The removal of COD, TSS and colour of black liquor by coagulation-flocculation process at optimized pH, settling and dosing rate

Pulp and Paper mills are generating millions of tons of wastewater and are major source of water pollution. In this research work, pulping wastes have been characterized and found to contain very high COD, TSS and colour. Coagulation-flocculation process was performed to find out the performance of different coagulants and flocculants like alum, ferric chloride, aluminium chloride, ferrous sulphate, poly aluminium chloride (PAC), cationic and anionic polyacrylamide polymers in individual form as well as in different combinations. The effects of dosing rate, settling time and pH were examined for reduction of COD, TSS and colour. Coagulants used in combinations were found to be more effective in reducing COD, TSS and colour instead of using individual form. The initial pH of the effluent for coagulation process was found to have remarkable effect on COD, TSS and colour removal. The most effective results were found using cationic and anionic polyacrylamide combination with ferric chloride and aluminium chloride and reduction of 76% COD, 95% TSS and 95% colour were observed at pH < 3.