High Cell Density Cultures of Microalgae Under Fed-batch and Continuous Growth

Abstract

Microalgae are pointed as one of the best alternatives for biofuels production due to high high lipid accumulation capacity. However, large scale production often results in low cell concentrations and low volumetric productivities. Heterotrophic cultures of microalgae can reach high biomass (over 100 g L^-1 DCW - dry cell weight) and lipid (over 50 % m/m) concentrations reducing downstream costs and increasing volumetric productivities. In this work fed-batch and continuous systems were evaluated for heterotrophic high cell density (> 10 g L^-1) cultures of microalgae Chlorella sp. for biomass and lipids production. In fed-batch growth a two stage feeding strategy (nitrogen sufficient and nitrogen limited) was employed. For continuous cultures different dilution rates were evaluated. Fed-batch culture achieved maximum biomass concentration and productivity of 58.8 g L^-1 DCW and 6.6 g L^-1 d^-1, respectively. Under nitrogen limitation an increase of 38 % in lipid content (from 21 to 29 % m/m) and 26 % in overall lipid productivity (from 1.25 to 1.58 g L^-1 d^-1) was observed. Continuous growth of microalgae started at a biomass concentration of 30 g L^-1 DCW. At the dilution rate of 0.02 h^-1 biomass concentration remained around 19 g · L^-1 DCW with a lipid content of 18 % under steady state conditions, resulting in biomass and lipid productivities of 9.1 and 1.5 g L^-1 d^-1, respectively. The results show that high biomass and lipid productivities can be attained in batch and continuous processes when high cell densities are applied.