Exploring the pressurized heterogeneous electro-Fenton process and modelling the system

In this research, a bench-scale installation was tested for the heterogeneous electro-Fenton treatment of clofibric acid. The setup consists of a pressurized flow-through electrochemical cell equipped with a catalyst fluidized-bed and aerated with a jet mixer. The novelty of the research is two-fold: the use of the pressurized-jet aerator on an electro-Fenton treatment is tested and it is one of the first studies combining pressure with heterogeneous catalysis in electro-Fenton. Moderate relative pressures, up to 2 bar, were analyzed. Initially, the electrogeneration of hydrogen peroxide was tested, showing that it is remarkably boosted by the application of pressure. Then, the elimination of clofibric acid by means of an electro-Fenton treatment was carried out at 0.12 and 0.25 A, using iron-containing alginate beads as the catalyst. Regardless of the current intensity, the increase from atmospheric pressure to 1 gauge bar boosted the elimination of the pollutant and reduced the specific energy consumption of the electrochemical cell. Specifically, at 0.25 A an abatement higher than 98% was achieved in 8 h at atmospheric pressure while only 1 h was required at 1 bar of gauge pressure. However, a further increase of the pressure to 2 bar did not report a major improvement. Moreover, the effect of pressure on the catalyst was analyzed, concluding that the integrity of the alginate beads was not compromised by pressure. In fact, the iron leaching was very similar at 0, 1 and 2 bar: around 30% after 8 h of treatment. Finally, a mathematical model was developed, using the experimental data to obtain the necessary fitting parameters, which allowed to understand better the behavior of the bench-scale reaction system.En esta investigación se probó una instalación a escala de banco para el tratamiento electro-Fenton heterogéneo del ácido clofíbrico. La configuración consta de una celda electroquímica de flujo presurizado equipada con un lecho fluidizado de catalizador y aireado con un mezclador de chorro. La novedad de la investigación es doble: se prueba el uso del aireador de chorro a presión en un tratamiento de electro-Fenton y es uno de los primeros estudios que combina presión con catálisis heterogénea en electro-Fenton. Se analizaron presiones relativas moderadas, hasta 2 bar. Inicialmente se probó la electrogeneración de peróxido de hidrógeno, demostrando que se potencia notablemente con la aplicación de presión. A continuación, se realizó la eliminación del ácido clofíbrico mediante un tratamiento electro-Fenton a 0,12 y 0,25 A, utilizando como catalizador perlas de alginato con contenido de hierro. Independientemente de la intensidad de la corriente, el aumento de la presión atmosférica a 1 bar manométrico potenció la eliminación del contaminante y redujo el consumo energético específico de la celda electroquímica. Concretamente, a 0,25 A se logró una reducción superior al 98% en 8 h a presión atmosférica mientras que solo se requirió 1 h a 1 bar de presión manométrica. Sin embargo, un aumento adicional de la presión a 2 bar no reportó una mejora importante. Además, se analizó el efecto de la presión sobre el catalizador, concluyendo que la integridad de las perlas de alginato no se vio comprometida por la presión. De hecho, la lixiviación del hierro fue muy similar a 0, 1 y 2 bar: en torno al 30% tras 8 h de tratamiento. Finalmente, se desarrolló un modelo matemático, utilizando los datos experimentales para obtener los parámetros de ajuste necesarios

Towards a more realistic heterogeneous electro-Fenton

With the aim of bringing the heterogeneous electro-Fenton (EF) treatment one step closer to a more realistic operation, the scaling-up of that technology was evaluated. Assays were performed firstly at lab scale in a stirred-tank reactor and then at bench scale in a flow setup including a jet aerator and a microfluidic flow-through electrochemical cell. A fluidized-bed reactor was added to the bench-scale installation in order to retain the solid catalyst, iron-containing alginate beads. To the best of the authors’ knowledge, there are no precedent studies reporting a heterogeneous EF treatment in a similar bench scale-configuration. Hydrogen peroxide generation and clofibric acid removal were assessed at both scales at current intensities of 0.12 and 0.25 A. Results showed that the scaled-up treatment was more efficient and cost-effective: at bench scale 18 times more volume was treated, the mass production of hydrogen peroxide was 28 higher and the specific cost for the removal of clofibric acid was cut by more than half. The most efficient treatment turned out to be the EF performed at 0.12 A at bench scale. Those results highlighted the importance of the reactor design in the scaling-up process. Additionally, aromatic intermediates were detected by liquid chromatography-mass spectrometry (LC-MS) and a degradation route was suggested. Carboxylic acids were also measured by HPLC confirming that the pollutant is mineralizing.Con el objetivo de acercar un paso más el tratamiento electro-Fenton heterogéneo (EF) a una operación más realista, se evaluó el escalamiento de esa tecnología. Los ensayos se realizaron primero a escala de laboratorio en un reactor de tanque agitado y luego a escala de banco en una configuración de flujo que incluía un aireador de chorro y una celda electroquímica de flujo continuo de microfluidos. Se agregó un reactor de lecho fluidizado a la instalación a escala de banco para retener el catalizador sólido, perlas de alginato que contienen hierro. Según el leal saber y entender de los autores, no existen estudios precedentes que informen un tratamiento de FE heterogéneo en una configuración de escala de banco similar. La generación de peróxido de hidrógeno y la eliminación de ácido clofíbrico se evaluaron en ambas escalas a intensidades de corriente de 0,12 y 0,25 A. Los resultados mostraron que el tratamiento ampliado fue más eficiente y rentable: a escala de banco se trató 18 veces más volumen, la producción masiva de peróxido de hidrógeno fue 28 veces mayor y el costo específico para la remoción de ácido clofíbrico se redujo a más de la mitad. El tratamiento más eficiente resultó ser el EF realizado a 0,12 A a escala de banco. Esos resultados destacaron la importancia del diseño del reactor en el proceso de ampliación. Además, los intermedios aromáticos se detectaron mediante cromatografía líquida-espectrometría de masas (LC-MS) y se sugirió una ruta de degradación. Los ácidos carboxílicos también se midieron por HPLC confirmando que el contaminante se está mineralizando. 12 A a escala de banco. Esos resultados destacaron la importancia del diseño del reactor en el proceso de ampliación. Además, los intermedios aromáticos se detectaron mediante cromatografía líquida-espectrometría de masas (LC-MS) y se sugirió una ruta de degradación. Los ácidos carboxílicos también se midieron por HPLC confirmando que el contaminante se está mineralizando. 12 A a escala de banco. Esos resultados destacaron la importancia del diseño del reactor en el proceso de ampliación. Además, los intermedios aromáticos se detectaron mediante cromatografía líquida-espectrometría de masas (LC-MS) y se sugirió una ruta de degradación. Los ácidos carboxílicos también se midieron por HPLC confirmando que el contaminante se está mineralizando

Cara a unha futura aplicación real do tratamento electro-Fenton heteroxéneo para a remediación de augas

In recent years, the Advanced Oxidation Processes (AOPs) have emerged as a promising alternative for the effluent treatment due to the great versatility that show in the degradation of organic pollutants of diverse origins. This versatility lies in the powerful action of the agent generated in all the AOPs: the hydroxyl radical. However, the increasing in the use of synthetic pollutants, related to the expansion of industrialization, makes it necessary to validate these new technologies for its application in the removal of new pollutants, such as the so-called emerging contaminants. In this context, this thesis is focused in optimizing and controlling the AOPs used for the treatment of emerging contaminants. Different AOPs will be studied: i) anodic oxidation, where an electric field generates hydroxyl radicals on the anode surface, ii) Fenton process, where hydroxyl radicals are obtained through the reaction of hydrogen peroxide and iron and iii) the electro-Fenton process, where an electric field is applied and iron is added in order to generate the hydroxyl radical in both the anode surface and through the reaction of hydrogen peroxide and iron. For the various AOPs, the treatment will be optimized depending on the selected pollutant and taking into account the operating variables and the type of reactor employed. This optimization will be carried out by performing a design of experiments using specialised software (e.g. Design expert) which allows evaluating and analysing the obtained results.En los últimos años los Procesos de Oxidación Avanzada (POAs) se han revelado como una interesante alternativa en el tratamiento de efluentes debido a la versatilidad que demuestran en la degradación de contaminantes orgánicos de diferente naturaleza. Esta versatilidad radica en la potente acción que demuestra el agente generado en todos ellos, el radical hidroxilo. No obstante el aumento de contaminantes sintéticos, producto del incremento de la industrialización, obliga a validar estas nuevas tecnologías para su aplicación en la degradación de nuevos contaminantes como son los denominados contaminantes emergentes. En este contexto, esta tesis se centrará en el uso de herramientas de optimización y control para las aplicaciones de los POAs en el tratamiento de contaminantes emergentes. Se plantea el estudio de distintos POAs: i) oxidación anódica, en el que el campo eléctrico genera radicales hidroxilo sobre la superficie del ánodo, ii) Proceso Fenton, donde se obtienen radicales hidroxilo mediante la reacción de hierro y peróxido de hidrógeno y iii) el proceso electro-Fenton, en el que se aplica un campo eléctrico y se añade hierro para generar el radical hidroxilo tanto en la superficie del ánodo como por reacción entre peróxido de hidrógeno e hierro. Para los distintos POAs, se optimizará el tratamiento en función del contaminante seleccionado y teniendo en cuenta las variables de operación y tipo de reactor utilizado. Esta optimización se realizará mediante un diseño de experimentos utilizando software especializado (ej Design expert) que permitirá la evaluación y análisis de los resultados obtenidos.Nos últimos anos, os Procesos de Oxidación Avanzada (POAs) reveláronse como unha interesante alternativa no tratamento de efluentes debido á versatilidade que mostran na degradación de contaminantes orgánicos de diferente natureza. Esta versatilidade radica na potente acción que demostra o axente xerado en todos eles: o radical hidroxilo. Non obstante, o aumento de contaminantes sintéticos, produto do incremento da industrialización, obriga a validar estas novas tecnoloxías para a súa aplicación na degradación de novos contaminantes, como son os denominados contaminantes emerxentes. Neste contexto, esta tese centrarase no uso de ferramentas de optimización e control para as aplicacións dos POAs no tratamento de contaminantes emerxentes. Proponse o estudo de distintos POAs: i) oxidación anódica, onde o campo eléctrico xera radicais hidroxilo sobre a superficie do ánodo, ii) proceso Fenton, no que se obteñen radicais hidroxilo mediante a reacción de peróxido de hidróxeno e ferro e iii) proceso electro-Fenton, no que se aplica un campo eléctrico e se engade ferro para xerar o radical hidroxilo tanto na superficie do ánodo como por reacción entre peróxido de hidróxeno e ferro. Para os distintos POAs, optimizarase o tratamento en función do contaminante seleccionado e tendo en conta as variables de operación e tipo de reactor empregado. Esta optimización levarase a cabo mediante un deseño de experimentos empregando software especializado (ex: Design expert) que permitirá a avaliación e análise dos resultados obtidos.Ministerio de Economía y Competitividad | Ref. CTM2014-52471-RAgencia Estatal de Investigación | Ref. CTM2017-87326-RXunta de Galicia | Ref. ED431C 2017/47Xunta de Galicia | Ref. and ED431C 2021/43Ministerio de Educación, Cultura y Deporte | Ref. FPU16/0264

Double benefit of electrochemical techniques: treatment and electroanalysis for remediation of water polluted with organic compounds

Concern about the current pollution of water environments and the inefficacy of conventional water treatments for the elimination of refractory contaminants has placed electrochemistry in the spotlight. With the objective of demonstrating the diverse applications that electrochemical techniques can have in the area of water remediation, this study is focused on the use of three different methods: (i) electro-Fenton process with heterogeneous catalyst as the treatment for the degradation of the target compounds; (ii) cyclic voltammetry for the characterization of the electrochemical system, and (iii) differential pulse voltammetry for the monitoring of the evolution of the degradation process. Four organic compounds were selected as target pollutants: the ionic liquid 1,3-Bis(2,4,6-trimethylphenyl)imidazolinium chloride, Mesitol, Mesidine and 2,5-Xylidine. Results were corroborated and complemented with chromatographic and total organic carbon (TOC) measurements. After 420 min of heterogeneous electro-Fenton treatment, almost 80% of TOC abatement was achieved for the ionic liquid and more than 90% for Mesitol, Mesidine and 2,5-Xylidine. Cyclic voltammetry studies for Mesitol and Mesidine suggested the formation of a polymeric film which remains adsorbed on the electrode surface. Finally, it was possible to conclude that the coupling of differential pulse voltammetry with the heterogeneous electro-Fenton process provides useful information about the evolution of the degradation process of pollutants in just a couple of minutes.Xunta de Galicia | Ref. ED431C 2017/47Agencia Estatal de Investigación | Ref. CTM2017-87326-RMinisterio de Educación, Cultura y Deporte | Ref. FPU16/0264

Current advances and trends in electro-Fenton process using heterogeneous catalysts – A review

Over the last decades, advanced oxidation processes have often been used alone, or combined with other techniques, for remediation of ground and surface water pollutants. The application of heterogeneous catalysis to electrochemical advanced oxidation processes is especially useful due to its efficiency and environmental safety. Among those processes, electro-Fenton stands out as the one in which heterogeneous catalysis has been broadly applied. Thus, this review has introduced an up-to-date collation of the current knowledge of the heterogeneous electro-Fenton process, highlighting recent advances in the use of different catalysts such as iron minerals (pyrite, magnetite or goethite), prepared catalysts by the load of metals in inorganic and organic materials, nanoparticles, and the inclusion of catalysts on the cathode. The effects of physical-chemical parameters as well as the mechanisms involved are critically assessed. Finally, although the utilization of this process to remediation of wastewater overwhelmingly outnumber other utilities, several applications have been described in the context of regeneration of adsorbent or the remediation of soils as clear examples of the feasibility of the electro-Fenton process to solve different environmental problems.Xunta de Galicia | Ref. ED431C 2017/47Ministerio de Economía y Competitividad (España) | Ref. CTM2014-52471-

Electroanalytical techniques applied to monitoring the electro-Fenton degradation of aromatic imidazolium-based ionic liquids

In this study, the degradation of the ionic liquid (IL) 1,3-dicyclohexylbenzimidazolium chloride ([DCy6bim][Cl]) was carried out by applying an heterogeneous electro-Fenton (HEF) treatment using iron alginate spheres (FeAS) as catalyst. Initial trials were performed at current between 50 and 250 mA, different FeAS dosages (1–5 g), and [DCy6bim][Cl] concentrations (70–280 mg L−1) as key parameters for the characterization of the HEF process. Comparative experiments suggest that high current, low FeAS dosage and low [DCy6bim][Cl] concentration are the best conditions to yield near complete total organic carbon decay after 4 h. In order to evaluate the catalyst behaviour and iron leaching during the degradation of [DCy6bim][Cl], differential pulse voltammetry (DPV), a sensitive and selective electroanalytical technique, was used to monitor the IL degradation, by-products and iron evolution into the solution at high concentration levels. The profile of the voltammetric curves obtained by DPV suggests almost complete cleavage of the cation structure of [DCy6bim][Cl] during the first 120 min. At longer treatment times, DPV revealed the generation of iron complex with chloride and carboxylic acids. Finally, chromatographic analysis of these carboxylic acids and inorganic anions permitted to validate the results obtained by DPV and demonstrated the feasibility of the HEF process for IL degradation. Graphical Abstract: [Figure not available: see fulltext.]Ministerio de Economía y Competitividad (España) | Ref. CTM2014-52471-RMinisterio de Educación, Cultura y Deporte (España) | Ref. FPU16/02644Xunta de Galicia | Ref. ED431C 2017/47Xunta de Galicia | Ref. ReGaLIs ED431 2017/11Xunta de Galicia | Ref. BIOAUGA ED431 2017/0

Exploring the use of carbon materials as cathodes in electrochemical advanced oxidation processes for the degradation of antibiotics

Three carbon materials from a varied origin, composition and porosity have been used as cost-effective cathodes in different electrochemical advanced oxidation processes (i.e. anodic oxidation (AO) and electro-Fenton (EF) in homogeneous and heterogeneous catalysis modalities) for the degradation of an antibiotic (e.g., metronidazole). In general, the efficiency towards the pollutant degradation increased as: AO < homogeneous EF < heterogeneous EF. The heterogeneous EF approach with iron pre-loaded in the carbon cathode outperformed the homogenous EF counterpart, despite a lower amount of iron. Reusability tests showed that iron-containing cathodes prepared from samples CQ (carbon obtained upon steam activation) and CB (carbon prepared by H3PO4 activation of biomass) were stable over at least three consecutive cycles. The best results were attained for cathode prepared with carbon CQ modified with iron, yielding over 97% removal of metronidazole after 150 min in all three reuses. Such better performance is related to the favorable adsorption of the pollutant on carbon CQ, thereby favoring the close contact between the generated oxidant species and the target antibiotic. The cathode based on carbon CQ was tested for the degradation of another recalcitrant antibiotic (sulfamethoxazole) in a real wastewater treatment plant effluent by means of a heterogeneous EF treatment, showing good degradation performance.Ministerio de Economía y Competitividad | Ref. CTM 2017-87326-RFondos FEDER | Ref. CTM 2017-87326-RRegion Centre Val de Loire | Ref. MOSAIK , APR-IA 2019Campus France (Program 'Make our planet great again')Ministerio de Educación, Cultura y Deporte | Ref. FPU16/0264

Exploring the pressurized heterogeneous electro-Fenton process and modelling the system

In this research, a bench-scale installation was tested for the heterogeneous electro-Fenton treatment of clofibric acid. The setup consists of a pressurized flow-through electrochemical cell equipped with a catalyst fluidized-bed and aerated with a jet mixer. The novelty of the research is two-fold: the use of the pressurized-jet aerator on an electro-Fenton treatment is tested and it is one of the first studies combining pressure with heterogeneous catalysis in electro-Fenton. Moderate relative pressures, up to 2 bar, were analyzed. Initially, the electrogeneration of hydrogen peroxide was tested, showing that it is remarkably boosted by the application of pressure. Then, the elimination of clofibric acid by means of an electro-Fenton treatment was carried out at 0.12 and 0.25 A, using iron-containing alginate beads as the catalyst. Regardless of the current intensity, the increase from atmospheric pressure to 1 gauge bar boosted the elimination of the pollutant and reduced the specific energy consumption of the electrochemical cell. Specifically, at 0.25 A an abatement higher than 98% was achieved in 8 h at atmospheric pressure while only 1 h was required at 1 bar of gauge pressure. However, a further increase of the pressure to 2 bar did not report a major improvement. Moreover, the effect of pressure on the catalyst was analyzed, concluding that the integrity of the alginate beads was not compromised by pressure. In fact, the iron leaching was very similar at 0, 1 and 2 bar: around 30% after 8 h of treatment. Finally, a mathematical model was developed, using the experimental data to obtain the necessary fitting parameters, which allowed to understand better the behavior of the bench-scale reaction system.Ministerio de Ciencia, Innovación y Universidades | Ref. CTQ2017-90659-REDTJunta de Comunidades de Castilla-La Mancha | Ref. SBPLY/17/180501/000396Ministerio de Educación, Cultura y Deporte | Ref. FPU16/02644Agencia Estatal de Investigación | Ref. CTM2017-87326-RAgencia Estatal de Investigación | Ref. PID2019-110904RB-I00Universidade de Vigo/CISU

Towards a more realistic heterogeneous electro-Fenton

With the aim of bringing the heterogeneous electro-Fenton (EF) treatment one step closer to a more realistic operation, the scaling-up of that technology was evaluated. Assays were performed firstly at lab scale in a stirred-tank reactor and then at bench scale in a flow setup including a jet aerator and a microfluidic flow-through electrochemical cell. A fluidized-bed reactor was added to the bench-scale installation in order to retain the solid catalyst, iron-containing alginate beads. To the best of the authors’ knowledge, there are no precedent studies reporting a heterogeneous EF treatment in a similar bench scale-configuration. Hydrogen peroxide generation and clofibric acid removal were assessed at both scales at current intensities of 0.12 and 0.25 A. Results showed that the scaled-up treatment was more efficient and cost-effective: at bench scale 18 times more volume was treated, the mass production of hydrogen peroxide was 28 higher and the specific cost for the removal of clofibric acid was cut by more than half. The most efficient treatment turned out to be the EF performed at 0.12 A at bench scale. Those results highlighted the importance of the reactor design in the scaling-up process. Additionally, aromatic intermediates were detected by liquid chromatography-mass spectrometry (LC-MS) and a degradation route was suggested. Carboxylic acids were also measured by HPLC confirming that the pollutant is mineralizing.Ministerio de Educación, Cultura y Deporte (España) I Ref. FPU16/02644Agencia Estatal de Investigación | Ref. CTM2017-87326-RAgencia Estatal de Investigación | Ref. PID2019-110904RB-I00Ministerio de Ciencia, Innovación y Universidades | Ref. CTQ2017-90659-REDTJunta de Comunidades de Castilla-La Mancha | Ref. SBPLY/17/180501/00039

Heterogeneous electro-Fenton as plausible technology for the degradation of imidazolinium-based ionic liquids

Conventional water treatments are generally inadequate for degradation of emerging pollutants such as ionic liquids (ILs). The use of heterogeneous electro-Fenton (HEF) has attracted great interest, due to its ability to efficiently oxidize a wide range of organic pollutants operating in cycles or in continuous mode. In this study, the removal of a complex IL from the imidazolinium family (1,3-Bis(2,4,6-trimethylphenyl)imidazolinium chloride), by means of HEF using iron alginate spheres as catalyst has been investigated, resulting in significant TOC decay after 6 h. The optimization of the key process parameters (current, IL concentration and catalyst dosage) has been performed using a Box-Behnken experimental design and achieving 76.98% of TOC abatement in 2 h of treatment. Current proved to be a crucial parameter and high catalyst dosage is required to achieve the maximum removal. In addition, an insight about the availability of iron into the reactor and the evolution of several intermediates has been carried out by employing differential pulse voltammetry on screen-printed carbon electrodes. The evolution of the different voltammetric peaks confirmed the influence of iron release, and the generation of several iron complexes has permitted the comprehension of the degradation pathway, which has been validated by chromatographic techniques.Ministerio de Economía y Competitividad (España) | Ref. CTM2014-52471-