Raw water treatment using bentonite-chitosan as a coagulant

Abstract

The effectiveness of bentonite using chitosan as a coagulant for raw water treatment was assessed in this study. The possible link between Alzheimer's disease with conventional aluminium based coagulants, has become an issue in water treatment. A method for treating water, using a natural approach as an alternate to achieve enhanced coagulation, might help to reduce risk to health, and be more environmentally friendly. One method for removing turbidity from raw water is by the adding of a primary coagulant (e.g., a natural polymer of chitosan) and a coagulant aid (e.g., natural clay of bentonite) to the raw water. A series of batch coagulation tests were conducted by jar test to obtain the optimum dosage, pH, ratio of coagulant aid and primary coagulant, and the efficiency time for the jar test, by evaluating the standard parameters, such as turbidity, pH, colour, aluminium, and chlorine. In terms of these parameters, chitosan:bentonite showed the best result, with a ratio of 30:70 in an optimal concentration of 1,000 mg/l with 0.15 g chitosan plus 0.35 g bentonite. The coagulants performed with an optimal pH of 5, with 30 min of mixing time during flocculation. However, the optimal pH condition during the jar test showed an improvement in the water alkalinity results, from pH 5 to 6.8. Coagulation with bentonite-chitosan successfully removed the turbidity with a highest efficiency of 98%. After water treatment in the optimal condition, results showed a great water quality standard, with 1.38 NTU, 10 TCU, 0.01 mg/l amount of chlorine and aluminium, and a pH of 6.8. However, data only showed slight differences of efficiency, between natural and conventional coagulants. In terms of the sludge volume index (SVI), the ratio of alum to bentonitechitosan was found to be 3:1 which indicated that less sludge was produced by the natural coagulant. In a cost comparison between these coagulants, based on a rough estimation, bentonitechitosan is nearly 10 times more expensive than the alum coagulant. However, with mass production and commercial availability, in the long run the price of chitosan could be reduced tremendously. © IWA Publishing 2012.