dynamic control of membrane fouling in mbr system pncwa- session 22-6 - mbr… · presentation...
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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