Developing a CO2 bicarbonation absorber for promoting microalgal growth rates with an improved photosynthesis pathway

In order to solve the problems of the short residence time and low utilization efficiency of carbon dioxide (CO 2 ) gas added directly to a raceway pond, a CO 2 bicarbonation absorber (CBA) was proposed to efficiently convert CO 2 gas and sodium carbonate (Na 2 CO 3 ) solution to sodium bicarbonate (NaHCO 3 ), which was dissolved easily in the culture medium and left to promote the microalgal growth rate. The CO 2 gas reacted with the Na 2 CO 3 solution (initial concentration = 200 mM L −1 and volume ratio in CBA = 60%) for 90 min at 0.3 MPa to give the optimized molar proportion (92%) of NaHCO 3 product in total inorganic carbon and increase the microalgal growth rate by 5.0 times. Quantitative label-free protein analysis showed that the expression levels of the photosystem II (PSII) reaction centre protein ( PsbH ) and PSII cytochrome ( PsbV2 ) in the photosynthesis pathway increased by 4.8 and 3.4 times, respectively, while that of the RuBisCO enzyme ( rbcL ) in the carbon fixation pathway increased by 3.5 times in Arthrospira platensis cells cultivated with the NaHCO 3 product in the CBA at 0.3 MPa. To increase the residence time of CO 2 gas added directly to the raceway pond, a CO 2 bicarbonation absorber was proposed to convert CO 2 gas and Na 2 CO 3 to NaHCO 3 , which was dissolved easily in the solution and left to promote the biomass growth rate.