Electro-selective fermentation enhances lipid extraction and biohydrogenation of Scenedesmus acutus biomass

Extraction of lipids from microalgae has been economically and energy prohibitive due to the requirement for pretreatment, and the use of toxic solvents in the process has exacerbated the problem. Selective Fermentation (SF) helps overcome these problems by selectively biodegrading carbohydrate and protein, while conserving lipids. We introduced and evaluated electro-selective fermentation (ESF), in which anode respiration in a microbial electrolysis cell (MEC) altered fermentation performance in ways that enhanced lipid wet-extraction. Using Scenedesmus acutus biomass, we evaluated ESF and compared it to SF. Compared to SF, ESF increased protein degradation by 4-fold, even though anode respiration represented <1% of the total electron input. Although ESF led to greater loss of total lipids, it improved lipid wet-extraction efficiency using a non-toxic solvent by 3-fold. Lipid loss was due to β-oxidation linked to biohydrogenation, and the long-chain fatty acid (LCFA) profile shifted from C18:1 to C16:0 and C14:0. Microbial community analysis emphasized the presence of protein-degrading bacteria and biohydrogenators in the ESF suspension and anode-respiring bacteria (ARB) on the ESF anode. Overall, ESF improved lipid extractability and biofuel quality despite current being a small component in the overall COD balance.