Study of Microalgae Biofixation with Bacteria Carbonic Anhydrase for Carbon Capture and Utilization

Climate change has been significantly affecting human activities due to the accumulation of greenhouse gases, such as carbon dioxide. Biofixation of carbon dioxide (CO2) has been investigated to reduce the atmospheric CO2 level and slow the rapid increase in the global temperature. Carbon capture and utilization (CCU) can be performed by either physio-chemical or biological methods. The latter takes place in ambient temperature and mild conditions, such that there is no need for high pressure and high energy consumption nor hazardous chemicals. Biofixation by microalgae has been utilized to capture CO2 and the microalgae biomass collected after the process can be further utilized in renewable biofuel generation. On the other hand, microbial enzymes, such as carbonic anhydrase (CA), have been investigated to speed up the whole biofixation process by increasing the conversion rate of CO2 into bicarbonate (HCO3−) in a culture medium and the latter can be readily used by microalgae to increase CO2 removal. In this study, in the presence of 20% CO2 (v/v) gas in air and 5 mL CA enzyme extract (0.5 mg mL−1 protein), we can significantly increase the biofixation rate using marine green microalgae, Tetraselmis sp. Results showed that the biofixation rate can be increased from 0.64 g L−1 day−1 (no CA and at 0.04% CO2) to 4.26 g L−1 day−1. The effects of different experimental conditions such as pH, nutrient levels and working CO2 concentration levels on Tetraselmis sp. growth and CO2 biofixation (CO2 removal) rate have been investigated. This study demonstrates a new alternative approach for effective carbon capture and utilization (CCU) using microalgae which can be applied to achieve the goal of carbon neutrality.