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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 Impact of flocfloc structurestructure

•• Other IssuesOther Issues

Principle Disadvantages of Principle Disadvantages of MBR ProcessMBR Process

•• Hydraulic Hydraulic

throughputthroughput

•• Membrane Membrane

foulingfouling

•• High MLSS High MLSS

concentrations concentrations

can result in can result in

rapid foulingrapid fouling

Some Perspective on High MLSS Some Perspective on High MLSS Concentrations in Concentrations in MBRsMBRs

•• Yamamoto et al., 1989 published the Yamamoto et al., 1989 published the

first paper on the SMBR configurationfirst paper on the SMBR configuration

•• Yamamoto, operation was possible up to Yamamoto, operation was possible up to

MLSSMLSSmaxmax= 40g/L= 40g/L

•• Ross et al., Ross et al., 1990 showed 1990 showed that that MLSSMLSSmaxmax→→→→→→→→60 g/L for an 60 g/L for an EMBREMBR

•• So, why are we So, why are we at 8 to 10 g/L?at 8 to 10 g/L?

Membrane TheoryMembrane Theory•• Membrane flux controls the rate of Membrane flux controls the rate of

material transported to the membrane material transported to the membrane

surface, Jsurface, JSSSS

•• The shear force controls the rate at The shear force controls the rate at

which rejected material is which rejected material is

resuspendedresuspended to the bulk solution, Vto the bulk solution, VLL

•• Simple modelSimple model

J =∆P

ηW ⋅RT

RM

RF

RC

––JssJss = to membrane= to membrane

––VVLL = away from membrane= away from membrane

––JssJss ≥≥ VVL L (rapid fouling)(rapid fouling)

Sustainable FluxSustainable Flux

•• Normal steady state operationNormal steady state operation

–– JssJss ≤≤ VVLL–– i.e. Operating at a sustainable fluxi.e. Operating at a sustainable flux

•• For a given flux and aeration rateFor a given flux and aeration rate

––Increasing the MLSS Increasing the MLSS

increases increases JssJss

––Increasing the MLSS Increasing the MLSS

reduces Vreduces VLL

––So, increasing the So, increasing the

MLSS has two MLSS has two

compounding effects compounding effects

that increase Rthat increase RCC

Effect of High MLSSEffect of High MLSS

•• Conditions that Conditions that

result in the result in the

accumulation of Raccumulation of RCC

–– Increase MLSSIncrease MLSS

–– Increase flux Increase flux

((JssJss))

–– Decrease VDecrease VLL»» Change in viscosityChange in viscosity

»» Reduced aeration Reduced aeration

intensity (plugged intensity (plugged

ports)ports)

•• Generally, high MLSS results in Generally, high MLSS results in membrane membrane ““sludgingsludging”” due to due to excessive Rexcessive RCC

•• Common claim or differentiator between Common claim or differentiator between

manufacturers is, manufacturers is, ““Our system can operate at higher Our system can operate at higher

MLSS concentrations than X can.MLSS concentrations than X can.””

•• Nobody is defying physics and the basic principles Nobody is defying physics and the basic principles

outlined in this talkoutlined in this talk

•• Either one of the following things is occurring:Either one of the following things is occurring:

–– The system has a higher aeration intensity (e.g. total aeration The system has a higher aeration intensity (e.g. total aeration

required for membranes/total membrane area)required for membranes/total membrane area)

–– The system is at a reduced flux rate (e.g. membrane The system is at a reduced flux rate (e.g. membrane

thickeners)thickeners)

•• Specific system hydraulics cannot totally be neglected, Specific system hydraulics cannot totally be neglected,

but generalizations can be madebut generalizations can be made

Operating at Higher MLSS Operating at Higher MLSS Is PossibleIs Possible

Experiments to Understand

High MLSS Fouling

Equipment and ApparatusEquipment and Apparatus

•• PilotPilot--scale SMBRscale SMBR

•• Capacity of 11,000 Capacity of 11,000

gpdgpd or 43 mor 43 m33/d/d

•• Treating primary Treating primary

effluent from the effluent from the

City of San City of San

FranciscoFrancisco’’s SEPs SEP

–– COD = 325 mg/LCOD = 325 mg/L

–– TSS = 98 mg/LTSS = 98 mg/L

Membrane Operation and Membrane Operation and CharacteristicsCharacteristics

•• Zenon 500C ModuleZenon 500C Module

•• Pore sizePore size

–– Nominal = 0.035 Nominal = 0.035 µµµµµµµµmm

–– Absolute = 0.1 Absolute = 0.1 µµµµµµµµmm

•• HydrophilicHydrophilic

•• Membrane fluxMembrane flux

30 L/m30 L/m2.2.h or 18 gfdh or 18 gfd

•• Coarse bubble airCoarse bubble air

14 L/s or 30 scfm14 L/s or 30 scfm

•• Intermittent aerationIntermittent aeration

•• 9 min operating cycle9 min operating cycle

with 30 sec relaxwith 30 sec relax

Experimental MethodsExperimental Methods

•• ShortShort--term and Longterm and Long--term experimentsterm experiments

•• ShortShort--termterm

–– Achieved steady state condition at Achieved steady state condition at MCRTsMCRTs of 10, 20 of 10, 20

and 30 d (MLSS = 12and 30 d (MLSS = 12--15 g/L)15 g/L)

–– Performed MLSS thickening experiments at constant Performed MLSS thickening experiments at constant

flux (30 LMH or 18 gfd)flux (30 LMH or 18 gfd)

»» Monitored membrane permeability, MLSS concentration and Monitored membrane permeability, MLSS concentration and

ML propertiesML properties

–– Shut off influent 15 minutes prior to experimentShut off influent 15 minutes prior to experiment

–– Performed 1 experiment per dayPerformed 1 experiment per day

–– Performed the experiment with different coarse bubble Performed the experiment with different coarse bubble

aeration rates (20, 30, 40 scfm or 9.4, 14.2, 18.9 aeration rates (20, 30, 40 scfm or 9.4, 14.2, 18.9

L/s)L/s)


•• LongLong--termterm

–– Used the previously achieved steady Used the previously achieved steady

state condition as starting points state condition as starting points

»» MCRTsMCRTs of 10, 20 and 30 dof 10, 20 and 30 d

»» MLSS 12MLSS 12--15 g/L15 g/L

–– Ceased ML wastingCeased ML wasting

–– Continue operationContinue operation

»» constant flux = 30 LMH (18 gfd)constant flux = 30 LMH (18 gfd)

»» Coarse bubble air = 14 L/s (30 scfm)Coarse bubble air = 14 L/s (30 scfm)

–– Monitored membrane performance, MLSS Monitored membrane performance, MLSS

concentration and ML propertiesconcentration and ML properties


•• ML ViscosityML Viscosity

–– Brookfield Rotational Brookfield Rotational Viscometer (LV2 Viscometer (LV2 spindle)spindle)

•• Additional ML Additional ML PropertiesProperties

–– Soluble CODSoluble COD

–– Soluble Microbial Soluble Microbial Products (SMP)Products (SMP)

–– Extracellular Extracellular Polymeric Substances Polymeric Substances (EPS)(EPS)

–– Colloidal materialColloidal material

Membrane PerformanceMembrane Performance

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200

Days of Operation

0

10

20

30

40

50

60

70

80

90

100

Flux, LMH

Specific Flux @ 20C Flux

10-d MCRT 20-d MCRT 30-d MCRT

Long-term

Experiments

Long-term

Experiment

Poor Sludge Filterability

Unable to Maintain Flux

at 30 LMH

Mixed Liquor ViscosityMixed Liquor Viscosity

y = 14676x-

0.7747

y = 2406.6x-

0.7019

y = 4617x-

0.6733

y = 6788.4x-

0.6958

10

100

1000

10000

100000

0.1 1 10 100

Spindle Speed, rpm

14.4 g/L 16.4 g/L 18.4 g/L 20.2 g/L


y = 6.357e0.1726x

R2 = 0.9393

y = 5.3776e0.2142x

R2 = 0.9348

y = 7.4013e0.1656x

R2 = 0.9885

0

100

200

300

400

500

600

700

10 12 14 16 18 20 22 24 26 28

MLSS, g/L


LV Spindle #2, 100 rpm

10-d MCRT:

20-d MCRT:

30-d MCRT:

Eiler’s EquationEilerEiler’’s Equations Equation

ηη o

= 1 +

η i

2φ

1 −φ

εMax

2

Where,

η = viscosity of suspension

ηο = viscosity of pure suspending fluid

ηI = intrinsic viscosity

φ = volume fraction≈MLSS/MLSSmax

εMax = maximum packing density

Eiler’s Equation vs. MLSSEilerEiler’’s Equation vs. MLSSs Equation vs. MLSS

1

2

3

4

5

6

7

8

9

10

0 5 10 15 20 25 30

MLSS, g/L

MLSS max =40 g/L

MLSS max =120 g/L

MLSS max =80 g/L

MLSS max =60 g/L

MLSS max =50 g/L

ShortShort--term term -- 20 scfm20 scfm

0.5

0.6

0.7

0.8

0.9

1.0

1.1

10 12 14 16 18 20 22 24 26 28

MLSS, g/L


Coarse Airflow Rate = 20 scfm (9.4 L/s)


0.5

0.6

0.7

0.8

0.9

1.0

1.1

10 12 14 16 18 20 22 24 26 28

MLSS, g/L



ShortShort--term term -- 1010--d MCRTd MCRT

0.5

0.6

0.7

0.8

0.9

1.0

1.1

10 12 14 16 18 20 22 24 26

MLSS, g/L

20 scfm 30 scfm 40 scfm

MCRT = 10 d

Importance of ViscosityImportance of Viscosity

0.5

0.6

0.7

0.8

0.9

1.0

1.1

0 50 100 150 200 250 300 350 400 450

Viscosity, mPa.s

1.5E-4 m/s 2.3E-4 m/s 3.0E-4 m/s

Critical Flux IllustrationCritical Flux Illustration

•• Normal steady state operationNormal steady state operation

–– JssJss ≤≤ VVLL–– i.e. Operating below critical fluxi.e. Operating below critical flux

•• ShortShort--term experimentsterm experiments

––JssJss increased as MLSS increased as MLSS

increasedincreased

––Membrane permeability Membrane permeability

varied with MLSS Conc.varied with MLSS Conc.

––Strong function of Strong function of

VVLL, not , not JssJss


Adapted from Cui et al., 2003 Journal of Membrane Science

Membrane Permeability RecoveryMembrane Permeability Recovery

Percent Post Experiment

Initial After Change Recovery Time, min

9.4 70.4 62.4 11% 0

9.4 same 69.7 1% 180

14.2 69.6 59.3 15% 5

14.2 same 68.6 1% 120

18.9 71.1 67 6% 2

18.9 same 70.5 1% 180

9.4 66.2 66.7 -1% 0

14.2 65.5 67 -2% 180

18.9 65.4 64.4 2% 0

9.4 79.8 75.7 5% 0

14.2 81.3 80.5 1% 0

18.9 77.2 76.4 1% 0

30

20

Coarse

Aeration Rate,

L/s

Specific Flux@20oC, LMH/bar

MCRT, d

10

•• No chemical cleans were performedNo chemical cleans were performed

•• Collected permeate and diluted ML Collected permeate and diluted ML to original MLSS concentrationto original MLSS concentration

Mixed Liquor PropertiesMixed Liquor Properties

1.5x10-4

2.3x10-4

3.0x10-4

1.5x10-4

2.3x10-4

3.0x10-4

1.5x10-4

2.3x10-4

3.0x10-4

t0 98 72 73 23 20 27 26 29 21

tF 86 77 - 27 32 23 46 38 48

Total SMP 29 45 105 41 30 46 33 32 35

SMPc 12 26 26 19 20 19 21 21 21

SMPp 17 19 79 22 10 27 12 11 14

SMP P/C - 1.4 0.7 3.0 1.2 0.5 1.4 0.6 0.5 0.7

Total SMP 45 53 166 45 35 48 33 35 39

SMPc 16 27 26 20 22 19 21 22 20

SMPp 29 26 140 25 13 29 12 13 19

SMP P/C - 1.8 1.0 5.4 1.3 0.6 1.5 0.6 0.6 1.0

Total EPS 81 87 102 115 104 114 103 103 105

EPSc 24 24 27 26 27 27 29 28 29

EPSp 57 62 74 88 77 87 74 75 76

EPS P/C - 2.4 2.6 2.7 3.4 2.8 3.2 2.6 2.6 2.6

t0 73 82 75 47 50 50 37 74 63

tF 101 115 113 70 62 57 71 59 92

t0

Colloidal

Material

tF

t0

Units

10-d MCRT

mg/g VSS

sCOD mg/L

mg/L

mg/L

NTU

Aeration Intensity, m/s

20-d MCRT 30-d MCRT

Sample*

Mixed

Liquor

Property

Mixed Liquor PropertiesMixed Liquor Properties

y = 4.1402x + 17.96

R2 = 0.7552

y = 1.79x + 35.777

R2 = 0.2364

y = 0.6978x + 48.644

R2 = 0.166

20

40

60

80

100

120

140

10 12 14 16 18 20 22 24 26 28

MLSS, g/L


LongLong--term Experimentsterm Experiments

0.5

0.6

0.7

0.8

0.9

1.0

1.1

10 15 20 25

MLSS, g/L


Coarse Airflow Rate = 30 scfm

What happened?What happened?•• LongLong--term experimentsterm experiments

–– JssJss is increasing with timeis increasing with time

–– VVLL is decreasing with time as coarse is decreasing with time as coarse

bubble aeration efficacy decreases with bubble aeration efficacy decreases with

increasing ML viscosityincreasing ML viscosity

•• Importance of TimeImportance of Time

–– Small difference Small difference between between JssJss and Vand VLLbecomes more important becomes more important with timewith time

––Slower MLSS thickening Slower MLSS thickening results in fouling at results in fouling at lower MLSS conc.lower MLSS conc.

Exposure Time to High MLSSExposure Time to High MLSS

0.5

0.6

0.7

0.8

0.9

1.0

1.1

10 12 14 16 18 20 22 24 26 28

MLSS, g/L

Short-term Exp Extended Short-term Exp No Wasting Exp

Data from 20-d and 30-d MCRTs

Aeration Intensity = 2.3E-4 m/s (14.2 L/s)

Membrane Flux = 30 L/(m2h)

Increasing Exposure

Time to High MLSS

Conditions

ConclusionsConclusions

•• High MLSS concentrations reduce High MLSS concentrations reduce

membrane permeabilitymembrane permeability

•• Increased coarse bubble aeration Increased coarse bubble aeration

rates improved permeabilityrates improved permeability

•• ML viscosity is important for ML viscosity is important for

backtransportbacktransport of rejected materialof rejected material

•• Exposure time to high MLSS is Exposure time to high MLSS is

importantimportant

Questions?Questions?

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