Improving hydrogen production by pH adjustment in pressurized gas fermentation

Area of Science:

• Biotechnology
• Chemical Engineering
• Microbiology

Background:

• Gas fermentation uses syngas from biomass or waste as feedstock.
• Bubble column reactors enhance gas-liquid mass transfer and reduce energy consumption.
• Thermococcus onnurineus is a hydrogenic CO-oxidizer relevant for gas fermentation.

Purpose of the Study:

• To design and evaluate a bubble column reactor for pressurized gas fermentation.
• To optimize hydrogen (H2) production by Thermococcus onnurineus.
• To assess the energy-saving potential of bubble column reactors in gas fermentation.

Main Methods:

• Culturing Thermococcus onnurineus under ambient and pressurized conditions.
• Utilizing a syngas mixture (60% CO, 40% N2) as feedstock.
• Monitoring and adjusting pH to optimize H2 productivity.
• Comparing H2 productivity with previously reported values from continuous stirred tank reactors.

Main Results:

• Maximum H2 productivity of 363 mmol/l/h was achieved at ambient pressure without pH control.
• Applying pressure led to a pH decline, likely due to increased CO2 solubility.
• pH control increased H2 productivity to 450 mmol/l/h, comparable to continuous stirred tank reactors.
• Bubble column reactors show potential for energy savings in gas fermentation.

Conclusions:

• Pressurized bubble column reactors can enhance H2 productivity in gas fermentation.
• pH control is crucial for optimizing microbial performance under pressure.
• This approach offers energy-saving potential for industrial gas fermentation processes.
• Findings are applicable to other gas fermentation processes involving CO2.