Chlorination control in a large water treatment works

The introduction of tighter drinking water quality standards and economic considerations has focused attention on ways to improve control systems for water treatment, and for the disinfection process in particular. This control problem has, however, proved difficult to tackle with automatic control systems, due to the long contact time between the water and the disinfectant needed to ensure reliable disinfection, and hence the long delay between a control action and its measurement. The variable quality of raw water, together with the large effect that seasonal changes in ambient temperature and pH have on the dissociation, and thus the disinfecting capability, of dosed chlorine-based disinfectants, compound the problem. This paper describes a simple and cost-effective approach to the control of water chlorination that is being implemented for a large UK water treatment works.