BACKGROUND: Combined use of permanganate and chlorine has been shown to have synergistic action in disinfection. However, according to the literature the effects of combined preoxidation on coagulation and filtration have not been thoroughly investigated. RESULTS: Laboratory and pilot experiments were conducted to evaluate the effect of the combined preoxidation by permanganate and chlorine on the treatment of River Luan water. Based on the reduction of the residual turbidity and UV254 after sedimentation and filtration, the optimum dosages of permanganate and chlorine were selected. The improvement of treated water quality was also achieved in the pilot processes. Permanganate reduced the amount of chlorine, while it enhanced chlorination and reduced trihalomethane production. The enhanced treatment efficiency could be explained by the synergistic effect of the preoxidants themselves and the effect of chlorine and intermediates such as hydrous manganese dioxide, which was formed in situ by permanganate reduction. CONCLUSION: Laboratory and pilot studies demonstrated that combined preoxidation by permanganate and chlorine could enhance water treatment. (C) 2009 Society of Chemical Industry