Membrane Fouling of Submerged Membrane Bioreactors:  Impact of Mean Cell Residence Time and the Contributing Factors

Abstract

In this study, four bench-scale pre-anoxic submerged membrane bioreactors (MBR) were operated simultaneously at different mean cell residence times (MCRTs) (3, 5, 10, and 20 days) to systematically elucidate the contributing factors of membrane fouling. Severe membrane fouling was first observed in the 3-day followed by the 5-day MCRT MBRs. Minimal membrane fouling was detected in the 10 and 20-day MCRT MBRs. The fouling of microfiltration membrane was not controlled by mixed liquor suspended solids concentration or zeta potential of biomass. Instead, membrane fouling rate increased with increasing soluble microbial products and extracellular polymeric substances concentrations, which both increased with decreasing MCRT. Total organic carbon, protein, carbohydrate, and UV254 absorbance in the mixed liquor supernatant increased with decreasing MCRT and were consistently higher than those of the effluent. Accumulation of carbohydrates rather than proteins in the mixed liquor supernatant was found to decrease with increasing MCRT. Normalized capilliary suction time value rather than the capilliary suction time value would indicate membrane fouling potential of a mixed liquor. Image analysis of the fouled membrane using scanning electron microscope and confocal laser scanning microscope showed that biofilm formation was the cause of membrane fouling.

Effect of sludge retention time on sludge characteristics and membrane fouling of membrane bioreactor

“…The fouled membrane surface could have created an additional resistance for the soluble EPS to permeate the membrane. The passage of polysaccharides and proteins across the membrane could be at different rates, thereby resulting in different rejection efficiencies (Ng et al, 2006). This might be a possible cause.…”

“…Ahmed et al (2007), operating their MBRs at SRTs of 20, 60 and 100 d, found that membrane fouling at shorter SRTs was rapid and the fouling rate declined with an increasing SRT. Ng et al (2006) had also demonstrated that long SRT reduced the membrane fouling rate.…”

“…Attention has been given to the relationship between SRT and extracellular polymeric substances (EPS) formation in recent studies (Cho et al, 2005;Masse et al, 2006). Ng et al (2006) operated MBRs at SRTs of 3, 5, 10 and 20 d, and found the concentrations of total organic carbon, proteins, and carbohydrates in the mixed liquor supernatant increased with decreasing SRT. In this study, the longest SRT was 20 d, while in real practice SRT might be much longer.…”

Development and testing of a fully gravitational submerged anaerobic membrane bioreactor for wastewater treatment

“…The MCRT controls the sludge growth rate and in many biological systems this is known to influence the production of extracellular polymeric (ECP) materials, which in turn may affect membrane fouling [7]. The current work did not investigate this or other microbiologically mediated factors that may contribute towards membrane fouling, but the importance of these and of the parameters controlling them should not be overlooked [7,22,28,29]. .…”

Performance and Fouling in Pre-Denitrification Membrane Bioreactors Treating High-Strength Wastewater from Food Waste Disposers

“…Soluble microbial products (SMP), which is believed identical to soluble EPS, are high molecular weight compounds released during cell lysis and cell growth, creating high resistance of the membrane and leading to a decline of permeate flux. Thus, investigation of EPS and SMP is an important issue in reducing membrane fouling in MBR [17,18]. However, there are only a few studies reporting process performance and investigation of EPS and SMP in the pre-denitrification MBR, especially for such system treating high-strength food wastewater.…”