Psychrophilic anaerobic digestion of semi-dry mixed municipal food waste: For North American context

Abstract

Treating municipal organic solid wastes economically is a challenge, predominantly in cold and high-altitude regions, where the temperature can be below 20°C. The aim of this research was to improve the anaerobic digestion (AD) of food waste (FW) with or without animal manure in a low-cost psychrophilic anaerobic digestion in sequencing batch reactor (PADSBR) at 20°C. Feed solid content was varied from 37% to 13%, mainly to validate the stability of digestion process suitable for different scenarios and OLR was increased from 0.8 to a maximum of 4.2kg VS/m3d. Results showed that methane production from FW mixture was feasible at low-temperature and specific methane yield of 0.401±0.01m3 CH4/kg VSfed was observed even at high OLR. When loading rates applied to bioreactors were increased by 225%, methane conversion rates decreased only by 10%, while maintaining the operational stability (e.g. no foaming, no acidification). Methane content was constantly in the range of 64–69%, which shows the quality of biogas is excellent and remained almost steady. The results suggest that PADSBR at 20°C is comparatively efficient in saving the heat energy and at the same time obtains the CH4 values close to mesophilic/thermophilic conditions. This concept is particularly vital for cold countries facing energy constrains.