PDF] Kinetics of tap water dechlorination and aquatic health impacts of selected dechlorination chemicals

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The kinetics of seven dechlorination agents (DA) was studied to identify the efficacy of dechlorination under variable dosage, mixing (periodic/continuous), and pH conditions (6.5 8.6 and/or >9). Dechlorination reactions at lx stoichiometric dosage (mg DA/ mg CI2) of the DAs are rapid in most cases, but not instantaneous and in some cases needed more than stoichiometric dosage to ensure a near zero residual level (0.02 mg/L total residual chlorine, as required by CEPA (1999)). Dechlorination kinetic analysis revealed reactions were either pseudo-first or zero order with respect to total chlorine concentration in solution at the lOx stoichiometric dosage and second order overall at 2 4x stoichiometric dosages. 48-hour aquatic toxicity tests were conducted using Daphnia magna to identify the acute (short-term) toxicity affects of the dechlorination chemicals over a range of concentrations (0 200 mg/L). Sodium sulfite and thiosulfate were found to have the least aquatic mortality effects while hydrogen peroxide and calcium thiosulfate had the most deleterious effects.