ANAEROBICWASTEWATERTREATMENTMICROBIOLOGY

ANAEROBICWASTEWATERTREATMENTMICROBIOLOGY

AnaerobicWastewaterTreatmentMicrobiology

A.AnaerobictreatmentoforganicmaBer‐AnaerobicdigesEon1.IntheabsenceofO2,organicmaBerisfermentedtocarbondioxideand

methane: 2CH2O‐‐‐‐‐‐‐‐>CH4+CO2

2.Morethan75%oftreatmentplantsintheUSuseanaerobicdigesEontoreducethesludgeyields,alsoenergyproduced.Sludge[thoughlessofit]issEllproduced.SomefaciliEesburnthesludge(costly),whileotherhaulitaway,e.g.landfillcover,off‐shoredumpsite,landapplicaEonof'biosolids'.

3.Alsouseddirectlyfortreatmentofmunicipalwastewater,mostlyinEurope,andforagriculture/farmwastes.InaddiEon,inEurope,usedforhighorganicindustrialwastes(e.g.canning/foodwastes).

4.GeneraEngenergyfromrefuse,20yrsagoenergycrisis‐fromfastgrowingplants,e.g.kelp;againbeingconsideredbyUSDA,DOE.

5.Municipalsolidwasteis60‐70%organicorcarbonbased.IfalltherefuseintheUSwereputintomethanedigesters11‐15%oftheenEreUSenergyconsumpEoncouldbesaEsfied.

B.Anumberofanaerobicprocessdesignsaredescribedintheliterature.VariaEonsaredesignedtolargelytoimprovetheoperaEonoftheprocess.

1.ConvenEonalflowthroughprocess θ=θc=6to30days

2.Anaerobiccontactprocess θ=0.5severaldays

3.Anaerobicfilter θ=fewhours,θc=~100days

4.Upflowanaerobicsludgeblanket(UASB) Anaerobicfluidizedbed(lowstrengthwastewater)

Allofthesecanseparatethehydraulicreten.on.mefromthecellreten.on.me.ThisismoreimportantwhentheprocessisbeingusedforwastetreatmentratherthanwhenitisusedforsolidsorsludgereducEon.

θ =1/D=V/F

θ  =hydraulicdetenEonEme

θ c=celldetenEonEme

1.ConvenEonalflowthroughprocess θ=θc=6to30days

2.Anaerobiccontactprocess θ=0.5severaldays

orACTIVATEDSLUDGE

3.Anaerobicfilterθ=fewhours,θc=~100days ‐simplest ‐verystable ‐relaEvelylowefficiency ofCODremoval ‐clogging,channeling

4.Upflowanaerobicsludgeblanket(UASB)Anaerobicfluidizedbed(lowstrengthwastewater)

5.  Thinfilmbioreactor(preferredforindustrialwastes)

Allthesetreatmentdesignsseparateθ fromθc

‐ biofilmonsand‐ goodcontactwithwaste‐ noclogging‐ hibiomass‐ shortθ ‐ highenergyreq.

C.Disadvantagesoftheanaerobicprocess‐almostallarerelatedtotheslowgrowthrateofanaerobicdigestercommuniEes,

e.g.Ksforaerobictreatmentsystems=1to20mg/L Ksforanaerobictreatmentsystems=200‐400mg/L

1.  LongdetenEonEme,14‐30days‐therefore,needalargerreactor–costfactor.

2. Longstart‐upperiod,uptoseveralmonths

3. HighsensiEvitytovaryingwasteloads,toxicinputs,adjustsveryslowly

4.  Hence,upsetsrequireverylongEmeforrecovery.

5. ProcessisverysensiEvetopH,cannotdropbelow6.2

6. OpEmumat85‐95°F,mayneedheaEng.

D.  Advantagesoftheanaerobicprocess(gotonextslide)

1.Loweryieldofbiologicalsolids(sludgeyield),e.g.Y=dx/‐dS

ae=equiv.cellsformed/equiv.e‐donorconsumed aerobic anaerobic ___ glucose 0.79 0.27 acetate 0.58 0.06 domesEcwaste 0.5 0.1 e.g.withoutoxygen,lessenergyavailable,lesscellssynthesized,butitalsomeanslesssludgetodisposeof.

Whatisadisadvantageforthecellisanadvantageforthedesignedprocess.

MICROBIALLY MEDIATED OXIDATION-REDUCTION REACTIONS

Electron donor reactions

glucose C6H12O6 }

benzene C6H6 } CO2 + H2O (+ cells)

toluene C7H8 }

xylenes C8H10 }

2.Higherdegreeof'wastestabilizaEon',e.g.highermineralizaEon,e.g.higherCOD,BODremoval,e.g.highertransformaEonfromtheorganictotheinorganic.

C10H19O3N+4.7H2O‐‐‐‐‐‐‐‐>0.145C5H7O2N+5.75CH4+2.48CO2 +0.81NH4

++0.81HCO3‐

Compareto C10H19O3N+9O2‐‐‐‐‐‐‐‐‐>C5H7O2N+5CO2+H2O

e.g.MostofthecarbonhasbeentransformedtoCO2andCH4,veryliBleremainsin theorganicform. Overallwithanaerobicprocesses80‐90%ofthewasteisconvertedtogasor inorganicformandis'stabilized'. IntheaboveequaEon,morethan90%isconvertedcomparedto50%inaerobic process.

3.lowerN&Prequirementsincelowercellyield

4.Nooxygenrequirement,therefore,noneedtoaerate,notlimitedbyoxygen transfer,importantreducEonincost. Note:mixinginanaerobicunitistokeepcellsmixed,whilemixingin aerobicunitsismuchmorevigorousinordertodeliveroxygen.

5.ProducEonofausefulproduct,fuel‐methane,usedtoheatandrundigester.

ConceptualModel(firstdescribedbyPerryMcCarty)

CO2,H2

1.  facultaEvemicrobes2.  nowastestabilizaEon3.  relaEvelyrapidprocess4.  co‐dependency

1.  anaerobes2.  relaEvelyslowprocess3.  ratelimiEngpartofprocess4.  co‐dependency

Thisisaconceptualmodel,andnotanactual2stepprocess.

HCOO-

CH3OH

CH3NH2 CH3COO-

Tracingthesourceofmethaneinananaerobicdigester

XCO2,H2formate

methanol,formatemethylamine,CO2,H2

DescripEonofoverallprocessofanoxicdecomposiEon

• Firstdescribedinanaerobicdigesters30yrsearlierbyanenvironmentalengineer

• Thisisthesameconceptualmodel

• Methanogensonlyuseacetate&singleCcompounds

• AcetateisoneofthemostimportantC‐sourcesinanoxichabitats

• Methanecannotcomefrompropionate

• Methanecanaccountfor30‐80%ofCfixedthroughprimaryproducEvityinfreshwaterenvironments

4.Methanebacteria‐alotwasknownaboutthembeforetheywereseparatedintotheirowndomain a)verysensiEvetoO2,ox‐redpotenEal<‐300mV b)sensiEvetopH,opEmum=6.6‐7.6.Below6.2digesterwilldie. Hence,organicacidscannotgettoohigh. c)slowgrowth d)limitednumberofspeciesandtheirlimitednumberofsubstrates

5.Sourceofmethane a)methylgroupcleavage *CH3COOH‐‐‐‐‐>*CH4+CO2 acetate 4CH3OH‐‐‐‐‐>3CH4+CO2+2H2Ob)CO2reducEon 4H2+CO2‐‐‐‐‐>2H2O+CH4 c)frompropionate? CH3CH2COOH+4H2O‐‐‐‐‐>2HCOOH+CO2+5H2 propionate formate d)fromformate HCOOH+3H2‐‐‐‐‐>CH4+2H2O

e)  “Methanobacteriumomelianskii”illustratesclosesyntrophicrelaEonshipinterspecieshydrogentransfer

2CH2H5OH+CO2‐‐‐‐‐>2CH3COOH+CH4

Actually2reacEonsmediatedby2differentorganisms 2CH2H5OH+2H2O‐‐‐‐‐>2CH3COOH+4H2 4H2+CO2‐‐‐‐‐>2H2O+CH4

6.MoredifficulttooperateProcessismuchlessforgivingthanaerobicprocess1.Unbalancecausedbysuddenchangesintemp.,organicloading,wastecharacter.

2.Noneofthesethingsaregoodforanybiologicalprocess,butanaerobicsystemsis muchlessforgivingandmoresensiEvetochangebecause a)ifonegroupisknockedout,amajorproporEonoftheorganismsareaffected and b)theirslowgrowthratesmeanthatitismoredifficultandslowertorecover.

3.The3parameterstomonitorare a)volaEleacidsbuildup‐formate,acetate,propionate,butyrate,etc b)pHdecrease c)hydrogenlevels