Background

Nanoscale zero-valent iron (nZVI) is commonly used for remediation of groundwater contaminated by chlorinated ethenes (CEs); however, its long-term reactivity and subsurface transport are limited. A novel nZVI–AC material, consisting of colloidal activated carbon (AC) with embedded nZVI clusters, was developed with the aim of overcoming the limitations of nZVI alone.

Results

Application of a limited amount of nZVI–AC to an oxic, nitrate-rich, highly permeable quaternary aquifer triggered time-limited transformation of CEs, with noticeable involvement of reductive dechlorination. Reductive dechlorination of CEs was dominantly abiotic, as an increase in the concentration of vinyl chloride (VC) and ethene did not coincide with an increase in the abundance of reductive biomarkers for complete dechlorination of CEs (Dehalococcoides, Dehalogenimonas, VC reductase genes vcrA and bvcA). Application of nZVI–AC under unfavourable hydrochemical conditions resulted in no dramatic change in the microbial community, the reducing effect resulting in temporal proliferation of nitrate and iron reducers only. At a later stage, generation of reduced iron induced an increase in iron-oxidizing bacteria. High concentrations and a continuous mass influx of competing electron acceptors (nitrate and dissolved oxygen) created unfavourable conditions for sulphate-reducers and organohalide-respiring bacteria, though it allowed the survival of aerobic microorganisms of the genera Pseudomonas, Polaromonas and Rhodoferax, known for their ability to assimilate VC or cis-1,2-dichloroethene. A potential for aerobic oxidative degradation of CE metabolites was also indicated by detection of the ethenotroph functional gene etnE.

Conclusions

This pilot study, based on the application of nZVI–AC, failed to provide a sustainable effect on CE contamination; however, it provided valuable insights into induced hydrogeochemical and microbial processes that could help in designing full-scale applications.

中文翻译：

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在活性炭中嵌入nZVI的原位试验应用，用于治理氯乙烯污染的地下水：对微生物群落的影响

背景

纳米级零价铁（nZVI）通常用于补救被氯化乙烯（CEs）污染的地下水。但是，它的长期反应性和地下运输受到限制。为了克服仅nZVI的局限性，开发了一种新型nZVI-AC材料，它由具有嵌入nZVI簇的胶体活性炭（AC）组成。

结果

在有氧，富含硝酸盐，高渗透性的第四层含水层中应用有限量的nZVI-AC会引发CE的限时转化，并明显涉及还原性脱氯。CE的还原脱氯是显性的非生物，如增加的氯乙烯（VC）的浓度和乙烯的增加的丰度还原的生物标志物的对CE设备（完全脱氯没有重合Dehalococcoides，Dehalogenimonas，VC还原酶基因vcrA和BVCA）。在不利的水化学条件下使用nZVI-AC不会导致微生物群落发生显着变化，其还原作用仅导致硝酸盐和铁还原剂的暂时扩散。在稍后的阶段，还原铁的产生引起铁氧化细菌的增加。高浓度和创建的硫酸盐减速器和有机卤化物-呼吸细菌不利的条件，虽然它允许属的需氧微生物的存活竞争电子受体的连续大量涌入（硝酸盐和溶解氧）假单胞菌，Polaromonas和Rhodoferax，已知其吸收VC或cis的能力-1,2-二氯乙烯。CE代谢产物的有氧氧化降解的潜力也通过检出嗜乙体营养功能基因etnE来指出。

结论

这项基于nZVI-AC的试点研究未能对CE污染提供可持续的影响。但是，它为诱导水文地球化学和微生物过程提供了宝贵的见识，可以帮助设计大规模应用。