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Evaluation of Monochloramine and Free Chlorine Penetration in a Drinking Water Storage Tank Sediment Using Microelectrodes
Citation:
Liu, H., D. Wahman, AND J. Pressman. Evaluation of Monochloramine and Free Chlorine Penetration in a Drinking Water Storage Tank Sediment Using Microelectrodes. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 53(16):9352-9360, (2019). https://doi.org/10.1021/acs.est.9b01189
Impact/Purpose:
This study evaluated the penetration of drinking water disinfectants into storage tank sediments that accumulate over time in drinking water distribution systems. Using microelectrodes capable of measuring micron scale water quality parameters, free chlorine, monochloramine, pH, dissolved oxygen, and several additional parameters were measured within storage tank sediments. The results demonstrated extremely limited penetration of disinfectants. This has important implications on the protection of pathogenic microorganisms that may occur in these sediments and the operational changes that water utilities might want to consider to improve disinfection in drinking water distribution systems. This research will be of high interest to water utilities and practitioners in the field of drinking water.
Description:
Sediment accumulation in water storage tanks may protect microorganisms from disinfectant exposure, causing water quality degradation. However, microbial activity and disinfectant penetration within water storage sediment remains largely uncharacterized. This study evaluated monochloramine and free chlorine penetration into a 2-cm (20,000 µm) deep drinking water storage tank sediment using microelectrodes. The sediment was successively exposed to 4-months monochloramine, 2-months free chlorine, and 2-months monochloramine. Temporal monochloramine, free chlorine, dissolved oxygen (DO), pH, ammonium, nitrite, and nitrate profiles were acquired using microelectrodes. Results showed that complete monochloramine or free chlorine penetration was not observed. Likewise, DO never fully penetrated the sediment, progressing inward with time to a maximum depth of 10,000 µm and indicating microbial activity remained during the entire 8 months. Decreasing ammonium and increasing nitrate concentrations, with minimal nitrite accumulation, further demonstrated microbial activity and indicated complete sediment nitrification. There was measurable ammonium, nitrite, and nitrate during free chlorine application and nitrification activity gradually resumed upon a switch back to monochloramine. These findings suggest that periodic sediment removal from drinking water storage facilities is desirable to remove potentially protected environments for microorganisms.
URLs/Downloads:
DOI: Evaluation of Monochloramine and Free Chlorine Penetration in a Drinking Water Storage Tank Sediment Using Microelectrodes
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