Co-cultivation of two freshwater microalgae species to improve biomass productivity and biodiesel production

This study aimed to investigate the symbiotic relationship of two freshwater microalgae species, Ettlia sp. and Chlorella sp. HS-2 to improve biomass productivity. The species were co-cultivated autotrophically under the inoculation ratios (Chlorella/Etdia) of 1:01, 1:04, 1:08, and 1:16. The performance of co-cultivation was compared with monoculture. It found that the co-cultivation returned higher biomass productivity (P < 0.05) than the monoculture under all inoculation ratios. The highest biomass productivity of 0.70 +/- 0.02 g L-1 day(-1) was achieved with an inoculation ratio of 1:08. The biomass productivity further increased to 0.74 +/- 0.06 g L-1 day(-1) by switching the cultivation mode to the mixotrophic condition. The biomass pro- ductivity of mixotrophic co-cultivation was higher P < 0.05 (0.74 +/- 0.06 g L-1 day(-1)) than the mixotrophic mono-culture of Ettlia (0.41 +/- 0.06 g L-1 day(-1)) but equal to mixotrophic mono-culture of Chlorella. FACS analysis revealed that the biomass obtained after co-cultivation contained 81% of Chlorella cells. In biochemical composition, co-cultivation (autotrophic) biomass contained protein 41%, carbohydrates 33%, lipids 11%, and pigments 2% of dry cell weight. The major fatty acids produced in the co-cultivation were C16-C18, which are favorable for biodiesel production. It is concluded that the co-cultivation is more favorable than the monoculture to obtain high biomass productivity and stable biomass composition.