Column test-based optimization of the permeable reactive barrier (PRB) technique for remediating groundwater contaminated by landfill leachates

• We investigated the PRB optimum composition and thickness using column tests.
• The optimum weight ratio of ZVI, Zeo and AC was 50%:10%:40%.
• We developed a method to estimate the thickness and longevity of PRB materials.
• A thickness (≥ 309.6 cm) is required for a practicable longevity (≥ 10 years).

We investigated the optimum composition of permeable reactive barrier (PRB) materials for remediating groundwater heavily contaminated by landfill leachate, in column tests using various mixtures of zero-valent iron (ZVI), zeolite (Zeo) and activated carbon (AC) with 0.01–0.25, 3.0–5.0 and 0.7–1.0 mm grain sizes, respectively. The main contributors to the removal of organic/inorganic contaminants were ZVI and AC, and the optimum weight ratio of the three PRB materials for removing the contaminants and maintaining adequate hydraulic conductivity was found to be 5:1:4. Average reductions in chemical oxygen demand (COD) and contents of total nitrogen (TN), ammonium, Ni, Pb and 16 polycyclic aromatic hydrocarbons (PAHs) from test samples using this mixture were 55.8%, 70.8%, 89.2%, 70.7%, 92.7% and 94.2%, respectively. We also developed a systematic method for estimating the minimum required thickness and longevity of the PRB materials. A ≥ 309.6 cm layer with the optimum composition is needed for satisfactory longevity, defined here as meeting the Grade III criteria (the Chinese National Bureau of Standards: GB/T14848/93) for in situ treatment of the sampled groundwater for ≥ 10 years.