Design of a multifunctional permeable reactive barrier for the treatment of landfill leachate contamination: laboratory column evaluation.

This study describes a laboratory-scale multifunctional permeable reactive barrier (multibarrier) for the removal of ammonium (NH4+: 313 +/- 51 mg N L(-1)), adsorbable organic halogens (AOX: 0.71 +/- 0.25 mg Cl L(-1)), chemical oxygen demand (COD: 389 +/- 36 mg L(-1)), and toxicity from leachate originating from a 40-year-old Belgian landfill. The complexity of the contamination required a sequential setup combining different reactive materials and removal processes. All target contaminants could be removed to levels below the regulatory discharge limits. Ammonium was efficiently removed in a first microbial nitrification compartment, which was equipped with diffusive oxygen emitters to ensure a sufficient oxygen supply. Ammonium was mainly oxidized to nitrite and to a lesser extent to nitrate, with an average mass recovery of 96%. Remaining ammonium concentrations could be further removed by ion exchange in a second compartment filled with clinoptilolite, exhibiting a total ammonium removal capacity of 46.7 mg N per g of clinoptilolite. Athird microbial denitrification compartment fed with sodium butyrate as a carbon source, was used to remove nitrate and nitrite formed in the first compartment. Maximum nitrification and denitrification rates at 12 degrees C indicated that hydraulic retention times of approximately 62 h and approximately 32 h were required in the columns to remove 400 mg N L(-1) by nitrification and denitrification, respectively. Leachate toxicity decreased to background levelstogetherwiththe removal of ammonium and its oxidation products. AOX and COD were efficiently removed by sorption in an additional compartment filled with granular activated carbon.