Date Published: October 10, 2017
Publisher: Springer Berlin Heidelberg
Author(s): Hongwu Cui, Fanping Meng, Feng Li, Yuejie Wang, Weiyan Duan, Yichen Lin.
This study proposes a two-stage mixotrophic process for cultivating Chlorella vulgaris. Heterotrophic growth is the dominant step in Phase I (to increase microalgal biomass) and photoautotrophic growth occurs in Phase II (to improve biomass concentration and lipid production). The results show that the addition of the low-cost antioxidant sodium erythorbate (8 g L−1) significantly accelerates the growth of microalgae in the first stage with air aeration. Furthermore, a higher CO2 fixation rate was obtained in the second stage (at least 344.32 mg CO2 L−1 day−1) with 10% CO2 aeration. This approximately corresponds to an increase of 177% over simple photoautotrophic cultivation with 10% CO2 aeration during the whole period. The two-stage cultivation strategy achieved a maximum C. vulgaris biomass concentration of 3.45 g L−1 and lipid productivity of 43.70 mg L−1 day−1, which are 1.85 and 1.64 times those arising due to simple photoautotrophy, respectively. Moreover, an analysis of the product’s fatty acid profile indicates that C. vulgaris might be an ideal candidate for two-stage mixotrophic cultivation of a renewable biomass for use in biodiesel applications. Another interesting point to note from the study is that it is an insufficiency of N and CO2 that probably limits the further growth of C. vulgaris.
The rapid development of human society and the inexpedient consumption of fossil fuels have caused an energy crisis. At the same time, huge amounts of greenhouse gases have been emitted into the atmosphere, which have induced unexpected climate changes and global warming. Among these greenhouse gases, carbon dioxide (CO2) is the primary contributor to global warming, accounting for 52% (Wilbanks and Fernandez 2014). On June 5, 2017, the global monthly mean CO2 concentration reached 406.05 ppm, which is much higher than the 280 ppm level encountered before the Industrial Revolution (ESRL 2017). The development of cost-effective technologies for achieving CO2 fixation is therefore one of the major challenges that we are faced with today (Kaiwan-arporn et al. 2012).
Mixotrophic cultivation is an attractive way of enhancing the concentration of algal biomasses (Yen and Chang 2013) and mode by which the microalgae can drive both photoautotrophy and heterotrophy and utilize both inorganic and organic carbon sources (Kang et al. 2004). In this study, a two-stage method of mixotrophic cultivation of C. vulgaris has been treated in detail. Phase I was used to improve the biomass concentration of the microalgae and Phase II to enhance the CO2 bio-fixation rate and lipid productivity.