Microfiltration of activated sludge wastewater - the effect of system operation parameters

Membrane or hollow fiber microfiltration is increasingly used with the activated sludge process in conventional wastewater treatment to produce a higher quality effluent. The major problem of such applications is membrane fouling, which has generally been attributed to the high contents of suspended solids in the wastewater. In this study, the operation of an integrated activated sludge bioreactor- membrane microfiltration system was investigated. It was found that the airflow rate of aeration, the mechanical mixing of the bioreactor and the circulation flow of the wastewater through the cross-flow microfiltration unit all affected the size distribution of the particles in the wastewater to be filtered, which consequently affected the performance of the microfiltration unit. The degree of membrane fouling by different size fractions of particles in the activated sludge wastewater was examined. The results reveal that the smaller particles played a more important role in membrane fouling. A relatively simple model is presented to predict cake growth and permeation flux decline in a cross-flow microfiltration. (C) 2002 Elsevier Science B.V. All rights reserved.