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[en] Nowadays, the reclamation of urban treated wastewater is attracting great interest due to the potential applications of these effluents in agriculture or industry sectors. In the treatment of this type of effluents, the removal of microorganisms (E. coli) and turbidity is always required to obtain a high-quality effluent. In literature, it has been described the disinfection stage by the addition of chemical reagents (chlorine, ozone, hydrogen peroxide…) and the removal of turbidity by chemical coagulation. In this context, electrochemical technologies emerge as a good alternative to carry out the on-site generation of disinfectant and coagulant agents from the species naturally contained in wastewater (electrodisinfection) and the dissolution of a sacrificial anode made of iron or aluminium (electrocoagulation). With this background, this lecture aims to describe the results obtained in the reclamation of actual effluents from municipal WWTP using a novel integrated electrochemical process: electrodisinfection-electrocoagulation (ED-EC). This combined technology allows to simultaneously decrease the turbidity and the Microbiological content present in these effluents. Likewise, the scaling up of this process has been carried out to check if the electrochemical technology is suitable for the reclamation of large volumes of urban treated wastewater. To do this, boron doped diamond (BDD) was used as anode, stainless steel as cathode and a perforated iron bipolar plate was placed between both electrodes to favor the production of coagulant agents in the electrochemical cell. The anode and bipolar electrode area was increased three and fifteen times, respectively, to check the scaling up of the technology. Results show that it is possible to completely removed the E. coli and turbidity present in the effluents during the ED-EC process using low current densities (< 10 A m-2) and applied electric charges (< 0.1 Ah dm-3) even at large scale. Electrogenerated free and combined chlorine species are the main responsible for disinfection whereas the generation of coagulant species from the electrodissolution of the anodic face of the iron bipolar electrode decrease the turbidity. These soft operation conditions lead to a low energy consumption and, therefore, this novel integrated electrochemical process could economically be a competitive technology for the reclamation of urban treated wastewater.
[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] Extreme-Mass-Ratio Inspirals (EMRIs) are one of the most promising sources of gravitational waves (GWs) for space-based detectors like the Laser Interferometer Space Antenna (LISA). EMRIs consist of a compact stellar object orbiting around a massive black hole (MBH). Since EMRI signals are expected to be long lasting (containing of the order of hundred thousand cycles), they will encode the structure of the MBH gravitational potential in a precise way such that features depending on the theory of gravity governing the system may be distinguished. That is, EMRI signals may be used to test gravity and the geometry of black holes. However, the development of a practical methodology for computing the generation and propagation of GWs from EMRIs in theories of gravity different than General Relativity (GR) has only recently begun. In this paper, we present a parameter estimation study of EMRIs in a particular modification of GR, which is described by a four-dimensional Chern-Simons (CS) gravitational term. We focus on determining to what extent a space-based GW observatory like LISA could distinguish between GR and CS gravity through the detection of GWs from EMRIs.
[en] Extreme mass ratio inspirals (EMRIs) occur when a compact object orbits a much larger one, like a solar-mass black hole around a supermassive black hole. The orbit has 3 frequencies which evolve through the inspiral. If the orbital radial frequency and polar frequency become commensurate, the system passes through a transient resonance . Evolving through resonance causes a jump in the evolution of the orbital parameters. We study these jumps and their impact on EMRI gravitational-wave detection. Jumps are smaller for lower eccentricity orbits; since most EMRIs have small eccentricities when passing through resonances, we expect that the impact on detection will be small. Neglecting the effects of transient resonances leads to a loss of ∼ 4% of detectable signals for an astrophysically motivated population of EMRIs. (paper)
[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] 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] Highlights: • The efficiency of the electrolysis of 2,4-D depends on the sp3/sp2 ratio of the diamond anode. • A higher sp3/sp2 ratio lowers the energy required to mineralize the pesticide. • The sp3/sp2 ratio influences the concentration but not the type of intermediates produced. • Chlorate and perchlorate production is favored at higher sp3/sp2 ratios. - Abstract: Boron-doped diamond films on silicon substrates (p-Si BDD) with different sp3/sp2 carbon ratios are systematically varied in electrodes used to oxidize 2,4-dichlorophenoxyacetic acid (2,4-D) in synthetic wastewater containing chlorides. 2,4-D is completely mineralized during the electrolysis. A higher sp3/sp2 ratio in the anode results in a more rapid and efficient oxidative removal of 2,4-D. Chlorinated compounds such as 4-chlororesorcinol, 2-chlorophenol, and 2,4-dichlorophenol form as intermediates during the oxidative treatment. Although these compounds are completely depleted during the electrolysis, their maximum observed concentrations decrease as the sp3 content increases in the anode. On the contrary, higher maximum concentrations are observed for non-chlorinated intermediates, especially hydroquinone, and there is a greater formation of chlorates and perchlorates in chloride-containing solutions as the sp3 content increases in the anode.