Inhibition of thermophilic anaerobic digestion of waste food by long chain fatty acids and propionate

Different initial concentrations of slurry waste food (discarded food), with and without the overlying layer of fat derived from the waste were anaerobically digested at 55C. At solids concentrations less than 20 g/l no significant difference was observed in terms of volatile fatty acids and methane production between samples containing fat layer and samples without it. However, at higher concentrations, differences became more obvious. Biogas released from a 50 g/l fat excluded sample was around 100% more than the gas generated from the fat included sample with the same initial solids concentration. Inhibition by propionate was not significant in concentrations less than 2000 mg/l. In the absence of fats, the inhibition caused by accumulation of propionate could be overcome partially by the methanogenic bacteria. Based on the energy generated in the form of methane, it was found that thermophilic anaerobic digestion of waste food could be an autothermal process for fat excluded feeds.