Anaerobic Co-Digestion of Sewage Sludge and Waste – A Review with a Focus on the Mixing Ratios, Pre- by IRJET Journal

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Abstract - Anaerobic digestion is a viable commercial option variety of wastes. However, there are several countriescontributeresult,combinationmethaneTobiodegradabilityyears.pcosewagepresentpublisheddigestionconsideredplant.digestionsubstratestolimitationstotheanaerobicdigestionofsinglesubstratesduesubstrateproperties.AnaerobiccodigestionoftwoormoreisaviableoptionforovercomingthemonodrawbacksandincreasingtheeconomicviabilityofaAtthemoment,anaerobiccodigestioncanbethemostsignificanttopicwithinanaerobicresearch,ashalfofthepublicationshavebeeninthelasttwoyears.Theaimofthispaperistoareviewoftheanaerobiccodigestionfoodwasteandsludgewithafocusonthemajorfactorsaffectingthedigestion,mixingratios,mixingstrategies,variousretreatmentstrategies,andmainchallengeswithinthelastInanaerobiccodigestion(AcoD),higherandvariabilityofFWarecriticalchallenges.minimizethechallengesofFoodWastesforincreasingproduction,optimizationforeachsubstrateandadequatepretreatmentarecritical.AsaAcoDhasthepotentialtobecommerciallyviableandtotheeconomy,particularlyindeveloping otherandOriginally,materialsindustrialclippPlanttheHydrolysis,hydrogensulphide,andmanurethroughouttheADprocess.acidogenesis,acetogenesis,andmethanogensaremainfourprocessesofanaerobicmetabolism[1],[2].andanimalwastes,cowmanure,wastepaper,grassings,leftoverfoodinmunicipalsolidwaste,home,andwastewater,andotherbiodegradableorganiccanallbehandledwithADtechnology[3],[4].theADprocesswasintendedforsewagesludgeanimalmanure[5].Sewagesludgeandmanure,onthehand,donothaveastrongpotentialforAD.Asaresult, biogasheatingpercentsolidsthananaerobicupatTraditionalmannertheappropriatetreatmenttoTheammopotentialreactor,production,singleimprovingsynergisticenhancenutrientsproductionCocombinedsubstratesnutrientsanaerobicandinFoodelementsSludgeprocessfedtoimprovetheefficiencyoftheprocess,thedigesterscanbewithtwoormoretypesoffeedstocksinacodigestion[6].containshighconcentrationsofnitrogenandtracebutislowinbiodegradableorganicmatter[7],[8].Waste(FW)isaproblematicorganicwastethatcomeslargequantities.ThevolatilesolidsinFWareabundant,theycanbeeasilyconvertedtomethaneviaanmethod.However,itusuallyhasalowamountof[9].AcoDisanapproachwheretwoormorewithcomplementarycharacteristicsaremixedfortreatment.digestionoffoodwasteacceleratestherateofmethaneandahighermethaneyield[10].Itcanusetheandbacterialdiversitiesindifferentwastestothedigestionprocess[11].Itseemstohaveaimpact,overcomingnutritionalimbalancesandbiodegradation.WhencomparedtotheADofawaste,thisimpactleadstoalargermethanewhichincreasestheorganiccontentinsidetheimprovesdigestatestabilization,anddilutesinhibitoryand/orhazardouschemicalssuchasnia,Na+,andsoon[12][14].energycontainedinwastewaterandsludgeispredictedbetentimesgreaterthantheenergyrequiredfor[15].ADofSShasbeenrecognizedasthemosttechniqueforrenewableenergyrecoveryandcreationofnutrientrichfertilizerinasustainableinrecentdecades[16].ADorAcoDofsewagesludgeisoftencarriedoutlowsolidconcentrations,whichmeansthatwatermakesthemajorityofthedigester'scontent.Highsolidsdigestion(HSAD)usesahighersolidsfeedstocklowsolidsanaerobicdigestion(LSAD),andthetotal(TS)percentageofthedigestateishigherthan1015[17].Smallerdigesters,lowerenergyusageforfeedstockanddigesters,andhighervolumetricgenerationaresomeofthebenefitsofHSAD[18]

Key Words: Anaerobic co digestion, Anaerobic digestion, FoodWaste,SewageSludge 1.INTRODUCTION Inoxygen depletedconditions,Anaerobicdigestion(AD)isa naturally occurring biological process of microbial degradation. Organic matter is broken down into simpler chemical components like methane, carbon dioxide,

International Research Journal of Engineering and Technology (IRJET) e ISSN: 2395 0056 Volume: 09 Issue: 03 | Mar 2022 www.irjet.net p ISSN: 2395 0072 © 2022, IRJET | Impact Factor value: 7.529 | ISO 9001:2008 Certified Journal | Page282 Anaerobic Co-Digestion of Sewage Sludge and Waste – A Review with a Focus on the Mixing Ratios, Pre-Treatment, and Challenges Hanan A. Fouad1 , Ahmed M. Aboulfotoh2, Rehab El-hefny3, Ahmed I. Marie4 1Professor, Sanitary Engineering Department of Civil Engineering, Shubra Faculty Benha University 2Assistant Professor, Sanitary Engineering Department of Civil Engineering, Faculty of engineering Zagazig University 3Assistant Professor, Sanitary Engineering Department of Civil Engineering, Shubra Faculty Benha University 4Lecturer Assistant, Sanitary Engineering Department of Civil Engineering, Shubra Faculty Benha University ***

AD is a set of complex biological processes that occur mostly in the absence of oxygen and involve bacteria hydrolyzing polymeric organic carbon molecules before hydrolysis,[19]hydrolysis,Thegasesrespectivelycarbonconvertingthemtobiogasandbiofertilizer.Themethaneanddioxidepercentagesareabout5065%and4050%fromthebiogas,andtraceamountsofothersuchashydrogensulphide,nitrousoxide,andothers.ADprocessinvolvesfourimportantbiochemicalsteps:acidogenesis,acetogenesis,andmethanogenesis[23].Thefourkeystagesofanaerobicdigestioninvolveacidogenesis,acetogenesis,andmethanogenesis.



 Methanogenesis: Methanogens transform the intermediate products from the previous stages into methane,carbondioxide,andwater.

Acetogenesis:Acetogensdigestthesimplemolecules produced during the acidogenesis phase to produce mostly acetic acid, as well as carbon dioxide and hydrogen.

3.1 Temperature

Thecarbon to nitrogen ratio(C/N)is theproportionof carbontonitrogeninorganicmatter.Thisratioiscriticalin

 Acidogenesis: breakdown of the remaining byproducts.dioxide,acidscomponentsbyacidogenicbacteria.Here,volatilefatty(VFAs)arecreated,alongwithammonia,carbonandhydrogensulfide,besidesother

3.2 pH

3.FACTORS AFFECTINGANAEROBIC CO DIGESTION

The temperature has a big impact on microbial communities,interferingintheprocessstability,microbial growth,therateofsubstrateutilization,andproductionof biogas [24]. In anaerobic digesters, four temperature schemescanbeemployedtoproducebiogas[25] [27]:(1) psychrophilictemperaturesrange(10 20°C)withoptimum at25°C;(2)mesophilictemperaturesrange(20 45°C)with thermophilic65°C)optimumat35°C;(3)thermophilictemperaturesrange(50withoptimumat55°C;and(4)extremelytemperaturesrangebetween65and70°C.

 Hydrolysis: Extracellular enzymes that convert carbohydrates, lipids, and proteins into sugars, long bychainfattyacids(LCFAs),andaminoacidsaresecretedhydrolyticbacteria.

Thebiologicalandchemicalreactionsoccurmoreslowly under psychotropic conditions [28], while underneath thermophilic conditions, the metabolic rate of microorganisms increases. Hence, thermophilic temperatures are commonly utilized in large scale biodigesters [25], [26]. Also, thermophilic temperatures guaranteethatpathogensbedestroyedatafasterrate[29]. However, using high temperatures needs higher energy costs, increased process control to ensure a uniform and stabletemperatureinsidethebiodigester[25].

3.4 C/N Ratio

technologyoptsubstrate((temperature,components.BiomassismadeupofavarietyofbiologicalandinorganicChemicalcomposition,operationalparameterspH,retentionduration,CarbontoNitrogenC/N)ratio,loadingrate,etc.),biodegradability,andcharacterizationareallimportantfactorsinimizingtheAcoDprocessofbiogasgeneration.

2. BIOCHEMISTRY OF ANAEROBIC DIGESTION

The perfect pH range for AD is very limited, usually ranging between 6.8 and 7.2 [30], Depending on the substrate utilized in the process as well as the digesting technique used [31]. The growth rate of methanogenic phaseprocesswhichbiodegradationFurthermore,ofabacteriaisdecreasedinconditionswithpHbelow6.6,whileveryalkalinepH(around8)mayleadtothedisintegrationmicrobialgranulesandsubsequentfailureoftheprocess.inmostcasesinvolvinghighalkalinity,theprocessproducesbicarbonatealkalinity,neutralizestheaciditycreatedbythebiodegradation[32].Therefore,anidealpHforthemethanogenicisusuallyaround7[30]

3.3 Retention Time

Hydraulic retention time (HRT) is the required time it thermophilicmesophilicsubstrateHRTtimetakesfortheorganicmattertocompletelybreakdownortheinwhichtheorganicmaterialstaysinthebiodigester.isaffectedbytheprocesstemperatureandthetypeoftobedigested[26].Usually,theHRTforschemesvariesfrom10to40days,whileforschemesthetimeisshorter,14days[26].

organicWhenactivityaccumulationnitrogen,methanogenesiscontentcarbon,steadytheorganicanaerobicthetheADprocesssincethetype,availability,andcomplexityofsubstrateallinfluencetheADrate[24],[26].Inthedegradationprocess,nitrogenmoleculesfromwastearetransformedintoammonia.Nitrogen,informofammonia,helpstokeepthepHofthemediumduringtheprocess[24].AhighC/NratioindicatesthatthematerialisrichinwhilealowC/Nratioindicatesthathighproteinisavailable[25].IftheC/Nratioishigh,themicroorganismsquicklyconsumetheresultinginlowergasproduction,whileanofammoniaoccursiftheratioislow.Theofmethanogenicbacteriaisnegativelyaffectedthemediumisalkaline(pH>8.5)[26].ForADofwaste,theC/Nratioshouldbebetween20and25

International Research Journal of Engineering and Technology (IRJET) e ISSN: 2395 0056 Volume: 09 Issue: 03 | Mar 2022 www.irjet.net p ISSN: 2395 0072 © 2022, IRJET | Impact Factor value: 7.529 | ISO 9001:2008 Certified Journal | Page284 ousingaccordingto[25].ThemaximumbiogasproductionachievedaC/Nratioof31[33],whileanotherstudystatedanptimumC/Nratioof28fortheproductionofbiogas[34].

4.1

biogasinconcentrationevolvesreleasecyclesusinbiogasvaryingmixingrecirculatedmixing,[38].hydrogenmethanogenictransfesyntrophicExcessivereleasefloatsedimentation,InadequatehydraulicWhenoperatingatahighorganicloadingrateandashortretentiontime,ADmixingbecomescritical.mixingappearstocausesignificantfoaming,scumming,andfrothingmaterialstoonthedigester'stopliquidsurface,obstructingtheofbiogasfromtheADliquid[36].Ontheotherhand,mixingintensitycausesthejuxtapositioningandbacterialinteractionsofinterspecieshydrogenrbetweencloselyattachedflocsofacetogenicandgranulestobreakdown,loweringthepartialpressureandnegativelyaffectingAD[37],Theimpellerorpropeller,oragitatorbasedmechanicalslurryrecirculatedhydraulicmixing,andbiogaspneumaticmixingarethethreetypesofADmodesused.Numerousresearchershavestudiedresultsabouttheeffectofthemixingmethodonyield.ThedigestibilityofHSADhasbeenenhancedbygperiodicmixingfollowedbywaitingasintermittentandattributedanoptimumconditionforbacteriatothebiogas[38].ItisstatedthattheroleofmixingmoresignificantlywithanincreaseinhighrateTSinthefeedslurrybecausethebiogasproducedthemixeddigesterisapproximately15%morethantheproducedfromtheunmixeddigester[39].

Methane production was found to be improved significantlybyincreasingthefractionofFWinSS,making cleartheimportanceoftheco digestionapproach.However, thereisalimitationtowhichaddingFWtoSScanleadtoan improvementinmethaneproduction.IftheFWisaddedto SSbeloworabovetheoptimummixingratiowhichdiffers fromonesystemtoanother,thedigestionperformancecan whenSS[55]completebelimitedandthereforedecreaseCH4production,orcauseafailurebecauseofinstabilityinthesystem[41],[57].Forhighermethaneproduction,differentratiosofFWandwerecodigestedinpriorresearch.AstudyfoundthattheFWandSSmixingratiois1:4,thehighestCH4

Theanaerobicdigestionandproductionofmethanecan be influenced by the amount of moisture content in the feedstock. Fujishima reported that the produced methane yield was reduced from 330 to 280 mL/g VSS when the moisturecontentreducedfrom97to89%ontheAD[35]. Thisindicatesthatanoptimumlevelofmoisturecontentis essentialfortheanaerobicdigestionprocess.

Moisture Content in Feedstock

[46].percthehazardousofyears,digestionofFWandSShasbeenwidelyusedinrecentwithnumerousresearchershighlightingthebenefitsenhancedmethane(CH4)generationanddilutionofchemicals[40][43].Duetopopulationincreaseandgrowinglivingstandards,generationrateofMSWisgraduallyincreasingby23enteveryyearamongthevariouswastesources[44]TheFW,whichrepresentsraw/cookedfooditems

LCH4 g−1 VS), because of the enhanced C/N ratio [59]. Regardless of the substrate ratio, micronutrients biogaswithbyimprovesDuringwassupplementation,eitherdirectlyorthroughleachatesources,foundtobeusefulforimprovedprocessefficiency.monoandcodigestionofFW,ironsupplementationprocessstabilityandrateofmethaneproduction1839%,accordingtoseveralstudies[60],[61].Accordingtoabiomethanepotentialassay,FWcombinedsludgeina1:2(VS)ratioproducedthemaximumof823mlgVS

methanogens.levels,process,theresultsnutrit30,optimumeconomicallyratiofromenhancedhasdifferentkeytheafter/beforemealpreparationinhouseholds,aswellasfrommanufacturing/productionandfoodservicesectors,isacomponentofMSWthatvariesfrom20to50percentinnations[47].Ingeneral,FWhasahigherC/Nratio(11.136.4),butSSalowerC/Nratio(69)andbymixingitcanbetoarangeof615[48].ThemethaneproductiontheadditionofFWtoSSdigestersenhancestheC/Nandkineticreaction,makingAcoDoperationsbothandpracticallypossible[10],[49][52].TheC/Nratiofordigesterperformanceisaround20andC/Nratioshigherthan30upsetthedigesterduetoionaldeficiency,whichaffectsmicrobialactivitiesandinadecreasedsubstrateremovalrate.However,ifC/Nratioislessthan6,ithasaharmfulimpactontheresultinginlowcarbonlevelsandhighammoniainhibitingthegrowthofhydrogenotrophic[10],[48],[53],[54].

yieldis215mLCH4g−1VS,whichis85.3%morethanthe mono digestionofFWalone[58].The1:1mixingratio(v/v) menhancedofOFMSW(particularlyFoodWaste)andSewageSludgealsotheproductionofmethaneby47.2percent(365

1 (21days)witha60%methane[62]. Marcelo et al., (2017) studied the co digestion of FW and primary sludge (PS) under thermophilic (55 :C) and mesophilic(35:C)conditions.TheoptimumFW:PSmixing ratio was 1:2 (VS) with an HRT of 21 days that obtained maximumspecificmethaneof270and205mlCH4/gVSat thermophilicandmesophilicconditionsrespectively[63].

4.ANAEROBIC CO DIGESTIONOF FOODWASTEAND SEWAGE SLUDGE Mixing Strategies

4.3 Effect of FW to SS Mixing Ratios

3.5

4.2 Benefits of Food Waste as A Co Substrate Co

4.4 Pre-treatment Strategies to Improve the Anaerobic Co Digestion improvealongintosconsideredbiologicalstabilizationAnaerobicdigestionneedsamuchlongerdurationfortheoftheorganicbecauseitisslowerthanaerobicdigestion.TheratelimitingstepoftheADistobethehydrolysisstepbecausethesubstrateurfaceadsorbsthehydrolyticenzymesandconvertthemsmallermoleculesforadditionaldegradationintoVFAwithadditionalbyproducts[66],[67].Inordertohydrolysis,severalpretreatmentshavebeen

International Research Journal of Engineering and Technology (IRJET) e ISSN: 2395 0056 Volume: 09 Issue: 03 | Mar 2022 www.irjet.net p ISSN: 2395 0072 © 2022, IRJET | Impact Factor value: 7.529 | ISO 9001:2008 Certified Journal | Page285 Mata Alvarezetal.(1990)studiedthemesophilic(35:C) anaerobicco digestionofa50:50mixtureofOFMSWandSS thatproducedthemaximumbiogasof0.36m3CH4kg 1VS 1 2.80attheHRTof14.5dayswithanorganicloadingrate(OLR)ofkgVSm 3d 1[23].Accordingtothethermophilic(55:C)

Moreover, pre treatment improved not only anaerobic reportedtreatmentswasteMenononfueldigestionbutalsothegenerationofelectricityinamicrobialcell[88]whichstudiedtheheat/alkalipretreatmentsdifferentwastewatersludge.Also,Maetal.[78]andetal.[89]useddifferentpretreatmentsonfoodforAD.However,themixedimpactofdifferentpreandcodigestiononWASandFWhasnotbeentothebestofourknowledge,althoughseveral

anaerobic co digestion performed by Del Borghi et al., (1999), OFMSW mixed with SS in a 50%:50% (VS) ratio producedthemaximumbiogasof.36m3kg 1VS 1(12days) witha64%methane[64].

Theanaerobicco digestionistheintegratedtreatmentof different wastes with various characteristics. Substrates consideredhydrolysisthecausedAcoDcomplicateddependshavedifferentpotentialenergyandcharacteristics,andthisontheiravailabilityandnature,soitisdifficultandtoselecttheappropriatesubstratesforAcoD.improvementmechanismshaveobservedissuesbythefeedstockcharacteristicsofthedigesterandstepsofhydrolysis[93],[94].SeparateratesofforeachparticulatecomponentshouldbeseparatelyintheAcoDprocessastheratesof

5. CHALLENGES OF FOOD WASTE CO-DIGESTION WITH SEWAGE SLUDGE

studies showed improved AD efﬁciency using various combinations of either FW with additional wastewater sludgeandviceversa[90] [92].

hydrolysisvarysigniﬁcantly.

highamountsbecomesinstability,productionmainTherefore,whilechoosingsubstratesforAcoD,C/NisonefactorinincreasingtheAcoDperformanceintheofbiogas.TheC/Nratiocausesprocesssystemfailure,andbiogasreductionwhenitlowerorhigherthantheoptimumvalue.LargeofVFAsproducedbythecosubstrateswiththeC/NratioduringtheAcidogenesisprocessbutthose

withlowC/Nratiohavehighbuﬀercapacityandduringthe Acidogenesis process, the ammonia increases. Also, the emissionsofN2OdependontheC/Nratio[100].AstheC/N ratio reduces, the emissions increase, and when the C/N increasestheemissionsdecrease.

WhencomparedtoSSmono digestion,theSS:FWratiosof thewith0.50:0.50showedsignificantlyincreasedmethanerecovery,themethaneproductivityincreasingby4.59timesandrateofhydrolysisincreasingby3.88times[65].

studied to enhance the efficiency of digestion of waste by differentchemicaltreatmentasandAcoD,electricalincludinghydrolysistreatmentchemicalhydrolysistreatmentmethaneinitialinfluencingimprovingthesolubilizingdecomposableorganicsubstancesanddecreasetimerequiredtotheoverallprocessingAD[68],[69].EffectivepretreatmentofbothsubstratesisessentialformethanerecoveryfromAcoDofFWandSS.BycrucialprocessparameterslikeOLRandHRT,feedcharacteristicscontrolthewholeprocessandproduction.HydrolysisisacriticalphaseintheofhighlyorganicwasteslikeFW,anditsishighlydependentonFWpropertiessuchascompositionsandparticlesize.Numerouspretreatmentshavebeendocumentedtoimproveefficacyforincreasedbiogasproduction,biological,chemical,physical,thermal,andmethods[46],[70][77].ForFWtreatmentpriortoavarietyofpretreatmenttechniqueswerestudied,highermethaneyieldswereproduced[46],[76][80].Inrecentyears,severalpretreatmentshavebeenstudiedthermalpretreatment[78],thermochemicalpre[81],ultrasonicpretreatment[82],[83],andpretreatment[84].Numerousstudiesutilizedpretreatmentstoimprovebiogasproductionand solubilization by using either specific FW or sludge [58], [66], (ultrasonicpreFurthermore,[85].manystudieshaveusedsingleorcombinedtreatmentlikechemical,ultrasonic,orcombinedwiththermal/chemicalonwasteactivatedsludgeWAS) and other wastes that are difficult to compare the efficacyofthepre treatments[83],[84],[86],[87],andfew studiesreportedmultiplepre treatmentsonWAS[58],[85].

uﬃcient to fulfill predictableenergyrequirements[97] [99].

rangingAnaerobicnitrogennutritionalfundamentalproducingcosubstratescharacterizationdigestedseparatingThebiogasproductionoptimizationwasmadepossiblebythecharacterizationandphasingofthecosubstratehydrolysis[95],[96].Asaresult,ofthevariouschemicalcompositionsofisusefulindecidingwhichsubstratestousefordigestionandpredictingtheentireAcoDprocessforbiogasusingamathematicalmodel.Thelimitationofanimalbyproductsistheimbalance,particularlythelowcarbontoratio,whichreducesmicrobialactivity.ThedigestionisstableattheoptimumoftheC/Nratiobetween2030,whichiss

ACKNOWLEDGEMENT

Becauseofthehighvariabilityoffoodwaste,co digestion offoodwastewithsludgemaybelimited.Thecomposition of food waste added to sewage sludge affects digestion performanceandchangingitmightinduceinstabilityinthe anaerobic population and, as a result, in the digestion process[101],[102].

eachWastescriticalAcoD,mixinganaerobicyears.halfmostAtdrawbacksisproperties.thevarietyAnaerobicprocessdecreasescontent,tostabilityrequiredAlthoughfromitBecauseitisarenewableenergysourcewithlowemissions,appearstobetheidealwastemanagementalternativeaneconomic,social,andenvironmentalstandpoint.amorethoroughknowledgeoftheprocessistoensuretheappropriatedevelopmentandofthemicrobialdegradation.Addingthefoodwastesewagesludgeanaerobicdigestersincreasesthenutrientweakensinhibitors,improvesthealkalinity,theformationofammonia,andenhancesthestability.digestionisaviablecommercialoptionforaofwastes.However,thereareseverallimitationstoanaerobicdigestionofsinglesubstratesduetosubstrateAnaerobiccodigestionoftwoormoresubstratesaviableoptionforovercomingthemonodigestionandincreasingtheeconomicviabilityofaplant.themoment,anaerobiccodigestioncanbeconsideredthesignificanttopicwithinanaerobicdigestionresearch,asofthepublicationshavebeenpublishedinthelasttwoTheaimofthispaperistopresentareviewofthecodigestionwithafocusonthemixingratios,strategies,andchallengeswithinthelastyears.InhigherbiodegradabilityandvariabilityofFWarechallenges.TominimizethechallengesofFoodforincreasingmethaneproduction,optimizationforsubstratecombinationandadequatepretreatmentare

[9] S.Esteves,“EnvironmentandSustainabilityCommittee E&S(4) 09 12 paper 1 Inquiry into energy policy and planninginWales EvidencefromWrittenEvidenceTo BeConsideredAsPartoftheInquiryIntoEnergyPolicy andPlanning in WalesAnaerobic Digestionin Wales,” 2012.

[5] N.Patha,“Chapter IVBIO GASTECHNOLOGYININDIA,” 2014. Accessed: Jul. 05, 2015. [Online]. Available: 598/14/14_chapter4.pdfhttps://shodhganga.inflibnet.ac.in/bitstream/10603/25

and

ThelightmetalionsareveryimportantinAnaerobicco digestionperformance.Itsconcentrationplaysanessential accumulatipointsubstratebiogas.toimportantADtoxicpopulationcompoundberoleinthesmoothperformanceoftheprocessbecauseitcanthemostpotentcauseoftoxicityinAD.Whenacausesanegativechangeinthemicrobialorbreaksbacterialgrowth,itcanbedefinedasorinhibitory[14].Thelightmetalionsincreasedintheduetotheincreaseofthefoodwastefraction,soitisverytomixthefoodwastewiththeoptimummixtureprotectthedigestionandgenerateahighamountofThechallengesofchoosingthefoodwasteasacowiththesewagesludgearenotstoppedatthisbutalsotheadditionofFWtoSSresultsinaninitialonintheconcentrationofVFAsbecauseofthe

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6. CONCLUSIONS

ADandAcoDseemtobereliableandpossiblesolutionsand technologiesforrecovering recyclingbothSSandFW.

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Praise and thanks be to Almighty ALLAH with whose gracioushelpthiswork was accomplished.Iwouldliketo expressmydeepgratitudetomysupervisorsintheFaculty ofEngineering,BenhaandZagazigUniversities;Prof.H.A. encouragementwife,Finally,forR.Fouad,Assoc.Prof.A.M.AboulFotohSalemandAssoc.Prof.M.Elhefny,attheEnvironmentalEngineeringDepartment,theirsincereguidance,encouragement,andhelp.Iwishtoexpressmygratitudetomymother,mymysons,andmysistersfortheircontinuoustocompletethiswork.

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