CO2 capture using limestone for cultivation of the freshwater microalga Chlorella sorokiniana PAZ and the cyanobacterium Arthrospira sp. VSJ

[Display omitted] •A practical approach for CO2 mitigation without a huge capital investment.•Strains isolated from saline soda lake of Lonar were explored.•An insight into enhanced chemo-photosynthetic CO2 sequestration.•Exposure to UVA radiation enhanced carbon dioxide mitigation and growth yield of microalgae. The present study reports a process wherein CO2 is captured in the form of bicarbonates using calcium oxide and photosynthetically fixed into biomass. Microalgal cultures viz. Chlorella sorokiniana PAZ and Arthrospira sp. VSJ were grown in the medium containing bicarbonates. The rate of bicarbonate utilization by C. sorokiniana PAZ was higher when CO2 trapped in the presence of 2.67mM calcium oxide than in the presence of 10mM sodium hydroxide and with direct addition of 10mM sodium bicarbonate. For Arthrospira sp. VSJ the bicarbonate utilization was 92.37%, 88.34% and 59.23% for the medium containing CaO, NaOH and NaHCO3, respectively. Illumination of photosynthetically active radiation (PAR)+ultraviolet A radiation (UVA) enhanced the yield of C. sorokiniana PAZ and Arthrospira sp. VSJ by 1.3 and 1.8 folds, respectively. FTIR analysis revealed elevation in the biosynthesis of specific metabolites in response to the UVA exposure.