scope:

Overview

Various forms of chlorine are commonly used in drinking water and reuse applications for their ability to disinfect and maintain a residual level of disinfectant throughout the distribution system. The majority of utilities in the United States use chlorine gas during treatment, although aproximately one-third of all drinking water treatment plants (DWTPs) in the United States use bulk hypochlorite for disinfection and around 8% of United States DWTPs use on-site hypochlorite generators or on-site generation (OSG) systems (AWWA 2008a, AWWA 2008b).

On-site generated hypochlorite, a water treatment disinfectant since the 1970s, initially was not widely embraced by the water industry because of intensive maintenance requirements and higher operating costs when compared with chlorine gas. Recent advances in OSG technology and increased concerns regarding the security and safety risks associated with chlorine gas have resulted in on-site generation of sodium hypochlorite becoming a more attractive and cost-effective option. Advantages of on-site generation over chlorine gas and bulk hypochlorite can include:

• Reduced volume of hazardous material that must be stored on-site
• Improved safety for the public and plant personnel
• Elimination of liabilities associated with transportation of hazardous materials
• Occupational Safety and Health Administration (OSHA) and US Environmental Protection Agency (USEPA) exemption from preparing emergency response plans