OutlineOutline •• IntroductionIntroduction •• Membrane IssuesMembrane Issues •• Other IssuesOther Issues OutlineOutline •• IntroductionIntroduction •• Membrane IssuesMembrane Issues ––General foulingGeneral fouling ––Impact of SRT or F/MImpact of SRT or F/M ––Impact of MLSSImpact of MLSS ––Impact of wet weatherImpact of wet weather •• Other IssuesOther Issues WhatWhat isis membranemembrane fouling?fouling? •• Membrane fouling is the loss of permeability with Membrane fouling is the loss of permeability with timetime •• In practice, this is observed as an increase in theIn practice, this is observed as an increase in the TMP required to maintain flow through the MBRTMP required to maintain flow through the MBR
•• For engineers, the increase in TMP For engineers, the increase in TMP needs to be related to the flux rate needs to be related to the flux rate and normalized for temperature and normalized for temperature this is called a temperature this is called a temperature corrected corrected ““PermeabilityPermeability ”” or or ““Specific FluxSpecific Flux ”” DefinitionDefinition ofof termsterms
Po
J = Q/A = membrane flux (m/s)
Membrane permeability = J/TMP
Pe TMP = P o Pe (Pa) A Membrane fouling: TMP
time PermeabilityPermeability J L = P TMP
Typical units in USA: gal/(ft 2. d.lb/in 2) or gfd/psi
Europe and Asia: L/(m 2. h.bar) or LMH/bar
Strict SI Units: m2. s/kg TemperatureTemperature correctedcorrected permeabilitypermeability
(-0.0239( T -20)) o J ⋅ e L20 C = P TMP
The above equation corrects for temperature effects on the viscosity of water. This equation is accurate within 5% for a temperature range of 5 to 40 oC.
WHY DO WE DO THIS?? Because changes in the viscosity of water directly impact TMP TemperatureTemperature correctioncorrection
2.0
1.8 As water temperature decreases - viscosity of water increases 1.6 s •
1.4
1.2
Actual 1.0 Calculated
0.8
0.6 Absolute viscosity of water, mPa 0.4 All other conditions equal -
0.2 this increases the TMP Need to Need equation different a use 0.0 0 5 10 15 20 25 30 35 40 45 Temperature, ºC Key MBR Research Projects ListList ofof KeyKey ResearchResearch ProjectsProjects
• 1999 2000 WERF study in San Diego • 1999 2000 Bureau of Reclamation II Study in San Diego • 2000 2004 STOWA project in the Netherlands • 2002 2005 WERF study in San Francisco • 2001 present King County in Seattle • 2003 2004 Bureau of Reclamation III Study in San Diego • 2002 present On going research by Anjou Recherche • 2006 present EU funded Amadeus initiative Understanding MBR Fouling MBRMBR foulingfouling theorytheory
• Basic fundamentals of membrane fouling in MBRs are the same regardless of the manufacturer or configuration (Pressure or Vacuum) • Membrane fouling results from the interaction between the mixed liquor and membrane material – Complex mixture of organics – Metabolic byproducts and possibly influent substrate or partiall y degraded influent substrate – Cells and microbes – Cellular and microbial debris – Inert suspended solids – Dissolved inorganics (possible precipitants) ResistanceResistance inin --seriesseries modelmodel •• Simplistic modelSimplistic model •• Widely used with lowWidely used with low pressure membranes pressure membranes (MF/UF/MBR)(MF/UF/MBR) •• Can be used to provide powerful insights to Can be used to provide powerful insights to MBR foulingMBR fouling
J = membrane flux, m/s TMP TMP = trans-membrane pressure, Pa J = . w = absolute viscosity of water, kg/m s -1 w ⋅ R T RT = total resistance to filtration, m ResistanceResistance inin --seriesseries modelmodel
•• RRT=R=R M+R+R F+R+R C
•• RRT = Total resistance= Total resistance
•• RRM = Membrane= Membrane
•• RRC = Cake Layer= Cake Layer
•• RRF = = FoulantsFoulants – Organic Adsorption – Inorganic Precipitation – Pore blocking MembraneMembrane resistance,resistance, RR MM
• RM is the hydraulic resistance due to the membrane alone Determining R M
• RM can be determined by 90000 performing a clean water flux 80000 profile on a clean membrane 70000 60000 • Record TMP and temperature 50000 12 -1 40000 RM = 3x10 m for 3 different flux rates TMP (Pa) 30000
20000 • Plot TMP vs. m*J, slope is R M y = 3E+12x + 21823 10000 R2 = 0.9996 0 5.E-09 6.E-09 7.E-09 8.E-09 9.E-09 1.E-08 Viscosity * Flux (kg/s 2) OtherOther resistanceresistance termsterms TMP • RT is obtained during normal MBR operation R T = – Increases with time or total volume filtered w ⋅ J
– Influenced by resistance of the filtration cake, R C
– Influenced by the degree of foulant present on the membrane, R F
• RF can be roughly estimated at any point in an operation cycle – Drain the mixed liquor from the membrane tank (air off) – Fill the membrane tank with membrane permeate and perform flux profile this provides R M+R F (possibly some residual R C that ’s why this is an estimate )
• Subtract R M (this was obtained before run began ) and you can approximate the amount of foulant , R F • Remainder of R T is attributed to R C HydrodynamicHydrodynamic forceforce balancebalance
• Membrane flux controls the rate of material transported
to the membrane surface, J SS • The lift force controls the rate at which rejected material
is re suspended to the bulk solution, V L
•• Normal MBR operationNormal MBR operation
–– JJss ≤≤ VVL –– i.e. Operating at subi.e. Operating at sub critical fluxcritical flux Critical Flux CriticalCritical fluxflux
• Conventionally denotes flux below which fouling does not take place – Membrane permeability remains as it was in pure water • Strict critical flux definition does not apply to MBR • Field et al., 1995 first adapted this concept to low pressure membranes • Le Clech et al., 2003 further developed the critical flux concept for MBRs IllustrationIllustration ofof criticalcritical fluxflux
20 gfd 8.7 MLSS = 8 g/L 18 gfd 10.9 SCFM = 30 scfm gfd 13.1 16 gfd 15.3 gfd 17.5 14
12
10
8
Vacuum Pressure, in Hg 6
4
2
0 0 2 4 6 8 10 Time, minutes FactorsFactors affectingaffecting criticalcritical fluxflux
•• Specific MBR hydrodynamicsSpecific MBR hydrodynamics – Hollow fiber versus flat sheet – Coarse aeration distribution – Pressure vs. Vacuum MBR systems •• Mixed liquor propertiesMixed liquor properties – Degree of flocculation » More disperse flocs with higher colloidal material is different than a well flocculated sludge – Viscosity
» The mixed liquor viscosity impacts the efficiency of V L » Higher viscosity lower scouring efficiency ImportanceImportance ofof coarsecoarse bubblebubble airair Cross-flow Adapted from Bérubé et al., 2005 AWWA MTC velocity
Constant flux experiments Single Phase = Water alone Dual Phase = Air/Water
Conclusion: Maintaining clean, well-functioning, and well-distributed coarse bubble air is critical SludgeSludge PropertiesProperties
Filamentous Colloidal Microorganisms Material
Particle Size
Extracellular Polymeric Substances (EPS) CriticalCritical FluxFlux IllustrationIllustration
MLSS = 10 12 g/L Air = 30 scfm
Adapted from Fan et al., 2006 Water Research V40 RM RC RF ––JssJss = to membrane= to membrane
––VVL = away from membrane= away from membrane
––JssJss ≥≥ VVL (rapid fouling)(rapid fouling) “Typical” MBR Fouling Mechanisms
Photos adapted from Miura et al., 2007 ““TypicalTypical ”” MBRMBR foulingfouling mechanismsmechanisms
• Organics are the most common foulant under normal operating conditions in MBRs – Conservative flux – Well functioning/distributed coarse aeration – Controlled MLSS • Organic fouling is primarily attributed to the soluble or colloidal organics present in the mixed liquor – Particles ≤ 6 m – Not incorporate into larger floc – Not yet clear whether colloidal or soluble is culprit (likely bo th) » Research has highlighted the importance of soluble carbohydrate or polysaccharides, but there is also literature to the contrary • Increased soluble/colloidal organic content results in increased membrane fouling rates ExtracellularExtracellular PolymericPolymeric SubstancesSubstances (EPS)(EPS) andand SolubleSoluble MicrobialMicrobial ProductsProducts (SMP)(SMP)
Hydrolysis EPS
Active Cell SMP Substrate
Adsorption and Diffusion/Shear flocculation OrganicOrganic foulingfouling
Adapted from Lesjean et al., 2005 Water Science and Technology OrganicOrganic foulingfouling
70
Total SMP = 7.0x + 36.8 2 60 R = 0.77
50
40
30
SMP concentration, mg/L 20 SMP = soluble microbial products 10 (soluble protein + soluble carbohydrate)
0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Steady state fouling rate, LMH/bar • d
Adapted from Trussell et al., 2006 InorganicInorganic foulantsfoulants
• Less severe than organic fouling for most municipal MBR applications • Certain waters (e.g. hard waters) can slowly develop an inorganic fouling layer – Low pH clean (most common is citric acid) will control this – This clean can be done as infrequently as annually at many facilities • Coagulants are typically used in municipal wastewater treatment facilities – High coagulant doses create hydroxide precipitants (e.g. Fe(OH) 3), or coagulant carryover (e.g. colloids not bound up in mixed liquor) that will result in inorganic fouling – It appears that an occasional low dose of coagulant can help reduce soluble and colloidal organic fouling CoagulantCoagulant AdditionAddition
Adapted from Holbrook et al., 2004 Water Environment Research PolymerPolymer AdditionAddition
•• Benefits of specialized polymer addition or Benefits of specialized polymer addition or ““flux flux enhancersenhancers ”” are currently being researchedare currently being researched – Reduces mixed liquor organic content (SMP) – Allows for increase in membrane flux by reducing colloidal organics •• Benefits have not been demonstrated on longBenefits have not been demonstrated on long term term basisbasis – Short term increase in mixed liquor filterability occurs – High doses required for longer run times – Long term impacts on sludge properties (e.g. post polymer addition) have not been demonstrated PolymerPolymer AdditionAddition
Adapted from Yoon et al., 2005 Water Science & Technology Other Important Fouling Mechanisms ChangesChanges inin MLSSMLSS concentrationconcentration • Increases in the MLSS concentration are important
– Increases the J SS to the membrane surface – Increases the mixed liquor viscosity – Combination can result in operation above the critical flux without changing the membrane flux • Different researchers have reached different conclusions on the “maximum ” MLSS concentration for membrane fouling • This is because the “maximum ” MLSS depends on – Membrane hydrodynamics (e.g. flat sheet, hollow fiber, pressure vs. vacuum, etc.) – Membrane flux rate – Re suspending efficiency (e.g. air rate, no air? cross flow velocity, “jet ”, mixed liquor viscosity) ChangesChanges inin mixedmixed liquorliquor propertiesproperties
• Mixed liquor viscosity can change dramatically without the MLSS concentration changing! – Mixed liquor viscosity has been > 2 times greater depending on properties (e.g. 200 vs. 400 mPa .s at 18 g/L) – Mixed liquor viscosity depends upon the degree of flocculation, extracellular polymeric substance (EPS) concentration, and filament concentration • Mixed liquor filterability can change without changing MLSS concentration
– If de flocculation occurs, a dramatic increase in the R C will occur » Increase in colloidal content » Disperse flocs and single cells » Dramatic changes can be quantified by time to filter (TTF) MixedMixed liquorliquor viscosityviscosity
Adapted from Cui et al., 2003 OtherOther importantimportant mixedmixed liquorliquor propertiesproperties forfor MBRMBR foulingfouling • Key foulants arise from biomass, termed extracellular polymeric substances (EPS) – unbound fraction often referred to as soluble microbial product (SMP) – bound fraction (EPS) • These can be further fractionated into chemical types, namely: – polysaccharide (or carbohydrate) – protein ChemicalChemical foulantfoulant studiesstudies
• Difficult to ubiquitously identify key foulant • Generally, high concentrations of SMP are a significant concern – Membrane fouling will increase – New research is showing importance of molecular weight of solubl e organic (e.g. >10 kDa and < 100 kDa ) • High concentrations of EPS do not always result in increased fou ling rates – High EPS can be a sign of good flocculation (e.g. low colloidal and soluble organic content)
– “Sticky ” EPS can result at low EPS concentrations and produce high R C Is Pore Size Important? MFMF vsvs UFUF •• A much debated topicA much debated topic •• Some believe that MF has a higher fouling Some believe that MF has a higher fouling tendenacytendenacy than UF membranesthan UF membranes •• Some believe the MF and UF membranes in Some believe the MF and UF membranes in MBRsMBRs will produce significantly different effluent waterwill produce significantly different effluent water qualities, possibly impact reactor design by the qualities, possibly impact reactor design by the retention of additional organicsretention of additional organics •• HermanowiczHermanowicz et. al (2006) clarified a Novak et. al (2006) clarified a Novak publication that suggested whether an MBR is MF or publication that suggested whether an MBR is MF or UF would impact the biological designUF would impact the biological design – Having either an MF or UF produced similar COD at the same conditions DynamicDynamic CakeCake LayerLayer (Lee(Lee etet al.al. 2001)2001) • Solids (microbial floc ) protect the membrane from direct exposure to organics • Acts as a “secondary ” membrane • Membrane fouling rate will increase with a less effective dynamic cake layer – Poor flocculation USUS BureauBureau ofof Rec.Rec. ReportReport (2000)(2000)
Rapid fouling Rapid fouling attributed to MF attributed to MF modulemodule Impact of SRT or F/M on Membrane Fouling RationaleRationale F S = o M θH ⋅ XMLVSS •• The SMBR process is currently The SMBR process is currently limited to an MLSS concentration of limited to an MLSS concentration of 10 g/L10 g/L •• The F/M ratio is a key parameter to The F/M ratio is a key parameter to optimize reactor tank designoptimize reactor tank design –– Small tank (low HRT)Small tank (low HRT) –– Small tank (high F:M)Small tank (high F:M) RationaleRationale
Capital O&M Present Worth, $ Worth, Present
θθθH, time EquipmentEquipment andand ApparatusApparatus
•• PilotPilot scale scale SMBRSMBR •• Treating Treating primary primary effluent from effluent from the City of San the City of San FranciscoFrancisco ’’s SEPs SEP – COD = 325 mg/L – TSS = 98 mg/L MembraneMembrane OperationOperation andand CharacteristicsCharacteristics •• Zenon 500C ModuleZenon 500C Module •• Nominal = 0.035 Nominal = 0.035 mm •• Flux = 30 L/mFlux = 30 L/m 2. hh •• Air = 14 L/sAir = 14 L/s •• Intermittent Intermittent aerationaeration •• 9 min operating 9 min operating cycle followed by cycle followed by 30 sec relax30 sec relax ExperimentalExperimental MethodsMethods
•• Initial operating conditions:Initial operating conditions: MCRT = 10 d (F/M = 0.34 gCOD/gVSSMCRT = 10 d (F/M = 0.34 gCOD/gVSS .d)d) •• Dissolved oxygen > 2 mg/LDissolved oxygen > 2 mg/L •• Constant MLSS = 8g/LConstant MLSS = 8g/L •• SteadySteady state data collection began state data collection began after 3 MCRTsafter 3 MCRTs •• 2 week steady2 week steady state data collection state data collection periodperiod •• MCRT was steadily decreased (5, 4, 3, 2 MCRT was steadily decreased (5, 4, 3, 2 d)d) – F/M (0.53, 0.73, 0.84, 1.4 gCOD/gVSS.d) MembraneMembrane PerformancePerformance atat 1010 --dd MCRTMCRT (F/M=0.34(F/M=0.34 gCOD/gVSSgCOD/gVSS .d)d)
Flux Specific Flux
40 300 Start-up Chemical Clean Large Foam Event
35 250
30
200 25 C, LMH/bar C, o
20 150
15 100
10 Specific Flux @ 20 @ Flux Specific
50 5
0 0 50 70 90 110 130 150 170 190 Days of Operation MembraneMembrane PerformancePerformance atat 55 --dd MCRTMCRT (F/M=0.53(F/M=0.53 gCOD/gVSSgCOD/gVSS .d)d)
Flux Specific Flux 40 300
35 250
30
200 25 C, LMH/bar o
20 150
15 100
10 @ Specific Flux 20
50 5
0 0 180 190 200 210 220 230 240 250 260 270 280 Days of Operation MembraneMembrane PerformancePerformance atat 44 --dd MCRTMCRT (F/M=0.73(F/M=0.73 gCOD/gVSSgCOD/gVSS .d)d)
Flux Specific Flux 40 300 Intermittent Coarse Air Failure Foam Event
35 250
30
200 25 C, LMH/bar C, o
20 150
15 100
10 Specific Flux @ 20 @ SpecificFlux
50 5
0 0 270 280 290 300 310 320 330 Days of Operation MembraneMembrane PerformancePerformance atat 33 --dd MCRTMCRT (F/M=0.84(F/M=0.84 gCOD/gVSSgCOD/gVSS .d)d)
Flux Specific Flux
40 300 Routine Feed Routine Feed Intermittent Coarse Line Cleaning Line Cleaning Air Failure
35 250
30
200 25 C, LMH/bar C, o
20 150
15 100
10 Specific Flux @ 20 Flux@ Specific
50 5
0 0 355 360 365 370 375 380 385 390 395 Days of Operation MembraneMembrane PerformancePerformance atat 22 --dd MCRTMCRT (F/M=1.4(F/M=1.4 gCOD/gVSSgCOD/gVSS .d)d)
Flux Specific Flux
40 300 Foam Event
35 250
30
200 25 C, LMH/bar o
20 150
15 100
10 Specific Flux @ 20
50 5
0 0 390 395 400 405 410 415 Days of Operation EffectEffect ofof F/MF/M onon SteadySteady --StateState FoulingFouling RateRate
MCRT, d 10 5 4 3 2 4.0
3.5
3.0 y = 1.661x2.1977 R2 = 0.9517
2.5
2.0
1.5
1.0
0.5
0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
F/M, g COD/g VSS.d SteadySteady --statestate FoulingFouling RateRate vsvs sCODsCOD
Soluble COD COD Rejection
90 100
80 sCOD = 3.8x + 61.3 90 R2 = 0.30 80 70
70 60 60 50 COD Rejection = -1.5x + 63.0 R2 = 0.24 50 40 40 30 30
20 COD Membrane Rejection, % 20
10 10
0 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Steady-state fouling rate, LMH/bar.d SteadySteady --statestate FoulingFouling RateRate vsvs SMPSMP
Protein Carbohydrate Total
70
Total SMP = 7.0x + 36.8 60 R2 = 0.77
50
40
30 SMPp = 2.8x + 20.5 R2 = 0.36
20 SMPc = 4.2x + 16.2 R2 = 0.72 10
0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Steady-state fouling rate, LMH/bar.d ConclusionsConclusions •• High organic loading rates (F/M) High organic loading rates (F/M) increased membrane fouling ratesincreased membrane fouling rates •• Biological foaming was controlled Biological foaming was controlled mechanicallymechanically •• Increased steadyIncreased steady state membrane fouling state membrane fouling rates correlated with SMP, not sCODrates correlated with SMP, not sCOD •• Understanding membrane fouling at high Understanding membrane fouling at high organic loading rates allows engineers organic loading rates allows engineers to design a compact SMBR without:to design a compact SMBR without: – excessive maintenance costs or – failing to meet the design capacity Why does high F/M cause membrane fouling EffectEffect ofof F/MF/M onon SteadySteady --StateState FoulingFouling RateRate
MCRT, d 10 5 4 3 2 4.0
3.5
3.0 y = 1.661x2.1977 R2 = 0.9517
2.5
2.0
1.5
1.0
0.5
0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
F/M, g COD/g VSS.d EquipmentEquipment andand ApparatusApparatus
•• BenchBench scale scale SMBRSMBR •• Treating Treating primary primary effluent from effluent from the City of San the City of San FranciscoFrancisco ’’s SEPs SEP – COD = 325 mg/L – TSS = 98 mg/L MembraneMembrane OperationOperation andand CharacteristicsCharacteristics •• Mitsubishi Mitsubishi SteraporeSterapore ® •• Nominal pore size Nominal pore size = 0.4 = 0.4 mm •• Membrane flux = 18 Membrane flux = 18 L/mL/m 2. hh •• Coarse bubble air Coarse bubble air = 0.4 L/s= 0.4 L/s •• 9 min operating 9 min operating cycle followed by cycle followed by 30 sec relax30 sec relax ExperimentalExperimental MethodsMethods
•• Operating conditions:Operating conditions: MCRT = 10 d (F/M = 0.50 gCOD/gVSSMCRT = 10 d (F/M = 0.50 gCOD/gVSS .d)d) MCRT = 2 d (F/M = 2.34 MCRT = 2 d (F/M = 2.34 gCOD/gVSSgCOD/gVSS .dd)) •• Dissolved oxygen > 2 mg/LDissolved oxygen > 2 mg/L •• Constant MLSS = 1.4 g/LConstant MLSS = 1.4 g/L •• SteadySteady state data collection began state data collection began after 3 MCRTsafter 3 MCRTs •• 2 week steady2 week steady state data collection state data collection periodperiod ToolsTools UsedUsed toto UnderstandUnderstand MembraneMembrane FoulingFouling • Steady state membrane fouling rate during operation • Molecular weight distribution of influent, SMP and effluent • FTIR of clean and fouled membranes • Batch filtration experiments expressed as Modified Fouling Index (MFI) – Stir cell filtration of steady state mixed liquor with UF (NMWCO = 300 kDa , PES) – Data presented as MFI at 20 oC and 210 kPa • Fouled membrane resistances FouledFouled MembraneMembrane ResistanceResistance TermsTerms
•• R=RR=R M+R+R F+R+R C •• RR = Total = Total resistanceresistance
•• RRM = Membrane= Membrane
•• RRC = Cake Layer= Cake Layer
•• RRF = Foulants= Foulants – Organics Adsorption – Inorganic Precipitation MembraneMembrane PerformancePerformance atat 1010 --dd MCRTMCRT (F/M=0.50(F/M=0.50 gCOD/gVSSgCOD/gVSS .d)d)
Flux Specific Flux
40 600 Start up 66 Days at 10-d MCRT (F/M = 0.50 gCOD/gVSS.d) 35 500
30
400 25 C, LMH/bar C, o
20 300
15 200
10 Steady-state fouling rate Specific Flux @Flux 20 Specific
100 Chemical Cleaning 5
0 0 0 10 20 30 40 50 60 70 80 Days of Operation MembraneMembrane PerformancePerformance atat 22 --dd MCRTMCRT (F/M=2.34(F/M=2.34 gCOD/gVSSgCOD/gVSS .d)d)
Flux Specific Flux
40 600 25 Days at 2-d MCRT (F/M = 2.34 gCOD/gVSS.d) 35 500
30 Chemical Chemical Cleaning Chemical Cleaning Cleaning 400 25 C, LMH/bar C, o
20 300
15 200 Steady- 10 state Specific Flux Specific @ 20
100 5 Improper Wasting Volumes 0 0 75 80 85 90 95 100 105 Days of Operation SteadySteady --StateState MembraneMembrane FoulingFouling RatesRates
Steady-state Fouling F/M MCRT SMP SMP Total SMP Rate @ 20oC c p . . gCOD/gVSS d d LMH/bar d mg/L mg/L mg/L 0.50 10 2.60 24 14 38 2.34 2 59.0 10 49 59 •• Membrane fouling rates increased Membrane fouling rates increased with F/Mwith F/M •• Total SMP concentration increased Total SMP concentration increased with F/Mwith F/M •• Unlike pilotUnlike pilot scale work, scale work, SMPcSMPc did did not increase with increasing F/Mnot increase with increasing F/M CarbohydrateCarbohydrate MolecularMolecular WeightWeight IncreasedIncreased atat LowLow MCRTMCRT (High(High F/M)F/M)
> 10 kDa 10 kDa - 1 kDa < 1 kDa
25
20
15
10
5 Carbohydrate concentration, mg/L
0 Influent SMP - 10 d SMP - 2 d Effluent - 10 d Effluent - 2 d Sample ProteinProtein MolecularMolecular WeightWeight IncreasedIncreased atat LowLow MCRTMCRT (High(High F/M)F/M)
> 10 kDa 10 kDa - 1 kDa < 1 kDa
70
60
50
40
30
20 Protein Concentration, mg/L 10
0 Influent SMP - 10 d SMP - 2 d EFF - 10 d EFF - 2 d Sample FouledFouled MembraneMembrane FTIRFTIR ResultsResults Virgin (Blue) 1 0 0 10-d MCRT (Green)
8 0
6 0 2-d MCRT %T
4 0
2 0 1 0 4 0 0 0 3 0 0 0 2 0 0 0 1 0 0 0 6 5 0 Wavenumber[cm-1]
3380 - indicates OH stretching 1660 and 1540 - indicates NH and COO - (protein) 1060 - indicates CO stretching of polysaccharides FouledFouled MembraneMembrane ResistanceResistance 1010 --dd MCRTMCRT Fouling Resistance During 10 days MCRT Operation
25
Before cleaning y = 4.2319x 20 R2 = 0.9979 y = 0.4014x 2 Physical R = 0.5914 15 y = 4.0956x Chemical R2 = 0.9757
10
5
0 0 5 10 15 20 25 30 35 40 Viscosity * Flux ( g/s2) After 66 d of operation without a chemical clean FouledFouled MembraneMembrane ResistanceResistance 22--dd MCRTMCRT
Fouling Resistance During 2 days MCRT Operation
25
Before cleaning y = 2.0627x R2 = 0.9919 20
15 y = 1.7468x Physical R2 = 0.9895 y = 0.4303x 10 R2 = 0.9315 Chemical
5
0 0 5 10 15 20 25 30 Viscosity * Flux ( g/s2) After 5 d of operation without a chemical clean FouledFouled MembraneMembrane ResistanceResistance TermsTerms
A B
RMembrane 9% RMembrane 21% RCake 3%
RCake 15% RFoulant 64%
RFoulant 88%
R = 4.23x1012 m-1 R = 2.07x1012 m-1 Fouled membrane R distribution for SMBR: A) 10-d MCRT (0.5 gCOD/gVSS .d) B) 2-d MCRT (2.34 gCOD/gVSS .d) BatchBatch FiltrationFiltration ResultsResults • Operating membrane permeability was similar when analyzed 63 and 71 LMH/bar for the 2 d and 10 d MCRTs • Factor of 2 in total fouled resistance • Used a batch filtration test to better understand these differences and importance of various components to fouling • Stir cell filtration of steady state mixed liquor with UF (NMWCO = 300 kDa , PES) • Data presented as MFI at 20 oC and 210 kPa BatchBatch FiltrationFiltration ResultsResults
Modified Fouling Index, 10 3 s/L 2 SRT, d Mixed Liquor Soluble SS Mixture Effect 10 17 11 2 4 2 47 27 12 8
• Higher sludge resistance observed at 2 d MCRT • Reduction in sludge filterability was observed as membrane fouling – Fouled resistances 4.23 (10 d) and 2.07 (2 d) with measurement was made on membrane permeate – Fouled permeability 71 (10 d) and 63 (2 d) with measurement was made during operation BatchBatch FiltrationFiltration ResultsResults
Modified Fouling Index, 10 3 s/L 2 SRT, d Mixed Liquor Soluble SS Mixture Effect 10 17 11 2 4 2 47 27 12 8
• MFI was higher for all fractions at MCRT = 2 d • Sludge was centrifuges at 12,000 g for 15 minutes – Soluble fraction was supernatant – Suspended solids (SS) fraction was pellet • SS was measured by resuspending pellet with batch stir cell permeate • Soluble MFI was almost 3 times higher at low MCRT • SS MFI increased 6 times at low MCRT (sticky cake) • Mixture effect was observed at both conditions SMBR Sludge- Low EPS/High Colloidal Material
Activated Sludge- High EPS/Low Colloidal Material EPSEPS DataData
Mean Concentration, mg/gVSS MCRT, d < 1 kDa 10 kDa - 1 kDa > 10 kDa Total Carbohydrate 10 4.3 17.6 7.8 29.7 2 5.5 6.8 18.3 30.6 Protein 10 30.6 46.2 14.4 91.2 2 48.5 11.3 60.9 120.7
No difference in total carbohydrate concentration most commonly cited foulant More total protein at low MCRT More high molecular weight organics at low MCRT CarbohydrateCarbohydrate EPSEPS
A B
< 1 kDa < 1 kDa 14% > 10 kDa 18% 26%
10 kDa - 1 > 10 kDa kDa 60% 22% 10 kDa - 1 kDa 60% Carbohydrate Carbohydrate Total Concentration: 29.7±1.7 mg/gVSS Total Concentration: 30.6±1.5 mg/gVSS Dramatic shift between the >10kDa and 10-1 kDa range A) 10-d MCRT (0.5 gCOD/gVSS .d) B) 2-d MCRT (2.34 gCOD/gVSS .d) ProteinProtein EPSEPS
A B
> 10 kDa 16% < 1 kDa 34% < 1 kDa 40% > 10 kDa 51%
10 kDa - 1 10 kDa - 1 kDa kDa 50% 9% Protein Protein Total Concentration: 91.2±6.6 mg/gVSS Total Concentration: 120.7±20.3 mg/gVSS AGAIN - a dramatic shift between the >10kDa and 10-1 kDa range A) 10-d MCRT (0.5 gCOD/gVSS .d) B) 2-d MCRT (2.34 gCOD/gVSS .d) ConclusionsConclusions
•• High organic loading rates (F/M) High organic loading rates (F/M) increased membrane fouling ratesincreased membrane fouling rates •• Increased steadyIncreased steady state membrane fouling state membrane fouling rates correlated with total SMPrates correlated with total SMP •• MW of carbohydrate and protein SMP MW of carbohydrate and protein SMP increased with F/Mincreased with F/M •• Membrane rejected higher MW SMPMembrane rejected higher MW SMP •• FTIR indicated protein and carbohydrate FTIR indicated protein and carbohydrate presence on fouled membranes with presence on fouled membranes with stronger adsorptions resulting from the stronger adsorptions resulting from the 22 d MCRT conditiond MCRT condition ConclusionsConclusions •• Membrane fouling was primarily due to Membrane fouling was primarily due to the adsorption of organics and Rthe adsorption of organics and R F was was dominate resistance term of fouled dominate resistance term of fouled membranesmembranes
•• RRC increased with F/M and this was increased with F/M and this was attributed to changes in attributed to changes in flocfloc properties properties that result in a that result in a ““stickysticky ”” cakecake •• Sludge filtration resistance (MFI) Sludge filtration resistance (MFI) increased with F/Mincreased with F/M •• MFI of suspended solids increased 6 MFI of suspended solids increased 6 times, supporting the increasing times, supporting the increasing importance of the cake layer with importance of the cake layer with increasing F/Mincreasing F/M