A mathematical investigation for the simulation and forecasting of a biodigester operations

Abstract

In this paper we formulate various mathematical models to describe the processes of anaerobic digestion of an organic waste treatment plant, based on its chemical kinetics, stoichiometry and on the biological aspects that influence the chemical reactions of anaerobic digestion. The latter is a process of degradation of the organic substance by microorganisms in the absence of oxygen, used in plants that have the purpose of producing biomethane and compost. This type of process is very complex and for its realization different chemical phases are involved as well as the presence of different bacterial families. The chemical reaction reagent represents the digester substrate; the products are biogas (methane and carbon dioxide) and digestate (degraded organic substances, from which compost is obtained). The populations modeled here are the reactants of chemical reactions and their products, as well as microorganisms. The latter play an important role as they carry the reactions inside the anaerobic reactor in which they live.Each mathematical model formulated consists of a system of ordinary differential equations, numerically integrated with the use of MATLAB software. The models are formulated both in non-operational and operational conditions. In the first case, in which neither new daily organic waste inputs nor product releases are expected, the system variables are studied at steady state as functions of the parameters. The operating models, on the other hand, also consider the daily input and output of the plant.