Effective biogas upgrading and production of biodiesel feedstocks by strategic cultivation of oleaginous microalgae

This study has shown the strategies to upgrade biogas and produce lipids as biodiesel feedstocks by cultivation of oleaginous microalgae. Three important growth factors for microalgae including light intensity, nitrogen source and CO2 supply, were strategically stepwise-increased during cultivation. The stepwise-increasing of CO2 supply was suitable for cell growth and lipid production while the stepwise-increasing of light intensity was more suitable for CO2 removal efficiency. Among the strategies attempted, the simultaneous stepwise-increasing of all three growth factors most effectively enhanced the performance of microalgae. Through this strategy, >96% of CO2 was continuously removed from biogas and the CH4 content in the purified biogas was >98%. This process also generated microalgal biomass at 4.40 ± 0.04 g L−1 with a lipid content of 34.10 ± 2.26%. The CO2 removal rate by this process was as high as 6.50 ± 0.21 g-CO2 day−1 per 1 L microalgal culture. The microalgal lipids contained long chain fatty acids (C16C18) >94% and their prospect fuel properties indicated their suitable use as biodiesel feedstocks. The integrated processes and strategies in this study would contribute greatly to the production of biogas and biodiesel feedstocks.