Carbon source and electro-stimulation modulates performance, microbial ecology, and metabolism in U (VI) bioreduction systems

Efficient removal and recovery of uranium from mining wastewater are essential for environmental protection and resource sustainability. Microbial reduction of soluble U(VI) to insoluble U(IV) is a promising strategy, but the role of biostimulation via tailored carbon sources and electrochemical inputs remains underexplored. This study investigated how carbon sources and electrode stimulation affect U(VI) reduction efficiency, product formation, microbial communities, and metabolic functions. U(VI) removal followed the order of carbon source: glucose > lactic acid > sodium acetate. Electro-stimulation markedly enhanced U(VI) reduction, especially under sodium acetate conditions with E_24h increased from 65.0% to 90.7% at 0.7 V, by promoting carbon sources utilization and accelerating the removal of competitive anions. Glucose and lactic acid promoted the formation of UO₂, while sodium acetate favored U₃O₈. Electro-stimulation facilitated the formation of compact uranium precipitates, enhancing recovery potential and minimizing reoxidation risk. Electrochemical analyses revealed that glucose and lactic acid exhibited superior electrochemical behavior compared to sodium acetate. Combined biostimulation enriched redox-active, electroactive, and EPS-secreting microbial taxa, along with functional genes related to U(VI) reduction, electron transfer, and carbon metabolism. Glucose and lactic acid imposed stronger selection on microbial and genetic structures than sodium acetate. Electro-stimulation promoted metabolic diversification, enhancing microbial resilience and functional redundancy. This study offers valuable insights into electrochemical enhancement of the biological treatment of uranium-bearing wastewater.