A study using coagulation-flocculation method for the treatment of pulp and paper mill wastewater has been carried out. The efficiency of alum and polyaluminum chloride (PACl) when used alone and in coupled with cationic polyacrylamide (C-PAM) and anionic polyacrylamide (A-PAM) on the treatment of pulp and paper mill wastewater were studied. The reduction efficiency of turbidity and chemical oxygen demand (COD), removal efficiency of total suspended solids (TSS), sludge volume index (SVI) and settling time are the main evaluating parameters. In coagulation-flocculation process using single coagulant, coagulant dosage and pH play an important role in determining the coagulation efficiency. At the optimum alum dosage of 1000 mg/L and optimum pH of 6.0, turbidity reduction is found to be 99.8%, TSS removal is 99.4% and COD reduction is 91 %. The optimum dosage and pH for PACl are 500 mg/L and 6.0, respectively, at which it gives 99.9% reduction of turbidity, 99.5% of TSS removal and 91.3% of COD reduction. A combination of inorganic coagulant and flocculant or polymer is applied in which alum and PACl are used coupled with the C-PAM (Organopol 5415) and A-PAM (Chemfloc 430A). Overall, alum coupled with Organopol 5415 is the best system among all systems studied. It gives 99.7% reduction of turbidity, 99.5% removal of TSS and 95.6% reduction of COD, and at the same time with low SVI (38 mL/g) and low settling time (12 s). (C) 2007 Elsevier B.V. All rights reserved.