CO2 biofixation at microalgae photobioreactors: hydrodynamics and mass transfer study

Carbon dioxide production due to fossil fuels and their effects on global warming has prompted researchers to find ways to reduce and fix it. There are various biological and chemical methods to remove these contaminants. Using microalgae is one of the leading methods to absorbing carbon dioxide. During this process, microalgae absorb carbon dioxide in photobioreactors and convert it into biomass eventually. This study investigated bubble size, gas velocity, and photobioreactor structure as effective parameters on CO2 fixation for removing carbon dioxide by microalgae. Increasing CO2 concentration is inversely related to bubble growth, and it is due to the concentration gradient between the bubble and the microalgae suspension. Also, by examining the dimensions of the photobioreactor, we can obtain information about the dynamics of the bubble. The dimensions of the photobioreactor and the operating conditions of the process have an interaction. For example, whatever the H/D ratio is high, the gas velocity is more significant on bubble size. The result of examining the effect of bubble velocity on the volumetric mass transfer coefficient shows that the concentration of liquid and gas contact decreases with increasing bubble velocity and vice versa. Also, when the gas flow is higher, the bubbles grow faster and the contact time is shorter, and bubbles tend to grow in the vertical direction. To complete the previous research in this study, which focuses on mass transfer in the process of biological absorption of carbon dioxide, the bubble behavior of the suspension in microalgae is investigated. [GRAPHICS] .