Coupling microscale zero-valent iron and autotrophic hydrogen-bacteria provides a sustainable remediation solution for trichloroethylene-contaminated groundwater: Mechanisms, regulation, and engineering implications

Controllable chemical redox reactions to couple microbial degradation for organic contaminated sites remediation: A review

Global environmental concern over organic contaminated sites has been progressively conspicuous during the process of urbanization and industrial restructuring. While traditional physical or chemical remediation technologies may significantly destroy the soil structure and function, coupling moderate chemical degradation with microbial remediation becomes a potential way for the green, economic, and efficient remediation of contaminated sites. Hence, this work systematically elucidates why and how to couple chemical technology with microbial remediation, mainly focused on the controllable redox reactions of organic contaminants. The rational design of materials structure, selective generation of reactive oxygen species, and estimation of degradation pathway are described for chemical oxidation. Meanwhile, current progress on efficient and selective reductions of organic contaminants (i.e., dechlorination, defluorination, -NO2 reduction) is introduced. Combined with the microbial remediation of contaminated sites, several consideration factors of how to couple chemical and microbial remediation are proposed based on both fundamental and practical points of view. This review will advance the understanding and development of chemical-microbial coupled remediation for organic contaminated sites.

Groundwater chlorinated solvent plumes remediation from the past to the future: a scientometric and visualization analysis

Contamination of groundwater with chlorinated hydrocarbons has serious adverse effects on human health. As research efforts in this area have expanded, a large body of literature has accumulated. However, traditional review writing suffers from limitations regarding efficiency, quantity, and timeliness, making it difficult to achieve a comprehensive and up-to-date understanding of developments in the field. There is a critical need for new tools to address emerging research challenges. This study evaluated 1619 publications related to this field using VOSviewer and CiteSpace visual tools. An extensive quantitative analysis and global overview of current research hotspots, as well as potential future research directions, were performed by reviewing publications from 2000 to 2022. Over the last 22 years, the USA has produced the most articles, making it the central country in the international collaboration network, with active cooperation with the other 7 most productive countries. Additionally, institutions have played a positive role in promoting the publication of science and technology research. In analyzing the distribution of institutions, it was found that the University of Waterloo conducted the majority of research in this field. This paper also identified the most productive journals, Environmental Science & Technology and Applied and Environmental Microbiology, which published 11,988 and 3253 scientific articles over the past 22 years, respectively. The main technologies are bioremediation and chemical reduction, which have garnered growing attention in academic publishing. Our findings offer a useful resource and a worldwide perspective for scientists engaged in this field, highlighting both the challenges and the possibilities associated with addressing groundwater chlorinated solvent plumes remediation.

Enhanced removal of cis-1,2-dichloroethene and vinyl chloride in groundwater using ball-milled sulfur- and biochar-modified zero-valent iron: From the laboratory to the field

Sulfidated zero-valent iron (ZVI) and biochar-supported ZVI have received increasing attention for their potential to dechlorinate trichloroethylene. However, minimal data are available regarding the combined effect of sulfur and biochar ZVI on trichloroethylene byproducts. The primary aim of the current study is to determine whether sulfur- and biochar-modified ZVI (ZVI-BC-S) enhances the removal of cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC) from groundwater. Results show that biochar and sulfur facilitated the milling of ZVI-BC-S into micro- and nanoscale particles and increased FeS formation. Moreover, the rates of cDCE and VC removal by ZVI-S increased by 30.1% and 30.2%, respectively, compared to those obtained with ZVI, owing to enhanced dechlorination via β-elimination by sulfur. Meanwhile, treatment with ZVI-BC-S harnessed the benefits of biochar and sulfur to enhance the cDCE and VC removal rates by 62.0% and 67.7%, respectively. Mechanistically, biochar enhanced the corrosion of ZVI-S to increase FeS production and enhance the electron transfer, β-elimination, and hydrogenolysis involved in cDCE and VC dechlorination. The effectiveness of ZVI-BC-S was confirmed in a field demonstration, during which cDCE and VC concentrations significantly decreased within 10 days following injection. The findings of this study can help inform the rational design of ZVI for in-situ remediation of chlorinated hydrocarbons in groundwater.

Impact of different zero valent iron-based particles on anaerobic microbial dechlorination of 2,4-dichlorophenol: Comparison of dechlorination performance and the underlying mechanism

The integration of iron-based materials and anaerobic microbial consortia has been extensively studied owing to its potential to enhance pollutant degradation. However, few studies have compared how different iron materials enhance the dechlorination of chlorophenols in coupled microbial systems. This study systematically compared the combined performances of microbial community (MC) and iron materials (Fe0/FeS2 +MC, S-nZVI+MC, n-ZVI+MC, and nFe/Ni+MC) for the dechlorination of 2,4-dichlorophenol (DCP) as one representative of chlorophenols. DCP dechlorination rate was significantly higher in Fe0/FeS2 +MC and S-nZVI+MC (1.92 and 1.67 times, with no significant difference between two groups) than in nZVI+MC and nFe/Ni+MC (1.29 and 1.25 times, with no significant difference between two groups). Fe0/FeS2 had better performance for the reductive dechlorination process as compared with other three iron-based materials via the consumption of any trace amount of oxygen in anoxic condition and accelerated electron transfer. On the other hand, nFe/Ni could induce different dechlorinating bacteria as compared to other iron materials. The enhanced microbial dechlorination was mainly due to some putative dechlorinating bacteria (Pseudomonas, Azotobacter, Propionibacterium), and due to improved electron transfer of sulfidated iron particles. Therefore, Fe0/FeS2 as a biocompatible as well as low-cost sulfidated material can be a good alternative for possible engineering applications in groundwater remediation.

Coupled microscale zero valent iron-autotrophic hydrogen bacteria dechlorination system is not always superior to its standalone counterparts: A sustainable remediation perspective

The coupling of microscale zero-valent iron with autotrophic hydrogen bacteria (mZVI-AHB) are often believed to show greater potential than the single abiotic or biotic systems in remediating chlorinated aliphatic hydrocarbon-contaminated groundwater. However, our understanding of the remediation performance of this system under real field conditions, especially by incorporating the concept of sustainable remediation, remains limited. In this study, the performances of the mZVI, H₂-AHB, and mZVI-AHB systems in dechlorinating groundwater containing complex electron acceptors were compared by evaluating their removal efficiency (RE), reaction products, and electron efficiency (EE), using trichloroethylene (TCE) as the target contaminant and NO₃^- and SO₄^2- as the coexisting natural electron acceptors. Ultimately, which of these systems had TCE removal superiority was dependent on the coexisting electron acceptor. mZVI-AHB and mZVI resulted in more complete dechlorination, whereas H₂-AHB exhibited higher N₂ selectivity in reducing NO₃^-. Regardless of the coexisting electron acceptor, the mZVI-alone system showed the highest EE. Finally, the sustainability concerns and applicability of the three systems were evaluated on the basis of their TCE RE, complete dechlorination ratio, N₂ selectivity, EE, and cost, which were integrated into a comparison of overall benefits. Our findings provide comprehensive and insightful information on the factors that determine remediation scheme selection in real practice.

Recent advances and trends of trichloroethylene biodegradation: A critical review

Trichloroethylene (TCE) is a ubiquitous chlorinated aliphatic hydrocarbon (CAH) in the environment, which is a Group 1 carcinogen with negative impacts on human health and ecosystems. Based on a series of recent advances, the environmental behavior and biodegradation process on TCE biodegradation need to be reviewed systematically. Four main biodegradation processes leading to TCE biodegradation by isolated bacteria and mixed cultures are anaerobic reductive dechlorination, anaerobic cometabolic reductive dichlorination, aerobic co-metabolism, and aerobic direct oxidation. More attention has been paid to the aerobic co-metabolism of TCE. Laboratory and field studies have demonstrated that bacterial isolates or mixed cultures containing Dehalococcoides or Dehalogenimonas can catalyze reductive dechlorination of TCE to ethene. The mechanisms, pathways, and enzymes of TCE biodegradation were reviewed, and the factors affecting the biodegradation process were discussed. Besides, the research progress on material-mediated enhanced biodegradation technologies of TCE through the combination of zero-valent iron (ZVI) or biochar with microorganisms was introduced. Furthermore, we reviewed the current research on TCE biodegradation in field applications, and finally provided the development prospects of TCE biodegradation based on the existing challenges. We hope that this review will provide guidance and specific recommendations for future studies on CAHs biodegradation in laboratory and field applications.

Trichloroethylene remediation using zero-valent iron with kaolin clay, activated carbon and bacteria

Nanoscale particles of zero-valent iron were used to form a permeable reactive barrier whose performance in dechlorinating a solution of trichloroethylene was compared with that of a barrier formed from limestone. The iron was combined with kaolin by calcination. The test liquid contained sewage sludge, and also added NH₄Cl and KH₂PO₄. The average removal rates of trichloroethylene and phosphorus over 365 days both exceeded 94%. Chemical oxygen demand was reduced by 92% and ammonium nitrogen by 43.6%. All were significantly greater than the removals with the limestone barrier. The ceramsite barrier retained 85% of its effectiveness even after 365 days of use. Dechloromonas sp. was the main dechlorinating bacterium, but its removal ability is limited. The removal of trichloroethylene in such a barrier mainly depends on reduction by the zero-valent iron and biodegradation. The results show that the prepared ceramsite is stable and effective in removing trichloroethylene from water. It is a promising in-situ remediation material for groundwater.