Effect of Feedstock Components on Thermophilic Solid-State Anaerobic Digestion of Yard Trimmings

Abstract

Solid-state anaerobic digestion of yard trimmings, composed of wood chips, lawn grass, and maple leaves, was conducted at 22% total solids at 55 °C for 45 days. Results showed digestion of mixed feedstocks generated earlier peaks and more methane than digestion of single components. The favorable peaking time (14 days) and methane yield (143 L/kg of VS) were achieved with equal fractions of the three components, increasing the methane yield by 80–200% compared to digestion of single components. Concentrations of volatile fatty acids and ammonia varied with component ratios and correlated with system performance. While organic components in mixtures were degraded differently, they were mostly degraded within 24 days and agreed with the methane yield. A mixture design model was established to predict the methane yield, and results showed that all interactions were synergistic, with the ternary interaction having the strongest effect. The model was verified using experimental data, which showed good agreement.