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

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