Chlorine Gas vs. Sodium Hypochlorite: What's the Best Option?

This article discusses a study by the city of Lakeville, Minnesota, to evaluate alternative disinfection technologies that was driven by U.S. Department of Homeland Security concerns about risks associated with handling, storing, and using toxic chlorine gas. The study evaluated alternative disinfection systems for the city's water treatment plant, considering the plant's existing system, safety, security, cost‐efficiency, and finished water quality. The Lakeville study did not evaluate ultraviolet, ozone, chloramine, or chlorine dioxide systems because of site and cost constraints. The study focused on sodium hypochlorite (NaOCl), that provides residual protection but is safer than chlorine gas and less expensive than other alternative disinfection systems. Installing a NaOCl system would require the city of Lakeville to make few modifications to its existing system, and finished water quality would be similar to what is presently produced. The article discusses the advantages and limitations of using sodium hypochlorite, and provides comparisons of capital costs and annual O&M costs of chlorine gas, commercial sodium hypochlorite, and on‐site sodium hypochlorite generation. The article includes a total present worth analysis for a 20‐mgd sodium hypochlorite disinfection system.