Bagasse compost pelletization: Sustainable densification for agricultural waste management

This study investigated the physical, mechanical, and microstructural properties of bagasse compost to optimize its densification into durable pellets for agricultural applications. Bagasse compost was initially subjected to hammer milling across various moisture contents (8-16% wet basis) and screen sizes (1-4 mm). Results showed that specific grinding energy increased exponentially with moisture content and decreased with larger screen sizes, ranging from 11 to 750 kJ/kg. Particle size distributions were characterized, revealing broader distributions with coarser screens. Pellets were subsequently produced using a closed-die hydraulic press under controlled pressures (50-150 MPa), moisture contents (8-20%), and particle sizes (1-4 mm). Compaction energy, fracture resistance, and pellet density were modeled using Response Surface Methodology. Increasing pressure significantly enhanced compaction energy, fracture resistance, and pellet density. Higher moisture content generally reduced compaction energy but improved fracture resistance, while pellet density exhibited an initial increase followed by a decrease. Particle size had a less pronounced effect on compaction energy and density but positively influenced fracture resistance. Microstructural analysis via Scanning Electron Microscopy (SEM) revealed more open fiber bundles and cracks in compost compared to raw bagasse, indicative of structural changes. X-Ray Diffraction (XRD) analysis showed an increased crystallinity index in compost due to the degradation of amorphous regions (hemicellulose and lignin), with crystalline cellulose remaining stable. Differential Scanning Calorimetry (DSC) identified the compost's average glass transition temperature at 89.7 °C, highlighting the importance of temperature control during densification to preserve beneficial microorganisms. Fourier Transform Infrared (FTIR) spectroscopy confirmed significant chemical changes, particularly the degradation of hemicellulose. These findings offer crucial insights for optimizing bagasse compost pelletization for sustainable and efficient utilization.