RESUMO
In this work, the influence of oxygen-containing surface groups of activated carbon electrodes on the charge efficiency of electro-assisted adsorption of As(V) was investigated. It was distinguished between activated carbons modified through acidic (oxidation) and thermal (reduction) treatments, starting with a granular pristine commercial activated carbon of bituminous origin. The textural characterization of the three materials showed that the treatments did not produce significant changes in the surface area and in the distribution of pores. The three carbon samples were used to fabricate packed electrodes with stainless-steel mesh as electric current collector. This work report that the application of anodic potentials (1.01 and 1.41 V vs. NHE) increased the adsorption capacity and rate of arsenate uptake in solutions containing only this contaminant (2.5 mg L-1) at pH 7. The oxidized carbon electrode presented the lowest capacitance and adsorption capacity during electroadsorption (0.33 mg g-1), compared to pristine material (1.77 mg g-1). On the other hand, the reduced electrode displayed the highest adsorption capacity of arsenate (3.14 mg g-1) when applying a potential of 1.01 V. The results were correlated with the potential of zero charge values. In addition, for this material, the rate of kinetics increased 26.7 % compared to experiments without applied potential.
RESUMO
The simultaneous removal of hydrated silica, fluoride and arsenic from deep well water (hydrated silica 72 mgL-1, fluoride 4.4 mgL-1, arsenic 106.2 µgL-1, sulfate 50 mgL-1, phosphate 0.99 mgL-1, pHâ¯=â¯8.2 and conductivity 659 µScm-1) by electrocoagulation (EC) was investigated. The EC was performed in a continuous electrochemical reactor using aluminum plates as sacrificial anodes coupled directly to a jar test device. The effect of current density (4â¯≤â¯jâ¯≤â¯8â¯mAâ¯cm-2) and mean linear flow rates in the EC reactor (0.057â¯≤â¯uâ¯≤â¯0.57â¯cmâ¯s-1) on the hydrated silica, fluoride, and arsenic removal efficiencies was analyzed. The abatement of hydrated silica was obtained at 8â¯mAâ¯cm-2 and 0.057â¯cmâ¯s-1, while the residual concentrations of F- and As after the same electrolysis were 0.19â¯mg L-1 and 9.8⯵g L-1, satisfying the WHO guidelines for F- (≤1.5â¯mg L-1) and As (≤10⯵g L-1). Spectroscopic analyses on aluminum flocs revealed that they are predominantly composed of aluminum silicates. Arsenates adsorb on aluminum flocs and fluoride replaces a hydroxyl group from aluminum aggregates.
Assuntos
Arsênio/química , Fluoretos/química , Água Subterrânea/química , Dióxido de Silício/química , Poluentes Químicos da Água/química , Purificação da Água/métodos , Adsorção , Alumínio/química , Poluentes Químicos da Água/análiseRESUMO
The degradation of solutions of the antibiotic levofloxacin (LVN) in sulfate medium at pH 3.0 has been investigated at pre-pilot scale by solar photoelectro-Fenton (SPEF) process. The flow plant included an FM01-LC filter-press cell equipped with a Ti|Pt anode and a three-dimensional-like air-diffusion cathode, connected to a compound parabolic collector as photoreactor and a continuous stirred tank under recirculation batch mode. The effect of volumetric flow rate on H2O2 electrogeneration from O2 reduction was assessed. Then, the influence of initial LVN concentration and Fe2+ concentration as catalyst on dissolved organic carbon (DOC) removal was thoroughly investigated. LVN was gradually mineralized by SPEF process, with faster DOC abatement at 0.50â¯mM Fe2+, yielding 100% after 360â¯minâ¯at applied cathodic potential of -0.30â¯V|SHE. The high mineralization current efficiency (MCE) and low specific energy consumption (ECDOC) revealed the extraordinary role of homogeneous hydroxyl radicals and natural UV light, which allowed the degradation of the antibiotic and its by-products with MCE values greater than 100%. Five cyclic by-products, N,N-diethylformamide and three short-chain linear carboxylic acids were detected by GC-MS and HPLC analyses. A parametric model to simulate the DOC decay versus electrolysis time was implemented for the SPEF pre-pilot flow plant, showing good agreement with experimental data.
Assuntos
Antibacterianos/análise , Peróxido de Hidrogênio/química , Ferro/química , Levofloxacino/análise , Modelos Teóricos , Raios Ultravioleta , Poluentes Químicos da Água/análise , Purificação da Água/métodos , Antibacterianos/efeitos da radiação , Catálise , Relação Dose-Resposta a Droga , Técnicas Eletroquímicas , Levofloxacino/efeitos da radiação , Projetos Piloto , Solubilidade , Fatores de Tempo , Poluentes Químicos da Água/efeitos da radiaçãoRESUMO
We investigated simultaneous arsenic and fluoride removal from ground water by electrocoagulation (EC) using aluminum as the sacrificial anode in a continuous filter-press reactor. The groundwater was collected at a depth of 320 m in the Bajío region in Guanajuato Mexico (arsenic 43 µg L(-1), fluoride 2.5 mg L(-1), sulfate 89.6 mg L(-1), phosphate 1.8 mg L(-1), hydrated silica 112.4 mg L(-1), hardness 9.8 mg L(-1), alkalinity 31.3 mg L(-1), pH 7.6 and conductivity 993 µS cm(-1)). EC was performed after arsenite was oxidized to arsenate by addition of 1 mg L(-1) hypochlorite. The EC tests revealed that at current densities of 4, 5 and 6 mA cm(-2) and flow velocities of 0.91 and 1.82 cm s(-1), arsenate was abated and residual fluoride concentration satisfies the WHO standard (CF < 1.5 mg L(-1)). Spectrometric analyses performed on aluminum flocs indicated that these are mainly composed of aluminum-silicates of calcium and magnesium. Arsenate removal by EC involves adsorption on aluminum flocs, while fluoride replaces a hydroxyl group from aluminum aggregates. The best EC was obtained at 4 mA cm(-2) and 1.82 cm s(-1) with electrolytic energy consumption of 0.34 KWh m(-3).
Assuntos
Alumínio/química , Arsênio/química , Eletrólise/métodos , Fluoretos/química , Poluentes Químicos da Água/química , Purificação da Água/métodos , Adsorção , Eletrodos , Eletrólise/instrumentação , Água Subterrânea/química , México , Purificação da Água/instrumentaçãoRESUMO
This paper explores the applicability of electrochemical oxidation on a triphenylmethane dye compound model, hexamethylpararosaniline chloride (or crystal violet, CV), using BDD anodes. The effect of the important electrochemical parameters: current density (2.5-15 m A cm(-2)), dye concentration (33-600 mg L(-1)), sodium sulphate concentration (7.1-50.0 g L(-1)) and initial pH (3-11) on the efficiency of the electrochemical process was evaluated. The results indicated that while the current density was lower than the limiting current density, no side products (hydrogen peroxide, peroxodisulphate, ozone and chlorinated oxidizing compounds) were generated and the degradation, through OH radical attack, occurred with high efficiency. Analysis of intermediates using GC-MS investigation identified several products: N-methylaniline, N,N-dimethylaniline, 4-methyl-N,N-dimethylaniline, 4-methyl-N-methylaniline, 4-dimethylaminophenol, 4-dimethylaminobenzoic acid, 4-(N,N-dimethylamino)-4'-(N',N'-dimethylamino) diphenylmethane, 4-(4-dimethylaminophenyl)-N,N-dimethylaniline, 4-(N,N-dimethylamino)-4'-(N',N'-dimethylamino) benzophenone. The presence of these aromatic structures showed that the main CV degradation pathway is related to the reaction of CV with the OH radical. Under optimal conditions, practically 100% of the initial substrate and COD were eliminated in approximately 35 min of electrolysis; indicating that the early CV by-products were completely degraded by the electrochemical system.