Enhancement of tannery wastewater treatment at low temperature by coagulation coupled with cationic polyacrylamide

Abstract

As one of the heavily polluted industrial wastewaters tannery wastewater, which is difficult to handle especially in winter at low temperature, has attracted intensive attention all over the world recently. This work investigated the application of coagulation-flocculation to improve the treatment of raw tannery wastewater at low temperature (10?). Parameters such as coagulant-flocculant combination, effective dosage and pH value etc. were optimized to enhance the removal of organic matter and suspended solids (SS). Ferric chloride, ferrous sulphate and polyaluminum chloride (PACl) were tested as conventional coagulants, and cationic polyacrylamide (C-PAM) was selected as flocculant. When coagulant was used alone, ferric chloride was found to be most efficient to remove chemical oxygen demand (COD) (42.8% removed) and SS (50.3% removed) and PACl was the lest affected by pH and produced less sludge than ferric chloride, as well as the least impact on the effluent pH. When coagulant was used in coupled with C-PAM, increased removal rate of COD and SS was achieved with a lower dosage demanded (4mg/L) for all coagulants and PACl showed the best performance of SS removal and the shortest sludge settling time (32s). The results illustrate this process can be an alternative pretreatment step prior to biological treatment at low temperature, especially for tannery wastewater.