Sequential Extraction of Carbohydrates and Lipids from Chlorella vulgaris Using Combined Physical and Chemical Pre-Treatments

A key focus of microalgae-based fuels/chemicals research and development has been on the lipids that many strains generate, but recent studies show that solely recovering these lipids may not be cost competitive with fossil-derived processes. However, if the carbohydrates can also be recovered and ultimately converted into useful chemical intermediates, this may improve the economics for microalgae-based sustainable product technologies. In the present work, physical and chemical pre-treatments were performed on the Chlorella vulgaris microalgae strain to recover the carbohydrates from the biomass primarily in the form of glucose and galactose. The effects of temperature, acid concentration, microalgae solid-to-liquid loading, and hydrolysis time on carbohydrate hydrolysis and recovery was explored to identify optimum conditions. The highest recovery of total carbohydrates, 90 ± 1.1 wt% at 95% confidence which represents 40 wt% of the initial biomass, was obtained using temperature-assisted weak-acid extraction. Sequential extraction of carbohydrates and lipids was then explored. The highest recovery of total lipids was 71 ± 1.8 wt%, which represents 22 ± 0.9 wt% of the initial biomass. The sequential extraction of carbohydrates followed by lipids resulted in an overall recovery of 60 ± 1.6 wt% of the initial biomass, which is higher than current single product recovery strategies. These results suggest that adding carbohydrate recovery may be a viable strategy for overcoming a major economic hurdle to microalgae-derived chemical and fuel production by significantly increasing the yield of usable materials from microalgae biomass.