Mixing and mass transfer in a pilot scale U-loop bioreactor.

Area of Science:

• Biotechnology and biochemical engineering
• Microbial fermentation technology
• Bioprocess engineering

Background:

• Efficient gas-liquid mass transfer is crucial for microbial processes like single-cell protein (SCP) production using Methylococcus capsulatus.
• Traditional bioreactors often struggle to handle large gas fractions while maintaining high mass transfer rates.

Purpose of the Study:

• To evaluate a novel forced flow U-loop fermenter for its ability to handle large gas fractions and achieve high gas-liquid mass transfer.
• To determine the effects of operating parameters on mixing time, mass transfer coefficients, and impeller power draw.

Main Methods:

• Characterization of mixing time and mass transfer coefficients in a 0.15 m³ U-loop fermenter.
• Investigation of impeller power draw under varying gas flow rates.
• Comparison with stirred tank reactors (STRs) and previous tubular loop reactors.

Main Results:

• Mixing time decreased and mass transfer increased with higher liquid flow rates and specific power input.
• The U-loop fermenter maintained high mass transfer even with large volumetric gas fractions.
• Significantly higher mass transfer coefficients were achieved compared to STRs and previous tubular loop reactors, especially with static mixers.

Conclusions:

• The novel U-loop fermenter is highly effective for processes requiring high gas-liquid mass transfer and handling large gas fractions, such as SCP production.
• The system offers superior performance over conventional bioreactors at modest flow rates.
• Static mixers further enhance the efficiency of the U-loop fermenter.