Session: Biogeochemical Transformation in Underground Environments: Natural Processes & Engineered Implementations for Contaminant Abatement:

Zero valent iron (ZVI) technology has been extensively researched for water treatment and subsurface remediation and amending ZVI with reduced sulfur species such as sulfide greatly enhances their efficiency in the removal of chlorinated solvents such as trichloroethene (TCE). This work examines the potential for in situ sulfidation of ZVI using sulfate-reducing bacteria (SRB), which may play an important role in subsurface chlorinated ethene remediation. Lab synthesized nanosized ZVI (nZVI) and commercially available ZVI materials were treated with reduced sulfur species produced by sulfate-reducing Desulfovibrio desulfuricans and freshwater sediment-derived enrichment culture (AMR-1). TCE reduction activity of biologically sulfidated ZVI particles was compared against the reactivity of ZVI sulfidated in a post-synthesis sulfidation approach (referred to herein as chemical sulfidation). Experiments show that TCE reduction efficiency improved in particles sulfidated using D. desulfuricans and AMR-1, compared to their respective untreated particles, and attachment of SRB to the particle surface was confirmed with SEM imaging. ZVIs conditioned in AMR-1 attained comparable TCE degradation rates as chemically sulfidated ZVIs, while D. desulfuricans-conditioned ZVI showed slower degradation of TCE. The product yield of biologically- and chemically-sulfidated ZVI systems were similar, suggesting that TCE degradation pathways were unaffected by the sulfidation method. To assess the potential influence of treated and untreated ZVI on indigenous bacteria, experiments monitored changes in AMR-1 community composition of following exposure to particles. Archaea and Eubacteria within AMR-1 culture were highly sensitive to untreated nZVI, which was not observed with micro-ZVI amendments and with sulfidated particles. Ongoing transcriptomic studies with treated ZVI particles and D. desulfuricans aim to identify changes in gene regulation following exposure to particles. Overall, the results from this study provided important insights on the interaction between SRB and ZVI and their impacts on in situ TCE remediation by ZVI materials.

Kayleigh Millerick

Texas Tech University

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