Committee:
     PRESIDENT: DOSTA PARRAS, JOAN
     SECRETARI: GIBERT AGULLO, ORIOL
     VOCAL NO PRESENCIAL: REZAKAZEMI, MASHALLAH
Thesis abstract: This comprehensive research represents a significant stride in the exploration of innovative strategies aimed at enhancing ammonia recovery within diverse wastewater streams. The study is structured into distinct phases, each addressing crucial aspects of the ammonia recovery process. In the initial phase, the research focuses on augmenting membrane contactor performance, employing coagulation-flocculation (C/F) and aeration as preliminary treatments. The outcomes of this phase demonstrate substantial increases in both the mass transfer coefficient and overall efficiency ofammonia recovery, particularly notable when treating the real sidestream centrate. A pivotal finding underscores the efficacy of dosing aluminum sulphate (Al2(SO4)3) at 30 mg Al+/L in the C/F process, yielding remarkable efficiencies in the removal of chemical oxygen demand (COD), turbidity, and total suspended solids (TSS). Into the second phase, the study delves into the sustainable application of liquid-liquid membrane contactors (LLMC) for ammonia recovery. An array of experimental conditions is meticulously explored, with the results illuminating the considerable impact of replacing the acid washing liquid between steps on the overall performance of the LLMC. Additionally, the study highlights the nuanced relationship between the initial ammonia concentration and the subsequent recovery, providing valuable insights. This phase effectively showcases the potential versatility and efficiency of LLMCs in the valorization of ammonia within wastewater streams. The third and final phase introduces a novel asymmetric hollow fiber liquid-liquid membrane contactor (HF-LLMC) with distinctive selectivity for ammonia over water. The investigation entails a comprehensive examination of various operational parameters, including feed and acid flow rates, mass transfer coefficients, and acid consumption. Notably, the results affirm the high selectivity of the HF-LLMC for ammonia, coupled with minimal water transfer. This establishes the HF-LLMC as a promising technology for the recovery and concentration of ammonium in diluted urban and industrial streams. The amalgamation of these findings, approached with a global perspective, significantly contributes not only to the advancement of sustainable nutrient recovery technologies but also underscores their pragmatic feasibility for implementation within the frameworks of the circular economy and efficient resource management.

Committee:
     PRESIDENT: MEDINA CABELLO, FRANCISCO
     SECRETARI: CABOT CODINA, ANDREU
     VOCAL: VELASCO VÉLEZ, JUAN JESÚS
Thesis abstract: The processes used nowadays for hydrogen and syngas production require more sustainable alternatives to advance in the necessary decarbonisation to fight against climate crisis. Currently, the main process is methane steam reforming (MSR) using natural gas. In this thesis, the use of dry reforming of methane (DRM) is proposed as a method of producing syngas. DRM is an attractive alternative since the two reactants, methane and carbon dioxide, are gases with a high global warming potential (GWP). Moreover, they are found together in the biogas resulting from the anaerobic digestion of organic matter. In the actual state-of-the-art, Ni catalysts supported on a wide range of metal oxides have been extensively studied. However, the main disadvantage is the accumulation of carbon that causes deactivation.In Chapter 4, the application of CoRu bimetallic catalysts supported on CeO2 has been studied. The catalysts have been prepared by conventional incipient wetness impregnation and by mechanochemical methods. A screening of catalytic activity has been conducted, and in-situ characterisation (NAP-XPS and XRD) has been used to get insight into the nature and behaviour of the catalytic active sites. It has been observed how the addition of ruthenium directly impacts the reducibility of cobalt species and results in smaller nanoparticles, as demonstrated by temperature-programmed reduction (H2-TPR) and XRD, respectively. The results of NAP-XPS show how ruthenium is able to modify the metal-support interaction, evidenced by a greater Ce3+/Ce ratio in the bimetallic samples. The synthesis method influences the dispersion of Co and Ru on the surface; NAP-XPS data suggested a higher Ru concentration on the surface of the bimetallic ball-milled samples, indicating the formation of small Ru clusters during milling, as confirmed by TEM analyses. Samples prepared by mechanochemistry, both mono- and bimetallic, have higher activity and stability than those synthesised by the conventional impregnation method, achieving higher CH4 and CO2 conversions. CoRu/CeO2-BM catalyst turns out as a stable catalyst for 24 hours at 700 C and with an average H2/CO ratio close to 1.In Chapter 5, the application of the same CoRu formulation supported on a Mg-Al-O mixed oxide has been studied. For these catalysts, the effect of Ru addition and the use of different precursors has also been studied, observing an effect on the catalytic activity and stability related to a synergy between Co and Ru. Through a "Design of Experiments" approach, the impact of various parameters of mechanochemical synthesis, such as milling frequency, milling time, and precursor addition order, has been studied. It should be highlighted that the samples synthesised by mechanochemistry show a lower amount of carbon deposits, which is ascribed to the particular architecture of the catalytic active sites.Finally, in Chapter 6, characterisation under operating conditions (X-ray absorption spectroscopy and X-ray diffraction) of the main samples synthesised in the previous chapter is performed. In addition to studying dry methane reforming, a small amount of water vapour is added to the reaction to study the combined reforming of methane (CRM), where steam reforming and dry reforming occur simultaneously. It is also observed that in CRM the carbon deposition in samples prepared by mechanochemical methods is substantially lower than those synthesised by conventional impregnation.

Committee:
     PRESIDENT NO PRESENCIAL: TROVARELLI, ALESSANDRO
     SECRETARI: ANDREU ARBELLA, TERESA
     VOCAL: ESCUDERO RODRÍGUEZ, CARLOS
Thesis abstract: Heterogeneous catalysis is one of the most important chemical technologies available today to produce most chemicals at the basis of industrial production. The transition to a greener energy production demands new challenges and new chemicals to be used as energy sources and vectors. Established processes such as methane steam reforming (MSR) are used to produce hydrogen to be used in fuel cells, and syngas which is the base reactant mixture for the synthesis of other chemicals. Bio-methane generated from biomass or other renewable sources can be used to produce hydrogen and syngas in a sustainable way.One way to improve the performance of a heterogeneous catalyst is to prepare bimetallic catalysts exploiting the synergy between two different metals for the active phase. Catalyst synthesis is also a fundamental step to control the catalytic properties of the material and ultimately to increase the sustainability of the whole process. In this PhD thesis, two bimetallic systems based on Ni-Fe and Pt-Ni were studied for methane steamreforming. Together with the incipient wetness impregnation synthesis, one of the most common industrial methods to prepare catalystsmechanochemistry synthesis was used as a green chemistry alternative.In Chapter 4, Ni-Fe bimetallic catalysts have been studied on different supports comparing the two synthesis methods, the effect of the support and the amount of Fe in the alloy. Iron is a redox promoter which can enhance the coke resistance of Ni-based catalysts, and it should provide sulphur resistance too. Thorough investigation with synchrotron in situ techniques such as XRD and NAP-XPS under reaction conditions allowedto study the catalyst structure during the reaction. The rearrangement of the Ni-Fe particles and theenrichment of Fe on the surface was observed under MSR conditions. Other catalysts based on different support have shown different behaviours: on non-reducible oxide supports, the activity of the bimetallic samples was equal or beter compared with the monometallic ones. For low-surface area CeO2, milled samples showed a great improvement of the catalytic activity due to the increased surface area and metal dispersion; for other non-reducible supports, the milled catalysts showed beter performances and in the case of the MG70 the activity of the bimetallic milled samples was as high as the monometallic, while theimpregnated samples showed lower activity with increasing Fe loading.In Chapter 5, PtNi/CeO­­2 catalysts have been prepared focusing on the mechanochemical synthesis and in finding the correlation between the synthesis parameters, the material’s structure, and the catalytic activity.Platinum addition to Ni-based catalysts increases the resistance to carbon formation and the stability of metallic Ni during the reaction. The characterisation of the catalysts by in situ NAP-XPS and XANES indicated that different levels of interaction between Ni, Pt and CeO2 were obtained during the synthesis, and this has been directly correlated with the different catalytic activity. Remarkably, the surface of the bimetallic catalystwas completely free of carbon atier the reaction, while the monometallic sample clearly showed theformation of solid coke.

Committee:
     PRESIDENT: SERRANO PURROY, DANIEL
     SECRETARI: MARTI GREGORIO, VICENÇ
     VOCAL: MAYORDOMO HERRANZ, NATALIA
Thesis abstract: High-level radioactive waste, such as spent nuclear fuel (SNF) from nuclear power plants, remains dangerous for hundreds of thousands of years. To manage them properly and avoid harm to human health and the environment, deep geological repository (DGR) is considered the internationally accepted management option. The DGR is based on a multi-barrier system that isolates waste from the biosphere until its radioactivity drops to safe levels. Understanding the processes that affect the SNF is essential to ensure the long-term safety of the DGR.The release of radionuclides upon contact with groundwater depends on their chemical state and location. While some are released instantaneously, the majority remain retained in the UO2 matrix, being their release controlled by the oxidative dissolution of UO2. The composition of groundwater, rich in bicarbonate ions, can change after interacting with the different barriers. Due to the presence of cement in the DGR design, its interaction with water can produce a very alkaline leachate (pH>13) rich in calcium and silicate ions. The addition of fly ash to cement can also introduce sulphur ions to the medium, which may affect the retention of radionuclides.Gadolinia (Gd2O3) is used as a neutron absorber in light water reactors to extend the life of the fuel cycle. The incorporation of Gd into the crystalline structure of UO2 could affect the oxidation of uranium. In this work, three different approaches have been studied to evaluate this effect:Gd2O3-doped UO2 samples with different levels of porosity (to simulate the microstructure of highly burned fuel) were exposed to different atmospheres in the presence of humidity. Porosity turned out to be a critical factor in oxidation, since, in its absence, Gd inhibited oxidation, while porous samples showed a dependence on the atmosphere present, with a reactivity: synthetic air>Ar>H2. Electrochemical experiments in the presence of silicate and calcium recorded lower values of current density and corrosion potentials as Gd content increased, indicating less surface oxidation. Finally, the dissolution rate was evaluated in bicarbonate solutions at pH>9. While bicarbonate influences the dissolution rate of UO2, samples doped with Gd2O3 showed very low and constant dissolution rates. XPS analysis of the samples suggests that Gd retards the oxidation of U(V) to U(VI) and, therefore, the dissolution of UO2. In summary, these studies determined a retarding effect of gadolinium on the oxidation/dissolution of UO2.Regarding the release and migration of radionuclides, those sensitive to redox potential, such as Mo and Tc, were studied. Leaching experiments demonstrated that Mo release increases at high pH through a surface complexation mechanism promoted by OH- and the oxidation of Mo(s) to Mo(VI), with a high contribution to the instantaneous release fraction. Since Mo could buffer the oxidation of UO2, knowing the chemical state of Mo in CNG would help predict the oxidation state of UO2, and therefore the release of radionuclides.The interaction of radionuclides with minerals, such as alumina, can affect their migration. Tc is a radionuclide of great environmental concern due to its long half-life, high toxicity and mobility under oxidizing conditions. The reductive immobilization of Tc(VII) to Tc(IV) by pre-adsorbed sulphide on alumina under anoxic conditions was studied. Although the presence of alumina did not improve the retention of Tc(VII), XAS analysis determined Tc(IV), and re-oxidation experiments suggested that the Tc species obtained are stable in the presence of oxygen.

Committee:
     PRESIDENT: CABALLERO SUÁREZ, JOSÉ ANTONIO
     SECRETARI: MONTASTRUC, LUDOVIC
     VOCAL NO PRESENCIAL: LEONARD, GRÉGOIRE
Thesis abstract: The quest for sustainable development is both urgent and complex. Paradigms like circular economy (CE) and industrial symbiosis (IS) aim to address this challenge by promoting strategies to achieve a more efficient use of available resources and a reduction of generated waste. However, the implementation of these paradigms faces significant practical challenges that hinder their widespread application. Despite the availability of process integration (PI) methods and tools to identify opportunities for sharing resources and closing material loops in the process industry, and the growing computational power to handle increasingly complex problems, the practical challenge remains to quantitatively, fairly, and transparently demonstrate that the proposed solutions satisfy the objectives of all decision-makers involved.Driven by this challenge, this Thesis aims to bridge the gap by developing frameworks that facilitate multi-actor multi-criteria decision-making. To achieve this, appropriate methods from game theory (GT) are identified to address the multi-actor problem, evaluating the alternatives based on Life Cycle Assessment (LCA) that allows for obtaining quantitative, comparable, and transparent indicators for the multi-criteria problem. Focusing on the process industry, all developed solution methods leverage process systems concepts and mathematical programming. In the first part of this Thesis, GT is utilized as a tool to find solutions that are fair and acceptable for all actors involved. To that end, cooperative profit allocation approaches are applied to PI problems, which have been designed using a proposed framework to reach targeted benefits (economic and environmental) through the introduction of waste-to-resource technologies. Moreover, a Stackelberg competition based framework for the identification of stable outcomes of non-cooperative bargaining between the actors in waste-to-resource pathways, in the absence of a regulatory authority, is proposed and applied a plastic waste recycling case. The second part employs LCA as a tool to quantify the environmental benefits of implementing CE and IS solutions, as a procedure to systematically consider interlinked phenomena such as burden-shifting. Furthermore, this Thesis advances life cycle optimization (LCO) by integrating mathematical programming with LCA to leverage extensive data from commercial Life Cycle Inventory (LCI) databases. Practical contributions include the development of the ``Python-based User-defined Lifecycle Product Optimization'' (PULPO) method, which exploits LCI databases to globally evaluate the individual decisions of the involved processes and their interdependencies. This approach allows the consideration of global supply chain targets in the decision-making of specific links in the chain.The third part synthesizes the insights and approaches developed in the previous two parts and proposes the cooperative PI-MAMCA framework, which includes quantitative procedures for evaluating the stability in the allocation of benefits, based on previously established approaches for multi-actor multi-criteria decision-making. For the first time, simultaneous allocation of various benefits among multiple actors is proposed, demonstrating that, even when considering multiple criteria, fair and acceptable solutions exist.

Committee:
     PRESIDENT: PAWLOWSKI, SYLWIN
     SECRETARI: GIBERT AGULLO, ORIOL
     VOCAL NO PRESENCIAL: LICON BERNAL, EDXON EDUARDO
Thesis abstract: Brines should be treated as waste and disposed accordingly. Nevertheless, brines are typically discharged back into water bodies, thereby affecting the marine environment, soil quality, and groundwater. However, the potential benefits and applications of these brines are worth further investigation. In addition to the high concentration of salt (NaCl), some important elements, such as Critical Raw Materials (e.g. Li, Sr, Ga, Ge) can be found. This has increased interest in using brines as an alternative source for recovering strategic elements, the large content of strong electrolytes (e.g., NaCl and Na2SO4) has opened the possibility of using brines as a source to produce chemical commodities (e.g., strong acid and bases). Specifically , owing to the highly saline nature of brines, they are well-suited for use in electro-membrane processes such as Electrodialysis with Bipolar Membranes (EDBM). EDBM allows for the generation of chemicals from their corresponding salts; the protons and hydroxide ions generated in the bipolar membranes generate, together with the cations and anions removed from the salts , acidic and alkaline solutions, respectively. However, EDBM technology still needs to be improved to reduce the high energy expenses and boost the concentration of products. EDBM remains a non-scale-up technology that requires more research and study to be able to compete with well-established technologies to produce acidic/alkali solutions from brines, including chlor-alkali technology.There fore, it is necessary to investigate mass transfer processes in complex systems such as those involving EDBM with solutions of high salt composition. Additionally, there are a limited number of bipolar membranes and limited information on the behaviour of the membranes in concentrated solutions .In this context, the present thesis aims to carry out an extensive evaluation of the production of acidic and alkaline solutions from brines using EDBM. This involved moving from theoretical proposals based on Computational Fluidic Dynamics (CFO) models to a comprehensive experimental campaign using synthetic brines, in which numerous operational parameters were examined. Two CFO models were introduced using 2-0 geometry, one was time-dependent and the other was not; both aimed to study the mass transpo rt, potential distribution, and water splitting phenomena.The results from both theoretical studies and experiments offered valuable insights into how to enhance the performance of EDBM and make them more competitive with current popular technologies, ultimately leading to the growth and expansion of this technology.

Committee:
     PRESIDENT: GIBERT AGULLO, ORIOL
     SECRETARI: CAMA I ROBERT, JORDI
     VOCAL: BRINGAS ELIZALDE, EUGENIO
Thesis abstract: The pyrometallurgical industry faces challenges in maintaining copper purity due to increasing impurities in the primary resources (Sb, Bi, and As) that can reach the electrorefining unit forming insoluble minerals, compromising copper purity. To address this, the copper industry is developing actions to reduce the presence of such impurities along different stages of the process flow sheet acting at: i) the final stages of the electrorefining process or ii) the mineral concentration stages (e.g. flotation). The main target objective of this PhD thesis has been centred in the evaluation of technological solutions to reduce such impurities (Sb, Bi and As) by introducing a sustainability concept, where elements considered as critics for the European Union (i.e. Sb and Bi) are recovered. In the case of acting in the final stage of electrorefining, ion-exchange (IX) technology is employed at industrial scale to continually treat the copper electrolyte of the electrorefining stage, removing Sb and Bi and ensuring a high copper purity. Upon IX resin saturation, regeneration with 6 M HCl produces a concentrated eluate containing Sb, Bi (7–14 g/L each), and As (1–4 g/L). Currently, lime treatment removes these impurities producing large volumes of waste containing As, Sb and Bi. Therefore, two valoriaztion routes of the eluate were evaluated based on solvent extraction (SX) and selective precipitation. SX route was based on the use of a solvated mixture of alkylphosphine oxides (commercialized as Cyanex 923) dissolved in kerosene and 1-decyl alcohol (10%) as a phase modifier. The separation factors of Sb, Biand As were evaluated and optimized as a function of extractant concentration and aqueous to organic (A/O) phase ratio. The results showed that 39% Bi and 78% Sb could be extracted with low co-extraction of As (<2.5%) working at the lowest Cyanex 923 concentration (0.15 mol/L) and A/O ratio of 1/3. Using 8M HNO3 as a stripping agent, both Sb and Bi were easily recovered (>90%). During the direct precipitation of eluate, As(V) forms an insoluble antimony arsenate (SbAsO4(s)). Therefore, it is necessary to pre-treat the eluent with SO2(g) or NaHSO3(s) to reduce As(V) to the (+III) state valence state. In this case, antimony oxychloride (Sb4O5Cl2, purity >93%) and bismuth oxychloride (BiOCl, purity >95%) can be obtained sequentially using NaOH, NaHCO3 and/or Na2CO3 under appropriate pH control. The recovered high purity Sb4O5Cl2(s) and BiOCl(s), still containing a low content of As, could be converted into oxides in alkaline media, improving the final purity making them suitable for commercial use. The techno-economic implications of Sb and Bi showed that the recovery of BiOCl(s)/Sb4O5Cl2(s) and BiOCl(s)/Sb2O3(s) is economically feasible in copper metallurgy facilities, especially when Sb and Bi prices are higher than 8.5 and 9.5 €/kg, respectively. Overall, the results highlighted the economic and technical potential of implementing Sb and Bi recovery routes in copper metallurgy plants, in line with the ambitious circular economy targets set by the European Union.In the case of approaching the reduction of the presence of impurities in the mineral copper concentrates, tetrahedrite (Cu12Sb4S13(s)) was selected as case study. Selective leaching of antimony using microwave-assisted technology in a laboratory scale was investigated at different concentrations of Na2S and NaOH, solid/liquid ratio, temperature, and microwave power. Results indicated that Sb dissolution is highly dependent on the concentrations of leaching reagents (Na2S/NaOH) and the temperature. The Sb content in the copper concentrate was successfully reduced from 1.1% to less than 0.2%, making it suitable for copper concentrate metallurgy processing. A proposal of potential integration of both alkaline leaching and selective precipitation of the Sb could provide a sustainable solution, promoting the recovery of a critical raw material for the European industry

Committee:
     PRESIDENT: PLANAS CUCHI, EULALIA
     SECRETARI: PALACIOS ROSAS, ADRIANA
     VOCAL: DEMICHELA, MICAELA
Thesis abstract: In recent decades, there has been an increase in the frequency of natural events, coinciding with the simultaneous development of industrial activities in many countries. Consequently, the frequency of Natech accidents, which are technological disasters triggered by natural hazards, has also risen. This trend has spurred researchers to explore new risk analysis methods to prevent and mitigate potential damage to populations, the environment, and industrial facilities. There is a growing awareness in the literature about the impact of natural events, particularly when they occur concurrently, cascade, or accumulate over time.This thesis proposes a research initiative to conduct a risk assessment that includes the Natech risk associated with strong winds. The primary objective is to develop a methodology for analyzing Natech risk in storage units in coastal zones that are particularly vulnerable to extreme weather events.Firstly, the thesis introduces the integration of natural events, specifically strong winds, into a quantitative Natech risk analysis methodology. This integration represents a significant advancement in assessing the potential impacts of technological accidents triggered by natural events. By incorporating strong winds as a hazard, the methodology offers a more comprehensive approach to evaluating the vulnerability of industrial facilities, especially storage tanks, to natural-technological events. This integration enables stakeholders to better understand and quantify the risks posed by Natech events involving strong winds, facilitating the implementation of targeted mitigation measures and enhancing preparedness. Ultimately, it contributes to improving the resilience of industrial facilities and surrounding communities to the risks posed by natural events.Secondly, the thesis describes the development of two models for environmental and socioeconomic risk assessment, respectively. These models provide a comprehensive framework for evaluating the potential environmental and socioeconomic impacts of Natech events, thereby enhancing the understanding of the overall risk landscape. By incorporating previously overlooked vulnerable elements, such as cultural heritage sites, sensitive environmental areas, water catchment sites, and so on, the models offer a more holistic perspective on Natech risks, ensuring that mitigation strategies can protect not only human safety and infrastructure, but also socioeconomic and environmental assets.Thirdly, the thesis outlines the development of a computational tool designed to facilitate the implementation of these models. This tool streamlines the risk assessment process, enabling stakeholders to analyze and manage Natech risks efficiently.Overall, the generation of these models and the accompanying computational tool represents a significant advancement in Natech risk management. By integrating environmental and socioeconomic considerations into the risk assessment process, these models provide a more robust foundation for decision-making and emergency preparedness, ultimately contributing to the resilience of communities and ecosystems in the face of Natech events. Finally, the methodology is applied in a case study to verify its applicability

Committee:
     PRESIDENT: OLIVERAS MENOR, IMMACULADA
     SECRETARI: ÁGUEDA COSTAFREDA, ALBA
     VOCAL: DE ALMEIDA, MIGUEL ABRANTES DE FIGUEIREDO BERNARDO
Thesis abstract: Human population is growing worldwide, so are the places where we live, move and work. These places, like neighbourhoods, networks for transportation of people and materials or industries are frequently near, or even immersed, within forested areas. These areas, where human activity meets with forestlands, are known as the wildland-urban interface. Here, we, our properties and our activities get exposed to forest fires, with a high potential for the loss of human lives and assets. The solution to this problem is complex, comprises various aspects and involves reducing the risk at the wildland-urban interface.One of the main features of this problem is the vegetation, that act as a natural fuel for the fire. Here, the ornamental vegetation has an active role driving the fire within the wildland-urban interface, while the wild vegetation drives the fire front from the forest where the fire ignites to the boundaries of our settlements.The goal of this thesis is to assess the fire hazard at the wildland-urban interface, addressing the problem from the perspective of these natural fuels. To meet this goal, the chapters of this thesis characterize and model the burning behaviour of ornamental and wild vegetation and develop documents, methodologies and tools to implement this knowledge.To characterize ornamental vegetation and the way it burns, this thesis shows detailed fuel samplings, real-scale burning experiments and a forensic study of a real fire in the wildland-urban interface. With this information it was possible to develop custom scripts to simulate ornamental vegetation fires in Fire Dynamics Simulator, which is a Computational Fluid Dynamic simulator specially designed to simulate heat and smoke transportation from the fire.To characterize fires burning wild vegetation, this thesis focuses on the boundaries of the wildland-urban interface and develops models able to predict flame geometry from the environmental conditions, which is necessary to forecast fire impact on the people and the structures. Finally, this thesis presents a software ready to be used by fire managers that uses the information obtained from these models to size the preventive infrastructures that surround our settlements.

Committee:
     PRESIDENT: PAIS VILAR, VÍTOR JORGE
     SECRETARI: SOLER TURU, LLUIS
     VOCAL: GARCIA MONTAÑO, JULIA
Thesis abstract: The objective of this thesis is to contribute to the development of mathematical modeling of Advanced Oxidation Processes (AOPs) aimed at the competent treatment of recalcitrant organic compounds in wastewater. In particular, the Ph.D. thesis first focuses on developing mathematical models of AOPs, implementing these models in software tools, and enabling a deeper understanding of the complex nature of these processes through the detailed simulation of the evolution of chemical species along the reaction time for diverse and unexplored scenarios. Hence, these tools are next used for fitting the models to the experimental data obtained in the laboratory in the course of the thesis or reported in the literature. The fitted models are analyzed and refined through sensitivity analysis techniques, and finally, they are validated and their accuracy assessed. Models are mainly used for addressing operational issues, but also design aspects are considered in regard of the simulation of integrated processes using AOPs and conventional biotreatment processes.The thesis specifically addresses the development of a model for AOPs, above all photo-Fenton processes, including flexible H2O2 supply given as a function of time. The model contributes a practical tool aimed at providing model-based simulation for solving the problem of the management of the H2O2 dosage profile of the photo-Fenton process.The thesis also addresses the problem of the pH dependency of the photo-Fenton by modeling the possibility of performing the photo-Fenton process at near-neutral pH. This is studied by considering the use of iron complexing agents such as ethylenediamine disuccinic acid (EDDS). In a subsequent stage, as a step forward in improving photo-Fenton processes, a reported kinetic model of the Fe(3+)-EDDS mediated photo-Fenton process is extended to include the reactions occurring in the absence of H2O2, when EDDS(• 3- )radical generated from the lysis of the Fe(3+)-EDDS complex is responsible for the organic matter degradation. This is achieved by adopting a novel semi-empirical approach based on lumping radical species.Ozonation of wastewater is also studied as a different case of AOPs, focusing in the modeling of ozone decay during the treatment of secondary effluents containing organic matter. This is addressed by proposing a new model, based again in the used of lumped or surrogate concentrations. The ozone model developed is shown to be capable of describing the complex profile of the ozone at different initial concentrations, and has proved accurate to describe the experimental data obtained in the lab, as well as data reported in the literature.The modeling approach adopted in this thesis has also been used to explore integrated processes combining AOPs with other processes, namely conventional biotreatment processes which main acknowledged limitation is the incapacity to remove recalcitrant compounds from wastewaters. The study combined the AOP models developed with standard models such as ASM1 to map the correspondence between the variables employed in each model, and produce the simulation of different scenarios combining these two technologies.As a final remark, the thesis has also addressed the design and development of chemical reactors, particularly prototypes for photo-Fenton processes using 3D-printing. This last study addresses the selection of materials according to different criteria for reactor prototyping and subsequent testing of the chemical suitability of the reactor for carrying out AOPs.

Committee:
     PRESIDENT: SASTRE REQUENA, ANA MARIA
     SECRETARI: SIRÉS SADORNIL, IGNACIO
     VOCAL NO PRESENCIAL: KOLODYNSKA, DOROTA
Thesis abstract: Nowadays, the increasing demand for raw materials caused by population growth and industrialisation moved the European Union (EU) to improve resource efficiency and as result the Critical Raw Materials/Strategic Raw Materials (CRMs/SRMs) list was created, which includes those raw materials with economic importance and/or supply risk for the EU. Seawater mining has emerged in the last years as a potential solution to resource scarcity. However, many valuable minerals present in seawater are considered Trace Elements (TEs) due to their low concentration (mg/L or µg/L), demanding energy-intensive and selective methods to extract them, which in the end can compromise their recovery from a technical and economic point of view. Research on Trapani saltworks (Sicily, Italy) and on the ones located at the Mediterranean basin revealed that the natural evaporation process in salt crystallisation ponds concentrates seawater components, producing a bittern (brine generated after NaCl(s) crystallisation in saltworks) with a concentration 40 times higher than seawater. Consequently, these bitterns, typically considered waste, present a potential viable source for extracting TEs identified as CRMs/SRMs.Evaluation of TEs extraction from bitterns using various sorbents demonstrated promising results. Whereas N- methylglucamine sorbents (S108, CRB03, CRB05) were highly efficient in terms of sorption/desorption for recovering B, Co, Ga and Ge, those containing aminophosphonic groups (S940, IRC747) effectively targeted Co, Ga and Sr. Similarly, one impregnated sorbent (MTX8010) exhibited outstanding selectivity towards Ga. Sorption mechanisms, based on bitterns’ speciation and sorbents’ functional group properties, were postulated to explain the extraction and selectivity patterns observed.Considering that some of the TEs were at concentrations of 0.5 mg/L in the bitterns, lab-scale packed-bed columns of these sorbents showed effective retention of TEs and high sorption capacities (e.g., 11 mg/g B for CRB03, >2.7 mg/g Co for S940, 0.9 mg/g Ga for MTX8010). The retained TEs were subsequently recovered from the sorbents by acidic desorption, resulting in a TEs-rich stream with a concentration of B up to 11-fold higher than seawater when CRB03 was used, 710-fold higher on Co when S940 was employed or 154-fold higher on Ga when MTX8010 was utilised, thus enhancing their extractionfeasibility.Diffusion Dialysis (DD) facilitated the recovery of the excess of acid used during the elution of the packed-bed resins. Flow rate and water to acid flow rate ratio effect were evaluated on acid recovery and the losses of metals. Under the optimum conditions (water to acid ratio of 1 working at 2.11 L/(m2 ·h)), 60% HCl was recovered while metallic TEs cations (i.e., Co, Ga, Sr) were completely rejected (>99%). However, certain leakage occurred for B (34%) and Ge (22%) due to their presence as neutral species (H3BO3(aq) and Ge(OH)4(aq)).The TEs could be recovered via precipitation/crystallisation from the packed-bed column eluates after treating them with DD.Co(OH)2(s), GaOOH(s) and SrSO4(s) were successfully precipitated using NaOH as precipitant agent. H3BO3(s) was crystallised from an eluate collected after processing a real bittern with N-methylglucamine packed-bed columns, leading to 70% of B recovery. In addition, a reaction with tannic acid allowed to recover 92% of Ge.Integration of sorption/desorption, DD, and precipitation/crystallisation processes enabled the definition of potential successful recovery schemes of several TEs minerals from bitterns, showcasing their potential as alternative CRMs/SRMs sources.