Future climate variability and land use changes can significantly impact organic matter (OM) contents of drinking water sources, thus affecting both the efficacy of water treatment unit processes and the formation potential for disinfection byproducts such as trihalomethanes (THMs). Storm events and associated runoff in watersheds trigger these water quality changes, resulting in large temporal increases in turbidity and OM concentrations in surface drinking water sources. To investigate these impacts and examine treatment optimization, a field study was conducted through systematic sample collection and chemical analysis along the treatment train of a drinking water treatment plant in the Midwestern United States for 72 hours, spanning the time before and after a storm event. THM concentrations were measured in the final product water entering distribution and THM formation potential was determined at each of the treatment units through chlorine spiking experiments. Results show that the multibarrier treatments employed at this plant, particularly the granular activated carbon (GAC) reactors, are effective at removing OM and reducing the effects of perturbation in the source water on THM formation potential. However, significant quantities of brominated-THMs were still observed in treated water. Together with the process operational parameters (<i>e.g.</i>, retention time, hydraulic loading rate, etc.), these chemical analyses serve as a basis to develop new quantitative process models for THM formation. Such models aim to assist plant operators and regulators in analysis of DBP Stage-II rule compliance and in developing process optimization options for improved treatment efficacy, even under projected future source water qualities.

Source water quality impacts on drinking water treatment plant performance and disinfection byproduct formation during a storm event

255th National Meeting (2018)

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