Bioelectrochemical modulation of sulfur oxidation enhances arsenic sequestration from sediments in Vallisneria natans through root iron plaque formation and arsenic oxidation: Processes and mechanisms.
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75% confidenceThis study investigated the use of bioelectrochemical systems to enhance arsenic sequestration in sulfur-rich sediments through the submerged aquatic plant Vallisneria natans. The results showed that arsenic accumulation and enrichment efficiency increased with applied voltage, and microbial electrolysis cells outperformed microbial fuel cells in enhancing root iron plaque development. The study proposed a mechanism involving bioelectrogenesis-driven sulfur oxidation, root iron plaque formation, and arsenic oxidation.
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Abstract
This study investigated the potential of bioelectrochemical systems (BESs) in enhancing arsenic (As) sequestration in sulfur-rich sediments through submerged aquatic plant Vallisneria natans (V. natans). A mechanism entailing bioelectrogenesis-driven sulfur oxidation, which facilitated root iron plaque (IP) formation and As oxidation, was proposed. A 125-day microcosm study was conducted using coupled plant-BES configurations, comprising: a microbial fuel cell (MFC), microbial electrolysis cells (MECs) with voltage gradients, and V. natans. Results showed that As accumulation and enrichment efficiency in IPs increased proportionally with applied voltage. Electrogenesis enhanced IP development, with MECs outperforming the MFC. Rhizospheric phosphorus deficiency in MFC stimulated radial oxygen loss (ROL) and microbial Fe 2+ oxidation for IP formation. In MECs, enhanced endogenous Fe 2+ availability and reduction in ΣH 2 S concentrations collectively facilitated IP development. As oxidation in MFC was significantly amplified within the rhizosphere by As-oxidizing microorganisms. Sulfite (SO 3 2- ), a metabolite of sulfur oxidation, was electrochemically activated in MECs to generate sulfite radicals (SO 3 •- ), demonstrating superior As oxidation efficacy compared to MFC. Metagenomic analysis revealed extracellular electron transfer (EET) efficiency dictated the sulfur oxidation pathway. MFC exhibited FeS 2 -dominated oxidation with terminal S 0 and intermediate S 2 O 3 2- formation, suppressing ΣH 2 S elimination. MECs displayed insufficient EET, driving ΣH 2 S oxidation, FeS consumption, and SO 3 2- accumulation. Intracellular sulfur oxidation pathways differed between systems: the rDsr pathway dominated in MFC, while Hdr process prevailed in MECs. Anode-associated keystone genera responsible for sulfur oxidation were Thiobacillus and Pseudomonas in MFC and MECs, respectively. Iron-oxidizing Collimonas and As oxidizing Halomonas/Acinetobacter were crucial for mediating IP formation and As oxidization, respectively in MFC. These findings demonstrate that BESs are effective tools for augmenting As sequestration by submerged aquatic plants. This investigation establishes foundational insights for practical implementation of integrated plant-BESs in As-contaminated sediment remediation strategies.