Multiple synergistic benefits of selective fermentation of Scenedesmus biomass for fuel recovery via wet-biomass extraction

Selective fermentation (SF), a novel alternative for microalgae-derived biofuel, ferments carbohydrates and proteins in microalgae biomass to volatile fatty acids (VFAs), which makes it easy to extract the lipid with low-toxicity solvents. A further advantage of SF is that the lipids are biohydrogenated to more valuable fuel precursors. This work evaluated SF using semi-continuous studies at pH values of 5 and 7 and with solids retention times (SRTs) of 2 to 15 days. SRT > 2 day enhanced VFA recovery from the non-lipid fractions by 4-fold (vs feed biomass), conserved the lipids, increased lipid wet-extraction (lipids assayed as fatty acid methyl esters, FAME) by at least 6900-fold (vs feed biomass), and shifted the FAME profile toward more saturated fatty acids through biohydrogenation. The performance benefits were accompanied by selective enrichment of biohydrogenating strains, e.g., Prevotella and Porphyromonodaceae, along with other fermenting bacteria that generate VFAs and H₂, e.g., Veillonellaceae. SF with a 5-day SRT had greater lipid wet extraction, compared to 2-day SRT, due to increased cell disruption and solvent permeability. By integrating multiple downstream processes into one step, SF offers important advantages for sustainable biofuel production from microalgae.