Disinfection byproducts (DBPs) are formed when an oxidizing agent like chlorine is added to water to eliminate pathogens. Some DBPs cause health problems; therefore, it is important to understand their formation during disinfection. One way to examine the potential for DBPs to form in water is through a formation potential (FP) test where chlorine is added to water under controlled conditions (e.g., pH, temperature, and contact time with chlorine). To stop the reaction at a particular time point and measure the DBP FP, the residual free chlorine has to be destroyed using a quenching agent (QA) like ascorbic acid, sodium bisulfite, sodium thiosulphate, sodium arsenite, 1,3,5-trimethoxy benzene, or ammonium chloride. However, the reaction rate (kinetics) of each quenching agent might be different with different dose ratios and might affect the DBP FP during storage prior to analysis. Ineffective quenching may produce inconsistent test results. Therefore, in this study, DBP FP with several QAs at different chlorine concentrations (3, 5, and 9 mg/L) and dose ratios (1:1, 1.3:1, 1.5:1, and 1.7:1; QA/chlorine molar ratio) were studied to understand the chlorine quenching effectiveness and its kinetics. The residual free chlorine was measured using the DPD standard method. Ascorbic acid and sodium bisulfite worked well for quenching residual free chlorine within 5 seconds starting from 1.3:1 QA/chlorine molar ratio. Future experiments will focus on the best performing QAs that have minimal effect on the stability of DBPs during sample storage, as well as minimal effect on excitation-emission fluorescence spectra.

Comparison of kinetics and dose ratios of different agents for quenching chlorine residual

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