Optimizing the gas distributor based on CO2 bubble dynamic behaviors to improve microalgal biomass production in an air-lift photo-bioreactor

Abstract

Dynamic behavior of bubbles would significantly affect CO2 mass transfer and may cause microalgae cells uneven distribution due to the bubble carrying effect. To improve microalgae growth, the gas distributor and aeration conditions was optimized according to the bubble rising behavior. The CO2 bubble rising trajectory is similar to a Zigzag. The amplitude and wavelength of the Zigzag, which reflected the influenced zone of microalgae suspension in horizontal direction and disturbance intensity on culture, respectively, was controlled by the structure of gas distributor and aeration conditions. An optimized round gas distributor that full of holes with an inner diameter of 0.5mm and spacing of 1.5mm was designed. When cultivated with the optimized gas distributor aerating 5% CO2 gas at 0.250vvm, the maximum biomass concentration of Chlorella pyrenoidosa achieved 2.88gL−1, increased by 83.44% compared to that of 1.57gL−1cultivated with the commercial micro-bubbles aerator.