Regulatory Mechanisms of Electron Supply Modes for Acetate Production in Microbial Electrosynthesis System

Abstract

Electrode electrons and hydrogen, as two main forms of electrons in the microbial electrosynthesis (MES) system, were used for product synthesis through direct or indirect electron transfer. However, their effects and regulatory mechanisms for acetate synthesis are unknown. In this study, different applied voltages and hydrogen partial pressures were applied to investigate acetate accumulation and the regulatory mechanisms of two electron supply modes. The results showed that the increased applied voltage promoted the rapid enrichment of acetogens (1.20 × 10⁹ ± 1.50 × 10⁸ copies·cm^–3) in biofilm and the electrochemical performance of the biocathode, demonstrating the direct regulation of the biofilm microbes by applied voltage. Whereas, the increased hydrogen partial pressure significantly increased the acetogen abundance (2.59 × 10⁹ ± 1.30 × 10⁸ copies·mL^–1) in suspension, resulting in the optimal acetate production performance (1117.63 mg/L) and Coulombic efficiency (71.06%) at P_H2-1.00, indicating the regulation on the planktonic microbes by hydrogen partial pressure. Moreover, either mode decreased the relative abundance of unclassified_f_Rhodocyclaceae and increased the relative abundance of Acetoanaerobium. The results clarified the interactive regulatory mechanisms of biofilm and planktonic microbes by applied voltage and hydrogen partial pressure in the MES system. This study provides novel insights into understanding direct and indirect electron transfer for product synthesis, potentially advancing MES system design and performance.