Colorado's oldest and largest public water provider has begun using ozone rather than chlorine to disinfect 2,645 miles of water mains.

A three-year study conducted by Denver Water and engineering firm CDM shows that, when combined with a high-pressure spray wash precleaning system that targets bacteria attached to pipe walls, ozone is an efficient disinfectant. It takes 20 to 30 minutes to work and converts to oxygen within an hour versus chlorine-based disinfection, a 24-hour process that requires dechlorination, which can take another 24 hours.

The research project involved three stages: laboratory, pipe-loop testing, and full-scale field trials. After developing a trailer-mounted precleaning system, Denver Water injected ozone into the water using a product developed by Mazzei Injector Corp. Based on the results, the utility is making this process part of its standard distribution system disinfection processes.

Water main disinfection isn't federally regulated, but the American Water Works Association is working with the EPA to establish ozone disinfection as a best practice.