A comparative study of fouling-related properties of sludge from conventional and membrane enhanced biological phosphorus removal processes

The physical and biochemical properties of activated sludge mixed liquor, including floc size distribution, zeta potential, relative hydrophobicity, and bound and unbound (soluble) extracellular polymeric substances (EPS), were examined in this study to evaluate their relationship to membrane fouling. Mixed liquors from a membrane enhanced biological phosphorus removal (MEBPR) process and a conventional enhanced biological phosphorus removal (CEBPR) process were compared. It was found that the floc size distribution and the amount of soluble EPS in the mixed liquor were the most important properties that significantly influenced the fouling propensity of sludge. Contrary to the literature, the content of EPS bound in activated sludge flocs was not found to be directly associated with membrane fouling, and sludge surface properties such as zeta potential and relative hydrophobicity were not closely related to the observed differences in the fouling tendencies of the two types of sludge.