Long-term operation of a permeable reactive barrier with diffusive exchange

Area of Science:

• Environmental Engineering
• Geochemistry
• Microbiology

Background:

• Acid mine drainage (AMD) poses significant environmental challenges due to high acidity and metal contamination.
• Permeable reactive barriers (PRBs) are passive treatment systems, but their long-term operational costs and effectiveness, especially for AMD, require further investigation.
• Sulfidic diffusive exchange (SDES) PRBs offer a promising approach for in-situ remediation by utilizing biologically produced sulfides.

Purpose of the Study:

• To evaluate the long-term operational performance and cost-effectiveness of a bench-scale SDES PRB for treating acid mine drainage.
• To assess the efficacy of SDES PRB in removing metals and acidity from both moderately and highly acidic AMD influents.
• To determine the stability of the microbial consortium and sulfate reduction rates under prolonged exposure to AMD conditions.

Main Methods:

• A bench-scale reactor simulating an SDES PRB was operated for 591 days.
• Two synthetic AMD influents were used: one moderately acidic (pH 4.9) and one highly acidic (pH 2.5) with varying metal and sulfate concentrations.
• Performance was monitored by measuring metal and acidity removal efficiencies and sulfate reduction rates.

Main Results:

• The SDES PRB achieved ~99% removal of metals and acidity from moderately acidic AMD.
• Significant removal of metals (up to 87% Fe, 79% Zn) was observed from highly acidic AMD.
• Sulfate reduction rates remained stable (~0.2 mol/m³-d) without significant inhibition, indicating microbial resilience.
• The system demonstrated long-term protection of the microbial consortium from toxicity.

Conclusions:

• SDES PRBs are suitable for long-term remediation of AMD-contaminated groundwater, even with high metal loads.
• The technology extends the operational range of conventional biological PRBs and shows potential for cost-competitive treatment compared to chemical precipitation.
• The study confirms the robustness and effectiveness of SDES PRB for sustainable AMD management.