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1, 1, 1-三氯乙烷(1, 1, 1-trichloroethane, 1, 1, 1-TCA)是一种常见的有机氯溶剂,工业上的广泛使用和不当处置使其成为全球地下水中普遍检出的污染物之一[1]。1, 1, 1-TCA易迁移扩散,化学性质稳定且不易降解,并具有“三致”效应,其一旦进入地下环境,将会严重危害生态安全和人类健康[2-3]。因此,如何高效治理1, 1, 1-TCA污染地下水已成为环境修复领域的研究热点。
原位强化还原脱氯是一种有效修复氯代烃污染地下水的方法,其中修复材料是影响修复效果的关键因素[4]。目前较为常用的修复材料包括具有化学还原脱氯能力的零价铁,以及能够促进微生物还原脱氯的有机碳源[5]。但这些修复材料存在易团聚和氧化、作用时效短及利用效率低等问题,从而限制了其应用范围[6-7]。设计并制备高效的功能复合材料是解决上述问题的一个新途径[8]。
将零价铁负载于生物炭(biochar,BC)上可显著降低零价铁的团聚程度,提高其对氯代烃的化学脱氯效果。DONG等[9]制备了一系列纳米零价铁基生物炭材料,发现其对水中三氯乙烯的去除率比单一纳米零价铁高14%以上。同时,生物炭具有丰富的孔隙结构,能够有效吸附污染物[10]。然而,生物炭中生物可利用性碳含量较低,无法进一步促进微生物的还原脱氯作用[11]。聚乳酸(polylactic acid,PLA)能够缓慢释放可被微生物利用的可溶性有机碳,是一种良好的缓释碳源[12]。因此,可以推测,将聚乳酸与负载零价铁的生物炭复合可增強材料的处理长效性。但目前有关这方面的研究尚未见报道。本研究制备了一种纳米零价铁-聚乳酸-生物炭复合材料,研究其协同胞外呼吸菌去除水中1, 1, 1-TCA的效果,并探讨协同体系还原降解污染物的机理。
纳米零价铁-聚乳酸-生物炭复合材料协同微生物去除水中1, 1, 1-三氯乙烷
1, 1, 1-trichloroethane removal from water by nano-zero valent iron-polylactic acid-biochar composite coupled with microorganism
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摘要: 针对地下水1, 1, 1-三氯乙烷污染问题,通过溶液插层和液相还原法制备了纳米零价铁-聚乳酸-生物炭复合材料;采用扫描电镜观察、热重分析、傅里叶变换红外光谱分析和X射线衍射分析等手段对复合材料进行了表征;研究了复合材料在厌氧条件下协同胞外呼吸菌(Shewanella oneidensis MR-1)去除水中1, 1, 1-三氯乙烷的效果;确定了材料的最佳使用条件;探讨了协同体系中污染物的去除机理。结果表明:复合材料中纳米零价铁和聚乳酸颗粒较为均匀地分散于生物炭表面;材料中生物炭、聚乳酸和纳米零价铁的最佳质量比为7∶1∶2,材料最佳投加量为1.0%,且其对不同浓度污染物均有明显去除效果;在最佳条件下,培养360 h后协同体系中1, 1, 1-三氯乙烷的最大去除率为94.61%;复合材料促进胞外呼吸菌的异化铁还原脱氯是协同体系去除污染物的主要机理。该铁基生物炭复合材料能够有效协同胞外呼吸菌提高水中1, 1, 1-三氯乙烷的去除率,且具有良好的缓释长效性。Abstract: Aiming at the problem of 1, 1, 1-trichloroethane pollution in groundwater, a nano-zero valent iron-polylactic acid-biochar composite was prepared by the solution intercalation and the liquid-phase reduction methods, and it was characterized by the following analysis methods: SEM, TGA, FT-IR and XRD. The performance of this composite coupled with extracellular respiratory bacteria (Shewanella oneidensis MR-1) on 1, 1, 1-trichloroethane removal under anaerobic conditions was studied, and the optimal conditions for this composite application was determined. Furthermore, the possible mechanisms of 1, 1, 1-trichloroethane removal in the synergistic system were discussed. The results showed that in this composite, both nano-zero valent iron and polylactic acid particles dispersed homogeneously on the biochar surface. The optimum mass ratio of biochar, polylactic acid and nano-zero valent iron in the composite was 7∶1∶2, and the optimal dosage of this composite was 1.0%, at which the contaminants with various concentrations could be removed effectively. After 360 h-incubation, the maximum removal rate of 1, 1, 1-trichloroethane was 94.61% under the optimal application conditions. In the synergistic system, the main mechanism of contaminant removal was the dissimilatory iron reduction dechlorination of extracellular respiratory bacteria promoted by this composite. An synergistic process between this iron-based biochar composite could effective couple with extracellular respiratory bacteria to improve the removal rate of 1, 1, 1-trichloroethane in aqueous solution, and had good slow-release and long-acting properties.
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