An Evaluation of UV and NaOCl for Wastewater Disinfection at the Pelham WWTP

A relatively new ultraviolet (UV) disinfection technology has been selected for the Pelham wastewater treatment plant (WWTP) operated by the Western Carolina Regional Sewer Authority (WCRSA). When completed, the Pelham WWTP will be the largest UV installation in South Carolina and one of the largest low pressure, high intensity UV systems in the United States.Presently, chlorine gas is used for effluent disinfection, and sulfur dioxide gas is used for dechlorination. Chlorine gas, sodium hypochlorite, and UV disinfection were evaluated during the predesign process with UV appearing to be the best alternative. The Pelham plant will receive effluent from the Taylors WWTP, another WCRSA plant, after decommissioning in five years. Differences in the two plants' effluent quality, color, transmittance, and dissolved inorganics were concerns for selection of the UV system. Therefore, plant-specific testing was done to confirm the UV design criteria.After completion of the site specific study, UV and liquid sodium hypochlorite (NaOCl) disinfection with sodium bisulfite (NaHSO3) dechlorination were considered for implementation. The disinfection system will have a design capacity equal to the expanded plant capacity of 22.5 mgd. This paper highlights the decision matrix used to evaluate disinfection alternatives including evaluation of UV technologies, plant specific testing, costs analyses, and the establishment of design criteria.