Synergistic and competitive interactions between solid carbon sources and current-driven sulfate reduction in a...

Conventional microbial sulfate reduction technologies for sulfate pollution control often suffer from low efficiency, insufficient sulfur immobilization, and poor stability under extreme carbon-to-sulfur (C/S) ratios, leading to secondary pollution. To overcome these limitations, this study combined electrical stimulation with a solid-phase carbon source (wheat straw) to construct a single-chamber microbial electrolysis cell for long-term operation. Under optimal conditions (hydraulic retention time = 2.0 d, C/S = 1.5, current density = 100 mA/m²), the sulfate removal efficiency and the accumulation rate of dissolved sulfide reached 92.45% and 26.30%, respectively. The system maintained stable performance over 293 days and during five shock events, demonstrating a pronounced synergistic effect between electrical input and the carbon source. The iron anode facilitated the directional conversion of sulfide into FeS and S⁰, enabling efficient sulfur immobilization and significantly suppressing secondary pollution. During operation, microbial activity was sustained at a high level (electron transport system activity = 0.357 μL O₂·g⁻¹·min⁻¹, ATP = 0.024 μmol). Metagenomic analysis revealed that electrical stimulation markedly enhanced the abundance of sulfur metabolism-related genes and promoted direct extracellular electron transfer process, whereas the wheat straw facilitated mediated extracellular electron transfer through the slow release of exogenous electron shuttles. The synergistic interaction between these processes optimized the electron transfer network within the system. This study elucidates the mechanisms underlying directional sulfur transformation and electron transfer during long-term operation, providing critical insights for optimizing microbial ecosystems involved in sulfate reduction and supporting the practical application of this technology in water in situ remediation.