Fouling behaviour of soluble microbial products and extracellular polymeric substances in a submerged anaerobic membrane bioreactor treating low-strength wastewater at room temperature

The properties of soluble microbial products (SMP) and extracellular polymeric substances (EPS) were determined and their role in membrane fouling behaviour was considered in an anaerobic membrane bioreactor (AnMBR) treating low-strength wastewater at room temperature. The SMP/EPS properties of interest were specific production, molecular weight distribution and adhesion force. The results showed the largest factor affecting the SMP/EPS properties and their diverse membrane fouling performances was the organic loading rate (OLR). An increase in the OLR resulted in an increase in the production of specific EPS and macromolecules in the SMP/EPS fractions, in effect exacerbating the flocculation ability of the mixed liquor in the AnMBR and thus facilitating the fast formation of cake layers. Furthermore, the EPS tended to be more viscoelastic and hydrophobic at a higher OLR and because the adhesion forces of the EPS-membrane and EPS-EPS were significantly enhanced as the OLR increased, cake fouling was significantly accelerated. The results indicated that the main cause of fouling was SMP-induced pore blockages, and that membrane resistance increased gradually until an OLR of 0.7 gCOD/L/d, but increased remarkably when the OLR was higher than 1.4 gCOD/L/d, caused by the EPS-induced fast-growth and compact cake layer on the membrane surface.