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 ~ RR%%%%%%&HRRRR%%%%%%%%%%&a&aa&HRRQHRRRH&mmmaeaaaaa aV4 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 aquaculture{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 broodstock 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