Biorefinery Processing of Waste to Supply Cost-Effective and Sustainable Inputs for Two-Stage Microalgal Cultivation

Overcoming obstacles to commercialization of algal-based processes for biofuels and co-products requires not just piecemeal incremental improvements, but rather a comprehensive and fundamental re-consideration starting with the selected algae and its associated cultivation, harvesting, biomass conversion, and refinement. A novel two-stage process designed to address challenges of mass outdoor microalgal cultivation for biofuels and co-products was previously demonstrated using an oleaginous, haloalkaline-tolerant, and multi-trophic green Chlorella vulgaris. ALP2 from a soda lake. This involved cultivating the microalgae in a fermenter heterotrophically or photobioreactor mixotrophically (first-stage) to rapidly obtain high cell densities and inoculate an open-pond phototrophic culture (second-stage) featuring high levels of NaHCO₃, pH, and salinity. An improved two-stage cultivation that instead sustainably used as more cheap and sustainable inputs the organic carbon, nitrogen, and phosphorous from fractionation of waste was here demonstrated in a small-scale biorefinery process. The first cultivation stage consisted of two simultaneous batch flask cultures featuring (1) mixotrophic cell productivity of 7.25 × 10⁷ cells mL⁻¹ day⁻¹ on BG-11₀ medium supplemented with 1.587 g L⁻¹ urea and an enzymatic hydrolysate of pretreated (torrefaction + grinding + ozonolysis + soaking ammonia) wheat-straw that corresponded to 10 g L⁻¹ glucose, and (2) mixotrophic cell productivity of 2.25 × 10⁷ cells mL⁻¹ day⁻¹ on BG-11₀ medium supplemented with 1.587 g L⁻¹ urea and a purified and de-toxified condensate of pre-treated (torrefaction + grinding) wheat straw that corresponded to 0.350 g L⁻¹ of potassium acetate. The second cultivation stage featured¹ H NMR-determined phototrophic lipid productivity of 0.045 g triacylglycerides (TAG) L⁻¹ day⁻¹ on BG-11₀ medium supplemented with 16.8 g L⁻¹ NaHCO₃ and fed batch-added 22% (v/v) anaerobically digested food waste effluent at HCl-mediated pH 9.