Effect of Leaching and Fungal Attacks During Storage on Chemical Properties of Raw and Torrefied Biomasses

Coffee husk, eucalyptus, and pine residues were torrefied at 290 °C in a screw reactor, during 5, 10, 15 or 20 min. The effects of feedstock type and torrefaction process parameters (holding time) on their energy characteristics were investigated. Raw and torrefied biomasses were then submitted successively to leaching and to white and brown rot fungi, to mimic storage conditions. Mass loss after leaching step, water content and weight loss due to fungal deterioration after 2, 4, 8, 12, 16 weeks were recorded. The chemical composition and high heating value (HHV) of the torrefied samples were measured to determine the alterations compared to raw biomass during their storage. Increasing torrefaction residence time improves the decay resistance of the biomasses. Variation of carbon content (%wt., dry basis) and HHV (kJ/kg, dry basis) were observed during native and torrefied biomasses fungal degradations. Carbon contents and HHV values of raw and torrefied biomasses decreased during Trametes versicolor exposure [49.65% > C > 44.07% and 19.71 kJ/kg > HHV > 17.19 kJ/kg, results from results from all tests combined.], whereas they increased during exposure to Coniophora puteana [46.15% < C < 52.70% and 17.43 kJ/kg < HHV < 20.74 kJ/kg]. Severe torrefaction is therefore a good way to improve coffee husk, eucalyptus, and pine energy properties while limiting loss of their energy properties during storage. Graphic Abstract