Biorefinery-oriented full utilization of food waste and sewage sludge by integrating anaerobic digestion and combustion: Synergistic enhancement and energy evaluation

Abstract

Biorefinery-oriented full utilization of organic wastes by integrating anaerobic digestion and combustion is a promising approach. The objectives of this study were to investigate the effect of the co-treatment of food waste and sewage sludge on the performance of the combined system in terms of methane production, combustion characteristics and total energy output. The anaerobic co-digestion of food waste with sewage sludge showed a clear synergistic enhancement at the optimal food waste/sewage sludge ratio of 2:2, where the methane yield increased by 99 mL/g VSadded compared with the theoretical value. The analysis of aqueous products suggested that the synergistic effect was attributed to reduced volatile fatty acids accumulation and ammonia inhibition. Furthermore, the digestate at a ratio of 2:2 showed the best combustion characteristics with the highest comprehensive combustion index and combustion stability index of 4.87 × 10−7%2 min−2 °C−3 and 4.80 × 103%2 min−2 °C−3, respectively, which could be resulted from the more stable organic components and the catalytic effects of inorganic minerals. Finally, the energy evaluation showed that the co-treatment would increase the daily energy output and specific energy output of 100 t/d full-scale plant by 14.3 GJ/day-33.7 GJ/day and 0.3 GJ/t-0.6 GJ/t, respectively. These findings could provide some valuable information for anaerobic digestion-combustion-based biorefinery of organic wastes.