Tertiary trickling filters at the Littleton/Englewood wastewater treatment plant provide concurrent nitrification and biological foul air treatment. Operation of the full-scale facilities during the past two years demonstrate highly efficient oxidation of ammonia and odorous sulfur compounds in the dual purpose process. Evaluation of performance data with a nitrification model demonstrate maximum theoretical reaction rates at the top of the filter media have been consistently achieved. Statistical analysis of operating variables indicated that influent suspended solids, temperature, and hydraulic application rate affect nitrification performance. Odorous compounds in foul air treated in the NTF, including hydrogen sulfide and methyl mercaptan, were reduced to concentrations less than 8 ug/m3.