Accumulation of organic substances in a submerged membrane bioreactor and its influence on membrane fouling

Abstract

A laboratory-scale submerged membrane bioreactor (SMBR) with a hollow-fibre membrane module was used to investigate the behaviour of organic substance accumulation in the sludge suspension and its impact on membrane fouling. The experimental study lasted for 12 months under different F/M ratio conditions. The results demonstrate the retention of organic solutes in the sludge mixture by membrane filtration. In addition to soluble microbial products (SMP), there was also a pool of non-filterable, large-sized organic substances, named biopolymer clusters (BPC), in the sludge suspension. BPC were shown to have a major impact on membrane fouling under different F/M conditions. The accumulation of BPC was more pronounced at a higher F/M ratio. Both polysaccharides and proteins appeared to be the main components of BPC. SMP were likely the main precursors of BPC. At a higher F/M ratio, more SMP would be produced, leading to more BPC formation and accumulation in the SMBR system. Based on the long-term experimental observation, it can be concluded that BPC are the major foulant in the SMBR that interact with sludge flocs to facilitate the fouling layer formation on the membrane surface.