A pilot-scale reactor, consisting of a set of two-stage-in-series biotrickling filters, an influent gas supply system and a liquid recirculation system, was utilized to treat ammonia in an airstream. Each stage of the biotrickling filter was constructed from a 20 cm × 200 cm (inner diameter × height) acrylic column packed with cokes (average diameter = 3.0 cm, specific area = 150 m2/m3) of 125 cm height. Experimental results indicate that a time of 30 days is required for development of biofilms for nitrification of the absorbed ammonia from the gas. Long-term (187 days) experimental results show that, in the conditions of EBRT (empty bed gas retention time) = 7.25 s, “circulation liquid/gas” flow rate ratio = 7.7 L/m3, and liquid pH = 6.65, the level of ammonia in the influent gas was reduced from 230 to 4.0 ppm. With the volumetric ammonia loading of less than 7.37 g NH3–N/m3.h, the system could achieve ammonia removal and nitrification efficiencies of 98 and 94%, respectively, without supplementary glucose as a carbon source. However, with a loading of 13.1 g NH3–N/m3.h, both decreased gradually due to a lack of carbon source and an accumulation of ammonium and nitrite ions in the recirculation liquid.