Bulk decay of chlorine in water distribution systems*

Mathematical models of chlorine concentration in water distribution systems require the bulk decay coefficient to be quantified. The coefficient needs to be determined with respect to independent variables if models are to maintain their predictive capability as seasonal and water treatment operational changes occur. Reported herein are experiments undertaken to determine the functional dependence of the bulk-free, chlorine decay rate coefficient on total organic carbon concentration, initial chlorine concentration, temperature, and the number of rechlorinations. The resulting equation gives satisfactory results during annual cycles and the introduction of granular activated carbon treatment at a water treatment plant.