Environmental Engineering Program, Department of Civil Engineering, 238 Harbert Engineering Center, Auburn University, Auburn, AL 36849, USA.
Water Res. 2011 Mar;45(7):2401-14. doi: 10.1016/j.watres.2011.01.028. Epub 2011 Mar 2.
Zero valent iron (ZVI) nanoparticles have been studied extensively for degradation of chlorinated solvents in the aqueous phase, and have been tested for in-situ remediation of contaminated soil and groundwater. However, little is known about its effectiveness for degrading soil-sorbed contaminants. This work studied reductive dechlorination of trichloroethylene (TCE) sorbed in two model soils (a potting soil and Smith Farm soil) using carboxymethyl cellulose (CMC) stabilized Fe-Pd bimetallic nanoparticles. Effects of sorption, surfactants and dissolved organic matter (DOC) were determined through batch kinetic experiments. While the nanoparticles can effectively degrade soil-sorbed TCE, the TCE degradation rate was strongly limited by desorption kinetics, especially for the potting soil which has a higher organic matter content of 8.2%. Under otherwise identical conditions, ∼ 44% of TCE sorbed in the potting soil was degraded in 30 h, compared to ∼ 82% for Smith Farm soil (organic matter content = 0.7%). DOC from the potting soil was found to inhibit TCE degradation. The presence of the extracted SOM at 40 ppm and 350 ppm as TOC reduced the degradation rate by 34% and 67%, respectively. Four prototype surfactants were tested for their effects on TCE desorption and degradation rates, including two anionic surfactants known as SDS (sodium dodecyl sulfate) and SDBS (sodium dodecyl benzene sulfonate), a cationic surfactant hexadecyltrimethylammonium (HDTMA) bromide, and a non-ionic surfactant Tween 80. All four surfactants were observed to enhance TCE desorption at concentrations below or above the critical micelle concentration (cmc), with the anionic surfactant SDS being most effective. Based on the pseudo-first-order reaction rate law, the presence of 1 × cmc SDS increased the reaction rate by a factor of 2.5 when the nanoparticles were used for degrading TCE in a water solution. SDS was effective for enhancing degradation of TCE sorbed in Smith Farm soil, the presence of SDS at sub-cmc increased TCE degraded by ∼ 10%. However, effect of SDS on degradation of TCE in the potting soil was more complex. The presence of SDS at sub-cmc decreased TCE degradation by 5%, but increased degradation by 5% when SDS dosage was raised to 5 × cmc. The opposing effects were attributed to combined effects of SDS on TCE desorption and degradation, release of soil organic matter and nanoparticle aggregation. The findings strongly suggest that effect of soil sorption on the effectiveness of Fe-Pd nanoparticles must be taken into account in process design, and soil organic content plays an important role in the overall degradation rate and in the effectiveness of surfactant uses.
零价铁 (ZVI) 纳米颗粒已被广泛研究用于降解水相中氯代溶剂，并已被测试用于污染土壤和地下水的原位修复。然而，对于其降解土壤吸附污染物的有效性知之甚少。本工作研究了羧甲基纤维素 (CMC) 稳定的 Fe-Pd 双金属纳米颗粒对两种模型土壤（盆栽土和史密斯农场土壤）中吸附的三氯乙烯 (TCE) 的还原脱氯作用。通过批处理动力学实验确定了吸附、表面活性剂和溶解有机物 (DOC) 的影响。尽管纳米颗粒可以有效地降解土壤吸附的 TCE，但 TCE 的降解速率受到解吸动力学的强烈限制，特别是对于有机物质含量为 8.2%的盆栽土。在其他条件相同的情况下，在 30 小时内，盆栽土中吸附的约 44%的 TCE 被降解，而史密斯农场土壤（有机物质含量=0.7%）中约 82%的 TCE 被降解。从盆栽土中提取的 DOC 被发现抑制 TCE 的降解。当 TOC 分别为 40ppm 和 350ppm 时，存在的提取的 SOM 分别降低了 34%和 67%的降解速率。测试了四种原型表面活性剂对 TCE 解吸和降解速率的影响，包括两种阴离子表面活性剂 SDS（十二烷基硫酸钠）和 SDBS（十二烷基苯磺酸钠）、阳离子表面活性剂十六烷基三甲基溴化铵 (HDTMA) 溴化物和非离子表面活性剂 Tween 80。所有四种表面活性剂在低于或高于临界胶束浓度 (cmc) 时均观察到增强 TCE 解吸的作用，阴离子表面活性剂 SDS 最有效。根据准一级反应速率定律，当纳米颗粒用于降解水溶液中的 TCE 时，1×cmc SDS 的存在将反应速率提高了 2.5 倍。SDS 有效增强了史密斯农场土壤中吸附的 TCE 的降解，在亚 cmc 存在下，SDS 增加了约 10%的 TCE 降解。然而，SDS 对盆栽土中 TCE 降解的影响更为复杂。在亚 cmc 存在下，SDS 降低了 5%的 TCE 降解，但当 SDS 剂量提高到 5×cmc 时，降解增加了 5%。这种相反的影响归因于 SDS 对 TCE 解吸和降解、土壤有机质释放和纳米颗粒聚集的综合影响。研究结果强烈表明，在工艺设计中必须考虑土壤吸附对 Fe-Pd 纳米颗粒有效性的影响，土壤有机含量在整体降解速率和表面活性剂使用效果中起着重要作用。
