In the United States, approved methods to measure free chlorine concentrations in drinking water systems adding sodium dichloroisocyanurate (dichlor) or trichloroisocyanuric acid (trichlor) as chlorine sources exhibit measurement bias from chlorinated cyanurate presence, leading to overestimated free chlorine concentrations for regulatory compliance. One option to overcome this limitation is to estimate free chlorine concentrations using an established water chemistry model (full model), but the full model 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. At 0 M ionic strength (μ), ln K 7a = - 4 , 671 T K + 4.95 or pK 7a = 2 , 028 T K - 2.15 , Δ H 7a 0 = 38.8 ± 6.0 kJ mol-1 (95% confidence interval, CI), ln K 9a = - 5 , 133 T K + 3.79 or pK 9a = 2 , 229 T K - 1.65 , and Δ H 9a 0 = 42.7 ± 3.0 kJ mol-1 (95% CI). At 25 °C and μ of 0 M, the simple model estimated pK7a and pK9a are 4.65 ± 0.059 (95% CI) and 5.83 ± 0.020 (95% CI), respectively. As an example of temperature's impact, the free chlorine concentration for a 2 mg Cl2 L-1 dichlor addition (pH 7.0) decreases from 0.90 mg Cl2 L-1 free chlorine at 25 °C to 0.60 mg Cl2 L-1 free chlorine at 5 °C. If temperature was not considered, a system operating at 5 °C would overestimate their free chlorine concentration by 50%, which could have significant implications for understanding disinfection efficacy, illustrating the developed model's significance.

中文翻译：

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5°C 至 35°C 范围内游离氯和氰尿酸系统的饮用水相关水化学模型

在美国，添加二氯异氰尿酸钠 (dichlor) 或三氯异氰尿酸 (trichlor) 作为氯源的饮用水系统中游离氯浓度的测量方法已获批准，这会因氯化氰尿酸盐的存在而导致测量偏差，从而导致游离氯浓度被高估以符合法规要求。克服此限制的一种选择是使用已建立的水化学模型（完整模型）估算游离氯浓度，但完整模型仅针对 25 °C 确定。当前的研究使用了完整模型（简单模型）的简化版本，并估计了简单模型所需的两个剩余平衡常数（K7a 和 K9a）的未知温度依赖性（5 至 35 °C）。在 0 M 离子强度 (μ) 时，输入 钾 7a = —— 4 , 671 吨 钾 + 4.95 或者 PK 7a = 2 , 028 吨 钾 —— 2.15 , Δ H 7a 0 = 38.8 ± 6.0 kJ mol-1（95% 置信区间，CI）， 输入 钾 9a = —— 5 , 133 吨 钾 + 3.79 或者 PK 9a = 2 , 229 吨 钾 —— 1.65 ， 和 Δ H 9a 0 = 42.7 ± 3.0 kJ mol-1 (95% CI)。在 25 °C 和 μ 为 0 M 时，简单模型估计的 pK7a 和 pK9a 分别为 4.65 ± 0.059（95% CI）和 5.83 ± 0.020（95% CI）。作为温度影响的示例，添加 2 mg Cl2 L-1 二氯 (pH 7.0) 的游离氯浓度从 25 °C 时的 0.90 mg Cl2 L-1 游离氯降低到 5 °C 时的 0.60 mg Cl2 L-1 游离氯℃。如果不考虑温度，在 5 °C 下运行的系统会将其游离氯浓度高估 50%，这可能对理解消毒功效具有重要意义，说明开发模型的重要性。