Energetic enhancement of thermal assistance in the cooling stage of biodrying by stimulating microbial degradation

Abstract In this study, thermal assistance was employed in the cooling stage of conventional biodrying. The results indicated that thermal assistance greatly enhanced water removal with improved vapor-carrying capacity of air-flow, and rapidly decreased moisture contents (MCs) from 45.15% to 49.42% to 15.20–25.85% in 6 days, which were much lower than those of conventional biodrying (CB, 34.90–40.85%). More importantly, a synergistic enhancement of physical and biological effects was observed in thermally assisted biodrying (TB) in terms of stimulated enzymes activity and microbial metabolism (higher oxygen uptake rate and degradation coefficient k). Among the degraded organics, lignocellulose was noted to be important for bio-heat generation in cooling stages, especially for straw as bulking agent. Heat balance results suggested that small fractions of thermal heat (19.76–24.73%) were required to upgrade CB processes for water evaporation with higher energy efficiency. Based on economic viability analysis and with consideration of the further drying for CB products, thermally assisted biodrying presented more economic benefits with less investment and shorter payback period. This research provided an efficient engineering approach to upgrade the cooling stage of conventional biodrying with low external heat cost.