Evaluation of Distribution System Water Quality During a Free Chlorine Conversion
Citation:
Alexander, M., P. Woodruff, J. Mistry, H. Buse, C. Muhlen, D. Lytle, J. Pressman, AND D. Wahman. Evaluation of Distribution System Water Quality During a Free Chlorine Conversion. AWWA Water Science. John Wiley & Sons, Inc., Hoboken, NJ, 6(3):e1377, (2024). https://doi.org/10.1002/aws2.1377
Impact/Purpose:
The environmental or health problem addressed by the study: Water quality and regulated disinfection byproducts before, during, and after a free chlorine conversion in a chloraminated system. A general description of the work and results: Water quality and regulated disinfection byproduct monitoring of a chloraminated drinking water distribution system before, during, and after a free chlorine conversion. The long-term importance or significance of the findings: Provides information on the changes in water quality and disinfection byproducts from a free chlorine conversion. Who would be interested in or could apply the results (e.g. program or regional partners, general public, local communities): Researchers, engineers, regulators, and drinking water utilities trying to understand water quality and disinfection byproduct impacts from a free chlorine conversion.
Description:
Chloraminated drinking water systems commonly implement a temporary free chlorine conversion (FCC) to control or minimize nitrification in the distribution system (DS), but unintended water quality changes may occur during the FCC, including increased disinfection byproducts (DBP) and metals concentrations. This study evaluated temporal water quality changes at multiple DS and residential sample locations in a United States (US) chloraminated drinking water DS before, during, and after an FCC. Water quality through the DS alternated between relatively consistent (steady state) and variable (non-steady state) periods when converting from chloramines to free chlorine and subsequently converting back to chloramines. At the DS maximum residence time sample location, approximately four days were required to stabilize disinfectant concentrations after switching disinfectants, but less time was required for sample locations closer to the DS entry point. Conversion to free chlorine increased the regulated four trihalomethane (THM4) and five haloacetic acid (HAA5) concentrations by four and seven times, respectively, compared to chloramines and exceeded THM4 and HAA5 maximum contaminant levels (MCLs) during the FCC. Furthermore, implications of requiring DBP regulatory compliance sampling during an FCC was quantified, resulting in a modified locational running annual average (mLRAA) calculation that accounted for the duration of increased DBP concentrations from an FCC. Systems implementing a single annual FCC with LRAAs relatively close to either the THM4 or HAA5 MCL, may exceed MCLs using an mLRAA calculation. For metals, the FCC had minor impacts to DS concentrations and did not appear to impact residential concentrations. Overall, variable water quality observed in this study appeared primarily associated with changing disinfectants where the duration depended on DS hydraulics to move water through the system.
URLs/Downloads:
DOI: Evaluation of Distribution System Water Quality During a Free Chlorine Conversion