Comparison of Commercial Dechlorination Chemicals used in Reverse Osmosis Processes

Objectives The objective of this study was to find a promising dechlorination chemical which can replace sodium bisulfite (SBS), which is mainly used as a dechlorination agent in reverse osmosis processes but can cause odor issues. Methods Candidate chemicals were selected in consideration of economic feasibility, ease of use, and toxicity. These included sodium metabisulfite (SM), sodium thiosulfate (ST), and sodium sulfite (SS). We investigated the effect of organic matters in water on residual chlorine decomposition and compared the appropriate injection amounts for each dechlorination chemicals. Also, the effect of the pH of treated water upon dechlorination was assessed. Results and Discussion Upon injection of dechlorination chemicals at the theoretical chlorine removal point, the chlorine was not completely removed but 10% to 40% remained. In ultrapure water, it was possible to completely dechlorinate by injecting 1.6 to 2.6 times more than the theoretical injection amount: 1.8, 2.2, and 3.1 times more for ST, SM, and SS, respectively. Considering only the injection amount, ST is an efficient dechlorination chemical for water with pH 9 or higher, and SM is for pH 9 or less Conclusion Considering the product price and user convenience, it is feasible to use ST, which can resolve the odor problem.