Solid state anaerobic co-digestion of yard waste and food waste for biogas production

► Solid state anaerobic digestion (SS-AD) of food waste and yard waste. ► The highest methane yields were obtained at feedstock/effluent (F/E) ratio 1. ► Increasing F/E ratio from 1 to 2 and 3 caused decreases in methane yield. ► The AD was upset at F/E ratio 3 except yard waste only. Food and yard wastes are available year round at low cost and have the potential to complement each other for SS-AD. The goal of this study was to determine optimal feedstock/effluent (F/E) and food waste/yard waste mixing ratios for optimal biogas production. Co-digestion of yard and food waste was carried out at F/E ratios of 1, 2, and 3. For each F/E ratio, food waste percentages of 0%, 10%, and 20%, based on dry volatile solids, were evaluated. Results showed increased methane yields and volumetric productivities as the percentage of food waste was increased to 10% and 20% of the substrate at F/E ratios of 2 and 1, respectively. This study showed that co-digestion of food waste with yard waste at specific ratios can improve digester operating characteristics and end performance metrics over SS-AD of yard waste alone.