Resumen
Biological treatment of landfill leachate faces some difficulties by influence of some physical and chemical characteristics of this sort of effluent, which usually presents high levels of nitrogen ? mainly ammonia nitrogen. High concentrations of ammonia nitrogen restrain biodegradation, requiring the nitrogen removal along with landfill leachate treatment in these cases. This work evaluated the nitrite formation in a pilot-scale biological treatment system applied to landfill leachate, aiming at posterior nitrogen removal by shortcut denitrification. Two pilot-scale units (250 L aeration tanks) were monitored simultaneously for 100 days. HRT in both cases was 5 days. Leachate applied on this experimental device was collected in a solid waste landfill in the city of Londrina, Paraná State. That landfill is active since 1972. In the operational conditions observed during this experiment, most of nitrogen removal occurred by ammonia volatilization. Anyway, nitrite formation was obtained in the pilot-scale units and nitrate remained at low levels.