H2 production potential in thermophilic mixed fermentation

Area of Science:

• Biotechnology and Bioengineering
• Microbiology
• Renewable Energy

Background:

• Dark fermentative hydrogen (H2) production is a promising bioenergy technology.
• Optimizing fermentation conditions, particularly pH, is crucial for maximizing H2 yields.
• Thermophilic mixed fermentation using diverse inocula presents unique challenges and opportunities.

Purpose of the Study:

• To investigate the effect of pH on dark fermentative H2 production at 55°C.
• To compare H2 yields using three different inocula: compost (G, H) and activated sludge (A).
• To identify optimal pH ranges for stable H2 production via specific fermentation pathways.

Main Methods:

• Sequential batch experiments were conducted using glucose (2 g/L) as substrate.
• pH was controlled at 5, 5.5, and 6 across experiments.
• Inocula included windrow yard waste compost (G), anaerobic organic waste compost (H), and activated sludge (A).

Main Results:

• Highest molar H2 yields were 1.7 (pH 5, G & H) and 1.6 (pH 5.5, A).
• Lactate fermentation caused significant drops in H2 yield in subsequent runs.
• At pH 5.5, stable H2 yields (~1.1) were observed with G via acetate-ethanol fermentation, with a shift from Clostridia to Thermoanaerobacterium species.

Conclusions:

• pH control between 5 and 5.5 is essential for stable H2 yield via acetate-butyrate fermentation using compost inocula (G, H) at 55°C.
• Microbial community shifts, indicated by the prevalence of Thermoanaerobacterium species at pH 5.5-6, influence fermentation pathways and H2 production.
• This study provides critical insights into optimizing thermophilic mixed fermentation for enhanced H2 generation.