We investigated arsenic removal from groundwater by electrocoagulation (EC) using aluminum as the sacrificial anode in a pre-pilot-scale continuous filter press reactor. The groundwater was collected ...at a depth of 320m in the Bajío region in central Mexico (arsenic 50μgL–1, carbonates 40mgL–1, hardness 80mgL–1, pH 7.5 and conductivity 150μScm–1). The influence of current density, mean linear flow and hypochlorite addition on the As removal efficiency was analyzed. Poor removal of total arsenic (<60%) in the absence of hypochlorite is due to a mixture of arsenite (HAsO2(aq) and H3AsO3(aq)) and arsenate (HAsO42−). Arsenic removal is more efficient when arsenite is oxidized to arsenate by addition of hypochlorite at a concentration typically used for disinfection (1mgL–1). Arsenate removal by EC might involve adsorption on aluminum hydroxides generated in the process. Complete arsenate removal by EC was satisfactory at a current density of 5mAcm–2 and mean linear flow of 0.91cms–1, with electrolytic energy consumption of 3.9kWhm3.
•Arsenic removal from groundwater by electrocoagulation.•Aluminum as sacrificial anodes.•Electrolyzes at different flow rates and current densities.•Electrocoagulation led to 100% arsenic removal (50μgL−1) with 3.9kWhm−3.•The influence of hypochlorite on arsenic removal efficiency was analyzed.
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•Enhanced electro-assisted adsorption of As(V) onto activated packed carbon anode.•Significant influence of the surface chemistry on the electrochemical parameters.•The textural ...properties of the adsorbents were not modified significantly.•The electrical stimulus could be used as control of the amount of surface charge.•The electrode with better performance was the thermally reduced activated carbon.
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.
Schwann cell (SC) transplantation represents a promising therapeutic approach for traumatic spinal cord injury but is frustrated by barrier formation, preventing cell migration, and axonal ...regeneration at the interface between grafted SCs and reactive resident astrocytes (ACs). Although regenerating axons successfully extend into SC grafts, only a few cross the SC–AC interface to re-enter lesioned neuropil. To date, research has focused on identifying and modifying the molecular mechanisms underlying such scarring cell–cell interactions, while the influence of substrate topography remains largely unexplored. Using a recently modified cell confrontation assay to model SC–AC barrier formation in vitro, highly oriented poly(ε-caprolactone) nanofibers were observed to reduce AC reactivity, induce extensive oriented intermingling between SCs and ACs, and ultimately enable substantial neurite outgrowth from the SC compartment into the AC territory. It is anticipated that these findings will have important implications for the future design of biomaterial-based scaffolds for nervous tissue repair.
This paper deals with hydrodynamics simulations in an up-flow pre-pilot electrochemical reactor with a stack containing eight cells in a serpentine array. Each cell contains horizontal parallel ...aluminum plate electrodes, open to the atmosphere at the top of the cell. The single-phase flow was simulated solving the Reynolds-Averaged Navier-Stokes (RANS) equations with k-ε turbulence model via finite element method. The residence time distribution (RTD) simulations were obtained solving the averaged diffusion-convection equation. The influence of mean linear flow velocity, 2.4 ≤ U ≤ 12.1 cm s−1, on the velocity profiles evidenced the presence of jet flow in the first channel of the stack, which is located close to the electrolyte inlet at the bottom of the reactor. Then, the flow pattern became homogeneous in the second and third channels, while the quasi-plug flow profile was developed from the fourth channel to the exit. Streamlines graphs showed that in channel 1 there was very little recirculation of the fluid elements; however, this phenomenon disappears in the subsequent channels. The RTD curves shows the absence of low velocity zones in the reactor, because the electrolyte outlet is open to the atmosphere. The experimental RTD curves showed excellent agreement with simulations.
•Simulation of hydrodynamics in a stack of eight cells in a serpentine array.•Horizontal parallel aluminum plate electrodes open to the atmosphere at the top.•The electrolyte velocity was different in each channel due to local turbulence.•The fluid behavior tends towards a plug flow pattern.•Close agreement between simulations and experimental data (95–98%) was obtained.
We present time-resolved spectral analysis of prompt emission from GRB 160625B, one of the brightest bursts ever detected by Fermi in its nine years of operations. Standard empirical functions fail ...to provide an acceptable fit to the GBM spectral data, which instead require the addition of a low-energy break to the fitting function. We introduce a new fitting function, called 2SBPL, consisting of three smoothly connected power laws. Fitting this model to the data, the goodness of the fits significantly improves and the spectral parameters are well constrained. We also test a spectral model that combines non-thermal and thermal (black body) components, but find that the 2SBPL model is systematically favoured. The spectral evolution shows that the spectral break is located around Ebreak ~100 keV, while the usual νFν peak energy feature Epeak evolves in the 0.5–6 MeV energy range. The slopes below and above Ebreak are consistent with the values –0.67 and –1.5, respectively, expected from synchrotron emission produced by a relativistic electron population with a low-energy cut-off. If Ebreak is interpreted as the synchrotron cooling frequency, the implied magnetic field in the emitting region is ~10 Gauss, i.e. orders of magnitudes smaller than the value expected for a dissipation region located at ~1013−14 cm from the central engine. The low ratio between Epeak and Ebreak implies that the radiative cooling is incomplete, contrary to what is expected in strongly magnetized and compact emitting regions.
This paper deals with the elimination of hydrated silica, arsenic, and phosphates from real groundwater collected in central Mexico (arsenic 22 μg L−1, hydrated silica 161 mg L−1, sulfate 50 mg L−1, ...phosphate 0.41 mg L−1, pH 7.6 and conductivity 508 μS cm−1) by electrocoagulation (EC), using a cascade-shaped up-flow reactor with a six-cell stack open to the atmosphere at the top. Aluminum plates were used as electrodes. The influence of both current density (4 ≤ j ≤ 10 mA cm−2) and mean linear flow rates (1.2 ≤ u ≤ 4.8 cm s−1) in the EC reactor on the removal efficiency of hydrated silica, arsenic, and phosphates were examined. The best removal of arsenic after EC (reaching a residual concentration, CAs = 1.5 μg L−1) was obtained at j = 10 mA cm−2 and u = 1.2 cm s−1, meeting the World Health Organization (WHO) recommendation (<10 μg L−1), while the residual concentrations of hydrated silica, phosphates and sulfates were Chs = 42 mg L−1, CPO43− = 0.03 mg L−1 and CSO42− = 35 mg L−1, respectively. The experimental conditions at j = 10 mA cm−2 and u = 1.2 cm s−1, produced a large amount of coagulant (85.4 mg L−1), so this condition was repeated in a second round of the EC process to further reduce the concentration of hydrated silica. This time, Chs = 2.6 mg L−1 and CSO42− = 30 mg L−1 were obtained with the complete abatement of arsenic and phosphates. The total cost of the EC was 1.093 USD m−3, which included the electrolytic energy consumption, the price of aluminum, the costs of pumping and confinement of sludge, emphasizing that the calculation was based on Mexican costs. SEM-EDS, XRD, XRF and FTIR analyses on flocs revealed that the coagulant reacted with silica forming aluminum silicates, while arsenic and phosphates were removed by adsorption on flocs. The partial removal of sulfates (40%) is associated with weak adsorption on aggregates.
•Elimination of hydrated silica, arsenic, phosphate and sulfate from groundwater.•Cascade-shaped up-flow electrocoagulation (EC) reactor with aluminum electrodes.•High coagulant doses are formed at current densities of 10 mA cm−2.•Silica reacts with coagulant to form aluminosilicates and silicates as flocs.•WHO guideline for As was satisfied after EC.
We study the problem of the escape and transport of cosmic rays (CRs) from a source embedded in a fully ionized, hot phase of the interstellar medium (HIM). In particular, we model the CR escape and ...their propagation in the source vicinity taking into account excitation of Alfv´enic turbulence by CR streaming and mechanisms damping the self-excited turbulence itself. Our estimates of escape radii and times result in large values (100 pc, 2 × 105 yr) for particle energies ≲ 20 GeV and smaller values for particles with increasing energies (35 pc and 14 kyr at 1 TeV). These escape times and radii, when used as initial conditions for the CR propagation outside the source, result in relevant suppression of the diffusion coefficient (by a factor 5–10) on time-scales comparable with their (energy dependent) escape time-scale. The damping mechanisms are fast enough that even on shorter time-scales, the Alfv´enic turbulence is efficiently damped, and the ratio between random and ordered component of the magnetic field is δB/B0 ≪ 1, justifying the use of quasi-linear theory. In spite of the suppressed diffusion coefficient, and then the increased residence time in the vicinity (≤200 pc) of their source, the grammage accumulated by CRs after their escape is found to be negligible (at all energies) as compared to the one accumulated while diffusing in the whole Galaxy, due to the low density of the HIM.
•Electrocoagulation (EC) and active chlorine-based photoelectro-Fenton-like (PEF-like).•Acid blue 29 (AB 29) dyestuff removal on iron flocs (76–58%) by EC.•Residual AB 29 after EC was mineralized ...(100%) by •OH generated in PEF-like.•AB 29 dyestuff solutions of 150–300 mg L−1 COD having 2000 mg L−1 chlorides.
This paper deals with the development of an innovative process combining electrocoagulation (EC) and active chlorine-based photoelectro-Fenton-like (PEF-like) methods for eliminating the Acid Blue 29 (AB 29) dye from synthetic water (initially having 150–300 mg L−1 COD, in 2000 mg L−1 NaCl at pH 7.3). The EC process was performed in a continuous EC reactor equipped with 1018 steel plates as sacrificial electrodes. The PEF-like electrolysis was carried out in a filter-press electrochemical reactor equipped with Ti|Ir-Sn-Sb oxides and stainless-steel plates as the anode and cathode, respectively. The hydrodynamics influence in terms of the mean linear flow rate (0.69 ≤ u ≤ 3.47 cm s−1) and current density (12 ≤ j ≤ 36 mA cm−2) in the continuous EC reactor was systematically examined. The best EC trial was achieved at j = 36 mA cm−2 and u = 0.69 cm s−1 reaching 62 % bleaching and 84 % COD removal. Then, the remaining solution after EC passed through the PEF-like process (adjusting the pH = 3 and the catalyst at 0.4 mM Fe2+), reaching complete discoloration and COD removal at 15 mA cm−2, 24.2 cm s−1. Hydroxyl radicals were responsible for the mineralization of the AB 29 dye in the PEF-like process. The obtained flocs after EC were analyzed by XRD, XRF, and FTIR to elucidate the removal pathway of the AB 29 dye on flocs. Finally, the carboxylic and inorganic byproducts produced during the incineration of AB 29 dye by PEF-like were followed by HPLC techniques.
Computational fluid dynamics (CFD) simulations were carried out for single-phase flow in a rotating cylinder electrode reactor (RCE) in a continuous operation mode. Velocity profiles and streamlines ...were obtained solving the Reynolds-averaged Navier-Stokes (RANS) equations with the k−ε turbulence model. Residence time distribution (RTD) was obtained solving the averaged diffusion-convection equation. Two configurations of RCE, varying the position of the electrolyte flow inlet and flow exit, were tested. Good agreement of simulations with experimental RTD was obtained. A constant rotational speed of 300rpm (peripheral velocity of 59.7cms−1, Re=22682) at the RCE surface was employed. Velocity profiles, streamlines, and RTD are obtained at different volumetric flow rates ranging from 0.1 to 0.8Lmin−1. The flow behavior shows the presence of recirculation zones, being less important for the configuration where the electrolyte inlet is situated at the bottom of the reactor, and the electrolyte outlet is set at the top of the reactor wall surface. The extent of recirculation zones increases with increasing flow rate.
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•Computational fluid dynamic simulations in a filter-press stack of three cells.•The fluid velocity was different in each cell due to local turbulence.•The upper cell link pipe of the ...filter press cell acts as a fluid mixer.•The fluid behaviour tends towards a continuous mixing flow pattern.•Close agreement between simulations and experimental data was achieved.
Computational fluid dynamics (CFD) simulations were carried out for single-phase flow in a pre-pilot filter press flow reactor with a stack of three cells. Velocity profiles and streamlines were obtained by solving the Reynolds-Averaged Navier-Stokes (RANS) equations with a standard k−ε turbulence model. The flow behaviour shows the appearance of jet flow at the entrance to each cell. At lengths from 12 to 15cm along the cells channels, a plug flow pattern is developed at all mean linear flow rates studied here, 1.2≤u≤2.1cms−1. The magnitude of the velocity profiles in each cell was different, due to the turbulence generated by the change of flow direction in the last fluid manifold. Residence time distribution (RTD) simulations indicated that the fluid behaviour tends towards a continuous mixing flow pattern, owing to flow at the output of each cell across the upper cell link pipe, which acts as a mixer. Close agreement between simulations and experimental RTD was obtained.
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