Performance of ozone as a disinectant for combined sewer overflow

Disinfection of combined sewer overflow (CSO) minimizes the number of disease-causing microorganisms (pathogens) released into receiving waters. Currently, the primary disinfecting agent used in the United States for wastewater treatment is chlorine (Cl-2); however, Cl-2 produces problems in aquatic ecosystems. As a result, alternative disinfectants are being investigated. This article presents the results of a state-of-the-art review of the effectiveness of ozone (O-3) for CSO disinfection. Data on major studies investigating CSO ozonation as well as its advantages and disadvantages are presented. Ozone inactivates a wider range of microorganisms than Cl-2. In addition, O-3 has a relatively high disinfection kill power, releases limited byproducts, is nonreactive with ammonia, and has an excellent ability for removing undesirable odor and color. The effectiveness of ozonation was found to be strongly dependent upon the occluding effects of suspended solids and influent quality. The reaction of O-3 with water impurities is a major limitation. In general, ozonation can be an effective, but expensive, technology for CSO disinfection.