Elduayen-Echave, B. (Beñat)

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    A CFD-based compartmental modelling approach for long-term dynamic simulation of water resource recovery facilities.
    (2024-07) Sanchez-Larraona, G. (Gorka); Elduayen-Echave, B. (Beñat); Hernández, B. (Borja); Romay-Gainza, A. (Asier); Arnau, R. (Rosario)
    This article presents a methodology for compartmental model (CM) creation for long-term simulation of water resource recovery facilities (WRRFs). CMs are often focused on reproducing with a lower computational cost than previously simulated scenarios. In contrast, the methodology presented here can represent variable hydraulic conditions, based on the interpolation of data gathered from a set of computational fluid dynamics simulations that reproduce representative hydraulic scenarios. This is achieved by modelling with bidirectional flows the exchange flows between fixed compartments, which are defined based on the geometry of the reactors. The resultant hydraulic surrogate model can be implemented in commercial water treatment software to solve biochemical kinetics. The methodology was applied to simulate in WEST (R)-DHI, a WRRF in Vila-Real, Spain. In this contribution, the CM was validated with real plant data. The developed CM provided a quick response simulation with a high level of hydraulic and biochemical detail. This allowed us to observe a spatial distribution of component concentration, which could help with sensor location or plant optimisation. The methodology presented here could also be a useful enabler of digital twins to be implemented in WRRF.
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    Struvite precipitation in wastewater treatment plants anaerobic digestion supernatants using a magnesium oxide by-product
    (2023) Guembe, M. (M.); García, I. (I.); Aguilar-Pozo, V.B. (V. B.); Gómez, J. (J.); Chimenos, J.M. (J. M.); Elduayen-Echave, B. (Beñat); Lopez, A. (A.); Olaciregui-Arizmendi, K. (K.); Ayesa-Iturrate, E. (Eduardo); Astals-García, S.(Sergi)
    Struvite precipitation is a well-known technology to recover and upcycle phosphorus from municipal wastewater as a slow-release fertiliser. However, the economic and environmental costs of struvite precipitation are constrained by using technical-grade reagents as a magnesium source. This research evaluates the feasibility of using a low-grade magnesium oxide (LG-MgO) by-product from the calcination of magnesite as a magnesium source to precipitate struvite from anaerobic digestion supernatants in wastewater treatment plants. Three distinct LG-MgOs were used in this research to capture the inherent variability of this by-product. The MgO content of the LG-MgOs varied from 42 % to 56 %, which governed the reactivity of the by-product. Experimental results showed that dosing LG-MgO at P:Mg molar ratio close to stoichiometry (i.e. 1:1 and 1:2) favoured struvite precipitation, whereas higher molar ratios (i.e. 1:4, 1:6 and 1:8) favoured calcium phosphate precipitation due to the higher calcium concentration and pH. At a P: Mg molar ratio of 1:1 and 1:2, the percentage of phosphate precipitated was 53-72 % and 89-97 %, respectively, depending on the LG-MgO reactivity. A final experiment was performed to examine the composition and morphology of the precipitate obtained under the most favourable conditions, which showed that (i) struvite was the mineral phase with the highest peaks intensity and (ii) struvite was present in two different shapes: hopper and polyhedral. Overall,
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    New mass-based population balance model including shear rate effects: Application to struvite recovery.
    (Servicio de Publicaciones. Universidad de Navarra, 2020-12) Elduayen-Echave, B. (Beñat); Sanchez-Larraona, G. (Gorka); Grau-Gumbau, P. (Paloma)
    Struvite (MgNH4PO4·6H2O) precipitation is a promising solution for phosphorus recovery in wastewater treatment plants. Controlled struvite precipitation can help to reduce eutrophication in the receiving waterways, fight global phosphorus scarcity and reduce operational problems generated by the uncontrolled precipitation of the mineral in the pipes. Due to the generated interest, the description of the precipitation process has been already included in existing wastewater treatment modelling libraries. However, following the classic wastewater treatment modelling approach, the process has been generally included as a one-step kinetic model. This one-step model type is limited for technological design and optimization purposes, as it does not include information about the mechanisms by which the precipitation occurs, nor the particle size distribution, a key variable for the performance of struvite as an effective fertilizer. Therefore, the aim of this thesis has been to upgrade existing one-step kinetic models by developing a mathematical model that could describe in detail the mechanisms occurring in struvite precipitation in order to be able to predict the resulting particle size distribution. This model is a population balance model in which hydrodynamic effects have been considered. The population balance model has been constructed according to Ceit’s plant wide model methodology, guaranteeing mass and charge balance. Therefore, it can be combined with the simulation of other unit processes used to describe wastewater treatment plants in a systematic and straightforward way. A sensitivity and collinearity analysis performed in the thesis, demonstrated that the model is coherent in its structure and valid to represent struvite precipitation processes. In order to incorporate the hydrodynamic effects to the model, results obtained in an experimental campaign where struvite precipitation was analysed under different mixing and saturation conditions in two different experimental set-ups, were used. Obtained results showed that a higher mixing intensity could be linked with a faster pH decay, an increasing particle density and lower particle size. These effects were included in the population balance model using a calibration procedure based on Bayesian Monte Carlo techniques. From the calibration procedure, new kinetic laws were proposed for struvite nucleation and growth, where the effect of the hydrodynamics had been decoupled by explicitly including the shear rate as a process variable.