Mathematical model and dynamic simulation of aerobic composting process

A structured dynamic model was developed to describe the aerobic composting process by system of nonlinear differential equations. The model takes into account: kinetics first order reaction with multiplicative influence of temperature, oxygen, moisture and free air space), mass transfer (oxygen, carbon dioxide, ammonia, water) and heat transfer (generated biological heat transfer, heat transfer from the reactor to surroundings, convective heat transfer between phases, heat transfer of the evaporated water) between three phases of the system. Some assumptions and hypothesis were made in the development of the model. The model can predict the composting dynamics through the degradation of organic matter, concentration of soluble gases (oxygen, carbon dioxide, ammonia), moisture content, gas composition in exhaust air (oxygen, carbon dioxide, ammonia, nitrogen, water vapour), temperature of exhaust air, temperature of composting material. For the preliminary test of the model, simulation results were compared with experimental data from pilot and laboratory scale studies. As composting material in the simulations, poultry waste was used. Numerical simulations provide a reliable approach to expected results.