activatesludgevs membrane reactor slide

8/14/2019 ActivateSludgeVS Membrane Reactor SLIDE

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Evaluation of ConventionalEvaluation of Conventional

Activated Sludge Compared toActivated Sludge Compared toMembrane BioreactorsMembrane Bioreactors

R. Shane Trussell, Ph.D., P.E.R. Shane Trussell, Ph.D., [email protected]@trusselltech.com

Short Course on Membrane BioreactorsShort Course on Membrane Bioreactors

3/22/063/22/06


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OutlineOutline

IntroductionIntroduction

Process DesignProcess Design

Effluent Water QualityEffluent Water Quality Peak FlowsPeak Flows

Mixed Liquor PropertiesMixed Liquor Properties

ConclusionsConclusions


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OutlineOutline







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Biological processes have become theBiological processes have become thepreferred municipal wastewaterpreferred municipal wastewatertreatment processtreatment process

Activated Sludge Process (ASP) hasActivated Sludge Process (ASP) has

developed into a mature process overdeveloped into a mature process overthe past centurythe past century

Membrane BioreactorMembrane Bioreactor(MBR) process is(MBR) process isrelatively new to wastewater treatmentrelatively new to wastewater treatment

with thewith the

concept of direct sludgeconcept of direct sludge

filtration emerging four decades agofiltration emerging four decades ago



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IntroductionIntroduction MembraneMembrane

Bioreactor (MBR)Bioreactor (MBR) Modified activatedModified activated

sludge processsludge process

UF/MF membraneUF/MF membrane

Two configurationsTwo configurations

External (EMBR)External (EMBR)

Submerged (SMBR)Submerged (SMBR)


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Flow Schemes for the MBR and Conventional

Activated Sludge Process

Flow Schemes for the MBR and ConventionalFlow Schemes for the MBR and Conventional

Activated Sludge ProcessActivated Sludge Process

Primary TreatedWastewaterPrimary TreatedWastewater

BackwashWaterBackwashWater

SecondaryClarifier

SecondaryClarifier

WASTEASTE

MicrofiltrationicrofiltrationConventionalConventionalConventional

Aeration Basineration Basin

TertiaryTreated

Wastewater

TertiaryTreated

Wastewater


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Flow Schemes for the MBR and Conventional

Activated Sludge Process

Flow Schemes for the MBR and ConventionalFlow Schemes for the MBR and Conventional

Activated Sludge ProcessActivated Sludge Process

BackwashWaterBackwashWater

SecondaryClarifier

SecondaryClarifier

WASTEASTE

TertiaryTreated

Wastewater

TertiaryTreated

Wastewater

MicrofiltrationicrofiltrationConventionalConventionalConventional


Primary TreatedWastewater


WASTEASTE

MBRMBR


(Equivalent toa 1-3 mm screen)

TertiaryQualityWastewater

TertiaryQualityWastewater


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Submerged MBR (SMBR)Submerged MBR (SMBR)Q



WASTEWASTE

EffluentffluentAeration BasinAeration Basin

Waste Activated Sludgeaste Activated SludgeSolids Recycleolids Recycle

QR = 3-5xQ


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External MBR (EMBR)External MBR (EMBR)

Primary TreatedWastewaterPrimary TreatedWastewater

Solids Recycleolids Recycle

EffluentffluentAeration Basineration BasinQ

QR = 20-30xQ

Waste Activated Sludgeaste Activated Sludge


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OutlineOutline







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MBRsMBRs combine activated sludgecombine activated sludgetechnology with membrane filtration totechnology with membrane filtration toexpand the normal operating regionexpand the normal operating region

MBRsMBRs can be designed at higher MLSScan be designed at higher MLSS

concentrations because they are notconcentrations because they are notaffected by theaffected by the limitations of gravitylimitations of gravity

sedimentation for solidsedimentation for solid--liquidliquidseparationseparation

SMBRsSMBRs are typically designed forare typically designed forMLSS concentrations 8MLSS concentrations 8--1212 g/Lg/L



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SMBRsSMBRs operate at 2 tooperate at 2 to >6 times>6 times ASPASP

MLSS concentrationsMLSS concentrations Higher MLSS concentrations translateHigher MLSS concentrations translate

into:into:

Advantages of High MLSSAdvantages of High MLSS

Longer SRTLonger SRTsame HRT, orsame HRT, or

Shorter HRTShorter HRTsame SRTsame SRT


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For a given HRT, the SMBR process canFor a given HRT, the SMBR process canoperate at 2 to >6 times the SRT of ASPoperate at 2 to >6 times the SRT of ASP

TraditionalTraditional SMBR design has been toSMBR design has been tooperate atoperate at conventionalconventional HRTsHRTs withwith longlongSRTsSRTs (i.e. > 20 days)(i.e. > 20 days)

LongLong SRTsSRTs have the following advantages:have the following advantages: Complete nitrification can occur even in coldComplete nitrification can occur even in cold

climatesclimates

Reduced biological sludge productionReduced biological sludge production

Complete oxidation of influent organicsComplete oxidation of influent organics

Possibility that slow growing microorganismsPossibility that slow growing microorganismscan degradecan degrade persistent organicspersistent organics

Longer SRT DesignsLonger SRT Designs


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In general, for a given SRT, the SMBR process canIn general, for a given SRT, the SMBR process cantreat wastewatertreat wastewaterin 1/2 toin 1/2 to 1/4 the HRT of ASP1/4 the HRT of ASP

ShortShort HRTsHRTs have the following advantages:have the following advantages:

Reduce overall plant footprintReduce overall plant footprint

Capital cost savings from reducedCapital cost savings from reduced land and tank volumeland and tank volume

Concept of shorterConcept of shorterHRTsHRTs brings about one of thebrings about one of theprinciple limitations ofprinciple limitations ofSMBRsSMBRs compared to ASPcompared to ASP

Minimum SRTMinimum SRT

There is a minimum SRT where membrane foulingThere is a minimum SRT where membrane foulingbecomes rapidbecomes rapid

A general design guideline is target the minimum SRTA general design guideline is target the minimum SRT

for nitrification plus an additional safety factorfor nitrification plus an additional safety factor

Some manufacturers have established their own lowerSome manufacturers have established their own lowerlimit at 12 dayslimit at 12 days

Shorter HRT DesignsShorter HRT Designs


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Effect of SRT on SteadyEffect of SRT on Steady--State Fouling RateState Fouling Rate

y = 1.661x2.1977

R2 = 0.9517

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

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

3 210 5 4MCRT, d

HRT = 4 h

HRT = 1 h


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Key difference is in solidKey difference is in solid--liquid separationliquid separation

ASPASP is not sensitive to lowis not sensitive to low SRTsSRTs and canand can

successfully operatesuccessfully operate in ain a conventionalconventional modemode SMBRsSMBRs are sensitive to loware sensitive to low SRTsSRTs and compactand compact

designs can result in increased membranedesigns can result in increased membrane

fouling ratesfouling rates This difference in solidThis difference in solid--liquid separationliquid separation

also makes pretreatmentalso makes pretreatment imperativeimperative

Fine screeningFine screening is an absolute must inis an absolute must in SMBRsSMBRs

The MBR community hasThe MBR community has been and is stillbeen and is stilllearning how importantlearning how important reliable screeningreliable screeningequipment isequipment is



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Krampe

andKauth,

2002

Higher MLSS concentrationsHigher MLSS concentrations influence theinfluence theoxygen transfer efficiencyoxygen transfer efficiency

Oxygen transfer from coarse bubbleOxygen transfer from coarse bubbleaeration required for membrane agitationaeration required for membrane agitationneeds to be consideredneeds to be considered



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OutlineOutline







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Biological processBiological process

applied to oxidizeapplied to oxidize

organics and removeorganics and remove

nutrientsnutrients

Principle difference isPrinciple difference issolidsolid--liquid separationliquid separation

mechanismmechanism Membrane provides aMembrane provides a

more consistent, highermore consistent, higher

quality effluentquality effluent

Effluent Water QualityEffluent Water Quality


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Membrane provides an absolute barrier and effluentMembrane provides an absolute barrier and effluent

quality is no longer a concern.quality is no longer a concern.

ND (


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MBR eliminatesMBR eliminates the needthe needfor monitoring sludgefor monitoring sludge

settleabilitysettleability as anas anoperational parameteroperational parameter

Effluent quality is notEffluent quality is not

dependent on operationsdependent on operations Not necessary to determineNot necessary to determine

TSS/VSS concentrations toTSS/VSS concentrations to

maintain desired SRTmaintain desired SRT Can use fixed waste rateCan use fixed waste rate

SRT=V/QSRT=V/QWASWAS



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Public Health BenefitPublic Health Benefit

membranesmembranes increase the distanceincrease the distance

between reclamation and the risk ofbetween reclamation and the risk ofmicrobial diseasemicrobial disease

pathogens are removed by sizepathogens are removed by sizeexclusionexclusion

not a highly selective chemical or photochemicalnot a highly selective chemical or photochemical

reactionreaction

pathogens can be rejected, not justpathogens can be rejected, not just

reducedreduced

Results fromResults from operating MBR plants:operating MBR plants:



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IndigenousIndigenous ColiphageColiphage

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

0 1000 2000 3000 4000 5000 6000 7000 8000

Hours of Operation

Primary Effluent Reactor #1Reactor #2 Reactor #1 (Non-Detect)

Reactor #2 (Non-Detect) Tertiary

Repaired

Integrity

New Membranes

Reactor # 2

Start -up

Period


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MBR Effluent AllowsMBR Effluent Allows Modern ObjectivesModern Objectives

to beto be RealizedRealized

Ideal for UV disinfectionIdeal for UV disinfection All particulate matter and suspended solids thatAll particulate matter and suspended solids that

can interfere with UV have been rejected atcan interfere with UV have been rejected at

membrane barriermembrane barrier High percentHigh percent transmissivitytransmissivity (>70%)(>70%)

Dose of 80 mJ/cmDose of 80 mJ/cm22 adequate for MBR effluent,adequate for MBR effluent,

while 100 mJ/cmwhile 100 mJ/cm22 required for granular filteredrequired for granular filteredwastewaterwastewater

Ideal pretreatment process for reducingIdeal pretreatment process for reducing TDSTDS

Suitable for direct feed to ROSuitable for direct feed to RO

ChloramineChloramine residual is requiredresidual is required



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0

25

50

75

100

125

150

175

200

0 250 500 750 1000 1250 1500 1750 2000

Time of Operation, h

Ne

tOperatingPress

ure,psi

0

5

10

15

20

25

30

35

40

Temperature,

C

Net Operating Pressure Temperature

Plant shutdow n

Feed TDS = 1200 mg/L

Aqua 2000 Bureau II StudyAqua 2000 Bureau II Study[[FilmtecFilmtec BW 30BW 30--4040, low pressure4040, low pressure TFC RO membranes]TFC RO membranes]

11 weeks


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OutlineOutline







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Peak flows are well addressed in ASP, butPeak flows are well addressed in ASP, butcan be troublesome forcan be troublesome forMBRsMBRs

Membranes are designed for a certainMembranes are designed for a certainthroughput (design flux)throughput (design flux)

MBRsMBRs areare typicallytypically limited to a peakinglimited to a peakingfactor of 1.5Qfactor of 1.5Q

Dependent onDependent on design fluxdesign flux (aggressive or conservative)(aggressive or conservative),,

temperature, and mixed liquor conditionstemperature, and mixed liquor conditions

ASP is capable of sustaining larger peakASP is capable of sustaining larger peak

flows (>2.5Q) for longer periods of timeflows (>2.5Q) for longer periods of time Possible deterioration in effluent qualityPossible deterioration in effluent quality

Peak FlowsPeak Flows


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MBR designs for large peak flows considerMBR designs for large peak flows considerthe following solutions:the following solutions:

Additional membrane area for peak flow serviceAdditional membrane area for peak flow service

Flow equalization tanks (frequently primaryFlow equalization tanks (frequently primary effeff))

Flux enhancingFlux enhancing polymers orpolymers orcoagulantcoagulant

additionaddition Currently, the most conservative and costCurrently, the most conservative and cost

effective solution is typically some kind ofeffective solution is typically some kind of

flow equalizationflow equalization Flux enhancing polymers and coagulantFlux enhancing polymers and coagulant

addition are showing great promise, butaddition are showing great promise, butresearch on longresearch on long--term effects is neededterm effects is needed



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Peak flows will become less of a disadvantagePeak flows will become less of a disadvantageforforMBRsMBRs as membrane costs continue toas membrane costs continue todecline and our understanding ofdecline and our understanding ofconditionsconditions

affectingaffectingmembrane fouling increasemembrane fouling increase



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OutlineOutline







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Mixed liquor properties are importantMixed liquor properties are important

because they determine how easily a sludgebecause they determine how easily a sludge

can be filtered through a membrane, settledcan be filtered through a membrane, settledor dewateredor dewatered

Differences in solidDifferences in solid--liquidliquid separation applyseparation applydifferent selective pressuresdifferent selective pressures

ASPASP requires a biology that flocculates andrequires a biology that flocculates and

settles well to remain in the systemsettles well to remain in the system

MBRsMBRs retain all biomass, even single cells in theretain all biomass, even single cells in the

mixed liquormixed liquor



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MerloMerlo et al. (2004) revealed some keyet al. (2004) revealed some key

findings comparing SMBR and ASP underfindings comparing SMBR and ASP under

steady state conditions forsteady state conditions for2, 3, 4, 5, 102, 3, 4, 5, 10--ddSRTsSRTs

SMBR has higher colloidal contentSMBR has higher colloidal content

SMBR has higher filament concentrationsSMBR has higher filament concentrations

Both SMBR/ASP particle size distributionBoth SMBR/ASP particle size distribution

(excluding colloidal(excluding colloidal -- i.e. >2i.e. >2 m) was controlledm) was controlledexclusively byexclusively by mixing intensity, Gmixing intensity, G


Particle Size DistributionParticle Size Distribution


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0.0

0.1

0.2

0.3

0.4

0.5

0.6

2-4 4-6 6-8 8-10 10-20 20-40 40-100 100-2000

Fre

quency

CMAS Hi

Particle Size DistributionParticle Size DistributionASP HiASP Hivsvs. SMBR. SMBR

0.0

0.1

0.2

0.3

0.4

0.5

0.6

2-4 4-6 6-8 8-10 10-20 20-40 40-100 100-2000

Characteristic Length, m

SMBR

ASP


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OutlineOutline







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SMBRsSMBRs have advantages compared to ASPhave advantages compared to ASP(compact, high quality effluent, high MLSS(compact, high quality effluent, high MLSS

concentrations)concentrations)

SMBRsSMBRs havehave disadvantages compared todisadvantages compared to ASP (lowASP (low

SRT limit, peak flow issues)SRT limit, peak flow issues)

Mixed liquor properties are differentMixed liquor properties are different inin SMBRsSMBRscompared to the ASP because of the reactorcompared to the ASP because of the reactor

conditionsconditions

Engineers have been studying mixed liquorEngineers have been studying mixed liquorproperties to improve theproperties to improve the settleabilitysettleability of ASPof ASP

Future of the SMBR processFuture of the SMBR process will be studyingwill be studyingmixed liquor properties that improve filterabilitymixed liquor properties that improve filterability



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Questions?Questions?

activatesludgevs membrane reactor slide

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