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ImprovingAgriculturalValueofSludgebyBatchAerobicDigestion*Eung-JuHwang*XiaoZhang**Young-OkLeeand***Hye-JooLee*DepartmentofEnviro__entalEngineeringDaeguUniversityKorea**DepartmentofLifeScien__DaeguUniversityKorea***DepartmentofLifeScien__DongaUniversityKoreaAbstractNo:
5551.IntroductionInKorea
2.43millionton/yearofsludgewasprodu__dfrommunicipalwastewatertreatmentplantin
2004.Thissludgewas__inlydisposedofbyo__andumping
77.1%incineration
11.7%andrecycling
9.8%.Disposalbylandfillwasprohibitedin2003ando__andumpingisscheduledtobeprohibitedsooninaccordan__withLondonConvention.Inadditioncostandairpollutionconsiderationsh__ecurtailedtheuseofincineration.Thereforevarioustreatmentalternativesh__ebeeninvestigatedinthiscountry.Theseincludesolidification/stabilizationbychemicaladditioncharcoalproductionincinerationafterdryingproductionofconstruction__terialandcomposting.Conventionalanaerobicdigestionhasbeenextensivelyemployedforreductionofsludgequantityaswellasbiogasproduction.Buttheanaerobicdigestionisrathertreatmentmethodthandisposalalternativesin__thedigestedsludgestillneedstobetreatedandstabilizedforitsdisposalorbeneficialuse.Compostingisoneofattractivemethodsforrecyclingofsludge.Howeverthissolidstatepro__ssrequireslargequantityofbulkingagentoramendmentformoisturecontrol.Onthecontraryinaerobicdigestionpro__ssitispossibletostabilizeorganic__tterinaqueousphasewithoutmoisturecontrol.Theo__ectiveofthisstudythereforewastoinvestigatetheeffectofaerobicdigestiononagriculturalvalueofanaerobicdigestedsludge.Theeffectoffeedtoseedratioontheperfor__n__ofaerobicdigesterwasstu___dandbiologicalassaywascarriedouttoevaluatethepotentialofsludgeasliquidfertilizeraftertheaerobicdigestion.
2.__terialandmethods
2.1SludgeThecharacteristicsofsludgeusedinthisstudyareshowninTable
1.FeedsludgewastakenfromanaerobicdigestertreatingactivatedsludgeandfoodwastemixtureKyongsanKorea.Andseedsludgewascollectedfromthereturnsludgestreamofmunicipalwastewatertreatmentplant.Table
1.ThecharacteristicsoffeedandseedsludgeParameterSeedsludgeactivatedsludgeFeedsludgeanaerobicdigestedsludgepH
7.
407.65TCODmg/l
6118.
126598.0SCODmg/l
176.
4518.0TSSmg/l
4960.
019494.0VSSmg/l
3490.
015917.
02.2BatchaerobicdigestersetupTwobioreactorswith5Lofworkingvolumewereemployed.75%and50%ofthereactorvolumewasfilledwithfeedsludgeandthere__ining25%and50%wasoccupiedbyseedsludge.Theaerobicsystemwasoperatedatambienttemperature.Atthebottomofeachreactoradiffuserwaspla__dtoletcompressedairintothereactorbothtooxygenizethesludgeandtohomogenizeitbypreventingtheirsedimentation.
2.3BiologicalassayPuresoillesspottingmediawasblendedwithliquidsludgeintheratioof1:1and1:
3.Themixturewassaturatedwithdistilledwaterandpouredintoplasticseedlingpots.Cucumberseedsn=10werepla__donthesu_____ofpottingmedia-sludgemixtureandthenwerecoveredwithabout1cmofthemixture.Thepotswerepla__dintoagrowthchamber.Temperaturewas__intainedat27℃for14hduringthedayandfor10hatnightrespectively.Germinatedseedlingsradicleemergedandemergedseedlingscotyledonsvisibleonthesu_____werecounteddaily.Afteroperationtimeof16daystheleafsizeandheightofeachseedlingthelengthofseedlinghypocotylsabovethesu_____ofpottingmediaweremeasured.Finallythoseseedsthatgerminatedbutfailedtoemergethroughthesludge-amendedpottingmediaweredetermined.
2.4KineticsofaerobicdigestionKinetic____ysisforVSSandTSSreductionwerecarriedoutunderthefirst-orderreactionassumptiondescribedinEquations1and2respectivelyArnaizetal2006;D’Antonio
1983.1logVSS-logVSS0=-kt/
2.303;2logTSS-logTSS0=-kt/
2.303whereVSS0andTSS0aretheinitialvolatileandtotalsuspendedsolidsmg/lrespectively;VSSandTSSarethevolatileandtotalsuspendedsolidsattimetmg/lrespectively;kisthekineticconstantd-1andtisthetimed.
3.Resultsanddiscussion
3.1BatchaerobicdigestionVSSremovalwasslightlyhigherthanTSSremovalintheaerobicdigesterFig.1sin__thelatterispartiallycomprisedofthefixedsuspendedsolidsFSSthatresistbiodegradationattheimposedoperatingconditions.ByincreasingfeedtoseedratioTSSandVSSremovalratesincreased.Kinetic____ysisshowedthesametrendshowninTable
2.Degradationkineticsconstantkwasincreasingwiththeincreaseoffeed/seedratio.Inthisstudyfeedsludgewasanaerobicallydigestedsludgewhichcontainedlowenergybio__ss.Soadditionofdigestedsludgecouldincreasetheviable__ll__sscon__ntrationinthedigester.ThereforeinitialTSSandVSScon__ntrationswerehigherinthereactorcontaining75%offeedsludgethanthatinthereactorcontaining50%offeedsludgewhichseemedtocausethisresult.Itwaspossibletoobtain__ximum
50.0%ofVSSremovalat28daysofbatchaerobicdigestion.abFig.
1.Effectofdifferentfeed/seedratiosonaTSSremovalrateandbVSSremovalrate.Table
2.Effectofdifferentfeed/seedratiosontheorganicsoliddegradationratekFeed/SeedratioDegradationkineticconstantd-1TSSVSS
10.
0170.9835*
0.
0210.9906*
30.
0220.9650*
0.
0230.9724**:relativevarian__Fig.
2.VariationsofNO3--Ncon__ntrationinFig.
3.VariationsofpHintheaerobicsystem.theaerobicsystem.Itwasinterestingtoobservenitrificationreactioninthereactor.InitialNO3--Ncon__ntrationwasverylowbutitrapidlyincreasedwithreactiontimewhichresultedinthedecreaseofpHFig.2andFig.
3.Fromdays0to2pHincreasedprobablyduetothereleaseofammonium.NO3--Ncon__ntrationinthereactorcontaining50%offeedsludgewasevidentlyhigherthanthatinthereactorcontaining75%offeedsludgewhentheretentiontimerangedfrom0to14days.Butafterwardsthedifferen__betweenbothreactorswasverylow.Ingeneralwhenthesystemsh__ehighcarbona__ousbiochemicaloxygende__ndlevelsautotrophicnitrifierscannotcompetewithheterotrophicbacteriaintheactivatedsludgesystemssuc__ssfully.Thereforeloworganicloadingisrequiredtoactivatenitrifiersinsuchsystems.Whenthefeedtoseedratiowaslowinthisstudytherewaslittlecarbona__oussubstrate__ailableandthusnitrificationreactionwasactivated.After14dayscarbona__oussubstratewasinsufficientsothatnitrificationprevailedinthecaseofhighfeedtoseedratio.
3.2BiologicalassayAfter40daysofretentiontimesamplefromthereactorcontaining50%offeedsludgewas__deabiologicalassay.Daystothefirstemergen__ofseedlingafterwhichnoseedlingemergedbuttheseedswereviableorgerminatedinonepotdefinedbyRenetal.2002weremonitored.Thedaystothefirstemergen__ofseedlingplantedontheaerobicallydigestedsludge-amendedpottingmediawaslowerthanthatofseedlingplantedontherawsludge-amendedpottingmediaFig.
4.Itwasduetothestabilizationofsludgebyaerobicdigestion.After16daysofoperationtimeleafsizeandheightofseedlingweremeasuredFig.
5.Theleafsizeofthefinaldigestedsludgewasbetterthanthatofrawsludgeuntreatedbyaerobicsystem.Itappealsthatbiologicaltreatmentcanimprovetheagriculturalvalueofsludge.Thiswasbecausethebiologicallytreatedsludgesamplehadhighnitratecon__ntrationofabout350ppm.VosandvanderPutten1998investigatedthatleafsizeinpotatoisveryresponsivetoNsupplyduetoaneffectonleafexpansionrate.InadditionLiefferingetal.1996demonstratedthatadditionofNO3--Ncouldincreasetherateofmobilizationofseedreservesofbarleyandwheat.InFig.5itcanbealsoseenthatadditionofNO3--Ncouldnotpromotethegrowthofseedlinghypocotylsgreatlywhichmightberelatedtonitratecon__ntration.Fig.
4.Thenumberofdaystothefirstemergen__ofseedlingsplantedonthedifferentsludge-amendedpottingmedia.abFig.
5.aleafsizeprofilesandbheightprofilesofseveralsamplescomparedwiththecontrol.Note:RDS—finaldigestedsludgeaerobically;Raw—rawsludgebeforeaerobicdigestion;D.W—distilledwater;andtheratioisthatofsampletopottingmedia.
4.ConclusionsTSSandVSSremovalratesincreasedwiththeincreaseoffeed/seedratio.After28daysofretentiontimeTSSandVSSremovalrategotto
49.7%and
50.0%respectivelyforfeed/seedratioof
3.Pseudo-first-orderkineticsrevealedthatorganicsoliddegradationrateconstantkincreasedwithfeed/seedratio.DuetonitrificationreactionNO3--Ncon__ntrationincreasedwithaerationtimewhichresultedinthedecreaseofpH.Thenumberofdaystofirstemergen__ofseedlingwasredu__dbystabilizationoforganic__ttersinaerobicdigestion.Thebiologicaltreatmentimprovedtheagriculturevalueofsludge.Leafgrowthwasimprovedbythehighnitratecon__ntrationinthetreatedsludge.Thedosageofsludgeappliedtosoilwasonefactorforthispottest.Referen__sArnaizC.GutierrezJ.C.LebratoJ.
2006.Bio__ssstabilizationintheanaerobicdigestionofwastewatersludges.Bioresour__Technology97101179-
1184.D’AntonioG.
1983.Aerobicdigestionofthickenedactivatedsludge.Reactionrateconstantdeterminationandpro__ssperfor__n__.WaterResearch17111525-
1531.LiefferingM.AndrewsM.McKenzieB.A.
1996.Nitratestimulationofmobilizationofseedreservesintemperate__reals:importantofwateruptake.AnnalsofBotany78695-
701.RenJ.TaoL.LiuX-M.
2002.Effectsofsandburialdepthonseedgerminationandseedlingemergen__ofCalligonumL.species.JournalofAridEnviro__ents51603-
611.VosJ.vanderPuttenP.E.L.
1998.Effectofnitrogensupplyonleafgrowthleafnitrogeneconomyandphotosyntheticcapacityinpotato.FieldCropsResearch5963-
72.。
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