Design and Optimization of a Two-Stage Microalgae-Assisted Lipid Production

Applying microalgae is a valuable strategy for CO2 removal, wastewater treatment, and biofuel production leading to valuable biomass production. However, the major challenge of biodiesel production by microalgae is achieving high lipid content while maintaining high biomass productivity. To do so, optimizing microalgal cultivation conditions is necessary. A novel two-stage process for increasing lipid productivity employing Chlorella vulgaris was introduced. The effect of three parameters; CO2 concentration (0.04-15.00% (v/v)), aeration rate (50-150 mL min(-1)), and photobioreactor diameter (7-14 cm), on microalgae growth, CO2, and nutrient removal in the first cultivation stage was studied. The effect of disconnecting CO2 aeration on the lipid content was then studied in the second cultivation stage. The results suggest that the maximum cell concentration (1.73 g L-1) is related to cultivation in a 10.5 cm diameter photobioreactor fed with 7.52% (v/v) CO2 concentration and 100 mL min(-1) flow rate. The CO2 removal rate of the latter photobioreactor was 100% after 7 days. Although significantly affected the growth and lipid content, the studied parameters had no obvious effect on the nutrient removal. The highest lipid content was 32.85 wt.% and the lipid content of microalgae increased up to 61.24 wt.% by detaching CO2 aeration, a sign of the feasibility of using the proposed two-stage process for commercialization of biodiesel production by microalgae. The lipid produced by this strategy seems promising for biodiesel production according to American and European standards.

Automated summary

Applying microalgae is valuable for CO2 removal, wastewater treatment, and biofuel production. Optimizing microalgal cultivation conditions is crucial for increasing lipid productivity. A two-stage process using Chlorella vulgaris showed promising results for commercial biodiesel production by microalgae.