DISINFECTION OPTIMIZATION OF THE CITY OF ATLANTA'S WEST SIDE CSO FACILITIES

The City of Atlanta's four west-side combined sewer overflow (CSO) facilities are highrate treatment facilities that utilize coarse and fine screening followed by sodium hypochlorite disinfection. This report describes the disinfection performance and optimization studies that were undertaken at these facilities to improve disinfection performance. The objectives of this work were:to satisfy the requirements set forth in the CSO Consent Decree negotiated between the City, Environmental Protection Agency, Georgia Environmental Division and citizen plaintiffs,determine the optimum chlorine dose while minimizing the total residual chlorine concentration in the effluent, anddetermine remedial measures necessary to meet fecal coliform requirements.The evaluation found that The City of Atlanta's CSOs exhibit a first flush, water quality varies throughout an event and between events, and the CSOs are currently contact time limited during the first flush in regards to the disinfection process. As a result, conctact times must be increased and variable chlorine doses are required to optimize dose and total residual chlorine concentrations. Methods found to be feasible in the control of the variable dose included conductivity, ammonium and flow measurements.