Beyond the digester: facility-wide greenhouse gas and pollutant emissions and energy performance of hybrid anaerobic-aerobic organic waste composting.

This study presents the first comprehensive facility-wide assessment of greenhouse-gas emissions and energy balance at a full-scale hybrid anaerobic-aerobic composting (AC) facility integrating high-solids anaerobic digestion with aerobic stabilization. Multi-season, phase-resolved monitoring was conducted using dynamic flux chambers for CO2, N2O, NH3, H2S, and NMVOCs, and UAV-based flux-curtain surveys for CH4, revealed distinct gas-specific emission patterns across operational stages. CH4, CO2, and H2S emissions were highest during curing, while NH3, N2O, and NMVOCs peaked during excavation, aerobic stabilization, and extended filling, respectively. The total operational carbon (OC) footprint was 20,300 ± 800 Mg CO2-eq yr-1 (0.460 ± 0.019 Mg CO2-eq Mg-1 dry waste). Accounting for net-positive energy generation (1,550 MWh yr-1) reduced this footprint to 19,800 Mg CO2-eq yr-1 (0.45 ± 0.018 Mg CO2-eq Mg-1 dry waste). Excluding curing-phase emissions decreased OC by ∼46%, to 10,760 Mg CO2-eq yr-1 (0.24 Mg CO2-eq Mg-1 dry waste), demonstrating that curing can nearly double total climate impacts. UAV-based CH4 fluxes (69 ± 8 kg h-1) exceeded chamber-based estimates (24 ± 3 kg h-1), highlighting the importance of multi-scale monitoring for capturing spatial variability. Fossil emissions from equipment averaged 8.2 kg CO2 Mg-1 dry waste and were dominated by diesel use. Targeted mitigation strategies, including improved aeration, optimized curing management, and equipment electrification, could reduce CH4 and N2O by up to 60% and 30%, respectively. The integrated OC-energy framework provides a robust basis for advancing cleaner production and circular-economy strategies in organic-waste management.