Evaluation of soluble microbial products (SMP) on membrane fouling in membrane bioreactors (MBRs) at the fractional and overall level: a review

Membrane fouling investigations in membrane bioreactors (MBRs) are a top research issue. The aim of this work is to study the combined effect of colloids and soluble microbial products (SMPs) on membrane fouling. Two lab-pilot MBRs were investigated for treating two types of wastewater (wwt), synthetic and domestic. Transmembrane pressure (TMP), SMP, particle size distribution and treatment efficiency were evaluated. Chemical Oxygen Demand (COD) removal and nitrification were successful for both kinds of sewage reaching up to 95–97% and 100%, respectively. Domestic wwt presented 5.5 times more SMP proteins and 11 times more SMP carbohydrates compared to the synthetic one. In contrast, synthetic wwt had around 20% more colloids in the mixed liquor with a size lower than membrane pore size (<400 nm) than domestic. Finally, the TMP at 36 days reached 16 kPa for synthetic wwt and 11 kPa for domestic. Therefore, synthetic wwt, despite its low concentration of SMPs, caused severe membrane fouling compared to domestic, a result that is attributed to the increased concentration of colloids. Consequently, the quantity of colloids and possibly their special characteristics play decisive and more important roles in membrane fouling compared to the SMP—a novel conclusion that can be used to mitigate membranes fouling.

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Changes in characteristics of soluble microbial products in membrane bioreactors associated with different solid retention times: Relation to membrane fouling

Water Research ◽

10.1016/j.watres.2008.11.024 ◽

2009 ◽

Vol 43 (4) ◽

pp. 1033-1039 ◽

Cited By ~ 147

Author(s):

Katsuki Kimura ◽

Takuro Naruse ◽

Yoshimasa Watanabe

Keyword(s):

Membrane Fouling ◽

Membrane Bioreactors ◽

Soluble Microbial Products ◽

Microbial Products

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Influences of electroosmosis and electrophoresis on permeate flux and membrane fouling in submerged membrane bioreactors (SMBRs)

Water Science & Technology ◽

10.2166/wst.2016.280 ◽

2016 ◽

Vol 74 (3) ◽

pp. 766-776 ◽

Cited By ~ 2

Author(s):

Secil Bayar ◽

Ahmet Karagunduz ◽

Bulent Keskinler

Keyword(s):

Membrane Fouling ◽

Membrane Surface ◽

Membrane Bioreactors ◽

Polymeric Membrane ◽

Soluble Microbial Products ◽

Permeate Flux ◽

Electrical Field ◽

Cake Layer ◽

Significant Process ◽

Microbial Products

The objective of this study was to investigate the influences of electroosmosis (EO) and electrophoresis (EP) on the permeate flux in submerged membrane bioreactors. When a polymeric membrane is placed in between an anode and a cathode, both EO and EP occur simultaneously, causing enhancement in flux. Results showed that after 150 min of filtration, the permeate fluxes were 60, 115, 175 and 260 L/m2/h at 0, 30, 40 and 50 V, respectively. It was shown that the EO was linearly changing with increasing voltage, reaching up to 54 L/m2/h at 50 V. EP was found to be a significant process in removing soluble microbial products from the membrane surface, resulting in an increase in permeate flux as the filtration progressed. About 20-fold of smaller protein and carbohydrate concentrations were found in the cake layer when the electrical field (EF) was applied. However, the EF application promoted pore fouling, because of the calcium and magnesium scaling.

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Fouling cake layer in a submerged anaerobic membrane bioreactor treating saline wastewaters: curse or a blessing?

Water Science & Technology ◽

10.2166/wst.2011.461 ◽

2011 ◽

Vol 63 (12) ◽

pp. 2902-2908 ◽

Cited By ~ 27

Author(s):

I. Vyrides ◽

D. C. Stuckey

Keyword(s):

Membrane Fouling ◽

Membrane Bioreactor ◽

Large Fraction ◽

Membrane Bioreactors ◽

Extracellular Polysaccharides ◽

Cake Layer ◽

Anaerobic Membrane Bioreactors ◽

Suspended Biomass ◽

Microbial Products

The treatment of inhibitory (saline) wastewaters is known to produce considerable amounts of soluble microbial products (SMPs), and this has been implicated in membrane fouling; the fate of these SMPs was of considerable interest in this work. This study also investigated the contribution of SMPs to membrane fouling of the; (a) cake layer/biofilm layer, (b) the compounds below the biofilm/cake layer and strongly attached to the surface of the membrane, (c) the compounds in the inner pores of the membrane, and (d) the membrane. It was found that the cake/biofilm layer was the main reason for fouling of the membrane. Interestingly, the bacteria attached to the cake/biofilm layer showed higher biodegradation rates compared with the bacteria in suspension. Moreover, the bacteria attached to the cake layer showed higher amounts of attached extracellular polysaccharides (EPS) compared with the bacteria in suspension, possibly due to accumulation of the released EPS from suspended biomass in the cake/biofilm layer. Molecular weight (MW) analysis of the effluent and reactor bulk showed that the cake layer can retain a large fraction of the SMPs in the reactor and prevent them from being released into the effluent. Hence, while cake layers lead to lower fluxes in submerged anaerobic membrane bioreactors (SAMBRs), and hence higher costs, they can improve the quality of the reactor effluent.

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Biomass Characteristics and Their Effect on Membrane Bioreactor Fouling

Molecules ◽

10.3390/molecules24162867 ◽

2019 ◽

Vol 24 (16) ◽

pp. 2867 ◽

Cited By ~ 5

Author(s):

Petros K. Gkotsis ◽

Anastasios I. Zouboulis

Keyword(s):

Membrane Fouling ◽

Membrane Bioreactor ◽

Suspended Solids ◽

Extracellular Polymeric Substances ◽

Membrane Surface ◽

Membrane Resistance ◽

Soluble Microbial Products ◽

Gelling Properties ◽

Microbial Products ◽

Soluble Part

Biomass characteristics are regarded as particularly influential for fouling in Membrane Bio-Reactors (MBRs). They primarily include the Mixed Liquor Suspended Solids (MLSS), the colloids and the Extracellular Polymeric Substances (EPS). Among them, the soluble part of EPS, which is also known as Soluble Microbial Products (SMP), is the most significant foulant, i.e., it is principally responsible for membrane fouling and affects all fundamental fouling indices, such as the Trans-Membrane Pressure (TMP) and the membrane resistance and permeability. Recent research in the field of MBRs, tends to consider the carbohydrate fraction of SMP (SMPc) the most important characteristic for fouling, mainly due to the hydrophilic and gelling properties, which are exhibited by polysaccharides and allow them to be easily attached on the membrane surface. Other wastewater and biomass characteristics, which affect indirectly membrane fouling, include temperature, viscosity, dissolved oxygen (DO), foaming, hydrophobicity and surface charge. The main methods employed for the characterization and assessment of biomass quality, in terms of filterability and fouling potential, can be divided into direct (such as FDT, SFI, TTF100, MFI, DFCM) or indirect (such as CST, TOC, PSA, RH) methods, and they are shortly presented in this review.

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