Ozone Treatment of Secondary Effluent at U.S. Municipal Wastewater Treatment Plants

Ozone is a strong oxidant used to treat a variety of constituents in potable water, wastewater, water reuse, and industrial water treatment applications. Ozone is effective at oxidizing a wide range of organic and inorganic compounds and disinfection. Well-known in potable water treatment, with about 400 US installations and 3,000 world-wide, ozone has limited application at wastewater treatments, with less than 10 operating facilities in the US. The ability of ozone to significantly reduce low level concentrations of trace organic compounds, including endocrine disrupting chemicals (EDCs), pharmaceuticals and personal care products (PPCPs), and other emerging contaminants have increased interest in applying ozone in potable water and wastewater treatment. Treating at the point source discharge rather than the water supply intake may be more effective. A recent American Water Works Research Foundation (AwwaRF) report indicated high removals of many EDCs and PPCPs at typical disinfection doses. Several wastewater utilities have installed or are in the process of installing ozone to treat secondary effluent. These utilities are using ozone in a variety of ways: as a primary disinfectant, for treatment of microconstituents, and in combination with other processes (e.g. membranes and UV) to produce high-quality water for indirect potable reuse (IPR). The different applications, treatment goals and basis of process selection are compared and contrasted. Secondary benefits of ozone treatment of secondary effluent, including the use of off-gas in biological treatment is also discussed.