Analysis of regulative variables on greenhouse gas emissions and spatial pore gas concentrations with modeling during large-scale trough composting

Abstract

Regulative composting variables, like aeration, turning and additive, are critical factors for low-emission and eco-friendly aerobic composting. The main variables (aeration, turning, and additive) on greenhouse gas (GHG) emission rates and spatial GHG concentrations in the pores of composting piles during the large-scale composting were investigated under a typical trough composting system. An engineering model combined momentum transfer was built to simulate the airflow, temperature, and oxygen concentration distribution; thus, the composting equipment parameters could be preliminarily ensured. The aeration period emitted more carbon dioxide per unit time than the non-aeration period. Over 83% of methane was emitted during nonaeration period. GHG emissions in after-turning period were lower than those both in the nonaeration and aeration periods. Through modeling, momentum lost around 34% by frictional resistance when air flows in pipes. The difference of inlet oxygen velocity distribution of pipe’s pores was not over 10%, because high pressure provided by a fan could slow down the frictional resistance along the pipeline. The temperature distribution simulation followed the rules of heat diffusion and convection. The oxygen concentration in piles was transferred by its concentration condition fitting Fick law. Model well simulated the actual condition and composting routine could provide support for composting system design and composting management. Because of the complex condition of large-scale composting, modeling of the airflow simulation on GHG emissions should be further investigated.