Membrane fouling and cleaning in microfiltration of activated sludge wastewater

A major obstacle in the widespread application of membrane microfiltration for activated sludge wastewater treatment is the rapid decline of the permeation flux with time as a result of membrane fouling. In this study, a hollow fiber membrane microfiltration unit was employed to treat two types of activated sludge wastewater of different particle size distributions. Theoretical models were used to fit the experimental flux data to identify the predominant membrane fouling mechanisms during microfiltration of each type of the activated sludge wastewater. A novel membrane cleaning method using sonication technique was evaluated. The performance of a combination of the various membrane cleaning methods, such as clean water backwashing, sonication, and chemical cleaning, was investigated. The results show that the main types of membrane fouling in microfiltration of activated sludge wastewater were attributed to initial pore blocking followed by cake formation. Periodic sonication of the membrane microfiltration module effectively removed the cake from the membrane surface and thus significantly recovered the permeation flux. However, sonication was not effective in flux recovery for membrane fouling caused by other mechanisms, such as pore blocking, and therefore the extent of flux recovery decreased with each sonication cleaning cycle. A combination of clean water backwashing, sonication and chemical cleaning with alkali and acid could achieve almost complete flux recovery. The underlying cleaning mechanisms and the effectiveness of each of the different cleaning methods to the different types of fouling are discussed. (C) 2003 Elsevier Science B.V. All rights reserved.