The Effect of Particle Size on Hydrolysis Kinetics of Food Waste

Food waste-related issues are currently considered a major concerning factor for sustainable development and waste management. Out of the available technologies, one good approach is solid-state anaerobic digestion (SS-AD), a biological process that converts organic waste into valuable biogas and nutrient-rich digestate. Among the various stages of solid-state anaerobic digestion (SS-AD), hydrolysis plays a crucial role in the overall efficiency of the process. Particle size may significantly affect the hydrolysis phase of the anaerobic digestion of food waste. In this study, the effect of particle size on the hydrolysis rate constant was found with laboratory-scale biogas digesters. The synthetic food waste with four different particle sizes (12.8, 6, 2, and 0.025 mm) was considered for the study. They were subjected to anaerobic digestion under mesophilic conditions with cow dung inoculum. Total solids content (TS) and volatile solids (VS) content from the hydrolysed phase in the digesters and the mass reduction of the digesters were measured. The VS measurements were modelled using modified first-order hydrolysis kinetics (MFK) using nonlinear regression curve fitting techniques. The rate constants of four particle sizes varied from 0.04–0.07/day for the MFK model. The optimum rate constant of 0.074/day was recorded for 2.5 mm, and it was found to be the best particle size for the food waste AD process.