Evaluation of Dewatering Devices for Producing High-solids...

GEPA

r- United States Municipal Environmental Research EPA-60012-79- 1 23 Environmental Protection Laboratory August 1979 Aeency Cincinnati OH 45268

, Research and Development

Evaluation of Dewatering Devices for Producing High-Solids Sludge Cake

RESEARCH REPORTING SERIES

Research reports of the Office of Research and Development U S Environmental Protection Agency have been grouped into nine series These nine broad cate- gories were established to facilitate further development and application of environmental technology Elimination of traditional grouping was consciously planned to foster technology transfer and a maximum interface in related fields The nine series are

1. 2. 3. 4. 5. 6. 7. 8. 9.

Environmental Health Effects Research Environmental Protection Technology Ecological Research Environmental Monitoring Socioeconomic Environmental Studies Scientific and Technical Assessment Reports (STAR) Interagency Energy-Environment Research and Development "Special" Reports Miscellaneous Reports

This report has been assigned to the ENVIRONMENTAL PROTECTION TECH- NOLOGY series. This series describes research performed to develop and dem- onstrate instrumentation, equipment, and methodology to repair or prevent environmental degradation from point.and non-point sources of pollution. This work provides the new or improved technology required for the control and treatment of pollution sources to meet environmental quality standards.

This document is available to the pubiic through the National Technical Informa- tion Service, Springfield, Virginia 221 61.

E P A - 6 0 0 / 2 - 7 9 - 1 2 3 A u g u s t 1979

EVALUATION OF DEWATERING D E V I C E S FOR

PRODUCING HIGH-SOLIDS SLUDGE CAKE

A l a n F. C a s s e l and

B e r i n d a P. Johnson

D i s t r i c t of C o l u m b i a G o v e r n m e n t D e p a r t m e n t of E n v i r o n m e n t a l Services

Water Resources M a n a g e m e n t A d m i n i s t r a t i o n Washington, D. C . 20032

C o n t r a c t N o . 68-03-2455

P r o j e c t O f f i c e r

R o l a n d V . V i l l i e r s W a s t e w a t e r Research D i v i s i o n

M u n i c i p a l E n v i r o n m e n t a l R e s e a r c h Laboratory C i n c i n n a t i , O h i o 45268

M U N I C I P A L ENVIRONMENTAL RESEARCH LABORATORY O F F I C E OF RESEARCH AND DEVELOPMENT

U.S. ENVIRONMENTAL PROTECTION AGENCY C I N C I N N A T I , O H I O 45268

r

DISCLAIMER

This r e p o r t has been reviewed by the Municipal Environmental Research Laboratory, U. S. Environmental P r o t e c t i o n Agency, and approved f o r publ ica- t i on . Approval does not s i g n i f y that t h e con ten t s n e c e s s a r i l y r e f l e c t t h e views and p o l i c i e s of t h e U. S. Environmental P r o t e c t i o n Agency, nor does rriention of t r a d e names o r commercial p roducts c o n s t i t u t e endorsement o r recommendation f o r use .

ii

h

FOREWORD

The Environmental P r o t e c t i o n Agency w a s c r ea t ed because of i nc reas ing pub l i c and government concern about t h e dangers of p o l l u t i o n t o t h e h e a l t h and we l fa re of t h e American people . Noxious a i r , f o u l water, and spo i l ed land are t r a g i c tes t imony t o t h e d e t e r i o r a t i o n of our n a t u r a l environment. The complexity of t h a t environment and t h e i n t e r p l a y between i t s components r e q u i r e a concent ra ted and i n t e g r a t e d a t t a c k on t h e problem.

Research and development is t h a t necessary f i r s t s t e p i n problem solu- t i o n and i t involves de f in ing t h e problem, measuring i t s impact, and search- ing f o r so lu t ions . The Municipal Environmental Research Laboratory develops new and improved technology and systems f o r t h e p reven t ion , t rea tment , and management of wastewater and s o l i d and hazardous w a s t e p o l l u t a n t d i scha rges from municipal and community sources , f o r t h e p r e s e r v a t i o n and t rea tment of pub l i c d r ink ing w a t e r s u p p l i e s , and t o minimize t h e adverse economic, s o c i a l , h e a l t h , and a e s t h e t i c e f f e c t s of p o l l u t i o n . This p u b l i c a t i o n i s one of t h e products of t h a t r e sea rch ; a most v i t a l communications l i n k between t h e r e sea rche r and t h e u s e r community.

Th i s r e p o r t p r e s e n t s t h e r e s u l t s of a year and a h a l f s tudy of t h e c a p a b i l i t y of va r ious mechanical dewatering dev ices t o produce h igh s o l i d s s ludge cake. a v a i l a b l e t h a t are capable of dewater ing municipal s ludge s o l i d s t o 30-40 percent cake dryness . This i s q u i t e s i g n i f i c a n t s i n c e i t impacts i n subsequent c o s t sav ings i n d i s p o s a l of s ludge s o l i d s . A t 30 pe rcen t s o l i d s , s ludge burns autogenously. This e l i m i n a t e s t h e need of c o s t l y a u x i l i a r y f u e l t o i n c i n e r a t e s ludge. Also, high cake s o l i d s means less s ludge t o haul and land dispose. Th i s dec reases land d i s p o s a l c o s t s .

Resu l t s show that a number of a l t e r n a t i v e methods are p r e s e n t l y

F ranc i s T. Mayo Di rec to r Municipal Environmental Research

Lab0 rat o ry , C i n c inna t i

iii

ABSTRACT

P i l o t - s c a l e dewater ing tests were made t o e s t a b l i s h des ign and ope ra t ing parameters f o r dewatering municipal wastewater s ludges on recessed p l a t e f i l t e r p r e s s e s (both diaphragm and f i x e d volume t y p e s ) , cont inuous b e l t presses, and r e t r o f i t u n i t s f o r a vacuum f i l t e r . s tudy showed t h a t when dewater ing lime and f e r r i c chlor ide-condi t ioned s ludges , t h e recessed p l a t e presses c o n s i s t e n t l y produced a 30-40% s o l i d s f i l t e r cake. Feed s o l i d s t o t h e u n i t s averaged 5% t o t a l s o l i d s wi th a range from 2.4 t o 10%. wi th emphasis on t h e 2 / 1 r a t i o , were t e s t e d . b e l t p r e s s e s on t h e Blue P la ins s ludge w a s l a r g e l y a f u n c t i o n of t h e percentage of waste a c t i v a t e d s ludge i n t h e feed mixture . Cake s o l i d s from 2>-30% were a t t a i n e d when t h e polymer condi t ion ing dosage w a s optimized. When used as a r e t r o f i t dev ice t o a vacuum f i l t e r , t h e b e l t p r e s s gave cake s o l i d s i n t h e 30-40% range dur ing l abora to ry - sca l e tests. demonstrat ion, however, w a s no t achieved because an adequate system f o r d e l i v e r i n g f i l t e r cake t o a b e l t f i l t e r has no t y e t been developed.

R e s u l t s from t h e 1.5-year

Various r a t i o s of waste-act ivated t o primary s ludge s o l i d s , Successfu l ope ra t ion of t h e

Fu l l - sca l e

Design parameters are developed t o dewater a mixture of 67% secondary and 33% primary s ludge i n a f u l l - s c a l e p l a n t i n s t a l l a t i o n . The es t imated c o s t s f o r dewater ing p l u s f i n a l d i s p o s a l by e i t h e r i n c i n e r a t i o n o r composting are a l s o presented.

This r e p o r t w a s submitted i n f u l f i l l m e n t of Contract No. 68-03-2455 by t h e Water Resources Management Adminis t ra t ion , Department of Environmental Se rv ices , D i s t r i c t of Columbia, under t h e sponsorship of t h e U. S. Environ- mental P r o t e c t i o n Agency.

i v

CONTENTS

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii Abst rac t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i v F igures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v i Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i x Abbrevia t ions and Symbols . . . . . . . . . . . . . . . . . . . . . . . . x i Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . x i i i

1 . 2 . 3 . 4 . . 5.

6 .

7 .

8 .

9 .

Background and I n t r o d u c t i o n . . . . . . . . . . . . . . . . . . 1 Summary and Conclusions . . . . . . . . . . . . . . . . . . . . 6

Sludge Condit ioning . . . . . . . . . . . . . . . . . . . . . . 14

Diaphragm f i l t e r p r e s s ( v a r i a b l e volume p r e s s ) . . . . . . . 20

Recommendations . . . . . . . . . . . . . . . . . . . . . . . . 10 Type of Sludge Processed . . . . . . . . . . . . . . . . . . . . 11

T e s t R e s u l t s . Dewatering Un i t s . . . . . . . . . . . . . . . . 20

Fixed volume f i l t e r p r e s s . . . . . . . . . . . . . . . . . . 59 Continuous b e l t f i l t e r p r e s s . . . . . . . . . . . . . . . . 75 Vacuum f i l t e r r e t r o f i t . Enviro tech h i - s o l i d s f i l t e r . . . . 84 V a c u u m f i l t e r . . . . . . . . . . . . . . . . . . . . . . . . 88

S p e c i a l T e s t s . . . . . . . . . . . . . . . . . . . . . . . . . . 90 C o r r e l a t i o n w i t h s p e c i f i c r e s i s t a n c e . . . . . . . . . . . . 90

Material ba lance . . . . . . . . . . . . . . . . . . . . . . 96 Condit ioning w i t h polymer . . . . . . . . . . . . . . . . . . 96 Tests on p r e s s cake process ing . . . . . . . . . . . . . . . 96

P rocess Design . . . . . . . . . . . . . . . . . . . . . . . . . 102 Continuous b e l t p r e s s . . . . . . . . . . . . . . . . . . . . 102 F i l t e r p r e s s . . . . . . . . . . . . . . . . . . . . . . . . 103 Chemical cond i t ion ing . . . . . . . . . . . . . . . . . . . . 103 F i l t e r p r e s s des ign . . . . . . . . . . . . . . . . . . . . . 105 Mul t ip le -hear th i n c i n e r a t o r des ign . . . . . . . . . . . . . 109

Dewatering and Disposa l Cos ts . . . . . . . . . . . . . . . . . 112

Dewatering of v a r i a b l e s ludge concen t r a t ions . . . . . . . . 94

App end ices A . Laboratory ana lyses . . . . . . . . . . . . . . . . . . . . . . 119 B . Data s h e e t s . . . . . . . . . . . . . . . . . . . . . . . . . . 121 C . Determinat ion of s p e c i f i c r e s i s t a n c e . . . . . . . . . . . . . . 138 D . Material ba lance . . . . . . . . . . . . . . . . . . . . . . . . 152 E . Der iva t ion of c o s t s . . . . . . . . . . . . . . . . . . . . . . 157 F . Ful l - sca l e u n i t s p e c i f i c a t i o n s . . . . . . . . . . . . . . . . . 174

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176

V

FIGURES

Page

2

Number

1 District of Columbia Wastewater Treatment Plant. Present Facilities

2 District of Columbia Wastewater Treatment Plant. Future Facilities

3

Lime Requirements vs. Percent Secondary Sludge 3 19

2 1

2 1

22

22

24

4

5

NGK Diaphragm Press

NGK Sludge Mix Tank

6 NGK Pump Assembly

NGK Control Panel 7

8 Process Schematic for NGK Diaphragm Press

9 Schematic of Filtration and Squeezing in Diaphragm Press

25

Schematic of Discharge and Washing in Diaphragm Press

10 27

32 Feed Volume vs. Time: NGK Runs on 3/4/77

Feed Pressure vs. Time: NGK Runs on 3/4/77

11

12

13

14

15

16

17

18

35

Filtrate Volume vs. Time: NGK Runs on 3/4/77

Effect of Increasing Squeeze Times - NGK Press Filtrate Volume vs. Time: NGK Runs on 11/1/77

37

38

39

50 Process Flowsheet for Continuous Run

52 Lasta Diaphragm Press

56 Schematic of Filtration, Discharge, and Washing in the Lasta Press

vi

Numbers

19

20

21

22

23

24

25

26

27

58

29

30

31

32

33

34

35

36

37

38

39

Passavant Filter Press

Sample Sections from Passavant Cake

Nichols Filter Press

Sample Sections from Nichols Cake

Comparative Yield Data

Schematic of Parkson Belt Press

Parkson Laboratory Belt Press

Magnum Press Test Results

Magnum Press Test Results

Unimat Belt Press

Schematic of Envirotech Hi-Solids Filter

Chemical Dosages vs. Percent Secondary Sludge. Envirotech Tests

Process Yield vs. Rv

Process Yield vs. Rp

Process Yield vs. CST/(Percent Solids of Conditioned Feed)

CST/(Percent Solids of Conditioned Feed) vs. Rv

CST/(Percent Solids of Conditioned Feed) vs. Rp

Rp vs. Rv

Cake from NGK Diaphragm Press

Cake Breaker

Incinerator Outlet Temperature vs. Percent Conditioners

Page

6 1

6 1

67

67

74

76

77

78

7 8

8 1

84

86

9 1

92

9 3

93

95

95

98

98

110

c- 1 Buchner Funnel Apparatus 1 4 2

v i i

Numbers

c- 2 Passavant Series 275 Resistance Meter

c- 3 CST Instrument

Page

1 4 2

145

v i i i

TABLES

Number

1

6

7

8

9

10

11

1 2

1 3

1 4

15

1 6

17

Blue Plains Wastewater Treatment Plant Operating Parameters

Page

1 2

Chemical Specifications 15

Material Balance Tests f o r Ca and Fe 16

Material Balance Tests for Total Solids 16

NGK Filter Performance vs. Chemical Conditioning

30

Runs to Optimize Pumping Time 3 3

Extended Runs - 3 / 8 / 7 7 41

Filtrate Quality vs. Chemical Conditioning 4 1

NGK Filter Cloths 4 2

NGK Runs on 211 Sludge 4 5

Typical Results on Diaphragm Press - August Runs

4 8

Lasta Runs on 2/1 Sludge 54

Comparison Runs on 2 / 1 Sludge 5 8

Typical Results on Model 2400 High-pressure Press ( 3 8 mm Plate) - August Runs

6 2

Runs on Model 2 4 0 0 High-pressure Press with 2 1 1 Secondary/Primary Sludge

6 4

Runs on Model 6 0 0 High-pressure Press 65

Typical Results on Low-Pressure Press - August Runs

6 8

ix

Number

18

19

20

21

22

23

24

25

26

27

28

29

F- 1

F- 2

Runs on Low-Pressure Press with 2/1 Secondary/Primary Sludge

Comparison Runs

Parkson Press as a Retrofit to Vacuum Filters

Unimat Belt Press Results on 2/1 Sludge

Unimat Press as a Retrofit to Vacuum Filters

Hi-Solids Filter Results

Comparison Runs - Vacuum Filter/Filter Press Dewatering Costs

Belt Press Costs

Incineration Costs

Land Disposal Costs

Total Disposal Costs

Filter Press Specifications

Filter Media Specifications

X

Page

70

72

79

82

83

87

89

113

114

115

116

116

174

175

ABBREVIATIONS AND SYMBOLS

ABBREVIATIONS

Btu/lb Cal/gm cm cfm d ft g (gm) gal gpd gpm hr in kg 1 lb m mg/l ml

MG MGD min min/rev (ME'R) mo N/m2 Ns /m2 RPM sec ( s ) wt

mm

SYMBOLS

BOD^ CaC03 Ca (OH) 2 CaO COD CST F:M

Btu per pound Calorie per gram Centimeter Cubic feet per minute Day Foot (feet) gram Gallon Gallons per day Gallons per minute Hour Inch Kilogram Liter Pound Meter Milligrams per liter Milliliter Millimeter Million Gallons Million gallons per day Minute Minutes per revolution Month Newtons per square meter Newtons-seconds per square meter Revolutions per minute Second Weight

Five Day Biochemical Oxygen Demand Calcium Carbonate Calcium Hydroxide Calcium Oxide Chemical Oxygen Demand Capillary Suction Time, sec Food to Mass Ratio in Secondary Aeration System

xi

FeC13 Fe (OH) 3 Hg (Inches Hg)

Rv

SRT TKN TS USDA

vs % t

P

Ferric Chloride Ferric Hydroxide Mercury (Inches of Mercury Pressure-

Mixed Liquor Suspended Solids Mixed Liquor Volatile Suspended Solids Millimeters of Water Pressure-Gage Ammonia Nitrate Total Phosphrous Hydrogen Ion Concentration Phosphate Pounds per square Inch-Gage Pressure Pressure Drop Specific Resistance to Filtration,

Specific Resistance to Filtration,

Sludge Retention Time Total Kjeldahl Nitrogen Total Solids United States Department of Agricul- ture

Volatile Solids P er c en t Pound Viscosity of water

Gage)

dimensionless (pressure)

cm/g (vacuum)

xii

ACKNOWLEDGEMENTS

W e would l i k e t o thank a l l t h e people whose d e d i c a t i o n and coopera t ion con t r ibu ted t o t h e success of t h e p r o j e c t . W e would l i k e t o extend a s p e c i a l thank you t o t h e s t a f f of o p e r a t o r s - Roger Benf ie ld , l e a d e r , J e r r y Ballengee, Dave W i l l h i t e , and Mark George - f o r t h e q u a l i t y of d a t a they c o l l e c t e d ; t o F e l i x Costanzo f o r assembling and main ta in ing t h e v a r i o u s t es t u n i t s ; t o B i l l Ruby f o r l a b o r a t o r y ana lyses ; and t o Marco Garcia and P e t e Repak f o r t h e s p e c i a l tests run throughout t h e cour se of t h e s tudy.

P a r t i c u l a r a p p r e c i a t i o n i s extended t o a l l t h e manufacturers who provided t h e i r time and equipment t o t h e s tudy. We are deeply indebted t o D r . James E. Smith, Jr . , of t h e EPA i n C inc inna t i , Ohio, who w a s i n s t r u - menta.? i n b r ing ing t h i s p r o j e c t i n t o be ing and provid ing t e c h n i c a l assist- ance i n g e t t i n g t h e s tudy underway. Thanks are a l s o due t o M r . R.V. Vi l l ie rs , p r o j e c t o f f i c e r , and D r . J. B. F a r r e l l , w i t h t h e Ul t imate Disposa l Sec t ion of EPA's Municipal Environmental Research Laboratory i n C inc inna t i , Ohio.

x i i i

SECTION 1

BACKGROUND AND INTRODUCTION

The District of Columbia's Wastewater Treatment Plant at Blue Plains receives flow from the District of Columbia and from suburban Maryland and Virginia jurisdictions. Approximately two million residents produce an average daily flow of 1.06 Mm3/day (280 MGD). Wastewater is treated by primary sedimentation and a secondary waste activated sludge process with chemical addition for solids capture and phosphorus removal. Sludge treatment is accomplished by two methods: gravity thickening and raw sludge dewatering with subsequent composting or trenching; or gravity thickening, anaerobic digestion, elutriation and dewatering with subsequent land spreading. (See Figure 1.)

An on-going expansion and upgrading of the plant, with completion scheduled for mid 1980, will add nitrification and multi-media filtration to the wastewater train. Sludge production will increase from its current level of approximately 150,000 kg/day dry solids (165 dry tons per day) to 340,000 kg/day solids (374 dry tons per day). To handle the additional sludge quantities, original plans had called for gravity thickening of primary sludge, air flotation thickening of all waste activated sludges, blending, vacuum filtration, and incineration. (See Figure 2.) All units except the incinerators have been installed. Because of the large amount of fuel oil which would be required to incinerate the vacuum filtered sludge cake, approval of the incinerators has been deferred by EPA pending further study. An initial study conducted by Camp, Dresser and McKee, Inca1 recommended a dual disposal system of composting and incineration and pointed out that if a high-solids sludge cake were produced, incineration could be accomplished with minimum quantities of auxiliary fuel. The study estimated that to incinerate 374 dry tons per day of an 18% vacuum filter cake, annual fuel oil usage would be approximately 16,000,000 gallons. Whereas, to incinerate a 35% solids cake, fuel usage would decrease to only 5,500,000 gallons per year. This 35% solids cake would be autocombustible and fuel would be required primarily for the afterburner to control toxic organics in the off-gas. Fuel usage in the multiple hearth furnace itself

~

1 Camp, Dresser & McKee, Inc. Alternative Sludge Disposal Systems for the District of Columbia Water Pollution Control Plant at Blue Plains. December , 1975.

1

c

U

c 01 v) 01 LA P

I

u $ E

U

k

aJ

'0

V

2

E

I: El

I E

0

.- c E! 0)

E

0 c

.- - A

3

m a,

b

a, U

0) U

m s" P

would be needed only f o r control of the position of the burning hearth. Camp, Dresser and McKee, therefore, recommended that the vacuum filters be replaced by filter presses so that an autocombustible sludge cake would be produced.

In mid-1976 the District of Columbia received approval from EPA to conduct a one year study of alternative dewatering devices for producing a high-solids sludge cake. The study was funded from two EPA sources. EPA Region I11 allowed expenses up to $186,992 as an addendum to an existing capital outlay project. EPA's Municipal Environmental Research Laboratory in Cincinnati, Ohio provided $49,693 and technical direction for the study.

The study was performed in the EPA-DC Pilot Plant using the existing equipment available in that facility as well as equipment provided by various manufacturers. A project engineer, a part-time chemical engineer, four sewage disposal planc operators, one chemist, and one mechanic conducted the entire study. The study period officially commenced on September 1, 1976 and ended on October 31, 1977; some preliminary test work actually began dn April, 1976. The study was completed with expenses well below the budgeted amount.

The purpose of the study was to compare the operation of the various dewatering devices on selected ratios of waste activated to primary sludges. Because the plmt had already purchased and installed 30 vacuum filter units, the District was interested only in evaluating devices that would produce significantly higher solids than the vacuum filters. Specifically, the District was interested in the results with a 2:l ratio of waste activated- to-primary sludge solids. All units were operated in an attempt to produce an auto-combustible sludge cake. For sludges conditioned with inert chemicals, this requires a solids content of approximately 35%. The type of units tested and their suppliers included:

1. 2.

Vacuum Filter - Pilot model owned by EPA. Vacuum Filter add-on devices - supplied by a) Envirotech Corporation, Salt Lake City, Utah, b) Parkson Corporation, Fort Lauderdale, Florida. c) Komline-Sanderson Corp., Peapack, New Jersey.

3. Belt Press - supplied by Parkson and Komline-Sanderson. 4 .

5.

6.

Filter Press - fixed volume @lo0 psig pressure supplied by Neptune-Nichols, Belle Mead, New Jersey. Filter Press - fixed volume @225 psig pressure supplied by Passavant Corp., Birmingham, Alabama. Filter Press - diaphragm type supplied by a) NGK Insulators, Ltd., Nagoya, Japan. Envirex Corporation has

since purchased the rights to manufacture and market this press in the United States.

4

b) Dart Industries, Paramus, New Jersey. c) Ingersoll-Rand Corp., Nashua, New Hampshire.

This report presents the results of testing the above dewatering units. Chemical conditioning with lime and ferric chloride was examined in detail t o establish the requirements as a function of the ratio of waste activated- to-primary sludge solids. A correlation between bench-scale filterability tests and filter press performance was developed to monitor the conditioning step. Polymer conditioning was evaluated as an alternative to lime and ferric chloride conditioning.

Detailed design parameters for each of the filter presses were developed for a 2 1 1 secondarylprimary sludge ratio. with the same batch of sludge provided valuable information on the advan- tagesldisadvantages of each. experiments to test cake shredding, incineration (solid waste furnace, multiple hearth furnace, and coal-fired boiler), and composting (static pile method).

Comparison runs on these presses

Filter press cake was used in a variety of

The belt presses were used to provide design criteria for the thickened sludges. These presses were also modified to function as add-on units to further dewater vacuum filter cake.

Capital and operating costs and utility consumption are detailed for the dewatering tinits. Total disposal costs for dewatering plus both incineration and composting are also presented.

5

SECTION 2

SUMMARY AND CONCLUSIONS

Chemical Conditioning

1.

2 .

3 .

4 .

5.

The lime and ferric chloride dosages required to produce a filterable sludge varied with the percentage of waste activated sludge. Fibrous primary sludge filtered quite readily; waste activated sludge required greater quantities of conditioners and was more difficult to dewater. Generally, a 311 ratio of lime-to-ferric chloride was optimum for conditioning the Blue Plains sludge.

Laboratory tests showed that over-agitation of the conditioned sludge was detrimental to the filtration process. Floc deterioration with both time and high shear was a major factor in determining chemical requirements.

The addition of lime and ferric chloride to the sludge mixture increased the final dry weight of the filter cake by a corresponding amount. All of the iron and 80% of the .calcium exited with the cake solids during filtration operations.

Bench-scale filterability tests were found to be useful when optimizing and controlling the lime and ferric chloride dosages.

Polymer conditioning of the 2/1 mixture of secondary-to-primary sludge was generally ineffectual. No single polymer was found which could adjust to the daily variations in the quality of sludge received from the primary and secondary treatment processes.

Filter Press-General

1. Each of the filter presses was capable of dewatering all sludge ratios in the range of 2.4-10% total feed solids to at least a 30% solids cake. The diaphragm press, however, was the only unit capable of dewatering the marginally conditioned sludges to the 35% solids required for an autocombustible cake.

2 . Once a minimum chemical conditioning requirement of lime and ferric chloride for adequate dewatering was established, increases in filtration yields (up to 20%) were obtained by slight increases in chemical dosages.

6

3 . In all the presses, suspended solids recovery in the filter cake was greater than 99%. The quantity of suspended solids in the filtrate was affected primarily by the type of filter cloth used and the degree of chemical conditioning.

4. The filter presses did not satisfactorily dewater polymer conditioned sludges.

5. The average specific resistance-to-filtration parameter was correlated directly with filter press yield.

Filter Press-Diaphragm Unit

1.

2.

3.

4 .

On the average, the NGK press, using conditioning of 19.6% lime and 6.5% FeCl3, dewatered the 211 secondary-to-primary sludge to a 38.7% solids cake with a yield of 2.39 kg/hr/m2 (0.49 lb/hr/ft2). The pum ing pressure required to feed the press was always less than 7 kg/cm3 (100 psig). The pumping cycle time averaged 17 minutes and was controlled by monitoring the total soiids feed rate. A squeezing pressure of 15.0 kg/cm2 (213 psig) was generally used. The squeezing cycle time (18 minutes) was controlled by filtering to a specified filtrate flow rate.

Equivalent results were obtained on the Ingersoll-Rand Lasta press. The full-scale yield for the unit, however, was somewhat higher at 2.93 kg/hr/m2 (0.60 lb/hr/f t2) for the 2/1 secondary-to-primary sludge.

Different filter cloths were tested on both the NGK and Lasta units. All gave ac-ceptable filtrate quality but cloth life, resistance to abrasion, etc., could not be effectively evaluated in our study.

The cloth washing system in each o f the presses also could not be adequately evaluated during the study. Maintenance of satisfactory cloth permeability by high-pressure sprays or acid washing is an area that generally requires more study.

Filter Press - Fixed Volume Unit

1.

2.

3.

The high-pressure press (225 psig) had an average filtration yield of 1.51 kg/hr/m2 (-31 lb/hr/ft2) and required 62.3% more filtration area than the NGK diaphragm unit to produce equivalent results. The low-pressure press (100 psi ) had an average full-scale yield of

the NGK diaphragm press to produce equivalent results. 1.07 kg/hr/m2 (.22 lb/hr/ft 4 ) and needed 126.8% more filter area than

Cycle time on the presses averaged 2-3 hours and was determined by filtering to a specified filtrate flow rate.

The cakes from the fixed volume presses always contained a dry outer section and a wetter inner core. This resulted in a substantial variation in the solids content across the cake.

7

Continuous Belt Press

1. Because of the highly variable sludge at Blue Plains, no polymer was found that could adjust to these variations and adequately condition the sludge at all times. The operation of the belt press, therefore, was not consistent.

2. With thickened sludge feeds, the press capacity, final cake solids, and polymer consumption were all affected by the percentage of waste- activated sludge. The unit performed best when dewatering high percentages of fibrous, primary sludge.

3. Suspended solids recovery in the filter cake averaged only 95%. Because of the stringent advanced waste treatment standards at Blue Plains, this level of recovery would be insufficient for continuous operation at this plant.

Vacuum Filter Retrofit Unit

1. The Envirotech Hi-Solids filter was discounted as an option for Blue * Plains. It was capable of increasing the cake from a rotary vacuum

filter to only 25% solids.

2. The use of the high-pressure section of the continuous belt press to further dewater the vacuum filter cake showed great promise. Cake solids of 35% were achieved in bench-scale work; however, demonstration of the system-in a full-scale test was not successful because of problems with feeding the vacuum filtered cake to the press.

Filter Cake Processing

1. The filter press cake was composted with wood chips by the static-pile method. than those for composting with vacuum filter cake.

A good final product was produced with projected costs less

2. Filter press cake with a solids content of at least 35% is considered a low-value fuel. It will burn in a multiple hearth incinerator without auxiliary fuel to produce an exit temperature of 800°F. It can also be co-burned with municipal refuse in a rocking-grate furnace. Because of the high ash content of the cake (up to 50%), however, it has been rejected as a fuel for a coal-fired boiler.

Economics

1. The belt press ($32.39 per ton) and the vacuum filter ($39.10 per ton) provide the lowest cost for dewatering.

2. Dewatering costs for each of the filter presses are nearly equal with unit costs of approximately $55.00 per ton.

8

3. Total disposal costs for filter pressing and incineration are approximately $88 per ton. This compares to the total cost for vacuum filtering and incineration at $130 per ton. Therefore, savings of nearly $4,000,000 per year for a 250 ton-per-day plant are possible by selecting filter presses for dewatering.

4 . Total disposal costs for filter pressing and composting (including the cost of hauling the press cake 25 miles) are approximately $102 per ton. This compares to the total cost of vacuum filtering and composting (including hauling) of $155 per ton. Choosing a filter press rather than a vacuum filter, therefore, will result in annual savings of nearly $5,000,000 for a 250 ton-per-day plant.

9

SECTION 3

RECOMMENDAT IONS

1. Filter presses should be installed at Blue Plains, designed to dewater the total quantity of sludge (average 374 dry tons per day) to be processed by either incineration or composting. This study showed that the diaphragm-type press offers the most flexibility and provides the best product. However, a final decision on the type of press to be utilized should be deferred until full-scale facilities of each type are inspected. Regardless of the type of unit chosen, a single large-scale unit should be purchased, installed and operated for . several months to provide valuable design information prior to a large-scale committment of funds.

2. Additional test work should also be conducted to determine whether the specific resistance parameter can be used to successfully monitor and control the chemical conditioning process. As outlined in Section 8 (Process Design) a pilot-scale horizontal vacuum filter, adjusted to simulate the Buchner funnel filtration test, would be used for this purpose. When a pilot-unit becomes available, this work can be carried out in conjunction with existing vacuum filter operations.

10

SECTION 4

TYPE OF SLUDGE PROCESSED

During t h e s tudy pe r iod , t h e wastewater t reatment system included d e g r i t - t i n g , primary sedimentat ion, and a h igh - ra t e waste a c t i v a t e d secondary process, wi th chemical a d d i t i o n f o r phosphorus removal. Table 1 shows average ope ra t ing parameters of t h e system f o r FY 1977 (October, 1976 through Septem- be r , 1977). ope ra t ion and a p o r t i o n of t h i s undigested s ludge is dewatered on vacuum f i l t e r s .

The primary and secondary s ludges are blended i n a th i cken ing

Throughout t h e s tudy pe r iod , t h e p l a n t experienced c o n t i n u a l o p e r a t i n g problems because of an overloaded s ludge processing system. Recycle loads , e s p e c i a l l y from g r a v i t y th i cken ing , c r e a t e d o p e r a t i n g d i f f i c u l t i e s i n secondary. The r e c y c l e flows (only 5% of t o t a l f low) c o n t r i b u t e d 22% of t h e BOD loading and 25% of t h e suspended s o l i d s load ing t o t h e wastewater t r ea tmen t t r a i n . This r e c y c l e problem, t o g e t h e r w i t h normal o p e r a t i n g problems expe- r ienced wi th chemical a d d i t i o n outages and t h e r a p i d l y changing biology i n secondary, caused a h igh ly v a r i a b l e s ludge product . i n t h e Distr ic t of Columbia a l s o c o n t r i b u t e d t o t h e problem; heavy r a i n s washed l a r g e q u a n t i t i e s of s o l i d s i n t o t h e primary s ludge t h u s changing t h e c h a r a c t e r of t h a t product. d a i l y .

The combined sewer system

As a r e s u l t , t h e s ludge d e w a t e r a b i l i t y v a r i e d

I n s e t t i n g up t h e s tudy , t h e eng inee r s a t tempted t o s imula t e t h e condi-

The t i o n s t h a t would e x i s t i n t h e f u t u r e f u l l - s c a l e p l a n t . When t h e systems are completed, a l l primary s ludge w i l l be g r a v i t y thickened s e p a r a t e l y . s ludges from secondary and n i t r i f i c a t i o n w i l l be combined and a i r f l o a t thickened. sludges. r e tu rned t o secondary. Ca lcu la t ions of f u t u r e s ludge product ion show that t h e p l a n t w i l l produce an average r a t i o of 33% primary s o l i d s / 6 7 % waste act i - vated s o l i d s .

All chemical p r e c i p i t a t e w i l l be included w i t h t h e waste a c t i v a t e d Backwash water and s o l i d s from t h e multi-media f i l t e r s w i l l be

The p i l o t p l a n t had t h e c a p a b i l i t y t o receive e i t h e r blended thickened I n i t i a l s ludge from t h e p l a n t o r primary and secondary s ludges s e p a r a t e l y .

test work wi th t h e p l a n t thickened s ludge gave good f i l t r a t i o n r e s u l t s ; however, t h e overloaded p l a n t t h i c k e n e r s tended t o wash ou t t h e f i n e s o l i d s . o rde r t o g e t a more real is t ic product f o r dewatering, s e p a r a t e p i l o t - s c a l e g r a v i t y t h i c k e n e r s f o r t h e primary and secondary s ludges were placed i n opera- t i o n . secondary t o primary s ludges, Consequently, t h e s e p a r a t e g r a v i t y th i cken ing systems were used and t h e two s ludges blended as necessary on a dry s o l i d s

I n

A major v a r i a b l e f o r s tudy w a s t h e d e w a t e r a b i l i t y of v a r i o u s r a t i o s of

11

TABLE 1. BLUE PLAINS WASTEWATER TREATMENT PLANT OPERATING PARAMETERS

Primary Treat men t Flow, Mm J/day (MGD) inc lud ing p l a n t r e c y c l e I n f l u e n t suspended s o l i d s , mg/l I n f l u e n t BOD^, mg/l Detent ion t i m e , hours Surface Loading Rate, m3/day/m2 (gpd / f t2> Suspended s o l i d s removal, % BOD5 removal, % Sludge Production, kg/Mm3 (Ib/MG) Sludge wasted, % t o t a l s o l i d s Sludge wasted, % v o l a t i l e s o l i d s

Secondary Treatment Aerat ion Tank

Flow, Mm3/daY (MGD) I n f l u e n t suspended s o l i d s , mg/l

* I n f l u e n t BOD^, mg/l I n f l u e n t phosphorus, mg/l as P MLSS/MLVSS concen t r a t ions , mg/l Detent ion t i m e , hours SRT, days F:M, days”

Sedimentation Tank Detent ion t i m e , hours Surface loading rate, m3/daY/m2 (gpd / f t2 )

F e r r i c c h l o r i d e , mg/l Polymer ( an ion ic ) , mg/l

Process Performance Suspended s o l i d s removal, % BOD5 removal, % P removal, % Sludge wasted, kg/Mm3 (Ib/MG) Sludge wasted, % t o t a l s o l i d s Sludge wasted, % v o l a t i l e s o l i d s Pe rcen t , b i o l o g i c a l so l id s / chemica l s o l i d s Fe content of waste s ludge, %

Chemical Addition

Gravi ty Thickenin Hydraulic loadinggrate , m3/da /m2 (f3Pd/ft2) So l ids loading rate, kg/daykm 5 9 ( l b s / d a y / f t 2 ) S o l i d s c a p t u r e e f f i c i e n c y ,

Mean 1.1 (292) 18 3 186 2.6 42.3 (1039) 45.0 37.0 78,960 (657.5) 0.525 72.4

1.1 (288) 102 121 6.2 1297/852 1.58 0.64 1.51

2.63 33.1 (813)

23 0.20

72 77 63 118,410 (986) 1.4 66.1 80/20 10.0

29.9 (734) 118.8 (24.3) 77

Vacuum F i l t r a t i o n Feed, % t o t a l s o l i d s 7.0 Lime a d d i t i o n , % of f eed s o l i d s 21.8

Cake s o l i d s con ten t , % 23.2 F i l t e r y i e l d , kg/hr/m2 ( l b / h r / f t 2 )

FeC13 a d d i t i o n , % of feed s o l i d s 7.5

15 .3 (3.12)

1 2

b a s i s . p r e f e r r e d method. ener proved too cumbersome. produce t h e r equ i r ed 4 t o 6% s o l i d s .

A i r f l o t a t i o n th i cken ing of t h e secondary s ludge would have been t h e Unfortunately, t h e l o g i s t i c s of running an a i r f l o a t t h i ck -

Gravi ty th i cken ing of t h e secondary s ludge d i d

The primary s ludge w a s d e l i v e r e d t o t h e p i l o t p l a n t and g r a v i t y thickened t o 6 t o 10% s o l i d s f o r use i n t h e s tudy. c o n t i n u a l l y from Monday morning t o Fr iday and wasted as necessary t o keep a s ludge b l anke t i n t h e th i ckene r . The c a p a c i t y of t h e t h i c k e n e r f a r exceeded t h e requirements f o r dewatering. The t h i c k e n e r w a s drained each Friday and f r e s h s ludge s t a r t e d each Monday. Because t h e primary s ludge a t Blue P l a i n s is very high i n f i b e r con ten t , a shredder w a s i n s t a l l e d i n t h e primary s ludge d e l i v e r y l i n e (0 .5% s o l i d s s t ream). It was used i n t e r m i t t e n t l y t o keep t h e r ags and t r a s h from plugging t h e t r a n s f e r pumps.

Normally, s ludge w a s d e l i v e r e d

The secondary waste s ludge w a s pumped d i r e c t l y from t h e secondary c lar i - f i e r s t o a g r a v i t y t h i c k e n e r i n t h e p i l o t p l a n t . p r i m a r i l y as a holding tank. rate. t o th i cken t o 4-6% s o l i d s con ten t . t h e day and t h e remaining c o n t e n t s d ra ined each af ternoon. kept t h e s ludge as f r e s h as p o s s i b l e . p r a c t i c a l l y a l l t h e f i n e s i n t h e secondary s ludge th i ckene r s were captured.

This t h i ckene r w a s used Each evening, s ludge w a s pumped i n a t a low flow

The flow w a s t hen c u t o f f e a r l y i n t h e morning and t h e c o n t e n t s allowed Sludge w a s used from t h i s source during

Such an o p e r a t i o n By seve re ly l i m i t i n g t h e overflow rate

A t y p i c a l 2 / 1 secondary/primary s ludge had t h e fol lowing c h a r a c t e r i s t i c s

Percent s o l i d s PH Density, gm/cc ( l b / g a l ) Temperature, w i n t e r O C Temperature, summer O C

% i r o n as Fe % v o l a t i l e s o l i d s

4 t o 6 6.2 t o 6 .8 1 .006 ( 8 . 4 ) 8-15 25-30 7 60-65

For a l l test runs, t h e s ludges were blended i n t h e fol lowing manner: Thickened secondary s ludge (at 4-6% s o l i d s ) w a s pumped wi th a Moyno pump t o a c a l i b r a t e d mixing tank; t h e volume w a s measured, t h e s ludge d e n s i t y measured, and a sample analyzed f o r pe rcen t s o l i d s on an O'Haus Moisture Balance. The q u a n t i t y of d ry s o l i d s i n t h e tank w a s t hen c a l c u l a t e d . The primary s ludge was a l s o analyzed f o r d e n s i t y and % s o l i d s , and t h e pounds of primary s ludge c a l c u l a t e d f o r a given volume. secondary t o primary s o l i d s r equ i r ed , t h e volume of primary s ludge was then Moyno pumped t o t h e mixing tank. e r r o r ; however, only approximate r a t i o s were r equ i r ed f o r t h e type of tests run.

Based on t h e r a t i o of

This method d i d g ive some experimental

When p l a n t thickened s ludge w a s used f o r t e s t i n g , it w a s pumped from t h e g r a v i t y t h i c k e n e r s t o a t ank t r u c k (700 g a l l o n s ) and then t r a n s p o r t e d one- q u a r t e r m i l e t o t h e p i l o t p l a n t . con ten t s t o t h e f i l t e r f eed tank.

A Moyno pump w a s used t o pump t h e t r u c k

13

SECTION 5

SLUDGE CONDITIONING

P r i o r t o e i t h e r p r e s s u r e o r vacuum f i l t r a t i o n , wastewater s ludges must A f i l t e r p r e s s w i l l gene ra l ly u s e f e r r i c c h l o r i d e A vacuum f i l t e r w i l l use e i t h e r f e r r i c c h l o r i d e

be chemically condi t ioned. and l i m e f o r cond i t ion ing . and l i m e o r f e r r i c c h l o r i d e and polymer; b e l t p r e s s e s w i l l gene ra l ly use polymer cond i t ion ing alone. For t h e purpose of t h i s s tudy , l i m e , f e r r i c c h l o r i d e and va r ious polymers, e i t h e r s i n g l y o r i n combination wi th one ano the r , were examined f o r t h e i r s u i t a b i l i t y i n cond i t ion ing t h e s ludge. s tudy attempted t o opt imize each of t h e s e chemicals f o r each of t h e dewatering h i t s . Other chemicals, such as aluminum chlorohydrate o r f e r r o u s s u l f a t e , were no t t e s t e d because rhey were e i t h e r t o o c o s t l y o r i n s h o r t supply.

The

CONDITIONING WITH LIME AND FERRIC CHLORIDE

The l i m e used f o r t h e s tudy w a s a bagged, pu lve r i zed , high calcium (94% Lime dosages are r epor t ed as t h e weight of t h e l i m e as pur- CaO) quicklime.

chased. The f e r r i c c h l o r i d e used was purchased as a 30% by weight s o l u t i o n and w a s diluted as necessary. Table 2 g ives t h e s p e c i f i c a t i o n s f o r t h e l i m e and ferric c h l o r i d e . Percent chemicals ( e i t h e r l i m e o r FeC13) are c a l c u l a t e d as:

Results are reported on a 100% FeC13 basis.

x 100 = % chemical l b s dry weight of chemical l b s dry incoming s ludge s o l i d s

Material Balance Tests

The a d d i t i o n of l i m e t o t h e thickened s ludge stream is expected t o form calcium carbonate ( i n s o l u b l e ) and calcium hydroxide ( s o l u b l e ) . The q u a n t i t i e s normally r equ i r ed w i l l raise t h e pH of t h e s o l u t i o n t o 11.0 o r above. Ferric c h l o r i d e reacts a t t h i s h igh pH t o form t h e i n s o l u b l e f e r r i c hydroxide (Fe(OH)3). w i t h a material balance test on a Buchner funnel . A t t h r e e d i f f e r e n t chemical dosages, approximately 225 m l of condi t ioned s ludge was f i l t e r e d ; t h e f eed , cake and f i l t r a t e were a l l analyzed f o r calcium (Ca) and i r o n (Fe) con ten t . The Ca and Fe determinat ions were made wi th an Atomic Absorption Spectropho- tometer. Table 3 shows t h e test r e s u l t s . Note t h a t t h e weight of Ca and Fe i n t h e feed do not balance e x a c t l y wi th t h e C a and Fe i n t h e f i l t r a t e and cake. However, t h e tests are u s e f u l i n t h a t t hey show t h a t appraximately 80% of t h e calcium and 100% of t h e i r o n w i l l e x i t w i t h t h e cake. -The remainder of t h e calcium s t a y s wi th t h e f i l t r a t e , probably as calcium hydroxide .

The d i s p o s i t i o n of t h e s e metal i o n s w a s determined

14

TABLE 2. CHEMICAL SPECIFICATIONS

Lime

S P e

C a O 94.84% Avai lable CaO 92.1% S ize

Concentration (as used) 1 l b / g a l l o n (11.3% by weight) S p e c i f i c g r a v i t y 1.06

Pulver ized CaO from Warner Co., Bel lef o n t e , Pa.

100% w i l l pa s s a 100-mesh s i e v e 1.95 micron average p a r t i c l e diameter

Ferric Chloride

. Concentration (as used) S p e c i f i c g r a v i t y

Liquid '2 30% by weight from DuPont t i t a n i u m d iox ide manufacture 1 l b / g a l l o n (10.9% by weight) 1.103

Add i t iona l tests were run on t h e Buchner funne l f o r t h e purpose of performing a t o t a l s o l i d s balance (determined by evaporat ing t h e samples t o dryness) . These tests, a t d i f f e r e n t chemical dosages, were c a r e f u l l y run t o determine t h e i n c r e a s e i n dry s o l i d s due t o t h e a d d i t i o n of l i m e and f e r r i c ch lo r ide . Thickened s ludge (primary and waste a c t i v a t e d ) w a s condi t ioned and approximately 200 m l were f i l t e r e d . unconditioned s ludge, t h e condi t ioned s ludge, t h e cake and t h e f i l t r a t e were measured. The r e s u l t s are shown i n Table 4. The tests show t h a t as chemicals are added, t h e weight of s o l i d s a c t u a l l y i n c r e a s e s above t h e i n i t i a l weight of s ludge p l u s chemicals added. The t o t a l s o l i d s i n t h e f i n a l cake, however, match very c l o s e l y w i t h t h e i n i t i a l weight of s ludge p l u s t h e weight of l i m e and f e r r i c c h l o r i d e added. The conclusion w e reached from t h e s e tests w a s t h a t both t h e l i m e and f e r r i c c h l o r i d e weights must be accounted f o r i n t h e f i l t e r cakes o f f e i t h e r a vacuum f i l t e r o r f i l t e r p r e s s . f o r every pound of l i m e and f e r r i c c h l o r i d e added f o r cond i t ion ing t h e f i n a l dry weight of t h e f i l t e r cake a l s o inc reased by an i d e n t i c a l amount.

Weights and t o t a l s o l i d s of t h e

This is most l i k e l y due t o CaC03 formation.

I n a l l c a l c u l a t i o n s w e t h e r e f o r e assumed t h a t

Important Considerat ions I n Condit ioning

A cons ide rab le amount of t r i a l - and-e r ro r work on t h e f i l t e r p r e s s e s and t h e bench s t u d i e s showed t h e following:

1. For Blue P l a i n s s ludge, t h e minimum amount of FeC13 needed f o r cond i t ion ing was approximately 5% by weight of s ludge s o l i d s .

15

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2. Three p a r t s of l i m e p e r p a r t of FeC13 worked a l l t h e t i m e . e v e r , t h e optimum lime:FeC13 r a t i o could be i n t h e range from 2 : l t o 4 : l .

How-

3. The FeC13 was always added f i r s t and allowed t o mix thoroughly be fo re adding t h e l i m e . The FeC13, however, forms a weak f l o c which can be e a s i l y broken up by too vigorous mixing; consequently care has t o be exe rc i sed during t h e mixing.

4. A f t e r t h e l i m e has been thoroughly mixed i n , t h e s ludge should be f i l t e r e d as soon as p o s s i b l e . assess f l o c d e t e r i o r a t i o n . S p e c i f i c r e s i s t a n c e tests were run wi th a Buchner funne l and t h e r e s u l t s r epor t ed as Rv. f i l t r a t i o n on t h e p i l o t - s c a l e NGK f i l t e r p r e s s t h e Rv va lue should be less than 27 x 1O1O cm/gm. These l a b o r a t o r y tests were conducted i n a 1500 m l beaker wi th a s i n g l e paddle stirrer (1" high x 3" wide). Maximum speed of t h e stirrer w a s 100 RPM. Sludge was added t o t h e beaker w i t h t h e mixer a t 100 RPM. (approximately 5 t o 6 minutes). L i m e (18.6%) w a s added and mixed i n (approximately 5 t o 6 minutes). When a v i s u a l check showed t h a t t h e chemicals were w e l l d i spe r sed , t h i s w a s c a l l e d t i m e = O . A t v a r i o u s t i m e i n t e r v a l s samples were grabbed and t h e Buchner funnel test made t o determine Rv.

The fol lowing tests were made t o

For good

(See Appendix C f o r t h e Rv procedure).

FeC13 (6.2%) w a s added and mixed i n thoroughly

I n Run #l, t h e mixer w a s allowed t o o p e r a t e a t 100 RPM f o r t h e du ra t ion of t h e test. r e s i s t a n c e inc reased r a t h e r quickly:

This run showed t h a t t h e s p e c i f i c

T i m e (min)

0 10 20

17.5 x 10" 94.8 x 10" 125 x 10"

I n Run 12, t h e mixer a l s o r a n a t 100 RPM f o r t h e e n t i r e test. By v i s u a l examination, t h e ope ra to r picked t h e t i m e a t which t h e s ludge appeared t o change. occurred i n approximately f i v e minutes:

This test showed t h a t t h e breakdown

Time (min)

0 5

11

Rv (cm/g)

23.1 x l o l o 76.1 x 1O1O sludge appeared

98.9 x 1O1O milky

I n Run #3, t h e mixer w a s slawed t o 20 RPM a f t e r t h e l i m e and FeCI3 had been mixed i n thoroughly. adequate t o keep t h e s ludge mixed. n o t i c e a b l e f l o c d e t e r i o r a t i o n :

This slow speed w a s b a r e l y A longe r t i m e w a s needed be fo re

17

Time (min)

0 10 20

30

Rv (cm/g>

10 11.8 x lolo 27.3 x lolo 43.5 x 10

10 93,2 x 10

floc began to deteriorate

The above tests confirmed the visual observations made throughout the entire test period; the same deterioration of sludge floc was observed many times in the NGK mixing tank. Marginally conditioned sludges were especially susceptible to over mixing or too-long storage times. If, however, the sludges were conditioned well above the marginal level, this rapid deterioration was less pronounced. Consequently, it should be noted that lime and FeCl usage can be minimized by proper design and operation of the conditioning system.

Chemical Reauirement vs. SecondarvIPrimarv Sludne Ratio

A test in a Buchner funnel was used to show the effect of the ratio of. secondary/primary shdge on chemical dosage requirements. This test was made for seven different sludge ratios. For each ratio, the sludges were blended in the proper proportions and then conditioned.with lime and ferric chloride. In all cases, a 3:l weight ratio of lime: FeCl was used. The dosage was considered to be optimum if the sludge could be filtered down to a good cake in less than 3-4 minutes. The results of this test are shown in Figure 3. It should be noted that this graph shows only a trend, rather than absolute chemical requirements. The Blue Plains sludge varies to the extent that these results would not be duplicated if the test was repeated on a subsequent day. This trend, however, is exactly what was found with all the filter press runs. Generally, primary sludge, because of its high fiber content, filters quite readily with only low chemical requirements. Secondary sludge which is composed of small biological solids is more difficult to condition and filter. A s the percentage of secondary sludge increases, the chemical requirements also increase. If enough lime and FeCl are added, though, the sludge can always be made to dewater.

3

3

COND IT ION ING WITH POLYMER

This topic will be discussed under each of the dewatering unit sections

18

30- -

=E--

26- -

P4- -

a=--

PO- -

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ak SECONDARY

Figure 3. Lime requirements vs percent secondary sludge.

19

SECTION 6

TEST RESULTS - DEWATERING UNITS

DIAPHRAGM FILTER PRESS (VARIABLE VOLUME PRESS)

The diaphragm-type f i l t e r p r e s s , a r e l a t i v e l y new innovat ion i n t h e wastewater t reatment i n d u s t r y i n t h e United S t a t e s , was t e s t e d most exten- s i v e l y during t h e study.

NGK Diaphragm Pres s

NGK I n s u l a t o r s , Nagoya, Japan, has been manufacturing and marketing a diaphragm-type f i l t e r p r e s s i n Japan f o r s e v e r a l yea r s . A p i l o t - s c a l e model of t h e i r NR-PF-I1 f i l t e r p r e s s was provided t o t h e District f o r t h e d u r a t i o n of t h e s tudy. This u n i t w a s used no t only t o provide design parameters f o r a diaphragm p r e s s , but a l s o t o s tudy several o t h e r f a c t o r s a s s o c i a t e d wi th any s ludge dewatering ope ra t ion . Envirex Corporation, Waukesha, Wisconsin, has s i n c e purchased t h e r i g h t s t o manufacture and market t h i s p r e s s i n t h e United S t a t e s .

F a c i l i t i e s - - The f i l t e r p r e s s system included t h e fol lowing equipment:

1. 2 p r e s s - 5.8 m2 (62.4 f t w i th twelve 800 mm (31.5 inches ) squa re p l a t e s . p l a t e s w a s 25 mm (1.0 inch ) . rubber diaphragms. A s i s t y p i c a l of f i l t e r p r e s s e s , t h e s u r f a c e of t h e p l a t e behind t h e f i l t e r c l o t h resembles t h e s u r f a c e of a w a f f l e i r o n , t o a l low removal of f i l t r a t e t h a t pas ses through t h e f i l t e r c l o t h . The s u r f a c e of t h e rubber diaphragm i n c o n t a c t w i th t h e f i l t e r c l o t h a l s o has a r a i s e d g r i d p a t t e r n f o r t h i s purpose. The p r e s s w a s equipped w i t h a hydrau l i c c l o s i n g mechanism and an overhead c l o t h v i b r a t i n g and washing u n i t .

f i l t r a t i o n area. Contained s i x chambers, Spacing between

Every o t h e r p l a t e was equipped w i t h

See F igu re 4 .

2 . Sludge mix t ank - 1.0 m3 (264 g a l l o n ) t ank , w i th var iable-speed mixer, equipped wi th t h r e e turbine-wing type a g i t a t o r b l ades . See Figure 5 .

3. Pump assembly - sludge f eed pump, squeezing water pump, and c l o t h washing pump. See F igu re 6 .

a. Feed pump - a diaphragm-type p i s t o n sump r a t e d a t 100 l /min (26 gpm) and p r e s s u r e s up t o 7 kg/cm (100 p s i g ) .

20

Figure 4 . NGK Diaphragm Press.

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39'l 4 Figure 5. NGK sludge mix tank,

2 1

Figure 6. NGK pump assembly.

Figure 7 . NGK c o n t r o l pane l .

22

b. Squeezing water pump - a mult i -s tage t u r b i n e pump rated a t 60 l /min (15.8 gpm) and p r e s s u r e s up t o 17.9 kg/cm2 (255 p s i g ) .

c . Cloth washing pump - plunger-type pump r a t e d a t 92 l /min (24 gpm) and p r e s s u r e s up t o 70 kg/cm2 (1000 PSig).

4. Water s t o r a g e t ank - 500 1 (132 g a l l o n s ) .

5. A i r compressors - wi th r e c e i v e r s (two), each r a t e d a t 7 kg/cm2 (100 p s i g ) f o r o p e r a t i n g b a l l va lves and c o r e blowing.

6. Control pane l - wi th r e l a y s , t i m e r s , etc. Allowed e i t h e r a t o t a l l y automatic o r manual mode of ope ra t ion . See F igu re 7.

The Dis t r ic t provided t h e fol lowing equipment t o complete t h e system.

1. Primary s ludge t h i c k e n e r - t o t 1 volum of 28.4 m3 (7500 g a l ) and overflow s u r f a c e area of 8.9 m2 (96 f t 5 ).

-2. Secondary s ludge t h i c k e n e r - t t a l v o l me of 20.8 m3 (5500 g a l ) and overflow s u r f a c e area of 6.0 m9 (65 f t j ) .

3. Moyno t r a n s f e r pumps - (two) each r a t e d a t 37.8 l /min (10 gpm).

4 . Lime s l u r r y makeup and s t o r a g e t ank - 757 1 (200 g a l ) w i th a g i t a t o r .

5. F e r r i c c h l o r i d e makeup and s t o r a g e t ank - 378 1 (100 g a l ) .

6. Batch feed t anks - f e r r i c c h l o r i d e t ank , 37.8 1 (10 g a l ) ; l i m e t a n k , 56.8 1 (15 g a l ) .

7. Ca l ib ra t ed f i l t r a t e c o l l e c t i o n t anks - 378 1 (100 g a l ) and 56.8 1 (15 g a l ) .

Operat ion--

and cake d i scha rge ope ra t ions . A t y p i c a l c y c l e was as fol lows. A complete c y c l e f o r t h e NGK f i l t e r p r e s s included pumping, squeezing,

See F igu re 8.

Primary and secondary sludges were pumped into the sludge mix tank at t h e d e s i r e d test r a t i o . S o l i d s con ten t of t h e mix w a s measured and t h e chemical dosage computed as a percentage of dry s ludge s o l i d s . 5-10% by weight of dry s ludge s o l i d s ) w a s added by g r a v i t y and mixed i n a t an a g i t a t o r speed of approximately 95 RPM. Lime (usua l ly 15-30% by weight of dry s ludge s o l i d s ) w a s a l s o added by g r a v i t y and mixed i n a t 95 RPM. v i s u a l examination showed t h e chemicals t o be w e l l mixed (about 10-15 min- u t e s ) , t h e mixer w a s slowed t o a speed j u s t s u f f i c i e n t t o prevent s t r a t i f i c a - t i o n ( approximatly 28 RPM). a c t u a t i n g t h e hydrau l i c u n i t , which he ld a cons t an t p r e s s u r e of 200 kg/cmz (2844 PSig) on t h e p l a t e s du r ing t h e e n t i r e p r e s s cyc le . The f i l t r a t i o n c y c l e began when t h e s ludge f eed pump w a s s t a r t e d . Pumping t i m e w a s normally 10 t o 20 min- u t e s , a l lowing a sludge f eed of 227 t o 303 liters (50 t o 80 g a l ) .

FeC13 (usua l ly

A f t e r

The f i l t e r p r e s s w a s c losed b

F igu re 9

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shows a d e t a i l e d view of t h e f i l t r a t i o n ope ra t ion . bottom feed p o r t i n t o t h e empty chamber. c l o t h s t o c o l l e c t i o n p o r t s on t h e ends of t h e p l a t e s . A t t h e end of t h e pumping cyc le , t h e squeezing pump was s t a r t e d immediately t o p r e s s u r i z e t h e diaphragm. Squeezing t i m e w a s u s u a l l y 10-25 minutes a t a p r e s s u r e of 15 kg/cm2 (213 p s i g ) . t h e rubber diaphragm behind one of t h e c l o t h s i n each chamber. compressed t o approximately h a l f its o r i g i n a l t h i ckness as t h e f i l t r a t e pas ses through both c l o t h s .

Sludge i s f e d through a F i l t e r e d water pas ses through both

Figure 9 a l s o shows how t h e p r e s s u r i z e d water expands The cake i s

A t t h e end of t h e squeezing c y c l e , t h e s ludge f eed l i n e s and f i l t r a t e l i n e s were blown o u t w i th p r e s s u r i z e d a i r . p l a t e s h i f t e r c a r r i a g e moved two p l a t e s i n t o p o s i t i o n f o r cake discharging. The overhead v i b r a t i n g u n i t subsequently pos i t i oned i t s e l f over t h e s e two p l a t e s , lowered i t s two v i b r a t i n g shoes onto t h e c l o t h support b a r s , and shook t h e f o u r c l o t h s wi th an e c c e n t r i c cam a c t i o n , thereby d i scha rg ing two cakes. The s h i f t e r c a r r i a g e then moved ano the r two p l a t e s and t h e p rocess repeated au tomat i ca l ly . The p i l o t u n i t discharged s i x cakes, each measuring 686 mm (27 i nches ) squa re and approximately 1 3 mm (0.5 inch ) t h i c k . A t t h e end of t h e d i scha rge c y c l e , t h e s h i f t e r c a r r i a g e , t h e v i b r a t i n g u n i t and t h e p l a t e s a l l moved back i n t o p o s i t i o n , ready f o r ano the r run. c l o t h washing c y c l e w a s i n i t i a t e d when r equ i r ed . The c y c l e w a s a l s o com- p l e t e l y automatic and similar i n o p e r a t i o n t o t h a t of t h e cake discharge. The overhead v i b r a t i n g and wash u n i t w a s equipped w i t h two spray b a r s , which washed f o u r c l o t h s a t one t i m e . evening, and depending on t h e type of tests, a f t e r each run. Figure 10 shows d e t a i l e d views of both t h e cake d i scha rge and washing ope ra t ions . The c l o t h s are a t t a c h e d t o t h e p l a t e s a t t h e bottom bu t are suspended from s p r i n g s a t t h e top. t h e d i scha rg ing and washing ope ra t ions .

The p r e s s ram w a s opened and t h e

A t t h i s p o i n t , t h e

The c l o t h s were washed each morning and

The c l o t h moves away from t h e top of t h e p l a t e t o f a c i l i t a t e both

Data s h e e t s 1 through 4 i n Appendix B were used i n r eco rd ing d a t a f o r t h e test runs. Raw d a t a w a s recorded on s h e e t s 1 through 3 and r e s u l t s summarized on d a t a s h e e t 4 . The d a t a s h e e t s are f i l l e d ou t f o r a t y p i c a l set of runs, w i th c a l c u l a t i o n s d e t a i l e d i n an accompanying explanat ion.

T e s t Data t o E s t a b l i s h Design Parameters-- In o r d e r t o develop design parameters f o r t h e dewatering of a 5% s o l i d s

s ludge t o produce a 35% s o l i d s cake on a diaphragm f i l t e r p r e s s , t h e follow- i n g parameters should be optimized:

1. 2. 3. 4 . 5. 6 . 7. 8.

Chemical requirements Feed pump p r e s s u r e Pumping t i m e Squeezing p r e s s u r e Squeezing t i m e F i l t r a t e q u a l i t y F i l t e r c l o t h s e l e c t i o n F i l t e r yield--as a f u n c t i o n of a l l of t h e above.

Because of t h e c o n s t a n t l y changing f i l t r a t i o n c h a r a c t e r i s t i c s of t h e s ludge, i t w a s extremely d i f f i c u l t t o compare test r e s u l t s from one day

26

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wi th those of another . Consequently, i t became necessary t o t r y t o c o l l e c t enough d a t a f o r a good comparison s tudy of t h e s e parameters from t h e same ba tch of s ludge, p r e f e r a b l y i n one days' t i m e . t h e methods used t o opt imize each of t h e parameters. y i e l d d i s c u s s e s average o v e r a l l r e s u l t s f o r t h e 2 / 1 secondary/primary s ludge.

The fol lowing s e c t i o n s d i s c u s s The s e c t i o n on f i l t e r

Chemical requirements--Generally, t h e r e are t h r e e p o s s i b l e ranges of chemical condi t ioning:

1. me level of lime/FeC13 dosages below which no dewatering w i l l occur. It is obvious t h a t t h i s l e v e l must be de f ined and a p p r o p r i a t e measures taken t o i n s u r e t h a t a l l s ludges are condi t ioned above it . Adding underconditioned s ludge t o a p r e s s w i l l cause many wasted manhours i n c l o t h r e juvena t ion , e i t h e r by high p r e s s u r e spray wash- i n g o r a c i d washing.

2. The level of chemical dosages i n t h e optimum range where good f i l t r a t i o n w i l l occur. g i v e s l i g h t l y h ighe r cake s o l i d s and f i l t e r y i e l d s . i n s t a l l a t i o n , t h e o p e r a t o r can choose t o o p e r a t e a t t h e upper o r lower end of t h i s range depending on s ludge q u a n t i t i e s t o be f i l - t e r e d . Obviously, c o s t s av ings i n chemical w i l l i n s p i r e t h e operator t o s t a y i n t h e lower end of t h e range as much as poss ib l e .

Higher chemical dosages w i t h i n t h i s range A t a p a r t i c u l a r

3. The level of chemical dosages a t very h igh lime/FeClg a d d i t i o n where t h e chemicals are overdosed bu t dewatering r e a d i l y occurs . a very s a f e level f o r ope ra t ion , w i th very l i t t l e chance of p r e s s f a i l u r e bu t chemical c o s t s are extremely high. The inc reased q u a n t i t i e s of i n e r t s o l i d s . i n t h e f i n a l cake a l s o r e s u l t i n decreased y i e l d s and could cause problems i n f u r t h e r processing.

This is

Table 5 shows t h e ef , fect of varying chemical dosages on t h e major f i l t e r p r e s s parameters , f i n a l cake s o l i d s content and f i l t e r y i e l d . Fu l l - sca l e y i e l d is de f ined as t h e weight of s ludge s o l i d s p e r square meter of f i l t r a t i o n area p e r hour. The t o t a l c y c l e t i m e used i n c a l c u l a t i n g t h i s f u l l - s c a l e y i e l d inc ludes t h e pumping and squeezing t i m e s p l u s 1 9 minutes mechanical t u rn - around t i m e (based on t h e manufacturer 's recommendation f o r t h e i r l a r g e s t p r e s s ) . See Appendix B, Explanation of Data Sheet 4. The runs on 2/18, 2/23, 3/4, 7/12 and 6/23 c l e a r l y show l e v e l s a t which t h e s ludge w i l l not dewater. With a l l of t h e s e poorly condi t ioned runs, t h e f i l t e r c l o t h s r equ i r ed cons ide rab le c leaning. dewatering, h ighe r chemical dosages gene ra l ly gave e i t h e r h ighe r cake s o l i d s and/or h ighe r y i e l d s . an i n c r e a s e of 5 percentage p o i n t s of l i m e and 2 of FeC13 can g ive a 20% i n c r e a s e i n f u l l - s c a l e y i e l d . But, i f t h e o b j e c t i v e i s t o o b t a i n a s p e c i f i c cake s o l i d s con ten t , f o r example 35%, a t minmum chemical a d d i t i o n , a p o i n t is reached beyond which chemical a d d i t i o n i s was te fu l . show t h a t no b e n e f i t i n y i e l d is gained by i n c r e a s i n g t h e chemical dosage above 22.8% lime/6.7% FeC13. lime/13.3% FeC13) a c t u a l l y showed a decreased y i e l d because of t h e q u a n t i t y of i n e r t chemicals i n t h e f i n a l s ludge cake.

I n cases where t h e cond i t ion ing w a s adequate f o r

Examination of t h e d a t a shows t h a t on t h e average,

The runs on 3/10

I n f a c t , t h e very h igh dosages (45.5%

28

Chemical dosage w a s , i n summary, l a r g e l y a func t ion of t h e s ludge c h a r a c t e r i s t i c s e x i s t i n g a t t h e t i m e . t r i a l - and-e r ro r procedure t h a t must be performed on each ba tch of s ludge t o be f i l t e r e d . Suction Time meter can a i d i n d e f i n i n g t h i s dosage. discussed f u r t h e r i n t h e s e c t i o n on s p e c i f i c r e s i s t a n c e tests.

Es tab l i sh ing t h e proper dosage is a

A simple Buchner funnel t es t and t h e use of t h e C a p i l l a r y These methods are

Feed pump pressure--The s ludge feed pump supp l i ed wi th t h e NGK p r e s s w a s capable of d e l i v e r i n g p r e s s u r e s from 3 t o 7 kg/cm2 (43 t o 100 p s i g ) . Numerous tests t o opt imize t h e t e rmina l pump p r e s s u r e were inconclusive. The more d i f f i c u l t s ludges gene ra l ly would g ive h ighe r f i l t e r y i e l d s i f t h e pump p r e s s u r e s w e r e above 5 kg/cm2 (71 p s i g ) . The easier t o f i l t e r s ludges, such as t h o s e wi th h igh primary r a t i o s , could be handled wi th lower p re s su res of 3 kg/cm2 (43 p s i g ) . I n l a r g e i n s t a l l a t i o n s , op t imiza t ion of pump p r e s s u r e should be done under continuous o p e r a t i n g c o n d i t i o n s , while cons ide r ing f i l t e r y i e l d , chemical cond i t ion ing requirements, and e s p e c i a l l y , f i l t e r c l o t h l i f e .

Pumping time--With a diaphragm p r e s s , t h e pumping as w e l l as t h e squeez- i n g c y c l e t i m e must be optimized so t h a t t h e f i l t e r y i e l d w i l l be maximized. The aatomatic c o n t r o l system supp l i ed wi th t h e p r e s s provided t h e op t ion of o p e r a t i n g wi th a p r e s e t pumping t i m e f o r each cycle . This mode of ope ra t ion is b e s t , however, only i f t h e s ludge f i l t e r a b i l i t y does no t change, i .e. , i f a cons t an t lime/FeC13 dosage g ives c o n s i s t e n t r e s u l t s on t h e f i l t e r p r e s s . With t h e Blue P l a i n s s ludge , t h i s w a s not t h e case. hence, r equ i r ed chemical dosages v a r i e d almost d a i l y . With some s ludges a pumping t i m e of 5 minutes was s u f f i c i e n t ; w i th o t h e r s , 25 minutes w a s b e s t . Figure 11 shows t h e v a r i a t i o n of t o t a l feed volume wi th t i m e i n s e v e r a l p r e s s runs wi th d i f f e r e n t levels of cond i t ion ing . Data f o r t h e s e runs of 3/4/77 are shown i n Table 5. For runs 1 and 2 i n which t h e s ludge w a s w e l l condi t ioned, t h e f eed rate remained q u i t e high (over 5 gpm) u n t i l t h e n i n t h minute. A f t e r t h a t t i m e , t h e s l o p e s began t o f l a t t e n ou t as t h e r e s i s t a n c e t o f i l t r a t i o n s t a r t e d t o inc rease . t h e feed rate dropped o f f and t h e r e s i s t a n c e t o f i l t r a t i o n began t o i n c r e a s e a f t e r only t h e f o u r t h minute.

Sludge f i l t e r a b i l i t y and,

I n run 3, a poorly condi t ioned s ludge ,

I n a diaphragm-type p r e s s , t h e pumping c y c l e is used p r i m a r i l y f o r adding f i l t e r a b l e s o l i d s t o t h e p r e s s , and t h e pumping c y c l e t i m e should be optimized t o t h i s end. For example, i n Table 6, s e v e r a l runs are shown f o r 4/1/77 and 4/6/77 i n which success ive ly longer pump t i m e s were used. t h e pump c y c l e w a s extended, a g r e a t e r q u a n t i t y of s o l i d s was added t o t h e p r e s s (as evidenced by cake dry weights) . Notice, though, t h a t a correspond- i n g i n c r e a s e i n y i e l d w a s n o t obtained. The key t o opt imizing t h e pumping cyc le , i.e. t o o b t a i n t h e maximum y i e l d f o r maximum s o l i d s inpu t t o t h e p r e s s , l i es i n knowing t h e s o l i d s a d d i t i o n rate f o r each success ive minute of pumping. t h e p r e s s (kg /h r ) , t hen t h e pumping c y c l e should be terminated. Determination of t h i s rate w a s made f o r a gene ra l i zed s ludge feed t o t h e NGK p r e s s and w a s c o r r e l a t e d t o a t e rmina l s ludge volume rate.

I n each case, as

Once t h i s rate drops below t h e expected average s o l i d s y i e l d on

From e a r l y test work, w e e s t a b l i s h e d an average ra te of 2.4 kg t o t a l sol ids/hr /m2 (0.5 I b / h r / f t 2 ) as a reasonable product ion rate f o r a f u l l - s c a l e

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3.4 k P s o l i d s / h r l & x 5.8 m2= .23 kg so l id s /min (.51 lb/min) 60 min/hr

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100 kg t o t a l feed 7.5 kg s o l i d s 1.02 x 1 k g / l

- 2 3 kg so l id s /min x = 3.0 l /min feed ( .8 gpm)

This t e rmina l pumping rate, through c a l i b r a t i o n of t h e NGK mix t ank , w a s found t o be equ iva len t t o 1/8 inch p e r minute. a f t e r 4/28/77) when t h e s ludge flow rate dropped t o 1/8 inch p e r minute f o r t h r e e consecut ive minutes, t h e pumping c y c l e w a s terminated. output of t h e s ludge f eed pump and t h e d i f f i c u l t i e s i n measuring 1/8 i nch n e c e s s i t a t e d a t h r e e minute t i m e t o ensu re t h a t a good measurement w a s taken.

During la ter test work ( i . e .

The v a r i a b l e

The runs on 5/19/77 (Table 6 ) show t h e e f f e c t s of t h i s procedure on t h r e e d i f f e r e n t l e v e l s of s ludge cond i t ion ing . t i o n i n g , gave a high y i e l d wi th a r a t h e r long pump t i m e of 19 minutes (low cake s o l i d s r e s u l t e d from an e r r o r i n t h e determinat ion of t h e squeezing rime). The second run w a s s t i l l w i t h good cond i t ion ing and a h igh y i e l d r e s u l t e d . The t h i r d run, w i t h marginal cond i t ion ing , achieved t h e r equ i r ed pumping rate i n only 13 minutes. s ludge w a s n o t w e l l condi t ioned. s l i g h t l y longer t i m e , so t h a t a good cake release would r e s u l t .

The f i r s t run, w i th good condi-

This i n d i c a t e d t o t h e o p e r a t o r s t h a t t h e It was then necessary t o squeeze f o r a

A secondary advantage of u s ing t h i s procedure involved t h e response of t h e p r e s s t o poorly condi t ioned s ludges. t i oned s ludge, t h i s rate w a s u s u a l l y achieved i n 5 t o 10 minutes and a t h i n cake w a s produced. This t h i n cake, however, would f u r t h e r dewater under extended squeezing t i m e s and t h u s g i v e a good d i scha rge from t h e f i l t e r c l o t h . Earlier runs showed t h a t poorly condi t ioned s ludge , when allowed t o form a t h i c k cake, d i d no t dewater w e l l under extended squeezing and cake s t i c k i n g and r e s u l t a n t c l o t h b l i n d i n g occurred. This new o p e r a t i o n a l procedure t h u s gave a way f o r t h e f i l t e r p r e s s t o compensate f o r e r r o r s t h a t had occurred i n t h e cond i t ion ing s t e p . This same method, a p p l i e d t o a w e l l condi t ioned s ludge produced a t h i c k cake wi th maximized y i e l d . In e f f e c t , t h i s method gave t h e b e s t f i l t e r performance f o r t h e s ludge and cond i t ion ing a v a i l a b l e .

I n gene ra l , w i th a poorly condi-

Recognizing t h e problems w i t h in s t rumen ta t ion t h a t could occur i n ob ta in - i n g a s ludge flow rate on a l a r g e r f i l t e r p r e s s , we examined two o t h e r methods f o r opt imizing t h e pump t i m e : 1) rate of pump p r e s s u r e bui ldup and 2) f i l t r a t e flow rate. i n d i c a t i o n of t h e r e s i s t a n c e t o f i l t r a t i o n t h a t e x i s t s during t h e dewatering process . It can be used t o i n d i c a t e a poorly condi t ioned s ludge and alert t h e o p e r a t o r t o t a k e c o r r e c t i v e a c t i o n . It cannot be used, however, t o d e f i n e t h e c y c l e endpoint f o r a w e l l condi t ioned sludge. I n Figure 12 , t h e f eed p r e s s u r e curves f o r t h e runs of 3/4/77 are shown. s ludge (Run #l) b u i l t up p r e s s u r e slowly, i n d i c a t i n g l i t t l e r e s i s t a n c e t o f i l t r a t i o n . At t h e end of t h e pumping c y c l e (16 minute mark), t h e p r e s s u r e

The rate of f eed pump p r e s s u r e bui ldup g ives an

The bes t - cond i t ioned

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35

w a s s t i l l r i s i n g a t a s t eady rate. The under-conditioned s l u d e (Run #3) b u i l t up p r e s s u r e very r a p i d l y . t h e p r e s s u r e reached a l i m i t i n g va lue w e l l be fo re t h e end of t h e c y c l e ( a l s o 16 minute mark).

Res i s t ance t o f i l t r a t i o n w a s t i g h and

The f i l t r a t e f low-rate i s an e a s i l y measured parameter and a c o r r e l a t i o n which would determine t h e end of t h e pumping c y c l e can be r e a d i l y developed from t h e f i l t r a t e flow rate d a t a c o l l e c t e d . Figure 13, f o r example, shows t h e f i l t r a t e c o l l e c t e d v s t i m e f o r t h e 3/4/77 runs. A t t h e 16 minute mark ( t h e end of t h e pump c y c l e ) , Runs 111 and #2 s t i l l had a f a i r l y s t e e p s l o p e , whereas Run f 3 had a l r e a d y begun t o f l a t t e n ou t . s i n c e f i l t r a t e f o r run #1 and #2 w a s s t i l l being discharged a t a h igh rate a t t h e end of t h e c y c l e , had t h e pumping t i m e s f o r t h e s e runs been extended h ighe r y i e l d s would have r e s u l t e d . Run f 3 pumping, though, should have been terminated nea r t h e 8 minute mark, where t h e s l o p e began t o f l a t t e n o u t .

These curves show t h a t

Because of t h e need t o test d i f f e r e n t r a t i o s of blended s ludges and v a r i a b l e t e rmina l pump p r e s s u r e s , w e decided t o use t h e more d i r e c t method of measuring t h e s ludge f eed rate t o determine t h e end of t h e pumping cycle . On a f u l l - s c a l e i n s t a l l a t i o n , however, e i t h e r s ludge f eed rate o r f i l t r a t e flow rate could be used.

Squeezing pressure--The squeezing p r e s s u r e w a s developed by applying

However, p r e s s u r i z e d water t o t h e diaphragms. During s t a r t u p , t h e NGK eng inee r s recommended t h a t t h e p r e s s be ope ra t ed a t 15 kg/cm2 t h e pump could d e l i v e r any p r e s s u r e up t o 17.6 kg/cmb (250 p s i g ) . Numerous tests were run throughout t h e s tudy pe r iod t o t r y t o opt imize t h e squeezing p r e s s u r e l e v e l and t h e rate a t which it w a s appl ied. None of t h e tests showed a marked d i f f e r e n c e i n f i n a l cake s o l i d s o r squeezing t i m e ove r t h e range of 7 t o 17.6 kg/cm2 (100 t o 250 p s i g ) . t o dewater independently of p r e s s u r e w i t h i n t h i s range. ope ra t ion , t h e f u l l p r e s s u r e w a s app l i ed t o t h e diaphragm immediately a f t e r t h e s ludge pump stopped. Tests were a l s o run applying t h e p r e s s u r e i n s t e p increments up t o t h e f i n a l squeezing p res su re . Again, no d i f f e r e n c e i n r e s u l t s could be determined. Therefore, i n n e a r l y a l l t h e p r e s s runs a squeezing p r e s s u r e of 15 kg/cm2 (213 p s i g ) , a p p l i e d ae per the manufacturer ' s design, was used.

213 p s i g ) .

The Blue P l a i n s s ludge appeared Under normal

Squeezing time--In an optimum pumping c y c l e f o r a w e l l condi t ioned s ludge i n t h e NGK p r e s s , approximately 75-85% of t h e f i l t r a t e w i l l be c o l l e c t e d during pumping. The squeezing c y c l e is then r e a l l y a cake conso l ida t ion s t e p removing r e l a t i v e l y small q u a n t i t i e s of f i l t r a t e . General ly , t h e squeezing c y c l e i n c r e a s e s t h e cake s o l i d s from approximately 20% a t t h e end of pumping t o 35-40% s o l i d s be fo re discharging. f o r example, shows t h e r e s u l t s of tests run on 4/13/77. t h e lime/FeC13 dosage w a s 20.7%/6.2%; t h e pump t i m e w a s 18 minutes. squeeze t i m e w a s i nc reased from 5 t o 25 minutes, t h e cake s o l i d s inc reased from 25% t o over 4 0 % , w i t h a corresponding dec rease i n p rocess y i e l d .

F igu re 1 4 , For t h e s e f i v e runs

As t h e

During t h e i n i t i a l p a r t of t h e s tudy ( p r i o r t o 4/28/77), t h e squeezing t i m e w a s p r e s e t by t h e ope ra to r . As w i t h t h e pumping t i m e , however, t h i s method w a s good only i f t h e s ludge and cond i t ion ing remained cons t an t . With

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a w e l l condi t ioned s ludge, squeezing t i m e s of 8 t o 10 minutes were normally s u f f i c i e n t t o produce t h e r equ i r ed 35% s o l i d s cake; w i t h t h e marginal ly condi t ioned s ludges squeezing t i m e s of over 20 minutes were requ i r ed t o reach t h i s l e v e l . Examination of many p r e s s runs showed a c o r r e l a t i o n between t h e t e rmina l f i l t r a t e flow rate and f i n a l cake s o l i d s . The d a t a from t h e runs on 4/13/77 is t y p i c a l :

Squeeze T i m e (min) % cake s o l i d s Terminal f i l t r a t e rate l /min (gpm)

5 10 15 20 25

25.5 31.3 35.0 37.3 40.6

3.78 (1.00) 1.89 (0.50) 0.87 (0.23) 0.57 (0.15) 0.00 (0.00)

Based on r e s u l t s such as t h e s e , a procedure w a s developed t o ensu re f i n a l cake s o l i d s of 35% f o r each run. Beginning on 4/28/77, a f t e r pumping t h e sJudge f eed t o a rate of 3.0 l /min, t h e squeezing c y c l e w a s extended u n t i l a t e rmina l f i l t r a t e rate of 0.57 l /min (0.15 gpm) was obtained. When t h i s rate he ld s t eady f o r t h r e e consecut ive minutes ( t o o b t a i n good measurement), t h e squeezing c y c l e w a s terminated. t e rmina l rate method worked w e l l w i t h all levels of condi t ioned sludge. F igu re 15 shows t h e f i l t r a t e curves on t h r e e l e v e l s of cond i t ion ing 100% secondary s ludge f o r t h i s procedure. i n Table 5. a t an average l e v e l , and Run #3 w a s marginal ly conditioned. t h e p r e s s c y c l e w a s t h e optimum f o r t h e type of s ludge dewatered; cake s o l i d s of about 35% r e s u l t e d f o r each run.

Subsequent tests showed t h a t t h i s

Data f o r t h e s e 11/1/77 runs are included Run #l.was s l i g h t l y over-conditioned; Run 8 2 w a s condi t ioned

I n each case

F i l t r a t e quality---The o v e r a l l q u a l i t y of t h e f i l t r a t e i s a f f e c t e d no t only by t h e s e l e c t i o n of c l o t h , bu t a l s o by t h e chemical cond i t ion ing . Normally, only t o t a l s o l i d s and suspended s o l i d s were analyzed on f i l t r a t e samples. On 3/8/77, tests were run t o c h a r a c t e r i z e t h e f i l t r a t e f o r o t h e r parameters. The f i l t e r c l o t h w a s n o t washed between these e i g h t r u n s , so t h a t a normal p l a n t o p e r a t i o n would be s imulated. Feed s o l i d s were 6.0% on a 1/1 r a t i o of secondary/primary sludge. Cycle t i m e f o r each of t h e runs w a s 16 minutes pumping and 8 minutes squeezing. Table 7 shows t h e f i l t r a t e parameters analyzed. Because of f i l t r a t i o n d i f f i c u l t i e s a t t h a t t i m e , a l l runs were made wi th high chemical dosages. Each of t h e p o l l u t a n t levels is c o n s i s t e n t w i t h t h a t f o r a water i n c o n t a c t w i th undigested sludge. The average pe rcen t t o t a l v o l a t i l e s o l i d s i n t h e f i l t r a t e w a s 24.8%, i n d i c a t i n g a high s o l u b l e chemical con ten t (mostly l ime). The average pe rcen t v o l a t i l e suspended s o l i d s w a s 60%, i n d i c a t i n g t h a t f i l t r a t e suspended s o l i d s were mostly organic .

Fu r the r tests were conducted t o determine t h e e f f e c t that chemical cond i t ion ing had on f i l t r a t e q u a l i t y . on 3/10/77 were w e l l condi t ioned and gave good cake r e s u l t s . Note t h a t t h e f i l t r a t e t o t a l s o l i d s (mostly l i m e ) decreased as t h e chemical a d d i t i o n rate decreased. The las t run was underconditioned and gave poor cake r e s u l t s and

See Table 8. The f i r s t t h r e e runs

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High f i l t r a t e suspended s o l i d s were common The f i n e p a r t i c l e s were n o t w e l l f l o c c u l a t e d

The runs on 11/1/77 show i d e n t i c a l

The fol lowing t y p i c a l run shows t h e f i l t r a t e s o l i d s as sampled a t va r ious t i m e i n t e r v a l s during t h e pumping cycle . #1 on 5/3/77 shown i n Table 5.

T i m e (min)

1.5 3.0 5.0

10.0 . 18.0

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mg/l

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mg/1

716 550

55 45 19

The t h e i n i t i a l f i l t r a t i o n being through t h e c l o t h . t h e chambers, t h e accumulated s o l i d s then act as t h e primary f i l t e r media. The composite sample of f i l t r a t e du r ing t h e pumping c y c l e averaged 7826 mg/l t o t a l s o l i d s and 308 mg/l suspended s o l i d s . same run showed 7713 mg/l t o t a l s o l i d s and t h a t t h e suspended s o l i d s were lower f o r t h e squeezing c y c l e than f o r t h e pumping cycle . (Table 8) show several cases i n which t h e f i l t r a t e c o l l e c t e d from t h e pumping and squeezing c y c l e s were analyzed s e p a r a t e l y .

suspended s o l i d s drop o f f r a p i d l y a f t e r t h r e e minutes. This i s due t o Once a - c a k e is formed i n

The squeezing c y c l e f o r t h e 50 mg/l suspended s o l i d s . Note

This w a s t r u e f o r a l l t h e p r e s s runs. The runs on 7/12/77

F i l t e r c l o t h eva lua t ion - -F i l t e r c l o t h s e l e c t i o n depends on r e s i s t a n c e t o wear and ab ras ion , t h e ease of cake release, and f i l t r a t e q u a l i t y d e s i r e d . Three d i f f e r e n t f i l t e r c l o t h s were supp l i ed wi th t h e NGK f i l t e r p r e s s , each of which w a s t e s t e d du r ing t h e s tudy. made and t h e method of o p e r a t i o n (day t i m e o n l y ) , r e s i s t a n c e t o wear and ab ras ion could no t be determined by t h i s s tudy. are given i n Table 9.

Because of t h e l i m i t e d number of runs

Cloth media s p e c i f i c a t i o n s

TABLE 9. NGK FILTER CLOTHS

A I R PERMEABILITY MATERIAL a t A P = 12.7 m y H20

TYPE CONSTRUCTION WARP /FILLING ~ m 3 / ~ e c / ~ m

NY 516 P l a i n polyamide/polypropylene 4 ..o TR 520 Herringbone p o l y e s t e r / p o l y e s t e r 11.0

t w i l l NY 51-4 T w i l l polyamide/polyester 93.0

42

The NY 516 c l o t h , t h e t i g h t e s t weave, w a s t h e f i r s t c l o t h t e s t e d . A t o t a l of 151 runs (5/26/76 t h r u 11/1/76) were made on t h i s c l o t h , mostly wi th p l a n t thickened sludge. F i l t r a t e ana lyses f o r 71 of t h e s e runs showed e x c e l l e n t r e s u l t s w i th an average of 16.7 mg/l suspended s o l i d s . Cake discharge, however, w a s n o t always t h e b e s t . For n e a r l y a l l t h e runs, except t hose t h a t were over condi t ioned, t h e c l o t h shaker w a s needed f o r cake discharge. The c l o t h s u r f a c e was rough and p a r t i c l e s of cake tended t o s t i c k . Underconditioned s ludges bl inded t h e c l o t h very r e a d i l y and excess ive scrubbing w a s required. The c l o t h washing system, ope ra t ed a t 350 p s i g , d i d l i t t l e t o r e juvena te t h e c l o t h a f t e r such a run. Res i s t ance t o ab ras ion and wear seemed t o be very high.

The second type c l o t h t e s t e d was t h e NY 51-4 media. and a very smooth s u r f a c e .

This c l o t h had t h e most open weave With t h e except ion of very poorly condi t ioned s ludges , cake d i scha rge w a s almost always good. The f i r s t set of NY 51-4 c l o t h s , operated from 11/2/75 through 4/7/77, were worn badly a f t e r 182 runs due t o over-zealous brushing wh i l e c l ean ing . brushing w a s r equ i r ed du r ing e a r l y 1977 when d i f f i c u l t i e s were encountered wi th dewatering t h e sludge. f o r 213 runs from 4/8/77 t o 10/7/77. both NY 51-4 c l o t h s averaged 525 mg/l suspended s o l i d s on a l l t ypes of s ludge. This c l o t h gave t h e b e s t o v e r a l l cake s o l i d s , s i n c e i t provided l i t t l e r e s i s t a n c e t o f i l t r a t i o n . F i l t r a t e q u a l i t y w a s , however, a drawback. The c l o t h a l s o seemed t o show l i t t l e r e s i s t a n c e t o w e a r . The second set were beginning t o tear i n p l a c e s a f t e r only 130 runs, bu t t h i s may have been due t o t h e a l t e r n a t e we t t ing and drying (which i s known t o s t r e t c h f i b e r s ) caused by our o p e r a t i o n a l schedule. is r equ i r ed be fo re any d e f i n i t e conclusions can be made.

The

The second set of NY 51-4 c l o t h s were operated F i l t r a t e ana lyses on 271 samples wi th

Fur the r eva lua t ion on a continuous b a s i s

The TR 520 c l o t h s were t e s t e d from 10/13/77 through 11/30/77 f o r a t o t a l of 80 runs. Only 22 of t h e s e runs were analyzed f o r f i l t r a t e q u a l i t y g iv ing 52.4 mg/l suspended s o l i d s . Even though t h i s w a s a t e x t u r e d , heavy c l o t h , cake d i scha rge w a s excellent--equal t o t h e NY 51-4 c l o t h . S u f f i c i e n t runs t o determine ab ras ion r e s i s t a n c e were n o t made, bu t t h e c l o t h seemed t o be more s t u r d y than t h e NY 51-4 c l o t h . b e s t compromise f o r both good d i scha rge and accep tab le f i l t r a t e q u a l i t y .

The TR 520 c l o t h appears t o provide t h e

Cloth washing requirements are more a f u n c t i o n of chemical cond i t ion ing than c l o t h s e l e c t i o n . were made on each of t h e c l o t h s b e f o r e they r equ i r ed washing. The c l o t h washing system, wh i l e designed t o o p e r a t e a t 70 kg/cm2 (1000 p s i g ) , only produced a maximum p r e s s u r e of 24.6 kg/cm2 (350 p s i g ) . gage and r e g u l a t o r valve caused t h i s problem bu t w a s no t discovered u n t i l all tests were completed.

When t h e cond i t ion ing w a s optimum, up t o 15 runs

A d e f e c t i v e p r e s s u r e

F i l t e r yield--A major purpose of t h e s tudy w a s t o develop design parameters t o dewater a 2 / 1 r a t i o of secondary/primary s ludge from an i n i t i a l 5% s o l i d s mixture t o a 35% s o l i d s cake. A t o t a l of 142 runs were made on t h i s s ludge r a t i o . Recognizing t h a t s ludge v a r i a b i l i t y was an important f a c t o r during t h e s tudy and t h a t many types of experiments were made, only t h e runs t h a t gave a t least a 35% s o l i d s cake were used t o produce r e p r e s e n t a t i v e

43

design cond i t ions f o r dewatering t h e Blue P l a i n s s ludge on a year-round b a s i s . According t o t h e manufacturer, scale-up from t h e p i l o t p r e s s d a t a t o a f u l l - scale u n i t can be made d i r e c t l y . F i l t r a t i o n (pumping) and squeezing c y c l e t i m e s w i l l be i d e n t i c a l . included i n t h e t o t a l c y c l e t i m e i n o r d e r t o o b t a i n t h e f u l l - s c a l e y i e l d . (See Appendix B, Explanation of Data Sheet 4 f o r d e t a i l s ) .

A mechanical t u n - a r o u n d t i m e , though, must be

These runs, t a b u l a t e d i n Table 10, are summarized below:

Chemical dosage Cycle t i m e

F i n a l cake s o l i d s Fu l l - sca l e y i e l d

19.6% lime/6.5% FeC13 16.9 min pumping/ 18.1 min squeezing 38.7% 2.39 kg/hr/m2 (0.49 l b / h r / f t 2 )

This d a t a w a s used t o develop average design parameters f o r a f u l l - s c a l e p r e s s i n s t a l l a t i o n a t Blue P l a i n s . Sect ion 9 , are based on t h e s e average values .

Cost estimates f o r t h e NGK p r e s s , given i n

Spec ia l Tests--

Dewatering of v a r i a b l e s ludge ratios--A secondary purpose of t h e s tudy was t o observe t h e e f f e c t of dewatering v a r i o u s r a t i o s of secondary t o primary s ludge s o l i d s . Tests on t h e Buchner funne l , Figure 3, had shown t h a t more chemicals were requ i r ed as t h e percentage of secondary s ludge inc reased . T e s t s on t h e NGK p r e s s confirmed t h e s e r e s u l t s and a l s o showed t h e e f f e c t s t h a t t h e s ludge r a t i o had on f i l t e r y i e l d . t h e s ludges were f a i r l y c o n s i s t e n t i n t h e i r f i l t e r a b i l i t y . During t h a t month, seven d i f f e r e n t s ludge r a t i o s w e r e , t e s t e d . With each s ludge r a t i o a t least t h r e e runs a t t h r e e d i f f e r e n t chemical dosages were made; one over- condi t ioned, one average condi t ioned, and one marginal ly condi t ioned. The r e s u l t s are averaged f o r - e a c h s ludge r a t i o i n Table 11. Note t h e gene ra l t r e n d t h a t s ludges high i n primary s o l i d s g i v e h igh cake s o l i d s and h igh y i e l d s wi th r e l a t i v e l y low chemical dosages. creases above 1/1 secondary t o primary, t h e secondary s ludge is t h e con t ro l - l i n g f a c t o r and t h e s ludges become more d i f f i c u l t t o dewater.

.During t h e month of August, 1977

Once t h e r a t i o of s o l i d s in -

Three day continuous run--From 10/4/77 - 10/7/77 t h e NGK p i l o t u n i t w a s operated cont inuously f o r a pe r iod of 72 hours. t h i s test were:

The primary o b j e c t i v e s of

a. To s imula t e a f u l l - s c a l e i n s t a l l a t i o n and thereby o b t a i n represen- t a t ive o p e r a t i n g parameters,

b. t o test t h e e f f e c t i v e n e s s of a continuous chemical cond i t ion ing scheme ;

c. t o e s t a b l i s h d i a g n o s t i c and monitoring procedures f o r a f u l l - s c a l e system,

d. t o o p e r a t e t h e u n i t under stress cond i t ions i n o r d e r t o e v a l u a t e t h e mechanical design, and

44

TABLE 10. NGK RUNS ON 211 SLUDGE

DATE

3-15-7 7

3- 16-7 7

3-30-77

3-31-77

4-1-77

4-5-77

4-7-77

4-12-7 7 4- 13- 7 7

4-26-77 4- 28-7 7

4-29-77

5-3-77

5-4-77

5-11-77 5-12-77

5-17-77 5-18-77 5-19-77

5-20-7 7 5-23-77

5- 24- 7 7 5-26-77

% CHEMICALS LIME/FeC13

26.018.1 16.014.6 15.914.6 19.615.7 21.616.3 21.616.3 14.914.2 15.014.2 15.414.5 15.114.3 21.916.4 21.916.4 20.816 .O 20.816.0 20.316.0 20.316.0 20.316.0 17.215.0 20.716.2 20.716.3 21.616.6 21.516.4 19.315.9 24.016.9 19.516.5 25.518.4 15.5/5.2 18.616.2 17.415.8 13.714.5 24.418.4 20.216.8 19.416.2 19.616.4 20.216.6 17.615.9 20.316.8 18.616.2 13.814.6 19,916.8 17.115.8 19.516.5 14.614.9

~~~ ~~

CYCLE TIME FULL-SCALE

-. - . 36.1 2.00 20.316.6 __ __ -

45

(MIN) PUblP/SQUEEZE

30115 30115 30115 20115 20115 2 01 15 20115 20115 5/15

10116 5/15

10115 5/15

10115 15/15 20115 25/15 18/25 18/15 18/20 18/25 20120 17/20 22/20 20119 21119 18125 18/19

9124 6120

19/14 16/16 15122 17/22 15/21 11/23 18/19 15/15 13/26 11/22 16/18 19/20 18/16 18/19

% CAKE SOLIDS

41.7 44.4 36.4 39.9 41.4 40.6 38.8 35.8 44.9 42.7 43.8 38.3 41.3 40.0 38.8 36.7 37.7 38.3 35.0 37.3 40.6 36.6 37.8 39.7 35.7 39.8 35.1 38.0 38.1 37.5 37.1 37.8 36.6 38.0 37.0 37.7 35.8 38.0 35.5 35.8 36.1

Yield kg/hr/m2

2.78 3.30 2.54 2.94 3.23 3.13 2.72 2.69 1.75 2.17 1.93 2.27 1.78 2.47 2.75 2.28 2.52 1.89 2.32 2.05 1.93 2.09 1.78 2.18 2.07 2.35 1.66 1.97 1.30 1.05 2.57 2.48 1.65 1.87 1.82 1.63 1.87 2.78 1.71 1.46 1 .91

38.1 2.17 17 - 6 2.48

B

TABLE 10.

CYCLE TIME FULL-SCALE % CHEMICALS (MINI % CAKE Y i e l d

DATE LIME/FeC13 PIJMP/SQUEEZE SOLIDS kg/m2/hr

6-15-77 6-22- 77

6-23-77

7-8-77 7-11-77

7-12-77 7-14-77 7-27-77 7-28-77 8-2-77

8-4-77 8-17-77

8-18- 7 7 8-19-77

8-23- 7 7 8-24- 7 7 8- 25-7 7

9-1-77 9-2-77

9-9-77

9-14-77

9- 21- 7 7 9-22-77 10- 13- 7 7 10-18-77

10-19-77

19.916.6 20.416.9 25.418.4 24.718.3 27.019.0 20.616.8 25.918.7 13.914.6 19.016.4 20.917 .O 26.818.9 16.815.6 22.117.4 17.915.9 14.714.9 18.016.0 17.515.8 19.616.6 21.517.2 14,214.8 16.615.5 18.316.2 20.116.7 19.316.5 17.916.0 18.916.3 17.816.0 19.116.4 19.116.4 24.318.1 29.219.7 27.719.2 24.118.0 15.015.0 23.417.8 20.116.6 14.815 .O 20.016.7 20.016.7 20.016.7 20.216.8 20.216.8 20.917.0

16/15 11121 17/18 15/18 16/18 16/16 1 7 I16 18/20 14/17 20122 16/14 17/19 21/16 20118 14/23 16/15 16/16 18/16 20116 18/21 15/20 21123 18/18 17/17 20120 15/18 16/21 16/22 12/22 13/22 19/17 16/16 18/20 20115 18/17 14/15 17/18 18/17 17/19 15/17 18/17 19/17 17/18

36.5 41.7 35.5 39.2 38.4 41.0 39.6 37.7 39.2 42.5 44.9 40.7 41.4 40.8 40.2 39.9 39.1 40.2 42.2 36.0 36.4 41.4 43.0 40.9 38.8 38.7 38.5 37.2 36.7 36.3 35.5 41.0 36.1 35.7 37.3 41.0 35.5 39.2 38.0 45.3 37.1 38.3 34.7

2.21 1.96 1.93 1.95 2.07 3.22 2.60 2.64 2.54 2.22 3.70 2.97 3.07 2.83 2.16 2.91 2.70 2.76 3.19 2.10 2.12 2.19 3.07 2.76 2.35 2.45 2.39 2.05 1.88 1.90 2.30 2.67 1.79 2.69 2.44 3.18 2.47 2.53 2.33 3.03 2.66 2.59 2.25

46

TABLE 10.

CYCLE TIME FULL-SCALE % CHENICALS (MINI % CAKE Yield

DATE LIME/FeC13 PUMP/ SQUEEZE SOLIDS kg/m2 /hr

10-25-77 19.316.4 10-26-77 25.718.5

15.815.3 15.815.3

12.114.0 10-27-77 12.0/4.0

10-28-77 19.7I6.6 11-2-77 20.416.8

Averages 19,616.5

19/15 19/14 18/18 16/18 18/20 15/21 20116 20117

16.9118.1

37.1 41.7 36.9 37.1 35.5 36.2 40.5 39.8

38.7

2.82 2.42 2.62 2.63 2.31 2.05 2.94 2.62

2.39

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e. t o acquaint p l a n t eng inee r s , maintenance, and o p e r a t i n g personnel w i th t h e design and o p e r a t i o n of a f i l t e r p r e s s .

The flowsheet f o r t h e p rocess is shown i n F igu re16 . Primary s ludge (1% s o l i d s ) and secondary s ludge (0.75% s o l i d s ) were g r a v i t y thickened t o 8% and 4% s o l i d s , r e s p e c t i v e l y , and mixed i n t h e blending t ank i n a secondary/primary s o l i d s r a t i o of 2/1. A r e c y c l e rate w i t h i n t h i s t ank of 10-20 gpm provided t h e necessary a g i t a t i o n f o r mixing. From he re , t h e blended s ludge (5.3% s o l i d s ) was pumped cont inuously a t 1 .5 gpm t o t h e chemical cond i t ion ing system. A Komline-Sanderson Rotary Drum Condit ioner , w i th i n t e r n a l b a f f l e s f o r mixing, w a s used as t h e cond i t ion ing tank. F e r r i c c h l o r i d e (13% weight s o l u t i o n ) w a s added by a p o s i t i v e displacement pump t o t h e s ludge f eed l i n e ; l i m e s l u r r y (6.5% - 13% weight s o l u t i o n ) w a s added t o t h e middle of t h e cond i t ion ing drum. In o r d e r t o minimize f l o c d e t e r i o - r a t i o n during t h e cond i t ion ing s t e p , drum speed was maintained a t one RPM, and t h e s ludge w a s de t a ined only a few minutes be fo re overflowing t o t h e p r e s s feed tank. average s ludge r e t e n t i o n t i m e of 1 .5 hours.

This t ank he ld enough s ludge f o r 2-3 p r e s s runs and had an

Automatic f i l t r a t i o n and squeezing c y c l e s of about 20 minutes each were used during p r e s s runs. These c y c l e s were checked and a d j u s t e d every f i f t h run by measuring t h e s ludge and f i l t r a t e flow rates. c y c l e was i n i t i a t e d only when r equ i r ed ; hence, t h e turn-around t i m e between success ive runs averaged only 10 minutes.

The c l o t h washing

Sludge f i l t e r a b i l i t y was monitored each run by Buchner funne l and CST tests on t h e s ludge l eav ing t h e cond i t ion ing tank. A CST of 15 seconds and a Buchner funne l f i l t r a t e rate of 80 m l / 2 min was used as an i n d i c a t o r of accep tab le f i l t e r a b i l i t y . Samples of s ludge, cake, and f i l t r a t e were taken every f i f t h run f o r l a b o r a t o r y a n a l y s i s .

A t o t a l of 76 runs were made, 72 on t h e 2 / 1 secondary/primary mixture Approximately 5600 g a l l o n s of s ludge P r e s s down-time w a s minimal and 59.3

and 4 on t h e 100% secondary sludge. were f i l t e r e d during t h e ope ra t ion . o p e r a t i n g hours were logged. r i z e d i n t h e fol lowing t a b l e :

Resu l t s of t h e l abora to ry ana lyses are summa-

Sludge f eed s o l i d s / v o l a t i l e s o l i d s 5.32%/67.5% Conditioned s ludge v o l a t i l e s o l i d s 46.9% Lime dosage (avegage) FeC13 dosage (average) Cycle t i m e (avg) pump/squeeze/

Cake w e t weight ( t o t a l ) Cake s o l i d s / v o l a t i l e s o l i d s Cake dry weight Cake s ludge s o l i d s Yield (average) F i l t r a t e suspended s o l i d s F i l t r a t e t o t a l s o l i d s Cloth washed Cloth used

mechanical

22.9% (of s ludge s o l i d s ) 7.3% (of s ludge s o l i d s )

20/20/5 minutes 2682 kg 36.3/48.2% 973 kg 748 kg 2.17 kg/hr/m2 83.2 mg/l 9465 mg/l 16 t i m e s (every 4.75 runs ) NY 51-4

49

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The chemical a d d i t i o n system proved t o be t h e major b o t t l e n e c k of t h e operat ion. Frequent plugging and clogging of t h e l i m e s l u r r y f eed l i n e caused t h e s ludge f eed t o b e under-conditioned f o r s e v e r a l of t h e runs. Consequently, poor cake d i scha rge and excess ive c l o t h b l i n d i n g occurred. Because of t h e s e problems i n t h e l i m e system, t h e bench-scale f i l t e r a b i l i t y tests were inva luab le . I n t e r r u p t i o n s i n t h e l i m e d e l i v e r y were immediately evident by high CST va lues (e.g. 257 sec) and low Buchner funne l f i l t r a t e rates (e.g. 14 m1/2 min). Thus, t h e o p e r a t o r s were a b l e t o s l u g dose t h e feed t ank i n o r d e r t o avoid d i s a s t r o u s p r e s s runs.

Problems w i t h t h e electrical f u n c t i o n s of t h e cake d i scha rge and c l o t h wash mechanisms caused some minor de l ays i n t h e automatic o p e r a t i o n of t h e p re s s . operat ion.

But otherwise, t h e p r e s s performed extremely w e l l du r ing t h e extended

P l a n t personnel , who i n i t i a l l y were unfami l i a r w i th t h e p r e s s , were gene ra l ly p l eased wi th its ope ra t ion .

The e n t i r e p r o j e c t , t h e r e f o r e , w a s considered h igh ly s u c c e s s f u l . Seve ra l important design sugges t ions evolved from t h e s e continuous runs and w i l l be discusded la te r i n t h e design s e c t i o n of t h e r e p o r t .

Lasta Diaphragm P r e s s

From 10/25/77 t o 11/3/77 Ingersoll-Rand, Nashua, New Hampshire, provided a t ra i ler mounted demonstration u n i t of t h e i r Lasta p r e s s f o r t e s t i n g . u n i t w a s a l s o a Japanese-made p r e s s and is manufactured under l i c e n s e from I s h i g a k i Mechanical Indus t ry Co., Ltd. Tests were run f o r comparison w i t h t h e NGK diaphragm p r e s s .

This

F a c i l i t i e s - -

1. P r e s s - 1.64 m2 (17.65 f t 2 ) f i l t r a t i o n area; contained fou r chambers wi th e i g h t 600 mm (23.6 i n c h e s ) squa re p l a t e s ; every o t h e r p l a t e was equipped wi th concave rubber diaphragms. See F igu re 1 7 .

2. Tank assembly

a. s ludge cond i t ion ing t ank - 0.7 m3 (184 g a l ) t ank w i t h v a r i a b l e speed mixer

s ludge s t o r a g e t ank - 1 . 3 m3 (350 g a l ) t a n k b.

c. l i m e s l u r r y t ank - 1 . 3 m3 (350 g a l ) t ank , w i t h cons t an t speed mixer

d. f e r r i c c h l o r i d e t ank - 0.6 m3 (150 g a l ) tank, w i t h cons t an t speed mixer

e. water s t o r a g e t ank - 0.6 m3 (150 g a l ) t ank

5 1

3 . Pump assembly

a. three (3) constant speed pumps - cake wash, cloth wash, diaphragm pressurization

b. three (3 ) variable speed pumps - sludge, lime, and ferric chloride delivery

c. one (1) vacuum pump - diaphragm deflation

d. hydraulic pump - opening and closing press

4. Air compressor with receiver - core blow and instrumentation control

5. Filter cake conveyor

Operation-- Conditioned sludge was prepared in the NGK mix tank and pumped to the

Lasta conditioning tank for use during the tests. L'asta press cycle included pumping, squeezing, cake discharging, and cloth washing operations. The pumping cycle, during which sludge was fed to the press, averaged 10 minutes at pressures of 4.6 - 7.0 kg/cm2 (65-100 psig). Sludge feed volume ranged from 4.5-60.9 liters (1.2-16.1 gallons) and entered the filtering chambers via special dispersion nozzles located at the top

A s with the NGK press, the

Figure 17. Lasta Diaphragm Press.

52

c e n t e r of t h e f i l t e r p l a t e s . F i l t r a t e w a s discharged through s i d e nozz le s a t t h e bottom of t h e f i l t e r p l a t e s .

A t t h e t e rmina t ion of t h e pumping c y c l e , t h e squeezing c y c l e began immediately. An average c y c l e l e n g t h was 20 minutes a t p r e s s u r e s of 14.8 kg/cm2 (210 p s i g ) provided by s t o r e d , r e c i r c u l a t e d water. t h e c y c l e , t h e s ludge and f i l t r a t e l i n e s were blown ou t by compressed a i r and t h e diaphragms were g r a v i t y d ra ined and r e tu rned t o t h e i r o r i g i n a l shape by vacuum suc t ion .

A t t h e end of

Cake d i scha rg ing and c l o t h washing o p e r a t i o n s began a t t h e conclusion of t h e squeezing cycle . As shown i n F igu re 18, t h e s e ope ra t ions were com- p l e t e l y d i f f e r e n t from those of t h e NGK p r e s s . The Lasta u n i t r e l e a s e d a l l f o u r cakes s imultaneously by a " t r ave l ing" motion of t h e f i l t e r c l o t h s . The c l o t h s moved downward around t h e bottom of t h e p l a t e s i n a u - t u r n f a s h i o n which caused t h e cakes t o release. A f t e r t h e d i scha rg ing was completed, t h e c l o t h s then r e tu rned t o t h e i r o r i g i n a l p o s i t i o n s . b l ades l o c a t e d a t t h e bottom of t h e p l a t e s t o assist i n d i f f i c u l t cake r e l e a s e s . ) both s i d e s by low p res su re , 7 kg/cm2 (100 PSig) , spray Showers l o c a t e d nea r t h e bottom of t h e p re s s . Drip pans were c losed over t h e d i scha rge p o r t i n o r d e r t o c a t c h spen t wash water and prevent r ewe t t ing of t h e f i l t e r cake.

(The p r e s s a l s o had doc to r

The f i l t e r c l o t h s moved downward a second t i m e f o r washing on

Standard l a b o r a t o r y ana lyses were performed on samples of t h e s ludge , cake, and f i l t r a t e .

T e s t data-- Over t h e two week test pe r iod , 35 runs were made on t h i s p r e s s ; t h e

r e s u l t s are p resen ted i n Table 1 2 . For each ba tch of s ludge, two t o t h r e e runs were u s u a l l y made a t va ry ing c y c l e t i m e s t o opt imize t h e y i e l d s and cake s o l i d s . t o g e t h e r i n Table 12 ; f o r t h e 100% secondary s ludge t e s t e d , t y p i c a l runs a t d i f f e r e n t cond i t ion ing l e v e l s are shown. A s shown by t h i s d a t a , t h e p r e s s performed q u i t e w e l l and produced cake s o l i d s of a t least 35% i n most cases. A t t h i s t i m e , though, t h e f eed s o l i d s content w a s high, and t h e s ludge was e a s i l y f i l t e r e d , even a t low chemical dosages. (Yields were c a l c u l a t e d by adding a f u l l - s c a l e mechanical t i m e of 10.5 minutes t o t h e p rocess c y c l e t i m e . )

For t h e 2 / 1 s ludge mixture t e s t e d , t h e s e runs are c l u s t e r e d

Three d i f f e r e n t f i l t e r c l o t h s , w i t h t h e fol lowing s p e c i f i c a t i o n s , were t e s t e d on t h e p re s s :

TYPE

891 920 940

AIR THICKN'ES S PERMEABILITY

CONSTRUCTION .FILLING mm cm3/min/cm2

2 x 2 t w i l l polypropylene 1.46 2 x 2 t w i l l polypropylene 1 .17 2 x 2 t w i l l polypropylene 1.02

1500 800

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The best filtrate quality was obtained using t h e 891 c l o t h ; suspended solids averaged 87.5 mg/l for runs made on the 2/1 sludge. Cake discharge was good for all three cloths, but sufficient runs were not made to evaluate resistance to wear and abrasion.

Comparison with NGK press-- During the test period, simultaneous runs were made on the NGK press.

Sludge was prepared in the NGK mix tank; a portion was pumped to the Lasta conditioning tank and the remainder was fed to the NGK unit.

In Table 13, comparable runs for the 2/1 sludge mixture are shown. The full-scale NGK yield assumes a 19 minute mechanical cycle every 20 runs. time with cloth washing every four runs. "Equivalent full-scale yields" were calculated for cycle times at which the lowest cake solids were achieved for either press. The performance of both presses, as shown by the average cake solids achieved, was essentially equal. The main advantage of the Lasta press was its shorter mechanical time (10.5 min vs. 19 min), positive cake discharge, and ease and speed of cloth washing. Additionally, the optimum cycle.on the Lasta unit usually had a shorter pump time than the NGK press, which resulted in a thinner cake for discharge.

with cloth washing The full-scale Lasta yield assumes a 10.5 minute mechanical

The main disadvantage of the Lasta unit is the quantity of total filtra- When tion area which is currently available on the full-scale Lasta unit.

comparing equivalent yields, the Lasta unit was much higher, averaging 3.31 kg/hr/m2 as compared to 2.70 kg/hr/m2 for the NGK press. represents an additional 22.6% filtration area that the NGK unit would require in order to dewater the same quantity of sludge to the same cake solids as the Lasta press. available than the largest Lasta unit (NGK-500 m2; Lasta-204 m2) ; therefore, fewer NGK units would be required.

This difference

However, the largest NGK press has 145% more filtration area

57

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58

FIXED VOLUME FILTER PRESS

The f i x e d volume p r e s s i s a s t anda rd r eces sed p l a t e f i l t e r p r e s s which produces cakes of a cons t an t t h i ckness . These p r e s s e s are designed t o o p e r a t e a t t e rmina l p r e s s u r e s ranging from 7 kg/cm2 (100 p s i g ) t o 15.8 kg/cm2 (225 p s i g ) . For t h e s tudy , a 225 p s i g u n i t was supp l i ed by Passavant Corp., and a 100 p s i g u n i t w a s supp l i ed by Neptune - Nichols Inc. This r e p o r t r e f e r s t o t h e 100 p s i g p r e s s as a "low-pressure unit" and t h e 225 p s i g p r e s s as a "high-pressure unit". Both p r e s s e s were ope ra t ed t o develop design d a t a f o r dewatering a v a r i e t y of s ludge r a t i o s , bu t most work w a s cen te red on t h e 2 / 1 secondary t o primary r a t i o . w i th each o t h e r and wi th t h e diaphragm type p r e s s .

The u n i t s were a l s o used f o r comparison tests

High-pressure P r e s s

F a c i l i t i e s - - The Passavant system included t h e fol lowing equipment.

1. P r e s s - Passavant Model 2400 - Produced up t o 6 c i r c u l a r cakes, each . 597 mm (23.5 inches ) i n diameter. Each chamber had a f i l t r a t i o n

area of 0.56 m2 (6.0 f t 2 ) . supp l i ed t o provide chamber th i cknesses of 30 mm (1.18 i n c h ) , 34 mm (1.34 i n c h ) , and 38 mm (1.50 inch ) . provided f o r p r e s s c l o s i n g .

Seve ra l s t a i n l e s s steel p l a t e s were

A h y d r a u l i c mechanism w a s (See Figure 1 9 . )

2. Feed t ank - 1135 1 (300 g a l ) c y l i n d r i c a l c losed t ank ; capable of w i ths t and ing air p r e s s u r e s up t o 21 kg/cm2 (300 p s i g ) .

3. A i r compressor - opera t ed a t p r e s s u r e s up t o 2 1 kg/cm2 (300 p s i g ) f o r f eed ing t h e p r e s s and c o r e blowing.

4. F i l t r a t e c o l l e c t i o n tank - 378 1 (100 g a l ) c a l i b r a t e d p l a s t i c v a t .

Operation--

p r i o r t o pumping t o t h e f eed tank. w i th t a p water and scrubbed wi th a s t i f f - b r i s t l e nylon brush. t hen c losed h y d r a u l i c a l l y . p r e s s u r e compressor s t a r t e d . 15.8 kg/cm2 (225 p s i g ) w a s a t t a i n e d and was h e l d f o r t h e remainder of t h e run, t hus providing t h e s o l e d r i v i n g f o r c e f o r dewatering t h e s l u d e. The run

hours f i l t r a t i o n t i m e had elapsed. Usually 3 cakes were made, bu t a t t i m e s when g r e a t e r q u a n t i t i e s of f eed s ludge were a v a i l a b l e , up t o 5 cakes could be produced. percent s o l i d s . General ly , t h e a v a i l a b i l i t y of l a b o r a t o r y oven space per- m i t t e d no more t h a n one o r two cake samples f o r a n a l y s i s f o r pe rcen t s o l i d s . Data s h e e t s 5 and 6 i n Appendix B summarize a t y p i c a l run on t h e high-pressure p re s s .

For a l l runs, t h e s ludge w a s blended and condi t ioned i n t h e NGK mix t ank Before each run t h e c l o t h s were wetted

The s ludge f eed valve was opened and t h e high- Within 15 t o 20 minutes t h e f u l l p r e s s u r e of

The p r e s s w a s

was ended when e i t h e r t h e f i l t r a t e rate reached 0.1 g a l / h r / f t f o r when t h r e e

A t t h e end of t h e run a l l cakes were weighed and analyzed f o r

Explanations are provided wi th each d a t a s h e e t .

59

Test Data--

September, 1977. During this time, sludge temperatures ranged from 2 4 O C to 30 OC. In August, the feed before conditioning averaged 5.7% solids and the sludge dewaterability was good. In September, the feed averaged from 3.4 to 4.0% solids before conditioning and the dewaterability was poor. higher chemical dosages were required to filter the sludges than during August .

All test runs with the high pressure-press were conducted in August and

Thus,

The data in Table 14 are typical results with this press for a variety These tests were all made in August of secondary to primary sludge ratios.

using a 38 mm (1.5 inch) cake.

The full-scale yields were computed by adding 20 minutes mechanical tum- around time to the process cycle time (based on the manufacturer's recommendation for their largest press). the chemical requirements increased, and the cake solids and yields decreased. Because of the open weave cloth on this press, the filtrate suspended solids were sometimes high, particulary when the sludge was marginally conditioned. The average cake density for the runs was 1123.0 kg/m3 (70.1 lb/ft3). discharge from this press was not the best; a thin mat of fibrous sludge remained on the cloth after each run, especially around the center feed hole. No precoat was used for any of these runs.

The filter cloth us d was a nylon monofilament of twill weave, with an air permeability of 76.7 cm 5 /s/cm2 @AP= 12.7" H20.0

As the ratio of secondary sludge increased,

Cake

The cake always showed a very dry outside portion and a much wetter inner section. Because of the limited size of the air compressor receiver, the core blow at the end of each run was generally ineffective in removing all the solids from the center feed hole. During cake sampling, pie shaped pieces were taken which included the proper proportions of this wet inner core and the dry outside section. To insure that these slices were indeed representative, the variation in dryness across the cake was periodically checked. A wedge was divided into four quarters as shown in Figure 20, and each quarter was analyzed for percent solids. These results were:

% solids (section) Theor. % solids of Date I I1 111 IV % solids adjacent wedge

8/15 17.4 21.7 37.7 39.3 32.5 31.2

8/17 19.7 33.0 43.9 42.5 38.5 37.0 8/18 21.6 28.7 41.2 41.9 36.5 36.6

8/23 16.1 23.4 36.5 40.8 32.8 33.6

8/16 41.6 47.4 52.1 49.0 48.9 47.5

8/19 26.1 35.9 41.7 42.3 39.2 37.4

Section I was 10.6% of the total volume; section I1 was 22.8%; section I11 was 35.1%; and section IV was 31.5%. The theoretical percent solids was calculated by multiplying these percentages by the percent solids in each section. The correlation of the last two columns is quite good, indicating that our method was correct. plate press will always have a variation in percent solids across the cake.

These results also show that a standard recessed

60

Figure 19. Passavant Filter Press.

Figure 20. Sample sections from Passavant cake.

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With the more d i f f i c u l t f i l t e r i n g s ludges t h i s v a r i a t i o n w a s even g r e a t e r as shown by t h e d a t a on 8-15 (100% secondary) , and 8-17 through 8-23 ( a l l 2 1 1 s ludge) . t h i s s ludge w a s e a s i l y f i l t e r e d .

The 8-16 run on 100% primary showed only s l i g h t v a r i a t i o n because

Table 15 p r e s e n t s t h e r e s u l t s of runs on t h e 211 secondary t o primary When t h e s ludge was p rope r ly condi t ioned, t h e high-pressure p r e s s

Marginally condi t ioned s ludges as shown on

sludge. gave accep tab le cake s o l i d s (over 35%), u s i n g t h e 38 mm cake, w i th c y c l e t i m e s approaching t h r e e hours. 8/4, 8/19, and 9 / 1 gave very poor r e s u l t s f o r t h i s t h i c k cake. In September, two new p l a t e s were i n s t a l l e d t o p rov ide cakes measuring 30 mm (1.18 inches ) . The end p l a t e s could no t be changed, however. So on subsequent runs, t h e two i n s i d e cakes measured 30 mm (1.18 i n c h e s ) , wh i l e t h e two o u t s i d e cakes measured 34 mm (1.34 inches ) . s e p a r a t e l y , a y i e l d w a s computed f o r each t h i c k n e s s ( runs on 9/21 and 9/22). The runs a f t e r 9/14 show t h a t t h e t h i n n e r cakes always contained s l i g h t l y higher cake s o l i d s , bu t w i th some measurable s a c r i f i c e i n o v e r a l l y i e l d . No comparisons could be made between t h e runs i n August and t h o s e i n September because t h e s ludge f i l t e r a b i l i t y had changed so d r a s t i c a l l y .

When t h e cakes could b e weighed and analyzed

During August, 1977, a d d i t i o n a l h igh p r e s s u r e runs were made on a Passavant Model 600 bench-scale p re s s . This p r e s s , 152 mm (6 i n c h e s ) i n diameter, could produce cakes of v a r i o u s th i cknesses from 25 mm t o 38 mm. The p r e s s w a s f e d from a small t ank p r e s s u r i z e d w i t h n i t r o g e n t o 15.8 kg/cm2 (225 p s i g ) . mix tank. t h a t h ighe r cake s o l i d s were produced by t h e t h i n n e r cakes (see t h e comparison tests on 8/17, 8/18, and 9/1) . Any change i n f u l l - s c a l e y i e l d because of t h e d i f f e r e n t cake t h i c k n e s s e s w a s n o t r e a d i l y apparent from t h i s d a t a .

For most runs, t h e condi t ioned s ludge w a s sampled from t h e NGK I n gene ra l , t h e tests showed R e s u l t s are p resen ted i n Table 16.

Some comparison runs between t h e Model 600 and Model 2400 p r e s s e s were conducted f o r t h e 38 mm (1.5 inches ) cake:

CYCLE TIME YIELD X CAKE b i n 1 (kg/hr/m2 1 SOLIDS

DATE M-600 M-2400 M-600 M-2400 M-600 M-2400

- 37.8 37.0 8-17-77 90 200 - - 8-18-77 120 190 3.12 1.81 35.8 36.6

8- 30- 7 7 115 180 2.54 1.47 26.7 28.4 8-30-77 110 180 3.37 1.54 39.2 31.9 9-1-77 130 180 2.83 1.54 35.9 29.3

The above t a b l e shows t h a t w i th t h e Model 600 p r e s s , c y c l e t i m e s were much s h o r t e r and the resultant y i e l d s were much higher . cake s o l i d s were a l s o achieved w i t h t h i s u n i t . has y e t been given f o r t h e s e appa ren t ly i n c o n s i s t e n t r e s u l t s .

I n some cases h ighe r No s a t i s f a c t o r y exp lana t ion

The scale-up f a c t o r ( f i l t r a t i o n area p e r p l a t e ) f o r t h e Model 2400 t o f u l l - s c a l e is on ly 12.9 t o 1.0, while f o r t h e Model 600, it is 198 t o 1.

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Therefore, Model 2400 d a t a w a s used f o r comparisons wi th t h e o t h e r p r e s s e s and f o r f u l l - s c a l e design. A s w i th t h e o t h e r p re s ses , scale-up from p i l o t d a t a t o t h e f u l l - s c a l e p r e s s can be made d i r e c t l y . The p rocess c y c l e t i m e ( f i l t r a t i o n t i m e ) is assumed t o be i d e n t i c a l f o r both s i z e u n i t s . The t o t a l c y c l e t i m e , however, must be a d j u s t e d t o inc lude t h e mechanical turn- around t i m e i n o r d e r t o o b t a i n t h e f u l l - s c a l e y i e l d .

Low-Pressure P r e s s

F a c i l i t i e s - - The Nichols system included t h e fol lowing equipment:

1. Pres s - 0.37 m2 (4 f t 2 ) f i l t r a t i o n area. cakes each measuring 330 mm (13 inches ) ac ross . coated steel , wi th a chamber t h i c k n e s s of 25 mm (1.0 inch ) . Spacers were a v a i l a b l e t o produce a cake t h i c k n e s s of 32 mm (1.25 inches ) . The p r e s s w a s c losed by a manually ope ra t ed screw. (See F igu re 21.)

Produced two octagon shaped P l a t e s were rubber

2. Feed t ank - 113.5 1 (30 g a l . ) c y l i n d r i c a l c losed t ank ; could be p r e s s u r i z e d w i t h a i r up t o 10.5 kg/cm2 (150 p s i g ) .

Operat ion--

i n t h e NGK mix t ank p r i o r t o pumping t o t h e f eed vessel-. t h e c l o t h s were wetted w i t h t a p water and scrubbed wi th a s t i f f - b r i s t l e nylon brush. t u r n i n g t h e screw. The i n l e t va lve t o t h e p r e s s w a s opened and t h e f eed t ank p r e s s u r i z e d slowly w i t h a i r t o reach a p r e s s u r e of 7 k g / d (100 p s i g ) w i t h i n 5 t o 10 minutes. provided t h e s o l e d r i v i n g f o r c e f o r dewatering. a d r a i n p i p e and a d r i p pan under t h e p l a t e s during t h e run. were no g a s k e t s between t h e f i l t e r p l a t e s , and t h e f i l t e r c l o t h s provided t h e only seals, up t o 50% of t h e f i l t r a t e w a s c o l l e c t e d from t h e d r i p pan. Early test work e s t a b l i s h e d t h a t t h e run was complete when t h e f i l t r a t e rate reached 25 ml/min o r less. A t t h e end of t h e run both cakes were weighed and sampled. A t r i a n g u l a r shaped s e c t i o n , as shown i n F igu re 22, w a s taken and analyzed f o r pe rcen t s o l i d s . t h e low-pressure p r e s s .

For a l l t h e runs on t h i s p r e s s , t h e s ludge was blended and condi t ioned Before each run,

The p r e s s w a s c losed and s e a l e d as t i g h t l y as p o s s i b l e by manually

This p r e s s u r e w a s maintained throughout t h e e n t i r e run and F i l t r a t e w a s c o l l e c t e d from

Because t h e r e

Data Sheets 7 and 8 in 'Appendix B summarize a t y p i c a l run on Explanations are provided w i t h each d a t a s h e e t .

T e s t Data--

t h e p r e s s could dewater s ludges over a range of s ludge temperatures from 11 "C t o 30 'C. on a v a r i e t y of secondary t o primary s ludge r a t i o s w i t h an average unconditioned f eed s o l i d s cqncen t r a t ion of 5.7%. These tests were a l l conducted i n August during comparison s t u d i e s w i t h t h e high-pressure u n i t and t h e diaphragm p r e s s . p ropor t ion of s e p t i c s o l i d s ; however, t h e i r d e w a t e r a b i l i t y w a s qui'te good even a t low chemical dosages. 20 minutes mechanical turn-around t i m e t o t h e c y c l e t i m e (based on- t h e manufacturer ' s recommendation f o r t h e l a r g e s t p r e s s a v a i l a b l e ) . run 100% primary s ludge on t h i s s m a l l p i l o t p r e s s f a i l e d because s o l i d s

T e s t work wi th t h e low-pressure p r e s s throughout t h e yea r showed t h a t

The d a t a i n Table 1 7 are t y p i c a l r e s u l t s w i t h t h i s p r e s s

The s ludges t e s t e d a t t h a t t i m e contained a h igh

The f u l l - s c a l e y i e l d w a s computed by adding

.Attempts t o

66

Figure 21. Nichols F i l t e r Press.

F igure 22. Sample s e c t i o n s from Nichols cake.

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plugged t h e s m a l l (1 i n c h diameter) feed l i n e .

The gene ra l t r e n d , as shown i n Table 17, was t h a t as t h e r a t i o of second- a r y s ludge inc reased , t h e chemical requirements increased, and t h e cake s o l i d s and y i e l d s decreased. The except ion t o t h i s w a s t h e 4 / 1 s ludges which seemed t o f i l t e r extremely w e l l . The f i l t r a t e q u a l i t y w a s una f fec t ed by changes i n t h e s ludge r a t i o s . The c l o t h used f o r a l l t h e s e runs w a s t h e Nichols 4709/40 c l o t h (a monofilament f a b r i c w i th a 2 x 2 t w i l l weave, and an a i r pe rmeab i l i t y of 20.3 c m 3 / s / c m 2 @ A P = 12.7 mm H20). d e n s i t y w a s 1141 kg/m3 (71.2 l b / f t 3 ) . s ludges, cake release from t h e c l o t h w a s g e n e r a l l y very good. But, as wi th t h e high-pressure u n i t s , t h e cake from t h i s p r e s s w a s d r i e r on t h e o u t e r s e c t i o n s than a t t h e i n n e r core .

The average cake Except f o r t h e marginal ly condi t ioned

Table 18 p r e s e n t s t h e r e s u l t s of t h e 1 3 i n d i v i d u a l runs on t h e 2 / 1 secondary/primary sludge. 8/4/77, show t h e e f f e c t of chemical cond i t ion ing . Low chemical dosages (marginal cond i t ion ing ) as i n t h e run on 8/4/77 gave poor r e s u l t s on t h i s p re s s . The f i r s t e i g h t runs i n t h e t a b l e were t h e r e s u l t s w i th t h e 25 mm (1 inch) t h i c k cake; t h e l as t 5 were wi th t h e 32 mm (1.25 inches ) t h i c k cake. I n c r e i s i n g t h e cake t h i c k n e s s t o 32 mm (1.25 inches) provided some t r a d e o f f s . The averages of t h e two sets of runs showed t h a t r e s u l t a n t cake s o l i d s were s l i g h t l y lower wi th t h e t h i c k e r cake, bu t t h e o v e r a l l f u l l - s c l e y i e l d s were n e a r l y i d e n t i c a l a t approximately 1.4 kg/hr m2 (0.29 l b / h r f t 1. creased cake t h i c k n e s s a l s o r equ i r ed inc reased c y c l e t i m e s .

The f i r s t t h r e e runs i n t h e t a b l e , 8/2/77 and

1 The in-

Comparison Runs

The comparison runs i n August, 1977, were designed t o e s t a b l i s h t h e ope ra t ing cond i t ions f o r t h e t h r e e types of presses-- low-pressure f i x e d volume, high-pressure f i x e d volume, and diaphragm. These tests were run on seven d i f f e r e n t secondary t o primary s ludge r a t i o s . With each r a t i o , a t least t h r e e runs were made: one wi th t h e s ludge over-conditioned; one wi th t h e s ludge condi t ioned i n a good, s a f e range; and one w i t h t h e s ludge marginally condi t ioned. cond i t ions were determined from experience; f i l t e r a b i l i t y w a s checked by s p e c i f i c r e s i s t a n c e and CST tests p r i o r t o each run.

The lime/FeC13 dosages r equ i r ed t o produce t h e above


1.

2.

Diaphragm p r e s s - NGK u n i t 5.8 m2 (62.4 f t 2 ) f i l t r a t i o n area*

High-pressure f i x e d volume - Passavant Model 2400 wi th 1.67 m2 (18 f t 2 ) f i l t r a t i o n area (3 cakes) .

Low-Pressure f i x e d volume - Nichols u n i t - .37 m2 (4 f t 2 ) f i l t r a t i o n area. Cake t h i c k n e s s w a s e i t h e r 25 mm o r 32 mm.

A l l tests used t h e 38 mm p l a t e s .

3.

Operation--

NGK mix t ank and blended i n t h e proper p ropor t ions f o r t h e test. s o l i d s of each s ludge were determined p r i o r t o blending t o be c e r t a i n t h a t

Thickened primary and secondary s ludges were independently pumped t o t h e Percent

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t h e blend was a c c u r a t e . mix i n . L ime s o l u t i o n a t one l b / g a l w a s then added and mixed i n . minutes a f t e r adding t h e l i m e , p o r t i o n s of t h e condi t ioned s ludge were pumped t o t h e Passavant and Nichols f eed t anks . The remainder w a s f e d t o t h e NGK p res s . The t h r e e p r e s s e s were a l l s t a r t e d a t t h e same t i m e . The o p e r a t i o n a l procedures, ( i . e . c y c l e t i m e s , p r e s s u r e s , e t c . ) were those desc r ibed previously.

FeC13 s o l u t i o n a t one l b / g a l w a s added and allowed t o Within 15

T e s t Data--

runs on t h e 2 / 1 s ludges are included, while only t h e b e s t runs wi th average cond i t ion ing are p resen ted f o r t h e o t h e r s ludge r a t i o s . were c a l c u l a t e d wi th t h e s e turn-around t i m e s : NGK - 19 minutes, Passavant - 20 minutes, and Nichols - 20 minutes. Seve ra l important conclusions were der ived from t h i s t a b l e :

I n d i v i d u a l t es t runs on t h e t h r e e p r e s s e s are p resen ted i n Table 19. A l l

The f u l l - s c a l e y i e l d s

1. With a p rope r ly condi t ioned s ludge, a l l t h r e e types of p r e s s e s pro- produced t h e r equ i r ed 35% cake s o l i d s .

2. On t h e average, t h e diaphragm p r e s s gave both h i g h e r cake s o l i d s * (40.0% vs 34.3% and 34.9%) and h ighe r y i e l d s t h a n t h e f i x e d volume

presses. Cake s o l i d s were approximately t h e same on both t h e h igh and low p r e s s u r e p r e s s e s , bu t t h e high-pressure p r e s s gave s i g n i - f i c a n t l y g r e a t e r y i e l d s than t h e low-pressure u n i t .

3. The diaphragm p r e s s w a s t h e only u n i t capable of s a t i s f a c t o r i l y dewatering t h e marginal ly condi t ioned s ludges. For example, on 8/4 and 8/30 both t h e Passavant and Nichols p r e s s e s had poor runs , w i th w e t , s loppy cakes and extremely low y i e l d s . With t h e same sludge t h e diaphragm p r e s s gave a good cake d i scha rge and h igh cake s o l i d s , bu t a t reduced y i e l d s . The diaphragm p r e s s , because of i ts s e p a r a t e squeezing c y c l e , provided a much more f l e x i b l e ope ra t ion . These poorly condi t ioned s ludges were pumped f o r s h o r t e r c y c l e s and t h e squeezing t i m e w a s i nc reased s l i g h t l y t o g i v e t h i n , dry cakes. t h e s ludge was f e d t o t h e s e p r e s s e s be taken.

The fixed-volume p r e s s e s d i d n o t have t h i s o p t i o n , so once no c o r r e c t i v e measures could

4. The marginal ly condi t ioned runs on 8/19 and 9 / 1 gave poor cake s o l i d s on t h e Passavant p r e s s , bu t accep tab le r e s u l t s on t h e Nichols p r e s s . This i n d i c a t e d that cake t h i c k n e s s had more of an e f f e c t t han p r e s s u r e i n determining cake s o l i d s con ten t .

5. A s t h e percentage of primary s ludge inc reased , t h e cake s o l i d s and y i e l d s improved f o r a l l p re s ses . Cake s o l i d s approached t h e 50% s o l i d s level f o r h igh primary r a t i o s .

6. For t h e p rope r ly condi t ioned 2 / 1 s ludge runs t h e average f i l t r a t e suspended s o l i d s were: NGK - 197 mg/l; Passavant - 26.5 mg/l; Nichols - 49.1 mg/l. The c a l c u l a t e d pe rcen t recovery of i n l e t suspended s o l i d s i n t h e f i l t e r cake is: NGK - 99.74%; Passavant - 99.97%; and Nichols - 99.93%.

71

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Overall, t h e diaphragm p r e s s performed b e t t e r t han e i t h e r of t h e f i x e d But s i n c e t h e s e p r e s s e s a l s o produced t h e r equ i r ed cake volume p res ses .

s o l i d s wi th t h e 2 / 1 s ludge, t h e comparison f o r c o s t and design purposes w a s based on t h e r e s p e c t i v e y i e l d s achieved i n reaching t h e 35% s o l i d s cake. The runs t h a t reached t h e r equ i r ed cake s o l i d s f o r t h e low and high-pressure p r e s s e s are shown i n F igu re 23. Fu l l - sca l e y i e l d s are p l o t t e d v s t h e d a t e of t h e run t i m e w a s t hen a d j u s t e d t o a l e v e l which would g i v e t h e same cake s o l i d s as ob ta ined on t h e o t h e r p re s ses . This w a s done by r e c a l c u l a t i n g t h e squeezing t i m e t o t h e p o i n t where t h e d e s i r e d pe rcen t s o l i d s were reached. t h e f i r s t NGK run on 8 / 2 had a pump/squeeze t i m e of 21/16 minutes and a f i n a l s o l i d s of 41.4%. The Passavant and Nichols cake s o l i d s were 37.4%. F i l t r a t e c o l l e c t i o n d a t a f o r t h e NGK run showed t h a t t h i s 37.4% s o l i d s l e v e l was reached a f t e r 9 minutes of squeezing. Therefore , a r e c a l c u l a t e d NGK c y c l e t i m e of 21 minutes pumping, 9 minutes squeezing, and 19 minutes mechanical t i m e w a s used, and a f u l l - s c a l e y i e l d of 2.94 kg/hr/m2 ob ta ined . These a d j u s t e d NGK y i e l d s are a l s o p l o t t e d i n F igu re 23 and t h e e i g h t runs averaged. To produce a 36.3% s o l i d s cake t h e N K average y i e l d was 3.31 kg/hr/m2;

s o l i d s ) w a s 1.46 kg/hr/m2.

and t h e e i g h t p o i n t s are averaged f o r each u n i t . The NGK c y c l e

For example,

t h e Passavant y i e l d w a s 2.04 kg/hr/m 8 ; and t h e Nichols y i e l d ( f o r 35.8%

Using t h e above y i e l d d a t a , t h e f i l t r a t i o n area requ i r ed t o p rocess a given q u a n t i t y of s ludge was then computed f o r each of t h e p r e s s types . example, t o p rocess 1000 kg /h r of dry s ludge s o l i d s , t h e NGK p r e s s would have r equ i r ed :

For

1000 kg;hr/= 302 m2 of f i l t r a t i o n area. 3.31 kg h r m2

Likewise, t h e Passavant and Nichols p r e s s e s would have r e q u i r e d 490 m2 and 685 m2 of f i l t r a t i o n area, r e s p e c t i v e l y . t h e Passavant u n i t r e q u i r e s 62.3% more f i l t e r area, and t h e Nichols p r e s s r e q u i r e s 126.8% more f i l t e r area than t h e NGK p r e s s t o dewatdr t h e same q u a n t i t y of sludge. s p e c i f i c a l l y f o r t h e Blue P l a i n s s ludge. relative f i l t e r areas r e f e r only t o t h e l a r g e s t p r e s s s i z e s a v a i l a b l e from each of t h e manufacturers: 628 m2. For comparisons of smaller s i z e p r e s s e s , a d i f f e r e n t mechanical t i m e must be used and a new f u l l - s c a l e y i e l d must be c a l c u l a t e d f o r each u n i t . For convenience, t h e fol lowing t a b l e shows t h e p rocess c y c l e time used t o d e r i v e F igu re 23:

Thus us ing t h e NGK p r e s s as a base,

It must be noted t h a t t h i s r e l a t i o n s h i p w a s de r ived It is f u r t h e r no ted t h a t t h e

NGK - 500 m2; Passavant - 1080 m2; and Nichols -

73

Process Cycle Times (min )

Date NGK Pass. Nich.

3.8

3.6

3.4

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-

-

-

-

-

-

2119 20 /9 16/11 18/11 20 /8 21/12 1817 17/10

120 150 200 190 180 190 160 180

100 120 110 150 140 170 130 140

See Table F-1 in Appendix F for specifications of the large-scale presses available from each of the manufacturers.

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Figure 23. Comparative yield data.

7 4

CONTINUOUS BELT FILTER PRESSES

Continuous b e l t p r e s s e s f o r s ludge dewatering were o r i g i n a l l y developed i n Europe and have g e n e r a l l y found wide acceptance i n many c o u n t r i e s . Seve ra l companies i n t h e United S t a t e s have purchased t h e technology and are now marketing t h e s e p r e s s e s i n t h i s country. Two manufacturers ' u n i t s were t e s t e d i n t h e s tudy - a Parkson Magnum p r e s s and a Komline Sanderson Unimat p r e s s . The u n i t s were used t o dewater both thickened s ludge and cake from a vacuum f i l t e r .

Parkson Magnum Pres s

The Magnum p r e s s w a s equipped wi th two continuous s c r e e n s made of polyester monofilament c l o t h (air pe rmeab i l i t y of 228 cm3/sec/cm2 GAP = 12.5 mm water) which r an through a system of guiding and p r e s s i n g r o l l e r s t h a t w e r e p e r f o r a t e d t o a l low f o r water drainage. There were t h r e e dewatering zones; a g r a v i t y drainage s t a g e , a low-pressure s t a g e - 0.5 kg/cm2 (7.5 p s i g ) , and a high-pressure s t a g e - up t o 7.7 kg/cm2 (110 p s i g ) . has a range of b e l t speeds from 1.2 t o 5.7 m/min.

Their f u l l - s c a l e p r e s s (See F igu re 2 4 . )


meter wide t ra i ler-mounted demonstration u n i t w a s t e s t e d i n October, 1977. A hopper and Moyno pump were supp l i ed wi th t h e demonstration u n i t t o test t h e vacuum f i l t e r cake as feed.

A 0.25 meter wide l a b o r a t o r y p r e s s w a s t e s t e d i n May, 1977. A 1 .0

Operation--

provide b a s i c information on dewatering polymer condi t ioned thickened s ludge blends. Data was a l s o c o l l e c t e d f o r t h e f u r t h e r dewatering of vacuum f i l t e r cake. Various r a t i o s of secondary t o primary s ludge were blended i n l abora to ry glassware, and t h e polymer w a s added and mixed i n . The condi t ioned s ludge w a s placed on t h e d ra inage s e c t i o n of t h e b e l t p r e s s and, a f t e r a s u i t a b l e d ra inage t i m e , t h e b e l t s moved t h e s ludge through t h e p r e s s u r e zones. Yield w a s computed from measurements of cake weight and b e l t speed. S o l i d s recovery on t h i s u n i t w a s e s t ima ted from experience. f i l t e r cake, samples were taken from t h e p l a n t ' s f u l l - s c a l e u n i t s and manually placed on t h e p r e s s .

The l a b o r a t o r y u n i t (0.25 meter), p i c t u r e d i n F igu re 25 , w a s used t o

When t e s t i n g vacuum

When t e s t i n g on t h e demonstration s i z e p r e s s , vacuum f i l t e r cake w a s c o l l e c t e d from t h e f u l l - s c a l e f i l t e r s i n a t r u c k , dumped on t h e ground, and then loaded i n t h e f eed hopper wi th a f r o n t end loade r . Moyno pump f e d t h e s ludge through a s ix- inch hose and a v a r i a b l e o r i f i c e f eed nozzle onto t h e drainage s e c t i o n of t h e p r e s s .

An open-throat

Test Data--

Laboratory (0.25 meter) unit--Results of t h e tests w i t h varying r a t i o s of secondary t o primary s ludge are p resen ted i n F igu res 26 and 27. f eed range of 5.5% t o 9.5% t o t a l s o l i d s , t h e f i n a l cake s o l i d s inc reased l i n e a r l y from 25% t o 41% as t h e percentage of primary inc reased .

With a

The p r e s s

75

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Figure 25. Parkson Laboratory Belt Press.

capacity exhibited an S-shaped curve, ranging from 248 to 1230 kg/hr/meter of belt width (547 to 2712 lbs/hr) for pure secondary and pure primary, respectively. Figure 27 shows that the polymer (Percol 721 @ $1.70/lb) consumption decreased from 5 . 5 to 1.6 lbs per ton dry solids, and estimated solids recovery (reflecting losses in both filtrate and washwater) increased from 95% to 98% with increasing percent primary. (greater than 84% by weight) the belt speeds were near maximum of 5 meters/min and high pressures of 7 kg/cm2 were attained. As the percent primary decreased, the belt speed was reduced to 3 meters/min and pressures of only 1.8 kg/cm2 (25 psig) were applied. With the high primary sludges, cake release from the cloth was excellent as is pictured in Figure 25. A s the percent primary decreased, a sharp scraper blade was needed to remove the cake. Some solids, however, usually remained imbedded in the cloth and high pressure washing was required to remove them.

With high primary sludge

The tests with vacuum filter cake showed excellent results. At that time, average conditioning chemicals of 19% lime, 6% FeC13, and 0.14% polymer were added to the vacuum filter feed. Cake solids from the vacuum filter averaged 20%; no additional chemicals were mixed with the belt press feed. The following table shows how the cake solids varied with throughput rate:

Capacity (kg total solids/hr/m) 378 7 02 972 1260 % Cake Solids 42 39 36 35

77

c

MAGNUM PRESS TEST RESULTS BluePlainr Plant Washington D C

4 400

O O ' 1; ' do ' do ' ' l o ' do ' 6L ' 70 ' A ' do ' l o o o %Primry(wt '. dry rdh)

l00 90 80 70 60 50 40 30 20 x) 0 %SecmdUy (wt %dry ads)

Figure 2 6 . Resu l t s of tests with vary ing r a t i o s of secondary t o primary s ludge (Parkson Corporat ion)

MAGNUM PRESS TEST RESULTS Blue Plains Plant. Washington. D C

' t 0 10 20 30 40 50 60 70 80 90 100

XPrimary(wt.% dry sol&)

100 90 80 70 60 50 40 30 20 10 0 %Secondary (wt.% dry solids)

Figure 27. vary ing r a t i o s of secondary t o primary s ludge (Parkson Corporat ion) .

78

Polymer dosage and s o l i d s recovery f o r

Solids retention on the belt was estimated at 99%. Cake release was excellent, similar to the release with 100% primary sludge. These tests clearly indicated that a belt press retrofitted to a vacuum filter could produce cake solids in the desired auto-combustible range. Further tests were therefore conducted on a full-scale unit.

Demonstration (1.0 meter) unit--Vacuum filter cake tests on the full- scale unit encountered difficulty and the good results with vacuum filter cake on the laboratory unit were not duplicated. in Table 20.

Test results are presented All the problems were related to the feeding and distribution

TABLE 20. PARKSON PRESS AS A RETROFIT TO VACUUM FILTERS

CAPACITY BELT SPEED HIGH PRESSURE % CAKE TOTAL SOLIDS

RUN NO. (m/min) (kg/cm2> SOLIDS (kg/hr/m width) REMARKS

Matl. directly :E] from filter 1 2 4.4 35.5 2. 3 3.9 35.8 3 3 2.1 35.1 376 4 3 2.3 28.0 5 3 1.8 29.4 6 3 2.1 29.0 7 3 2.1 30.6 8 1 2.3 35.1 115

Matl. from 303 screw conveyor

of the vacuum filter cake (cake solids at 20%). Table 20, cake directly from the vacuum filter was used. was that previously described. The sticky nature of the sludge caused it to hang up on the walls of the hopper and form a bridge across the pump inlet. Some wash water was added to the hopper to facilitate feeding the pump, but interruptions of flow to the press were numerous, and the cake had to be forced manually into the bottom of the hopper. In Run #l, the feed layer was too thick the high-pressure section resulted. This condition caused the screen to wrinkle and crease under pressure. point (approximately 2.1 kg/cm2) where the material would not extrude from the sides at the high pressure roller. Because of these feed problems, the yields were low in these first three runs. Filtrate suspended solids were measured at 1328 mg/l in Run #1, thus giving only a 95% solids retention on the press.

In Runs #1 through #3 in The feed system

and a shearing and rolling effect at the beginning of

In Run 83, the pressure was lowered to a

The vacuum filter cake was then processed through a screw feeder in This material was easily fed through

Runs 14 through 118 show that the material, order to make the cake more fluid. the hopper/pump arrangement. although more fluid, also became more difficult to press as the floc deteriorated with the screw action. The speed on the press had to be reduced by one-third in order to achieve the 35% cake solids. Filtrate suspended solids increased to approximately 1900 mg/l and solids retention in the press was only 93%. Much more work in developing an acceptable feed system

79

P

is required in order to use the belt press in this application.

Komline-Sanderson Unimat Belt Press

Facilities-- The Unimat press was similar in concept to the Parkson press. The

Unimat press, pictured in Figure 28, had four dewatering zones: drainage stage; and low, medium, and high pressure stages. Pressures in the high-pressure section were in excess of 2.1 kg/cm2 (30 PSig). mounted unit tested was their GM2H - effective width of 0.5 meter.

a gravity

The trailer 5/7 pilot plant model, with an

Operation-- For the thickened sludge tests, the primary and secondary sludges

were thickened separately and blended in an 11.4 m3 (3000 gal) tank to produce a 2/1 secondary to primary sludge solids ratio. sludge was metered to a flocculation tank and polymer was added prior to feeding the press. The final cake and filtrate were analyzed for total solids. Yield was determined from measurements of the total solids and flow rate of the feed.

The blended

For the vacuum filter cake tests, a truck-load of 20% solids cake was taken from the plant's full-scale units and delivered to a point adjacent to the trailer. The cake was manually fed to the low-pressure section of the belt press in bucket loads. per unit time. During these tests with the vacuum filter cake, problems were encountered with the motor drive on the press. overloaded and kept kicking out; should have been used to handle this feed.

The yield was estimated by counting buckets

At times, the motor was a slightly larger motor and drive probably

Test Data--

Thickened sludge feed--(2/1 secondary/primary). Table 21 summarizes During this test the results of the tests run with the thickened sludge.

period, the plant experienced some upset conditions and the sludge was septic when received. days when the polymer would not flocculate the sludge to days when the same polymer worked very well. Laboratory tests were made each morning to determine which of the two available polymers would work. that were achieved, depending on whether the sludge would respond to the polymer at that time. the polymer rate had only marginal results on the final cake solids. other chemical conditioning agents, the polymers appeared to be quite selective and worked only within a very narrow range. 7/26 were the best for the-entire series, and seem to be representative of what the belt press can produce with the proper polymer conditioning. The overall average results were cake solids of 31 to 33% at a rate of 307 kg/hr/meter of belt width with a polymer cost of approximately $9.00 per ton of sludge solids. Unfortunately, because the Blue Plains sludge is so variable, these results would not be obtained every day. With our type of sludge, a number of polymers would have to be readily available for

The sludge characteristics varied considerably from

Thus, the results were quite inconsistent.

These results show the range of cake solids

The first two runs on 7/26 show that a doubling of Unlike

The last three runs on

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82

immediate use as the sludge characteristics changed. were not measured during any of these tests, therefore solids recovery was not computed.

Washwater flow rates

TABLE 22. UNIMAT PRESS AS A RETROFIT TO VACUUM FILTER

DATE

7-13-77 7-13-77 7-13-77

7-14-77 7-14-77

7-25-77 7-25-77

% FEED SOLIDS

22.1 22.3 22.3

22.0 22.8

23.0 23.6

% CAKE SOLIDS

34.3 35.5 30.4

37.6 35.3

33.2 34.1

TOTAL SOLIDS YIELD

kg/hr/meter width

655 595 947

543 5 85

613 1399

FILTRATE SOLIDS mgll

TOTALISUSPENDED

- 1 - - 1 -

2800 / -

- 1 - - / -

1776 / 1244 - / -

Vacuum filter cake--Table 22 shows results for the vacuum filter cake feed. Because the vacuum filter cake was originally conditioned with lime and ferric chloride, and because it was hand fed to the press, these results are consistent. The runs on 7/13 show that as the yield (i.e. belt speed) was increased, the final cake solids decreased. Cake samples taken from the intermediate-pressure zones during these runs showed that the first two zones increased the cake solids from 22% to approximately 27%. The high- pressure zone, on the other hand, increased cake solids from about 27% to approximately 35% and was responsible for the majority of the dewatering These results look promising and indicate that further tests, perhaps using only a high-pressure section of the press, are warranted.

83

VACUUM FILTER RETROFIT - ENVIROTECH HI-SOLIDS FILTER

Envirotech Corporation has developed a retrofit unit for a belt-type vacuum filter. This "Hi-Solids'' filter is an expression device which extracts additional moisture from a vacuum filter cake. It is equipped with an air compressor and associated controls, in addition to the standard auxiliary equipment needed for a vacuum filter. Figure 29. The filter cloth leaves the drum at its uppermost point and travels over a stationary grid. applies pressure to the cloth and the filter cake. A vacuum is pulled on the bottom of the grid to carry away extracted moisture. The operation of the unit is on a discontinuous cycle. A typical cycle takes either 5 . 2 or 7 . 2 minutes per revolution, corresponding to a 20 second or 40 second press time. For a 20 second press time the following sequence occurs: the cake forms on the drum for 20 seconds, the drum progresses 1/5 a revolution

The unit is pictured in

Above the grid is a rubber diaphragm which

Hi-Solids Assemb 1 y

Cloth

Figure 29. Schematic of Envirotech Hi-Solids Filter

84

and stops; the cake dries under vacuum for 20 seconds and the drum progresses another 1/5 revolution, etc. When the cake reaches the press zone, it is squeezed by the diaphragm for 20 seconds; then it progresses 1/5 revolution and is discharged. The cloth is subsequently washed and the cycle repeated. Diaphragm pressure is a maximum of 10.5 kg/cm2 (150 psig).

Facilities--

mounted, 3 ft. diameter by 3 ft. face filter. Auxiliary equipment included a sludge feed tank, three chemical feed tanks, flocculator, air compressor, transfer pumps, vacuum pump, filtrate pump and receiver.

Test work was conducted in April, 1976 on Envirotech's trailer-

Operation--

media and optimum chemical dosage for each of six different sludge ratios. Candidate filter media were evaluated by conducting five consecutive top feed leaf tests. Selection was based on good cake discharge, filtrate quality, and apparent resistance to cloth blinding, Chemical dosages were optimized by determining the minimum concentrations which gave the maximum filtrate volume for the total dewatering time.

A vacuum filter leaf apparatus was used to evaluate the proper filter

For the tests on the Hi-Solids Filter, primary sludge was obtained from a pilot plant primary clarifier, and secondary sludge was obtained from the plant's secondary clarifiers. Both sludges were thickened and delivered to the trailer feed tank for blending. Using the predetermined chemical dosages, the Hi-Solids Filter was operated at two different test conditions for each sludge:

Condition Press Time Cycle Time

1 2

20 seconds 40 seconds

5.2 min/rev. 7.2 midrev.

Test Data--

secondary sludge in Figure 30. ratio, performance tests on the Hi-Solids Filter were conducted. are presented in Table 23. solids and yields with increasing ratio of secondary sludge.

The results of the chemical conditioning tests are plotted vs percent Using these chemical dosages for each sludge

The results Once again the results show decreasing cake

The 2/1 ratio was used for comparison with a standard vacuum filter installation. Review of the data showed that a vacuum filter gave a 17% solids cake at 5.2 MPR, and 17.5% solids at 7.2 MPR cycle time. The Hi- Solids Filter increased this to 24 and 25% solids, but wasmot able to achieve the desired 35% cake sol-ids. with optimum chemical conditioning is expected to be 14.6 kg/hr/m2. Because of the Hi-Solids Filter attachment, this yield was not achieved at the 20 second press time (5.2 MPR) (14.0 kg/hr/m2) and was even further reduced (11.3 kg/hr/mZ) with the 40 second press time (7.2 MPR). cake solids above the 25% range were not produced, the Hi-Solids Filter was not considered as a dewatering option for the plant.

Full-scale yield on a vacuum filter

Because

85

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86

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VACUUM FILTER

During the August, 1977 comparison runs on the filter presses, samples of the conditioned sludge were also used to run a series of optimizing tests on a vacuum filter leaf. Tests were conducted according to the procedure described in the Komline-Sanderson Engineering Corporation instruction manual entitled "Test Leaf Instructions - Rotary Drum Vacuum Filter" (Document Number KSM029). excellent correlations with actual full-scale vacuum filter operation.

The 0.1 ft2 leaf, when used properly, can give

For each sludge sample, at least five different form and dry times The best of were run to show a range of possible operating conditions.

each of these runs is shown and compared to the corresponding NGK run in Table 2 4 . Generally, vacuum filter performance was adversely affected by high ratios of secondary sludge; cake solids above 20% were easily achieved when the percentage of secondary sludge was 50% or less. The filter press usually gave approximately twice the percent solids achieved with a vacuum filter; however, because of its continuous operation, the vacuum filter yields were much higher than the filter press yields (i.e. the total filtration area required was much less for a vacuum filter). In all cases, and especially with the higher percentages of secondary sludge, the filter press could more easily dewater varying sludge feeds. Marginally conditioned sludges, o r the difficult 100% secondary sludges, gave poor results on the vacuum filter but gave acceptable yields and cake solids on the filter press.

88

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SECTION 7

SPECIAL TESTS

CORRELATION WITH SPECIFIC RESISTANCE

During the latter part of the study, bench-scale filterability tests were performed in conjunction with experimental work on the pilot filter presses. Capillary suction time (CST), modified Buchner funnel (Rv), and high pressure (Rp) methods were used to determine the average specific resistance to filtration of the conditioned sludge mixture and provide correlations with press performance. methods are given in Appendix C.

Detailed descriptions of these test

Samples of the conditioned mixture were taken directly from the NGK

The filterability tests were mix tank to insure that the bench-scale tests were made on the same sludge mixture that was fed to the pilot filters. begun simultaneously with the start of the press cycles. measured first, followed by the pressure and modified Buchner funnel determinations, respectively.

The CST was

In Figures 31-33, the results of these tests for the NGK press are plotted. These graphs show that a definite empirical correlation existed between the average specific resistance of the conditioned sludge mixture and press performance. to filtration increased i.e. a process

obtained using a least squares linear regression analysis of the data in Figures 31-33). Results similar to this were also found for each of the fixed volume presses.

In general, press yields decreased as the resistance and minimum acceptable filtration for this press,

ield of 3.17 kg/hr/m2 to give cake solids of 35%, occurred at Rv = 27 x 10 4T 0 cm/g, Rp = 7 and CST = 15 seconds (these values were

At a plant similar to Blue Plains where sludge characteristics and, hence, chemical conditioning demand varies daily, correlations such as these can provide an invaluable tool for controlling full-scale press operations. measure of the specific resistance gave a good indication of press performance, regardless of either sludge blend ratio or quantity of conditioning chemicals added. In the calculation of the specific resistance parameter (See Appendix C.). the effect of these variables is minimized so.that

Tests on the pilot press units showed that the quantitative

consistent comparable the run on

resistance values have comparable press yields. the 4/1 secondarylprimary sludge required a conditioning dosage of

For example,

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91

RATIO % CHEMICALS Rv CST PROCESS YIELD SEC / PRIM Lime / FeC 13 RP 1010 cm/g sec kgl hr /m2

211 18.316.2 3.02 32.76 12.4 3.12 16.615.5 3.10 28.71 12.5 3.27

2/1 14.214.8 - 25.86 15.3 3.12 411 29.619.9 1.33 10.74 11.0 5.42 111 15.215.0 1.28 9.57 12.8 5.81 112 15.515.2 0.86 5.20 9.3 6.79 111 18.916.4 0.69 4.04 8.4 6.20

2/1

29.6% lime and 9.9% FeC13; specific resistance values of Rp = 1.33, Rv = 10.74 x 1010 cm/g, and CST = 11.0 sec were obtained; and a yield of 5.42 kg/hr/m2 resulted. however, a chemical dosage of only 15.2% lime and 5.0% FeC13 was required, yet nearly identical resistance values of Rp, Rv, and CST equal to 1.28, 9.57 x 1010 cm/g, and 12.8 sec, respectively, were obtained.

Because of correlations of this type between the specific resistance and the press yield, these bench-scale resistance tests provide a quick method whereby press output can be approximated prior to filtration. And within the span of only a few moments for testing, hours which would be wasted on inadequate filtration can be avoided.

In the subsequent run on the 111 sludge mixture,

The resulting press yield, therefore, was also nearly identical at 5.81 kgIhrlm2.

It is evident *from the above table, however, that the CST, although a good indicator of filterability, does not give consistent results. Other researchers2 have found that the test is extremely sensitive to the feed solids concentration of the sludge and, hence, is most useful only when correlated with results from the pressure and modified Buchner funnel tests. In Figures'34 and 35, these correlations, in which the CST has been corrected for feed solids, are shown. While the CST would be the preferred method of determining filterability since it requires only a few seconds to perform, the considerable amount of data scattering suggests that this method introduces a significant error in resistance determinations.

Several manufacturers have indicated that for high pressure filtrations, the pressure method is preferred, In Figure 36, however, the correlation between Rp and Rv shows that the modified Buchner funnel and pressure tests produced comparable results (correlation coefficient = 0.902) for our particular sludge. This indicates that the Buchner test, which requires less time and is much easier to operate, can at times be used with equal accuracy in high-pressure filtration work. Moreover, where precise determinations of actual resistance values are not required, the modified Buchner test can be reduced to a simpler form in which only the quantity of filtrate collected within a given period of time is noted. Compilation

2. Baskerville, R.C. and R.S. Gale, "A Simple Automatic Instrument for Determining the Filterability of Sewage Sludges, "Water Pollution Control, - 67, 233 (1968).

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93

of all the data collected for the Blue Plains sludge showed that if 80 mls of filtrate were collected within two minutes, the filter cake would cow pletely form and a resistance value of Rv = 27 x 1010 cm/g would result.

The specific resistance tests were also used to evaluate the effect of varying chemical dosages on the different sludge mixtures. As stated previously and shown in the following table, the filterability of the conditioned sludge generally increased with increasing chemical addition; this change was reflected in decreasing values of the specific resistance:

% CHEMICALS Rv CST PROCESS YIELD DATE LIME/FeC13 Rp 1010 cm/g sec kg/m2/ hr

8-19 19.6/6.5 1.16 6.84 10.5 6.69 8-10 15.2/5.0 1.28 9.57 12.8 5.8. 8-10 12.1/4.0 2.06 19.49 12.6 5.17

(Ratio secondary/primary = 1/1)

Theoretically, the point at which optimum chemical conditioning occurs, i.e.

obtained from resistance measurements. a determination of this type, a substantial cost savings in chemicals can be realized since the unnecessary addition of conditioners would be avoided.

. the greatest increase in press yield per unit addition of chemicals, can be In a full-scale installation, with

DEWATERING OF VARIABLE SLUDGE CONCENTRATIONS

Throughout the study, the unconditioned sludges averaged 5% total solids. to 6.0% - 6.5% for feeding to the press. Because gravity thickening and air flotation thickening will produce a consistent 5% solids feed, no special tests were run to determine quantitatively the effect that variable feed concentrations had on filter press results; however, the NGK press was capable of handling a range of feed solids from a low of 2.4% (1.8% before conditioning) to a high of 10.0% (8.4% before conditioning). In the low solids region, the press yields were slightly lower because more water had to be processed; but because of the separate squeezing cycle in the diaphragm press, cake solids were not affected. In the high solids region, two adverse effects were noted:

Conditioning with lime and ferric chloride raised the total solids

1. Conditioning in the mix tank was difficult because the high sludge solids were very viscous and chemical dispersion was hindered.

2. The sludge pump and the feed ports in the press were more easily plugged with trash and heavy solids.

Total feed solids of 10% appear to be the upper concentration that the diaphragm press can handle. Tests to evaluate feed concentration5 were not run for the fixed volume presses.

94

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95

MATERIAL BALANCE

The NGK press was the only unit tested for which all input and output streams could easily be measured. used to calculate a sample material balance. The calculations, detailed in Appendix D, show a very good balance between input and output total solids.

Test data from a run on 10/18/77 were

CONDITIONING WITH POLYMER

Over thirty polymers were screened in an attempt to find a polymer that could adequately condition the sludge for dewatering on a filter press. Allied Colloid's Percol 776 was found to give the best results in the conditioning step. This polymer, a high activity cationic formulation, worked quite well in conjunction with ferric chloride on a vacuum filter. Tests on the Buchner funnel also showed good filterability. Full-scale tests on the NGK press, however, gave rather poor results. Cake solids no greater than 28.6% were achieved, even with extended squeezing cycle times. were, therefore, quite low. The largest problem, however, was the almost *immediate cloth blinding. the cloths, thus requiring them to be removed for acid washing.

Yields

High pressure sprays were ineffective in cleaning

It is believed that the floc formed by the polymer was too weak to withstand the high pressures in the press. But, with proper cloth selection and care in conditioned sludge handling and feeding, the filter press can probably be adapted to dewater a polymer conditioned sludge. The sludge at Blue Plains, however, varies to the extent that one polymer that will work effectively 100% of the time has not yet been found. In contrast, the lime/FeC13 conditioning system can be adjusted to always give satisfactory results.

TESTS ON PRESS CAKE PROCESSING

The automatic operating mode on the NGK press allowed the production of relatively large quantities of filter press cake for other purposes. Throughout the entire study, the filter press cakes were used for composting trials at the Beltsville, Md. compost site. A number of cakes were analyzed for their calorific value and used in incineration tests conducted in both a multiple hearth incinerator and a rocking grate solid waste incinerator. A local power utility also analyzed the press cake for possible use in coal fired boilers.

Cake Physical Properties

The cake, when discharged from a diaphragm press, resembles a large

3 up waffle. Generally, it is rigid and free-standing but break (see Figure 37). The density ranges from 1121 to 1185 kg/m This press cake, when conditioned with lime and FeC13, dries out in several days. Sludge cakes that were conditioned with 20% lime/6.7% FeC13 were exposed to ambient weather conditions. exposed to sunlight, rain, etc. Another cake was placed in the center of a

(70-74 lb/ft3

One cake was placed in the open,

96

61 cm (2 foot) high "pyramid" of sludge cakes. cake was analyzed for percent solids.

Each day a portion of the

TEMPERATURE % SOLIDS % SOLIDS DAY WEATHER WHEN SAMPLED OPEN PYRAMID

0 Cloudy 27 O C 39 41.6 1 hin/clearing 14 OC 44.7 41.1 3 Sunny 20 o c 72 40.8 4 Cloudy 24 OC 77.5 40.7 5 Rain/clearing 24 OC 77.2 41.7

These results show that the press cake does air dry when spread in a thin layer or if stacked vertically. impervious to rain and was very hard and brittle. The material in the center of the pyramid did not dry; however, further observations of the cakein the interior of taller piles up to 122 cm (4 feet) showed some self heating after 3 to 4 weeks as aerobic decomposition (composting) proceeded. However, when the cake was broken up into 5 cm (2 inch) pieces prior to piling outside, it was easily rewetted by rain and became difficult to handle. These observations were quite useful when conducting the composting trials.

A s the*cake dried it became

Cake Breaking

In a large-scale installation, some type of cake breaker will be required prior to any further processing. Fortunately, the diaphragm press gives a fairly uniform product which can be easily handled in a controlled situation. Test work centered around finding acceptable methods of cake breaking and establishing the parameters that affected this step.

Three types of units were found to work:

1. A small tree and branch chipper, operated at high speeds, was capable of breaking up fresh press cakes. The high speeds, however, caused the machine to gum up easily. reduced any partially dried cake to dust.

The unit also

2. A garden rototiller, run through the cakes while piled on the ground, was used to prepare the sludge prior to composting. This slow speed unit did an acceptable job for small test quantities of cake.

3 . A make shift variable speed screw, pictured in Figure 38, worked quite well to produce chunks in the 5 cm (2 inch) range. on this unit showed that slow speeds gave the best results. The effectiveness of this machine was found to be a function of percent cake solids. Cake solids below approximately 27% tended to stick

Tests

97

Figure 37. Cake from NGK Diaphragm Press.

Figure 38. Cake Breaker.

98

to moving parts. Above the 27% level, the cakes responded to mechanical handling with no sticking. This unit was also effective in breaking up the cakes from the fixed volume presses. The wetter inner sections of the cakes from these presses caused no problems as long as there were sufficient guantities of the dry outside cake sections to help scour the internal screw.

Compost Trials

Tests were conducted at U.S.D.A.'s compost research facility at Belts- ville, Maryland, in which the filter press cakes were composted via the static pile method. filter cake at 20% solids. For the vacuum filter cake, the sludge is mixed with wood chips ( 2 : l chips to sludge volumetric ratio; 1:l weight basis) and stacked to a height of approximately 2 . 4 m (8 feet) over a perforated pipe. the pile for a period of 21 days, causing temperatures to reach a normal 70 OC. The mixture is sufficiently deodorized in this time period and the pile is then moved to a stationary curing pile approximately 4.6 m (15 ft) tall for 30 days. The curing period ensures maximum pathogen kill. After screening out the wood chips for reuse, the product is ready for distribution.

This method is quite successful for composting vacuum

A layer of finished compost blankets the pile. Air is drawn through

The wood chips are needed to reduce the initial moisture of the mix, The to provide air passages, and to provide an additional carbon source,

wood chips are the major operating cost of this operation. that with the filter press cake, the wood chips could be eliminated o r substantially reduced in quantity. Initial composting tests on the press cake without wood chips did produce the required temperatures in the pile, but complete deodorization of the mass was not achieved; the larger chunks of cake had crusted over and contained an anaerobic inner core.

It was hoped

Good results with the filter press cake were obtained by breaking up the cake to a size of 7.6 cm ( 3 inch) or less with a rototiller, and mixing with wood chips to a volumetric ratio of 0.5:l chips/sludge cake (approximately 0.2:l .O weight basis). composting and 30 days curing were required for the process. though, are only preliminary since much larger quantities of press cake are required for a full-scale demonstration test. that if filter press cake is available, cost savings of up to 60% over the vacuum filter operation can be obtained.

The same time periods of about 21 days These results,

It is projected, however,

Incinerator Tests

A number of the press cake samples were analyzed in a Parr adiabatic oxygen bomb for their calorific value. An average of 32 samples of 2/1 secondary/primary sludge press cake showed that the press cake can be considered to be a low-value fuel that will burn without auxiliary fuel oil.

99

Dry solids basis 3228 cal/gm (5806 Btu/lb) Wet solids basis 1225 cal/gm (2204 Btu/lb) Dry volatile solids basis 6293 cal/gm (11318 Btu/lb)

Multiple hearth unit--

meter (18 inch) single hearth furnace at the Nichols Engineering Research Facility. The purpose of the tests was to determine if the high chemical content of the Blue Plains filter-pressed sludge would cause any clinkering problems. Prior to one of the tests, the Blue Plains secondary plant was overdosed with FeC13 to simulate the approximate iron and phosphate content in the sludge that is expected when the advanced waste treatment facilities are completed. FeC13 for conditioning prior to filter pressing. had the normal amounts of iron and phosphate that were available from the plant at that time.

Samples of the filter press cake were incinerated in a 45.7 cm dia-

This sludge was then overdosed with lime and A second sludge tested

The following table identifies the sludges tested.

% CHEMICALS % VOLATILE SLUOGE CAKE LIME/FeC13 X Fe* % SOLIDS SOLIDS

1 24.4/8.2 8 42.8 2 15.6/5.1 8 39.3 3 25.9/8.7 5 39.6 4 13..9/4.6 5 37.7

*estimated by calculation

45.4 50.1 47.2 53.5

Each of the sludge samples were incinerated t complet

BTU/lb DRY SOLIDS

4872 5373 4995 5789

burnout t temperatures from 927 OC to 1038 O C (1700 OF to 1900 OF). fed to the furnace ranged from 2.5 to 7.5 cm (1 to 3 inches). burnout was achieved with no clinker formation. It was concluded that the filter press cake and the high chemical addition would pose no special problems for the incineration of the Blue Plains sludge.

Particle size Excellent

Solid Waste Incinerator Tests-- A qualitative test was conducted to determine if the filter press

cake combined with solid waste would burn in a solid waste incinerator. The test unit was a Flynn ti Emrich rocking grate design with underfire and overfire air controls. pit, had an average solids detention time of 45 minutes. Approximately 6600 wet kg (3000 lbs) of press cake at 35% solids were dumped into the furnace along with solid waste. above the furnace dropped from its normal 677 OC (1250 OF) to 593 OC (1100 OF) when the sludge was in the burning zone. residue, however, showed no signs of the sludge cake and it was assumed to be completely burned. burn well in a co-disposal scheme with solid waste. cake moisture, however, there is a limit to the amount that can be blended.

The furnace, fed by cranes from a storage

The temperature in the combustion chamber

Examination of the

These tests indicated that the press cake would Because of the press

100

Calculations show that with a 35% solids cake, approximately 20 to 40% of the wet feed to the incinerator can be sludge cake.

Evaluation of Press Cake in a Coal F i r e d Boiler

Samples of filter press cake were given to a local utility, Potomac Electric Power Company, for their routine fuel analysis. The purpose was to determine if a filter cake-coal mixture could be fed to a boiler to produce electricity. They analyzed the cake sample for ash, sulfur, moisture, and calorific content:

As received Dry basis

Ash Sulfur Water Cal/gm (Btu/lb)

12.7%

62.5% 1171 (2108)

0.14% 33.9% 0.37% -

3123 (5621)

This analysis caused them to reject the press cake as a fuel. that, "Although there are no chemical reasons that we can see which would preclude the use of this sludge as a fuel, the amount of ash is extremely high and would considerably increase our ash handling problems." Because of possible pluggage problems, "our suppliers of coal mills express concern with the fibrous material in the filter press cake,,.. The amount of gas flow handled by the induced draft fans would increase because of the high moisture content of the sludge. Considering the additional costs for fan power and ash handling and the additional expense of the added new equipment for handling the sludge, it is doubtful if there is any economic benefit to be gained from the burning of sludge. Further study would be required to confirm this preliminary cost estimate,"3 of filter press cake were not available for a full-scale test.

They stated

Sufficient quantities

3Letter R. C. Ungemach (Pepco) to R. C. McDonell (Montgomery County Council) June 3, 1977.

101

SECTION 8

PROCESS DESIGN

The purpose of the study was to evaluate the various dewatering devices that are capable of producing an auto-combustible cake and to develop design parameters for those units that actually achieved this goal. For auto- combustion, approximately 35% total solids in cakes containing lime and FeC13 conditioning and 30% solids in polymer-conditioned cakes are required from the dewatering process. The continuous belt press and each of the filter presses met these requirements.

CONTINUOUS BELT PRESS

A continuous belt press can produce a 30% solids cake with polymer conditioning. While theoretically this is acceptable for auto-combustion, some practical problems negated consideration of this press for use at the Blue Plains plant:

1.

2.

The need to rely solely on polymer conditioning is unacceptable. During the testing on the belt press, the variability of the sludge feed was so pronounced that no single polymer was found that properly conditioned the feed at all times. rate secondary process produces a variable waste sludge that has a highly variable response to polymer conditioning. While the use of lime as a conditioning agent would reduce this variability, scaling and cloth plugging problems normally associated with using lime have made belt press suppliers somewhat reluctant to rely on it for conditioning.

Apparently the high-

The high solids content of the filtrate can cause recycle problems in a plant where effluent suspended solids must be controlled to very low levels. Suspended solids capture in the belt press was estimated at 95% for the 2/1 secondary/primary sludge. However, the poor cake discharge generally experienced with this sludge led us to believe that this figure could be an over-estimation of the actual recovery. When advanced waste treatment facilities are completed at Blue Plains, the wastewater effluent must meet a required 7 mg/l suspended solids and 0.22 mg/l total phosphorus standard. Because of the necessity to recycle all water streams from solids processing, the thickening and dewatering systems must have a high degree of solids capture. The entire plant is self- contained with only two effluent streams: the wastewater discharge

102

to the river and the sludge. stream, they will be recirculated through the treatment system and even- tually discharged to the river. Calculations show that if only a 95% solids recovery was achieved in dewatering, the filtrate stream returned to the head of the plant would raise the suspended solids level in the influent raw wastewater by approximately 15 mg/l. This influx of fine solids, together with the recycle solids from thickening operations (which would raise the influent level another 22 mg/l), would pose an additional burden on the wastewater treatment train. Because of the uncertainties in operating advanced waste treatment with multi-media filters, the authors believe that unless a 98-99% solids capture is achieved in the dewatering operation, thus minimizing recycle fines buildup in the system, the plant may have difficulty in achieving its effluent standards.

If solids are not removed via the sludge

For these reasons, the belt press was considered unsuitable for use at Blue Plains to dewater thickened sludge. The unit, though, has many advantages that warrent full investigation at other facilities. In a plant that has a fairly consistent sludge that responds well to polymer conditioning, $he press can provide a low capital, low operating cost process for producing an auto-combustible cake.

When used as a retrofit device to a vacuum filter, test work showed that the high-pressure section of the belt press can further dewater the vacuum filter cake to the same final cake solids as a filter press. lime and FeC13, rather than polymer, were used in conditioning the thickened sludge. No additional chemicals were used to condition the vacuum filter cake prior to dewatering on the belt press. Thus, if the problems encountered during the demonstration of this process can be overcome, the use of the press as a retrofit unit can be a very cost-effective alternative to the filter press, especially for existing vacuum filter installations. Further test work, however, is needed to evaluate possible feeding and distribution systems. add-on device should also be assessed.

In this case,

Long-range problems associated with the use of lime and FeC13 on the

FILTER PRESS

Chemical conditioning

The addition of lime and FeC13 to the sludge is necessary for the operation of the filter press. Throughout the study period the chemical dosages required for good filterability varied with the sludge characteristics. priorities should be placed on defining the variables in the wastewater processing train that most affect the sludge characteristics and operating the treatment plant in a manner that will minimize their effect on sludge filterability. operation, but will also save many dollars in chemical conditioning costs.

In a full-scale continuous dewatering operation one of the highest

Doing this will not only provide a smoother dewatering

Another high priority should be placed on the conditioning step itself. During the course of the study several important large-scale design considerations evolved:

103

1. Because of (a) the cost of chemicals and (b) the increase in final disposal costs due to the addition of inert conditioning chemicals, optimization of the dosage is necessary. A method of predicting this optimum dosage was not found; however, bench-scale methods (CST, Buchner funnel, pressure tests) were developed which gave an indication of how well the conditioned sludge would dewater on a filter press. To avoid the necessity of running a large number of these tests, the authors feel that a small pilot-model horizontal vacuum filter could be used as a Buchner funnel to continuously monitor the specific resistance filtration parameter. A small slip stream from the conditioning tank would be fed to this filter and, with the unit running at a constant speed, the time needed to produce a dry cake would provide an indication of the dewaterability of the conditioned sludge. The bench-scale tests had shown that if the conditioned sludge could be filtered down to a good cake within 3 to 4 minutes on the Buchner funnel, that same sludge would also filter easily on the pilot press and a 35% solids cake would be produced. By adjusting the feed rate and belt speed of the horizontal vacuum filter, this correlation could be established for the full-scale press. If the cake dries too quickly, the sludge has been over conditioned and the chemicals can be cut back slightly. If the cake takes too long a time to form, the chemical dosage is insufficient and can be increased. The unit would obviously have to be calibrated in the field under continuous operating conditions. A small unit, costing less than $20,000, could provide the necessary information to control a multi- million dollar filter press installation.

2.

A horizontal vacuum filter was not obtained in time to be tested in the study. When a unit becomes available, however, tests will be conducted to prove this concept.

Because of the wide range of sludge feed rates to the press, better control of the conditioning chemicals could be obtained by conditioning at a constant flow rate. The arrangement used during the continuous run on the NGK press (depicted in Figure 16) is a good example. In addition to the conditioning tank, a small surge tank was used to hold the conditioned sludge for feed to the press. The sludge leaving the conditioner could then be sampled and checked for filterability. The conditioning tank must be designed to provide good mixing without shearing the floc. The surge tank should be sized for a maximum of 30 minutes detention time with only enough agitation to keep the solids in suspension. Both tanks must be designed so that miscellaneous trash and small fibers do not build up on the moving parts. A shredder (mazorator) installed in the sludge feed line to the tanks will keep the trash to a manageable size and avoid plugging in the filter press.

3 . Careful handling of the conditioned sludge at all times is a necessity if chemical costs are to be optimized. feed pump must be of a design to minimize shearing of the sludge

The filter press

104

floc as the material is delivered to the press under pressure.

4 . The corrosiveness of the FeC13 solution is an important consideration in selecting materials of contruction for both the filter press system and the final disposal system. Sludge cake that has been conditioned with FeC13 is generally mildly corrosive.

5. During the design phase, close attention must be given to lime slurry handling. Experience at Blue Plains has shown that scaling will occur not only in the lime slurry lines feed lines and filtrate lines. Injection of an anti-scalant solution in the lime slurry can assist in alleviating these problems. Careful design of all piping systems including access for periodic clean-out is a necessity.

but also in the sludge

Filter Press Design

The following section on costs shows that the three types of presses-- diaphragm, high-pressure, and low-pressure - can all provide the required cake Solids at approximately the same unit costs. Several advantages and disadvantages of each type are not, however, readily apparent from these tables.

The diaphragm-type press generally gave higher cake solids, shorter cycle times, and a more uniform cake than the fixed volume presses. Essentially this improved performance was related to cake thickness. The diaphragm press operates best with a 13 t o 19 mm (1/2 to 3/4 inch) cake; the low-pressure press with a 25 to 32 mm (1.0 to 1.25 inch) cake; and the high-pressure press with a 30 to 40 mm (1.18 to 1.57 inch) cake. The low-pressure press (100 psig) generally gave shorter cycle times than the high-pressure press (225 psig), although the final overall yield was greater with the high-pressure unit. Apparently, the higher pressures have the advantage of being able to handle the thicker cakes and, therefore, give higher yields per press cycle.

Cake discharge with the high-pressure press was not, however, completely acceptable. improve the discharge or the use of a precoat would be required for a full- scale installation. pressure press The diaphragm press used low pressures to feed the sludge (<lo0 psig), but squeezed at pressures of 213 psig. tioned and no precoat would be required.

Either the selection of a filter media which would

Cake discharge was generally very good on the low- and no precoat would be required.

Cake discharge was always good when the sludge was well condi-

An additional advantage of the diaphragm-type press is that it is the only type of press that can successfully dewater marginally conditioned sludges. ter capacity is available, less chemicals could be used to marginally condition the sludge. Longer squeeze times would be needed to achieve the required 35% cake solids. Thus, the squeezing diaphragm can be used to minimize the overall chemical costs.

Therefore, during periods of low sludge production, when extra fil-

105

This increased flexibility of a diaphragm-type press can also be used to give any desired cake solids on normally conditioned sludges (by using extended squeeze times) up to the limit of filterability (approximately 40-45% total solids for a 2/1 sludge). press are developed by the squeezing water pump, a relatively low maintenance item. feed pump, generally a higher maintenance item.

The high pressures in the diaphragm

High pressures in a fixed volume press are developed by the sludge

The production of sludge cake with a diaphragm-type press gives the process advantages as mentioned above; however, from a mechanical standpoint, this also means more mechanical movement of the press components per ton of sludge filtered as compared to the fixed volume presses. This increased mechanical movement could mean not only higher maintenance costs, but also increased instrumentation to control the cycle. In addition, a diaphragm-type press will be discharging cakes every 30-60 minutes, while the fixed volume presses will discharge thicker cakes every three hours. Unless these discharge operations can be made totally automatic and trouble- free, an operator should be present. Accordingly, in the cost estimates for the NGK press, the automatic shaker was eliminated and was replaced by increased manpower. The discharge operation on the diaphragm-type press that releases all cakes at one time (e.g. Ingersoll-Rand, Lasta design) appears to have some advantages over the single or two cake discharge operation.

Diaphragm and cloth replacement costs represent another disadvantage for the diaphragm-type press. Cloth wear occurs in the initial sludge feed portion of each cycle. Once the cake is formed, filtration occurs through the cake and the cloth essentially sees only relatively clear water. Cloth life for all types of presses is estimated at 3000 cycles. With a fixed volume press this equates to changing a set of cloths each year; with a diaphragm press, every three months. designs is quite difficult and long periods of downtime are required. Considerably more field testing is required to find more wear resistant cloths and to define the parameters that extend cloth life.

Cloth replacement with some filter

Based on the manufacturer's recommendation, diaphragm life is estimated at 20,000 cycles. under full-scale operating conditions.

Verification of this cycle life must also be established

Design Parameters--

NGK diaphragm press--For the 2/1 secondary/primary sludge ratio, Table It 10 in the report shows an average of 95 runs over a seven month period.

is assumed that these results would be representative of a full years operation. A 17-minute pump time, 18-minute squeeze time, and a 19-minute mechanical time would be required per cycle (54-minute total). Cake solids of 35-40% would be attained at an average yield of 2.39 kg/hr/m2 (0.49 lb/hr/ft2). The cloth shaker is not included in the mechanical time; it would add another 6 minutes to the cycle for cake discharge. every 20 cycles.

On the average, the chemical dose would be 20% lime and 7% FeC13,

The cloth wash is assumed to be required

106

When ore production is required, increased chemical dosages (another 5 percentage points of lime and 2 of FeC13) can increase the yield by a factor of 1.2 (based on full-scale yield data derived from Table 5). diaphragm-type filter press installation can therefore be sized for average sludge production figures, but it has a built-in capability to increase sludge throughput by slightly overdosing the chemicals.

A

The sludge feed system should include a pump to deliver pressures up to A feed pressure recorder would provide a useful indica- 7 kg/cm2 (100 psig).

tion of whether the rate of pressure rise is too great (indicating pluggage or underconditioned sludge). A sludge flowrate meter, correlated with total solids of the sludge feed, could be used to stop the feed pump at the optimum feed rate. water pump that will deliver variable pressures up to 1 7 . 6 kg/cm2 (250 psig) . The filtrate during both the pumping and squeezing cycles should be monitored for flowrate and total flow per cycle. The rate monitor would signal the end of either the pumping or squeezing cycle. The flow totalizer would be used to indicate differences between runs and provide a monitor on cloth pluggage.

The diaphragm pressurization system should include a squeezing

Based on the information available, the cloth of choice would be the TR 520'type (described in Table 9). evaluation. achieved during the study. kglcm2 (350 psig) and this was not always sufficient to clean the cloths. acid wash system may be necessary for units that use lime for conditioning. Acid washing is quite effective at removing calcuim carbonate and lime deposits both from the cloth and the filtrate passages on the plates. large-scale installations, both acid washing and high-pressure spray washing should be available. Acid is used to free the system of lime deposits; high pressure sprays are used to remove imbedded sludge particles from the filter media.

The cloth wash system needs further The full system pressure of 70 kg/cm2 (1000 psig) was never

The operating pressure available was only 24.6 An

For

The large number of electrical functions necessary for the diaphragm- type press would best be served by using solid state components which could be programmed to indicate malfunctions in both machine and circuit operations. Some problems were encountered with the limit switches and relays that were not easily located and/or correctable.

The NGK pilot press was provided with a 25 mm (1-inch) filtration chamber. with much thicker cakes, we recommend that a thicker chamber be provided on a full-scale design. increase the overall yield substantially. compromise the advantages of the diaphragm-type press. With easily filterable sludges, more cake per cycle can be discharged. If, however, the sludge filterability is poor, short pump times could still be used to provide a thin, dry cake. with a thicker chamber because of the increased distance of diaphragm movement. would be less likely to be plugged with rags and trash.

Because the sludge was easily filtered on the fixed volume presses

Chamber thickness up to 38 mm (1.5 inches) should A larger chamber would not

Diaphragm and cloth life must each be evaluated

An added benefit of a larger chamber is that the feed opening

107

Y

Lasta Diaphragm Press--Comparison testing showed that the Lasta press would give both equivalent cake solids and somewhat higher yields than the NGK press. An average of seven runs on both presses indicated that the full- scale Lasta yield was 22.6% higher than the NGK yield for the Blue Plains sludge. Because of this limited amount of data, design parameters for this press were developed by scaling results from the NGK press. Using the seven month average on the NGK press and applying the 22.6% factor, the full-scale average yield for the Lasta press is then 2.93 kg/hr/m2 (0.60 lb/hr/ft2). The number of Lasta filter press units required for installation, though, will be greater than that for NGK. filtration area, whereas the largest NGK press has 500 m2.

The largest Lasta press has only 204 m2

The main advantage of the Lasta desi n is the shorter mechanical turn- around time (10.5 minutes for their 204 m 5 press), since all chambers discharge at once. Additionally, the cake discharge and cloth washing operations are almost completely automatic and the operator attention required would be minimal.

Because of Lasta's shorter mechanical time and, consequently, higher yield, the optimum pumping cycle (as determined from the solids addition rate) is slightly shorter. This provides for a thinner cake and, therefore, somewhat shortened squeezing times. Sufficient data was not collected to compute average cycle times; however, an estimate would be in the range of 30 to 40 minutes total. This assumes that during cloth washing, accomplished by low-pressure (100 psig) sprays, only 1/4 of the filter cloths will be washed each cycle.

The same type of controls as discussed for the NGK press would also be required for the Lasta design. in this press, however, the main disadvantages of a diaphragm-type press, i.e. filter cloth and diaphragm replacement costs, could possibly be even more pronounced with the-Lasta-type design.

Because of the shorter cycle times

High-pressure press (Passavant)--The full-scale design for the Passavant press is based on the comparison runs in August, 1977. During that time the results showed that the high-pressure press could process the same quantity of sludge but would require 62.3% more filtration area than the NGK press. Design parameters for this press were also developed by scaling the results from the NGK diaphragm unit. Taking the seven month average of data on the NGK press and applying the 62.3% factor gives a Passavant design yield of 1.51 kg/hr/m2 (0.31 lb/hr/ft2) with a 40 mm (1.57 inch) chamber thickness. A mechanical time of 20 minutes is required for their Model 20 press (11,625 ft2). solids of 34 to 37% will be produced in an average cycle time of 3-1/3 hours. Increasing this chemical dosage (another 5 percentage points of lime and 2 of FeC13) should result in an increased yield of approximately 20%. the NGK press, a built in capacity exists for handling increased sludge production by increasing the chemical dosage.

Using 20% lime and 7% FeC13 for conditioning, cake

As with

The sludge feed system should include a pump to deliver pressures up to 15.8 kg/cm2 (225 psig). A feed pressure recorder is necessary but a flowrate indicator would not be needed with this press. Filtrate rate and

108

total filtrate flow is the preferred method of monitoring the operation, The sludge feed system surge tank should be shared with several presses so that the conditioned sludge detention time does not increase above the 30 minute limit (to avoid floc deterioration).

Low-pressure press (Nichols)--The full-scale design for the Nichols press is based on the comparison runs in August, 1977. During that time the results showed that the low-pressure press could also process an equivalent quantity of sludge but would require 126.8% more filtration area than the NGK press. Again, design parameters were developed by scaling NGK press results because of the limited amount of data available. Taking the seven month data on the NGK press and applying the 126.8% factor gives a Nichols design yield of 1.07 kg/hr/m2 (0.22 lb/hr/ft2), with a 32 mm (1.25 inch) chamber thickness. A mechanical time of 20 minutes is required for their largest press (6760 ft2 with 115 chambers). 7% FeC13 for conditioning, cake solids of 34 to 37% will be produced in an average cycle time of 3 hours. Increasing the chemical dosage will give an increase in yield similar to the high-pressure press. With the exception of using a feed pump of 7.0 kg/cm2 (100 psig), all other comments for process cont5ol are identical to those made for the high-pressure press.

Using 20% lime and

MULTIPLE-HEARTH INCINERATOR DESIGN

Tests run on the single-hearth incinerator showed that there would be no clinkering problem with the filter press cake. We were unable to run any tests to prove that the press cake was auto-combustible; however, the calculations are fairly well known and have been verified in large-scale installations. Figure 39 is a plot showing incinerator outlet temperature as a function of cake total solids and percent conditioners. Any combination that gives an outlet temperature above 800 OF is auto-combustible. The graph was provided by Whitman, Requardt and Associates, Baltimore, Mary- land. Assumptions were:

Feed rate: 507,000 lbs/day sludge solids Volatile solids before conditioning: 60% Heating value: 10,000 Btu/lb V . S . Excess air: 75%

The figure shows that with 27% conditioners (20% lime, 7% FeC13) and 35% cake solids the feed is auto-combustibile with an 800 OF outlet temperature. If the quantity of conditioners increases, then there must be a corresponding increase in percent cake solids. For example, if the dosage rate is increased to 33% (25% lime, 8% FeC13), then the cake solids must increase to approximately 36.2%. This increase in cake solids is easily accomplished with any of the filter presses. Essentially the figure shows that large increases in chemical addition rates require only small increases in final cake solids to maintain the 800 O F temperature. chemical conditioning, increasing the cake dryness by extending cycle times in the press has the effect of raising the incinerator outlet temperature. If an afterburner is used immediately downstream of the incinerator, this increase in outlet temperature may result in some fuel savings. In

For a given

109

actuality, however, it is more cost-effective to remove the water vapor thus reducing the amount of gas to be heated prior to raising the outlet gas temperature (for toxic pollutant control @ 1350 OF). There is then, little benefit to achieving a very dry cake above the auto-combustible range. However, if a waste-heat boiler is used for steam generation, the higher outlet temperatures could increase the steam production, and fn this case there may be some benefit to increasing the cake solids from the press. The alternatives are too complex for any generalized calculations to show the tradeoffs; hence each design must be evaluated on an fndividual basis.

111

SECTION 9

DEWATERING AND DISPOSAL COSTS

Estimates of capital and operating costs are presented in Tables 25 through 29. These estimates are for a large municipal wastewater treatment plant generating 250 dry tons of sludge per day (roughly equivalent to a wastewater flow of 200-250 MGD). These estimates are purposely generalized and not specific to the Blue Plains plant. The dewatering options costed are vacuum filters, filter presses, and belt presses. Final disposal costs for both incineration and composting are included.

*

The reader is referred to Appendix E f o r details of a l l calculations. The following general assumptions were used in developing the tables.

1.

2.

3.

4 .

5.

6.

7.

Sludge: 500,000 lbs/day dry incoming sludge solids @ a concentration of 5% (before conditioning); 2/1 secondary/primary sludge solids ratio.

Chemical conditioners: For vacuum filter and filter presses, lime @ 20%, FeC13 @ 7% of dry sludge solids. Lime cost @ $0.022/ lb; FeC13 cost @ $0.065/lb. lime deposits. For belt press, polymer costs @ $15.00 per ton of sludge solids,

Anti-scalant needed to help prevent

Yield: Based on test data and expressed as pounds of sludge solids per hour per square foot of filtration area. expressed as pounds per hour per meter of belt width.

On belt press,

Number of Units: Based on largest size unit available. (See Appendix F for specifications.)

Capital cost (1978 dollars): Includes chemical feed system, sludge feed pumps, dewatering unit with all necessary accessories, and conveyor system to transport cake to next process. The total capital cost was obtained by multiplying the manufacturers' equipment cost by a factor of 3 to include installation, piping, utilities, building and engineering.

Amortization: Computed at 6-3/8% and 20-year life. Capital cost x 0.09 = annual amortization cost.

Power: Cost at $0.04 per kwhr.

112

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TABLE 26. BELT PRESS COSTS

Sludge Solids (Tons/day) Yield (lb/hr/meter of width) % Cake Solids Unit size No. of units*

Capital Cost, $

Annual Costs, $

Amortization Chemicals Power Water Operating Labor Maintenance Total

Belt Press

250 675 30 3 meter 12

7,050,000

634,500 1,368,800

81,300 108,400 672,000 90,500

2,955,500

Vac. Filter +

Belt Press

250 3.0 - 1180** 20 - 35 ** 600 ft2 - 2 meter ** 13 - lo** 12,400,000

1,116,000 1,663,400 398,240 153,700 840,000 143,750

4,315,090

Unit Costs, $/ton 32.39 47.29

* Includes one standby unit. ** First entry for vacuum filter; second for belt press

114

TABLE 27. INCINERATION COSTS

Vacuum Filter Filter Press Feed Feed

Total Feed, tonslday 317.5 2 Feed Solids 20 % Volatile Solids 47.2 Furnace Diameter 25' - 9" No. Hearths 12 Furnace Capacity,

10 l b s wet f eed/hr/f t2

317.5 35 b7.2

12 25 1- - g"

10

20 , 000 10 , 000 Capital Cost, $1,000

Annual Costs, $1,000

Amortization Power Fuel Operating Labor Maintenance Ash Disposal Total

1,800.0 899.2

4,110.0 504.0 400.0 610.0

8,323.2

900.0 405.2 630.0 336.0 200.0 610.0

3,081.2

Unit Cost, $/ton of sludge solids 91.21 33.77

115

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8 Water: City water, at a cost of $0.53 per 1000 gallons, required for high-pressure washes on the filter presses, Filtered and disinfected water for low-pressure sprays such as required on a vacuum filter and belt press is supplied at a cost of $0.25 per 1000 gallons. at no cost from filtrate or plant effluent.

Chemical makeup water supplied

9. Operating labor: $21,000 per man year; 4 crews required per week to cover a 7-day operation. Includes supervision.

10. Maintenance: Based on a percentage of equipment purchase costs plus cloth replacement costs.

11. Unit cost: $/ton of incoming dry sludge solids.

In Table 25, costs for the vacuum filter and the high-pressure and low-pressure press are based on the costs for actual operating installations in the United States and are considered fairly accurate. operations of the diaDhragm-type press are currently on line in the United States; hence, the costs for these units are based on the best information available from the manufacturer. filter presses are essentially equal at $54 to $55 per ton. Selection of one type versus the other can, therefore, be based on the operating parameters desired and/or competitive bidding. For dewatering only, the vacuum filter provides a cheaper alternative than filter presses. the major differences are essentially due to the amortization costs. Out-of- pocket annual operating cbsts, exclusive of amortization, for either the vacuum filter or any of the filter press types are approximately $30 to $32 per ton.

No large scale

Operating costs for the three types of

However,

Table 26 presents some cost estimates for the belt press, both as a single unit or as a retrofit to a vacuum filter. As with the diaphragm press, no large-scale belt press installations are currently on line in the United States to provide actual cost data. Therefore, the estimates given are based on information available from the manufacturers. It is assumed that a suitable polymer at a reasonable cost can be provided for sludge conditioning. potential for providing a very reasonable alternative ($32.39 per ton) to either a vacuum filter or a filter press. However, because of problems detailed in the previous section of this report, the belt press was not considered suitable for Blue Plains.

The estimates show that the belt press has the

The use of a belt press as a retrofit to a vacuum filter installation shows a reasonable cost ($47.29 per ton). This estimate assumes the full price for a new vacuum filter installation; enough information is presented in Appendix E to fully cost this option for a specific existing facility. As detailed in the previous section, however, further work must be initiated to develop a workable system prior to implementhg this option.

117

a

Table 27 shows approximate costs for a multiple-hearth incineration facility. A single train includes a 12-hearth incinerator, electrostatic precipitator, sub-cooler, and fume furnace. Emissions are controlled to the EPA limit of 1.3 pounds of particulate matter per dry ton of solids input. Fuel costs are based on producing an 800 OF exhaust temperature from the furnace and then further raising the stack gases to 1350 OF. For the 20% feed, considerable fuel is required in the furnace; for the 35% feed, the sludge is auto-combustible and fuel is required only to raise the stack gas temperature. Table 27 shows considerable savings when incinerating a cake in the auto-combustible range. in fuel requirements, fewer furnaces (2 vs 4 units) are required, thereby realizing additional savings in power, labor, and maintenance costs.

Along with the savings

The hauling costs in Table 28 are based on a 25 mile haul distance to a processing or disposal site. open-air static pile method developed at Beltsville, Maryland. These costs are for processing only, and do not include any costs or revenues derived from the marketing/disposal of the final product. transport distance, the costs per dry ton for hauling are nearly equal to ‘the composting costs.

The composting costs are based on the

Because of the long

The total disposal costs in Table 29 show:

1. Total disposal costs for filter pressing and incineration are approximately $88 per ton. vacuum filtering and incineration at $130 per ton. Therefore, savings of nearly $4,000,000 per year for a 250 ton-per-day plant are possible by selecting filter presses for dewatering.

This compares to the total cost for

2. Total disposal costs for filter pressing and composting (including

This compares t o the total cost of vacuum filtering the cost of hauling the press cake 25 miles) are approximately $102 per ton. and composting (including hauling) of $155 per ton. Choosing a filter press rather than a vacuum filter, therefore, will result in annual savings of nearly $5,000,000 for a 250 ton-per-day plant.

118

APPENDIX A

LABORATORY ANALYSES

The fol lowing r o u t i n e l abora to ry ana lyses were performed. De ta i l ed de- s c r i p t i o n s of i nd iv idua l procedures can be found i n Standard Methods f o r t h e Examination of Water and Wastewater, 1 4 t h e d i t i o n .

Primary, Secondary Sludge

To ta l So l ids

Spec i f i c Gravi ty PH

Sludge Feed

To ta l So l ids V o l a t i l e So l ids PH Spec i f i c Gravi ty Few

F i l t e r Cake

To ta l So l ids V o l a t i l e So l ids Density

Fe BTU

F i l t r a t e

To ta l So l ids

119

Method

O'Haus moisture balance Glass e l e c t r o d e Referred t o weight of 1 l i t e r of water a t room temperature

Dried a t 103-105 O C overnight I g n i t i o n of d r i e d r e s idue a t 61OoC Same as above Same as above Atomic absorp t ion spectroscopy us ing Varian kA-6 Spectrophotometer

Dried a t 103-105 O C overnight Same as above Variable-volume p r e s s - determined from volume of water d i sp laced by a known weight of f i l t e r cake Fixed volume p r e s s - determined from t h e t o t a l weight of f i l t e r cake d iv ided by t o t a l chamber volume Same as above Determined us ing P a r r a d i a b a t i c Oxygen Bomb Calorimeter

Same as above

Suspended Solids

PH c1-

COD

Total Phosphate

Total Nitrogen, Nitrate

Determined according to Standard Methods Same as above Determined according to Standard Me tho d s Determined according to Standard Methods Determined according to Standard Methods Determined according to Standard Methods

120

APPENDIX B - DATA SHEETS

xE:PERATURE- 25°C GRINDING-

PRIKARY/SECONDARY (pH) ., RUN #

P" CO?lB€NED SLUDGE-uncond . - c o n d .

LEVEL-be fo re& a f te r cond. (INCH)

LEVEL ( a f t e r p u m p i n g )

LIME ADDED ( G A L S )

FECL3 ADDED(GAL.S)

SLUDGE PUT.lF'ED-(GALS)

FILTRATE COLLECTED (PUMPING)

FILTRATE COLLECTED (SQUEEZE)

FILTRATE COLLECTED (TOTAL)

FILTRATE :pH

FILTRATE APPEARANCE

CAKE:WEIGHT (WET)

CAKE:CONSISTENCY/DISCHARGE

PUMPING TIME

DATA SHEET 1

Yes 1

tl

1 - 1 -- - 1 -

232/3' 2l1I1

30-7 I 8

16-314

5.6 61.6 -

35.7 10.9146.6

52.9 -

clear

74 excellent

15

DATE- 6/23/77 - PPESS- NGK SQUEEZING PFXSSCRE- 213 CLOTH TYPE NY51-4

SLUDGE TYPE- P r i m & S e c APPEARANCE- Brown color

- II 2

- 1 - 8 3 04 15

- I - , - 1 - - 1 -

PUMPING PRESSURE (TERMINAL)

SQUEEZING TIME

CLOTH WASH: be fo re r u n

CAKE THICKNESS

- 58 53 95

18 18 18 Yes no no

114-112 114-112 114-112

CST (of c o n d i t i o n e d s l u d g e )

CAKE DENSITY

TANKED DRAINED

PRIMARY- S P E C I F I C GRAVITY-

SECONDARY-SPECIFIC GRAVITY-

MMBINED -UNCOND.(SP.GR.)

COMBINED-COND. (SP.GR.1 1.0208 1.007 1.0065

14.8 10.8 24.2

1.1757 1.18 1.12 Yes yes yes

1.027 1.014

1.0114 1.0058 1.0027

PRIMARY-INCHES- 4-113 SECON DARY-IN MES- 20 RATIO-#II PRI./SEC. 32168

REMARKS: ph m e t e r inoperative

1 2 1

Explanation of Data Sheet 1

1.

2.

3.

4.

Information a t top of page i s se l f -explana tory . cates i f t h e primary s ludge mazorator w a s used.

The gr inding e n t r y ind i -

pH - w a s normally measured on each of t h e s ludges , both be fo re and a f t e r condi t ion ing , ( and on t h e f i l t r a t e . when used wi th s ludge and were inope ra t ive on t h i s p a r t i c u l a r day.

The pH probes f a i l e d q u i t e o f t e n

The "LEVEL" e n t r i e s show t h e amount of s ludge i n t h e tank a t va r ious i n t e r v a l s , measured from a r e fe rence po in t a t t h e top of t h e tank , The t o t a l t ank depth from t h i s po in t w a s 48 inches. w a s 6.4 ga l lons / inch .

Tank c a l i b r a t i o n

The l i m e and FeC13 ga l lons added are a l s o equiva len t t o t h e pounds of each added. c a l i b r a t i o n .

Note t h a t l i m e and FeC13 used were both .1 l b / g a l f o r easy

Lime makeup i n t h e l i m e s l u r r y tank w a s as fol lows:

An 80 l b bag of l i m e was added t o 75.5 ga l lons water The r e s u l t a n t t o t a l volume was 80 ga l lons .

FeC13 makeup i n t h e holding tank w a s as fol lows:

28.6 ga l lons FeC13 (30% by weight; 3.5 1bs FeC13 Per ga l lon ; Spec i f i c g r a v i t y = 1.362) w a s added t o t h e vat. The vat w a s f i l l e d t o 100 ga l lons wi th water and mixed w e l l .

5.

6 .

7.

8.

The " f i l t r a t e c o l l e c t e d (pumping)" w a s measured i n ga l lons by a d i p s t i c k reading i n t h e 100 ga l lon c o l l e c t i o n vat.

The " f i l t r a t e c o l l e c t e d (squeeze)" w a s measured i n g a l l o n s by a d i p s t i c k reading i n t h e 15 ga l lon c o l l e c t i o n vat. q u a n t i t y c o l l e c t e d dur ing the squeeze c y c l e only; t h e second e n t r y shows t h e volume c o l l e c t e d i n t h e pumping and squeezing cyc le s combined.

The f i r s t e n t r y shows the

The " f i l t r a t e c o l l e c t e d ( t o t a l ) " shows t h e t o t a l amount i n the vats a f t e r t h e pump and squeeze cyc le s p l u s the f i l t r a t e and s ludge blowing cyc les . The blow cyc le s con t r ibu ted approximately s i x ga l lons . The f i l t r a t e samples were c o l l e c t e d p r i o r t o the blowing cyc les .

Cake weight w a s measured i n pounds by c o l l e c t i n g a l l t h e discharged cake and weighing on a beam scale.

122

9. Cake: cons is tancy/d ischarge is t h e o p e r a t o r ' s opinion on t h e hardness and q u a l i t y of t h e discharged cake.

10. Pumping t i m e is t h e t o t a l t i m e t h a t t h e s ludge pump w a s running. t akes approximately 1.5 t o 2.0 minutes t o f i l l t h e chambers i n t h e NGK p i l o t p re s s . of f i l t r a t i o n a f t e r t h e chambers are f i l l e d .

It

Some p r e s s manufacturers r e f e r t o pump t i m e as t h e t i m e

11. Terminal pump p res su re is t h e reading taken on t h e d ischarge of t h e diaphragm pump a t t h e end of t h e cycle . pump, t h e p re s su re gage pulsed and t h e reading i s only approximate t o

Because t h i s w a s a p i s t o n

+ - 5 ps ig .

12. Squeezing t i m e i s t h e t o t a l t i m e t h a t t h e squeezing pump w a s running. It took only 15-20 seconds t o f i l l t h e chambers on t h e p i l o t p re s s . Larger p re s ses may r e q u i r e 2 t o 3 minutes t o f i l l t h e chambers, t hus extending t h i s t i m e i n a c t u a l la rge-sca le opera t ion .

13. The "c lo th wash" i s se l f -explana tory . The automatic system w a s used.

14. Cake th i ckness w a s measured i n inches a t va r ious p o i n t s on va r ious cakes.

15. CST ( c a p i l l a r y s u c t i o n t i m e ) i n seconds shows t h e relative f i l t e r a b i l - i t y of t h e condi t ioned s ludge.

16. Cake dens i ty (gm/cc) w a s measured by p l ac ing a one l i t e r graduated cy l inde r on a balance and measuring both t h e weight of cake added and t h e volume of water d isp laced .

17. "Tank Drained" r e f e r s t o t h e s t a t u s of t h e mixing t ank a t t h e end of t h e run.

18. The s p e c i f i c g r a v i t y of t h e primary s ludge , secondary s ludge , uncondi- t ioned , and condi t ioned combined s ludges were a l l measured by weighing one l i t e r of t h e sample. Because of gas bubbles and p i eces of t r a s h i n ind iv idua l samples, t h i s method was no t completely accura te . How- ever, t h e averages of many samples can be used f o r most c a l c u l a t i o n s wi th l i t t l e e r r o r .

19. The primary and secondary "inches" r e f e r t o volume i n t h e mixing tank. Note t h e h igh volume r a t i o (4.6/1) i n c o n t r a s t t o t h e low weight r a t i o (2/1)

20. The s p e c i f i c g r a v i t y of t h e 1 l b / g a l l o n chemical s o l u t i o n s were measured p e r i o d i c a l l y .

123

DATA SHEET 2

18

19

20

18 314 46.6

BLOWDOWI 52.9

IE

total cumulative gallons

Pump filtrate in 100 gallon vat - 2.67 gal/inch

Squeeze filtrate in 15 gallon vat - 0.58 gallinch of filtrate

124


1.

2.

3 .

4.

5 .

6 .

7.

8.

9 .

During each run, d i p s t i c k readings of t h e s ludge and f i l t r a t e l e v e l s were s imultaneously taken by two opera tors .

Column 1 shows t h e t i m e i n minutes.

Column 2 shows the inches of s ludge i n t h e mixing tank as measured from t h e top r e fe rence poin t .

Column 3 shows the volume of s ludge pumped, corresponding t o t h e measurement i n column 2 .

Column 4 shows t h e s ludge feed pump d ischarge p res su re i n ps ig .

Column 5 shows t h e inches of f i l t r a t e c o l l e c t e d i n t h e 100 ga l lon vat during t h e pumping c y c l e as measured by d i p s t i c k from t h e bottom.

Column 6 shows t h e volume of f i l t r a t e corresponding t o t h e readings i n column 5.

Column 7 shows t h e inches of f i l t r a t e c o l l e c t e d i n t h e 1 5 ga l lon v a t during t h e squeezing cyc le , as measured by d i p s t i c k from t h e bottom. This smaller vat w a s used so that low f i l t r a t e readings could be observed.

Column 8 shows t h e volume of f i l t r a t e corresponding t o t h e readings i n column 7 and added t o t h e t o t a l volume c o l l e c t e d during t h e pumping cyc le .

Note t h a t t h e cyc le t i m e s f o r th i s run were 15 minutes of pumping, f o l - lowed by 18 minutes of squeezing. Normally, t h e pumping c y c l e was terminated when the l e v e l i n t h e s ludge tank dropped t o 1/8" pe r minute f o r t h r e e conse- c u t i v e minutes. dropped t o 1/4" pe r minute f o r three consecut ive minutes.

The squeezing cyc le w a s terminated when t h e f i l t r a t e rate

125

E

DATA SHEET 3

ANALYSIS REQUEST AND RE=

Analytical Services Laboratory FWPCA-DC Pilot Plant

Washington, D. C.

Analysis Requested

Submitted by: W. Ruby

Date Submitted: 6/23/77

Date Reported: 6/24/77

LAB NO. [SAMPLE IDENTIFICATION 1

6/23/77 Primary 9.26 Secondary 4.34

NGK R1 Pump 5.15 NGK R1 Squeeze - NGK R2 Pump 5.68 NGK R2 Squeeze - NGK R3 Pump 5.90 NGK R3 Squeeze -

1 I

I I

a JI d a c

$ 3

a m k

a c d U

a /' c n d U g

a d 4

cn

W

12 6


Laboratory procedures are explained f u r t h e r i n Appendix A. The following analyses were determined f o r each f i l t e r p re s s run.

1. Primary sludge - % t o t a l s o l i d s X v o l a t i l e s o l i d s

2. Secondary sludge - X t o t a l s o l i d s % v o l a t i l e s o l i d s

3 3. Combined sludge - unconditioned feed X t o t a l s o l i d s % v o l a t i l e s o l i d s

4. Combined sludge - conditioned feed X t o t a l s o l i d s X v o l a t i l e s o l i d s

5 . F i l t e r Cake - X t o t a l s o l i d s % v o l a t i l e s o l i d s

6 . Fi l t r a t e - t o t a l s o l i d s as mg/l suspended s o l i d s as mg/l

The primary and secondary sludge samples were composites taken e i t h e r from t h e NGK mixing tank o r d i r e c t l y from t h e discharge of t h e thickeners .

The combined sludge samples, both unconditioned and conditioned, were dipped from t h e NGK mix tank.

F i l t e r cake samples were taken a t random from various sec t ions of a t least four of t h e s i x cakes. Tests were run t o show t h a t t h e cakes were uniform throughout with respec t t o % s o l i d s . % s o l i d s of t h e s i x cakes w a s ever observed.

No appreciable d i f f e rence i n

F i l t r a t e samples were dipped from t h e f i l t r a t e c o l l e c t i o n tanks a f t e r a g i t a t i o n t o ensure a r ep resen ta t ive sample. from the pumping and squeezing cyc les were analyzed separa te ly .

For some runs t h e f i l t r a t e s

127

DATA SHEET 4

--_ ___ - DATE- R L R U - 6 / 2 3 / 7 7

TYPE SLUDGE-

RATIO- P/I'-PR. f SEC. -__ FEED S O L I D S - % S O L . f % V O L T ( u n c o n L

PRIMARY-%SOL. /%VOL& pH.-

SE COY DARY -%SOL. 1 %VOL . f pH. - - FEED S O L I D S - % S O L . / % V O L . - ( c o n d L

PRIMARY- S P . GR. ( g r . / c c . ) __

SECONDARY -SP . GR. - (gr . / c c . FkED S 0 ~ 1 - ~ ~ - 5 ~ , G R . - (un cond . ) - ;H .-- F E E D SOLIDS-SP . G R . - ( c o n d . ) - AH .- - LIME ( a d d e d ) %-

FECL3 ( a d d e d ) %-

i 'OLUME-(feea t o 9ress)-GALS. __

P L W T I P E - ( k n s . )

SQUEEZE T I M E - ( K n s .) -

TERMINAL PRESSURE-Pump p s i g . -

SQLEEZING PRESSURE-usig

FILTRATE VOLUME-(gals .)PLWXNG-

FILTRATE V O L L m - ( G a l s . ) SQUEEZE-

FILTRATE VOL.-(Ga&.l TOTAL+B.D.

_______

~ _ _ _ - _ _ - _ - -

~ _ _ _ - ~

-

FILTER CAKE-(Wet w e i g h t )

F I L l E R CAKE-(ZSol . /%Vol.)

FILTER CAKE (Dry Weight ) Corr.

CAKE THI CKNE SS - ( I n c h e s )

YIELD ( l b s . / f t . Z h r . ) P r o c e s s

* NS indicates no s a m p l e was t a k e n

CLOTH T Y P E - ~ ~ 5 1 - 4 TEIPERATURE- 2 5 0 ~ PRESS MECHANICAL TIME-5 min. PRESS FILTER AREA- 6 2 . 4 f t2

C7YCLCSIONS- T e s t s show Rood f i l t r a m n and -igihuzhad-

LOW l i m e (17 .2%) w o u l d not d e w a t e r effectively. N o t e l o w r a k e a n l i d - .

128


Data Sheet 4 combines t h e da t a co l l ec t ed from t h e run (Data Sheets 1 and 2) with t h e labora tory r e s u l t s (Data Sheet 3) and seve ra l c a l c u l a t i o n s t o summarize t h e series of tests run. A l l examples use Run #l.

1. The a c t u a l weight r a t i o of primary t o secondary s ludge was ca l cu la t ed from t h e measurements taken of t h e volume, s p e c i f i c grav i ty , and labora tory % s o l i d s of each sludge.

l b s s o l i d s = (inches i n tank) x ( tank c a l i b r a t i o n ) x ( s p e c i f i c g rav i ty ) x (densi ty of water) x % s o l i d s

100

9.26 l b s primary s ludge = 4.33 i n x 6.4 g a l / i n x 1.027 x 8.3453 l b / g a l x - 100 = 22.0 l b s

4.34 l b s secondary sludge = 20 i n x 6.4 g a l / i n x 1.014 x 8.3453 l b / g a l x- 100 = 47.0 l b s

RAtio: l b s pr imary/ lbs secondary = - 22 o r 31.7% 47 68.3%

2. Percentages of t o t a l and v o l a t i l e s o l i d s , pH ( i f a v a i l a b l e ) , and s p e c i f i c g rav i ty were summarized.

3. The percentages of l i m e and FeC13 were ca l cu la t ed as follows. ing t h e chemical dosages, t h e t o t a l l b s of solids i n t h e tank w e r e determined from t h e feed s o l i d s (unconditioned) measurement and t h e volume.

5.15 l b s s o l i d s = 24.33 i n x 6.4 g a l / i n x 1.0114 x 8.3453 l b / g a l x - 100

In comput-

= 67.7 l b s

L ime added = 16.75 g a l x 1 l b l g a l = 16.75 l b s

16 75 67.7 % l i m e = - x 100 =24.7%

FeC13 added = 5.6 g a l x 1 l b / g a l = 5.6 l b s

4. F i l t e r cake cor rec ted dry weight is given. The f i n a l cake weight was

129

cor rec t ed f o r t h e

Cake dry weight =

chemicals added.

% s o l i d s 100 w e t weight x

39.2 74 l b s x - 100

29 l b s

Corrected dry weight = (cake dry weight)-(chemical weight) The chemical weight i s known as a percentage of t h e incoming s ludge s o l i d s ; t h e proper formula i s then:

- - 1 + (24.7 + 8.3)

100

= 21.8 l b s

5. Yield is repor ted as:

co r rec t ed dry weight (cyc le t i m e ) x ( f i l t r a t i o n area)

Corrected dry weight = 21.8 lbs

cyc le t i m e = 15 min + 18 min = 33 min = 0.55 h r 60 min/hr

2 F i l t r a t i o n area = 62.4 f t

Yield = 21.8 l b s (0.55 h r ) x (62.4 f t L )

= 0.63 l b / h r / f t 2

This y i e l d is c a l l e d t h e process y i e l d , s i n c e i t inc ludes only pump and squeezing t i m e s . It is a good f i g u r e f o r comparing runs i n a set t o e s t a b l i s h t r ends . For scale-up, t h e mechanical t i m e of t h e f u l l - s c a l e p r e s s must be included i n t h e " fu l l - sca l e yield" . p re s s , t h i s mechanical t i m e is 19 minutes. It inc ludes t i m e t o open and c l o s e t h e p re s s , d i scharge cake, and f i l l t h e squeezing chambers, etc. The f u l l - s c a l e cyc le t i m e is then:

For t h e 500 m3 NGK

33 min + 19 min = 52 min = 0.87 h r 60 min/hr

Ful l - sca le y i e l d = 21.8 lbs (0.87 hr) x (62.4 ft*) = 0.40 l b s / h r / f t 2

130

DATA SHEET 5

'FILTRATE PASSAVANT BRESS - OPERATIONAL DATA EILTRATE

REMARKS: Comparison with NGK and Nichols.

65

70

60 I 225 111-718 I 31.7

225 12-112 33.4

105 110

E 1 225 112-314 1 34.0 90 225 13-114 35.4

225 , 13-718 37.0

120

125

130 135 140

145 150

155 160

225 14-114 38.0

225 14-318 38.4

225 14-518 39.0

225 14-718 39.7

225 14-718 39.7

131


Data Sheet 5 was used to collect information during each run on the Passavant press.

1. The data in the column on the left is self-explanatory. Some information was taken from the referenced corresponding NGK run.

2 . Pressure and filtrate readings were normally taken every ten minutes during the run. Filtrate w a s collected in a 100 gallon plastic vat. Vat calibration was 2.67 gal/inch.

132

DATA SHEET 6

CAKE THICKNESS:( INCHES ) CAKE DENSITY: ( l b s . / f t . )

YIELD: ( l b s . / f t . 2/ hr . ) Process YIELD: ( f u l l s c a l e )

Terminal f i l t r a t e rate (Ral/hr/ft*)

3 1 . 5 76.8

0.52

0.46

0

CONCLUSIONS: Good run for 2/1 sludge -

V

133


on

1.

2.

3.

4 .

5.

6.

Data Sheet 6 w a s used t o summarize a l l d a t a c o l l e c t e d on each run t h e Passavant p re s s .

Data on t h e s ludge r a t i o , t h e % feed s o l i d s , and t h e chemical rates were taken from t h e corresponding NGK run.

F i l t r a t e s o l i d s were determined from a composite sample of t h e f i l t r a t e .

Cake s o l i d s were determined by averaging t h e % s o l i d s f o r each of t h e two cakes sampled.

Corrected dry weight w a s determined by t h e same procedure descr ibed i n t h e explana t ion f o r Data Sheet 4.

Process y i e l d w a s repor ted as:

Corrected dry weight (cyc le t i m e ) 'x ( f i l t r a t i o n area)

Yield = 25.0 l b s n

(160/60 h r ) x (18.0 f t " )

= 0.52 l b / h r / f t 2

Ful l - sca le y i e l d w a s c a l c u l a t e d by adding 20 minutes t o t h e process cyc le t i m e ( t u r n around t i m e r equ i r ed f o r a large-scale p r e s s ) .

Fu l l - sca l e cyc le t i m e = 160 min + 20 min = 180 min 3.0 h r m 25.0 lbs

F u l l scale y i e l d = (3.0 h r ) x (18.0 ft?)

= 0.46 l b / h r / f t 2

134

DATA SHEET 7

150

155 160

165 170

175 180

FILTRATE EILTRATE NICHOLS PRESS - OPERATrONAL DATA ?.ESSLXE VOLL?E PATE

-_

-_

R U #

CAKE THICKNESS I 1"

TOTAL CYCLE TIME (MINS.) 130

REMARKS: Comparison with NGK and Pasaavant

Time Pressure Filtrate rate Total Volume b i n ) (psig) (ml) (ml)

1 15 850 2 30 2500 3 50 1500 4 75 1950 5 100 1300

850 3350 4850 6800 8100

0

5 100 8100 8100 10 115 12300 4200 13

20 95 16250 3950 25

30 110 18600 2350 33

40 85 20050 1450

50 I 107 I 21100 I 1050 I I . 1

55 I 1 1 60 93 21650 550

70 I 100 22090 440

80 103 22430 340

90 95 I 22690 I 260 I 1 1

120 I 100 I 23150 I 120 I 1 1

145 I 1

135

DATA SHEET a

TYPE SLUDGE:

RATIO: # /# P r . / S e c .

FEED SOLIDS:%SOL./% VOL.(uncond.)/pH.

FEED SOLIDS:%SOL.I% VOL.(cond.)/ OH.

LIME % :

FEERRIC I: CYCLE TIME : ( X N S . ) TERMINAL FEED PRESSUFS?.(psig) :

FILTRATE VOLlME : (MLS .)

FILTRATE pH. :

FILTRATE : (mg/l) TOTAL SOLIDS

F I L T W E : ( m g / l ) SUS.SOLIDS

FILTRR CAKE: (WET WEIGHT)

FILTER CAKE : (%SOL. / ZVOL .)

FILTER CAKE:(CORR. DRY WEIGHT)

CAKE THICKNESS:( INCHES )

CAKE DENSITY: ( l b ~ . / f t . ~ )

YIELD: ( l b s .If t . 2 / h r .) Drocess

Termina l f i l t r a t e rate ml/min

F u l l scale y i e l d ( l b s / f t 2 / h r )

CLOTH TYPE: 4709140 TEMPER

CONCLUSIONS:

-

1 I

Pr imISec 1 1 2

31.6168.4

7.59142.91-

5.65160.41-

101

23250 - - I I I

49 I I I _ ~ _ ~~

9.55 l b s

36.2147.3 2 .7 l b s

I I

0.31 I 10 0.27 I I 1

TURE: 28' C PRESS AREA: 4 f t2

136


Data Sheet 7 w a s used t o c o l l e c t information during each run on t h e Nichols p re s s .

1. This d a t a shee t is nea r ly i d e n t i c a l t o Data Sheet 5 and t h e same remarks are appropr ia te .

2. The f i r s t f i v e minutes of t h e run were programed t o inc rease t h e p re s su re i n t h e feed tank slowly by us ing a r e g u l a t o r valve.

3. Pressure and f i l t r a t e readings were normally taken every t e n minutes dur ing t h e run. composited during t h e run. The p res su re f l u c t u a t e d s l i g h t l y because of o t h e r demands on t h e a i r supply system.

F i l t r a t e w a s c o l l e c t e d i n a graduated cy l inde r and


Data Sheet 8 w a s used t o summarize a l l d a t a c o l l e c t e d on each run on t h e Nichols p r e s s . This d a t a shee t i s i d e n t i c a l t o Data Sheet 6 .

137

APPENDIX C

DETERMINATION OF SPECIFIC RESISTANCE TO FILTRATION

From June through October 1977, laboratory measurements of the filterability of the conditioned sludge mixtures were made using three different techniques:

1. Modified Buchner funnel method

2 . Positive pressure method

3. Capillary suction method

The modified Buchner funnel and pressure methods give quantitative measurements of the filterability of a sludge by determination of its average specific resistance to filtration. The specific resistance is defined as the pressure difference required to produce a unit rate of filtrate flow of unit viscosity through a unit weight of cake and is calculated from the following equation:

R = 2PA2b

Where

k C

R = average specific resistance P = the filtration pressure A = the filter area E l = the viscosity of the filtrate c = the weight of cake solids per unit volume of filtrate b = slope of filtrate discharge curve, i.e. time/volume

versus volume

A more detailed discussion of the theoretical derivation of this equation can be found in the literature.4

The capillary suction test was developed as an alternative to the Buchner funnel and pressure tests. filtrate to drain from a given volume of sludge and is easily correlated

It measures the time required for

4. Carman, P.C. "Fundamental Principles of Industrial Filtration (A Critical Review of Present Knowledge)." of Chemical Engineers, 1938, 16, 168.

Transactions of the-Institution

138

with the specific resistance parameter.

MODIFIED BUCHNER FUNNEL METHOD

This technique is used most frequently in studies of sewage sludge filtrations.5~6 Essentially, it consists of effecting the filtration process by the use of a vacuum pressure.

Facilities

The filter consisted of a white, porcelain Buchner funnel (9.1 cm plate diameter). Standard laboratory paper (9 cm diameter) graded for a fast filtering speed was used as the filter media. Suction was provided by a 24 inch gage vacuum pump. Accessory equipment included a 250 ml graduated cylinder with side arm, stand, stopwatch, and thermometer. The funnel, with accessories, was assembled as shown in Figure C-1.

Operat ion

A filter paper was wetted and placed in the bottom of the funnel. The conditioned sludge was prepared by pouring twice from one beaker to another to resuspend any solid particles which had settled out. The temperature of the sample was noted and a 200 ml portion was measured into the funnel. The vacuum was then started immediately, and simultaneous readings of filtrate quantity and time were recorded as the filtrate collected. These readings were taken at 10 or 15 second intervals for an elapsed time of 240 seconds or until the vacuum broke, i.e. the filter cake was completely formed . Analysis

R = Rv = 2PA2b PC

Experimental parameters were measured in the metric system and Rv reported in units of cm/g. A filtration vacuum differential of 24 inches Hg (81360

5. Coackley, P. and B.R.S. Jones. "Vacuum Sludge Filtration I. Interpretation of Results by the Concept of Specific Resistance. Sewage and Industrial Wastes, 1956,28, - 963.

6. Swanwick, J.D., F.W. Lussignea, and K.J. White. "The Measurement of the Specific Resistance to Filtration and Its Application in Studies of Sludge Dewatering.'' Purification, 1961, - 6 487.

Journal of the Institute of Sewage

13 9

N/m2) was used. The filtration area was taken to be that of the filter paper, 63.62 cm2. The filtrate viscosity,p , was assumed to be that of water, measured at the temperature of the sample and converted to units of Ns/m2. The weight of dry cake solids per unit volume of filtrate, c (g/cm3) , was approximated from the sample feed solids concentration according to the relationship:

TS S 1000-TS S

C'

where TSS is the total suspended solids of the feed, g/l.

The slope of the filtrate curve, b (s/cm6), was obtained by plotting e / V vs V, where V is the filtrate volume collected in time 8. Carman 7 noted that in the determination of by the initial readings of 0 and V represent the initial resistance of the filter medium rather than the specific resistance of the solids. Hence, 8 and V should not be measured from the beginning of the filtration; rather, the filtration pressure should be raised slowly to its full value to minimize the effect of this 4nitial resistance. Once the pressure reaches constancy, the readings should then be taken. pressures were raised immediately to full value and measurements of 0 and V were taken from the start of the experiment. circumvent the problem posed by resistance of the filter medium, these first initial readings were not used in computing the slope of the filtrate curve. By doing this, the procedure was simplified and standardized for all operating personnel, yet experimental accuracy was still maintained.

In our determinations, this procedure was not used;

However, in order to

A sample of the data collected and its analysis is shown for this method in the following data sheet.

POSITIVE PRESSURE METHOD

This method has been used by several researchers8S9 during studies of high-pressure filtration. Buchner funnel method, except that the filtration pressure is provided by positive instead of vacuum pressure.

It is similar in operation to the modified

7. Carman, P.C. op. cit.

8. Coackley, P and B.R.S. Jones. "Vacuum Sludge Filtration I. Interpretation of Results by the Concept of Specific Resistance." Sewage and Industrial Wastes, 1956, - 28, 963.

9. "Pressure Filtration of Waste Water Sludge with Ash Filter Aid." Environmental Protection Agency (EPA) Technology Series, 1978, EPA-R2-7 3-231.

140

P

Figure C-1. Buchner Funnel Apparatus.

Figure C-2. Passavant Series 275 Resistance Meter.

14 1

Facilities

A Passavant Series 275 Resistance Meter was used. It included a 7 cm diameter stainless steel body and support screen. A 7 cm diameter filter cloth together with a standardized laboratory filter paper served as the filter media. Required additional equipment included a cylinder of compressed nitrogen gas, a 100 ml buret, stand, and stopwatch. The instrument was assembled as shown in Figure C-2.

Operation

The filter cloth was wetted and placed in the meter over the support One of the laboratory filter papers was wetted and placed on top screen.

of this cloth. A 250 ml sample of the conditioned sludge was measured into the meter, and the top was attached and secured. The 100 ml buret was initially filled to its lower 100 ml mark; and the meter was then pressurized to 225 psig with the compressed gas. Simultaneous readings of filtrate quantity and time were subsequently recorded. Readings were taken at 15 second intervals for a period of 240 seconds or until the f.iltration was completed and blow-by occurred, with gas passing through the filter.

Analysis

The specific resistance equation was revised by Passavant Corp. to give:

2PA2b = Kb R = R p = - - PC C

In this equation, Rp is measured as a dimensionless quantity. K is an index constant developed by Passavant, measured in arbitrary units of g-cm3/s. It is a function of the pressure, temperature, and viscosity of the sludge being dewatered. The slope, b (s/cm6>, of the filtrate curve and the weight of dry cake solids per unit volume of filtrate, c (g/cm3), were obtained as described in the previous section. earlier that this pressure test is essentially a Buchner funnel test run under positive pressure. Results, therefore, could also be interpreted by the same formula used for the Buchner funnel test.

It was noted

A sample of the data for this test and its analysis is shown in the accompanying data sheet.

CAPILLARY SUCTION METHOD

The .use of this method for determining the filterability of sewage sludges was developed as the result of research studies at the Water Pollution Research Laboratory in Stevenage, England. It was developed as an alternative to the modified Buchner funnel test to permiErapid assessment of the filterability of a sewage sludge.

14 2

The principle of the method is that filtration occurs by the suction applied to the sludge by the capillary action of a standard grade, absorbent filter paper. The rate at which the paper becomes wetted gives an indication of the filterability of the sludge.

Facilities

A capillary suction time meter, which consisted of two transparent plates separated by a filter paper and an automatic timer, was used. The lower plate measured 9 cm x 9 cm x 0.6 cm high. One edge of this plate was raised to a height of 1.2 cm and served to position the filter paper. (The type of filter paper used was the Whatman No. 17 chromatography grade). The upper plate measured 7 cm x 9 cm x 2.3 cm high and contained a central hole approximately 1.9 cm in diameter. On the under side of the plate, concentric with the center hole, were two circular marks of diameters 3.2 cm and 4.5 cm; these marks were connected electrically to an automatic timer. A stainless steel cylinder, 2.5 cm high and 1.8 cm inner diameter, fitted into the central hole of the upper plate and served as a reservoir for the sludge sample.

Operation

The filter paper was positioned on the lower plate along the raised edge. The upper plate, with electrical connections touching the filter paper, was placed on top of the filter paper along the raised edge of the lower plate. The stainless steel cylinder was placed in the hole in the upper plate and a small volume of the sludge sample poured into it. A s the suction pressure of the filter paper drained the filtrate from the sample, the automatic timer started when the outward progression of the filtrate reached the first connection and stopped when it reached the second. the timer.

The capillary suction time or CST (in seconds) was then read from

A picture of the CST instrument is shown in Figure C-3 and sample data is shown in the data sheet.

Analysis

The CST only provides an indication of the filterability of the sludge. Through calibration with the modified Buchner funnel and pressure methods, however, it can be correlated with the specific resistance parameter. (See Section 7, Special Tests).

10. Gale, R.S. and R.C. Baskerville. "Capillary Suction Method for Determination of the Filtration Properties of a Solid/Liquid Suspension." Chemistry and Industry, 1967, p 355.

11. Gale, R.S. and R.C. Baskerville. "A Simple Automatic Instrument for determining the Filtrability of Sewage Sludges." Control, 1968, - 67, p. 233.

Water Pollution

14 3

Figure C-3. CST Instrument

144

Date: 7/28/77 Run: #1 Sludge Description: Conditioning Additives:

Ratio Secondary/Primary @ 2/1 FeC13 - 3.67 gals Lime -11 gals

Test #l CST = 10.9 sec.

Test #2 Pressure Method

Temperature: 29 OC Pressure: 225 psig

Volume (V) eiv 3 s/cm S cm 3 cm

Time ( 8 ) Reading (v)

0 15 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240

100.0 84.0 75.8 68.8 63.2 58.0 53.2 48.6 45.0 41.0 37.2 34.0 31.0 27.8 24.6 21.8 18.8

0 16.0 24.2 31.2 36.8 42.0 46.8 51.4 55.0 59.0 62.8 66.0 69.0 72.2 75.4 78.2 81.2

Test I 3 Modified Buchner Funnel Method

Temperature: 2 9 O C

Time ( 0 ) S

0 10 20 30 4 0 5 0 60 7 0 8 0 9 0

100 110 1 2 0 130 1 4 0 1 5 0 160

Pressure: 24 I ' Hg

Volume (V) cm3

0 34 4 8 5 4 6 4 72 7 6 8 6 90 96

100 1 0 4 1 0 8 1 1 2 116 1 2 0 Vacuum broke

- 0.938 1.240 1.442 1.630 1.786 1.923 2.043 2.182 2.288 2.389 2.500 2.609 2.701 2.785 2.877 2.956

e/v slcm

- 0 . 2 9 4 0.417 0 .556 0 .625 0 .694 0 .789 0 .814 0.888 0 .938 1.000 1.058 1.111 1 .161 1 . 2 0 7 1 . 2 5 0

@ 2' 38"

145

ANALYSIS

T e s t f 1 CST = 10.9 s e c

T e s t B 2 P res su re Method

a ) Ca lcu la t ion of c

Unconditioned s ludge:

21.0 inches x 6.4 gal x 3.785 1 = 500.76 1 inch g a

500.76 1 x 5.96% x 0.995 g x 1000 ml = 29725.65g - - 100% m l 1

Lime :

11 g a l s x 3.785 1 = 41.64 1 g a

11 g a l s x 1 l b x 454 g = 4994.0g g z i l b

FeCl : 3 3.57 g a l s x 3.785 1 = 13.89 1

g a i

3.67 g a l s x 1 l b x 454 g = 1666.18g g i i l b

1 g - Sludge 29725.65 500.76 L i m e 4994.00 41.64 FeC13

TSS =

1666.18 36385.83

13.89 556.29

36385*83 = 65.41 g /1 556.29

= 0.070 g/cm3 TSS 1000 - TSS

C'

b) @ 29 O C and 225 p s i g , K = 5.43 g-cm3 (see c h a r t ) S

6 c )

kb d ) Rp = -

from graph, b = 0.0235 s / c m

C

14 6

= 5.43 g-cm3/s x 0.0235 s/cm 6 0.070 g/cm3

= 1.82 (dimensionless)

e. Alternatively, if Rp is analyzed according to the equation

Rp = 2PA2b F-

A = 38.5 em2; A2 = 1482.3 cm 4

P = 225 psig = 155.133 x lo4 N/m2

e29 'C,pH20 = 8.21 x loh4 Ns/m 2

Rp = 2PA2b PC

= 2 x 155.133 x lo4 N/m2 x 1482.3 cm4 x 0.0235 s/cm6 8.21 x 10-4 Ns/m2 x 0.070 g/cm3

= 1.88 x 10l2 cm/g

Test #3 Modified Buchner Funnel Method

3 a) c = 0.070 g/cm

b) P = 24"Hg = 81360 N/m2

c) @ 29'C,pH20 = 8.21~10'~ Ns/m2

d)

e )

A = 63.6 cm; A2 a4047.5 cm4

from graph, b = 0.00775 s/cm6

f) Rv = 2PA2b Pc

= 2 x 81360N/m2 x 4047.5 cm4 x 0.00775s/cm6 8.21~10'~ Ns/m*X 0.070 g/cm3

= 8.88 x 1O1O cm/g

147

H P E A ~ C E - Black and grainy _-

CAKE THICKNESS-

PRIMARY-INCHES- 4 SECONDARY-INCHES- 1 7 RATIO-#f # P R I . f SEC. 32/68

REMARKS: Primary So l ids = 10.8% Secondary So l ids = 5.76% Combined Sol ids = 5.96%

148

b

* **a

co

mm

h

0O

U

ah

co

o

\D

64

**

ou*

oomu

CV

dc

oO

dmdu

oc

oc

om

d

m- d m

-

uu

39

.... muwh

UelWrl

... "U

h

ld

rl

aqC

Oco

mm

m0

00

0

....... ~~

........

149

3.0

El.0

c f P c ? D

1.0

1.0

LI

m z m !? Y

> ' .I

0

-

-

b

/ 50

V tCM% 100

T C l T 3 MOOlFlCO BUCHNER FUNNEL METHOD

-

-

I I I

0

t

60 100

V CCM%

110

150

K-Factor as a Function of Temperature

Temperature OC OF - - 0 32.0

1 33.8 2 35.6 3 37.4 4 39.2 5 41.0

6 42.8 7 44.6 8 46.4 9 48.2

10 50.0

11 51.8 12 . 53.6 13 55.4 14 57.2 15 59.0

16 60.8 17 62.6 18 64.4 19 66.2 20 68.0

21 69.8 22 71.6 23 73.4 24 75.2 25 77.0

26 78.8 27 80.6 28 82.4 29 84.2 30 86.0

31 87.8 32 89.6 33 91.4 34 93.2 35 95.0

K -

2.48

2.57 2.66 2.74 2.83 2.93

3.02 3.11 3.21 3.30 3.40

3.49 3.59 3.69 3.80 3.90

4.00 4.10 4.21 4.31 4.43

4.53 4.64 4.75 4.86 4.97

5.09 5.20 5.31 5.43 5.55

5.67 5.79 5.91 6.03 6.15

* Temperature * OC * - OF - * * * 36 96.8 * 37 98.6 * 38 100.4 * 39 102.2 * 40 104.0

* 41 105.8 * 42 107.6 * 43 109.4 * 44 111.2 * 45 113.0

* 46 114.8 * 47 116.6 * 48 118.4 * 49 120.2 * 50 122.0

* 51 123.8 * 52 125.6 * 53 127.4 * 54 129.2 * 55 131.0

* 56 132.8 * 57 134.6 * 58 136.4 * 59 138.2 * 60 140.0

* 61 141.8 * 62 143.6 * 63 145.4 * 64 147.2 * 65 149.0

*

*

*

*

*

* * * 66 150.8 * 67 152.6 * 68 154.4 * 69 156.2 * 70 158.0

K * Temperature - OF - * o c * -

* *

159.8 6.27 * 71 6.40 * 72 161.6 6.52 * 73 163.4 6.65 * 74 165.2 6.77 * 75 167.0

6.90 * 76 168.8 170.6 7.03 * 77

7.16 * 78 172.4 174.2 7.29 * 79

7.42 * 80 176.0

177.8 7.55 * 81 7.68 * 82 179.6 7.82 * 83 181.4 7.95 * 84 183.2 8.09 * 85 185.0

8.23 * 86 186.8 8.36 * 87 188.6 8.50 * 88 190.4

192.2 8.63 * 89 8.77 * 90 194.0

195.8 8.91 * 91 9.05 * 92 197.6 9.20 * 93 199.4

201.2 9.34 * 94 9.48 * 95 203.0

9.62 * 96 204.8 206.6 9.77 * 97

9.91 * 98 208.4 10.1 * 99 210.2 10.2 * 100 212.0

*

*

*

*

*

* *

10.3 * 10.5 * 10.6 * 10.9 * 10.8 *

11.1 11.2 11.4 11.5 11.7

11.9 12.0 12.2 12.3 12.5

12.6 12;8 12.9 13.1 13.2

13.4 13.5 13.7 13.8 14.0

14.2 14.3 14.5 14.6 14.8

15.0 15.2 15.3 15.5 15.7

This table subsumes a constant pressure of 225 psig, a filtration area equal to that of the PASSAVANT Series 275 Resistance Meter, and the dynamic viscosity of the filtrate to be equivalent to that of water.

Source: Passavant Corporation

151

P

APPENDIX D

MATERIAL BALANCE

Data f o r t h i s t e s t was c o l l e c t e d on 10/18/77. of t h i s s e c t i o n .

Refer t o Data Sheet a t end

Sludge I 1

INPUT, l b s t o t a l s o l i d s

Sludge 37.5 Chemicals 10 .0

OUTPUT, l b s t o t a l s o l i d s

F i l t e r Cake Sludge 32 .7 Chemicals 8.7

F i l t r a t e 4.2 Sludge Blowdown

Sludge 1.6 Chemicals 0.4

F i l t r a t e Blowdown 0.2

T o t a l 47.5 T o t a l 47.8

Er ro r i n Analys is = 47*8-47*5 x 100 47.5

= 0.63%

152

Ca 1 cu l a t ions

Sol id input t o t h e p r e s s c o n s i s t s of the s ludge and chemical s o l i d s i n t h e feed. The fol lowing parameters were measured:

i. feed volume t o t h e p r e s s - 77.6 g a l s s o l i d conten t of feed - 7.10% s p e c i f i c g r a v i t y of feed - 1.033 chemical content of feed - 26.7% of dry s ludge s o l i d s

ii, iii. i v .

The t o t a l mass of s o l i d s i n the feed i s ca l cu la t ed as: Mass t o t a l s o l i d s = Mass Feed x % s o l i d s

l b s 7.10% g a l i E r = (77:6 g a l s x 8.345 - x 1.033) x

= 47.5 l b s

aqd c o n s i s t s of bo th chemical and s ludge s o l i d s .

The mass of chemical s o l i d s is: Mass chemical s o l i d s = Mass t o t a l s o l i d s x % chemical s o l i d s

Chemical conten t of t h e feed i s 26.7% of t h e dry s ludge solids; t h e r e f o r e based on t h e t o t a l feed s o l i d s , i . e . , s ludge f chemicals, thechemica l conten t i s :

- 26 7 x 100 = 21.1% 126.7

21.1% Mass chemical s o l i d s = 47.5 l b s x- 100 %

= 10.0 l b s

The mass of dry s ludge s o l i d s is: Mass sludge s o l i d s = Mass t o t a l s o l i d s - Mass chemical s o l i d s

= 37.5 l b s

153

INPUT SUMMARY

chemical s o l i d s 10.0 l b s s ludge s o l i d s 37.5 l b s

47.5 l b s

2. output

Output from t h e p re s s c o n s i s t s of s o l i d s i n t h e cake, f i l t r a t e and blowdown. The fol lowing output v a r i a b l e s were measured:

i. F i l t e r cake weight - 101.0 l b s ii. So l id conten t of f i l t e r cake - 41.0% i v .

iii. Volume of f i l t r a t e c o l l e c t e d - 58.3 g a l s To ta l s o l i d s concent ra t ion of f i l t r a t e - 8569 mg/l

v. Volume of blowdown - 6.4 g a l s

a. F i l t e r Cake

To ta l mass of t h e cake is 101.0 l b s ; t o t a l mass of t h e s o l i d s f r ac - * t i o n of t h e cake is

Mass t o t a l s o l i d s =

I

c a l c u l a t e d as:

Mass cake x % s o l i d s

41.0% 101.0 l b s x 0 l O O X

41.4 l b s

The mass of chemical s o l i d s in. t h e cake is ca l cu la t ed as: Mass chemical s o l i d s = Mass t o t a l s o l i d s x % chemical s o l i d s

21.1% = 41.4 l b s x - 100%

= 8.7 lbs

and t h e mass of s ludge s o l i d s is: Mass s ludge s o l i d s = Mass t o t a l s o l i d s - Mass chemical s o l i d s

= 32.7 l b s

b. F i l t r a t e

A t o t a l volume of 58.3 ga l lons of f i l t r a t e w a s c o l l e c t e d dur ing t h e f i l t e r p r e s s cycle . is c a l c u l a t e d as: Mass f i l t r a t e s o l i d s = Volume f i l t r a t e x Concentration f i l t r a t e s o l i d s

The mass of s o l i d p a r t i c l e s w i th in t h e f i l t r a t e

6 W g a l mg/l = 58.3 g a l x 8569 mg/l x 8.345 x 10-

= 4.2 l b s

154

c. Blowdown

t h e blowdown cycle . equal volumes of each.

The blowdown volume c o n s i s t s of s ludge and f i l t r a t e c o l l e c t e d during It is assumed t h a t t h e blowdown is composed of

Sludge Rlowdown

This s ludge has a t o t a l mass of : The volume of s ludge c o l l e c t e d during blowdown is assumed t o be 3.2

ga l lons . Mass sludge blowdown = Volume sludge blowdown x dens i ty s ludge

= 3.2 g a l x 8.345 l b / g a l x 1.033 = 27.6 l b s

The t o t a l mass of s o l i d s wi th in t h e blowdown is , the re fo re : Mass t o t a l s o l i d s = Mass sludge blowdown x % s o l i d s

7.10% = 27.6 l b s X- 100% = 2.0 l b s

The mass of chemical s o l i d s is c a l c u l a t e d as: Mass c'hemical s o l i d s = Mass t o t a l s o l i d s x % chemical s o l i d s

21.1% = 2.0 l b s x

= 0.4 l b s

and, t h e mass of s ludge s o l i d s is: Mass sludge s o l i d s = Mass t o t a l s o l i d s - Mass chemical s o l i d s

= 1 .6 l b s

F i l t r a t e Blowdown The volume of f i l t r a t e c o l l e c t e d is assumed t o be 3.2 ga l lons . The

mass of s o l i d p a r t i c l e s w i th in t h e f i l t r a t e is , t h e r e f o r e , c a l c u l a t e d as : Mass f i l t r a t e s o l i d s = Volume f i l t r a t e x Concentration f i l t r a t e s o l i d s

- -6 l b / g a l = 3.2 g a l x 8569 mg/l x 8.345 x 10

= 0.2 l b s mg,l

OUTPUT SUMMARY

F i l t e r Cake l b s Sludge s o l i d s 32.7 Chemical s o l i d s 8.7

F i l t r a t e 4.2 Sludge Blowdown

Sludge s o l i d s 1 .6 Chemical s o l i d s 0.4

F i l t r a t e blowdown 0.2 To ta l 47.8

155

FILTRATE (mg/l) TOLAL SOLIDS-

FILTRATE (mg/l) SUS. SOLIDS-

FILTER CAKE-(Wet w e i g h t ) lbs. F I L l E R CAKE-(ZSol. / % V O l . )

FILTER CAKE ( D r y W e i g h t ) lbs. CAKE THICKNESS-(Inches)

YIELD ( l b s . l f t . 2 h r . )

156

8 5 6 9 I

59 I l O t O I 4 1 . 0 - 4 8 . 3 ! 32.7

318 - 314

1.08

APPENDIX E

DERIVATION OF COSTS

Costs are derived for a plant generating 250 ~ r y tons,. lbs/ day 2 00- 2 5 0

lay (500,000 ) of sludge solids (roughly equivalent to a wastewater flow of MGD) .

VACUUM FILTER

Number of Units

2 Full-scale yield = 3.0 lb/hr/ft Filtration area = 600 ft2/unit

Number of units = 500,000 lb/day 3 . 0 lb/hr/ft2 x 24 hr/day x 600 ftz/unit

= 11.6 units or 12 units + 1 spare = 13 units

Capital Costs

1. Filters--from Komline-Sanderson, the cost per unit is $158,000.

Total installed cost = $158,000 x 13 units x 3 = $6,162,000

2. Lime System--for feeding an average of 50 tons/day

Total installed cost = $1,000,000

and includes conveyors, bins, slakers, pumps, etc.

Ferric Chloride System--for feeding 16.7 tons/day of 10% solution 3.

Total installed cost = $500,000

and includes storage tanks, pumps, etc.

4 . Conveyors--to transport filter cake to next process.

Total cost = $1,000,000

157

5. Total Capital Costs--

Filters $6,162,000 Lime 1 , 000,000 Ferric Chloride 500 , 000 Conveyors 1,000,000

Total $8,662,000

Annual Costs

1. Amortization--

Amortized cost = $8,700,000 x 0.09 = $783,000

2. Chemicals--chemical usage consists of lime @ 20%, ferric chloride @ 7%, and anti-scalant (to counteract lime scale).

Lime cost = 100,000 lb/day x $.022/lb x 365 days/yr = $803,000

FeC13 cost = 35,000 lb/day x $.065/lb x 365 days/yr = $830,375

Anti-scalant cost = $30,000

Total chemical costs = $1,663,375

3. Power--power co'sts assume 100% duty cycle usage.

Filters - 12 units @ 90 Hp/unit Sludge pumps - 12 @ 10 Hp/pump FeC13 system Lime system Conveyors

Total

1080 Hp 120 22 87 37

1346 Hp

Power cost = 1346 Hp x .746 Kw/Hp x $.O4/Kw-hr x 8760 hr/yr = $ 351,900

4. Water--the cloth washing system requires 60 gpm/unit.

Water cost = 60 gpm/unit x 12 units x $.25/1000 gal x 525,600 min/yr = $94,600

5. Operating Labor--labor costs assume each crew consists of 1 supervisor, 5 men to operate the filters and 1 man to operate the chemical.system. To cover a 7 day/week operation, 4 crews will be required, and 28 man- years (7 men/crew x 4 crews) will be expended.

Labor cost = 28 man-years x $21,000/man-year = $588,000

158

6. Maintenance--maintenance costs consist of the costs for both normal maintenance (materials and labor) and filter cloth replacement. Normal maintenance is based on 2% of the purchase price of all equipment, i.e. (Total capital cost)/3. 2000 hrs at a cost of $550 per cloth. the cloths are included in the cost for operating labor.

The filter cloths must be replaced once every The labor costs for changing

$8,662yooo x $.02 = $58,000 3 Normal maintenance cost =

Cloth replacement cost - - 8760 hr/yr x 12 units x $550/cloth 2000 hr/cloth/unit

= $29,150

Total maintenance costs = $87,150

7. Total Annual Costs--

Amortization Chemicals Power Water Labor Maintenance

Unit Cost

$ 783,000 1,663,000 351,900 94,600 588,000 87,150

Total $3,567,650

For processing 250 tons/day of dry sludge solids.

Unit cost = $ 3,567,650lyr = $39.10/ton 250 tons/day x 365 days/yr

FILTER PRESS--VARIABLE VOLUME UNIT

Number of Units

Full-scale yield = 0.49 lb/hr/ft2 Filtration area = 5380 ft2/unit

Number of units = 500,000 Ib/day 0.49 lb/hr/ftL x 24 hr/day x 5380 ftL/unit


159

Capital Costs

1. Presses--from Envirex, the cost for 9 units is $6,500,000.

Total installed cost = $6,500,000 x 3 = $19,500,000

2. Chemical System--for lime and FeC13; see vacuum filter costs.


3. Flight Conveyors--



Presses $19,500,000 Chemical System 1,500,000 Flight Conveyors 2,000,000

Total $23,000,000

Annual Costs

1. Amortization--

Amortized cost = $23,000,000 x .09 = $2,070,000

3. Power--costs assume 100% duty cycle usage

Press plus accessories--

Power usage = 37 Kw-hr/ton

Associated systems--

Lime system 81 Hp FeC13 system 14 Sludge pumping-4 pumps @ 15 Hp ea. 60

Conditioning system 20 Conveyors 260

435 Hp

Power usage = 435 Hp x .746 Kw/Hp x 24 hr/day = 31.2 Kw-hr/ton 2 5 0 t on/day

160

b

Power Costs--total power usage is 68.2 Kw-hr/ton

Power cost = 68.2 Kw-hr/ton x 250 ton/day x 365 days/yr x $.04/kw-hr = $248,900

4.

5.

6.

Water--filter cloths will require washing once every 20 press cycles. With a 54-minute cycle per press, the filter cloths will be washed 1.35 times per day and each wash will consume 3000 gallons. City water will be used.

Water cost = 3000 gal/cycle x 1.35 cycles/day/unit x 365 days/yr

x 8 units x $.5267/1000 gal = $6400

Operating Labor--costs assume each crew consists of 1 supervisor, 4 men to operate the presses, and 1 man to operate the chemical system. Four crews will be required for a 7 day/week operation and 24 man-years will be expended.

Labor cost = 24 man-years x $2lY000/man-year = $504,000

Maintenance--maintenance costs consist of the costs for normal equipment maintenance and filter cloth and diaphragm replacement. equipment maintenance is based on 2% of the purchase price of all equipment. at a material cost of $6500/unit. Diaphragms will require replacement once every 20,000 cycles at a material cost of $26,00O/unit. labor will change the filter cloths and diaphragms; 1.5 man-years will be expended.

Normal

Filter cloths will require replacement once every 3000 cycles

Operating

Normal maintenance cost = $23,000,000/3 x .O2 = $153,000

x 9 units

= $195,000

Diaphragm replacement cost = 27 cYcles/daY X 365 days/yr 20,000 cycles

x $26,00O/unit x 9 units

= $117,000

Labor cost = 1.5 man-years x $21,000/man-year = $31,500

Total maiatenance cost = $496,500

161

7. Total Annual Costs

Amortization Chemicals Power Water Operating Labor Maintenance

$ 2,070,000 1,663,400 248,900 6,400

504,000 496,500

Total $ 4,989,200

Unit Cost

For processing 250 tons/day of dry sludge solids

Unit cost = $ 4,989,200/yr = $54.68/ton 250 tons/day x 365 days/yr

FILTER PRESS--HIGH-PRESSURE FIXED VOLUME UNIT

Muhber of Units

Full-scale yield = 0.31 lb/hr/ft2 Filtration area = 11625 ft2/unit Chamber size = 40 mm (1.57 inches)

Number of 'units = 500,000 lb/day 0.31 lb/hr/ftL x 24 h rlday x 11623 f t L / unit


Capital Costs

From Passavant, the cost for 7 units, including all chemical systems, conveyors, etc., is $8,450,000.

Total installed cost = $8;450,000 x 3 = $25,350,000

Annual Costs

1. Amortization--

Amortized cost = $25,350,000 x .09 = $2,281,500

2. Chemicals--for lime, FeC13, and anti-scalant; see vacuum filter costs.

Chemical cost = $1,663,400

3. Power--for 6 presses in operation, power usage is 57.3 Kw-hr/ton

Power cost = 57.3 Kw-hr/ton x 250 tons/day x 365 days/yr x $.04/Kw-hr = $210,000

162

4 . Water--filter cloths will require washing once per month; each wash will consume 36,000 gallons of water.

Water cost = 36,000 gal/cycle x 1 cycle/mo/unit x 12 mo/yr

x 7 units x $ .5267/1000 gal

= $1600

5. Operating Labor--costs assume each crew consists of 1 supervisor, 3 men to operate the presses, and 1 man to operate the chemical system. For a 7 day/week operation, 20 man-years will be expended.

Labor cost = 20 man-years x $21,000/man-year = $420,000

6. Maintenance--maintenance costs consist of the costs for normal equipment maintenance and filter cloth replacement. Equipment maintenance is based on 2% of the purchase price of all equipment. Filter cloths will require replacement once per year at a cost of $240,000 for materials and $40,000 for labor (includes 2 men on ‘day shift year-round).

Normal maintenance cost = $25,350,000/3 x .02 = $170,000

Cloth replacement cost = $240,000

Labor cost = $40,000


7. Total Annual Costs--

Amortization Chemicals Power Water Operating Labor Maintenance

$2,281,500 1,663,400 210,000 1,600

420,000 450,000

Total $5,026,500

Unit Cost


Unit cost = $5,026,500 /yr . = $55.08/ton 250 tons/day x 365 days/yr

163

FILTER PRESS - LOW-PRESSURE FIXED V0Lb.E UNIT

Lumber of Units

Full-scale yield = 0.22 lb/hr/ft2 Filtration area = 6760 ft2/unit Chamber size = 32 mm (1.25 inches)

500,000 lb/day x 24 hr/day x 6760 ft2/unit Number of units = Q . ~ ~ 1b/hr/ft2

= 14 units or 14 units + 1 spare = 15 units

Capital Costs

1. Presses--from Nichols, the cost for each press is $400,000.

Total installed cost = $400,00O/unit x 15 units x 3 = $18,000,000

2. Chemical System--for lime and FeC13, see vacuum filter costs.


3. Conveyors--


4 . T o t a l Capital Costs--

Presses Chemical System Conveyors

Total

$18,000,000 1,500,000 2,300,000

$21,800,000

Annual Costs

1. Amortization--

Amortized cost = $21,800,000 x .09 = $1,962,000

2. Chemicals--for lime, FeC13, and anti-scalant; see vacuum filter costs.


3. Power--

Press--includes sludge and chemical feed systems.

Power usage = 65.3 Kw-hr/ton

164

F

Transfer conveyors--power usage is 330 hp.

Power usage = 330 Hp x .746 Kw/Hp x 24 hrlday = 23.6 Kw-hr/ton 250 tonslday

Power costs - total power usage is 88.9 kw-tirlton

Power cost = 88.9 Kw-hrlton x 250 tonslday x 365 dayslyr x $.04/Kw-hr = $324,500

4. Water--filter cloths on one press only will be washed each day. Each wash will consume 5000 gallons of water.

Water cost = 5000 gallcycle x 1 cyclelday x 365 dayslyr x S.526711000 gal = $1,000

5. Operating Labor--costs assume each crew consists of 1 supervisor, 7 press operators, and 1 man to operate the chemical system. For a 7 daylweek operation, 36 man-years will be expended.


6. Maintenance--maintenance costs consist of the costs for normal equipment maintenance and cloth replacement. Equipment maintenance is based on 2% of the purchase price of all equipment. Filter cloths will require replacement once per year at a cost of $4600/unit for materials and $6,000 for labor (600 man-hrlyr).

Normal maintenance cost = $21,500,00013 x .02 = $143,000

Clotn replacement cost = $4600/unit x 15 units = $69,000

Labor cost = $6,000


7. Total Annual Costs-- Amortization Chemicals Power Water Operating Labor Maintenance

$1,962,000 1 , 663 , 000 324 , 500 1,000

756,000 218,000

Total $4,924,500

165

Unit Cost

To process 250 tons/day of dry sludge solids.

= $53.97/ton 84,924,500/yr Unit cost = 250 tonslday x 365 days/yr

BELT PRESS

iiumber of Units

Full-scale yield = 675 lb/hr/m width Eelt width = 3m/unit

500,000 lb/day 675 lb/hr/m x 24 hr/day x 3m/unit units

or 11 + 1 spare=12 Number of units =

Capital Costs units.

1. Presses--frorr, Komline Sanderson, the cost per unit is $147,000.


2. Polymer Feed System - includes storage, mixing, pumping, etc.

Total installed cost = 5750,OaO

3. Conveyors--


4 . Total Capital Costs--

Presses $5,300,000 Chemical System 753,000

Total $7,050,000 Conveyors 1,000 , 000

Annual Costs

1. Amortization--

Amortized cost = $7,050,000 x .09 = $634,500

2. Chemicals--test work indicated $9.00 per ton of sludge processed. However, because of uncertainty of polymer suitability, assume $15.00 per ton.

Chemical cost = 250 tonslday x 365 dayslyr x $15.00/ton = $1,368,800

166

3.

4 .

5.

6 .

7.

Power--

Press - 12.75 Hp/unit x 11 units 140 Iip 110

Folymer system 31 Conveyors 30

Sludge pumps - 10 Elp/unit x 11 units

Total 31i kip

Fower cost = 311 Hp x .746 Kw-hr/Iip x 8760 hr/yr x $.04/Kw-hr = $81,300

Water--each unit will consume 75 gpm.

Water cost = 75 gal/min/unit x 11 units x 525,600 min/yr x $.25/1000 gal

= $108,400

Labor--costs assume each crew consists of 1 supervisor, 6 men to operate the presses, and 1 man to operate the chemical system. For a 7 day/week operation, 32 man-years will be expended.


Maintenance--mantenance costs consist of the costs for normal maintenance and belt replacement. Normal maintenance costs for materials and labor are based on 3X of the purchase price of all equipment. Belt replacement costs will total $20,000 per year.

Normal maintenance cost = $7,050,000/3 x .03 = $70,500

Belt replacement cost = $20,000


Total Annual Costs--

Am0 r t i z a t ion Chemicals Power Water Operating Labor Maintenance

$ 634,500 1 , 368,800

81,300 108 , 4.00 672 , 000 90,500

$2,955,500

Unit Cost


= $32.39/ton $2,955,500 Unit cost = 250 tons/day x 365 days/yr

167

VACUUM FILTER FLUS BELT PRESS

Number of Units

Vacuum filters - 12 units + 1 spare = 13 units Full-scale yield for belt press = 1181 lb/hr/m width (Parkson tests) Belt width - 2 m/uriit

500,000 lb/day 1181 lb/hr/m x 24 hr/day x 2m/unit Number of units =


CaDital Costs

1. Vacuum Filters--


2. Belt Presses--from Parkson, the cost per unit is $72,000


3. Distribution and Feeding System--


4 . Additional Conveyors--

Total installed cost = $500,000


Vacuum Filters $8,700,000 Belt Fresses 2,160,000 Distribution/Feed System 1 , 000 , 000 Additional Conveyor 500 , 090

Total $12,400,000

Annual Costs

1. Amortization--

Amortized cost = $12,400,000 x .09 = $1,116,000

2. Chemicals--same as costs for vacuun filters.


168

3. Power--

Vacuum Filter System 1346 IIp Belt Fresses - 12.5 Hp/unit x 9 units 112.5 Distribution/Feed System 50 Additional Conveyors

Total 15

1523.5 Hp

Power cost = 1523.5 Hp x .746 Kw/Ep x $.04/Kwhr x S760 hr/yr

= $398,240

4. Water--the vacuum filter system will consume 60 gpm/unit; the belt press system will consume 50 gpm/unit.

Water consumption = 60 gpm/unit x 12 units + 50 gpm/unit x 9 units

= 1170 gpm

Water cost = 1170 gal/min x 525,600 min/yr x $.25/100@ gal = $153,700

5. Operating Labor - costs assume a 7-man crew will operate the vacuum filter system and a 3-man crew will operate the belt press system. For a 7 day/week operation, 40 man-years will be expended.


6. Maintenance--maintenance costs consist of normal maintenance costs on both the vacuum filters and the belt presses and belt replacement costs on the belt press. Vacuum filter maintenance costs will total $37,150 per year (see vacuum filter costs). Belt press maintenance costs are based on 3X of the purchase price of the additional equipment associated with the belt press. Belt replacement costs will total $20,000 per year.

Vacuum filter maintenance costs = $87,150

Belt press maintenance costs = $3,663,000/3 x .03 = $36,600

Belt replacement costs = $20,000


163

7 . T o t a l Annual Costs--

Amor t iza t ion Chemic a1 s Power Water Opera t ing Labor Maintenance

$1,116,009 1,663,400

398,240 153,700 849,000 143,750

$4,315,090

Unit Cost

For p r o c e s s i n g 250 t o n s l d a y of s l u d g e s o l i d s .

54,315,090 = $47.29/ ton 250 t o n s l d a y x 365 d a y s l y r Unit c o s t =

IN INERAT I O N

The c o s t s i n t h i s s e c t i o n are rough approximations developed from on-going d e s i g n work f o r t h e D i s t r i c t of Columbia.

Number of U n i t s

I n c i n e r a t o r r a t i n g = 10 l b w e t f e e d l h r l f t Burning area f o r a 12 h e a r t h u n i t = 4584 f t 2 / u n i t (25.75 f t d i a m e t e r ) Feed c a p a c i t y = 45,480 l b w e t feed, /hr Feed ra te = 317.5 t o n s l d a y of d r y s o l i d s (253 tons /day of d r y s l u d g e

s o l i d s + 27% chemica ls ) A v a i l a b i l i t y f a c t o r = 85X

2 of burn ing area

For a 202 f e e d

317.5 t o n s l d a y x 2000 l b s l t o n 45,480 lb w e t feed x .2 lb d r y feed x 24 h r x 0.85 Number of u n i t s = .

h r l u n i t l b w e t feed day = 3.4 o r 4 u n i t s

S i m i l a r l y , f o r a 35% feed

Number of u n i t s = 1.9 o r 2 u n i t s

C a p i t a l Cos ts

I n c l u d e s a i r p o l l u t i o n c o n t r o l equipment ( e l e c t r o s t a t i c p r e c i p i t a t o r ) t o meet emiss ion requi rements , i n s t a l l a t i o n , b u i l d i n g , u t i l i t i e s , and e n g i n e e r i n g .

T o t a l i n s t a l l e d c o s t = $5,000,000/uni t

170

1. Amortization--

Annual Costs

For a 20% feed, amortized cost = $20,000,000 x .09 = $1,800,000

For a 35% feed, amortized cost = $900,000

2. Power--

For a 20% feed, power usage is 860 Eplunit

Fower cost = 860 hplunit x 4 units x .746Iiw/iip x 8760 hrlyr x S .04/Kw-hr

= $899,200

For a 35Z feed, power usage is 775 Hplunit

Fower cost = $405,200

3. Fuel--the incinerator will produce an 800 O F outlet temperature. A fume furnace will raise all stack gases to 1350 O F before discharge. Water vapor will be removed in a subcooler, prior to reheating the stack gases. oil will be required for incineration, and 7,133 gal/day of 112 fuel oil will be required for the fume iurnace, for a total fuel usage of 28,133 gallday. With a 35): solids feed, 4306 gallday of # 2 fuel oil will be required for the fume furnace only.

With a 20% solids feed, 21,000 gallday of #2 fuel

For a 20% feed, fuel cost = 28,133 gallday x 365 dayslyr x $ .40/gal = $4,110,000

For a 352 feed, fuel cost = $630,000

4. Operating Labor--costs assume each crew consists of 1 supervisor, 1 operator per unit and 1 helper. Four crews will be required to cover a 7 daylweek operation. for a 35% feed, 16 man-years will be expended.

For a 20% feed, 24 man-years will be expended;

For a 20% feed, labor cost = 24 man-years x $2lY000/man-year = $504,000

For a 35% feed, labor c o s t = $336,000

5. Maintenance--costs assume $100,00O/unit per year.

For a 20% feed, maintenance cost = $100,00O/unit x 4 units = $400,000

For a 35% feed, maintenance cost = $200,000

17 1

6. Asn d isposa l - -haul ing and d i s p o s a l c o s t s w i l l t o t a l $10.00/ ton of a s h and are computed based on 40% of t h e incoming feed t o t h e ciewatering p r o c e s s p l u s lOOTd of t h e i n e r t chemicals added.

T o t a l a s h q u a n t i t y = 167.5 t o n s l d a y

Ash d i s p o s a l c o s t s = 167.5 t o n l d a y x 365 d a y s l y r x S10.00l ton = $61a,000

7 . T o t a l Annual Costs--

Amor t iza t ion F’ower Fuel Opera t ing Labor Maintenance

20% Feed 35% Feed

$1,800,000 s 900,000 899,200 405,200

4,110,000 630 , 000 504,000 336,000 400,000 200,000

Ash D i s p o s a l 610,000 T o t a l $8,323,200

610,000 $3,081,200

Unit Cost

For p r o c e s s i n g 250 t o n s l d a y of s l u d g e s o l i d s .

= V91.21lton $8,323,200/yr For a 207; f e e d , u n i t c o s t = 25U tons /day x 365 d a y s l y r

For a 3570 f e e d , u n i t c o s t = $33.77/ton

HAULING

h a u l i n g c o s t s are based on a c t u a l c o s t s now i n c u r r e d a t Blue P l a i n s t o h a u l s l u d g e cake a 25 m i l e d i s t a n c e . Undigested vacuum-f i l te r cake must be t r a n s p o r t e d i n enc losed v e h i c l e s , e .g . , a c o n c r e t e mixer; hence c o s t s are $9.40 p e r w e t ton . enough t o c a r r y i n a n open dump t r u c k ; hence c o s t s of $6.25 p e r w e t ton .

F i l t e r - p r e s s cake is assumed t o b e d r y

The c o s t s per d r y t o n of s l u d g e s o l i d s were developed by c o r r e c t i n g t h e above f i g u r e s f o r t h e p e r c e n t cake s o l i d s and q u a n t i t i e s of chemica ls added. For example, t h e c o s t of h a u l i n g vacuum f i l t e r cake a t 207: s o l i d s is c a l c u l a t e d as

$9.40/wet t o n 1 . 2 7 t o n s t o t a l s o l i d s h a u l i n g c o s t = X 0.2 d r y ton/wet t o n 1.0 t o n s l u d g e s o l i d s

= $59.69/dry t o n of s l u d g e s o l i d s

172

COMPOSTING

Costs were obtained from a paper entitled "Composting Filter Press Cake"; presented at Compost Science Meeting, April, 1978 at Omaha, Nebraska; Maryland. received. as described under hauling costs.

G. Wilson, D. Colacicco, and D. Casey, USDA, Beltsville, Costs in this paper are presented in $/wet ton of sludge as To convert to $/dry ton of sludge solids, use the procedure

17 3

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Sludge Solids: Total Solids: Process Yield:

Full-scale Yield:

GLOSSARY OF TERMS

Sewage sludge solids only. Sewage sludge plus chemical solids. Calculated as kilograms of sludge solids per hour of filtration time per square meter of filtration area.

except that cycle time includes both filtration and mechanical cycle time for a full-scale press.

Same calculation as process yield

17 6

R E P O R T NO. 12.

E PA- 6 00/ 2 - 7 9 - 1 2 3 T I T L E A N D S U B T I T L E

I

3. RECIPIENT'S ACCESSIONNO.

EVALUATION OF DEWATERING DEVICES FOR PRODUCING HIGH- SOLIDS SLUDGE CAKE

8. PERFORMING O R G A N I Z A T I O N REPORT NO. AUTHORW

Alan F. Cassel and Berinda P. Johnson 10. P R O G R A M E L E M E N T NO. PERFORMING O R G A N I Z A T I O N N A M E A N D ADDRESS

1BC821, SOS #1, Task A38 D i s t r i c t of Columbia Government Department of Environmental Serv ices 11. C O N T R A C T / G R A N T NO.

6 , P E R F O R M l N ~ O R G A N l ~ A T 1 0 N C O D E

Water Resources Management Adminis t ra t ion I 68-03-2455

U. S. Environmental P ro tec t ion Agency Cinc inna t i , Ohio 45268

5000 Overlook Avenue, Washington, D. C . 20032 13. TYPE OF REPORT A N D PERIOD C O V E R E D 2. SPONSORING AGENCY N A M E A N D ADDRESS

EPA/600/14

Municipal Environmental Research Laboratory Off ice of Research and Development

Res- St i idv 14. SPONSORING AGENCY'CODE

P i l o t - s c a l e dewatering tes ts were made t o e s t a b l i s h design and ope ra t ing parameters f o r dewatering municipal wastewater s ludges on recessed p l a t e f i l t e r p re s ses (both diaphragm and f ixed volume types ) , continuous b e l t p re s ses , and r e t r o f i t u n i t s f o r a vacuum f i l t e r . Resul t s from t h e 1.5-year s tudy showed t h a t when dewatering lime and f e r r i c ch lor ide-condi t ioned s ludges , t h e recessed p l a t e p re s ses c o n s i s t e n t l y produced a 30-40% s o l i d s f i l t e r cake. Feed s o l i d s t o t h e u n i t s averaged 5% t o t a l s o l i d s wi th a range from 2.4 t o 10%. was te-ac t iva ted t o primary s ludge s o l i d s , wi th emphasis on t h e 2 / 1 r a t i o , were t e s t e d . Bel t p re s ses produced cake s o l i d s from 25-30% when t h e polymer condi- t i o n i n g dosage was optimized. t he b e l t p re s s gave cake s o l i d s i n t h e 30-40% range during l abora to ry - sca l e t e s t s . Design parameters are developed t o dewater a mixture of 67% secondary and 33% primary s ludge i n a f u l l - s c a l e p l a n t i n s t a l l a t i o n . dewatering p l u s f i n a l d i sposa l by e i t h e r i n c i n e r a t i o n o r composting a r e a l s o presented .

Various r a t i o s of

When used as a r e t r o f i t device t o a vacuum f i l t e r ,

The es t imated c o s t s f o r

7. K E Y WORDS A N D D(

DESCRIPTORS

Sludge Dewatering Sludge d i sposa l Waste t rea tment Economic an a 1 ys i s Cost es t imates

Release t o pub l i c

EPA Form 2220-1 (9-73) 1

:UMENT A N A L Y S I S

I.IDENTIFIERS/OPEN ENDED TERMS IC. COSATI Field/Group

Sludge process ing P i l o t s tudy Performance da ta Design gu ide l ines Sludge condi t ion ing Sludge dewatering

19. SECURITY CLASS (This Report)

Unclas s i f i ed 20. SECURITY CLASS (Thispage)

13B

!1. NO. OF PAGES

191 !2. PRICE

1 U S GOVERNM~NlPRlNl lNGDff ICt 1979 -657-06015436

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