Biogas production from co-digestion of different proportions of food waste and fresh bovine manure

The present study aimed to evaluate the process of anaerobic co-digestion of different proportions of food waste and fresh bovine manure. The experiments were carried out in the laboratory (using 250-mL reactors) and in a pilot-scale biodigester (8 m3). The laboratory experiment was conducted with batch feed systems testing three food waste (FW) and bovine manure (BM) ratios: 0:1, 1:2, and 3:1 (equivalent to 0, 33, and 75 % of food waste in the digester substrate, respectively). The pilot-scale biodigester had a continuous feed system and received a 1:2 FW:BM mixture ratio. The highest accumulated biogas production in the laboratory was 273 mL g-1 of volatile solids (VS) in the treatment with the 1:2 FW:BM ratio. Concentrations of volatile fatty acids (VFA) greater than 8 g L-1 inhibited methane production, except in the treatment without food waste. In the pilot-scale biodigester, concentrations of VFA were below the inhibitory threshold, and the biogas and methane yields were 271 L kgVS-1 and 220 L kgVS-1, respectively. Therefore, food waste can be successfully co-digested with fresh bovine manure in continuous feed digesters, with an initial organic load rate of at least 2.74 kgVS m-3 day-1. Future studies should aim to test progressive increases in food waste load to identify the threshold for inhibition.