Thermal drying of industrial sludge using forced aeration

This study investigated an industrial biosludge drying system using hot gases from a coal furnace, seeking to increase the solids content of the biosludge above 50% (w.b.), considered suitable for combustion in biomass boilers. Biosludge was collected from a paper mill activated sludge plant. Biosludge mixtures with eucalyptus chips and eucalyptus bark in two different proportions (15% and 25%) were placed into a drying chamber. Hot gases generated by the furnace, with a flowrate of 0.64 ± 0.02 m³ s^-1 at 100 ± 20°C, were applied to the piles through a blowing system. The results demonstrated that the 75% biosludge/25% eucalyptus bark mixture achieved the best drying ratio, increasing the total solids content from 31% to 72%, over a 5-h drying period. Nevertheless, all other treatments involving the addition of a bulking agent achieved solids content above 50%, confirming the positive effect of adding dried material to the sludge. These results indicate a potential use of hot gases that are currently available and released into the atmosphere by paper mills.