Evaluation of Ozone for Cryptosporidium Inactivation and Atrazine Oxidation in a Lime Softening Plant

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Abstract
This case study evaluates the integration of ozone in a softening plant with emphasis on the feasibility of high pH ozonation. The softening plant in Jefferson City, Missouri, treats Missouri River water characterized by high hardness, TOC of up to 8.0 mg/L, and occurrences of atrazine at concentrations up to 20 μg/L. As part of the predesign effort for rehabilitation of the existing WTP, ozone was evaluated to achieve current and anticipated future disinfection requirements, as well as atrazine removal. Testing using a continuous flow bench scale unit was conducted to evaluate ozone for 2-log Cryptosporidium inactivation and to oxidize 10 to 14 μ/L of atrazine. Because of the high CT required for 2-log Cryptosporidium inactivation, it was found that practicing an AOP was not necessary to reduce the atrazine level to below the current maximum contaminant level (MCL) of 3 μg/L. In this case, the long term disinfection requirements for Cryptosporidium likely will drive the ozone system design criteria despite the high levels of atrazine occurring in the raw water supply.