Studies on chlorination of greywater

In view of the growing implementation of systems for treated greywater reuse, and as chlorination is an eventual step of the treatment to assure disinfection, a study of variables affecting the residual chlorine decay in greywater are reported in this paper. The investigation was carried out at laboratory scale with chlorinated samples, and the residual chlorine was measured spectrophotometrically with o-tolidine. To discuss the effects of these variables, decay curves were compared, or alternatively, fitted to a parallel first order decay model. Studied variables were: pH, surfactants, coliform bacteria, ammonia concentration, coagulant agents, potassium permanganate concentration, filtration and storage time. The obtained results showed that residual chlorine can be stabilized by: ammonia, by preoxidation with potassium permanganate or by treatment with coagulanting–flocculanting agents. Surfactants and bacteria were shown to favoured chlorine consumption. Results from this study can be useful to define the working conditions of full-scale systems where the reduction of chlorination dose is a matter of great interest to minimize the environmental impact of the systems.