Reactive and hydraulic behavior of pilot scale H₂O₂-assisted PRB in remediating landfill contaminated groundwater

The performance of a pilot-scale H₂O₂-assisted permeable reactive barrier (PRB) system was evaluated for landfill leachate-contaminated groundwater remediation. H₂O₂ pre-oxidation achieved 40-60 % COD removal at source concentrations > 75 mg/L. Carbon layers in PRB provided ∼42 % additional COD removal through catalyzed oxidation and adsorption, with BC+Fe₃O₄ (PRB2) outperforming AC (PRB1). BC+Fe₃O₄ also achieved 78.6 % NH₄⁺ removal ⁽vs. 30.8 % for AC), potentially through enhanced biological activity, thereby preserving zeolite ion-exchange capacity. After 8-month operation, 292.96 and 378.36 m³ of groundwater were remediated by PRB1 and PRB2, respectively. Effluent concentrations were reduced to10∼30 mg/L COD and < 1.5 mg/L NH₄⁺, from source levels of 50-240 mg/L COD and 40-230 mg/L NH₄⁺. Advection-diffusion^-adsorption model effectively described NH₄⁺ transport but underestimated early COD peaks due to complex oxidation. Coexisting contaminants reduced retardation factors by an order of magnitude. Temporary O₂ accumulation and potential precipitation of CaCO₃ and Fe/Mn hydroxides contributed to clogging in the front carbon layers, while biological activity and possible N₂ gas accumulation dominated in zeolite and rear carbon layers. Hydraulic conductivity reductions reached 80 % in carbon and 50-75 % in zeolite layers but were operationally controllable. These findings provide critical design recommendations for implementing H₂O₂-assisted PRB systems in long-term landfill risk management.