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

Results taken from microfiltration and ultrafiltration of the activated sludge effluent taken from a municipal wasterwater treatment plant in Victoria revealed that microfiltration fouling was governed by pore adsorption of the particles smaller than the pores during the first 20-30 minutes of filtration and then follow cake filtration model. UF fouling could be described by the cake filtration model throughout the course of filtration. Coagulation with alum and (poly)aluminium chlorohydrate (ACH) altered the MF fouling mechanism to follow the cake filtration model from the beginning of filtration. The MF and UF flux improvement by coagulation was due to the removal of some of the foulants in the raw AS effluent by the coagulants. The MF flux improvement was greater for alum than for ACH whereas the two coagulants performed equally well in UF. Coagulation also reduced hydraulically irreversible fouling on the membranes and this effect was more prominent in MF than in UF. The unified membrane fouling index (UMFI) was used to quantitatively evaluate the effectiveness of coagulation on membrane flux enhancement.