Growing Chlorella vulgaris on mixed wastewaters for biodiesel feedstock production and nutrient removal

BACKGROUND: Large water footprint and nutrients demand are two of the major issues during microalgae cultivation. In this study, anaerobically digested swine manure was mixed with centrate at different minimal dilution multiples (2×, 3×, 4×, 6× and 8×), which was used as media to cultivate Chlorella vulgaris (UTEX 2714) for reducing the production cost of algae cultivation and balancing the nutrient profiles of culture media. RESULTS: Chlorella vulgaris (UTEX 2714) grew well on the mixed wastewaters with a biomass productivity of 132.2 to 440.3 mg L⁻¹ d⁻¹. Nutrients in the mixed wastewaters were removed effectively by this alga, and the removal efficiencies of ammonium (NH₄ ⁺-N), total nitrogen (TN), chemical oxygen demand (COD) and total phosphorus (TP) ranged from 98.3, 46.9, 30.2 and 21.8 to 99.3, 71.4, 42.2 and 80.4%, respectively. Additionally, chemical compositions, such as pigments, carbohydrate, protein and lipids, in this alga varied with the change of dilution multiple due to the different nutrient profiles of culture media. Predicted properties of biodiesel from the oils of this alga satisfied the specifications of biodiesel, ASTM D6751-08 and EN 14214 standards. CONCLUSION: Biomass of C. vulgaris (UTEX 2714) can be used as a good-quality feedstock for biodiesel production when grown on mixed wastewaters. This novel integration of using mixed wastewaters to cultivate microalgae would be an effective way to reduce the production cost of algal biomass.