Blad1Par.Short descriptionUoMa=projected width of a gas collection platema=mixed liquor recirculation factor(-)(from nitrification zone to pre-D zone)Aa=total area occupied by apertures in a UASB reactorm2Ad=surface area of final settlerm2Admin=minimum final settler surface aream2ai,n=annualisation factor(-)AIC=annualized investment costsUS$.yr-1Alk=alkalinitymg CaCO3.l-1Alk=final alkalinity after complete decay of active sludge in aerobic digestermg CaCO3.l-1Alkd=alkalinity consumed in the aerobic digestermg CaCO3.l-1Alki=initial alkalinity concentration (aerobic digestion)mg CaCO3.l-1Alke=final alkalinity concentration (aerobic digestion)mg CaCO3.l-1Am=membrane surface aream2Amod=membrane surface area in a modulem2Ao=overflow area in UASB reactorm2ath=specific thickener surface aream2.d.kg-1 CODAth=thickener surface aream2Au=surface area of UASB reactorm2Aumin=minimum UASB surface aream2b=projected height of a gas collection platemban=anaerobic decay rated-1bh=decay rate for heterotrophic bacteria (non bio-P)d-1bhT=decay rate for heterotrophic bacteria (non bio-P)d-1at temperature TBn=mass balance recovery factor for nitrogenous material(-)bn=decay rate for nitrifiersd-1Bo=mass balance recovery factor for COD(-)BODvss=BOD value of a unit of organic sludge (aerobic digestion)mg BOD.mg-1 VSSBp=mass balance recovery factor for phosphorus(-)bp=decay rate of bio-P organismsd-1bv=apparent decay constant of heterotrophic bacteria (non bio-P)d-1Cae=unit construction costs of aeration systemUS$.kW-1Cd=unit volume construction costs of final settlerUS$.m-3Cd1=unit volume construction costs of the primary settlerUS$.m-3Cda=unit volume construction costs of aerobic digesterUS$.m-3Cdi=unit volume construction costs of anaerobic digesterUS$.m-3Cdl=costs of discharge to sewer (levies)US$.PE-1Cel=price of electricityUS$.kWh-1Cgen=unit construction cost of power generationUS$.kW-1Ch=costs of heating (e.g. with gas or oil)US$.m-3 gas orUS$.kg-1 fuel[CH4]eq=equilibrium methane concentrationmg CH4.l-1cp=proportionality constant between stirred and diluted(-)sludge volume indexCr=unit volume construction costs of the aeration tankUS$.m-3Cr=specific active biomass production per unit mass daily applied biodegradable CODmg VSS.d.mg-1 CODCrh=specific active biomass production of heterotrophic organisms per unit mass daily applied biodegradable CODmg VSS.d.mg-1 CODCrn=specific active nitrifiers production of per unit mass of daily applied nitrogenmg VSS.d.mg-1 NCrp=specific active biomass production of bio-P organisms per unit mass daily applied biodegradable CODmg VSS.d.mg-1 CODCsd=costs of sludge disposalUS$.ton-1 TSSCth=unit volume construction costs of a sludge thickenerUS$.m-3Cu=unit volume construction costs of a UASB reactorUS$.m-3Dc=denitrification capacitymg N.l-1 influentDc1=denitrification capacity in pre-D zonemg N.l-1 influentDc1p=denitrification capacity from utilization of easilymg N.l-1 influentbiodegradable CODDc1s=denitrification capacity from utilization of slowlymg N.l-1 influentbiodegradable CODDc3=denitrification capacity in post-D zonemg N.l-1 influentDcd=denitrification capacity in the final settlermg N.l-1 influentDd=diameter of final settlermDOav=average oxygen concentration during OUR testmg O2.l-1DOl=oxygen concentration in the liquid phasemg O2.l-1DOm=oxygen concentration measured by oxygen sensormg O2.l-1DOmt=oxygen concentration in the membrane tankmg O2.l-1DOs=saturation concentration of dissolved oxygen in the mixed liquor at pressure pmg O2.l-1DOs20=saturation concentration of dissolved oxygen at 20Cmg O2.l-1DOsa=saturation concentration of dissolved oxygen under actual conditionsmg O2.l-1DOsp=saturation concentration of dissolved oxygen at standard pressuremg O2.l-1DOss=saturation concentration of dissolved oxygen at 20C and 1 atm (9.1 mg.l-1)mg O2.l-1DOsT=saturation concentration of dissolved oxygen at temperature Tmg O2.l-1f=fraction of the influent flow discharged to the first reactor in step feed systems(-)f=endogenous residuemg VSS.mg-1 VSSF=fouling factor(-)F=solids fluxkg TSS.m-2.d-1F/P=feed to permeate ratio(-)fa(N-1)=active sludge fraction in the sludge entering the Nth digestermg VSS.mg-1 VSSfac=fraction of construction costs required for construction of additional (non-specified) unitsmg VSS.mg-1 VSSfae=active sludge concentration in aerobic digestermg VSS.mg-1 VSSfaer=aerobic sludge mass fractionkg TSS.kg-1 TSSfai=initial active sludge concentration (aerobic digestion)mg VSS.mg-1 VSSfaN=active sludge fraction in the sludge leaving the Nth aerobic digestermg VSS.mg-1 VSSfan=anaerobic sludge mass fractionkg TSS.kg-1 TSSfat=active fraction of sludgemg VSS.mg-1 TSSfav=active fraction of organic sludgemg VSS.mg-1 VSSfav1=active fraction of organic sludge from primary settlingmg VSS.mg-1 VSSfav2=active fraction of organic sludge from activated sludge systemmg VSS.mg-1 VSSfave=active fraction of organic stabilised sludgemg VSS.mg-1 VSSfbh=fraction of Sbi consumed by normal heterotrophic biomassmg COD.mg-1 CODfbp=fraction of Sbi sequestered by bio-P organismsmg COD.mg-1 CODfbp=slowly biodegradable (particulate) COD fraction in the raw wastewatermg COD.mg-1 CODf'bp=slowly biodegradable (particulate) COD fraction in the pre-settled wastewatermg COD.mg-1 CODfbpu=biodegradable particulate fraction of organic CODmg COD.mg-1 CODin anaerobic effluentfbs=easily biodegradable (soluble) COD fraction in the raw wastewatermg COD.mg-1 CODf'bs=easily biodegradable (soluble) COD fraction in the pre-settled wastewatermg COD.mg-1 CODfbsh=fraction of Sbsi consumed by normal heterotrophic bacteriamg COD.mg-1 CODfbsp=fraction of Sbsi sequestered by bio-P organismsmg COD.mg-1 CODfbsu=biodegradable soluble fraction of organic COD in anaerobic effluentmg COD.mg-1 CODfcv=proportionality constant between bacterial mass and mass of CODmg COD.mg-1 VSSfd=activity factor for a bivalent ion(-)fdn=denitrification constant = (1 - fcvY)/2.86(-)fep=endogenous residue of bio-P organismsmg VSS.mg-1 VSSfh2s=inorganic H2S-COD in UASB effluent expressed as fraction of influent CODmg COD.mg-1 CODfh2su=inorganic H2S-COD fraction in anaerobic effluentmg COD.mg-1 CODfi=additional investment costs (non-construction related)(-)Fl=limiting solids fluxkg TSS.m-2.d-1Fm=membrane fluxl.m-2.h1fm=maximum anoxic sludge fraction allowed form3.m-3selected sludge age (when Nae = Nad)fm=activity coefficient for a monovalent ion in the mixed liquor(-)fmax=maximum allowed anoxic mass fractionm3.m-3fmi=mineral fraction influentmg ISS.mg-1 CODfn=nitrogen fraction in organic biomassmg N.mg-1 VSSf'np=inert particulate COD fraction after primary settlingmg COD.mg-1 CODfnp=inert particulate influent COD fractionmg COD.mg-1 CODfnpu=inert particulate fraction of COD in anaerobic effluentmg COD.mg-1 CODf'ns=inert soluble COD fraction after primary settlingmg COD.mg-1 CODfns=non biodegradable, soluble influent COD fractionmg COD.mg-1 CODfnsu=non biodegradable, soluble COD fraction in anaerobic effluentmg COD.mg-1 CODfp=phosphorus fraction in organic biomassmg P.mg-1 VSSfpd=fraction of bio-P organisms capable of denitrification(-)fpp=maximum poly-P fraction of bio-P organismsmg P.mg-1 VSSfpr=phosphorus release constantmg P.mg-1 CODfpu=putrescible fraction of anaerobic sludgemg VSS.mg-1 VSSfr=average frequency of exposure at the chlorine injection pointd-1Fs=applied solids load (drying beds)kg TSS.m-2f'sb=fraction of biodegradable COD that is easily biodegradable remaining after primary settlingmg COD.mg-1 BCODfsb=fraction of biodegradable COD that is easily biodegradablemg COD.mg-1 BCODFsol=solids loading ratekg TSS.m2.d-1Ft=total solids flux in final settlerkg TSS.m2.d-1Fu=solids flux due to sludge abstractionkg TSS.m2.d-1fv=organic sludge fraction = ratio between volatile and total sludge concentrationmg VSS.mg-1 TSSFv=solids flux due to sludge settlingkg TSS.m2.d-1fve=organic sludge fraction in stabilised sludgemg VSS.mg-1 TSSfvp=organic sludge fraction of bio-P organismsmg VSS.mg-1 TSSfvu=organic sludge fraction anaerobic sludgemg VSS.mg-1 TSSfx=total anoxic sludge mass fractionkg TSS.kg-1 TSSfx1=pre-D anoxic sludge mass fractionkg TSS.kg-1 TSSfx3=post-D anoxic sludge mass fractionkg TSS.kg-1 TSSfxd=sludge mass fraction located in final settlerkg TSS.kg-1 TSSfxvd=fraction of final settler volume filled with sludgem3.m-3g=gravitational acceleration constantm.s-2h=liquid height above base of V-notch or above perforationmH1=thickener inlet zone / thickening zone (ATV)mH2=thickener clarification zone / sludge storage zone (ATV)mH3=thickener compression zone / separation zone (ATV)mH4=thickener sludge removal zone / clear water zone (ATV)mHd=height of final settlermHdav=average depth of final settlermHdb=height of the sludge buffer zonemHdf=deflector heightmHdif=level of air diffusers above reactor bottommHdig=height of digestion zone in UASB reactormHfb=height of freeboard of UASB reactormHgb=liquid height of gas boxmHgls=liquid GLS heightmHliq=liquid height UASB reactormHth=height of sludge thickenermHu=total height of UASB reactormi=interest rate%I=investment costsUS$Idsv=diluted sludge volume indexml.g-1 TSSIssv=stirred sludge volume indexml.g-1 TSSk=Vesilind constantl.g-1 TSSK1=rate constant for denitrification on easily biodegradablemg N.g-1 Xa-VSS.d-1organic materialk1=equilibrium constant for CO2 dissociationmol.l-1k1*=real equilibrium constant for CO2 dissociation,mol.l-1corrected for ionic activityK2=rate constant for denitrification on slowly biodegradable organic materialmg N.g-1 Xa-VSS.d-1k2=equilibrium constant for bicarbonate dissociationmol.l-1k2*=real equilibrium constant of the bicarbonate dissociation, corrected for ionic activitymol.l-1K3=rate constant for denitrification due to endogenous respirationmg N.g-1 Xa-VSS.d-1Ka=adsorption rate constantlitre.mg-1 Xa.d-1kabs=adsorption constanth-1Kap=adsorption saturation constantmg COD.mg-1 XaKc=fermentation constantl.mg-1 Xa-VSS.d-1Kh=Henry constantatm or mg.l-1.atm-1kla=oxygen transfer coefficienth-1klaa=oxygen transfer coefficient under actual conditionsh-1klas=oxygen transfer constant at 20Ch-1klaT=oxygen transfer constant at TCh-1Km=specific utilisation rate constantmg COD.mg-1 Xa.d-1Kmp=specific utilisation rate of slowly bio-degradable (adsorbed) organic materialmg COD.mg-1 Xa.d-1Kms=specific utilisation rate of easily biodegradable organic materialmg COD.mg-1 Xa.d-1Kn=saturation constant for nitrifiersmg N.l-1Ko=half saturation constant for aerobic processesmg O2.l-1kr=relaxation constanth-1Ks=saturation constant (Monod)mg COD.l-1Ksp=saturation constant (Monod) for growth on slowly biodegradable, adsorbed substratemg COD.mg-1 XaKss=saturation constant (Monod) for growth on easilymg COD.l-1biodegradable substratekw=equilibrium constant for the dissociation of watermol2.l-2kw*=real equilibrium constant for the dissociation of water, corrected for ionic activitymol2.l-2Le=height of water layer remaining at end of drying periodmmLi=height of initial water layer applied to sludge bedmmLu=length of UASB reactormm=maintenance costs% of TIC per yearmciv=maintenance costs for civil part of plant% of TIC per yearMCrd=construction costs of aeration tank and final settlerUS$MCthdi=total construction costs of thickener and anaerobic digesterUS$MDc1=total pre-D denitrification capacitykg N.d-1MDc3=total post-D denitrification capacitykg N.d-1MEchem=total chemical excess sludge productionkg TSS.d-1mEd=specific digested sludge masskg VSS.kg-1 CODMEd=digested sludge masskg VSS.d-1MEmeoh=chemical excess sludge production (metal oxides)kg TSS.d-1MEmep=chemical excess sludge production (metal phosphates)kg TSS.d-1mEt=specific excess sludge production (equal to apparent yield Yap)mg TSS.mg-1 CODMEt=excess sludge productionkg TSS.d-1mEt1=specific primary excess sludge productionmg TSS.mg-1 CODMEt1=primary excess sludge productionkg TSS.d-1mEt2=specific secondary excess sludge productionmg TSS.mg-1 CODMEt2=secondary excess sludge productionkg TSS.d-1mEte=specific stabilised excess sludge productionmg TSS.mg-1 CODMEte=stabilised excess sludge productionkg TSS.d-1mEtu=specific anaerobic excess sludge productionmg TSS.mg-1 CODMEtu=anaerobic excess sludge productionkg TSS.d-1MEtx=total (secondary) excess sludge production corrected for loss of suspended solids in the effluentkg TSS.d-1mEv=specific organic sludge production (= apparent yield Yap)mg VSS.mg-1 CODMEv=volatile or organic excess sludge productionkg VSS.d-1MEv1=organic primary excess sludge productionkg VSS.d-1MEv2=organic secondary excess sludge productionkg VSS.d-1mEve=specific stabilised organic excess sludge productionmg VSS.mg-1 CODMEve=stabilised organic excess sludge productionkg VSS.d-1MEvu=organic anaerobic excess sludge productionkg VSS.d-1mEvxa=specific active excess sludge productionmg VSS.mg-1 CODmExvna=specific inactive excess sludge productionmg VSS.mg-1 CODmMd=specific methane productionkg CH4.kg-1 CODMMd=methane productionkg CH4.d-1MME=consumption of metal saltskg.d-1mme&i=maintenance costs for mechanical, electrical and instrumentation part of plant% of TICMNav1=mass of nitrate available in (i.e. returned to) the pre-D zonekg N.d-1MNd=mass of denitrified nitrogenkg N.d-1MNd1=mass of nitrate denitrified in the pre-D reactorkg N.d-1MNd3=mass of nitrate denitrified in the post-D reactorkg N.d-1MNdd=mass of nitrate denitrified in the final settlerkg N.d-1MNdp=denitrification due to consumption of slowlykg N.d-1biodegradable CODMNds=denitrification due to consumption of easily biodegradable CODkg N.d-1mNl=specific nitrogen discharge with the excess sludgemg N.mg-1 CODMNl=nitrogen removal with produced excess sludgekg N.d-1mNld=specific nitrogen release in digestermg N.mg-1 CODMNld=mass of nitrogen released in digesterkg N.d-1mNle=specific nitrogen removal due to discharge with the stabilised excess sludgemg N.mg-1 CODMNle=mass of nitrogen removed with stabilised excess sludgekg N.d-1MNlx=mass of nitrogen removed with the excess sludge corrected for the loss of organic nitrogen with the effluentkg N.d-1MNte=nitrogen load in effluentkg N.d-1MNti=nitrogen load in influentkg N.d-1MOc=oxygen demand for COD oxidation (= MSo)kg O2.d-1MOeq=equivalent oxygen demandkg O2.d-1(recovered oxygen from denitrification)MOn=oxygen demand for nitrificationkg O2.d-1MOt=total oxygen demandkg O2.d-1MPchem=mass of phosphorus removed by chemical precipitationkg P.d-1mPel=specific power productionkWh.kg-1 CODMPl=phosphorus removal with excess sludge productionkg P.d-1mPl=specific phosphorus discharge with the excess sludgemg P.mg-1 CODMPl1=mass of phosphorus removed with the primary excess sludgekg P.d-1mPle=specific phosphorus removal due to discharge with the stabilised excess sludgemg P.mg-1 CODMPle=mass of phosphorus removed with stabilised excess sludgekg P.d-1MPlex2=mass of phosphorus removed with the secondary excess sludge, corrected for the loss of organic nitrogen with the effluentkg P.d-1MPlx=mass of phosphorus removed with the excess sludge, corrected for loss of organic phosphorus in the effluentkg P.d-1MPte=phosphorus load in the effluentkg P.d-1mq1=specific primary excess sludge flow ratem3.kg-1 CODmq2=specific secondary excess sludge flow ratem3.kg-1 CODmqth=specific thickened sludge productionm3.kg-1 CODmSbu=fraction of total COD present as biodegradable CODmg COD.mg-1 CODin UASB effluentmSd=fraction of influent COD that is digestedmg COD.mg-1 CODMSd=mass of COD digested in the systemkg COD.d-1MSda=COD mass digested in UASB and emitted to atmospherekg COD.d-1mSdu=fraction of influent COD digested in UASBmg COD.mg-1 CODMSdu=COD mass digested in UASBkg COD.d-1mSe=fraction of influent COD leaving the system with the effluent (soluble COD only)mg COD.mg-1 CODmSeu=fraction of influent COD ending up as non-settleable COD in the UASB effluentmg COD.mg-1 CODMSeu=non settleable COD load in UASB effluentkg COD.d-1mSmb=fraction of influent COD metabolizedmg COD.mg-1 CODMSmb=metabolized sludge masskg COD.d-1mSo=fraction of influent COD that is oxidizedmg COD.mg-1 CODMSo=mass of COD oxidized in the system (= MOc)kg COD.d-1mSod=fraction of influent COD oxidized in aerobic digestermg COD.mg-1 CODMSseq=mass of COD sequestered by bio-P organismskg COD.d-1mSte=fraction of influent COD leaving the system with the effluent (includes particulate COD)mg COD.mg-1 CODMSte=COD load in the effluentkg COD.d-1MSti=applied COD loadkg COD.d-1MSxv=mass of COD discharged from the system in the excess sludgekg COD.d-1mSxv=fraction of influent COD discharged from the systemmg COD.mg-1 CODin the excess sludgemSxv1=fraction of influent COD leaving the system in the primary excess sludgekg COD.d-1mSxv2=fraction of influent COD discharged from the systemkg COD.d-1in the secondary excess sludgemSxve=fraction of influent COD leaving the system with stabilised excess sludgemg COD.mg-1 CODMSxve=mass of COD discharged from the system in the stabilised excess sludgekg COD.d-1mSxvu=influent COD fraction converted into anaerobic excess sludgemg COD.mg-1 CODMSxvu=COD mass discharged as anaerobic excess sludge from UASBkg COD.d-1mwmeoh=mole weight metal hydroxideg.mol-1mwmp=mole weight metal phosphateg.mol-1mwms=mole weight metal saltg.mol-1mXa=active sludge mass per unit mass daily applied CODmg VSS.d.mg-1 CODMXa=total active sludge mass in systemkg VSSMXah=total active heterotrophic sludge mass in systemkg VSSMXan=total active nitrifier sludge mass in systemkg VSSMXap=total mass of active bio-P organisms in systemkg VSSmXau=active anaerobic sludge mass per unit mass daily applied CODmg VSS.d.mg-1 CODMXau=total active anaerobic sludge mass in systemkg VSSmXbpu=non-degraded biodegradable sludge mass per unit mass daily applied CODmg VSS.d.mg-1 CODMXbpu=total mass of non-degraded biodegradable sludge mass in systemkg VSSMXchem=total mass of chemical sludge in systemkg TSSmXe=endogenous sludge mass per unit mass daily applied CODmg VSS.mg-1 COD.d-1MXe=total mass of endogenous sludge in systemkg VSSMXen=total mass of endogenous nitrifier sludge in systemkg VSSMXep=total mass of endogenous bio-P sludge in systemkg VSSmXeu=endogenous anaerobic sludge mass per unit massmg VSS.d.mg-1 CODdaily applied CODMXeu=total mass of endogenous anaerobic sludgekg VSSmXi=inert sludge mass per unit mass daily applied CODmg VSS.d.mg-1 CODMXi=total mass of inert sludge in systemkg VSSmXiu=non-biodegradable particulate anaerobic sludge massmg VSS.d.mg-1 CODper unit mass daily applied CODMXiu=total mass of non-biodegradable particulate anaerobickg VSSsludge in systemmXmu=inorganic anaerobic sludge mass per unit massmg ISS.d.mg-1 CODdaily applied CODMXmu=total mass of inorganic anaerobic sludge in systemkg VSSMXn=total nitrifier mass in systemkg VSSmXt=total sludge mass per unit mass daily applied CODmg TSS.d.mg-1 CODMXt=total sludge mass in systemkg TSSMXtba=available sludge mass storage capacity in final settlerkg TSSMXtbr=required sludge mass storage capacity in final settlerkg TSSMXtd=total sludge mass in final settlerkg TSSmXtu=anaerobic sludge mass per unit mass daily applied CODmg TSS.mg-1 COD.d-1MXtu=total mas of anaerobic sludge in systemkg TSSmXv=volatile sludge mass per unit mass daily applied CODmg VSS.mg-1 COD.d-1MXv=total volatile sludge mass in systemkg VSSMXvh=total organic heterotrophic biomass in systemkg VSSmXvu=anaerobic organic sludge per unit mass daily applied CODmg VSS.mg-1 COD.d-1MXvu=total anaerobic organic sludge mass in systemkg VSSn=economical lifetimeyearsn=number of gas boxes(-)n=insurance costs% of TIC per yearN=number of UASB reactors(-)N=number of aerobic digesters(-)Nad=desired/required effluent ammonium concentrationmg N.l-1Nae=ammonium effluent concentrationmg N.l-1Nav1=nitrate available in pre-D zonemg N.l-1 influentNav3=nitrate available in post-D zonemg N.l-1 influentNc=nitrification capacity (= nitrified ammonium concentration)mg N.l-1 influentNc/Sbi=ratio between nitrification capacity and biodegradablemg N/mg CODinfluent COD(Nc/Sbi)l=limiting ratio between nitrification capacity and biodegradable influent COD for the applicability of the Bardenpho processmg N.mg-1 COD(Nc/Sbi)o=maximum ratio between nitrification capacity and biodegradable influent COD allowing full nitrogen removalmg N.mg-1 CODNd=denitrified nitrogen concentrationmg N.l-1 influentNdd=concentration of nitrate that will be denitrified in the return sludge stream per passage through the final settlermg N.l-1Nddmax=maximum allowable production of nitrogen gas in the return sludge flow during its passage through the final settler to the abstraction pointmg N.l-1Ndp=denitrification due to consumption of slowlymg N.l-1 influentbiodegradable CODNds=denitrification due to consumption of easily biodegradable CODmg N.l-1 influentNke=effluent Kjeldahl nitrogen concentrationmg N.l-1Nki=influent Kjeldahl nitrogen concentrationmg N.l-1Nl=nitrogen concentration removed with the excess sludgemg N.l-1 influentNld=nitrogen concentration released in digestermg N.l-1 influentNle=nitrogen concentration removed with the stabilisedmg N.l-1 influentexcess sludgeNlh=nitrogen concentration removed with the heterotrophicmg N.l-1 influentexcess sludgeNln=nitrogen concentration removed with the nitrifiermg N.l-1 influentexcess sludgeNlx=nitrogen concentration discharged with excess sludgemg N.l-1 influent(corrected for loss of organic nitrogen in the effluent)NN2eq=equilibrium dissolved nitrogen gas concentration at the maximum liquid depth of the final settler, assuming an atmosphere of 100% nitrogenmg N.l-1NN2in=dissolved nitrogen gas concentration in the incomingmg N.l-1mixed liquor flowNn=nitrate concentration when decay of active sludge is complete (aerobic digestion)mg N.l-1Nnd=nitrate production in the aerobic digestermg N.l-1Nne=nitrate/nitrate effluent concentrationmg N.l-1Nni=initial nitrate concentration (aerobic digestion)mg N.l-1Nni=influent nitrate/nitrite concentrationmg N.l-1Noe=organic nitrogen in effluentmg N.l-1Noi=influent organic nitrogen concentrationmg N.l-1Nope=particulate organic nitrogen in effluentmg N.l-1Nose=soluble organic nitrogen in effluentmg N.l-1Np=nitrification potentialmg N.l-1 influent(= maximum ammonium concentration that can be nitrified)Nte=effluent total nitrogen concentrationmg N.l-1Nte,max=maximum nitrogen effluent concentrationmg N.l-1(all released nitrogen recycled to aeration tank)Nte,min=minimum nitrogen effluent concentrationmg N.l-1(no recycle of released nitrogen to aeration tank)Nti=influent Kjeldahl nitrogen concentrationmg N.l-1(Nti/Sti)l=limiting ratio between influent TKN and total influent COD for the applicability of the Bardenpho processmg N.mg-1 COD(Nti/Sti)o=maximum ratio between influent TKN and total influent COD allowing full nitrogen removalmg N.mg-1 CODo=operational costs% of TIC per yearOc=oxygen uptake rate (respiration) for COD oxidationmg O2.l-1.d-1Oen=endogenous respiration ratemg O2.l-1.d-1Oeq=oxygen recovery rate (equivalent oxygen uptake rate)mg O2.l-1.d-1due to denitrificationOex=exogenous respiration ratemg O2.l-1.d-1Oex,sbp=exogenous respiration rate due to consumption of slowly biodegradable (adsorbed) substratemg O2.l-1.d-1Oex,sbs=exogenous respiration rate due to consumption of easily biodegradable substratemg O2.l-1.d-1On=oxygen uptake rate for nitrificationmg O2.l-1.d-1Ot=total oxygen uptake ratemg O2.l-1.d-1OT4,5=oxygen transfer efficiency at 4.5 m submergence%OTa=actual oxygen transfer efficiencykg O2.kWh-1 or %Otd=total oxygen uptake rate (aerobic digester)mg O2.l-1.d-1OTs=standard oxygen transfer efficiencykg O2.kWh-1 or %OUR=oxygen uptake ratemg O2.l-1.h-1OURa=apparent OURmg O2.l-1.h-1OURabs=rate of change of oxygen concentration in reactor due to hydraulic effectsmg O2.l-1.h-1OURen=endogenous respiration ratemg O2.l-1.h-1OURh=rate of change of oxygen concentration in reactor due to adsorption of atmospheric oxygenmg O2.l-1.h-1OURm=maximum oxygen uptake rate due to nitrificationmg O2.l-1.h-1p=personnel costs% of TIC per yearp=atmospheric pressurebarP=static point(-)Paer=required aeration powerkWPaerm=installed aeration powerkWpch4=partial methane pressureatmPchem=concentration of phosphorus to be chemically removedmg P.l-1 influentpdis=discharge pressurebar or m liquidPdiss=dissipated powerW.m-3Pel=power productionkWPel=electrical power consumption (pumps)kWPEres=residual pollution load in wastewater after treatmentUS$.PE-1Ph=required heating powerm3 gas or kg fuel.d-1Pl=influent phosphorus concentration removed withmg P.l-1 influentthe excess sludgePld=influent phosphorus concentration in digested sludgemg P.l-1 influent(i.e. released to liquid phase)Ple=influent phosphorus concentration removed withmg P.l-1 influentthe stabilised excess sludgePlx=phosphorus concentration discharged with excess sludge (corrected for loss of organic phosphorus with the effluent)mg P.l-1 influentPmin=minimum required energy required to keep sludge in suspensionW.m-3po2=partial oxygen pressureatmPope=particulate organic phosphorus in effluentmg P.l-1Pose=soluble organic phosphorus in effluentmg P.l-1Ppe=phosphate concentration in effluentmg P.l-1ps=standard pressurebarPtd=desired/required total phosphorus concentration in the effluentmg P.l-1Pte=effluent total phosphorus concentrationmg P.l-1Pte,max=maximum phosphorus effluent concentrationmg P.l-1(all released phosphorus recycled to aeration tank)Pte,min=minimum phosphorus effluent concentrationmg P.l-1(no recycle of released phosphorus to aeration tank)Pti=influent phosphorus concentrationmg P.l-1pw=water vapor pressurebarQ=flow ratem3.h-1 or m3.s-1q=excess sludge flowm3.d-1q1=primary excess sludge flowm3.d-1q2=secondary excess sludge flowm3.d-1Qair=air flowkg.h-1 or Nm3.h-1Qch4=methane gas flow rateNm3.h-1Qbg=biogas flow rateNm3.h-1Qf=module feed flow (cross-flow membranes)m3.h-1Qi=influent flow ratem3.d-1 or m3.h-1Qp=permeate flow ratem3.h-1Qpf=influent peak flow ratem3.h-1Qrec=recirculation flow (cross-flow MBR)m3.h-1qth=thickened excess sludge flowm3.d-1qw=excess sludge flowm3.d-1r=recirculation factor from pre-D zone to anaerobic zone(-)R=gas constantkJ.mol-1.K-1ra=adsorption rate of slowly biodegradable materialmg COD.l-1.d-1rd=decay ratemg VSS.l-1.d-1rd=denitrification ratemg N.l-1.d-1Rd=retention time in aerobic digesterdaysRdi=retention time in anaerobic digesterdaysRdmin=theoretical minimum total aerobic digestiondaysretention time for N rdp=denitrification rate on slowly biodegradable CODmg N.l-1.d-1rds=denitrification rate on easily biodegradable CODmg N.l-1.d-1Rdtot=minimum total aerobic digestion retention timedaysrg=growth ratemg VSS.l-1.d-1Rh=hydraulic retention timedaysRh1=hydraulic retention time in pre-D reactordaysrhi=hydrolysis rate of stored slowly biodegradable materialmg COD.l-1.d-1Rhth=thickening time final settler (ATV)daysRhu=hydraulic retention time UASBhrRmin=minimum retention time for complete utilisation of the Sbs present in the influent in the pre-D reactordaysrn=nitrification ratemg N.l-1.d-1RN=retention time in Nth aerobic digesterdaysRrel=relative evaporation rate of water in the exposed sludge batch(-)Rs=sludge agedaysRsa=true sludge age (including sludge mass present in final settler)daysrsbp=net production of slowly biodegradable materialmg COD.l-1.d-1rsbs=net production of easily biodegradable materialmg COD.l-1.d-1rsbs=feeding rate of easily biodegradable material to the pre-D reactormg COD.l-1.d-1Rsm=minimum sludge age required to achieve desireddayseffluent ammonium concentrationRsn=minimum sludge age required for nitrificationdaysrspa=net production of adsorbed biodegradable materialmg COD.l-1.d-1Rsu=anaerobic sludge agedaysru=utilisation rate of organic materialmg COD.l-1.d-1rus=utilisation rate of easily biodegradable influent organic materialmg COD.l-1.d-1rv=decay rate of volatile solidsmg VSS.l-1.d-1Rw=water evaporation ratemm.day-1rxa=net production of active sludgemg VSS.l-1.d-1rxe=production rate of endogenous residuemg VSS.l-1.d-1s=sludge recycle factor(-)Sbh=biodegradable COD consumed by normal heterotrophic biomassmg COD.l-1 influentSbi=biodegradable influent COD concentrationmg COD.l-1 influentSbp=biodegradable COD sequestered by bio-organismsmg COD.l-1 influentSbp=slowly biodegradable COD concentration (reactor)mg COD.l-1 influentSbs=easily biodegradable COD concentration (reactor)mg COD.l-1 influentSbsh=easily biodegradable COD consumed by normalmg COD.l-1 influentheterotrophic biomassS'bsi=influent concentration of easily biodegradable material after correction for denitrification in the anaerobic zonemg COD.l-1 influentSbsi=easily biodegradable influent COD concentrationmg COD.l-1 influentSbsN=residual concentration of the easily biodegradable material in the effluent of the Nth reactor of a seriesmg COD.l-1Sbsp=easily biodegradable COD sequestered by bio-P organismsmg COD.l-1 influentsc=critical sludge recirculation factor(-)sd=safety factor used to allow for locally increased dissolved nitrogen gas concentrations(-)Seu=soluble (non settleable) COD concentration in UASB effluentmg COD.l-1 influentsfd=safety factor used in design final settler(-)sfth=safety factor used in design sludge thickener(-)Shab=COD discharge per capitag COD.inhab-1smin=minimum value of sludge recirculation flow (MBR)(-)Sni=non biodegradable influent COD concentrationmg COD.l-1 influentSnsi=non biodegradable soluble influent COD concentrationmg COD.l-1 influentSpa=concentration of absorbed slowly biodegradable material (reactor)mg COD.l-1 influentspf=return sludge ratio during peak flow (ATV)(-)Spi=particulate influent COD concentrationmg COD.l-1 influentSte=total effluent COD concentrationmg COD.l-1Sti=total influent COD concentrationmg COD.l-1 influentStu=total UASB effluent COD concentrationmg COD.l-1SVFA=VFA concentrationmg COD.l-1 influentt=aerobic digestion timedaysT=sewage temperatureCt1=time required for preparation of the sludge bed anddaysapplication onto the bed of the sludge to be driedt2=time required for percolationdayst3=time required for evaporationdayst4=time required for removal of the dried sludge anddayscleaning of the bed for the next batchtc=total drying cycle timedaysTCC=total construction costsUS$tcomp=compression time (thickener)daysTdig=temperature in the anaerobic digesterCTIC=total investment costsUS$Tin=blower inlet temperatureCTmax=maximum reactor temperatureCTmin=minimum reactor temperatureC(often equal to design temperature)TOC=total operational costsUS$tp=duration of primary phase (denitrification)dTs=hydraulic loading ratem.h-1Tsm=maximum allowable hydraulic loading ratem.h-1Tspf=hydraulic loading rate during peak flow (ATV)m.h-1Tvx=sludge volume loading ratel.m-2.h1Tvxm=maximum sludge volume loading ratel.m-2.h1u=downward liquid velocity in settlerm.h-1U=humidity%Ue=final humidity%Ui=initial humidity%v0=Vesilind constantm.d-1 or m.h-1va=liquid velocity in UASB aperturesm.h-1Vaer=volume aerobic zonem3Van=volume of anaerobic zone (bio-P removal)m3Vc=volume of settler conem3vd=hydraulic retention time in final settlerdaysVd=volume of final settlerm3Vd1=volume of primary settlerm3Vda=aerobic digestion volumem3vda=specific aerobic digestion volumem3.d.kg-1 CODVdb=available volume for sludge buffering in the final settlerm3Vdi=anaerobic digester volumem3Vhab=reactor volume required per capitam3.inhab-1vl=liquid upflow velocity in UASB reactorm.h-1vo=liquid overflow velocity in UASB reactorm.h-1Vr=volume of aeration tankm3vr=biological reactor volumem3.d.kg-1 CODVt=total volumem3vth=specific thickener volumem3.d.kg-1 CODVth=thickener volumem3Vtp=molar gas volume at actual temperature and pressureliter.mol-1Vu=UASB volumem3vx=sludge volumeml.l-1Vx1=volume pre-D zonem3Vx3=volume post-D zonem3Wa=width of single aperture in UASB reactormWgb=outer width of gas boxmWu=width of UASB reactormXa=active sludge concentration in reactorkg VSS.m-3Xa(N-1)=active sludge concentration in (N-1)th digester and its effluent (aerobic digestion)kg VSS.m-3Xad=digested active sludge concentration (aerobic digestion)kg VSS.m-3Xae=active sludge concentration in digester and its effluentkg VSS.m-3(aerobic digestion)Xah,an=active heterotrophic sludge concentration in anaerobic zonekg VSS.m-3Xai=initial or incoming active sludge concentrationkg VSS.m-3(aerobic digestion)XaN=active sludge concentration in N-th digester and its effluent (aerobic digestion)kg VSS.m-3Xan=active nitrifier concentrationkg VSS.m-3Xav=average concentration at which sludge will accumulate in the final settlerkg TSS.m-3Xbpu=non degraded biodegradable solids concentrationkg VSS.m-3Xc=critical sludge concentrationkg TSS.m-3xch4=mole fraction of dissolved methane gas in watermole.mole-1Xd1=primary sludge concentrationkg TSS.m-3Xe=concentration of endogenous residue in reactorkg VSS.m-3Xee=endogenous sludge concentration formed in aerobic digesterkg VSS.m-3Xen=concentration of endogenous residue from nitrifierskg VSS.m-3Xf=average sludge concentration on settler bottom (ATV)kg TSS.m-3Xi=inert organic sludge concentration in reactorkg VSS.m-3Xl=limiting sludge concentrationkg TSS.m-3Xm=minimum sludge concentrationkg TSS.m-3Xmi=concentration of inorganic solids in influentmg ISS.l-1Xmu=inorganic sludge concentration in reactorkg ISS.m-3Xnae=inactive sludge concentration in digester (aerobic digestion)kg VSS.m-3Xnai=initial or incoming inactive sludge concentrationkg VSS.m-3(aerobic digestion)Xr=return sludge concentrationkg TSS.m-3Xrm=maximum return sludge concentrationkg TSS.m-3Xrmax=maximum allowed sludge concentration in membrane tankkg TSS.m-3Xt=total sludge concentration in reactorkg TSS.m-3Xt1=sludge concentration in first reactor (step feed systems)kg TSS.m-3Xt2=sludge concentration in second reactor (step feed systems)kg TSS.m-3Xte=total stabilised sludge concentrationkg TSS.m-3Xte=effluent total solids concentrationmg TSS.l-1Xth=thickened excess sludge concentrationkg TSS.m-3Xthl=limiting thickening sludge concentrationkg TSS.m-3Xtpf=sludge concentration in the reactor during peak flowkg TSS.m-3Xtu=average UASB sludge concentration in reactorkg TSS.m-3Xtud=average UASB sludge concentration in digestion zonekg TSS.m-3Xv=volatile sludge concentration in reactorkg VSS.m-3Xv=final volatile sludge concentration when decay of active sludge is complete (aerobic digestion)kg VSS.m-3Xvd=digested organic sludge concentrationkg VSS.m-3Xve=stabilised organic sludge concentrationkg VSS.m-3Xvi=initial volatile sludge concentration (aerobic digestion)kg VSS.m-3Xvu=organic anaerobic sludge concentrationkg VSS.m-3Xw=waste sludge concentrationkg TSS.m-3Yan=anaerobic yieldmg VSS.mg-1 CODYao=yield of ammonia oxidisersmg VSS.mg-1 NYap=apparent yieldmg VSS.mg-1 COD or mg TSS.mg-1 CODY or Yh=heterotrophic yieldmg VSS.mg-1 CODYn=nitrifier yieldmg VSS.mg-1 NYno=yield of nitrite oxidisersmg VSS.mg-1 N=inclinationmm.m-1=ratio of the oxygen transfer rate in mixed liquor and(-)in pure water=plate inclination=angle of base of V-notch=ratio of the saturation concentration of DO in mixed liquor(-)and in pure waterAlkam=alkalinity change from ammonificationmg CaCO3.l-1 influentAlkd=alkalinity change from denitrificationmg CaCO3.l-1 influentAlkn=alkalinity change from nitrificationmg CaCO3.l-1 influentAlkt=total alkalinity changemg CaCO3.l-1 influentDc1=reduction in pre-D denitrification capacity due tomg N.l-1recycle of oxygen to pre-D zoneDc3=reduction in post-D denitrification capacity due to influx of oxygen in post-D zonemg N.l-1L=height of water layer removed during drying periodmmMXt=mass of sludge transferred from the reactor to the final settler during peak flowkg TSSNa=variation of ammonium concentrationmg N.l-1 influentNam=ammonified nitrogen concentration in themg N.l-1 influentactivated sludge processNn=variation of nitrate concentrationmg N.l-1 influentp=differential pressurebarpmod=differential pressure over a membrane modulebarpTM=trans membrane pressurebarXt=change in reactor sludge concentration during peak flowg TSS.l-1aer=efficiency of blower%ch4=methane fraction in biogas%COD=COD removal efficiency%d=efficiency factor to account for short circuiting between inlet- and outlet of final settler (ATV)(-)dn=maximum solids removal efficiency of inactive sludge fraction%dp=maximum solids removal efficiency of active sludge fraction%el=electrical efficiency of pump, biogas engine and gas motor%m=ratio between net and gross membrane flux(-)sb=sludge drying bed productivitykg TSS.m-2.d-1xv=fraction of solids converted in digester%1=COD removal efficiency of primary settler%dn=degree of solids conversion inert and endogenous sludge(-)dp=degree of solids conversion active sludge(-)x1=solids removal efficiency of primary settler%'m=(apparent) maximum specific nitrifier growth rate in systems with non aerated zonesd-1=specific growth rate of nitrifiersd-1m=maximum specific nitrifier growth rated-1T=sweet water viscosity at process temperaturecPT,ref=sweet water viscosity at reference temperature (1.288 at T = 15)cP=densitykg.m-3=membrane permeabilitylitre.m-2.h-1.bar-1T=membrane permeability at process temperaturelitre.m-2.h-1.bar-1T,ref=membrane permeability at T = 15Clitre.m-2.h-1.bar-1=temperature dependency coefficient (Arrhenius)(-)=contraction coefficient(-)

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