NITROGEN REMOVAL FROM SEPTIC TANK EFFLUENT USING …

NITROGEN REMOVAL FROM SEPTIC TANK EFFLUENT USING

SAND FILTRATION AND SULFUR/LIMESTONE DENITRIFICATION

A

Thesis

Submitted to the Faculty of Graduate Studies and Research

In Partial Fulfillment of the Requirements

For the Degree of

Master of Applied Science

in Environmental Systems Engineering

University of Regina

by

Vivek Mariappan

Regina, Saskatchewan

April, 2002

Copyright 2002: Mariappan, Vivek

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

NITROGEN REMOVAL FROM SEPTIC TANK EFFLUENT USING

SAND FILTRATION AND SULFUR/LIMESTONE DENITRIFICATION

A

Thesis

Submitted to the Faculty of Graduate Studies and Research

In Partial Fulfillment o f the Requirements

For the Degree of

Master of Applied Science

in Environmental Systems Engineering

University o f Regina

by

Vivek Mariappan

Regina, Saskatchewan

April, 2002

Copyright 2002: Mariappan, Vivek


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CanadaReproduced with permission of the copyright owner. Further reproduction prohibited without permission.

UNIVERSITY OF REGINA

FACULTY OF GRADUATE STUDIES AND RESEARCH

CERTIFICATION OF THESIS WORK

We, the undersigned, certify that Vivek Mariappan, candidate for the Degree of Master of Applied Science, has presented a thesis titled Nitrogen Removal from Septic Tank Effluent using Sand Filtration and Sulfur/Limestone Denitrification, that the thesis is acceptable in form and content, and that the student demonstrated a satisfactory knowledge of the field covered by the thesis in an oral examination held on September 9, 2002.

External Examiner:

Internal Examiners:

Dr. Pritam Jain, Saskatchewan Environment

/ Vey' Dr. T. Viraraghavan, S ervisor




C E R T IF IC A T IO N O F T H E S IS W O R K

We, the undersigned, certify that Vivek Mariappan, candidate for the Degree of Master of Applied Science, has presented a thesis titled Nitrogen Removal from Septic Tank Effluent using Sand Filtration and Sulfur/Limestone Denitrification, that the thesis is acceptable in form and content, and that the student demonstrated a satisfactory knowledge of the field covered by the thesis in an oral examination held on September 9, 2002.

External Examiner:Dr. Pritam Jain, Saskatchewan Environment

Internal Examiners:Dr. T. Viraraghavan, Supervisor




PERMISSION TO USE POSTGRADUATE THESIS

TITLE OF THESIS: Nitrogen Removal from Septic Tank Effluent using Sand Filtration and Sulfur/Limestone Denitrification

NAME OF AUTHOR: Vivek Mariappan

DEGREE: Master of Applied Science

In presenting this thesis in partial fulfillment of the requirements for a postgraduate degree from the University of Regina, I agree that the Libraries of this University shall make it freely available for inspection. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the professor or professors who supervised my thesis work, or in their absence, by the Head of the Department or the Dean of the Faculty in which my thesis work was done. It is understood that with the exception of UMI Dissertations Publishing (UMI) that any copying, publication or use of this thesis or parts thereof for financial gain shall not be allowed without my written permission. It is also understood that due recognition shall be given to me and to the University of Regina in any scholarly use which may be made of my material in my thesis.

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DATE:




P E R M IS S IO N T O U S E P O S T G R A D U A T E T H E S IS

TITLE OF THESIS: Nitrogen Removal from Septic Tank Effluent using Sand Filtration andSulfur/Limestone Denitrification

NAME OF AUTHOR: Vivek Mariappan

DEGREE: Master of Applied Science

In presenting this thesis in partial fulfillment of the requirements for a postgraduate degree from the University of Regina, I agree that the Libraries of this University shall make it freely available for inspection. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the professor or professors who supervised my thesis work, or in their absence, by the Head of the Department or the Dean of the Faculty in which my thesis work was done. It is understood that with the exception of UMI Dissertations Publishing (UMI) that any copying, publication or use of this thesis or parts thereof for financial gain shall not be allowed without my written permission. It is also understood that due recognition shall be given to me and to the University of Regina in any scholarly use which may be made of my material in my thesis.

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ABSTRACT

The control of nitrogen from on-site effluents has been identified as an important

measure to minimize groundwater pollution by nitrates. A study was conducted to

remove nitrogen from a septic tank effluent. The primary objectives of the study were: 1)

to investigate the applicability of a sand filter system for nitrification of STE (septic tank

effluent) and sulfur/limestone autotrophic denitrification (SLAD) layer to treat the

nitrified effluent as a single pass system; and 2) to determine an optimum ratio of sulfur

to limestone in the SLAD layer.

Column based studies were conducted to achieve the objectives. Studies include

conducting experiments and plotting nitrogen, COD, alkalinity, and sulfate profiles along

the system. The systems were dosed intermittently with 6 h resting period between

application at uniform rates of 4 and 8.1 cm/d of STE for 160 and 40 days respectively

(for a total of 200 consecutive study days).

The results demonstrate that significant nitrification would be achieved with an

intermittent sand filter system dosed twice daily. The sand filter system needed

approximately two months for stabilization before attaining significant nitrification

capability. The effluent from the sand filter showed a 70 percent conversion of influent

TKN to nitrate and nitrite nitrogen. An overall average removal of COD in the sand filter

during the entire period of study was found to be between 80 and 90 percent. Phosphate

and alkalinity reductions were over 60 and 15 percent respectively.

Denitrification using sulfur/limestone has shown to be a very effective method in

achieving a nearly complete nitrogen removal from nitrified effluent of the sand filter.

Studies to determine a proper ratio of sulfur limestone mixture and applicability in real

i


ABSTRACT

The control of nitrogen from on-site effluents has been identified as an important

measure to minimize groundwater pollution by nitrates. A study was conducted to

remove nitrogen from a septic tank effluent. The primary objectives of the study were: 1)

to investigate the applicability o f a sand filter system for nitrification of STE (septic tank

effluent) and sulfur/limestone autotrophic denitrification (SLAD) layer to treat the

nitrified effluent as a single pass system; and 2) to determine an optimum ratio of sulfur

to limestone in the SLAD layer.

Column based studies were conducted to achieve the objectives. Studies include

conducting experiments and plotting nitrogen, COD, alkalinity, and sulfate profiles along

the system. The systems were dosed intermittently with 6 h resting period between

application at uniform rates o f 4 and 8.1 cm/d o f STE for 160 and 40 days respectively

(for a total o f 200 consecutive study days).

The results demonstrate that significant nitrification would be achieved with an

intermittent sand filter system dosed twice daily. The sand filter system needed

approximately two months for stabilization before attaining significant nitrification

capability. The effluent from the sand filter showed a 70 percent conversion of influent

TKN to nitrate and nitrite nitrogen. An overall average removal o f COD in the sand filter

during the entire period of study was found to be between 80 and 90 percent. Phosphate

and alkalinity reductions were over 60 and 15 percent respectively.

Denitrification using sulfur/limestone has shown to be a very effective method in

achieving a nearly complete nitrogen removal from nitrified effluent o f the sand filter.

Studies to determine a proper ratio o f sulfur limestone mixture and applicability in real

i


life, three ratios (mass to mass) 1/1, 2/1, and 3/1 of sulfur and limestone were examined.

A near 100% denitrification was achieved in all three ratios, while sulfate and alkalinity

production to a range of 150-250 mg/L and 500-900 mg/L as CaCO3 were observed in

the effluent from SLAD layers. The production of high concentration of sulfate and

alkalinity may be a limiting factor in its application.

ii


life, three ratios (mass to mass) 1/1, 2/1, and 3/1 of sulfur and limestone were examined.

A near 100% denitrification was achieved in all three ratios, while sulfate and alkalinity

production to a range o f 150-250 mg/L and 500-900 mg/L as CaCCL were observed in

the effluent from SLAD layers. The production of high concentration of sulfate and

alkalinity may be a limiting factor in its application.

n


ACKNOWLEDGEMENTS

I am thankful to my supervisor, Dr. T. Viraraghavan for providing me with an

opportunity to work in his research group. His guidance helped me in undertaking my

study with enthusiasm.

I appreciate the understanding and cooperation shown by Mr. Jay Ram and his

family during the collection of septic tank effluent samples. I thank Ashref Darbi, for

helping me in the task of sample collection. My friends Thyagarajan, Kei Lo, and Vijay

were always there to help me with my work on and off campus. I thank Dr. Helen

Christiansen and family for their guidance and concern.

I am thankful to the Faculty of Engineering for providing me teaching

assistantship position. I thank my parents and sister, who have been a constant source of

inspiration and moral support during my studies.

iii


ACKNOW LEDGEMENTS

I am thankful to my supervisor, Dr. T. Viraraghavan for providing me with an

opportunity to work in his research group. His guidance helped me in undertaking my

study with enthusiasm.

I appreciate the understanding and cooperation shown by Mr. Jay Ram and his

family during the collection of septic tank effluent samples. I thank Ashref Darbi, for

helping me in the task of sample collection. My friends Thyagarajan, Kei Lo, and Vijay

were always there to help me with my work on and off campus. I thank Dr. Helen

Christiansen and family for their guidance and concern.

I am thankful to the Faculty of Engineering for providing me teaching

assistantship position. I thank my parents and sister, who have been a constant source o f

inspiration and moral support during my studies.

Ill


TABLE OF CONTENTS

ABSTRACT

ACKNOWLEDGEMENTS III

LIST OF TABLES VII

LIST OF FIGURES IX

NOTATION X

INTRODUCTION 1

1.1 Objectives and scope of the study 3

2 LITERATURE REVIEW 4

2.1 Nitrification 4

2.2 Denitrification 8

2.3 Treatment process 10

2.3.1 Aerobic Treatment Units 10

2.3.2 Evaporation systems 11

2.3.3 Subsurface disposal mechanism 11

2.3.4 Wetlands 14

2.3.5 Sand Filters 15

2.4 Alternative Nitrogen removal system 18

2.4.1 RUCK system 19

2.4.2 Kitchen Waste 20

2.4.3 Alcohol 20

2.4.4 Bio-textile 21

2.4.5 Peat 22

2.4.6 Sawdust 23

2.4.7 Sulfur 24

iv


TABLE OF CONTENTS

ABSTRACT........................................................................................................................................... I

ACK NO W LEDG EM ENTS......................................................................................................... I ll

LIST OF TA B LES.................................................................................................................. VII

LIST OF FIG U R ES.................................................................................................................. IX

NOTATION......................................................................................................................................... X

INTRODUCTION............................................................................................................................... 1

1.1 Objectives and scope of the study...................................................................................... 3

2 LITERATURE REVIEW .........................................................................................................4

2.1 N itrification ........................... 4

2.2 D enitrification........................................................................................................................... 8

2.3 Treatment process.................................................................................................................. 10

2.3.1 Aerobic Treatment U nits............................................................................................10

2.3.2 Evaporation systems....................................................................................................11

2.3.3 Subsurface disposal mechanism................................................................................11

2.3.4 Wetlands....................................................................................................................... 14

2.3.5 Sand Filters...................................................................................................................15

2.4 Alternative Nitrogen removal system ..............................................................................18

2.4.1 RUCK system.............................................................................................................. 19

2.4.2 Kitchen W aste.............................................................................................................20

2.4.3 Alcohol.........................................................................................................................20

2.4.4 Bio-textile.................................................................................................................... 21

2.4.5 Peat............................................................................................................................... 22

2.4.6 Sawdust........................................................................................................................23

2.4.7 Sulfur............................................................................................................................24

iv


3 MATERIALS AND METHODS 27

3.1 Septic tank effluent used in the study 27

3.2 Sand, Sulfur and Limestone used in the column 27

3.3 Thiobacillus denitrificans culture 28

3.4 Experimental Set-up 30

3.4.1 Culturing Thiobacillus denitrificans in SLAD layer 32

3.5 Column Studies 33

3.5.1 Analytical Methods 34

3.6 Sampling, transport, and storage methods 35

4 RESULTS AND DISCUSSION 36

4.1 Characteristics of septic tank effluent 36

4.1.1 p1-1 36

4.1.2 Ammonia, nitrate, nitrite and total Kjeldahl nitrogen 38

4.1.3 COD 38

4.1.4 Phosphates 38

4.1.5 Alkalinity 38

4.2 Performance of sand filter 39

4.2.1 pH 39

4.2.2. Nitrogen removal 39

4.2.2 COD 51

4.2.3 Alkalinity 52

4.2.4 Phosphate 53

4.2.5 Dissolved oxygen 57

4.2.6 Crust formation 57

4.3 Treatment efficiency of SLAD layer 58

4.3.1 pH and alkalinity 58

4.3.2 Nitrogen removal 64

4.3.3 Sulfate 69

4.3.4 COD 73

v


3 MATERIALS AND M E T H O D S.........................................................................................27

3.1 Septic tank effluent used in the stu d y .............................................................................27

3.2 Sand, Sulfur and Limestone used in the colum n......................................................... 27

3.3 Thiobacillus denitrificans culture.....................................................................................28

3.4 Experimental Set-up ............................................................................................................. 30

3.4.1 Culturing Thiobacillus denitrificans in SLAD layer............................................... 32

3.5 Column Studies.......................................................................................................................33

3.5.1 Analytical M ethods....................................................................................................34

3.6 Sampling, transport, and storage m ethods................................................................... 35

4 RESULTS AND D ISC U SSIO N ...........................................................................................36

4.1 Characteristics o f septic tank effluent.............................................................................36

4.1.1 p H ................................................................................................................................. 36

4.1.2 Ammonia, nitrate, nitrite and total Kjeldahl nitrogen...........................................38

4.1.3 C O D ............................................................................................................................. 38

4.1.4 Phosphates................................................................................................................... 38

4.1.5 Alkalinity................................................................. 38

4.2 Performance of sand filter.................................................................................................. 39

4.2.1 pH ................................................................................................................................. 39

4.2.2. Nitrogen removal........................................................................................................ 39

4.2.2 C O D .............................................................................................................................51

4.2.3 Alkalinity..................................................................................................................... 52

4.2.4 Phosphate.................................................................................................................... 53

4.2.5 Dissolved oxygen.......................................................................................................57

4.2.6 Crust formation.......................................................................................................... 57

4.3 Treatment efficiency o f SLAD la y e r .............................................................................. 58

4.3.1 pH and alkalinity........................................................................................................ 58

4.3.2 Nitrogen removal........................................................................................................64

4.3.3 Sulfate.......................................................................................................................... 69

4.3.4 C O D ............................................................................................................................ 73

v


4.3.5 Phosphate 76

4.4 General Discussion 79

5. CONCLUSIONS AND RECOMMENDATIONS FOR FURTHER STUDY 81

5.1 Conclusions 81

5.2 Recommendations for further study 82

REFERENCE 83

APPENDIX A 96

vi


4.3.5 Phosphate................................................................................................................... 76

4.4 General Discussion............................................................................................................. 79

5. CONCLUSIONS AND RECOM M ENDATIONS FOR FURTHER ST U D Y . 81

5.1 Conclusions...........................................................................................................................81

5.2 Recommendations for further study ........................................................................... 82

REFERENCE.................................................................................................................................... 83

APPENDIX A .................................................................................................................................... 96

V I


LIST OF TABLES

Table 3.1. Culture preparation medium 29

Table 3.2. Trace element composition 29

Table 4.1. Septic tank effluent characteristics 37

Table 4.2 Nitrification percentage across the sand filter 40

Table 4.3. Alkalinity removal efficiency across sand filter 54

Table 4.4. Percentage increase of alkalinity in SLAD effluent at 4.0 cm/d 63

Table 4.5. Percentage increase of alkalinity in SLAD effluent 8.1 cm/d 63

Table 4.6. Comparison of nitrogen removal efficiency in sand filter and SLAD

layers 67

Table 4.7. COD removal efficiency of SLAD layers 74

Table 4.8. Percentage increase in phosphate in SLAD layer 78

Table A.1. Influent TKN and ammonia-nitrogen to the sand filter. 96

Table A.2. Ammonia-nitrogen results from sand filter effluent columns 1, 2, 3 97

Table A.3. Nitrate-nitrogen results from sand filter effluent columns 1, 2, 3. 98

Table A.4. Nitrite-nitrogen results from sand filter effluent columns 1, 2, 3. 99

Table A.S. Ammonia-nitrogen results from sand filter effluent columns 1, 2, 3 100

Table A.6. Dissolved oxygen concentration from sand filter columns 1, 2, 3. 101

Table A.7. STE COD results 102

Table A.B. COD results from sand filter effluent columns 1, 2, 3. 103

Table A.9. STE Alkalinity results 104

Table A.10. Alkalinity results from sand filter effluent columns 1, 2, 3. 105

Table A.11. STE phosphate as P results. 106

Table A.12. Phosphate as P results from sand filter effluent columns 1, 2, 3 107

vii


LIST OF TABLES

Table 3.1. Culture preparation m edium ...................................................................................29

Table 3.2. Trace element com position....................................................................................... 29

Table 4.1. Septic tank effluent characteristics........................................................................ 37

Table 4.2 Nitrification percentage across the sand filter.................................................... 40

Table 4.3. Alkalinity removal efficiency across sand filter ................................................54

Table 4.4. Percentage increase of alkalinity in SLAD effluent at 4.0 cm /d ..................63

Table 4.5. Percentage increase o f alkalinity in SLAD effluent 8.1 cm /d........................63

Table 4.6. Comparison of nitrogen removal efficiency in sand filter and S L A D .........

layers..............................................................................................................................................67

Table 4.7. COD removal efficiency of SLAD la y ers .............................................................74

Table 4.8. Percentage increase in phosphate in SLAD layer............................................ 78

Table A .I. Influent TKN and ammonia-nitrogen to the sand filter................................ 96

Table A.2. Ammonia-nitrogen results from sand filter effluent columns 1, 2, 3.........97

Table A.3. Nitrate-nitrogen results from sand filter effluent columns 1, 2, 3.............. 98

Table A.4. Nitrite-nitrogen results from sand filter effluent columns 1, 2, 3 ............... 99

Table A.5. Ammonia-nitrogen results from sand filter effluent columns 1, 2, 3 .......100

Table A.6 . Dissolved oxygen concentration from sand filter columns 1, 2, 3 .............101

Table A.7. STE COD results.......................................................................................................102

Table A.8 . COD results from sand filter effluent columns 1, 2, 3.................................. 103

Table A.9. STE Alkalinity results............................................................................................. 104

Table A.10. Alkalinity results from sand filter effluent columns 1, 2, 3 ...................... 105

Table A .l l . STE phosphate as P results..................................................................................106

Table A.12. Phosphate as P results from sand filter effluent columns 1, 2, 3 .............. 107

vii


Table A.13. Nitrate as nitrogen results from SLAD effluent columns 1, 2, 3. 108

Table A.14. Nitrite as nitrogen results from SLAD effluent columns 1, 2, 3. 109

Table A.15. Sulfate results from SLAD effluent columns 1, 2, 3. 110

Table A.16. COD results from SLAD effluent columns 1, 2, 3 111

Table A.17. Phosphate-as P results from SLAD effluent columns 1, 2, 3. 112

Table A.18. Alkalinity results from SLAD effluent columns 1, 2, 3. 113

viii


Table A.13. Nitrate as nitrogen results from SLAD effluent columns 1, 2,..3............108

Table A.M . Nitrite as nitrogen results from SLAD effluent columns 1, 2, 3 ............109

Table A.15. Sulfate results from SLAD effluent columns 1, 2, 3.................................... 110

Table A.16. COD results from SLAD effluent columns 1, 2, 3 ........................................I l l

Table A.17. Phosphate-as P results from SLAD effluent columns 1, 2, 3 ....................112

Table A .18. Alkalinity results from SLAD effluent columns 1, 2, 3.............................. 113

V I 11


LIST OF FIGURES

Figure 3.1. Experimental Set up 31

Figure 4.1. Septic tank effluent nitrogen composition 41

Figure 4.2. Oxidation of influent NH4-N to NO2-N and NO3-N in sand filters 42

Figure 4.3. Mass balance (influent NI-14--N Vs effluent total nitrogen) of nitrogen in

sand filter 43

Figure 4.4. Comparison of the sand filter effluent NH4-N to NO3-N and NO2-N 44

Figure 4.5. Sand filter effluent COD comparison 45

Figure 4.6. Sand filter effluent COD removal efficiency 46

Figure 4.7. Sand filter effluent alkalinity comparison 47

Figure 4.8. Phosphate removal in sand filter 56

Figure 4.9. Alkalinity profile in column 1 60



Figure 4.12. Nitrate and nitrite nitrogen in SLAD layer effluent 65

Figure 4.13. Nitrogen levels in SLAD layer effluent 66

Figure 4.14. Influence of Ammonia nitrogen on sulfate levels 70

Figure 4.15. A comparison of sulfate production and nitrate levels in SLAD layer

effluent 71

Figure 4.16. Comparison of SLAD effluent SO4 and alkalinity 72

Figure 4.17. COD profile across the system 75

Figure 4.18. Phosphate profile 77

ix


LIST OF FIGURES

Figure 3.1. Experimental Set u p ..................................................................................................31

Figure 4.1. Septic tank effluent nitrogen com position......................................................... 41

Figure 4.2. Oxidation of influent NH4 -N to NO 2 -N and NO3 -N in sand filters..............42

Figure 4.3. Mass balance (influent NH 4 -N Vs effluent total nitrogen) of nitrogen in

sand filter .....................................................................................................................................43

Figure 4.4. Comparison of the sand filter effluent NH 4 -N to NO3 -N and NO 2 - N 44

Figure 4.5. Sand filter effluent COD com parison................................................................. 45

Figure 4.6. Sand filter effluent COD removal efficiency.................................................... 46

Figure 4.7. Sand filter effluent alkalinity com parison......................................................... 47

Figure 4.8. Phosphate removal in sand filter...........................................................................56

Figure 4.9. Alkalinity profile in column 1.................................................................................60

Figure 4.10. Alkalinity profile in column 2.............................................................................. 61

Figure 4.11. Alkalinity profile in column 3 .............................................................................. 62

Figure 4.12. Nitrate and nitrite nitrogen in SLAD layer effluent.....................................65

Figure 4.13. Nitrogen levels in SLAD layer effluent.............................................................6 6

Figure 4.14. Influence o f Ammonia nitrogen on sulfate levels.......................................... 70

Figure 4.15. A comparison of sulfate production and nitrate levels in SLAD layer

effluent...........................................................................................................................................71

Figure 4.16. Comparison o f SLAD effluent SO 4 and alkalinity........................................72

Figure 4.17. COD profile across the sy stem ............................................................................75

Figure 4.18. Phosphate profile..................................................................................................... 77

i.\


NOTATION

AS automated sampler

ATCC American Type Culture Collection

atm atmosphere

BLWRS barriered landscape water renovation system

BOD biological oxygen demand

c concentration

C/N carbon to nitrogen ratio

CEC cation exchange capacity

cm centimeter

cm/d centimeter per day

Co concentration at time "0"

COD chemical oxygen demand

Ct concentration at time t

DO dissolved oxygen

exp exponential

h hour

HLR hydraulic loading rate

HRT hydraulic retention time

(1) hydraulic head

IC Ion chromatography

K reaction rate constant

kg kilogram

x


NOTATION

AS automated sampler

ATCC American Type Culture Collection

atm atmosphere

BLWRS barriered landscape water renovation system

BOD biological oxygen demand

c concentration

C/N carbon to nitrogen ratio

CEC cation exchange capacity

cm centimeter

cm/d centimeter per day

Co concentration at time “0”

COD chemical oxygen demand

Ct concentration at time t

DO dissolved oxygen

exp exponential

h hour

HLR hydraulic loading rate

HRT hydraulic retention time

(j) hydraulic head

IC Ion chromatography

K reaction rate constant

kg kilogram


km kilometer

L liter

L/h liter per hour

M molarity

MAC maximum acceptable concentration

MCL maximum contaminant level

me milli equivalence

mg milligram

mg/L milligram per liter

mL milliliter

psi pound per square inch

PVC polyvinyl chloride

RSF Recirculating sand filter

SFE sand filter effluent

SLAD sulfur/limestone autotrophic denitrification

SS suspended solids

STE septic tank effluent


t time

TKN total kjeldahl nitrogen

TSS total suspended solids

u macroscopic flow velocity

°C degree centigrade

xi


km kilometer

L liter

L/h liter per hour

M molarity

MAC maximum acceptable concentration

MCL maximum contaminant level

me milli equivalence

mg milligram

mg/L milligram per liter

mL milliliter

psi pound per square inch

PVC polyvinyl chloride

RSF Recirculating sand fdter

SFE sand fdter effluent

SLAD sulfur/limestone autotrophic denitrification

SS suspended solids

STE septic tank effluent


t time

TKN total kjeldahl nitrogen

TSS total suspended solids

u macroscopic flow velocity

°C degree centigrade


INTRODUCTION

The growing demand for water has generated a need for effective water and

wastewater treatment strategies. This need has enhanced our understanding of common

principles of the behavior of various pollutants in soil and water, leading to measures to

minimize pollution. The control of nitrogen has been identified as an important

environmental activity as demonstrated by the adverse effects that excess levels of

different forms of nitrogen have had on aquatic systems leading to eutrophication and

health hazards (United States Environmental Agency 1993).

The increase in population of semi urban areas has required the use of onsite treatment

methods to treat and dispose of household wastewater. One-third of the population in the

United States of America (U.S.A.) uses septic systems for wastewater disposal,

registering an increase of 15% from 1980 to 1990. Septic systems are the largest source

of effluent disposal to the groundwater zone (Widrig et al 1996; Robertson and Cherry

1995). Conventional onsite treatment of domestic wastewater would generally comprise

of a septic tank for primary treatment, followed by subsurface soil absorption system for

secondary treatment. The effluent of an average septic tank comprises of solids, plant

fertilizing nutrients such as nitrogen, phosphorous, and microorganisms (Viraraghavan

and Warnock 1976). Walker et al. (1973) reported that in household of four an average

contribution of nitrogen would be approximately 33 kg N/year. The nitrogen after

anaerobic treatment in the septic tank consists of predominantly soluble ammonium

nitrogen (86%), combined nitrite and nitrate nitrogen (1%) and organic nitrogen (13%)

(Nichols et al. 1997). The nitrogenous compounds in black water (toilet water) present as

fecal matter and urine converts into ammonium ion by either hydrolysis or microbial


INTRODUCTION

The growing demand for water has generated a need for effective water and

wastewater treatment strategies. This need has enhanced our understanding of common

principles of the behavior of various pollutants in soil and water, leading to measures to

minimize pollution. The control of nitrogen has been identified as an important

environmental activity as demonstrated by the adverse effects that excess levels of

different forms of nitrogen have had on aquatic systems leading to eutrophication and

health hazards (United States Environmental Agency 1993).

The increase in population of semi urban areas has required the use of onsite treatment

methods to treat and dispose o f household wastewater. One-third of the population in the

United States of America (U.S.A.) uses septic systems for wastewater disposal,

registering an increase of 15% from 1980 to 1990. Septic systems are the largest source

o f effluent disposal to the groundwater zone (Widrig et al 1996; Robertson and Cherry

1995). Conventional onsite treatment of domestic wastewater would generally comprise

of a septic tank for primary treatment, followed by subsurface soil absorption system for

secondary treatment. The effluent of an average septic tank comprises of solids, plant

fertilizing nutrients such as nitrogen, phosphorous, and microorganisms (Viraraghavan

and Warnock 1976). Walker et al. (1973) reported that in household o f four an average

contribution of nitrogen would be approximately 33 kg N/year. The nitrogen after

anaerobic treatment in the septic tank consists of predominantly soluble ammonium

nitrogen (86%), combined nitrite and nitrate nitrogen (1%) and organic nitrogen (13%)

(Nichols et al. 1997). The nitrogenous compounds in black water (toilet water) present as

fecal matter and urine converts into ammonium ion by either hydrolysis or microbial

1


digestion in aerobic or anaerobic conditions (Andreoli et al. 1979). The major reaction in

septic systems can be summarized as partial anaerobic digestion of organic matter in the

septic tank and aerobic oxidation of organic carbon to carbon dioxide with a conversion

of nitrogen to nitrate in the unsaturated or oxidation zone (Wilhelm et al. 1996). The

conventional method of treatment is not designed for nitrogen removal and with reduced

dispersive and dilution potential, nitrate contamination leads to groundwater pollution

(Robertson and Anderson 1999; Lamb et al. 1990; Sikora and Corey 1976).

The maximum contaminant levels (MCL) in the drinking water for nitrate and

nitrite stipulated by the Canadian Drinking Water Guidelines, World Health Organization

(WHO) and the United States Environmental Protection Agency (U.S.EPA) are 10 mg/L

as nitrate nitrogen (NO3—N) and 1 mg/L as nitrite-nitrogen (NO2--N) (Guidelines for

Canadian Drinking Water Quality 1996; AWWA 1990).

These limits were set to prevent the development of methemoglobinemia or "blue

baby syndrome" in infants (Schubert et al. 1999; Kapoor and Viraraghavan 1997). This is

a potentially lethal condition when the nitrate is converted to nitrite in the gastrointestinal

tract which, then oxidizes the iron content present as ferrous in hemoglobin to a

methemoglobin, a ferric form of hemoglobin that cannot transport oxygen (Schubert et al.

1999; Packham 1992). Methemoglobinemia as a disease is more likely to affect infants

than adults hemoglobin in infants is more readily oxidizable to methemoglobin and intake

of liquids is ten times more in infants than in adults (Mirvish 1991). Schubert et al.

(1999) reported that the recent incidence of methemoglobin as a disease was unknown as

it is not a reportable disease, and nitrates could be a cause in gastric cancer, lymphoma,

thyroid disorder, abortion, and birth defects to a child born to a mother drinking high-


digestion in aerobic or anaerobic conditions (Andreoli et al. 1979). The major reaction in

septic systems can be summarized as partial anaerobic digestion of organic matter in the

septic tank and aerobic oxidation of organic carbon to carbon dioxide with a conversion

of nitrogen to nitrate in the unsaturated or oxidation zone (Wilhelm et al. 1996). The

conventional method of treatment is not designed for nitrogen removal and with reduced

dispersive and dilution potential, nitrate contamination leads to groundwater pollution

(Robertson and Anderson 1999; Lamb et al. 1990; Sikora and Corey 1976).

The maximum contaminant levels (MCL) in the drinking water for nitrate and

nitrite stipulated by the Canadian Drinking Water Guidelines, World Health Organization

(WHO) and the United States Environmental Protection Agency (U.S.EPA) are 10 mg/L

as nitrate nitrogen (NCET'!) and 1 mg/L as nitrite-nitrogen (NOi’-N) (Guidelines for

Canadian Drinking Water Quality 1996; AWWA 1990).

These limits were set to prevent the development of methemoglobinemia or “blue

baby syndrome” in infants (Schubert et al. 1999; Kapoor and Viraraghavan 1997). This is

a potentially lethal condition when the nitrate is converted to nitrite in the gastrointestinal

tract which, then oxidizes the iron content present as ferrous in hemoglobin to a

methemoglobin, a ferric form of hemoglobin that cannot transport oxygen (Schubert et al.

1999; Packham 1992). Methemoglobinemia as a disease is more likely to affect infants

than adults hemoglobin in infants is more readily oxidizable to methemoglobin and intake

of liquids is ten times more in infants than in adults (Mirvish 1991). Schubert et al.

(1999) reported that the recent incidence of methemoglobin as a disease was unknown as

it is not a reportable disease, and nitrates could be a cause in gastric cancer, lymphoma,

thyroid disorder, abortion, and birth defects to a child born to a mother drinking high-

?


nitrate water. However, Henderson (2000) reported that no clear evidence was available

to indicate nitrate as a carcinogen causing gastric cancer in the case of humans and

animals.

The methodology for effective nitrogen removal involves effective oxidation of

ammonia to nitrate in an aerobic stage, followed by denitrification in an anaerobic or

anoxic environment. Controlled nitrification and denitrification would reduce the

nitrogen pollution caused by onsite effluents to a considerable degree.

1.1 Objectives and scope of the study

The objectives of the study were as follows:

i. to assess the potential of intermittent sand filtration in nitrifying STE;

ii. to examine the potential of sulfur/limestone autotrophic denitrification (SLAD) in

denitrifying nitrified STE, identifying the suitable ratio of sulfur and limestone

required;

iii. to examine the effect of hydraulic loading rate on nitrification and denitrification

potential of sand filter and SLAD layer, respectively

The scope of the study consists of the following tasks:

i. a review of literature on nitrogen removal from onsite effluents using different

treatment methods;

ii. culturing Thiobacillus denhrificans for a laboratory study and seeding of

sulfur/limestone with the same; and

iii. Conducting experimental studies to evaluate nitrogen removal from a unified

filtration system with layers of sand and sulfur/limestone.

3


nitrate water. However, Henderson (2000) reported that no clear evidence was available

to indicate nitrate as a carcinogen causing gastric cancer in the case of humans and

animals.

The methodology for effective nitrogen removal involves effective oxidation of

ammonia to nitrate in an aerobic stage, followed by denitrification in an anaerobic or

anoxic environment. Controlled nitrification and denitrification would reduce the

nitrogen pollution caused by onsite effluents to a considerable degree.

1.1 Objectives and scope o f the study

The objectives of the study were as follows:

i. to assess the potential of intermittent sand filtration in nitrifying STE;

ii. to examine the potential of sulfur/limestone autotrophic denitrification (SLAD) in

denitrifying nitrified STE, identifying the suitable ratio o f sulfur and limestone

required;

iii. to examine the effect of hydraulic loading rate on nitrification and denitrification

potential o f sand filter and SLAD layer, respectively

The scope of the study consists of the following tasks:

i. a review of literature on nitrogen removal from onsite effluents using different

treatment methods;

ii. culturing Thiobacillus denitrificans for a laboratory study and seeding of

sulfur/limestone with the same; and

iii. Conducting experimental studies to evaluate nitrogen removal from a unified

filtration system with layers of sand and sulfur/limestone.


2 LITERATURE REVIEW

2.1 Nitrification

Nitrification can be defined as biological oxidation of ammonium-nitrogen to

nitrate nitrogen with nitrite nitrogen as an intermediate. However, biological nitrification

could be enhanced by certain physical parameters such as volatilization, adsorption, and

mineralization depending on cation exchange capacity (CEC), and plant uptake (Lance

1972).

Volatilization can be defined as a natural process of releasing ammonia (NH3+) to

the atmosphere depending on temperature and pH of the effluent. At normal conditions,

the ammonium ion present in effluent exists in equilibrium with ammonia at 10%; with

an increase in temperature, the pH shifts to the right (as in equation 2.1) releasing

ammonia in gaseous form (Sawyer and McCarty 1978). According to Lance (1972)

volatilization accounts for a loss of 10% of ammonium as ammonia from onsite effluents.

NH: NH3 +H+ (2.1)

The positively charged ammonium compounds gets adsorbed on

negatively charged particles such as organic and clay minerals, which have high cation

exchange capacity (CEC). The adsorbed ammonium ions then oxidize and leach

gradually as nitrite and nitrate ions, depending on the availability of oxygen. The

oxidized nitrite and nitrates undergo no further adsorption due to the anionic capacity and

mobility. Lance (1972) reported that amount of ammonium ions adsorbed in clay

minerals can be explained by the ammonium adsorption ratio (AAR), defined as follows:

4


2 LITERATURE REVIEW

2.1 Nitrification

Nitrification can be defined as biological oxidation of ammonium-nitrogen to

nitrate nitrogen with nitrite nitrogen as an intermediate. However, biological nitrification

could be enhanced by certain physical parameters such as volatilization, adsorption, and

mineralization depending on cation exchange capacity (CEC), and plant uptake (Lance

1972).

Volatilization can be defined as a natural process of releasing ammonia (NH3 +) to

the atmosphere depending on temperature and pH of the effluent. At normal conditions,

the ammonium ion present in effluent exists in equilibrium with ammonia at 10%; with

an increase in temperature, the pH shifts to the right (as in equation 2.1) releasing

ammonia in gaseous form (Sawyer and McCarty 1978). According to Lance (1972)

volatilization accounts for a loss of 10% of ammonium as ammonia from onsite effluents.

N H ; — ^ N H 3 T + H + (2.1)

The positively charged ammonium compounds gets adsorbed on

negatively charged particles such as organic and clay minerals, which have high cation

exchange capacity (CEC). The adsorbed ammonium ions then oxidize and leach

gradually as nitrite and nitrate ions, depending on the availability o f oxygen. The

oxidized nitrite and nitrates undergo no further adsorption due to the anionic capacity and

mobility. Lance (1972) reported that amount of ammonium ions adsorbed in clay

minerals can be explained by the ammonium adsorption ratio (AAR), defined as follows:

4


AAR= NH: (me I L) (2.2)

VY2 [Ca 2 1 + {Mg 2+

The biological conversion of ammonium to subsequent nitrogen form requires the

presence of oxygen for the growth of nitrifiers. This could be achieved by either diffusing

air through aerators or through natural oxidation upon exposure to the atmosphere. The

biological transformation takes place in the presence of organisms that could be

classified, on the nutrient uptake as autotrophic and heterotrophic bacteria. The

competition between heterotrophic and autotrophic bacteria and their ability to grow

depends on environmental conditions such as pH, oxygen demand, temperature, and

toxicity (Van Niel et al. 1993). Robertson and Kuenen (1992b) reported that autotrophs

are more common in normal conditions in particular chemolithoautotrophic nitrifiers of

the family Nitrobacteraceae such as Nitrobacter, Nitrosomanas that are major

contributors of nitrification. They also reported that the presence of compounds as

ammonium ions is preferred to ammonia, for better nitrification. Nitrosomanas bacteria

are responsible for the conversion of ammonium compounds to nitrite where they are first

converted to hydroxylamine on production of hydroxylamine oxidoreductase to nitrites.

The nitrites are then oxidized by nitrite oxidoreductase in Nitrobacter to nitrates. Sharma

and Ahlert (1977) reported that the amount of oxygen required by Nitrobacter is 1.14 mg,

and Nitrosomonas requires 3.43 mg to oxidize 1 mg of NO2---N and NH3—N respectively.

The amount required by the organisms in real life would be less than the stoichiometric

calculation.

NH4 +1.502 ''"r"'""""'"' 2 Hi- + H ,0 + NO2- + 58 — 84kcal (2.3)

NO; + 0.50, \arohckter NO- +15.4 — 20.9kcal (2.4)


The biological conversion of ammonium to subsequent nitrogen form requires the

presence of oxygen for the growth of nitrifiers. This could be achieved by either diffusing

air through aerators or through natural oxidation upon exposure to the atmosphere. The

biological transformation takes place in the presence of organisms that could be

classified, on the nutrient uptake as autotrophic and heterotrophic bacteria. The

competition between heterotrophic and autotrophic bacteria and their ability to grow

depends on environmental conditions such as pH, oxygen demand, temperature, and

toxicity (Van Niel et al. 1993). Robertson and Kuenen (1992b) reported that autotrophs

are more common in normal conditions in particular chemolithoautotrophic nitrifiers of

the family Nitrobacteraceae such as Nitrobacter, Nitrosomanas that are major

contributors of nitrification. They also reported that the presence of compounds as

ammonium ions is preferred to ammonia, for better nitrification. Nitrosomanas bacteria

are responsible for the conversion of ammonium compounds to nitrite where they are first

converted to hydroxylamine on production of hydroxylamine oxidoreductase to nitrites.

The nitrites are then oxidized by nitrite oxidoreductase in Nitrobacter to nitrates. Sharma

and Ahlert (1977) reported that the amount o f oxygen required by Nitrobacter is 1.14 mg,

and Nitrosomonas requires 3.43 mg to oxidize 1 mg of N02*-N and NH3~N respectively.

The amount required by the organisms in real life would be less than the stoichiometric

calculation.

N H 4+ +1 .50 , AV/ro— ^ 2 / / + + H 20 + NO; + 5 8 - 8 4 kcal (2.3)

NO; + 0.50, NO; + 15.4 - 20.9kcal (2.4)

5


Smith et al. (1997) reported that ineffective oxidation of ammonium compounds

would lead to a build up of nitrite. They also reported that a major contribution of the

nitrite build up would be the presence of free ammonia, which occurs in the presence of

high temperature and pH, where ammonium ion equilibrium shifts to free ammonia.

The heterotrophic nitrifiers include species of Psettdomonas dentrificans,

Alcaligenes and Thiosphaera pantotropha, which act as an aerobic denitrifier (Robertson

and Kuenen 1992a).

RNH2 -> RNHOH R-NO --> RN024 NO3- (2.5)

RNH4+ NI-120H -› NOH NO2- 4 NO3- (2.6)

Liu and Capdeville (1996) reported that the population of the nitrifying organisms

increases with ammonium concentration and mineralization of compounds on the biofilm

of nitrifiers. McCarty (1999) reported that the growth rate of Nitrosomanas was higher

when compared with Nitrobacter.

Toxicity effects by various compounds, which determine the growth factor leads

to several months for proper stabilization. Nitrification could be inhibited by the presence

of ammonia-ammonium and nitrite-nitrous acid equilibrium (McCarty 1999; Sharma and

Ahlert 1977). Toxicity effects of nitrogenous compounds studied by McCarty (1999)

showed that free ammonia and nitrous acid along with other non-nitrogenous compounds

have shown greater inhibiting qualities when exceeding the limits. Lamb et al. (1991)

reported that temperature, pH, and alkalinity are the primary limiting factors in a

nitrification process.

6


Smith et al. (1997) reported that ineffective oxidation of ammonium compounds

would lead to a build up of nitrite. They also reported that a major contribution o f the

nitrite build up would be the presence of free ammonia, which occurs in the presence of

high temperature and pH, where ammonium ion equilibrium shifts to free ammonia.

The heterotrophic nitrifiers include species of Pseudomonas dentrificans,

Alcaligenes and Thiosphaera pantotropha, which act as an aerobic denitrifier (Robertson

and Kuenen 1992a).

RN Ih -> RNHOH -> R-NO RN()2 NOR (2.5)

RNHR -> NH2OH -> NOH -> NOR -> NOR (2.6)

Liu and Capdeville (1996) reported that the population of the nitrifying organisms

increases with ammonium concentration and mineralization of compounds on the biofilm

of nitrifiers. McCarty (1999) reported that the growth rate of Nitrosomanas was higher

when compared with Nitrobacter.

Toxicity effects by various compounds, which determine the growth factor leads

to several months for proper stabilization. Nitrification could be inhibited by the presence

of ammonia-ammonium and nitrite-nitrous acid equilibrium (McCarty 1999; Sharma and

Ahlert 1977). Toxicity effects of nitrogenous compounds studied by McCarty (1999)

showed that free ammonia and nitrous acid along with other non-nitrogenous compounds

have shown greater inhibiting qualities when exceeding the limits. Lamb et al. (1991)

reported that temperature, pH, and alkalinity are the primary limiting factors in a

nitrification process.

6


Van Niel et al. (1993) reported that heterotrophic nitrifier such as T Pantotropha

could substitute the autotrophs for nitrification as they require less oxygen demand of 1-2

mg, and has the ability to withstand fluctuations in pH and temperature. Their studies

further showed that they had higher nitrification ability than autotrophs at C/N above 10

and the growth rate was less than autotrophs at normal conditions.

Nitrification also depends on physical parameters such hydraulic conductivity,

retention time and oxygen demand which depend on the application of hydraulic loading

rate. Jones and Taylor (1965) reported that providing more retention time of the effluent

in the media increased the nitrification efficiency of the system while, an increase in

hydraulic loading rate would lead to saturation of media thus increasing the conductivity

rate. Cogger and Carlile (1984) reported that long term saturation of media would lead to

an anaerobic environment, increasing oxygen demand of nitrifiers, which would lead to a

decrease in nitrification capability. The hydraulic conductivity (K) of the media

depending on the loading rate determines the nitrogen removal capacity of the system,

which could be calculated by using Darcy's law (U.S.EPA 1980).

u =—Kgrad.(1) (2.7)

Where,

u is the macroscopic flow velocity;

(I) is the hydraulic head.

Another important process, which determines the nitrification of the system, is the

crust formation. Crust formation is common and was reported by Magdoff et al. (1974),

to occur in all soil absorption systems. Crust is formed on the surface of the filter media

either in conventional or alternative treatment system. Siegrist (1987) reported that crust

7


Van Niel et al. (1993) reported that heterotrophic nitrifier such as T. Pantotropha

could substitute the autotrophs for nitrification as they require less oxygen demand of 1-2

mg, and has the ability to withstand fluctuations in pH and temperature. Their studies

further showed that they had higher nitrification ability than autotrophs at C/N above 10

and the growth rate was less than autotrophs at normal conditions.

Nitrification also depends on physical parameters such hydraulic conductivity,

retention time and oxygen demand which depend on the application of hydraulic loading

rate. Jones and Taylor (1965) reported that providing more retention time of the effluent

in the media increased the nitrification efficiency of the system while, an increase in

hydraulic loading rate would lead to saturation o f media thus increasing the conductivity

rate. Cogger and Carlile (1984) reported that long term saturation of media would lead to

an anaerobic environment, increasing oxygen demand o f nitrifiers, which would lead to a

decrease in nitrification capability. The hydraulic conductivity (K) of the media

depending on the loading rate determines the nitrogen removal capacity of the system,

which could be calculated by using Darcy’s law (U.S.EPA 1980).

o = -Kgrad.§ (2.7)

Where,

u is the macroscopic flow velocity;

<(> is the hydraulic head.

Another important process, which determines the nitrification o f the system, is the

crust formation. Crust formation is common and was reported by Magdoff et al. (1974),

to occur in all soil absorption systems. Crust is formed on the surface of the filter media

either in conventional or alternative treatment system. Siegrist (1987) reported that crust

7


formed is due to an anaerobic decomposition of polysaccharides on the surface of the

filter media. He also reported that the crust formed on the surface clogs the pores on the

soil and thus decreases the nitrification capacity. Jones and Taylor (1965) suggested that

the use of the entire infiltrative surface for loading followed by an extended period of

resting would increase the efficiency of a soil absorption system. They also reported that

periodic loading of large volumes of effluent would temporally increase the height of

ponding, and hydraulic gradients, and providing more aeration time.

Liu and Capdeville (1994) suggested the use of different filter media such as

porous glass beads, textile materials and other synthetic material with large surface area,

and void volume as a substitute for sand filter; their study showed equivalent or better

results in the terms of nitrification in a sand filter.

2.2 Denitrification

Denitrification can be defined as a biological reduction of nitrate to nitrogen gas.

This process could proceed through several steps in biochemical pathways with an

ultimate production of nitrogen gas (U.S.EPA 1993). Denitrification is the most plausible

mechanism for reducing nitrate contamination in groundwater. (Bouma 1971) reported

that in an optimal functioning disposal system less denitrification would occur and then

only in anaerobic microsites. The general reaction process occurring during

denitrification could be described as follows:

2NO; —> (HNO — NOH)—> A1,0 —> N, (2.8)

Denitrification can take place in an anoxic or anaerobic medium with either

autotrophic or heterotrophic bacteria as denitrifying organisms with the requirement of

organic carbon as a substrate (Reneau Jr. 1977; Sikora and Corey 1976). Robertson and

8


formed is due to an anaerobic decomposition of polysaccharides on the surface of the

filter media. He also reported that the crust formed on the surface clogs the pores on the

soil and thus decreases the nitrification capacity. Jones and Taylor (1965) suggested that

the use of the entire infiltrative surface for loading followed by an extended period of

resting would increase the efficiency of a soil absorption system. They also reported that

periodic loading o f large volumes of effluent would temporally increase the height of

ponding, and hydraulic gradients, and providing more aeration time.

Liu and Capdeville (1994) suggested the use of different filter media such as

porous glass beads, textile materials and other synthetic material with large surface area,

and void volume as a substitute for sand filter; their study showed equivalent or better

results in the terms o f nitrification in a sand filter.

2.2 Denitrification

Denitrification can be defined as a biological reduction of nitrate to nitrogen gas.

This process could proceed through several steps in biochemical pathways with an

ultimate production o f nitrogen gas (U.S.EPA 1993). Denitrification is the most plausible

mechanism for reducing nitrate contamination in groundwater. (Bouma 1971) reported

that in an optimal functioning disposal system less denitrification would occur and then

only in anaerobic microsites. The general reaction process occurring during

denitrification could be described as follows:

2NO' -> 2NO; -> (HNO - NOH) - + N 2O ^ N 2 ON(Z.S)

Denitrification can take place in an anoxic or anaerobic medium with either

autotrophic or heterotrophic bacteria as denitrifying organisms with the requirement of

organic carbon as a substrate (Reneau Jr. 1977; Sikora and Corey 1976). Robertson and

8


Cherry (1995) and Reneau Jr. (1979) reported that an attenuation or diffusion of nitrate

into the anaerobic zone from the aerobic zone took place with a gradient build up and

decreased as denitrification took place.

NO3- + organic carbon ->NO2 + organic carbon ( 1\1, + carbon dioxide + water) (2.9)

C + CO, + N, + H,0 (2.10)

A broad range of heterotrophic bacteria are involved in the process of

denitrification with a requirement of organic carbon as an energy source. The selection of

a carbon source has mainly been made with an objective of providing a longer life, ability

to withstand extreme conditions and availability. In order for denitrification to take place,

two main conditions must be satisfied. First, denitrifying bacteria must have an electron

donor or organic carbon as a substrate and the bacteria must have an anaerobic/anoxic

environment for denitrification to be initiated. Some of the heterotrophic denitrification

methods that have been applied so far are gray water (Laak 1972), alcohol as ethanol and

methanol (Sikora and Keeney 1975), kitchen waste (Biswas and Warnock 1985), peat

(Rock et al. 1984), sawdust (Robertson and Cherry 1995), and molasses (Erickson et al.

1971).

Denitrification using autotrophic bacteria such as Thiobacillus denitrificans takes

place in an anaerobic medium, using sulfur as a substrate and bicarbonate producer

limestone as a carbon source (Zhang and Shan 1999; Sikora and Keeney 1976; Mann et

al. 1972). Reneau et al. (1989) reported that by providing sufficient nitrification zone and

with a restricted drainage conditions for denitrification to occur in an anoxic or anaerobic

layer with the presence of soluble carbon, denitrification would be possible in a

conventional septic system.


Cherry (1995) and Reneau Jr. (1979) reported that an attenuation or diffusion of nitrate

into the anaerobic zone from the aerobic zone took place with a gradient build up and

decreased as denitrification took place.

N 03'+ organic carbon ->N02~ + organic carbon ( N2 + carbon dioxide + water) (2.9)

c + n o ; - > co2 + n 2 + h 2 o (2 j 0)

A broad range of heterotrophic bacteria are involved in the process of

denitrification with a requirement of organic carbon as an energy source. The selection of

a carbon source has mainly been made with an objective of providing a longer life, ability

to withstand extreme conditions and availability. In order for denitrification to take place,

two main conditions must be satisfied. First, denitrifying bacteria must have an electron

donor or organic carbon as a substrate and the bacteria must have an anaerobic/anoxic

environment for denitrification to be initiated. Some of the heterotrophic denitrification

methods that have been applied so far are gray water (Laak 1972), alcohol as ethanol and

methanol (Sikora and Keeney 1975), kitchen waste (Biswas and Wamock 1985), peat

(Rock et al. 1984), sawdust (Robertson and Cherry 1995), and molasses (Erickson et al.

1971).

Denitrification using autotrophic bacteria such as Thiobacillus denitrificans takes

place in an anaerobic medium, using sulfur as a substrate and bicarbonate producer

limestone as a carbon source (Zhang and Shan 1999; Sikora and Keeney 1976; Mann et

al. 1972). Reneau et al. (1989) reported that by providing sufficient nitrification zone and

with a restricted drainage conditions for denitrification to occur in an anoxic or anaerobic

layer with the presence of soluble carbon, denitrification would be possible in a

conventional septic system.

9


2.3 Treatment process

Onsite treatment processes include aerobic, evaporation, subsurface disposal,

wetland, and sand filter systems each having their own merits and demerits. The general

approach for an onsite treatment system for a single household would be a septic tank as

a primary treatment and subsurface disposal system as a secondary treatment option.

Septic tanks have shown to be reliable and widely practiced primary treatment option.

The secondary treatment option has been a concern because of variable parameters to be

considered such as type and permeability of the native soils, slope and drainage pattern of

the site, depth of groundwater, proximity of wells nearby, and distance from the surface

water. Other influences apart from pollution perspective would be quality of construction,

installation procedures and operation and maintenance practices (White 1995).

Several studies have shown that complete nitrogen removal from septic tank was

not achieved in a conventional system (Franks 1993; Dillaha et al. 1985; Cogger and

Carlile 1984; De Walle and Schaff 1980; DeVaries 1972). An efficient and consistent

nitrogen removal process would include a system where maximum nitrification and

denitrification could be achieved. The treatment processes are discussed in brief

concentrating on nitrification and denitrification processes.

2.3.1 Aerobic Treatment Units

Aerobic or extended/suspended growth systems generally comprise of septic tank

with an induced aeration or fixed aerators followed by a fixed film system consisting of

either a trickling filter, a rotating biological contractor or an up-flow filter. The use of

aerobic units has not been commonly used because of the disadvantages posed in

operation and maintenance of the system (U.S.EPA 1980). Induced oxidation in the

10


2.3 Treatment process

Onsite treatment processes include aerobic, evaporation, subsurface disposal,

wetland, and sand filter systems each having their own merits and demerits. The general

approach for an onsite treatment system for a single household would be a septic tank as

a primary treatment and subsurface disposal system as a secondary treatment option.

Septic tanks have shown to be reliable and widely practiced primary treatment option.

The secondary treatment option has been a concern because of variable parameters to be

considered such as type and permeability of the native soils, slope and drainage pattern of

the site, depth of groundwater, proximity o f wells nearby, and distance from the surface

water. Other influences apart from pollution perspective would be quality of construction,

installation procedures and operation and maintenance practices (White 1995).

Several studies have shown that complete nitrogen removal from septic tank was

not achieved in a conventional system (Franks 1993; Dillaha et al. 1985; Cogger and

Carlile 1984; De Walle and Schaff 1980; DeVaries 1972). An efficient and consistent

nitrogen removal process would include a system where maximum nitrification and

denitrification could be achieved. The treatment processes are discussed in brief

concentrating on nitrification and denitrification processes.

2.3.1 Aerobic Treatment Units

Aerobic or extended/suspended growth systems generally comprise of septic tank

with an induced aeration or fixed aerators followed by a fixed film system consisting of

either a trickling filter, a rotating biological contractor or an up-flow filter. The use of

aerobic units has not been commonly used because of the disadvantages posed in

operation and maintenance of the system (U.S.EPA 1980). Induced oxidation in the

10


septic tank reduces BOD, COD and produces an effluent rich in carbon dioxide and

metabolized biomass. The study done by Brewer et al. (1978) on the operation and use of

aerobic units across U.S.A. showed that 36% of the operating units faced problems

during the first year and well operated units produced partial oxidation of ammonium

compounds into nitrates with no denitrification taking place.

2.3.2 Evaporation systems

Onsite evaporation systems are divided into two categories, evapotranspiration

and lagoons, either with or without infiltration. These systems are being used in areas of

high groundwater or with impermeable soils where subsurface disposal cannot be used.

The factors for consideration for the installation of the system are climate variability,

hydraulic loading rate, cover soil, vegetation, construction technique, salt accumulation

and soil permeability. Treatment mainly depends on evaporation and plant uptake in the

beds and lagoons; thus, nitrogen contamination in groundwater through an evaporation

system is minimal (U.S.EPA 1980). Though these systems are widely used across the

United State of America, there has not been enough documentation on nitrogen removal.

2.3.3 Subsurface disposal mechanism

Subsurface disposal has been in use as an effective treatment of onsite effluents

and nearly one third of the population in the USA who use onsite treatment treat them

through subsurface disposal methods (Kropf et al. 1977). Subsurface disposal through

trenches and mounds is more expensive but has been useful in places of high

groundwater level and unsuitable soil permeability condition (Franks 1993; U.S.EPA

1980). These disposal methods were to provide economical, effective remediation of

1 1


septic tank reduces BOD, COD and produces an effluent rich in carbon dioxide and

metabolized biomass. The study done by Brewer et al. (1978) on the operation and use of

aerobic units across U.S.A. showed that 36% of the operating units faced problems

during the first year and well operated units produced partial oxidation of ammonium

compounds into nitrates with no denitrification taking place.

2.3.2 Evaporation systems

Onsite evaporation systems are divided into two categories, evapotranspiration

and lagoons, either with or without infiltration. These systems are being used in areas of

high groundwater or with impermeable soils where subsurface disposal cannot be used.

The factors for consideration for the installation o f the system are climate variability,

hydraulic loading rate, cover soil, vegetation, construction technique, salt accumulation

and soil permeability. Treatment mainly depends on evaporation and plant uptake in the

beds and lagoons; thus, nitrogen contamination in groundwater through an evaporation

system is minimal (U.S.EPA 1980). Though these systems are widely used across the

United State of America, there has not been enough documentation on nitrogen removal.

2.3.3 Subsurface disposal mechanism

Subsurface disposal has been in use as an effective treatment o f onsite effluents

and nearly one third of the population in the USA who use onsite treatment treat them

through subsurface disposal methods (Kropf et al. 1977). Subsurface disposal through

trenches and mounds is more expensive but has been useful in places of high

groundwater level and unsuitable soil permeability condition (Franks 1993; U.S.EPA

1980). These disposal methods were to provide economical, effective remediation of

11


wastewater so as not to contaminate the groundwater. The soil absorption system is a

secondary treatment option or in most cases the final treatment. It was relied as a

treatment option for the natural treatment by microbial colonies in soil to biodegrade the

septic tank effluent (White 1995). A mound system is used in areas of shallow

groundwater table and impermeable soils. Cogger and Carlile (1984) reported that the

aerobic nature of the soil absorption system provided nitrification of the ammonium

nitrogen into nitrates and denitrification occurs in microsites present in the soil, while

saturated fields had a higher ammonium nitrogen concentration in the groundwater.

Reneau Jr. (1979; 1977) reported that an increase in depth of the aerobic zone would

decrease the groundwater contamination, though a depth of more than three feet had less

effect on increasing nitrification, which could be achieved by providing more horizontal

movement of the effluent. Reneau (1979) reported that denitrification was possible in the

plinthic horizon and depended on the fluctuating groundwater table. He also reported

that, denitrification mainly occurred in anaerobic regions of the soil with nitrate

movement depending on mass flow and concentration gradient created by the

denitrification layer. Viraraghavan and Warnock (1976) reported that the effectiveness of

a soil treatment system varied with a number of environmental factors such as soil and air

temperatures, groundwater table and amount of oxygen present in the soil. They also

reported that no significant denitrification took place under tile condition.

Most of the studies done by researchers have shown that complete nitrogen

removal could not be achieved in a conventional subsurface disposal site due to the lack

of soluble carbon present as a substrate for denitrification. Dillaha et al. (1985) examined

the applicability of the Niimi process in a trench system. Niimi's process suggested on

12


wastewater so as not to contaminate the groundwater. The soil absorption system is a

secondary treatment option or in most cases the final treatment. It was relied as a

treatment option for the natural treatment by microbial colonies in soil to biodegrade the

septic tank effluent (White 1995). A mound system is used in areas of shallow

groundwater table and impermeable soils. Cogger and Carlile (1984) reported that the

aerobic nature of the soil absorption system provided nitrification of the ammonium

nitrogen into nitrates and denitrification occurs in microsites present in the soil, while

saturated fields had a higher ammonium nitrogen concentration in the groundwater.

Reneau Jr. (1979; 1977) reported that an increase in depth of the aerobic zone would

decrease the groundwater contamination, though a depth of more than three feet had less

effect on increasing nitrification, which could be achieved by providing more horizontal

movement of the effluent. Reneau (1979) reported that denitrification was possible in the

plinthic horizon and depended on the fluctuating groundwater table. He also reported

that, denitrification mainly occurred in anaerobic regions of the soil with nitrate

movement depending on mass flow and concentration gradient created by the

denitrification layer. Viraraghavan and Warnock (1976) reported that the effectiveness of

a soil treatment system varied with a number o f environmental factors such as soil and air

temperatures, groundwater table and amount o f oxygen present in the soil. They also

reported that no significant denitrification took place under tile condition.

Most of the studies done by researchers have shown that complete nitrogen

removal could not be achieved in a conventional subsurface disposal site due to the lack

of soluble carbon present as a substrate for denitrification. Dillaha et al. (1985) examined

the applicability of the Niimi process in a trench system. Niimi’s process suggested on

12


using STE as a carbon source for denitrification by providing 10-15 cm impermeable pan

filled with capillary sand under a reduced condition. They reported that in a trench

condition, Niimi process worked primarily under influence of soil types, hydraulic

loading and transport, and had a nitrogen removal of 27 to 38 %.

Subsurface disposal depends on the hydraulic loading rate, which directly affects

the aerobic, anaerobic and crust formation (Loudon et al. 1992; Simons and Magdoff

1979; Bouma et al. 1971). Studies done by Cogger and Carlile (1984) and Erickson et al.

(1971) have shown that subsurface disposal has been effective in nitrification and

mineralization of the organic nitrogen, which later oxidizes to ammonium. To study the

possibility of the denitrification in a conventional soil absorption system, Robertson and

Anderson (1999) and Erickson et al. (1971) conducted studies by providing an anaerobic

zone with sufficient carbon source for denitrification to take place. Erickson et al. (1971)

performed studies on barriered landscape water renovation system (BLWRS) a modified

version of the mound system by providing a barrier of limestone as a buffering agent

between the unsaturated and saturated zone with molasses as a carbon source. These

studies reported an overall removal over 95% of the inlet ammonia nitrogen with an

effluent nitrate concentration below MCL. The use of several carbon sources as a

substrate and provision of an anaerobic zone beneath the aerobic zone had been

experimented at laboratory and field scale studies. Some of the materials used for the

application are saw dust (Robertson and Cherry 1995), sulfur (Koenig and Liu 1996;

Kanter et al. 1994) and peat (Rock 1984). Franks (1995) reported that the criteria for

maintaining a proper disposal method in achieving an anaerobic zone beneath the aerobic

layer rely on an efficient dispersal mechanism. Dispersal mechanisms have shown more

13


using STE as a carbon source for denitrification by providing 10-15 cm impermeable pan

filled with capillary sand under a reduced condition. They reported that in a trench

condition, Niimi process worked primarily under influence of soil types, hydraulic

loading and transport, and had a nitrogen removal of 27 to 38 %.

Subsurface disposal depends on the hydraulic loading rate, which directly affects

the aerobic, anaerobic and crust formation (Loudon et al. 1992; Simons and Magdoff

1979; Bouma et al. 1971). Studies done by Cogger and Carlile (1984) and Erickson et al.

(1971) have shown that subsurface disposal has been effective in nitrification and

mineralization of the organic nitrogen, which later oxidizes to ammonium. To study the

possibility o f the denitrification in a conventional soil absorption system, Robertson and

Anderson (1999) and Erickson et al. (1971) conducted studies by providing an anaerobic

zone with sufficient carbon source for denitrification to take place. Erickson et al. (1971)

performed studies on barriered landscape water renovation system (BLWRS) a modified

version of the mound system by providing a barrier o f limestone as a buffering agent

between the unsaturated and saturated zone with molasses as a carbon source. These

studies reported an overall removal over 95% of the inlet ammonia nitrogen with an

effluent nitrate concentration below MCL. The use of several carbon sources as a

substrate and provision of an anaerobic zone beneath the aerobic zone had been

experimented at laboratory and field scale studies. Some of the materials used for the

application are saw dust (Robertson and Cherry 1995), sulfur (Koenig and Liu 1996;

Kanter et al. 1994) and peat (Rock 1984). Franks (1995) reported that the criteria for

maintaining a proper disposal method in achieving an anaerobic zone beneath the aerobic

layer rely on an efficient dispersal mechanism. Dispersal mechanisms have shown more

13


advantages in increasing the life span of the system in operation by providing a uniform

application of the load. Magdoff et al. (1974) reported that the crust formation reduced

the nitrification capacity of the media. Studies done by Simons and Magdoff (1979) have

shown that the crust formation in the aerobic zone disturbed nitrogen transformation by

providing insufficient aeration with longer wetting periods by making the soil anaerobic.

Kropf et al. (1977) and Erickson et al. (1971) reported that, disposal of effluent with less

suspended solids at a regularized hydraulic loading rate would provide more aeration,

which will reduce the growth of crust.

Studies conducted by Franks (1993) on a continuous nitrification and

denitrification system using a leachfield and an impermeable pan for denitrification using

methanol as the carbon source found that, stratification of the native soil provided more

horizontal movement than vertical resulting in 75 % loss of fluid from the system. He

suggested on using a shield with sufficient slope such that allowing the leachate to travel

the entire length and prevent short-circuiting. Franks (1993) and Andreoli et al. (1979)

reported that an engineered site with a shield would prevent horizontal movement of

effluent to the groundwater and a provision of separate gas vent from the denitrification

zone would prevent nitrogen from passing through the aerobic zone by displacing

oxygen.

2.3.4 Wetlands

Thom et al. (1998) studied wetland treatment applicability for onsite systems and

reported that effective treatment for nitrogen removal would require a more controlled

environment. The principal operation of wetland treatment involves a saturated emergent

and submergent vegetation, open to atmosphere with animal life, and the biological

14


advantages in increasing the life span of the system in operation by providing a uniform

application of the load. Magdoff et al. (1974) reported that the crust formation reduced

the nitrification capacity of the media. Studies done by Simons and Magdoff (1979) have

shown that the crust formation in the aerobic zone disturbed nitrogen transformation by

providing insufficient aeration with longer wetting periods by making the soil anaerobic.

Kropf et al. (1977) and Erickson et al. (1971) reported that, disposal of effluent with less

suspended solids at a regularized hydraulic loading rate would provide more aeration,

which will reduce the growth of crust.

Studies conducted by Franks (1993) on a continuous nitrification and

denitrification system using a leachfield and an impermeable pan for denitrification using

methanol as the carbon source found that, stratification of the native soil provided more

horizontal movement than vertical resulting in 75 % loss of fluid from the system. He

suggested on using a shield with sufficient slope such that allowing the leachate to travel

the entire length and prevent short-circuiting. Franks (1993) and Andreoli et al. (1979)

reported that an engineered site with a shield would prevent horizontal movement of

effluent to the groundwater and a provision o f separate gas vent from the denitrification

zone would prevent nitrogen from passing through the aerobic zone by displacing

oxygen.

2.3.4 W etlands

Thom et al. (1998) studied wetland treatment applicability for onsite systems and

reported that effective treatment for nitrogen removal would require a more controlled

environment. The principal operation of wetland treatment involves a saturated emergent

and submergent vegetation, open to atmosphere with animal life, and the biological

14


environment accompanied by physical and chemical activities that purify the wastewater

(Knight and Kadlec 1996). In the treatment by wetlands more storage or residence time is

needed for nitrification/denitrification to occur. Johns et al. (1998) reported that a

treatment efficiency of over 80% was achieved in terms of ammonium removal with a

residence time of 2.9 days, with an influent concentration in the range 13-25 mg/L of

NH3-N, while a reduction up to 30% was attributed to plant uptake. Their studies also

showed that ammonium removal efficiency decreased with residence time. Long term

studies in subsurface constructed wetlands by Thom et al. (1998) showed a reduction of

60% total nitrogen and 65% ammonia nitrogen with less conversion to nitrates. In order

to consider the wetland process as an alternative treatment method for onsite effluents,

more studies are needed on the depth, subsoil texture, vegetation, effects of climate and

other design parameters.

2.3.5 Sand Filters

Sand filters as a secondary treatment procedure are being used in the treatment of

wastewater for its efficient reduction of BOD, COD and microorganisms. Harris et al.

(1977) reported that sand filters would be an ideal secondary treatment procedure for

onsite effluent as it requires less maintenance and are inexpensive to operate, with no

secondary sludge and over 90% reduction of microorganisms, COD and BOD. Widrig et

al. (1996) showed that variables that influenced the treatment performance in a sand filter

were the filter depth, particle size distribution and mineral composition of the media,

pretreatment of the wastewater, hydraulic and organic loading rate, temperature and

dosing technique. A typical sand filter system would contain no additives with less cation

exchange capacity (CEC), sufficient porosity for ammonium reducing bacteria to grow

I5


environment accompanied by physical and chemical activities that purify the wastewater

(Knight and Kadlec 1996). In the treatment by wetlands more storage or residence time is

needed for nitrification/denitrification to occur. Johns et al. (1998) reported that a

treatment efficiency of over 80% was achieved in terms of ammonium removal with a

residence time of 2.9 days, with an influent concentration in the range 13-25 mg/L of

NH3 -N, while a reduction up to 30% was attributed to plant uptake. Their studies also

showed that ammonium removal efficiency decreased with residence time. Long term

studies in subsurface constructed wetlands by Thom et al. (1998) showed a reduction of

60% total nitrogen and 65% ammonia nitrogen with less conversion to nitrates. In order

to consider the wetland process as an alternative treatment method for onsite effluents,

more studies are needed on the depth, subsoil texture, vegetation, effects of climate and

other design parameters.

2.3.5 Sand Filters

Sand filters as a secondary treatment procedure are being used in the treatment of

wastewater for its efficient reduction of BOD, COD and microorganisms. Harris et al.

(1977) reported that sand filters would be an ideal secondary treatment procedure for

onsite effluent as it requires less maintenance and are inexpensive to operate, with no

secondary sludge and over 90% reduction of microorganisms, COD and BOD. Widrig et

al. (1996) showed that variables that influenced the treatment performance in a sand filter

were the filter depth, particle size distribution and mineral composition of the media,

pretreatment o f the wastewater, hydraulic and organic loading rate, temperature and

dosing technique. A typical sand filter system would contain no additives with less cation

exchange capacity (CEC), sufficient porosity for ammonium reducing bacteria to grow

15


and less adsorption capability. The operation can either be free access, open, buried or

recirculating filters with sufficient aeration and alkalinity; nitrification can then be

achieved (U.S.EPA 1980).

Widrig et al. (1996) recommended the use of intermittent sand filter for onsite

effluent treatment due to the reliability, cost-effectiveness and increased land

developmental pressure on environmentally sensitive areas like shorelines and high relief

regions. Efficient nitrification could be achieved with a longer resting period thus

providing more retention time for oxidation of ammonium and organic nitrogen through

physico-chemical and biological processes. It was reported that ccontinuous operation of

the sand filter led to saturation of the media making it anaerobic where the requirement

for nitrification was not favorable (Harris et al. 1977; Brandes 1974; Lance 1972).

Brandes (1974) reported that sand particle size ranging from 0.3 to 0.6 mm would

provide sufficient nitrification (over 85%) with 90% reduction of BOD and COD while

operating with a hydraulic loading rate of 0.04 m3/m2.d.

Recirculating sand filter (RSF) studies by Lamb et al. (1990) and Loudon et al.

(1985) showed that they could achieve a significant nitrification of STE with a sufficient

dosing frequency. Lamb et al. (1991) reported that the use of RSF in nitrifying STE

followed by denitrification using rock tanks or other means of a denitrification system

would show a significant nitrogen removal in the system.

Lance and Whisler (1972) performed studies using a clay loam (25% clay) with a

bulk density of 1.6 g/cc on the removal of nitrogen by varying flooding and resting

periods. Nitrification along with volatilization, mineralization and ammonification of

organic nitrogen to nitrates increased with longer flooding days and denitrification was

16


and less adsorption capability. The operation can either be free access, open, buried or

recirculating filters with sufficient aeration and alkalinity; nitrification can then be

achieved (U.S.EPA 1980).

Widrig et al. (1996) recommended the use of intermittent sand filter for onsite

effluent treatment due to the reliability, cost-effectiveness and increased land

developmental pressure on environmentally sensitive areas like shorelines and high relief

regions. Efficient nitrification could be achieved with a longer resting period thus

providing more retention time for oxidation o f ammonium and organic nitrogen through

physico-chemical and biological processes. It was reported that ccontinuous operation of

the sand filter led to saturation of the media making it anaerobic where the requirement

for nitrification was not favorable (Harris et al. 1977; Brandes 1974; Lance 1972).

Brandes (1974) reported that sand particle size ranging from 0.3 to 0.6 mm would

provide sufficient nitrification (over 85%) with 90% reduction o f BOD and COD while

operating with a hydraulic loading rate o f 0.04 m3/m 2 .d.

Recirculating sand filter (RSF) studies by Lamb et al. (1990) and Loudon et al.

(1985) showed that they could achieve a significant nitrification of STE with a sufficient

dosing frequency. Lamb et al. (1991) reported that the use of RSF in nitrifying STE

followed by denitrification using rock tanks or other means of a denitrification system

would show a significant nitrogen removal in the system.

Lance and Whisler (1972) performed studies using a clay loam (25% clay) with a

bulk density of 1 . 6 g/cc on the removal o f nitrogen by varying flooding and resting

periods. Nitrification along with volatilization, mineralization and ammonification of

organic nitrogen to nitrates increased with longer flooding days and denitrification was

16


reported to occur in lesser quantities. Kropf et al. (1977) reported that intermittent

flooding decreased the amount of effluent treated providing less treatment efficiency.

Complete nitrification would be necessary for an efficient denitrification of the

effluent. Brandes (1978) reported that with additives such as "red mud" a mixture of

compounds containing aluminum, iron, calcium, sodium and silica, limestone, added to

the sand filter the effluent quality was not significantly different from typical sand filter

effluent. Laboratory studies by Lance (1972) showed that addition of clay minerals with

higher CEC to the sand exhibited more nitrification capacity on an intermittent operation.

Zhang and Shan (1999) and Lance (1977) reported that column height of 0.91 m provided

sufficient nitrification with 86% occurring in the first 0.6 m; the increase in height above

0.91 m provided not much of an effect in increasing nitrification.

Studies conducted by Nichols et al. (1997) and Reneau Jr. (1977) showed that the

use of stratified filter with decreasing coarseness of sand particle along the height was

able to achieve a near complete nitrification with a hydraulic loading rate of 0.4 m3/m2.d.

Nichols et al. (1997) studied the efficiency of stratified filter with sand particle sized 0.4

to 1.4 mm at the top 20 cm, 12 cm filled with 0.2 to 0.7 mm and bottom 18 cm filled with

1 to 0.5 mm, layer in between the packed sand was filled with pea gravel. They reported

an ammonium nitrogen conversion of nearly 100 % when operated with 'A of the filter

loading capacity of 51 L/m2.d. When operated to 50 L/m2.d the effluent was reported to

have a mean inorganic nitrogen of (nitrate and nitrite) 20.5 mg/ L and a mean ammonium

nitrogen 6.2 mg/L. The suction developed by the lower size particles created a more

aerobic state in the upper region of the filter by allowing water to seep thorough. The

17


reported to occur in lesser quantities. Kropf et al. (1977) reported that intermittent

Hooding decreased the amount of effluent treated providing less treatment efficiency.

Complete nitrification would be necessary for an efficient denitrification of the

effluent. Brandes (1978) reported that with additives such as '‘red mud” a mixture of

compounds containing aluminum, iron, calcium, sodium and silica, limestone, added to

the sand filter the effluent quality was not significantly different from typical sand filter

effluent. Laboratory studies by Lance (1972) showed that addition of clay minerals with

higher CEC to the sand exhibited more nitrification capacity on an intermittent operation.

Zhang and Shan (1999) and Lance (1977) reported that column height of 0.91 m provided

sufficient nitrification with 8 6 % occurring in the first 0 . 6 m; the increase in height above

0.91 m provided not much of an effect in increasing nitrification.

Studies conducted by Nichols et al. (1997) and Reneau Jr. (1977) showed that the

use of stratified filter with decreasing coarseness of sand particle along the height was

able to achieve a near complete nitrification with a hydraulic loading rate of 0.4 m3/m 2 .d.

Nichols et al. (1997) studied the efficiency o f stratified filter with sand particle sized 0.4

to 1.4 mm at the top 20 cm, 12 cm filled with 0.2 to 0.7 mm and bottom 18 cm filled with

1 to 0.5 mm, layer in between the packed sand was filled with pea gravel. They reported

an ammonium nitrogen conversion of nearly 1 0 0 % when operated with % of the filter

2 2 loading capacity of 51 L/m .d. When operated to 50 L/m .d the effluent was reported to

have a mean inorganic nitrogen of (nitrate and nitrite) 20.5 mg/ L and a mean ammonium

nitrogen 6.2 mg/L. The suction developed by the lower size particles created a more

aerobic state in the upper region of the filter by allowing water to seep thorough. The

17


factors that would affect nitrification would be a higher loading rate, a decrease in

temperature, and crusting.

Siegrist (1987) reported that crusting or clogging was a deposition of poly amino

saccharides, which could inhibit the aeration capacity and increase saturation. Studies by

Daniel and Bouma (1974) and Jones and Taylor (1965) have shown that increased

aeration or providing more resting period of the media lessened the crust formation by

decomposing the organic compounds. Reducing solid concentration and periodic removal

of upper 10-15 cm of sand layer with replacement could prevent crusting (Siegrist 1987).

The overall process of nitrification reduces alkalinity by 7.14 mg as CaCO3 for 1 mg of

nitrate nitrogen with the release of hydrogen ions, which increase the acidity of the

effluent and can be neutralized with addition buffering agents (Lamb et al. 1990).

H+ + HCO3- H H2CO3 H CO2 T +H20 (2.11)

The degree of nitrification depends on the depth of the filter while the major

portion of nitrification occurs in the top layers of the media in the start-up stage, which

gradually increases over a period, though hydraulic conductivity decreases with the age

of the filter irrespective of depth. Studies by Loundon (1985) on the use of sand filters in

areas of severe winter climates showed that it could be operated efficiently if appropriate

design parameters were considered.

2.4 Alternative Nitrogen removal system

A conventional soil absorption system was able to achieve 20% removal of

nitrogen and effective reduction of BOD, COD and phosphate from the STE (Siegrist and

Jenssen 1989). In areas found unsuitable to dispose of effluent because of incomplete

nitrogen removal, alternate systems with selective nitrogen removal mechanisms have to

18


factors that would affect nitrification would be a higher loading rate, a decrease in

temperature, and crusting.

Siegrist (1987) reported that crusting or clogging was a deposition of poly amino

saccharides, which could inhibit the aeration capacity and increase saturation. Studies by

Daniel and Bouma (1974) and Jones and Taylor (1965) have shown that increased

aeration or providing more resting period of the media lessened the crust formation by

decomposing the organic compounds. Reducing solid concentration and periodic removal

of upper 10-15 cm of sand layer with replacement could prevent crusting (Siegrist 1987).

The overall process o f nitrification reduces alkalinity by 7.14 mg as CaCC>3 for 1 mg of

nitrate nitrogen with the release of hydrogen ions, which increase the acidity of the

effluent and can be neutralized with addition buffering agents (Lamb et al. 1990).

H + + HCO~ <-> H 2C03 <-> C02 t +H20 (2.11)

The degree of nitrification depends on the depth of the filter while the major

portion of nitrification occurs in the top layers o f the media in the start-up stage, which

gradually increases over a period, though hydraulic conductivity decreases with the age

of the filter irrespective of depth. Studies by Loundon (1985) on the use o f sand filters in

areas of severe winter climates showed that it could be operated efficiently if appropriate

design parameters were considered.

2.4 Alternative Nitrogen removal system

A conventional soil absorption system was able to achieve 20% removal of

nitrogen and effective reduction of BOD, COD and phosphate from the STE (Siegrist and

Jenssen 1989). In areas found unsuitable to dispose o f effluent because of incomplete

nitrogen removal, alternate systems with selective nitrogen removal mechanisms have to

18


be relied upon. Effective or complete nitrogen removal can be achieved by

denitrification, which, should be preceded by complete nitrification using conventional

and alternate methods. Denitrification as an anaerobic or anoxic operating system

depends on natural or alternate sources of carbon as a substrate. Several carbon rich

materials have been used as a substrate including gray water (Laak 1982) in RUCK

system, kitchen waste (Biswas and Warnock 1985), alcohol in forms of methanol and

ethanol (Sikora and Keeney 1975), peat (Viraraghavan and Rana 1991; Rock 1984),

molasses (Erickson et al. 1971), biotextile (Townshend, 1997), sawdust (Robertson and

Cherry 1995), sulfur and limestone (Zhang and Shan, 1999; Koenig and Liu 1996; Kanter

et al. 1994).

2.4.1 RUCK system

A modification of the conventional septic tank system, the RUCK system treats

the toilet wastewater (black water) and kitchen wastewater (gray water) in separate tanks.

The black water is then nitrified using a sand filter and gray water rich in organic carbon

is used as a substrate in an upflow rock filter. This is on the basis that the gray water has

more carbonaceous content while the black water contains more nitrogen content

(Siegrist et al. 1976). Studies conducted by Laak (1982) using a passive RUCK system,

reported an average total nitrogen removal of 70% with a ratio of organic carbon in the

gray to black water of 0.7, with an HRT of 3-5 days. Laak (1986) reported that

temperature and pH had an influence on the operation, and the alkalinity content of the

nitrified black water was considered as a limiting factor. Studies done by Lamb et al.

(1991) on buried RUCK and sand filter system used across New Jersey showed nitrogen

removal of over 80%. They reported that denitrification using greywater with a ratio of

19


be relied upon. Effective or complete nitrogen removal can be achieved by

denitrification, which, should be preceded by complete nitrification using conventional

and alternate methods. Denitrification as an anaerobic or anoxic operating system

depends on natural or alternate sources of carbon as a substrate. Several carbon rich

materials have been used as a substrate including gray water (Laak 1982) in RUCK,

system, kitchen waste (Biswas and Warnock 1985), alcohol in forms of methanol and

ethanol (Sikora and Keeney 1975), peat (Viraraghavan and Rana 1991; Rock 1984),

molasses (Erickson et al. 1971), biotextile (Townshend, 1997), sawdust (Robertson and

Cherry 1995), sulfur and limestone (Zhang and Shan, 1999; Koenig and Liu 1996; Kanter

et al. 1994).

2.4.1 RUCK system

A modification o f the conventional septic tank system, the RUCK system treats

the toilet wastewater (black water) and kitchen wastewater (gray water) in separate tanks.

The black water is then nitrified using a sand filter and gray water rich in organic carbon

is used as a substrate in an upflow rock filter. This is on the basis that the gray water has

more carbonaceous content while the black water contains more nitrogen content

(Siegrist et al. 1976). Studies conducted by Laak (1982) using a passive RUCK system,

reported an average total nitrogen removal o f 70% with a ratio of organic carbon in the

gray to black water o f 0.7, with an HRT of 3-5 days. Laak (1986) reported that

temperature and pH had an influence on the operation, and the alkalinity content o f the

nitrified black water was considered as a limiting factor. Studies done by Lamb et al.

(1991) on buried RUCK and sand filter system used across New Jersey showed nitrogen

removal of over 80%. They reported that denitrification using greywater with a ratio of

19


carbon present to nitrate from the sand filter effluent at 3: 1 was successful in achieving a

near complete nitrogen removal from the system. They also reported that not a complete

removal of nitrogen was achieved in sand filter/greywater system due to the incomplete

nitrification in the sand fi lter system, which would have been achievable in buried or

above ground sand filters with high alkaline media or water supply.

2.4.2 Kitchen Waste

Similar to the use of gray water in the denitrification of the nitrified effluent

Warnock and Biswas (1976) used kitchen waste as a substitute. By varying the nitrate

concentration in the system, denitrification capability of kitchen waste was tested. A

maximum removal of 90% was reported at an application rate of 0.035 m3/m2.d and C/N

ratio of 4.

2.4.3 Alcohol

Methanol has been the most commonly used biological. energy source in

achieving denitrification for nitrified STE and has been used and studied widely for the

use in treating nitrogen from individual onsite treatment (Franks 1993). Methanol as an

alternative carbon source is an effective denitrification source in achieving complete

nitrogen removal

NO3- + 5/6 CH3OH -> 1/2 N2 + 516 CO2 1- 7/6 H2O + OH- (2.12)

Sikora and Keeney (1976) achieved an average of 90% removal of nitrogen with

12 h of residence time on providing 1:2 of methanol to effluent; on adding twice the

required ratio of methanol, same removal efficiency was achieved with a retention time

of 8.33 hours. Andreoli et al. (1979) reported that denitrification occurred within a 2-hour

20


carbon present to nitrate from the sand filter effluent at 3: 1 was successful in achieving a

near complete nitrogen removal from the system. They also reported that not a complete

removal of nitrogen was achieved in sand filter/greywater system due to the incomplete

nitrification in the sand filter system, which would have been achievable in buried or

above ground sand filters with high alkaline media or water supply.

2.4.2 Kitchen W aste

Similar to the use of gray water in the denitrification o f the nitrified effluent

Warnock and Biswas (1976) used kitchen waste as a substitute. By varying the nitrate

concentration in the system, denitrification capability of kitchen waste was tested. A

3 2maximum removal of 90% was reported at an application rate of 0.035 m /m .d and C/N

ratio of 4.

2.4.3 Alcohol

Methanol has been the most commonly used biological, energy source in

achieving denitrification for nitrified STE and has been used and studied widely for the

use in treating nitrogen from individual onsite treatment (Franks 1993). Methanol as an

alternative carbon source is an effective denitrification source in achieving complete

nitrogen removal

NOT + 5/6 CH3 0H -» % N 2 + 5/6 C 0 2 f- 7/6 H20 + OH' (2.12)

Sikora and Keeney (1976) achieved an average of 90% removal of nitrogen with

1 2 h of residence time on providing 1 : 2 of methanol to effluent; on adding twice the

required ratio o f methanol, same removal efficiency was achieved with a retention time

of 8.33 hours. Andreoli et al. (1979) reported that denitrification occurred within a 2-hour

20


contact time with methanol and over 90% removal occurred in the upper layers of the

denitrification zone but decreased when influent DO increased. Lamb et al. (1990)

reported that methanol mixed with sand fi lter effluent at a ratio of 1: 2000 and C/N of 4:1

produced 99 % removal of nitrogen. Franks (1993) reported that some of the

disadvantages of using methanol as a denitrification agent would be repair and

monitoring by the homeowner and service personnel, as methanol use require frequent

maintenance.

Ethanol is used, as the amount of carbon present is higher than in methanol

decreasing the amount required as carbon with a lesser risk. Lamb et al. (1990) reported

that a mixture of C:N, 1:7000 from the sand filter effluent, produced the same degree of

denitrification while methanol required 1:2000 C: N. Loudon et al. (1985) reported that

the use of alcohol as a supplement to an external carbon source had less effect on

application in cold regions unless they were below ground.

2.4.4 Bio-textile

A biotextile was used in the study conducted by Townshend (1997) to determine

the nitrification and denitrification potential with recirculation of the effluent and carbon

material present in the sawdust as a denitrifying agent. The study reported that nitrogen

removal of over 76% in the non-winter months and 67% in the winter months was

achieved. The mean percentage of efficiency in denitrification was 78% with a mean

effluent concentration of ammonia nitrogen at 20 mg/L.

21


contact time with methanol and over 90% removal occurred in the upper layers of the

denitrification zone but decreased when influent DO increased. Lamb et al. (1990)

reported that methanol mixed with sand filter effluent at a ratio of 1: 2000 and C/N of 4:1

produced 99 % removal of nitrogen. Franks (1993) reported that some of the

disadvantages of using methanol as a denitrification agent would be repair and

monitoring by the homeowner and service personnel, as methanol use require frequent

maintenance.

Ethanol is used, as the amount of carbon present is higher than in methanol

decreasing the amount required as carbon with a lesser risk. Lamb et al. (1990) reported

that a mixture of C:N, 1:7000 from the sand filter effluent, produced the same degree of

denitrification while methanol required 1:2000 C: N. Loudon et al. (1985) reported that

the use of alcohol as a supplement to an external carbon source had less effect on

application in cold regions unless they were below ground.

2.4.4 Bio-textile

A biotextile was used in the study conducted by Townshend (1997) to determine

the nitrification and denitrification potential with recirculation of the effluent and carbon

material present in the sawdust as a denitrifying agent. The study reported that nitrogen

removal of over 76% in the non-winter months and 67% in the winter months was

achieved. The mean percentage of efficiency in denitrification was 78% with a mean

effluent concentration o f ammonia nitrogen at 20 mg/L.

2 1


2.4.5 Peat

Peat is a partially fossilized plant matter whose major constituents are

cellulose and lignin. The polar activity of the peat favors adsorption of transition metals

and organic compounds; this activity is related to the presence of polar functional groups

such as ketones, aldehydes, alcohols, acids and ethers present in the lignin of the peat

(Viraraghavan 1993). The effectiveness of peat in nitrogen removal is attributed to acidic

nature and organic content present and is used in the treatment of wastewater as a

filtration and adsorbent medium. Peat has provided more attenuation of ammonium ions

resulting in gradual nitrification to nitrates (White 1995; Viraraghavan 1993; Rana and

Viraraghavan 1987; Rock et al. 1984; Sikora and Kenney 1975). Robertson and Cherry

(1995) and Brooks et al. (1984) reported that the attenuation was mainly due to the

organic nitrogen bound to the fungal biomass, which utilizes the organic and inorganic

nitrogen for its growth in an aerobic state.

The degree of nitrification and denitrification on a peat based. system depends on

the hydraulic loading rate and compactness. Rana and Viraraghavan (1987) conducted a

laboratory column study with varying depth of peat and constant surface area of 314 cm2.

Their study showed 95 % removal of TKN and NH3-N in a column with depth 20, 30 and

50 cm of peat at a hydraulic loading rate of 63.7 mm/d. The increase in hydraulic loading

rate to 89 mm/d, decreased the nitrification efficiency to 35 % at 20 and 30 cm depths

while 50 cm column showed 75 and 84 % removal of NH3-N and TKN. Viraraghavan

and Rana (1991) reported that at a loading rate of 63.7 mm/day the column achieved a

removal of over 95% NH3-N and TKN with removal decreasing over an increase in depth

and loading rate.


2.4.5 Peat

Peat is a partially fossilized plant matter whose major constituents are

cellulose and lignin. The polar activity of the peat favors adsorption of transition metals

and organic compounds; this activity is related to the presence of polar functional groups

such as ketones, aldehydes, alcohols, acids and ethers present in the lignin of the peat

(Viraraghavan 1993). The effectiveness of peat in nitrogen removal is attributed to acidic

nature and organic content present and is used in the treatment of wastewater as a

filtration and adsorbent medium. Peat has provided more attenuation of ammonium ions

resulting in gradual nitrification to nitrates (White 1995; Viraraghavan 1993; Rana and

Viraraghavan 1987; Rock et al. 1984; Sikora and Kenney 1975). Robertson and Cherry

(1995) and Brooks et al. (1984) reported that the attenuation was mainly due to the

organic nitrogen bound to the fungal biomass, which utilizes the organic and inorganic

nitrogen for its growth in an aerobic state.

The degree of nitrification and denitrification on a peat based, system depends on

the hydraulic loading rate and compactness. Rana and Viraraghavan (1987) conducted a

laboratory column study with varying depth o f peat and constant surface area o f 314 cm2.

Their study showed 95 % removal of TKN and NH3 -N in a column with depth 20, 30 and

50 cm of peat at a hydraulic loading rate o f 63.7 mm/d. The increase in hydraulic loading

rate to 89 mm/d, decreased the nitrification efficiency to 35 % at 20 and 30 cm depths

while 50 cm column showed 75 and 84 % removal o f NH3 -N and TKN. Viraraghavan

and Rana (1991) reported that at a loading rate o f 63.7 mm/day the column achieved a

removal of over 95% NH 3 -N and TKN with removal decreasing over an increase in depth

and loading rate.

22


Franks (1993) reported that the compactness of peat at a range of 0.1- 0.12 g/cm3 could

take a hydraulic loading rate up to 4.1 cm/d with a filter of minimum 30 cm depth, while

an increase in hydraulic loading rate would lead to crust formation and channeling thus

making the system anaerobic. Brooks et al. (1984) reported that intermittent operation led

to a better result with same hydraulic capacity of the peat fi lter than continuous operation.

Denitrification was reported by Rock et al. (1984) in anaerobic conditions accounting to

62 % reduction of total nitrogen. Nichols and Boelter (1982) showed a 90% removal and

pH of 6.3-6.9 can be achieved using peat-sand fi lter bed with 30 mg/L as the initial total

nitrogen content. The efficiency of the bed decreased with time; at the end of 5 years the

nitrogen conversion decreased to 50% releasing ammonia nitrogen. Studies done by the

researchers show that the peat filter bed had a higher percentage nitrogen conversion of

ammonium compounds to nitrates with an increase in color and pH of 3-3.3 (White 1995;

Rock et al. 1984).

2.4.6 Sawdust

The use of sawdust as an alternate carbon treatment media in denitrification was

experimented by providing a barrier attenuation to increase the efficiency through an

anaerobic zone below the tile bed for denitrification. Effluent from the denitrification

layer had a low ammonia and nitrate concentration, showing a total nitrogen removal of

over 90% and a near complete denitrification (Robertson and Cherry 1995). The removal

of nitrate was attributed to adsorption on the surface of the material due to decrease in

sulfate and chloride level in the effluent, which also provided growth for anaerobic

bacteria. Insufficient organic carbon present in the sawdust surface, which supported the


Franks (1993) reported that the compactness of peat at a range of 0.1- 0.12 g/cmJ could

take a hydraulic loading rate up to 4.1 cm/d with a filter of minimum 30 cm depth, while

an increase in hydraulic loading rate would lead to crust formation and channeling thus

making the system anaerobic. Brooks et al. (1984) reported that intermittent operation led

to a better result with same hydraulic capacity of the peat filter than continuous operation.

Denitrification was reported by Rock et al. (1984) in anaerobic conditions accounting to

62 % reduction of total nitrogen. Nichols and Boelter (1982) showed a 90% removal and

pH of 6 .3-6.9 can be achieved using peat-sand filter bed with 30 mg/L as the initial total

nitrogen content. The efficiency of the bed decreased with time; at the end of 5 years the

nitrogen conversion decreased to 50% releasing ammonia nitrogen. Studies done by the

researchers show that the peat filter bed had a higher percentage nitrogen conversion of

ammonium compounds to nitrates with an increase in color and pH of 3-3.3 (White 1995;

R ocketal. 1984).

2.4.6 Sawdust

The use of sawdust as an alternate carbon treatment media in denitrification was

experimented by providing a barrier attenuation to increase the efficiency through an

anaerobic zone below the tile bed for denitrification. Effluent from the denitrification

layer had a low ammonia and nitrate concentration, showing a total nitrogen removal of

over 90% and a near complete denitrification (Robertson and Cherry 1995). The removal

of nitrate was attributed to adsorption on the surface of the material due to decrease in

sulfate and chloride level in the effluent, which also provided growth for anaerobic

bacteria. Insufficient organic carbon present in the sawdust surface, which supported the

23


growth of heterotrophic denitrificans in the biofilm, was reasoned to be the cause of

lesser denitrification.

2.4.7 Sulfur

Biological nitrification followed by autotrophic denitrification using sulfur

growing organisms such as Thiobacillus, Thiomicrospira and Paracoccus denitrificans

has shown promising results in reliability providing an efficient method of nitrogen

removal (Gayle et al. 1989). The sulfur oxidizing bacteria provides an optimal growth in

both acidic and alkaline media by adapting to the pH of the effluent and could be grown

heterotrophically in the presence of organic carbon (Kanter et al. 1994; Sikora and

Keeney 1976; Mann et al. 1972). The autotrohphic denitrificans (Thiobacillus

denitrificans and Thiomicrospira denitrificans) use the inorganic carbon compounds and

bicarbonate compounds as their carbon source and nitrate as their electron acceptor. The

stoichometric equation of the reaction is (Batchelor and Lawrence 1978)

55 S + 20 CO2 + 50 NO3" + 38 H20 + 4 NH4+

25 N2 + 4 C5H7NO2 + 55 S042- + 64 fr (2.13)

The maximum growth rate of Thiobacillus denitrificans was observed in the pH

range of 6 to 8 at a temperature range of 12 to 30 °C (Batchelor and Lawrence 1978).

6N0,- + 5S +2H,0 -÷ 3N2 T +4E504 + SO + energy (2.14)

The release of hydrogen ions and subsequent reaction with sulfate produces sulfuric acid,

which decreases the pH of the effluent. The use of carbonate or bicarbonate ions would

likely increase the pH; limestone and dolomite has been used to supplement the

requirement with the release of carbon dioxide, which, would be used for synthesis of

24


growth of heterotrophic denitrificans in the biofilm, was reasoned to be the cause of

lesser denitrification.

2.4.7 Sulfur

Biological nitrification followed by autotrophic denitrification using sulfur

growing organisms such as Thiobacillus, Thiomicrospira and Paracoccus denitrificans

has shown promising results in reliability providing an efficient method of nitrogen

removal (Gayle et al. 1989). The sulfur oxidizing bacteria provides an optimal growth in

both acidic and alkaline media by adapting to the pH of the effluent and could be grown

heterotrophically in the presence o f organic carbon (Kanter et al. 1994; Sikora and

Keeney 1976; Mann et al. 1972). The autotrohphic denitrificans (Thiobacillus

denitrificans and Thiomicrospira denitrificans) use the inorganic carbon compounds and

bicarbonate compounds as their carbon source and nitrate as their electron acceptor. The

stoichometric equation of the reaction is (Batchelor and Lawrence 1978)

55 S + 20 CO? + 50 N O i + 38 H20 + 4 N H f

25 N2 + 4 C5 H 7NO 2 + 55 S O /- + 64 f t (2.13)

The maximum growth rate o f Thiobacillus denitrificans was observed in the pH

range of 6 to 8 at a temperature range of 12 to 30 °C (Batchelor and Lawrence 1978).

6 NO f + 5S + 2 H 2O -> 3N 2 t +4HSOf + SO f + energy (2.14)

The release of hydrogen ions and subsequent reaction with sulfate produces sulfuric acid,

which decreases the pH of the effluent. The use of carbonate or bicarbonate ions would

likely increase the pH; limestone and dolomite has been used to supplement the

requirement with the release o f carbon dioxide, which, would be used for synthesis of

24


cellular material (Zhang and Shan 1999; Kanter et al. 1994; Sikora and Keeney 1976;

Mann et al. 1972).

S0 + 11,0 +1.50, —> 2802-4 +2H+ (2.15)

H, S0, +CaCO, —> CaSO +CO-, + H,0 (2.16)

The utilization of nitrate as a terminal electron acceptor occurs when the demand

for oxygen exceeds the supply, thus the need for an anaerobic or a reduced potential

system is necessary (Mann et al. 1972). Denitrification can be increased by reducing the

particle size of the sulfur, providing more surface area for the growth of biofilm, and

providing more retention time (Koenig and Liu 1996; Sikora and Keeney 1976).

The application of sulfur as a denitrifying agent below the ground over an

impermeable layer has shown considerable success in removing nitrate (Koenig and Liu

1996; Kanter et al. 1998). Mann et al. (1972) studied the efficiency of nitrate removal in a

four column study containing Hanford sandy loam and Moreno silty clay loam treated

and untreated with sulfur and limestone. They reported that columns with sulfur

limestone showed a significant removal at operating conditions of ranging from 1.9 to 2.6

cm/d for Hanford treated columns and 2.13 to 2.23 cm/d for Moreno treated columns.

The loading rate experimented were higher than the untreated columns and was reported

to have a removal percentage over 90 of influent nitrate nitrogen (425 mg/L). The

removal of nitrate would depend upon the application rate of the effluent over the layer.

Sikora and Kenney (1976) studied the effect of denitrification using sulfur and dolomite,

1/1 weight ratio and mechanically aerated STE. The STE then were diluted to 1:36 to

resemble seepage bed effluent, the effluent was then added the required nitrate to

maintain the influent concentration to the denitrification to 40 mg/L as nitrate nitrogen. A


cellular material (Zhang and Shan 1999; Kanter et al. 1994; Sikora and Keeney 1976;

Mann et al. 1972).

The utilization of nitrate as a terminal electron acceptor occurs when the demand

for oxygen exceeds the supply, thus the need for an anaerobic or a reduced potential

system is necessary (Mann et al. 1972). Denitrification can be increased by reducing the

particle size of the sulfur, providing more surface area for the growth of biofilm, and

providing more retention time (Koenig and Liu 1996; Sikora and Keeney 1976).

The application of sulfur as a denitrifying agent below the ground over an

impermeable layer has shown considerable success in removing nitrate (Koenig and Liu

1996; Kanter et al. 1998). Mann et al. (1972) studied the efficiency of nitrate removal in a

four column study containing Hanford sandy loam and Moreno silty clay loam treated

and untreated with sulfur and limestone. They reported that columns with sulfur

limestone showed a significant removal at operating conditions of ranging from 1.9 to 2.6

cm/d for Hanford treated columns and 2.13 to 2.23 cm/d for Moreno treated columns.

The loading rate experimented were higher than the untreated columns and was reported

to have a removal percentage over 90 of influent nitrate nitrogen (425 mg/L). The

removal of nitrate would depend upon the application rate of the effluent over the layer.

Sikora and Kenney (1976) studied the effect o f denitrification using sulfur and dolomite,

1/1 weight ratio and mechanically aerated STE. The STE then were diluted to 1:36 to

resemble seepage bed effluent, the effluent was then added the required nitrate to

maintain the influent concentration to the denitrification to 40 mg/L as nitrate nitrogen. A

S° + H 20 + \ .5 0 2 -> 2 S O \+ 2 H (2.15)

H 2SOa + GaCO, CaSO , + C 0 2 + H 20 (2.16)

25


near complete removal of nitrate was achieved in less than 3.3 hours of residence time

and an increase in sulfate and alkalinity was observed. They also reported that

autotrophic denitrification alone would be possible in an anaerobic system as little

soluble carbon would be present.

The application of sulfur/limestone in a mound system was performed by Kanter et al.

(1998) where, the mound was split into 8 cells of 36 cm width. Effluent quality of less

than 10 mg N/L was achieved with influent application of 0.26 m3/m2.d and

concentration of 52 mg N/L. Studies by Zhang and Shan (1999) on an in-situ application

of sulfur/limestone in a conventional lateral field with a primary sedimentation tank

effluent showed over 90% removal of nitrogen from an initial concentration of 40 mg

N/L. Mann et al. (1972) suggested that the addition of sulfur to energy deficient soils

may be more practical than addition of exogenous carbon source as the competition for

available carbon among non-denitrifying bacteria is also very keen.

26


near complete removal of nitrate was achieved in less than 3.3 hours of residence time

and an increase in sulfate and alkalinity was observed. They also reported that

autotrophic denitrification alone would be possible in an anaerobic system as little

soluble carbon would be present.

The application of sulfur/limestone in a mound system was performed by Kanter et al.

(1998) where, the mound was split into 8 cells of 36 cm width. Effluent quality of less

than 10 mg N/L was achieved with influent application of 0.26 m 3/m2.d and

concentration of 52 mg N/L. Studies by Zhang and Shan (1999) on an in-situ application

of sulfur/limestone in a conventional lateral field with a primary sedimentation tank

effluent showed over 90% removal of nitrogen from an initial concentration o f 40 mg

N/L. Mann et al. (1972) suggested that the addition of sulfur to energy deficient soils

may be more practical than addition of exogenous carbon source as the competition for

available carbon among non-denitrifying bacteria is also very keen.

26


3 MATERIALS AND METHODS

3.1 Septic tank effluent used in the study

The septic tank effluent was collected from a four-member household in White

City, approximately 20 km east of Regina on Highway No. 1. Grab samples of the

effluent were collected from a two compartmented septic tank having capacities of 1575

and 675 L, respectively. The average detention time of both compartments is

approximately three days and the collected sludge is cleaned once in two years.

3.2 Sand, Sulfur and Limestone used in the column

Red flint sand of particle size 0.45 — 0.55 mm with a uniformity coefficient of 1.35-

1.70 was used in the study in the column. The sand was purchased from USF Water

Group Inc. Regina, Saskatchewan. Sand was sieved to remove the dirt and packed in a

similar manner in all three columns used in the study.

Granular elemental sulfur and limestone of particle size 2.38-4.76 mm (U.S. sieve

sizes #8 to #4) were used in the study to facilitate the growth of autotrophic Thiobacillus

denitrificans and as a pH limiter respectively. Sulfur and limestone were obtained from

Consumers' Co-operative Refinery Ltd., Regina and Regal Flooring Ltd., Regina,

respectively. Sulfur and limestone were washed with tap water to remove the dirt and

sieved to the specific size before packing them to respective ratios in the column.

27


3 MATERIALS AND METHODS

3.1 Septic tank effluent used in the study

The septic tank effluent was collected from a four-member household in White

City, approximately 20 km east of Regina on Highway No. 1. Grab samples of the

effluent were collected from a two compartmented septic tank having capacities of 1575

and 675 L, respectively. The average detention time of both compartments is

approximately three days and the collected sludge is cleaned once in two years.

3.2 Sand, Sulfur and Limestone used in the column

Red flint sand of particle size 0.45 - 0.55 mm with a uniformity coefficient of 1.35-

1.70 was used in the study in the column. The sand was purchased from USF Water

Group Inc. Regina, Saskatchewan. Sand was sieved to remove the dirt and packed in a

similar manner in all three columns used in the study.

Granular elemental sulfur and limestone o f particle size 2.38-4.76 mm (U.S. sieve

sizes # 8 to #4) were used in the study to facilitate the growth of autotrophic Thiobacillus

denitrificans and as a pH limiter respectively. Sulfur and limestone were obtained from

Consumers' Co-operative Refinery Ltd., Regina and Regal Flooring Ltd., Regina,

respectively. Sulfur and limestone were washed with tap water to remove the dirt and

sieved to the specific size before packing them to respective ratios in the column.

27


3.3 Thiobacillus denitrificans culture

Thiobacillus denitrificans as a freeze-dried culture ATCC strain # 23642 was

obtained from American Type Culture Collection (ATCC) Rockville, Maryland, U.S.A.

The culture was grown in a medium described by Lampe and Zhang (1996) (Tables 3.1

and 3.2.) The solutions were prepared with tap water. The stock culture was inoculated

into 1 L of medium and incubated under nitrogen at the room temperature 20 ± 3 °C for

14 days. The culture was routinely maintained by transferring 200 mL of previously

prepared culture and made to one liter by adding freshly prepared feed solution. The

bacterial culture was cultivated inside the reactor by adding 300 mL of the originally

prepared culture into a flask of 1 L and remaining volume was fi lled with culture feed

solution without sodium thiosulfate. The feed solution was passed in an upflow manner at

0.02 m3/m2.d so that more retention time is available for the initial culture growth. The

feed solution was recirculated over a three-day period. After three days, 600 mL of the

solution was wasted daily from the day onwards, and was replaced with 150 mL of

culture and 450 mL of feed solution without thiosulfate. The system was kept in

operation for a period of 14 days prior to the start up of the whole system. The culture of

Thiobacillus denitrificans was used as a seed source to grow the organisms in the reactor

until the reactor was ready for operation. System readiness was identified by the nitrogen

bubble formation at the top of the column; no specific test was done to identify the gas as

nitrogen.

78


3.3 Thiobacillus denitrificans culture

Thiobacillus denitrificans as a freeze-dried culture ATCC strain # 23642 was

obtained from American Type Culture Collection (ATCC) Rockville, Maryland, U.S.A.

The culture was grown in a medium described by Lampe and Zhang (1996) (Tables 3.1

and 3.2.) The solutions were prepared with tap water. The stock culture was inoculated

into 1 L of medium and incubated under nitrogen at the room temperature 20 ± 3 °C for

14 days. The culture was routinely maintained by transferring 200 mL of previously

prepared culture and made to one liter by adding freshly prepared feed solution. The

bacterial culture was cultivated inside the reactor by adding 300 mL of the originally

prepared culture into a flask of 1 L and remaining volume was filled with culture feed

solution without sodium thiosulfate. The feed solution was passed in an up flow manner at

0.02 m3/m2.d so that more retention time is available for the initial culture growth. The

feed solution was recirculated over a three-day period. After three days, 600 mL of the

solution was wasted daily from the day onwards, and was replaced with 150 mL of

culture and 450 mL of feed solution without thiosulfate. The system was kept in

operation for a period of 14 days prior to the start up o f the whole system. The culture of

Thiobacillus denitrificans was used as a seed source to grow the organisms in the reactor

until the reactor was ready for operation. System readiness was identified by the nitrogen

bubble formation at the top of the column; no specific test was done to identify the gas as

nitrogen.

28


Table 3.1. Culture preparation medium

Material Amount (g/L)

Sodium thiosulfate (Na2S203.5H20)

Sodium hydrogen carbonate (NaHCO3) 1.5

Potassium nitrate (KNO3) 3

Sodium hydrogen phosphate (Na2HPO4) 1.5

Potassium hydrogen phosphate (KH2PO4) ().3

Magnesium sulfate heptahydrate 0.4

(MgSO4.7H20)

Trace element 1 mL/L

Table 3.2. Trace element composition

Material Amount (mg/L)

Potassium hydrogen phosphate (K2HPO4) 56.25

Ammonium Chloride (NH4C1) 5.74

Magnesium chloride (MgC12.6H20) 1

Manganese sulfate (MgSO4.H20) 1

Calcium chloride (CaC12) 1

Ferric chloride (FeC12.6H20) 1

29


Table 3.1. Culture preparation medium

Material Amount (g/L)

Sodium thiosulfate (Na2 S2 0 3 .5 H2 0 ) 6

Sodium hydrogen carbonate (NaHCCF) 1.5

Potassium nitrate (KNO3 ) ->

Sodium hydrogen phosphate (Na2 FlP0 4 ) 1.5

Potassium hydrogen phosphate (KH2 PO4 ) 0.3

Magnesium sulfate heptahydrate 0.4

(M gS04 .7H2 0 )

Trace element 1 mL/L

Table 3.2. Trace element composition

Material Amount (mg/L)

Potassium hydrogen phosphate (K2 HPO4 ) 56.25

Ammonium Chloride (NH4 C1) 5.74

Magnesium chloride (MgCl2 .6H2 0 ) 1

Manganese sulfate (M gS0 4 .H20 ) 1

Calcium chloride (CaCl2) 1

Ferric chloride (FeCl2 .6H2 0 ) 1


3.4 Experimental Set-up

Three polyvinyl chloride (PVC) transparent columns with a height of 137 cm and

5 cm in diameter were used in the study. Washed crushed stones of approximately 0.5

mm in size were placed underneath the sulfur limestone mixture to prevent the sulfur and

limestone particles being blocked in the effluent tubing. Sulfur and limestone were

mixed according to the mass ratio 1/1, 2/1, and 3/1 and were placed above crushed-stones

to a height of 30.5 cm.

Red flint sand of particle size 0.45-0.55 mm in diameter was used in designing the

sand filter setup. The sand was filled to a height of 91.4 cm above the sulfur limestone

mixture. The columns were tapped at the sides so that the sand particles were logged on

to each other leaving sufficient space for the hydraulic movement across the filter.

The septic tank effluent from a container was fed to the top of the column through

three separate tubings using a peristaltic pump. The pumping rate was controlled using a

speed controller. The effluent from the sand filter was collected at the sampling port

located at 91.5 cm from top of the sand filter. The effluent from the SLAD layer was

collected from the bottom of the reactor, with the collection point at 30.5 cm from the

bottom to provide full submergence of the reactor creating anoxic conditions. A port

located at a height of 30.5 cm from the bottom. This was done to provide sufficient

hydraulic retention time to the SLAD layer and maintain an anaerobic zone. The

experimental setup of the study is shown in Figure 3.1 .

30


3.4 Experim ental Set-up

Three polyvinyl chloride (PVC) transparent columns with a height of 137 cm and

5 cm in diameter were used in the study. Washed crushed stones of approximately 0.5

mm in size were placed underneath the sulfur limestone mixture to prevent the sulfur and

limestone particles being blocked in the effluent tubing. Sulfur and limestone were

mixed according to the mass ratio 1/1, 2/1, and 3/1 and were placed above crushed-stones

to a height of 30.5 cm.

Red flint sand of particle size 0.45-0.55 mm in diameter was used in designing the

sand filter setup. The sand was filled to a height of 91.4 cm above the sulfur limestone

mixture. The columns were tapped at the sides so that the sand particles were logged on

to each other leaving sufficient space for the hydraulic movement across the filter.

The septic tank effluent from a container was fed to the top of the column through

three separate tubings using a peristaltic pump. The pumping rate was controlled using a

speed controller. The effluent from the sand filter was collected at the sampling port

located at 91.5 cm from top of the sand filter. The effluent from the SLAD layer was

collected from the bottom of the reactor, with the collection point at 30.5 cm from the

bottom to provide full submergence of the reactor creating anoxic conditions. A port

located at a height o f 30.5 cm from the bottom. This was done to provide sufficient

hydraulic retention time to the SLAD layer and maintain an anaerobic zone. The

experimental setup of the study is shown in Figure 3.1.

30


Sand filter Sulfur/limestone SLAD layer

110

rtirti

3/1

Peristaltic Pump

Figure 3.1. Experimental Set up

31

Effluent sampling ports

Sand filter sampling ports

Crushed stones


Sand filter W v Sulfur/limestone SLAD layer

Effluent sampling ports

Sand filter sampling ports

+ w iv+++++ .'.H

£++++++h#+ X +X #t¥&<i+X+i+KX+X+X+X*;X+X+X v$X+X+X+XqX+X+X+X+<X+X wSwX1► ♦X+Xwtoml+X+X+X+X+X+X+X+XKwX■& & X +X+X+X+X+Xh+X+X+X+S+X+X+X+XL+X+XtX+X’

mm.

mmmm.&XM4K+1-K+L+?XwX«X+X+Xs+X*

sssss

ssssss-st-a mm

Crushed stones

Influent

PeristalticPump

Figure 3.1. Experimental Set up


3.4.1 Culturing Thiobacillus denitrificans in SLAD layer

A one-liter flask was used to prepare original culture solution of which 200 mL of

original culture was introduced along with 800 mL of nutrient solution without

thiosulfate. The solution was then introduced in the SLAD layer in an upflow fashion and

recirculated over a period of three days at 0.5 mL/min. This was to provide more

retention time to the growth of biofilm in the sulfur. After three days, 600 mL of the

solution was wasted daily, and was replaced with 150 mL of culture and 450 mL of feed

solution without thiosulfate. After 15 days, the attached growth was considered

substantial enough to stop the recirculation.

To prepare the reactors for the column tests, 300 mL of bacterial culture was

initially introduced into each anaerobic fixed-bed reactors. The remaining volume in each

column was filled with feed solution used to culture autotrophic denitrifying bacteria

without thiosulfate. To enable the denitrifying bacteria to accumulate and form a biofilm

on the granular sulfur-limestone media, the contents of the columns were repeatedly

recirculated over a three-day period.

The hydraulic loading rate was 4 cm/d for a study period of 155 days and 8.1

cm/d for 40 days. The hydraulic retention time (HRT) based on gross volume of reactor

in the reactor was 30.5 days during the first period and 15.2 days during the second

period.

32


3.4.1 Culturing Thiobacillus denitrificans in SLAD layer

A one-liter flask was used to prepare original culture solution of which 200 mL of

original culture was introduced along with 800 mL of nutrient solution without

thiosulfate. The solution was then introduced in the SLAD layer in an upflow fashion and

recirculated over a period of three days at 0.5 mL/min. This was to provide more

retention time to the growth of biofilm in the sulfur. After three days, 600 mL of the

solution was wasted daily, and was replaced with 150 mL of culture and 450 mL of feed

solution without thiosulfate. After 15 days, the attached growth was considered

substantial enough to stop the recirculation.

To prepare the reactors for the column tests, 300 mL of bacterial culture was

initially introduced into each anaerobic fixed-bed reactors. The remaining volume in each

column was filled with feed solution used to culture autotrophic denitrifying bacteria

without thiosulfate. To enable the denitrifying bacteria to accumulate and form a biofilm

on the granular sulfur-limestone media, the contents o f the columns were repeatedly

recirculated over a three-day period.

The hydraulic loading rate was 4 cm/d for a study period of 155 days and 8.1

cm/d for 40 days. The hydraulic retention time (HRT) based on gross volume of reactor

in the reactor was 30.5 days during the first period and 15.2 days during the second

period.

32


3.5 Column Studies

All the three columns were operated at room temperature (approximately 20 ± 2

°C) and were fed twice in 24 h with a gap of 6 h in between. The column studies were

divided into two different hydraulic loading stages of 4 and 8.1 cm/d. It took one month

for the system to stabilize and produce a consistent reading. The experiments were

conducted for 200 days continuous. The influent samples were collected in acid washed

plastic bottles and physical and chemical analyzes were then performed on them. The

effluent samples were collected in acid washed plastic bottles and refrigerated at 4 °C and

tests were performed on them. All the samples were analyzed within a span of 24 hours

after collection.

33


3.5 Column Studies

All the three columns were operated at room temperature (approximately 20 ± 2

°C) and were fed twice in 24 h with a gap o f 6 h in between. The column studies were

divided into two different hydraulic loading stages of 4 and 8.1 cm/d. It took one month

for the system to stabilize and produce a consistent reading. The experiments were

conducted for 200 days continuous. The influent samples were collected in acid washed

plastic bottles and physical and chemical analyzes were then performed on them. The

effluent samples were collected in acid washed plastic bottles and refrigerated at 4 °C and

tests were performed on them. All the samples were analyzed within a span of 24 hours

after collection.


3.5.1 Analytical Methods

Influent and effluent samples were analyzed in accordance with the "Standard

Methods", (APHA 1999) for parameters analyzed. The specific methods used in the

determination of each parameter are given below.

The pH of all samples was tested using a Fisher Accumet model 600-pH meter.

Nitrate-nitrogen (NO3--N), nitrite-nitrogen (N0,--N), sulfate (S042-) and phosphate as

phosphorus (PO4-) were determined for the effluent and influent by Dionex 600 Ion

Chromatography (IC) equipped with CD25 conductivity detector. The Dionex Ionpac

AS17 column was thermostated at 35°C on LC25 chromatography oven and the sample

was filtered through the AS40 automated sampler, which was used along with the IC

system. Dissolved oxygen was measured using a YSI 52 Dissolved Oxygen Meter. The

dichromate reflex method (Section 5220B of "Standard Methods") was adopted for COD

determination. Total kjeldhal nitrogen was estimated using a digestion apparatus and a

distillation apparatus (Tecator Digestion System 6, 1007 digester and Tecator Kjectec I

1002 Distilling Unit). Higher influent ammonia nitrogen concentration was determined

using Tecator Kjectec I 1002 distilling unit (Section 4500B and 4500 C of "Standard

Methods") and the effluent containing less ammonia nitrogen was measured using Hach

(1992). The alkalinity measurement was done in accordance with "Standard Methods"

(Section 2320). The suspended solids were determined by the glass fiber method

described in "Standard Methods" (Section 2540).

34


3.5.1 Analytical Methods

Influent and effluent samples were analyzed in accordance with the “Standard

Methods”, (APHA 1999) for parameters analyzed. The specific methods used in the

determination of each parameter are given below.

The pH of all samples was tested using a Fisher Accumet model 600-pH meter.

Nitrate-nitrogen (NCV-N), nitrite-nitrogen (NCV-N), sulfate (S 042') and phosphate as

phosphorus (POT) were determined for the effluent and influent by Dionex 600 Ion

Chromatography (IC) equipped with CD25 conductivity detector. The Dionex Ionpac

AS 17 column was thermostated at 35°C on LC25 chromatography oven and the sample

was filtered through the AS40 automated sampler, which was used along with the IC

system. Dissolved oxygen was measured using a YSI 52 Dissolved Oxygen Meter. The

dichromate reflex method (Section 5220B of “Standard Methods”) was adopted for COD

determination. Total kjeldhal nitrogen was estimated using a digestion apparatus and a

distillation apparatus (Tecator Digestion System 6 , 1007 digester and Tecator Kjectec I

1002 Distilling Unit). Higher influent ammonia nitrogen concentration was determined

using Tecator Kjectec I 1002 distilling unit (Section 4500B and 4500 C of “Standard

Methods”) and the effluent containing less ammonia nitrogen was measured using Hach

(1992). The alkalinity measurement was done in accordance with “Standard Methods”

(Section 2320). The suspended solids were determined by the glass fiber method

described in “Standard Methods” (Section 2540).

34


3.6 Sampling, transport, and storage methods

The septic tank effluent samples collected from White City were transported to the

laboratory within one hour of collection and stored in airtight plastic containers in

refrigerator at 4° C. The effluent samples collected were all grab samples using a bucket

and a rope. All the samples were analyzed for physical and chemical characteristics

within 24 hours of collection.


3.6 Sampling, transport, and storage methods

The septic tank effluent samples collected from White City were transported to the

laboratory within one hour of collection and stored in airtight plastic containers in

refrigerator at 4° C. The effluent samples collected were all grab samples using a bucket

and a rope. All the samples were analyzed for physical and chemical characteristics

within 24 hours of collection.

35


4 RESULTS AND DISCUSSION

The treatment efficiency of the columns observed is discussed in regard to the

various parameters selected for the study purpose. Tables A. 1 to A. 18 (Appendix A)

contain raw data. The effect of physical and chemical characteristics of the influent STE,

sand fi lter effluent and SLAD layer effluent are discussed for the two hydraulic loading

rates.

4.1 Characteristics of septic tank effluent

The physical and chemical characteristics of the septic tank effluent were analyzed

on a periodic basis through the study period and are shown in the Table 4.1. These values

were comparable to the data in the literature (Widrig et al 1996; Viraraghavan 1993) and

previous studies done at University of Regina, Water Resources Laboratory on the same

septic tank (Viraraghavan and Rana 1991).

4.1.1 pH

The pH of the septic tank effluent was in range of 6.9 to 7.9. The detention

available in the septic tank and anaerobic digestion that takes place in the septic tank

brought the mean pH of the effluent near to neutral.

36


4 RESULTS AND DISCUSSION

The treatment efficiency of the columns observed is discussed in regard to the

various parameters selected for the study purpose. Tables A. 1 to A. 18 (Appendix A)

contain raw data. The effect of physical and chemical characteristics of the influent STE,

sand filter effluent and SLAD layer effluent are discussed for the two hydraulic loading

rates.

4.1 Characteristics of septic tank effluent

The physical and chemical characteristics o f the septic tank effluent were analyzed

on a periodic basis through the study period and are shown in the Table 4.1. These values

were comparable to the data in the literature (Widrig et al 1996; Viraraghavan 1993) and

previous studies done at University of Regina, Water Resources Laboratory on the same

septic tank (Viraraghavan and Rana 1991).

4.1.1 pH

The pH of the septic tank effluent was in range of 6.9 to 7.9. The detention

available in the septic tank and anaerobic digestion that takes place in the septic tank

brought the mean pH of the effluent near to neutral.

36


Table 4.1. Septic tank effluent characteristics

No. Parameter Range Mean Standard deviation

1. pH 6 — 7.9 7.2 0.7

2. Alkalinity (as CaCO3) 490 - 600 539 25

3. Turbidity (NTU) 208 - 243 228 24

4. Total soluble solids 105 - 186 126 57

5. Total COD 172 - 535 333 84

6. Soluble COD 150 — 400 312 61

7. Total TKN 25 - 37 31 3

8. Total soluble TKN 28 - 29 29 0.7

9. Total Ammonia as N 23 - 29 25 3

10. Chloride 169 - 456 256 203

11. Nitrite as N

12. Nitrate as N 0.1 - 0.8 0.6

13. Sulfate 165 - 276 191 60

14. Phosphate as P 0.7 - 7.9 4.9 2

Note: All parameters except pH, turbidity are represented as mg/L.

37


Table 4.1. Septic tank effluent characteristics

No. Parameter Range Mean Standard deviation

1 . pH 6 .9 -7 .9 7.2 0.7

2 . Alkalinity (as CaC 03) 490 - 600 539 25

oJ. Turbidity (NTU) 208 - 243 228 24

4. Total soluble solids 105 - 186 126 57

5. Total COD 172 - 535 333 84

6 . Soluble COD 1 5 0 -4 0 0 312 61

7. Total TKN 2 5 -3 7 31 3

8 . Total soluble TKN 2 8 -2 9 29 0.7

9. Total Ammonia as N 2 3 -2 9 25 3

1 0 . Chloride 169-456 256 203

1 1 . Nitrite as N - -

1 2 . Nitrate as N 0 . 1 - 0 . 8 0 . 6

13. Sulfate 165 -276 191 60

14. Phosphate as P 0.7 - 7.9 4.9 2

Note: All parameters except pH, turbidity are represented as mg/L.

37


4.1.2 Ammonia, nitrate, nitrite and total Kjeldahl nitrogen

The nitrogen content of STE was predominantly in ammonia form and partial

oxidation of effluent inside the septic tank left behind traces of nitrate and nitrites. At

normal effluent pH of 7.2, the ammonia nitrogen exits as ammonium ion NH4 form

rather than as ammonia NH3- (Lance 1972).

The total kjeldahl nitrogen as a combination of organic and ammonia nitrogen

varied from 32 to 35 mg/L.

4.1.3 COD

The chemical oxygen demand (COD) of the effluent varied between 215 and 432

mg/L, with a mean value of 333 mg/L and the soluble COD varied between 150 and 400

mg/L with a mean value of 312 mg/L.

4.1.4 Phosphates

The total phosphates as phosphorus in the effluent were in the range of 0.7 to 7.9

mg/L with a mean value of 4.9 mg/L. The anaerobic digestion which takes place in the

septic tank converts most of the phosphorus (both organic and condensed form) to

soluble orthophosphate (Sikora and Corey 1976).

4.1.5 Alkalinity

The alkalinity of the effluent varied between 490 and 600 mg/L as CaCO3 with a

mean value of 539 mg/L as CaCO3 with a standard deviation of 25. The presence of

hydroxides, carbonates, and bicarbonates of elements such as calcium, magnesium,

38


4.1.2 Ammonia, nitrate, nitrite and total Kjeldahl nitrogen

The nitrogen content of STE was predominantly in ammonia form and partial

oxidation of effluent inside the septic tank left behind traces of nitrate and nitrites. At

normal effluent pH of 7.2, the ammonia nitrogen exits as ammonium ion NH^form

rather than as ammonia NH 3 _ (Lance 1972).

The total kjeldahl nitrogen as a combination of organic and ammonia nitrogen

varied from 32 to 35 mg/L.

4.1.3 COD

The chemical oxygen demand (COD) of the effluent varied between 215 and 432

mg/L, with a mean value o f 333 mg/L and the soluble COD varied between 150 and 400

mg/L with a mean value o f 312 mg/L.

4.1.4 Phosphates

The total phosphates as phosphorus in the effluent were in the range o f 0.7 to 7.9

mg/L with a mean value o f 4.9 mg/L. The anaerobic digestion which takes place in the

septic tank converts most of the phosphorus (both organic and condensed form) to

soluble orthophosphate (Sikora and Corey 1976).

4.1.5 Alkalinity

The alkalinity of the effluent varied between 490 and 600 mg/L as CaCC>3 with a

mean value of 539 mg/L as CaCC>3 with a standard deviation of 25. The presence of

hydroxides, carbonates, and bicarbonates o f elements such as calcium, magnesium,

38


sodium, potassium, or of ammonia contribute to the alkalinity presence in STE

(Tchobaoglous and Burton 1991).

4.2 Performance of sand filter

The treatment efficiency of the columns observed are reported and discussed in

regard to the various pollution parameters recorded and analyzed. The sand filter

(operated in three columns) took 64 days from start to convert 50 % of the influent

nitrogen present as TKN to oxidized form as nitrate and nitrite nitrogen. This was

understood as a stabilization period for the growth of nitrifiers in the system. Table 4.2

and Figures 4.1 to 4.7 show the behavior of the parameter across the sand filter.

4.2.1 pH

The pH of the effluent from the sand filters was 7.1 ± 3 °C throughout the study.

The shift in loading rate from 4 cm/d to 8.1 cm/d did not influence the pH of the effluent.

4.2.2. Nitrogen removal

Nitrification as a conversion of initial TKN to subsequent nitrate and nitrite

nitrogen was studied as a part of nitrogen removal in sand filter system. The results from

operating sand filter system at loading rates of 4 and 8.1 cm/d have shown that sand filter

could be applied in real life operation in the field with an intermittent loading at 6-hour

intervals. Nitrification of over 60 % was achieved in three sand filter columns operated.

Sand filter studies were done using two hydraulic loading rates of 4 cm/d and 8.1 cm/d.

The sand filter columns took 64 days to achieve a 50 % conversion of initial TKN present

in the influent to subsequent nitrate and nitrite nitrogen.

39


sodium, potassium, or of ammonia contribute to the alkalinity presence in STE

(Tchobaoglous and Burton 1991).

4.2 Performance of sand filter

The treatment efficiency o f the columns observed are reported and discussed in

regard to the various pollution parameters recorded and analyzed. The sand filter

(operated in three columns) took 64 days from start to convert 50 % of the influent

nitrogen present as TKN to oxidized form as nitrate and nitrite nitrogen. This was

understood as a stabilization period for the growth of nitrifiers in the system. Table 4.2

and Figures 4.1 to 4.7 show the behavior o f the parameter across the sand filter.

4.2.1 pH

The pH of the effluent from the sand filters was 7.1 + 3 °C throughout the study.

The shift in loading rate from 4 cm/d to 8.1 cm/d did not influence the pH of the effluent.

4.2.2. Nitrogen removal

Nitrification as a conversion of initial TKN to subsequent nitrate and nitrite

nitrogen was studied as a part o f nitrogen removal in sand filter system. The results from

operating sand filter system at loading rates of 4 and 8.1 cm/d have shown that sand filter

could be applied in real life operation in the field with an intermittent loading at 6-hour

intervals. Nitrification of over 60 % was achieved in three sand filter columns operated.

Sand filter studies were done using two hydraulic loading rates of 4 cm/d and 8.1 cm/d.

The sand filter columns took 64 days to achieve a 50 % conversion o f initial TKN present

in the influent to subsequent nitrate and nitrite nitrogen.

39


Table 4.2 Nitrification percentage across the sand filter

Time Days

Column 1

Nitrification Column 2

Nitrification

Column 3

Nitrification

0 4.8 0.5 5.0 8 35.4 11 22.3 11.3 35.8 16 38.0 20.9 29.1 19 38.2 20.8 29.0 46 40.9 27.3 43.8 54 38.8 26.3 30.9 60 37.4 31.0 32.7 64 50.9 34.9 74 54.0 50.9 60.8 82 56.4 60.1 66.0 89 69.4 83.9 64.4 97 59.6 51.0 66.2 102 57.1 60.0 60.2 110 54.3 67.2 64.4 114 60.4 61.3 69.5 123 70.8 64.0 78.2 131 76.4 56.4 78.8 140 79.6 63.8 80.8 169 55.6 64.4 64.0 181 53.2 54.4 60.8 186 61.5 61.1 65.6 195 68.8 71.3 75.4

Mean 51.5 48.0 54.4 Std. Dev 17.7 22.4 20.6

Note: Loading rate 4 cm/d from 0 to 160 days

Loading rate 8 cm/d from 160 to 195 days

40


Table 4.2 Nitrification percentage across the sand fdter

Column 1 Column 2 Column 3Time Nitrification Nitrification NitrificationDays % % %

0 4.8 0.5 5.08 35.411 22.3 11.3 35.816 38.0 20.9 29.119 38.2 20.8 29.046 40.9 27.3 43.854 38.8 26.3 30.960 37.4 31.0 32.764 50.9 34.974 54.0 50.9 60.882 56.4 60.1 66.089 69.4 83.9 64.497 59.6 51.0 66.2102 57.1 60.0 60.2110 54.3 67.2 64.4114 60.4 61.3 69.5123 70.8 64.0 78.2131 76.4 56.4 78.8140 79.6 63.8 80.8169 55.6 64.4 64.0181 53.2 54.4 60.8186 61.5 61.1 65.6195 68.8 71.3 75.4

Mean 51.5 48.0 54.4Std. Dev 17.7 22.4 20.6



40


Reproduced w

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f the copyright owner.

Further reproduction prohibited w

ithout permission.

40 1

35

30

25 E

E 20 on

z 15

10

5

0

0

TKN —0— NH4-N

4 cm/d 8.1 cm/d

ti

20 40 60 80 100 120 140 160 180 200

Time (days)

Figure 4.1. Septic tank effluent nitrogen composition

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Figure 4.1. Septic tank effluent nitrogen composition

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)

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Column 2

35

30

25

20

15

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- - - -In NH3-N A E-NO2-N

E-NO3-N

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0 50 100 Time (days)

150 200

100

Figure 4.2. Oxidation of influent NI-14-N to NO2-N and NO3-N in sand filters

150 200

Reproduced

with perm

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copyright ow

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reproduction prohibited

without

permission.

Column 1 Column 2

to

♦ - - In NH3-N -A— E-N02-N

•E-N03-N

4 cm/d

».......3 25OX 5 20

0 too 150 20050Time (days)

Column 3

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020015050 1000

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15

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00 50 100 150 200

Time (days)

Figure 4.2. Oxidation o f influent NH 4 -N to NO 2 -N and NO 3 -N in sand filters

Reproduced w

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Column 1 35

30

a 25 -3,1)

20

u 15

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Column 2

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- - 1- - - In NH4-N Nitrogen

8.1 1 +c

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50 100 150 200 Time (days)

150

Figure 4.3. Mass balance (influent NH4-N Vs effluent total nitrogen) of nitrogen in sand filter

200

Reproduced

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without

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Column 1

-&■CJ

,8.1cm/i4 cm/d

Z 10

0 100 150 20050

Column 2 35

In NH4-N — ■— E- Nitrogen

Time (days)

Column 3

30

25

20

15

10

5

0

4 cm/d-

50 100

4 cm/d

Z 10

0 50 100 150 200

150 200

Time (days)

Figure 4.3. Mass balance (influent NEU'-N Vs effluent total nitrogen) of nitrogen in sand filter

Reproduced w

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Column 1 35

30

2 25 co E 20

0 15

2 to

5

0

'44 4 cm/d •44 8.1

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Column 3 35

30

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Column 2 35

30

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••• ► • • •

0

100

50 100 150 200

Time (days)

150

Figure 4.4. Comparison of the sand filter effluent NH4-N to NO3-N and NO2-N

200

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without

permission.

-c-

Column 1 35

30

Column 2 - - In NH3-N • E- Nitrogen-*8.1 J4 cm/d w

cm/d !

Z 10

100 2000 50 150

354 cm/d cm/d30

25

20

15

10

5

0200100 1500 50

Time (days)

Column 335

4 cm/d30

25w>20

a 15

z 1 0

50 100 Time (days)

150 200

Figure 4.4. Comparison o f the sand filter effluent NH 4 -N to NO 3 -N and NO 2-N

Reproduced w

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70

60

50

s 40

0 C-) 30

20

10

CO 1- 1 COI - 2 -4-- Col - 3

4 cm/d 8.1 cm/d

1

0 20 40 60 80 100 120 140 160 180 200 Time (days)

Figure 4.5. Sand filter effluent COD comparison

0 V1I©U+oU+

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Figure 4.5. Sand filter effluent COD comparison

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CO

D R

emoval

°A

100

95

90

85

80

75

70

65

60

0

—+— Col - 1 —II— Col - 2 —A-- Col - 3

20 40 60 80 100 120 140 160 180 200

Time (days)

Figure 4.6. Sand filter effluent COD removal efficiency

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00

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Figure 4.6. Sand filter effluent COD removal efficiency

Reproduced w

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ithout permission.

700

600

500 M

400

t300

:1 200

100

0

• - + - - Influent Col - 1 Col - 2 Col - 3

cm/d 4 8.1 cm/d

•

• . • •-

,

•

„- • .

••.- - . . . . ... . . . . - ..

... .

0 20 40 60 80 100

Time (days)

120 140

Figure 4.7. Sand filter effluent alkalinity comparison

160 180 200

■ Influent — ■— Col - 1 — *— Col - 2 — • — Col -73

00

O

♦

"O00

oo

oo

ooo

oo

(£03*0 SB 'T/S™)47

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Figure 4.7. Sand filter effluent alkalinity comparison

The increase in nitrification efficiency was gradual in the sand filters through the entire

period of study. Nitrifiers are slow growing autotrophic organisms; initially competition

between autotrophic and heterotrophic organisms in the upper surface of the sand filter

would be the reason for the delay in conversion of the initial TKN to nitrites and nitrates.

Pell and Nyberg (1989b) reported that in a sand filter system operated at 6.7 cm/d

heterotrophic aerobic microorganisms were established before ammonium and nitrite

oxidizers, which took 75 to 95 days to equal the number of hetrotrophs. A decrease in the

nitrification was observed when hydraulic loading rate was increased to 8.1 cm/d from

4.0 cm/d, but was above 50 %. All three columns, which were set up identically, showed

a maximum nitrification of 80, 83, and 80 % in columns 1,2 and 3 respectively. On a

comparison of mass balance of nitrogen in the influent to effluent from of the sand filters

(Figure 4.2), only once in the entire period of study the effluent total nitrogen equaled the

influent TKN. During the study period of 200 days, approximately 70 % of influent

nitrogen as TKN was converted to nitrate and nitrite nitrogen with a complete oxidation

of organic nitrogen. The remaining 30% was accounted as loss of nitrogen which could

have volatilized or denitrified in the micro-anaerobic systems present in the sand filter; a

15 to 20 % loss of nitrogen in a sand filter system used in nitrification of on-site effluent

was also reported by Tchobanoglous and Burton (1991). According to Lance (1972) 10-

15 % of the nitrogen are lost due to volatilization when STE is applied to the soil. An

initial nitrite buildup was seen across the sand filter columns but decreased when nitrate

concentration in the effluent started to increase. Oxidation of ammonia nitrogen to nitrate

and nitrite nitrogen could take place by chemical or biological processes. The red fl int

sand contains no chemicals in it so; the adsorption of NH4-N could not have been

48


The increase in nitrification efficiency was gradual in the sand filters through the entire

period of study. Nitrifiers are slow growing autotrophic organisms; initially competition

between autotrophic and heterotrophic organisms in the upper surface of the sand filter

would be the reason for the delay in conversion of the initial TKN to nitrites and nitrates.

Pell and Nyberg (1989b) reported that in a sand filter system operated at 6.7 cm/d

heterotrophic aerobic microorganisms were established before ammonium and nitrite

oxidizers, which took 75 to 95 days to equal the number of hetrotrophs. A decrease in the

nitrification was observed when hydraulic loading rate was increased to 8.1 cm/d from

4.0 cm/d, but was above 50 %. All three columns, which were set up identically, showed

a maximum nitrification of 80, 83, and 80 % in columns 1,2 and 3 respectively. On a

comparison of mass balance o f nitrogen in the influent to effluent from of the sand filters

(Figure 4.2), only once in the entire period of study the effluent total nitrogen equaled the

influent TKN. During the study period of 200 days, approximately 70 % of influent

nitrogen as TKN was converted to nitrate and nitrite nitrogen with a complete oxidation

of organic nitrogen. The remaining 30% was accounted as loss o f nitrogen which could

have volatilized or denitrified in the micro-anaerobic systems present in the sand filter; a

15 to 20 % loss of nitrogen in a sand filter system used in nitrification of on-site effluent

was also reported by Tchobanoglous and Burton (1991). According to Lance (1972) 10-

15 % of the nitrogen are lost due to volatilization when STE is applied to the soil. An

initial nitrite buildup was seen across the sand filter columns but decreased when nitrate

concentration in the effluent started to increase. Oxidation of ammonia nitrogen to nitrate

and nitrite nitrogen could take place by chemical or biological processes. The red flint

sand contains no chemicals in it so; the adsorption of NH4-N could not have been

48


possible. The loss of nitrogen by denitrification in anaerobic microsites present in the

sand fi lter is possible; Pell and Nyberg (1989b) reported a formation of significant

population of denitrifiers in the sand filter, which at times was reported to be more than

aerobic bacteria present. U.S.EPA (1993) reported that growth kinetics of Nitrosomonas

and Nitrobacter are dependent on concentration of ammonium and nitrite respectively,

and under steady state condition the maximum growth rate of Nitrobacter is higher than

the Nitrosomonas. During the initial period of the study, it was found that sand filter

effluent had nitrite concentration higher than MAC of 1 mg/L. The reason behind the

initial nitrite nitrogen build up in the effluent of the sand filter could be due to the

deficiency of dissolved oxygen in the lower part of the sand filter. The oxygen deficiency

created by oxidation of organic matter and uptake by the ammonium oxidizers such as

Nitrosomonas, could have led to insufficient nitrite oxidizers in the system. The delay in

the growth of nitrite oxidizers was also reported in the study conducted by Stout et al.

(1984) on natural silt loam; they found that ammonium oxidizers were 10 times more

abundant than the nitrite oxidizers. The sand filter system took 70 days to produce an

effluent less 2 mg/L of nitrite nitrogen with occasional increase in concentration; this

would be rationalized, as time required for the development of hetrotrophs and

ammonium oxidizers in the sand filter. Ammonium present in the effluent gradually

decreased with time but a steep decrease was seen during the period of 60 to 80 days of

operation (Figure 4.3). The effluent contained less than 2 mg/L as ammonia nitrogen with

no organic nitrogen present. The decrease in the ammonia nitrogen and increase in nitrate

and nitrite nitrogen in the effluent of sand filter shows a clear indication of nitrification

process under going in the sand filter. Increasing the hydraulic loading rate to 8.1 cm/d at

49


possible. The loss of nitrogen by denitrification in anaerobic microsites present in the

sand filter is possible; Pell and Nyberg (1989b) reported a formation of significant

population of denitrifiers in the sand filter, which at times was reported to be more than

aerobic bacteria present. U.S.EPA (1993) reported that growth kinetics of Nitrosomonas

and Nitrobacter are dependent on concentration o f ammonium and nitrite respectively,

and under steady state condition the maximum growth rate of Nitrobacter is higher than

the Nitrosomonas. During the initial period o f the study, it was found that sand filter

effluent had nitrite concentration higher than MAC of 1 mg/L. The reason behind the

initial nitrite nitrogen build up in the effluent o f the sand filter could be due to the

deficiency of dissolved oxygen in the lower part o f the sand filter. The oxygen deficiency

created by oxidation of organic matter and uptake by the ammonium oxidizers such as

Nitrosomonas, could have led to insufficient nitrite oxidizers in the system. The delay in

the growth of nitrite oxidizers was also reported in the study conducted by Stout et al.

(1984) on natural silt loam; they found that ammonium oxidizers were 10 times more

abundant than the nitrite oxidizers. The sand filter system took 70 days to produce an

effluent less 2 mg/L of nitrite nitrogen with occasional increase in concentration; this

would be rationalized, as time required for the development of hetrotrophs and

ammonium oxidizers in the sand filter. Ammonium present in the effluent gradually

decreased with time but a steep decrease was seen during the period o f 60 to 80 days of

operation (Figure 4.3). The effluent contained less than 2 mg/L as ammonia nitrogen with

no organic nitrogen present. The decrease in the ammonia nitrogen and increase in nitrate

and nitrite nitrogen in the effluent of sand filter shows a clear indication of nitrification

process under going in the sand filter. Increasing the hydraulic loading rate to 8.1 cm/d at

49


the end of 160 days of operation decreased the nitrification percentage (Figure 4.1). The

sand fi lters took 15 days to acclimatize itself to the loading rate of 8.1 cm/d to provide

greater than 50 % nitrification of initial nitrogen (Table 4.1). At the end of 27 day run of

8.1 cm/d all three sand filters reached 70% removal of ammonia nitrogen with the

effluent containing mean nitrate, nitrite and ammonia as nitrogen of 15, 1, and 1.5 mg/L,

respectively.

The ratio of COD/TKN plays a significant role in the process of nitrification. The

oxygen demand created by the chemicals and oxidizable organics inhibit the oxygen

transfer to the nitrifiers. The COD/TKN of the septic tank effluent ranged from 6.5 to

19.1 with a mean of 7.2. Eckenfelder (1980) reported that a COD/TKN ratio of less than

5 would be optimum for the nitrification process to proceed and a ratio above 5 would

inhibit the growth of nitrifiers. Rittmann and McCarty (2001) reported that for a

successful nitrification process to operate the ratio of BOD/TKN should be between 5

and 10, where nitrifiers constitute 20% of the active biomass and if the ratio is more than

25, little or no reduced nitrogen would be available for nitrification. They further reported

that a higher BOD/TKN ratio would tend to increase the competition between hetrotrophs

and autotrophs incurring greater resistance for the nitrifier substrates particularly NH4+

and oxygen.

50


the end of 160 days of operation decreased the nitrification percentage (Figure 4.1). The

sand filters took 15 days to acclimatize itself to the loading rate of 8.1 cm/d to provide

greater than 50 % nitrification of initial nitrogen (Table 4.1). At the end of 27 day run of

8.1 cm/d all three sand filters reached 70% removal of ammonia nitrogen with the

effluent containing mean nitrate, nitrite and ammonia as nitrogen of 15, 1, and 1.5 mg/L,

respectively.

The ratio of COD/TKN plays a significant role in the process of nitrification. The

oxygen demand created by the chemicals and oxidizable organics inhibit the oxygen

transfer to the nitrifiers. The COD/TKN of the septic tank effluent ranged from 6.5 to

19.1 with a mean of 7.2. Eckenfelder (1980) reported that a COD/TKN ratio of less than

5 would be optimum for the nitrification process to proceed and a ratio above 5 would

inhibit the growth of nitrifiers. Rittmann and McCarty (2001) reported that for a

successful nitrification process to operate the ratio of BOD/TKN should be between 5

and 10, where nitrifiers constitute 20% of the active biomass and if the ratio is more than

25, little or no reduced nitrogen would be available for nitrification. They further reported

that a higher BOD/TKN ratio would tend to increase the competition between hetrotrophs

and autotrophs incurring greater resistance for the nitrifier substrates particularly NFLf1"

and oxygen.

50


4.2.2 COD

A decrease in COD was recorded in all three-sand filter columns of identical

design parameters. The COD reduction was consistent through the period of study and

was in accordance to the sand filter effluent COD data as observed in literature (Widrig et

al. 1996; Pell and Nyberg 1989a; Brandes et al. 1974). A maximum removal of 95 % was

achieved in all the three columns.

The sand filter columns reached over 90 % removal of COD within two weeks of

operation and remained consistent through the entire period of study. From Figure 4.5 it

can be observed that the COD decreased from a mean initial value of 333 mg/L to 33

mg/L at 160 days of operation at a hydraulic loading rate of 4.1 cm/d. The reduction in

the COD was immediate and concentration in the effluent remained stable through the

entire period except on when loading rate was increased from 4 cm/d to 8.1 cm/d. Pell

and Nyberg (1989a) reported that major reduction of COD took place in upper 15 cm of

the sand filter where the amount of aerobic microorganisms are at, the maximum. An

increase in hydraulic loading rate to 8.1 cm/d decreased the COD removal percentage but

over 80 % removal was achieved. The initial days of operation upon the increase in

loading rate, caused an increase in the COD value to 50 mg/L from the sand filter

effluent, but COD values were below 40 mg/L after 16 days of operation at the same

loading rate. Pell and Nyberg (1989a) reported that the fluctuations in COD in effluent

from the columns indicate a lack of stability in the decomposition process. Thus, the

increase in COD could be that some of the microorganisms were flushed out or a

development of anaerobic condition in the system. The time required bringing back to

original removal percentage or acclimatization of the heterotrophic organisms in the sand

51


4.2.2 COD

A decrease in COD was recorded in all three-sand filter columns of identical

design parameters. The COD reduction was consistent through the period of study and

was in accordance to the sand filter effluent COD data as observed in literature (Widrig et

al. 1996; Pell and Nyberg 1989a; Brandes et al. 1974). A maximum removal of 95 % was

achieved in all the three columns.

The sand filter columns reached over 90 % removal of COD within two weeks of

operation and remained consistent through the entire period of study. From Figure 4.5 it

can be observed that the COD decreased from a mean initial value of 333 mg/L to 33

mg/L at 160 days of operation at a hydraulic loading rate of 4.1 cm/d. The reduction in

the COD was immediate and concentration in the effluent remained stable through the

entire period except on when loading rate was increased from 4 cm/d to 8.1 cm/d. Pell

and Nyberg (1989a) reported that major reduction o f COD took place in upper 15 cm o f

the sand filter where the amount of aerobic microorganisms are at. the maximum. An

increase in hydraulic loading rate to 8.1 cm/d decreased the COD removal percentage but

over 80 % removal was achieved. The initial days o f operation upon the increase in

loading rate, caused an increase in the COD value to 50 mg/L from the sand filter

effluent, but COD values were below 40 mg/L after 16 days of operation at the same

loading rate. Pell and Nyberg (1989a) reported that the fluctuations in COD in effluent

from the columns indicate a lack of stability in the decomposition process. Thus, the

increase in COD could be that some of the microorganisms were flushed out or a

development of anaerobic condition in the system. The time required bringing back to

original removal percentage or acclimatization of the heterotrophic organisms in the sand

51


fi lter to higher loading rate and stagnation of the STE in the sand fi lter was less than 21

days.

The sand filter columns achieved a mean COD removal percentage over 80 with

the lowest in column 3 of 74 % and the highest of 95 % recorded in all three columns

(Figure 4.6). The sand filter columns were able to produce an effluent with a mean COD

of less than 60 mg/L and with more consistency with a standard deviation of less than 20

mg/L. These results agree with data from similar investigations. Magdoff et al. (1974)

reported over 90% removal of COD in sand columns operated under aerobic conditions;

40% removal was achieved when finer sand was used. The decrease in the COD removal

percentage was reported to be caused by ponding and anaerobic conditions. Magdoff and

Keeney (1975) reported that a sand filter system when loaded with 8 cm of septic tank

effluent as one daily dose or as a 2 cm load every 6 h, a 96% reduction of COD could be

achieved.

4.2.3 Alkalinity

Alkalinity data obtained from the effluent after a single pass through the sand

filter of the three columns were almost similar to each other. The sand filter effluents

showed a 10 % decrease in alkalinity levels. Wilhelm et al. (1996) reported that, aerobic

oxidation of the nitrogen and sulfur (equation 4.1, 4.2) would release hydrogen ions

thereby decreasing the pH of the effluent. The denitrification in an anaerobic

environment would increase the pH of the effluent as the hydrogen ions, would be

consumed by the carbon present.

N1/4 '+- 2 0, ---> NO3+ 2 H+ +2 H,0 (4.1)

2 0 2 + H,S (or organic S) ---> so/ + 2 fr (4.2)

52


filter to higher loading rate and stagnation of the STE in the sand filter was less than 21

days.

The sand filter columns achieved a mean COD removal percentage over 80 with

the lowest in column 3 of 74 % and the highest of 95 % recorded in all three columns

(Figure 4.6). The sand filter columns were able to produce an effluent with a mean COD

of less than 60 mg/L and with more consistency with a standard deviation of less than 20

mg/L. These results agree with data from similar investigations. Magdoff et al. (1974)

reported over 90% removal of COD in sand columns operated under aerobic conditions;

40% removal was achieved when finer sand was used. The decrease in the COD removal

percentage was reported to be caused by ponding and anaerobic conditions. Magdoff and

Keeney (1975) reported that a sand filter system when loaded with 8 cm of septic tank

effluent as one daily dose or as a 2 cm load every 6 h, a 96% reduction of COD could be

achieved.

4.2.3 Alkalinity

Alkalinity data obtained from the effluent after a single pass through the sand

filter o f the three columns were almost similar to each other. The sand filter effluents

showed a 10 % decrease in alkalinity levels. Wilhelm et al. (1996) reported that, aerobic

oxidation of the nitrogen and sulfur (equation 4.1, 4.2) would release hydrogen ions

thereby decreasing the pH of the effluent. The denitrification in an anaerobic

environment would increase the pH of the effluent as the hydrogen ions, would be

consumed by the carbon present.

N H /+ 2 0 2 NO}+ 2 f t +2 H20 (4.1)

2 O? + H?S (or organic S) ---> S O /' + 2 I f (4.2)

52


5 CH,0 + 4 NO3- + 4 H4 2N? + 5 CO? + 7 H20 (4.3)

It is estimated that a theoretical destruction of 7.1 mg of alkalinity as CaCO3 per

mg of ammonia nitrogen oxidized would occur (U.S.EPA 1993). An initial removal of

alkalinity from mean value of 539 mg/L across the sand filters to 340 mg/L as CaCO3

was achieved in the first eight days of operation and a consistent removal of 20% was

achieved later.

A complete oxidation of the total ammonia nitrogen of mean value 25 mg/L

present in the effluent would reduce the alkalinity to 178 mg/L as CaCO3 from the sand

filter effluent. The difference between the initial and final sand filter alkalinity was 80

mg/L as CaCO3, which is a 14% decrease in alkalinity. To record a 14% decrease of the

alkalinity the NH4+-N needed would be 12 mg/L, which is 50% of the original NH4+-N

present. The theoretical consideration and the results obtained did not agree considering a

maximum of 20% volatilization but the remaining 30% of NH4+-N could not be

accounted. This was also observed in the study done by Nasr (1983)

An increase in alkalinity removal percentage to 20 was seen at the end of the

study period of 4.0 cm/d at 148 days of operation and 8.1 cm/d at 41 days of operation,

(Table 4.3). The pH of the sand filter effluent was nearly neutral through the entire period

of study.

4.2.4 Phosphate

The effluent from the sand filters recorded a low phosphorus content, which

accounts for a high removal of phosphorus in the sand filters. The phosphorus present in

the STE is inorganic, and is predominantly in the orthophosphate form.

53


5 CH20 + 4 NO 3 + 4 I f ' ---» 2Ni + 5 C 0 2 + 7 H?0 (4.3)

It is estimated that a theoretical destruction of 7.1 mg of alkalinity as CaCCfi per

mg of ammonia nitrogen oxidized would occur (U.S.EPA 1993). An initial removal of

alkalinity from mean value of 539 mg/L across the sand filters to 340 mg/L as CaCCfi

was achieved in the first eight days of operation and a consistent removal of 20% was

achieved later.

A complete oxidation of the total ammonia nitrogen of mean value 25 mg/L

present in the effluent would reduce the alkalinity to 178 mg/L as CaCCfi from the sand

filter effluent. The difference between the initial and final sand filter alkalinity was 80

mg/L as CaCCL, which is a 14% decrease in alkalinity. To record a 14% decrease o f the

alkalinity the N H /-N needed would be 12 mg/L, which is 50% of the original NH 4 +-N

present. The theoretical consideration and the results obtained did not agree considering a

maximum of 20% volatilization but the remaining 30% of N H /-N could not be

accounted. This was also observed in the study done by Nasr (1983)

An increase in alkalinity removal percentage to 20 was seen at the end of the

study period of 4.0 cm/d at 148 days of operation and 8.1 cm/d at 41 days o f operation,

(Table 4.3). The pH of the sand filter effluent was nearly neutral through the entire period

of study.

4.2.4 Phosphate

The effluent from the sand filters recorded a low phosphorus content, which

accounts for a high removal of phosphorus in the sand filters. The phosphorus present in

the STE is inorganic, and is predominantly in the orthophosphate form.

%


Table 4.3. Alkalinity removal efficiency across sand filter

Column 1 Column 2 Column 3

Time

Days

Removal efficiency Removal efficiency Removal efficiency OA

0

8 44 35 31

22 21 13 14

36 18 14 16

50 -15 -10 -12

64 3 1 10

78 11 6 12

92 23 23 19

106 21 13 14

120 17 16 13

134 14 14 10

148 21 18 11

162 6 3 8

176 14 9 16

190 17 13 13

197 16 17 22

Mean 13.2 10.5 14.8

STD.Dev 5.0 6.1 -6.1



54


Table 4.3. Alkalinity removal efficiency across sand filter

Column 1 Column 2 Column 3Time Removal efficiency Removal efficiency Removal efficiencyDays % % %

08 44 35 31

22 21 13 1436 18 14 1650 -15 -10 -1264 1 1078 11 6 1292 23 23 19106 21 13 14120 17 16 13134 14 14 10148 21 18 11162 6 3 8176 14 9 16190 17 13 13197 16 17 22

Mean 13.2 10.5 14.8STD.Dev 5.0 6.1 6.1




The inorganic phosphate present as polyphosphate and organic phosphate is eventually

converted to orthophosphates within a few centimeters of the soil infiltrative surface (Otis

et al. 1975). The p1-1 and composition of the soil govern the retention of phosphate. Sikora

and Corey (1976) reported that a decrease in pH of the soil in the presence of iron and

aluminum would retain the phosphate to form their respective phosphate compounds,

while the presence of calcium helps in retaining only when the pH ranged from neutral to

strongly alkaline. Phosphate adsorption on sand particles was reported by Pell and

Nyberg (1989a) and Magdoff et al. (1974), the researchers reported that adsorption would

occur through the entire sand filter column with over 80% reduction occurring in the

upper aerobic zone of 3 cm of the sand filter. The red flint sand has less or no aluminum,

iron and calcium present in it, chemisorption of phosphate on the particles of the sand is

not possible and the pH obtained from the effluent of the sand filter ranged between 6.9

and 7.9, which was near neutral. The behavioral pattern of phosphate in sand filter was

similar in all columns. The phosphate as phosphorus in STE fluctuated from 1 to 8 mg/L;

these fluctuations had less effect on the effluent. During the period between 65 and 110

days from the start of operation the STE phosphate concentration fluctuated between 2

and 8 mg/L, while the sand filter effluent had concentration increased from less than 1 to

2.8 mg/L. The increase in sand filter effluent phosphate concentration coincided with the

increase in influent concentration, thus it can be concluded that saturation of the filter had

not occurred as some of the researchers reported phosphate saturation of the filter would

occur soon (Pell and Nyberg 1989a; Magdoff et al. 1974). Sand filter always produced an

effluent of less than 3 mg/L phosphate as P, except when the hydraulic loading rate was

increased to 8.0 cm/d. From Figure 4.8, it was observed, on changing the hydraulic

55


The inorganic phosphate present as polyphosphate and organic phosphate is eventually

converted to orthophosphates within a few centimeters of the soil infiltrative surface (Otis

et al. 1975). The pH and composition of the soil govern the retention of phosphate. Sikora

and Corey (1976) reported that a decrease in pH of the soil in the presence of iron and

aluminum would retain the phosphate to form their respective phosphate compounds,

while the presence of calcium helps in retaining only when the pH ranged from neutral to

strongly alkaline. Phosphate adsorption on sand particles was reported by Pell and

Nyberg (1989a) and Magdoff et al. (1974), the researchers reported that adsorption would

occur through the entire sand filter column with over 80% reduction occurring in the

upper aerobic zone of 3 cm of the sand filter. The red flint sand has less or no aluminum,

iron and calcium present in it, chemisorption of phosphate on the particles of the sand is

not possible and the pH obtained from the effluent of the sand filter ranged between 6.9

and 7.9, which was near neutral. The behavioral pattern of phosphate in sand filter was

similar in all columns. The phosphate as phosphorus in STE fluctuated from 1 to 8 mg/L;

these fluctuations had less effect on the effluent. During the period between 65 and 110

days from the start of operation the STE phosphate concentration fluctuated between 2

and 8 mg/L, while the sand filter effluent had concentration increased from less than 1 to

2.8 mg/L. The increase in sand filter effluent phosphate concentration coincided with the

increase in influent concentration, thus it can be concluded that saturation of the filter had

not occurred as some of the researchers reported phosphate saturation of the filter would

occur soon (Pell and Nyberg 1989a; Magdoff et al. 1974). Sand filter always produced an

effluent of less than 3 mg/L phosphate as P, except when the hydraulic loading rate was

increased to 8.0 cm/d. From Figure 4.8, it was observed, on changing the hydraulic

55


Reproduced w

ith permission o


Furth


ithout perm

ission.

9

8

7

6 bn

ai 5 A

2 4

© 3

2

1

0

- - - In PO4 Col 1 Col 2 —4-- Col 3

4 cm/d 8.1 cm/d ---. ►

0',

, _... .

. ,

'•

t f -•• • .. . , '

, .

, . A, ..„ . i,A, v ....

A . r-.._...._,,_, ...,

0 20 40 60 80 100

Time (days)

Figure 4.8. Phosphate removal in sand filter

120 140 160 180 200

0000

<N©Ui©UrrOOhCl-H♦

00

o(N

00

o('T

/Sul) j sb ojeq

dsoj

Reproduced w


ner. F


ission.

Figure 4.8. Phosphate removal in sand filter

loading rate to 8.0 cm/d from 4.1 cm/d, phosphate concentration in the effluent increased,

flushing of the retained phosphate in the sand filter could be a reason. Flocculation or

coagulation inside the sand particles or retention in the biological mat could be the reason

for the decrease in phosphate from the sand filter effluent.

4.2.5 Dissolved oxygen

The dissolved oxygen decreased along the height of the reactor, indicating DO

consumption and COD removal and nitrification. The dissolved oxygen at the end of sand

filters ranged between 1 and 2 mg/L, thus the upper part SLAD systems are in an anoxic

state. Justin and Kelly (1978) reported that dissolved oxygen higher than 4 mg/L will

inhibit the SLAD process.

4.2.6 Crust formation

At the end of the complete experimental run for a total of 200 days, sand filter and

SLAD layer were carefully taken out and examined for physical changes in the layers.

Biological mat had formed at the top of the intermittent sand filters for a depth of 2.5, 2.6

and 2.6 cm in columns 1, 2 and 3, respectively. Magdoff et al. (1974) reported that crust

formation at the top of sand filter is an accumulation of decomposed polysaccharides

products from the anaerobic action from the septic tank. These products clog the soil

pores. The crust could have been the reason behind retaining the phosphate from STE and

in filtering out the solids.

57


loading rate to 8.0 cm/d from 4.1 cm/d, phosphate concentration in the effluent increased,

flushing of the retained phosphate in the sand filter could be a reason. Flocculation or

coagulation inside the sand particles or retention in the biological mat could be the reason

for the decrease in phosphate from the sand filter effluent.

4.2.5 Dissolved oxygen

The dissolved oxygen decreased along the height of the reactor, indicating DO

consumption and COD removal and nitrification. The dissolved oxygen at the end of sand

filters ranged between 1 and 2 mg/L, thus the upper part SLAD systems are in an anoxic

state. Justin and Kelly (1978) reported that dissolved oxygen higher than 4 mg/L will

inhibit the SLAD process.

4.2.6 Crust formation

At the end of the complete experimental run for a total o f 200 days, sand filter and

SLAD layer were carefully taken out and examined for physical changes in the layers.

Biological mat had formed at the top o f the intermittent sand filters for a depth of 2.5, 2.6

and 2.6 cm in columns 1, 2 and 3, respectively. Magdoff et al. (1974) reported that crust

formation at the top of sand filter is an accumulation of decomposed polysaccharides

products from the anaerobic action from the septic tank. These products clog the soil

pores. The crust could have been the reason behind retaining the phosphate from STE and

in filtering out the solids.

57


4.3 Treatment efficiency of SLAD layer

4.3.1 pH and alkalinity

The p1-1 of the SLAD column effluent was stable through the study ranging from

6.2 to 7.6. Other researchers have showed a similar reading with a stable p1-1 environment

in the SLAD column such as 6.4 to 7.6 (Zhang and Shan 1999), and 6.8 to 7.1 (Koening

and Liu 1996). The sulfur oxidizing bacteria, Thiobacillus denitriflcans present in the

SLAD layer reduces the nitrate to nitrogen gas and oxidizes sulfur to sulfates with a net

release of hydrogen ions, which decreases the pH to acidic level. The limestone present in

the SLAD layer acts as a pH neutralizer by reducing the sulfuric acid to produce

alkalinity as bicarbonates in the effluent and a provider of inorganic carbon source for the

growth of autotrophic bacteria (Zhang and Shan 1999; Kanter et al. 1998). According to

equation 4.4 and 4.5, oxidation of sulfur to sulfate causes a subsequent evolution of

hydrogen ions, which decrease the pH with the release of sulfuric acid. The sulfuric acid

produced reacts with the limestone, which contributes to the alkalinity (Kanter et al.

1998).

55 S + 20 CO? + 50 NO3- + 38 H?0 + 4 NH4+ -4

25 N7 + 4 C3117NO2 + 55 SO/ + 64 H+ (4.4)

S° + ff,0 + 1.5 0? 4 2 S042- + 211+ (4.5)

The reduction of hydrogen ions by limestone (CaCO3 ) releases bicarbonate ions

in the effluent. The possible reasons for the reduction of pH and utilization of CaCO3 can

be explained by the equations below,

58


4.3 Treatm ent efficiency of SLAD layer

4.3.1 pH and alkalinity

The pH of the SLAD column effluent was stable through the study ranging from

6.2 to 7.6. Other researchers have showed a similar reading with a stable pH environment

in the SLAD column such as 6.4 to 7.6 (Zhang and Shan 1999), and 6.8 to 7.1 (Koening

and Liu 1996). The sulfur oxidizing bacteria, Thiobacillus denitrificans present in the

SLAD layer reduces the nitrate to nitrogen gas and oxidizes sulfur to sulfates with a net

release o f hydrogen ions, which decreases the pH to acidic level. The limestone present in

the SLAD layer acts as a pH neutralizer by reducing the sulfuric acid to produce

alkalinity as bicarbonates in the effluent and a provider of inorganic carbon source for the

growth o f autotrophic bacteria (Zhang and Shan 1999; Kanter et al. 1998). According to

equation 4.4 and 4.5, oxidation of sulfur to sulfate causes a subsequent evolution of

hydrogen ions, which decrease the pH with the release of sulfuric acid. The sulfuric acid

produced reacts with the limestone, which contributes to the alkalinity (Kanter et al.

1998).

55 S + 20 CO2 + 50 N O i + 38 H20 + 4 N H / -»

25 N2 + 4 C5H 7N 0 2 + 55 S O / + 64 i t (4.4)

^ + H jO + 1.5 O: -> 2 S O /- + 2H* (4.5)

The reduction of hydrogen ions by limestone (CaCCL) releases bicarbonate ions

in the effluent. The possible reasons for the reduction of pH and utilization of C aC 03 can

be explained by the equations below,

58


CaCO3 + f-120 4 Ca2+ + HCO3- + Off (4.6)

CaCO3 + H2CO3- ---> Ca2+ + 211CO3- (4.7)

CaCO3 + H2O 4 Ca2+ +HCO3 + Off (4.8)

The equation proposed by Batchelor and Lawrence (1978) for possible reduction

of nitrate using sulfur oxidizing bacteria Thiobacillus denitrificans would produce 7.5 mg

of sulfate for every one mg of nitrate nitrogen reduced.

According to Zhang and Shan (1999) equation 4.8 is a more possible mechanism

of reduction to limestone in the SLAD layer, while equation 4.6 requires a pH of less than

3 and equation 4.7 would not occur with the partial pressure of carbon dioxide PCO2, of

less than 0.03 atm or when pH of the effluent is between 6 and 7. From equation, 4.8 and

4.6 the ratio of alkalinity produced to the nitrogen removal was 4.62, which is close to

those - 4.46 (Zhang and Shan 1999), 4.19 (Koenig and Liu 1996), and 4.39 (Hashimoto et

al. 1987). During the initial phase of the study, total alkalinity and phenolphthalein

alkalinity were recorded. The phenolphthalein alkalinity (representing the carbonates)

gradually decreased over a period of time and was not observed in later stages of the

study. Total alkalinity data were used in comparison and plotting profiles. Alkalinity

from sand filter effluent at 300 to 446 mg/L as CaCO3, increased to 511 to 939 mg/L as

CaCO3 in the effluent of the SLAD layer during the first 22 days of operation (Figures

4.9, 4.10, 4.11). The increase in alkalinity was almost twice of the initial SFE alkalinity

and was comparable to STE alkalinity. The SLAD effluent alkalinity gradually decreased

from 64th day onwards to produce an effluent alkalinity in the range of 520 to 600 mg/L

of CaCO3, which was an increase of 10 to 40 % from the SFE alkalinity. On comparison

of columns 1, 2 and 3 (Tables 4.4 and 4.5) it was observed that a slight fluctuation in

59


CaCOj + 11,0 O Ca2+ + HCOs + O ff (4.6)

CaCOi + H2C O i -> Ca2+ + 2 H C 0 f (4.7)

CaCOj + H20 -> Ca2+ +HCO3 ' + O ff (4.8)

The equation proposed by Batchelor and Lawrence (1978) for possible reduction

of nitrate using sulfur oxidizing bacteria Thiobacillus denitrificans would produce 7.5 mg

of sulfate for every one mg of nitrate nitrogen reduced.

According to Zhang and Shan (1999) equation 4.8 is a more possible mechanism

of reduction to limestone in the SLAD layer, while equation 4.6 requires a pH of less than

3 and equation 4.7 would not occur with the partial pressure of carbon dioxide Pco2 , of

less than 0.03 atm or when pH o f the effluent is between 6 and 7. From equation, 4.8 and

4.6 the ratio of alkalinity produced to the nitrogen removal was 4.62, which is close to

those - 4.46 (Zhang and Shan 1999), 4.19 (Koenig and Liu 1996), and 4.39 (Hashimoto et

al. 1987). During the initial phase o f the study, total alkalinity and phenolphthalein

alkalinity were recorded. The phenolphthalein alkalinity (representing the carbonates)

gradually decreased over a period o f time and was not observed in later stages o f the

study. Total alkalinity data were used in comparison and plotting profiles. Alkalinity

from sand filter effluent at 300 to 446 mg/L as C aC 03, increased to 511 to 939 mg/L as

CaC03 in the effluent o f the SLAD layer during the first 22 days of operation (Figures

4.9, 4.10, 4.11). The increase in alkalinity was almost twice of the initial SFE alkalinity

and was comparable to STE alkalinity. The SLAD effluent alkalinity gradually decreased

from 64th day onwards to produce an effluent alkalinity in the range of 520 to 600 mg/L

of CaC03j which was an increase o f 10 to 40 % from the SFE alkalinity. On comparison

of columns 1, 2 and 3 (Tables 4.4 and 4.5) it was observed that a slight fluctuation in

59


Reproduced w

ith permission o



ithout permission.

Alk

alin

ity

(m

g/L

as

CaC

O3)

1000

900

800

700

600

500

400

300

200

100

0

- - + - - Influent SLAD-1 --A---- SFE

4.0 cm/d 8.1 cm/d --0.

. . ..• .. - ----m---2:4W111

0 20 40 60 80 100

Time (days)

120 140 160 180 200

Figure 4.9. Alkalinity profile in column 1

Reproduced

with perm

ission of the

copyright ow

ner. Further


without

permission.

- - ♦ - ■ Influent — ■— SLAD-1 — *— SFE

10008 . 1 cm/d4.0 cm/d

900

800

5 700

« 600 «

w> 500 S,

6 400 c

1 300<

200

100

0 20 40 60 80 100 140 160 200120 180

Time (days)


Reproduced w

ith permission o


Furth


ithout perm

ission.

Alk

alin

ity

(m

g/L

as

CaC

O3)

1000

900

800

700

600

500

400

300

200

100

0

0

- - * - - Influent —fa-- SFE —A-- SLAD

4.0 cm/d 81 cm/d

. . ... ----- •• . • • .. .

, 1 i

20 40 60 80 100 120 140 160 180 200

Time (days)


Reproduced

with perm

ission of the

copyright ow

ner. Further


without

permission.

Influent — ■— SFE — *— SLAD

10008 . 1 cm/d4.0 cm/d

900

800rr,0 700Cl* 600 «sJm 500s£ 400 a

1 300

200

100

•”T'

200140 160 180100 120

Time (days)


Reproduced w

ith permission o



ithout permission.

Alk

ali

nit

y (

mg

/L a

s C

aC

O3

) 1000

900

800

700

600

500

400

300

200

100

0

- - + - - Influent SFE --Ar--- SLAD

-1 4.0 cm/d 8.1 cm/d —►

0 20 40 60 80 100 120 140 160 180 200

Time (days)


Reproduced

with perm

ission of the

copyright ow

ner. Further


without

permission.

oto

- - ♦ - - Influent — ■— SFE — *— SLAD

10008.1 cm/d4.0 cm/d

900

- 8000U 700 uC5

m 500 S,

5 400

1 300

< 200

600

100

140 160 180 20080 100 120

Time (days)


Table 4.4. Percentage increase of alkalinity in SLAD effluent at 4.0 cm/d

No.

Time

Days

Column 1

% Increase

Column 2

% Increase

Column 3

% Increase

1 0

2 8 82.8 45.7 39.1 3 22 119.0 110.6 111.1

4 36 60.6 26.0 21.8

5 50 41.0 66.3 47.1

6 64 22.6 10.7 24.1

7 78 27.4 21.0 28.0 8 92 26.1 24.7 12.4 9 106 40.9 27.0 18.0 10 120 29.7 19.7 14.0 11 134 17.2 16.4 12.5 12 148 20.8 16.9 10.0

Mean 44.4 35.0 30.7

STD.Dev 6.4 1.7 29.1

Table 4.5. Percentage increase of alkalinity in SLAD effluent 8.1 cm/d

No.

Time

Days


% Increase % Increase % Increase

13 162 6.2 6.2 12.9

14 176 6.7 6.2 13.7 15 190 16.5 11.5 15.2 16 197 18.0 16.2 24.9

Mean 11.9 10.0 16.7

STD.Dev 6.2 4.8 5.6

63


Table 4.4. Percentage increase o f alkalinity in SLAD effluent at 4.0 cm/d

Time Column 1 Column 2 Column 3

No. Days % Increase % Increase % Increase

1 02 8 82.8 45.7 39.1J 22 119.0 110.6 111.14 36 60.6 26.0 21.85 50 41.0 66.3 47.16 64 22.6 10.7 24.17 78 27.4 21.0 28.08 92 26.1 24.7 12.49 106 40.9 27.0 18.010 120 29.7 19.7 14.011 134 17.2 16.4 12.512 148 20.8 16.9 10.0

Mean 44.4 35.0 30.7STD.Dev 6.4 1.7 29.1

Table 4.5. Percentage increase of alkalinity in SLAD effluent 8.1 cm/d


No. Days % Increase % Increase % Increase

13 162 6.2 6.2 12.914 176 6.7 6.2 13.715 190 16.5 11.5 15.216 197 18.0 16.2 24.9

Mean 11.9 10.0 16.7STD.Dev 6.2 4.8 5.6


alkalinity was seen in column 2 effluent while the other two columns produced a gradual

decrease in the alkalinity compared to the initial sand filter effluent alkalinity.

The increase in the hydraulic loading rate increased the alkalinity in the effluent

of SLAD layer in all the three columns. An increase of 22 % alkalinity was seen from 1/1

column while a marginal increase of 5 and 6 %in the 2/1 and 3/1 columns respectively.

From the data it could be conceived that higher the limestone present, higher the

alkalinity in the effluent. The mean alkalinity produced at hydraulic loading rate of 4.1

cm/d, was lower in the case of column 3 but had a higher standard deviation. Column 3

had two peaks above 800 mg/L as CaCO3 but decreased to below 600 mg/L within a

week of operation, while other columns showed a gradual decrease.

4.3.2 Nitrogen removal

Results of this work had shown that SLAD layers could serve as an effective

denitrification agent for nitrate rich sand filter effluent (See Figures 4.12, and 4.13). A

near complete denitrification was achieved in three ratios 1/1, 2/1, 3/1 of sulfur/limestone

of SLAD layer studied and the effect of hydraulic loading rate was minimal (Table 4.6).

The average nitrate nitrogen concentration in the effluent from the three columns was

below 1 mg/L, which was much lower than the MAC of 10 mg/L as nitrate nitrogen. An

occasional increase in the nitrate level to 4.68 and 4.26 was seen in the SLAD layer of

columns 2 and 3 during 11 and 46th day of operation. Column 3 produced a more

consistent reading reaching 1.0 mg/L on two occasions during the operation at the

hydraulic loading rate of 4.0 cm/d.

64


alkalinity was seen in column 2 effluent while the other two columns produced a gradual

decrease in the alkalinity compared to the initial sand filter effluent alkalinity.

The increase in the hydraulic loading rate increased the alkalinity in the effluent

of SLAD layer in all the three columns. An increase of 22 % alkalinity was seen from 1/1

column while a marginal increase o f 5 and 6 %in the 2/1 and 3/1 columns respectively.

From the data it could be conceived that higher the limestone present, higher the

alkalinity in the effluent. The mean alkalinity produced at hydraulic loading rate of 4.1

cm/d, was lower in the case of column 3 but had a higher standard deviation. Column 3

had two peaks above 800 mg/L as CaCCL but decreased to below 600 mg/L within a

week of operation, while other columns showed a gradual decrease.

4.3.2 Nitrogen removal

Results of this work had shown that SLAD layers could serve as an effective

denitrification agent for nitrate rich sand filter effluent (See Figures 4.12, and 4.13). A

near complete denitrification was achieved in three ratios 1/1, 2/1, 3/1 o f sulfur/limestone

of SLAD layer studied and the effect of hydraulic loading rate was minimal (Table 4.6).

The average nitrate nitrogen concentration in the effluent from the three columns was

below 1 mg/L, which was much lower than the MAC of 10 mg/L as nitrate nitrogen. An

occasional increase in the nitrate level to 4.68 and 4.26 was seen in the SLAD layer of

thcolumns 2 and 3 during 11 and 46 day of operation. Column 3 produced a more

consistent reading reaching 1.0 mg/L on two occasions during the operation at the

hydraulic loading rate o f 4.0 cm/d.

64


Reproduced w

ith permission o



ithout permission.

'J

Column 1 25

1 20

E 15

y 10

0

4 cm/d

50 100 Time (days)

25

20

5

0

150

A 8.1* cm/d

200 0

Column 3

1 4 cm/d 81. cm/d


150

Sand N

200

--f—SLAD N

100 150 200

Figure 4.12. Nitrate and nitrite nitrogen profile in SLAD layer

Reproduced

with perm

ission of the

copyright ow

ner. Further


without

permission.

Column 1 Column 2 Sand N •SLAD N

'ox

eox©u

Time (days)

(Jan

258.1 i

cm/d4 cm/d

20

15

10

5

0200100 1500 50

Column 3

25 4 cm/d

20

15

10

5

100

0150 2000 50

254 cm/d

cm/d20

15

10

5

0150 20050 100

Time (days)

Figure 4.12. Nitrate and nitrite nitrogen profile in SLAD layer

Reproduced w

ith permission o



ithout permission.

Column 1

25

20

bn E 15

9 g 10

5

0

0

4 cm/d

50 100 150 Time (days)

Column 3

25

20

5

200

Column 2

25

20

15

10

5

0

0

N —11— SLAD- N

4 cm/d 0.1.4 8 10: cm/d ;

50

1;411---- 4 cm/d 8

.1

* cm/d

0

0 50 100 150 200 Time (days)

SFE- N: SLAD- N:

100

Nitrate nitrogen + Nitrite nitrogen (mg/L) Nitrate nitrogen + Nitrite nitrogen (mg/L)

Figure 4.13. Nitrogen levels in SLAD effluent

150 200

Reproduced

with perm

ission of the

copyright ow

ner. Further


without

permission.

Column 1 Column 2 ■SFE-N •SLAD-N25

4 cm/d20

15

5

0100 150 2000 50

Time (days)

Column 3

4 cm/d cm/d20

on15

^10

5

0100 150 200500

Time (days)

SFE- N: Nitrate nitrogen + Nitrite nitrogen (mg/L)SLAD- N: Nitrate nitrogen + Nitrite nitrogen (mg/L)

254 cm/d

20

15

10

5

0150 2001000 50

Figure 4.13. Nitrogen levels in SLAD effluent

Table 4.6. Comparison of nitrogen removal efficiency in sand filter and SLAD layers

Hydraulic loading rate: 4.0 cm/d.

Sand filter Nitrification SLAD Denitrification

Time -------

Days

Column 1 Column 2 Column 3 Column 1 Column 2 Column 3

0 4.8 0.5 5.0 92.8 -17.6 96.0 8 35.4 98.4 11 22.3 11.3 35.8 97.6 -74.4 95.6

16 38.0 20.9 29.1 98.3 98.8 35.5

19 38.2 20.8 29.0 99.2 99.0 96.9

46 40.9 27.3 43.8 99.1 98.6 60.5 54 38.8 26.3 30.9 82.5 98.0 86.2

60 37.4 31.0 32.7 96.5 99.8 99.9 64 50.9 34.9 94.7 99.5 74 54.0 50.9 60.8 98.8 98.8 89.2 82 56.4 60.1 66.0 93.5 99.4 99.3

89 69.4 83.9 64.4 98.2 99.2 98.3

97 59.6 51.0 66.2 96.9 81.7 92.8 102 57.1 60.0 60.2 98.2 97.8 98.6 110 54.3 67.2 64.4 87.7 96.4 94.4

114 60.4 61.3 69.5 96.7 96.9 98.9 123 70.8 64.0 78.2 99.0 98.6 99.5 131 76,4 56.4 78.8 93.1 92.6 99.0 140 79.6 63.8 80.8 95.0 99.2 98.3 153 74.4 65.6 48.9 95.4 99.2 87.1

Mean 50.9 45.7 51.5 95.6 81.2 90.8

Hydraulic loading rate: 8.1cm/d.

Sand filter Nitrification SLAD Denitrification

Time Days

Column 1 Column 2 Column 3 Column 1 Column 2 Column 3

169 55.6 64.4 64.0 75.7 90.8 96.4

181 53.2 54.4 60.8 87.4 81.7 93.9

186 61.5 61.1 65.6 94.2 93.1 96.2 195 68.8 71.3 75.4 92.4 95.8 96.5

Mean 59.8 62.8 66.4 87.4 90.3 95.7

67


Table 4.6. Comparison o f nitrogen removal efficiency in sand filter and SLADlayers


Sand filter Nitrification SLAD DenitrificationTime Column 1 Column 2 Column 3 Column 1 Column 2 Column 3Days % % % % % %

0 4.8 0.5 5.0 92.8 -17.6 96.08 35.4 98.411 22.3 11.3 35.8 97.6 -74.4 95.616 38.0 20.9 29.1 98.3 98.8 35.519 38.2 20.8 29.0 99.2 99.0 96.946 40.9 27.3 43.8 99.1 98.6 60.554 38.8 26.3 30.9 82.5 98.0 86.260 37.4 31.0 32.7 96.5 99.8 99.964 50.9 34.9 94.7 99.574 54.0 50.9 60.8 98.8 98.8 89.282 56.4 60.1 66.0 93.5 99.4 99.389 69.4 83.9 64.4 98.2 99.2 98.397 59.6 51.0 66.2 96.9 81.7 92.8102 57.1 60.0 60.2 98.2 97.8 98.6110 54.3 67.2 64.4 87.7 96.4 94.4114 60.4 61.3 69.5 96.7 96.9 98.9123 70.8 64.0 78.2 99.0 98.6 99.5131 76.4 56.4 78.8 93.1 92.6 99.0140 79.6 63.8 80.8 95.0 99.2 98.3153 74.4 65.6 48.9 95.4 99.2 87.1

Mean 50.9 45.7 51.5 95.6 81.2 90.8

Hydraulic loading rate: 8.1cm/d.

Sand filter Nitrification SLAD DenitrificationTime Column 1 Column 2 Column 3 Column 1 Column 2 Column 3Days % % % % % %169 55.6 64.4 64.0 75.7 90.8 96.4181 53.2 54.4 60.8 87.4 81.7 93.9186 61.5 61.1 65.6 94.2 93.1 96.2195 68.8 71.3 75.4 92.4 95.8 96.5

Mean 59.8 62.8 66.4 87.4 90.3 95.7

67


Nitrite nitrogen concentration in the effluent was below the MAC of 1 mg/L with

an occasional increase in the effluent nitrite during the operation. Nitrite and nitrate

nitrogen present in the effluent have been consistently well below the MCL throughout

the period of study. On a comparison of effluent nitrate and nitrite, columns 1 and 2

effluents had a higher concentration of nitrite nitrogen than of nitrate nitrogen. During the

period 64 to 160 days of operation, nitrites in the effluents of columns 1 and 2 were

higher than nitrates. The number of nitrite peaks decreased with the sulfur/limestone ratio

showing that higher the sulfur content lesser the nitrite concentration in the effluent.

Column 3 had two peaks of nitrite nitrogen higher than the nitrate nitrogen and produced

more consistent result than the other two columns. There was an increase in the nitrate

and nitrite concentration in the effluent on increasing the hydraulic loading rate to 8.1

cm/d. The nitrite nitrogen in the effluent was just above 1 mg/L in columns 1 and 2 but

decreased to less than 1 mg/L in 10 days of continuous operation at the same loading rate.

The column 3 was less affected by the change in hydraulic loading. rate though nitrate

levels were higher than at the previous loading rate but below 1 mg/L. The decrease in

concentration of nitrate and nitrite paralleled in column 1 but a more gradual decrease of

nitrite level was seen in column 2. The column 2 produced a fluctuation of values on

comparison with the other two columns. The effect of ammonia nitrogen on the decrease

of nitrate was not found to be significant, as by equation 4.4, ammonia nitrogen is

required by the biomass for metabolism. The increase in ammonia nitrogen from the sand

filter effluent had less effect in terms of sulfate or alkalinity increase in the SLAD layer

effluent. This phenomenon was also reported by Kanter et al. (1998). Thus we could

68


Nitrite nitrogen concentration in the effluent was below the MAC of 1 mg/L with

an occasional increase in the effluent nitrite during the operation. Nitrite and nitrate

nitrogen present in the effluent have been consistently well below the MCL throughout

the period of study. On a comparison of effluent nitrate and nitrite, columns 1 and 2

effluents had a higher concentration of nitrite nitrogen than of nitrate nitrogen. During the

period 64 to 160 days of operation, nitrites in the effluents of columns 1 and 2 were

higher than nitrates. The number of nitrite peaks decreased with the sulfur/limestone ratio

showing that higher the sulfur content lesser the nitrite concentration in the effluent.

Column 3 had two peaks of nitrite nitrogen higher than the nitrate nitrogen and produced

more consistent result than the other two columns. There was an increase in the nitrate

and nitrite concentration in the effluent on increasing the hydraulic loading rate to 8.1

cm/d. The nitrite nitrogen in the effluent was just above 1 mg/L in columns 1 and 2 but

decreased to less than 1 mg/L in 10 days o f continuous operation at the same loading rate.

The column 3 was less affected by the change in hydraulic loading, rate though nitrate

levels were higher than at the previous loading rate but below 1 mg/L. The decrease in

concentration of nitrate and nitrite paralleled in column 1 but a more gradual decrease of

nitrite level was seen in column 2. The column 2 produced a fluctuation of values on

comparison with the other two columns. The effect o f ammonia nitrogen on the decrease

o f nitrate was not found to be significant, as by equation 4.4, ammonia nitrogen is

required by the biomass for metabolism. The increase in ammonia nitrogen from the sand

filter effluent had less effect in terms o f sulfate or alkalinity increase in the SLAD layer

effluent. This phenomenon was also reported by Kanter et al. (1998). Thus we could

68


conclude that ineffective nitrification in the nitrification zone reduces the overall nitrogen

removal but has less effect on the denitrification efficiency.

Denitrification by sulfur oxidizing bacteria was successful in all three columns

reaching close to 100 % denitrification capability. Denitrification was significant from

day 1 in columns 1 and 3 while column 2 took time to stabilize (16 days) to produce a

similar level of nitrate. The increase in hydraulic loading rate deterred the removal

percentage in column 1 while columns 2 and 3 achieved 90 and 96 % removal efficiency.

4.3.3 Sulfate

Sulfate production caused by the oxidation of sulfur by the Thiobacillus

denitrificans was seen in the SLAD effluent of three ratios. The first week of operation

produced an effluent containing nearly 2000 mg/L of sulfate among the three columns

and decreased over the period (Figures 4.14 and 4.15).

The initial start up studies produced an effluent over 2000 mg/L of sulfate among

the three different ratios and decreased over the period. The decrease in the sulfate was

more than 60 % within 8 days of operation. The decrease of sulfate in the effluent was

evident for the initial 53 days of study, before fluctuations began. The steep decrease and

fluctuations in effluent concentration were evident in all three columns with of different

sulfur/limestone ratios. The effluent sulfate and alkalinity increased with influent

ammonia concentration from the sand filter. The sulfate increase coincided with the

increase in alkalinity levels in the effluent, which coincided with the influent ammonia

nitrogen. This phenomenon was also reported in studies done by Zhang and Shan (1999).

Figure 4.16 shows the effect of effluent sulfate concentration on alkalinity. Sikora and

Keeney (1976) reported that accumulation of sulfate products depend on external factors

69


conclude that ineffective nitrification in the nitrification zone reduces the overall nitrogen

removal but has less effect on the denitrification efficiency.

Denitrification by sulfur oxidizing bacteria was successful in all three columns

reaching close to 100 % denitrification capability. Denitrification was significant from

day 1 in columns 1 and 3 while column 2 took time to stabilize (16 days) to produce a

similar level of nitrate. The increase in hydraulic loading rate deterred the removal

percentage in column 1 while columns 2 and 3 achieved 90 and 96 % removal efficiency.

4.3.3 Sulfate

Sulfate production caused by the oxidation of sulfur by the Thiobacillus

denitrificans was seen in the SLAD effluent of three ratios. The first week of operation

produced an effluent containing nearly 2000 mg/L o f sulfate among the three columns

and decreased over the period (Figures 4.14 and 4.15).

The initial start up studies produced an effluent over 2000 mg/L o f sulfate among

the three different ratios and decreased over the period. The decrease in the sulfate was

more than 60 % within 8 days o f operation. The decrease of sulfate in the effluent was

evident for the initial 53 days o f study, before fluctuations began. The steep decrease and

fluctuations in effluent concentration were evident in all three columns with of different

sulfur/limestone ratios. The effluent sulfate and alkalinity increased with influent

ammonia concentration from the sand filter. The sulfate increase coincided with the

increase in alkalinity levels in the effluent, which coincided with the influent ammonia

nitrogen. This phenomenon was also reported in studies done by Zhang and Shan (1999).

Figure 4.16 shows the effect of effluent sulfate concentration on alkalinity. Sikora and

Keeney (1976) reported that accumulation o f sulfate products depend on external factors

69


Reproduced w

ith permission o



ithout permission.

Column 1

20

5

0

4 cm/d


150

Column 3 20

0

0

8 .14 cm/d

200

50

3500

3000

2500 ^

Column 2 SO4

3500

3000

2500 a

NH3-N

20 81* 4 cm/d ► emid

q 15

2000 g w E 2000 g 4.) z 10

1500 'cis' ,- 4. 1500= =

1000 v) Z 1000

500 500

0 0

0 50 100 150 200 Time (days)

4 cm/d ►

100

Time (days)

150

8.1* I cm/d 3000

3500

2500

2000

1500

1000

-I 500

200

0

Sul

fate

(m

g/L

)

Figure 4.14. Influence of Ammonium nitrogen on sulfate levels

Reproduced

with perm

ission of the

copyright ow

ner. Further


without

permission.

Column 1 Column 2 •NH3-N •S04

E

•*TXz

204 cm/d

15 2500 s e;M2000 S

101500 «

1000 <»5500

0200100 1500 50

Time (days)

Column 3

JOX>E,ZITfXz

Oil

33Z

20 35004 cm/d

15 * 2500

200010

1500

10005500

0150 2000 50 100

Time (days)

3500204 cm/d

15 2500

200010

1500

10005500

0100 150 200

Time (days)

Figure 4.14. Influence o f Ammonium nitrogen on sulfate levels

Sulfa

te

(mg/

L)

Reproduced w

ith permission o



ithout permission.

Column 1

5

4

2 0 z

I 4 cm/d 0.14 8.1* cm/d


NO

3-N

(m

g/L

) 150

3500

3000

- 2500 •-•

- 2000 g - 1500 5

- 1000 w)

- 500

0

200

NO

3-N

(m

g/L

)

3

2

1

0

Column 2 NO3-N

4 cm/d

-41— SO4

8.1 3500

cm/r 3000

4 cm/d

50 100 Time (days)

150

50 100 150 Time (days)

11 8 3500

.4 . 1* cm/d 3000

200

2500

2000

1500

1000

500

0

Sul

fate

(m

g/L

)

Figure 4.15. A comparison of sulfate production to nitrate levels in SLAD effluent

- 2500

- 2000 g

1500 *4

1000 Cl)

500

0

200

Reproduced

with perm

ission of the

copyright ow

ner. Further


without

permission.

Column 1 Column 2 •N03-N •S04

j'SiEWzIoz

5 35004 cm/d

30004

2500 ~■JOX’

2000 E3

1500 «21000 n

1500

050 100 150 2000

Time (days)

Column 3

sJac

oz

Jw>E,zIrr>Oz

35005 4 cm/d3000

42500

3 2000

150021000

1500

0100 150 2000 50

Time (days)

35005 4 cm/dcm/d 3000

42500

3 2000

150021000

1500

0200100 150

0>

3cn

Time (days)

Figure 4.15. A comparison o f sulfate production to nitrate levels in SLAD effluent

Sulfa

te

(mg/

L)

Reproduced w

ith permission o



ithout permission.

Column 1

1000

800

E r",;600 >,

:E C.)

7 (7) 400

200

11--- 4 cm/d 0+48.1* cm/d 3000

3500

2500

2000 g

1500 5.

— 1000 v)

— 500

Column 2

1000

800

E el 600 O

U 400

'e▪ t 200

-4—Alkalinity —U—SO4

4 cm/ H 8.1* cm/d 3000

3500

2500

- 2000 g

L 1500 a

1000

- 500

0 0 0 --

0 50 100 150 200 0 50 100 150 200 Time (days) Time (days)

Column 3

1000

800

on "e4-7 600

aO

(..) 400

200

4 cm/d 10. 8.1 cm/d 1 3000

3500

0 50 100 150 Time (days)

• 'SINAI

200

2500

200014

1500 1-4

1000 cip

500

0

Figure 4.16. Comparison of sulfate and alkalinity from SLAD effluent

0

Reproduced

with perm

ission of the

copyright ow

ner. Further


without

permission.

Column 1 Column 2 ■Alkalinity •S04

1000 T 3500

cm/d “ 30004 cm/d

8002500 ^

OJ)2000 E

OX'£ n 600

OI y•■= U 400 1500 $

200500

0 50 100 150 200Time (days)

Column 3

1000 ----------- 3500< 8.1

cm/d~ 30004 cm/d

800250001

600 2000

1500U 4001000

200500

0 100 150 20050Time (days)

1000 ------ 3500< 8.1 ►cm/d I 3000

4 cm/d

8002500

2000

s 1500400a< 1000

200500

0 50 100 150 200

'So

Time (days)

Figure 4.16. Comparison o f sulfate and alkalinity from SLAD effluent

Sulfa

te

(mg/

L)

such as pH, oxygen and phosphate concentration. The stiochiometric equation (equation

2.13) indicates that 7.5 mg S042 would be produced for every 1 mg nitrate-N reduced

(Batchelor and Lawrence 1978). Other researchers gave similar ratios such as 6.39

(Sikora and Keeney 1976), 7.75 (Hashimoto et al. 1987), 7.89 (Koenig and Liu 1996) and

7.53 (Zhang and Shan 1999). This study has shown that ratio of sulfate produced to

nitrogen removed ranged between 7.12 and 12.87. The ratio was highest on initial days

of operation and gradually decreased, except when the hydraulic loading rate was

changed to 8.1 cm/d from 4.0 cm/d.

The aesthetic objective of sulfate in drinking water is 500 mg/L as stipulated by the

Canadian Drinking Water Guidelines, U.S.EPA, and WHO (AWWA 1990). The average

sulfate concentration was 209, 227, and 219 mg/L for columns 1, 2 and 3 respectively,

for the period between 64 and 195 days.

4.3.4 COD

An increase in COD from SLAD Layers was seen from initial sand filter effluent

(Tables A.7 and A.15). An overall decrease of COD over 60 % values from initial STE

from 2/1 and 3/1 SLAD effluent was seen, while 1/1 SLAD effluent recorded a 52 %

decrease of COD (Table 4.7 and Figure 4.17). An increase in COD was seen when

hydraulic loading rate was changed to 8.1 from 4.0 cm/d. An overall consistency of COD

removal with a standard deviation of 9.74 was seen from 2/1 SLAD ratio, while 3/1

showed a higher degree of COD removal with a lesser standard deviation of 8.8. 1/1

column effluent recorded the highest COD value compared with the other two ratios with

a standard deviation of 12.19. Zhang and Shan (1999) reported a decrease in COD from

an influent concentration of 300 to 30 mg/L.

73


such as pH, oxygen and phosphate concentration. The stiochiometric equation (equation

2.13) indicates that 7.5 mg SO4 2' would be produced for every lmg nitrate-N reduced

(Batchelor and Lawrence 1978). Other researchers gave similar ratios such as 6.39

(Sikora and Keeney 1976), 7.75 (Hashimoto et al. 1987), 7.89 (Koenig and Liu 1996) and

7.53 (Zhang and Shan 1999). This study has shown that ratio of sulfate produced to

nitrogen removed ranged between 7.12 and 12.87. The ratio was highest on initial days

of operation and gradually decreased, except when the hydraulic loading rate was

changed to 8.1 cm/d from 4.0 cm/d.

The aesthetic objective of sulfate in drinking water is 500 mg/L as stipulated by the

Canadian Drinking Water Guidelines, U.S.EPA, and WHO (AWWA 1990). The average

sulfate concentration was 209, 227, and 219 mg/L for columns 1, 2 and 3 respectively,

for the period between 64 and 195 days.

4.3.4 COD

An increase in COD from SLAD Layers was seen from initial sand filter effluent

(Tables A.7 and A. 15). An overall decrease of COD over 60 % values from initial STE

from 2/1 and 3/1 SLAD effluent was seen, while 1/1 SLAD effluent recorded a 52 %

decrease of COD (Table 4.7 and Figure 4.17). An increase in COD was seen when

hydraulic loading rate was changed to 8.1 from 4.0 cm/d. An overall consistency o f COD

removal with a standard deviation o f 9.74 was seen from 2/1 SLAD ratio, while 3/1

showed a higher degree of COD removal with a lesser standard deviation of 8 .8 . 1/1

column effluent recorded the highest COD value compared with the other two ratios with

a standard deviation of 12.19. Zhang and Shan (1999) reported a decrease in COD from

an influent concentration of 300 to 30 mg/L.

7.3


Table 4.7. COD removal efficiency of SLAD layers


Time

Days

Column 1 Removal

Column 2 Removal

Column 3 Removal

0 8 70.8 73.8 68.8 16 28.5 44.8 18.6 46 45.8 69.0 63.9 60 35.2 54.4 61.6 74 55.2 61.6 63.1 82 55.3 66.3 65.8 89 67.4 68.6 59.3 97 47.0 65.7 61.3 110 43.0 58.0 65.4 123 63.6 66.9 71.9 131 52.2 57.4 79.5 140 62.1 66.3 83.7 153 53.5 41.4 65.6

Mean: 52.0 61.0 64.0 Std. Dev. 12.4 9.6 15.3


Time Column I Column 2 Column 3

Days Removal Removal Removal

169 47.5 62.0 59.1 181 67.6 70.2 74.8 195 65.4 77.6 74.4

Mean: 60.0 70.0 69.3 Std. Dev. 11.1 7.8 8.9

74


Table 4.7. COD removal efficiency of SLAD layers



Days Removal%

Removal%

Removal%

08 70.8 73.8 68.816 28.5 44.8 18.646 45.8 69.0 63.960 35.2 54.4 61.674 55.2 61.6 63.182 55.3 66.3 65.889 67.4 68.6 59.397 47.0 65.7 61.3110 43.0 58.0 65.4123 63.6 66.9 71.9131 52.2 57.4 79.5140 62.1 66.3 83.7153 53.5 41.4 65.6

Mean: Std. Dev.

52.012.4

61.09.6

64.015.3



Days Removal%

Removal%

Removal%

169 47.5 62.0 59.1181 67.6 70.2 74.8195 65.4 77.6 74.4

Mean: 60.0 70.0 69.3Std. Dev. 11.1 7.8 8.9


Reproduced w

ith permission o



ithout permission.

Column 1 600

500

a 400 1

300

0 C.) 200

100

0

0

4 cm/d

50 100 Time (days)

Column 3

600

+8.1 .00-cm/d

150 200

Column 2 600

500

400 an

1. 300

C U 200

4 4 cm/d

500

a 400

:11 300

O U 200

100

0

0

100

50 100 Time (days)

150

IN SFE —A— SLAD

50 100 Time (days)

8.1* cm/d

Figure 4.17. COD profile across the system

200

150 200

Reproduced

with perm

ission of the

copyright ow

ner. Further


without

permission.

Column600

cm/d- j4 cm/d

500

£ 400

300QOU 200

100*

50 100 Time (days)

Column 3

150

-Jw>a,Qo

200

IN SFE SLADColumn 2 600 r

*4 8.1 ►cm/d

4 cm/d500

400

300

200

100

050 100

Time (days)150 200

600< 8.1 ►

cm/d4 cm/d

500

400

300

200

100

0100 150 2000 50

Time (days)

Figure 4.17. COD profile across the system

4.3.5 Phosphate

The phosphate was present in the effluent of the SLAD layers thorough the study

period (Table A.16 and Figure 4.18). The initial phase of study showed an increase in

concentration of phosphate as phosphorus, in the effluent in the range of 5 to 8 mg/L. The

influent concentration to the SLAD layers from the sand fi lters was in range of 0.5 to 2

mg/L. Acidity produced by the nitrification of STE helps in retention of phosphates in the

sand filter. Thus, phosphates are retained by soil when they precipitate out of solution

(Sikora and Keeney 1976).

The phosphate production in the SLAD layers increased to greater than 500 % of

initial concentration during first 64 days of operation (Table 4.8). The phosphate

concentration gradually decreased along the period of study but showed rapid

fluctuations. A steep increase was observed when changing the hydraulic loading rate to

8.1 from 4.0 cm/d. The possibility of phosphate present in the SLAD layers could be the

result of seeding procedures followed to grow Thiobacillus denitrificans. Phosphate as

potassium hydrogen phosphate (KH2PO4), sodium phosphate (Na2HPO4) and

micronutrient as di-potassium hydrogen phosphate (K2HPO4) was added as a nutrient to

grow the culture and to seed in the SLAD layers for a period of 2 weeks. The phosphate

would have been retained in the column and with a gradual release in the effluent.

76


4.3.5 Phosphate

The phosphate was present in the effluent of the SLAD layers thorough the study

period (Table A. 16 and Figure 4.18). The initial phase of study showed an increase in

concentration of phosphate as phosphorus, in the effluent in the range of 5 to 8 mg/L. The

influent concentration to the SLAD layers from the sand filters was in range of 0.5 to 2

mg/L. Acidity produced by the nitrification o f STE helps in retention of phosphates in the

sand filter. Thus, phosphates are retained by soil when they precipitate out of solution

(Sikora and Keeney 1976).

The phosphate production in the SLAD layers increased to greater than 500 % of

initial concentration during first 64 days o f operation (Table 4.8). The phosphate

concentration gradually decreased along the period of study but showed rapid

fluctuations. A steep increase was observed when changing the hydraulic loading rate to

8.1 from 4.0 cm/d. The possibility of phosphate present in the SLAD layers could be the

result o f seeding procedures followed to grow Thiobacillus denitrificans. Phosphate as

potassium hydrogen phosphate (KH2 PO4 ), sodium phosphate (Na2H P04) and

micronutrient as di-potassium hydrogen phosphate (K2 HPO4 ) was added as a nutrient to

grow the culture and to seed in the SLAD layers for a period of 2 weeks. The phosphate

would have been retained in the column and with a gradual release in the effluent.

76


Reproduced w

ith permission o



ithout permission.

Column 1

10

Pho

spha

te a

s P

(m

g/L

)

0

0

4 cm/d

50 100 Time (days)

Column 3

10

Pho

spha

te a

s P

(m

g/L

)

8

6

4

2

150

*14 8.1 101. cm/d

200 0 50 100 Time (days)

0

4 cm/d

50 100 Time (days)

150

Figure 4.18. Phosphate profile

8.1*_ cm/d

200

150 200

Column 1 Column 2 —♦—IN SFE ♦ SLAD

00

00rs

®

®IT)

c:® T3 ® w—

<yEH

®IT)

(T/8

iu) j

s

b a

jBq

ds

oq

j

00

oo®

®id

<n

® *oO w<y

®tn

T3

ID

eI

o00

so Tf

(T/S

ui) j

s

b 3

)Bq

dso

q<

]

r<o

(q/tiu

i) j

sb

ajB

qd

so

qj

77

Reproduced w


ner. F


ission.

Time (days)

Figure 4.18. Phosphate profile

Table 4.8. Percentage increase in phosphate in SLAD layer


Time

Days

Column 1 Increase

OA

Column 2 Increase

Column 3 Increase

OA

10 1483.3 418.7 216.2 21 709.1 1336.6 1150.5 26 134.7 110.5 97.6 29 70.5 94.2 42.3 56 718.4 452.1 352.1 64 475.6 539.0 714.0 70 248.0 290.4 242.3 74 492.5 705.5 294.8 84 123.6 312.1 31.6 92 59.8 -5.6 19.4 99 60.8 24.6 -15.0 107 76.4 44.1 87.5 112 83.5 113.7 24.3 124 96.4 56.7 209.4 133 61.8 68.9 47.5 141 27.5 7.2 4.8 154 34.8 30.0 70.5



DaysIncrease Increase Increase

169 32.4 61.0 18.9 183 90.5 -31.6 -40.0 187 14.3 35.7 63.6 192 75.4 75.0 35.8

78


Table 4.8. Percentage increase in phosphate in SLAD layer



Days Increase%

Increase%

Increase%

10 1483.3 418.7 216.221 709.1 1336.6 1150.526 134.7 110.5 97.629 70.5 94.2 42.356 718.4 452.1 352.164 475.6 539.0 714.070 248.0 290.4 242.374 492.5 705.5 294.884 123.6 312.1 31.692 59.8 -5.6 19.499 60.8 24.6 -15.0107 76.4 44.1 87.5112 83.5 113.7 24.3124 96.4 56.7 209.4133 61.8 68.9 47.5141 27.5 7.2 4.8154 34.8 30.0 70.5



Days Increase%

Increase%

Increase%

169 32.4 61.0 18.9183 90.5 -31.6 -40.0187 14.3 35.7 63.6192 75.4 75.0 35.8

78


4.4 General Discussion

Column studies were performed as a unified system with sand filter and SLAD

layer of height 0.91 and 0.3 m respectively with a loading rate 4.0 and 8.1 cm/d applied

intermittently at 6 h intervals. Sand filter system needed 64 days of operation at loading

rate 4.0 cm/d to achieve 50 percent conversion of mean influent TKN of 29 mg/L to

nitrate and nitrite nitrogen. The effluent nitrate nitrogen from the sand filter effluent

ranged between 12 and 20 mg/L from 64 day onwards, with a drop in nitrate nitrogen

when the loading rate was changed to 8.1 cm/d at the end of 160 days. Three sulfur:

limestone ratios (mass: mass) 1:1, 2:1 and 3:1 were studied to identify the denitrification

ability. All three ratios showed significant denitrifying capacity. Ratio 3:1 showed a

better adaptability to change in loading rate, production of sulfate and alkalinity to the

reduction of nitrate nitrogen. Denitrification of the sand filter effluent in SLAD layer

was effective from the day of operation producing effluent nitrate nitrogen ranging from

1.1 to 0.1 mg/L during the study period of 195 days. The sulfate and alkalinity production

in the SLAD effluent was proportional to the increase in influent ammonia nitrogen to the

sand filter and nitrate nitrogen from the sand filter effluent. Sand filter effluent ammonia

nitrogen decreased from a mean of 3.7 mg/L to less than 1 mg/L from SLAD layer

effluent. The sulfate produced from the SLAD layer was in the range of 112 to 329 mg/L

and the ratio of sulfate produced to the nitrogen decreased ranged between 7.1 and 12.8.

The alkalinity production was in the range of 526 to 612 mg/L as CaCO3 and alkalinity

production to nitrogen decrease was 4.6. COD from the SLAD effluent was in the range

of 67 to 167 mg/L from a mean initial sand filter effluent COD of 33 mg/L. The sulfate

present in the SLAD effluent could be the cause of the COD increase.

79


4.4 General Discussion

Column studies were performed as a unified system with sand filter and SLAD

layer of height 0.91 and 0.3 m respectively with a loading rate 4.0 and 8.1 cm/d applied

intermittently at 6 h intervals. Sand filter system needed 64 days of operation at loading

rate 4.0 cm/d to achieve 50 percent conversion of mean influent TKN of 29 mg/L to

nitrate and nitrite nitrogen. The effluent nitrate nitrogen from the sand filter effluent

ranged between 12 and 20 mg/L from 64 day onwards, with a drop in nitrate nitrogen

when the loading rate was changed to 8.1 cm/d at the end of 160 days. Three sulfur:

limestone ratios (mass: mass) 1:1, 2:1 and 3:1 were studied to identify the denitrification

ability. All three ratios showed significant denitrifying capacity. Ratio 3:1 showed a

better adaptability to change in loading rate, production of sulfate and alkalinity to the

reduction of nitrate nitrogen. Denitrification of the sand filter effluent in SLAD layer

was effective from the day of operation producing effluent nitrate nitrogen ranging from

1.1 to 0.1 mg/L during the study period of 195 days. The sulfate and alkalinity production

in the SLAD effluent was proportional to the increase in influent ammonia nitrogen to the

sand filter and nitrate nitrogen from the sand filter effluent. Sand filter effluent ammonia

nitrogen decreased from a mean of 3.7 mg/L to less than lmg/L from SLAD layer

effluent. The sulfate produced from the SLAD layer was in the range of 112 to 329 mg/L

and the ratio of sulfate produced to the nitrogen decreased ranged between 7.1 and 12.8.

The alkalinity production was in the range o f 526 to 612 mg/L as C aC 03 and alkalinity

production to nitrogen decrease was 4.6. COD from the SLAD effluent was in the range

of 67 to 167 mg/L from a mean initial sand filter effluent COD of 33 mg/L. The sulfate

present in the SLAD effluent could be the cause of the COD increase.

79


The limitation for an operation as a unified system in real life would be the

production of sulfate and alkalinity from the SLAD effluent, which depends on the

nitrification ability in the nitrifying zone. This study showed that the sand filter system

accompanied by a SLAD layer with ratio of sulfur: limestone of 3:1 operated as a single

stage system can be used in reducing nitrogen present in the septic tank effluent.

80


The limitation for an operation as a unified system in real life would be the

production of sulfate and alkalinity from the SLAD effluent, which depends on the

nitrification ability in the nitrifying zone. This study showed that the sand filter system

accompanied by a SLAD layer with ratio o f sulfur: limestone of 3:1 operated as a single

stage system can be used in reducing nitrogen present in the septic tank effluent.

80


5. CONCLUSIONS AND RECOMMENDATIONS FOR FURTHER

STUDY

5.1 Conclusions

The following conclusions were drawn from the study:

1. The intermittent operation of the sand filters showed a significant reduction of

COD, and phosphate when operated at two loading rate of 4 and 8.1 cm/d.

2. Nitrification of over 60% was achieved in the sand filters at the two loading rates.

3. Nitrification capability of the sand filter increased after a stabilization period of

one month and the increase in nitrification was directly proportional to the

ammonia nitrogen present in the influent (STE) and hydraulic loading rate.

4. Nitrified effluent from the sand filter showed a near complete oxidation of the

organic nitrogen to nitrate nitrogen at both loading rates.

5. An increase in hydraulic loading rate decreased the reduction of alkalinity and

phosphate from the sand filter.

6. Dissolved oxygen in the sand filter effluent was between 1 and 2 mg/L thus,

facilitating an anoxic environment while entering the SLAD layer.

7. The SLAD system was found to be successful in denitrifying nitrified sand filter

effluent. Significant nitrogen removal was achieved on operation with two

hydraulic loading rates. SLAD layer of 3/1 ratio of sulfur and limestone was

identified to be suitable in accordance with its ability to adapt with the change in

hydraulic loading rate, production of sulfate to alkalinity ratio and nitrite to nitrate

ratio.

81


5. CONCLUSIONS AND RECOM M ENDATIONS FOR FURTHER

STUDY

5.1 Conclusions

The following conclusions were drawn from the study:

1. The intermittent operation of the sand filters showed a significant reduction of

COD, and phosphate when operated at two loading rate of 4 and 8.1 cm/d.

2. Nitrification of over 60% was achieved in the sand filters at the two loading rates.

3. Nitrification capability o f the sand filter increased after a stabilization period of

one month and the increase in nitrification was directly proportional to the

ammonia nitrogen present in the influent (STE) and hydraulic loading rate.

4. Nitrified effluent from the sand filter showed a near complete oxidation of the

organic nitrogen to nitrate nitrogen at both loading rates.

5. An increase in hydraulic loading rate decreased the reduction of alkalinity and

phosphate from the sand filter.

6. Dissolved oxygen in the sand filter effluent was between 1 and 2 mg/L thus,

facilitating an anoxic environment while entering the SLAD layer.

7. The SLAD system was found to be successful in denitrifying nitrified sand filter

effluent. Significant nitrogen removal was achieved on operation with two

hydraulic loading rates. SLAD layer of 3/1 ratio of sulfur and limestone was

identified to be suitable in accordance with its ability to adapt with the change in

hydraulic loading rate, production o f sulfate to alkalinity ratio and nitrite to nitrate

ratio.

81


8. Nitrate nitrogen was well below MAC during the entire run of the system, while

nitrite nitrogen concentration during the initial run of the system was above MAC,

which gradually decreased with time.

9. The increase in sulfate concentration was directly proportional to alkalinity in the

effluent of the SLAD system.

10. Nitrogen removal and the production of sulfate and alkalinity followed the

stoichiometric equation.

5.2 Recommendations for further study

Further study is suggested in the following areas:

1 To identify the effect in nitrification by adding higher CEC materials like clay in

the sand filter.

2 To identify the degree of nitrification along the height of the sand filter system.

3 The effect of temperature on the SLAD system and its applicability in severe

winter conditions.

4 The ability of the SLAD system to withstand variable influent concentrations,

such as higher concentration of ammonia-nitrogen.

5 To identify a method for reduction of sulfate and alkalinity from the effluent

either following a different procedure or an addition of separate treatment system

such that it will be a viable process in field.

6 Identification of reaction order for nitrification in the sand filter and

denitrification in SLAD layer.

82


8. Nitrate nitrogen was well below MAC during the entire run of the system, while

nitrite nitrogen concentration during the initial run of the system was above MAC,

which gradually decreased with time.

9. The increase in sulfate concentration was directly proportional to alkalinity in the

effluent of the SLAD system.

10. Nitrogen removal and the production of sulfate and alkalinity followed the

stoichiometric equation.

5.2 Recommendations for further study

Further study is suggested in the following areas:

1 To identify the effect in nitrification by adding higher CEC materials like clay in

the sand filter.

2 To identify the degree o f nitrification along the height of the sand filter system.

3 The effect of temperature on the SLAD system and its applicability in severe

winter conditions.

4 The ability of the SLAD system to withstand variable influent concentrations,

such as higher concentration o f ammonia-nitrogen.

5 To identify a method for reduction of sulfate and alkalinity from the effluent

either following a different procedure or an addition of separate treatment system

such that it will be a viable process in field.

6 Identification of reaction order for nitrification in the sand filter and

denitrification in SLAD layer.

82


REFERENCE

American public health Association (APHA) (1999) "Standard methods for the

examination of water and wastewater." Twentieth edition. Am. Public Health

Assoc., Washington DC.

American Water Works Association (AWWA) (1990) "Water quality and treatment: a

handbook of community water supplies." Ed. Pontius, F. W., fourth edition

McGraw-Hill Inc., New York.

Anderoli, A., Bartilluci, N., and Reynold, R. (1979) "Nitrogen removal in a subsurface

disposal system." J. Water Pollution Control Fedn. 51(4), 841-854.

Audic, J. M., Faup, G. M., and Navarro, J. M. (1984) "Specific activity of nitrobacter

through attachment on granular media." Water Res. 18(6), 745-750.

Aulakh, S. M., Kehra, S. T., and Doran, J. W., (2000) "Mineralization and denitrification

in upland, nearly saturated and flooded subtropical soil II. Effect of organic

manures varying in N content and C:N ratio." Biology and Fertility of Soils.

31(2), 168-172.

Batchelor, B. and Lawrence, A.W. (1978) "Autotrophic denitrification using sulfur." J.

Water Pollution. Control Fedn. 1986-2001.

Benefield, L.D., and Randall, C. W. (1980) "Biological process design for wastewater

treatment." Prentice-Hall Inc. Englewood Cliffs, NJ.

Biswas, N. and Warnock, R. G. (1985) "Nitrogen transformation and fate of other

parameters in columnar denitrification." Water Res. 19(8), 1065-1071.

Blanc, J., Audic, J. M., and Faup, G. M. (1986) "Enhancement of Nitrobacter activity by

heterotrophic bacteria." Water. Res. 20(1 1), 1375-1381.

8_3


REFERENCE

American public health Association (APHA) (1999) “Standard methods for the

examination of water and wastewater.” Twentieth edition. Am. Public Health

Assoc., Washington DC.

American Water Works Association (AWWA) (1990) “Water quality and treatment: a

handbook of community water supplies.” Ed. Pontius, F. W., fourth edition

McGraw-Hill Inc., New York.

Anderoli, A., Bartilluci, N., and Reynold, R. (1979) “Nitrogen removal in a subsurface

disposal system.” J. Water Pollution Control Fedn. 51(4), 841-854.

Audic, J. M., Faup, G. M., and Navarro, J. M. (1984) “Specific activity of nitrobacter

through attachment on granular media.” Water Res. 18(6), 745-750.

Aulakh, S. M., Kehra, S. T., and Doran, J. W., (2000) “Mineralization and denitrification

in upland, nearly saturated and flooded subtropical soil II. Effect o f organic

manures varying in N content and C:N ratio.” Biology and Fertility o f Soils.

31(2), 168-172.

Batchelor, B. and Lawrence, A.W. (1978) “Autotrophic denitrification using sulfur.” J.

Water Pollution. Control Fedn. 1986-2001.

Benefield, L.D., and Randall, C. W. (1980) “Biological process design for wastewater

treatment.” Prentice-Hall Inc. Englewood Cliffs, NJ.

Biswas, N. and Warnock, R. G. (1985) “Nitrogen transformation and fate o f other

parameters in columnar denitrification.” Water Res. 19(8), 1065-1071.

Blanc, J., Audic, J. M., and Faup, G. M. (1986) “Enhancement of Nitrobacter activity by

heterotrophic bacteria.” Water. Res. 20(1 1), 1375-1381.


Bouma, J. (1971) "Evaluation of the field percolation and alternative procedure to test

soil potential for disposal of septic tank effluent." Soil Sci. Soc. of America. Proc.

35, 871-875.

Bouma, J., Converse, J. C. Otis, R. J., Waker, W. G. and Ziebell, W. A. (1975) "A mound

system for onsite disposal of septic tank effluent in slowly permeable soils with

seasonally perched water tables."J. Environ. Qual. 4(3), 382-388.

Brandes M. (1974) "Experimental study on removal of pollutants from domestic sewage

by underdrained soil filter." Procc. National Home Sewage Disposal Symposium.

American Society of Agricultural Engineers. St.Joseph, Mich. ASAE. 29-34

Brandes M. (1978) "Characteristics of effluents from gray and black water septic tanks."

J. Water Poll. Control Fed. 2547-2559.

Brewer, W. S., Lucas, J., and Prascak, G. (1978) "An evaluation of the performance of

household aerobic sewage treatment units." J. Environ. Health 41(2), 82-85.

Brooks, J. L., Rock, C. A., and Struchtemeyer, R.A. (1984) "Use of peat for onsite

wastewater treatment: II. Field studies." J. Environ. Qual. 13, 524-530.

Calaway, W. T. (1957) "Intermittent sand filters and their biology." Sewage and Ind.

Wastes J. 29(1), 1-5.

Cogger, C. G., and Carlile, B. L. (1984) "Field performance of conventional and

alternative septic systems in wet soils." J. Environ. Qual. 13, 137-142.

Daniel, T. C. and Bouma, J. (1974) "Column studies of soil in a slowly permeable soil as

a function of effluent quality." J. Environ. Qual., 3(4), 321-327.

84


Bouma, J. (1971) “Evaluation of the field percolation and alternative procedure to test

soil potential for disposal of septic tank effluent.” Soil Sci. Soc. o f America. Proc.

35, 871-875.

Bouma, J., Converse, J. C. Otis, R. J., Waker, W. G. and Ziebell, W. A. (1975) “A mound

system for onsite disposal of septic tank effluent in slowly permeable soils with

seasonally perched water tables.” J. Environ. Qual. 4(3), 382-388.

Brandes M. (1974) “Experimental study on removal o f pollutants from domestic sewage

by underdrained soil filter.” Procc. National Home Sewage Disposal Symposium.

American Society of Agricultural Engineers. St.Joseph, Mich. ASAE. 29-34

Brandes M. (1978) “Characteristics of effluents from gray and black water septic tanks.”

J. Water Poll. Control Fed. 2547-2559.

Brewer, W. S., Lucas, J., and Prascak, G. (1978) “An evaluation of the performance of

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APPENDIX A

Raw Experimental Data

Table A.I. Influent TKN and ammonia-nitrogen to the sand filter.

Time

Days

Septic tank effluent (Influent to sand filter)

Ammonia nitrogen TKN (mg/L) (mg/L)

0 23 26 8 23 28

11 24 28 16 20 25 19 26 34 46 26 32 54 27 27 60 29 35 64 28 36 74 23 30 82 26 30 89 23 29 97 25 29 102 25 32 110 29 34 114 27 37 123 25 31 131 25 27 140 24 32 153 27 33 169 25 33 181 25 32 186 27 35 195 24 34

96


APPENDIX A

Raw Experim ental Data

Table A.I. Influent TKN and ammonia-nitrogen to the sand fdter.

TimeSeptic tank effluent

(Influent to sand filter)

Days Ammonia nitrogen (mg/L)

TKN(mg/L)

0 23 268 23 28

1 1 24 2816 2 0 2519 26 3446 26 3254 27 2760 29 3564 28 3674 23 3082 26 3089 23 2997 25 29

1 0 2 25 321 1 0 29 34114 27 37123 25 31131 25 27140 24 32153 27 33169 25 33181 25 32186 27 35195 24 34


Table A.2. Ammonia-nitrogen results from sand filter effluent columns 1, 2, 3.

Time

Days

Column 1 Column 2 Column 3 Ammonium-nitrogen

(mg/1_) Ammonium-nitrogen Ammonium-nitrogen

(mg/L) (mg/L)

0 17.6 16.7 17.6

8 16.7 12.4

11 12.4 16.7 10.3

16 10..3 15.4 9.5

19 9.5 10.8 10.5

46 10.5 9.5 9.2

54 8.7 9.1 10.8

60 9.3 9.2 7.6

64 7.6

74 6.9 7.2 8.2

82 4.8 5.6 7.6

89 3.7 3.1 7.2

97 2.3 3.7 2.3

102 2.1 2.3 2.1

110 1.1 2.1 1.1

114 1.7 1.1 1.7

123 1.7 1.7 1.7

131 0.7 1.7 2.5

140 0.7 0.7 1.7

153 0.8 0.7 7.1

169 7.9 0.8 5.9

181 3.3 7.9 3.3 186 2.1 3.3 2.1

195 1.3 2.1 1.3

97




Days Ammonium-nitrogen Ammonium-nitrogen Ammonium-nitrogen (mg/L) (mg/L) (mg/L)

0 17.6 16.7 17.68 16.7 12.4

1 1 12.4 16.7 10.316 10.3 15.4 9.519 9.5 1 0 . 8 10.546 10.5 9.5 9.254 8.7 9.1 1 0 . 8

60 9.3 9.2 7.664 7.674 6.9 7.2 8 . 2

82 4.8 5.6 7.689 3.7 3.1 7.297 2.3 3.7 2.3

1 0 2 2 . 1 2.3 2 . 1

1 1 0 1 . 1 2 . 1 1 . 1

114 1.7 1 . 1 1.7123 1.7 1.7 1.7131 0.7 1.7 2.5140 0.7 0.7 1.7153 0 . 8 0.7 7.1169 7.9 0 . 8 5.9181 3.3 7.9 3.3186 2 . 1 3.3 2 . 1

195 1.3 2 . 1 1.3

97


Table A.3. Nitrate-nitrogen results from sand filter effluent columns 1, 2, 3.


(Days) Nitrate-nitrogen

(mg/L) Nitrate-nitrogen

(mg/L) Nitrate-nitrogen

(mg/L)

0 1.0 0.0 1.1

8 _3.1 3.6

11 3.6 2.1 4.0

16 4.2 2.4 4.2

19 6.6 3.7 8.1

46 8.6 5.0 6.3

54 9.1 5.8 8.1

60 8.6 7.6 7.5

64 13.2

74 11.3 10.5 12.9

82 13.2 14.5 16.0

89 15.1 16.7 13.4 97 13.9 11.9 15.7

102 14.0 14.0 14.0

110 15.7 17.2 18.4 114 16.2 16.5 18.7

123 17.4 15.9 19.5

131 17.9 13.8 19.4

140 18.3 14.2 18.2 153 19.6 17.1 12.7

169 12.6 14.3 15.3

181 13.2 12.7 15.1

186 15.2 15.6 16.3

195 15.7 16.2 17.3

98


Table A.3. Nitrate-nitrogen results from sand filter effluent columns 1, 2, 3.


(Days) Nitrate-nitrogen(mg/L)

Nitrate-nitrogen(mg/L)

Nitrate-nitrogen(mg/L)

0 1 . 0 0 . 0 1 . 1

8 3.1 3.61 1 3.6 2 . 1 4.016 4.2 2.4 4.219 6 . 6 3.7 8 . 1

46 8 . 6 5.0 6.354 9.1 5.8 8 . 1

60 8 . 6 7.6 7.564 13.274 11.3 10.5 12.982 13.2 14.5 16.089 15.1 16.7 13.497 13.9 11.9 15.7

1 0 2 14.0 14.0 14.01 1 0 15.7 17.2 18.4114 16.2 16.5 18.7123 17.4 15.9 19.5131 17.9 13.8 19.4140 18.3 14.2 18.2153 19.6 17.1 12.7169 1 2 . 6 14.3 15.3181 13.2 12.7 15.1186 15.2 15.6 16.3195 15.7 16.2 17.3

98


Table A.4. Nitrite-nitrogen results from sand filter effluent columns 1, 2, 3.


Days Nitrite-nitrogen

(mg/L) Nitrite-nitrogen

(mg/L) Nitrite-nitrogen

(mg/L)

0 0.1 0.1 0.1

8 5.0 5.0

11 1.8 0.6 1.8

16 3.4 1.8 3.4

19 3.3 1.7 3.3

46 2.0 2.1 2.0

54 1.4 1.3 1.4

60 2.2 1.4 2.2

64 1.0

74 1.1 1.2 1.0

82 1.5 1.1 1.1 89 0.9 2.6 1.5

97 1.0 0.9 0.9

102 0.3 1.0 1.0

110 0.1 2.3 0.3 114 0.1 0.1 0.1

123 0.3 0.1 0.1

131 1.2 0.3 0.3

140 0.8 1.1 1.2

153 0.5 0.6 0.5

169 1.3 1.8 0.7

181 0.1 0.9 0.1 186 1.4 0.9 1.4 195 0.8 0.9 0.8

99


Table A.4. Nitrite-nitrogen results from sand filter effluent columns 1, 2, 3.


DaysNitrite-nitrogen

(mg/L)Nitrite-nitrogen

(mg/L)Nitrite-nitrogen

(mg/L)0 0 . 1 0 . 1 0 . 1

8 5.0 5.01 1 1 . 8 0 . 6 1 . 8

16 3.4 1 . 8 3.419 3.3 1.7 3.346 2 . 0 2 . 1 2 . 0

54 1.4 1.3 1.460 2 . 2 1.4 2 . 2

64 1 . 0

74 1 . 1 1 . 2 1 . 0

82 1.5 1 . 1 1 . 1

89 0.9 2 . 6 1.597 1 . 0 0.9 0.9

1 0 2 0.3 1 . 0 1 . 0

1 1 0 0 . 1 2.3 0.3114 0 . 1 0 . 1 0 . 1

123 0.3 0 . 1 0 . 1

131 1 . 2 0.3 0.3140 0 . 8 1 . 1 1 . 2

153 0.5 0 . 6 0.5169 1.3 1 . 8 0.7181 0 . 1 0.9 0 . 1

186 1.4 0.9 1.4195 0 . 8 0.9 0 . 8

99




Days Ammonia-nitrogen Ammonia-nitrogen Ammonia-nitrogen

(mg/L) (mg/L) (mg/L) 0 17.6 16.7 17.6

8 16.7 12.4

11 12.4 16.7 10.3

16 10.3 15.4 9.5

19 9.5 10.8 10.5

46 10.5 9.5 9.2

54 8.7 9.1 10.8

60 9.3 9.2 7.6

64 7.6

74 6.9 7.2 8.2

82 4.8 5.6 7.6

89 3.7 3.1 7.2 97 2.3 3.7 2.3

102 2.1 2.3 2.1

110 1.1 2.1 1.1

114 1.7 1.1 1.7

123 1.7 1.7 1.7

131 0.7 1.7 2.5 140 0.7 0.7 1.7 153 0.8 0.7 7.1 169 7.9 0.8 5.9 181 3.3 7.9 3.3 186 2.1 3.3 2.1 195 1.3 2.1 1.3

100


Table A.5. Ammonia-nitrogen results from sand filter effluent columns 1 ,2 ,3 .


DaysAmmonia-nitrogen Ammonia-nitrogen Ammonia-nitrogen

(mg/L) (mg/L) (mg/L)0 17.6 16.7 17.68 16.7 12.4

1 1 12.4 16.7 10.316 10.3 15.4 9.519 9.5 1 0 . 8 10.546 10.5 9.5 9.254 8.7 9.1 1 0 . 8

60 9.3 9.2 7.664 7.674 6.9 7.2 8 . 2

82 4.8 5.6 7.689 3.7 3.1 7.297 2.3 3.7 2.3

1 0 2 2 . 1 2.3 2 . 1

1 1 0 1 . 1 2 . 1 1 . 1

114 1.7 1 . 1 1.7123 1.7 1.7 1.7131 0.7 1.7 2.5140 0.7 0.7 1.7153 0 . 8 0.7 7.1169 7.9 0 . 8 5.9181 3.3 7.9 3.3186 2 . 1 3.3 2 . 1

195 1.3 2 . 1 1.3

100


Table A.6. Dissolved oxygen concentration from sand filter columns 1, 2, 3.

Time

Days


mg/L mg/L mg/L

0 5 6 6

11 4 5 5

19 4 4 4

54 2 2 2

64 2 2 2

82 1 1 1

97 1 1 1

110 1 1 1

123 0.8 0.8 0.7

140 0.5 0.4 0.5

169 3 2.8 2.8

186 1 1.2 1.2

195 0.5 0.6 0.5

101


Table A.6. Dissolved oxygen concentration from sand filter columns 1, 2, 3.


Days mg/L mg/L mg/L

0 5 6 6

1 1 4 5 519 4 4 454 2 2 2

64 2 2 2

82 1 1 1

97 1 1 1

1 1 0 1 1 1

123 0 . 8 0 . 8 0.7140 0.5 0.4 0.5169 3 2 . 8 2 . 8

186 1 1 . 2 1 . 2

195 0.5 0 . 6 0.5

101


Table A.7. STE COD results

Time Days

Influent to Sand Filter COD mg/L)

8 5.35

16 172

46 432

60 318

74 344

82 365

89 344

97 274

110 312 123 338

131 326

140 412 153 215

169 276

181 346

195 312

102


Table A.7. STE COD results

TimeDays

0816466074828997110123131140153169181195

Influent to Sand Filter COD

(mg/L)

535172432318344365344274312338326412215276346312

102


Table A.8. COD results from sand filter effluent columns 1, 2, 3.

Time

(Days)

Column 1 COD

(mg/L)

Column 2 COD

(mg/L)

Column 3 COD

(mg/L)

0

8 49 44 51

16 16 18 21

46 26 32 35

60 61 32 -,-, _.)..)

74 17 17 17

82 22 24 23

89 35 39 32

97 36 29 17

110 42 37 24

123 56 42 39

131 45 44 29

140 44 21 61

153 15 35 55

169 53 46 47

181 32 43 39

195 29 36 35

103


Table A.8. COD results from sand fdter effluent columns 1, 2, 3.


(Days) COD(mg/L)

COD(mg/L)

COD(mg/L)

08 49 44 5116 16 18 2146 26 32 3560 61 32 O ">

74 17 17 1782 22 24 2389 35 39 3297 36 29 17110 42 37 24123 56 42 39131 45 44 29140 44 21 61153 15 35 55169 53 46 47181 32 43 39195 29 36 35

103


Table A.9. STE Alkalinity results

Time Influent to Sand Filter

(Days) Alkalinity

(mg/L as CaCO3) 0

8 536

22 515

36 523

50 490

64 550

78 526 92 600

106 534 120 557

134 526

148 540 162 546 176 573

190 531

197 543

104


Table A.9. STE Alkalinity results

Time Influent to Sand Filter

(Days) Alkalinity (mg/L as CaCC>3 )

0

8 5362 2 51536 52350 49064 55078 52692 600106 5341 2 0 557134 526148 540162 546176 573190 531197 543

104


Table A.10. Alkalinity results from sand filter effluent columns 1, 2, 3.


Days Alkalinity

(mg/L as CaCO3) Alkalinity

(mg/L as CaCO3Alkalinity

(mg/L as CaCO30

8 300 351 369 22 407 446 445

36 429 450 437 50 563 538 549

64 535 542 493

78 468 496 461

92 460 465 486

106 421 467 460

120 465 468 485

134 453 450 473 148 427 443 481

162 514 531 503 176 490 520 483

190 443 463 461 197 456 450 421

105


Table A.10. Alkalinity results from sand filter effluent columns 1, 2, 3.


DaysAlkalinity

(mg/L as CaCOa)Alkalinity

(mg/L as CaCC>3

Alkalinity (mg/L as CaCCL

0

8 300 351 3692 2 407 446 44536 429 450 43750 563 538 54964 535 542 49378 468 496 46192 460 465 486106 421 467 4601 2 0 465 468 485134 453 450 473148 427 443 481162 514 531 503176 490 520 483190 443 463 461197 456 450 421

105


Table A.11. STE phosphate as P results.

Time

(Days)

Influent to Sand Filter

Phosphate-as P

(mg/L)

10 4.5

21 0.7 26 4.6 29 4.7

56 3.1 64 1.6

70 1.7

74 3.2 84 4.1

92 7.5 99 6.8 107 5.3 112 6.4 124 7.9 133 7.7 141 7.6 154 6.6

169 5.4 183 5.7

187 6.1 192 5.2

106


Table A .l l . STE phosphate as P results.

Time(Days)

Influent to Sand Filter Phosphate-as P

(mg/L)1 0 4.5

2 1 0.726 4.629 4.756 3.164 1 . 6

70 1.774 3.284 4.192 7.599 6 . 8

107 5.31 1 2 6.4124 7.9133 7.7141 7.6154 6 . 6

169 5.4183 5.7187 6 . 1

192 5.2


Table A.12. Phosphate as P results from sand filter effluent columns 1, 2, 3.

Column 1

Phosphate-as P

(mg/L)

Column 2 Column 3

Time

(Days)

Phosphate-as P

(mg/L)

Phosphate-as P (mg/L)

10 0.5 1.5 2.1

21 0.6 0.3 0.6

26 1.4 1.6 1.9

29 1.7 1.4 1.6

56 0.6 0.8 1.1

64 0.7 0.7 0.5 70 0.8 0.9 0.9 74 0.7 0.5 1.1

84 1.2 0.6 1.9 92 1.4 2.8 1.8 99 1.3 2.1 2.5

107 1.3 1.8 1.4

112 1.6 1.4 1.1 124 2.0 2.1 1.8 133 2.3 2.3 1.4 141 2.0 2.0 2.1 154 1.6 1.1 1.9 169 3.7 2.9 2.7 183 1.7 3.1 2.0 187 2.1 1.4 1.1

192 1.2 0.8 0.6

107


Table A .12. Phosphate as P results from sand fdter effluent columns 1, 2, 3.

Column 1 Column 2 Column 3Time

(Days)Phosphate-as P

(mg/L)Phosphate-as P

(mg/L)Phosphate-as P

(mg/L)1 0 0.5 1.5 2 . 1

2 1 0 . 6 0.3 0 . 6

26 1.4 1 . 6 1.929 1.7 1.4 1 . 6

56 0 . 6 0 . 8 1 . 1

64 0.7 0.7 0.570 0 . 8 0.9 0.974 0.7 0.5 1 . 1

84 1 . 2 0 . 6 1.992 1.4 2 . 8 1 . 8

99 1.3 2 . 1 2.5107 1.3 1 . 8 1.41 1 2 1 . 6 1.4 1 . 1

124 2 . 0 2 . 1 1 . 8

133 2.3 2.3 1.4141 2 . 0 2 . 0 2 . 1

154 1 . 6 1 . 1 1.9169 3.7 2.9 2.7183 1.7 3.1 2 . 0

187 2 . 1 1.4 1 . 1

192 1 . 2 0 . 8 0 . 6

107


Table A.13. Nitrate as nitrogen results from SLAD effluent columns 1, 2, 3.

Time

(Days)

Column 1 NO3-N (mg/L)



0 0.07 0.05 0.04 8 0.12 0.03

11 0.1 4.68 0.05 16 0.07 0.02 0.02 19 0.03 0.06 4.26 46 0.03 0.06 1.06 54 1.76 0.02 0.00 60 0.31 0.01 0.04 64 0.67 74 0.01 0.02 1.46 82 0.16 0.01 0.02 89 0.16 0.01 0.05 97 0.16 0.05 0.24 102 0.02 0.03 0.02 110 1.84 0.39 1.01 114 0.01 0.05 0.02 123 0.02 0.05 0.01 131 0.02 0.01 0.07 140 0.31 0.04 0.18 153 0.42 0.09 1.59 169 1.91 0.19 0.53 181 1.04 1.47 0.76 186 0.8 0.34 0.64 195 0.9 0.71 0.58

108


Table A.13. Nitrate as nitrogen results from SLAD effluent columns 1, 2, 3.


(Days) N 0 3-N(mg/L)

NO3 -N(mg/L)

NO3 -N(mg/L)

0 0.07 0.05 0.048 0 . 1 2 0.03

1 1 0 . 1 4.68 0.0516 0.07 0 . 0 2 0 . 0 2

19 0.03 0.06 4.2646 0.03 0.06 1.0654 1.76 0 . 0 2 0 . 0 0

60 0.31 0 . 0 1 0.0464 0.6774 0 . 0 1 0 . 0 2 1.4682 0.16 0 . 0 1 0 . 0 2

89 0.16 0 . 0 1 0.0597 0.16 0.05 0.24

1 0 2 0 . 0 2 0.03 0 . 0 2

1 1 0 1.84 0.39 1 . 0 1

114 0 . 0 1 0.05 0 . 0 2

123 0 . 0 2 0.05 0 . 0 1

131 0 . 0 2 0 . 0 1 0.07140 0.31 0.04 0.18153 0.42 0.09 1.59169 1.91 0.19 0.53181 1.04 1.47 0.76186 0 . 8 0.34 0.64195 0.9 0.71 0.58

108


Table A.14. Nitrite as nitrogen results from SLAD effluent columns 1, 2, 3.

Time

(Days)

Column 1 Nitrite as nitrogen

(mg/L)


(mg/L)


(mg/L) 0 0.1 0.1 0.1

8 5.0 5.0

11 1.8 0.6 1.8

16 3.4 1.8 3.4

19 3.3 1.7 3.3

46 2.0 2.1 2.0

54 1.4 1.3 1.4

60 2.2 1.4 2.2

64 1.0

74 1.1 1.2 1.0

82 1.5 1.1 1.1

89 0.9 2.6 1.5 97 1.0 0.9 0.9

102 0.3 1.0 1.0 110 0.1 2.3 0.3 114 0.1 0.1 0.1

123 0.3 0.1 0.1

131 1.2 0.3 0.3 140 0.8 1.1 1.2

153 0.5 0.6 0.5 169 1.3 1.8 0.7 181 0.1 0.9 0.1 186 1.4 0.9 1.4 195 0.8 0.9 0.8

109


Table A.14. Nitrite as nitrogen results from SLAD effluent columns 1, 2, 3.


(Days) Nitrite as nitrogen (mg/L)

Nitrite as nitrogen (mg/L)

Nitrite as nitrogen (mg/L)

0 0 . 1 0 . 1 0 . 1

8 5.0 5.01 1 1 . 8 0 . 6 1 . 8

16 3.4 1 . 8 3.419 3.3 1.7 3.346 2 . 0 2 . 1 2 . 0

54 1.4 1.3 1.460 2 . 2 1.4 2 . 2

64 1 . 0

74 1 . 1 1 . 2 1 . 0

82 1.5 1 . 1 1 . 1

89 0.9 2 . 6 1.597 1 . 0 0.9 0.9

1 0 2 0.3 1 . 0 1 . 0

1 1 0 0 . 1 2.3 0.3114 0 . 1 0 . 1 0 . 1

123 0.3 0 . 1 0 . 1

131 1 . 2 0.3 0.3140 0 . 8 1 . 1 1 . 2

153 0.5 0 . 6 0.5169 1.3 1 . 8 0.7181 0 . 1 0.9 0 . 1

186 1.4 0.9 1.4195 0 . 8 0.9 0 . 8

109


Table A.15. Sulfate results from SLAD effluent columns 1, 2, 3.

Time

(Days)

Column 1

Sulfate (mg/L)

Column 2 Sulfate (mg/L)

Column 3 Sulfate (mg/L)

0 2061.6 3180.0 3142.0

8 1045.6 911.5

11 597.9 2068.3 1037.7

16 643.3 2173.6 1472.6

19 766.5 2266.0 317.3

46 301.7 775.2 340.0

54 184.3 536.8 214.7

60 260.5 242.8 223.6

64 223.2

74 227.0 240.7 270.8

82 358.2 611.6 323.8

89 294.1 289.1 328.6 97 171.6 276.9 179.1

102 257.2 279.6 283.9

110 197.2 105.3 104.4

114 480.7 294.9 298.7

123 148.6 167.7 111.9

131 110.5 153.2 139.0

140 134.7 168.7 142.6

153 143.9 172.3 235.4

169 270.3 268.1 264.6

181 220.5 256.4 183.2 186 167.9 194.3 167.9

195 180.3 189.3 173.7

110


Table A.15. Sulfate results from SLAD effluent columns 1, 2, 3.


(Days) Sulfate(mg/L)

Sulfate(mg/L)

Sulfate(mg/L)

0 2061.6 3180.0 3142.08 1045.6 911.5

1 1 597.9 2068.3 1037.716 643.3 2173.6 1472.619 766.5 2266.0 317.346 301.7 775.2 340.054 184.3 536.8 214.760 260.5 242.8 223.664 223.274 227.0 240.7 270.882 358.2 611.6 323.889 294.1 289.1 328.697 171.6 276.9 179.1

1 0 2 257.2 279.6 283.91 1 0 197.2 105.3 104.4114 480.7 294.9 298.7123 148.6 167.7 111.9131 110.5 153.2 139.0140 134.7 168.7 142.6153 143.9 172.3 235.4169 270.3 268.1 264.6181 220.5 256.4 183.2186 167.9 194.3 167.9195 180.3 189.3 173.7

110


Table A.16. COD results from SLAD effluent columns 1, 2, 3.


(Days) COD

(mg/L) COD

(mg/L) COD

(mg/L)

0

8 156 140 167

16 123 95 140

46 234 134 156

60 206 145 122

74 154 132 127

82 163 123 125

89 112 108 140

97 145 94 106 110 178 131 108

123 123 112 95

131 156 139 67

140 156 139 67

153 100 126 74

169 145 105 113

181 112 103 88

195 108 70 80

I 1 1


Table A.16. COD results from SLAD effluent columns 1, 2, 3.


(Days) COD COD COD(mg/L) (mg/L) (mg/L)

0

8 156 140 16716 123 95 14046 234 134 15660 206 145 1 2 2

74 154 132 12782 163 123 12589 1 1 2 108 14097 145 94 106

1 1 0 178 131 108123 123 1 1 2 95131 156 139 67140 156 139 67153 1 0 0 126 74169 145 105 113181 1 1 2 103 8 8

195 108 70 80

111


Table A.17. Phosphate-as P results from SLAD effluent columns 1, 2, 3.

Column 1

Phosphate-as P

(mg/L)

Column 2 Column 3

Time

(Days)

Phosphate-as P

(mg/L)

Phosphate-as P

(mg/L)

10 7.9 7.8 6.6

21 4.9 4.3 7.5

26 3.2 3.4 3.8

29 3.0 2.7 2.3

56 4.7 4.4 5.0

64 4.0 4.5 4.1

70 2.9 3.5 3.1

74 4.4 4.0 4.3

84 2.6 2.5 2.5

92 2.2 2.6 2.2

99 2.1 2.6 2.1

107 2.3 2.6 2.6

112 2.9 3.0 1.4

124 3.9 3.3 5.6

133 3.8 3.9 2.1

141 2.5 2.1 2.2

154 2.2 1.4 3.2

169 4.9 4.7 3.2

183 3.2 2.1 1.2

187 2.4 1.9 1.8

192 2.1 1.4 0.8

1 1 2


Table A.17. Phosphate-as P results from SLAD effluent columns 1, 2, 3.

Column 1 Column 2 Column 3Time Phosphate-as P Phosphate-as P Phosphate-as P

(Days) (mg/L) (mg/L) (mg/L)1 0 7.9 7.8 6 . 6

2 1 4.9 4.3 7.526 3.2 3.4 3.829 3.0 2.7 2.356 4.7 4.4 5.064 4.0 4.5 4.170 2.9 3.5 3.174 4.4 4.0 4.384 2 . 6 2.5 2.592 2 . 2 2 . 6 2 . 2

99 2 . 1 2 . 6 2 . 1

107 2.3 2 . 6 2 . 6

1 1 2 2.9 3.0 1.4124 3.9 3.3 5.6133 3.8 3.9 2 . 1

141 2.5 2 . 1 2 . 2

154 2 . 2 1.4 • 3.2169 4.9 4.7 3.2183 3.2 2 . 1 1 . 2

187 2.4 1.9 1 . 8

192 2 . 1 1.4 0 . 8

112


Table A.18. Alkalinity results from SLAD effluent columns 1, 2, 3.


(Days) Alkalinity

(mg/1, as CaCO3) Alkalinity

(mg/L as CaCO3) Alkalinity

(mg/L as CaCO3)

0

8 549 511 513

22 892 939 939

36 688 567 532

50 794 895 808

64 656 600 612

78 596 600 590

92 580 580 546

106 593 593 543

120 603 560 553

134 531 524 532

148 516 518 529

162 546 564 568

176 523 552 549

190 516 516 531

197 538 523 526

113


Table A.18. Alkalinity results from SLAD effluent columns 1, 2, 3.


(Days)Alkalinity

(mg/L as CaC 03)Alkalinity

(mg/L as C aC 03)Alkalinity

(mg/L as C aC 03)

08 549 511 513

22 892 939 93936 688 567 53250 794 895 80864 656 600 61278 596 600 59092 580 580 546106 593 593 543

120 603 560 553134 531 524 532

148 516 518 529

162 546 564 568176 523 552 549190 516 516 531197 538 523 526

113


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