2004 Volume 41 Issue 11 Pages 798-805
Filtration behaviors of sewage secondary effluent pretreated with flocculant were studied under constant filtration rate condition using ceramic microfiltration membranes. The process consisted of the periodic operations of the filtration (fouling) and backwashing (cleaning) cycles. The system was capable of selecting two modes of membrane backwashing, i. e., physical backwashing or chemically enhanced backwashing. The time dependency of pressure drop across the filter cake in an operating cycle mainly due to the cake build-up was well described by the constant rate filtration equation for the compressible filter cake, and the increase with the cycle number in pressure drop across the membrane mainly due to the pore blocking was adequately correlated by the intermediate blocking law. Our experimental data clearly showed that the combined operation of physical and chemically enhanced backwashing was highly effective for the filtration of sewage secondary effluent when accompanied by the flocculation operation. The increased dosage of flocculant substantially reduced the cake resistance and irreversible pore plugging. Particularly, less frequent physical backwashing by addition of flocculant led to an increase in the average filtration rate.