Abstract
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 pre-treated (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 featured 1H 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.
Highlights
Commercialization of algal-based processes for biofuels and co-products is constrained upstream during cultivation by low productivity, contamination by invasive species, unsustainable and inefficient supply of nutrients, inorganic carbon, and water, exposure to environmental factors, and limited available land acreage for inoculum and subsequent large-scale cultures
Results from Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and Py-gas chromatography (GC)-MS all suggest that the torrefaction temperatures of 280 ◦ C and 300 ◦ C were sufficient to alter physical properties of wheat straw
The 45× enlargement shows that the biomass began to lose its bound fibrous structure and highly irregularly shaped particles with similar diameters formed upon torrefaction
Summary
Commercialization of algal-based processes for biofuels and co-products is constrained upstream during cultivation by low productivity, contamination by invasive species, unsustainable and inefficient supply of nutrients (e.g., nitrogen, sulfur, and phosphorous), inorganic carbon, and water, exposure to environmental factors, and limited available land acreage for inoculum and subsequent large-scale cultures It is constrained downstream by costly and inefficient harvesting, cell disruption, product extraction, thermochemical conversion, hydrotreatment, and upgrading. The combination of high cell densities and extreme haloalkaline conditions in the second phototrophic stage could minimize residence time and limit contamination [2], facilitate auto-flocculation harvesting [3], efficiently supply inorganic carbon [4], and enhance neutral lipid accumulation [5]. This two-stage process can be further improved upon with sustainable supplies of organic carbon for the first stage and nitrogen and phosphorous nutrients for the second stage
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