Editorial of the special issue on advanced electrochemical technologies for environmental applications

This special issue of Separation and Purification Technology gathers 27 articles, which are related to keynotes and oral or poster presentations at the 2nd European Workshop of Electrochemical Engineering entitled ‘New Bridges for a New Knowledge on Electrochemical Engineering’. The workshop was held from 1st to 5th October 2017 in Barcelona (Spain), as a Joint Event of the 10th World Congress of Chemical Engineering (WCCE10). This congress was promoted by the World Chemical Engineering Council (WCEC), the European Federation of Chemical Engineering (EFCE) and the European Society of Biochemical Engineering Sciences (ESBES) to approach researchers and specialists in all areas of chemical engineering and to improve their strategy for the development of innovative processes that will be vital for the society of tomorrow. The joint event was promoted by the Working Party on Electrochemical Engineering (WPEE) of the EFCE and co-organized with the Spanish Excellence Network on Environmental and Energy Applications of the Electrochemical Technology (thus being the 2nd Workshop of E3TECH Network). It took place at Fira de Barcelona, one of the most important trade fair institutions in Europe

Chitosan-derived nitrogen-doped carbon electrocatalyst for a sustainable upgrade of oxygen reduction to hydrogen peroxide in UV-assisted electro-Fenton water treatment

The urgency to move from critical raw materials to highly available and renewable feedstock is currently driving the scientific and technical developments. Within this context, the abundance of natural resources like chitosan paves the way to synthesize biomass-derived nitrogen-doped carbons. This work describes the synthesis of chitosan-derived N-doped mesoporous carbon in the absence (MC-C) and presence (N-MC-C) of 1,10-phenanthroline, which acted as both a porogen agent and a second nitrogen source. The as-prepared MC-C and N-MC-C were thoroughly characterized and further employed as catalytic materials in gas-diffusion electrodes (GDEs), aiming to develop a sustainable alternative to conventional GDEs for H2O2 electrogeneration and photoelectro-Fenton (PEF) treatment of a drug pollutant. N-MC-C presented a higher content of key surface N-functionalities like the pyrrole group, as well as an increased graphitization degree and surface area (63 vs 6 m2/g), comparable to commercial carbon black. These properties entailed a superior activity of N-MC-C for the oxygen reduction reaction, as confirmed from its voltammetric behavior at a rotating ring-disk electrode. The GDE prepared with the N-MC-C catalyst showed greater H2O2 accumulation, attaining values close to those obtained with a commercial GDE. N-MC-C- and MC-C-derived GDEs were employed to treat drug solutions at pH 3.0 by the PEF process, which outperformed electro-oxidation. The fastest drug removal was achieved using N-MC-C, requiring only 16 min at 30 mA/cm2 instead of 20 min required with MC-C. The replacement of the dimensionally stable anode by a boron-doped diamond accelerated the degradation process, reaching an almost complete mineralization in 360 min. The main degradation products were identified, revealing the formation of six different aromatic intermediates, alongside five aliphatic compounds that comprised three nitrogenated structures. The initial N was preferentially converted into ammonium.Peer ReviewedPostprint (published version

Electrochemical treatment of Acid Red 1 by electro-Fenton and photoelectro-Fenton processes

Small volumes (100 mL) of acidic aqueous solutions with 30-200 mg L-1 TOC of the toxic azo dye Acid Red 1 (AR1) have been comparatively treated by various electrochemical advanced oxidation processes (EAOPs). The electrolytic system consisted of a BDD anode able to produce ·OH and an air-diffusion cathode that generated H2O2, which subsequently reacted with added Fe2+ to yield additional ·OH from Fenton’s reaction. Under optimized conditions (i.e., 1.0 mM Fe2+, 60 mA cm-2, pH 3.0, 35 ºC), the analysis of the initial rates for decolourization and AR1 decay assuming a pseudo-first-order kinetics revealed a much higher rate constant for photoelectro-Fenton (PEF, ~ 2.7x10-3 s-1) compared to electro-Fenton (EF, ~ 0.6x10-3 s-1). Mineralization after 180 min was also greater in the former treatment (90 % vs 63 %). The use of UV radiation in PEF contributed to Fe(III) photoreduction as well as to photodecarboxylation of refractory intermediates, yielding a mineralization current efficiency as high as 85% during the treatment of solutions of 200 mg L-1 TOC. Primary reaction intermediates included three aromatic derivatives with the initial naphthalenic structure and four molecules only featuring benzenic rings, which were totally mineralized in PEF

Valorization of bottom ash from municipal solid waste incineration: recovery of copper by electrowinning

Postprint (published version

Performance of the Electro-Oxidation and Electro-Fenton Processes with a BDD Anode for the Treatment of Low Contents of Pharmaceuticals in a Real Water Matrix

本文报告了采用掺硼金刚石阳极（BDD）电氧化和电芬顿工艺处理真实水体中注入含有少量药物残留物的单组分和多组分溶液（即1 mg·L-1对乙酰氨基酚和/或1 mg·L-1水杨酸，pH=3）的研究结果. 以恒定电流密度方式在BDD/Pt电解池中进行电氧化，而在BDD/空气扩散电解池中进行电芬顿，从而在阴极电生H2O2. 结果表明，由于乙酰氨基酚和水杨酸均与溶液中氯离子氧化所产生的活性氯物种发生反应，因此，电氧化处理真实水体中两种药物的降解要比超纯水中添加0.05 mol·L-1 Na2SO4快. 这种含氯氧化剂的反应活性甚至超过了阳极形成的有限的羟基活性基，提高电流密度大大加速了两种污染物的消除. 在真实水体自然碱性pH下得到了类似的结果. 当电氧化处理两种药物的混合物时，两种药物上面产生的氧化剂的竞争作用，导致药物的降解变慢，只有电芬顿处理真实水体时药物的降解才稍微加快，这是由于H2O2与Cl-的反应，生成了反应活性弱得多的含氯活性基，从而抑制了电生的H2O2和添加的Fe2+之间发生的芬顿反应所形成的同相羟基活性基的累积. 对于添加了药物的真实水体，在较高的电流密度下电氧化可得到较好的天然有机物成分（NOM）矿化度，且添加0.05 mol·L-1 Na2SO4效果会更好. 虽然在药物溶液的电氧化中检测出微量的氧化副产物，如对苯醌、NO3-和NH4+ 离子，但在本研究条件下无法去除真实水体中所含有的氮基化合物.Here, we report the performance of electro-oxidation and electro-Fenton with a boron-doped diamond (BDD) anode for the treatment of single and multicomponent solutions containing small amounts of pharmaceutical residues (i.e., 1 mg·L-1 paracetamol and/or 1 mg·L-1 salicylic acid) spiked into a real water matrix at pH 3.0. Electro-oxidation was performed in a BDD/Pt cell, whereas electro-Fenton was carried out in a BDD/air-diffusion cell to electrogenerate H2O2 at the cathode, always operating at constant current density. It was found that the decay of both pharmaceuticals by electro-oxidation was more rapid in the real water matrix than in ultrapure water with 0.05 mol·L-1 Na2SO4 because of their additional reaction with active chlorine species produced at the bulk from the oxidation of Cl ion. Such chlorinated oxidants exhibited even higher reactivity than hydroxyl radicals formed and confined at the anode. The increase in current density largely enhanced the removal of both pollutants. Similar results were found using the real water matrix at natural alkaline pH. When the mixture of both pharmaceuticals was treated by electro-oxidation, their abatement became slower owing to the competitive attack of generated oxidants over them. Only a slight acceleration of pharmaceutical decay was obtained for the real water matrix using electro-Fenton, since the accumulation of additional homogeneous hydroxyl radical formed from Fenton’s reaction between generated H2O2 and added Fe2+ was inhibited by its reaction with Cl- to form much less reactive chlorinated radicals. For the real water matrix with added pharmaceuticals, a high degree of mineralization of the natural organic matter content (NOM) was reached at high current densities by electro-oxidation, which was even improved upon addition of 0.05 mol·L-1 Na2SO4. Traces of oxidation by-products like p-benzoquinone, as well as NO3- and NH4+ ions, were detected during the electro-oxidation of paracetamol solutions, but the N-compounds contained in the real water matrix were not removed under the investigated conditions.The authors thank the financial support from Ministerio de Ciencia e Innovación, Spain (MICINN) through project CTQ2010-16164/BQU co-financed with FEDER funds.The authors thank the financial support from Ministerio de Ciencia e Innovación, Spain (MICINN) through project CTQ2010-16164/BQU co-financed with FEDER funds.作者联系地址：Laboratori d’Electroquímica dels Materials i del Medi Ambient, Departament de Química Física, Facultat de Química, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, SpainAuthor's Address: Laboratori d’Electroquímica dels Materials i del Medi Ambient, Departament de Química Física, Facultat de Química, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain通讯作者E-mail：[email protected]

Electrochemically-assisted thermal-based technologies for soil remediation

In situ thermal remediation (ISTR) technologies are considered a good option to both, evaporate volatile organic contaminants (VOCs) and enhance the mass transport of dissolved chemicals, avoiding the drawbacks associated with soil excavation. Subsurface heating can be promoted by using direct current (DC) or alternating current (AC), thanks to the Joule effect that arises when electricity is converted into heat as it flows through a low conductivity medium like soil. In this chapter, after a short introduction about existing ISTR technologies, electrochemical ISTR (i.e., electrothermal methods), is reviewed with detail. The fundamentals, mathematical considerations, and modelling are described, thereby presenting some examples that clearly reveal the temperature dependence of key physical properties of soil and water, as well as the scale effect. Several companies that have successfully scaled-up the DC and AC electrothermal techniques are mentioned throughout the chapter. A key idea to keep in mind is that the lowest effective temperature should be the one chosen in ISTR to avoid collateral effects like excessive energy consumption and negative effects on soil properties, including loss of fertility. Coupling of electrical heating with simultaneous in situ chemical oxidation (ISCO) via generation of highly oxidizing species like sulfate radicals enables the operation at milder temperature, thus reducing the electrical power consumption and allowing the degradation of pollutants in addition to their desorption/volatilization.Peer ReviewedPostprint (published version

Crosslinking of poly(vinylpyrrolidone) activated by electrogenerated hydroxyl radicals: A first step towards a simple and cheap synthetic route of nanogel vectors

A facile electrosynthesis route for the preparation of polymer nanogels based on the in situ production of hydroxyl radicals is reported for the first time. Electro-Fenton process with continuous H2O2 electrogeneration and Fe2+ regeneration performs better than electro-oxidation with a boron-doped diamond or dimensionally stable anode for promoting crosslinking of poly(vinylpyrrolidone). Keywords: Electrogenerated hydroxyl radicals, BDD, DSA, Electro-Fenton, Polymer modification, Nanoge

Paired electrochemical removal of nitrate and terbuthylazine pesticide from groundwater using mesh electrodes

Groundwater is one of the main freshwater resources on Earth, but its contamination with NO3- and pesticides jeopardizes its viability as a source of drinking water. In this work, a detailed study of single electro-oxidation (EO) and electrodenitrification and paired EO/electrodenitrification processes has been undertaken with simulated and actual groundwater matrices containing 100 mg dm-3 NO3- and/or 5 mg dm-3 terbuthylazine pesticide. Galvanostatic electrolyses were made with 500 cm3 of solutions at pH 4.0-10.5 and 250-1000 mA in tank reactors with a RuO2 or boron-doped diamond (BDD) anode and one or two Fe cathodes, all of them in the form of meshes. Most of NO3- removals agreed with a pseudo-first-order kinetics. In Cl--free media, NH4+ predominated as electroreduction product. In chloride media, a greater amount of N-volatiles was determined alongside a slower electrodenitrification, especially with RuO2 due to the partial re-oxidation of electroreduction products like NH4+ by active chlorine. The pesticide decays were also fitted to a pseudo-first order kinetics, and its presence led to a smaller release of N-volatiles. Overall, BDD always favored the pesticide degradation thanks to the action of BDD( OH), whereas RuO2 was preferred for electrodenitrification under some conditions. The EO/electrodenitrification of groundwater was successful once the matrix was softened to minimize its hardness. The NO3- concentration was reduced below the limit established by the WHO. Overall, the BDD/Fe cell was more suitable than the RuO2/Fe cell because it accelerated the pesticide removal with a simultaneous high degree of NO3- electroreduction. However, it produced toxic chlorate and perchlorate. A final post-treatment with an anion exchange resin ensured a significant removal of both ions, thus increasing the viability of the electrochemical approach to treat this type of water. Chromatographic analyses revealed the formation of ten heteroaromatic products like desethyl-terbuthylazine and cyanuric acid, alongside oxalic and oxamic as final short-chain carboxylic acids.Peer ReviewedPostprint (author's final draft

On the stationarity of linearly forced turbulence in finite domains

7th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2011, Volume 2011-July, 2011© 2011 International Symposium on Turbulence and Shear Flow Phenomena, TSFP07. All rights reserved. A simple scheme of forcing turbulence away from decay was introduced by Lundgren some time ago, the 'linear forcing', which amounts to a force term linear in the velocity field with a constant coefficient. The evolution of linearly forced turbulence towards a stationary final state, as indicated by direct numerical simulations (DNS), is examined from a theoretical point of view based on symmetry arguments. In order to follow closely the DNS the flow is assumed to live in a cubic domain with periodic boundary conditions. The simplicity of the linear forcing scheme allows one to re-write the problem as one of decaying turbulence with a decreasing viscosity. Scaling symmetry considerations suggest that the system evolves to a stationary state, evolution that may be understood as the gradual breaking of a larger approximate symmetry to a smaller exact symmetry. The same arguments show that the finiteness of the domain is intimately related to the evolution of the system to a stationary state at late times, as well as the consistency of this state with a high degree of isotropy imposed by the symmetries of the domain itself. The fluctuations observed in the DNS for all quantities in the stationary state can be associated with deviations from isotropy. Indeed, self-preserving isotropic turbulence models are used to study evolution from a direct dynamical point of view, emphasizing the naturalness of the Taylor microscale as a self-similarity scale in this system. In this context the stationary state emerges as a stable fixed point. Self-preservation seems to be the reason behind a noted similarity of the third order structure function between the linearly forced and freely decaying turbulence, where again the finiteness of the domain plays an significant role