Key Laboratory of Urban Environment and Health, Ningbo Observation and Research Station, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, PR China; Department of Geosciences, Environmental Mineralogy and Chemistry, Eberhard Karls University Tübingen, 72074 Tübingen, Germany.
Key Laboratory of Urban Environment and Health, Ningbo Observation and Research Station, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, PR China.
J Hazard Mater. 2023 Jun 15;452:131266. doi: 10.1016/j.jhazmat.2023.131266. Epub 2023 Mar 24.
Produced water (PW) is the largest waste stream generated by hydraulic fracturing in an unconventional shale gas reservoir. Oxidation processes (OPs) are frequently used as advanced treatment method in highly complicated water matrix treatments. However, the degradation efficiency is the main focus of research, organic compounds and their toxicity have not been properly explored. Here, we obtained the characterization and transformation of dissolved organic matters of PW samples from the first shale gas field of China by two selected OPs using FT-ICR MS. CHO, CHON, CHOS, and CHONS heterocyclic compounds associated with lignins/CRAM-like, aliphatic/proteins, and carbohydrates compounds were the major organic compounds identified. Electrochemical Fe/HClO oxidation preferentially removed aromatic structures, unsaturated hydrocarbons, and tannin compounds with a double-bond equivalence (DBE) value below 7 to more saturated compounds. Nevertheless, Fe (VI) degradation manifested in CHOS compounds with low DBE values, especially single bond compounds. Oxygen- and Sulfur-containing substances, primarily O, SO-SO, NSO, and NSO classes, were the main recalcitrant components in OPs. The toxicity assessment showed that the free-radical-formed Fe/HClO oxidation could cause significant DNA damage. Therefore, the toxicity response byproducts need spcial attention when conducting OPs. Our results led to discussions on designing appropriate treatment strategies and the development of PW discharge or reuse standards.
产出水（PW）是非常规页岩气藏水力压裂过程中产生的最大废水。氧化工艺（OPs）常被用作高度复杂水基质处理的高级处理方法。然而，降解效率是研究的主要关注点，有机化合物及其毒性尚未得到充分探讨。在这里，我们通过两种选定的 OPs 从中国第一个页岩气田获得 PW 样品中溶解有机物的特性和转化，使用 FT-ICR MS。与木质素/CRAM 样、脂肪族/蛋白质和碳水化合物化合物相关的 CHO、CHON、CHOS 和 CHONS 杂环化合物是鉴定出的主要有机化合物。电化学 Fe/HClO 氧化优先去除芳香结构、不饱和烃和单宁化合物，这些化合物的双键等价物（DBE）值低于 7，转化为更饱和的化合物。然而，Fe（VI）降解表现在 DBE 值较低的 CHOS 化合物中，特别是单键化合物。含氧和含硫物质，主要是 O、SO-SO、NSO 和 NSO 类，是 OPs 中的主要难处理成分。毒性评估表明，自由基形成的 Fe/HClO 氧化会导致明显的 DNA 损伤。因此，在进行 OPs 时，需要特别注意毒性副产物。我们的结果引发了关于设计适当处理策略和制定 PW 排放或再利用标准的讨论。
