外文文献翻译循环水网箱养殖系统其他专业Word文档格式.docx

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ProductionSystems

AnOverviewofCriticalConsiderations

ThomasM.Losordo,MichaelP.MasserandJamesRakocy

Traditionalaquacultureproductioninpondsrequireslargequantitiesofwater.Approximately1milliongallonsofwaterperacrearerequiredtofillapondandanequivalentvolumeisrequiredtocompensateforevaporationandseepageduringtheyear.Assuminganannualpondyieldof5,000poundsoffishperacre,approximately100gallonsofwaterarerequiredperpoundoffishproduction.InmanyareasoftheUnitedStates,traditionalaquacultureinpondsisnotpossiblebecauseoflimitedwatersuppliesoranabsenceofsuitablelandforpondconstruction.

Recirculatingaquacultureproductionsystemsmayofferanalternativetopondaquaculturetechnology.Throughwatertreatmentandreuse,recirculatingsystemsuseafractionofthewaterrequiredbypondstoproducesimilaryields.Becauserecirculatingsystemsusuallyusetanksforaquacultureproduction,substantiallylesslandisrequired.

Aquaticcropproductionintanksandracewayswheretheenvironmentiscontrolledthroughwatertreatmentandrecirculationhasbeenstudiedfordecades.Althoughthesetechnologieshavebeencostly,claimsofimpressiveyieldswithyear-roundproductioninlocationsclosetomajormarketsandwithextremelylittlewaterusagehaveattractedtheinterestofprospectiveaquaculturists.Inrecentyears,avarietyofproductionfacilitiesthatuserecirculatingtechnologyhavebeenbuilt.Resultshavebeenmixed.Whiletherehavebeensomenotablelarge-scalebusinessfailuresinthissector,numeroussmall-tomedium-scaleeffortscontinueproduction.

Prospectiveaquaculturistsandinvestorsneedtobeawareofthebasictechnicalandeconomicrisksinvolvedinthistypeofaquacultureproductiontechnology.Thisfactsheetandothersinthisseriesaredesignedtoprovidebasicinformationonrecirculatingaquaculturetechnology.

Criticalproductionconsiderations

Allaquacultureproductionsystemsmustprovideasuitableenvironmenttopromotethegrowthoftheaquaticcrop.Criticalenvironmentalparametersincludetheconcentrationsofdissolvedoxygen,un-ionizedammonia-nitrogen,nitrite-nitrogen,andcarbondioxideinthewateroftheculturesystem.Nitrateconcentration,pH,andalkalinitylevelswithinthesystemarealsoimportant.Toproducefishinacosteffectivemanner,aquacultureproductionsystemsmustmaintaingoodwaterqualityduringperiodsofrapidfishgrowth.Toensuresuchgrowth,fisharefedhigh-proteinpelleteddietsatratesrangingfromto15percentoftheirbodyweightperdaydependingupontheirsizeandspecies（15percentforjuveniles,percentformarketsize）.Feedingrate,feedcomposition,fishmetabolicrateandthequantityofwastedfeedaffecttankwaterquality.Aspelletedfeedsareintroducedtothefish,theyareeitherconsumedorlefttodecomposewithinthesystem.Theby-productsoffishmetabolismincludecarbondioxide,ammonia-nitrogen,andfecalsolids.Ifuneatenfeedsandmetabolicbyproductsareleftwithintheculturesystem,theywillgenerateadditionalcarbondioxideandammonia-nitrogen,reducetheoxygencontentofthewater,andhaveadirectdetrimentalimpactonthehealthoftheculturedproduct.

Inaquacultureponds,properenvironmentalconditionsaremaintainedbybalancingtheinputsoffeedwiththeassimilativecapacityofthepond.Thepondnaturalbiologicalproductivity（algae,higherplants,zooplanktonandbacteria）servesasabiologicalfilterthatprocessesthewastes.Aspondproductionintensifiesandfeedratesincrease,supplementaland/oremergencyaerationarerequired.Athigherratesoffeeding,watermustbeexchangedtomaintaingoodwaterquality.Thecarryingcapacityofpondswithsupplementalaerationisgenerallyconsideredtobe5,000to7,000poundsoffishperacre（topoundoffishpergallonofpondwater）.

Thecarryingcapacityoftanksystemsmustbehightoprovideforcost-effectivefishproductionbecauseofthehigherinitialcapitalcostsoftankscomparedtoearthenponds.Becauseofthisexpenseandthelimitedcapacityofthe“natural”biologicalfiltrationofatank,theproducermustrelyupontheflowofwaterthroughthetankstowashoutthewasteby-products.Additionally,theoxygenconcentrationwithinthetankmustbemaintainedthroughcontinuousaeration,eitherwithatmosphericoxygen

（air）orpuregaseousoxygen.

Therateofwaterexchangerequiredtomaintaingoodwaterqualityintanksisbestdescribedusinganexample.Assumethata5,000-gallonproductiontankistobemaintainedataculturedensityofpoundoffishpergallonoftankvolume.Ifthe2,500poundsoffisharefeda32%proteinfeedatarateofpercentoftheirbodyweightperday,thenpoundsoffeedwouldproduceapproximatelypoundsofammonia-nitrogenperday.（Approximately3percentofthefeedbecomesammonia-nitrogen.）Additionally,iftheammonianitrogenconcentrationinthetankistobemaintainedatmg/l,thenamassbalancecalculationonammonia-nitrogenindicatesthattherequiredflowrateofnewwaterthroughthetankwouldbeapproximately5,600gallonsperhour（93gpm）tomaintainthespecifiedammonia-nitrogenconcentration.Evenatthishighflowrate,thesystemalsowould

requireaerationtosupplementtheoxygenaddedbythenewwater.

Recirculatingsystemsdesign

Recirculatingproductiontechnologyismostoftenusedintanksystemsbecausesufficientwaterisnotavailableonsiteto“wash”fishwastesoutofproductiontanksinaflow-throughconfigurationorproductionsystemthatuseswateronlyonce.Inmostcases,aflow-throughrequirementofnearly100gallonsperminutetomaintainoneproductiontankwouldseverelylimitproductioncapacity.Byrecirculatingtank

waterthroughawatertreatmentsystemthat“removes”ammoniaandotherwasteproducts,thesameeffectisachievedaswiththeflow-throughconfiguration.Theefficiencywithwhichthetreatmentsystem“removes”ammoniafromthesystem,theammoniaproductionrate,andthedesiredconcentrationofammonia-nitrogenwithinthetankdeterminetherecirculatingflowratefromthetanktothetreatmentunit.Usingtheexampleoutlinedabove,ifatreatmentsystemremoves50percentoftheammonia-nitrogeninthewateronasinglepass,thentheflowratefromthetankwouldneedtobetwicetheflowrequirediffreshwaterwereusedtoflushthetank（93gpm/=186gpm）.Akeytosuccessfulrecirculatingproductionsystemsistheuseofcost-effectivewatertreatmentsystemcomponents.Allrecirculatingproductionsystemsremovewastesolids,oxidizeammoniaandnitrite-nitrogen,removecarbondioxide,andaerateoroxygenatethewaterbeforereturningittothefishtank（seeFig.1）.Moreintensivesystemsorsystemsculturingsensitivespeciesmayrequireadditionaltreatmentprocessessuchasfinesolidsremoval,dissolvedorganicsremoval,orsomeformofdisinfection.

Wastesolidsconstraints

Pelletedfeedsusedinaquacultureproductionconsistofprotein,carbohydrates,fat,mineralsandwater.Theportionnotassimilatedbythefishisexcretedasahighlyorganicwaste（fecalsolids）.Whenbrokendownbybacteriawithinthesystem,fecalsolidsanduneatenfeedwillconsumedissolvedoxygenandgenerateammonia-nitrogen.Forthisreason,wastesolidsshouldberemovedfromthesystemasquicklyaspossible.Wastesolidscanbeclassifiedintofourcategories:

settleable,suspended,floatableanddissolvedsolids.Inrecirculatingsystems,thefirsttwoareofprimaryconcern.Dissolvedorganicsolidscanbecomeaprobleminsystemswithverylittlewaterexchange.

Settleablesolidscontrol:

Settleablesolidsaregenerallytheeasiestofthefourcategoriestodealwithandshouldberemovedfromthetankandfiltrationcomponentsasrapidlyaspossible.Settleablesolidsarethosethatwillgenerallysettleoutofthewaterwithin1hourunderstillconditions.Settleablesolidscanberemovedastheyaccumulateonthetankbottomthroughproperplacementofdrains,ortheycanbekeptinsuspensionwithcontinuousagitationandremovedwithasedimentationtank（clarifier）,mechanicalfilter（granularorscreen）,orswirlseparator.Thesedimentationandswirlseparatorprocessescanbeenhancedbyaddingsteepinclinetubes（tubesettlers）inthesedimentationtanktoreduceflowturbulenceandpromoteuniformflowdistribution.

Suspendedsolidscontrol:

Fromanaquaculturalengineeringpointofview,thedifferencebetweensuspendedsolidsandsettleablesolidsisapracticalone.Suspendedsolidswillnotsettletothebottomofthefishculturetankandcannotberemovedeasilyinconventionalsettlingbasins.Suspendedsolidsarenotalwaysdealtwithadequatelyinarecirculatingproductionsystem.Ifnotremoved,suspendedsolidscansignificantlylimittheamountoffishthatcanbegrowninthesystemandcanirritatethegillsoffish.Themostpopulartreatmentmethodforremovingsuspendedsolidsgenerallyinvolvessomeformofmechanicalfiltration.Thetwotypesofmechanicalfiltrationmostcommonlyusedarescreenfiltrationandgranularmediafiltration（sandorpelletedmedia）.FormoreinformationonthesedevicesseeSRAC453,RecirculatingAquacultureTankProductionSystems:

AReviewofComponentOptions.

Fineanddissolvedsolidscontrol:

Finesuspendedsolids（<

30micrometers）havebeenshowntocontributemorethan50percentofthetotalsuspendedsolidsinarecirculatingsystem.Finesuspendedsolidsincreasetheoxygendemandofthesystemandcausegillirritationanddamageinfinfish.Dissolvedorganicsolids（protein）cancontributesignificantlytotheoxygendemandofthetotalsystem.