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[en] Recently, the electrochemical oxidation with boron doped diamond anodes (BDD) has become one of the most promising technologies for the treatment of industrial wastes and for the electro-synthesis of oxidants. Boron doped diamond anodes present high chemical and electrochemical stability, as well as great current efficiency for the mineralization of organic matter and for the production of oxidants. Among the spectra of oxidants that can be produced by BDD electrochemical oxidation, perchlorate outstands due to its potential applications. Thus, perchlorate salts are used in pyrotechnics, in manufacture of matches, munitions and in the chemical analytical industry. Furthermore, the production of drinking water by seawater reverses osmosis (SWRO) is becoming the key solution for high water-stressed countries. Nevertheless, the management of the brine produced as rejected stream is one of the challenges that remains unsolved nowadays. In this scenario, the main goal of this work is to present a possible solution for the valorization of the rejected stream of SWRO processes, consisting in using this stream as a raw material for the electrochemical production of high added value chlorine derivates by BDD electrochemical oxidation. In this work, solutions with NaCl concentration ranging from 1 M to 2 M (from 58.4 to 116.8 g L-1) were used as raw material for the production of perchlorates with commercial BDD electrochemical cells (from Adamant technologies). The effect of the key parameters, such as the current density or the initial NaCl concentration, in the rate and efficiency of perchlorate production was evaluated. The results show that it is possible to convert almost 100% of initial chloride to perchlorate regardless the initial concentration of sodium chloride. Moreover, it was observed that the current density play an important role on the efficiency of the production of the different chlorine oxoanions. Conversely, the results obtained do not depend on the initial concentration of NaCl, because the high concentration used avoids the appearance of mass transfer limitations. According to the results obtained, the electrochemical production of perchlorate by BDD electrochemical oxidation outstands as a promising novel technology for the valorization of the brine produced in SWRO processes.
[en] Electrochemical advanced oxidation processes (EAOPs) are envisaged as promising technologies to comply with an ever-increasing legal framework and the required environmental protection, especially when it comes to deal with hardly-biodegradable effluents.
[en] Hospital activities generate multiple quantities of effluents as function of numerous factors suchas number of beds, existent of general services, number and type of wards and blocks, number of inpatients and outpatients, etc (Oliveira et al., 2018).
[en] We present results from three Suzaku observations of the z = 3.91 gravitationally lensed broad absorption line quasar APM 08279+5255. We detect strong and broad absorption at rest-frame energies of ∼<2 keV (low energy) and 7-12 keV (high energy). The detection of these features confirms the results of previous long-exposure (80-90 ks) Chandra and XMM-Newton observations. The low- and high-energy absorption is detected in both the back-illuminated (BI) and front-illuminated (FI) Suzaku X-ray Imaging Spectrometer spectra (with an F-test significance of ∼>99%). We interpret the low-energy absorption as arising from a low-ionization absorber with log N H ∼ 23 and the high-energy absorption as due to lines arising from highly ionized (2.75 ∼< logξ ∼< 4.0, where ξ is the ionization parameter) iron in a near-relativistic outflowing wind. Assuming this interpretation we find that the velocities in the outflow range between 0.1c and 0.6c. We constrain the angle between the outflow direction of the X-ray absorber and our line of sight to be ∼<36 deg. We also detect likely variability of the absorption lines (at the ∼>99.9% and ∼>98% significance levels in the FI and BI spectra, respectively) with a rest-frame timescale of ∼1 month. Assuming that the detected high-energy absorption features arise from Fe XXV, we estimate that the fraction of the total bolometric energy injected over the quasar's lifetime into the intergalactic medium in the form of kinetic energy to be ∼>10%.
[en] We analyze the long-term (rest-frame 3-30 yr) X-ray variability of 11 broad absorption line (BAL) quasars, mainly to constrain the variation properties of the X-ray absorbing shielding gas that is thought to play a critical role in BAL wind launching. Our BAL quasar sample has coverage with multiple X-ray observatories including Chandra, XMM-Newton, BeppoSAX, ASCA, ROSAT, and Einstein; 3-11 observations are available for each source. For seven of the eleven sources we have obtained and analyzed new Chandra observations suitable for searching for any strong X-ray variability. We find highly significant X-ray variability in three sources (PG 1001+054, PG 1004+130, and PG 2112+059). The maximum observed amplitude of the 2-8 keV variability is a factor of 3.8 ± 1.3, 1.5 ± 0.2, and 9.9 ± 2.3 for PG 1001+054, PG 1004+130, and PG 2112+059, respectively, and these sources show detectable variability on rest-frame timescales down to 5.8, 1.4, and 0.5 yr. For PG 1004+130 and PG 2112+059 we also find significant X-ray spectral variability associated with the flux variability. Considering our sample as a whole, we do not find that BAL quasars exhibit exceptional long-term X-ray variability when compared to the quasar population in general. We do not find evidence for common strong changes in the shielding gas owing to physical rearrangement or accretion-disk rotation, although some changes are found; this has implications for modeling observed ultraviolet BAL variability. Finally, we report for the first time an X-ray detection of the highly polarized and well-studied BAL quasar IRAS 14026+4341 in its new Chandra observation.
[en] Highlights: • Numerical model for electrokinetic remediation of polluted soil with 2,4-D is shown. • Periodic polarity reversal processes has been included in the module M4EKR. • Improvements of the application of polarity reversal strategy has been studied. • Periodic polarity reversal at 6 h enhances the yield of EKR a 94.5%. - Abstract: This article presents a numerical study of the transport phenomena involved in the electrokinetic remediation of soils polluted with polar pesticides. 2,4-Dichlorophenoxyacetic acid is used as a representative of this pesticide type. A one-dimensional configuration with two facing electrodes placed in electrolyte compartments and a cathodic overflow pollutant extraction system has been used for that purpose. The conventional electrokinetic remediation process is evaluated by keeping the electrode polarity constant, and to obtain acceptable yields, it is necessary to extend the treatment for more than 250 days. The application of periodic polarity reversals is proposed to improve these results. This strategy maximises the pesticide concentration in the cathodic compartment, thus maximising the pollutant extraction rate. The results show that by applying polarity reversals over 6-h periods, it is possible to accelerate the treatment, thus improving its overall efficiency up to 94.5% compared with the treatment using a constant electrode polarity.
[en] We present results from multi-epoch spectral analysis of XMM-Newton and Chandra observations of the broad absorption line (BAL) quasar APM 08279+5255. Our analysis shows significant X-ray BALs in all epochs with rest-frame energies lying in the range of ∼6.7-18 keV. The X-ray BALs and 0.2-10 keV continuum show significant variability on timescales as short as 3.3 days (proper time) implying a source size-scale of ∼10 rg, where rg is the gravitational radius. We find a large gradient in the outflow velocity of the X-ray absorbers with projected outflow velocities of up to 0.76c. The maximum outflow velocity constrains the angle between the wind velocity and our line of sight to be less than ∼22 deg. Based on our spectral analysis, we identify the following components of the outflow: (1) highly ionized X-ray absorbing material with an ionization parameter in the range of 2.9 ∼< log ξ ∼< 3.9 (the units of ξ are erg cm s-1) and a column density of log N H ∼ 23 (the units of N H are cm-2) outflowing at velocities of up to 0.76c; and (2) low-ionization X-ray absorbing gas with log NH ∼ 22.8. We find a possible trend between the X-ray photon index and the maximum outflow velocity of the ionized absorber in the sense that flatter spectra appear to result in lower outflow velocities. Based on our spectral analysis of observations of APM 08279+5255 over a period of 1.2 yr (proper time), we estimate the mass-outflow rate and efficiency of the outflow to have varied between 16+12-8 Msun yr-1 to 64+66-40 Msun yr-1 and 0.18+0.15-0.11 to 1.7+1.9-1.2, respectively. Assuming that the outflow properties of APM 08279+5255 are a common property of most quasars at similar redshifts, our results then imply that quasar winds are massive and energetic enough to significantly influence the formation of the host galaxy, provide significant metal enrichment to the interstellar medium and intergalactic medium, and are a viable mechanism for feedback at redshifts near the peak in the number density of galaxy mergers.
[en] The electrochemical oxidation of 2,4-dinitrophenol (2,4-DNP) aqueous wastes has been studied using both, bulk electrolysis and voltammetric techniques. To carry out the bulk electrolysis, a bench-scale plant with a single compartment electrochemical flow cell was used. Boron-doped diamond (BDD) materials were used as the anode and stainless steel (AISI 304) as the cathode. According to the obtained results, a simple mechanistic model has been proposed. The oxidation of 2,4-DNP leads to the appearance of phenol and quinonic compounds and to the release of the nitro groups from the aromatic ring, in a first step. In a second step, these organics are transformed into carboxylic acids (mainly maleic and oxalic acid). The process ends with the formation of carbon dioxide (CO2). The effects of the waste characteristics (composition and pH) and of the operation parameters of the process (temperature and current density) have also been studied in this work. The complete removal of the organic compounds contained in the waste has been obtained in all essays
[en] We report spectral, imaging, and variability results from four new XMM-Newton observations and two new Chandra observations of high-redshift (z ∼> 4) radio-loud quasars (RLQs). Our targets span lower, and more representative, values of radio loudness than those of past samples of high-redshift RLQs studied in the X-ray regime. Our spectral analyses show power-law X-ray continua with a mean photon index, (Γ) = 1.74 ± 0.11, that is consistent with measurements of lower redshift RLQs. These continua are likely dominated by jet-linked X-ray emission, and they follow the expected anticorrelation between photon index and radio loudness. We find no evidence of iron Kα emission lines or Compton-reflection continua. Our data also constrain intrinsic X-ray absorption in these RLQs. We find evidence for significant absorption (NH ∼ 1.7 x 1022cm-2) in one RLQ of our sample (SDSS J0011+1446); the incidence of X-ray absorption in our sample appears plausibly consistent with that for high-redshift RLQs that have higher values of radio loudness. In the Chandra observation of PMN J2219-2719 we detect apparent extended (∼14 kpc) X-ray emission that is most likely due to a jet; the X-ray luminosity of this putative jet is ∼2% that of the core. The analysis of a 4.9 GHz Very Large Array image of PMN J2219-2719 reveals a structure that matches the X-ray extension found in this source. We also find evidence for long-term (450-460 days) X-ray variability by 80%-100% in two of our targets.
[en] The effluents of ink-manufacturing processes contain a large variety of pollutants such as dyes, surfactants, biocides, water soluble solvents, etc. In this work, the electrochemical oxidation of several dyes (methylene blue and rhodamine B), solvents (monoethylene glycol, diethylene glycol and glycerol) and surfactants (sodium dodecylbenzenesulfonate) has been studied. To carry out the electrolyses, a bench-scale plant with a single-compartment electrochemical flow-cell was used. Boron doped diamond (BDD) was used as anode and stainless steel (AISI 304) as cathode. For all the compounds tested, the conductive diamond electrooxidation allows achieving the almost complete removal of COD of the waste with a very high current efficiency. The efficiencies of the electrochemical processes seem to depend on the current density and on the nature of the anions contained in the waste (chlorine, sulphate, phosphate). Thus, it has been observed that the use of chloride media favours the treatment of dyes. On the contrary, the use of sulphate- or phosphate-containing solutions improves the removal of the aliphatic compounds studied (solvents). These results suggest an important role of the mediated electrochemical processes on the overall performance of the reaction system