Dynamic behavior and transfer characteristics of CO2-enriched bubbles within Spirulina sp. suspension under various aeration conditions using the high-speed imaging technique

Abstract

The biological CO₂ fixation method through microalgae photosynthesis has received considerable attention to alleviate the trend of global warming. CO₂-enriched gas is generally aerated into the microalgae suspension in the form of bubbles through the gas distributors. Dynamic behavior and transfer characteristics of CO₂-enriched bubbles are crucial to microalgae cells growth and CO₂ bio-fixation. A visual experimental system based on the high-speed camera was constructed in this work to obtain the dynamic behavior and transfer characteristics of CO₂-enriched bubbles within Spirulina sp. suspension. CO₂-enriched bubbles movement and dissolution characteristics were comprehensively investigated under various CO₂ concentrations, gas distributor aperture size, aeration rates, and Spirulina sp. biomass densities. Experimental results indicate that the optimal CO₂ dissolution mass transfer and absorption rate were attained under the CO₂ concentration of 5 %, gas distributor aperture diameter of 10 μm, and aeration rate of 0.1–0.3 vvm. Moreover, as Spirulina sp. biomass density increased, the bubble average diameter decreased, and rising velocity slowed while the volumetric mass transfer coefficient and CO₂ absorption rate elevated. To summarize, this work may guide future efforts to enhance the photobioreactors (PBRs) performance from the perspective of aeration conditions optimization.