DBP Impacts From Increased Chlorine Residual Requirements: Fid-Bau Portal

DBP Impacts From Increased Chlorine Residual Requirements

Roth, Damon K. / Cornwell, David A.

Since the Surface Water Treatment Rule (SWTR) was implemented in 1989, the US Environmental Protection Agency (USEPA) has required utilities to maintain a chlorine residual (free or total) throughout the distribution system. Although many states have established numerical minimum values for the chlorine concentration to be maintained, the SWTR only requires a “detectable” residual. In 2015, AWWA's Disinfectant Residual Strategy Panel recommended that USEPA consider establishing numeric minimums for analytical methods used for disinfectant analysis to help utilities assess whether they are successfully maintaining disinfectant residuals in their systems. Implementing numeric minimums will require some utilities to increase chlorine dosages to maintain higher residuals than their current practice. In this study, water samples from 21 utilities across the United States were collected for testing to determine the impact that increasing residual chlorine levels would have on disinfection byproduct (DBP) formation. The results indicated that many systems are able to maintain detectable chlorine residuals without feeding sufficient chlorine to exhaust the inherent chlorine demand of the bulk water. Therefore, significantly more additional chlorine is required to raise the free chlorine residual from a trace level to a concentration of about 0.2–0.5 mg/L; after that concentration is reached, significantly less chlorine is required to increase residual. Accordingly, systems that currently maintain trace chlorine residuals in their distribution system will see increased DBP formation if they begin feeding sufficient chlorine to increase residuals. Systems that already maintain free chlorine residuals in excess of 0.2 mg/L would expect to see minimal incremental DPB formation if required to increase chlorine residuals.