Thermal pre-treatment as a tool for energy recovery from food waste through anaerobic digestion. Effect on kinetic and physicochemical characteristics of the substrate

Abstract Hydrolysis is the rate limiting stage in the anaerobic digestion (AD) of solid waste, such as food waste (FW), due to the presence of lignocellulosic material, which affects methane production. Mitigation strategies, such as thermal pre-treatment of the substrate, can be used to accelerate hydrolysis. In this study, the influence of temperature (72 – 128 °C) and exposure time (15 – 33 min) on the physicochemical properties of the substrate, biochemical methane potential (BMP) hydrolysis, the balance of organic matter (as measured by the chemical oxygen demand (COD)), and net energy production were determined. In terms of the substrate, positive results were obtained: a 50% reduction in lignin; up to a 34% increase in hemicellulose; up to a 99% reduction in Fe, Mn, Cu and Zn; an 83% decrease in Mg; and a 150% increase in K. In addition, methane production was higher than for the untreated substrate (120 vs 90 mLCH4 ⋅ gVS−1). The modified first-order kinetic model and adjusted Gompertz models, showed that the pre-treatment reduced the lag-phase (by less than 1 d), and increased the hydrolysis constant to above 40%. The optimal preteatment condition was approximately 72 °C-22 min, promoted hydrolysis, increased the COD soluble and produced a positive energy balance (7821.07 kJ).