Optimizing dark fermentation for hydrogen production: lessons from Thermoactinomyces mirandus

Area of Science:

• Biotechnology and Bioengineering
• Renewable Energy
• Microbial Physiology

Background:

• Biological hydrogen (H2) production via dark fermentation (DF) is a promising renewable energy strategy.
• Process efficiency in DF is often limited by strain-specific characteristics and suboptimal operating conditions.

Purpose of the Study:

• To characterize the fermentation physiology of the thermophilic anaerobe Thermoactinomyces mirandus.
• To optimize small-scale H2 production by T. mirandus through screening various conditions.

Main Methods:

• Batch cultivations were performed at 52 °C to screen carbon sources, nitrogen sources, C/N ratios, and inhibitory factors.
• Small-scale, closed-flask pH control was implemented and compared to uncontrolled conditions.
• Fermentation product profiles and H2 production rates were analyzed under different conditions.

Main Results:

• Yeast extract as a nitrogen source and fructose, xylose, or lactose as carbon sources supported the highest H2 yields.
• Implementing pH control at pH 7.2 increased H2 yield 4.2-fold and improved lactose consumption to 99.4%.
• An optimal pH range of 7.5-8.0 was identified for maximum H2 production rate (VHPR), and higher lactose loads increased VHPR but decreased yield.

Conclusions:

• pH control is a critical factor for significantly enhancing H2 yield in T. mirandus fermentation.
• Quantitative operating windows for T. mirandus were defined, including optimal pH and substrate loading.
• The study provides a transferable workflow for optimizing DF processes and mitigating inhibitory factors.