PERFORMANCE TESTING OF COMBINED SEWER OVERFLOW CONTROL TECHNOLOGIES DEMONSTRATES CHEMICAL AND NONCHEMICAL DISINFECTION ALTERNATIVES AND SATISFIES EPA CSO POLICY

Columbus, Georgia, through the Columbus Water Works implemented a 95 million combined sewer overflow (CSO) control program including full-scale alternative technology testing, watershed monitoring and compliance demonstration with the US EPA CSO Policy to satisfy site-specific water quality standards. The Uptown Park CSO facility in Columbus, one of two CSO treatment systems, is the home of a national demonstration program sponsored through a Congressional appropriation and EPA grant for technology testing with peer review by a team of experts coordinated by the Water Environment Research Foundation (WERF). This facility also known as the CSO Advanced Demonstration Facility (ADF) was constructed to examine the performance of various wet weather treatment technologies for solids removal and alternative methods of disinfection.Four disinfection technologies have been examined in full-scale side-by-side comparisons to evaluate performance and operation criteria under similar CSO quality conditions. Vortex separators were used as contact chambers for three types of chemical disinfection including sodium hypochlorite (with and without sodium bisulfite dechlorination), chlorine dioxide and peracetic acid. A compressed media filter followed by UV disinfection was also evaluated at various vortex pre-treatment levels to provide high quality control for the more frequent, more concentrated events.Disinfection performance relationships were developed between effluent bacteria, chemical or UV dose and the quality conditions to the process influent. These relationships also provided algorithms that were used to automatically control the chemical disinfection process for the enormously varying conditions during an event and for differing antecedent periods. Methods are described for quantifying the statistical distribution loading on the receiving waters for a given solids removal and disinfection control scheme. Methods are also described for operation of disinfection process control.Study applications show how the loading and technology performance relationships can be used to formulate a waste load allocation (WLA) for the CSO in comparison with other WLA's and non-point load allocations (LA's) for compliance with a total maximum daily load (TMDL). Formulation strategies are demonstrated using the Columbus area example involving interstate sources of point and nonpoint contributions to wet weather bacteria impairment.