To address the challenge of massive emissions of greenhouse gas carbon dioxide (CO₂), carbon biosequestration represented by microalgae CO₂ biofixation gets much attention due to its environmental friendliness and sustainability in recent years. The carbon fixation efficiency of microalgae depends on the mass transfer of CO₂ (from flue gas) to microalgae liquid medium largely, however, there is rare literature focusing on factors which could influence the absorption of CO₂ in microlagae culture. 

In order to elucidate the mass transfer of CO₂ in microalgae medium, the Micoralga Biotechnology Research Group led by Prof. LI Yeguang from Wuhan Botanical Garden explored the effects of three main physicochemical factors, which were carbon concentration, pH and bubbling depth, on CO₂ absorption in the process of microalgae culture for CO₂ sequestration. 

Results revealed that the absorption of supplied CO₂ could be improved significantly with increasing CO₂ bubbling depth from 14.5 to 80 cm, to yield remarkable benefits for CO₂ sequestration in microalgae mass culture.  

In the range of pH10.6–7.0, when carbon concentrations were below 9.52 mmol/L, pH had no significant effect on CO₂ absorption ratio (P>0.05), while carbon concentration was above 9.52 mmol/L, pH affected CO₂ absorption ratio significantly (P<0.05).  

In microalgae culture, maintaining the culture pH above the equilibrium pH can avoid CO₂ escaping from the solution. 

This study enhanced the understanding on effects of carbon concentration, pH, and bubbling depth on CO₂ absorption in the process of microalgae culture for CO₂ sequestration, and provided a conclusion with wide adaptability and guiding significance for CO₂ fixation by different microalgae further more. 

This work was funded by the National Natural Science Foundation of China. Relevant research results have been published in Environmental Science and Pollution Research entitled "Effects of carbon concentration, pH, and bubbling depth on carbon dioxide absorption ratio in microalgae medium". 

Regression curves of CO₂ absorption ratio responding to bubbling depth and different carbon concentrations (Image by WAMG Zhongjie)