DEMONSTRATION TESTING OF ON-SITE ELECTROLYTIC GENERATION OF DISINFECTANTS

In recent years, water and wastewater utilities that use chlorine gas, particularly treatment plants located in populated areas, have conducted alternative disinfectant evaluations out of concern to public health, damage to the environment and safety of their workers from an accidental release of chlorine. On-site disinfectant generation technologies including electrolytic have been commercially available for several years. However, there has been little research regarding disinfection effectiveness, production of by-products and cost comparisons for application in mid to large water treatment plants.A ten week pilot plant study of two electrolytic disinfectant technologies was conducted at an 18 MGD water treatment plant in St. Louis County in Missouri and compared to the simultaneous disinfection using chlorine gas and ammonia.The study was also conducted to determine preliminary dosage and effectiveness of the electrolytic generated disinfectants on combined sanitary and storm sewer overflow. This was done because the potential exists for future disinfection of these waters prior to discharge and the on-site technologies provide a safer alternative to the use of chlorine gas at multiple locations in the collection system.The Electric Power Research Institute (EPRI) provided guidance and funding assistance for the project. Missouri-American Water Company provided water treatment facilities. The Metropolitan St. Louis Sewer District provided laboratory testing of disinfected combined sewer overflows. The St. Louis City – Water Division provided the laboratory analysis for the water samples collected at the water treatment and pilot plants.The results demonstrated that on-site generation of sodium hypochlorite and mixed oxidants provide effective disinfectants that produce less by-products than chlorine with ammonia. However, the increase observed in chlorate is a potential concern. The on-site generation technologies operating costs were significantly greater than chlorine at this site. Also, the addition of a chlorine gas scrubber was more economical than switching over to the new technologies. However, on-site generation may be cost effective for smaller new facilities or those existing that are facing extensive modification to meet safety concerns or regulatory requirements.