Fouling deposition and removal during filtration with short periodical backwash was investigated by direct observation coupled with hydraulic resistance measurement. Using a model mixture of bentonite and alginate, it was found that short periodical backwash only (i.e. without air scouring) expanded the foulant cake, which is subsequently recompressed back to membrane surface when the filtration resumes. With air-scouring aided backwash, the fouling material is convected away from the effective filtration zone, thus limiting re-deposition. However, due to the potential fractionation of foulant species at high air scouring rate, the deposition of more highly resistant components was observed over multiple filtration and backwash cycles. The results indicated that the changes in cake height, composition and structure were affected not only by the initial composition of the feed, but also by the hydrodynamics of the backwash and air scouring present. (C) 2011 Elsevier B.V. All rights reserved.