Temperature-oxygen regulated pore-gas distribution and emissions revealed by coupled heat-mass-momentum modeling during membrane-covered aerobic composting.

Membrane-covered aerobic composting (MCAC) has shown potential for mitigating gaseous emissions; however, the coupled mechanisms governing gas distribution and transport within the system remain unclear. In this study, pore-gas distributions and emission characteristics of carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ammonia (NH3) were investigated in an MCAC system. Meanwhile, a coupled heat-mass-momentum transfer model was developed to simulate the spatiotemporal evolution of temperature and oxygen concentration under membrane-covered conditions. Results showed that pore-gas concentrations exhibited no significant vertical differences (p > 0.05), indicating relatively homogeneous gas distribution within the pile under MCAC conditions. MCAC reduced cumulative greenhouse gas emissions by 2.46%-11.32% and NH3 emissions by 3.86%-10.86%. NH3 emissions were significantly correlated with temperature and oxygen concentration (p < 0.01), whereas CO2, CH4, and N2O emissions showed no significant correlations. The developed model successfully reproduced the transient dynamics of temperature and oxygen concentration, with R2 values of 0.92-0.93 and 0.89-0.93, respectively. Simulation results revealed pronounced temperature stratification but comparatively weaker oxygen gradients within the pile. In contrast, pore-gas concentrations remained relatively uniform, suggesting that membrane covering coupled with forced aeration substantially enhanced airflow-driven gas mixing. These findings indicate that gas distribution in MCAC systems is governed primarily by convective transport induced by modified boundary conditions, whereas temperature and oxygen distributions are regulated by coupled heat generation, transport, and oxygen consumption processes. This study provides a physically based heat-mass-momentum coupled framework for understanding gas transport behavior during MCAC.