Membrane foulants and fouling mechanisms in microfiltration and ultrafiltration of an activated sludge effluent

摘要

Membrane fouling in microfiltration (MF) and ultrafiltration (UF) of an activated sludge (AS)neffluent was investigated. It was found that the major membrane foulants were polysaccharides,nproteins, polysaccharide-like and protein-like materials and humic substances. MF fouling bynthe raw effluent was governed by pore adsorption of particles smaller than the pores during thenfirst 30 minutes of filtration and then followed the cake filtration model. UF fouling could bendescribed by the cake filtration model throughout the course of filtration. Coagulation with alumnand (poly)aluminium chlorohydrate (ACH) altered the MF fouling mechanism to follow the cakenfiltration model from the beginning of filtration. The MF and UF flux improvement byncoagulation was due to the removal of some of the foulants in the raw AS effluent bynthe coagulants. The MF flux improvement was greater for alum than for ACH whereas thentwo coagulants performed equally well in UF. Coagulation also reduced hydraulically irreversiblenfouling on the membranes and this effect was more prominent in MF than in UF. The unifiednmembrane fouling index (UMFI) was used to quantitatively evaluate the effectiveness ofncoagulation on membrane flux enhancement.