Insights into microplastic migration through polymer-modified geosynthetic clay liners under dry-wet cycles

Area of Science:

• Geotechnical Engineering
• Environmental Science
• Materials Science

Background:

• Geosynthetic clay liners (GCLs) are crucial for landfill containment.
• Polymer modification, like xanthan gum (XG) addition, aims to enhance GCL performance.
• Understanding GCL behavior under environmental stress, such as dry-wet cycling, is vital for long-term barrier integrity.

Purpose of the Study:

• To investigate the impact of dry-wet cycling on the hydraulic conductivity and polyethylene (PE) migration of xanthan gum (XG)-modified GCLs (XG GCLs).
• To elucidate the mechanisms behind the deterioration of barrier performance in XG GCLs under simulated landfill conditions.

Main Methods:

• Flexible-wall permeametry was employed to conduct six dry-wet cycles using simulated landfill leachate (SLL).
• Multiscale analyses included quantitative crack imaging, residual polymer quantification, and SEM-EDS microstructural analysis.
• XG GCLs with XG loadings from 3% to 12% were tested.

Main Results:

• Dry-wet cycling led to crack expansion, reduced residual XG, and increased hydraulic conductivity.
• Polyethylene (PE) was detected in effluents after three cycles, with concentrations increasing over time.
• SEM-EDS revealed PE primarily within XG hydrogel along preferential flow paths.

Conclusions:

• Coupled effects of flow path enlargement and polymer elution significantly degrade XG GCL barrier performance.
• Dry-wet cycling poses risks of barrier failure and PE breakthrough, necessitating careful design and monitoring.
• Findings highlight the importance of considering long-term performance and potential contaminant migration in landfill barrier systems using modified GCLs.