Membrane fouling - a review on the role of EPS

Abstract

Extracellular polymeric substances (EPS) in either bound or soluble/colloidal form are currently considered as the major cause of membrane fouling in membrane bioreactors. Several factors like the type of wastewater, sludge loading rate, sludge age, MLSS concentration, mechanical stress, and microbial growth phase are known to influence the concentration of EPS in one way or another [1–4]. Also, unsteady states like intermittent feeding, irregular sludge wastage or shifts in the oxygen supply [5–7] have been identified as additional factors leading to an increase in EPS formation or to a change in its fouling propensity (Fig. 1). Despite the large number of technical publications on membrane fouling and EPS, many questions remain unanswered to date. A number of attempts have been made to correlate flux with MLSS concentration, floc size, sludge rheology [1], and soluble EPS concentration [8], but due to the complex nature of the biological system and the difference in experimental and analytical methods applied these are inconsistent and often even contradictory. This paper reviews results from the authors’ own and other labs and thereby aims at establishing a general evaluation of the role of EPS for membrane fouling.