Ozone-Enhanced UV Disinfection at the Indianapolis Belmont Advanced Wastewater Treatment Plant

Considering the need for a doubling of its current disinfection capacity at the Belmont Advanced Wastewater Treatment Plant, the City of Indianapolis embarked on an extensive conceptual evaluation of disinfection alternatives including permutations between ozonation, UV irradiation and chlorination/dechlorination. The objectives were to maximize the use and benefits from the existing assets, while providing additional disinfection capacity that is both reliable and cost-effective. Key points of the conceptual evaluation, which includes both monetary and non-monetary considerations, are presented. The selected disinfection plan relies on an unusual hybrid of three methods of disinfection (UV irradiation preceded by low dose ozonation during dry weather, augmented with chlorination/dechlorination during wet weather) and presents multiple synergies (UV transmittance, double-barrier approach) and benefits (dissolved oxygen, utilization of existing ozone system). The case of the Indianapolis Belmont plant provides a large-scale illustration of the challenges associated with designing a pre-ozonated UV system within an existing plant, including the assessment of the benefits from pre-ozonation that are specific to this utility, the selection of appropriate design UV transmittance values, the retrofit design of a UV system into a restricted hydraulic profile, and the development of design documents to allow competitive bidding of multiple equipment suppliers.