Nitrifying biofilms were constructed on low density polyester Dacron for the bioremediation of nitrogen from wastewater effluent of a municipal treatment plant. Dacron disks were inoculated with wastewater sludge enriched for 15 days for either ammonia- or nitrite-oxidizing bacteria (AOB or NOB, respectively) and packed into glass bioreactors. Wastewater effluent containing high levels of ammonia, nitrite, and phosphate was collected and fed to inoculated and uninoculated bioreactors. Both inoculated bioreactors showed stable nitrification efficiencies, removing 96 and 76% of the ammonia and 12 and 35% of the nitrite for AOB- and NOB-inoculated bioreactors, respectively. Efficiencies of phosphate removal were similar in both inoculated and uninoculated bioreactors, indicating that nitrifiers were not required for this process. AOB-inoculated bioreactors accumulated nitrite mid-way through the experiment and had low rates of conversion to nitrate, suggesting slow nitrite oxidizer growth. DGGE and sequence analysis of AOB 16S rRNA genes showed enrichment of Nitrosomonas spp. in both inoculated bioreactors, and a dominance of Nitrosospira spp. in non-inoculated bioreactors. This study describes an inexpensive and efficient technology for removing ammonia and nitrite from wastewater effluents of municipal treatment plants before its release to the environment.