Evaluation of the Methane Potential and Kinetics of Supermarket Food Waste

Abstract

The methane potential of supermarket food waste (SMW) has scarcely been determined, especially at 55 °C. In this paper, the different types of SMW generated in a chain of supermarkets have been characterized over a period of 1 year. Batch anaerobic digestion tests employing six different mixtures of SMW were conducted under thermophilic conditions. Start-up was very rapid, with lag-phase values < 1 day, reaching peak methane production rates before day 5. The observed methane yields ranged between 453 and 678 L/kg VS. The highest value was obtained with the mixture including waste generated from all the different sections of the supermarket (fish, fruit and vegetables, butchery, bakery, and charcuterie), followed by the mixture not including fruit and vegetable waste, with no statistical significant differences between these values. The lowest value was obtained when bakery waste was not included in the mixture. The results are consistent with the observed degradation in volatile solids, ranging from 78 to 91%. The modified Gompertz kinetic model provided a better fit than the first-order kinetic model, with R2 values higher than 0.994 and deviations between experimental and theoretical values ranging from 1.5 to 6.1%. The technical digestion time (t80–t90) was calculated to range between 11.5 and 14 days, with the exception of the substrate containing all five types of waste generated in the supermarket, which ranged between 14.5 and 17 days. Scanning electron microscopy (SEM) images showed the further deterioration and size reduction of particles in the substrate producing the highest methane yield.