|Research Summary, CSO Disinfection Pilot Study: Spring Creek CSO Storage Facility Upgrade (EPA/600/R-02/077) November 2003
This research summary presents the results of a pilot-scale disinfection study performed for the New York City Department of Environmental Protection and EPA. The main objective of the pilot study was to demonstrate alternatives to hypochlorite disinfection for application to the Spring Creek facility and potentially to other combined sewer overflow (CSO) facilities.
The pilot testing was divided into two phases. Phase I was performed from December 1996 through March 1997; Phase II was performed from August through November 1999. EPA provided technical assistance for the entire study.
Phase I evaluated treatment performance of five technologies: ultraviolet (UV) irradiation; ozonation (O3); chlorine dioxide (ClO2) disinfection; chlorination/dechlorination (Cl2/deCl2); and electron beam irradiation (E-Beam). The fifth technology, E-Beam, was evaluated during supplemental Phase I pilot testing sponsored by the New York Power Authority and the Electric Power Research Institute.
Using the results from Phase I, Phase II provided additional evaluation of technologies that had shown potential for CSO applications. These were UV, ClO2, and Cl2/deCl2. This research summary concentrates on these three technologies, but the overall results of both phases for each technology along with the cost are also discussed.
Generally, all tested disinfection technologies, with the exception of E-beam, achieved targeted bacterial reductions of 3 to 4 logs. Cl2/deCl2, ClO2, and O3 at the doses tested provided these levels of disinfection over the full range of wastewater quality tested. To date, ozonation was not found to be cost effective for CSO applications. While ClO2 was superior in effectiveness and similar in cost to Cl2/deCl2, the generation technology for ClO2 negates the need for gaseous Cl2; however, further development is needed. Because an effective Cl2-gas-free process of ClO2 generation has not been proven to be reliable and, because Cl2 gas cannot be transported within New York City, disinfection with ClO2 cannot be recommended for use within New York City at this time.
The Spring Creek facility upgrade construction was scheduled for the fall of 2002. The upgraded Spring Creek facility will continue to use sodium hypochlorite for disinfection, with provisions to add dechlorination at a later date. Improvements will be made to increase disinfectant flash mixing and to automate hypochlorite feed and residual control. While the decision to continue the use of hypochlorination for the upgraded facility was based on the Phase I study, it is recognized that the overall pilot results (Phases I and II) will be used to guide decisions at other CSO facilities.
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