A. Lopes

Electrochemical degradation of aromatic amines on BDD electrodes

The electrochemical oxidation of four aromatic amines, with different substituent groups, 3-amino-4-hydroxy-5-nitrobenzenesulfonic acid (A1), 5-amino-2-methoxybenzenesulfonic acid (A2), 2,4-dihydroxyaniline hydrochloride (A3) and benzene-1,4-diamine (A4), was performed using as anode a boron-doped diamond electrode, commercially available at Adamant Technologies. Tests were run at room temperature with model solutions of the different amines, with concentrations of 200 ppm, using as electrolyte 0.035 M Na(2)SO(4) aqueous solutions, in a batch cell with recirculation, at different current densities (200 and 300 A m(-2)). The following analyses were performed with the samples collected during the assays: UV-Vis spectrophotometry, chemical oxygen demand (COD), total organic carbon (TOC), total Kjeldahl nitrogen, ammonia nitrogen, nitrates and HPLC. Results have shown a good electrodegradation of all the amines tested, with COD removals, after 6 h assays, higher than 90% and TOC removals between 60 and 80%. Combustion efficiency (η(C)), which measures the tendency to convert organic carbon to CO(2), was also determined for all the amines, being η(CA1)

Electrochemical degradation of sulfonated amines on SI/BDD electrodes.

The electrochemical oxidation of aniline (AN) and ortanilic (OA), metanilic (MA) and sulfanilic (SA) acids was performed using as anode a boron-doped diamond (BDD) electrode. Tests were performed with model solutions of the different amines, with concentrations of 200mg L(-1), using as electrolyte 0.035 M Na2SO4, in a batch cell, with re-circulation, at different current densities (200 and 300 A m(-2)). Samples were collected at pre-selected intervals and absorbance measurements, Chemical Oxygen Demand (COD), Total Organic Carbon (TOC), Total Kjeldahl Nitrogen, Ammonia Nitrogen, Nitrates and Nitrites and HPLC analysis were performed. Results have shown a good elimination of the persistent pollutant, with COD and TOC removals always higher than, respectively: AN--91% and 90%; OA--75% and 82%; MA--88% and 87%; and SA--85% and 79%. The combustion efficiencies, calculated for the first hour of the runs, for the 300 A m(-2) assays, were the following: AN--0.93; OA--0.28; MA--0.82; and SA--0.83. For all the amines studied, after 6h degradation only oxalic and maleic acids were identified by HPLC.

Anodic oxidation of a biologically treated leachate on a boron-doped diamond anode

In the present study, the anodic oxidation of a leachate from an intermunicipal sanitary landfill was evaluated using a boron-doped diamond anode as a possible post-treatment to the biological one, in order to diminish the remaining bio-refractory organic matter. The influence of the dilution of the leachate sample and the applied current density on the performance of electrochemical oxidation was investigated. For the different assays performed, a comparison between the theoretical kinetic model for organic mineralization, proposed in the literature, and experimental data was done and the best correspondences were attained at lower applied current density for sample without dilution and at higher applied current density for the more diluted sample. However, the energetic most favourable treatment is attained for sample without dilution at very low current density. The DOC/COD ratio was also analysed and apparently, the mineralization of the organic matter improves with the dilution of the leachate samples.

ACTIVITY COEFFICIENTS OF SODIUM CHLORIDE IN WATER – ETHANOL MIXTURES: A COMPARATIVE STUDY OF PITZER AND PITZER – SIMONSON MODELS

Activity coefficients of NaCl were determined in water–ethanol solvents, in the range 5–20% (w/w) ethanol, from emf data. The molalities varied from 0.1 mol-kg−1 to near saturation and measurements were taken in the temperature range 25–50°C. The Pitzer model was used to describe the nonideal behavior of the electrolyte and the corresponding coefficients were determined for each solvent. The Pitzer–Simonson equations were also applied and a detailed study, involving the short- and long-range forces, was done in order to better understand the different results obtained with both models.

Effect of alpha-tocopherol on superoxide radical and toxicity of cadmium exposure

Contamination with cadmium compounds poses high potential risk for the health of populations and for this reason the treatment of their toxic effects should urgently be established. The present study was carried out to determine whether alpha-tocopherol intake can protect tissues against damage induced by cadmium, and to clarify the contribution of superoxide radicals (O 2 - ) in this process. Cadmium chloride was tested for tissue damage by a single intraperitoneal injection of Cd 2+ ions (2 mg Kg -1 ). To determine the potential therapeutic effect of vitamin E, a group of Cd 2+ -treated rats received a drinking solution of alpha-tocopherol (40 mg l -1 ) for 15 days. Cadmium induced increased serum creatinine and total lactate dehydrogenase, reflecting renal and cardiac damage. The increased lipoperoxide and decreased Cu-Zn superoxide dismutase levels indicated the generation of superoxide radicals in cadmium-treated rats. Tocopherol induced increased serum high-density lipoprotein and depressed the toxic effects of Ca 2+ alone, since creatinine and lactate dehydrogenase determinations were recovered to the control values. Tocopherol decreased lipoperoxide and led the superoxide dismutase activities to approach those of the control values. We concluded that superoxide radicals are produced as mediators of cadmium toxicity. Tocopherol possesses a significant anti-radical activity and inhibits the cadmium effect on superoxide dismutase activity. Tocopherol also protected tissues from the toxic effects of cadmium by a direct antioxidant action which decreased lipoperoxide formation.

Activity Coefficients of Potassium Chloride in Water–Ethanol Mixtures

Activity coefficients of KCl were determined in water–ethanol solvents in the range 5–20% (w/w) ethanol, from experimental electromotive force (emf) data. The molalities varied from 0.1 mol-kg−1 to near saturation and measurements were taken in the temperature range 25 to 45°C. The Pitzer model was used to describe the nonideal behavior of the electrolyte and the corresponding coefficients were determined for each solvent. The Pitzer–Simonson equations were also applied and found superior in the study of KCl in those nonaqueous solutions.

Electrochemical oxidation of humic acid and sanitary landfill leachate: Influence of anode material, chloride concentration and current density

The influence of applied current density and chloride ion concentration on the ability of Ti/Pt/PbO2 and Ti/Pt/SnO2-Sb2O4 anodes for the electrochemical oxidation of humic acid and sanitary landfill leachate samples was assessed and compared with that of BDD anode. For the experimental conditions used, results show that both organic load and nitrogen removal rates increase with the applied current density and chloride ion concentration, although there is an optimum COD/[Cl-]0 ratio below which there is no further increase in COD removal. Metal oxide anodes present a similar performance to that of BDD, being the results obtained for Ti/Pt/PbO2 slightly better than for Ti/Pt/SnO2-Sb2O4. Contrary to BDD, Ti/Pt/PbO2 promotes lower nitrate formation and is the most suitable material for total nitrogen elimination. The importance of the optimum ratio of Cl-/COD/NH4 +initial concentrations is discussed.

Electrochemical treatment of concentrate from reverse osmosis of sanitary landfill leachate.

Conventional sanitary landfill leachate treatment has recently been complemented and, in some cases, completely replaced by reverse osmosis technology. Despite the good quality of treated water, the efficiency of the process is low and a large volume of reverse osmosis concentrate has to be either discharged or further treated. In this study, the use of anodic oxidation combined with electro-Fenton processes to treat the concentrate obtained in the reverse osmosis of sanitary landfill leachate was evaluated. The anodic oxidation pretreatment was performed in a pilot plant using an electrochemical cell with boron-doped diamond electrodes. In the electro-Fenton experiments, a boron-doped diamond anode and carbon-felt cathode were used, and the influence of the initial pH and iron concentration were studied. For the experimental conditions, the electro-Fenton assays performed at an initial pH of 3 had higher organic load removal levels, whereas the best nitrogen removal was attained when the electrochemical process was performed at the natural pH of 8.8. The increase in the iron concentration had an adverse impact on treatment under natural pH conditions, but it enhanced the nitrogen removal in the electro-Fenton assays performed at an initial pH of 3. The combined anodic oxidation and electro-Fenton process is useful for treating the reverse osmosis concentrate because it is effective at removing the organic load and nitrogen-containing species. Additionally, this process potentiates the increase in the biodegradability index of the treated effluent.

Activity Coefficients of Potassium Chloride and Sodium Chloride in the Quaternary System KCl-NaCl-Water-Ethanol

Activity coefficients of KCl and NaCl were determined in the quaternary system KCl-NaCl-water-ethanol, for 10 and 20% (w/w) ethanol in the solvent, from experimental electromotive force data. The molalities varied from 0.1 mol kg−1 to near saturation and measurements were taken in the temperature range 20 to 50°C. The Pitzer-Simonson equations were used to describe the nonideal behavior of both electrolytes and the corresponding activity coefficients were determined for each solvent and temperature.

Superoxide radical and nephrotoxic effect of cadmium exposure

Pollution and industrial practices result in concentrations of metals and other environmental agents that are related to environmental toxicity. Concentrations of metals are widely related to biochemicals values which are used in disease diagnosis due to environmental toxicity. This work was carried out in order to verify the nephrotoxic effect of cadmium and to clarify the contribution of reactive oxygen species (ROS) in this process. Cadmium chloride was tested for nephrotoxic damage in rats by a single intraperitoneal (i.p.) injection Cd2+ (2 mg/kg) and oral intake (Cd2+ -100mg/l-from CdCl2). The cadmium-induced biochemical alterations included significant increased levels of serum creatinine concentrations, in rats with i.p. injection. Total urinary protein concentrations were only increased in rats with cadmium intake. Lipoperoxide was also increased after 3 and 7 days of the Cd2+ treatment. No changes were observed in glutathione peroxidase activities. Cadmium-induced damage might be due to superoxi...