School of Environment, South China Normal University, Guangzhou, Guangdong 510006, China.
Bureau of Hydrology and Water Resources, Pearl River Water Resources Commission of Ministry of Water Resources, Guangzhou, Guangdong 510611, China.
Water Res. 2022 Oct 1;224:119046. doi: 10.1016/j.watres.2022.119046. Epub 2022 Sep 1.
Thermally activated peroxydisulfate In Situ Chemical Oxidation (TAP-ISCO) is often applied for the remediation of soil-sorbed hydrophobic organic contaminants (HOCs) and nonaqueous phase liquids (NAPLs), which act as long-term sources of groundwater contamination. TAP-ISCO benefits from improved desorption/dissolution of organic contaminants into the aqueous phase and efficient activation of peroxydisulfate at elevated temperatures, but the primary limitation of TAP-ISCO is the short lifetime of peroxydisulfate (therefore the availability of reactive radical species). To resolve this problem, coupling of peroxide stabilizers with TAP were tested. The compatibility of seven representative commercial organic and inorganic peroxide stabilizers, including sodium stannate, trisodium phosphate, sodium pyrophosphate, sodium silicate, sodium citrate, ethylene diamine tetra methylene phosphonic acid and ethylenediaminetetraacetic acid disodium salt, with TAP in aqueous solutions and solutions containing goethite or soil particles were first studied. The effects of stabilizers on the formation, distribution and reactivity of reactive oxygen species were then investigated through electron paramagnetic resonance (EPR) spin-trapping experiments using 5,5-dimethyl-1-pyrroline-N-oxide, chemical probe experiments using anisole, nitrobenzene and hexachloroethane, and biphasic trichloroethylene (TCE) dense nonaqueous phase liquids (DNAPLs) TAP-ISCO mimicking experiments. The results indicate that organic stabilizers significantly accelerate peroxydisulfate decomposition at both ambient and elevated temperatures. In contrast, inorganic stabilizers can markedly increase peroxydisulfate longevity by suppressing the acid-catalyzed peroxydisulfate decomposition, quenching radical-chain acceleration, and sequestering transition metal species. In addition, TAP systems containing inorganic stabilizers can effectively generate a variety of reactive radical species, including SO, HO, and O, and improve the oxidation of anisole and nitrobenzene, though suppressing the reduction of hexachloroethane to some extent. Especially, suitable inorganic stabilizers (e.g., trisodium phosphate) can effectively improve TAP oxidation of TCE DNAPL while suppressing peroxydisulfate decomposition. Overall, this study provides the fundamental basis of coupling TAP-ISCO with peroxide stabilizers.
热激活过硫酸盐原位化学氧化（TAP-ISCO）常用于修复土壤吸附的疏水性有机污染物（HOCs）和非水相液体（NAPLs），这些污染物是地下水污染的长期来源。TAP-ISCO 受益于有机污染物在水相中的解吸/溶解的改善和过硫酸盐在高温下的有效激活，但 TAP-ISCO 的主要限制是过硫酸盐的短寿命（因此反应性自由基的可用性）。为了解决这个问题，测试了过氧化物稳定剂与 TAP 的耦合。首先研究了七种代表性的商业有机和无机过氧化物稳定剂，包括偏锡酸钠、磷酸三钠、焦磷酸钠、硅酸钠、柠檬酸钠、乙二胺四甲叉膦酸和乙二胺四乙酸二钠盐，在水溶液中和含有针铁矿或土壤颗粒的溶液中与 TAP 的相容性。然后通过使用 5,5-二甲基-1-吡咯啉-N-氧化物的电子顺磁共振（EPR）自旋捕获实验、使用茴香醚、硝基苯和六氯乙烷的化学探针实验以及两相三氯乙烯（TCE）稠密非水相液体（DNAPLs）TAP-ISCO 模拟实验，研究了稳定剂对活性氧物质的形成、分布和反应性的影响。结果表明，有机稳定剂在环境温度和高温下都能显著加速过硫酸盐的分解。相比之下，无机稳定剂通过抑制酸催化的过硫酸盐分解、淬灭自由基链加速和螯合过渡金属物种，可以显著延长过硫酸盐的寿命。此外，含有无机稳定剂的 TAP 系统可以有效地生成各种活性自由基，包括 SO、HO 和 O，并改善茴香醚和硝基苯的氧化，但在一定程度上抑制了六氯乙烷的还原。特别是，合适的无机稳定剂（如磷酸三钠）可以有效地提高 TAP 对 TCE DNAPL 的氧化作用，同时抑制过硫酸盐的分解。总的来说，这项研究为 TAP-ISCO 与过氧化物稳定剂的结合提供了基础。
