The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

Pablo Canizares - One of the best experts on this subject based on the ideXlab platform.

  • effect of the Polarity Reversal frequency in the electrokinetic biological remediation of oxyfluorfen polluted soil
    Chemosphere, 2017
    Co-Authors: Silvia Barba, J Villasenor, Manuel A Rodrigo, Pablo Canizares
    Abstract:

    Abstract This work studies the feasibility of the periodic Polarity Reversal strategy (PRS) in a combined electrokinetic-biological process for the remediation of clayey soil polluted with a herbicide. Five two-weeks duration electrobioremediation batch experiments were performed in a bench scale set-up using spiked clay soil polluted with oxyfluorfen (20 mg kg−1) under potentiostatic conditions applying an electric field between the electrodes of 1.0 V cm−1 (20.0 V) and using PRS with five frequencies (f) ranging from 0 to 6 d−1. Additionally, two complementary reference tests were done: single bioremediation and single electrokinetic. The microbial consortium used was obtained from an oil refinery wastewater treatment plant and acclimated to oxyfluorfen degradation. Main soil conditions (temperature, pH, moisture and conductivity) were correctly controlled using PRS. On the contrary, the electroosmotic flow clearly decreased as f increased. The uniform soil microbial distribution at the end of the experiments indicated that the microbial activity remained in every parts of the soil after two weeks when applying PRS. Despite the adapted microbial culture was capable of degrade 100% of oxyfluorfen in water, the remediation efficiency in soil in a reference test, without the application of electric current, was negligible. However, under the low voltage gradients and Polarity Reversal, removal efficiencies between 5% and 15% were obtained, and it suggested that oxyfluorfen had difficulties to interact with the microbial culture or nutrients and that PRS promoted transport of species, which caused a positive influence on remediation. An optimal f value was observed between 2 and 3 d−1.

  • electrokinetic remediation of soil polluted with insoluble organics using biological permeable reactive barriers effect of periodic Polarity Reversal and voltage gradient
    Chemical Engineering Journal, 2016
    Co-Authors: Esperanza Mena, J Villasenor, Manuel A Rodrigo, Pablo Canizares
    Abstract:

    Abstract This study investigated the remediation of clay soil polluted with low-solubility organics (diesel hydrocarbons) using a combined electrochemical-biological technology. Electrokinetic soil flushing was used, coupled with a biological permeable reactive barrier, which was placed into soil away from electrodes to prevent the negative effects of the acidic and basic fronts on the viability of microorganisms. Three two-week long batch experiments were performed in a lab-scale installation specifically designed to evaluate the remediation of polluted soil. The primary variable under study was the electric field applied to the soil (0.5, 1.0 and 1.5 V cm−1), and the experimental procedure included daily Polarity Reversal of the electrodes and the addition of anionic surfactant in the electrode wells. The Polarity Reversal was observed to be a key strategy, which allowed adequate experimental conditions to be maintained in the soil (especially temperature and pH) for the success of the organic biodegradation process. The surfactant was evenly distributed across the soil, which helped the pollutant be transported. The biological activity was not limited to the barrier area but extended to the entire soil portion due to the microbial transport and growth far from the central barrier position. The voltage gradient did not have a strong influence on the measured experimental conditions (soil temperature, pH and moisture) but affected the electroosmotic flow. A higher diesel removal efficiency (36%) was observed when using the higher voltage gradient (1.5 V cm−1) after two weeks, which demonstrates a promising performance of the studied technology for a future real in-situ application.

  • effect of electric field on the performance of soil electro bioremediation with a periodic Polarity Reversal strategy
    Chemosphere, 2016
    Co-Authors: Esperanza Mena, J Villasenor, Pablo Canizares, Manuel A Rodrigo
    Abstract:

    In this work, it is studied the effect of the electric fields (within the range 0.0-1.5 V cm(-1)) on the performance of electrobioremediation with Polarity Reversal, using a bench scale plant with diesel-spiked kaolinite with 14-d long tests. Results obtained show that the periodic changes in the Polarity of the electric field results in a more efficient treatment as compared with the single electro-bioremediation process, and it does not require the addition of a buffer to keep the pH within a suitable range. The soil heating was not very important and it did not cause a change in the temperature of the soil up to values incompatible with the life of microorganisms. Low values of water transported by the electro-osmosis process were attained with this strategy. After only 14 d of treatment, by using the highest electric field studied in this work (1.5 V cm(-1)), up to 35.40% of the diesel added at the beginning of the test was removed, value much higher than the 10.5% obtained by the single bioremediation technology in the same period.

M Vazquez - One of the best experts on this subject based on the ideXlab platform.

  • magnetization Reversal of the transverse domain wall confined between two clusters of magnetic impurities in a ferromagnetic planar nanowire
    Journal of Magnetism and Magnetic Materials, 2016
    Co-Authors: D Toscano, S A Leonel, P Z Coura, Fernando Sato, B V Costa, M Vazquez
    Abstract:

    Abstract Numerical simulations have been used to investigate the Polarity Reversal of the transverse domain wall in rectangular magnetic nanowires and the stabilization of the domain wall position after occurring the Polarity Reversal. In order to control the wall position we have considered two clusters of magnetic impurities, identical and equidistant from the nanowire width axis. Traps of pinning and blocking for the transverse domain wall can be originated from magnetic impurities, consisting of a local variation of the exchange constant. Under suitable excitation amplitudes it is possible to switch the Polarity of the transverse domain wall by applying a nanosecond axial magnetic field pulse in a fast and controllable way.

Andrew J Biggin - One of the best experts on this subject based on the ideXlab platform.

  • subduction flux modulates the geomagnetic Polarity Reversal rate
    AGU Fall Meeting Abstracts, 2018
    Co-Authors: Mark W Hounslow, Mathew Domeier, Andrew J Biggin
    Abstract:

    The cause of variations in the frequency of geomagnetic Polarity Reversals through the Phanerozoic has remained a primary research question straddling palaeomagnetism and geodynamics for decades. Numerical models suggest the primary control on geomagnetic Reversal rate on 10 to 100 Ma timescales is the changing heat flux across the core-mantle boundary, a flux which is expected to be influenced by variations in the lithosphere subducted into the mantle. A positive relationship between the time-dependent global subduction flux and magnetic Reversal rate is expected, with a time delay to transmit the thermal imprint into the lowermost mantle. We perform the first test of this hypothesis using subduction flux estimates and geomagnetic Reversal rate data back to the early Paleozoic. Subduction area flux is derived from global, full-plate tectonic models, and evaluated against independent subduction flux proxies based on strontium isotopes and age distribution of detrital zircons . A continuous Phanerozoic Reversal rate model is built from pre-existing compilations back to ~320 Ma plus a new Reversal rate model in the data-sparse mid-to-early Paleozoic. Cross-correlation of the time-dependent subduction flux and geomagnetic Reversal rate series reveals a significant correlation with a time delay of ~120 Ma (with Reversals trailing the subduction flux). This time delay represents a value intermediate between the seismologically constrained time expected for a subducted slab to transit from the surface to the core-mantle boundary (~150-300 Ma), and the much shorter lag time predicted by some numerical models of mantle flow (~30-60 Ma). Our novel estimate of lag time, encouragingly represents a compromise between them. Important uncertainties in our proposed relationship remain, but the results cast new light on the dynamic connections between the surface and deep Earth, and will help to constrain new models linking mantle convection, the thermal evolution of the lowermost mantle, and the geodynamo.

  • subduction flux modulates the geomagnetic Polarity Reversal rate
    Tectonophysics, 2018
    Co-Authors: Mark W Hounslow, Mathew Domeier, Andrew J Biggin
    Abstract:

    Abstract Ascertaining the cause of variations in the frequency of geomagnetic Polarity Reversals through the Phanerozoic has remained a primary research question straddling paleomagnetism and geodynamics for decades. Numerical models suggest the primary control on geomagnetic Reversal rates on 10 to 100 Ma timescales is the changing heat flux across the core-mantle boundary and that this is itself expected to be strongly influenced by variations in the flux of lithosphere subducted into the mantle. A positive relationship between the time-dependent global subduction flux and magnetic Reversal rate is expected, with a time delay to transmit the thermal imprint into the lowermost mantle. We perform the first test of this hypothesis using subduction flux estimates and geomagnetic Reversal rate data back to the early Paleozoic. Subduction area flux estimates are derived from global, full-plate tectonic models, and are evaluated against independent subduction flux proxies based on the global age distribution of detrital zircons and strontium isotopes. A continuous Phanerozoic Reversal rate model is built from pre-existing compilations back to ~320 Ma plus a new Reversal rate model in the data-sparse mid-to-early Paleozoic. Cross-correlation of the time-dependent subduction flux and geomagnetic Reversal rate series reveals a significant correlation with a time delay of ~120 Ma (with Reversals trailing the subduction flux). This time delay represents a value intermediate between the seismologically constrained time expected for a subducted slab to transit from the surface to the core-mantle boundary (~150–300 Ma), and the much shorter lag time predicted by some numerical models of mantle flow (~30–60 Ma). While the reason for this large discrepancy remains unclear, it is encouraging that our novel estimate of lag time represents a compromise between them. Although important uncertainties in our proposed relationship remain, these results cast new light on the dynamic connections between the surface and deep Earth, and will help to constrain new models linking mantle convection, the thermal evolution of the lowermost mantle and the geodynamo.

Manuel A Rodrigo - One of the best experts on this subject based on the ideXlab platform.

  • effect of the Polarity Reversal frequency in the electrokinetic biological remediation of oxyfluorfen polluted soil
    Chemosphere, 2017
    Co-Authors: Silvia Barba, J Villasenor, Manuel A Rodrigo, Pablo Canizares
    Abstract:

    Abstract This work studies the feasibility of the periodic Polarity Reversal strategy (PRS) in a combined electrokinetic-biological process for the remediation of clayey soil polluted with a herbicide. Five two-weeks duration electrobioremediation batch experiments were performed in a bench scale set-up using spiked clay soil polluted with oxyfluorfen (20 mg kg−1) under potentiostatic conditions applying an electric field between the electrodes of 1.0 V cm−1 (20.0 V) and using PRS with five frequencies (f) ranging from 0 to 6 d−1. Additionally, two complementary reference tests were done: single bioremediation and single electrokinetic. The microbial consortium used was obtained from an oil refinery wastewater treatment plant and acclimated to oxyfluorfen degradation. Main soil conditions (temperature, pH, moisture and conductivity) were correctly controlled using PRS. On the contrary, the electroosmotic flow clearly decreased as f increased. The uniform soil microbial distribution at the end of the experiments indicated that the microbial activity remained in every parts of the soil after two weeks when applying PRS. Despite the adapted microbial culture was capable of degrade 100% of oxyfluorfen in water, the remediation efficiency in soil in a reference test, without the application of electric current, was negligible. However, under the low voltage gradients and Polarity Reversal, removal efficiencies between 5% and 15% were obtained, and it suggested that oxyfluorfen had difficulties to interact with the microbial culture or nutrients and that PRS promoted transport of species, which caused a positive influence on remediation. An optimal f value was observed between 2 and 3 d−1.

  • electrokinetic remediation of soil polluted with insoluble organics using biological permeable reactive barriers effect of periodic Polarity Reversal and voltage gradient
    Chemical Engineering Journal, 2016
    Co-Authors: Esperanza Mena, J Villasenor, Manuel A Rodrigo, Pablo Canizares
    Abstract:

    Abstract This study investigated the remediation of clay soil polluted with low-solubility organics (diesel hydrocarbons) using a combined electrochemical-biological technology. Electrokinetic soil flushing was used, coupled with a biological permeable reactive barrier, which was placed into soil away from electrodes to prevent the negative effects of the acidic and basic fronts on the viability of microorganisms. Three two-week long batch experiments were performed in a lab-scale installation specifically designed to evaluate the remediation of polluted soil. The primary variable under study was the electric field applied to the soil (0.5, 1.0 and 1.5 V cm−1), and the experimental procedure included daily Polarity Reversal of the electrodes and the addition of anionic surfactant in the electrode wells. The Polarity Reversal was observed to be a key strategy, which allowed adequate experimental conditions to be maintained in the soil (especially temperature and pH) for the success of the organic biodegradation process. The surfactant was evenly distributed across the soil, which helped the pollutant be transported. The biological activity was not limited to the barrier area but extended to the entire soil portion due to the microbial transport and growth far from the central barrier position. The voltage gradient did not have a strong influence on the measured experimental conditions (soil temperature, pH and moisture) but affected the electroosmotic flow. A higher diesel removal efficiency (36%) was observed when using the higher voltage gradient (1.5 V cm−1) after two weeks, which demonstrates a promising performance of the studied technology for a future real in-situ application.

  • effect of electric field on the performance of soil electro bioremediation with a periodic Polarity Reversal strategy
    Chemosphere, 2016
    Co-Authors: Esperanza Mena, J Villasenor, Pablo Canizares, Manuel A Rodrigo
    Abstract:

    In this work, it is studied the effect of the electric fields (within the range 0.0-1.5 V cm(-1)) on the performance of electrobioremediation with Polarity Reversal, using a bench scale plant with diesel-spiked kaolinite with 14-d long tests. Results obtained show that the periodic changes in the Polarity of the electric field results in a more efficient treatment as compared with the single electro-bioremediation process, and it does not require the addition of a buffer to keep the pH within a suitable range. The soil heating was not very important and it did not cause a change in the temperature of the soil up to values incompatible with the life of microorganisms. Low values of water transported by the electro-osmosis process were attained with this strategy. After only 14 d of treatment, by using the highest electric field studied in this work (1.5 V cm(-1)), up to 35.40% of the diesel added at the beginning of the test was removed, value much higher than the 10.5% obtained by the single bioremediation technology in the same period.

D Toscano - One of the best experts on this subject based on the ideXlab platform.

  • magnetization Reversal of the transverse domain wall confined between two clusters of magnetic impurities in a ferromagnetic planar nanowire
    Journal of Magnetism and Magnetic Materials, 2016
    Co-Authors: D Toscano, S A Leonel, P Z Coura, Fernando Sato, B V Costa, M Vazquez
    Abstract:

    Abstract Numerical simulations have been used to investigate the Polarity Reversal of the transverse domain wall in rectangular magnetic nanowires and the stabilization of the domain wall position after occurring the Polarity Reversal. In order to control the wall position we have considered two clusters of magnetic impurities, identical and equidistant from the nanowire width axis. Traps of pinning and blocking for the transverse domain wall can be originated from magnetic impurities, consisting of a local variation of the exchange constant. Under suitable excitation amplitudes it is possible to switch the Polarity of the transverse domain wall by applying a nanosecond axial magnetic field pulse in a fast and controllable way.