October 10, 2019
The aim of the paper is to de-mystify the science and operational practice around the use of contact time (Ct) in management of disinfection of drinking water supplies. Disinfection of water with a chemical disinfectant (chlorine or chloramine) requires time for the chemical to react with and kill target pathogens. In an ideal situation the required time for the disinfection to take place is facilitated by a purpose-built reactor or contact tank, specifically designed for this purpose to provide a controllable process.
In reality the situation across the water industry is often quite different. Most water suppliers rely on disinfection to occur in their treated water storages (clear water tanks and reservoirs) of various sizes, with various arrangements of inlet and outlet structures and varying levels of short circuiting. The effective contact time is often much less than is assumed, potentially compromising disinfection efficacy. It is hoped that the Ct paper will provide valuable information and insight to water utilities to assist them in optimising their disinfection processes.
In addition to thanking WIOA for the opportunity to collaborate on the publication of this paper, WaterRA would like to congratulate Andrew Lanchbery (Victorian Department of Health & Human Services) on his authorship, as well as acknowledge the generous support from Coliban Water and expert review and input from Aaron Ward, Zlatko Tonkovic, Peter Mosse and Bruce Murray.