Geophysical Monitoring at Laboratory Scale of Aerobic Degradation of Diesel Oil

The study is aimed to monitor bioremediation of hydrocarbon-polluted soils by measuring geophysical electromagnetic parameters. A previous study at lab scale showed that biostimulated indigenous microorganisms can remove diesel oil from soil successfully. Herein, we focused on the result of a laboratory test using Time Domain Reflectometry (TDR) probes to measure electrical conductivity and dielectric permittivity in a column of sandy soil artificially contaminated with diesel oil. To simulate aerobic degradation of hydrocarbons, mesocosms were set-up in two Plexiglas columns (inner diameter = 13.8 cm) with 3.4 kg of soil (layer height = 14 cm) spiked with 0.24 kg of diesel oil and hydrated with 0.4 kg of Mineral Salt Medium for Bacteria. One mesocosm was aerated by air injection from the bottom of the column, while the other had only natural aeration due to air diffusion through the soil itself. In each column, electrical conductivity and dielectric permittivity were monitored by TDR probes for 105 days. TDR measurements were supported by microbiological and gas chromatographic analyses, along with SEM images. The findings showed that air injection heavily influenced the TDR monitoring, probably due to generation of air bubbles around the probe that interfered with probe-soil coupling. Therefore, the measurement accuracy was reduced in an irreversible way. In the non-aerated system, a slight (2%) and linear decrease of dielectric permittivity was observed over time, meanwhile electrical conductivity decreased by about 30%

Open-ended coaxial probe measurements of complex dielectric permittivity in diesel-contaminated soil during bioremediation

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

Production of polyhydroxyalcanoates (PHAs) using milk whey and dairywastewater activated sludgeProduction of bioplastics using dairy residues

The production of polyhydroxyalcanoates (PHAs), which are biodegradable plastics, was studied using milk whey and dairy wastewater activated sludge to define a suitable C/N ratio, the pre-treatments required to reduce the protein content, and the effect of pH correction. The results show good production of PHAs at a C/N=50 and without pH correction. The use of dairy wastewater activated sludge has the advantage of not requiring aseptic conditions