Dry batch anaerobic digestion of food waste in a box-type reactor system: Inoculum preparation and reactor performance

A box-type reactor system with liquid inoculum has been studied for the dry anaerobic digestion of foodwaste. The food waste was processed without any pre-treatment to remove physical impurities, neitherwater addition to dilute and slurry the feedstock. The experiment was carried out with inoculum tosubstrate ratios of 1:1 (w/w) and 0.08:1 (VS basis). Previous acclimation of liquid inoculum enhanced theprocess, assuring a fast start up of the box digester and preventing from process failure by volatile fattyacids accumulation. The percolate recirculation strategy was shown to have a relevant effect on theprogress of the process. The results suggest that the process can be optimized by providing low percolaterecirculation rate during the start-up of the box digester followed by an increase in the percolaterecirculation rate when volatile fatty acids decrease and methane content in the biogas increases. Themethane yield obtained in the box digester from the food waste was in the range 460e477 L CH4kg 1VS,being the VS removal efficiency between 91.1 and 91.4%. Globally, the process operated at an organicloading rate of 2.5 kg VS m 3d 1and yielded a volumetric methane production rate of 1.0 m3CH4m3d 1. These results show the high potential of food waste for its conversion in renewable energy by usingthe dry batch anaerobic technology