Revealing GHG-NH3 emission mechanisms: A comparison of food waste composting and biogas residue composting

Composting is a vital technology for the resource utilization of food waste (FW) and biogas residue (BR); however, it faces challenges such as greenhouse gas (GHG) and odor emissions. This study compares the gas emission characteristics of FW and BR composting and investigates the effect of phosphate slag, with the aim of elucidating the emission mechanisms and providing guidance for optimizing composting practices. FW composting maintained a thermophilic phase (>55 °C) for over 7 days, while BR composting, limited by its low organic matter content, failed to sustain a similar thermophilic phase. CH4 was the dominant GHG emitted during BR composting, accounting for 97.8 % of total GHG (CO2-eq). Phosphate slag amendment effectively reduced CH4 emissions by 68.3 %. CH4 release from BR composting was concentrated within the first two days, driven by residual methanogens from the anaerobic digestion (AD) process and anaerobic conditions within the pile. Additionally, BR composting emitted significantly more NH3 (0.42–0.60 g/kg BR) than FW composting (0.15–0.16 g/kg FW), due to the conversion of organic-N to NH4+ during AD process. Overall, AD increased CH4 and NH3 emissions during subsequent BR composting. In contrast, N2O was the primary GHG emitted during FW composting, contributing 75.0 %–87.0 % of total GHG emissions (CO2-eq). Higher N2O emissions occurred during the early stages of FW composting, coinciding with a Pseudomonas relative abundance exceeding 25 %. These findings highlight the distinct emission profiles of FW and BR composting and provide a basis for developing targeted emission reduction strategies tailored to different organic waste streams.