Numerical predictive modelling for groundwater remediation using nanotechnology

Successful remediation of contaminated groundwater resources is known to have many barriers1. These limitations are more significant for ex-situ techniques compared to in-situ ones. An ex-situ technique such as excavation of contaminated soil for landfill or incineration, although a move toward total contaminant removal, poses a risk to business disruption. For the two candidate contaminated sites we are studying the source and plume locations are situated within operating facilities of active businesses. A halt in production (needed for a safe soil excavation and removal) presents a scenario with concerning socio-economic impacts to local business. In-situ remediation techniques address spatial disadvantages as they do not require removal of contaminated soil for remediation. Instead, injection of reactive material (chemicals or particles) offer a remediating solution addressing the contaminated area in-situ. In-situ remediation can be achieved through chemical degradation. However, in-situ chemical oxidation of chlorinated solvents using potassium permanganate can cause formation of a precipitate resulting in reduction in fluid mobility within the pore structure.
Nanoscale zero valent iron (nZVI) is an emerging technique within in-situ remediation. Nanoremediation is an attractive proposition as it has been shown to improve reaction time due to a large surface area when compared to microscale zero valent iron. This reaction rate is especially an advantage when compared to bioremediation. Remediation by nZVI is effective for a range of contaminants, including chlorinated solvents. The goal of this study is to study the application of nanoremediation technology for in-situ degradation of chlorinated solvents in two contaminated sites in Brazil. This technology is chosen based on the small footprint for nZVI injection, reducing the invasiveness of this technique.
The two contaminated sites we study are located in the outskirts of the city of Sao Paulo. A pore-scale study has recently shown that nanoremediation can cause remobilisation of previously trapped droplets of chlorinated solvents2. Building on this study we are using field-scale 3D aquifer models (constructed in PetraSim software) to solve multiphase flow in porous media to focus on contamination transport in these two groundwater systems. 3D models were built based on cross sectional maps and data (e.g. hydraulic conductivity and porosity) extracted from publicly available environmental reports. These models are used to study the (i) preferential flow pathways through the contamination source and plume for each site induced and exacerbated by heterogeneity of the aquifer system, and (ii) the viscous displacement of the trapped contaminant as a function of nZVI concentration that leads to varying degree of piston-like displacement.
This study offers the opportunity to model and explore the difference in tropical soil and high levels of rainfall have on groundwater contamination and how remediation may need to be adjusted to account for this.
The outcomes of this work inform a pilot-scale nanoremediation project, currently at the design stage, as part of the GRUN project (UK-Brazil collaborative research). Performing these sensitivity analysis on the key parameters contributing to a successful process at the field scale. This will enable us to identify the most suitable site(s) for effective application of nanoremediation.