von Gunten Urs
Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600 Duebendorf, Switzerland; ENAC, School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale, CH-1000, Lausanne, Switzerland.
Water Res. 2024 Apr 1;253:121148. doi: 10.1016/j.watres.2024.121148. Epub 2024 Jan 16.
This publication summarizes my journey in the field of chemical oxidation processes for water treatment over the last 30+ years. Initially, the efficiency of the application of chemical oxidants for micropollutant abatement was assessed by the abatement of the target compounds only. This is controlled by reaction kinetics and therefore, second-order rate constant for these reactions are the pre-requisite to assess the efficiency and feasibility of such processes. Due to the tremendous efforts in this area, we currently have a good experimental data base for second-order rate constants for many chemical oxidants, including radicals. Based on this, predictions can be made for compounds without experimental data with Quantitative Structure Activity Relationships with Hammet/Taft constants or energies of highest occupied molecular orbitals from quantum chemical computations. Chemical oxidation in water treatment has to be economically feasible and therefore, the extent of transformation of micropollutants is often limited and mineralization of target compounds cannot be achieved under realistic conditions. The formation of transformation products from the reactions of the target compounds with chemical oxidants is inherent to oxidation processes and the following questions have evolved over the years: Are the formed transformation products biologically less active than the target compounds? Is there a new toxicity associated with transformation products? Are transformation products more biodegradable than the corresponding target compounds? In addition to the positive effects on water quality related to abatement of micropollutants, chemical oxidants react mainly with water matrix components such as the dissolved organic matter (DOM), bromide and iodide. As a matter of fact, the fraction of oxidants consumed by the DOM is typically > 99%, which makes such processes inherently inefficient. The consequences are loss of oxidation capacity and the formation of organic and inorganic disinfection byproducts also involving bromide and iodide, which can be oxidized to reactive bromine and iodine with their ensuing reactions with DOM. Overall, it has turned out in the last three decades, that chemical oxidation processes are complex to understand and to manage. However, the tremendous research efforts have led to a good understanding of the underlying processes and allow a widespread and optimized application of such processes in water treatment practice such as drinking water, municipal and industrial wastewater and water reuse systems.
本出版物总结了我在过去30多年里在水处理化学氧化工艺领域的历程。最初，化学氧化剂用于微污染物去除的应用效率仅通过目标化合物的去除来评估。这由反应动力学控制，因此，这些反应的二级速率常数是评估此类工艺效率和可行性的先决条件。由于该领域的巨大努力，我们目前拥有许多化学氧化剂（包括自由基）二级速率常数的良好实验数据库。基于此，可以利用哈米特/塔夫脱常数或量子化学计算得出的最高占据分子轨道能量，通过定量结构活性关系对没有实验数据的化合物进行预测。水处理中的化学氧化必须在经济上可行，因此，微污染物的转化程度往往有限，在实际条件下无法实现目标化合物的矿化。目标化合物与化学氧化剂反应形成转化产物是氧化过程固有的，多年来出现了以下问题：形成的转化产物在生物学上比目标化合物活性更低吗？转化产物是否有新的毒性？转化产物比相应的目标化合物更易生物降解吗？除了对与微污染物去除相关的水质有积极影响外，化学氧化剂主要与水基质成分反应，如溶解有机物（DOM）、溴化物和碘化物。事实上，DOM消耗的氧化剂比例通常>99%，这使得此类工艺本质上效率低下。其后果是氧化能力丧失以及形成有机和无机消毒副产物，其中也涉及溴化物和碘化物，它们可被氧化为活性溴和碘，随后与DOM发生反应。总体而言，在过去三十年中发现，化学氧化过程难以理解和管理。然而，巨大的研究努力使人们对其基本过程有了很好的理解，并允许此类工艺在饮用水、市政和工业废水以及水回用系统等水处理实践中得到广泛和优化的应用。
