Removal of ammoniacal-nitrogen from an artificial landfill leachate in downflow reed beds

摘要

The fate of ammoniacal-nitrogen (NH_4-N) was studied in a lab-scale downflow reed bed system treating an artificial landfill leachate. Individual reed beds were saturated by the leachate, then drained and rinsed by tap water. NH_4-N was removed by a two-stage process, adsorption onto the reed bed media followed by nitrification into nitrite-nitrogen (NO_2-N) and nitrate-nitrogen (NO_3-N). Decrease of the NH_4-N level of the leachate was observed when the reed beds were saturated. By rinsing the beds, part of the NH_4-N adsorbed inside the bed matrices was released into the rinse water. The presence of NO_2- and NO_3-N in the rinse water demonstrated that nitrification took place while NH_4-N was retained inside the bed matrices. For artificial leachates with NH_4-N levels of 150 +- 5 mg/l, an average removal rate of 44% in a 3h treatment was achieved. Mass balance analysis indicated that adsorption, transformations into NO_2- and NO_3-N accounted for 64,4 and 24% of the NH_4-N removal, respectively. This study also demonstrated that in general a greater rate of effluent recirculation around downflow reed beds gives higher NH_4-N removal.