Comparison of reaction kinetics under varying conditions for dechlorination chemicals

The rate of dechlorination using seven different chemicals was studied under a range of dosages, mixing intensities and pH conditions. This kinetic study demonstrates that sodium sulfite, sodium bisulfite, sodium metabisulfite, sodium thiosulfate, and ascorbic acid are needed in excess of the stoichiometric dosage (mg Dechlorination Agent/mg Cl2) to achieve complete dechlorination within less than 1 minute and that the dechlorination reactions were pseudo-first order in terms of the total chlorine concentration in solution. Calcium thiosulfate and hydrogen peroxide on the other hand displayed first order dechlorination kinetics with 1x and 0.1x stoichiometric dosage, respectively achieving complete dechlorination in ≤1 minute. Acute toxicity of the various dechlorination chemicals was completed to help determine which dechlorination agent is also safest for release into the aquatic environment. Hydrogen peroxide was found to have the highest dechlorination rate but was the most toxic compound with respect to Daphnia magna.