Particle-Scale Modeling of Methane Emission during Pig Manure/Wheat Straw Aerobic Composting

Inefficient aerobic composting techniques significantly contribute to the atmospheric methane (CH₄) levels. Macro-scale models assuming completely aerobic conditions cannot be used to analyze CH₄ generation in strictly anaerobic environments. This study presents a particle-scale model for aerobic pig manure/wheat straw composting that incorporates CH₄ generation and oxidation kinetics. Parameter estimation revealed that pig manure is characterized by high CH₄ yield coefficient (0.6414 mol CH₄ mol^–1 <i>C</i>_man) and maximum CH₄ oxidation rate (0.0205 mol CH₄ kg^–1 VS_aero h^–1). The model accurately predicted CH₄ emissions (<i>R</i>² = 0.94, RMSE = 2888 ppmv, peak time deviation = 0 h), particularly in the self-heating and cooling phases. During mesophilic and thermophilic stages, a rapid increase of CH₄ generation (0.0130 mol CH₄ kg^–1 VS h^–1) and methanotroph inactivation were simulated, implying that additional measures should be performed during these phases to mitigate CH₄ emissions. Furthermore, CH₄ oxidation efficiency was related to oxygen permeation through the composting particles. Reducing the ambient temperature and extending the aeration duration can decrease CH₄ emission, but the threshold temperature is required to trigger the self-heating phase. These findings provide insights into CH₄ emission during composting and may inform responsible strategies to counteract climate change