Dairy Wastewater Treatment by Coagulation with Chitosan

Abstract

The pre-treatment of dairy wastewater is important as it reduces the load to small municipal wastewater treatment plants and is attractive as it produces sludge valuable as a food additive. Only non-toxic organic polymers of biological origin are suitable for this purpose. Anionic polymers such as sodium carboxymethyl cellulose (CMC) are commonly used for treating dairy wastewater, after the pH is adjusted to 4.2–4.5, however, this process consumes both acid and base while the process stability is highly dependent on the pH. In this study, a novel coagulant, chitosan, was tested in dairy wastewater. Chitosan is made from shrimp- and crab-shell waste and is a non-toxic cationic polymer. The results indicate very good performance even at pH = 5.5. The zeta potential studies on chitosan coagulation reveals the possibility for specific chemical adsorption of the polymer. The zeta potential at which coagulation occurs seems not to be constant for a given wastewater type and coagulant, thus it is not possible to use it as a “set-point” for coagulant dosing unless combined with other parameters.