Research Progress in Membrane Fouling of Membrane Bioreactor

Frontier of Environmental Science December 2015, Volume 4, Issue 4, PP.99-103

Research Progress in Membrane Fouling of Membrane Bioreactor Fa Tan, Dunqiu Wang†College of Environmental Science and Engineering, Guilin University of Technology, Guilin 541004, China â€

Email: wangdunqiu@sohu.com

Abstract Membrane bioreactor (MBR) has been becoming a popular technology in wastewater treatment due to its advantages with good treatment efficiency. However, membrane fouling prevented its wide application in water treatment. In this paper, the mechanism of membrane fouling was summarized, and the improvement methods were introduced. Operational parameters were emphasized in the running plants.

Keywords: MBR; Membrane Fouling; Operational Parameters

1

INTRODUCTION

Membrane bioreactor (MBR) is a process, which combines membrane technology and biological treatment in one unit. MBR has been widely used in sewage and industrial wastewater treatment due to its efficient solid-liquid separation under high sludge concentration. However, membrane fouling is the key factor, which restricts its application. The problem of membrane fouling strictly impacts the life cycle of the expensive membrane unit, then the running cost turns very high. Therefore, the research of membrane fouling is very urgent in developing MBR technology.

2

MECHANISMS OF MEMBRANE FOULING

Membrane fouling is a proceeding, during which suspended substances or dissolved matters attach on the surface or in the pore of membrane [1]. The membrane fouling might be led by the interaction force, concentration polarization, formation and compression of the block cake, absorption, filtration pore block between the particles and membrane [2].

2.1 Pollutants The composition of treated liquid plays a key role on membrane fouling. Published investigations of membrane fouling show that the macromolecular organic substance are main pollutants of membrane fouling, which contain the polysaccharide and protein content of extracellular polymeric substances (EPS), humic acids, suspended substance, colloid, and soluble substance, etc. [3]. The properties of the above pollutants are also the main reason of membrane fouling.

Harada et al [4] found that the filtration performance decreased with the increasing concentration of soluble organic matter. Nagaoka et al [5] have also observed increasing filtration resistance with increasing supernatant total organic carbon. Wisniewski et al [6] concluded that the dissolved fraction of mixed liquor was responsible for 50%-75% of the total fouling resistance. Defrance et al [7] investigated the relative contributions of suspended solids, colloids, and dissolved matter to filtration resistance and concluded that their impact was 65%, 30% and 5%, respectively. Liu et al [8] studied the effect of EPS on short term membrane fouling in submerged membrane bioreactor and found that the membrane fouling was caused by increasing EPS concentration and the protein was the dominant component of the membrane fouling.

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Microbial EPS can be divided into soluble EPS and bound EPS [9-10]. Bound EPS presents rheological double deck, and it consists of inner tightly bound EPS (TB-EPS) and outer loosely bound EPS (LB-EPS) [11]. The major components of LB-EPS and TB-ESP are macromolecular compound of polysaccharide and protein. Fan [12] concluded that colloidal particles (around 1Îźm diameter) might play a critical role in membrane fouling in MBR. As EPSs are one of the major components of colloidal particles, and they have been widely recognized as the main membrane pollutants. Tamesh [13] suggested that the main of soluble EPSs are the soluble microbial products (SMP), and they generate from the metabolism of microorganism. SMP are the compound substances of protein, polysaccharide, humus, nucleic acid, and antibiotics. Zhang et al [14] suggested that EPS and SMP are organic substances, which are the secondary products of microorganism.

2.2 Cake and Proceeding There is a certain relationship between membrane fouling and formed cake on the surface of membrane. With constantly accumulating cake layer, the phenomenon of membrane fouling will be more obvious following with declining flux. Bae [15] suggested that membrane fouling can be divided into three different phases based on flux variety: the flux sharply declines at the initial stage; the flux declining rate slows down the pace; and the flux remains stable. Lin [16] studied the permeability of MBR and found that the variation of filtration resistance obeys the standard blocking filtration model in initial process, and then fits to cake filtration model in later process. It was found that cake layer makes up over 90% of total resistance and the contributions of the sludge fractions, suspended solids, colloids and solutes, were calculated as 87.98%, 6.20%, and 5.82%, respectively.

3

ALLEVIATION OF MEMBRANE FOULING

3.1 Membrane Material Shen et al [3] suggested that the current focus of membrane material research is to use surface engineering technique in alleviating membrane fouling, such as modifying hydrophilicity and hydrophobicity, biological compatibility improvement, nano material application, etc. Organic materials are popular for membranes, such as polyvinylidene fluoride (PVDF), polythene (PE), polyfluoroethylene (PE), polyfluortetraethylene (PTFE), polyvinyl chloride (PVC), etc. Inorganic membrane is also widely used in recent years. Alumina ceramic membrane is one of the typical inorganic membranes.

Xu et al [17] showed that the surface decoration of polypropylene has improved the filtration process. Yu et al [18] have added alumina nanometer particles into PVDF membrane surface to modify phase inversion, and then hydropholicity and mechanical strength of membrane surface have been improved significantly. Chang et al [19] found that hydropholic membrane material has effect on anti-pollution, and hydropholic membrane is less affected by sorption with stable flux. Shimazu et al found that electronegative ceramic membrane flux was improved comparing with uncharged electropositive membrane [20]. Therefore, membrane materials are very important in treating defined wastewater.

Dong et al [21] found that adding nanometer particles into ultrafiltration membrane could change the surface property of membrane by nanoparticle-embedded. This method could improve the anti-pollutant performance of ultrafiltration membrane unit, which was caused by enhancing anti-adhesiveness of colon bacillus.

3.2 Operational Parameters Arabi et al [22] found that the membrane fouling could be improved with optimum calcium and sodium concentrations of 36 mg/L and 140mg/L, respectively. High sodium concentration could decrease the floc size and increase the fouling rate. However, introduction of magnesium was beneficial in reducing the fouling rate by increasing the floc size and the function of cationic bridges. Nakhla et al [23] found that the concentrations of calcium could impact the membrane fouling. The influent calcium concentration of 280 mg/L improved the membrane permeability, and the concentration of 830 mg/L led to substantial inorganic fouling of the membrane.

Ding et al [24] found that adding granular activated carbon (GAC) into expanded granular sludge bed (EGSB) not only improved the COD removal efficiency, but also alleviated membrane fouling efficiently. The results showed - 100 http://www.ivypub.org/fes

GAC could reduce SMP and tryptophan protein–like, aromatic protein-like and fulvic-like substances. Chen et al [25] concluded that the membrane fouling could be effectively controlled with the increase of calcium concentration, and the best permeability was achieved at calcium concentration of 200 mg/L. While high concentration above 200 mg/L was proved to stimulate membrane fouling due to increasing the inorganic fouling.

Cao et al [26] showed that the addition of powder activated carbon (PAC) could alleviate membrane fouling with increasing flux and reduce transfer membrane pressure (TMP) during long-term run. The addition of PAC reduced the amount of soluble substances, which caused membrane fouling by blogging in the pores of the membrane. Li et al [27] also reported that the addition of PAC played a critical role in the permeability performance. The PAC concentration of 1.2 g/L could enhance the permeability significantly, and the critical membrane flux increased 32% with only 44% of former TMP. Gong [28] reported that the cake layer could enhance membrane flux, improve rejection rate of organic compounds and mitigate the irreversible membrane fouling during the test of ultrafiltration unit. The formation of coagulation floc by diatomite could increase the floc size; therefore the formed cake layer improved the filtration performance.

Alleviating membrane fouling by forcing electric field is one of research heats during recent years. Forcing electric field can make the surface charge of membrane more electricity, and electronegative foulants can’t adhere to the surface of membrane permanently [29]. As a result, the chance of membrane pore block is reduced and stable flux might be maintained in reasonable time.

4

CONCLUSIONS

Membrane fouling is still the main problem of membrane technique application. The mechanism of membrane fouling is dedicated in several models. The substances, such as EPS, SMP are regarded as the key pollutants.

Numerous efforts were made by using advanced membrane material and improving operation parameters.

However, new methods with reasonable cost are still expected.

ACKNOWLEDGEMENTS This research was supported by the National Natural Science Foundation of China (No. 51108108), Guangxi Natural Science Foundation (2013GXNSFCA019018; 2014 GXNSFBA118265), Research Projects of the Education Department of Guangxi Government (2013ZD031; KY2015WZ015; KY2015WZ016), Guangxi Key Laboratory of New Energy and Building Energy Saving (12-J-21-2).

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AUTHORS 1

Fa Tan was born in Guangxi Province, China, on January 23, 1990. He earned the bachelor degree of Guilin

University of Technology in 2014.And Fa Tan is a student with master’s degree of Guilin University of Technology, Guilin, China. The major field of study is water pollution control technology.

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2

Dunqiu Wang was born in Jiangsu Province, China, on April 2, 1969. Dun-qiu Wang earned the bachelor

degree in Kunming University of Technology in 1993. And he earned the master degree and doctor degree in CHONGQING UNIVERSITY in 2000 and 2004, respectively.

The major field of study is water pollution control technology and promising waste treatment technology. He is the Professor in Guilin University of Technology, Guilin, China

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