Potential of Redox Control in Microbial Fermentation: A Mini Review

Abstract

The manipulation of oxidation–reduction potential (ORP) has emerged as a pivotal strategy for optimizing microbial activity and hydrogen yields in anaerobic fermentation processes. This review systematically analyzes open-access research articles published between 2020 and 2025 that investigate the role of ORP in dark fermentation and biohydrogen production. By focusing on 16S rRNA-based microbial profiling, metabolic outcomes, and ORP-controlled operational strategies, we highlight how specific ORP levels selectively enrich hydrogen-producing genera such as Clostridium and suppress less efficient or competing microbes like Veillonellaceae or Enterobacteriaceae. Optimal ORP ranges (e.g., –284 to –322 mV) were consistently associated with increased H₂ productivity (30–70%) and metabolic shifts favoring acetate and butyrate pathways. Chemical agents such as ferricyanide and H₂O₂ were frequently employed to modulate ORP, influencing microbial redox balance and community stability. Additionally, the review discusses the mechanisms linking redox state to electron flow, enzyme activation, and microbial dominance. Despite recent advances, significant research gaps remain in scaling ORP control strategies, standardizing ORP setpoints for various substrates, and integrating real-time ORP monitoring in bioreactors. We conclude that ORP is not merely a passive indicator but a controllable parameter that can guide microbial ecology and improve fermentative hydrogen production. This review provides a foundation for future research on coupling redox management with microbial engineering to design more efficient, resilient, and predictable biohydrogen systems.