Jang Min, Min Soo-hong, Park Jae Kwang, Tlachac Eric J
Department of Civil and Environmental Engineering, University of Wisconsin-Madison, 1415 Engineering Drive, Madison, Wisconsin 53706, USA.
Environ Sci Technol. 2007 May 1;41(9):3322-8. doi: 10.1021/es062359e.
Two reactive media [zerovalent iron (ZVI, Fisher Fe0) and amorphous hydrous ferric oxide (HFO)-incorporated porous, naturally occurring aluminum silicate diatomite [designated as Fe (25%)-diatomite]], were tested for batch kinetic, pH-controlled differential column batch reactors (DCBRs), in small- and large-scale column tests (about 50 and 900 mL of bed volume) with groundwater from a hazardous waste site containing high concentrations of arsenic (both organic and inorganic species), as well as other toxic or carcinogenic volatile and semivolatile organic compounds (VOC/SVOCs). Granular activated carbon (GAC) was also included as a reactive media since a permeable reactive barrier (PRB) at the subject site would need to address the hazardous VOC/SVOC contamination as well as arsenic. The groundwater contained an extremely high arsenic concentration (341 mg L(-1)) and the results of ion chromatography and inductively coupled plasma mass spectrometry (IC-ICP-MS) analysis showed that the dominant arsenic species were arsenite (45.1%) and monomethyl arsenic acid (MMAA, 22.7%), while dimethyl arsenic acid (DMAA) and arsenate were only 2.4 and 1.3%, respectively. Based on these proportions of arsenic species and the initial As-to-Fe molar ratio (0.15 molAs mole(-1)), batch kinetic tests revealed that the sorption density (0.076 molAs molFe(-1)) for Fe (25%)-diatomite seems to be less than the expected value (0.086 molAs molFe(-1) calculated from the sorption density data reported by Lafferty and Loeppert (Environ. Sci. Technol. 2005, 39, 2120-2127), implying that natural organic matters (NOMs) might play a significant role in reducing arsenic removal efficiency. The results of pH-controlled DCBR tests using different synthetic species of arsenic solution showed that the humic acid inhibited the MMAA removal of Fe (25%)-diatomite more than arsenite. The mixed system of GAC and Fe (25%)-diatomite increased the arsenic sorption speed to more than that of either individual media alone. This increase might be deduced by the fact that the addition of GAC could enhance arsenic removal performance of Fe (25%)-diatomite through removing comparably high portions of NOMs. Small- and large-scale column studies demonstrated that the empty bed contact time (EBCT) significantly affected sorpton capacities at breakthrough (C = 0.5 C0) forthe Fe0/sand (50/50, w/w) mixture, but notfor GAC preloaded Fe (25%)-diatomite. In the large-scale column tests with actual groundwater conditions, the GAC preloaded Fe (25%)-diatomite effectively reduced arsenic to below 50 microg L(-1) for 44 days; additionally, most species of VOC/SVOCs were also simultaneously attenuated to levels below detection.
对两种反应介质[零价铁（ZVI，Fisher Fe0）和负载无定形水合氧化铁（HFO）的天然多孔硅酸铝硅藻土[命名为Fe（25%）-硅藻土]]进行了间歇动力学、pH控制的微分柱间歇反应器（DCBR）测试，并在小规模和大规模柱试验（床层体积分别约为50和900 mL）中使用了来自一个危险废物场地的地下水，该地下水中含有高浓度的砷（有机和无机形态）以及其他有毒或致癌的挥发性和半挥发性有机化合物（VOC/SVOCs）。还纳入了颗粒活性炭（GAC）作为反应介质，因为该场地的可渗透反应屏障（PRB）需要同时解决有害的VOC/SVOC污染以及砷污染问题。该地下水中砷浓度极高（341 mg L⁻¹），离子色谱和电感耦合等离子体质谱（IC-ICP-MS）分析结果表明，主要的砷形态为亚砷酸盐（45.1%）和一甲基砷酸（MMAA，22.7%），而二甲基砷酸（DMAA）和砷酸盐分别仅占2.4%和1.3%。基于这些砷形态比例以及初始砷与铁的摩尔比（0.15 molAs mol⁻¹），间歇动力学测试表明，Fe（25%）-硅藻土的吸附密度（0.076 molAs molFe⁻¹）似乎低于预期值（根据Lafferty和Loeppert（《环境科学与技术》，2005年，39卷，2120 - 2127页）报道的吸附密度数据计算得出的0.086 molAs molFe⁻¹），这意味着天然有机物（NOMs）可能在降低砷去除效率方面发挥了重要作用。使用不同合成砷溶液进行的pH控制DCBR测试结果表明，腐殖酸对Fe（25%）-硅藻土去除MMAA的抑制作用比对亚砷酸盐的抑制作用更强。GAC和Fe（25%）-硅藻土的混合体系使砷的吸附速度提高到超过单独使用任何一种介质的速度。这种提高可能是由于添加GAC可以通过去除相当一部分NOMs来增强Fe（25%）-硅藻土的砷去除性能。小规模和大规模柱研究表明，空床接触时间（EBCT）对Fe0/砂（50/50，w/w）混合物在穿透时（C = 0.5 C0）的吸附容量有显著影响，但对预加载GAC的Fe（25%）-硅藻土没有影响。在实际地下水条件下的大规模柱试验中，预加载GAC的Fe（25%）-硅藻土在44天内有效地将砷浓度降低到50 μg L⁻¹以下；此外，大多数VOC/SVOC种类也同时被衰减到检测限以下。
