Panaro, Daniele Bernardo (2021) Mathematical modeling of anaerobic digestion in plug-flow reactors. [Tesi di dottorato]

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Abstract

Anaerobic digestion is one of the most used technology for the treatment of organic compounds contained in a great variety of waste through which the production of a renewable energy is obtained, the biogas. Mathematical modelling plays a key role in providing tools supporting the designing and managing of plants performing this kind of process. The vast majority of mathematical models describing the anaerobic digestion process focus their attention on systems in wet conditions, whose mathematical problem consists in non-linear systems of ordinary differential equations. Dry anaerobic digestion modelling, due to the reactors where it is performed, needs more complex systems of partial differential equations to describe properly the dynamics of the process. The lack of scientific literature on this topic drove the interests and the efforts of the research activities of the three years of Ph.D, concretized in the scientific articles that are presented in this work of thesis. Research activities were aimed to the development of a mathematical model describing the dynamics of the main compounds involved in a dry anaerobic digestion process in plug-flow reactors. The thesis is divided in 6 chapters. In chapter 1 the main topic is introduced. Chapter 2 presents the calibration and validation of an ADM1-based model, performed using the results of experimental campaigns of anaerobic digestion of potato waste having the characteristic dimension of the particles varying in a wide range. Chapter 3 describe the derived mathematical model of anaerobic digestion in plug-flow reactors: model equations and hypothesis are presented and model consistency with experimental observations is shown through numerical simulations. The model considers the variation of compounds concentrations in both space and time and takes into account the mass/volume variation of the treated matrix along the reactor. Moreover, a new equation describing the gas-transfer phenomenon is presented in this chapter. A global aensitivity analysis and uncertainty quantification for the model of dry anaerobic digestion in plug-flow reactors is performed in Chapter 4. These activities revealed the most important model parameters influencing the methane production, the main output of the model. In Chapter 5, based on the global sensitivity analysis and uncertainty quantification results, model parameters have been calibrated and validated. Results of two experimental campaigns of dry anaerobic digestion in a plug-flow reactor have been used to this purpose. Lastly, in Chapter 6 a general discussion for future research developments is given.

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