Hydrogen Production via Dual-Stage Biofilm Reactors: A Modular Theoretical System Combining Dark Fermentation, Photofermentation, and CO₂ Sequestration

This paper presents a modular, dual-stage biofilm reactor for enhanced hydrogen production, integrating Clostridium butyricum for dark fermentation and Rhodobacter sphaeroides for photofermentation. By transitioning from suspended-cell cultures to surface-anchored biofilms, the system achieves improved microbial retention, greater gas yield, and reduced energy input. Hydrogen output exceeds 1010 liters per day per matched unit (1 m² Clostridium + 3.7 m² Rhodobacter), supported by real-time sensor feedback and autonomous mist-based substrate delivery.To enable continuous operation, a solvent-based liquid-liquid extraction module—termed the Continuous VFA Extraction Reactor (CVER)—isolates VFAs from residual glucose and reintroduces them into the photofermentation stage via a back-extracted aqueous stream. This decouples microbial pacing between stages and preserves substrate integrity.Carbon neutrality is achieved through a high-efficiency sugarcane-based CO₂ fixation loop, capable of absorbing all system-generated emissions within a <1 m² footprint. Economic modeling estimates a capital efficiency of ~$1.97 per kg H₂ produced, with minimal operating cost and strong scalability.The result is a compact, regenerative platform built for autonomous hydrogen production in research labs, pilot facilities, and future decentralized energy systems.