Comparison of Reaction Rates and Relative Efficiencies for Various Dechlorination Chemicals

Abstract

Dechlorination of chlorinated water and wastewater is most often achieved by chemical reduction through the addition of sulfur-IV compounds before discharge into the aquatic receiving environment or upon entry in the distribution system. However, reasonable doubts subsist about the efficiency of sulfur-IV compounds as dechlorination mediators for the reduction of chlorine and organic chloramines. As a consequence, alternative treatments have been investigated over the past few years but little information remains available on the kinetics of dechlorination at different dosages. In this study, the kinetics of dechlorination promoted by five selected dechlorination agents were observed at different stoichiometric ratios (1x, 3x, and 10x), and ANOVA was applied to the results in order to assess their statistical significance. Hydrogen peroxide (HP) was shown to promote faster than expected dechlorination; ascorbic acid and calcium thiosulfate also presented viable alternatives to treatment by sulfur-IV compounds represented by sodium sulfite and bisulfite in this study. This study challenges the common perception that HP dechlorination is slow and provides a comparative analysis for dechlorination kinetics using regression analysis, half-life values, and rate constants.