Anaerobic Co-digestion of Grass, Alfalfa, and Red Clover for Methane Production and the Kinetic Analysis

The residual of perennials in landscape trimming and agricultural interval planting are produced massively, and they can provide an innovative way to increase anaerobic digestion efficiency via co-digestion process. In this study, the bio-methane potential (BMP) of different perennial crops (grass, alfalfa, and red clover) in various feedstock concentrations based on volatile solid (VS) and the kinetic analysis of the co-digestion process were investigated. The results showed that grass and legumes reached the highest methane yield at 5 VS/L and 20 VS/L, respectively. Co-digestion of grass and perennials had better methane production of 338 mL/g VS, which is 9.1% higher than mono-digestion. Further analysis demonstrated that VS removal efficiency of mono-legumes digestion was below 60%, while co-digestion of grass and legumes can improve VS removal efficiency dramatically. Volatile fatty acids (VFAs) and ammonia in the digestate accumulated at 40 VSadded/L. Additionally, kinetic analysis was employed to predict and evaluate the performance of anaerobic digestion, with the Cone model showing the best fitting curve.