Coupling a Boron Doped Diamond Anode with a Solid Polymer Electrolyte to Avoid the Addition of Supporting Electrolyte in Electrochemical Advanced Oxidation Processes

The application of electrochemical technologies to wastewater treatment is limited by solution conductivity. In this paper, a solid polymer electrolyte Nafion\uae membrane has been used sandwiched between a boron doped diamond (BDD) anode and Ti/RuO2 cathode meshes to treat Bismarck Brown Y (BBY) solutions with very low conductivity. BBY has been chosen as model compound to the system, and the influence of several process parameters has been investigated. During the experiments the evolution of chemical oxygen demand (COD), color removal and nitrogen compounds have been monitored. The performances were strongly related with applied current and stirring rate, changed in a range of 0.5\u20132 A and 200 and 850 rpm, respectively. Their increment leads to a decrease of oxidation time required to remove BBY completely. The effect of the presence of Na2SO4 (2 and 7 mM) as supporting electrolyte has been also evaluated. Results were compared with a removal treatment carried out with a conventional batch system, using a flow cell containing liquid supporting electrolyte (Na2SO4). This comparison highlighted that the new cell setup is performing better in removing organic compounds, and thus, can be considered as effective process for the treatment of solutions with a low conductivity

Application of diamond electrodes to electrochemical processes

Conducting diamond thin film is a new electrode material that has received great attention recently because it possesses several technologically important characteristics such as an inert surface with low adsorption properties, remarkable corrosion stability, even in strong acidic media, and an extremely wide potential window in aqueous and non-aqueous electrolytes. Thanks to these properties diamond electrodes meet the requirements for a wide range of electrochemical applications. The object of this article is to summarise and discuss the recent results available in the literature concerning the application of diamond electrodes to electrochemical processes such as water treatment and electro-synthesis of organic and inorganic compounds

Electrochemical generation of H2O2 in low ionic strength media on gas diffusion cathode fed with air

The electrogeneration of hydrogen peroxide in solution with low ionic strength using a gas diffusion cathode fed with air was investigated by linear sweep voltammetries and bulk electrolyses. The effect of applied current (15\u201345mAcm 122), solution pH (4\u201310), temperature (15\u201360 \u25e6C) and cell configuration (divided or undivided) on the H2O2 generation rate and current efficiency was evaluated. Experimental results showed that in Na2SO4 0.05MH2O2 can be produced with a satisfactory efficiency, i.e. 53%. Higher production rate was obtained in a two-compartment cell by increasing current density and pH and by decreasing solution temperature. A much lower efficiency (i.e. 30%) was obtained using the undivided cell, because, under these conditions, electrogenerated hydrogen peroxide was decomposed by anodic oxidation on Pt electrode

Influence of thickness on mechanical properties and crack-bridging ability of coatings for concrete

Different variables can influence the crack-bridging ability (CBA) of a coating. These parameters can be related to: (i) the substrate, i.e. the way the crack opens and develops in the concrete; (ii) the substrate/coating interface, i.e. the adhesion of the organic coating to the concrete; (iii) the coating, i.e. its thickness and mechanical properties; (iv) the external conditions, i.e. the temperature in field and the mechanical solicitation of the structure. In the present paper, some experiments were performed to analyse the third point, i.e. to find possible relationships between the variation of the CBA (in situ failure of the coating applied to the concrete substrate) and the mechanical properties (free-film failure) of coatings with thickness. Experimental results suggest that the value of strain at break is a key factor in the variation of CBA of a coating with thickness

Applicability of electrochemical methods to carwash wastewaters for reuse. Part 2: Electrocoagulation and anodic oxidation integrated process.

In this work a combined two-step process consisting in the electrochemical coagulation with iron anodes and the electrochemical oxidation with boron-doped diamond anode (BDD) was developed for the treatment of a real carwash wastewater. The effects of important operating parameters such as current density, electrolysis time and pH on the surfactants oxidation, COD removal and energy consumptions during electrocoagulation have been explored. Furthermore, the effect of current density on the performance of anodic oxidation has been studied. The experimental results revealed that in the optimal experimental conditions (actual pH 6.4, electrolysis time 6 minutes and applied current 2 mA cm-2) the electrocoagulation method is able to remove 75% of COD in with low energy consumption, about 0.14 kWh m-3. The complete COD removal of the wastewater was achieved by the overall combined process where the residual organics coming from the electrocoagulation are degraded by electrochemical oxidation applying a current of 10 mA cm-2. The energy consumption and the electrolysis time for the complete mineralization of the carwash wastewater were 12 kWh m-3 and 100 minutes, respectively

Electrochemical Oxidation as a Final Treatment of Synthetic Tannery Wastewater

Vegetable tannery wastewaters contain high concentrations of organics and other chemicals that inhibit the activity of microorganisms during biological oxidations, so biorefractory organics that are not removed by biological treatment must be eliminated by a tertiary or advanced wastewater treatment. In this paper, the applicability of electrochemical oxidation as a tertiary treatment of a vegetable tannery wastewater was investigated by performing galvanostatic electrolysis using lead dioxide (Ti/PbO2) and mixed titanium and ruthenium oxide (Ti/TiRuO2) as anodes under different experimental conditions. The experimental results showed that both the electrodes performed complete mineralization of the wastewater. In particular, the oxidation took place on the PbO2 anode by direct electron transfer and indirect oxidation mediated by active chlorine, while it occurred on the Ti/TiRuO2 anode only by indirect oxidation. Furthermore, the Ti/PbO2 gave a somewhat higher oxidation rate than that observed for the Ti/TiRuO2 anode. Although the Ti/TiRuO2 required almost the same energy consumption for complete COD removal, it was more stable and did not release toxic ions, so it was the best candidate for industrial applications. With the Ti/TiRuO2 anode, the rate of tannery wastewater oxidation increased with the current density, pH, and temperature of the solution. These results strongly indicate that electrochemical methods can be applied effectively as a final treatment of vegetable tannery wastewater allowing the complete removal of COD, tannin, and ammonium and decolorization

Electrochemical Oxidation Of Aromatic Sulphonated Acids On A Boron-Doped Diamond Electrode

The electrochemical oxidation of an industrial wastewater containing aromatic sulphonated acids on a boron-doped diamond electrode (BDD) was studied using cyclic voltammetry and bulk electrolysis. The influence of the current density and flow-rate was investigated in order to find the optimum conditions. It was found that a polymeric film, which caused BDD deactivation, was formed in the potential region of water stability during oxidation, however it was removed by high-potential anodic polarisation in the region of O2 evolution. The complete mineralisation of the wastewater was achieved over the whole range of experimental conditions examined, due to the production of hydroxyl radicals on the diamond surface. The oxidation of the aromatic sulphonated acids was favoured by a low current density and a high flow-rate meaning that the oxidation was a diffusion-controlled process

Influence of anode material on the electrochemical oxidation of 2-naphthol. Part 2: Bulk electrolysis experiments

The electrochemical oxidation of 2-naphthol has been studied by galvanostatic electrolysis, using a range of electrode materials such as lead dioxide, boron-doped diamond (BDD) and Ti\u2013Ru\u2013Sn ternary oxide anodes. The influence of some operating parameters, such as current density, flow-rate and chloride concentration on naphthol oxidation has been investigated in order to find the optimum experimental conditions. Measurements of chemical oxygen demand, HPLC and total organic carbon have been used to follow the oxidation. The experimental data indicate that on PbO2 and BDD, naphthol oxidation takes place by reaction with electrogenerated hydroxyl radicals and is favoured by low current density and high flow-rate. On the contrary, on a Ti\u2013Ru\u2013Sn ternary oxide the mineralisation of naphthol occurs only in the presence of chloride ions that act as redox mediators and COD removal is affected by chloride concentration and is not significantly influenced by the current density and mass-transfer coefficient. From a comparison of the results of the three electrodes it has been found that boron-doped diamond gives a faster oxidation rate and better current efficiency

Removal of colour and COD from wastewater containing acid blue 22 by electrochemical oxidation

Electrochemical oxidation of synthetic wastewater containing acid blue 22 on a boron-doped diamond electrode (BDD) was studied, using cyclic voltammetry and bulk electrolysis. The influence of current density, dye concentration, flow rate, and temperature was investigated, in order to find the best conditions for COD and colour removal. It was found that, during oxidation, a polymeric film, causing BDD deactivation, was formed in the potential region of water stability, and that it was removed by anodic polarisation at high potentials in the region of O2 evolution. Bulk electrolysis results showed that the electrochemical process was suitable for completely removing COD and effectively decolourising wastewaters, due to the production of hydroxyl radicals on the diamond surface. In particular, under optimal experimental conditions of flow rates (i.e. 300 dm3 h 121) and current density (i.e. 20mAcm 122), 97% of COD was removed in 12 h electrolysis, with 70 kWhm 123energy consumption