Enhancing the physical quality of barley straw pellets by optimizing biological pretreatment

Abstract. Pelleting can increase the efficiency of handing and transportation of biomass for conversion into biofuels. Pretreatment of biomass makes lignin fragments accessible by disrupting the lignocellulosic structure, and ensures the production of high-quality pellets. In this study, biological pretreatment using solid-state fermentation (SSF) was investigated as a means to improve the quality of pellets produced from barley straw. SSF of barley straw using Trametes versicolor 52J and Phanerochaete chrysosporium were conducted. Response surface methodology was employed by using a four-factor, three-level Box-Behnken design with moisture content (%, w. b.), hammer mill screen size used for chopping barley straw (mm), fermentation time (days) and fermentation temperature (°C) as material/process parameters. Pellet density, dimensional stability and tensile strength were the measured response variables. The optimization variables of moisture content (70%, w. b.), hammer mill screen size (50-62.18 mm), fermentation temperature (22℃) and fermentation time (29.14-34.93 days) of barley straw with pretreatment using the two fungal strains were obtained. The microscopic structural changes induced by microbial pretreatment were examined by scanning electron microscopy (SEM). Results showed that the combination between single fibers became relatively loose, and the connection was never tight which was advantageous to improve the physical quality of the compressed pellets.