In recent years, the interest on modelling activated sludge (AS) systems by means of Computational Fluid Dynamics (CFD) techniques has significantly increased. This work shows a successful case study combining CFD hydrodynamics and biokinetic modelling. The hydrodynamics is analysed by using the Reynolds-averaged Navier-Stokes equation for incompressible non-Newtonian fluids and SST turbulence model. Biokinetics has been included into the CFD as transport equations with source and sink terms defined by the Activated Sludge Model nº1 (ASM1). Furthermore, a strategy for reducing the computational cost while maintaining accuracy of the results of these calculations has been proposed. This strategy is based on a two-step solver configuration and the definition of a variable timestep scheme. The resulting CFD-ASM approach permits a proper evaluation of denitrification in the anoxic tanks as well as the reproduction of nitrate and readily biodegradable substrate distributions. To demonstrate the strength of the proposed CFD-ASM, it has been used to evaluate the operation of a full-scale AS system and optimize its performance through changes in the biological reactor anoxic zone. The original configuration has been retrofitted and modified after detecting intrinsic defects on the fluid behaviour within the tank. This study has been assessed by analysing hydrodynamics in detail and validating the simulation results with tracer tests and flow velocity measurements. Substantial variations on the Residence Time Distribution have been confirmed when modifying the internal elements of the tank configuration: the wall-bushing and the stirrer positioning. As a result of this work, an influential short circuiting was corrected improving hydrodynamics and increasing mean residence time, all favouring denitrification efficiency. Outcomes of this study show the benefit of CFD when applied to AS tanks.

This work exhibits the importance of the experimental validation when full-scale computational fluid dynamics (CFD) models are developed to provide a detailed analysis of the spatial variations in 3D of the fluid flow inside aerated tanks. Single-phase and two-phase CFD models were performed to study the fluid behaviour carefully by means of the velocity profiles and the aeration pattern in a full-scale oxidation ditch. Air holdup , bubble size distribution and interfacial area density were calculated by polydisperse models where Population Balance Model (PBM) was governed by break-up and coalescence; the free-surface approach allowed the CFD model to describe the threedimensional effect of bubbly plumes in large scales in detail. Tracer tests were carried out to obtain the flow pattern and the hydraulic distribution of the flow into two wastewater treatment lanes in order to define the boundary conditions for the model correctly. Despite the difficulty of performing velocity measurements of the fluid in 3D, with and without air bubbles, these provided essential information to validate the CFD model. From this analysis, several simulations were performed to improve the hydrodynamics and the operation of the process by relocating the propellers.

Registro de acceso restringido Este recurso no está disponible en acceso abierto por política de la editorial. No obstante, se puede acceder al texto completo desde la Universitat Jaume I o si el usuario cuenta con suscripción. Registre d'accés restringit Aquest recurs no està disponible en accés obert per política de l'editorial. No obstant això, es pot accedir al text complet des de la Universitat Jaume I o si l'usuari compta amb subscripció. Restricted access item This item isn't open access because of publisher's policy. The full--text version is only available from Jaume I University or if the user has a running suscription to the publisher's contents.

In this work, we have tested a photocatalytic material consisting of a core of SiO2/Fe3O4 coated with TiO2 (Magnox) for plausible tertiary wastewater treatment. For this, a pilot plant of 45 L equipped with an Ultraviolet light (UVC) lamp was employed to study the degradation of a model contaminant, enrofloxacin (ENR), as well as water disinfection (elimination of Escherichia coli and Clostridium perfringens). The influence of different operational conditions was explored by means of dye (rhodamine-B) decolorization rates, analyzing the effects of photocatalyst quantity, pH and recirculation flow rates. The magnox/UVC process was also compared with other four Advanced Oxidation Processes (AOPs): (i) UVC irradiation alone, (ii) hydrogen peroxide with UVC (H2O2/UVC), (iii) Fenton, and (iv) photo-Fenton. Although UVC irradiation was efficient enough to produce total water disinfection, only when employing the AOPs, significant degradations of ENR were observed, with photo-Fenton being the most efficient process (total enrofloxacin removal in 5 min and c.a. 80% mineralization in 120 min, at pH0 2.8). However, Magnox/UVC has shown great pollutant abatement effectiveness under neutral conditions, with the additional advantage of no acid or H2O2 addition, as well as its plausible reuse and simple separation due to its magnetic properties.

Aquest text està subjecte a una llicència Reconeixement-CompartirIgual de Creative Commons, que permet copiar, distribuir i comunicar pública ment l'obra sempre que s'especifique l'autor i el nom de la publicació fins i tot amb objectius comercials i també permet crear obres derivades, sempre que siguen distribuïdes amb aquesta mateixa llicència.