Tissue composition and higher heating values differ among six bioenergy grasses

Abstract

Perennial crops are considered as one of the most promising substitutions for fossil fuels for both ethanol production and direct combustion, but the quality and suitability of bioenergy feedstock is species dependent. The bioenergy feedstock value of different perennial crops is mainly determined by tissue composition and higher heating value (HHV). A common garden field experiment with four replications was conducted to investigate differences in cellulose, hemicellulose, lignin, ash, and 14 different tissue elemental concentrations as well as HHV from tissues of switchgrass (Panicum virgatum L.), Miscanthus (Miscanthus×giganteus), indiangrass (Sorghastrum nutans), eastern gamagrass (Tripsacum dactyloides), reed canary grass (Phalaris arundinacea), and giant reed (Arundo donax L.) grown in 2020 and 2021 in Midwest USA. Results showed that Miscanthus, switchgrass, and indiangrass exhibited higher holocellulose (cellulose + hemicellulose) concentrations compared with eastern gamagrass, reed canary grass as well as giant reed: 684–687 g kg-1 vs 597–646 g kg-1 (2-yr averages). Switchgrass and Miscanthus had higher lignin concentrations (97–108 g kg-1) than the other four species (66–84 g kg-1). Greater 2-yr averaged HHVs were observed in switchgrass (18.1 MJ kg-1) and Miscanthus (17.8 MJ kg-1) than for giant reed (17.3 MJ kg-1), eastern gamagrass (17.0 MJ kg-1), indiangrass (16.9 MJ kg-1), and reed canary grass (16.5 MJ kg-1), which was correlated with differences in ash concentration between switchgrass and Miscanthus (25–29 g kg-1) and the other four species (42–91 g kg-1). Switchgrass, Miscanthus, and indiangrass exhibited significantly lower nitrogen, sulfur, and potassium concentrations than the other grass species, which would lead to less NOx and SOx emission, and sintering or slag formation in the combustion chamber. Giant reed obtained the greatest potential ethanol and combustion yields on a single plant basis, followed by Miscanthus, switchgrass, indiangrass, eastern gamagrass, and reed canary grass; however, further studies are needed to evaluate biomass yields on an area basis.