When PAC was added into the pretreatment supernatant, the rejection rate was 91% in the membrane severation. Rejection rate in the cute of without PAC was 69%. The permeate flux in the membrane separation with PAC was lower than in the case of non-PAC, but the recovery of permeability by cleaning in the case of PAC addition(J_f/J_o : 91.90%) was higher than in the case of non-PAC(J_f/J_o : 74.64%). It is thought that PAC is cause of membrane fouling and it's adsorption with soluble organic materials