Computational fluid dynamics techniques for fixed-bed biofilm systems modeling: numerical simulations and experimental characterization
- Autores: Lledó Prades
- Directores de la Tesis: Xavier Gamisans Noguera (dir. tes.), Antonio David Dorado Castaño (codir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2018
- Idioma: español
- Tribunal Calificador de la Tesis: Sergio Chiva Vicent (presid.), David Gabriel Buguña (secret.), Cristian Picioreanu (voc.)
- Programa de doctorado: Programa de Doctorado en Recursos Naturales y Medio Ambiente por la Universidad Politécnica de Catalunya
- Materias:
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- Resumen
This thesis is focused on the development of one-phase and multiphase models using computational fluid dynamics (CFD) techniques to analyze biosystems behavior at mesoscale. In the first part, the operation of a fixed-bed biofilm reactor was simulated using Eulerian one-phase models, coupling fluid flow dynamics with biokinetics. The results reproduced accurately bioreactor performance, being experimentally verified hydrodynamics and species transport. However, the models had to be adapted to reproduce real scenarios where the biofilm motion can play a key role. On further consideration, this thesis suggested the development of Eulerian two-phase models using volume of fluid (VOF) method, defining the biofilm as an independent fluid phase by means of a comprehensive analysis of its rheological properties. This characterization became essential for accurately reproducing the fluid-biofilm interaction, describing the biofilm as a non-Newtonian fluid, which parameters were strongly dependent on its density. Thus, in the second part of this thesis, this novel continuum approach for biosystems modeling was tested, considering the required implementations to reproduce the species transfer at the interface (liquid-biofilm), and the possible growth of the biofilm phase. This new approach coupled fluid dynamics under laminar conditions with biochemical phenomena and/or biofilm mechanical behavior, so being able to reproduce the fluid stress over the biofilm, and its motion. The simulated results were experimentally verified evaluating transport mechanisms under different hydrodynamic conditions, and the model capability to reproduce shear-induced deformation and detachment, and recoil in biofilms was stated. In the third part of this thesis, the capacities of the new approach of continuum model were further tested, in order to reproduce wide range of hydrodynamic conditions to which biosystems can be exposed. Particularly, Eulerian multiphase models were developed and solved to characterize turbulent gas flows behavior over biofilms attached to walls. A coupled method of VOF and level-set, and shear stress transport (SST) k-omega model were used, reproducing accurately gas-biofilm interactions, turbulence and near-wall treatment. The simulated results were experimentally verified to confer identity to developed CFD approach, correctly describing the interfacial instabilities on the fixed-bed biofilm, such as ripples formation, and biofilm displacement and removal from its original position. The results also revealed that biofilm fluidization was the mechanisms behind the impact of turbulent air flows. Finally, in the last part of this thesis, the work was focused on the accurate analysis of fluid-biofilm interface, and on the necessity of acquiring local experimental data to verify models. The applicability of needle-probes as an innovative technique for in-situ biofilm layer and fluid interfaces detection was examined. The sensor probe performance was calibrated and verified in multiphase systems, revealing its practicability for interface detection, depth measuring, and surface reconstruction. So, a feasible tool for the experimental characterization of biosystems and models verification at mesoscale was provided. Therefore, the Eulerian multiphase approach proposed in this thesis, together with the experimental analyses, revealed the potential of CFD techniques as an alternative tool for fixed-bed biofilm systems modeling, allowing to reproduce simultaneous spatial and temporal, physical and biochemical phenomena under different operating conditions and biosystems configurations. The proposed approach helped to address key aspects of biofilm modeling such as its deformation and detachment under laminar and turbulent conditions.
