Samuel Ouoba

A New Experimental Method to Determine the Sorption Isotherm of a Liquid in a Porous Medium

Sorption from the vapor phase is an important factor controlling the transport of volatile organic compounds (VOCs) in the vadose zone. Therefore, an accurate description of sorption behavior is essential to predict the ultimate fate of contaminants. Several measurement techniques are available in the case of water, however, when dealing with VOCs, the determination of sorption characteristics generally relies on gas chromatography. To avoid some drawbacks associated with this technology, we propose a new method to determine the sorption isotherm of any liquid compounds adsorbed in a soil. This method is based on standard and costless transducers (gas pressure, temperature) leading to a simple and transportable experimental device. A numerical estimation underlines the good accuracy and this technique is validated on two examples. Finally, this method is applied to determine the sorption isotherm of three liquid compounds (water, heptane, and trichloroethylene) in a clayey soil.

A New Experimental Method to Determine the Henry’s Law Constant of a Volatile Organic Compound Adsorbed in Soil

This paper presents a new mechanical method to determine Henry’s law constant (HLC) of a volatile organic compound (VOC). This method is an extension of the one proposed by Ouoba et al. (2010) to determine the water activity in porous media. This work focuses on TCE and aims at characterizing its liquid-vapor equilibrium in various cases in the form of a pure liquid phase or dissolved in an aqueous solution, adsorbed or not in a natural soil. A liquid phase is disposed in a closed chamber whose volume can be incrementally increased. The recording of the total gas pressure leads to evaluating the vapor partial pressure of a volatile compound even in the case of an aqueous solution. This method has been validated using various aqueous solutions of TCE and the HLC obtained is in agreement with the literature. Then, the validity of Henry’s law has been asserted in the case of an aqueous solution of TCE adsorbed in a hygroscopic soil. Indeed, a linear relation between the vapor partial pressure of TCE and its concentration has been obtained while the HLC is about 16% lower. This result highlights the influence of adsorption phenomena on vapor/liquid equilibrium.

Influence of Ambient Pressure on the Evaporation of Volatile Organic Pollutants (VOP) during Soil Decontamination: Case of the Trichloroethylene (TCE)

This article presents the results on the volatilization of the volatile organic pollutants (VOP) during decontamination process from the soil. The choice of TCE as a volatile organic pollutant is explained by the fact that it is relatively highly soluble in water, compared to other compounds, which excludes any possibility of adsorption of its vapors on the walls of the experimental device during testing. Its saturation vapor pressure very high (≈7700 Pa at 20oC and nearly 12,000 Pa at 30oC) facilitates its monitoring using a pressure transducer relatively less accurate and less expensive. The results obtained on the evaporation of TCE show a linear dependence with the pressure. The coefficient of volatilization is 3.2 times greater for an atmospheric pressure of 90 kPa than for a pressure of 100 kPa. This coefficient would be multiplied by 20 when the pressure passes from 100 kPa to 10 kPa.

A New Experimental Method to Determine the Evaporation Coefficient of Trichloroethylene (TCE) in an Arid Soil

This paper presents a new method to determine the evaporation coefficient of trichloroethylene using a new experimental device called “activity-meter”. This device and the associated method have been developed in the Laboratory of Mechanical Engineering of the University of Montpellier 2 (France). The influence of diffusion on the vapor pressure of trichloroethylene and the influence of temperature at the liquid–gas interface were first determined. The results show that diffusion phenomena have no influence on the vapor pressure of trichloroethylene beyond 400 s of experimental time and the temperature is almost constant during experiments. Thus, in order to take into account the effects that are only due to the variation of partial pressure of trichloroethylene at the liquid–gas interface, the time interval used is between 400 s and the time required to reach equilibrium. The influence of pressure and temperature on the evaporation coefficient of pure trichloroethylene in an arid soil was then highlighted. The results show that the evaporation coefficient of trichloroethylene decreases with total vapor pressure but increases with temperature. A comparative study on evaporation coefficients conducted on water, heptane, and trichloroethylene shows that our results are in good agreement with results on volatility.

Highlighting of a local non-equilibrium thermodynamics during the transfer of trichlorethylene (TCE) in the superficial layers of arid soils

In this paper, we analyse and model the mass transfer of trichloroethylene in the surface layer of soil. Our study essentially focuses on arid soils taking into account the phase change liquid–vapour. We have then examined the validity of the assumption of local equilibrium by comparing the values of instantaneous pressure of the trichloroethylene during transfer process and the equilibrium vapour pressure. It appears that the assumption of local equilibrium during the transfer of trichloroethylene cannot be admitted.