Theoretical and observed biogas production from plant biomass of different fibre contents

The methane productivity of silage of four crop species – Zea mays L., Sorghum saccharatum, Miscanthus × giganteus and Miscanthus sacchariflorus – was investigated. The experiments revealed that at a hydraulic retention time of 60 days the volumetric methane yields from the Z. mays L. or S. saccharatum silages were higher than those from the Miscanthus × giganteus or M. sacchariflorus silages because of the higher crude fibre content in Miscanthus spp. However, at comparable lignin concentrations in the feedstock, methane productivity for M. sacchariflorus (0.19 ± 0.08 L/g volatile solids) was twice that of Miscanthus × giganteus (0.10 ± 0.03 L/g volatile solids). The efficiency of cellulose conversion varied from 83.6% (S. saccharatum) to 52.1% (Miscanthus × giganteus), and hemicellulose from 88.9% (Z. mays L.) to 59.7% (Miscanthus × giganteus). Conversion of cellulose and hemicellulose depended on the ratio of these polysaccharides to the lignin concentration of the feedstock.