An efficiency analysis for the production of chlorine dioxide by the electrolysis of brine in seawater desalination plants

A previous study by the authors evaluated the efficiency of producing multi-oxidants using anodes coated in precious metal. This study showed that a titanium anode coated in ruthenium generates the largest amount of active chlorine (chlorine dioxide). The results from the efficiency evaluation also show that DuPont Nafion N-2030 ion film is the most efficient of the diaphragms that were tested. To increase the recovery rate for ClO2, this study optimizes the composition of the anode electrolyte. Sodium chlorite is added into the brine and an electrolysis reaction is performed at 40 °C and 12 V for batch operation. The principal product is ClO2 with a maximum concentration of 1,074 mg L−1. During continuous electrolysis, when the inflow rate for the anode electrolyte is increased to 120 mL min−1, ClO2 is produced at a constant concentration of 60 mg L−1 after 30 minutes. An analysis of the multi-oxidants generated from brine to detect disinfection byproducts shows very little trichloromethane is formed, much less than the standard for total trihalomethanes in drinking water in Taiwan (0.1 mg L−1). The disinfection efficiency of the multi-oxidant produced in this study is about three times greater than that of commercial hypochlorous acid. These results show that multi-oxidant products retrieved by recycling brine from desalination plants are commercially applicable and have economic value.