The Effect of On-Site Generated Ultra Pure Hypochlorite~TM on Water and Wastewater Disinfection

摘要

Chlorine is the most common disinfectant used in water and wastewater treatment systems in the United States, although the use of ultraviolet light and ozone are becoming more common. Historically, gaseous chlorine was the most prevalent form of chlorination in the United States; however, the use of an aqueous solution of sodium hypochlorite is increasing in water and wastewater treatment applications due to safety concerns associated with the use, storage and transportation of chlorine gas. The implementation of the Risk Management Plan (RMP) by the USEPA for the storage of hazardous chemicals (June 1999) and the re-registration of chlorine gas by the USEPA Office of Pesticide Programs as a pesticide (Fall 2001) also has accelerated the use of sodium hypochlorite in the water and wastewater treatment industry. It should be noted that while the disinfection of drinking water using either ultraviolet light or ozone can be viable alternatives to gaseous chlorine, additional disinfection will be required to provide the USEPA mandated disinfectant residual in drinking water distribution systems. Sodium hypochlorite solution is typically applied at concentrations up to 15% by weight chlorine. Problems associated with the use of sodium hypochlorite may include availability of sodium hypochlorite in some areas, high transportation costs, increasing production costs, a lack of long-term stability and the final pH of the chlorinated water. The rate at which sodium hypochlorite concentration decays during storage is a function of both the sodium hypochlorite concentration and storage temperature. On-site electrochemical generation of low strength sodium hypochlorite (0.8% chlorine concentration) may mitigate sodium hypochlorite degradation problems. However, storing large volumes of low-concentration sodium hypochlorite and adding these low-concentrations of sodium hypochlorite has many disadvantages that may include high salt usage, large storage requirements and increased salt concentrations in the finished water. On-site electrochemical generation of atmospheric pressure chlorine gas and sodium hydroxide and /or high strength sodium hypochlorite (12 % chlorine) is a viable solution to the problems discussed above.