Development of a gas-permeable bag photobioreactor for energy-efficient oxygen removal from algal culture

Closed photobioreactors are ideal for the production of high-purity and high-value microalgal and cyanobacterial products. However, dissolved oxygen accumulation in closed reactors is detrimental to the growth. Conventional aeration for oxygen removal comprises up to 40% of the total culture cost, and energy-efficient dissolved oxygen removal is demanded. In this study, a novel gas-permeable bag photobioreactor was developed by the incorporation of a gas-permeable film. A hydrophobic microporous film was the most effective for both oxygen permeability and cost compared to silicone or fluororesin. The microporous film was placed on the backside of the reactor as an irradiation reflector. In a culture of Euhalothece sp., less than half of the steady-state dissolved oxygen concentration was demonstrated in the gas-permeable reactor than a non-permeable reactor. The gas-permeable reactor exhibited an oxygen transfer coefficient of 0.084 min(-1) under continuous mixing, which is high enough to maintain approximately 300% dissolved oxygen concentration with 58 mg L-1 h(-1) biomass productivity without aeration (equivalent to 1.4 g L-1 d(-1) under 24-h light). The estimated energy requirement for the gas-permeable reactor can be less than 1% of the aerated reactor of the same size. These results suggested the effectiveness of the gas-permeable reactor for energy-efficient algal mass culture.

Automated summary

A novel gas-permeable bag photobioreactor was developed to efficiently eliminate oxygen and enable energy-efficient large-scale cultivation of microalgae.