Coagulation–flocculation studies of tannery wastewater using cationic polymers as a replacement of metal salts

Abstract

Studies were conducted to evaluate the efficiency of cationic polymers as a suitable replacement of metal salts for the treatment of a local tannery wastewater. Eleven cationic polymers of varying molecular weights (MW) and charge densities (CD) were examined using jar test apparatus. Three cationic polymers: one with MW of 4 million Dalton and CD of 55%; second with MW of 6 million Dalton and CD of 40%; and the third with MW of 8 million Dalton and CD of 40% were found suitable for tannery wastewater treatment at an optimum dose of 20 mg/L for each. Percentage removals with these three cationic polymers for turbidity, total suspended solids (TSS), total chemical oxygen demand (TCOD) and chromium lied in a range of 91–95%, 69–83%, 25–29% and 96–97%, respectively with respect to plain settled wastewater. The cost of the most suitable cationic polymer C-496 at its optimum dose was $0.09 per cubic metre of wastewater and sludge production was 35 mL/L. The results demonstrated that treatment of tannery wastewater with cationic polymers is a viable and economical option when compared with metal salts.