RESUMO
Heterogeneous electro-Fenton (HEF) is as an alternative to the conventional electro-Fenton (EF) process. HEF uses a solid phase catalyst, whereas EF employs a solubilized one. This implies that in HEF, material can be recovered through a simple separation process such as filtration or magnetic separation in HEF. HEF also has the advantage of not requires a previous pH adjustment, which facilitates working in a higher pH range. In this work, Fe, Cu and Fe/Cu bimetallic nanoparticles (Fe/Cu NPs) were synthesized, characterized and used for the degradation of Nafcillin (NAF). The effect of the adsorption and the anodic oxidation (AO-H2O2) process was tested to assess their influence on HEF. NAF adsorption did not exceed 24% of antibiotic removal and the AO-H2O2 process eliminated the total NAF after 240 min of electrolysis. Through the HEF process, the antibiotic was completely removed using Fe/Cu NPs after 7.0 min of electrolysis, while these NPs, mineralization reached 41% after 240 min. In this case, NAF degradation occurs mainly due to the generation of hydroxyl radicals in the BDD electrode, and the Fenton reaction with Fe and Cu NPs. The main organic intermediates produced during the degradation of NAF by HEF were identified allowing the proposal of degradation pathway. Finally, the antibiotic was also completely eliminated from a wastewater from slaughterhouse after 15 min of treatment by HEF and using Fe/Cu bimetallic NPs.
Assuntos
Cobre/química , Peróxido de Hidrogênio/química , Ferro/química , Nanopartículas Metálicas/química , Nafcilina/química , Antibacterianos/química , Catálise , Técnicas Eletroquímicas , Eletrólise/instrumentação , Eletrólise/métodos , Radical Hidroxila/química , Oxirredução , Águas Residuárias/química , Poluentes Químicos da Água/análise , Poluentes Químicos da Água/químicaRESUMO
This study investigated the anodic oxidation of phenolic wastewater generated by cashew-nut processing industry (CNPI) using active (Ti/RuO2-TiO2) and inactive (boron doped diamond, BDD) anodes. During electrochemical treatment, various operating parameters were investigated, such as current density, chemical oxygen demand (COD), total phenols, O2 production, temperature, pH, as well as current efficiency and energy consumption. After electrolysis under optimized working conditions, samples were evaluated by chromatography and toxicological tests against L. sativa. When both electrode materials were compared under the same operating conditions, higher COD removal efficiency was achieved for BDD anode; achieving lower energy requirements when compared with the values estimated for Ti/RuO2-TiO2. The presence of Cl- in the wastewater promoted the electrogeneration of strong oxidant species as chlorine, hypochlorite and mainly hypochlorous acid, increasing the efficiency of degradation process. Regarding the temperature effect, BDD showed slower performances than those achieved for Ti/RuO2-TiO2. Chromatographic and phytotoxicity studies indicated formation of some by-products after electrolytic process, regardless of the anode evaluated, and phytotoxic action of the effluent. Results encourage the applicability of the electrochemical method as wastewater treatment process for the CNPI, reducing depuration time.
Assuntos
Diamante/química , Eletrólise/métodos , Fenóis/análise , Águas Residuárias/química , Poluentes Químicos da Água/análise , Purificação da Água/métodos , Anacardium/química , Boro/química , Eletrodos , Eletrólise/instrumentação , Indústria Alimentícia , Lactuca/efeitos dos fármacos , Nozes/química , Oxirredução , Fenóis/toxicidade , Compostos de Rutênio/química , Titânio/química , Poluentes Químicos da Água/toxicidade , Purificação da Água/instrumentaçãoRESUMO
In this study, the electrochemical degradation process of 5-fluorouracil (5-FU) in aqueous media was performed using a continuous flow reactor in an undivided cell (system I), and in a divided cell with a cationic membrane (Nafion® 424) (system II). In system I, 75% of 5-FU degradation was achieved (50â¯mgâ¯L-1) with a applied current density jappâ¯=â¯150 A m-2, volumetric flow rate qvâ¯=â¯13â¯Lâ¯h-1, after 6â¯h of electrolysis (kappâ¯=â¯0.004 min-1). The removal efficiency of 5-FU was higher (95%) when the concentration was 5â¯mgâ¯L-1 under the same conditions. Nitrates (22% of initial amount of N), fluorides (27%) and ammonium (10%) were quantified after 6â¯h of electrolysis. System II, 77% of 5-FU degradation was achieved (50â¯mgâ¯L-1) after 6â¯h of electrolysis (kappâ¯=â¯0.004 min-1). The degradation rate of 5-FU was complete when the concentration was 5â¯mgâ¯L-1 under the same conditions. Nitrates (29% of initial amount of N), fluorides (25%) and ammonium (5%) were quantified after 6â¯h of electrolysis. In addition, the main organic byproducts identified by mass spectroscopy were aliphatic compound with carbonyl and carboxyl functionalities. Due to, the mineralization of 5-FU with acceptable efficiency of 88% found in system II (japp of 200 A m-2), this system seems to be more promising in the cytostatic drug removal. Moreover the efficiency of 5-FU removal in diluted solutions is better in system II than in system I.
Assuntos
Boro/química , Diamante/química , Eletrólise/métodos , Fluoruracila/análise , Poluentes Químicos da Água/análise , Purificação da Água/métodos , Eletrodos , Eletrólise/instrumentação , Fluoruracila/química , Cinética , Oxirredução , Poluentes Químicos da Água/química , Purificação da Água/instrumentaçãoRESUMO
In this work we report on the hydrogen production capacity of single-chamber microbial electrohydrogenesis cell (MEC) with optimized design characteristics, in particular cathode surface area and anode-cathode spacing using acetate as substrate. The results showed that the maximal H2 production rates and best energetic performances could be obtained using the smallest, 71 cm2 stainless steel cathode and 4 cm electrode distances, employing a 60 cm2 bioanode. Cyclic voltammetric analysis was employed to investigate the dominant electron transfer mechanism of the architecturally optimized system.
Assuntos
Fontes de Energia Bioelétrica , Eletrólise/instrumentação , Hidrogênio/metabolismo , Acetatos/metabolismo , Eletrodos , Transporte de Elétrons , Aço InoxidávelRESUMO
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
The appearance of pharmaceutical compounds and their bioactive transformation products in aquatic environments is becoming an issue of increasing concern. In this study, the electrochemical oxidation of the widely used antibiotic sulfamethoxazole (SMX) was investigated using a commercial mixed oxide anode (Ti/Ru0.3Ti0.7O2) and a single compartment filter press-type flow reactor. The kinetics of SMX degradation was determined as a function of electrolyte composition, applied current density, and initial pH. Almost complete (98 %) degradation of SMX could be achieved within 30 min of electrolysis in 0.1 mol L(-1) NaCl solution at pH 3 with applied current densities ≥20 mA cm(-2). Nine major intermediates of the reaction were identified by LC-ESI-Q-TOF-MS (e.g., C6H9NO2S (m/z = 179), C6H4NOCl (m/z = 141), and C6H6O2 (m/z = 110)). The degradation followed various routes involving cleavage of the oxazole and benzene rings by hydroxyl and/or chlorine radicals, processes that could occur before or after rupture of the N-S bond, followed by oxidation of the remaining moieties. Analysis of the total organic carbon content revealed that the antibiotic was partially mineralized under the conditions employed and some inorganic ions, including NO3 (-) and SO4 (2-), could be identified. The results presented herein demonstrate the efficacy of the electrochemical process using a Ti/Ru0.3Ti0.7O2 anode for the remediation of wastewater containing the antibiotic SMX.
Assuntos
Antibacterianos/química , Eletrólise/instrumentação , Óxidos/química , Sulfametoxazol/química , Poluentes Químicos da Água/química , Eletrodos , Cinética , Oxirredução , Titânio/química , Águas Residuárias/químicaRESUMO
Iron electrodes were used for electrocoagulation (EC) treatment of wastewater from a dairy plant. Electrolysis time, pH, current density and distance between electrodes were considered to assess the removal efficiency of chemical oxygen demand (COD), total solids (TS) and their fractions and turbidity. Samples were collected from the effluent of a dairy plant using a sampling methodology proportional to the flow. The treatments were applied according to design factorial of half fraction with two levels of treatments and three repetitions at the central point. The optimization of parameters for treating dairy industry effluent by electrocoagulation using iron electrodes showed that electric current application for 15 minutes, an initial sample pH close to neutral (pH 7.0) and a current density of 50 A (.)(m-2) resulted in a significant reduction in COD by 58 %; removal of turbidity, suspended solids and volatile suspended solids by 95 %; and a final treated effluent pH of approximately 9.5. Negative consequences of the type of electrode used were the emergence of an undesirable color and an increase in the proportion of dissolved solids in the treated effluent.
Assuntos
Eletrólise/métodos , Esgotos/química , Purificação da Água/métodos , Criação de Animais Domésticos , Animais , Análise da Demanda Biológica de Oxigênio , Eletrodos , Eletrólise/instrumentação , Concentração de Íons de Hidrogênio , Ferro/química , Purificação da Água/instrumentaçãoRESUMO
The EU Directive 1999/77/EC, prohibiting new applications of chrysotile, exempted diaphragms used in electrolysis to produce chorine and caustic soda in existing chlor-alkali plants until they reach the end of their service life, or until suitable asbestos-free substitutes become available, whichever is sooner. There is no technical justification for extending this exemption after January 2008, when it is scheduled for review. Economic interests should not take precedence over the social and environmental costs imposed by the asbestos production required for this industry. The EU Scientific Committee on Toxicity, Ecotoxicity and the Environment should not further delay the necessary decision on a total and immediate worldwide ban of the mining, manufacturing, and all uses of asbestos.
Assuntos
Amianto/toxicidade , Indústria Química/normas , Eletrólise/instrumentação , Exposição Ocupacional/prevenção & controle , Exposição Ocupacional/normas , Brasil , Cloro , União Europeia , Humanos , Fatores de Risco , Hidróxido de SódioRESUMO
STATEMENT OF PROBLEM: Titanium has been suggested as a replacement for alloys currently used in single-tooth restorations and fixed partial dentures. However, difficulties in casting have resulted in incomplete margins and discrepancies in marginal fit. PURPOSE: This study evaluated and compared the marginal fit of crowns fabricated from a commercially pure titanium (CP Ti) and from Ti-6Al-4V alloy with crowns fabricated from a Pd-Ag alloy that served as a control. Evaluations were performed before and after marginal refinement by electrical discharge machining (EDM). MATERIAL AND METHODS: Forty-five bovine teeth were prepared to receive complete cast crowns. Stone and copper-plated dies were obtained from impressions. Fifteen crowns were cast with each alloy (CP Ti, Ti-6Al-4V, and Pd-Ag). Marginal fit measurements (in micrometers) were recorded at 4 reference points on each casting with a traveling microscope. Marginal refinement with EDM was conducted on the titanium-based crowns, and measurements were repeated. Data were analyzed with the Kruskal-Wallis test, paired t test, and independent t test at a 1% probability level. RESULTS: The Kruskal-Wallis test showed significant differences among mean values of marginal fit for the as-cast CP Ti crowns (mean [SD], 83.9 [26.1] microm) and the other groups: Ti-6Al-4V (50.8 [17.2] microm) and Pd-Ag (45.2 [10.4] microm). After EDM marginal refinement, significant differences were detected among the Ti-6Al-4V crowns (24.5 [10.9] microm) and the other 2 groups: CP Ti (50.6 [20.0] microm) and Pd-Ag (not modified by EDM). Paired t test results indicated that marginal refinement with EDM effectively improved the fit of CP Ti crowns (from 83.9 to 50.6 microm) and Ti-6Al-4V crowns (from 50.8 to 24.5 microm). However, the difference in improvement between the two groups was not significant by t test. CONCLUSION: Within the limitations of this study, despite the superior results for Ti-6Al-4V, both groups of titanium-based crowns had clinically acceptable marginal fits. After EDM marginal refinement, the fit of cast CP Ti and Ti-6Al-4V crowns improved significantly.