Outline
• Introduction
• Membrane Issues
• Other Issues
Outline
• Introduction
• Membrane Issues
–General fouling
–Impact of SRT or F/M
–Impact of MLSS
–Impact of wet weather
• Other Issues
What is membrane fouling?
• Membrane fouling is the loss of permeability with
time
• In practice, this is observed as an increase in the
TMP required to maintain flow through the MBR
• For engineers, the increase in TMP
needs to be related to the flux rate
and normalized for temperature this is called a temperature
corrected “Permeability” or
“Specific Flux”
Definition of terms
Po
J = Q/A = membrane flux (m/s)
Membrane permeability = J/TMP
Pe
TMP = Po-Pe (Pa)
A
Membrane fouling:
TMP
time
Permeability
J
LP =
TMP
Typical units in USA:
gal/(ft2.d.lb/in2) or gfd/psi
Europe and Asia:
L/(m2.h.bar) or LMH/bar
Strict SI Units:
m2.s/kg
Temperature corrected permeability
o
20 C
P
L
=
J⋅e
(-0.0239(T -20))
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 40oC.
WHY DO WE DO THIS??
Because changes in the viscosity of water directly impact TMP
Temperature correction
2.0
1.6
Absolute viscosity of water, mPa•s
As water temperature decreases viscosity of water increases
Need to use a different equation
1.8
1.4
1.2
1.0
0.8
0.6
0.4
0.2
Actual
Calculated
All other conditions equal this increases the TMP
0.0
0
5
10
15
20
25
Temperature, ºC
30
35
40
45
Key MBR
Research Projects
List of Key Research Projects
• 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
MBR fouling theory
• 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 partially
degraded influent substrate
– Cells and microbes
– Cellular and microbial debris
– Inert suspended solids
– Dissolved inorganics (possible precipitants)
Resistance in-series model
• Simplistic model
• Widely used with low-pressure membranes
(MF/UF/MBR)
• Can be used to provide powerful insights to
MBR fouling
TMP
J=
µw ⋅ R T
J = membrane flux, m/s
TMP = trans-membrane pressure, Pa
µw = absolute viscosity of water, kg/m.s
RT = total resistance to filtration, m-1
Resistance in-series model
•
•
•
•
•
RT=RM+RF+RC
RT = Total resistance
RM = Membrane
RC = Cake Layer
RF = Foulants
–
–
–
Organic Adsorption
Inorganic Precipitation
Pore blocking
Membrane resistance, RM
Determining RM
90000
80000
70000
60000
TMP (Pa)
• RM is the hydraulic resistance
due to the membrane alone
• RM can be determined by
performing a clean water flux
profile on a clean membrane
• Record TMP and temperature
for 3 different flux rates
• Plot TMP vs. m*J, slope is RM
50000
RM = 3x1012 m-1
40000
30000
20000
y = 3E+12x + 21823
R2 = 0.9996
10000
0
5.E-09
6.E-09
7.E-09
8.E-09
9.E-09
Viscosity * Flux (kg/s 2 )
1.E-08
Other resistance terms
• RT is obtained during normal MBR operation R T =
–
–
–
TMP
µw ⋅ J
Increases with time or total volume filtered
Influenced by resistance of the filtration cake, RC
Influenced by the degree of foulant present on the membrane, RF
• 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 RM+RF (possibly some residual RC that’s why this is an estimate)
• Subtract RM (this was obtained before run began) and you
can approximate the amount of foulant, RF
• Remainder of RT is attributed to RC
Hydrodynamic force balance
• Membrane flux controls the rate of material transported
to the membrane surface, JSS
• The lift force controls the rate at which rejected material
is re-suspended to the bulk solution, VL
• Normal MBR operation
– Jss ≤ VL
– i.e. Operating at subcritical flux
Critical
Flux
Critical flux
• 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
Illustration of critical flux
20
MLSS = 8 g/L
SCFM = 30 scfm
gfd 8.7
18
gfd 10.9
gfd 13.1
gfd 15.3
gfd 17.5
Vacuum Pressure, in Hg
16
14
12
10
8
6
4
2
0
0
2
4
6
Time, minutes
8
10
Factors affecting critical flux
• Specific MBR hydrodynamics
– Hollow fiber versus flat sheet
– Coarse aeration distribution
– Pressure vs. Vacuum MBR systems
• Mixed 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 VL
» Higher viscosity - lower scouring efficiency
Importance of coarse bubble air
Adapted from Bérubé et al., 2005 AWWA MTC
Constant flux experiments
Single Phase = Water alone
Dual Phase = Air/Water
Conclusion: Maintaining clean, well-functioning,
and well-distributed coarse bubble air is critical
Cross-flow
velocity
Sludge Properties
Colloidal
Material
Filamentous
Microorganisms
Particle Size
Extracellular Polymeric
Substances (EPS)
Critical Flux Illustration
MLSS = 10-12 g/L
Air = 30 scfm
Adapted from Fan et al., 2006 Water Research V40
RM
RF
RC
–Jss = to membrane
–VL = away from membrane
–Jss ≥ VL (rapid fouling)
“Typical” MBR
Fouling Mechanisms
Photos adapted from Miura et al., 2007
“Typical” MBR fouling mechanisms
• 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 µm
– Not incorporate into larger floc
– Not yet clear whether colloidal or soluble is culprit (likely both)
» 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
Extracellular Polymeric Substances
(EPS) and Soluble Microbial Products
(SMP)
Hydrolysis
EPS
Active Cell
SMP
Diffusion/Shear
Adsorption and
flocculation
Substrate
Organic fouling
Adapted from Lesjean et al., 2005 Water Science and Technology
Organic fouling
70
Total SMP = 7.0x + 36.8
2
R = 0.77
SMP concentration, mg/L
60
50
40
30
20
SMP = soluble microbial products
(soluble protein + soluble carbohydrate)
10
0
0.0
0.5
1.0
1.5
2.0
2.5
Steady-state fouling rate, LMH/bar • d
Adapted from Trussell et al., 2006
3.0
3.5
4.0
Inorganic foulants
• 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
Coagulant Addition
Adapted from Holbrook et al., 2004 Water Environment Research
Polymer Addition
• Benefits of specialized polymer addition or “flux
enhancers” are 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 long-term
basis
– 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
Polymer Addition
Adapted from Yoon et al., 2005 Water Science & Technology
Other Important
Fouling Mechanisms
Changes in MLSS concentration
• Increases in the MLSS concentration are important
– Increases the JSS 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)
Changes in mixed liquor properties
• 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 RC will occur
»
»
»
Increase in colloidal content
Disperse flocs and single cells
Dramatic changes can be quantified by time to filter (TTF)
Mixed liquor viscosity
Adapted from Cui et al., 2003
Other important mixed liquor
properties for MBR fouling
• 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
Chemical foulant studies
• 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 soluble organic
(e.g. >10 kDa and < 100 kDa)
• High concentrations of EPS do not always result in increased fouling
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 RC
Is Pore Size Important?
MF vs UF
• A much debated topic
• Some believe that MF has a higher fouling tendenacy
than UF membranes
• Some believe the MF and UF membranes in MBRs
will produce significantly different effluent water
qualities, possibly impact reactor design by the
retention of additional organics
• Hermanowicz et. al (2006) clarified a Novak
publication that suggested whether an MBR is MF or
UF would impact the biological design
– Having either an MF or UF produced similar COD at the
same conditions
Dynamic Cake Layer
(Lee et al. 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
US Bureau of Rec. Report
(2000)
Rapid fouling
attributed to MF
module
Impact of SRT or F/M on
Membrane Fouling
Rationale
F
So
=
M θ H ⋅ X MLVSS
• The SMBR process is currently
limited to an MLSS concentration of
10 g/L
• The F/M ratio is a key parameter to
optimize reactor tank design
– Small tank (low HRT)
– Small tank (high F:M)
Rationale
Present Worth, $
Capital
O&M
θH, time
Equipment and Apparatus
• Pilot-scale
SMBR
• Treating
primary
effluent from
the City of San
Francisco’s SEP
– COD = 325 mg/L
– TSS = 98 mg/L
Membrane Operation and
Characteristics
Zenon 500C Module
Nominal = 0.035 µm
Flux = 30 L/m2.h
Air = 14 L/s
Intermittent
aeration
• 9 min operating
cycle followed by
30 sec relax
•
•
•
•
•
Experimental Methods
• Initial operating conditions:
MCRT = 10 d (F/M = 0.34 gCOD/gVSS.d)
• Dissolved oxygen > 2 mg/L
• Constant MLSS = 8g/L
• Steady-state data collection began
after 3 MCRTs
• 2 week steady-state data collection
period
• MCRT was steadily decreased (5, 4, 3, 2
d)
– F/M (0.53, 0.73, 0.84, 1.4 gCOD/gVSS.d)
Membrane Performance at 10-d
MCRT (F/M=0.34 gCOD/gVSS.d)
Flux
Specific Flux
300
40
Start-up
Chemical Clean
Large Foam Event
35
30
200
o
25
Specific Flux @ 20 C, LMH/bar
250
20
150
15
100
10
50
5
0
50
70
90
110
130
Days of Operation
150
170
0
190
Membrane Performance at 5-d MCRT
(F/M=0.53 gCOD/gVSS.d)
Flux
Specific Flux
40
300
35
30
200
25
150
20
15
100
10
50
5
0
180
190
200
210
220
230
240
Days of Operation
250
260
270
0
280
Specific Flux @ 20oC, LMH/bar
250
Membrane Performance at 4-d MCRT
(F/M=0.73 gCOD/gVSS.d)
Flux
Specific Flux
40
300
Intermittent Coarse Air Failure
Foam Event
35
30
200
25
150
20
15
100
10
50
5
0
270
280
290
300
Days of Operation
310
320
0
330
Specific Flux @ 20oC, LMH/bar
250
Membrane Performance at 3-d MCRT
(F/M=0.84 gCOD/gVSS.d)
Flux
Specific Flux
300
40
Routine Feed
Line Cleaning
Routine Feed
Line Cleaning
Intermittent Coarse
Air Failure
35
30
200
25
20
150
15
100
10
50
5
0
355
360
365
370
375
380
Days of Operation
385
390
0
395
Specific Flux @ 20oC, LMH/bar
250
Membrane Performance at 2-d MCRT
(F/M=1.4 gCOD/gVSS.d)
Flux
Specific Flux
40
300
Foam Event
35
30
200
25
20
150
15
100
10
50
5
0
390
395
400
405
Days of Operation
410
0
415
Specific Flux @ 20oC, LMH/bar
250
Effect of F/M on Steady-State Fouling Rate
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
F/M, g COD/g VSS.d
1.0
1.2
1.4
1.6
Steady-state Fouling Rate vs sCOD
Soluble COD
COD Rejection
100
90
sCOD = 3.8x + 61.3
80
90
2
R = 0.30
70
60
60
50
COD Rejection = -1.5x + 63.0
50
R2 = 0.24
40
40
30
30
20
20
10
10
0
0
0.0
0.5
1.0
1.5
2.0
2.5
Steady-state fouling rate, LMH/bar.d
3.0
3.5
4.0
COD Membrane Rejection, %
80
70
Steady-state Fouling Rate vs SMP
Protein
Carbohydrate
Total
70
Total SMP = 7.0x + 36.8
R2 = 0.77
60
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
Steady-state fouling rate, LMH/bar.d
3.0
3.5
4.0
Conclusions
• High organic loading rates (F/M)
increased membrane fouling rates
• Biological foaming was controlled
mechanically
• Increased steady-state membrane fouling
rates correlated with SMP, not sCOD
• Understanding membrane fouling at high
organic loading rates allows engineers
to design a compact SMBR without:
– excessive maintenance costs or
– failing to meet the design capacity
Why does high F/M cause
membrane fouling
Effect of F/M on Steady-State Fouling Rate
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
F/M, g COD/g VSS.d
1.0
1.2
1.4
1.6
Equipment and Apparatus
• Bench-scale
SMBR
• Treating
primary
effluent from
the City of San
Francisco’s SEP
– COD = 325 mg/L
– TSS = 98 mg/L
Membrane Operation and
Characteristics
• Mitsubishi
Sterapore®
• Nominal pore size
= 0.4 µm
• Membrane flux = 18
L/m2.h
• Coarse bubble air
= 0.4 L/s
• 9 min operating
cycle followed by
30 sec relax
Experimental Methods
• Operating conditions:
MCRT = 10 d (F/M = 0.50 gCOD/gVSS.d)
MCRT = 2 d (F/M = 2.34 gCOD/gVSS.d)
• Dissolved oxygen > 2 mg/L
• Constant MLSS = 1.4 g/L
• Steady-state data collection began
after 3 MCRTs
• 2 week steady-state data collection
period
Tools Used to Understand
Membrane Fouling
• 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 20oC and 210 kPa
• Fouled membrane resistances
Fouled Membrane Resistance
Terms
• R=RM+RF+RC
• R = Total
resistance
• RM = Membrane
• RC = Cake Layer
• RF = Foulants
– Organics Adsorption
– Inorganic
Precipitation
Membrane Performance at 10-d
MCRT (F/M=0.50 gCOD/gVSS.d)
Flux
Specific Flux
600
40
Start up
66 Days at 10-d MCRT
(F/M = 0.50 gCOD/gVSS.d)
35
30
400
25
20
300
15
200
10
Steady-state fouling rate
100
Chemical Cleaning
5
0
0
0
10
20
30
40
Days of Operation
50
60
70
80
Specific Flux @ 20oC, LMH/bar
500
Membrane Performance at 2-d MCRT
(F/M=2.34 gCOD/gVSS.d)
Flux
Specific Flux
40
600
25 Days at 2-d MCRT
(F/M = 2.34 gCOD/gVSS.d)
35
30
Chemical
Cleaning
Chemical Cleaning
Chemical Cleaning
400
25
20
300
15
200
Steadystate
10
100
5
Improper
Wasting
Volumes
0
75
80
85
90
Days of Operation
95
100
0
105
Specific Flux @ 20oC, LMH/bar
500
Steady-State Membrane
Fouling Rates
F/M
MCRT
gCOD/gVSS.d
d
10
2
0.50
2.34
Steady-state Fouling
Rate @ 20oC
LMH/bar.d
2.60
59.0
SMPc
SMPp
Total SMP
mg/L
24
10
mg/L
14
49
mg/L
38
59
• Membrane fouling rates increased
with F/M
• Total SMP concentration increased
with F/M
• Unlike pilot-scale work, SMPc did
not increase with increasing F/M
Carbohydrate Molecular Weight
Increased at Low MCRT (High F/M)
> 10 kDa
10 kDa - 1 kDa
< 1 kDa
Carbohydrate concentration, mg/L
25
20
15
10
5
0
Influent
SMP - 10 d
SMP - 2 d
Sample
Effluent - 10 d Effluent - 2 d
Protein Molecular Weight Increased
at Low MCRT (High F/M)
> 10 kDa
10 kDa - 1 kDa
< 1 kDa
Protein Concentration, mg/L
70
60
50
40
30
20
10
0
Influent
SMP - 10 d
SMP - 2 d
Sample
EFF - 10 d
EFF - 2 d
Fouled Membrane FTIR Results
100
10-d MCRT (Green)
Virgin (Blue)
80
60
2-d MCRT
%T
40
20
10
4000
3000
2000
W a v e n u m b e r[c m -1 ]
3380 - indicates OH stretching
1660 and 1540 - indicates NH and COO- (protein)
1060 - indicates CO stretching of polysaccharides
1000
650
Fouled Membrane Resistance
10-d MCRT
Fouling Resistance During 10 days MCRT Operation
25
Before
cleaning
20
y = 4.2319x
R2 = 0.9979
y = 0.4014x
R2 = 0.5914
Physical
y = 4.0956x
15
Chemical
R2 = 0.9757
10
5
0
0
5
10
15
20
25
Viscosity * Flux
(µ
µg/s2)
After 66 d of operation without a chemical clean
30
35
40
Fouled Membrane Resistance
2-d MCRT
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
Viscosity * Flux
(µ
µg/s2)
After 5 d of operation without a chemical clean
25
30
Fouled Membrane Resistance
Terms
B
A
RMembrane
9%
RMembrane
21%
RCake
3%
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)
RCake
15%
Batch Filtration Results
• 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 20oC
and 210 kPa
Batch Filtration Results
SRT, d
10
2
Modified Fouling Index, 10-3 s/L2
Mixed Liquor Soluble
SS
Mixture Effect
17
11
2
4
47
27
12
8
• Higher sludge resistance observed
d MCRT
• Reduction in sludge filterability
observed as membrane fouling
at 2was
– Fouled resistances 4.23 (10-d) and 2.07 (2d) with measurement was made on membrane
permeate
– Fouled permeability 71 (10-d) and 63 (2-d)
with measurement was made during operation
Batch Filtration Results
SRT, d
10
2
Modified Fouling Index, 10-3 s/L2
Mixed Liquor Soluble
SS
Mixture Effect
17
11
2
4
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
EPS Data
Mean Concentration, mg/gVSS
MCRT, d
< 1 kDa 10 kDa - 1 kDa
> 10 kDa
Carbohydrate
10
4.3
17.6
7.8
2
5.5
6.8
18.3
Protein
10
30.6
46.2
14.4
2
48.5
11.3
60.9
Total
29.7
30.6
91.2
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
Carbohydrate EPS
B
A
< 1 kDa
14%
> 10 kDa
26%
< 1 kDa
18%
10 kDa - 1
kDa
22%
> 10 kDa
60%
10 kDa - 1
kDa
60%
Carbohydrate
Total Concentration: 29.7±1.7 mg/gVSS
Carbohydrate
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)
Protein EPS
B
A
> 10 kDa
16%
< 1 kDa
34%
< 1 kDa
40%
10 kDa - 1
kDa
50%
Protein
Total Concentration: 91.2±6.6 mg/gVSS
> 10 kDa
51%
10 kDa - 1
kDa
9%
Protein
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)
Conclusions
• High organic loading rates (F/M)
increased membrane fouling rates
• Increased steady-state membrane fouling
rates correlated with total SMP
• MW of carbohydrate and protein SMP
increased with F/M
• Membrane rejected higher MW SMP
• FTIR indicated protein and carbohydrate
presence on fouled membranes with
stronger adsorptions resulting from the
2-d MCRT condition
Conclusions
• Membrane fouling was primarily due to
the adsorption of organics and RF was
dominate resistance term of fouled
membranes
• RC increased with F/M and this was
attributed to changes in floc properties
that result in a “sticky” cake
• Sludge filtration resistance (MFI)
increased with F/M
• MFI of suspended solids increased 6
times, supporting the increasing
importance of the cake layer with
increasing F/M