Co-Digestion of Food Waste and Dairy Manure for Biogas Production

Abstract

Co-digestion of food waste and dairy manure in a mesophilic, completely mixed anaerobic digester was studied in the laboratory. Two mixtures of food waste and dairy manure were tested. The first mixture was composed of 32% food waste, based on volatile solids (VS) content, and 68% dairy manure; the second mixture was composed of 48% food waste and 52% dairy manure. For each mixture, the performance of the anaerobic digester was evaluated at two different organic loading rates (2 and 4 g VS L-1 d-1). The results showed that at 2 g VS L-1 d-1, the digesters were stable when fed with either mixture. The second mixture yielded a higher biogas production yield and rate (504 mL g-1 VS and 1010 mL L-1 d-1, respectively) than the first mixture (398 mL g-1 VS and 780 mL L-1 d-1, respectively). At 4 g VS L-1 d-1, the digester fed with the first mixture had stable performance, but the digester fed with the second mixture had large fluctuation in daily biogas production. The average biogas yields were 476 and 504 mL g-1 VS, respectively, and biogas production rates were 1910 and 2020 mL L-1 d-1, respectively, for the first and second mixture. No significant differences were found for VS removal between different conditions tested. Based on the measurement data, the energy generation potential of a farm digester was calculated for co-digestion of different amounts of manure and food waste.