Malone, R,F,, and A. A. DeLosReyes,Jr. 1997. Categoriesof recirculating aquaculhue systems.In: AquaculturalEngineering Society Proceedings, ISTA IV, Orlando,FL, November 9-12, 1997, pp, 197-208, LSU-R-97-025 C2 ~ % R % % a R m a A 'a w 0 % %w % % %& R R R R % % R R R % R % %Q %Q R % R R 0 % %% R % %% a a m m e 0 I Categoriesof RecirculatingAquaculture Systems

Ronald F, Malone I I Chevron U5,A. Professor

AurelioA. DelasReyes,Jr. Postdoctoral ResearchAssociate

Departmentof Qvil andEnvironmental Enghmuing LouisianaState University BatonRouge, LA 70803~5 fI II

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Abstract

This paperpresents a systematiccategorization of recirculatingsystems based upon their ecologicalmimicry. Although natural aquaticsystems are almost endlessin their variationof physicaland chemicalcharacteristics, recirculating systems are normallydesigned to approximateonly their mostfundamental aspects. The authors' proposed classification system basedon the mostbasic divisions with respectto a system'ssalinity, temperature, and trophic statewould permit the definitionof integratedsystem design criteria for the vastmajority of aquacultureapplications. Specialization of systemsbased upon pH regimenmay also be justified in a few specializedcases. The prcrposedclassification system identifies twelve combinationsof temperature warmwater or coldwater!,salinity marine or fresh!, and trophic status oligotrophic,mcsotrogkic, or eutrophic!. The trophic states are assigned water quality criteria thatreflect a blendof nahnmland recirculating conditions that are normally observed. Of the12 possiblecombmations, 9 categories seem to representthe vast majorityof recirculating aquaculturesystems, and would @gear to justify developmentof broadcriteria. Oneadditional systemclass that falls outside the basic structure because of its pH constraintsseems worthy of addition,bringing the total number of practicalcategories to 10. Commonnames are assigned to the 10 categoriesto representtheir naturalcounterpart or function. Thesenames mask the underlyingrationale for development,but shouldfacilitate their adoption by theaquaculture community.The establishment of a classificationsystem will facilitatethe developmentof treatmentstrategies and design criteria in supportof the variousrecirculating categories. Commentson thedraft classification system are being encouraged by posting of thecriteria in thelntemet at 4ttpJ/la-sea-grant.lsu.edu/recirculatingsystems/Recirqua/RecirquaDefault.htm>. Refinementswill bemade in responseto comments prior to 6aalpublication.

197 Introduction

Overthe last decade the unit processesrequired for treatmentof recirculatingsystems have been clearlydefined Lucchettiand Gray, 1988;Huguenin and Colt, 1989;Roscnthal and Black, 1993!, The four most critical processesare aeration oxygen!, clarification solids,SOD!, biofiltration BOD, ammonia, nitrite!, and degasification carbon dioxide!. Systemswith extendedhydraulic retentiontimes must generallyhave an alkalinity replenishmentregime to compensatefor the alkalinity~nsuming nitrification reaction. Additional treatment components including denitrification nitrate, alkalinity!, ozonation BOD, color!, disinfection pathogens!, andfoam fractionation surfactants!are provided to complywith specifi productionneeds.

Therationale for implementation,including both deviceselection and sizing criteria, vary widely Parker 1981;Kaiser and Schmitz, 1988;Losordo and Westcrman,1994; Heinen, et al. 1996; Arbiv andVan Rijn, 1995;Summerfelt, 1995; DeLosReyes and Lawson, 1996; Twarowska et al. 199S!. In fact, there are so many combinationsof technologiesthat the industry is caughtin a developmenteddy. Clearly,some assemblies of technologiesarc morereliable and costeffective than others. However,each system design is virtually unique;yet, thereare so many variations in purpose,device interactions,and water quality objectivesthat it is difficult for ineaningful advancementsto be recognized. While individual treatmentdevices display a high level of technologicalrefinemen, integration af technologiesfor cohesive treatment packagesis faltering.

This paperproposes a recirculatingclassification system with the intent that the classification systemwill serve as a foundationfor the systematicgeneration of integrateddesign criteria. Focusedrefinement of integrateddesigns with respectto reliability and cost minimizationwill increasethe prospectsfor profitableoperations by avoidingunnecessary capital and operational costs, an essentialfeature in the cost-sensitiveaquaculture area Muir, 1981; Losordo and Westeraian,1994!. Thc following sectionpresents the underlyingrationale for selectionof the parametersutilized to conductthe initial partitioningof thc productionsystems.

Classification Scheme

In reviewingthe diversity of recirculatingsystems, it becomesapparent that they vny widely accordingto the waterquality objectives.The water quality divisionscan be clusteredaccording to levelof organicloading or trophic level: thc lightly loadedsystems displaying the bestwater quality,and the heaviestloaded systems representing the worstacross a wide bandof water quality variables. Additional resolutioncan be obtainedby examinitigthe tempcraturcand salinity regimeappropriate for the speciescultured. In a few cases,there is further refinemcnt accordingto thepH or alkalinity of the system. Impacton the designof treatmentsystems was theprimary rationale used for inclusionor exclusionof thesepotential classification parameters.

198 The conceptof trophic level is used in the classificationof lakes to distinguishthe level of nutrientenrichment Holum, 1977;Wetzel, 1983!. Nutrient loadinggenerally controls the level of algal growthin the lake, andthus, controls the productivityof the food chain in the lake. The cleanest lakes, as estitnatcd by ared nutrient loading, are classifiicd as "oligotrophic". Oligotrophiclakes tend to be very clear andhold the most pristinewaters, but low productivity levelsrestrict fish populations.As a lakeages, internal cycling of mitrients&om the sediments builds up, the lake becomesvery productive,supporting algal growths, healthy zooplankton populations,and ultimately, a robustfish population.Thee lakesare classified as "mesotrophic" or moderately enriched. As nutrient loading levels increase fiirther, the system becomes "eutrophic" indicating that the productivity is so high that the systemdisplays water quality instability. This is evidencedtypically by algal blooms, dissolved oxygen crashes,and intermittent ammonia peaks. Only tolerant Gsh speciestend to prosper in a eutrophic environment.

By analogy fish production systemscan be categorizedas oligotrophic, mesotrophic,or eutrophicby thc level of the water'senrichment as driven by the feedapplication rates. Thereis a general trend towards water quality deterioration as feed loading increases.However, in this case,the classificationis morcclosely associated with the waterquality objectivesrather than the feedloading since thc treatmentcomponents can be sizedto partially offset loading,invalidating the use of a strict loadmg guideline.The bestwater quality conditionsare associatedwith the oligotrophicsystems, and the worst with the eutrophicsystems.

A classificationsystem with at leastthree levels appears to be a justifiablerefineinent of earlier attemptsto establishgeneral water quality criteria for {e.g., Rogersand Klemetson, 1985!. In all cases,thc water quality criteria are selectedto assurea relatively stress-&ee environment Tomasso, 1996! for the culturedspecies and to meetthe productionobjectives.

Oligotrophic recircuhiting systems,with their excellent water quality Table 1!, are most &eqqmtly usedfor brccdiiigpurposes. Valuable are own held at low densitieswith oversizedtreatment units to assurestress-&ec development. For example,the bestwater quality is often demandedfor shrimpmaturation Lawrenceand Hunter, 1987!. Eggsand.fry of many speciesarc very sensitiveto waterpollution and mostparameters must be held below detection limits. Similarly, displayaquaria are often kept in an oligotrophicstate to assurethat the highest aestheticstandards are met, Recirculatingsoft~ Callinectessapidus! sheddingsystems Malone and Burden, 1988a! and soft~wfish {ProcaInbarusclarkiI and P. zonanydws! sheddingsystems Malone and Burden, 1988b;Malone et al. 1996! are designedto display ohgotrophicconditions to protect the aninuils as they pass through the vulnerablemolting process. In somecases, sensitive species must be kept in oligotrophicconditions throughout their life.

The mesotrophicclassification describes the bulk of high~ity productionsystems where risk andeconomics must be carefiilly balanced to achieveprofitability e.g., trout [Salvo gairdnen]- Heinenet al. 1996;Kaisar and Schmitz,1988!; tilapia [Oreochromisniloticus] - DeLosReyes, 1996;Twarowska et al. 1995!. Heresome deterioration in aestheticsis permittedand water qualityis held at safe levels to avoid growth inhibition and disease problems. Dissolved oxygen levelsare &equent1y permitted to dropto 5 mg/L,and total ammonia nitrogen TAN! and nitrite nitrogen NO2-N! are allowed to Qucnuleto ashigh as 1 mg-N/L,a level widely recognized as tolerablefor growoutof mostfood species. Deterioration in water color and turbidity is permittedasthese parameters areweakly correlated toSsh health. Total suspended solids levels andthe assocratcd BOD! are allowed to creepup to about15 mg/L, gust below the level that maybe of damage tothe more sensitive species, and below the level where biofouling problems beginto occur within pipes and treatment components. Table1: Water quahty shmdards areproposed foreach trophic level allowing engineers tomore appropriatelydevelop integrated design guidelines.

WaterQuality Oligotrophic Mesotrophic Eutrophic Pmuncter Dissolved Essential, low levels induce Ox en m >6.0 >5.0 >4.0 stress reduce or kill High concentrationsimpact Carbo~ dioxide respiratoryprocesses and can mg/L! <1.0 <5.0 reducepH to levelsthat inhibit nitrifiers Total Ammonia NH3toxic, high levelsreduce m -N/L <1.0 <2.0 induce stress,or kill Nitrite mg-N/L! <0.3 <1.0 <2.0 Toxic,induces respiratory stress and kills Toxic to some ornamental and Nitrate m -N/L <50 marUlc Ns Biochemical Contributesto biofouhngand OxygenDemand <5.0 <10 <20 promotes bacterial blooms -N/L that can contribute to stress. Contributesto biofouling, Total Suspended <5.0 <15.0 <25.0 causesgill datnagein Solids m scGsitlvc les Aesthetics,clear water helps Turbidity NTU! <10 <100 with diseaseprevention and mana ent LowpH caninhibit nitrifying H >7.0' >7.0 >7.0 htcteria in bio61ters Alkalinity Low alkalinity caninhibit -CaCO >80' >80 nitri hmteria in biofilters Color Not Ae4mtics, causedby inert abs. 436 nm A h cable rc&acto anics Canbe importantto cultured Hardness Not Not Not species,but has little impact -CaCO A licable A 'cable licablc on desi ~ ApH range of 5.0-7.0and alkalinity of <80mg-CaCO3/L applies to "TropicalRain Forest" category only. The eutrophiccategory exists for the growoutaf the most tolerantspecies [e.g., carp Cyprinus carpio! - Arbiv andVan Rijn, 1995;snakehead Chan@a stnatus!, Qin et al. 1997;Kemp's ridley turtles LepidochelyshmJn! - Malone et al. 1990; alligators Alligator mississippiensis!- DeLasReyeset al. 1995!that showvigorous growth under moderately deteriorated water quality conditions. Here, dissolvedoxygen lcvcls are allowedto drop ta an economicoptiiiium level usually dcfined thraugh net growth studies. For example,Papoutsog1ou and 'Tztha 996! demonstrateda least-costoxygen level of 3.8 mg/L for blue tilapia &eoclN omis mucus! in rccirculatcdwater. The toxic compoundsammonia and nitrite are allowedto rise to 2 mg-N/L, bclawthe level adverselyimpacting growth or inducingchronic disease for tolerantspecies Qin et aL, 1997!. Aestheticand convenience criteria are nearly abandoned at this level with the water allowedto literally becomeopaque due to turbidity <100 NTU! andcolor. Suspendedsolids < 25 mg/L! and BODs <20 mg/L! are not allowed to rise to the level where heterotrophic dominationlimits biofiltration Harremoes,1982; Rogersand Klemetson,1985; Zhanget al 1995!. Despite the relatively low sbmdardsfor water quality set for eutrophic production conditians,a numberof species,having presumablyevolved under similar natural conditions, can prosper under these conditions.

In summary,it appearsthat a three-tierdivision of recirculatingsystems is well justified. Three divisionsare suf5cient to reflectthe diversityof systemqualities without becomingburdensome. Carefulattention needs to be givento the establishmentaf the waterquality standardsassociated with eachclassification, assuring that one parameterdoes not dFectively limit the breadthof application of the classification.

Further subdivision of the classification system by temperature appears mandatory. Temperatureimpacts the rates of chemicaland biological processesat thc most fundamental level. Of primary concernare the metabolicrates of the speciescultured and of bacterial populationstraditionally used to purifyrecirculating wats. A simplistictwo stepclassification betweencoldwatcr <15 'C! andwarmwater 5 'C! is proposedto allow rationalsizing of componentswhose efIicicncies arc impacted by temperieire. In the caseof oxygen,for example,this would allow engineers'to makesizing adjustmentsto compensatefor changesin the saturationlevel and transfer constants induced by tempmture Hugueninand Colt, 1989!, Areal nitrification in biofiltcrs are generallybclievcd to declinewith temperature,impacting the suttee arearequirements for treitmcnt of a givenload Shannaand Ahlert, 1977;Knowles et al. 1965;Srna and Baggalcy, 1975; Wortman and Wheaton, 1991!.

Althoughtempcrahirc responses of individualspecies of fish,crustiiceuis, and mollusks has been generallystudied, the more globalrelationship.between temperature and metabolicactivity acrossspecies is muchmorc vagueowing to the evolutionaryvariations in enzymaticsystems. Thus,it cannotbe assumedthat the grossmetabolic level of a coldwatersystem is lessthan that of a wannwatersystem, although clearly someelements such as the biofiltration unit will be adverselyimpacted. Giventhis stateof affairs,a simpledivision of systemsinto a coldwater andwarmwater classification seems appropriate, however, furtlwr subdivisions may be justified astemperature effects on integrateddesigns become better known.

201 Salinityhas a majoreffect an the saturation level and transfer kinetics of oxygen.As the salinity level increases,maintenance of a selectedoxygen level becomesmore difficult. It is also recognizedthat foam fractionatar performance improves with salinity, whereas, clari6crs which dependon settlingmay be adversely impacted. Thc impact on bio6ltrationunits is notclear, althoughevidence of signi6cant difFerences hasbeen presented Nijhof and Bovendeur, 1095!. Theimpact of salinityon gastransfer alone justi6es a divisionbetween aurrine >10 ppt! and freshwater <10 ppt! applications,but docsnot seemta justify an intermediatebrackish water classi6cation.

Froma waterquality perspective, water arc oftendescribed as acidic <7.0!,neutral .0!, or alkaline .0! onthe basis of thehydrogen ion cancentratian.Alkaline waters are domiruwd by hydroxideions, and acidic waters by hydrogenions. ThepH canhave a majorimpact on the rate of chemical and biological reactions. The principal impact on system design relates to bio6ltrationdesign, and more speci6callythe impactof pH on bacterialactivities. As a general statement,both heterotrophicand nitrifying bacteriaare inhibited by low pH. The critical nitrifyingbacteria are clearly im~ by cithcrlow pH or low alkalinity Sharmaand Ahlcrt, 1977;Paw 1984!. A signi6cantdecline in nitri6cationkinetics occurs at pH valuesjust below neutral,usually in associationwith alkaliniticsbeLow 80 mg-CaCO~.

Froman perspective, pH is a volatileparameter since it is alsodefined by theratio of carbondioxide and the bicirbonatcion concentrationin most applications.Once the carbonate alkalinity of a systemis de6ned,the pH fluctuateswith the carbondioxide level. It may bc more appropriateto classifyrecirculating systems by their alkalinityas acidic <80 mg-CaCO~!or alkaline > 80 mg&aC~! underthe presumptionthat only low alkalinity systemscan display low pH values.An exceptioncan be inducedby a poordegasi6cation camponent. However, acidic low alkalinity!systems are rare, being used primarily for thebreeding of SouthAmerican -rainforest ornamental species Weaver, 1991!. 'Hase systemscan have pH levelsas low as 5.0, andare almostalways oligotrophic. Acidic systemsare rarelyused outside of this unique applicationarea. Instead, even rainwater species are reared in systemswith pH valuesnear 7.0, where bacterial kinetics are much more favorable and bio61tration requirements are greatly reduced.

Acidic conditionsare not naturallyconducive to growout,thus, rcpartitioning based on a pH or alkalinity does not seemjusti6ed. Establishmentof a unique chesi6catian to supportthe productionof rainforest ornamental 6sh, however, is vnLrrantedby theeconomic impact of this industry Chapmanet aL 1997!.

202 Hardness

Hardnessis technicallya measurementof the cumulativeconcentration of the divalentcations commonlyfound in water. In mostaquaculture applications it primarily refiects the calcium ion con tration.Calcium is animportant water quality parameter with watersfrequently being classifiedas hard highcalcium levels! or soft low calciumlevels!. Although a numberofo recommendationsexist for theinaximum or ininimalhaidiiess levels for a varietyof species, hardnesshas little or no impacton theinajority of treatmentdevices used in recirculating systems.Partitioning of the recirculatingsysteins according to hardnesswould servelittle functionin the generationof designcriteria.

RecirculatingSystem ClassiYications

Reviewof the significantpartitioning parameters indicates that a reasonabledelineation of recirculatingsystems can be achieved in a 2x 2 x 3 matrix,based upon a system'ssalinity, temperature,and trophic level. Figure 1 illustratesthe classification system and assigns common namesto theresulting recirculating system classes. Three eutrophic classi6cations fresh/cold, cold/marine,and warm/marine! arenot commonly utilized and can be dropped as categories. Theresulting classifications aresufficiently different to justify unique design criteria, and should provideaquaculturists with suf6cient diversity to covermost applications. The "Tropical" classi6cation fresh/warm/oligotrophic! warrants further refinement, as generalcriteria wou1d notserve the production of thecommerciaHy important South American ornamental fish. Acidic conditionsinhibit nitrification, demanding adjustments in bio61tration design rationale. Thus, a "TropicalRain Forest" acidic! and a "TropicalDisplay and Breeding" neutral to basic! categorywere established. This adjustment iHustrates the potential for furtherexpansion and refinementofthe classification system asrecirculating industries become more sophisticated. Table2 iHustratesrelationships between the 10 classes of recirculating systems and the specific applications.A given species may appear under more than one classification based'upon the systole'sproposed function broodstock conditioning, spawning, fry production,fingerling headstart,or growout!.Thus, redfish/red drum Scfaenopsocellutus! broodstock may be conditionedunder "Manne Reef," but fingerlingsmay be rearedunder "Marine Growout" warm/mesotrophic!.Also, based upon the production philosophy of the aquaculturist, tilapia maybe grown in systemsfollowing "Waimwater Growout" fresh/mesotrophic!, or "Hardy WarmwaterGrowout" fresh/eutrophic!, or,given their tolenmce for salinity, "Marine Growout" warm/mesotrophic!guidelines. Ultimately, the authors trust that commercial experience wiH identifyclassifications that provemost reliable and costwffective, allowing production associationsto mah; firm recommendationsto their members.

ThechLssi6cation system does not preclude further refinements in recommendations.Additional treatmentrequirements that are not inherently covered in thebasic water quality guidelines can beappended tothe basic classification. 'Ihe specification foroyster depuration, forexamp1e, maybe presented as"Marine Growout with Disinfection." Or, cephalopods may demand "MarineReef with Denitri6cation" Whitson et al, 1993!.The variations wiH stemfrom a commonlyaccepted base, however, and adoption of such refinements fora particularappHcation

203

Table2: The existen~of the recirculatingclassification system permits engineers to develop integrateddesign guidelines,and, independently,production associationscan make clear recommendationsas to appropriatecategories for productionactivities by their membership.

Ackamvledgement

This researchis supportedby the LouisianaSea Grant CollegeProgram, a part of the national SeaGrant CoHegepmgram under the auspicesof the NationalOceanic and Atmospheric Administration,U. S. Departnientof Commerce.

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gg CooperativeExtension NRAES->05

AquaculturalEngineering Society Proceedings 111 Advancesin Aquacultural Engineering

Proceedingsfrom the Aquacultural Engineering Society {AES}Technical Sessions at the FourthInternational SymposiumonTilapia in Aquaculture

CoronadoSprings Resort, Watt Disney World Orlando,Florida November9-12, 1997

Editedby

Michael B. Timmons Professor~Department ofAgricultural and Biological Engineering CornellUniversity

Thomas Losordo AssociateProfessor and Extension Aquaculture Specialist Departmentof Zoology k Biologicaland Agricultural Engineering NorthCarolina State University

NortheastRegional AgricUltural Engineering Service CooperativeExtension I 52 Riley-RobbHall ithaca,New York 14B53-5703