Highly selective acetate production from wine lees through acidogenic fermentation

Among winery wastes wine lees have a high, unexplored potential for the production of carboxylic acids and more particularly acetate. In fact, they have a high ethanol and low carbohydrate content which can make thermodynamically feasible the oxidation of ethanol to acetate. In this study, the potential of wine lees for anaerobic acetate production was assessed in batch conditions, 37 °C and pH 5.5. White wine lees (WWL) and red wine lees (RWL) were fermented with and without inoculum, and RWL were also co-fermented with waste activated sludge at 20, 40, 70 and 100 gCOD/L. Endogenous microbiome had the same fermentation performances than the external inoculum in WWL, while it led to almost no carboxylates production in RWL, where the community was dominated by the H₂-producer Klebsiella (81.6%). Overall, acetate always represented the majority of carboxylates (58-72% on COD basis). H₂ production was low (0.31-6.97 mL H₂/g bCOD_in), thus enabling anaerobic ethanol oxidation to acetate (ΔG = -26.6/-7.4 kJ/mol). In co-fermentation, at 70 and 100 gCOD/L caproate (10.0-16.0%) and heptanoate (1.6-5.4%) appeared, alongside a microbiome enriched in lactate-producers (up to 24.5%). Overall, the high acetate selectivity obtained is promising for biorefinery process coupling.