STUDY OF THE TRANSPORT OF HEAVY METAL IONS THROUGH CATION-EXCHANGE MEMBRANES APPLIED TO THE TREATMENT OF INDUSTRIAL EFFLUENTS

La presente Tesis Doctoral consiste en la determinación de las propiedades de transporte de diferentes especies catiónicas a través de membranas de intercambio catiónico. Las membranas de intercambio iónico son un componente clave de los reactores electroquímicos y de los sistemas de electrodiálisis, puesto que determinan el consumo energético y la eficiencia del proceso. La utilización de este tipo de membranas para el tratamiento de efluentes industriales no es muy extendida debido a los requisitos de elevada resistencia química y durabilidad que deben cumplir las membranas. Otro asunto importante radica en la eficiencia en el transporte de los iones que se quieren eliminar a través de la membrana. Normalmente, existe una competencia por el paso a través de las membranas entre diferentes especies debido al carácter multicomponente de los efluentes a tratar. Sin embargo, una mejora en las propiedades de las membranas de intercambio iónico permitiría la implantación del tratamiento mediante reactores electroquímicos de efluentes industriales con un contenido importante en compuestos metálicos, tales como los baños agotados de las industrias de cromado. La utilización de una tecnología limpia como la electrodiálisis conllevaría diferentes ventajas, entre las cuales destacan la recuperación de los efluentes para su reutilización en el proceso industrial, el ahorro en el consumo de agua y la disminución de la descarga de contaminantes al medio ambiente. La determinación de las condiciones de operación óptimas así como la mejora de las propiedades de transporte de las membranas constituye el principal tema de la presente investigación. Para ello, se emplearán diferentes tipos de membrana. En primer lugar, se estudiará el comportamiento de las membranas poliméricas comerciales que poseen unas propiedades de resistencia química elevadas, las cuales se tomarán como referencia. De forma paralela, se producirán membranas conductoras de iones a partir de materiales cerámicos económicos, ya que la resistencia de los materiales cerámicos a sustancias oxidantes y muy ácidas es mayor que la de los materiales poliméricos. Este punto constituye la parte más innovadora de la investigación, puesto que la mayoría de las membranas de intercambio iónico comerciales están basadas en materiales poliméricos que no pueden resistir las condiciones específicas de los efluentes industriales. Una vez determinadas las condiciones de operación óptimas, se realizarán ensayos en plantas piloto con el fin de confirmar los resultados obtenidos mediante las técnicas de caracterización y determinar el grado de recuperación y coste energético asociado a los procesos electrodialíticos de tratamiento de efluentes industriales.Martí Calatayud, MC. (2014). STUDY OF THE TRANSPORT OF HEAVY METAL IONS THROUGH CATION-EXCHANGE MEMBRANES APPLIED TO THE TREATMENT OF INDUSTRIAL EFFLUENTS [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/46004TESISPremios Extraordinarios de tesis doctorale

Interplay between physical cleaning, membrane pore size and fluid rheology during the evolution of fouling in membrane bioreactors

[EN] Fouling is one of the most pressing limitations during operation of membrane bioreactors, as it increases operating costs and is the cause of short membrane lifespans. Conducting effective physical cleanings is thus essential for keeping membrane operation above viable performance limits. The nature of organic foulants present in the sludge and the membrane properties are among the most influential factors determining fouling development and thus, efficiency of fouling mitigation approaches. The role of other factors like sludge viscosity on fouling is still unclear, given that contradictory effects have been reported in the literature. In the present study we use a new research approach by which the complex interplay between fouling type, levels of permeate flux, membrane material and feed properties is analyzed, and the influence of these factors on critical flux and membrane permeability is evaluated. A variety of systems including activated sludge and model solutions with distinct rheological behavior has been investigated for two membranes differing in pore size distribution. We present a novel method for assessing the efficiency of fouling removal by backwash and compare it with the efficiency achieved by means of relaxation. Results obtained have proven that backwash delays development of critical fouling as compared with relaxation and reduces fouling irreversibility regardless of fluid rheology. It was shown that backwash is especially effective for membranes for which internal fouling is the main cause of loss in permeability. Nonetheless, we found out that for membranes with tight pores, both relaxation and backwash are equally effective. The critical flux decreases significantly for high-viscosity fluids, such as activated sludge. This effect is mainly caused by an intensified concentration polarization at the feed side rather than by internal fouling events. However, membrane permeability has been proven to rely more on the permeate viscosity than on the feed viscosity: poor rejection of organic fractions showcasing high viscosity causes an acute decline in membrane permeability as a consequence of increased shear stress inside the membrane pores. (C) 2018 Elsevier Ltd. All rights reserved.M.W. acknowledges the support through an Alexander-von-Humboldt Professorship. M.C. Marti-Calatayud acknowledges the support to Generalitat Valenciana through the funding APOSTD2017. M.C. Marti-Calatayud thanks the contributions of Sybille Hanisch, Sanchita Khandelwal and Sara Vivanco. This work was supported by the German Federal Ministry of Education and Research (BMBF) through the project BRAMAR (02WCL1334A). We thank Synder Filtration for the supplied membranesMartí Calatayud, MC.; Schneider, S.; Yüce, S.; Wessling, M. (2018). Interplay between physical cleaning, membrane pore size and fluid rheology during the evolution of fouling in membrane bioreactors. Water Research. 147:393-402. https://doi.org/10.1016/j.watres.2018.10.017S39340214

Trade-off between operating time and energy consumption in pulsed electric field electrodialysis: A comprehensive simulation study

[EN] Electrodialysis (ED) has been recently introduced in a variety of processes where the recovery of valuable resources is needed; thus, enabling sustainable production routes for a circular economy. However, new applications of ED require optimized operating modes ensuring low energy consumptions. The application of pulsed electric field (PEF) electrodialysis has been demonstrated to be an effective option to modulate concentration polarization and reduce energy consumption in ED systems, but the savings in energy are usually attained by extending the operating time. In the present work, we conduct a comprehensive simulation study about the effects of PEF signal parameters on the time and energy consumption associated with ED processes. Ion transport of NaCl solutions through homogeneous cation-exchange membranes is simulated using a 1-D model solved by a finite-difference method. Increasing the pulse frequency up to a threshold value is effective in reducing the specific energy consumption, with threshold frequencies increasing with the applied current density. Varying the duty cycle causes opposed effects in the time and energy usage needed for a given ED operation. More interestingly, a new mode of PEF functions with the application of low values of current during the relaxation phases has been investigated. This novel PEF strategy has been demonstrated to simultaneously improve the time and the specific energy consumption of ED processes.The authors acknowledge the support of the Ibero-American CYTED network 318RT0551.Martí Calatayud, MC.; Sancho-Cirer Poczatek, M.; Pérez-Herranz, V. (2021). Trade-off between operating time and energy consumption in pulsed electric field electrodialysis: A comprehensive simulation study. Membranes. 11(1):1-15. https://doi.org/10.3390/membranes11010043S11511

Mass transfer phenomena during electrodialysis of multivalent ions: chemical equilibria and overlimiting currents

[EN] Electrodialysis is utilized for the deionization of saline streams, usually formed by strong electrolytes. Recently, interest in new applications involving the transport of weak electrolytes through ion-exchangemembranes has increased. Clear examples of such applications are the recovery of valuable metal ions from industrial effluents, such as electronic wastes or mining industries. Weak electrolytes give rise to a variety of ions with different valence, charge sign and transport properties. Moreover, development of concentration polarization under the application of an electric field promotes changes in the chemical equilibrium, thus making more complex understanding of mass transfer phenomena in such systems. This investigation presents a set of experiments conducted with salts of multivalent metals with the aim to provide better understanding on the involved mass transfer phenomena. Chronopotentiometric experiments and current-voltage characteristics confirm that shifts in chemical equilibria can take place simultaneous to the activation of overlimiting mass transfer mechanisms, that is, electroconvection and water dissociation. Electroconvection has been proven to affect the type of precipitates formed at the membrane surface thus suppressing the simultaneous dissociation of water. For some electrolytes, shifts in the chemical equilibria forced by an imposed electric field generate new charge carriers at specific current regimes, thus reducing the system resistance.Manuel Cesar Marti-Calatayud acknowledges the funding received from Generalitat Valenciana (ASPOSTD/2017/059).Martí Calatayud, MC.; García Gabaldón, M.; Pérez-Herranz, V. (2018). Mass transfer phenomena during electrodialysis of multivalent ions: chemical equilibria and overlimiting currents. Applied Sciences (Basel). 8(9):1-13. https://doi.org/10.3390/app8091566S11389Barry, E., McBride, S. P., Jaeger, H. M., & Lin, X.-M. (2014). Ion transport controlled by nanoparticle-functionalized membranes. Nature Communications, 5(1). doi:10.1038/ncomms6847Ran, J., Wu, L., He, Y., Yang, Z., Wang, Y., Jiang, C., … Xu, T. (2017). Ion exchange membranes: New developments and applications. Journal of Membrane Science, 522, 267-291. doi:10.1016/j.memsci.2016.09.033Zhao, W.-Y., Zhou, M., Yan, B., Sun, X., Liu, Y., Wang, Y., … Zhang, Y. (2018). Waste Conversion and Resource Recovery from Wastewater by Ion Exchange Membranes: State-of-the-Art and Perspective. Industrial & Engineering Chemistry Research, 57(18), 6025-6039. doi:10.1021/acs.iecr.8b00519Feng, J., Graf, M., Liu, K., Ovchinnikov, D., Dumcenco, D., Heiranian, M., … Radenovic, A. (2016). Single-layer MoS2 nanopores as nanopower generators. Nature, 536(7615), 197-200. doi:10.1038/nature18593Zhu, X., Hatzell, M. C., Cusick, R. D., & Logan, B. E. (2013). Microbial reverse-electrodialysis chemical-production cell for acid and alkali production. Electrochemistry Communications, 31, 52-55. doi:10.1016/j.elecom.2013.03.010Strathmann, H. (2010). Electrodialysis, a mature technology with a multitude of new applications. Desalination, 264(3), 268-288. doi:10.1016/j.desal.2010.04.069Martí-Calatayud, M. C., Buzzi, D. C., García-Gabaldón, M., Ortega, E., Bernardes, A. M., Tenório, J. A. S., & Pérez-Herranz, V. (2014). Sulfuric acid recovery from acid mine drainage by means of electrodialysis. Desalination, 343, 120-127. doi:10.1016/j.desal.2013.11.031Chen, D., Hickner, M. A., Agar, E., & Kumbur, E. C. (2013). Selective anion exchange membranes for high coulombic efficiency vanadium redox flow batteries. Electrochemistry Communications, 26, 37-40. doi:10.1016/j.elecom.2012.10.007Hou, L., Wu, B., Yu, D., Wang, S., Shehzad, M. A., Fu, R., … Xu, T. (2018). Asymmetric porous monovalent cation perm-selective membranes with an ultrathin polyamide selective layer for cations separation. Journal of Membrane Science, 557, 49-57. doi:10.1016/j.memsci.2018.04.022Pham, S. V., Kwon, H., Kim, B., White, J. K., Lim, G., & Han, J. (2016). Helical vortex formation in three-dimensional electrochemical systems with ion-selective membranes. Physical Review E, 93(3). doi:10.1103/physreve.93.033114Belashova, E. D., Melnik, N. A., Pismenskaya, N. D., Shevtsova, K. A., Nebavsky, A. V., Lebedev, K. A., & Nikonenko, V. V. (2012). Overlimiting mass transfer through cation-exchange membranes modified by Nafion film and carbon nanotubes. Electrochimica Acta, 59, 412-423. doi:10.1016/j.electacta.2011.10.077Nebavskaya, K. A., Sarapulova, V. V., Sabbatovskiy, K. G., Sobolev, V. D., Pismenskaya, N. D., Sistat, P., … Nikonenko, V. V. (2017). Impact of ion exchange membrane surface charge and hydrophobicity on electroconvection at underlimiting and overlimiting currents. Journal of Membrane Science, 523, 36-44. doi:10.1016/j.memsci.2016.09.038Choi, J.-H., Lee, H.-J., & Moon, S.-H. (2001). Effects of Electrolytes on the Transport Phenomena in a Cation-Exchange Membrane. Journal of Colloid and Interface Science, 238(1), 188-195. doi:10.1006/jcis.2001.7510Martí-Calatayud, M. C., García-Gabaldón, M., & Pérez-Herranz, V. (2013). Effect of the equilibria of multivalent metal sulfates on the transport through cation-exchange membranes at different current regimes. Journal of Membrane Science, 443, 181-192. doi:10.1016/j.memsci.2013.04.058Nikonenko, V. V., Pismenskaya, N. D., Belova, E. I., Sistat, P., Huguet, P., Pourcelly, G., & Larchet, C. (2010). Intensive current transfer in membrane systems: Modelling, mechanisms and application in electrodialysis. Advances in Colloid and Interface Science, 160(1-2), 101-123. doi:10.1016/j.cis.2010.08.001Pismenskaya, N. D., Belova, E. I., Nikonenko, V. V., & Larchet, C. (2008). Electrical conductivity of cation-and anion-exchange membranes in ampholyte solutions. Russian Journal of Electrochemistry, 44(11), 1285-1291. doi:10.1134/s1023193508110141Martí-Calatayud, M. C., García-Gabaldón, M., Pérez-Herranz, V., & Ortega, E. (2011). Determination of transport properties of Ni(II) through a Nafion cation-exchange membrane in chromic acid solutions. Journal of Membrane Science, 379(1-2), 449-458. doi:10.1016/j.memsci.2011.06.014Martí-Calatayud, M. C., García-Gabaldón, M., Pérez-Herranz, V., Sales, S., & Mestre, S. (2015). Ceramic anion-exchange membranes based on microporous supports infiltrated with hydrated zirconium dioxide. RSC Advances, 5(57), 46348-46358. doi:10.1039/c5ra04169dCowan, D. A., & Brown, J. H. (1959). Effect of Turbulence on Limiting Current in Electrodialysis Cells. Industrial & Engineering Chemistry, 51(12), 1445-1448. doi:10.1021/ie50600a026Sarapulova, V., Nevakshenova, E., Pismenskaya, N., Dammak, L., & Nikonenko, V. (2015). Unusual concentration dependence of ion-exchange membrane conductivity in ampholyte-containing solutions: Effect of ampholyte nature. Journal of Membrane Science, 479, 28-38. doi:10.1016/j.memsci.2015.01.015Tanaka, Y. (2007). Acceleration of water dissociation generated in an ion exchange membrane. Journal of Membrane Science, 303(1-2), 234-243. doi:10.1016/j.memsci.2007.07.020Mel’nikov, S. S., Shapovalova, O. V., Shel’deshov, N. V., & Zabolotskii, V. I. (2011). Effect of d-metal hydroxides on water dissociation in bipolar membranes. Petroleum Chemistry, 51(7), 577-584. doi:10.1134/s0965544111070097Gil, V. V., Andreeva, M. A., Jansezian, L., Han, J., Pismenskaya, N. D., Nikonenko, V. V., … Dammak, L. (2018). Impact of heterogeneous cation-exchange membrane surface modification on chronopotentiometric and current–voltage characteristics in NaCl, CaCl 2 and MgCl 2 solutions. Electrochimica Acta, 281, 472-485. doi:10.1016/j.electacta.2018.05.19

Chronopotentiometric study of ceramic cation-exchange membranes based on zirconium phosphate in contact with nickel sulfate solutions

In this article, the innovative cation-exchange membranes obtained from ceramic materials are presented. Different microporous ceramic supports were obtained from an initial mixture of alumina and kaolin, to which a varying content of starch was added in order to obtain supports with different pore size distributions. The deposition of zirconium phosphate into the porous supports generates membranes with cation-exchange properties. The fabrication of ion-exchange membranes which could resist aggressive electrolytes such as strong oxidizing spent chromium plating baths or radioactive solutions would allow the application of electrodialysis for the decontamination and regeneration of these industrial effluents. The performance of the manufactured membranes was studied in nickel sulfate solutions by means of chronopotentiometry. An increase of the membrane voltage drop during chronopotentiometric measurements was observed in some membranes, which seems to be a consequence of concentration polarization phenomena resulting from the ionic transfer occurred through the membranes. Current voltage curves were obtained for the different ceramic membranes, allowing the calculation of their ohmic resistance. The ohmic resistance of the membranes increased when the open porosity (OP) of the samples was incremented up to a value of 50%. For values of OP higher than 50%, the resistance of the membranes decreased significantly with porosity.Martí Calatayud, MC.; García Gabaldón, M.; Pérez-Herranz, V.; Sales, S.; Mestre, S. (2013). Chronopotentiometric study of ceramic cation-exchange membranes based on zirconium phosphate in contact with nickel sulfate solutions. Desalination and Water Treatment. 51(1-3):597-605. doi:10.1080/19443994.2012.714629597605511-3L. Harttinger, Handbook of Effluent Treatment and Recycling for The Metal Finishing Industry, Finishing Publications Ltd.; ASM International, Stevenage 1994.Balagopal, S., Landro, T., Zecevic, S., Sutija, D., Elangovan, S., & Khandkar, A. (1999). Selective sodium removal from aqueous waste streams with NaSicon ceramics. Separation and Purification Technology, 15(3), 231-237. doi:10.1016/s1383-5866(98)00104-xHobbs, D. . (1999). Caustic recovery from alkaline nuclear waste by an electrochemical separation process. Separation and Purification Technology, 15(3), 239-253. doi:10.1016/s1383-5866(98)00105-1Dzyazko, Y. S., Mahmoud, A., Lapicque, F., & Belyakov, V. N. (2006). Cr(VI) transport through ceramic ion-exchange membranes for treatment of industrial wastewaters. Journal of Applied Electrochemistry, 37(2), 209-217. doi:10.1007/s10800-006-9243-7García-Gabaldón, M., Pérez-Herranz, V., Sánchez, E., & Mestre, S. (2006). Effect of porosity on the effective electrical conductivity of different ceramic membranes used as separators in eletrochemical reactors. Journal of Membrane Science, 280(1-2), 536-544. doi:10.1016/j.memsci.2006.02.007Linkov, V. ., & Belyakov, V. . (2001). Novel ceramic membranes for electrodialysis. Separation and Purification Technology, 25(1-3), 57-63. doi:10.1016/s1383-5866(01)00090-9Tripathi, B. P., & Shahi, V. K. (2007). SPEEK–zirconium hydrogen phosphate composite membranes with low methanol permeability prepared by electro-migration and in situ precipitation. Journal of Colloid and Interface Science, 316(2), 612-621. doi:10.1016/j.jcis.2007.08.038Clearfield, A., & Smith, G. D. (1969). Crystallography and structure of .alpha.-zirconium bis(monohydrogen orthophosphate) monohydrate. Inorganic Chemistry, 8(3), 431-436. doi:10.1021/ic50073a005Alberti, G., Bernasconi, M. G., Casciola, M., & Costantino, U. (1978). Ion exchange of some divalent and trivalent cations on the surface of zirconium acid phosphate micro-crystals. Journal of Chromatography A, 160(1), 109-115. doi:10.1016/s0021-9673(00)91786-2Yaroslavtsev, A. B. (2003). Ion DiffusionThrow Interface in Heterogeneous Solid Systems with the Modified Surface. Defect and Diffusion Forum, 216-217, 133-140. doi:10.4028/www.scientific.net/ddf.216-217.133Yaroslavtsev, A. B. (2009). Composite materials with ionic conductivity: from inorganic composites to hybrid membranes. Russian Chemical Reviews, 78(11), 1013-1029. doi:10.1070/rc2009v078n11abeh004066Yaroslavtsev, A. B., Nikonenko, V. V., & Zabolotsky, V. I. (2003). Ion transfer in ion-exchange and membrane materials. Russian Chemical Reviews, 72(5), 393-421. doi:10.1070/rc2003v072n05abeh000797Davis, M. E. (2002). Ordered porous materials for emerging applications. Nature, 417(6891), 813-821. doi:10.1038/nature00785Taky, M., Pourcelly, G., Lebon, F., & Gavach, C. (1992). Polarization phenomena at the interfaces between an electrolyte solution and an ion exchange membrane. Journal of Electroanalytical Chemistry, 336(1-2), 171-194. doi:10.1016/0022-0728(92)80270-eSistat, P., & Pourcelly, G. (1997). Chronopotentiometric response of an ion-exchange membrane in the underlimiting current-range. Transport phenomena within the diffusion layers. Journal of Membrane Science, 123(1), 121-131. doi:10.1016/s0376-7388(96)00210-4Pismenskaia, N., Sistat, P., Huguet, P., Nikonenko, V., & Pourcelly, G. (2004). Chronopotentiometry applied to the study of ion transfer through anion exchange membranes. Journal of Membrane Science, 228(1), 65-76. doi:10.1016/j.memsci.2003.09.012Martí-Calatayud, M. C., García-Gabaldón, M., Pérez-Herranz, V., & Ortega, E. (2011). Determination of transport properties of Ni(II) through a Nafion cation-exchange membrane in chromic acid solutions. Journal of Membrane Science, 379(1-2), 449-458. doi:10.1016/j.memsci.2011.06.014García-Gabaldón, M., Pérez-Herranz, V., & Ortega, E. (2011). Evaluation of two ion-exchange membranes for the transport of tin in the presence of hydrochloric acid. Journal of Membrane Science, 371(1-2), 65-74. doi:10.1016/j.memsci.2011.01.015GARCIAGABALDON, M., PEREZHERRANZ, V., SANCHEZ, E., & MESTRE, S. (2008). Effect of tin concentration on the electrical properties of ceramic membranes used as separators in electrochemical reactors. Journal of Membrane Science, 323(1), 213-220. doi:10.1016/j.memsci.2008.06.03

Study on the difficulties of the students in chemical engineering in the interpretation of ternary phase diagrams

[EN] The present study has been carried out in an experimental subject of the Degree in Chemical Engineering of the Universitat Politècnica de València. The study is focused on the results of a test answered by the students about the use of ternary diagrams in one of the laboratory practice sessions. In particular, we analyzed the interpretation by the students of the ternary phase diagrams applied to the solid-liquid extraction process. From the analysis of the answer of 56 students, it can be concluded that the interpretation of binary and pure systems was successful for the major part of the students. However, the students made more mistakes in the interpretation of ternary systems.[ES] La presente investigación se ha llevado a cabo en una asignatura experimental del Grado en Ingeniería Química de la Universitat Politècnica de València. Se han analizado los resultados de los tests que han realizado los estudiantes acerca de los conceptos desarrollados en una de las prácticas de laboratorio. En particular, se ha evaluado la interpretación de diagramas triangulares rectangulares por parte de los estudiantes en su aplicación al proceso de extracción sólido-líquido. Tras analizar las respuestas de 56 estudiantes, se ha concluido que la interpretación de sistemas binarios y de un solo componente se ha llevado a cabo de forma correcta en la mayoría de casos. Sin embargo, en la interpretación de sistemas ternarios los estudiantes han incurrido en errores en una mayor proporción.Hernández Pérez, L.; Martí Calatayud, MC.; Montañés Sanjuan, MT. (2022). Estudio sobre las dificultades de los estudiantes de ingeniería química en la interpretación de diagramas triangulares rectangulares. Editorial Universitat Politècnica de València. 401-409. https://doi.org/10.4995/INRED2022.2022.1591440140

Norfloxacin mineralization under light exposure using Sb-SnO2 ceramic anodes coated with BiFeO3 photocatalyst

Advanced Oxidation Processes have been proven to be an efficient way to remove organic pollutants from wastewaters. In this work, a ceramic electrode of Sb–SnO2 (BCE) with a layer of the photocatalytic material BiFeO3 (BFO-BCE), has been characterized electrochemically and further tested for norfloxacin photo-electrooxidation in the presence and absence of light. The electrode photoactivity was highly enhanced thanks to the presence of BiFeO3, as confirmed by Linear Sweep Voltammetry, chronoamperometry and potentiometry, and Electrochemical Impedance Spectroscopy. Additionally, working in galvanostatic mode, a high mineralization of norfloxacin was achieved after 240 min, reaching 62% at 25 mA cm−2 under light conditions. This value is comparatively higher than the 40% achieved with the BCE. The oxidation byproducts were followed by ionic chromatography and HPLC analysis, which also allowed us to propose an oxidation pathway of the norfloxacin molecule. Finally, some indicators of the reactor performance such as the Mineralization Current Efficiency and the specific energy consumption were analyzed, revealing that lower current densities (8.3 mA cm−2) led to higher current efficiencies, and that light improved both the current efficiency and energy consumption

Comparison of two different ceramic electrodes based on Sb-SnO2 coated with BiFeO3 and Bi2WO6 for the photoelectrooxidation of an emerging pollutant

In this work, a comparison between novel photoanodes based on Sb-SnO2 (BCE) coated with BiFeO3 (BFO-BCE) and Bi2WO6 (BWO-BCE) was carried out. An improvement in the catalytic activity of the electrodes under light exposure was demonstrated by means of Linear Sweep Voltammetry, light pulsed chronoamperometry and Electrochemical Impedance Spectroscopy, being more notorious at current densities below 25 mA·cm−2 for the BFO-BCE and above 25 mA·cm−2 for the BWO-BCE. This improved performance was caused by an increase of the photogenerated oxidizing species. As compared with the uncoated BCE anode used without light, photoelectrooxidation tests led to improvements of around 40% in the degradation degree of norfloxacin (NOR) using both photoanodes at 8.33 mA·cm−2. This improvement was also observed in the mineralization degree of the model wastewaters, with an increase of 36% and 28% at 25 mA·cm−2 for the BWO-BCE and BFO-BCE, respectively. The degradation and formation of subproducts was followed by ion chromatography and HPLC analysis, where some of the main intermediates were detected, allowing us to elaborate a degradation route for NOR with these novel electrodes. The Mineralization Current Efficiency (MCE), energy consumption and extent of electrochemical combustion (Φ) showed improvements with light application for both electrodes at high current densities, being the BWO-BCE the one with the highest MCE and Φ at the cost of a slightly higher energy consumption. This showed the importance of light for these electrodes and its impact in the general process performance, which can be of great advantage in future applications

Tracking homogeneous reactions during electrodialysis of organic acids via EIS

[EN] Organic acids are highly valuable platform chemicals that can be obtained from bioresources and subsequently transformed into a wide spectrum of profitable consumer goods. After their synthesis, organic acids need to be separated from other by-products and conveniently upconcentrated. Based on the ionic nature of organic acids, electromembrane processes are viable technologies for their recovery. Transport of weak acids through ion- exchange membranes is a complex process influenced by multiple phenomena, i.e. concentration polarization, water dissociation and counterion-membrane interactions. In the present study, the transport of two different organic acids (citric and oxalic acid) through anion-exchange membranes is investigated by means of using linear sweep voltammetry, chronopotentiometry and electrochemical impedance spectroscopy (EIS). Results have shown that, at pH values where multivalent acid anions predominate in solution, a first limiting current density is registered in the current-voltage curves, followed by an increase in membrane resistance. A further increase in current leads to a second limiting current density and a steeper increase in membrane resistance associated with an intensified ion depletion. A strong correlation between polarization curves and electrochemical impedance measurements reveals that such increase in resistance is prompted by generation of Hþ and OH? ions and the concomitant onset of homogeneous reactions in very thin solution layers. The generation of Hþ and OH? ions is tracked by a Gerischer arc in the impedance spectra. As the polarization level increases, the subsequent reaction of multivalent anions into lower-charge acid anions involves the evolution of additional Gerischer arcs. Furthermore, the lower conductivity of the reaction products correlates with the increased system resistance. The characteristic times of these reactions are in the order of milliseconds, thus being only directly accessible with the use of frequency response analysis techniques, such as EIS.M.C. Marti-Calatayud acknowledges the support of Generalitat Valenciana through the funding APOSTD/2017/059.Martí Calatayud, MC.; Evdochenko, E.; Bär, J.; García Gabaldón, M.; Wessling, M.; Pérez-Herranz, V. (2020). Tracking homogeneous reactions during electrodialysis of organic acids via EIS. Journal of Membrane Science. 595:1-10. https://doi.org/10.1016/j.memsci.2019.117592S110595Kiss, A. A., Lange, J.-P., Schuur, B., Brilman, D. W. F., van der Ham, A. G. J., & Kersten, S. R. A. (2016). Separation technology–Making a difference in biorefineries. Biomass and Bioenergy, 95, 296-309. doi:10.1016/j.biombioe.2016.05.021Abels, C., Carstensen, F., & Wessling, M. (2013). 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Analysis and optimization of the influence of operating conditions in the ultrafiltration of macromolecules using a response surface methodological approach

[EN] In this work, the ultrafiltration of macromolecules was analysed using a response surface methodological approach. The behaviour of two different inorganic membranes was investigated. The membranes selected were a Carbosep M2 membrane (Orelis, France) with a molecular weight cut-off (MWCO) of 15 kDa and a Tami MSKT membrane (Tami Industries, France) with a MWCO of 5 kDa. The solute employed was polyethylene glycol of 35 kDa molecular weight. The influence of transmembrane pressure (0.1, 0.2, 0.3, 0.4 and 0.5 MPa), crossflow velocity (1, 2 and 3 m/s) and feed concentration (5, 10 and 15 g/L) on permeate flux and permeate flux decline was investigated. Analysis of variance was proved to be a useful tool to determine the effect of operating variables on both parameters. The method used demonstrated the presence of coupled effects between factors as well as squared effects that are relevant to the ultrafiltration process. The surface contours obtained from fitted models were used for the optimization of the operating conditions. The goal was to simultaneously maximize the average permeate flux and minimize the flux decline. The optimal operating conditions for the Carbosep M2 membrane were a transmembrane pressure of 0.38 MPa and a crossflow velocity of 3 m/s. The optimal operating conditions for the Tami MSKT membrane could not be determined by means of multiple response optimization due to the low accuracy of the regression model obtained for the cumulative permeate flux decline (SFD) response variable. (C) 2009 Elsevier B.V. All rights reserved.The authors of this work wish to gratefully acknowledge the financial support of the Spanish Ministry of Science and Technology (MCYT) through the project no. CTQ2005-03398.Martí Calatayud, MC.; Vincent Vela, MC.; Alvarez Blanco, S.; Lora-García, J.; Bergantinos Rodríguez, E. (2010). Analysis and optimization of the influence of operating conditions in the ultrafiltration of macromolecules using a response surface methodological approach. Chemical Engineering Journal. 156(2):337-346. https://doi.org/10.1016/j.cej.2009.10.031S337346156