Comparison of Photofermentative Hydrogen Production in Cylindrical Photobioreactors Using Different Mixing Systems

Area of Science:

• Microbiology
• Biotechnology
• Renewable Energy

Background:

• Photosynthetic purple non-sulfur bacteria are promising for biological hydrogen production.
• Photobioreactor (PBR) design and mixing are critical for optimizing microbial H₂ generation.
• Scaling up H₂ production processes requires careful consideration of reactor parameters.

Purpose of the Study:

• To investigate the H₂ production capabilities of Rhodopseudomonas sp. in different photobioreactor volumes.
• To compare the effectiveness of two mixing methods (paddle vs. spiral rotor) in a larger PBR.
• To assess the light conversion efficiency (LCE) under various conditions and evaluate process scale-up.

Main Methods:

• Cultivation of Rhodopseudomonas sp. in 0.2 L and 4.0 L cylindrical photobioreactors.
• Comparison of H₂ production and LCE using a paddle rotor versus a spiral rotor in the 4.0 L PBR.
• Analysis of H₂ volume, production rate, productivity, and LCE for each tested condition.

Main Results:

• The 0.2 L PBR yielded 142.15 mL H₂ with 0.59% LCE.
• The 4.0 L PBR with a paddle rotor produced 806.05 mL H₂ (2.29 mL/h rate) and 0.58% LCE.
• The 4.0 L PBR with a spiral rotor achieved 1642 mL H₂ (2.87 mL/h rate) and a higher LCE of 0.72%.

Conclusions:

• The spiral rotor provided more uniform mixing, enhancing cell efficiency and LCE in the larger PBR.
• Successful scale-up of Rhodopseudomonas sp. photofermentation from 0.2 L to 4.0 L was demonstrated.
• Optimized mixing is crucial for efficient biological hydrogen production in scaled-up photobioreactors.