Development and validation of a dynamic first order kinetics model of a periodically operated well-mixed vessel for anaerobic digestion

Abstract The transition towards a decarbonised electrical power system has consequences for the operation of Anaerobic Digestion (AD) providing an incentive to respond to the dynamic demand for electricity. Therefore, dynamic models to predict and control the AD process are of interest. A large number of models of AD exist, however, none seems fit for routine use in industry, being either too simple and inaccurate, or too complex. Consequently, the aim of this paper is to develop a new moderately complex dynamic model for process design and operational control of AD for intra-day on-demand electricity generation. The model interprets AD as three irreversible first order chemical reactions in series. The periodic nature of the usual feeding regime is used to develop a new general chemical kinetic analysis for a well-mixed tank subject to periodic feeding that is also industry friendly and fit for purpose with AD. The use of the model for AD is validated with eight datasets for different experimental conditions each mimicking demand-driven biogas production from sewage sludge obtained at pilot scale (0.05 m3). The model is accurate in predicting the biogas production rate, and the significant operational parameters of the process. The periodic version of the model performs generally better than a dynamic version that performs a bespoke mass balance at each feed and integrates the modelling equations until the next feed. It is concluded that the periodic model is fit for the purpose of predicting the operational parameters needed for dynamic biogas production and on-demand electricity generation.