A critical review on latest innovations and future challenges of electrochemical technology for the abatement of organics in water

Updated water directives and ambitious targets like the United Nations’ Sustainable Development Goals (SDGs) have emerged in the last decade to tackle water scarcity and contamination. Although numerous strategies have been developed to remove water pollutants, it is still necessary to enhance their effectiveness against toxic and biorefractory organic molecules. Comprehensive reviews have highlighted the appealing features of the electrochemical technologies, but much progress has been made in recent years. In this timely review, a critical discussion on latest innovations and perspectives of the most promising electrochemical tools for wastewater treatment is presented. The work describes the performance of electrocatalytic anodes for direct electrochemical oxidation, the oxidation mediated by electrogenerated active chlorine, the electrocatalytic reduction as well as coupled approaches for synchronous anodic and cathodic processes combined with homogeneous and heterogeneous catalysis. The last section is devoted to the assessment of scale-up issues and the increase in the technology readiness level

TRATAMIENTO ELECTROQUIMICO DE CONTAMINANTES ORGANOCLORADOS ALIFATICOS. ELUCIDACION DE LOS CAMINOS DE REACCION.

Los hidrocarburos alifáticos clorados conjugan toxicidad con una alta estabilidad química, capacidad de bioacumulación y difusión de largo alcance. Los cloroetanos son particularmente ubicuos en la industria y en los productos domésticos, y su introducción en el medio ambiente puede entrañar riesgos para los seres vivos. Actualmente, la USEPA (US Environmental Protection Agency) está llevando a cabo el llamado “Endocrine Disruptor Screening Program (EDSP)”, en el cual tanto el 1,2-dicloroetano (DCA) como el 1,1,2,2-tetracloroetano (TCA) son considerados prioritarios debido a sus efectos potenciales sobre el sistema endocrino. El DCA se encuentra también en la lista de substancias prioritarias establecida recientemente por la Comisión Europea.1 Para evitar o, cuando menos, minimizar la entrada de cloroetanos en el medio acuático es necesaria la aplicación de tecnologías de tratamiento de aguas más eficaces que las tradicionalmente empleadas en las plantas de tratamiento de aguas residuales, como por ejemplo los procesos de oxidación avanzada (AOPs). De entre éstos, los AOPs electroquímicos (EAOPs) como la oxidación anódica (OA) y el proceso electro-Fenton (EF) vienen suscitando un gran interés para la degradación de compuestos orgánicos debido a sus excepcionales características técnicas y al uso reducido de compuestos químicos de elevado coste. Sin embargo, hasta la fecha, la electrorreducción con cátodos de plata ha sido el método electroquímico más utilizado para la destrucción de cloroetanos, observándose en general una conversión parcial de los contaminantes iniciales en lugar de su mineralización total. En este trabajo, se han tratado disoluciones acuosas ácidas de DCA y TCA mediante los procesos EF y OA. Las electrólisis se han realizado a corriente constante usando un ánodo de diamante dopado con boro (BDD) y un cátodo a difusión de aire (ADE) capaz de generar H2O2 in situ, el cual reacciona con el Fe2+ añadido para obtener •OH en el seno de la disolución a partir de la conocida reacción de Fenton. A los 420 min de tratamiento EF a 300 mA, se alcanzó la mineralización prácticamente total de disoluciones con 4 mM de DCA o TCA. Tratamientos comparativos en ausencia de Fe2+ (es decir, OA) o con un ánodo de menor poder oxidante como el Pt condujeron a una mineralización más pobre. Los resultados tan positivos obtenidos mediante el proceso EF con BDD se pueden atribuir a la acción sinérgica de los radicales oxidantes, es decir, BDD(•OH) en la superficie del ánodo y •OH en el seno de la disolución, además de la minimización de las limitaciones difusivas. El descenso de la concentración del contaminante inicial se ajusta perfectamente a una cinética de pseudo primer orden. Los subproductos acumulados en mayor concentración durante la degradación del DCA y el TCA son los ácidos cloroacético y dicloroacético, respectivamente. Así mismo, se han identificado los ácidos acético, oxálico y fórmico. Los caminos de reacción propuestos incluyen etapas de decloración oxidativa y reductiva (catódica). Por otra parte, se ha encontrado que el cloro se libera inicialmente como ion Cl, el cual es oxidado a ion ClO3 y, fundamentalmente, a ion ClO4, gracias a la acción de los radicales BDD(•OH) y •OH generados en gran proporción. En conclusión, se ha demostrado que el proceso EF con una celda BDD/ADE es una tecnología muy efectiva para la descontaminación de disoluciones acuosas de DCA y TCA, así como de mezclas de ambos, lo cual constituye un resultado importante de cara a proseguir con su tratamiento en matrices de agua real. Referencias 1. European Commission, Identification of Priority Hazardous Substances under the Water Framework Directive, Directorate-General Environment, 2000

Importance of lysosomal cysteine proteases in lung disease

The human lysosomal cysteine proteases are a family of 11 proteases whose members include cathepsins B, C, H, L, and S. The biology of these proteases was largely ignored for decades because of their lysosomal location and the belief that their function was limited to the terminal degradation of proteins. In the past 10 years, this view has changed as these proteases have been found to have specific functions within cells. This review highlights some of these functions, specifically their roles in matrix remodeling and in regulating the immune response, and their relationship to lung diseases

Matrix metalloproteinases in lung biology

Despite much information on their catalytic properties and gene regulation, we actually know very little of what matrix metalloproteinases (MMPs) do in tissues. The catalytic activity of these enzymes has been implicated to function in normal lung biology by participating in branching morphogenesis, homeostasis, and repair, among other events. Overexpression of MMPs, however, has also been blamed for much of the tissue destruction associated with lung inflammation and disease. Beyond their role in the turnover and degradation of extracellular matrix proteins, MMPs also process, activate, and deactivate a variety of soluble factors, and seldom is it readily apparent by presence alone if a specific proteinase in an inflammatory setting is contributing to a reparative or disease process. An important goal of MMP research will be to identify the actual substrates upon which specific enzymes act. This information, in turn, will lead to a clearer understanding of how these extracellular proteinases function in lung development, repair, and disease

Electrochemical process for the treatment of landfill leachate

In this paper, the anodic oxidation of a real leachate from an old municipal solid waste landfill has been studied using an electrolytic flow cell equipped with a lead dioxide (PbO2) anode and stainless steel as the cathode. The influence of several operation parameters such as (i) the applied current (from 0.5 to 3 A), (ii) liquid flow rate (from 50 to 420 L h-1), (iii) temperature (from 25 to 50 \ub0C), and (iv) pH (from 3.5 to 8.2) on the COD removal rate, current efficiency, and energy consumption has been evaluated. The galvanostatic electrolyses always yielded COD values below the discharge limit (COD p mg L-1); the COD removal rate increased with rising applied current, solution pH, and temperature, whereas it remained almost unaffected by the recirculation flow rate. These results indicate that the organic compounds were mainly removed by their indirect oxidation by the active chlorine generated from chlorides oxidation. The specific energy consumption necessary to reduce the organic load to below the disposal limit was 90 kWh m-

Anodic oxidation of mecoprop herbicide at lead dioxide

The electrochemical oxidation of an aqueous solution containing mecoprop (2-(2-methyl-4-chlorophenoxy) propionic acid) has been studied at PbO2 anodes by cyclic voltammetry and bulk electrolysis. The influence of current density, hydrodynamic conditions, temperature and pH on the degradation rate and current efficiency is reported. The results obtained show that the use of PbO2 leads to total mineralization of mecoprop due to the production of oxidant hydroxyl radical electrogenerated from water discharge. The current efficiency for the electrooxidation of mecoprop is enhanced by low current density, high recycle flow-rates and high temperature. In contrast, the pH effect was not significant. It has also been observed that mecoprop decay kinetics follows a pseudo-first-order reaction and the rate constant increases with rising current density

Comparative depollution of mecoprop aqueous solutions by electrochemical incineration using BDD and PbO2 as high oxidation power anodes

The oxidation ability of the two most used high oxidation power anodes (i.e., anodes with high overpotential for O2 evolution), lead dioxide (PbO2) and boron-doped diamond (BDD), has been compared for the electrochemical incineration of solutions containing the herbicide mecoprop (MCPP) by using an electrolytic flow cell. The influence of several operating parameters such as current, liquid flow rate and MCPP concentration on the performance of both systems with a stainless steel cathode has been studied. Galvanostatic electrolyses always lead to complete mineralization due to the high amounts of effective hydroxyl radicals generated from water oxidation at each anode. The current efficiency using PbO2 is low, thus yielding extremely high energy consumption, while BDD anode exhibits faster oxidation rate and greater current efficiencies, along with a significantly lower energy cost. In this system MCPP disappears at a time similar to that required for overall mineralization, following a pseudo first-order kinetics that is typical of a constant excess of oxidizing hydroxyl radical. GC\u2013MS analyses reveal that the electrochemical degradation pathway involves the same aromatic and carboxylic acid intermediates when using PbO2 or BDD anodes and that oxalic acid is the ultimate by-product prior to conversion to CO2

Comparative electrochemical treatments of two chlorinated aliphatic hydrocarbons. Time course of the main reaction by-products

Acidic aqueous solutions of the chlorinated aliphatic hydrocarbons 1,2-dichloroethane (DCA) and 1,1,2,2-tetrachloroethane (TCA) have been treated by the electro-Fenton (EF) process. Bulk electrolyses were performed at constant current using a BDD anode and an air diffusion cathode able to generate H2O2 in situ, which reacts with added Fe2+ to yield •OH from Fenton’s reaction. At 300 mA, almost total mineralization was achieved at 420 min for solutions containing 4 mM of either DCA or TCA. Comparative treatments without Fe2+ (anodic oxidation) or with a Pt anode led to a poorer mineralization. The better performance of the EF process with BDD is explained by the synergistic action of the oxidizing radicals, BDD(•OH) at the anode surface and •OH in the bulk, and the minimization of diffusional limitations. The decay of the initial pollutant accomplished with pseudo first-order kinetics. Chloroacetic and dichloroacetic acids were the major by-products during the degradation of DCA and TCA, respectively. Acetic, oxalic and formic acids were also identified. The proposed reaction pathways include oxidative and reductive (cathodic) dechlorination steps. Chlorine was released as Cl, being further oxidized to ClO3 and, mostly, to ClO4, due to the action of the largely generated BDD(•OH) and •OH

The preparation of PbO2 coatings on reticulated vitreous carbon for the electro-oxidation of organic pollutants

The preparation of PbO2 coatings on reticulated vitreous carbon (RVC) has been carried out at constant current from electrolytic baths containing aqueous Pb(II) and methanesulfonic acid (MSA, CH3SO3H). The morphological and structural analysis of the RVC/PbO2 deposits carried out by scanning electron microscopy (SEM) and X-ray diffraction revealed that a thick (100 ?m), homogeneous, nanostructured ?-PbO2 film can be successfully formed. As a result, three-dimensional ?-PbO2 structures were obtained, being particularly interesting for their use as anodes in wastewater treatment. The high oxidation ability of these anodes has been verified by the electro-oxidation of Methyl Orange aqueous solutions. Quick decolourisation was achieved, with total colour removal in less than 60 min at 600 mA due to the production of large amounts of reactive OH radicals from the oxidation of water at high anodic potentials. The progressive mineralisation of the solutions was also ascertained from the total organic carbon (TOC) removal, which was much quicker at a higher applied current. All the coated RVC electrodes exhibited excellent long-term stability and remained unaltered after prolonged electrolyses. In addition, novel PbO2 composite coatings were prepared in the presence of hydrothermally synthesized titanate nanotubes (TiNT). The SEM images showed the presence of TiNT agglomerates along the PbO2 surface, which led to higher anodic current in the cyclic voltammetries carried out with Methyl Orange solutions. It is suggested that TiNT favour the adsorption of the organic molecules, facilitating the contact with the OH radicals and thus accelerating the electro-oxidation process. This was confirmed by the faster TOC removal compared to that yielded by the RVC/PbO2, being 45% instead of 24% at 120 mi

Action (verb) fluency: test-retest reliability, normative standards, and construct validity

Action (verb) fluency is a newly developed verbal fluency task that requires the examinee to rapidly generate as many verbs (i.e., things that people do ) as possible within 1 min. Existing literature indicates that action fluency may be more sensitive to frontal-basal ganglia loop pathophysiology than traditional noun fluency tasks (e.g., animal fluency), which is consistent with the hypothesized neural dissociation between noun and verb retrieval. In the current study, a series of analyses were undertaken to examine the psychometric properties of action fluency in a sample of 174 younger healthy participants. The first set of analyses describes the development of demographically adjusted normative data for action fluency. Next, a group of hypothesis-driven correlational analyses reveals significant associations between action fluency and putative tests of executive functions, verbal working memory, verbal fluency, and information processing speed, but not between action fluency and tests of learning or constructional praxis. The final set of analyses demonstrates the test-retest stability of the action fluency test and provides standards for determining statistically reliable changes in performance. In sum, this study enhances the potential clinical applicability of action fluency by providing demographically adjusted normative data and demonstrating evidence for its reliability and construct validity