Guide to the measurement and use of Ct

Disinfection of water (potable or recycled) with a chemical disinfectant (chlorine or chloramine) requires time for the chemical to react with and kill the target microbial pathogens. Ideally the time for the reaction is provided in a purpose-built reactor or contact tank as this is specifically designed for this purpose and provides a controllable process. The reality however is quite different. Most water supplies rely on disinfection to occur in clear water tanks and reservoirs of various size, with various arrangements of inlet and outlet structures and varying levels of short circuiting. The effective contact time is often less than is assumed.

Many water utilities use a target free or total chlorine residual in their treatment systems to achieve a level of disinfection that they understand to be adequate. This approach to disinfection can be improved in most cases.

About the Author

Andrew Lanchbery

Andrew is a senior chemical and environmental engineer who has completed full scale tracer testing at Water Treatment Plants across Victoria and is currently employed at the Victorian Department of Health and Human Services Water Unit as a technical specialist.

PDF

Guide to the measurement and use of Ct (PDF)

Excel

Baffling Factor tracer test template (XLSX)