Continuous H-B-E fermentation by Clostridium carboxidivorans: CO vs syngas

Area of Science:

• Biotechnology and Bioengineering
• Renewable Energy
• Microbial Fermentation

Background:

• Renewable carbon sources are crucial for reducing fossil fuel dependence.
• Syngas fermentation by bacteria like Clostridia offers a pathway to convert CO or CO2 + H2 into valuable chemicals and biofuels.
• Clostridium carboxidivorans is a key microorganism for syngas fermentation.

Purpose of the Study:

• To evaluate the performance of Clostridium carboxidivorans in a continuously operated stirred tank reactor.
• To assess acid and solvent production using pure CO or synthetic syngas at pH 5.6 under varying dilution rates.
• To understand the impact of substrate composition and operating conditions on fermentation outcomes.

Main Methods:

• Continuous fermentation of Clostridium carboxidivorans in a stirred tank reactor.
• Feeding pure CO or synthetic syngas at different dilution rates (0.034-0.25 h⁻¹).
• Monitoring cell growth, acid, and solvent (ethanol, butanol, hexanol) production.

Main Results:

• Fermentation pathways were similar for CO and syngas, with consistent growth and metabolite production at pH 5.6 across dilution rates.
• Wash-out occurred at a dilution rate of 0.25 h⁻¹ for both substrates.
• Ethanol was the primary solvent, with a shift towards butanol using CO and hexanol using syngas.
• Maximum cell concentration (0.5 gDM/L) achieved with pure CO at 0.05 h⁻¹.
• Highest total solvent productivity (60 mg/L*h) achieved with synthetic syngas at 0.17 h⁻¹.

Conclusions:

• Substrate composition and operating conditions significantly impact syngas fermentation efficiency.
• Clostridium carboxidivorans demonstrates robust performance in continuous culture for biofuel and chemical production.
• Optimized syngas fermentation is vital for sustainable energy and chemical manufacturing.