Aerobic composting with hydrothermal carbonization aqueous phase conditioning: Stabilized active gaseous nitrogen...

The losses of reactive gaseous nitrogen (N), including ammonia (NH₃) and nitrous oxide (N₂O), represent a pressing environmental issue during composting. However, the impact of hydrothermal carbonization aqueous phase (HAP) on compost gaseous N emissions and the underlying mechanisms remain largely unexplored. Herein, Quercus acutissima leaves-derived HAP and its modified HAP (MHAP) were added to the chicken manure compost at 5 % (w/w) and 10 % (w/w) applied rates to observe changes in NH₃ and N₂O fluxes, compost properties and bacterial communities. Results showed that high application of HAP significantly decreased compost cumulative NH₃ volatilization by 23-26 % compared to the control and MHAP. Compost NH₃ and N₂O emissions were significantly influenced by compost temperature and inorganic N concentrations. Moreover, HAP and MHAP at high rates reduced the relative abundance of Bacteroidota (5-29 %) and Proteobacteria (11-35 %), compared to those at low rates. Compost environmental factors and bacterial diversity were identified as dominant factors affecting gaseous N emissions, with 54 % and 25 % explanatory rates, respectively. Furthermore, high application rates of HAP are expected to reduce annual NH₃ emissions from poultry manure compost by 40000 t. These findings provide insights into rational resource utilization of HAP and gaseous N emission reduction from composting.