Semi-conductive materials for engineered bioremediation: From surface properties to microbial diversity

Engineered bioremediation has gained attention in recent years as a speedy and efficient option for environmental pollution control. Solid materials can speed up in situ bioremediation processes because they offer a platform for microbial attachment and immobilization, and serve as electron donor and energy source, acceptor, and/or redox mediator to promote biological reaction rates. These materials can impact microbial community composition, behavior, and growth. This work evaluates anaerobic bacterial responses to two different semi-conductive materials used in subsurface remediation, granular activated carbon (GAC) and zerovalent iron (ZVI), with the goal of elucidating relationships between material properties and microbial activity.

GAC studies investigate the influence of solution chemistry and surface oxidation treatments, mimicking natural weathering processes, on Geobacter sulfurreducens strain PCA’s ability to colonize GAC and utilize the material as a solid-phase electron acceptor. Results show that surface oxidation most significantly affects PCA catabolism at elevated pH, compared to neutral or acidic pH conditions. Effects of GAC oxidation are most pronounced for highly weathered GAC under growth conditions. However, similar improvements in respiration and biological growth rates are not observed using a freshwater sediment-derived enrichment consortia containing PCA and active sulfate reducers. These findings provide evidence that increased GAC oxidation promotes enrichment of Geobacter under unfavorable aqueous conditions (high pH) only if strong reductants (sulfide) are absent.

ZVI studies compare the impact of sulfidated and non-sulfidated ZVI particles on bacterial culture Desulfovibrio desulfuricans and sulfate-reducing enrichment culture AMR-1. Experiments with D. desulfuricans show that sulfidation of the particles can significantly (p < 0.05) decrease rates of sulfate reduction, but the extent to which respiration rates decline depends upon whether ZVI is pure and nanoscale (nZVI) or mesoscale with impurities (Peerless). When AMR-1 is present, non-sulfidated nZVI enriches Archaea, yet sulfidated nZVI does not promote methanogenic growth. Both sulfidated and non-sulfidated Peerless particles suppress methanogens and maintain the richness and diversity of the consortia. Our results indicate that ZVI source material may be more influential than surface sulfidation on the enrichment and behavior of sulfate-reducing bacteria.

Overall, this work shows that tailoring surface properties of semi-conductive materials can influence microbial enrichment and biotransformation reactions under appropriate environmental and microbial conditions. These findings address critical knowledge gaps related to microbial responses to material amendments, critical frontiers in establishing solid-phase amendments as an effective and reliable bioremediation strategy.

Embargo status: Restricted until 01/2023. To request the author grant access, click on the PDF link to the left.