Decentralised Bioenergy from Automatically Controlled Anaerobic Digestion of Food Waste

Transporting waste afar to automatically centralised anaerobic digestion plants logically means more carbon footprint and inconvenience. Better local approaches are desirable in a sustainable circular economy. Consequently, the performance of an automatically controlled small-scale prototype digestion plant is presented herein. This is done in terms of energy efficiency and technical
suitability to valorise biogas as fuel for electrical and thermal energy. The microplant operated in recirculation mode to enhance food waste conversion and improve volatile solids degradation. An energy assessment is considered with a combined heat and power (CHP) unit. The microplant nearly attained self-sufficient electrical energy use, as reflected by 0.95 of overall performance
coefficient (COPel) estimated at 22.5% ratio between energy production and consumption, at 360 L methane (kg VS)-1 and an organic loading rate (OLR) of 1.06 g VS (L d)-1. Evidently, assessing energy at low OLR required warming up the feed to the desired process conditions, and consequently demanded thermal energy accounting for 80% of the total energy demand of the micro-plant, and thus highly compromising efficiency. Conversely, at higher OLR (2.7 g VS (L d)
1) the plant reached self-sufficient electrical energy use at the process conditions (COPel of 1.68).