Progress of studies on soluble microbial products in a membrane bioreactor

A review concerning the production of soluble microbial products (SMP) and their impact in a membrane bioreactor is presented in this paper. The high performance of membrane separation in the membrane bioreactor not only results in an increased organic loading rate and an improved effluent quality, but also builds the bioreactor as a relatively closed system. SMP, most of which have been identified as humic acid, polysaccharide and protein released from substrate metabolism and microbial endogenous growth, are found to comprise the majority of soluble TOC or COD in the biologically treated effluent. SMP accumulation was always observed in a membrane bioreactor due to its considerable macromolecular content and its slow biodegradable nature. Too much accumulated SMP may decrease the stability of the effluent quality, repress microbial viability, as well as result in serious membrane fouling. SMP formation is greatly influenced by influent concentration and sludge concentration. The knowledge about SMP in a membrane bioreactor is far from completion. Much work is still required to be done.