LowCostBiofilters0305.pdf

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Aquaculture Extension Bulletin Spring 2005

Low-Cost Biofiltration Systems

James P. Szyper1,2,3,, Clyde Tamaru2, Harry Ako4,Kathleen McGovern-Hopkins2, and Robert Howerton2

1Corresponding author: 875 Komohana St., Hilo, HI96720, tel. 808 981-5199, email [email protected]

2Hawaii Aquaculture Extension Service (sponsored by

University of Hawaii Sea Grant College Program and Stateof Hawaii Aquaculture Development Program)

3Cooperative Extension Service, UH Manoa College of Tropical Agriculture and Human Resources

4Dept. of Molecular Biosciences & Bioengineering, UHManoa College of Tropical Agriculture and HumanResources

Water for agricultural uses including aqua-culture is a limited resource in most places.In Hawaii as in other island locations, waterconservation and optimal use of the avail-able resource will be increasingly importantas population grows and businesses develop

(Leone 2003, New Internationalist 2003).Biofiltration systems reduce consump-

tive water use and waste discharge in aqua-culture systems, often dramatically, butbusiness operators may lack the capital orotherwise hesitate to make the initial invest-ment. Commercial systems can appear andsometimes be complex. Low cost systemsserve to demonstrate principles, structure,and function. They provide encouragementto observers that a system can be operated

conveniently and that investment will berecovered within a reasonable time.

This bulletin describes the approachesand demonstration systems developed foraquaculture extension efforts in Hawaii dur-ing recent years. The primary purpose of

these demonstrations is to show possibilitiesthat are immediately applicable for existingbusinesses or for readily-envisioned devel-opments among our clientele. No attempthas been made to review this large field of endeavor nor to make a comprehensive test

of possible approaches. We welcome infor-mation from readers of this bulletin to im-prove this document for future editions.

Water Use and Conservation Potential

Recirculating biofiltration technology doesnot aim to completely eliminate addition of new water or discharge of used water duringa crop production cycle. The primary pur-pose is to keep concentrations of total am-

monia nitrogen (TAN) low with minimalcost for water replacement. During a recentworkshop session in Hawaii, Tom Losordoof North Carolina State University defined"closed" recirculating systems as those inwhich up to 20% of the water volume is ex-changed for new water each day, with 5 to10% being typical. These percentages areminimal and necessary in systems that re-move settleable or filterable solids, in addi-tion to processing ammonia.

Non-recirculating culture systems usevarious amounts of new water during pro-duction, depending on stocking density andthe degree of ammonia processing and othersupport by natural or artificial processes.Fishes and shrimps can be grown in earthen



ponds without discharge of used water dur-ing the entire crop production cycle undersome conditions. However, replacement of evaporation losses may require addition of water at a rate of 1 to 3 percent or more of the pond volume per day. In non-recirculating (flow-through) tank systems,considerable water exchange is required todilute the ammonia produced by the fish atmost commercially useful stocking densi-ties. For example, we took a biofilter off-line for a few days’ modification during oneof our recent trials in Hilo, in which wewere maintaining a tilapia stock at 5-6kg/m3 in a 2.4 m diameter tank in the green-house. The biofilter had been maintainingammonia concentrations below 0.3 ppm,with water exchange of only about 10% perweek. Without the biofilter, a flow rate of about 7 liters per minute of new water(more than 200% per day volume exchange)was necessary to prevent ammonia concen-trations from increasing, even at this com-mercially modest stocking density. Consid-ering only the need for ammonia removal,the biofilter was saving more than 9 m3 of water per day. At recent public water rates

in Hawaii County, this amounts to a cost of $4.23 per day or about $127 per month,which would amount to a significant frac-tion of the production costs and marketvalue of the crop.

Demonstration Systems in Hawaii

Seven different recirculating biofiltrationsystems are described here (Table 1). Theperformance of 5 of these was assessed dur-

ing support of working culture systems. The designs are mostly adaptations of well-known strategies, made by the authors of this document. In one case, a creative adap-tation of a commercial system was given tous by colleagues as noted in the Acknowl-edgments. These are “small-scale” systems,

meaning in this case that the filter containervolumes ranged from 20-125 liters (e.g., 5gallon buckets, 33 gallon plastic trash cans). The supported culture volumes ranged from0.6 to 8 m3. The systems are labeled in Ta-ble 1 as “Outdoor” and “Indoor,” indicatingour particular test conditions; the designsare adaptable to many settings.

Quantitative assessments are reportedhere to lend credence to the workability of these approaches, but the results should notbe taken as definitive or limiting. All of thesystems can readily be improved upon andadapted to new uses, including use of multi-ple filter units or much larger containers tosupport larger culture units.

Outdoor Green Water Biofilters

Systems A, B, and C were developed at theUniversity of Hawaii’s freshwater aquacul-ture research facility at Windward Commu-nity College on the island Oahu. They wereaimed at facilitating increased productioncapacity (stocking density) and water con-servation on freshwater ornamental fishfarms (Asano et al. 2003). All were made

in 20 liter white plastic buckets and de-ployed on the edge or submerged in cylin-drical plastic tanks of water volume 2080liters (Figure 1). Each bucket contained0.028 m3 (1 ft3) of pvc ribbon (Bio-Fill,Aquatic Ecosystems, www.aquaticeco.com)for bacterial substrate. System A (tricklingfilter) had water pumped to the open top of the bucket, through homemade spray bars,from where it trickled to the bottom and re-turned to the culture tank through a short

pipe. Water was lifted from the culture tankby a 15 W electric pump set to deliver 9 li-ters per minute, which amounted to about 6culture tank volumes per day. System B(submerged filter, similar to the box filtersfamiliar to aquarium hobbyists) was drivenby air lift of tank water out of the center of



Figure 2. Students at UH Hilo farm selecting breeders.This and all remaining photos by Jim Szyper.

Figure 1. Air lift—driven biofilter in a plastic trash can.

.

_________________________________________________________________________________________

Table 1. Seven recirculating biofiltration systems demonstrated in Hawaii. Approximate materialscosts reflect prices in Hawaii during the late 1990’s – early 2000’s. Costs of air pumps for air lifts arenot included; research facility air systems were used in these cases.

____________________________________________________________________________________

System Filter Container Culture System Biofilter Materials Cost ____________________________________________________________________________________

A. Outdoor Green Water plastic bucket cylindrical plastic tank $ 60* Trickling Filter 20 liters (5 gal) 2080 liters(pump driven)

B. Outdoor Green Water plastic bucket cylindrical plastic tank $ 45** Submerged Filter 20 liters 2080 liters(air lift driven)

C. Outdoor Green Water plastic bucket cylindrical plastic tank $ 45** Trickling Filter 20 liters 2080 liters

(air lift driven)

D. Indoor Trash Can plastic trash can cylindrical plastic tank $ 110** Up-flow Filter 125 liters (33 gal) 4700-8000 liters(air lift driven)

E. Indoor Shelf System plastic water bottle 75 liter (20 gal) glass $ 150* Up-flow Filter 20 liters aquaria x 8: 600 liters(pump driven)

F. Indoor Fluidized 12” dia. pvc pipe cylindrical plastic tank $ 300*** Bed Sand Filter 60 liters 4700 liters(pump driven)

G. Outdoor Green Water plastic bucket cylindrical plastic tank $ 50* Trickling Filter 20 liters 2500 liters(pump driven)

* Includes small (15-25 W AC) submersible water pump.** Does not include an air pump to drive air lift.*** Includes 186W (0.25 hp) AC electric water pump.

_________________________________________________________________________________________

the submerged bucket, which had smallholes drilled in its sides to admit tank water.Water flow was 3 liters per minute, about 2tank volumes per day. Air was provided bythe facility’s blower system. System C wassimilar to system A, but was driven by airlift.

A demonstration system on Maui Island(System G) is based on a trickling filter in a

bucket like System A, but is undergoingcontinuing development of added functionsby Aecio D’Silva of the University of Ari-zona. Water passes from the culture tank toa settling basin (55 gallon drum) to removesolids. Water goes from there to the biofilterand then through a hydroponic vegetableproduction system. One of the innovativedevelopments was to remove solids to an



Figure 1. Outdoor green water biofilters at Windward CommunityCollege. Top: trickling filter mounted on tank rim. Bottom: sub-merged filter in tank. Photos by K. McGovern-Hopkins.

anaerobic digestion container to produce anadditional by-product, methane. The biofil-ter used non-biodegradable packaging"peanuts" as a substrate which substantiallyreduced costs. Although quantitative testresults are not available, this inexpensive

biofiltration unit performed comparably tobiofilters using much more expensive sub-strates such as bio balls.

The performance of systems A and Bwas assessed in a controlled experiment inwhich 9 tanks were stocked with juvenilekoi (ornamental carps) at an initial densityof 1 kg/m3, with fish added later to attain 3kg/m3, which finally grew to 4.6 kg/m3. Three tanks each were allocated to 3 treat-ments: support by systems A and B, and a

set of unsupported controls. Details are pre-sented by Asano et al. (2003). Initial fertili-zation of the tanks and the waste producedby the initial stocks of fish fostered densegreen water blooms, which kept the concen-trations of total ammonia, nitrite, and nitrateat nearly undetectable levels through 16days. It was presumed that the filters were

conditioned by that time. Upon tripling of the fish biomass on day 17, concentrationsof nitrogen rose in all tanks. The biofiltersin general held the nitrogen concentrationsat lower levels than were seen in the controltanks, but required some time to becomeconditioned to the new biomass and N-loading. Between days 17-75, all biofiltersystems reduced total ammonia to 2 mg/l orless, and nitrite to low levels. The controlswere taken down on day 76, when ammoniahad reached high levels and some fish died.One of three submerged filter systems had apartial mortality event. The trickling filtersmarginally outperformed the submergedfilters, with better ammonia removal andsome advantage in oxygen concentrations.New water was added only to make upevaporation until day 76, after which waterwas exchanged at about 30% per week. Thevalue of these results for the farming of freshwater ornamental fish in Hawaii is thatthe supported densities are much higherthan those typical of local farming practices,and this was done with minimal water ex-change.

Indoor Biofilters

Systems D, E, and F were developed andtested on Hawaii Island in the aquaculturelaboratory greenhouse at the research andteaching farm of the University of Hawaii atHilo College of Agriculture, Forestry, andNatural Resource Management. The pri-mary purpose was to provide demonstra-tions of workable systems that are applica-ble to a variety of products and farm situa-

tions. Quantitative assessments of perform-ance were made, but no formal experimentswere performed.

The up-flow biofilter contained in a plas-tic trash can (system D), is an adaptation of a traditional design described by Szyper(1989; Figure 2 here), with the current ver-



Figure 2. Trash can biofilter. Top: diagram from Backyard Aqua-culture in Hawaii. Bottom: working biofilter at UH Hilo farm.Photo by J. Szyper.

sion shown in detailed photographs atwww.uhh.hawaii.edu/~pacrc/bigisaquapg/(Select Education and Training from thehome page). Tank water is air-lifted in a 4cm (1.5 in) pvc pipe into the filter bodyalongside the tank. A larger open tube de-

livers the water to the bottom dead spacewhere solids can collect for manual drain-age through a bottom valve. Water fills thecan moving upward through a 5-10 cm thicklayer of crushed coral for pH control andalkalinity addition, then through a layerconsisting of 0.04 m3 (1.5 ft3) of the plasticribbon used in systems A, B, and C. Theselayered materials are supported above thedead space by a plastic grate resting on pipesections of 15-20 cm length. Water returns

from the top of the filter to the culture tankby passive overflow. This system has sup-ported cylindrical tanks of 4.5 to 8 m3 vol-ume containing tilapia stocks up to 5 kg/ m3 for more than two years’ nearly continuousoperation. For maintenance of modest fishstocks, minimal water exchange and infre-quent cleaning are sufficient, with total am-

monia concentrations kept well below 1ppm. The facility water’s relatively lowalkalinity (30-40 ppm) is maintained orslightly increased. This biofilter was able toreplace and match the performance of thesand biofilter in a trial described below.Nitrogen processing is discussed quantita-tively in a separate section below.

A smaller biofilter of similar designstrategy (system E, Figure 3) was assembledin an inverted 20 liter plastic drinking waterbottle. A valve was installed in the neck of the bottle for solids removal. A bottle withthis feature was originally obtained com-mercially, but later filters were made inhouse. Used water is delivered by a 1.3 cm(1/2 in) pipe passing through a bulkheadfitting placed about 10 cm above the bottomof the filter. Water fills the system passingupward through a 5 cm thick layer of crushed coral and 0.01 m3 (0.33 ft3) of plas-tic ribbon supported on a plastic grate as insystem D, exiting through a bulkhead fittingnear the top into a 75 liter reservoir tank.From there, a 15 W electric pump deliverswater to an overhead 5 cm (2 in) pipe run-ning lengthwise over the aquarium shelf.

Taps from this pipe deliver water by gravityto each of eight 75 liter (20 gallon ‘high’)glass aquaria. Used water leaves eachaquarium near the bottom, through a bulk-head fitting to an outside standpipe, fromwhich water falls into a lengthwise, downsloping 5 cm pipe that returns water to thefilter by gravity. An important feature of

Figure 3. Aquarium shelf biofilter system. Left: close-up of filtervessel showing layers of Bio Fill and crushed coral. Right: systemoverview. Photo by J . Szyper.



the water pathway is the prevention of si-phoning in case of pump failure: there is alack of continuous pipe connection when 1)water enters the aquaria, and 2) used waterenters the return pipe.

This shelf system was filled with freshwater and stocked with juvenile (2.5 - 5 cmlength) pink convict cichlids, which wereavailable on the facility from earlier work.Each aquarium was stocked initially with 3small fish; when the filter took total ammo-nia concentrations to nearly undetectablelevels after 10 days, fish were added everyfew days in an attempt to approach theprocessing capacity of the system. Fish ad-ditions after about 30 days caused brief am-monia spikes; earlier additions did not. Anaddition at about 40 days’ operation causeda large ammonia spike, a reduction after afew days, followed by rising concentrations.At this point, fish stocking densities wereabout 2 kg/m3, the aquaria appeared heavilystocked, the water had notable color andsuspended particulate matter (though aquar-ium bottoms were siphoned manuallydaily), and the first two fish mortalitieswere found over two days. The trial was

terminated at this point. This relativelysmall and inexpensive filtration system sup-ported fish biomass densities reasonable forcommercial production of ornamental fisheswhen aquarium systems are appropriate. Inaddition, these densities are higher than acommercial shop would display, and so thesystem could be used in that setting.

An identical system was installed on anearby shelf, and filled with artificial sea-water (Instant Ocean). After conditioning,

the filter held total ammonia at genuinelyundetectable levels with low to modest fishstocks, in contrast with the low but detect-able levels at low fish densities in the fresh-water system. This difference was consis-tent over a two year period. The seawatersystem kept clownfish pairs for nearly two

years, and a variety of other marine fishes(e.g., reef grouper, white ulua (jack cre-valle), Pacific threadfin, greater amberjack)for periods of days to months. In order totest a less expensive artificial seawater for-mula, the freshwater shelf was drained andrefilled with the new seawater, called “FiveComp” for its five components (Table 2).Reef grouper and white ulua were stockedat low densities and kept for 16 days. Thebiofilter adapted to Five Comp, taking TANlevels below 1 ppm for the last 5 days.

Finally for Hawaii Island systems, a flu-idized bed sand biofilter (System F, Figure4) was built in an upright 1.2 m (4 ft) lengthof 30 cm diameter (12 in) pvc pipe, cappedon one end, and having 44 kg (100 lb) of No. 20 graded sand as substrate for bacterialgrowth. The sand was kept in motion byinjection of water to the bottom of the sandbed by a 186 W (0.25 hp) AC water pumpthrough a 0.4 cm (1.5 in) pipe ending in ahomemade spray head. The pump was in-stalled in and near the top of a trash can thatwas set up similarly to System D above, butwithout plastic ribbon. This vessel served

as pump reservoir, clarifier (discussed be-low), and water conditioner with its layer of crushed coral. Pumped water was directedto the bottom of the sand biofilter vessel,filled it, and overflowed into the fish tank (a2.4 m diameter (8 ft) cylindrical plastic tankcontaining about 4.6 m3 of water. Watercompleted its cycle by returning from thefish tank to the trash can by passive over-flow through an exit port near the top of thetank wall. This system was stocked (with

hybrid tilapia) and monitored similarly tothe aquarium shelf system in the trial de-scribed above. The time course of TANconcentrations showed a qualitativelysimilar pattern of performance for the sandbiofilter. After conditioning, the filter kept TAN at low levels until total fish biomass



__________________________________________________________________________

Table 2. Ingredients for “Five Comp” artificial salt water. Weights of salts used to make 100 liters and50 gallons of salt water are given.

Ingredient Formula Weight for 100 liters Weight for 50 galg oz

Sodium chloride NaCl 2500 167(table salt)

Magnesium sulfate MgSO4 600 40(Epsom salt)

Potassium chloride KCl 60 4.0

Calcium chloride CaCl2 120 8.0

Sodium bicarbonate NaHCO3 20 1.3

(baking soda)

Total 3300 230

__________________________________________________________________________

Figure 4. Fluidized bed sand biofilter system including trash canclarifier / pump sump. Photo by J . Szyper.

exceeded 50 kg (>10 kg/m3). A major dif-ference from the shelf system is that thesand biofilter adapted, presumably by anincrease in bacterial population, to the lastbiomass addition and reduced total ammo-nia to low levels. At this point, the sandbiofilter was taken off line, and a condi-

tioned trash can biofilter (System D) wasinstalled on the fish tank. This filter tookthe remaining total ammonia concentrationof about 1 ppm to nearly undetectable over1.5 days (including two daily feedings), atwhich time the trial was terminated.

System Performance: Solids, Oxygen, & pH

Recirculating biofiltration systems mustdeal with solid wastes produced in any cul-

ture system of substantial intensity. Noneof the demonstration systems described herewas designed to remove solids efficiently;the primary consideration was to demon-strate low cost ammonia processing. Theperformance of the systems with ammoniais discussed in further detail below. Neither



were the systems designed for optimalmaintenance of dissolved oxygen concen-trations. In general, modest levels of airbubble aeration and the aerating effect of airlifts was relied upon to support oxygen de-mand in the systems. Similarly, mainte-nance of pH is somewhat addressed by aera-tion, in that high concentrations of carbondioxide are degassed by aeration at lowerpH values, providing a partially effectivenegative feedback. That is, more carbondioxide is removed when systems are pro-ducing higher amounts, and this works toincrease pH. This factor was handled dif-ferently between the indoor and outdoorfilter systems, the latter having some carbondioxide taken up by the blooms. All of these factors can be improved with avail-able low cost technology, and we have con-tinued to expand and improve some of thesesystems.

The Outdoor Green Water Biofilters were manually cleaned of solids every twoweeks during the latter, highest-stocking-density stage (day 76 onward) of their for-mal trials (Asano et al., 2003). This wassufficient to keep the systems working well.

The culture tanks contained some settledsolids, mainly clumped microalgae from theactive blooms, which were not removed. The aeration was not intended to, and didnot, keep all solids well mixed in the water.Settling of solids in a culture vessel is be-nign up to a point because they are readilyremoved by siphoning. In general, manualsolids removal is an effective strategy insmall scale systems. Automating the proc-ess is an important effort to save personnel

costs for commercial settings. The greenwater blooms acted to increase dissolvedoxygen and pH levels during the day, and tolower them at night, resulting in greater ex-tremes than would be seen in clear watersystems. Nonetheless, the systems main-tained with few exceptions, dissolved oxy-

gen above 4 ppm and pH above 6.0. The Indoor Biofilters were different in

each case. The trash can filter (System D),in its original deployment on the tilapiatank, became a green water system like theoutdoor systems. Solids were occasionallyemptied through the bottom valve, and otherparts of the system were cleaned only infre-quently, mainly by manual siphoning of sol-ids from the bottom of the culture tank. Airstone aeration and the effect of air lift main-tained the system for several years withgreat stability. Solids were manually si-phoned from the aquarium systems (SystemE) daily during the stocking density trial. This was adequate to support the trial, butleft enough solids suspended in the water(by fish activity and the single bubblestream from a pipette) to have the aquari-ums look dirty (with turbidity and largerparticles) during later stages. Aerationmaintained dissolved oxygen levels above 5ppm in the reservoir at all times, and above4 ppm in the aquaria until the last 2 weeks. The crushed coral layer in this system pro-vided notable advantages. The pH neverfell below 6.9, and only rarely below 7.0.

Total alkalinity increased during the trialfrom about 40 to 80 ppm. The sand biofil-ter system (System F) was taken to higherfish stocking densities than any other sys-tem, greater than 10 kg/m3. Dissolved oxy-gen levels declined steadily during the trial,but did not fall below 4 ppm. The crushedcoral layer effectively maintained total alka-linity, increasing it from an initial 30 ppm to50 ppm. The aeration effectively mixedsuspended solids throughout the water,

which means that solids were being sent tothe clarifier quantitatively. Very little set-tled on the culture tank bottom; the fish be-ing somewhat underfed may have contrib-uted to this condition. Solids were removednearly daily from the bottom port of theclarifier trash can. However, the clarifier



design permitted too much of suspendedsolids to reach the water pump, which hadto be manually cleaned during much of thetrial.

System Performance: Ammonia Processing

The amount of ammonia processing to beexpected from various filter media materialsunder different conditions is the subject of voluminous literature, which is not re-viewed here. Rather, the systems are as-sessed in terms of the summary of expectedprocessing capacities graciously providedby Kevin Hopkins of the University of Ha-waii at Hilo (personal communication),which was compiled from original literatureand from estimates tabulated by a commer-cial supplier. Assessments provided hereapply generally to warm water situations,but are not adjusted for different tempera-tures, which were well within the range 20 -30 oC on Hawaii Island and similar onOahu, with possibly greater extremes out-doors there.

Because ammonia processing bacteriaoccupy thin layers on the surface of filter

media, it is reasonable to consider the rateof total ammonia nitrogen (TAN) processedper unit of surface area, when the area canbe determined. The summary of capacitiesshows some variation, but the most com-mon estimate, 0.807 g TAN / m2 / day, issufficient for this discussion. Commercialmaterials may be sold in volume quantities(cubic feet or meters), and catalogued orpackaged with an indication of the surfacearea provided by each unit of volume, that

is, the effective surface area as m2/m3.Because production of TAN in a culture

system depends mainly on the rate of inputof nitrogen in the protein fraction of thefeed, the loading of a biofiltration system ismost directly expressed as g TAN/day forthe system. This input rate might derive

from a variety of combinations of biomass,feeding rate, and protein content of feed.Other important estimates of culture systemcapacity (e.g., fish stocking density in termsof numbers or biomass) are best interpretedas consequences of the loading rate that canbe processed by the filter. For present pur-poses, we will use a conservative estimatethat about one third of the nitrogen contentof the feed eaten by fish will appear as TAN, a soluble excretion product, the re-mainder being eliminated as solid waste orincorporated into biomass.

The Outdoor Green Water Biofilters were packed with 0.028 m3 (1 ft3) of plasticribbon (Bio Fill) as noted above. Thisamount of the material (1 package at about$37 before shipping) has an effective sur-face rating of 820 m2/m3, and thus an ex-pected ammonia processing capacity of 820x 0.807 x 0.028 =18.5 g TAN/day (Table3), which Asano et al. (2003) noted wasmore than sufficient for the loading ratesused in the trials. The maximum feedingrate was 125 g/day of feed with 45% proteincontent. Nitrogen content is usually esti-mated as 1/6.5 =0.154 of the weight of pro-

tein. TAN loading rate can thus be esti-mated as 125 x 0.45 x 0.154 x 0.333 =2.9 g TAN/day. This suggests that the biofilterscould have handled six times the actualloading rate, which came from a final fishbiomass density of 4.6 kg/ m3. If biomassdensity were increased substantially underthese conditions, it is likely, as we haveseen elsewhere, that factors such as solids,dissolved oxygen, and pH would becomeproblematic before TAN loading. Table 3

compares the demonstration systems dis-cussed here in terms of estimated TANprocessing capacity and loading rates duringtrials. These calculations neglect the am-monia processing that takes place on theunderwater interior surfaces of the culturetanks and biofilter containers. In the case of



System D, the tank walls add about 7.5 m2 and the trash can about 1.5 m2 of substrate

for bacterial habitation, a total addition of about 27% to the surface area of the filtra-tion media (Table 3). This capacity may beconsidered from the first in system design,or left as an engineering buffer. Note thatthe walls' contribution was already operat-ing during the large water consumption ex-ample discussed above.

The only quantitative test of the trashcan filter was its replacement of the sandbiofilter at the end of the latter’s formal

trial. Because the trash can was the onlysource of TAN processing support for 1.5days including 2 feedings, and because TAN levels dropped to near zero during thisperiod, it must have processed the TAN in-put. The capacity estimate for the sandbiofilter is based on the guideline provided

by Carlos Martinez of the University of Florida, that 100 lbs of sand can support

100 lbs of fish fed typical feeds at 5% bodyweight per day. The 52 kg (114 lb) of fishin our trial were taking only about 2% perday near the end. We have found no esti-mate for the effective surface area of thesand. The design of the sand biofilter sys-tem specified silica sand; only size-gradedcommon sand was readily available on Ha-waii Island. Some of the carbonate compo-nents of the sand dissolved during the trial,about 14 of 120 lb. The pumped water was

effective in keeping the sand in motion; op-timal system performance requires a par-ticular volume increase upon fluidization,ideally to 150-200% of still volume, to per-mit optimal colonization of sand grains bybacteria. We generally had less volumethan this, but still attained sufficient TAN

__________________________________________________________________________

Table 3. Performance summary for demonstration biofiltration systems. Capacity estimates use astandard rate of 0.807 g TAN / m2 / day; observed rates presume 1/3 of nitrogen in feed appears as TAN.

____________________________________________________________________________________

System Total Water Volume Filtration Medium TAN Processing Rate

m3 name volume area g /daym3 m2 capacity observed

____________________________________________________________________________________

A. Green Water 2.1 Bio Fill 0.03 23.0 18.5 2.9 Trickling Filter

B. Green Water 2.1 Bio Fill 0.03 23.0 18.5 2.9Submerged Filter

D. Trash Can 4.7 Bio Fill 0.04 32.8 26.5 15+*

E. Shelf System 0.75 Bio Fill 0.01 8.2 6.6 0.9

F. Fluidized Bed 4.8 #20 sand 0.03 n/a 50 15+Sand Biofilter

* When trash can replaced sand biofilter at end of trial.

__________________________________________________________________________



processing to support the trial.

Adoption of Systems by Farmers

These designs and strategies are reasonablywell known, particularly the bucket andtrash can ideas. A locally-built turnkeybackyard culture system with biofiltrationwas available on Maui during the 1970'sand 1980's. Commercial uses of informallow cost systems in Hawaii began well be-fore our demonstrations. Since we beganthese demonstrations and described them inprint and in public presentations, more Ha-waii aquaculture businesses have adoptedrecirculating biofiltration technology, somewith commercially-purchased systems,some with homemade systems includingthese approaches, and some with combina-tions of the two. We appreciate the collabo-ration we have had with many of these busi-nesses, and the opportunities to learn fromand assist them.

Acknowledgements

We are particularly grateful to Carlos Marti-

nez and Craig Watson of the Tropical Aqua-culture Laboratory of the University of Florida Institute for Food and AgriculturalSciences for sharing Watson’s design of thesand biofilter and for discussion. Modifica-tions of the design and limitations of thesystem described here are entirely the re-sponsibility of the senior author. We appre-ciate Kevin Hopkins of the University of Hawaii at Hilo (UHH) sharing his table of processing capacities prepared for his engi-

neering class, and for discussion of the Ha-waii Island systems. The trials could nothave been completed without the skillfulattention of the UHH student assistants ToluRasmussen, Mahealani Kaneshiro, CristinGallagher, and Jeanette Kondo. This workwas supported by the University of Hawaii

Sea Grant College Program, the Aquacul-ture Development Program of the HawaiiDept. of Agriculture (contract numbers48499, 49855, and 51063), and the HawaiiCounty Dept. of Research and Development(contract numbers 03061 and 04081).

Single copies of this work may be obtainedfrom the corresponding author. For multi-ple copies contact Sea Grant Communica-tions, 2525 Correa Road, Honolulu, HI96822, telephone 808 956-7410, fax 808956-3014, email [email protected].

References

Asano, L., H. Ako, E. Shimizu, and C.S. Tamaru, 2003. Limited water exchangeproduction systems for freshwater ornamen-tal fish. Aquaculture Research34:937-941.

Leone, D., 2003. Federal report warns of isle water shortage. Honolulu Star-Bulletin,Friday, July 11, 2003. www.starbullletin.com/2003/07/11/news/story3.html.

New Internationalist, 2003. Water - The

Facts. New Internationalist, Issue 354,March 2003. www.newint.org/issue354/facts.htm.

Szyper, J .P., 1989. Backyard Aquaculturein Hawaii: a Practical Manual. Universityof Hawaii, Windward Community College,87p.

This publication is funded, in part, by a grant/cooperative agree-ment from the National Oceanic and Atmospheric Administration,Project #A/AS-1, which is sponsored by the University of HawaiiSea Grant College Program, SOEST, under Institutional GrantNo. NA16RG2254 from NOAA Office of Sea Grant, Departmentof Commerce. The views expressed herein are those of the author(s) and do not necessarily reflect the views of NOAA or any of itssubagencies. UNIHI-SEAGRANT-AB-03-01.

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