Dissolved oxygen (DO) is essential for the health of aquatic ecosystems, supporting biogeochemical cycles and the decomposition of organic matter. However, continuous untreated external inputs from illicit discharges or sewer overflows, coupled with inadequate ecological base flow, have led to widespread river deoxygenation and serious ecological crises. This study demonstrates that chlorinated wastewater treatment plant (WWTP) effluent can significantly enhance DO levels in downstream rivers, particularly in areas with high pollution loads or poor ecological base flow. Notably, DO increases in receiving waters were positively correlated with initial chorine doses. Residual chlorine in WWTP effluent reduced inorganic nitrogen and dissolved organic matter (DOM). Analysis of DOM and molecular properties showed that residual chlorine preferentially reacts with low-molecular-weight organics like amino acids, increasing their hydrophobicity and electrophilicity. These molecular changes inhibit enzyme interactions, reducing the bioavailability of these compounds for oxygen-consuming processes. Field studies demonstrated that through on-site optimization of the full-scale WWTP disinfection process, specifically by controlling residual chlorine levels in effluents, DO levels downstream increased by an average of 15%, with a maximum of 48% compared to upstream levels, while typical disinfection byproducts (i.e., trihalomethanes, haloacetic acids and haloacetonitriles) remained below regulatory thresholds. This work provides new insights into the positive effects of chlorinated WWTP effluent on DO levels in receiving waters.

中文翻译：

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污水处理厂排放的含氯污水增加了接收河流中的溶解氧：从实验室研究到实际应用


溶解氧 （DO） 对水生生态系统的健康至关重要，支持生物地球化学循环和有机物的分解。然而，非法排放或下水道溢流的持续未经处理的外部输入，加上生态基流不足，导致了广泛的河流脱氧和严重的生态危机。本研究表明，氯化污水处理厂 （WWTP） 出水可以显著提高下游河流的溶解氧水平，尤其是在污染负荷高或生态基流较差的地区。值得注意的是，接收水域的 DO 增加与初始绒毛蛋白剂量呈正相关。污水处理厂污水中的余氯减少了无机氮和溶解有机物 （DOM）。DOM 和分子性质分析表明，余氯优先与氨基酸等低分子量有机物反应，增加了它们的疏水性和亲电性。这些分子变化抑制了酶相互作用，降低了这些化合物在耗氧过程中的生物利用度。现场研究表明，通过现场优化全尺寸污水处理厂消毒过程，特别是通过控制污水中的余氯水平，下游的溶解氧水平平均增加了 15%，与上游水平相比最高增加了 48%，而典型的消毒副产物（即三卤甲烷、卤代乙酸和卤代乙腈）仍低于监管阈值。这项工作为氯化污水处理厂污水对受纳水溶氧水平的积极影响提供了新的见解。