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1988

Development and Design of a Fluidized Bed/Upflow Sand Filter Configuration for Use inRecirculating Aquaculture Systems.Daniel G. BurdenLouisiana State University and Agricultural & Mechanical College

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D evelopm ent and design of a fluidized bed /upflow sand filter configuration for use in recirculating aquaculture system s

Burden, Daniel G., Ph.D.

The Louisiana State University and Agricultural and Mechanical Col., 1988

300 N. Zeeb Rd.Ann Arbor, MI 48106



DEVELOPMENT AND DESIGN OF A FLUIDIZED BED/UPFLOW SAND FILTER CONFIGURATION FOR USE IN RECIRCULATING

AQUACULTURE SYSTEMS

A Dissertation

Submitted to the Graduate Faculty of the Louisiana State University and

Agricultural and Mechanical College in partial fulfillment of the

requirements for the degree of Doctor of Philosophy

in

The Department of Civil Engineering

byDaniel G. Burden

B.S., Harding University, 1978 M.E., Louisiana State University, 1985

December 1988


ACKNOWLEDGEMENTS

This research was supported by the Louisiana Sea Grant College

Program, an element of the National Sea Grant College Program, under the

auspices of the National Oceanic and Atmospheric Adminstration, U.S.

Department of Commerce. Special thanks goes out to Mr. Ron Becker,

Associate Director of the Louisiana Sea Grant College Program, who has

continually supported this research effort throughout the past two

years. Invaluable advice was received from Drs. Dudley D. Culley and

Leon Duobinis-Gray at LSU's School of Forestry, W'ildlife, and Fisheries.

Much of the initial research depended on crawfish from off-season

production ponds provided by these individuals. The author would also

like to acknowledge Herman "Bubby" and Steve Oufnac of Baton Rouge,

Louisiana, whose commercial facility was used for verification testing

of design criteria on full-scale filter units. Crabs and invaluable

technical advice were provided by Mr. Cultus Pearson through his

commercial operation in Lacombe, Louisiana. Special thanks also goes

out to Ms. Ann Mannino and Mr. Jim Robin who gave invaluable laboratory

and field assistance.

ii


FORWARD

I would like to extend my sincere thanks to Dr. Ron Malone for his

assistance, guidance, and encouragement as my major professor in

addition to being a good friend. The numerous accomplishments I have

achieved over the past six years in no doubt reflect our working

relationship. I would like to extend my thanks to the other members of

the committee, Drs. Flora Wang, Marty Tittlebaum, Dipak Roy, and Dudley

Culley.

I would like to thank my brother and close friends whom I have

enjoyed working with over the past years: David S. Burden 'soon to be

Dr. David S. Burden), Dr. Constantine "Dean" Mericas, Don Manthe,

Kevin Cange, and Paul Gremillion. I also would like to acknowledge

members of the research group: Dr. Walter "Wink" Zachritz, deEtte

Ferguson, and Kelly Rusch, for their support and editorial assistance

over the last year. I also owe a great deal of gratitude to Dr. David

N. Richardson, a former employer and now a faculty member at the

University of Missouri at Rolla, whose encouragement to attend

graduate school in civil engineering was a turning point in my career.

Most of all, I am deeply indebted to my "closest" friend— my wife,

Betsy. Without her love, understanding, and constant companionship,

this accomplishment would have never been possible.

Some individuals have referred to this occasion as the end of a

"dynasty", but in the words of T.S. Eliot "In the end is my new

beginning". Well, call it whatever you want, I'm glad its over (and

so is my wife). Farewell Tiger fans.

iii


TABLE OF CONTENTS

Page

ACKNOWLEDGMENTS . . . . . . ................................ ii

FORWARD ................... iii

LIST OF TABLES . . . . . . . . . . . . . . . . ............ vii

LIST OF FIGURES ....................... viii

A B S T R A C T ............ xi

CHAPTER

I. Introduction.......... 1

II. The Effect of Sand Grain Size on Fluidized Bed Filter Performance in Recirculating,Soft-Shell Crawfish Production Systems ........ 6

Abstract.................................... 6

Introduction . ............................. 7

Background .................................. 9

Methodology............ 12

Results .......... 18

Fine Sand (20/40) 18

Medium Sand (12/20) 21

Coarse Sand (8/16)..................... 24

Discussion . . . . . . . . . . . .......... 26

Conclusions and Recommendations . . . . . . 29

III. Evaluation of a Fluidized Bed/Upflow Sand Filter Combination Proposed for a Recirculating Blue Crab Shedding S y s t e m ............ 31

Abstract........................... 31

Introduction ....................... 32

Background.................................. 33

Nitrification . . . .......... 33

iv


CHAPTER Page

Oxygen Consumption . ................... 34

Fluidized Bed Filter . ............. 36

Upflow Sand Filter . . . . . . . . . . . 37

M e t h o d s .................................. . 38

Filter Studies ............................. 39

Waste Characterization Study .............. 45

Results . 4 7

Filter Studies ............................. 47

Fluidized Bed/Upflow SandFilter Combination . . . . . . . 48

Fluidized B e d ....................... 50

Upflow Sand Filter.................. 54

Excretion S t u d y ........................... 56

Discussion..................................... 56

Oxygen Consumption ......................... 58

Nitrification ...................... 62

Relative Filter Ability . . . . . . . . 65

Summary ............... . . . . . . . . 66

Conclusions ................................. 67

IV. Fluidized Bed/Upflow Sand Filter Performance in a RecirculatingSoft-Shell Crawfish Facility . . . . . . . . . . 69

Abstract ................... . . . . . . . . 69

Introduction . . 70

Background . . . . . . . ............... . . 71

Commercial Facility Description. . . . . . . 80

Methodology..................................... 82


CHAPTER Page

Results . . ................... 84

Discussion............ 89

Conclusions and Recommendations . ......... 94

BIBLIOGRAPHY . ........................................... 96

APPENDICES . . . . ............................. 102

A. Water Quality Data ........................ 103

1. Grain Size Determination D a t a ............... 104

2. Filter Evaluation Data .......... 116

B. Crab Waste Characterization Data . . . . . . . . . 128

C. Filter Fluxrate D a t a ........... 130

D. Commercial Facility D a t a ............... .......... 137

VITA ........................................ 140

vi


LIST OF TABLES

Table Page

1 Water quality parameters and methodsused with the filtration research ............. 17

2 Analytical data summary for the steady-state analyses using thefine, medium, and coarse s a n d s ................. 20

3 Dimensions of the experimentalsetup used for determining filtercarrying capacity .................................... 41

4 Water quality methods and instrumentsused with the filtration research................ . 46

5 Steady-state data obtained on the fluidized bed (FB) and upflow sand(UFS) filters when running inparallel operation ......................... 51

6 Steady-state data obtained on (a) the single fluidized bed filter and (b) thesingle upflow sand filter ............... 53

7 Statistical summary for all waste characterization data collected onthe blue c r a b ....................... 57

8 Major components of a recirculatingshedding system ................. 74

9 Summary of interim design criteria for shedding systems employing fluidized bed/upflow sand filter configurations (taken from Maloneand Burden, 1988) . . ............................. 75

10 Summary of water quality and field data collected at the commercial soft-shell crawfish facility in Baton Rouge, Louisiana. All measurements of water qualitydata were taken in sump # 2 ......................... 86

vii


LIST OF FIGURES

Figure Page

1 Experimental apparatus used with thegrain size determinations . . ....................... 13

2 Detailed schematic of the fluidized bedfilter (not to scale)................................ 14

3 Loading, ammonia, nitrite, effluent dissolved oxygen, and pH data observed on the fine (20/40) grain sand when usedas a media with the fluidized bed f i l t e r ............. 19

4 Flowrates expressed as a percentage of the initial flowrate observed onthe fine, medium, and coarse sands . . . . . . . . . 22

5 Loading, ammonia, nitrite, effluent dissolved oxygen, and pH data observed on the medium (12/20) grain sand when used as a media with the fluidized bedf i l t e r ............................................... 23

6 Loading, ammonia, nitrite, effluent dissolved oxygen, and pH data observed on the coarse (8/16) grain sand when used as a media with the fluidized bedf i l t e r .......................................... 25

7 A schematic of the experimental setup used with the three filter configurations.The fluidized bed/upflow sand filter combination and the single upflow sand filter (circumvented by the dashed line) configurations are denoted in (a). The single fluidized bed filter is illustratedin (b) .......... ............ ..................... . 40

8 A detailed illustration of the fluidized bed filter used with the study (not toscale) ............................................... 42

9 Normal and intermittent operation of theupflow sand filter (not to scale) .............. 44

10 Water quality monitoring results and loading curves obtained on the fluidizedbed/upflow sand filter combination . . . . . . . . . 49

11 Monitoring results obtained on the fluidized bed filter using flosspre-filtration.... .................................... 52

vm


Figure Page

12 Loading curves and water quality monitoring data obtained on the single upflow sand filter configuration . . . . . . . . . . . . . ............... 55

13 Gamma distributions for OLR data on the fluidized bed and submerged rock filter configurations. Mean values are indicated in parentheses and denoted by the horizontal lines oneach distribution . . .......... . . ................ 59

14 Pie diagrams illustrating the representative portions of total OLR on the upflow sand andfluidized bed filters . . . . . 61

15 Results of the linear regression analyses performed on total nitrogen accumulation in the three filter configurations. R-square valuesindicated in parentheses.............. 64

16 Components of a recirculating systemfor a soft-shell crawfish facility ........... . . . 73

17 Unpressurized fluidized bed filter designs for diameters ranging from10 to 20 inches (25 to 50 cm) ......... 76

18 Unpressurized upflow sand filter designed for diameters ranging from10 to 20 inches (25 to 50 c m ) ....................... 78

19 Schematic of the commercial soft-shell crawfish facility located in BatonRouge, L o u i s i a n a .................................... 81

20 Total ammonia, nitrite, and pH monitoring data obtained on the commercial soft-shell facility in Baton Rouge, LA. Filter design capacity (150 lbs/ft3) indicatedby the vertical line . . . . . . . . . . . . . . . . 87

21 Total ammonia and nitrite removal efficiency data obtained on the commercial facility in Baton Rouge LA. Solid diagonal lines representremoval efficiencies . . . . ........................ 88

ix


Figure Page

22 Fluidized bed and upflow sand filterOCF observations taken at the commercial facility. Reported values for the upflow sand filter represent a mean with upper and lower standard deviations for thethree filters at a given filter loading . . . . . . . 91


ABSTRACT

A fluidized bed/upflow sand filter configuration, was developed and

designed for utilization in recirculating aquaculture systems, specifi

cally the soft-shell crab and soft-shell crawfish industries. These

filters were selected and designed because of their ability to withstand

clogging and still maintain high levels of water quality for aquaculture

production. The effectiveness of sand grain size was used to evaluate

fluidized bed filter performance with filter loadings ranging from 16 to

1285 pounds of crawfish per cubic foot of filter sand. A coarse sand

grain size was recommended as a filter media because of it's ability to

shear excessive biofilm growth from the sand, thus prohibiting clogging

from occurring within the filter bed. The fluidized bed/upflow sand

filter combination was evaluated in terms of nitrification and oxygen

consumption when used with a recirculating crab shedding system. The

filter combination's carrying capacity (700 crabs per cubic foot of sand

media) exceeded that observed with the submerged rock filter by more

than 20 times and was largely explained by the filter's solids removal

ability which significantly reduced the filter's oxygen loading rate

(OLR). Nitrification rates with the filter combination were extremely

high as total ammonia and nitrite levels remained below 1.0 mg-N/L.

Verification of a volumetric loading criteria (150 pounds per cubic

foot) for this filter combination was further established with

performance data obtained from a commercial soft-shell crawfish

facility. Water quality monitoring results indicated that the filters

maintained total ammonia and nitrite levels below 1.0 mg-N/L under

typical operating conditions. Shock loading, pH control, and over-

xi


feeding, rather than filter capacity, dominated water quality fluctua

tions, thereby indicating that the loading criteria was sufficient for

commercial operation.

xii


CHAPTER I

INTRODUCTION

The Gulf Coast states have recently experienced a re-growth and

re-expansion of the soft shell crab industry as reported landings have

increased tremendously over the last few years. Most of this increase

was attributed to the development of engineering designs for closed,

recirculating systems to hold and shed peeler crabs. These systems

centered on using low-rate biological treatment, such as the submerged

rock filter.

More recent activities have centered on culturing soft-shell

crawfish as a potential aquaculture industry in Louisiana and other Gulf

states. This past year (1988) marked the first year when several

large-scale producers, ranging from 500 to 2000 pounds, went into

commercial operation using flow-through systems. However, economic

constraints and the lack of reliable design criteria for maintaining

adequate water quality in shedding systems prohibited the initial

growth of the industry. Consequently, efforts focused on using new

technology, specifically recirculating systems, for producing the

soft-shells.

The low-rate submerged rock filter used with the crab industry was

limited in its inability to withstand clogging and still maintain

adequate water quality during periods of high loadings. For the soft-

shell crab industry to maintain its current growth and for the newly

developed soft-shell crawfish industry to increase its efficiency,

other filter designs were necessary to provide filters of a reasonable

size which would still maintain water quality. Consequently, research

■1


efforts were directed toward developing high-rate biological filters

that both industries could incorporate into recirculating designs.

Dissertation Objective and Approach

This dissertation consists of three manuscripts, each describing an

integral part of a two-year research project directed toward developing

and designing high-rate biological filters for recirculating systems.

The first manuscript focuses on the fluidized bed, a high-rate biologi

cal filter. Because of the limited amount of research conducted on the

filter, inconclusive data were available concerning the appropriate sand

grain size to employ as a filter media. Consequently, the initial

experimental work centered on investigating several sand grain sizes to

substantiate design criteria. Filter testing was carried out using

scaled-down recirculating systems for holding red swamp crawfish

(Procambarus clarkii). Chapter II, "The Effect of Sand Grain Size on

Fluidized Bed Filter Performance in Recirculating, Soft-Shell Crawfish

Production Systems", describes the results of this research. This

manuscript has been accepted for publication in The Journal of

Aquacultural Engineering.

The second portion of the research involved determining the most

effective filter design to use with a recirculating system. Following a

comprehensive literature search, a combination of the fluidized bed and

upflow sand filter appeared most appropriate for maintaining adequate

water quality in both soft-shell crab and crawfish shedding systems.

The upflow sand filter was added to the filter configuration because of

its ability to remove solids and consequently reduce BOD loading in the

system. Therefore, filter testing centered on analyzing this con

figuration, as well as its individual components, to determine filter


performance in terms of both nitrification and oxygen stability. Filter

evaluations were performed with blue crabs (Callinectes sapidus) , those

commonly used for shedding operations in the Gulf Coast region. In

addition to this study, a separate waste characterization analyses was

conducted to determine the relative effect of solids removal on

crab-excreted wastes. Chapter III, "Evaluation of the Fluidized

Bed/Upflow Sand Filter Combination Proposed for a Recirculating Blue

Crab Shedding System", describes the results of this work and makes

recommendations as to why the filter combination is well suited for

recirculating system designs.

Finally, Chapter IV, "Fluidized Bed/Upflow Sand Filter Performance

in a Recirculating Soft-Shell Crawfish Facility", presents verification

data based on the developed design criteria. Filter designs depended

upon several different aspects: (I) fed or unfed systems, (2) filter

media and size, (3) pumping requirements, (4) filter hydraulics, and

(5) filter carrying capacity. Design verification was carried out in a

1600 pound commercial crawfish shedding operation located in Baton

Rouge, Louisiana. The relative ability of the filter combination was

tested and analyzed in terms of both nitrification and dissolved oxygen

requirements and covered in Chapters III and IV. Both chapters have

also been submitted for publication in The Journal of Aquacultural

Engineering.

Conclusions

The high-rate fluidized bed and upflow sand filter combination was

proven as an extremely effective method to achieve water treatment in a

recirculating aquaculture system. Filter carrying capacities exceeded

those historically observed with the submerged rock filters by more than


4

20 times while still maintaining adequate water quality for shedding

operations. Total ammonia and nitrite levels remained below 1.0 mg-N/L

without experiencing any harmful impacts on molting crabs or crawfish.

The filter combination's higher efficiency was explained by the high

kinetic transport rates resulting from surface abrasion and hydraulic

distribution of blofilm in the fluidized bed and by the enhanced solids

removal ability of the upflow sand filter.

From the results of this research effort, one can readily see the

immediate impact that these high-rate filters are having on the aqua

culture industry. Because of the industry's continued growth rate,

efforts should be made to improve and enhance current system designs.

Continued research should focus on improving kinetic transport rates,

reducing water/volume ratios, and investigating the impact of CO^

accumulations, as applied to these filters. A more thorough under

standing of these concepts will increase the efficiency of the

recirculating system when utilized in the aquaculture industry.

Industrial Impact

Commercial dissemination of filter designs was initiated in April,

1988 when an advisory agent workshop, sponsored by the Louisiana Sea

Grant College Program, was conducted on the Louisiana State University

campus. Information on design of recirculating systems incorporating

the new filter technology was distributed to extension agents in

Louisiana, Florida, Minnesota, Mississippi, South Carolina, and Texas

for their use in the public sector. Consequently, the development of

recirculating soft-shell crawfish facilities in Louisiana and other Gulf

states has rapidly expanded and continues to do so. Commercial systems

ranging in size from 500 to 6000 pounds have been built and new


5

facilities are currently in construction for the 1988-1989 season. The

new filter technologies are also being implemented in other aquaculture

areas outside the Gulf Coast region as well. These areas include Morgan

Hill Aqua Farms in California, Sea Hatcheries Limited in Australia,

Norton Brothers, Inc. in Florida (tropical fish hatcheries), Early Times

Distillery in Kentucky (catfish production), and the Public Service of

Colorado (co-generation talapia grow-out system) just to mention a few.


CHAPTER II

THE EFFECT OF SAND GRAIN SIZE ON FLUIDIZED BED FILTER PERFORMANCE IN RECIRCULATING, SOFT-SHELL CRAWFISH PRODUCTION SYSTEMS*

Daniel G. Burden and Ronald F. Malone Department of Civil Engineering, Louisiana State University

Baton Rouge, Louisiana 70803

ABSTRACT

The effectiveness of media size was investigated when using a

fluidized bed filter in a recirculating system for soft-shell crawfish

production. Three different sand grain sizes, 0.42-0.84 mm, 0.84-

1.68 mm, and 1.19-2.38 mm were used to evaluate filter performance with3 3crawfish loadings ranging from 256 to 20,600 kg/m (16 to 1285 lbs/ft ).

Results of the study indicated that the hydraulic behavior of the fine

and medium grain sands prohibits using them as filter media at high3crawfish loadings, typically greater than 4633 kg/m of sand

3(300 lbs/ft ). During these high loading periods, excessive floe

developed within the filter causing the sand media to "gel" and effluent

oxygen levels to collapse. Conversely, the coarse sand exhibited no3 3clogging at loadings as high as 20,600 kg/m (1285 lbs/ft ). The coarse

sand's ability to shear excessive biofilm growth from the sand prohi

bited clogging from occurring within the filter bed and therefore made

it a superior media to use with a fluidized bed in a soft-shell crawfish

system.

*In Press, The Journal of Aquacultural Engineering

6


7

INTRODUCTION

Soft-shell crawfish have recently been considered a seafood

delicacy although availability has been severely limited by production.

Newly developed technology, however, now permits commercial production

of soft-shell crawfish on a small scale. Total production for this

growing industry rose from an estimated 2950 kg (6500 lbs) in the

1985-1986 season to over 6800 kg (15,000 lbs) during 1986-1987 season.

Current projections indicate somewhere between 22,700 and 34,000 kilo

grams (50,000 and 75,000 pounds) will be produced during the 1987-1988

season. Production levels in excess of 454,000 kilograms (one million

pounds) per year are expected within a few years only if the industry

can overcome certain obstacles. These problems include: (1) guaran

teeing a source of immature hard crawfish and extension of season,

(2) difficulties with acclimating pond-raised or wild immature crawfish

into soft-shell facilities, and (3) the lack of reliable design criteria

for maintaining adequate water quality in a shedding system.

Industry has placed its current focus on improving water quality by

developing reliable design criteria for shedding facilities. The

earliest commercial systems employed flow-through systems for holding

and separating soft-shell crawfish. Operational costs associated with

this technology, however, are high because of the water use and

heating costs. Flow-through systems require freshwater, usually drawn

from wells or municipal water systems, at a continuous flushing rate

ranging from 0.42 to 0.83 L/min-kg (0.05 to 0.1 gpm/lb). Thus, a

small facility with a 454 kg (1000.1b) holding capacity demands 8 to

16 billion liters (17 to 35 million gallons) of heated groundwater

over an eight month season. Furthermore, the annual costs associated


8

with heating the groundwater from 21 to 27°C (70 to 80°F) will exceed

$15,000. Assuming a 2 percent daily production rate and the current

wholesale market price of $17.6/kg ($9.00/lb), a 454 kg (1000 lb)

facility can generate approximately $43,000 a year in gross income. If

heating costs account for nearly 30 percent of this income, the

economical viability of the entire operation becomes questionable.

A more cost-effective means of producing the soft-shell crawfish

can be achieved by using a closed recirculating system. These systems,

characterized by their reuse of water, contain filtration components

which process animal wastes to a relatively inert and harmless state

(Manthe et al. 1984). Annual heating costs are relatively low ranging

from $1,000 to $2,000 for an insulated recirculating system. Research

has therefore centered on developing high-rate filters which can support

exceedingly large amounts of biomass and still maintain adequate water

quality. One of the biological filters proposed for this purpose is the

fluidized bed filter.

The fluidized bed filter operates as a "fixed-film" biological

filter, but involves an upward movement of fluid, or wastewater, through

a sand bed at a velocity sufficient enough to "fluidize" the sand. Sand

has been historically used as a granular media because it is durable and

relatively inexpensive. The sand grain size defines the hydraulic

environment within a fluidized bed and thus, is the major factor con

trolling the filter's effectiveness. Therefore, research was directed

toward determining an appropriate grain size to employ with a fluidized

bed filter when used in a recirculating system. This article compares

the effectiveness of three sand grain sizes and makes recommendations on


an effective grain size to use with a fluidized bed filter in a recircu

lating soft-shell crawfish system.

BACKGROUND

In a typical soft-shell crawfish culture system, pond-raised

immature crawfish (Procambarus clarkii) are placed in shallow, indoor

culture trays and fed until they develop color patterns which indicate

the approach of molting (or ecdvsis). Premolt crawfish are isolated

in "molting trays" and then removed by hand within a few hours of the

molting process and immediately frozen (Culley et al. 1.985). Systems

are designed based on holding capacity (kilograms or pounds). Most

systems in Louisiana are small with holding capacities ranging from 227

to 908 kilograms (500 to 2,000 pounds). These systems currently produce

1.5 to 2.0 percent of capacity per day when properly operated at 27°C

(80°F).

While in the system, crawfish continuously excrete ammonia

(Hartenstein, 1970). This direct excretion of total ammonia associated

with the crawfish, as well as that produced from the decay of uneaten

feed, continually contribute total ammonia to the recirculating system.

Cange (1987) demonstrated that crawfish total ammonia excretion rates

vary from 58 to 86 mg-N per pound of crawfish per day depending on the

protein content of the feed. High protein foods (43 percent) can

contribute as much as 130 mg-N per gram of food if left to decay in a

system (Cange, 1987). Consequently, high mortalities have been often

associated with total ammonia and possibly nitrite accumulations in both

flow-through and recirculating systems.


10

Reported total ammonia toxicity limits for crawfish (P^ clarkii)

range from a maximum of 2.65 mg-N/L (pH=8.6), associated with juvenile

crawfish (based on 96-hr LC-50's), to as low as 1.00 mg-N/L observed

during the molting process (Hymel, 1985; Cange, 1987). Hymel (1985)

also reported mean nitrite toxicity levels of 5.94 mg-N/L (96-hr LC-

50's) on intermolt crawfish while no mortalities were observed when

concentrations were maintained at 1.00 mg-N/L. Additional nitrite

toxicity research on intermolt crawfish (|\_ clarkii) by Gutzmer and

Tomasso (1985) indicated a 96-hr LC-50 of 8.5 +0. 5 mg-N/L. Observa

tions made on commercial facilities lead the authors to conclude that

molting losses become significant at levels well below the indicated

acute toxicity levels (96-hr LC-50's) because of the intermolt's

increased sensitivity and long exposure periods (up to 50 days).

Considering the lack of data on chronic toxicity levels, the authors

assumed that ammonia (total) and nitrite concentrations should be

maintained below 1.0 mg-N/L to avoid high molting losses. The success

of a recirculating system thus depends on designing filtration

components, which can adequately maintain total ammonia and nitrite

levels when used in an aquaculture setting.

Weber et al. (1970) first recognized the ability of the biological

fluidized bed filter when he used fluidized beds of activated carbon to

remove dissolved organic compounds from chemically-treated sewage.

Weber noticed the biomass growth occurring on the particles and likewise

the reduction in nitrite concentrations through the bed. Similar to a

fixed-film filter, the sand or carbon particles become evenly coated

with both heterotrophic and chemoautotrophic bacteria. Heterotrophs

obtain their energy from organic compounds (excreted by the crawfish)


11

and convert them to an inorganic state while the chemoautotrophs obtain

their energy by converting the inorganics. Nitrosomonas and Nitro-

bacter, the principal genera of the autotrophic bacteria, convert total

ammonia to nitrite and nitrite to the relatively harmless state of

nitrate, respectively. The active biomass concentration in the filter

is large because of the greater amount of surface area available for

biological growth.

The range of media sizes used with fluidized bed filters varies by

almost 200 percent. Jeris et al. (1974) employed fluidized beds for

denitrification of domestic and industrial wastewaters using sand

ranging in diameter from 0.8 to 1.1 mm as a medium for biological

growth. Short (1973) also developed a fluidized bed filter for

oxidizing low concentrations of total ammonia (0.5 - 2.0 mg NH^-N/L)

found in river water when used as a water supply. Short assumed that by

providing a larger surface area for bacterial growth more treatment

could be achieved and, therefore, used sand ranging in diameter from

0.05 to 0.15 mm. Additional research on fluidized bed filters, where

sand is employed as the granular media, has been based on particle

diameters ranging in size from 0.3 to 0.9 mm (Cooper, 1981; Nutt et al.

1984).

Selecting an appropriate grain size insures that (1) a suitable

amount of surface area is available for biological growth, (2) an

adequate oxygen supply is maintained across the filter bed, and (3)

a sufficient amount of abrasion is provided to avoid filter clogging

as a result of excessive biofilm growth. The methods used for

determining the effect of grain size on filter performance are

presented in the following section.


12

METHODOLOGY

Three independent fluidized bed filters were used to examine the

effect of grain size on the removal of total ammonia and nitrite in a

recirculating system. As implied by Standard Methods, the test for

ammonia nitrogen (NH^) measures all nitrogen in the form of NH^, NHÔH,

and NH^. Therefore, throughout the remainder of the text, reference to

'ammonia’ or 'NH^' implies 'total ammonia'.

Each system consisted of a fluidized bed reactor with a holding

tank containing a known weight of live crawfish. Live crawfish were

used to assure that the waste load imposed on each system was

representative of a commercial facility, thus assuring that the

filters would hold representative populations of both hetertrophic and

autotrophic bacteria. Crawfish were not fed while in the system so

that loading information could be accurately determined for

comparative purposes.

The holding tank consisted of a 521 mm (21.5 inches) square plastic

tub with a 330 mm depth (13 inches). A 25.4 mm (1 inch i.d.) drain pipe

was located in the tank's front center (Figure 1). Total system volume

was equivalent to 98 liters (26.0 gal.). A 250 x 500 mm sheet of

plastic louvering was placed inside the tank and elevated at a height of

approximately 70 mm to allow additional surface area for the crawfish

during periods of high loading.

Each fluidized bed filter was constructed using 38.1 mm (1.5 inch

i.d.) diameter clear PVC tubing (762 mm long) with appropriate PVC

fittings on the intake and outlet similar to those illustrated in

Figure 2. Recirculation of water through the filter was maintained

using a Cole-Palmer 1/25 HP centrifugal pump with magnetic drive.


13

TO AIR PUMP

M S*neFLUIDIZED

MEDIA HOLDINGTANK

PUMP

Figure 1. Experimental apparatus used with the grain size determinations.


14

19 mm (3 /4 " )

DISCHARGE BACK TO SYSTEM

3 8 mm

100 PERCENT EXPA NSIO N

PACKED H EIG H T

— 2 5 m m ( I ) OF GRADED GRAVELSUPPORT PLATE

3 .2 mm HOLES

SCREENED IN FLOW

BALL VALVESECTION A-A

Figure 2. Detailed schematic fo the fluidized bed filter (not to scale).


15

Flowrates were based on maintaining 100 percent expansion of the bed at

all times by using a 1.9 cm (3/A") ball valve on the filter's intake

side. Aeration was provided to the system by using two Whisper 600

pumps with airstones placed in each holding tank.

Three different sand grain sizes were used for comparative work in

this study: (1) a 1.19-2.38 mm coarse filter sand (graded to pass a #8

mesh and retain on a #16 mesh screen), (2) a 0.8A-1.68 mm medium filter

sand (graded to pass a #12 mesh and retain on a #40 mesh screen) , and

(3) a 0.42-0.84 mm fine filter sand (graded to pass a #20 mesh and

retain on a #40 mesh screen). All sands were pre- washed with ammonia-

free dechlorinated water to remove excess debris. Packed bed height of

each filter was equivalent to 30.5 cm (1 ft.) corresponding to a total3 3media volume of 347 cm (0.012 ft ). Because the fluidized bed operates

in a turbulent environment, excreted solids (which are continuously

released by the crawfish) remain within the system. Therefore, a small3

floss bed filter (volume = 709 cm ) was positioned at the effluent

discharge and changed on a daily basis. The floss bed, which removed

excreted solids, was used to simulate commercial operations which employ

some means of solids removal in the treatment scheme.

Experimental protocol consisted of filling each tank with 41 liters

(10.83 gal.) of ammonia-free, dechlorinated tap water. A known "wet

weight" of crawfish, ranging in carapace width from 18 to 20 mm

(14 + 1 gram), were then loaded into each system. Crawfish were not fed

while in the experimental tanks and were replaced every 48 to 72 hours

with crawfish taken from a separate 7600 liter (2000 gallon) recircu

lating holding system where feeding was conducted. Purina Trout Chow

Checkerettes #4 (w/ 43 percent protein) were used for feeding in the


16

support system. Ammonia excretion rates for these crawfish were

estimated at 36 mg-N/lb-day (Cange, 1987). Mortalities were removed

every 3 to 4 hours and replaced with healthy crawfish from the main

holding system. Total system weights were checked once a day and

adjusted accordingly. All systems were maintained at 24 + 1°C.

Physical and chemical parameters were monitored daily between

9:00 am and 11:00 am. Parameters included pH, dissolved oxygen (DO),

temperature, flowrate, ammonia nitrogen (NH^-N) and nitrite nitrogen

(NOn-N). When each system stabilized at a given loading of crawfish

weight, a "steady-state" analysis was conducted to indicate typical

filter performance. Steady-state analyses included biochemical oxygen

demand (BOD), and alkalinity (ALK) in addition to those parameters run

on a daily basis. At the end of a steady-state analysis, each system

was completely drained; replaced with fresh ammonia-free, dechlorinated

tap water; and adjusted for optimum pH by adding sodium bicarbonate.

The in-tank crawfish weight was then increased and maintained until the

next steady-state condition. The methods and instrumentation used with

each analysis are outlined in Table 1. All analyses were conducted

according to procedures outlined in Standard Methods (APHA, 1985).

Bicarbonate addition was used to maintain pH levels (7.5-8.3), as

well as alkalinity levels (>100 mg/L as CaC03), in an optimum range for

nitrification (Paz, 1984; USEPA, 1975). Below a pH of 7.0, a reduction

in nitrification occurs but does not cease completely (Hirayama, 1970).

pH levels were therefore adjusted at the beginning of each steady-state

analysis by chemical adding 2.4 to 4.8 mg/lb of sodium bicarbonate

(NaHC03) per day (Malone and Burden, 1987). All adjustments were made

following each day's sampling routine.


Table 1. Water quality parameters and methods used with the filtration research.

Water Quality Parameter Analysis Method

Total Ammonia Nitrogen Distillation, Nesslerization

Nitrite Nitrogen Sulfanilamide-basedColorimetric

Nitrate Nitrogen Orion Nitrate Ion Electrode - Model 93-07, Orion Double Junction Reference Electrode - Model 90-02

Total Kjeldahl Nitrogen Digestion, Distillation, Nesslerization

Biochemical Oxygen Demand

Winkler Method

Alkalinity Titration/Potentiometric

Total Suspended Solids Gravimetric

Dissolved Oxygen Yellow Springs Instrument Model 57 Oxygen Meter

PH Cole-Palmer Mini pH Meter


18

RESULTS

Filter performance between the three grain sizes was evaluated

based on relative nitrification ability, maintaining adequate dissolved

oxygen in the effluent water, and maintaining adequate pH. A comparison

of the three grain sizes was made based on a crawfish loading rate of 3 34633 kg/m (289 lbs/ft ), the highest load successfully sustained by all

three sands.

Fine Sand (20/40). A total of four steady-state analyses (June 16,

July 3, July 22, and August 7), with loadings ranging from 256 to3 34633 kg/m (16 to 289 lbs/ft ), were performed on the fine media. Time

trace data for both daily ammonia and nitrite data are compared with

corresponding loadings in Figure 3. Steady-state values for ammonia and

nitrite all increased with carrying capacity (Table 2). At a loading of 3 34633 kg/m (289 lbs/ft ), steady-state ammonia and nitrite concentra

tions were equivalent to 1.26 and 0.08 mg-N/L, respectively. The

volume/weight ratio, defined as the ratio of total water volume to the

crawfish weight (loading) held in the system, was equivalent to

25.5 L/kg (3.0 gal/lb). The previous loading rate of 946 kg/m^3(59 lbs/ft ) displayed moderate steady-state ammonia levels

(0.62 mg-N/L) and non-detectable nitrite concentrations.

Monitoring was only performed for a 12-day period following the3steady-state analyses at the maximum loading of 4633 kg/m (August 7).

3System failure occurred with a capacity equivalent to 9266 kg/m 3(578 lbs/ft ) when the excess floe development caused the filter to

"gel" and oxygen levels in the effluent water collapsed. The dramatic

increase in ammonia and nitrite concentrations (11.99 and 0.68 mg-N/L,

respectively) on August 16 reflects this two-fold increase in loading.


19

Figure 3

pH

O X 0 0

»

7-«£ 6

000

3 00

400

500

100

E2AY29 JU5I0 JUS) 50 JU L13 J u t 30 &UGI3 AUG 31 K P T 13 SEPT 30SAUPLB40 DATE

Loading, ammonia, nitrite, effluent dissolved oxygen, and pH data observed on the fine (20/40) grain sand when used as a media with the fluidized bed filter..


Reproduced

with perm

ission of the

copyright ow

ner. Further

reproduction prohibited

without

permission.

Table 2. Analytical data summary for the steady-state analyses using the fine, medium, and coarse sands.

Loading(kg/m )„ 256 475 946 4633 9266 11,590 15,454 20,600(lbs/ft ) 16 30 59 289 578 723 964 1285

Fine Sand:Temp. (°C) 23.9 23.9 23.4 23.4pH 7.50 7.00 7.40 8.00Flowrate (L/rain) 1.27 0.77 1.02 0.69NH3-N (mg/L) 0.49 0.61 0.62 1.26N02-N (mg/L) < 0.01 < 0.01 <0.01 0.08BOD5 (mg/L) , 1 4ALK (mg/L as CaC03) • • 2 9

Medium Sand:Temp. (°C) 24,0 23.9 23.7 23.7 23.1 23.8pH 7.50 6.95 7.50 7.15 7.05 7.50Flowrate (L/min) 3.25 3.22 3.19 2.64 1.38 1.23HH3-N (mg/L) 0.55 0.54 0.64 1.16 1.78 1.45N02-N (mg/L) 0.02 0.02 0.01 0.12 0.19 0.19B0D5 (mg/L) , . 1 4 7 12ALK (mg/L as CaC03) • • 79 86 242 263

Coarse Sand:Temp. (°C) 24.1 23.9 23.7 23.7 23.3 24.0 23.0 21.4PH 7.60 6.85 7.40 7.85 7.35 7.75 7.90 8.2Flowrate (L/min) 5.49 5.80 5.67 6.35 6.06 5.71 6.04 6.31NH3-N (mg/L) 0.47 0.64 0.68 1.03 1.96 1.68 2.15 1.61N02-N (mg/L) < 0.01 0.02 0.01 0.16 0.78 0.47 0.46 0.30B0D5 (mg/L) . . 1 4 10 10 49 30ALK (mg/L as CaC03) • • 102 348 540 304 • 537

denotes no data to

Although the data indicates rapid conversion of ammonia to nitrite, the

filter became inoperative when clogging occurred approximately three

days later. Flowrate during this short interval averaged less than

0.6 L/min, a 50 percent decrease from the initial flowrate observed on

June 16 (Figure. 4). Additionally, effluent dissolved oxygen concentra

tions decreased with loading as the flowrate decreased and bacterial

activity (biofilm growth) increased. Mean effluent DO remained con-

sistently below 1.0 mg/L at the maximum loading (578 lbs/ft ).

Medium Sand (12/20). Six steady-state analyses (June 16, July 3 and 22,

August 4 and 19, and September 2), with loadings ranging from 256 to3 311,590 kg/m (16 to 723 lbs/ft ), were performed on the medium grain

sand. Time trace data for daily ammonia and nitrite levels in the

filter are compared with respective carrying capacities in Figure 5.

Nitrite levels in the system remained consistently below 0.50 mg-N/L for3

the entire 113 day period. When carrying capacities exceeded 4633 kg/m 3

(289 lbs/ft ), steady-state ammonia levels generally exceeded 1.5

mg-N/L. For the duration of testing, steady-state values for nitrite

steadily increased with loading (Table 2). Steady-state ammonia,

however, was reduced by almost 20 percent when loading was increased

from 9266 to 11,590 kg/m'* (578 to 723 lbs/ft'*). The higher ammonia3

level observed at 9266 kg/m appears to result from the system's pH

(7.05) falling below the optimum range for nitrification (7.5-8.3).

Ammonia and nitrite levels peaked around August 15 when a pump

failure occurred. The largest ammonia peak of almost 16 mg-N/L

(September 11) occurred some seven days after the final loading of 3 315,454 kg/m (964 lbs/ft ). Mean flowrates steadily decreased from

3.8 to less than 1.0 L/min with increased loading (see Figure 4).


Reproduced

with perm

ission of the

copyright ow

ner. Further


without

permission.

COARSE (8 /1 6 )1.00.9

0.80.7

FINE ( 2 0 /4 0 )£ 0.6-J 0.5

MEDIUM (1 2 /4 0 )_! 0.4

0.3

CC 0.20.1

0.00 100 200 300 400 500 600 700 800 9 0 0 1000 1100 1200 1300

LOADING (lbs/ft3)

Figure 4. Flowrates expressed as a percentage of the initial flowrate observed on the fine, medium, and coarse sands.

horo

23

Figure 5

3 o

DO.

PUUP

1000

coo« 700

o 600

500

200100

UAY20 JUWI3 AW 50 A l i a JUL30 &U0t3 E£PT >3 SEPT 50CAMPLING DATE

Loading, ammonia, nitrite, effluent dissolved oxygen, and pH data observed on the medium (12/20) grain sand when used as a media with the fluidized bed filter.


Filter failure (caused by excessive floe development and clogging)

occurred with a loading of 15,454 kg/in'* where mean flowrate decreased to

25 percent of the initial flowrate. Effluent dissolved oxygen levels

were consistently low during this period averaging less than 1.2 mg/L.

At the maximum steady-state loading (11,590 kg/mJ) , where filter

clogging was not observed, nitrite levels remained below 0.3 mg-N/L,

although ammonia levels exceeded 1.0 mg-N/L. The volume/weight ratio at

this loading was equivalent to 10.2 L/kg (1.2 gal/lb).

Coarse Sand (8/16). A total of eight steady-state analyses (June 4;

July 3 and 22; August 7 and 23; September 2, 19, and 28) were performed3 3with loadings ranging from 256 to 20,600 kg/m (16 to 1285 lbs/ft').

Figure 6 illustrates daily ammonia and nitrite levels with corresponding

loading values observed over the entire 129 day study period. After the

seventh steady-state analysis (15,454 kg/m ), system volume was

increased from 41 to 82 liters by plumbing a second identical tank to

the existing system and increasing the pump size from 1/25 HP to 1/10

HP. This additional volume increase was required to provide more

surface area for crawfish at the next loading level of 20,600 kg/m"*3(1285 lbs/ft ). By doubling the volume, the density of crawfish was

2 2reduced by almost 35 percent (from 2.6 lbs/ft to 1.7 lbs/ft ) and the

volume/weight ratio was increased by more than 50 percent (from 0.9

gal/lb to 1.4 gal/lb). Aeration in the system was essentially doubled

by placing an additional sprayhead, which discharged effluent water back

into the system, along the tank's side. This setup also provided

additional circulation. A siphon, constructed of 38.1 mm (1.5" i.d.)

PVC, was placed across the two tanks to maintain equivalent head.


25

Figure 6

DO

to <

■ NH.'N

1300 -

1200 -

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- £00 - n 800-£3

Z TOO ' © 600 • | 5 00 -

§ 4 0 0 -

“ * 3 0 0 -

£00 - 100 •

CAY 2 0 «A#(I3 JU N 30 JU L15 JIB. 3 0 A U 313 AUG 31 E£PTIS C2PT 30

8M9PUNQ DATE

Loading, ammonia, nitrite, effluent dissolved oxygen, and pH data observed on the coarse (8/16) grain sand when used as a media with the fluidized bed filter.


Steady-state ammonia levels ranged from 0.47 to 2.15 mg-N/L while

nitrite levels ranged from below detection limits to 0.78 mg-N/L

(Table 2). As with the two previous grain sizes, the dramatic peaks in

ammonia and nitrite concentrations (13.1 and 0.68 mg-N/L, respectively)

observed on August 16 resulted from a two-fold increase in loading and a

lack of dilution volume in the system. However, the filter's ability to

quickly recover demonstrates the extreme robustness of the fluidized bed

under high loading regimes. With the exception of this loading period

and a pump failure on August 27, effluent nitrite levels remained, for

the most part, consistently below 0.50 mg-N/L. High ammonia levels,

however, were evident in the latter part of the analyses. Carrying3 3capacities which exceeded 4633 kg/m (289 lbs/ft ) consistently

demonstrated steady-state ammonia levels in the range between 1.6 and

2.1 mg-N/L. Analyses were abruptly halted on September 30 when the

seasonal supply of crawfish ended.

Results indicated the coarse media sustained a maximum carrying 3 3capacity of 20,600 kg/m (1285 lbs/ft ) without experiencing filter

clogging. Mean flowrate through the filter was 5.7 L/min and demon

strated no significant reduction throughout the entire study (Figure 4).

The larger grain size appears to contribute to abrasion which shears

excessive biofilm growth from the sand thereby prohibiting clogging in

the loading regime evaluated in this experiment. Unlike the fine and

medium grain sands, effluent dissolved oxygen levels remained above

2.0 mg/L for the majority of the study reflecting, in part, the constant

flowrate maintained throughout the study.


DISCUSSION

During normal operation, the fluidized bed expands and contracts in

response to flowrate changes and/or biomass (biofilm) growth on the sand

particles. As the biofilm thickens, the effective volume of the sand

particle increases and lowers the terminal velocity. Thus, the flow1

required for maintaining 100 percent expansion decreases. Further, if

filter loading becomes excessive, the biofilm can increase in thickness

to the point that particle movement gradually becomes restricted, and

the filter bed gels and becomes inoperative. This event was readily

apparent with the medium (12/20) and fine (20/40) grain sands as the two

media demonstrated a slow, yet gradual, flow restriction through the

filter bed as loading was continually increased (Figure 4). Likewise,

the decline in flowrate allowed effluent dissolved oxygen concentrations

to decrease below 2.0 mg/L, thereby limiting the filter's nitrification

ability. Conversely, the coarse (8/16) grain sand showed no effect of

clogging whatsoever even at higher loadings. The larger grain size

appears to contribute to the filter's ability to shear excessive biofilm

growth on the particle thereby reducing its chances of clogging (at

least within the loading conditions examined in this experiment).

Based on the results of this study (Table 2), no appreciable

differences were apparent when comparing the relative abilities of each

grain size with respect to nitrification. Results from this study do

not substantiate findings from past research which indicates that media

surface area has a significant effect on the overall nitrification

ability. In fact, the larger grain size, which had less surface area

for biofilm growth in comparison to the two smaller grain sizes, had an

equal, if not slightly better, nitrification ability based on compari-


28

sons made at equivalent carrying capacities. More importantly, the

coarse (8/16) grain sand appears most suitable as a media since it has a

more predictable hydraulic behavior with respect to filter clogging.

Additionally, the coarse sand can safely maintain loadings equivalent to 3 34800 kg/m (300 lbs/ft ) of unfed crawfish while keeping ammonia and

nitrite concentrations below 1.0 mg/L and 0.5 mg/L, respectively. Based

on these observations, the coarse sand must be considered the superior

media to use with a fluidized bed filter in a recirculating aquaculture

system.

Several experimental factors must be considered as limitations if

one attempts to use these results for determining actual filter carrying

capacity. First, the results of this research are based on an unfed

system. Commercial soft-shell crawfish systems, which employ feeding,

require more nitrification ability as a result of the additional

nitrogen load contributed by uneaten food which remains in the system.

Second, the extremely high loading rates which were used with the medium

and coarse grain sands were not anticipated in the original experimental

design. Consequently, insufficient volume/weight ratios (less than

2 gal/lb) were maintained for the shock ammonia loadings which occurred

within each individual system when crawfish loadings were suddenly

increased. Finally, an inadequate amount of aeration was apparent with

the higher loading rates which led to intermittent oxygen depressions,

pH declines, and CC^ accumulation within the system. Loadings that 3 2exceeded 4800 kg/m (300 lbs/ft ) appear to show no significant

differences in effluent quality (particularly ammonia), thus leading

the authors to believe that either a trace element deficiency, C02


29

accumulation, pH decline, or combination of these factors has a direct

effect on the kinetics governing the nitrification process.

While the fluidized bed has enormous advantages over the conven

tional treatment methods such as the submerged rock filter (Manthe,

1984), the filter also has three major disadvantages. The first

involves the required chemical addition needed to stabilize pH levels.

In this case, sodium bicarbonate was used to maintain an adequate pH and

assure that sufficient amounts of bicarbonate ion were available for

nitrification. Without chemical addition, the filter will not achieve

optimum levels of nitrification and consequently fail to maintain

adequate water quality. A second disadvantage involves the filter's

inability to capture solids. Since the fluidized bed specializes

primarily in nitrification, the filter must be used in conjunction with

a filter which can remove solids, such as an upflow sand filter.

Finally, a higher filter flowrate is required to maintain sufficient

fluidizatlon, thus increasing the energy costs required for operation.

CONCLUSIONS AND RECOMMENDATIONS

Based on the results of this study, the three sand grain sizes

demonstrated no appreciable differences in terms of carrying capacities

for maintaining ammonia levels below 1.0 mg-N/L. However, with respect

to observed maximum carrying capacities, only the coarse sand (1.19-

2.38 mm) maintained its ability to withstand clogging and consequent

oxygen failure. The larger grain size appears to contribute to the

filter's ability to shear excessive bacterial growth from the sand

particles thereby making the media more hydraulically predictable. The

coarse sand must therefore be considered a superior media to use with a


30

fluidized bed filter in a recirculating aquaculture system. Fluidized

bed filters employing the coarse sand as a media should be capable of3 3

safely supporting loadings equivalent to 4800 kg/m (300 lbs/ft ) of

unfed crawfish while maintaining ammonia concentrations at or below

1.0 mg/L and nitrite levels below 0.5 mg/L.

Future research regarding fluidized bed filters and recirculating

aquaculture systems should investigate specific ammonia and nitrite

toxicity limits for molting crawfish. Chronic toxicity testing should

be conducted on conditions that realistically simulate commercial

operating requirements for recirculating systems. Additionally, factors

which limit filter effluent quality (such as trace elements, CC^, and

pH) should be determined so that more efficient filter designs can be

implemented in commercial facilities.


CHAPTER III

EVALUATION OF A FLUIDIZED BED/UPFLOW SAND FILTER COMBINATION PROPOSED FOR A RECIRCULATING BLUE CRAB SHEDDING SYSTEM*

Daniel G. Burden and Ronald F. Malone Department of Civil Engineering, Louisiana State University

Baton Rouge, Louisiana 70803

ABSTRACT

A fluidized bed and upflow sand filter combination were evaluated

in terms of nitrification and oxygen consumption when used in a

recirculating crab shedding system. Systems using the filter

technology can expect carrying capacities of over 700 crabs per cubic

foot of sand media while maintaining adequate water quality for a

shedding operation. This filter combination's carrying capacity

exceeded that observed with the submerged rock filter by more than 20

times and was largely explained by the filter's ability to remove

solids to reduce the oxygen loading rate (OLR). The fluidized bed

exhibited a 56 percent decrease in OLR when compared to the best

submerged rock filter design. This substantial reduction was

principally attributed to biomass attrition occurring within the

individual filter itself. Nitrification rates with the filter

combination were extremely high as total ammonia and nitrite levels

remained below 1.0 mg-N/L.

*Submitted to The Journal of Aquacultural Engineering for publication.

31


32

INTRODUCTION

The use of recirculating systems for producing soft-shell crabs has

gained wide acceptance in Louisiana and the surrounding Gulf States.

Filtration components are utilized to maintain high water quality as

required by molting crabs. The historical filtration method used by the

industry has been the submerged rock filter. The submerged rock filter

combines the advantages of nitrification, solids removal, and pH control

into one unit, thus eliminating the need for additional treatment.

Furthermore, these filters reauire .little or no maintenance over an entire

shedding season.

Current design criteria for the submerged rock filter stipulate a3 3carrying capacity of 33 crabs/ft (132 kg/m ) of filter media although3 3capacities as high as 50 crabs/ft (200 kg/m ) have been observed under

experimental conditions (Manthe et al. 1988). As their carrying

capacities indicate, these filters can only operate at low loading

rates. Bacteria in the filters are maintained in a state of endongenous

respiration which assures that there is no net production of bacterial

biomass. As loading rates are increased, filter clogging generally

results from excessive bacterial growth which fill void spaces in the

rock bed. This clogging prevents a uniform distribution of oxygen

throughout the filter bed, causing localized oxygen deficiencies which

lead to filter failure and eventual loss of crab stocks.

Aside from clogging, pH control becomes increasingly difficult

because of rapid fluctuations in carbon dioxide concentrations. As the

system's buffering capacity becomes limited, the nitrifying bacteria's

ability to adequately reduce ammonia and nitrite levels in a recircu

lating system becomes severely inhibited (Gaudy and Gaudy, 1978; Paz,


33

1984). Consequently, toxic nitrite concentrations rapidly increase to

exceedingly high levels, sometimes greater than 20 mg-N/L (Manthe et al.

1984). Molting crabs were found to be adversely affected by nitrite

levels as low as 0.5 mg-N/L. When toxic nitrite concentrations were

present during molting, crabs often died halfway out of their old shell.

As a result, water quality often controls the economic viability of the

shedding operation.

Research efforts have therefore been directed toward developing

high-rate filters which are small in volume, can withstand clogging, and

yet maintain adequate water quality. This manuscript presents results

of laboratory studies which evaluate the carrying capacity of a

fluidized bed and upflow sand filter combination when used in a crab

shedding facility. Independent evaluations of carrying capacity on the

fluidized bed and the upflow sand filter, as well as waste characteriza

tion studies on the blue crab, were also conducted to provide supporting

data.

BACKGROUND

Nitrification. Biological filters are designed to optimize natural

waste degradation processes whether aerobic or anaerobic. Although

anaerobic filters have been proposed for removing nitrate from system

waters, most biological filtration schemes are based upon enhancing

aerobic processes. The most critical degradation step, nitrification,

depends upon bacteria genera (principally Nitrosomonas and Nitrobacter)

that are strictly aerobic. These bacteria transform the toxic forms of

ammonia and nitrite to the relatively harmless form of nitrate. The

overall reaction is summarized as follows:


34

NH? + 20„ '-*■ NO" + 2H+ 4- Ho0 Cl)4 2 3 2

On a stoichiometric basis, 4.57 milligrams of oxygen are required for

each milligram of ammonium-N which is oxidized to nitrate-N. In a

recirculating system's biological filter, however, nitrification is not

the only oxvgen-consuming phenomenon which takes place (Manthe et al.

1985). Other processes such as mineralization of animal wastes and

respiration by carbonaceous organisms during BOD assimilation

simultaneously compete for oxygen. Filter designs must therefore

satisfy not only the oxygen demand for nitrification, but that amount

for these additional processes as well.

While the nitrification process requires oxygen, its end products,

hydrogen ions and carbon dioxide, reduce both pH and alkalinity.

Alkalinity reduction occurs at a rate of 7.14 moles for every mole of

ammonium oxidized during nitrification (USEPA, 1974). Recirculating

systems must therefore maintain adequate alkalinity levels to appease

the inorganic carbon levels required by the nitrifying bacteria.

Typical water quality guidelines for recirculating systems require a

minimum alkalinity of 100 mg/L as CaC03 (Malone and Burden, 1988).

Optimum pH levels for soft-shell crab production systems lie between 7.5

and 8.3 (Haefner and Garten, 1974). This pH range will adequately

sustain aquatic life, as well as the nitrifying bacteria, and minimize

the dissolution of ions in a recirculating system.

Oxygen Consumption. The amount of oxygen consumed by a biological

filter indicates the amount of bacterial activity, which in turn,

relates to the waste loading imparted to a recirculating system.


35

The relationship of oxygen consumption to waste loading, coupled with

the fact that oxygen frequently limits filter performance, has led to

the development of filter designs based on these concepts.

Manthe et al. (1988) more recently presented submerged rock filter

designs for blue crab shedding systems based on oxygen supply. The

authors based their methodology on a mass balance of dissolved oxygen

using two design parameters: the oxygen consumed during filtration

(OCF) and the oxygen loading rate (OLR). The OCF parameter was based on

oxygen consumption and flowrate across the filter:

OCF = Q * (C± - Co) (2)

where

OCF = oxygen consumed during filtration (mg-O^/day),

Q = flowrate through the filter (L/day),

C^ = filter influent DO concentration (mg-O^/L), and

Cq = filter effluent DO concentration (mg-O^/L).

The OCF measures the amount of oxygen consumed in the filter as a result

of BOD exertion and bacterial respiration. The OCF varies continuously,

even with a constant population of aquatic species in the system, as a

result of subtle water quality changes.

The mean oxygen demand on the filter on a per crab basis is

expressed as:

NOLR = Z (OCF./R.) (3)

1 = 1 3 3


26

where

OLR = the mean oxygen loading rate (mg-O^/crab-day);

R = the number of crabs in the system;

N = the number of OCF observations; and

j = observation number.

The OLR parameter estimates the oxygen demand (BOD) on the filter as

wastes from a unit number of crabs are degraded. Submerged rock filters

provide for degradation of captured solids, dissolved wastes, and

bacterial biomass; thus, the potential oxygen demand is completely

expressed. Addition of pre-filtration components or upflow sand filters

reduces the OLR by removing solids from the system before they

stabilize.

The ability of the submerged rock filter to operate at high loading

rates is constrained by the bacteria's spatial demands and oxygen

transfer rates (Haug and McCarty, 1972; Manthe et al. 1984). The

proposed fluidized bed/upflow sand filter combination is designed to

alleviate clogging problems at high loadings, provide a robust oxygen

supply, and maximize solids removal in an effort to minimize oxygen

demand (or OLR) on the filter. Each filter component is briefly

discussed in the following section.

Fluidized Bed Filter. Fluidized bed filters have been historically used

in the chemical engineering field but recently emerged in the late

1970's as a means of upgrading existing sewage treatment plants (Cooper

and Sutton, 1983). Design criteria for these biological reactors have

been primarily developed for treating high influent BOD concentrations

commonly found in overloaded facilities.


37

The fluidized bed simulates the submerged rock filter in many

respects, but the packing medium, typically sand, expands by an upward

movement of fluid through the bed. Fluidization of the media increases

the effective surface area available for bacterial growth per unit of

reactor volume and provides a favorable environment for kinetic

transport in a relatively small reactor volume. Furthermore, the

fluidized bed minimizes operational problems such as clogging since the

bed can expand to accommodate the extra volume necessary for bacterial

growth (Jeris et al. 1974; Andrews and Tien, 1979; Cooper, 1981). The

limiting factor with using the fluidized bed filter lies in its

inability to capture solids. Since the filter operates in an expanded,

turbulent environment, biofilm which adhere to the sand grains are

continually abraded as a direct result of fluid shearing and particle

abrasion (Powell and Slater, 1982). This continual abrasion of biofilm,

or "biomass attrition", combined with the filter's inability to capture

solids, therefore mandate combining the fluidized bed with some

mechanism for solids removal. The upflow sand filter provides one such

option.

Upflow Sand Filter. Because of the desire to maintain suitable water

quality in a recirculating system and the inability of the fluidized bed

to remove solids, filtration for a recirculating system must be

supplemented with additional treatment. A granular-medium filter such

as the upflow sand filter serves such a purpose. The upflow sand filter

consists of a packed bed of sand through which water flows upward from

the filter bottom and discharges back to the system or to a waste line,

depending on the mode of operation. During normal operation, the filter

remains packed, capturing solids within or on the filter surface,


38

returning clean effluent waters back to the system. Solids capture

occurs through the process of physical straining and sedimentation

within the filter media (USEPA, 1980). Although solids capture is the

filter's primary objective, a high degree of nitrification also takes

place within the filter bed (Rich, 1980; Wheaton, 1985).

As solids buildup occurs within the filter, flowrate declines,

headloss increases across the filter bed, and effluent quality, in

general, decreases. Consequently, intermittent backwashing (or

cleaning) of the upflow sand filter is required on a routine basis.

Backwashing is accomplished by increasing the flowrate to expand the

bed. As the flowrate increases, trapped solids within the filter bed

are removed by fluid shearing and particle abrasion. Backwashing is

normally directed to a slow sand filter which removes solids discharged

from the backwash waters prior to re-entering the recirculating system.

Backwash water is applied to the filter bed surface through a distri

bution manifold which insures uniform flooding of the bed surface.

Solids are removed in a surface mat which forms on the filter's upper

layer of fine sand. The trapped layer of solids and sand is periodi

cally removed, discarded, and replaced with new sand.

METHODS

Two different experiments were conducted in this study: filter

studies and waste characterization studies. The filter studies were

conducted to determine carrying capacities on the fluidized bed/upflow

sand filter combination, as well as each individual component, using

unfed premolt crabs. The waste characterization studies were performed

to provide supporting data on the amount of ammonia and excessive solids


39

material which were excreted by blue crabs. The methods used with each

experiment are described below.

Filter Studies. Three different filter configurations were tested:

(1) a fluidized bed/upflow sand filter combination , (2) a fluidized bed

with floss pre-filtration, and (3) an upflow sand filter. Each filter

was constructed from clear acrylic tubing, 4 inches (10.2 cm) in

diameter, using PVC fittings on the inlet and outlet. All systems,

consisting of three plexiglass holding tanks, a sump, and a pump, were

plumbed with polyvinylchloride (PVC). An American Products 1/2 HP pump,

capable of delivering a maximum of 53 gpm (200 L/min) at 20 feet of

head, was used to assure a flowrate which exceeded the system's

requirements throughout the experimental regime. Flowrates were

controlled using 3/4 inch (1.9 cm) ball valves on each filter.

A general schematic and dimensions of the experimental setup are

presented in Figure 7 and Table 3, respectively. Aeration was supplied

by plumbing spray nozzles into each holding tank from a manifold off the

pump output line. Each independent system had a total volume equivalent

to 67.4 gal. (255 liters). The single filter configurations, systems

utilizing a single fluidized bed (Figure 7a) or a single upflow sand

filter, had a filter media volume equivalent to 0.116 ft"". The con

figuration consisting of both filters operating in parallel (Figure 7b)3had a filter media volume equivalent to 0.233 ft or twice that of the

single filter configuration.

The fluidized bed filter (Figure 8) consisted of a sand bed, 16

inches (40.6 cm) in depth, through which a constant upflow of water

continuously maintained the filter in its expanded mode. Typically,

bed expansion was maintained between 25 and 50 percent. A medium


Reproduced

with perm

ission of the

copyright ow

ner. Further


without

permission

Figure 7

(a) (b )

(ISLOWSANDFILTER

u p fl owSANDFILTER

OALL VALVE_ra- FLUIOIZE0 DED

-pj 1

HOLDING TANK 3

HOLDING TANK 2

HOLDING TANK I

l— — h r* SUtSP * *

T >1/2 HP PUMP

(C)

QALL VALVE

1o-JoX TANK 3

HOLDING TANK 2

HOLDING TANK!

FLOSSFILTER

» SUUP

FLUIDIZED DED " O -1/2 HP PUKP

A schematic of the experimental setup used with the three filter configurations. The fluidized bed/upflow sand filter combination and the single upflow sand filter (circumvented by the dashed line) configurations are denoted in (a).The single fluidized bed filter is illustrated in (b).

-E~O

41

Table 3. Dimensions of the experimental setup used for determining filter carrying capacity.

Component Length(ft)

Width(ft)

Depth(ft)

WaterDepth(ft)

CrossSectional

Area( f O

Volume(ftJ)

Holding Tanks 3 2 1 0.479 6 2.875

Sump 3 ? 1 0.542 6 3.250

Fluidized Bed Filter (Media)

- - 1.33 - 0.087 0.116

Upflow Sand Filter (Media)

- - 1.33 - 0.087 0.116

Fluidized Bed/ Up flow Sand Filter (Media)

— . — 1.33 0.174 0.233

Slow Sand Filter (Media)

1.167 1 0.67 ~ 1.167 0.778


DISCHARGETO SYSTEM

100 PERCENT EXPANSION

PACKED BED HEIGHT ( 16“)

S OP GRADED GRAVEL (1/2 - I/O")

SUPPORT.PLATE

SECTION 4 - 4

DALL VALVE

Figure 8. A detailed illustration of the fluidized bed filter used with the study (not to scale).


43

grain sand, ranging in diameter from 0.84 to 1.68 mm, was used as a

filter medium. Solids removal was accomplished by placing polyester

aquarium filter floss in a mechanical filtration box at the filter's

discharge. Floss was changed on a daily basis.

The upflow sand filter (Figure 9) consisted of a 16 inch (40.6 cm)

packed bed of dolomite (4.76 - 7.93 mm in diameter). Backwashing was

performed once a day by temporarily shutting off the normal flow dis

charged back to the sump, thereby directing the backwash waters to a

slow sand filter (Figure 7a) via a 1.5 inch (3.8 cm) drain line. Clean

effluent water was returned to the sump.

Each system was initially filled with ammonia-free, dechlorinated

tap water and adjusted for salinity to 5 ppt using artificial sea salts

(Instant Ocean). A specified number of medium crabs (Callinectes

sapidus), ranging in carapace width from 10 to 15 cm, were then loaded

into each system. Crab loadings were increased only after each system

stabilized at the specified crab loading so that representative water

quality samples could be collected. Stabilization merely indicated that

the population of nitrifying bacteria within the filter had approached

an equilibrium state with the ammonia and nitrite concentrations present

in the system.

Crabs were not fed while in the experimental tanks to simulate a

commercial shedding operation. To prevent cannibalism, weak animals and

mortalities (approximately two percent daily) were removed and replaced

every two to four hours. Crab populations in each system were routinely

replaced with a healthy crab population every 5 days. Replacement crabs

were held in a separate 600 gal. (2250 L) recirculating system where

feeding was conducted. Purina Trout Chow Checlcerettes it4 (w/ 43 percent


Reproduced

with perm

ission of the

copyright ow

ner. Further


without

permission. Figure

NO R M A L OPERATION IN T E R M IT T E N T E X P A N S IO N

3C

, VWASTE WATER / ' > DISCHARGE TO.

SLOW SAND { FILTER V

DISCHARGE TO SYSTEM

BALL VALVE BALL VALVE

- 5 0 PERCENT EXPANSION

B R EA K-BAR

PACKED BED HEIGHT

3" OF GRADED GRAVEL ( 1 /2 - 1/B")

SUPPO R T-PLA TE 3/0 Holes

INFLOW

SECTION 4 - 4BALL VALVE

Normal and intermittent operation of the upflow sand filter (not to scale)

p -p -

45

protein) and live crawfish were used for feeding in the support system.

All crabs were obtained from a commercial soft-shell crab fisherman

(Lacombe, Louisiana) two to three times a week. Both the holding and

experimental systems were maintained at room temperature (23 + 1 °C).

Water loss due to evaporation was replaced daily using dechlorinated tap

water.

Monitoring was performed on a daily basis for total ammonia-

nitrogen (NH^), nitrite-nitrogen (NO^)» dissolved oxygen (DO), pH,

temperature (Temp), flowrate (Q), and salinity. All monitoring was

conducted between 9:00 and 11:00 am. When each system stabilized at

the specified crab loading, an expanded "steady-state" analysis was

conducted to determine filter performance. Steady-state analysis

included nitrate-nitrogen (NO^) , biochemical oxygen demand (BOD,.),

alkalinity (ALK), and total suspended solids (TSS) in addition to those

parameters run on a daily basis. The methods and instrumentation used

with each analysis are outlined in Table 4. All analyses were conducted

according to procedures outlined in Standard Methods (APHA, 1985). At

the end of a steady-state analysis, the crab loading in each system was

increased and maintained until the system stabilized at the new loading.

Bicarbonate addition was necessary to maintain pH levels (7.0-

8.3), as well as alkalinity levels (> 100 mg/L as CaCO^), in an optimum

range for oxidation rates of the Nitrosomonas and Nitrobacter bacteria

(Paz, 1984; USEPA, 1975). pH levels were adjusted by adding 2.4 to 4.8

mg of sodium bicarbonate (NaHCO^) per pound of crab following each day's

sampling routine (Malone and Burden, 1987).

Waste Characterization Study. Separate from the individual filter

studies, a waste characterization study was conducted on the blue crab


46

Table 4. Water quality parameters and methods used with the filtration research.

Water Quality Parameter Analysis Method

Total Ammonia Nitrogen Distillation, Nesslerization

Nitrite Nitrogen Sulfanilamide-basedColorimetric

Nitrate Nitrogen Orion Nitrate Ion Electrode - Model 93-07, Orion Double Junction Reference Electrode - Model 90-02

Total Kjeldahl Nitrogen Digestion, Distillation, Nesslerization

Biochemical Oxygen Demand

Winkler Method

Alkalinity Titration/PotentimetricEndpoint

Total Suspended Solids Gravimetric

Dissolved Oxygen Yellow Springs Instrument Model 57 Oxygen Meter

pH Cole-Palmer Mini pH Meter


to determine ammonia excretion rate and subsequent solids loading.

These data allow generalization of design findings by defining carrying

capacities in terms of parameters that could be used in any application.

Crabs used in the study were taken from a main holding system where they

were fed whole crawfish and Purina Trout Chow Checkerettes #4 prior to

their isolation. Methods used with the study are similar to those

followed by Cange (1988). A total of six water quality parameters were

analyzed: ammonia nitrogen, nitrite nitrogen, total Kjeldahl nitrogen

(TKN), biochemical oxygen demand, total suspended solids, and volatile

suspended solids (VSS). Analyses for the BOD and TKN parameters were

conducted on both filtered and unfiltered samples, using a 0.45 micron

filter, to determine the impact of suspended solids upon water quality.

All analyses were conducted in triplicate on the same day of sampling

according to procedures outlined in Standard Methods (APHA, 1985).

RESULTS

Filter Studies.

Initial filter acclimation was accomplished with each system

configuration in 20 days (June 19) after successive loadings of3 343 crabs/ft (9 days) and 86 crabs/ft ('11 days). Startup curves for

ammonia and nitrite followed the typical pattern for biological filters

as described by Manthe et al. (1984). Subsequent to acclimation, crab

loadings were increased and steady-state analyses were conducted

accordingly. pH levels gradually declined within each system

illustrating the inability of the silica-based sand and dolomictic media

to effectively buffer pH changes. Following approximately 40 days of

monitoring, chemical addition of sodium bicarbonate was implemented in


48

all three filter systems to maintain pH levels in an effective range for

nitrification. Results of the daily and steady-state monitoring for the

combination and individual filter configurations are presented below.

Fluidized Bed/Upflow Sand Filter Combination. Results of the daily

monitoring of ammonia, nitrite, effluent dissolved oxygen, and pH data

with respect to crab loading are illustrated in Figure 10. Since the

filter combination essentially doubled the filter media volume,3

volumetric carrying capacities, ranging from 86 to 773 crabs/ft , were

consequently lower in contrast to the individual filter configurations.

Monitoring was discontinued after September 16 as a result of external

factors.

The inability of the sand and dolomite media to provide adequate

buffering capacity, as well as pH control, was readily apparent after

40 days of continuous operation. At this point, pH levels dropped below

7.0, a critical level with regard to high nitrification rates. The high

ammonia peak observed on July 17 (day 49) resulted from a steady decline

in pH levels (prior to chemical addition) coupled with shock loading the3

system to a total of 172 crabs/ft . This loading period also had a

short-term, diminishing effect on the effluent DO levels in the upflow

sand filter as illustrated in Figure 10. Smaller ammonia peaks observed

throughout the remainder of the study appear to result from shock

loading on the system. Effluent DO in the upflow sand filter briefly

fell below 2.0 mg/L during this period, but remained, in general, above

3.0 mg/L while DO levels in the fluidized bed typically stayed above

5.0 mg/L.


49

pH

< 9h- Z N. gO < MH_. N

1600

o 1200

1000

GOO

° GOO

SAY50 JUNEI9 JUfS50 JUIYI3 JULT30 AUG 15 AUG91 GCPIGSA M P LIN G OATE

Figure 10. Water quality monitoring results and loading curves obtained on the fluidized bed/upflow sand filter combination.


50

A total of six steady-state analyses, beyond that of initial filter

acclimation, were conducted on the system (Table 5). Ammonia and

nitrite levels for the most part, remained below 1.0 and 0.5 mg-N/L,

respectively, for the entire study. These low levels appear to reflect

a somewhat less rigorous test on the filter combination since maximum

carrying capacities were not reached in this experimental regime.

Fluidized Bed. Daily ammonia, nitrite, pH, and effluent dissolved

oxygen data are illustrated along with crab loading data in Figure 11.3

Following filter acclimation with a loading capacity of 86 crabs/ft ,3crab loading on the system was doubled to 172 crabs/ft . Steady-state

3analyses were conducted on loadings ranging from 172 to 688 crabs/ft

corresponding with sampling dates June 28, July 9, and August 7

(Table 6a). Steady-state ammonia, nitrite, nitrate, and BOD levels

steadily increased with loading. Mean flowrate over the entire study

was equivalent to 9.8 L/min. As a result, oxygen transport in the

filter never became limited as effluent dissolved oxygen levels remained

above 4.0 mg/L.

The large ammonia peak (8.2 mg-N/L) observed on July 17 (day 49)

resulted from both shock loading and a steady decline in pH levels

(< 7.0) before bicarbonate addition was implemented on July 18. Crab

loading was essentially doubled five days previous to this ammonia peak.

Furthermore, with the increased loading the water/volume ratio fell

below 1 gal/crab. Shock loadings, like those experienced here, can be

avoided if a ratio of 2 gal/crab or greater is provided based on

previous recommendations by Manthe et al. (1987).

Routine monitoring of ammonia and nitrite was carried out for

an additional 20 days beyond that of the last steady-state analyses


Table 5. Steady-state data obtained on the fluidized bed (FB)and upflow sand (UFS) filters when running in parallel operation. Flowrates denoted by 'Q'.

Loading(crabs/ft3)(lbs/ft3)

8620

17240

33980

430100

645150

773180

Q-FB (L/min) 14.1 11.0 10.3 10.8 16.8 16.8

Q-UFS (L/min) 3.3 1.6 3.6 2.6 2.3 O 0 • 4.

NH3 (mg-N/L) 0.08 0.23 0.28 0.29 0.31 0.60

N02 (mg-N/L) 0.05 0.12 0.33 0.28 0.29 0.46

N03 (mg-N/L) 87 148 348 313 395 459

BOD,. (mg/L) 3 n 7 5 3 4

ALK (mg/L as CaCO^ ) • 14 192 190 135 144

pH 7.8 6.6 7.5 7.5 6.7 6.9

TSS (mg/L) 10 9 16 3 14 12

Temp. (°C) 22.0 22.0 23.5 24.0 22.5 23.0


o «

< ?

coo

zoo

UAYSO JUNEI9 AURESO JULYI9 JULYIO AUOI9 AU03I CEP 168AUPMN0 DATE

Figure 11. Monitoring results obtained on the fluidized bed filter using floss pre-filtration.


Table 6. Steady-state data obtained on (a) the single fluidized bed filter and (b) the single upflow sand filter.

Loading(crabs/ft3)(lbs/ft3)

17240

34480

688160

1289300

1547360

(a) FTuiaized Bedr

Q (L/min) 9.0 9.5 10.6

NH3 (mg-N/L) 0.19 0.13 0.74

NO£ (mg-N/L) 0.16 0.18 0.63

N03 (mg-N/L) 63 110 333

BOD5 (mg/L) 4 4 13

ALK (mg/L as CaC03) • 43 289

pH 7.9 7.0 7.6

TSS (mg/L) 8 8 21

Temp. (°C) 22.0 22.0 23.5

(b) UpFlow Sand Filter:

0 (L/min) 4.7 2.2 3.6 1.9 1.7

NH3 (mg-N/L) 0.28 0.59 0.61 0.77 0.98

N02 (mg-N/L) 0.27 0.33 0.50 0.53 0.55

. NO (mg-N/L) 69 204 296 342 421

BOD5 (mg/L) 3 8 5 6 9

ALK (mg/L as CaC03) • 112 262 155 198

pH 7.9 7.5 7.6 7.6 7.6

TSS (mg/L) 7 17 8 18 4

Temp. (°C) 22.0 22.0 23.5 22.5 22.5


54

3on August 7 (day 70). Crab loadings which exceeded 158 lbs/ft resulted

in heavy mortalities, typically greater than 10 percent/day, as ammonia

and nitrite levels reached levels as high as 5.5 and 1.3 mg-N/L,

respectively. The filter failed to exhibit any signs of recovery and

consequently, the system was shut down.

Upflow Sand Filter. Five steady-state analyses beyond initial

filter acclimation were conducted on the upflow sand filter with3

loadings ranging from 172 to 1549 crabs/ft (Table 6b). Ammonia,

nitrite, and nitrate levels steadily increased with loading. Flowrates

and consequently effluent dissolved oxygen levels consistently decreased

with increased loading as biofilm growth increased throughout the

dolomitic filter bed. Although backwashing was performed on a routine

daily basis, the ever increasing solids loads resulting from biofilm

growth and crab loading largely contributed to the flowrate decline.

Prior to the last steady-state analyses, effluent dissolved oxygen

levels remained below 1.0 mg/L.

Routine daily monitoring of ammonia, nitrite, pH, and effluent

dissolved oxygen concentrations are illustrated in Figure 12. Beyond

filter acclimation, three large ammonia peaks ranging from 2.5 to

5.7 rag-N/L were observed in the data. The first peak (July 17)

directly ensues the day when system pH (6.5) was at a minimum.

Immediately following that day's sampling, bicarbonate addition was

implemented in the system. The two subsequent peaks, one of which

displayed the highest ammonia level (5.7 mg-N/L), were observed on

August 3 and 27 (days 66 and 90) with loadings of 344 and 1289 3crabs/ft , respectively. Effluent dissolved oxygen levels were

extremely low, below 1.0 mg/L, prior to these periods. Nitrification in


55

or

DO

o < ?

1400

g 1200

1000

000 ■

200

MAY 3 0 <UmCt8 JULY 13 JULYSO AUGI3 AUQ 3I 8EPIC8A U P L IN 0 OATE

Figure 12. Loading curves and water quality monitoring data obtained on the single upflow sand filter configuration.


56

the filter was undoubtedly inhibited to a large extent as a result of

these oxygen deficiencies.

Excretion Study.

Results of the excretion study are summarized in Table 7. Mean

excretion rate for the blue crab was equivalent to 0.219 +0.076 mg

NH^+N^/g-day based on a mean crab weight of 105.6 grams. The large

amount of variability displayed by the excretion data was attributed to

three factors: (1) crabs used in the study were based on "wet weight",

(2) the wide range of crab weights used throughout the study, and (3)

the physiological state of the crabs as a result of time spent in the

holding system. Additional factors such as the natural variability in

both sampling and laboratory procedures, as well as the crab's feeding

and metabolic rates, may have also contributed to the observed

variability.

The unfiltered and filtered BOD and TKN samples represent the

solids partitioning portion of this study. Solids removal reduced BOD

loading by 0.169 mg/g-dav (62 percent) while only a small decrease

(7 percent) in nitrogen loading was apparent. This large reduction of

BOD indicates the need for a solids removal mechanism such as the upflow

sand filter in a recirculating shedding operation.

DISCUSSION

The fluidized bed/upflow sand filter combination provided superior

nitrification treatment when compared to the submerged rock filter.3

Maximum carrying capacity (773 crabs/ft ) observed on the filter com

bination exceeded the rock filter by more than 20 times while main

taining suitable water quality for a crab shedding operation. Higher


57

Table 7. Statistical summary for all waste characterization data collected on the blue crab.

Parameter n XStandardDeviation Range

Crab Weight (g) 15 104.1 11.48 83 - 125

Excretion(mg/g-day)

14 0.219 0.076 0.102 - 0.383

Nit (mg-N/g-day) 14 0.194 0.083 0.083 - 0.375

N02 (mg-N/g-day) 14 0.025 0.016 0.005 - 0.059

Unfiltered TKN (mg/g-day)

15 0.330 0.132 0.160 - 0.610

Filtered TKN (mg/g-day)

14 0.315 0.139 0.094 - 0.581

Unfiltered BOD5 (mg/g-day)

15 0.262 0.120 0.083 - 0.542

Filtered BOD5 (mg/g-day)

15 0.093 0.055 0.026 - 0.216

TSS (mg/g-day) 14 0.711 0.376 0.309 - 1.77

VSS (mg/g-day) 14 0.468 0.186 0.218 - 0.887


58

carrying capacities may have been possible, but were unobtainable

because of a limited crab supply.

Oxygen Consumption. Examination of the oxygen loading rates (OLR) for

each filter configuration demonstrates why the fluidized bed/upflow sand

filter combination yields superior performance. Oxygen loading rates

were determined on each filter configuration based on the following

criteria: (1) effluent dissolved oxygen concentrations must be greater

than 2.0 mg/L to assure the expressed OLR was not oxygen-limited and (2)

ammonia concentrations must not exceed 1.0 mg-N/L to avoid the effect

that shock loadings may have on system operation. These criteria follow

the guidelines set forth by Manthe et al. (1988) in their OLR evaluation

on the submerged rock filter.

Results of the OLR analyses revealed mean values of 68, 139, and

140 mg-0o/crab-day for the fluidized bed w/ floss pre-filtration, the

upflow sand filter, and the fluidized bed/upflow sand filter combina

tion, respectively. To gain a more thorough understanding of the OLR

evaluation, the mean values (and their standard deviations) for the

individual filters were examined by using probability distributions.

Distributions used in these analyses were chosen in the form of a gamma

density function based on data skewness (Ward et al. 1982).

Gamma distributions for the individual fluidized bed filter

w/ pre-filtration along with those for the two submerged rock filter

configurations are compared in Figure 13. Observation of the

distributions illustrates the highly variable nature of the OLR

parameter. The two separate distributions for the submerged rock

filter are based on data taken from Manthe et al. (1988): (1) an

OLR of 500 mg-0?/crab-day without pre-filtration and (2) an OLR of


Reproduced

with perm

ission of the

copyright ow

ner. Further


without

permission.

O.OI2r

> 0.009 um 0.008

S 0.007

U- 0.006

2 0.005 UiE 0.004lil^ 0003

0.0020001OOOO

BIOMASS

ATTRITION

SOLIDS

REMOVAL

FLUIDIZED BED W/PRE-FILTRATION

(1 = 68)

SUBMERGED ROCK FILTER W/ PRE-FILTRAT ION

(x =344)

SUBMERGED ROCK FILTER W/0 PRE-FILTRATION

(x =500)

Id I100 200 300 4 0 0 500 600 700 800 900 1000

OXYGEN LOADING RATE ( m g - 0 2 / c r a b - d a y )

Figure 13. Gamma distributions for OLR data on the fluidized bed and submerged rock filter configurations. Mean values are indicated in parentheses and denoted by the horizontal lines on each distribution. Ul

\ D

60

344 mg-O^/crab-day using floss pre-filtration. The 31 percent dif

ference in the mean OLR values results from the floss bed filter's

ability to remove the larger solids which would otherwise decompose and

exert additional, oxygen demand. When compared with the results from the

excretion study, the floss filter is relatively inefficient in solids

capture since a BOD reduction of nearly 65 percent was percent was

possible with total solids removal (see Table 7).

As indicated by the vertical line to the right of the fluidized

bed distribution, the mean OLR was reduced an additional 55 percent

beyond the original reduction realized by floss pre-filtration with

the submerged rock filter. This additional reduction in OLR was

principally attributed to biomass attrition, thus supporting the

filter's ability to continually abrade biofilm when operating in a

turbulent environment. In contrast to the submerged rock filter w/o

pre-filtration, the fluidized bed/floss combination realizes an

impressive 86 percent reduction in OLR reflecting both biomass

attrition and solids removal. Consequently, the relative amount of

OLR exerted (OLR^) by the fluidized bed was equivalent to 13 percent of

the total, or 68 mg-On/crab-day. Each component is readily illustrated

in Figure 14a. Thus, the total, or unimpaired, OLR (OLR^) on the system

can be expressed as follows:

OLR = OLR, + OLR + OLR (4)t b s e

where

OLR^ = OLR removal due to biomass attrition,

OLR = OLR due to solids waste removal, ands ’OLR = OLR exerted in the filter,e


Reproduced

with perm

ission of the

copyright ow

ner. Further


without

permission.

UPFLOW SAND FILTER FLUIDIZED BED FILTER

EXPRESSED OLR (O L R 0 ) =

28 °/<OLR DUE TO

BIOMASS ATTRITION ( O L R b) =41%

OLR DUE TO SOLID WASTE REMOVAL

( O L R a ) =3 1 %

OLR DUE TO BIOMASS ATTR IT IO N

(O L R b ) =5 5 %

OLR DUE TO SOLID WASTE REMOVAL

(O L R j , ) =31

Figure 14. Pie diagrams illustrating the representative portions of total OLR on the upflow sand and fluidized bed filters.

62

Based on a similar analysis with the upflow sand filter, the mean

OLR decreased by 41 percent as a result of biomass attrition thus,

making the combined OLR (OLR^ and OLRs) reduction equivalent to

72 percent or 359 mg-O^/crab-day (Figure 14b). Under the assumption

that OLR^ (floss bed) equals the OLRg (upflow sand filter), estimates

indicate the OLR^ (upflow sand filter) is less than the OLR^ since

solids are not removed instantaneously as they are held for longer

detention times. In summary, the higher OLR^ observed with the upflow

sand filter (139 mg-O^/crab-day) justifies using the fluidized bed in

combination as a treatment method. Although not illustrated, the OLR^

of the fluidized bed/upflow sand filter combination was reduced by

almost 60 percent when compared to the best submerged rock filter

design.

Nitrification. Further scrutiny of the nitrogen data lends some insight

as to why the fluidized bed/upflow sand filter provides superior water

quality. The most apparent advantage of the filter combination stems

from the relatively short time (20 days) required for filter accli

mation. Because of the fluidized bed's favorable environmental for

bacterial growth, kinetic transport rates are higher and acclimation

periods are consequently shorter. In contrast, acclimation for the

submerged rock filter typically takes between 30 to over 100 days

(Hirayama, 1974; Manthe and Malone, 1987). By decreasing the acclima

tion period, productivity and economic viability of the shedding system

increases. Additionally, system water quality remains more stable

because of the filter's enhanced ability to handle heavy crab loadings.

These factors have been a major obstacle with using the submerged rock

filter in commercial systems.


63

Although maximum carrying capacities were not reached with the

filter combination, acceptable water quality was maintained throughout

the experimental run. Ammonia and nitrite levels, for the most part,

remained below concentrations considered safe for commercial operation.

Furthermore, these conditions were maintained at pH levels considered

less than optimum since inhibition of the nitrifying bacteria generally

occurs at pH levels below 7.0. Thus, the authors firmly believe that

higher carrying capacities could have been attained with the filter

combination.

From the results of this study, the system's reserve capacity (in

terms of nitrification) rests in the fluidized bed filter when the

upflow sand filter is near its pratical operational capacity. Higher

ammonia and nitrite levels would have nonetheless impacted the entire

system had only the upflow sand filter been in operation. The

fluidized bed also complements the upflow sand filter in its inherent

ability to impose a lower oxygen demand (OLR^) on the system as

previously discussed.

The effect of nitrogen loading on each filter configuration system

was further examined by using a regression analysis. Total nitrogen

(summation of ammonia, nitrite, and nitrate) was designated as the

dependent variable and crabday as the independent variable for each

filter system. Crabday was defined as one crab held in the system for

one day; thus, 10 crabs held for 5 days would equal 50 crabdays.

Results of the regression analyses are illustrated in Figure 15 for each

filter configuration. Of the three filter configurations tested, the

fluidized bed filter was best represented by a linear model (P<0.0i,

R2=0.998).


Reproduced

with perm

ission of the

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ner. Further


without

permission. Figure

500

„ 400

o>E

ZU1CDOccK-

<I-O

300

200

100

FLUIDIZED BED ( r2 =0.99)

FLUIDIZED BED/ UPFLOW SAND FILTER

COMBINATION{(■2 = 0.92) / ,

y s' UPFLOW SAND FILTER/ s ' ' (r2 1 0.86)

_L_ _1_ _L _l1000 2000 3000 4 0 0 0 5000 6000 T000 8000 9000

CRABDAY

L5. Results of the linear regression analyses performed on total nitrogen accumulations in the three filter configurations. R-square values indicated in parentheses. o\■C-

65

Based on the slope of each regression line, the average nitrogen

accumulation rate in each system was determined based on a system volume

of 255 liters. Total nitrogen accumulation rates were equivalent to 48,

52, and 103 mg-N/lb-day for the upflow sand filter, the fluidized

bed/upflow sand filter combination, and the fluidized bed using

pre-filtration, respectively. The accumulation rate observed on the

fluidized bed compares favorably well with the excretion rate observed

on the crab (102 mg-N/lb-day) while those the remaining filter

configurations do not. The lower accumulation rates observed with the

fluidized bed/upflow sand filter combination and the upflow sand filter

reflect an approximate 50 percent reduction in accumulated total

nitrogen, principally nitrate. Assuming this reduction occurs as a

result of denitrification, this appears to result from using the slow

sand filter with the two upflow sand filter configurations. In

contrast, denitrification does not take place with the individual

fluidized bed and upflow sand filter configurations since the floss bed

system (used for pre- filtration) maintains an aerobic environment as it

was changed on a daily basis. While no significant toxicity effects of

accumulated nitrate are known to occur in a recirculating system, this

reduction improves the overall water quality in the shedding system.

Relative Filter Ability. The clogging problems associated with the

submerged rock filter during periods of high loading did not hinder

performance of either filter until maximum carrying capacities were

obtained. The upflow sand filter provided acceptable water quality for

maintaining a shedding facility up to a maximum carrying capacity of 31547 crabs/ft . Beyond this point, the filter failed to support the

system as a result of flow restriction and dissolved oxygen limitations


66

in the effluent water. Higher carrying capacities may have been

possible if baclcwashing had been performed on a more frequent basis,

perhaps three or four times a day.

As discussed earlier, the fluidized bed operates in an environment

conducive to high-rate nitrification treatment principally because of

the greater surface area available for biofilm growth. However, based

on the results of this study, the fluidized bed exhibited a lower

carrying capacity in comparison to the upflow sand filter, which was

initially Included for solids removal. Two possible reasons may explain

this markedly large difference. First, the highly turbulent environment

in which the fluidized bed filter operates may in fact contribute an

excessive amount of shear, as well as abrasion, on the biofilm thereby

causing more harm than good. The percentage of bed expansion, pre

dominated by fluid dynamics, may therefore control substrate removal,

thus explaining the lower carrying capacity of the fluidized bed.

Secondly, the dramatic differences in filter performance may also be

linked to excessive biofilm detachment but for reasons other than

shearing (Turakhia et al. 1983). Thus, while both filters provide

nitrification, the fluidized bed appears to function more as a roughing

filter while the upflow sand filter functions as a polishing filter.

Summary. The fluidized bed/upflow sand filter combination provided

superior water quality in comparison to the submerged rock filter

designs typically used with crab shedding systems. Both filter

acclimation time and the actual amount of oxygen demand exerted

(OLR^) by the filter combination were reduced significantly. The

reduction in OLR is particularly significant since system designs are

commonly based on oxygen consumption.


67

A design criteria based on a fluidized bed/upflow sand filter

combination would provide a significantly higher treatment capacity for

a recirculating system. Holding systems can be configured to hold the

maximum density of crabs without degrading water quality and virtually

eliminate loss of crab stocks due to filtration failures. With this

ability, the production of soft-shell crabs in can be increased

tremendously. Production rates can also be more reliable and

predictable permitting the soft-shell crab industry to become more

competitive on a national basis.

CONCLUSIONS

The following conclusions can be made with regards to the research

conducted on fluidized bed and upflow sand filters when utilized with

recirculating crab shedding systems:

(1) The fluidized bed/upflow sand filter combination provided

superior treatment in comparison to the submerged rock filter. These

high-rate biological filters have carrying capacities of at least

20 times higher than historically observed with the submerged rock3

filter and were observed to support 773 crabs/ft while still main

taining satisfactory water quality for a blue crab shedding operation.

(2) The fluidized bed/upflow sand filter combination increased

carrying capacity over that of the submerged rock filter can be

explained in large by the enhanced solids removal ability and corre

sponding OLR reduction. Total oxygen loading rates (0LRt> were reduced

an additional 41 and 56 percent for the upflow sand filter and fluidized

bed filter, respectively when compared with the submerged rock filter

using floss pre-filtration.


68

(3) The upflow sand filter alone provides acceptable water quality3treatment up to a maximum of 1547 crabs/ft at which time the filter

failed as a result of flow restriction and dissolved oxygen failure in

the effluent water. Bacterial respiration rates in the filter compare

favorably with that of the fluidized bed filter.

(4) Bicarbonate addition is a mandatory requirement for pH control

in recirculating systems using these high-rate filtration components

over extended periods of time, as the system's alkalinity will rapidly

decrease.

(5) Mean excretion rate for fed crabs was equivalent to 0.219 mg/g

of total nitrogen per day. Solids partitioning studies indicated that

solids removal accounts for an approximate 64 percent reduction in BOD

loading.

(6) The slow sand filter appeared to contribute a significant

amount of denitrification to the system by reducing total nitrate

accumulation to approximately 50 percent of those levels found in

the fluidized bed using only floss pre-filtration.


CHAPTER IV

ASSESSMENT OF A VOLUMETRIC LOADING CRITERIA FOR A FLUIDIZED BED/UPFLOW SAND FILTER CONFIGURATION*

Ronald F. Malone and Daniel G. Burden Department of Civil Engineering, Louisiana State University

Baton Rouge, LA 70803

ABSTRACT

A volumetric loading criteria of 150 pounds of fed crawfish per

cubic foot of filter sand was used for designing fluidized bed and

upflow sand filters in several commercial recirculating soft-shell

crawfish (Procambarus clarkii) facilities. One particular facility was

monitored to provide representative data on filter performance. Water

quality results indicated the filters sufficiently maintain total

ammonia and nitrite levels below 1.0 mg-N/L under typical commercial

conditions. The upflow sand filter was principally responsible for

solids removal and nitrification in the system. The fluidized bed was

biologically active, but appeared to support heterotrophic bacteria

which reduce the biological oxygen demand. Normal aeration in the

system provided sufficient oxygen levels for the crawfish and bacteria,

but failed to control carbon dioxide accumulations causing difficulties

in pH control. Shock loading and overfeeding, rather than filter

capacity, appeared to dominate water quality fluctuations, thereby

indicating the volumetric loading guideline was sufficient for

commercial adoption.

*Submitted to Aquacultural Engineering for publication.

69


70

INTRODUCTION

The red swamp crawfish (Procambarus clarkii) experiences the growth

process of molting (or ecdysis) a minimum of eleven times before

reaching maturity (Huner and Barr, 1984). The crawfish remains in the

vulnerably "soft-shell" state for several hours after each molt. At

this stage, the soft-shell crawfish is considered a seafood delicacy

although availability has been severely limited by production as well as

technology. Recent designs of crawfish shedding systems, however, have

stimulated the rapid growth of this emerging industry (Cullev et al.

1985a) . Production during the 1987-88 season (November to June) appears

to have increased from 50,000 to 75,000 pounds in comparison with just

7,000 pounds in the 1985-86 season. Although the production process

appears straightforward, the process is labor intensive and production

rates are still somewhat low, ranging from 1.5 to 2.0 percent per day of

the system's total holding capacity.

Earlier shedding systems were based primarily on flow-through

technologies utilizing fresh water, usually drawn from wells or

municipal water systems, at a continuous flushing rate ranging from

0.025 to 0.1 gpm/lb of crawfish (Cange, 1987). However, water quality

problems and energy costs associated with flow-through designs

confronted operators. Iron and ammonia levels in many groundwaters

lead to mortalities when crawfish were in the sensitive molting stage,

thus prohibiting the use of this technology. Additionally, the cool

groundwater (typically 70°F or 21°C) required that flow-through systems

bear the high cost of pre-heating water.

Soft-shell crab (Callinectes sapidus) production facilities in the

Gulf States, to a large extent, use recirculating systems which employ


71

submerged rock filtration for maintaining water quality (Perry et al.

1982, Manthe et al. 1983). The most inherent advantage of this

technology lies in using filtration components which process metabolic

wastes to a relatively harmless, non-toxic state. Recirculating

systems also reduce heating costs by approximately a factor of ten,

providing a strong financial incentive for adopting the technology.

Because of these advantages, the recirculating system was immediately

considered as an alternative to the flow-through technology currently

employed for soft-shell crawfish production. However, the submerged

rock filters, used for soft-shell crab production, proved inadequate

for crawfish shedding systems where feeding was necessary to encourage

growth and molting. Design criteria based upon fluidized bed and

upflow sand technologies under development for the soft-shell crab

industry (Malone and Burden, 1987) were, therefore, modified and

refined in cooperation with the commercial sector.

This paper presents recirculating design criteria which have proven

acceptable for producing soft-shell crawfish. Monitoring results from a

commercial facility constructed on these criteria are presented and

relative filter performance is evaluated. Emphasis is placed upon the

suitability of a volumetric loading criteria (pounds of crawfish per

cubic foot of sand) which is used for designing the fluidized bed and

upflow sand filters.

BACKGROUND

Commercial production of the soft-shell crawfish requires several

critical steps: capture, transport, acclimation, sorting, shedding,

processing, and sale. These steps have been described in detail by


72

several authors (Bitterner and Kopanda, 1973; Culley et al. 1985a,

1985b; Culley and Duobinis-Gray, 1988a, 1988b; Huner, 1980; Huner and

Avault, 1976; Scudamore, 1948; Stephens, 1955). This article focuses

on the shedding aspect where recirculating systems are used for

commercial production.

The recirculating system used for producing soft-shell crawfish

consists of six functional components: culture and molting trays,

biological filters, screen boxes, a reservoir, a sump, and a pump

(Figure 16). The function of each component and the criteria used for

design are provided in Tables 8 and 9, respectively. The biological

filters (specifically the fluidized bed and upflow sand filters),

which provide water purification, alleviate oxygen supply and clogging

constraints that limited the submerged rock filter (discussed in

Chapter III). The fluidized bed was intended to provide rapid BOD

reduction and high-rate nitrification. The upflow sand filter was

originally included to provide a mechanism of solids removal. Design

guidelines for these filters have proven critical to commercial

adoption (Malone and Burden, 1988).

Figure 17 presents a generic configuration for unpressurized

fluidized beds that can be used with filters ranging in diameter from 10

to 20 inches (25 to 50 cm). Water flows into the filter bottom, up

through the underdrain plate and support gravel bed, finally fluidizing

the filter media (sand) prior to exiting the overdrain port. Bacteria

attached to the sand grains effectuate nitrification and BOD reduction.

Fluxrates through the filter are high, typically ranging from 45 to 652 3 2gpm/ft (2640 to 3820 m -day/m ). Filter media selection (1.2-2.4 mm

3filter sand) and the loading criteria (150 lbs/ft of sand) preclude


73

BIOLOGICAL FILTERSWASH WATER DISCHARGE SCREEN BOXES

PUMP

MAKE-UPWATER

HOLDING OR MOLTING TRAYS

SUMPS R RESERVOIRS

Figure 16. Components of a recirculating system for a soft-shell crawfish facility.


74

Table 8. Major components of a recirculating shedding system.

Function Design Factors

Culture and Molting Trays

Provide easily accessed for holding, separating, molting of crawfish

spaceand

Tray surface area, aeration rates, water circulation, lighting, access

Biological Filter

Capture solids, degrade dissolved wastes, remove ammonia and nitrite

Volume, media composition, media surface area, aeration, water flowrate

Screens

Capture debris, prevent clogging of spray heads

Mesh size, box size, placement

Reservoir

Provide dilution volume stabilize the system

to Volume, circulation rate

Sump

Provide water for pump intake and control system water levels

Volume, turbulence, circulation rate

Pump

Provide circulation and aeration of system water

Pump type, flowrate, pressure


75

Table 9. Summary of interim design criteria for shedding systemsemploying fluidized bed/upflow sand filter configurations (taken from Malone and Burden, 1988).

Parameter Value Comment

Tray Area 1 lb/ft2 Normal loading density for trays

Water Depth 1 inch Recommended water depth in trays

Sand Size 1.2-2.4 mm Diameter of 8/16 filter sand

Sand Volume 150 lbs/ft3 At least 50 precent of the total sand volume must be in the upflow sand filter

Bed Depth 15 inch Assumed bed depth in sand filters

Volume/WeightRatio

5 gallons/lb Total operational water volume ratio for all components

Flowrates 0.07 gpm/lb Minimum flowrate to trays

65 gpm/ft2 Normal operational fluxrate for fluidized bed filter

i10 gpm/ft“ Normal operational fluxrate to

upflow sand filter

65 gpm/ft2 Expansion fluxrate for upflow sand filter


Figure 17

76

w

w

o o o o o o o o o oo o o o o o o o o < Ho o o o o o o o o o ]0000000090o o o o O O O o o o e O O O Q o e o o o o o o o o o o o o o o o o e o o o o o o o o o o o o o o o o n o o Q . n o o a a o

5/16* HOLES

£— 5 1 5 ' H O L E S

SECT'ON A A BOX FILTERS W SECTION A A

c y l i n d e r f i l t e r s

>NIET & OUTLET PIPES CENTERED ON SIDE WALLS

BRASSBAR

" s> 3 8 H C L E S B O T T O M -h a .F OF PiPF O N I V

Unpressurized fluidized bed filter designed for diameters ranging from 10 to 20 inches (25 to 50 cm).


77

clogging and/or oxygen depletion problems during periods of high

loading. However, the filter bed is incapable of capturing solids and,

in fact, adds to the solids loading by continually abrading bacterial

biomass generated in the waste conversion process.

The generic upflow sand filter configuration (Figure 18) is similar

to the fluidized bed. In contrast, the upflow sand filter captures and

removes waste solids from the system. The filter also supports

bacterial populations on the sand grain surfaces which contribute to BOD

reduction and nitrification in the system. The coarse sand (1.2-2.4 mm? 3 ?

filter sand) permits a moderate fluxrate (9.4 gpm/ft“ or 551 m -day/m“)

without expanding the bed. Thus, solids are captured in the bed while

the solids-free water returns to the system via the two-inch discharge2pipe. Once or twice a day, the fluxrate is increased (45-65 gpm/ft ) by

backwashing (or expanding) the filter bed to flush out accumulated

solids. The two-inch discharge line is closed forcing the wash waters

out of the system. Following the backwashing sequence, the fluxrate is

decreased returning the filter to normal operation. Replenishment of

wash waters from an external source (groundwater or tap water) permits

periodic water overturn in the system.

Low and variable fluxrates through the upflow sand filter preclude

sequential filtration. A single fluidized bed typically operates in

parallel with two or three identically sized upflow sand filters

receiving influent waters from a centralized sump (see Figure 16). The

fluidized bed's flow can be diverted to expand each sand filter during

the backwashing cycle. Water treated by the fluidized bed discharges

directly back to the sump while solids-free water from the upflow sand

filter discharges into the large reservoir. The reservoir's high


78

w

ty

O O O O O O O O O O( o e o o o o e o o d o o o o o o o o o o ] o o o o o o o o o o l o o o e o e e o o o o o o o o o o o o o o o e o o o o o o o o o o o o o o o o o o o o o o o o o o oOft ft _fl 6 Oft ft n Q

5/18* HOLES

*T ■

SECTION AA BOX FILTERS ty

5/10* HOLES

SECTION A-A CYUNOER FILTERS

TOP OPEN

INLET fi OUTLET PIPESCENTEREO ON SIDE WALLS

48

8/10SANDGRAVEL1/2-1/0*

i\ 3/0" HOLES BOTTOM HALF OF PIPE ONLY

Figure 18. Unpressurized upflow sand filter designs for diameters ranging from 10 to 20 inches (25 to 50 cm).


79

dilution volume provides stability following shock loading when large

quantities of immature crawfish are introduced into the system.

The volumetric loading criteria relates the pounds of fed crawfish

(measured in pounds or kilograms) that can be safely supported by a unit

volume of sand (measured in cubic feet or cubic meters). By estab

lishing a a practical volumetric loading criteria, the recirculating

shedding system can sustain a maximum load of crawfish for extended

periods with total ammonia and nitrite levels at or below 0.5 mg-N/L.

These quality objectives are conservative, particularly since mortality

problems observed in both laboratory and commercial shedding systems

over the last three years appear to be associated with concentrations

above 1 mg-N/L for each parameter. Research defining the chronic

effects of long term exposure (30-45 days) must be conducted before

quality objectives can be more specifically defined. The criteria does

not discriminate between sand placed in the fluidized bed or upflow sand

filter. However, at least fifty percent of the sand volume must be in

the upflow sand filters to assure solids capture and removal. A system

may be designed employing the upflow sand filter only; however, filter

failure, caused by oxygen depletion, can be catastrophic. Systems

subjected to high waste concentrations, caused by overfeeding or sudden

increases in animal populations (shock loadings), benefit from the

robust reserve capacity that the fluidized bed offers. The volumetric

loading criteria assumes feeding rates of about one percent of crawfish

weight per day based on food protein levels between 25 and 35 percent.


80

COMMERCIAL FACILITY DESCRIPTION

A 1600 pound soft-shell crawfish production facility (Figure 19)

located in Baton Rouge, Louisiana was used for monitoring the perfor

mance of the fluidized bed and upflow sand filters. The commercial

facility, constructed in February 1988, employs four equivalently sized

filters, one fluidized bed and three upflow sand filters, operating in a

parallel configuration. All filters were unpressurized, nearly square

in shape, constructed with marine plywood, and fiberglassed to prevent

leakage. Filter dimensions consisted of a 17-inch cross-sectional area

at the bottom with slightly slanted sides ("V 3 deg.) to facilitate media

expansion and backwashing. Filter designs were based on design

guidelines presented in Table 9.

Each filter contained a coarse filter sand, 15 inches in depth,3 3with a volume of 2.62 ft (0.297 m ). Based on the recommended

3150 lb/ft design capacity (Malone and Burden, 1988), the total combined

3 3filter volume (10.477 ft or 0.297 m ) could support 1600 pounds of

crawfish. All the upflow sand filters in the system were backwashed

twice-a-day, once in the early morning and again in the early evening.

Makeup water used to compensate for backwashing and evaporation was

taken from a quarter-acre pond located adjacent to the facility. pH

control was maintained in the facility by periodically adding

sodium bicarbonate (1 to 5 lbs) to the water.

Aside from the filters, the shedding system consisted of two sumps,

four 1.5 HP pumps, 112 culture trays, 14 molting trays, and a gas water

heater. During normal operation, the system held approximately 2700 3gallons (10.2 m ) of water making the volume/weight ratio equivalent to

1.7 gallons per pound of crawfish. This ratio was significantly lower


Reproduced

with perm

ission of the

copyright ow

ner. Further


without

permission.

UAREUP WATER FROtf POND

4"0PVC

4"<* PVC

WASTE0A3 HEATER 100,000 0TU10 HP

PUtJPGATE VALVE

I3HPPUUP.OACKUrQALL VALVE Q GATE VALVE

TRATS

UPFLOWSANDfilter

UPFLOWSANDfilter

UPFLOWSANDFILTER

SUMP HO. 2 550 GALLONS

SUMP KO I 1150 GALLONS

Figure 19. Schematic of the commercial soft-shell crawfish facility located in Baton Rouge, Louisiana.

82

than the 5.0 gallon per pound criteria recommended by Malone and Burden

(1988).

Four rows of culture trays (28/row) were constructed with an indi-?vidual tray surface area of 10 ft*". These tray dimensions were smaller

2than those normally recommended for commercial use (24 ft^/tray). One

row of molting trays (14 total) was constructed, although only six to 2eight trays (8 ft /tray) were normally used during peak loadings. Thus,

the smaller molting trays were used for culture trays whenever

necessary. All trays were loaded at density of one pound per square

foot. Sprayheads discharging water to the trays originated from a

1-inch diameter PVC manifold extending the length of each tray run.

Stainless steel ball valves installed on the manifold head were used for

controlling flowrates. Both culture and molting trays emptied to common

4-inch PVC drainlines which returned water to the sump.

METHODOLOGY

Two different sampling programs were conducted at the commercial

facility: (1) a general water quality survey of the facility and (2) an

evaluation of filter performance. The sampling methodology used with

each survey, in addition to the analytical methods, are presented below.

Data obtained during the first portion of the study was used to

evaluate system water quality in terms of nitrification, pH, and oxygen

stability. A total of 13 sampling events spread over a 45 day period

(April 26 - June 6) were monitored at the facility. All sampling was

conducted between 7:00 and 9:00 am.

Ideally, the volumetric loading criteria should be evaluated under

a constant loading. However, at this stage, such conditions are rarely


83

observed in the soft-shell crawfish industry. Source of supply for high

quality immature crawfish remains a problem for most operators and pur

chases tend to be made in large quantities. Evaluation of the

volumetric loading criteria in this commercial facility was complexed

because the system lacked sufficient volume to dilute accumulated wastes

following intermittent shock loading (200-400 pounds crawfish per day).

Approximately three days are required for the nitrifying population to

adjust to increased ammonia production. Efforts were made to avoid

sampling within 72 hours of a population increase of more than 10

percent per day. However, residual effects of shock loading undoubtedly

influenced a number of the observations.

Samples used to evaluate the system's nitrification ability were

analyzed for both total ammonia-nitrogen (NH^) and nj.trite-nitrogen

(NO^). Filter performance in terms of oxygen stability was obtained by

measuring influent and effluent dissolved oxygen (DO) and corresponding

flowrates (Q) on each filter. Influent DO measurements were made near

the pump intake in sump //2 (see Figure 19) to provide a representative

sampling of filter influent. Field analyses also included monitoring

pH, temperature, and alkalinity (ALK). pH measurements were taken in

each individual filter, the sump ( i l l ) , and randomly selected culture and

molting trays. Temperature monitoring was conducted in the trays as

well as the sump (//2) . Alkal inity samples were taken from the sump

(112).

Loading estimates were made in the system by randomly selecting

holding trays and measuring "wet weights" of crawfish. Based on the

number of trays currently online, a loading estimate was calculated.

Records were maintained by the operators on the amounts of immature


84

crawfish added to the system, mortalities removed, and the daily

quantities of soft-shells produced in the facility.

Separate from the water quality survey, six evaluations of filter

performance were conducted over a 20 day period. These evaluations were

performed to lend further insight into the relative nitrification

ability of each filter. Influent and effluent samples were taken on

each filter for total ammonia-nitrogen and nitrite-nitrogen analyses.

All influent samples were taken near the pump intake in sump f/2 while

effluent samples were taken from each filter's discharge line.

Loading estimates were made using the procedure previously discussed.

All analyses (for both studies) were conducted according to the

procedures outline in Standard Methods (APHA, 1985). Total ammonia and

nitrite laboratory analyses were performed using the nesselerization and

the sulfanilamide-based colorimetric procedures, respectively.

Alkalinity analyses were conducted on-site using the titration/potentio-

metric endpoint method. Titrant standardization was conducted with each

sampling event. Dissolved oxygen measurements were made using a Yellow

Springs Model 57 oxygen meter. pH monitoring was conducted using a

Cole-Palmer Mini pH meter.

RESULTS

The commercial facility was monitored on thirteen different

occasions while the system was near or slightly above its design

capacity of 1600 pounds or, in terms of the filter loading criteria,

150 lbs/ft'" of filter sand. Filter design capacity was exceeded on3

two occasions with loadings of 160 and 165 lbs/ft . Mortalities in

the system were normal for commercial system (between 2 and 3 percent


85

per day) and soft-shell production was moderate, averaging approximately

2 percent per day of the system's loading. A statistical summary of the

loading and water quality data is presented in Table 10.

Ammonia and nitrite levels observed at the various filter loadings

are presented in Figure 20. Although the total ammonia and nitrite

levels fluctuate above the authors recommended guideline of 0.5 mg-N/L,

the facility operated reasonably well during the entire monitoring

period. The filters consistently maintained total ammonia and nitrite

below the 1.0 mg-N/L threshold level. The highest ammonia concentra

tion, 2.3 mg-N/L, was observed following a combined shock load of

760 pounds of crawfish over two consecutive days. Ammonia levels,

averaging 0.57 mg-N/L, were slightly lower than the nitrite levels,

averaging 0.62 mg-N/L.

Alkalinity in the facility averaged 216 mg/L (as CaCO^) and

remained above the minimum recommended level of 100 mg/L (as CaCO^) for

safe commercial operation. Despite efforts by the operators, however,

pH levels (Figure 20c) remained below the desirable range of 7.5 to 8.0.

Normal aeration in the system maintained dissolved oxygen levels in the

sump between 4.9 and 7.0 mg/L throughout the monitoring period. Mean

water temperature (30.1 + 2.1°C) in the system remained consistently

higher than normally recommended (22 - 28°C).

Figure 21 illustrates ammonia and nitrite removal efficiency data

obtained from the independent filter evaluations conducted on the

fluidized bed and upflow sand filters. Removal efficiencies are

bounded by the diagonal lines marked 0 and 50 percent removal while

the x-axis denotes 100 percent removal. Close examination of the data

indicates that the ammonia conversion efficiencies for the fluidized


86

Table 10. Summary of water quality and field data collected at the commercial soft-shell crawfish facility in Baton Rouge, Louisiana. All measurements of water quality data were taken in sump #2 (see Figure 19)

Parameter n XStandardDeviation Range

Loading (lbs) 13 1351 238 900 - 1725

NH3 (mg-N/L) 13 0.57 0.56 0.20 - 2.30

NO^ (mg-N/L) 13 0.62 0.22 0.24 - 0.93

Alkalinity (mg/L as CaCO,,)

12 216 91 100 - 423

00 (mg/L) 13 5.8 0.6 4.9 - 7.0

pH 13 7.1 0.2 6.7 - 7.7

Temp. (°C) 13 30.1 2.1 27.5 - 34.0

Flowrate (gpm)

- Fluidized Bed Filter

13 103 24 33 - 126

- Upflow Sand Filters

39 18 6 5 - 29


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Figure 20. Total ammonia (a), nitrite (b), and pH (c) monitoring data obtained on the commercial soft-shell facility„in Baton Rouge, LA. Filter design capacity (150 lbs/ft ) indicated by the vertical line.


88

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89

bed are erratic with reductions averaging only 12 percent. Similarly,

net nitrite reductions in the fluidized beds averaged less than one

percent. Conversely, important contributions were made by the three

upflow sand filters with regard to system nitrification. The filters

consistently demonstrate reductions in both ammonia (averaging 34 per

cent) and net nitrite (averaging 18 percent). Thus, the upflow sand

filters not only play an important role in solids removal (as discussed

in Chapter III) but have a major influence on controlling ammonia and

nitrite levels in the recirculating system.

DISCUSSION

During the monitoring period, the system was repeatedly subjected

to shock loadings. Crawfish loadings, ranging from 200 to 400 pounds

per day (12.5 to 25 percent of capacity), were imposed to maintain the

system at design capacity. For example, the highest observed ammonia

level (2.3 mg-N/L) occurred following the addition of 760 pounds of

crawfish to the system over a two day period. This increased loading

not only doubled the filter loading in a three day period, but also3exceeded the system's 150 lbs/ft design capacity. With a

volume/weight ratio of less than 2 gallons per pound of crawfish, this

facility lacked the dilution capacity necessary for stabilization while

the filters acclimated to the increased loading.

Difficulties with pH control (as illustrated in Figure 20c) and

overfeeding, caused by operator inexperience, contributed additional

instability to the system. Consequently, no apparent relationship

was evident between filter loading and system water quality. However,

these filters appear to maintain ammonia and nitrite below 1.0 mg-N/L


90

under typical commercial operational conditions when loaded to the3criteria level of 150 lbs/ft . Further improvements in water quality

will, undoubtedly, result as the facility's managing personnel gain

experience operating the filters, managing loading patterns,

controlling feeding rates, and controlling pH.

While the upflow sand filters demonstrated consistent reductions in

ammonia and nitrite concentrations, contributions of the fluidized bed

filter are not readily discernible as demonstrated in Figure 21. A- more

in-depth analyses of the filter's ability considers the oxygen consump

tion rate (OCF), a direct measure of the bacterial activity of the

filter (Hirayama, 1965; Manthe et al. 1988). Results of the analyses

for both the fluidized bed and upflow sand filter are illustrated in

Figure 22. Single OCF observations are illustrated for the fluidized

bed filter while mean OCF values, with upper and lower standard

deviations, represent the three upflow sand filters at a given loading.

Based on these results, the fluidized bed appears bacteriallv active

and, intermittently, responsible for most of the waste conversion,

particularly when filter loading exceeds the design carrying capacity.

Results of filter removal efficiencies (Figure 21), however, suggest

that heterotrophic bacteria, rather than the slower growing nitrifiers,

dominate the filter. Thus, the upflow sand filters are reducing ammonia

and nitrite concentrations below those levels required to support

nitrifiers in the abrasive environment provided by the fluidized bed.

The BOD reduction effectuated by the fluidized bed filter, however,

decreases the load on the upflow sand filters contributing indirectly to

their nitrification rates.


Reproduced

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'DESIGNCARRYINGCAPACITY

_1______ l80 90 100 110 120 130 140 150

FILTER LOADING CAPACITY ( Ib s /f f3 )160 170

Fluidized bed and upflow sand filter OCF observations taken at the commercial facility. Reported values for the upflow sand filter represent a mean with upper and lower standard devications for the three filters at a given filter loading.

Failure of submerged filters is most often associated with oxygen

depletion (Hirayama, 1965, 1974; Manthe and Malone, 1988). Comparison

of the mean oxygen consumption rates to the oxygen fluxrates indicates

that these filters are operating safely below their maximum carrying

capacity. Nitrifying bacteria are severely inhibited when dissolved

oxygen levels in the filters are allowed to drop below 2.0 mg-09 (Gaudy

and Gaudy, 1978). Thus, the useful oxygen flux or oxygen carrying

capacity (OCC) can be computed as the product of the flowrate and the

difference between the influent oxygen level and the minimum allowable

filter effluent level of 2.0 mg-0o (Manthe et al. 1988). Designi.

flowrates (Table 9) coupled with maintenance of a sump dissolved oxygen

level of 6.0 mg-On/L define the OCC as 429 and 2966 g-0?/day for a

upflow sand filter and fluidized bed, respectively. The average OCF for

the upflow sand filters (292 g-09/day) was observed when the system

operated between 75 and 100 percent of capacity (113 and 150 lbs/ftJ),

thus indicating that 68 percent of the OCC was utilized. In contrast,

the fluidized bed's OCF averaged only 461 g-09/day, or 16 percent of

capacity, in the same operational range. Recognizing that the some

filter capacity must be reserved to absorb daily fluctuations, the

upflow sand filters are near their practical operational capacity. The

majority of the system’s reserve capacity rests in the fluidized bed (as

intermittently illustrated in Figure 22) .

Based on these observations, the fluidized bed and upflow sand

filters compliment each other when used in a recirculating shedding

system. First, the upflow sand filters appear responsible for most of

the waste conversion and removal (as solids) during normal loading

conditions. However, the fluidized bed contributes to the waste


93

removal as a result of biomass attrition in the abrasive, fluidized

environment. A second means by which the two filters complement each

other involves the upflow sand filter's inability to maintain oxygen

supplies during peak loadings. During these periods, the fluidized

bed appears to support the bulk of the waste load, thus protecting the

system from catastrophic failure.

The high level of filter bacterial activity contributes to dif

ficulties with pH control in commercial systems. The crawfish,

Procambarus clarkii, tolerates a wide pH range without adverse effect

(Huner and Barr, 1984). However, above 8.0 the toxic un-ionized ammonia

species becomes increasingly dominate over ionized ammonia (ammonium),

thereby increasing the animals sensitivity to total ammonia accumula

tions. Conversely, pH values below 7.0 inhibit the activities of the

nitrifying bacteria in biological filters (Paz, 1984). Recognizing that

pH values within a filter can decline significantly as a consequence of

nitrification, the influent (sump) pH level should be maintained between

7.5 and 8.0.

Despite an average alkalinity of 216 mg-CaCO^, pH in the sump

ranged from a low of 6.7 to a maximum of only 7.7, averaging 7.1.

Although normal aeration levels in the system adequately maintained

dissolved oxygen levels in the sump above 5.0 mg/L, they were not

sufficient to contend with the large amounts of carbon dioxide

produced by respiration activities of the crawfish and the bacterial

population. Theoretical pH/alkalinity calculations reveal carbon

dioxide levels, ranging from 17 to 174 mg-CO^/L, persisted throughout

the monitoring period. Given the known sensitivity of the nitrifying


94

bacteria to depressed pH levels, some type of supplemental aeration

(or air stripping) apparatus would seem justified for pH control.

CONCLUSIONS AND RECOMMENDATIONS3The recommended volumetric loading criteria of 150 lbs/ft is a

sufficient criteria for designing fluidized bed and upflow sand filters

when employed with recirculating soft-shell crawfish production

facilities. The filters are robust, controlling total ammonia and

nitrite levels below 1.0 mg-N/L. Results indicated that water quality

fluctuations were not related to filter carrying capacity. Water

quality in systems which follow design guidelines are controlled mostly

by system management rather than by the maximum carrying capacity of

filters. Careful attention must be given to managing pH levels in the

system, reducing shock loadings, and avoiding overfeeding.

The upflow sand filter provides most of the waste processing during

periods of normal loading. In addition to its crucial solids removal

function, the upflow sand filter appears responsible for most of the

system's nitrification. Effluent waters from the upflow sand filters

were not completely nitrified indicating that additional water quality

improvements can be realized if factors controlling the nitrification

rates can be identified. The fluidized bed remained active throughout

the study, but appeared primarily responsible for BOD reduction rather

than nitrification.

Addition of sodium bicarbonate was not sufficient for pH control jn

the system. Normal aeration adequately supplied oxygen to the crawfish

and biological filters but failed to control carbon dioxide accumula

tions. The pH declined rapidly during periods of peak biological


activity and high carbon dioxide production. Methodologies capable

stripping carbon dioxide from the recirculating waters should be

investigated and included in future designs.


BIBLIOGRAPHY

APHA, 1985. Standard Methods for the Treatment of Water and Wastewater,

16th ed. , American Public Health Administration, New York.

Andrews, G.F. and C. Tien, 1979. The expansion of a fluidized bed

containing biomass, Amer. Inst. Chem. Eng. Journ., 25(4): 720- 723.

Bitterner, G.D. and R. Kopanda, 1973. Factors influencing molting in

the crayfish Procambarus clarkii, Journ. of Exp. Zoology, 186(1):

7-16.

Cange, K.M., 1987. Water quality management strategies for production of

the soft-shelled red swamp crawfish (Procambarus clarkii), Master's

thesis, Louisiana State University, Baton Rouge, Louisiana 70803.

Chidester, F.E., 1912. The biology of the crayfish, American

Naturalist, 46: 279-293.

Cooper, P.F., 1981. The use of biological fluidized beds for the

treatment of domestic and industrial wastewaters, Chem. Eng.,

371(2): 373-376.

Cooper, P.F. and P.M. Sutton, 1983. Treatment of wTastewaters using

biological fluidized beds, Chem. Eng., 392:65.

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crawfish: A status report, Louisiana Sea Grant College Program,

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Culley, D.D., M.Z. Said, and P.T. Culley, 1985b. Procedures affecting

the production and processing of soft-shell crawfish. Journ. World

Mariculture Society, 16: 183-192.

96


97

Culley, D.D. and L. Duobinis-Gray, 1988a. Effects of temperature on

molting and mortality rates of red swamp crawfish (Procambarus

clarkii) in a soft-shell culture system, In Review.

Culley, D.D. and L. Duobinis-Gray, 1988b. Effects of dissolved oxygen

on molting and mortality rates of red swamp crawfish (Procambarus

clarkii) in a soft-shell culture system, In Review.

Culley, D.D. and L. Duobinis-Gray, 1988c. Molting, mortality, and the

effects of density in a commercial soft-shell crawfish operation.

Journ. World Mariculture Society, in Press.

Gaudy, M.S. and Gaudy, E.T., 1978. Microbiology for Environmental

Engineers, Wiley-Interscience, New York.

Gutzmer, M.P. and J.R. Tomasso, 1985. Nitrite toxicity to the crayfish

Procambarus clarkii, Bull. Environ. Contain. Toxicol. 34: 369-376.

Haefner, P.A. and D. Garten, 1974. Methods of handling shedding blue

crabs, Callinectes sapidus, Marine Advisory Series No.8, Virginia

Institute of Marine Science, Gloucester Point, Virginia.

Hartenstein, R., 1970. Nitrogen metabolism in non-insect arthropods, in

Comparative biochemistry of nitrogen metabolism, Vol. 1, ed. J.W.

Campbell, Academic Press, New York, pp. 299-372.

Haug, R.T. and P.I. McCarty, 1972. Nitrification with submerged

filters, Journ. WPCF, 44: 2086-2102.

Hirayama, K., 1965. Studies on water control by filtration through sand

beds in a marine aquarium with a closed circulating system - I.

Oxygen consumption during filtration as an index in evaluating the

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Fish. , 31: 877-892.


98

Hirayama, K., 1970. Studies on water control by filtration through sand

bed in a marine aquarium with closed circulating system - VI.

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36(1):26-34.

Hirayama, K., 1974. Water control by filtration in closed systems,

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Huner, J.V. 1980. Molting in the red crawfish, Proc. of the First

National Crawfish Culture Workshop, D. Gooch and J. Huner, ed.,

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Huner, J.V. and J.W. Avault, 1976. The molt cycle of subadult red swamp

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Hymel, T.M., 1985. Water quality dynamics in commercial crawfish ponds

and toxicity of selected water quality variables to Procambarus

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Jaspers, E.J., 1969. Environmental conditions in burrows and ponds of

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Jeris, J.S., C. Beer, and J.A. Mueller, 1974. High rate biological

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f ■ ■ ' ' ' ' '


99

Johnson, S.K., 1982. Water quality in crawfish farming. Proc. Crawfish

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100

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science, New York.


APPENDICES

102


APPENDIX A

WATER QUALITY DATA

This appendix provides a listing of the raw water quality data used with Chapter II (Grain Size Determinations) and Chapter III (FilterEvaluations). Appendix A-l presents the grain size data as sort by sandsize: Fine (0.42 - 0.84 mm), Medium (0.84 - 1.68), and Coarse (1.19 -2.38 mm) while Appendix A-2 presents filter evaluation data as sorted byfilter design: Fluidized Bed, Upflow Sand Filter, and FluidizedBed/Upflow Sand Filter Combination.

Total ammonia nitrogen (NH3), nitrite nitrogen (N02), nitrate nitrogen (N03), total kjeldahl nitrogen (TKN), dissolved oxygen, total suspended solids (TSS), volatile suspended solids (VSS), and biochemical oxygen demand (BOD) are reported in units of milligrams per liter (mg/L). Alkalinity (ALK) units are mg/L as calcium carbonate. Temperature units are in degrees Celsius. pH data is reported in standard units. Unreported data is denoted by a

103


APPENDIX A-l

GRAIN SIZE DETERMINATION DATA

Influent dissolved oxygen data is denoted under the heading 'DOINF' while effluent dissolved oxygen is designated under 'DOEFF'. Total wet weight of crawfish (reported in grams) held each system is designated as 'WGT'.

104


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APPENDIX A-2

FILTER EVALUATION DATA

Effluent dissolved oxygen data for the single filter configurations and for the fluidized bed filter, when used in combination with the upflow sand filter, are denoted by the symbol 'DOEFFB'. Effluent dissolved oxygen data for the upflow sand filter when used in combination with the fluidized bed are denoted by 'DOEFSF'. Influent dissolved oxygen for all configurations is denoted by 'DOINF'. All dissolved oxygen data are reported in units of mg/L. Flowrate data for the single filter configurations are reported as 'FL0W1'. Flowrates for the combination filter design are designated as 'FL0W1' for the fluidized bed and 'FL0W2' for the upflow sand filter. Number of crabs held in the system are denoted by 'POP' while the number of crab mortalities are reported under 'MORT'.

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APPENDIX B

CRAB WASTE CHARACTERIZATION DATA

This appendix contains raw data from the waste characterization studies conducted on the blue crab (Callinectes sapidus) which was used in Chapter III. Total ammonia nitrogen (NH3), nitrite nitrogen (N02), unfiltered TKN (UNFTKN), filtered TKN (FILTKN), unfiltered BOD (I1NFB0D), filtered BOD(FILBOD), total suspended solids (TSS), and volatile suspended solids (VSS) are reported in units of mg/’L. Individual crab weight is reported as 'WGT'.

128


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APPENDIX C

FILTER FLUXRATE DATA

This appendix contains experimental fluxrate data needed for fluidizing a filter at a given expansion rate and backwashing an upflow sand filter based on several media. All experiments were conducted on a 6 inch plexiglass column 43 inches high. A 1.5" ball valve was used for flowrate control and connected the column and a 1.0 HP pump (American Products, Model it 381084) . The column contained a 3" gravel underdrain of which the bottom layer consisted of 1.5" of gravel which passed a 1/2" sieve and was retained on a 3/8" sieve. The upper 1.5" layer consisted of gravel which passed a 3/8" sieve and was retained on a 3/16" sieve. On top of the gravel underdrain, one of three media was loaded at a specified height. The three media types included: 1) coarse "8/16" sand (1.19 - 2.38 mm), 2) medium "12/20" sand (0.84 - 1.68 mm), and 3) commercial dolomite (4.76 - 7.93 mm). Dry bed heights of 12 and 15 inches (denoted as 'BEDHT'in the appendix)) were used for all three media types.

A total of five different expansions were used: 0, 25, 50, 75,and 100 percent. These are designated as FLOWO, FL0W25, FL0W50, FLOW75, and FLOW100 in the appendix. Maximum flowrate at 0 percent expansion was determined when the upper particle layer on the filter bed began to expand. Bed expansion heights were marked on the column and adjusted with the use of the 1.5" ball valve. Flowrate determinations were made using a microcomputer, an analog/digital converter, and a level sensoring device. A software program, written in Turbo Pascal (Borland, 1985) was developed in conjunction with the hardware configuration and designed to measure a total of five replicates as denoted by 'RUN' in the appendix. To detect precision in flowrate measurements, a total of 3 independent analyses were conducted making a total of 15 replicates for each media at a given expansion rate.

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363

APPENDIX D

COMMERCIAL FACILITY DATA

This appendix contains the commercial facility data used in conjunction with Chapter IV. Table D-l contains system data while Table D-2 contains the filter performance data. The system consists of four filters: one fluidized bed filter (FB) and three upflow sand filters (designated as USF1, USF2, and USF3). Total ammonia (NH4-N), nitrite (N02-N), and dissolved oxygen data are reported in units of mg-N/L. Influent dissolved oxygen data for each filter is designated as 'Sump DO'. Alkalinity data is reported as mg/L of calcium carbonate. pH data (taken from the sump) is reported in standard units while temperature data is reported in degrees Celsius. The number of crawfish held in the system during each sample event is designated as 'Loading' and reported in units of pounds. All sampling was conducted in 1988.

1 3 7


TABLE

D-l.

SYSTEM

DATA

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VITA

Daniel George Burden was born April 19, 1955 in Orlando, Florida.

His family later moved to Gainesville, Florida where he graduated with

honors from Gainesville High School in 1973. He attended Harding

University in Searcy, Arkansas and graduated with a B.S. in General

Science. He spent the following two years working as an engineering

assistant with Richardson Engineering and Testing Laboratories and

later became manager of the firm in 1980. A year later he entered

LSU's graduate program in 1982 and received his Master's in Civil

Engineering in 1985. After completing his Ph.D. program he accepted a

position with James M. Montgomery, Consulting Engineers, Inc. in Fort

Lauderdale, Florida.

140


DOCTORAL EXAMINATION AND DISSERTATION REPORT

Candidate:

M ajor Field:

Title of Dissertation:

Date of Examination:

September 12,

Daniel G. Burden

Civil Engineering

Development and Design of a Fluidized Bed/Upflow Sand Filter

Configuration For Use In Recirculating Aquaculture Systems

Approved:

Major Professor and Chairman

Dean of the Graduafe^scbbol

EXAM INING COM M ITTEE:

A ' M A / Q . U / y y \

( A x J U u

1988


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