Impacts of Disinfectant Switching Practices on Chloraminating Utilities

Sponsor: American Water Works Association Research Foundation

Co-PIs: Nancy Love (Virginia Tech) and Francis DiGiano (UNC-Chapel Hill)

This ongoing project is examining the impacts of a temporal switch in disinfectant type on water quality in drinking water distribution systems. To minimize the potential for nitrification, many plants employing chloramination for secondary disinfection convert their residual from chloramines to free chlorine on a periodic basis. The concept behind this switch, known as ‘temporal disinfectant switching', is that free chlorine will oxidize any ammonia (the food source for nitrifying bacteria) and will reduce the number of nitrifying bacteria present within the distribution system. Although the benefits of temporal disinfectant switching have been empirically assumed on the basis of full-scale studies, the assumption that this practice minimizes nitrification occurrence has never been verified under controlled conditions as can only be done at the pilot-scale level in a laboratory experiment. The overall goal of this project is to improve our understanding of how water quality changes as a result of a temporal switch from a monochloramine residual to a free chlorine residual. The following research priorities have been the focus of our efforts:

1. To document the effectiveness of free chlorine for the control of nitrifying bacteria.
2. To evaluate how distribution system pipe materials affect nitrifying biofilm consortia.
3. To determine how disinfection byproduct (DBP) concentrations change as a result of the switch from monochloramine to free chlorine.
4. To examine how disinfectant switching impacts the stability of the biofilm.

Presentations