Color Removal Using Alum and Cationic Polymers

摘要

Color in natural waters is often due to the presence of humic materials. Humic materials may be precursors for trihalomethanes (THM's)in water that is chlorinated for disinfection. The removal of humic compounds before chlorination of drinking water helps to prevent the formation of THM's. A common operation employed to lower the humic content or color of a natural water is that of coagulation, with alum and synthetic polymers being common coagulants. The objectives of this research were to determine the feasibility of applying alum and polymers in combination and to compare the coagulation characteristics of systems where alum, polymers, and alum-polymer combinations were used. Also, an attempt was made to determine the reaction mechanisms between coagulants and humic compounds for each of the systems studied. Batch flocculation experiments were conducted using a synthetic colored water with a humic acid concentration of 20 mg/l (400 color units) at a pH of 6. Alum and two commercial cationic polyelectrolytes were the coagulants employed. Measurements were made on the true color, residual turbidity, and electrophoretic mobility of the treated solutions. The color-removing ability of each of the coagulants was assessed from the standpoints of color removal, operational problems, and cost. For the system studied, alum was found to provide the best removal efficiency at the lowest cost with the widest operational flexibility. It was determined that it is feasible to apply alum and polymers in combination to achieve color removal.