case history - mbr plant achieves higher flow with permacare
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Case Study CH-573
MBR plant achieves 50 – 65% higher flowrates with PermaCare® MPE50™ polymer
SituationSituationSituationSituationSituationOur client, a membrane bioreactor
plant that treats municipal waste-
water, used Nalco’s Membrane
Performance Enhancer™ (MPE)
solution to increase plant filtration
rates. The product, PermaCare
MPE50 polymer:
• Enabled the plant to operate at
50% higher flow rates, reducing
the need to purchase additional
membrane units and associated
equipment
• Reduced the plant’s frequency of
membrane cleaning
• Increased the plant’s filtration
capabilities, allowing it to accom-
modate peak flow rate conditions
PermaCare MPE50 polymer offers
additional benefits for membrane
bioreactor plants, such as:
• Higher peak flow operation
without flux loss
• Lower membrane operating
costs, such as scouring air
• Better permeate quality: reduc-
tion in TOC, COD, TSS, color
and turbidity; increased removal
of pathogens, including viruses
and phages
• Better performance at low
temperature
• Better biological stability to upset
conditions
• Foam removal and prevention
ProblemProblemProblemProblemProblemOur client had a limited capacity
to handle their high influent
wastewater flow. The options that
addressed this problem were:
• Install additional membrane
units to increase filtration
capacity, which would require
new membranes and associ-
ated process equipment.
• Clean the membrane more
frequently, to try to restore lost
filtration performance.
PermaCare MPE50 polymer
enabled the plant to both increase
throughput and reduce membrane
fouling. Membrane fouling occurs
because microbes produce
extracellular polysaccharides and
proteins known as soluble micro-
bial products (SMP), which build
up, bind to, and foul membrane
surfaces, impeding the flow of
water through the membrane.
To minimize membrane fouling,
operators at membrane bioreactor
treatment (MBR) plants are forced
to decrease their operating flux.
But decreased operating flux
reduces the throughput of the
MBR and can force the plant to
bypass untreated wastewater.
Alternatively, the MBR can operate
at a higher flux, but this typically
results in a high rate of membrane
fouling, which in turn forces an
increase in the frequency of
membrane cleaning.
The addition of
PermaCare MPE50
polymer improved the
performance of a
membrane bioreactor
operating on municipal
wastewater
Until this recent increase in influent
flow, the plant flow had varied
between 140 – 200 m3/day.
Recently, the flow rate reached
the design flow rate of 240 m3/day.
A system diagram is shown in
Figure 1.
This plant could have installed
additional membrane units to
increase filtration capacity, but this
would require additional capital
expenditure for new membranes
and associated process equipment.
So the plant started frequent
membrane cleaning to try to restore
lost filtration performance.
SolutionSolutionSolutionSolutionSolutionPermaCare MPE50 polymer
consists of specially formulated
cationic polymers, and the product
is compatible with all commercially
available membranes for MBRs. It
is theorized that the MPE products
react with the soluble microbial
products (SMP), and, through a
process of coagulation, collapse
the extended structure of the SMP
into a more compact shape that’s
readily incorporated into the
biofloc. That means that there is
less SMP that is able to contact
and foul the membrane surfaces.
Figures 2a and 2b photos
(magnified 100x and stained with
India ink) show the difference in
the mixed liquor before and after
treatment with Nalco’s MPE
products. The white color is the
biopolymers that cause the buildup
and subsequent membrane fouling.
Notice in Figure 2b the reduction in
the available biopolymers after the
treatment with PermaCare MPE50
polymer.
PermaCare MPE50 polymer was
added to the plant-mixed liquor and
helped increase membrane plant
filtration rates by:
• Mitigating the negative effects of
membrane-fouling biopolymers
and other membrane foulants.
• Increasing cake porosity on the
membrane.
This reduced membrane fouling
and increased MBR throughput.
Figure 2a – PermaCare MPE50 polymermixed liquor stained with India ink
Figure 2b – Bioreactor mixed liquortreated with PermaCare MPE50polymer and stained with India ink
Figure 1 – Membrane bioreactor plant flow diagram and basic data
5.4 hr anoxic(56 m3)
9.3 hr anoxic(97 m3)
Influentwastewater
240 m3/day
3–5Q
450 m3 air/hr
To river
Design flow rate: 240 m3/day
Wastewater: Municipal
Membrane area: 150 cartridges x 5 units x 0.8 m2 = 600 m2
HRT: 5.4 hr in anoxic tank (56 m3) + 9.3 hr in oxic tank (97 m3)Total HRT = 14.7 hr (153 m3)
MLSS range: 8,000 – 15,000 mg/L (11,000 mg/L average)
Sludge removal: Infrequent
Influent: BOD 150 ppm, SS 150 ppm, TN 42 ppm at 6/2/2003
Aeration: Coarse bubble to membrane units (90 m3/hr for each unit),and no fine bubble biological air
ResultsResultsResultsResultsResultsWe concluded that 100 PPM of
PermaCare MPE50 polymer
increased the critical flux value by
more than 100%. The following
sections discuss how we ap-
proached the test.
Basic test
For the test, we followed this
process:
• Cleaned the five membrane units
according to the manufacturer’s
recommended procedure.
• Measured the critical flux value
(CFV), or the largest flux that can
be achieved before any signifi-
cant membrane fouling occurs,
for each module, by increasing
the membrane flux in incremental
steps. At each step, we main-
tained the flux constantly for 10
minutes and stopped when the
transmembrane pressure (TMP)
increased during the 10 minute
test interval, because this
increase indicates that particu-
late matter was accumulating on
the membrane surface, which
could result in membrane fouling.
• Added approximately 100 PPM
of the PermaCare MPE50
polymer to the bioreactor mixed
liquor and repeated the critical
flux value test.
• During the control CFV test (no
PermaCare MPE50 polymer
added), the transmembrane
pressure (TMP) deviated from
the trend line when the flux
increased from 25 LMH to 29
LMH, indicating that the mem-
brane was fouling. We concluded
that the control critical flux value
was 25 LMH. See Figure 3.
Figure 3 – Critical Flux – Control versus MPE50 polymer treated Mixed Liquor
Trend line
Treatment with 100 ppm MPE50
Control
Flux - LMH (L/m2/hr)
Tra
ns-M
embr
ane
Pre
ssur
e (k
Pa)
• After the addition of 100 ppm
PermaCare MPE50 polymer the
transmembrane pressure did not
deviate from the trend line even
at 55 LMH, which was the
maximum flow available from
the suction pump.
Longer duration test
We also conducted a longer
duration test by taking one of the
five modules offline in order to
increase the flux through the other
four modules. The permeation rate
was measured as a function of
transmembrane pressure. Table 1
shows that the permeability
increased substantially during the
PermaCare MPE50 polymer
treatment period.
ConclusionConclusionConclusionConclusionConclusionThe addition of PermaCare MPE50
polymer improved the performance
of a membrane bioreactor operating
on municipal wastewater and:
• allowed stable operation at an
increased flux rate
• decreased membrane fouling
• increased membrane permeability
• decreased the TMP required to
reach design flow
As a result, the MBR throughput
was increased without the need
to increase the size of the plant or
the amount of membrane in the
installation.
Table 1 – Permeability increase comparison
Note: If 5 modules were used with MPE50 the throughput of the plant reached
the design flow of 240 m3/day at a 80% reduction in transmembrane pressure.
Conversion Factors
1 LMH (liter/meter2-hour) = 0.6 GFD (gallon/foot2-hour) = 0.04 m/day
( meters/day)
1 kPa (kilo Pascal ) = 0.145 psig ( pound/in2)
1 m3/hour = 0.22 GPM, 1.57 x 10-4 GPD, 9469.7 MGD
Before MPE50 polymer Treatment After MPE50 polymer Treatment
Control: 5 modules operating 4 modules operating
Flow: 187 m3/day Flow: 196 m3/day
Avg. TMP: 31.8 kPa Avg. TMP: 6.0 kPa
Flux: 13 LMH Flux: 17 LMH
MPE50, PermaCare, NALCO and the logo are Trademarks of Nalco and its related companies©2004, 2005 Nalco Company All Rights Reserved 9-05
NALCO COMPANY OPERATIONS
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