The effect of appending direct electric field on the membrane flux of an antifouling membrane bioreactor (MBR) designed and built in our laboratory was investigated. The results showed that appending electric field had significant influence on the membrane flux. At an operation pressure of Delta P = 0.1 MPa, membrane flux increased with electric field strength from E = 15 V/cm to 20 V/cm, then kept almost constant after E arrived 20 V/cm. This might result from the fact that charged coarse particle and colloid accounted for 80% of CODCr and BOD5 in urban domestic sewage. Those particles and colloid moved away from the membrane surface in the electric field and their speed increased with the increase of electric field strength. When the electric field strength was strong enough to make the deposited layer on the membrane surface no longer a limiting factor in the membrane flux, no much effect was observed after the electric field strength exceeded the critical point. (c) 2006 Elsevier B.V. All rights reserved.