Challenges associated with intermediate ozonation in drinking water treatment during cold weather: A case study
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2021-05
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Booth, Robert D. Masters Environmental Assessment. Challenges Associated with Intermediate Ozonation in Drinking Water Treatment during Cold Weather: A Case Study
The Charles Horne Water Treatment Plant in Greenville, North Carolina is the only water plant in the state that uses intermediate ozonation as the primary disinfection process for the inactivation of dangerous pathogens. Recently the plant experienced erratic filter turbidity readings during cold weather. The water plant is served by seven dual media filters consisting of anthracite or granulated activated carbon and sand. High turbidity readings reduce the production
capacity of the plant and can ultimately result in a violation of the Surface Water Treatment Rule prompting a boil water notice for the service population. Further investigation suggests that microbubble formation due to gas supersaturation in the filter media is likely causing the erratic turbidity readings. This issue has been observed twice over the past three years during the winter months. Each event has strained the operational capacity of the plant by not only reducing the
capacity to treat water and remain in compliance, but also depleting the storage of already treated water due to increasing the frequency of cleaning filters with already treated drinking water.
These events have threatened the ability of the water plant’s ability to maintain system pressure and provide a safe and adequate supply of drinking water for its customer base. Greenville Utilities received approval from the North Carolina Division of Environmental Quality (NCDEQ) to use ozonation as a primary disinfectant in 2007. Ozonation is a much more powerful oxidizing agent than chlorine. Ozone is used for its ability to deactivate a variety of microorganisms such as cryptosporidium and giardia without reacting with organics and forming
disinfection byproducts like trihalomethanes (THMs) and halo acetic acids (HAAs). Ozonation is not without its problems, however. The equipment used to generate ozone is very expensive, ozone does not persist in water, therefore a secondary disinfectant is required in the distribution system, and ozone has been shown to cause problems with supersaturation of dissolved oxygen
under certain conditions. Intermediate ozonation refers to the application of ozone prior to filtration. This review focuses on intermediate ozonation systems, filter turbidity issues, and how facilities can manage microbubble formation in filtrations to maintain treatment efficacy.
Specifically reducing flow velocities through filtration and reducing the amount of ozone used during disinfection. Water treatment facilities looking to add intermediate ozonation in the future should consider their source water, their system water production demands, and the loading rates of their filters.
