Reactions and interactions of drinking water treatment by-products: Characterization of the electrochemical formation of inorganic by-products of the electrolysis of salt brine.

摘要

Chlorine is the most widely used oxidant for water disinfection in the United States. However, recent concern over the carcinogenicity of inorganic by-products has prompted the USEPA to set maximum contamination limits for chlorite ion and bromate ion. To comply with USEPA regulations, research has focused on alternative water disinfection techniques.; Chlorine dioxide has been considered as an alternative oxidant for water disinfection, however generation is costly and inorganic by-products (chlorite ion and chlorate ion) are still formed. Ozone is another alternative oxidant for water disinfection. Unfortunately, bromate ion is formed by the reaction of bromide ion and ozone, but more importantly ozone does not remain as a residual in the distribution system and microbial regrowth can occur.; The electrolysis of salt brine is a well known technology dating back to the early 1800's. In recent years, manufacturers have claimed that the electrolysis of salt brine can be used as a water disinfection technique by generating a mixture of chlorine, chlorine dioxide, ozone and hydrogen peroxide. Reports also indicate an increase in microbial kill along with reduced disinfection by-product formation. However, the electrolyzed brine solutions have never been fully chemically characterized.; This research is conducted to develop methods to characterize the electrolyzed brine solutions for oxidants and inorganic by-products. The difficulty in method development is to analyze for low levels of analyte in the presence of high concentrations of chlorine typically present in electrolyzed brine solutions.; Two electrolysis units are evaluated: a bench top laboratory unit (BPS) and a full-scale unit (SAL-20). Experimental results show that the electrolyzed brine solutions contain between 200 to 400 mg/L of free available chlorine (FAC: Cl₂, HOCl, OCl−). Neither ozone nor chlorine dioxide are detected. The inorganic by-products are measured for each unit. The BPS electrolyzed brine contains 4–5 mg/L chlorate ion, 0.05 mg/L chlorite ion and 0.05 mg/L bromate ion. The full-scale electrolyzed brine contains 1–2 mg/L chlorate ion, 0.05 mg/L chlorite ion and 1–2 mg/L bromate ion. The inorganic by-products measured will be correlated to the possible oxidants produced during the electrolysis of salt brine in order to formulate a chemical model.