Membrane fouling was observed using microbial suspensions obtained from a sequencing batch reactor operated for simultaneous partial nitrification and anammox. Combined effects of particle size distributions in microbial suspensions taken from the SBR and membrane pore sizes on membrane fouling are presented. With the smallest membrane pore size tested (0.1 mu m), a supernatant solution led to higher fouling rate than the mixed liquor suspension having relatively bigger particle sizes and larger quantity. However, the fouling rate with two different solutions was not different significantly as the glass-fiber filter (1.2 mu m pore size) was used. For the smallest membrane pore size, best fittings based upon pore blocking models showed that cake filtration played a key role in the membrane fouling. However, intermediate pore blocking was classified as dominant fouling mechanisms for the glass-fiber filter tested. This study showed that the surface morphology of the fouling layer deposited on membrane surface could vary depending upon the surface properties of the fresh membranes and glass-fiber filter such as surface roughness. A higher surface roughness of the membrane resulted in a higher fouling rate with rougher surface of the fouling layer formed on the membrane. This study also suggested that soluble microbial products (SMP) resulted in a higher flux decline than that observed with extracellular polymeric substances (EPS) in the supernatant solution taken from the anammox SBR. (C) 2015 Elsevier B.V. All rights reserved.