Key Takeaways & Executive Findings
- •• • Biochar matrix and AQDS individually enhance Cr(VI) bioreduction by S. oneidensis MR-1, but their combination exhibits antagonism, reducing removal efficiency compared to single amendments. • • The antagonistic effect is attributed to increased repulsive forces between the biochar-AQDS complex and bacterial cells, which inhibit electron transfer to Cr(VI) during the fast reduction phase. • • The study highlights the importance of considering co-existing e-DOM when applying biochar for Cr(VI) remediation, as interactions can negate expected benefits. • • Findings provide mechanistic insights into biochar's environmental fate and its impact on microbial electron transfer processes, informing risk assessment for biochar-amended soils.
Abstract
Chromium is a common environmental metal pollutant. Shewanella oneidensis MR-1 can generate extracellular electrons, facilitating the reduction of Cr(VI) to Cr(III), thereby mitigating its toxicity. Both biochar and electroactive dissolved organic matter (e-DOM) regulate extracellular electron transfer during Cr(VI) bioreduction. In practice, surface DOM on biochar can detach and enter the environment, while the biochar matrix (BCM) remains the predominant form and coexists with e-DOM. However, the combined effects of BCM and e-DOM on microbial Cr(VI) removal are unclear. This study investigated the individual and combined impacts of biochar matrix and AQDS (a model e-DOM) on Cr(VI) reduction by S. oneidensis MR-1. Results showed that biochar matrix or AQDS alone promoted Cr(VI) removal, primarily by accelerating electron transfer during the fast reduction phase. However, when both were added, an antagonistic effect was observed, attributed to increased repulsive forces between the biochar matrix-AQDS complex and the bacterial cells, which inhibited electron transfer to Cr(VI). This research elucidates the electrochemical interactions between biochar matrix and e-DOM, providing a theoretical basis for biochar applications in environmental remediation and risk assessment.
1. Introduction
Hexavalent chromium (Cr(VI)) contamination poses significant environmental and health risks due to its high toxicity and mobility. Bioremediation using electroactive bacteria like Shewanella oneidensis MR-1 offers a sustainable approach, as these bacteria can transfer electrons to reduce Cr(VI) to less toxic Cr(III). Biochar amendments have been shown to enhance this process by facilitating electron transfer, but the presence of dissolved organic matter (DOM) in natural environments can alter biochar's surface properties and microbial interactions. Specifically, biochar-derived DOM may detach and interact with microbial cells, potentially affecting the efficiency of Cr(VI) reduction.
This study addresses the critical knowledge gap regarding the combined effects of biochar matrix and e-DOM (modeled by AQDS) on Cr(VI) bioreduction. While individual effects are known, their interaction remains unexplored. The research reveals an antagonistic effect when both are present, attributed to increased electrostatic repulsion between the biochar-AQDS complex and bacterial cells, which impedes electron transfer. These findings underscore the necessity of considering co-existing e-DOM in biochar-based remediation strategies, as they can significantly influence treatment outcomes. The mechanistic insights provided are essential for optimizing biochar applications and predicting their environmental impact.
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LIU Lijuan, REN Hao, WANG Xue, ZHU Bingqian, CHENG Chen, ZHANG Peng (2026). Antagonistic Effects of Anthraquinone-2,6-Disulfonic Acid Sodium Salt and Biochar Matrix on Shewanella oneidensis MR-1 Mediated Cr(VI) Reduction. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2025040705
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Frequently Asked Questions
What is the specific antagonistic mechanism when biochar matrix and AQDS are combined?
The antagonistic effect arises from increased repulsive forces between the biochar-AQDS complex and S. oneidensis MR-1 cells, which inhibit electron transfer to Cr(VI). This was observed during the fast Cr(VI) bioreduction phase, where the promotion seen with individual amendments was negated.
How does the presence of AQDS affect the electron transfer capacity of biochar matrix?
AQDS alone enhances electron transfer, but when combined with biochar matrix, the complex exhibits higher repulsion towards bacteria, reducing the overall electron transfer efficiency. This suggests that AQDS may alter the surface charge of biochar, impacting microbial attachment and electron shuttling.
What are the implications for biochar application in Cr(VI)-contaminated environments with high DOM content?
In environments rich in e-DOM, biochar may not effectively enhance Cr(VI) bioreduction due to antagonistic interactions. Therefore, biochar application should be evaluated considering DOM levels, and alternative strategies may be needed to overcome the inhibitory effects.
What experimental conditions were used to observe the antagonistic effect?
The study used S. oneidensis MR-1 with Cr(VI) in the presence of biochar matrix and AQDS, both individually and combined. The antagonistic effect was observed in the fast reduction phase, with electron transfer inhibition attributed to increased repulsive forces.
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