Three parallel membrane bioreactors (MBR) were operated to verify the effect of powdered activated carbon (PAC) dosage on membrane fouling for domestic wastewater treatment at PAC dosage of 0, 0.75 and 1.5 g/L, respectively. The results showed that the application of PAC was effective in decreasing the content of extracellular polymeric substances (EPS) inside the microbial floc at PAC dosage of 0.75 g/L. And the EPS deposited on the membrane was reduced with addition of PAC. This suggests that the permeable PAC particulate layer filter out microbial cells and colloids, and prevent them from reaching the membrane surface. The cake resistance decreased with the increase of PAC dosage. However, the irreversible fouling resistance was reduced effectively at PAC dosage of 0.75 g/L, and this effect weakened significantly at a higher dosage of 1.5 g/L. The degree of irreversible fouling was equal at PAC dosage of 0 and 1.5 g/L. Detailed studies on the effect of PAC dosage indicated that a PAC dosage of 0.75 g/L was the optimum in terms of organic removal and filtration flux. (c) 2006 Elsevier B.V. All rights reserved.