TiO₂ Nano-photocatalyst-driven CO₂ Biofixation and Lipid Accumulation in Brackish Water Cyanobacteria for Sustainable Biodiesel Production

This study focused on the effect of CO2 concentration on cyanobacterial cultivation using BG-11 medium to enhance biomass and lipid productivity. Different cyanobacterial species isolated from brackish water were screened and identified using molecular characterisation. From the isolated cyanobacterial species, two rapidly growing species, Phormidium uncinatum and Oscillatoria salina were selected. Their biomass and lipid productivity were optimised by varying the CO2 concentration. These strains were subjected to tolerance tests by changing the conditions of the cyanobacterial growth medium, pH, CO2 concentration, and temperature. Biochemical parameters were also estimated. Oscillatoria salina exhibited the highest biomass production, reaching 956 ± 0.04 mg/L at a 15 % CO2 concentration. A high protein content of 25.23 ± 0.32% was found in P. uncinatum compared to O. salina, whereas O. salina showed higher lipid and biomass productivity than P. uncinatum. Furthermore, O. salina was utilised for the production of biodiesel using a nanophotocatalyst (TiO2). It was found to enhance the biodiesel up to 98%. The biodiesel was tested for fuel properties and compared with the ASTM Standards.