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A Drinking Water Relevant Water Chemistry Model for the Free Chlorine and Cyanuric Acid System from 5°C to 35°C
Citation:
Wahman, D. AND M. Alexander. A Drinking Water Relevant Water Chemistry Model for the Free Chlorine and Cyanuric Acid System from 5°C to 35°C. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 36(3):283-294, (2019). https://doi.org/10.1089/ees.2018.0387
Impact/Purpose:
Determine temperature dependence on equilibrium expressions. In July 2001, dichlor (anhydrous sodium dichloroisocyanurate or sodium dichloroisocyanurate dihydrate) and trichlor (trichloroisocyanuric acid) use for the routine treatment of drinking water in the United States (US) was first approved. Their use is equivalent to adding free chlorine (hypochlorous acid plus hypochlorite ion) and cyanuric acid in a fixed proportion. In the US, currently approved methods to measure the free chlorine concentration in systems adding dichlor or trichlor exhibit measurement bias from chlorinated cyanurate presence; therefore, accurate free chlorine concentration determination is practically impossible and overestimated for regulatory compliance. One possible option to overcome this limitation is to estimate free chlorine concentrations using the established water chemistry of the free chlorine and cyanuric acid system (full model), but the water chemistry has only been determined for 25 °C. The current research used a simplified version of the full model (simple model) and estimated the unknown temperature dependence (5 to 35 °C) of the two remaining equilibrium constants (K7a and K9a) required for the simple model.
Description:
In July 2001, dichlor (anhydrous sodium dichloroisocyanurate or sodium dichloroisocyanurate dihydrate) and trichlor (trichloroisocyanuric acid) use for the routine treatment of drinking water in the United States (US) was first approved. Their use is equivalent to adding free chlorine (hypochlorous acid plus hypochlorite ion) and cyanuric acid in a fixed proportion. In the US, currently approved methods to measure the free chlorine concentration in systems adding dichlor or trichlor exhibit measurement bias from chlorinated cyanurate presence; therefore, accurate free chlorine concentration determination is practically impossible and overestimated for regulatory compliance. One possible option to overcome this limitation is to estimate free chlorine concentrations using the established water chemistry of the free chlorine and cyanuric acid system (full model), but the water chemistry has only been determined for 25 °C. The current research used a simplified version of the full model (simple model) and estimated the unknown temperature dependence (5 to 35 °C) of the two remaining equilibrium constants (K7a and K9a) required for the simple model.
URLs/Downloads:
DOI: A Drinking Water Relevant Water Chemistry Model for the Free Chlorine and Cyanuric Acid System from 5°C to 35°C
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