Dynamic Control of Membrane Fouling in MBR Systemin MBR System

Chinh Hoang, Hong Zhao and Michael Sparks

Presentation Outline

� MBR Technology Overview� Membrane Fouling – Number One Issue Facing

MBR OperationMBR Operation� Factors Influence MBR performance� Pilot Study Results� Dynamic Control of Membrane Fouling� Summary

WAS

Influent Wastewater

Aeration Tank Final Clarifier

Air

UV

Tertiary Filter

Conventional Activated Sludge WWTPConventional Activated Sludge WWTP

Membrane Biological Reactor SystemsMembrane Biological Reactor Systems

WAS

Membrane Tank

Influent Wastewater

Air

UV

Aeration Tank

Membrane Biological Reactor SystemsMembrane Biological Reactor Systems

Small Footprint (HRT 4-7 hrs)

TANK VOLUMEActivated Sludge Process

Membrane Bioreactor Process

CONVENTIONAL AS

Activated Sludge Process

MBR

MBR

Features and Advantages of MBR Systems

� No need for secondary clarifiers or tertiary filters

� Absolute Barrier � Very compact footprint (MLSS 9 – 14,000 mg/L)mg/L)

� Long SRT• Complete nitrification• Reduced sludge generation

� Exceptional effluent quality• Typical ND on TSS and BOD• < 0.1 NTU Turbidity

MBR Major ComponentsMBR Major Components

Recirculation Pump

UV

Aeration Tank Membrane Tank

Permeate Pump

Fine Screen

Blower

A Closer Look

Treated water

Sludge

Membrane Bioreactor

Water/Air

Flow

Sludge

Membrane

Aeration

Fouling – Number One Issue Facing MBR Operation

� Over time membrane fouling is inevitable in MBR� Permeate flux decline (constant TMP operation) or TMP

increase (constant flux rate operation)� Two types of fouling – Reversible and Irreversible� Reversible fouling cause by deposition of large particles � Reversible fouling cause by deposition of large particles

and flocs on surface, can be managed with effective physical cleaning methods

� Irreversible Fouling cause by small colloids and solute that plugging membrane pores, CIP cleaning may be required

Fouling – Number One Issue Facing MBR Operation(con’t)

� Fouling usually lead to:• Increase in high air scour flow rate – higher energy

consumption• Increase in CIP frequency – higher chemical

consumption, shorter membrane life expectancyconsumption, shorter membrane life expectancy

� Fouling must be managed to sustain operation of MBR system

Factors Influence Fouling of Membrane

� Sludge characteristics:• MLSS level – generally higher the level faster the

formation of cake layer on membrane• The level of EPS in sludge – high level of EPS will

increase bio-fouling on membraneincrease bio-fouling on membrane• Size of particles – smaller particles combine with EPS

can form a denser cake layer and will be harder to get rid of the membrane surface

Factors Influence Fouling of Membrane (con’t)

� Permeate Flux Rate • Determine the rate of transport fouling components

toward membrane • The higher the flux rate the faster the formation of

cake layer on membranecake layer on membrane• TMP rise more quickly when operate above critical

flux• Membrane “prefer” to operate at sub-critical flux rate,

however fouling is inevitable in long term operation

� Air Scouring Flow Rate • Provide shear forces that will help remove the solids

on membrane surface• Determine the rate of back-transport of foulants away

from membrane surface

Factors Influence Fouling of Membrane (con’t)

from membrane surface• Generally higher flux rate would require higher air

scour rate

Factors Influence Fouling of Membrane (Con’t)

� Relaxation• Permeation is suspended, membrane sheets are

loose • Air scour cleaning is more effective

Scour Aeration

9 mins 1 min 1 min1 min9 mins 9 mins

Filtration

Pilot Study at Cary, NC

Pilot Study: Identifying Critical Flux

20

25

30

35

40

Permeate Discharge Flow, gpm

3.2

4.0

4.8

5.6

6.4

Transm

embrane Pressure, PSI

PERM_DIS_FLOW_EU

TMP_PSI_CALC

Y = 0.0036X

Y = 0.0094X

Y = 0.029X

0

5

10

15

20

11/30/06 14:00

11/30/06 14:10

11/30/06 14:20

11/30/06 14:30

11/30/06 14:40

11/30/06 14:50

11/30/06 15:00

11/30/06 15:10

11/30/06 15:20

11/30/06 15:30

11/30/06 15:40

11/30/06 15:50

11/30/06 16:00

Permeate Discharge Flow, gpm

0.0

0.8

1.6

2.4

3.2

Transm

embrane Pressure, PSI

Pilot Study: Sludge property Affecting Membrane Performance

0.30

0.35

0.40

0.45

0.50

Rate of TMP Increase within One Cycle,

PSI/m

in

Alum addition at 30 mg/L & Temp < 15oC

Alum addition at 75 mg/L & Temp > 15oCBiomass Killed &

Temp < 12oC

0.00

0.05

0.10

0.15

0.20

0.25

5 10 15 20 25 30 35 40 45

Permeate Flux Rate, GFD

Rate of TMP Increase within One Cycle,

PSI/m

in

F/M < 0.1 & Temp > 18oC

& Temp < 15oC

F/M > 0.2 Or Temp < 15oC

Pilot Study: Effect of Flux Rate on TMP (con’t)

30

35

40

45

50

Permeate flow, G

PM & Sco

uring Airflo

w,

SCFM & Tem

perature, oC

4.0

4.5

5.0

5.5

6.0

Transm

embrane Pressure, P

SIPermeate Flow

Scour Air

Temperature

TMP

Y = 0.156X

0

5

10

15

20

25

30

11/5/0617:07

11/5/0617:12

11/5/0617:17

11/5/0617:22

11/5/0617:27

11/5/0617:32

11/5/0617:37

11/5/0617:42

11/5/0617:47

11/5/0617:52

Permeate flow, G

PM & Sco

uring Airflo

w,

SCFM & Tem

perature,

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Transm

embrane Pressure, P

SI

TMP

Y = 0.020X

Y = 0.061X

Pilot Study: Ineffective Fouling Control Lead to Rising in TMP

30

35

40

45

50

Permeate flow, GPM & Scouring Airflow, SCFM &

Tem

perature, C 3.5

4

4.5

5

5.5

Transmem

brane Pressure, PSI

PERM_DIS_FLOW_EUMBR_AIR_FLOW_EUPERM_TEMP_EUTMP_PSI_CALC

Y = 0.15X

Y = 0.19

Y = 0.25X

Y = 0.32X

0

5

10

15

20

25

30

1/22/07 14:45 1/22/07 14:55 1/22/07 15:05 1/22/07 15:15 1/22/07 15:25 1/22/07 15:35

Permeate flow, GPM & Scouring Airflow, SCFM &

Tem

perature, C

0.5

1

1.5

2

2.5

3

3.5

Transmem

brane Pressure, PSI

Y = 0.11X

Pilot Study: Effect of Scour Air Flow Rates on TMP

40

50

60

70

Permeate flow, G

PM & Scouring airflow, SCFM & Tem

p, C

3.2

4

4.8

5.6

TMP, PSI

Permeate FlowScour Air FlowTemperatureTMP

0

10

20

30

2/1/07 8:52 2/1/07 9:07 2/1/07 9:21 2/1/07 9:36 2/1/07 9:50 2/1/0710:04

2/1/0710:19

2/1/0710:33

2/1/0710:48

2/1/0711:02

2/1/0711:16

Permeate flow, G

PM & Scouring airflow, SCFM & Tem

p, C

0

0.8

1.6

2.4 TMP, PSI

TMP

Effect of Relaxation Duration on TMP

30

35

40

45

50

Permeate flow, GPM & Scouring Airlfow, SCFM &

1.5

2

2.5

PERM_DIS_FLOW_EU

MBR_AIR_FLOW_EU

PERM_TEMP_EUTMP_PSI_CALC

0

5

10

15

20

25

30

2/2/07 8:21 2/2/07 8:28 2/2/07 8:35 2/2/07 8:42 2/2/07 8:49 2/2/07 8:57 2/2/07 9:04 2/2/07 9:11 2/2/07 9:18 2/2/07 9:25

Permeate flow, GPM & Scouring Airlfow, SCFM &

Tem

pe

0

0.5

1

1.5

TMP, PSI

1 min Relaxation, TMP not stable

2 min Relaxation,TMP stablized

Effect of Relaxation on TMP – No “True” Relaxation Leads to TMP Increase

40

45

50

55

60

65

Permeate flow, GPM & Scouring Airflow, SCFM & Tem

p, C

3.0

3.5

4.0

4.5

5.0

5.5

TMP, PSI

PERM_DIS_FLOW_EU

MBR_AIR_FLOW_EU

PERM_TEMP_EU

Temper adjusted TMP

TMP_PSI_CALC

TMP Jump

10

15

20

25

30

35

31-Dec

1-Jan2-Jan3-Jan4-Jan5-Jan6-Jan7-Jan8-Jan9-Jan

10-Jan

11-Jan

12-Jan

13-Jan

14-Jan

15-Jan

16-Jan

17-Jan

18-Jan

19-Jan

20-Jan

21-Jan

Permeate flow, GPM & Scouring Airflow, SCFM & Tem

p, C

0.0

0.5

1.0

1.5

2.0

2.5

TMP, PSI

Permeate siphoning during relaxation

Dynamic Control of Fouling

� A dynamic model can be employed to effectively control fouling

� Aim to control constant TMP� By adjusting one or more of the following control � By adjusting one or more of the following control

variables • Scour Air Flow Rate, V• Membrane Flux Rate, F• Relaxation Phase, TR• Permeate Phase, TP

Control Logic Scheme

� A hierarchal order logic scheme� Priorities of process control variables are

defined� Control variables must satisfy set of pre-defined � Control variables must satisfy set of pre-defined

conditions in order to be adjusted� Adjusting one or more process control variables

will be made in the next cycle

Filtration Cycles: Permeation and Relaxation Phases

Change in TMP within One or Two Filtration Cycles

Control Logic Scheme

Conclusions

� Fouling must be controlled in order to sustain operation of an MBR system

� MBR fouling can be managed by different techniques such as air scour, relaxation, and techniques such as air scour, relaxation, and reasonable flux (e.g. sub-critical) operation

� A dynamic model can be employed to effectively control fouling and avoid unnecessary over-scouring