Conversion of Food Waste into Energy: Impact of Thermal Pre-Treatment on Hydrogen and Methane Production

In the framework of the waste circular economy, anaerobic digestion (AD) is a promising treatment option, due to both renewable energy and fertilizer production. Nevertheless, in mesophilic conditions a part of the organic carbon fed is not degraded, reducing the possibility to fully exploit the waste energy potential, and opening the research to advanced processes that can increase AD efficiency. In this study, AD of food waste was investigated in thermophilic conditions. Scope of this work was to evaluate the efficiency of a mild thermal pre-treatment on the solubilisation of complex organics and the digestion enhancement potential in terms of H2 and CH4 conversion rates. Thermal pre-treatment promoted complex organics solubilisation (soluble COD up to +40%) in particular with reference to starch and hemi-cellulose fraction. The high amount of released sugars was rapidly transformed into H2 in the first hours of AD, with high yields (up to 2.6 mol H2/mol glucose) and significant gain with respect to untreated waste. Ultimate methane yield was not affected by the substrate pre-treatment, but the positive impact was shown by the increase in anaerobic biodegradability, and kinetics.