Simulation of greenhouse gas emission during sewage-sludge composting with high-concentration oxygen aeration

Continuous emission of greenhouse gases (CH4, N2O) is still one of key issues inhibiting the sustainability of the composting industry, which is regulated by aeration combined with porosity of the matrix via varying dissolvedoxygen (DO) distribution of in compost particles. Numerical simulation is considered to be an emerging tool for optimizing oxygen supply and porosity of the matrix. Therefore, in this study, a novel numerical simulation approach was developed, which includes a DO distribution model and fitting equations of GHG based on DO distribution. The parameters (porosity distribution, coefficients) were obtained from pilot experiments of sewage-sludge composting at aeration of two oxygen concentrations (20.9 %, OC20.9; 40.0 %, OC40.0) respectively. As a result, when the air-immobile region ranged from 0.2 to 0.5 and the O2 concentration was increased from 20.9 % (OC20.9) to 100.0 % (OC100.0), the CH4 emission rate decreased by a range of 53 %-96 %, while the N2O emission rate varied from a decrease of 7 % to an increase of 59 %. The developed simulation approach can be used to assist in establishing novel technologies to reduce GHGs emission in composting via optimizing oxygen supply combined with matrix's porosity.