Abstract
The main residual of beer production, referred as Brewery’s Spent Grain (BSG), is an excellent raw biomass for biogas production. However, the C/N (organic carbon/organic nitrogen) ratio is not centered within the optimal range defined for the anaerobic digestion process, suggesting that the process efficiency could be enhanced by addition of appropriately selected agricultural residuals. In this regard, walnuts, produced from wood-production trees and therefore non-food-competitive, were selected. Walnuts show higher organic carbon content than BSG and their addition can mitigate the abundancy of nitrogen, typical of this latter biomass. Moreover, the presence of shredded woody walnut shell, will make the residual digestate highly predisposed for final composting, since the presence of solid and, at the same time, highly bio-degradable, woody particles, could ensure higher permeability to the whole residual, thus favouring the aerobic reactions required for the final composting. The present study deals with biogas production from sole BSG, sole walnuts and mixtures containing both. The results were discussed in terms of overall quantity of biogas produced, time duration of the whole process and daily production.
