This study was conducted to investigate the chemical precipitation (CP) and membrane bioreactor (MBR) hybrid process for the treatment of piggery wastewater. Average removal efficiencies for BOD, COD and turbidity in CP process were 64.3%, 77.3% and 96.4%, respectively. CP process had a moderate effect on NH(3)-N removal (40.4%) which improved up to 98.2% mainly due to nitrification and filtration processes in MBR. The average removal efficiencies of BOD, COD and turbidity in MBR were 99.5%, 99.4% and 99.8%, respectively. Monod equation was used to explain the microbial activities in terms of specific growth rate. The specific growth rate of bacteria in aeration tank (N-batch) and anoxic tank (D-batch) were 0.013 and 0.005 d(-1) with a biomass yield of 0.78 and 0.43 mg MLSS produced/mg COD utilized, respectively. Microorganisms from the N-batch and D-batch showed a low-level of nitrifying and moderate-evel of denitrifying capabilities which were 1.08 mg NH(3)-N/(g MLVSS.h) and 2.82 mg NO(3)/(g MLVSS.h), respectively. Carbohydrates were the main component in extracellular polymeric substance (EPS) compounds that could be attached to the membrane surface easily and led to membrane biofouling. increase of MLSS, EPS and sludge viscosity concentration, decrease of sludge floc size and incomplete chemical cleaning procedure resulted in the increase of membrane resistance. Total membrane resistance increased from 3.19 x 10(12) m(-1) to 5.43 x 10(14) m(-1). Crown Copyright (c) 2008 Published by Elsevier Ltd. All rights reserved.