A numerical integrated model of composting processes using finite elements methods

CSBE100824 - Presented at 8th World Congress on Computers in Agriculture (WCCA) Symposium ABSTRACT A dynamic finite element computer model of a composting system was created; it was temporally and spatially explicit. The modeled system was a cylindrical vessel, but it was conceptualized as a two-dimensional system on the assumption of radial symmetry. Air was blown in at the bottom through a distribution plenum and exited freely at the top. The evolution of the model was computed over time and space using multi-physics finite element modeling software (COMSOL™ version 3.5a). At each time step, the stationary solutions of the differential equations describing convection or diffusion were chosen, because those processes were assumed to occur much faster than any changes in the biomass. The compost was studied as a three-phase system. The water film around the solid particles hydrolyzed the nutriments that sustained the biomass and its chemical activities. Gases produced or consumed by the biomass - oxygen, carbon dioxide, ammonia - were exchanged with the gas phase through the water film. The gas concentrations and the temperature in the liquid or vapor phases were separately represented. Heat transfer was modeled as conductive through the liquid and solid phases, convective in the gas phase, and both convective and conductive therein. The population of micro-organisms was considered to be composed of mesophiles and thermophiles with different temperature-related growth coefficients. In order to model the heat and mass transfer between phases, a total of n growth characteristics were accounted for. Their development was computed through time and space. The modeling results and validation against physical experimental data are discussed.