Biofixation of CO2 from a power plant through large-scale cultivation of Spirulina maxima

Abstract

Using microalgae for biological fixation of CO2 is an attractive option for limiting the amount of CO2 emissions from power plants. In this experiment, Spirulina maxima was successfully grown utilizing direct flue gas emitted from the Ratchaburi Electricity Generating Company Limited, Thailand. The aims of this study were to determine the optimal conditions for large-scale culturing of this alga for maximum biomass as well as CO2 abatement. The results showed that the carbon source of NaHCO3 can be reduced from standard Zarrouk medium of 16.8 down to 8 g/L, producing fresh and dry weight biomass yields of 206 and 21.57 kg, respectively, within 30 days of cultivation. The optimal initial pH was 9.0, thereby reducing the lag phase of algal growth and producing the best fresh weight yield. The natural light intensity (with CO2) prevented stressed and weakened the algal cells, resulting in extending the algal life and producing the highest yields of fresh and dry weight. The morphology of algal cells was examined following culturing at pH 9 and pH10.5. The algal cells produced at pH 9 had a helical shape of the trichome, a separate septum and thylakoids, and the vacuoles were distributed throughout the cell, while algal cells cultured in medium with an initial pH of 10.5 mostly had the straight form, with the septum and thylakoids being unclear. The maximum CO2 level used was 2.5 times base level of the CO2 (141.75 g CO2/h) produced the highest biomass of fresh and dry weights. The optimal culture for CO2 gas was the continuous culture system and using CO2 efficiently, which encouraged algal growth and produced higher biomass yields than those from the batch culture system. There was no significant difference in nutritional value terms for the protein and pigments contents between the algal biomass products in assay with and without CO2 Furthermore, there was no metal contamination in algal biomass. The results indicate that the use of waste CO2 from a power plant can be successfully used for large-scale Spirulina production.