Treatment of paper and pulp mill effluent by coagulation

Pulp and paper mill effluent is highly polluting and is a subject of great environmental concern. In the present research we studied the removal of chemical oxygen demand (COD) and colour from paper mill effluent, using the coagulation process. A batch coagulation study was conducted using various coagulants such as aluminium chloride (AlCl(3)), polyaluminium chloride (PAC) and copper sulphate (CuSO(4)center dot 5H(2)0). The initial pH of the effluent had a tremendous effect on the COD and colour removal. The PAC reduced COD by 83% and reduced colour by 92% at an optimum pH of 5.0 and a coagulant dose of 8 mL L(-1). With AlCl(3), at an optimum pH of 4.0 and a coagulant dose of 5 g L(-1), 72% COD removal and 84% colour removal were observed. At an optimum pH of 6.0 and a mass loading of 5 g L(-1), 76% COD reduction and 78% colour reduction were obtained with copper sulphate. It was also observed that, after addition of coagulant, the pH of the effluent decreased. The decrease in the pH was highest with AlCl(3), followed by PAC and then CuSO(4)center dot 5H(2)0.