1

Performance of Bio-Fouling Reducers In Aerobic

Submerged Membrane Bioreactor For Palm Oil Mill

Effluent Treatment

Adhi Yuniarto1, Zaini Ujang

2, Zainura Zainon Noor

3*

1,2,&3 Institute of Environmental and Water Resource Management (IPASA),

Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia. * Corresponding Author Email: zainura@fkkksa.utm.my

Published in

JURNAL TEKNOLOGI UTM

No. 49 (F), Dis. 2008

pp. 555-566

2

Performance of Bio-Fouling Reducers in Aerobic

Submerged Membrane Bioreactor For Palm Oil Mill

Effluent Treatment

Adhi Yuniarto1, Zaini Ujang

2, Zainura Zainon Noor

3*

1,2,&3 Institute of Environmental and Water Resource Management (IPASA),

Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia. * Corresponding Author Email: zainura@fkkksa.utm.my

Abstract. Bio-fouling is one of the major challenges of submerged membrane

bioreactor operation, which reduces productivity and increases operational/main-

tenance cost. Powdered activated carbon, granular activated carbon and fine grained

zeolite were used as bio-fouling reducer (BFR) to reduce bio-fouling in membrane

and improve effluent qualities. A bench scale aerobic submerged membrane

bioreactor (ASMBR) was used to study bio-fouling behavior for palm oil mill

effluent (POME) treatment. A 20-liter reactor was set up using a flat sheet

microfiltration membrane equipped with continues fine air bubbles for bio-oxidation

and membrane scouring. Comparative result on ASMBR with and without BFR

adjunction was performed at constant flux and in a defined organic loading.

Experiments showed positive changes in trans membrane pressure (TMP), as well as

the improvement in effluent qualities. However a jelly-like biofilm layer was the

main reason for TMP increasing and bio-fouling.

Keywords : Bio-fouling reducer; membrane bioreactor; ASMBR; POME.

Abstrak. Bio-fouling merupakan salah satu daripada masalah utama di dalam

operasi membran bioreactor separa-tengelam. Serbuk karbon teraktif, granular karbon

teraktif dan serbuk halus zeolite telah digunakan untuk mengatasi masalah bio-

fouling di dalam membran dan juga untuk meningkatkan kualiti effluen. Membran

bioreaktor separa-tenggelam aerobik (ASMBR) telah digunakan di dalam kajian

berskala makmal untuk mengkaji ciri-ciri bio-fouling di dalam perawatan effluen air

sisa kelapa sawit. Reaktor bersaiz 20 liter telah dibina dengan mengggunakan 1

kepingan membrane penurasan mikro bersama gelembung udara halus secara

berterusan untuk proses bio-oksidasi dan untuk menggosok membrane. Perbandingan

ke atas ASMBR dengan Pengurang Bio-fouling (BFR) dan tiada BFR telah

dijalankan dengan aliran kekal dan pemuatan organik yang telah ditetapkan. Kajian

ini telah menunjukkan perubahan positif di dalam tekanan antara membran (TMP)

dan kualiti effluent. Walau bagaimanapun, didapati pembentukan lapisan lender pada

permukaan membrane masih merupakan punca utama peningkatan TMP dan

terjadinya bio-fouling.

Keywords : Pengurang Bio-fouling; membran bioreaktor; ASMBR; POME.

3

1.0. INTRODUCTION

Palm oil is the most important agriculture crop in Malaysia, covering about more than

three million hectares of the cultivated area. In 2007 Malaysia and Indonesia

remained as the world’s largest producers and exporters of palm oil, contributed for

87% of global production [1]. Unfortunately, this big agricultural and industry

activity generates a great amount of by product, known as palm oil mills effluent

(POME). Every ton of crude palm oil produced in factory, about 2.5-3.5 tons of

POME is generated [2]. In the year 2004, more than 40 million tonnes of POME was

generated from more than 370 mills in Malaysia. If the effluent is discharged

untreated properly, it can indisputably cause substantial environmental problems.

Raw POME is a colloidal suspension that contains 95–96% of water, 0.6–0.7% of

oil and grease and 4–5% of total solids including 2–4% suspended solids originated

from the mixture of sterilized condensate, separator sludge and hydrocyclone

wastewater [3]. Typically with very high content of organic and oil, the resulting

POME is a thick brownish color liquid and discharged at a temperature between 80

and 90 oC. It is fairly acidic with pH ranging from 4.0 to 5.0. The POME

characteristic and standard discharge limit is summarized in Table 1.

Table 1 Characteristics of raw combine POME and its standard discharge limit by the

Malaysian Department of the Environment

Parameters Concentrations Standart Limit,

mg/L mg/L

pH 4.2 – 5.1 5 - 9

BOD 31,300 - 34,050 100

COD 62,500 - 67,100 ---

Suspended solids 20,540 - 24,200 400

Total nitrogen 872 - 912 150

Ammoniacal nitrogen 36 - 46 ---

Oil and grease 90,100 - 99,700 50

Temperature 85 - 91 45

Except pH and temperature all other parameters are in mg/L, temperature in oC

By increasing in number of replacing the conventional water and wastewater

treatment process, the membrane bioreactor (MBR) process has proved become a

feasible technology for water reclamation and producing of high quality treated water

[4]. MBR provides biological activated sludge treatment with filtration separation

where the membrane mainly uses to replace the clarifier as in the conventional

wastewater treatment. Among MBR are small footprint, low sludge production, and

high quality effluent. More specific advantages included complete separation of

suspended solids and bacteria by the membrane, possible to nitrify easily, reduce

hydraulic retention time (HRT) to a minimum by separating it with the sludge

retention time (SRT), uncomplicated operation especially because bulking

4

phenomenon does not effect to the liquid-solid separation, and MBR can also

function as a small-scale system [5].

In the late of 1980s, submerged low pressure configurations of MBR was a

significant development to answer the lack of older MBR systems and also to reduce

operating cost. In this new configuration, membrane was directly submerged in

aeration tank containing the biological sludge and extracted the treated permeate [6].

Several methods that showed the development of submerged MBRs during 1980s -

1990s has been also affecting world-spread uses of submerged MBRs, including

submerged MBRs as an upgrade option for existing wastewater treatment plant [4, 7].

It is generally known that fouling reduces the performance of the membrane.

When fouling occurs, a thick gel layer and cake layer is formed on and into the

membrane, resulting the permeate flux to decline, increase in hydraulic resistance and

operating costs due to the need for cleaning or changing the membrane. Fouling is

usually attributed to a number of parameters, such as sludge particle deposition,

adhesion of macromolecules such as extracellular polymeric substance (EPS), soluble

microbial products (SMP) and pore clogging by small molecules [8 - 11].

A number of previous studies have focused on various factors that affect

membrane fouling in MBRs. Factors like the type of wastewater, sludge loading rate,

sludge age, mixed liquor suspended solid (MLSS) concentration, mechanical stress,

solid retention time, food-to-microorganism ratio and microbial growth phase are

known to affect the concentration of EPS and in turn to the evolution of membrane

fouling [12 - 14].

Various techniques have been used to reduce membrane fouling. In aerobic

submerged membrane bioreactors, air bubbles can prevent the deposit forming on the

membrane surface [15]. Periodic backwashing improves membrane permeability and

reduces fouling, thus leading to optimal, stable hydraulic operating conditions [6, 10].

Adding flocculation–coagulation agents limits membrane fouling by aggrega-tion of

the colloidal fraction, thus reducing internal clogging of the membranes [16]. Several

materials have been added to the ASMBR to reduce bio-fouling. Previous studies

concerning activated carbon dosing in MBR have pointed out an increase in sludge

filterability and a decrease in the membrane fouling rate [17 – 21]. The addition of

zeolite on the membrane filter bioreactor has been enhanced the membrane

permeability [22].

This paper aimed to conduct a better understanding on the effectiveness of Bio-

fouling Reducers in POME treatment, particularly to the membrane fouling

phenomenon and organic removal.

2.0. METHODOLOGY

The raw POME was obtained from Kilang Pertubuhan Petani Negeri Johor, Kahang

Johor, has a typical COD of about 65000 mg/L and had to be cooled and diluted

several times before feeding the reactor. Feed preparation in influent tanks and

sampling of its quality were done daily. The feeding characteristics are showed in

Table 2.

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Table 2 Feeding characteristics (diluted POME)

Parameter Range (mg/L, except pH)

COD 1000 89

TS 780 32

Total N 14 2.1

Total P 3.2 1.29

Ammoniacal Nitrogen 0.83 0.23

pH 6.11 0.12

The laboratory experimental set-up is shown in Fig.1. The ASMBR consist of a

twenty liters reactor, where single module of flat sheet membrane was immersed in

the aerobic zone. The chlorinated polyethylene membrane module was provided by

Kubota Japan with nominal pore size of 0.4 m and effective area of 0.1 m2. The air

transported by the compressed air pipeline was fed into the reactor with a micro-

bubble diffuser installed beneath the membrane. It provided adequate oxygen to

maintain aerobic conditions for biomass growth as well as scoured the fouling on the

membrane surface to prevent cake accumulation on it. This air flow was monitored

with an air flow meter. The influent flow rate was controlled by a water level sensor

set in the reactor. Constant permeate flux was maintained with a variable speed

peristaltic pump. However the flux also controlled by measure it manually using a

calibrated cylinder and a stopwatch twice a day. A pressure transducer (PG-30 Copal

Elect.) measured trans membrane pressure and its data was recorded with RS232 Data

Logger software using a data logging system. The reactor was operated at room

temperature, and it was maintained to neutral pH.

The working volume and operating condition of ASMBR are summarized in Table

3. The ASMBR was seeded with activated sludge obtained from a sewage treatment

plan in Kulai Johor Bahru. After run for achieving steady-state condition, the

experiments were initiated. The operational parameters during filtration process were

trans membrane pressure, organics removal (as COD) and permeate color. Initiate

experiment was the operation of BFR without bio-fouling reducer, and then followed

by BFR addition. No sludge was discharged during the operation period except

samplings and there was no further addition of BFR during ASMBR experimental

period.

Table 3 Operating conditions of the ASMBR

Parameter Value

Working volume, l 20

Temp., oC 25 – 27

pH 6.8 – 7.7

Organicin, mg COD/l

Qin, m3/d (l/h)

1000

0.024 (1)

Organic loading, kg COD/m3.d 0.024

6

Permeate Flux at constant rate, LMH 10

MLSS, mg/L 4000 to 8000 4200 – 5400

HRT, h 20

DO, mg/L 6.6 – 7.9

Air flow, l/min 6

Computer

Water Leveler

Pressure Gauge

Pump

Flat sheet membrane

Air Diffuser

Air Compressor

Effluent Container

Influent Container

Figure 1 Flow diagram of ASMBR system

Table 4 shows BFR type that used in this experiment. BFR have been dried for 24

hours and store in dry place before introduced it into ASMBR. Adsorption

experiment has been conducted as an approach method to determine BFR

concentration to be filled into ASMBR. A conventional jar apparatus with six-spindle

of steel paddles was used in this test. Six beakers with 0.5 liter of POME stirred

concurrently. Initial concentration of POME is 1000 mg COD/L. After adding BFR

into the suspension, the beakers were mixed for 1 min at 200 RPM and continued

with 20 hours at 50 RPM. After full stopped, suspensions were allowed to sediment

for 1 h with the supernatant being analyzed for organic concentrations. Variation of

BFR concentrations in the suspension were set in the range of 1 – 30 g/L.

7

Table 4 BFR characteristics

BFR type Origin Quality Supplier

BFR1 PAC, charcoal PA Fisher Scientific, Ltd.

BFR2 GAC, charcoal PA Kanto Chemical Co. Inc.

BFR3 Zeolite Powder Commercial Harta Semarak, Sdn. Bhd.

Laboratory experiments associated with this study were carried out in the

Environmental Engineering Lab, Faculty of Civil Engineering, Universiti Teknologi

Malaysia. The activated sludge quality was regularly tested for mixed liquor

suspended solids (MLSS). Dissolved Oxygen (DO) concentration and temperature of

the activated sludge were measured using portable YSI 55 Dissolved Oxygen (YSI

Inc, Ohio USA). Also, pH was measured on site using Hanna pH211 pH meter

(Hanna Instruments, Bedfordshire UK). Color was analyzed using a

spectrophotometer (HACH/DR 5000). Parameter analyses were carried out according

to standard methods [23] immediately after samples were collected.

3.0. RESULTS AND DISCUSSION

Prior to the ASMBR experiment, adsorption experiment were carried out to

determine concentration of BFR. Figure 2 shows the organic removal percentage by

adsorption using BFR. BFR1 achieved the best performance in low concentration (1-

5 g/L) with 80 – 92% removal. The performance increased until almost 94.7% when

the BFR1 concentration was 8 gr/L, before the removal efficiency decreased even its

concentration increased to 30 gr/L. BFR2 removed 64% of organic at concentration 1

g/L and increased to 81% (8 g/L). Organic removal was only 83% when BFR2

concentration was 20 g/L. BFR3 had a better performance with 90.3% organic

removal on 8 g/L and still achieved higher organic removal when the concentration

was 30 g/L (93.3%).

It was also proved that the concentration of BFR in the powder form was more

effective compared to the granular form. This is due to larger surface area of the BFR

powder and granular form. However the main reason why BFR2 considered to be

used in further experiment was in term of initial cost and ease of handle.

From Figure 2 below, BFR1 of 8 g/L was selected to be filled into the ASMBR

because at higher concentration of BFR1, organic removal efficiency tended to

decrease. For BFR2 and BFR3, 8 g/L was also chosen as a dosage for further use,

because at higher BFR3 dosage there was no significant improvement of organic

removal.

When the ASMBR operated without BFR, the increasing of TMP took place

gradually from the initiation to the end of the ASMBR operation at 120 hours, as

shows in Figure 3. The last TMP recorded was 13.6 kPa. The generation of gel layer

on the membrane surface of this operation was much thicker than other experiments

with BFR. This layer was observed in plain view after stopped the experiment and

removed the membrane. The layer generation was due to the production of SMP,

8

which could block membrane pores. Their accumulation demonstrated the natural

factor for membrane bio-fouling [11].

0 5 10 15 20 25 30 35

BFR Concentration (g/L)

60

65

70

75

80

85

90

95

100

Org

anic

(as

CO

D)

rem

ov

al (

%)

BFR1 BFR2 BFR3

Selected Dose

Figure 2 Organic removal by BFR

Figure 3 also shows that the ASMBR with BFR had lower TMP development

compared to the system without BFR. TMP was remained stable at lowest pressure as

it was initiated when BFR1 and BFR2 were introduced into ASMBR; 2.8 kPa and 3.1

kPa, respectively. This is due to the direct adsorption of dissolved organic matters

onto BFR.

BFR2, which is a granular form, tended to float or settle in the ASMBR. This

made it more difficult to disperse evenly in the activated sludge, resulting in a less

adsorption capacity to adsorb organic material. Therefore it is easier for organic

material to form cake layer on membrane surface, which made TMP in this system

higher than other BFR.

On the other hand, the cake layer of the activated sludge was replaced by BF1 and

BF3 precoat layer with large porosity and non-compressibility, which reduced cake

resistance to water and oxygen transfer. As a result, TMP was decreased. These

phenomenon proved that the use of BFR mitigate the membrane fouling.

Organic removal efficiency was measured during 120 hours of the ASMBR

system operation, which is shown in Figure 4. The results indicated that all systems

achieved excellent organic removals of over 94%. The addition of BFR increased the

ASMBR system to produce better permeate quality. This was due to the BFR

simultaneous functions of biodegradations (i.e. through attachment of biomass on its

surface) and adsorption of organic fractions. It was noted that BFR3 had a better

performance than other BFR.

9

0 20 40 60 80 100 120

Operation Time (hours)

0

2

4

6

8

10

12

14

16

TM

P (

kP

a)

NoBFR

BFR3

BFR1

BFR2

Figure 3 Trendline of Membrane Bio-fouling with BFR.

0 20 40 60 80 100 120

SMBR Operation Time (hours)

85

90

95

100

Re

mo

va

l E

ffic

ien

cy (

% C

OD

)

CODrem NoBFR

CODrem BFR1

CODrem BFR2

CODrem BFR3

BFR2

BFR3

BFR1

NoBFR

Figure 4 Organic Removal

The average organic removal during ASMBR operation without BFR, with BFR1,

BFR2 and BFR3 were 94.38%, 96.89%, 95.25% and 98.18%, respectively. It means

that organic removal for ASMBR with BFR1, BFR2 and BFR3 were increased by

10

2.46%, 0.87%, and 3.80%, respectively. It seems that these increments were not

significant, but it would be rewarded by the ASMBR longer operation time.

0 20 40 60 80 100 120

SMBR Operation Time (hours)

0

20

40

60

80

100

120

140

160

180

200

Efflu

en

t C

olo

r (P

tCu

)

Color Eff NoBFR Color Eff BFR1 Color Eff BFR2 Color Eff BFR3

NoBFR

BFR1

BFR3

BFR2

Figure 5 Effluent color of ASMBR system

The ASMBR without BFR produced higher effluent color then others. This soluble

natural color is known as the other problem in POME treatment. By adding BFR into

the ASMBR, the quality of effluent color improved as indicated in Figure 5. This was

due to adsorption of the small molecule material onto BFR surface or BFR-biomass

surface.

Effluent color in ASMBR without BFR was decreasing even the gel layer was

generated on membrane surface. It was possibly because the gel layer blocked

membrane pore, made the pore size smaller, so that bigger substances was rejected. It

also explained why its organic removal still tended to increase. As illustrated in

Figure 6(a). When BFR added into the ASMBR, it was found that the organic

removal remained high during the experiment, it probably due to the BFR adsorption

of SMP produced. This adsorption could improve the organic removal and improved

the quality of permeate. Even though with the use of BFR1 and BFR3, effluent color

tended to increase again after 20 hours of operation, despite high organic removal.

The color remains high because the membrane layer was not blocked by the

formation of gel layer or cake, thus soluble organic which not attached to BFR could

pass through the membrane pore to permeate side as illustrated in Figure 6(b).

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Figure 6 Conceptual removal of soluble materials in ASMBR operation

(Adapted from [17])

4.0. CONCLUSIONS

From these experiments, it can be concluded that BFR demonstrated a significant role

in bio-fouling reduction by maintained TMP as low as 2.3 – 3.6 kPa at the end of

ASMBR operations. It was also found that the organic removal of ASMBR with

BFR1, BFR2 and BFR3 was further improved by 2.46%, 0.87% and 3.80%

respectively, compared to the operation of ASMBR without BFR. In addition, the

reduction of the thickness of gel layer and the organic cake formation on membrane

surface thereafter demonstrated the capability of BFR in adsorption and reducing bio-

fouling.

ACKNOWLEDGEMENT

The authors wish to express gratitude the Research Management Center (RMC) of

Universiti Teknologi Malaysia for the financial assistance under VOT no. 79903.

REFERENCES

[1] USDA, Foreign Agricultural Service (2007) Indonesia : Palm Oil Production

Prospects Continue to Grow. http://www.pecad.fas.usda.gov /highlights/2007/

12/Indonesia_palmoil.

[2] Ahmad, A.L., Ismail, S. and Bhatia, S. (2005) Membrane treatment for palm

oil mill effluent: effect of transmembrane pressure and crossflow velocity.

Desalination 179:245-255.

(a) (b)

12

[3] Ma, A.N. (2000) Environmental management for the palm oil industry. Palm

Oil Developments 30:1-10.

[4] Judd, S, (2007) The status of membrane bioreactor technology. Trends in

biotechnology 26(2):109-116.

[5] Jeong, T.Y., Cha, G.C., Yoo, I.K. and Kim, D.J. (2007) Characteristics of bio-

fouling in a submerge MBR. Desalination 207:107-113.

[6] Cote, P., Buisson, H. and Praderie, M. (1998) Immersed membranes activated

sludge process applied to the treatment of municipal wastewater. Water Sci.

Technol. 38:437–442.

[7] Buisson, H., Cote, P., Praderie, M. and Paillard, H. (1998) The use of immersed

membranes for upgrading wastewater treatment plants. Water Sci. Technol.

37:89–95.

[8] Nagaoka, H., Ueda, S. and Miya, A. (1996) Influence of bacterial extracellular

polymers on the membrane separation activated sludge process. Wat. Sci. Tech.

34:165–172.

[9] Bouhabila, E.H., Aim, R.B. and Buisson, H. (2001) Fouling characterisation in

membrane bioreactors. Sep. Purif. Tech. 22–23:123–132.

[10] Bouhabila, E.H., Aim, R.B. and Buisson, H. (1998) Microfiltration of activated

sludge using submerged membrane with air bubbling: application to wastewater

treatment. Desalination 118:315–322.

[11] Drews, A., Lee, C.H. and Kraume, M. (2006) Membrane fouling - a review on

the role of EPS, Desalination 200:186–188.

[12] Chang, I.S. and Lee, C.H. (1998) Membrane filtration characteristic in

membrane coupled activated sludge system the effect of physiological states of

activated sludge on membrane fouling. Desalination 120:221–233.

[13] Chang, I.S., Le Clech, P., Jefferson, B. and Judd, S. (2002) Membrane fouling

in membrane bioreactors for wastewater treatment, J. Environ. Eng. 128:1018–

1029.

[14] Li, X.Y. and Yang, S.F. (2007) Influence of loosely bound extracellular

polymeric substances (EPS) on the flocculation, sedimentation and

dewaterability of activated sludge. Water Res. 41(5):1022–1030.

[15] Ueda, T., Hata, K., Kikuoka, Y. and Seino, O. (1997) Effects of aeration on

suction pressure in a submerged membrane bioreactor. Water Res. 31(3):489–

494.

[16] Bhatia, S., Othman, Z. and Ahmad, A.L. (2007) Coagulation–flocculation

process for POME treatment using Moringa oleifera seeds extract:

Optimization studies. Chem. Eng. Journal 133:205–212.

[17] Ujang, Z., Au, Y.L. and Nagaoka, H. (2002) Comparative study on microbial

removal in immersed membrane filtration (IMF) with and without powdered

activated carbon (PAC). Water Sci. Technol. 46(9):109–115.

[18] Seo, G.T., Moon, C.D., Chang, S.W. and Lee, S.H. (2004) Long term operation

of high concentration powdered activated carbon membrane bio-reactor for

advanced water treatment. Water Sci. Technol. 50(8):81–87.

13

[19] Liu, Y., Wang, L., Wang, B., Cui, H. and Zhang, J. (2005) Performance

improvement of hybrid membrane bioreactor with PAC addition for water

reuse. Wat. Sci. Tech. 52(10–11):383–391.

[20] Munz, G., Gori, R., Mori, G. and Lubelloa, C. (2007) Powdered activated

carbon and membrane bioreactors (MBR-PAC) for tannery wastewater

treatment: long term effect on biological and filtration process performances.

Desalination 207:349–360.

[21] Guojun, Z., Shulan, J., Xue, G. and Zhongzhou, L. (2008) Adsorptive fouling

of extracellular polymeric substances with polymeric ultrafiltration membranes.

J. Membrane Science 309:28–35.

[22] Lee, J.C., Kim, J.S, Kang, I.J., Cho, M.H., Park, P.K. and Lee, C.H. (2001)

Potential and limitations of alum or zeolite addition to improve the performance

of a submerged membrane bioreactor. Water Sci. Technol. 43(11):59–66.

[23] APHA (1992). Standard Methods for Examination of Water and Wastewater.

18th ed. American Public Health Association, American Water Works

Association and Water Environment Federation, Washington DC, USA.