Irradiated electrochemical processes for the removal of persistent organic pollutants from waters and wastewaters (original) (raw)
Related papers
Journal of Hazardous Materials, 2016
This paper analyzes the advantages and drawbacks of the combination of UV irradiation with electrolysis with the aim to give insight about the feasibility of the application of this technology for the reclaiming of conventionally-treated wastewater. The oxidation of synthetic solutions containing five selected model complex pollutants has been compared, showing that UV irradiation improves the results of electrolysis for progesterone, metoprolol and caffeine and deteriorates the performance for the degradation of sulfamethoxazole and dimethyl-phthalate. Differences observed becomes lower when mineralization is compared showing that the effects of UV irradiation are diluted when a mixture of species is oxidized. Results suggest that high ThOD/TOC (Theoretical oxygen demand/Total organic carbon) 2 ratios improve the synergistic coupling of technologies while low values lead to a clear antagonistic effect. Because during oxidation progress this ratio is decreased, the observed effect on mineralization is much lower than in the oxidation of the raw molecule. Opposite to this low effect on the oxidation of organics, the improvement in the performance of the disinfection by coupling UV to electrolysis is much clearer. In addition, UV irradiation modifies significantly the chlorine speciation and helps to prevent the formation of hazardous species such as chlorate and perchlorate during the electrochemical processes.
Journal of Applied Electrochemistry, 2015
This work focused on the removal of Persistent Organic Pollutants (POPs) from wastewater using irradiation-assisted electrochemical technologies, i.e., sonoelectrolysis, photoelectrolysis and sono-photoelectrolysis. Single-irradiation processes (sonolysis and photolysis) and electrochemical oxidation using conductive diamond anodes (current density of 30 mA cm-2) were also evaluated for comparison. Three POPs with different molecular structures (sulfamethoxazole, metoprolol and caffeine, initial concentration of 100 mg dm-3) were studied to evaluate the robustness of the selected technologies and the oxidation mechanisms involved in each case. Results show that the single application of the irradiation technologies led to the removal of only a small amount of POPs and no mineralisation, with the nature of the pollutant showing a marked effect; the opposite was observed for the single application of Conductive Diamond Electrochemical Oxidation (CDEO), which is a highly robust and efficient technology for the degradation of all types of POPs. Sonoelectrolysis, photoelectrolysis and sono-photoelectrolysis processes (ultrasound conditions: 200 W, ultraviolet conditions: 254 nm, 4 W) may show synergistic, antagonistic or nil effects with respect to a single electrochemical oxidation event, depending on the nature of the treated molecule. The differences observed may be related to the different chemical nature of the organic species studied, indicating an important role of mediated oxidation processes, which may be enhanced with ultrasounds and ultraviolet radiation techniques.
Chemosphere, 2018
Boron doped diamond (BDD) anode has been used to oxidatively remove Rhodamine B (RhB), as persistent organic pollutant, from synthetic wastewater by electrolysis, photoelectrolysis and chemical oxidation containing sulfate and phosphate as supporting electrolytes. RhB is effectively oxidized by electrolysis and by chemical oxidation with the oxidants separately produced by electrolyzing sulfate or phosphate solutions (peroxodisulfate and peroxodiphosphate, respectively). The results showed that light irradiation improved the electrolysis of RhB due to the activation of oxidants under irradiation at high current densities. Meanwhile, the efficiency of the chemical oxidation approach by ex situ electrochemical production of oxidants was not efficient to degrade RhB.
Chemical Engineering Journal, 2012
The electrochemical oxidation of organics in water at boron doped diamonds (BDD) was experimentally investigated with the aim to discuss the correlations among the conversion of the pollutants and the instantaneous current efficiency ICE with the operative conditions. A simple theoretical model previously developed for the oxidation of oxalic acid accounting for the cases of mass transfer control, oxidation reaction control and mixed kinetic regimes was adopted and extended to challenge its predictive capability in the case of organics of different nature and in systems with more pollutants. A quite good agreement, between theoretical predictions and experimental data pertaining to the electrochemical oxidation of numerous organics, including some carboxylic acids and aliphatic chlorides, was observed, both for experiments performed in the presence of one or more organics. Results clearly indicate that such a simple model can be used to describe properly the "direct oxidation" (including oxidation by anodic electron transfer or by means of hydroxyl radicals) of organics at BDD. The comparison between the theoretical model and the experimental data strongly sustained the hypothesis that oxalic acid is oxidized by anodic electron transfer exchange while formic and maleic acids by reaction with hydroxyl radicals.
Chemical Engineering Journal, 2012
h i g h l i g h t s " Electrolysis with conductive-diamond anodes assures the disinfection of urban treated wastewaters. " It assures the total removal of coliforms without the addition of any reagent. " Hypochlorite and chloramines have been identified as the main disinfectants produced. " Formation of hazardous compounds is not obtained by this technology using low current densities. " Power consumptions as low as 0.2 kW h m À3 is enough to assure the complete disinfection of treated wastewater.
Chemosphere, 2018
This work focuses on the treatment of synthetic wastewater polluted with dye Procion Red MX-5B by different Electrochemical Advanced Oxidation Processes (EAOP) based on diamond anodes. The influence of the current density and the supporting electrolyte has been studied on dye removal and total mineralization of the organic matter. Results show that electrolysis with diamond electrodes is a suitable technology for an efficient degradation of dye. Nonetheless, the process efficiency increases when using chloride as supporting electrolyte because of the electrochemical generation of hypochlorite in wastewater which significantly contribute to dye removal. On the contrary, the total mineralization of the organic matter is more efficient in sulfate media. In this case, large amounts of peroxodisulfate are electrogenerated, favoring the complete removal of total organic carbon (TOC). On the other hand, lower current densities (10 mA cm) lead to a more efficient removal of both dye and TOC...
Electrocatalysis, 2013
A numerical model has been developed to estimate the role of hydroxyl radicals in the competition of organic compounds during electrolysis using a boron-doped diamond (BDD) anode. It is well established that hydroxyl radicals are generated during water discharge. These radicals are free at the surface and act locally, their sphere of activity was estimated by the model to be 20 nm maximum from the anode. The implementation of the model taking account the presence of one and then two organic compounds in the solution can be used to predict the variation of the concentration of each organic with time during the electrolysis and their space profile in the electrochemical reactor too without using adjustable parameters. The role of hydroxyl radicals was highlighted in the competitive reaction with organics: the electrolysis of a solution containing an equimolar mixture of formic acid (FA) and maleic acid (MA) shows that FA oxidation only began when the MA had completely disappeared. The numerical model is in good agreement with the experiment and is thus suitable to describe the competition of two organics during electrolysis with a BDD anode. Keywords Boron-doped diamond . Hydroxyl radicals . Numerical model . Electrooxidation of organics . Wastewater treatment Abbreviations C Concentration (in mole per cubic meter) C°Initial concentration (in mole per cubic meter) D i Diffusion coefficient of the compound i (in square meter per second) j Current density (in Ampere in square meter) j lim Limiting current density (in Ampere in square meter) J Flux (in mole per square meter per second) k d Mass transfer coefficient (in meter per second) k i Rate constant of chemical reaction involving • OH and the organic compound i L Thickness of the diffusion layer (in meter) M i Molar mass of the compound i (in grams per mole) S Electrode area (in square meter) V T Volume of the solution (in square meter)
Applied Catalysis B: Environmental, 2014
In this work, the improvements obtained in the conductive-diamond electrochemical oxidation (CDEO) by simultaneous coupling of ultrasounds (US) and UV-light irradiation are studied for the treatment of synthetic wastes containing dimethyl phthalate (DMP). Results show that both irradiation technologies improve significantly the rates of oxidation and mineralization of the electrolytic process, but their coupled effect on results is smaller to the effect observed when they operate separately. Results are explained in terms of the formation of radicals in the reaction media by UV-light or US decomposition of powerful oxidants formed electrochemically on the conductivediamond surface. Oxidation of DMP proceeds thought the removal of the methyl esters group, ring breakage and carboxylic acid mineralization. Concentration of intermediates is very small in electrolytes with sulfates. When chlorides are present in the electrolyte, chlorophenols are also observed and concentration of intermediates becomes greater. In terms of energy consumed, sonolysis processes are more expensive than photolysis processes to attain similar removal percentages.
Journal of Electroanalytical Chemistry, 2019
This work is focused on the evaluation of the performance of bulk electrosynthesis of chlorine oxoanions and peroxodisulfate with diamond electrodes, made with the same conductive-diamond coating deposited on three different substrates (niobium, tantalum and silicon). Results point out an important influence of the substrate on the efficiency of the processes. The diamond coatings on tantalum substrate leads to higher concentrations of hypochlorite and perchlorate from the electrolysis of synthetic brines. Specifically, the most remarkable influence has been observed at 1500 A m-2. This can be attributed to a production of large amounts of hydroxyl radicals which significantly contribute to the generation of hypochlorite and perchlorate by mediated oxidation of chloride and hypochlorite, respectively. On the contrary, the electrochemical production of peroxodisulfate is favored when using silicon as diamond substrate, as well at current densities higher than 1000 A m-2. Although the formation of peroxodisulfate depends on the production of hydroxyl radicals, this better performance of silicon (and even niobium) 2 can be related to the decomposition of peroxodisulfate by means of its reaction with the excessively high concentrations of hydroxyl radicals produced with diamond coatings deposited on tantalum. These results are of extreme significance for the tailoring of electrodes for specific applications, because they demonstrate that the boron doping and the sp 3 /sp 2 ratios are not the only inputs to be considered.