Optimization of hydrogen production from food waste using anaerobic mixed cultures pretreated with waste frying oil

The fermentation of food waste by anaerobic mixed cultures pretreated with waste frying oil (WFO) was examined in this study. Waste frying oil was used as a stressing agent to suppress hydrogenotrophic methanogens and enrich H₂-producing bacteria. Lipid-rich compounds can be adsorbed onto the cell wall of some species, including methanogens, and they can reduce the permeability of the membranes and limit nutrient transport into cells. The optimization of H₂ yield was performed using a three-factor, three-level Box-Behnken design method. Initial pH, pretreatment duration and waste frying oil concentration were considered the experimental factors. Pretreatment with waste frying oil decreased the production of CH₄ significantly and, in turn, improved H₂ accumulation. The response surface model predicted complete inhibition of methanogens with 7.74 g/L waste frying oil, an initial pH of 5.5 and a duration of 42.67 h for the pretreatment conditions. Applying these conditions led to an experimental H₂ yield of 71.34 mL/gVS, which was significantly higher than that of untreated cultures (12.97 mL/gVS).