The fate of ammoniacal-nitrogen (NH4-N) was studied in a lab-scale downflow reed bed system treating an artificial landfill leachate. Individual reed beds were submerged by the leachate, then drained and rinsed by tap water. It was discovered that NH4-N was removed by a two-staged process, adsorption onto the reed bed media followed by nitrification into nitrite-nitrogen (NO2-N) and nitrate-nitrogen (NO3-N). A drop of NH4-N level of the leachate was observed when the reed beds were submerged. By rinsing of the beds, part of the NH4-N adsorbed inside the bed matrices was re-released into the rinse water. The presence of NO2-N and NO3-N in the rinse water demonstrated that nitrification process took place while the NH4-N was being retained inside the bed matrices. For artificial leachates with NH4-N levels of 150±5 mg/l, an average removal rate of 43.8% in a three-hour treatment was achieved; mass balance analysis indicated that processes of adsorption, and transformation into NO2-N and NO3-N accounted for 63.7%, 4.3% and 24.4% of the NH4-N removal, respectively. This study also demonstrated that in general greater recirculation rate of effluent around the downflow reed beds gives higher NH4-N removal.
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