Investigating algal CO2 capture through screening of Qatari desert microalgae & cyanobacteria strains

Abstract

CO2 fixation by phototrophic microalgae has been addressed as a possible global carbon emissions reducer, whilst simultaneously producing useful products. Especially in Qatar, the prospect of using microalgae for CO2 abatement is promising: high solar irradiance, large areas of non-arable land, and large amounts of CO2 emissions make it seemingly the ideal place for algae cultivation. In order to promote high biomass productivities, and subsequent CO2 uptake rates, effective CO2 supply to the cultivation system is of high importance. However, the low solubility of CO2 in water, as well as the limiting tolerance of microalgae to increased CO2 concentrations, results in low efficiency of CO2 capture by microalgal production systems. In order to overcome these hurdles, this research focused on selecting local desert microalgae strains with high tolerance to increased CO2 levels, and developing growth media in order to increase the solubility of CO2. Forty-five locally isolated marine microalgae strains were screened for growth under increased CO2 concentrations, ranging from 0.04% to 30% (v/v). A number of different trends in CO2 tolerance could be identified from the results; a number of strains showed a clear inhibition of growth with CO2 concentrations of 5% and higher, whilst others showed increasing growth rates for increasing CO2 concentrations up to 30%. The trend in growth rate suggests that even higher CO2 concentration could be applied without growth-limiting effects, and could even stimulate higher growth-rates. In order to further increase the productivity of high CO2-tolerant strains, as well as to investigate the effects of pH on the CO2 tolerance of low-tolerant strains, various strains were cultivated in alkaline media and high CO2 concentrations. Besides leading to an increased solubility of CO2 in the culture media, increasing the pH is thought to balance the acidification effect of CO2 - possibly leading to higher CO2 tolerances. Overall, applying these strains and media adaptations for large-scale applications is expected to increase the CO2 transfer efficiency to the culture, resulting in decreased operational costs and higher overall productivities.