Doctorado en Ciencias de la Ingeniería (DOCI)

Permanent URI for this collection

https://repositorio.uandes.cl/handle/uandes/989

Browse

Browsing Doctorado en Ciencias de la Ingeniería (DOCI) by Subject "Ciencias Naturales"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    A novel fluid dynamic study of the gas-liquid flows in biotrickling filters through CFD simulations and digital imaging techniques
    (Universidad de los Andes, 2022) Carreño López, Felipe Antonio; Moreno Casas, Felipe; Vergara Fernández, Alberto
    Daily, tons of volatile organic compounds (VOCs) which negatively affect the environment and human health are emitted into the atmosphere from anthropogenic and natural sources. Biotrickling filtration (BTF) is becoming one of the most promising treatment technologies for odor control. Within the last decades, the treatment of pollutants have been studied, and diverse numerical models for predicting the mass transfer have been intensively developed. However, the current state of the art is mainly based on using the two-film, penetration, and surface renewal theories which do not account for local variations of the fluid velocities, physical properties, or flow regimes. To account for variations on the local physical processes, a detail description of porous media, the multiphase fluid dynamics, and the biomass film is required. This work investigates and extends a three-dimensional computational fluid dynamic (CFD) model coupled with computerized tomography (CT) with the novel incorporation of a contrast agent as a first attempt to assess the local biofilm formation inside a realistic porous structure used in biotrickling filtration of VOCs. The validation of these models was accomplished in terms of the gas and liquid phase residence time distribution (RTD), and the volumetric mass transfer coefficient. The gas phase RTD was obtained using a novel methodology based low cost MOx sensor; the liquid phase RTD was obtained from a methylene blue pulse method, while the mass transfer characterization was carried out by using the sulphite method. Finally, the column was operated for the treatment of toluene vapours and a contrast agent was added after reaching the steady state in order to obtain a 3D description of the local biofilm formation. These results were used to validate the CFD-CT models. The mean RTD and the normalized variance estimated in the simulation were 43.709 s and 0.326, respectively. Compared with the experimental results, a relative difference of 4.167% for the mean RTD and 32.515% for the normalized variance were found. The computed surface area was available for biodegradation was 0.366 m2. This work results in a validated gas RTD model, whereas for the liquid RTD and mass transfer coefficient the proposed approaches seem promising but requires additional computational resources to assess the steady state behavior. This methodology demonstrated the feasibility to obtain the local biofilm formation but additional imaging procedures are required to reconstruct the closed manifold geometry to use this image as a computational mesh.
  • Thumbnail Image
    Item
    Efficient uncertainty quantification and propagation in performance-based earthquake engineering
    (Universidad de los Andes, 2025-04) Birrell Arangua, Matías; Astroza Eulufí, Rodrigo
    In recent decades, the constant deterioration of existing infrastructure and the increasing exposure to natural hazards driven by geological processes and changing climate conditions have motivated the development of a new philosophical approach to structural engineering, known as performance-based engineering. Its goal is to provide a rigorous, science-based framework through a comprehensive assessment of structural risk, ultimately delivering a decision variable that is useful for practical decision-making. To this end, performance-based engineering establishes a probabilistic framework that aims to address uncertainty regarding (i) the hazards to which the structure is exposed, (ii) the actual behavior of the structure versus that predicted by the engineering model, and (iii) the damage caused when certain intensity levels are exceeded. At each of these stages, properly quantifying uncertainty and subsequently propagating it through the following stages is critical for a successful risk assessment. In this context, methodological progress has been gradual, supported by technological advances that have enabled the implementation of probabilistic methods. However, the cost of adopting a probabilistic framework has been high, especially due to the need for largescale simulation of finite element models, which requires significant computational and time investment. For this reason, developing methods that enable efficient uncertainty quantification and propagation in performance-based engineering remains an open challenge and a key area of current research. This thesis presents two approaches aimed at providing efficient methods for uncertainty quantification and propagation by supporting structural simulations with machine learning surrogate models using Gaussian processes. The first approach focuses on quantifying and decomposing parameter-induced uncertainty in structural responses under specific hazard scenarios. Its goal is to support probabilistic sampling-based analyses, including model calibration and updating, iterative performancebased design, and sensitivity analysis. The second approach focuses on the quantification, propagation, and decomposition of uncertainty in structural vulnerability assessment under a broad range of seismic events. This approach implements and discusses the performance-based engineering framework from a philosophical standpoint, although applied to a real-world case study. Available definitions of damage states in bridge components and the relationships between these and their consequences are discussed. Both approaches are developed in a fully probabilistic setting, including probabilistic seismic hazard analysis, probabilistic structural modeling, and uncertainty decomposition.
  • Thumbnail Image
    Item
    Study of alternative metabolic pathways for the production of (R)-3-hydroxybutyric acid in polyhydroxybutyrate producing bacteria
    (Universidad de los Andes, 2022) Yañez Meneses, Luz Francy
    Considerable rich literature has accumulated concerning biochemical, physiological, and genetic aspects of polyhydroxybutyrate (PHB) intracellular accumulation in bacteria. The costs of substrates and processing, including the extraction of the polymer accumulated in intracellular granules, still hampers a more widespread use of this family of polymers. The PHB monomeric unit, (R)-3-hydroxybutyric acid (R3HBA) has found uses at the biomedical, chemical and supplement industries. The literature shows that two main process engineering and metabolic engineering strategies have been identified aimed at the production of chiral R3HBA: (i) production from the accumulated polymer (polymerization and depolymerization system, PDS); (ii) by bypassing the accumulation of PHB using metabolically engineered bacteria. The later includes the use of thioesterases (thioesterase shortcut system, TSS) that removes CoA from R3HBA-CoA, resulting in the R3HBA release to extracellular medium. This PhD thesis aims at broadening the understanding of the genetic and operational factors leading to PHB polymerization and R3HBA production in Azohydromonas lata DSM 1123, Cupriavidus necator H16 and Methylocystis parvus OBBP. Results showed that the growth associated PHB production observed in A. lata mimics an overflow metabolism, additionally, a successful PHB depolymerization in a two stage chemostat was obtained. The feasibility of producing R3HBA through in-vivo depolymerization of the intracellularly accumulated PHB in M. parvus was investigated. A PHB to R3HBA conversion of 77.2 ± 0.9% (R3HBA titer of 0.153 ± 0.002 g L⁻¹) can be attained in a mineral medium containing 1.0 g L⁻¹ KNO₃ at 30 °C with shaking at 200 rpm and a constant pH of 11 for 72 hours. Nitrogen deprivation, oxygen limitation, the supplementation with exogenous R3HBA and neutral or acidic pHs strongly reduced the excreted R3HBA concentration and yield. The implementation of the TSS system in M. parvus and C. necator by the construction of an expression vector containing tesB was hampered by inconsistencies in the constructed plasmids pLY01 and pLY02. Finally, the production of R3HBA by redirecting fluxes in the PHB metabolic pathway was investigated in C. necator; two mutant strains were constructed using the suicide vector pT18mobsacB: C. necator ∆phaC and C. necator ∆phaC ∆hbd, both unable to polymerize PHB and the last one incapable to transform R3HBA into acetoacetate. The mutant trains released pyruvate and R3HBA, suggesting that a native thioesterase of C. necator may play a role in the release of R3HBA by removing CoA from 3HBA-CoA. A protein homology on the genome of C. necator showed an enzyme encoded as WP_037025319.1 with a percent identity of 44 % in comparison with Ycia that may trigger R3HBA release. The results obtained in this work demonstrated the feasibility of R3HBA production by reducing or eliminating the fluxes of the reactions consuming R3HBA via operational manipulation as described in M. parvus and A. lata or via gene knock outs in C. necator.