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. 2020 Nov 22;20(22):6677.
doi: 10.3390/s20226677.

Open-Ended Coaxial Probe Measurements of Complex Dielectric Permittivity in Diesel-Contaminated Soil during Bioremediation

Andrea Vergnano  1 , Alberto Godio  1 , Carla Maria Raffa  2 , Fulvia Chiampo  2 , Jorge A Tobon Vasquez  3 , Francesca Vipiana  3
Affiliations

Open-Ended Coaxial Probe Measurements of Complex Dielectric Permittivity in Diesel-Contaminated Soil during Bioremediation

Andrea Vergnano et al. Sensors (Basel). .

Abstract

In the bioremediation field, geophysical techniques are commonly applied, at lab scale and field scale, to perform the characterization and the monitoring of contaminated soils. We propose a method for detecting the dielectric properties of contaminated soil during a process of bioremediation. An open-ended coaxial probe measured the complex dielectric permittivity (between 0.2 and 20 GHz) on a series of six soil microcosms contaminated by diesel oil (13.5% Voil/Vtot). The microcosms had different moisture content (13%, 19%, and 24% Vw/Vtot) and different salinity due to the addition of nutrients (22 and 15 g/L). The real and the imaginary component of the complex dielectric permittivity were evaluated at the initial stage of contamination and after 130 days. In almost all microcosms, the real component showed a significant decrease (up to 2 units) at all frequencies. The results revealed that the changes in the real part of the dielectric permittivity are related to the amount of degradation and loss in moisture content. The imaginary component, mainly linked to the electrical conductivity of the soil, shows a significant drop to almost 0 at low frequencies. This could be explained by a salt depletion during bioremediation. Despite a moderate accuracy reduction compared to measurements performed on liquid media, this technology can be successfully applied to granular materials such as soil. The open-ended coaxial probe is a promising instrument to check the dielectric properties of soil to characterize or monitor a bioremediation process.

Keywords: bioremediation; complex dielectric permittivity; contaminated soil; diesel oil; open-ended coaxial probe.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Different polarization effects in solid materials [32].
Figure 2
Figure 2
Contaminated soil microcosms.
Figure 3
Figure 3
Network analyzer and dielectric probe measuring the permittivity of contaminated soil: (a) instrument, (b) apparatus scheme, and (c) open-ended coaxial probe scheme.
Figure 4
Figure 4
Real and imaginary dielectric permittivity measured on distilled water.
Figure 5
Figure 5
Complex dielectric permittivity before bioremediation and after 130 days: real part (a), imaginary part (b). Microcosm: C/N = 120, volumetric water content = 13%.
Figure 6
Figure 6
Complex dielectric permittivity before bioremediation and after 130 days: real part (a), imaginary part (b). Microcosm: C/N = 120. Volumetric water content = 19%.
Figure 7
Figure 7
Complex dielectric permittivity before bioremediation and after 130 days: real part (a), imaginary part (b). Microcosm: C/N = 120. Volumetric water content = 24%.
Figure 8
Figure 8
Complex dielectric permittivity before bioremediation and after 130 days: real part (a), imaginary part (b). Microcosm: C/N = 180. Volumetric water content = 13%.
Figure 9
Figure 9
Complex dielectric permittivity before bioremediation and after 130 days: real part (a), imaginary part (b). Microcosm: C/N = 180. Volumetric water content = 19%.
Figure 10
Figure 10
Complex dielectric permittivity before bioremediation and after 130 days: real part (a), imaginary part (b). Microcosm: C/N = 180. Volumetric water content = 24%.
Figure 11
Figure 11
Electrical conductivity derived from the mean of the imaginary component of dielectric permittivity. Microcosm: C/N = 120. Volumetric water content = 13%.
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