Assessing the Synergistic Effects of Co-digestion of Maize Silage and Red Chicory Waste

Nowadays, the anaerobic digestion of organic wastes to produce renewable energy is a reality in many countries. Many feedstocks can be processed by anaerobic digestion to produce biogas, however, anaerobic digestion of single substrates can have drawbacks that could be eliminated by the anaerobic co-digestion of their mixtures (two or more). In this paper, the anaerobic co-digestion of maize silage and red chicory (radicchio) waste is presented. Several batch anaerobic biodegradability tests were performed in order to compare the methane production of the blend with those of the two substrates digested separately. The methane production was modelled by a first order kinetic model, focusing on the initial substrate solubilization. The specific methane productions of maize silage and red chicory as single substrates were 0.346 L CH4 g–1 ODM and 0.326 L CH4 g–1 ODM. The first solubilization rate constants (ksol) were 0.231 d–1 for the digestion of maize silage, and 0.389 d–1 for the radicchio waste. Two parameters representing the relative changes in specific methane production and solubilization rate were calculated in order to evaluate the synergistic effects due to co-digestion of studied substrates. Results showed that blending the two substrates enhanced the performances of the AD process, mainly with respect to biogas production kinetics with low increments in the ultimate methane potential.