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ISSN : 1226-0088(Print)
ISSN : 2288-7253(Online)
Membrane Journal Vol.30 No.1 pp.1-8

Effect of Antifouling Composite Membrane on Membrane Bioreactor: A Review

Bo Woo Lee*, Sunwoo Lee**, Rajkumar Patel***
*Life Science and Biotechnology Department (LSBT), Underwood Division (UD), Underwood International College, Yonsei University, Sinchon, Seoul 03722, South Korea
**Bio-Convergence, Integrated Science and Engineering Division (ISED), Underwood International College, Yonsei University, 85 Songdogwahak-ro, Yeonsu-gu, Incheon 21983, South Korea
***Energy and Environmental Science and Engineering (EESE), Integrated Science and Engineering Division (ISED), Underwood International College, Yonsei University, 85 Songdogwahak-ro, Yeonsu-gu, Incheon 21983, South Korea
Corresponding author(
February 23, 2020 ; February 26, 2020 ; February 27, 2020


In membrane bioreactor (MBR), activated sludge degrade the biological component and membrane process separate this bacterial flocks as well the suspended solids. However, membrane fouling is one of the major issues in MBR. In this review, composite membrane used in MBR to overcome fouling is discussed. It is classified into membrane containing carbon and noncarbon materials. Introducing graphene, graphene oxide (GO) and carbon nanotubes or their modified part into pristine membrane enhance hydrophilicity of the composite membrane. Inorganic materials like silicon dioxide (SiO2) or titanium dioxide (TiO2) are also incorporated for preparing composite membrane to increase its water flux.

방오성 복합막의 막생물반응기에 대한 영향

이 보 우*, 이 선 우**, 라 즈쿠마 파텔***
*연세대학교 언더우드학부 생명과학공학과
**연세대학교 융합과학공학부 바이오융합과
***연세대학교 융합과학공학부 에너지환경융합과


막 생물 반응기(MBR)에서, 활성화 된 슬러지는 생물학적 성분을 분해하고 막 공정은 이 부유 물질인 박테리아를 분리시킨다. 그러나 MBR에서의 주요 문제는 ‘막 오염’이다. 이 리뷰에서는 ‘막 오염’을 극복하기 위하여 제시된 ‘복합막’을 논의하고 있다. ‘복합막’은 탄소 또는 비탄소 재료 포함하는 막으로 분류할 수 있다. 이 복합막의 친수성은 그래핀, 산화그래핀 (GO) 및 탄소 나노 튜브 또는 그들의 변형 된 부분을 깨끗한 막에 도입시킬 때 향상된다. 이산화규소(SiO2) 또는 이산화티타 늄(TiO2)과 같은 무기 물질 또한 막의 물 흐름을 증가시키기 위해 복합막 형성에 통합된다.

    1. Introduction

    Increasing population and growing urbanization make it pivotal for efficient wastewater treatment. Membrane bioreactor (MBR) process is an efficient method for treatment of wastewater. Activated sludge treatment and solid-liquid separation by membrane technology is the method followed in MBR. Ultrafiltration membrane (UF) and microfiltration membrane (MF) are most suitable due to their pore size. However, fouling of the membrane is mainly by extracellular polymeric substances and natural organic matter[1-6]. Biofouling block the membrane pore, reducing membrane flux and lifetime of the membrane drastically.

    Carbon based materials are important class of additive that reduces the biofouling when introduced in the pristine membrane[7]. More specifically graphene oxide has antibacterial and antifouling properties oxidative degradation of the cell membrane and generation of hydrophilicity respectively. Similar kind of properties are shown by carbon nanotube. Dispersion of carbon additive on to the pristine membrane results in phase separation of composite membrane. Modification of the additive by functionalization with carboxyl group or linking to polyethylene glycol (PEG) enhance antifouling properties due to hinderance on biofilm formation.

    Metal oxide nanoparticles like titanium oxide (TiO2) and silicon dioxide (SiO2) brings in hydrophilicity to the composite membrane. As a result, water flux of the composite membrane increases which is reflected in MBR. In this review composite membrane is classified into two parts. One, composite membrane containing carbon materials and second part consist of metal oxide nanoparticles.

    2. Antifouling Composite Membrane-based Membrane Bioreactor

    2.1. Composite containing carbon material

    Polyvinylidene fluoride (PVDF) is mixed with graphene oxide (GO) nanosheets to prepare composite microfiltration membrane[8]. Non solvent induced phase separation method was followed to cast the composite membrane. The pore size of the composite membrane was 0.089 μm as observed by SEM indicating be microfiltration membrane. The antifouling performance of the PVDF/GO composite membrane was compared to that of a commercial PVDF membrane using long-term MBR tests. Composite membrane has 1/6th lower pore blocking resistance than the pristine PVDF membrane. Also, the composite membrane collected 5.97 g/m2 of extracellular polymeric substances (EPS) which was lower than that on the PVDF membrane (17.87 g/m2). The lower pore blocking resistance and EPS concentration all show the superior antifouling properties of the composite membrane. Ravishankar et al. reported preparation of polyether sulfone (PSF) and GO composite membrane for application in Anaerobic-anoxic-oxic membrane bioreactor (A2O MBR)[9]. The A2O MBR was tested for removal of wastewater containing 5 mg/L of lead. When compared with pristine PSF, composite membrane demonstrated better rejection of lead and higher critical flux. The composite membrane also took longer time to reach trans-membrane pressure (TMP) of 55 kPa (around 85 days) compared to 60 days for the pristine membrane when operated below the membrane’s critical flux. Durability of the PSF/GO composite membrane is about 1.4 times higher than the pristine membrane. However, much of the lead removal is by its aggregation on biomass in the MBR. Same group reported another PSF/GO composite microfiltration membrane prepared by non-solvent induced phase inversion method[10]. Ratio GO and PSF was varied to prepare four different kind of composite membrane and tested for critical flux using a laboratory scale MBR system. Intermittent mode and continuous modes with backwash were used to evaluate critical flux and found out that mode of operation has insignificant effect on critical flux in presence of lower concentration of GO in the composite membrane. But when GO percentage is increased than intermittent mode is favored. Overall effect of presence of GO was studied in detail and optimum operation condition was found out. Presence of GO enhance antifouling ability, reduce filtration time leading to efficient wastewater treatment process. Zinadini et al., reported composite membrane prepared from polyethersulfone (PES) and GO instead of PSF [11]. Percentage of GO nanoplates are varied and composite membrane was prepared by nonsolvent induced phase separation method. Biological suspension was used to measure the flux recovery ratio (FRR), fouling resistance (Rr) and irreversible fouling resistance (Rir) of the membranes. The results showed that the addition of GO nanoplates improved the membrane's FRR and in the best case, the 0.5 wt% GO membranes with polymer percentage of 13, 15 and 17 wt% showed FRRs of 90, 92.8 and 94%, respectively. The unfilled PES membrane (13 wt%) showed the highest irreversible fouling resistance of 30%, indicating that the addition of the nanoplates reduced the resistance factor of the membrane. These results showed the improved antifouling properties of the GO incorporated PES membranes. Removal of organic matters by MBR in terms of biochemical oxygen demand (BOD) and chemical oxygen demand (COD) from milk processing wastewater are improved emphasizing the effect of PES/GO composite membrane.

    Beygmohammdi et al. prepared new type of composite membrane by grafting of GO to polyvinylpyrrolidone (PVP) by surface initiated free radical polymerization and mixing with polyvinylidene fluoride (PVDF)[12]. Presence of PVP-g-GO in the PVDF/PVP-g-GO composite enhance the compatibility due to presence of PVP that is linked to GO and it was compared with PVDF/ GO. From field emission scanning electron microscopy (FESEM), study it was confirmed that PVP does interact the PVDF matrix that enhance the GO dispersion compared to pristine GO. Composite membrane was prepared by non-solvent induced phase separation method and antifouling properties of PVDF/GO (1.5 wt%) and PVDF/PVP-g-GO (1.5 wt%) were compared with that of the neat PVDF in MBR system. The results show the neat PVDF membrane to have a total fouling ratio (TFR) value of 88.12% which was higher the values for PVDF/GO (1.5 wt%) and PVDG/PVP-g-GO (1.5 wt%) membranes which were 86.92% and 83.84%, respectively. The irreversible fouling ratio (IFR) for neat PVDF membrane was 39.49% and this value decreased to 25.38% and 19.25% for PVDF/GO (1.5 wt%) and PVDF/PVP-g-GO (1.5 wt%) membranes, respectively. All these results show that the addition of GO and PVP-g-GO nanoparticles significantly improved the antifouling properties of the PVDF membrane with PVDF/ PVP-GO (1.5 wt%) membrane having the highest fouling resistance. Another group followed similar approach and replaced PVP with cellulose nanocrystal (CNC) keeping PVDF matrix fixed[13]. CNC is mixed with GO unlike earlier study in which it was grafted with PVP. In this case two composite systems of GO/PVDF, GO-CNC/PVDF was prepared. Unlike earlier study, this group prepared CNC/PVDF blend and compared with composites and pristine PVDF. Non solvent induced phase inversion method was followed to prepare four different types of microfiltration membrane and than measured the water flux. The results showed that GO-CNC/PVDF has the highest water flux and thus the highest antifouling property. Laboratory scale MBR systems were used to test GO-CNC/PVDF, CNC/PVDF, and PVDF membranes which were operated side by side in the same MBR tank. The evolution of TMP was used to examine the fouling activities of the membranes at a steady effluent flux. The average TMP increasing rates of GO-CNC/PVDF was around 43.7% lower than that of CNC/PVDF and 69.2% lower than that of pristine PVDF membrane. The slower TMP increasing rate of GO-CNC/PVDF ratio compared with the other two membranes showed that the addition of hydrophilic GO-CNC composite onto the pristine PVDF can reduce its membrane fouling rates significantly. During the long-term MBR operation, GO-CNC/PVDF membrane also showed lower irreversible fouling, loosely thin cake layer, lower extracellular polymeric substance (EPS) accumulation, longer cleaning cycle, and higher flux recovery, all of which indicated better antifouling performances. In a similar type of work, GO was modified to attach sulfonic group (SGO) and mixed with PVDF to prepare SGO/PVDF composite material[14]. SGO was mixed with PVDF and PVP in n-methyl- 2-pyrrolidone (NMP) in certain ratio and composite membrane was prepared by non-solvent induced phase separation method. In this work, fouling caused by antibiotic resistant bacteria (ARB) was studied. ARB is the bacteria E2 which has resistance against antibiotics such as ampicillin, cefotaxime, vancomycin, tetracycline, and gentamicin; and the experiment is done on the PVDF/SGO composite membrane. The antifouling performance through the lytic cycle of P2 in E2 is assessed by measuring the flux change that has membrane contaminated by E2. There is 57 % enhancement of flux for P2 phase treated composite membrane which conclude that lytic phase inhibits the formation of biofilm. Figs. 1 and 2 represent the TEM and SEM image which further corroborate these facts.

    In this work GO is replaced with functionalized carbon nanotube (CNT)[15]. At first CNT was treated with nitric acid to attach carboxyl group and further reacted with polyethylene glycol (PEG) to prepare PEG terminated CNT (PEG-CNT). PSU was mixed with PEG-CNT and PVP in dimethyl acetamide (DMAc) and membrane was prepared by non-solvent induced phase separation process. Mechanical properties of the composite membrane were tested by tensile test and morphology was checked by SEM. Membrane performance was performed by permeation of water and protein solution. Composite membrane consisting of 0.25 wt% of PEG-CNT has four times higher permeability than the pristine membrane. PEG lyation of composite membrane due to CNT modification enhance resistance to fouling by 72.9 ± 1% for which it useful in MBR to treat wastewater. In a similar work, PEG-CNT was replaced by amine terminated multiwall carbon nanotube (MWCNT-NH2)[16]. First, MWCNT was treated with mixture of nitric and sulfuric acid, followed by thionyl chloride and finally with diamine of 4,4-diamino biphenyl methane (DDM) to prepare MWCNT-NH2. Polyether sulfone (PES) was mixed with MWCNT-NH2 and PVP in DMAc in certain ratio and MWCNT-NH2/ PES ultrafiltration composite membrane was prepared by non-solvent induced phase separation method. Ratio of MWCNT-NH2 to PES was varied to prepare three different kinds of membranes. Membrane resistance to fouling was studied by suspension separation of activated sludge and then flux recovery ratio was measured. Composite ultrafiltration membranes which had FRRs of more than 73% showed better antifouling performance than the pristine PES with 70% of FRR. Among the composite membranes, the 0.1 wt% NH2-MWCNTs membrane had the highest FRR of 89.7%, indicating that it has the best antifouling properties.

    Nanodiamond was used as source of carbon material to prepare high density polyethylene (HDPE) composite membrane[17]. Nanodiamond was modified with carboxylic group or PEG to enhance its compatibility with HDPE. At 430°C under circulation of air nanodiamond was converted to carboxylated nanodiamond (ND-COOH). ND-COOH was treated with thionyl chloride and followed by reaction with PEG to prepare PEG terminated nanodiamond (ND-PEG).

    Composite membrane of HDPE/ND-COOH and HDPE/ ND-PEG was fabricated by mixing with mineral oil in thermally induced phase separation process. Pristine HDPE exhibit significant decrease in the water flux as the time passed and the fouling continued, whereas PE/ND-COOH membrane showed less decrease in water flux. Presence of carboxyl terminated ND and PEG linked PD brings in hydrophilicity to the composite membrane and hence antifouling properties enhanced as compared to pristine membrane. Prepared membrane module was immersed in pure water present in membrane bioreactor to measure pure water flux (PWF) (J0). Then the membrane module was placed in MBR and the flux of activated sludge filtration was determined. The membranes were then moved to a water tank so that the PWF of the fouled membranes (J1) could be measured. The fouled membranes were then cleaned and the PWF of the cleaned membranes (J2) was measured again. The values of J0, J1, and J2 were used to calculate total fouling ratio (TFR), irreversible fouling ratio (IFR), reversible fouling ratio (RFR), and flux recovery ratio (FRR). The results show that the fouling parameters of neat PE and PE/ND-COOH (0.50 wt%) membranes are nearly the same, but PE/ND-PEG (0.75 wt%) membrane has lower total fouling ratio, lower irreversible fouling ratio and higher flux recovery ratio which shows its higher fouling resistance. PE/ND-PEG (0.75 wt%) membrane’s superior antifouling performance can be attributed to the antibacterial properties of PEG-NP and also the way the ether group PEG forms strong hydrogen bonds with water molecules which prevents adhesion of bacteria, proteins and other foulants on the membrane. In a similar work, cellulose acetate was used as the matrix and mixed with ND-COOH to prepare CN/ND-COOH[18]. Critical flux, fouling behavior, and anti-fouling properties against extracellular polymeric substances (EPS) were examined in order to compare the nanocomposite membranes with CA membrane. CA/ND-COOH (0.5 wt.% of NDs) nanocomposite membrane showed higher critical flux and lower attachment of filamentous bacteria. When extractable EPS was analyzed, CA/ND-COOH (0.5 wt.%) membrane had lower concentrations of proteins and carbohydrates in the EPS and soluble microbial products (SMP) than other membranes.

    Another group synthesized composite nanoparticle of silver phosphate (Ag3PO4) and graphitic carbon nitride (g-C3N3) and incorporated with PES to prepare PES/ Ag3PO4/g-C3N4 microfiltration composite membrane by non-solvent induced phase separation method[19]. The membranes underwent filtration experiments using water and bovine serum albumin (BSA) solution to measure the membrane’s steady pure water flux (Jw1) and the bovine serum albumin (BSA) solution flux (JP). The results showed that the membranes modified with Ag3PO4-NH2/g-C3N4 had better fouling resistance ratios and higher FRR values than the bare PES membrane which indicates that the modified membranes have better antifouling properties.

    2.2 Composite containing non-carbon material

    Incorporation of silicon dioxide (SiO2) into HDPE matrix lower the hydrophobicity of the composite[20]. HDPE/SiO2 composite membrane was prepared by thermally induced phase separation method. Antifouling characteristics of the HDPE/SiO2 membranes were evaluated through constant-pressure filtration tests and the fouling analysis showed that the incorporation of SiO2 reduced the total fouling ratio by 27% and the irreversible fouling ratio by more than 70% while increasing the reversible fouling ratio by 16%. Hermia’s model was used to identify the most likely fouling mechanism and it was shown that there are two fouling phases. In the first phase, cake filtration is shown to be the main fouling mechanism and in the second phase, blockage model is revealed to be the main fouling mechanism. Titanium dioxide is another kind of nanoparticle incorporated into polypropylene matrix to enhance hydrophilicity of the material. PP/TiO2 composite membrane was prepared by thermally induced phase separation method[21]. Membrane bioreactor (MBR) system was used to investigate the effect of the aeration rate on the antifouling performance of polypropylene (PP)/TiO2 nanocomposite membrane. The antifouling performance of both the neat PP and composite PP was tested in different aeration rates (0.5,1, and 1.5 m3/m2h). When the neat PP and PP/TiO2 membranes were compared, the composite membrane had a higher reversible fouling ratio (RFR) and lower irreversible fouling ratio (IRF) which indicates its superior antifouling performance. Another group reported similar work of PP/TiO2 composite membrane prepared above reported process[22]. When pristine and composite membranes were compared, the results showed that the addition of TiO2 nano particles lowered the intrinsic, cake layer and irreversible fouling resistances. The main fouling mechanism was shown to be cake formation for both membranes, but the nanocomposite membrane showed lower irreversible fouling. Similarly, by incorporation of titania into PES ultrafiltration membrane enhanced the antifouling properties of the composite membrane[23] (Fig. 3).

    3. Conclusion

    Membrane bioreactor is a process in which activated sludge induce biological degradation and simultaneous separation of the solid and liquid by membrane process. However, during the process, separating membrane easily fouled due formation biofilm by bacteria on the surface of the membrane. This review discussed the control of fouling by composite membrane consisting of engineering polymers like PSF, PES, HDPE, PP etc. Another part of the composite membranes are carbon materials represented by GO, CNT or ND and noncarbon materials SiO2 or TiO2. Modification of nanomaterials with functional group enhance the composite compatibility and reduce membrane fouling substantially.



    Morphological and chemical characterization of the filler nanoparticles and PVDF-SGO composite membrane (a-SGO TEM, b-FTIR spectrum of GO and SGO, c-XPS spectrum of GO and SGO, and d-SEM cross section image of the PVDF-SGO membrane) (Reproduced from Ayyaru et al., 14 with permission of Royal Society of Chemistry).


    SEM images of an E. coli fouled membrane (a and c), phage treated membranes (b and d) and initial phage infection (e and f) (Reproduced from Ayyaru et al., 14 with permission of Royal Society of Chemistry).


    Generation of microvoid in PES composite membrane by the presence of titania (Reproduced from Low et al. 23 with permission of American Chemical Society).



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