Developing microporous fibrous-diaphragm aerator to decrease bubble generation diameter for improving microalgal growth with CO2 fixation in a raceway pond

•A fibrous-diaphragm aerator generates bubbles through pores of expanded diaphragm.•An installation angle of 22° resulted in the minimum bubble generation diameter.•Bubble generation diameter and time decreased by 60% and 50%.•Mixing time decreased by 22% and mass-transfer coefficient increased by 40%.•Microalgal biomass yield and photochemical efficiency increased by 38.5% and 80%. A novel microporous fibrous-diaphragm aerator (FDA) was proposed to generate pressurized gas with check valve to penetrate through millions of micropores (6–126 μm) of expanded fibrous diaphragm on internal support, thus decreasing bubble generation diameter and increasing bubble residence time for improving microalgal growth with CO2 fixation in a raceway pond. When installation angle of FDA internal support increased from 0° to 45°, bubble generation time and diameter first decreased (to valley bottoms of 4 ms and 0.45 mm at 22°) and then increased. Compared to traditional strip aerator, bubble generation time and diameter decreased by 50% and 60% through FDA with support installation angle of 22° and average pore diameter of 28 µm, while gas-solution mixing time decreased by 22% and mass transfer coefficient increased by 40%, leading to increased actual photochemical efficiency (by 80%) and increased biomass yield (by 38.5%) of Arthrospira cells with pure CO2 aeration through FDA.