Dual Effects of Humic Acid in Trichloroethylene Removal from Groundwater by Zero-Valent Iron: Hydrophobic Partition and Surface Adsorption
Dual Effects of Humic Acid in Trichloroethylene Removal from Groundwater by Zero-Valent Iron: Hydrophobic Partition and Surface Adsorption
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DOI：
10.1007/s11270-016-2832-0
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发表时间：
2016-04
期刊：
影响因子：
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通讯作者：
P. Rao;Tongzhou Liu;Xihua Liang;Guoyu Ding
中科院分区：
文献类型：
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作者：
P. Rao;Tongzhou Liu;Xihua Liang;Guoyu Ding
地下水中的天然有机物(NOM)是影响Fe0可渗透反应墙(PRB)长期运行的一个重要因素。在间歇实验和柱式实验中，NOM的主要成分腐植酸对模拟地下水中三氯乙烯(TCE)的去除表现出双重效应。在与Fe0接触的初始阶段，腐植酸对TCE的疏水分配和随后在Fe0表面的快速吸附促进了TCE的去除。从长远来看，腐植酸抑制了TCE的去除，因为吸附在FeO表面的腐植酸阻碍了FeO的反应活性，限制了TCE的传质。Ca~(2+)使腐植酸与FeO腐蚀产物的共聚作用增强，使FeO基质孔隙率降低，导致TCE去除能力更快耗尽。FTIR分析表明，通过疏水分配去除的部分TCE保留在Fe0表面积累的腐植酸中，而不是被Fe0还原降解。提出了用Fe0PRB处理富含氮地下水中有机污染物的问题。一旦累积的NOM从FeO表面解吸或分离，滞留在NOM中的有机污染物可能会释放回来，导致地下水中的有机污染物反弹到PRB的界限之外。
Natural organic matter (NOM) in groundwater is a factor of concern in long-term operation of Fe0permeable reactive barrier (PRB). In this study, humic acid, a major component of NOM, showed dual effects in trichloroethylene (TCE) removal from simulated groundwater by Fe0in batch and column experiments. In the initial stage of contacting with Fe0, humic acid promoted TCE removal due to its hydrophobic partitioning towards TCE and the subsequent fast adsorption onto Fe0surfaces. In a long run, humic acid inhibited TCE removal because the buildup of adsorbed humic acid on Fe0surfaces passivated Fe0reactivity and limited TCE mass transfer. Ca2+enhanced the co-aggregation of humic acid with Fe0corrosion products and led to a faster depletion of TCE removal capacity by diminishing Fe0matrix porosity. Revealed by FTIR analysis, part of TCE removed through hydrophobic partitioning was retained in humic acid accumulated on Fe0surfaces rather than reductively degraded by Fe0. It raises a concern of using Fe0PRB to treat organic contaminants in NOM-rich groundwater. Releasing back of NOM retained organic contaminants might take place once the accumulated NOM is desorbed or detached from Fe0surfaces, resulting in a rebound of organic contaminants in the groundwater beyond the confine of PRB.