Assessing the Impact and Causes of Brominated DBPs for Stage 2 Compliance

Authors:

  • David Briley - Hazen and Sawyer

As utilities adjust to complying with the Stage 2 Disinfectant / Disinfection Byproduct Rule, the impact of brominated species of THMs and HAAs are being scrutinized. In the presence of chlorine, bromide is oxidized to hypobromous acid, which is a stronger halogen substitution agent than hypochlorous acid. When bromide is present in the raw water at levels as low as 100 ppb, it has been found to impact DBP formation in several ways, including acceleration of DBP kinetics, and through direct incorporation if bromide into DBPs. The latter is of particular importance, because the bromine atom is significantly heavier than the chlorine atom and DBPs are measure on a mass basis. As an example, a molecule of bromoform (CHBr3) weighs 2.1 times as much as a mole of chloroform (CHCl3). This discrepancy can significantly increase the risk of a Stage 2 DBPR violation. Other properties of the molecules are affected by bromine incorporation as well, including Henry’s Law Constants which governing removal of THMs through air-stripping, a post-treatment technique which has recently gained favor in many parts of the country.

Several utilities have observed elevated levels of bromine in their source waters for a myriad of reasons, including industrial discharges, natural sources, and other unknown inputs, and have observed significant related impacts on the DBP concentrations and speciation. One utility evaluated recently came across an anomalous, brief, one week period of high bromide levels and correspondingly exceedingly high levels of TTHMs in their distribution system. Follow-up sampling designed to confirm the elevated DBPs found bromide was no longer in the source water, and DBPs had reduced back to normal levels. As these and other utilities prepare for Stage 2 DBPR compliance, the impact of bromine species has been exacerbated in certain situations.

This presentation will provide background information regarding formation of brominated DBPs and the problems associated with them, along with a series of case studies outlining the experiences of several utilities with brominated DBPs and solutions provided for understanding and reducing associated impacts.

For more information, please contact the author at dbriley@hazenandsawyer.com.

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