Co-digestion of by-products and agricultural residues: A bioeconomy perspective for a Mediterranean feedstock mixture

This study focused on applying batch and continuous co-digestion approaches to investigate the effects of a feedstock mixture (FM) constituted by ten Mediterranean feedstocks highly available in the Mediterranean area (i.e., olive pomace, olive mill wastewater, citrus pulp, poultry litter, poultry and cattle manure, whey and cereal straw) on methane production for bioenergy generation. For the same feedstock mixture (FM), two different anaerobic digestion (AD) tests were carried out to evaluate the possible inhibitory effects of some biomasses on the biological process. The first AD test showed a methane yield equal to 229 Nm3CH4/tVS (27% lower than that measured during the batch test). During the second AD test, the specific production was 272 m3CH4/tVS. Both tests showed a similar methane content of methane in the biogas, equal to about 57%. The first AD test showed an inhibition effect of the process: total conversion of the organic matter into biogas was not ended. The second batch test demonstrated that the selected FM could be viable to carry out the co-digestion and could provide a flexible solution to generate advanced biofuels in biogas plants located in the Mediterranean area.