Ultrasonic pretreatment of DDGS for anaerobic digestion

In the last years the need to face both climate change and energy supply requirements has promoted the interest towards biofuels. Among the most promising ones there is bioethanol, whose production relies for approximately 80% on biomass fermentation. The main obstacle in spreading the production of bioethanol is related to its productive process competitiveness. In order to improve ethanol plant energy balance, anaerobic digestion has been suggested for the treatment of DDGS (Distilled Dried Grains with Solubles), which is one of the main process by-products. This study aims to evaluate anaerobic digestion yields of DDGS and its variation after ultrasonic pretreatment. Sonolysis is a promising disruptive technique, whose effects are generated by the collapse of cavitational bubbles. It has been proved that low frequency ultrasound can promote mainly physical effects. In this study, the basic unit of a low frequency commercial ultrasonic device was used. Its effects were expected to result in carbon and nitrogen solubilisation improvement and, consequently, in the enhancement of anaerobic digestion yields of sonicated substrates. Main results were provided in order to highlight both chemical-physical and biological effects of sonolysis on DDGS. Their analysis highlighted the absence of a relation between solubilisation and anaerobic digestion yields in terms of biogas production. This evidence highlighted the tight relation between sonolysis effects and investigated substrate composition, which can result in relevant variation in anaerobic digestion yields of sonicated substrates to be treated by means of anaerobic digestion.