Anaerobic bacterial responses to carbonaceous materials and implications for contaminant transformation: Cellular, metabolic, and community level findings.

Carbonaceous materials (CM) enhance the abundance and activity of bacteria capable of persistent organic (micro)pollutant (POP) degradation. This review synthesizes anaerobic bacterial responses to minimally modified CM in non-fuel cell bioremediation applications at three stages: attachment, metabolism, and biofilm genetic composition. Established relationships between biological behavior and CM surface properties are identified, but temporal relationships are not well understood, making it difficult to connect substratum properties and "pioneer" bacteria with mature microorganism-CM systems. Stark differences in laboratory methodology at each temporal stage results in observational, but not causative, linkages as system complexity increases. This review is the first to critically examine relationships between material and cellular properties with respect to time. The work highlights critical knowledge gaps that must be addressed to accurately predict microorganism-CM behavior and to tailor CM properties for optimized microbial activity, critical frontiers in establishing this approach as an effective bioremediation strategy.

Effect of Copresence of Zerovalent Iron and Sulfate Reducing Bacteria on Reductive Dechlorination of Trichloroethylene.

Sulfur amendment of zerovalent iron (ZVI) materials has been shown to improve the reactivity and selectivity of ZVI toward a select group of organohalide contaminants in groundwater, most notably trichloroethene (TCE). In previous studies, chemical or mechanochemical sulfidation methods were used; however, the potential of using sulfate-reducing bacteria (SRB) to enable sulfur amendment has not been closely examined. In this study, lab-synthesized nanoscale ZVI (nZVI) and Peerless iron particles (ZVIPLS) were treated in a sulfate-reducing monoculture (D. desulfuricans) and an enrichment culture derived from freshwater sediments (AMR-1) prior to reactivity assessments with TCE as the model contaminant. ZVI conditioned in both cultures exhibited higher dechlorination efficiencies compared to unamended ZVIs. Remarkably, nZVI and ZVIPLS exposed to AMR-1 attained similar TCE dechlorination rates as their counterparts receiving chemical sulfidation (i.e., S-nZVI) using previously reported method. Product distribution data show that, in the SRB-ZVI system, abiotic dechlorination is the dominant TCE reduction pathway. In addition to dissolved sulfide, biogenic or synthesized FeS particles can enhance nZVI reactivity even as nZVI and FeS were not in direct contact, implying that SRB may influence the reactivity of ZVI via multiple mechanisms in different remediation situations. A shift in Archaea abundance in AMR-1 with nZVI amendment was observed but not with ZVIPLS. Overall, the synergy exhibited in the SRB-ZVI system may offer a valuable remediation strategy to overcome limitations of standalone biological or abiotic dechlorination approaches for chlorinated solvent abatement.