Surfactant foam injection for remediation of diesel-contaminated soil: A comprehensive study on the role of co-surfactant in foaming formulation enhancement.

Aqueous foam injection is a promising technique for in-situ remediation of soil and aquifers contaminated by petroleum products. However, the application efficiency is strongly hindered by foam's instability upon contact with hydrocarbons. Addressing this, we propose a new binary surfactant mixture of Sodium Dodecyl Sulfate (SDS) and Cocamidopropyl Hydroxysultaine (CAHS). This study investigates CAHS's role as a co-surfactant in enhancing foam stability against antifoaming diesel oil under static and dynamic conditions. Using a dynamic foam analyzer (DFA-100), we assessed static foam's stability by monitoring decay profiles and bubble growth over time. The results revealed that the highest stability can be reached at a CAHS to SDS ratio of 50:50, increasing the half-life of the foam by 7.7 times. Remarkably, our analyses at bulk and bubble scales also elucidated the mechanisms behind the enhanced foam stability of the proposed binary surfactant mixture in the absence and presence of diesel. Additionally, in a 1D sand column, the SDS-CAHS mixture demonstrated more than twofold improvement of the Resistance Factor, attributed to the better survival of the lamellae due to the reduced rate of their destruction. This formulation also yielded a recovery improvement of >10 % compared to SDS foam. The significant improvements in stability and performance of the SDS-CAHS (50:50) mixture were credited to a robust pseudo-emulsion film formation, creating a higher oil entry barrier. This reinforcement and the surfactant molecules' synergistic interactions at the gas-liquid-oil interface significantly contributed to the overall effectiveness.

Microwave-enhanced thermal removal of organochlorine pesticide (chlordecone) from contaminated soils.

Soil contamination with chlordecone, an organochlorine pesticide, is causing serious health problems, affecting crop production and local livestock valorization in the French West Indies. In-situ chemical reduction (ISCR) processes for soil remediation have shown promise but need improvement in terms of time, cost and effective treatment, particularly for andosol soil types. Our study shows that a 10-min microwave treatment significantly reduces chlordecone concentrations (50-90%) in contaminated andosol and nitisol soils. Dry andosol soils show the highest removal yields and reach a higher final temperature (350 °C). Microwave treatment is in all cases more effective or at least as effective as 60 min of conventional heating at a target temperature of 200 °C. The thermal response of andosol and nitisol to microwave exposure is different, as the former is likely to undergo thermal runaway, reaching high temperatures in a short time, resulting in highly efficient thermal removal of chlordecone. These results encourage further scale-up, particularly for the treatment of andosol soils due to their strong microwave response.

Experimental study of DNAPL displacement by a new densified polymer solution and upscaling problems of aqueous polymer flow in porous media.

The remediation of DNAPL-contaminated soil with lower-density fluids is ineffective due to the over-riding of displacing fluid. The densification of biopolymers is experimentally studied to develop a solution with the same density as a pollutant. Polymer solutions and contaminants are characterized through rheometer. A 1D column filled with monodisperse glass beads was used to measure their apparent viscosity in porous media. The displacement of pollutants by biopolymers (such as xanthan gum, guar gum, and carboxymethyl cellulose) and densified solutions based on barite are investigated in the 1D porous column. In addition, the polymer solution flow is studied using an upscaling method based on the shear viscosity measured with rheometer. The upscaling results are compared with the 1D column experimental outcomes. We found that carboxymethyl cellulose is the best for densifying polymer and showed the highest remediation yield for DNAPL remediation. The polymers' rheology was represented well through the Carreau rheological model. The discrepancy of apparent viscosity in porous media from polymers' shear viscosity measured with rheometer is explained by the adsorption of polymers on pore surfaces and deposition of barite particles in a porous medium, which led to a decrease in permeability. The upscaling results are in good agreement with experimental outcomes at low-pressure gradients. The impact of porous media geometry on polymer flow in porous media is described.

Influence of water saturation and soil properties on the removal of organic pollutants using microwave heating.

Properties of fluids and media, such as soil moisture, may play a significant role in the absorption of microwave and heat distribution during the remediation of soil contaminated with volatile and semi-volatile compounds. Previous studies have been performed on soil samples placed inside a microwave oven cavity in a reactor far from the waveguide outlet or directly inside the metal waveguides. These conditions are far from in situ applications where the unsaturated soil is directly exposed to microwaves through the antenna slots. The objective of this study was therefore to understand better how soil temperature and pollutant recovery change during microwave and conduction heating and how soil properties, liquid type, and saturation influence that. We developed a unique experimental setup that consists of a splittable soil column inserted inside the cavity of a modified domestic microwave oven (power 1000 W and frequency 2.45 GHz) so that the soil surface is in direct contact with the radiated microwaves. Experiments with electrical resistance heating using the same column but with a modified design were conducted for comparison. We used three types of soils spanning fine, medium, and coarse sands, and two semi-volatile pollutants (xylene and diesel fuel). The pollutants and water of different volumes (12% and 25%) were mixed with soils to make the artificially contaminated soils. Temperature values were measured at different points along the sand-packed column using fiber-based optical thermocouples. We evaluated treatment efficiency in space (soil analysis) and time (outlet phase decantation). The experimental results show that microwave heating technology is optimal for water saturation of around 12%, which gives the best compromise between the overall dielectric properties and allows rapid and efficient heating. The temperature increases fast at the beginning of the microwave heating and stabilizes because of the latent heat of the water and pollutant vaporization and then increases again but slowly for dry soil conditions. A maximum temperature of 170 °C was achieved after 140 min of microwave heating. The type of soil and pollution can drastically affect remediation efficiency through mechanical mechanisms (because of a pressure increase) in addition to physical mechanisms (evaporation) for pollutant removal. The removal efficiencies, using the outlet fluids decantation, were 67%, 73%, and 75% for fine, medium, and coarse sand, respectively, for the applied heating time. We found that microwave heating works better in coarser sand where classical conduction heating usually failed. Comparing the two types of heating (microwave and conductive heating) under the same conditions highlights that the use of microwaves makes it possible to reach very high temperatures in a shorter time than with thermal conduction heating.

Numerical simulations of high viscosity DNAPL recovery in highly permeable porous media under isothermal and non-isothermal conditions.

We developed a decimetric size model based on coupling generalized Darcy's law and heat-transfer equations to model viscous dense non-aqueous phase liquid (DNAPL) pumping through highly permeable porous media under non-isothermal conditions. The presence of fingering and non-wetting phase ganglia was modeled through an unsteady capillary diffusion coefficient and an arbitrary heterogeneous permeability field. The model was validated using existing experimental data of a simple case, an oil injection in a 2D tank packed with glass beads. Next, we compared the results of this model against a DNAPL extracting situation in the 2D tank to better understand the two-phase flow behavior in highly permeable porous media. We found that natural convection during heating plays an essential role in heat transfer, especially in the wetting phase zone. By adding the dynamic effect (unsteady conditions) we were better able to describe the presence of the ganglia in porous media. We observed good agreement between modeled and experimental oil saturation curves until the breakthrough point, with a mean relative error of about 10% for low and high flow rates, and 8% and 16% after breakthrough for low and high flow rates, respectively. Extracting viscous oil at low flow rates and high temperature generates less fingering and is well described by the generalized Darcy's law. The remobilization of residual non-wetting ganglia after the breakthrough point at the outlet is, however, difficult to simulate using the generalized Darcy's law. In the end, we treated this issue by using a perturbed permeability field to simulate the observed fingering in the 2D tank.