Enhancing direct air carbon capture into microalgae: A membrane sparger design with carbonic anhydrase integration

In this study, a novel membrane gas sparger incorporating a carbonic anhydrase (CA) coated electrospun polysulfone membrane is proposed, to enhance the CO₂ sequestration rate from atmospheric air into photobioreactors and open raceway ponds. Firstly, an electrospinning technique is employed to fabricate a strong and permeable polysulfone membrane. Then, multiple layers of CA are coated onto the polysulfone membrane through a layer-by-layer method and molecular dynamics simulation is adopted to verify the CA coating. To fortify the mechanical strength, the membrane is integrated within a metal mesh module as an air sparger. Finally, the microalgae growth is tested within a laboratory scale raceway pond. The CA coating more than doubles the uptake of CO₂ by the algae relative to air sparging through an open tube, and by 70 % compared to a commercial air stone, with activity retained for 35 days. Further, the resistance to air flow is less than that of a commercial air stone. Importantly, the membrane can readily be replaced within the metal mesh module for minimal cost, providing a facile approach to maintaining high direct air capture rates into outdoor algal ponds over long periods.