Effect of granular activated carbon and other porous materials on thermal decomposition of per- and polyfluoroalkyl substances: Mechanisms and implications for water purification
Effect of granular activated carbon and other porous materials on thermal decomposition of per- and polyfluoroalkyl substances: Mechanisms and implications for water purification
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DOI：
10.1016/j.watres.2021.117271
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发表时间：
2021-05-31
期刊：
影响因子：
12.8
通讯作者：
Xiao, Feng
中科院分区：
文献类型：
--
作者：
Sasi, Pavankumar Challa;Alinezhad, Ali;Xiao, Feng
热处理通常用于再活化来自水净化设施的用过的颗粒活性炭（GAC）。它也是污水污泥处理和城市固体废物管理的一个组成部分。本研究详细调查了全氟烷基和多氟烷基物质（PFAS）以及一种PFAS替代品（GenX）在热处理过程中的命运，重点关注GAC的影响。我们证明了全氟烷基羧酸（PFCAs），包括全氟辛酸（PFOA）和GenX的热分解可以在150-200摄氏度的温度下发生。发现PFOA有三个温度区，包括稳定区和非挥发区（= 400 ℃）。热分解开始于PFCAs羧基附近的C-C键的均裂，其形成不稳定的全氟烷基自由基。似乎存在双重分解途径。添加高度多孔的吸附剂，如GAC或共聚物树脂，压缩了PFCA的中间升华区，改变了它们的热分解途径，并在250 ℃下将分解速率常数提高了150倍。结果表明，所观察到的热分解加速与GAC上的气相PFCA分子的吸附。对PFOA具有低亲和力的非活性炭/生物炭的存在并没有加速其热分解，这表明与吸附剂的孔隙率相比，炭/GAC的富含π电子的聚芳族表面发挥了微不足道的作用。总的来说，结果表明：（1）在传统的热GAC/污泥/废物处理过程中，PFCAs和GenX的大量分解是非常可能的;（2）GAC或其他高度多孔材料的存在或添加可以加速PFAS的热分解并改变分解途径。(C)2021爱思唯尔有限公司保留所有权利。
Thermal treatment is routinely used to reactivate the spent granular activated carbon (GAC) from water purification facilities. It is also an integral part of sewage sludge treatment and municipal solid waste management. This study presents a detailed investigation of the fate of per- and polyfluoroalkyl substances (PFAS) and one PFAS alternative (GenX) in thermal processes, focusing on the effect of GAC. We demonstrate that the thermolysis of perfluoroalkyl carboxylic acids (PFCAs), including perfluorooctanoic acid (PFOA), and GenX can occur at temperatures of 150-200 degrees C. Three temperature zones were discovered for PFOA, including a stable and nonvolatile zone (= 400 degrees C). The thermal decomposition began with the homolysis of a C-C bond next to the carboxyl group of PFCAs, which formed unstable perfluoroalkyl radicals. Dual decomposition pathways seem to exist. The addition of a highly porous adsorbent, such as GAC or a copolymer resin, compressed the intermediate sublimation zone of PFCAs, changed their thermal decomposition pathways, and increased the decomposition rate constant by up to 150-fold at 250 degrees C. The results indicate that the observed thermal decomposition acceleration was linked to the adsorption of gas-phase PFCA molecules on GAC. The presence of non-activated charcoals/biochars with a low affinity for PFOA did not accelerate its thermal decomposition, suggesting that the pi electron-rich, polyaromatic surface of charcoal/GAC played an insignificant role compared to the adsorbent's porosity. Overall, the results indicate that (1) substantial decomposition of PFCAs and GenX during conventional thermal GAC/sludge/waste treatment is very likely, and (2) the presence or addition of GAC or other highly porous materials can accelerate thermal PFAS decomposition and alter decomposition pathways. (C) 2021 Elsevier Ltd. All rights reserved.