recirculating aquaculture system (ras) technologies

Recirculating Aquaculture System (RAS)TechnologiesPart 2

by Nigel Timmons, Michael B. Timmons, and James M. Ebeling

If RAS technology is going to besuccessful, tben the aquaeulturalistmust expect to compete against the

other commodity meats and large scalefish farming such as currently beingpracticed by the net-pen salmon industryor the US catfish industry. (See Figure Ifor historical production levels).

The dismal truth is that there has been20 years of generally negative resultsand viability associated with RAS.Generalizing, most of the problemshave not been so much related to thetechnology as the mismanagement ofsystems and attempts at growing speciesthat were not suited towards RAS. Theauthors also disagree with the idea thatRAS can only be used to produce highvalue products. Like any business,success is built upon a whole series ofcritical factors, any one of which that ismissing will lead to a business failure.

General misconceptions that arecommonly associated with RAStechnology include:

• Overly complicated• Prone to catastrophic failure• Expensive• Suited only for high-value species• Only highly educated people can be

trained in their useThese labels may have been

warranted a few years ago, but today,RAS technology is none of the above.Of course, you can make any technologyoverly complicated, expensive, andprone to failure - but we are well beyondthat {or at least we should be) in theRAS industry today. The unit processesassociated with a RAS are depicted inFigure 2 (p. 33; taken from Timmonset al., 2002). All unit processes shownare generally not used in any particularRAS application, but al! these processesshould be considered during the designand planning stages, particularly in

Figure I. World yearly production ofsalmonids, tilapia and catfish (FAO. 2002).

relation to the level of water qualitycontrol and quality desired.REQUIREMENTS FORINFRASTRUCTURE ANDCAPITALIZATION

An aquaculture development projectwill require significant infrastructure interms of water, waste disposal eapacity,enclosed building space, electricalenergy and load demand supply, andtransportation logisties. While each

site considered will require a thoroughengineering analysis, approximateminimal site requirements are given inTable I.WATER SOURCE

The major advantage of RAS is thatthe water requirements for productionare reduced dramatically. What newwater is introduced into a RAS must bebiologically secure. The major vectorfor introducing disease organisms into

Table 1. Approximate infrastructure and utility requirements

Production per year (kg)

Footprint of buildings, square meter

Water Required & Discharge per day, m3

Heating Requirements, MJ/day(peak seasonal demand)

Electrical Requirements, kWh/day

Liquid Oxygen, cubic meter/day

Cool Water(Trout)

454,000

5,600

3,000

20,000

6,000

1,000

Warm Water(TJIapia)

454,000

3,700

300

40,000

4,000

1,000

32 Aquaculture Magazine September/October 2006

Disinfection• • • • • * •

Fine & DissolvedSolids Removal

Chapter 6

Aeration/Oxygenation

Chapter 8

COj RemovalChapter 8

Water QualityChapter 3Loading

Chapter 4Culture Units

Chapters

Biofiltration/NitrificationChapter 7

SolidsCapture

Chapter 6

Monitoring &System Control

Chapter 9

BiosecurityChapter 13

NutritionChapter 16

ManagementChapter 11 Economics

Chapter 15

AquaponicsChapter 18

Figure 2. Unit processes associated with Recirculating AquacultureSystem (RAS) Technology (from Tttnmons et al. 2002: Reference

given to the book chapters that cover these topics.)

Table 2: Most important Unit Precesses

Unit Process

Biofiltration

SolidsSeparation

Carbon Dioxide Stripping

Oxygenation

pH Balance

Water Quality Parameter Addressed

Ammonia & Nitrite Nitrogen Removal

Excess feed and fish waste removal

Carbon dioxide concentration in water

Dissolved oxygen concentration

pH, C02 concentration, Alkalinity

a production site is through the water orthrough the animals being brought intothe farm. If both of these vectors areclean, then the occurrence for losses dueto disease are practically non existent.

Great effort must go into making afarm biologically secure. The sourcewater ideally should be deep wellsproviding drinking water quality water.There is no substitute for a biologically

secure source of water. Do not build onany site until water sourcing issues areestablished. You should assume that asa minimum site requirement, you willneed one system volume of water perday. even though typical usage rateswill be 20% of system volume per dayor less. Treating non-biosecure watersources will require some combinationof mechanical fi l tering, ozone,ultraviolet, and chemical processes.(See Timmons et al., 2002: Chapter 13Fish Health Management, Chapter 12Ozonation & UV-Irradiation, Chapter 6Solids Capture).

The quality of the water necessarywill depend upon the species beinggrown and the stage of production beingimplemented. Water quality for an eggrearing operation will be more stringentthan an advanced growout system fortilapia. In terms of water quality, criteriamust be specific to species and stageof production.COSTS OF PRODUCTIONAND CAPiTALiZATION.

A list of the most important unitprocesses of indoor recirculatingaquaculture and the water qualityparameters they address are presented inTable 2.

The equipment used to performthese individual unit processes allcontribute to overall capitalizationcosts. Economically competitive foodfish production will depend uponcollectively reducing capitalizationcosts to be at least nearly as efficient asthe salmon industry, e.g. $0,40/kg peryear of system capacity production (seecalculation later in this section).

Inventive new ideas or managementmethods must be developed as tohow to combine unit operations or toreduce costs associated with presenttechnologies. Probably more than anyother factor that can contribute towardsthis goal is to increase the scale of theproduction operations. Just as dairy, hogsand poultry have increased productionper farm and therein improved laborefficiency and other cost of goodscomponents, the aquaculture RAS basedindustry must also do so.

A photo of a current intensive RASis shown in Figure 3 (p. 34) and a unitprocess figure for this system is given

Aquaculture Magazine September/October 2006 33

Figure 3. A RAS u^ing a CycloBio Filter. Low Head Oxygenation(LHO) Unit and Stripping CoUunns. Water flow exiting the top

of the fluidized-sand biofilter flows by gravity through a cascadestripping column, an LHO unit, and a UV irradiation unit beforebeing piped by gravity to the culttire tank. Photo courtesy of theConservation Fund Freshwater Institute (Shepherds(own, WV).

in Figure 4.A simplified unit process diagram

is shown in Figure 5 (p. 35; fromFingerlakes Aquaculture, Groton, NY)that is used for rearing of tilapia. Figtire 6is a photo of such a system (p. 35). Notethe differences in complexity basedupon the use of the CFFI system beingused to rear arctic char (a sensitivewater quality species) versus theFingerlakes system that is used to raisetilapia (a less sensitive animal to waterquality conditions).

A cost analysis for a generic tilapiaRAS based farm can be seen in Table 3(p. 36; software available in Timmonset al., 2002) and Table 4 (p. 36). Datain Table 3 is considered representativefor a current state-of-the-art tilapia farmproducing in excess of 1,000 ton/year (2million pounds per year). Using the inputdata shown in Table 3, the predictedcosts of production for such a farm isshown in Table 4 (model developed byCornell University). These numbers

UV:optlonal)

Air<GiL =

•S t. 03Teed Gas

StripperVent

FluldlzeoSand

BlofUter

VentDff-Gas

Culture Tankor Row of

Culture Tanks

90-95H Of -total -tank f lof

Make-upWater

rioa-tValve

DrunFilter

aettled flow is reusedor aent to discharge

Sunp

footvolvss

Punp<s)

Dv*rfto«

Solnb r 0*4 or lolal nn«r«l no»>

.

pHControl

Liquid To Dischargel-8y. of to ta l reclrc flow)

Figure 4. A Process Flow Drawing of the 4.800 Umin RAS at the Conservation Fund Freshwater Institute (CFFI).


LHO

CO2 Stripping

Oxygen Addition

CycloBio

90% Flow from Tanks

Solids Settling"•"Chamber

Figure 5. Unit process flow diagram indicating CycloBio locationwithin a Fingcrlakes Aquacuiture Production 'Pod'used lo rear tilapia

in a RAS (courtesy of Fingerlakes Aquacuiture. Groton, NY).

Figure 6. Overview of a CycloBio System al Fingerlake.s Aquacuiture(10 meter diameter fbh tank is show in front of CycloBio. notemixing fans that are blowing air through waterfall from top of

distribution channel leaving CycloBio and delivering water to LHOunits). Courtesy of Fingerlakes Aquacuiture (Groton, NY).

Co.st

Ib= 0.168

kWh•5mTDH-\.5fg

w TDH-kg,,,.

Figure 7. Formula to determine cost of pumping.

$0.10 $0.126kg,,,

indicate that a large commercial tilapiafarm could compete quite effectivelywith offshore protluction in the filletfresh market if processing costs canbe achieved competitively (a majorchallenge still). A series of 1,000ton (multi-million pound) productionfarms would be required lo support anautomated processing facility.

The capitalization costs for theabove example are $1.83 per kg peryear of production capacity. Laborcosts are relatively high comparedto salmon farming. In comparison,Atlantic salmon capitalization costs for10 to 20 net pens per site are 550,000per pen (good for stocking 50,000smolts). the capitalization cost expressedbased upon system produetion capacityper year is: $/(kg per year capacity)- S500,000/(1,300.000 kg/year) =$0.40/kg/year.

Note that the tilapia capitalization($I.83/kg/year) is over 4 times largerthan the salmon capitalization. Table 4summarizes the impact of capitalizationcosts (investment) upon costs ofproduction. The salmon costs are by farthe lowest in the aquacuiture industryand this can be attributed to its largescale fanning approach and a concertedapplication of research to provide theneeded equipment and managementtechniques for this industry.COST OF PUMPING

A primary disadvantage of RAStechnology is that water must be movedfrom the culture tank to the differentunit processes thai restore used waterto aeceptabic levels of quality for fishgrowth. Table 6 (p. 37) summarizes thecosts associated with pumping basedupon the amount of lift required (howhigh the water must be elevated abovethe culture tank free water surface) andthe flow rate required to support fishgrowth. As a nile-of-thumb. one can use8 Lpin of flow per kg of feed fed per day(5 gpm per pound of feed fed per day)(for supplying o.xygen and requirednitrification). Table 6 illustrates the costof pumping using various flow rates andwater lifting heights.

For example, looking at the formulain Figure 7, we can see what the eost ofpumping would be if the TDH neededto run the RAS system were 5 m. e.g..

Aquacuiture Magazine September/Oetober 2U06 35

Table 3

Building Costs, Maintenance, and Labor

Days of Operation perYear

365

Equipment DepreciationPeriod

7 years

Building DepreciationPeriod

12 years

Total Building FloorArea

60,000 sq. ft.

Total Labor Cost perBuilding

$200,000

Number of Podsin Building

100,000

Initial Cost of Building

$200,000

Gallons in Tanks.Sump, Biofilte

100,000 per pod

Building Backup &Monitoring Costs

$50,000

Complete Pod Systemw/ access

S125,000perpod

Fisb Needs - Oxygen, Feed, and Fingerlings

Oncost

$0.04 per Ib.

Mortality over GrowtliPeriod

50%

0^ Supplied per FeedFed

0.75 lbs.

Fingerling Cost

$0.05 each

Feed Cost

$0.14 per Ib.

Selling Size

2 lbs.

Feed to Gain Ratio

1.20

Mm. Feed per Pod

400 lbs.

Max. Feed per Pod

822 lbs.

Heating and Electricity

Water Temp

82.0° F

Cost of Energyper 100,000 BTU

$0.75

Makeup Water Temp

50.0" F

Kilowatts

12.0 per pod system

Daily Water ExchangeRate

10.0%

Electrical Cost

$0,04 per kWh

High ExchangeEfficiency

0.0%

Overall R value forBIdg. (hr'ft^*F/Btu}

20.0

Air Volume Changes(ftVhr)

2.0

Note: Oxygen efficiency of use is reflected in the supplied oxygen level per unit of feed fed.Note: Assumes heating of air and water is based on cost of energy shov/n.

Farm Output: 2,000,000 lbs. per year

Table 4: Predicted Production Costs for Tilapia

Feed/Pod (kg/day) and 8 pods

Production (kg/week)(whole fish)

Electric Cost

Feed Cost

Water Heating

Air Heating

Oxygen

Labor

Fingerling

Depreciation & Repairs

Total Cost (S/kg)

374

17,045

$0.04

$0.37

$0.07

$0.07

$0.09

$0.22

S0.06

S0.31

$1.23

% Total

3%

30%

6%

6%

7%

18%

5%

25%

100%

Predicted production costs for a 1.000 ton (l-MiUion

Ih) per year tilapia farm (costs in S/kg)

for a fluidized sand bed, and the feed

to gain ratio for the system is 1.5 and

assuming 30 Lpm of flow per kg of feed

fed per day.

Thus, it can be seen that production

costs for pumping are proportional to:

• Pumping pressure (total dynamic

head the pump works against, TDH)

• Feed to gain ratio (fg)

• Electricity cost

Design and planning should address

lowering all three of these contributing

factors to pump operating costs during

the first stages of RAS farm planning.

Design considerations should include

how to incorporate low head pumps and

water treatment methods that minimize

requirements for lifting water.

BIOFiLTRATiON

Effective and cost efficientbiofiltration is one of the keys elementsto cost effective indoor aquaculture


Taliie 5: Depreciation Costs

Capital Cost $ perkg/yr

S0.40

$0.50

$1.00

$2,00

$3.00

Depreciation Period, Years

4

$0.10

$0.13

$0.25

$0.50

$0.75

7

$0.06

$0.07

$0,14

$0.29

$0.43

10

$0.04

$0.05

$0.10

$0.20

$0.30

Depreciation Cost ($/kg) Fish Produced as Affected hy Depreciation Period

Table 6: Pumping Costs

Lpm/(kgfeed/day)

5

10

20

30

40

TDHm

1

1

1

1

1

BHPkW

0.001

0.002

0.005

0.007

0.009

kWh,kg*

0.028

0.056

0.112

0.168

0.224

Cost/kg(whole fish)

0.003

0.006

0.011

0.017

0.022

Cost of pumping per unit offish produced (kg) assuming electricity. SO. 10per kWh. efficiency of pump (a) 70% and feed to gain ratio of } .00. Note:WHP = Qx TDHxSG/0.012 where WHP = kWandQin m3/s and TDHin m. Assumes that each flow rate is supporting I kg of feed fed per day

Table 7. Blofllter Capital Costs

Biofilter Type

Rotating Biological Contactor

Trickling Biofilter

Bead Filter {not microbead Aquafilter type - seenote below)

Conventional Fluidized-Sand Biofilter

CycloBio '̂*̂ Fluidized-Sand Biofilter

Farm Cost

$668,000

$620,000

$296,000

$124,000

$76,000

Cost ($ per kg/yr)

$1.50

$1.36

$0.66

$0.26

$0.18

Capital Costs Estimates Associated With Biofilter Choices fora Tilapia Farm Producing 454 M ton (I million Ih) Annually.

Cost is listed as S per kg per year of production.

production. Biofiltration (short for toxic byproduct of food digestion andbiological filtration) is the biological synthesis, into nitrate, a nearly harmlessprocess of nitrification in which salt. For aquaculture applications,bacteria convert ammonia nitrogen, the biofiltration typically occurs under

aerobic conditions (with oxygen) in avessel or tank that contains substrateonto which ihe nitrifying bacteria canattach and grow. Examples of biofiltersthat are common to the wastewatcrtreatment and aquaculture industriesinclude trickling filters, rotatingbiological contactors, sand biofillers,bead biofilters, and neutral-buoyantpacking material biofilters. In all cases,ammonia nitrogen present in the waterpassing through the biofilters undergoesbiological transformation that ultimatelyconverts ammonia to nitrate nitrogen.

The choice of biofilter will impactthe dynamic head that tbe pump systemmust work again.st. Fluidized sandbeds will work against 5 to 10 metersof head, while trickle type filters canbe operated at much shallower depths,e.g.. 2 m. Floating bead biofilters aresimilar in head requirements to tricklefilters and provide large surface areaslor nitrification comparable lo fluidizedsand beds. Al! biofilters have advantagesand disadvantages, and for small scalesystems, e.g. feeding around 50 kg offeed per day, the choice of biofilter isprobably irrelevant. Based upon theauthors' experiences, we summarizecosts for various biofilter choices (seeTable 7) based upon their capitalizationcost to support a 454 ton per year tiiapiafarm (I M lb/year).

TheCycioBio""*^ referred to in Tahle 7is a patented up-flow sand biofiltermanufactured by Marine Biotech ofBeverly. MA. Tbe CycloBio technologyhas been applied to Chilean salmonsmolt production (more informationavailable from the Fundacion Chile. Dr.Gustavo Parada, Santiago). Microbeadfilters (see Timmons et al., 2006) are acombination of trickling filter design andbead filter principles and cost similar toand operate similar to a conventionaltrickling filter. Currently, moving bedbiofilters are also a favored design(more details can be seen at WaterManagement Technologies website; seehttp://w-:m-t.com). Moving bed filtersuse a vessel filled to about half depthwith plastic media (Kaldness media asan example) and then fish lank water ismoved through the vessel much as if itwere holding fish. Vigorous agitation andaeration is required. Primary advantages

.Aquaculture Magazine September/October 2006 37

of the moving bed filter is low headrequirements and minimal movingparts or complexity. Costs are similar toconventional trickling filters or micro-bead filters.

Tbe most important factors in thedesign of a biofilter are (I) the massof TAN tbat it removes per day, i.e..the product of the flow rate across thebiofiiterand the change in concentrationofammonia across the biofilter; and, (2)the TAN removal efficiency (frcm) ofthe biofilter. Tbe mass of TAN removedper day can often be increased as thehydraulic loading rate Is increasedacross a biofilter. However, increasedhydraulic loading rate can decrease theTAN removal efficiency as increasedhydraulic loading rates shorten the waterretention time within the biofilter andincreases the mass load on the filter. Asa rough estimate, one can assume thatbiological filters will remove from 0.5to 1.0 kg TAN/day per m3 of media inthe system. Coolwater systems will becloser to the low end of this design rangeand warm water systems will be nearerthe upper end of the design values. These

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design values are minimally impacted bythe choice of media. However, properlymanaging a biofitler and in particularcontrolling the solids loading on abiofilter can have enormous impact onperfomiance. More details are providedin Timmons et al., 2002.

Trout, char and salmon requirerelatively clean water and low levels ofun-ionized ammonia, so high percentremoval efficiencies per hydraulic passare required when designing systemsto raise tbese species. For this reason,fluidized-sand biofilters containing finesands are commonly used in cold-waterrecirculating systems because tbesebiofilters will often achieve 70-90%TAN removal efficiencies. Fluidized-sand biofilters using fme sands arealso capable of providing completenitrification (due to tbeir excess supplyof surface area), which helps to maintainlow nitrite-nitrogen concentrationswithin the recirculating system(generally < 0.1-0.2 mg/L as nitrogen).As can be seen from this discussion,the choice of species will affect thechoice of equipment and biofiltration

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technology employed. The eosts ofproduction as affected by capitalizationand water quality maintenance must bekept in the forefront if RAS technologyis to be applied on an economicallysuccessful basis. It is a relativelyeasy design task to develop a systemthat will create high water qualityconditions, but designing a system thatcan produce fish economically is anentirely different design task and is infact quite challenging.GAS STRiPPING ANDCONDITIONiNG COSTS ANDPH CONTROL

RAS systems can require pro-activedesign components to remove dissolvedcarbon dioxide and to supply sufficientoxygen to maintain fish productivity. Atypical gas transfer device that combinesboth functions is shown in Figure 8(p. 39).

Controlling CO; stripping ratescan be used to control water pH andpH control can be used to mitigateproblems associated with highammonia. These unit process devicesare continually being improved forpractical implementation.SOLIDS REMOVAL.

The effective control of solids inRAS is probably the most criticalparameter for long term economicsuccess. Poor solids removal destroyswater quality and hence fish perfonnanceand compromises biofilter perfomiance.Currently the most generally used methodfor solids removal is mechanical screensusing 60 to 120 micron mesh sizes.Unfortunately, mechanical screeningfor solids removal is typically now themost expensive single component of anentire RAS system. Settling basins withfrequent cleaning (e.g. twice per day)may be appropriate where labor costsarc relatively low in less developedcountries. Design details for solidsremoval are provided by Timmons et al.(2002. Chapter 6. p 164-204).OTHER COSTS.

Feeding systems, alarm and controlsystems and all other capital costcomponents are often the same equipmentbeing used on outdoor or flow-throughnon-RAS systems. Consideration shouldbe given tbat a different environment canexist within RAS farms tbat are generally


t CASCADECOtUMNPACKRO

WITH

CASCADECOLUMN

ACKED w m I

j

NOWAC

Figure 8, Stacked C02 stripper/LHO unit supported over a cone

bottom sump tank to simplifydediment removal, (drawing by

PRAqt/a Technologies Ltd.. Nanaimo.British Columbia, Canada).

indoors, e.g. high humidity. Buildingconstruction, insulation materials,heating and ventilation systems -mustall be considered to create an effectivefarm design. (Timmons. et al., 2002,Chapter 14 Building EnvironmentalControl, pp 467-482).REFERENCES

Delgado, C . Rosegrant, M, Meijer,S, Wada, N, & Ahmed, M. (2002). Fishas Food: Projections to 2020. Paperpresented in the IIFET2002 The BiennialMeeting of International Institute forFisheries Economics and Trade, August19-23. Wellington, NZ.

Delmarva Poultry Industry. Inc.(2002) 16686 County Seat Highway.Georgetown, DE 19947

Forster. J. (1999) Aquaculturechickens, salmon- a case study. WorldAquaculture 30(3): 33-38, 40. 69,70.

Hicks, B. and Holder, J.L. (2001) NetPen Farming. Proceedings 2001 AESIssues Forum, Shepherdstown, WV.November 1M4, 2001, NRAES-I57Publication, Cornell University, Ithaca,NY 14850.

Macinko, S. and D.W. Bromley(2002) Who owns America's Fisheries,Report provided and sponsored by thePew Charitable Trusts.

Timmons. M.B., Ebeling. .I.M.,Wheaton, F., Summerfelt, S.T.. Vinci,B.J. (2002) Recirculating AquacultureSystems. 2nd Ed. p 760. Cayuga AquaVentures, Ithaca, NY.

Timmons, M.B. (2005). Competitivepotential for USA urban aquaculture.In: Urban AquacuUure. Eds. B. Costa-Pierce, A. Desbonnet, P. Edwards, andD. Baker, pp 137-158. CABI Publishing,Cambridge. MA.

Timmons, M.B., Holder, J.L., andEbeling. J.M.. 2006. Application ofmicrobead biological filters. AquaculturalEngineering 34:332-343.

Weirich. C.R., Browdy, C.L.,Bratvold, D., McAbee, B.J., and Stokes,A.D.. 2(X)2. Preliminary characterizationof a prototype minimal exchange super-intensive shrimp production system.In: Proceedings of the 4th InternationalConference of Recirculating Aquaculture,Roanoke, VA, July, pp 255-270.

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recirculating aquaculture system (ras) technologies

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