Morphological structures of wheat straw strongly impacts its anaerobic digestion

Abstract

Anaerobic digestion (AD) of lignocellulosic residues, such as cereal straws, depends on many factors that influence substrate characteristics, particularly its biochemical composition, and thus biogas production: straw variety, growing stage, storage conditions, etc. However, impacts of straw morphological fractions on AD have never been evaluated. For the first time, the anaerobic degradation of five different fractions of wheat straw (internodes, leaves, nodes, chaffs and rachis) was evaluated. The results indicate that these fractions present strong and significant differences in terms of ash content, organic matter, soluble phase and fibers distribution. Based on their biomethane potential, it is possible to classify these fractions into three categories: stem structures (internodes and nodes) with a methane potential of 141±14NmLgVS-1, ear structures (chaffs and rachis) with 186±4NmLgVS-1 and leaves with 242±7NmLgVS-1. However, similar and low biohydrogen potential was found for every fraction (around 10±2NmLgVS-1). These results show that selection of straws with higher contents of leaves, rachis and chaffs could significantly increase methane potential, while biohydrogen production would require pretreatment steps. The study suggests to investigate on optimization of the wheat straw variety or harvesting methods as a low cost approach to increase methane potential of agricultural residues. © 2013 Elsevier B.V.