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The control of membrane fouling is an essential issue in membrane bioreactor (MBR) process. It has been recognized that the most important factors that affect membrane fouling are presence of soluble microbial products (SMP) and extracellular polymeric substances (EPS) in a reactor. The objective of this study was to examine the effect of the coagulant addition on the membrane fouling in the MBR process. Accordingly, laboratory scale batch experiments and MBR experiments were conducted using coagulant. In batch experiments, effective SMP removal and control of EPS release were observed by coagulant addition. Fe coagulant was slightly more effective than Al coagulant in the addition of same mole amount. Therefore, Fe was used as coagulant in MBR experiments. In MBR experiments, Fe solutions of 0 mg/L, 2,260 mg/L and 4,520 mg/L were added into the tanks (Run1, Run2 and Run3, respectively) with the flow rate of 200 mL/d. COD removal efficiencies of 97% and phosphorus removal efficiencies of 92% were observed by Fe addition in the MBR experiment. Membrane fouling occurred more often in Run1 than in the other two Runs. Membrane was cleaned 18, 9 and 5 times in Run1, Run2 and Run3, respectively during 40 days runs. This suggested that the membrane fouling was reduced by the coagulant addition. The protein and carbohydrate concentrations of the SMP in the fraction of 1 microm-0.4 microm in Run2 and Run3 were significantly lower than that in Run1 and the particle size of the activated sludge was obviously increased in Run2 and Run3. These results suggested that the coagulant addition is effective to control the membrane fouling.