Co-digestion of mushroom compost with switchgrass using solid–state anaerobic digester

Abstract

Spent Mushroom Compost (SMC) already broken down into smaller particles by fungal action is an ideal material for producing biogas. Two cycles of five Solid State Anaerobic Digesters (SS-ADs) with different mix-ratio of SMC and Switchgrass (SG) were operated at feedstock-to-effluent ratio (F/E) of 2 at a temperature 35±2°C. The total solids concentration of the digester was kept at ∼17%. Initial biogas production observed during the start-up of the digester confirmed the presence of readily available extractives for digestion. In the first cycle, the highest methane yield was observed in SMC 0 (0% SMC + 100% SG) of 28.82 L/kg VS/d and the lowest yield was observed in SMC 4 (100% SMC + 0% SG) as 10.32 L/kg VS/d. The substrate containing 100% SG (SMC 0) recorded the highest cumulative biogas yield of 295.43 L/kg VS in 63 days. The digesters with higher SMC fraction showed lower methane production, low pH value, and high VFA content upon decomposition. The SS-ADs having SMC/SG of 50:50 showed more than 2 times methane production in comparison with SS-ADs having SMC as sole substrate. An estimation of volumetric productivity also established a linear relationship with the SMC/SG ratio.