The Effects of Xanthan Gum as a Synergistic Delivery Reagent on Perchloroethylene Remediation in Lower-Permeability Zones of Aquifers

Treating contamination plumes in relatively lower-permeability zones (LPZs) presents a significant challenge for injection-based remediation due to aquifer heterogeneity. Currently, xanthan gum, as a co-remediation agent, has been confirmed to enhance the removal efficiency of contaminants in these zones. However, its associated effects on plume migration remain to be clarified. This study revealed the mechanisms by which xanthan addition enhances the removal rate of perchloroethylene (PCE), as well as its effects on plume migration. The results demonstrated that the injection of xanthan induces adverse migration of contamination plumes. A nonlinear relationship was observed between xanthan concentration, injection rate, and remediation performance. Within the studied range (0 g/L–0.8 g/L; 10 mL/min–40 mL/min), an optimal xanthan concentration (0.8 g/L) and injection rate (25 mL/min) were identified, at which the PCE removal efficiency was significantly improved, and the contamination plume migration was effectively inhibited. For combinations of porous media with a lower permeability contrast, adding xanthan led to better performance. To provide a comprehensive assessment of the remediation performance, four key indicators were proposed: remediation measurement factor, PCE removal rate, sweeping uniformity, and injection pressure. The results identified the optimal remediation conditions: M-F combination with the lowest permeability contrast (4.9), 0.4 g/L xanthan, and an injection rate of 25 mL/min. These findings contribute valuable insights for the formulation of more efficient remediation strategies.