Boron doped diamond electrode for the wastewater treatment

Electrochemical studies of diamond were started more than fifteen years ago with the first paper on diamond electrochemistry published by Pleskov. After that, work started in Japan, United States of America, France, Switzerland and other countries. Over the last few years, the number of publications has increased considerably. Diamond films have been the subject of applications and fundamental research in electrochemistry, opening up a new branch known as the electrochemistry of diamond electrodes. Here, we first present a brief history and the process of diamond film synthesis. The principal objective of this work is to summarize the most important results in the electrochemical oxidation using diamond electrodes. Os estudos sobre eletroquímica do diamante iniciaram-se há mais de quinze anos, com o primeiro artigo publicado nessa área, por Pleskov. Depois disso, pesquisas começaram no Japão, Estados Unidos, França, Suíssa e outros países, sendo que nos últimos anos o número de publicações aumentou consideravelmente. Filmes de diamante têm sido o objeto de aplicações e pesquisa fundamental em eletroquímica, abrindo um novo campo conhecido como eletroquímica de eletrodos de diamante. Aqui, nós apresentamos uma breve história e o processo de síntese de filme de diamante. O principal objetivo deste trabalho é resumir os resultados mais importantes em oxidação eletroquímica, usando-se eletrodos de diamante

Conductive diamond electrodes for water purification

Nowadays, synthetic diamond has been studied for its application in wastewater treatment, electroanalysis, organic synthesis and sensor areas; however, its use in the water disinfection/purification is its most relevant application. The new electrochemistry applications of diamond electrodes open new perspectives for an easy, effective, and chemical free water treatment. This article highlights and summarizes the results of a selection of papers dealing with electrochemical disinfection using synthetic diamond films

Electrochemical behaviour of dopamine at covalent modified glassy carbon electrode with l-cysteine: preliminary results

The surface of glassy carbon (GC) electrode has been modified by oxidation of L-cysteine. The covalent modified GC electrode with L-Cysteine has been studied, according the supporting electrolyte used. Favourable interactions between the L-cysteine film and DA enhance the current response compared to that at the Nafion GC and bare GC electrodes, achieving better performances than those other electrodes. This behaviour was as result of the adsorption of the cysteine layer film, compact and uniform formation; depending on L-cysteine solution (phosphate buffer or chloridric acid supporting electrolyte) used for modifying GC surface. In cyclic voltammetric measurements, modified electrodes can successfully separate the oxidation/reduction DA peaks in different buffer solutions, but an evident dependence in the response was obtained as function of pH and modified electrode. The modified electrode prepared with L-cysteine/HCl solution was used to obtain the calibration curve and it exhibited a stable and sensitive response to DA. The results are described and discussed in the light of the existing literature

Degradation of 2-hydroxybenzoic acid by advanced oxidation processes

In this study, advanced oxidation processes (AOPs) such as the UV/H2O2 and Fenton processes were investigated for the degradation of 2-hydroxybenzoic acid (2-HBA) in lab-scale experiments. Different [H2O2]/[2-HBA] molar ratios and pH values were used in order to establish the most favorable experimental conditions for the Fenton process. For comparison purposes, degradation of 2-HBA was carried out by the UV/H2O2 process under Fenton experimental conditions. The study showed that the Fenton process (a mixture of hydrogen peroxide and Fe2+ ion) was the most effective under acidic conditions, leading to the highest rate of 2-hydroxybenzoic acid degradation in a very short time interval. This same process led to a six-fold acceleration of the oxidation rate compared with the UV/H2O2 process. The degradation of 2-hydroxybenzoic acid was found to follow first-order kinetics and to be influenced by the type of process and the experimental conditions. The experimental results showed that the most favorable conditions for 2-HBA degradation by the Fenton process are pH around 4-5, [Fe2+] = 0.6 mmol.L-1, and [H2O2]/[2-HBA] molar ratio = 7. The hydroxylation route is explained here for the two processes, and the results are discussed in the light of literature information

Towards Sustainability: Photochemical and electrochemical processes applied for environmental protection

In the last century, public policy around the globe was mainly focused on economic growth leaving out of this perspective, social concerns and the environment detriment that this merely economic approach was causing. It was until the last quarter of the 20th century that people started to be aware of the growing poverty and of the jeopardy of the planet as a result of human being activities. In consequence, the concept of sustainable development emerged in the United Nations as a call to all countries to integrate economic growth with social needs and environmental protection, in such a way that our activities as earth inhabitants stopped compromising the quality of life and needs satisfaction of future generations

Renewable energies driven electrochemical wastewater/soil decontamination technologies: A critical review of fundamental concepts and applications

Electrochemical wastewater and soil treatments are exciting set of technologies that has been well-studied over the recent years as one of the most-effective remediation techniques for the removal of hazardous pollutants from liquids effluents and soil. The main requirement of these technologies is electricity and their sustainability can be largely improved if they are powered by renewable energy sources. Likewise, this green energy powering can help to apply these technologies in remote areas, such as rural communities in developing countries, where no electricity grid is available. This review presents a comprehensive discussion on fundamental concepts and applications of renewable energy driven electrochemical technologies for treating hazardous pollutants in wastewater and contaminated soils. In the first section, the fundamentals of different electrochemical remediation technologies are presented, whereas the next two sections focused on the most applied technologies for powering these electrochemical devices: the solar photovoltaic (PV) (Section 3) and the wind turbines (Section 4). After that, the non-near future is faced with the study of the principles of biomass energy production and how bioelectrochemical systems are starting to be evaluated for powering electrochemical technologies (Section 5). Then, new approaches in the renewable energy driven electrochemical technologies such as triboelectric nanogenerators and photocatalytic fuel cells are described in Section 6. The last section focused on the challenges expected for the near future, describing the most promising storage system and evaluating the scale-up, environmental and economic concerns of the technologies studied in this work

Modelling electro-scrubbers for removal of VOCs

This work focuses on the development and testing of simple phenomenological models for understanding the behaviour of processes happening at the same time in the electro-scrubbers during the electrochemically assisted absorption of two relevant volatile organic compounds: perchloroethylene and toluene. Formulation of the model considers physical absorption of the organics into the electrolyte and reactivity according to experimental observations. Different experimental case studies have been used to validate the model obtaining regression coefficients higher than 0.9 and 0.85 for perchloroethylene and toluene, respectively. The model points out the high relevance of the absorption technology and of the presence of cobalt. In the case of perchloroethylene, the model also highlighted the important contribution of the wet decomposition of this chlorinated hydrocarbon. Results obtained clearly evidence the industrial application of the electro-scrubbers technologies

Continuous electro-scrubbers for the removal of perchloroethylene: Keys for selection

In this work, the removal of perchloroethylene (PCE) using continuous-operation electro-scrubbers is evaluated. Two types of electro-scrubbers were made by combining a jet mixer or a packed absorption column with a single flow-cell. The absorbent/electrolyte is recirculated between both devices, being electrolyzed in the cell and retaining the pollutant in the scrubber. In both scrubber’s system, an important amount of PCE was absorbed into the electrolyte and the application of electric current significantly improved the results, highlighting the efficiency of the integration of technologies. Tests in the absence of absorbent/electrolyte confirmed the reactivity of the PCE in the wet gas phase. The jet-mixer system turned out to be more efficient than the packed column, yielding better results both in absorption and electro-absorption modes, and reaching a PCE removal greater than 90%. Meanwhile, the addition of cobalt mediators did not improve the electro-scrubbing efficiency as initially expected: in the case of the packed column electro-scrubber there were no changes while in the case of the jet mixer surprisingly it is generated a negative effect

Electrolysis with diamond anodes of the effluents of a combined soil washing – ZVI dechlorination process

In this work, a new soil washing process in which Soil-Liquid extraction technology is enhanced by adding iron particles (zero valent iron nanoparticles or granules) was investigated to remove clopyralid from spiked soils. This novel approach can be efficiently used to extract chlorinated hydrocarbons from soil and aims to obtain soil-washing wastes with low content of hazardous chlorinated species. The iron particles used were subsequently removed from the treated soil using magnetic fields. Then, the complete mineralization of the produced soil washing effluents was successfully achieved by applying anodic oxidation with diamond anodes in an electrochemical flow cell. Results demonstrated that, opposite to what it was initially expected, no improvements in the efficiency of the electrochemical process were observed by adding iron particles during the soil washing. This behavior is explained in terms of the lower electrochemical reactivity of the dechlorinated derivatives produced. Although results are not as promising as initially expected, it does not mean a completely negative outcome for the use of ZVI during washing, because the hazardousness of the pollutants is rapidly decreased in the initial stages of the soil-washing, opening the possibility for the combination of this technology with other processes, such as biological treatment

Treatment of ex-situ soil-washing fluids polluted with petroleum by anodic oxidation, photolysis, sonolysis and combined approaches

In this research, the treatment of soil spiked with petroleum was studied using a surfactant-aided soil-washing (SASW) process followed by sonolysis (US), photolysis and boron doped diamond electrolysis (BDD-electrolysis) for washing liquid treatment. Results clearly demonstrate that SASW is a very efficient approach in the treatment of soil, removing completely the petrochemical compounds by using dosages about 5 g of extracting surfactant (sodium dodecyl sulfate (SDS)) per kg of soil. The main characteristics of the effluents produced in this soil remediation technology as well as the efficiency of the treatment (US, photolysis and BDD-electrolysis) depend on the dosage of SDS. Depollution of the effluents (degradation and mineralization of the organic matter) is related to the reduction in size of micelles formed by SDS and petroleum, and it depends on the treatment used. US and photolysis were inefficient decontamination processes, while BDD-electrolysis favors the complete depletion of micelles. However, the intensification of the efficiency was attained by synergic degradation effects when UV light irradiation and US were coupled with BDD-electrolysis, US/BDD-electrolysis and photo/BDD-electrolysis, respectively. Sulfate (coming from SDS) ions play an important role during the BDD-electrolysis, US/BDD-electrolysis and photo/BDD-electrolysis because persulfate and persulfate radicals are produced (by sulfate activation applying US or photolysis), improving the efficiency of the processes