Acidogenic fermentation of the main substrates of food waste to produce volatile fatty acids

Food waste is ideal for producing energy and value-added chemicals (e.g., biohydrogen and volatile fatty acids (VFAs)) in biorefineries. The main food waste components are carbohydrates, proteins, and lipids. Three substrates (glucose, peptone, and glycerol, representing carbohydrates, proteins, and lipids, respectively) were acidogenically fermented in this study. For each substrate, we investigated fermentation type and VFAs produced. We used a stoichiometric approach to identify the metabolic pathways through which the substrates were converted. The maximum VFA concentrations for glucose, peptone, glycerol, and a mixture were 38.2, 32.2, 31.1, and 38.5 gCOD/L, respectively. Mixing the substrates increased VFA production, indicating that synergistic effects between microorganisms improved acidogenic fermentation. Different fermentation types occurred for different substrates. Butyric, acetic, and propionic acids were the main products for glucose, peptone, and glycerol, respectively. Glucose was metabolized through three pathways. The metabolism of glycerol was similar to glucose through the “glycerol-pyruvate-VFA” pathway.