A combined ammonia gas absorption and nitrification was conducted in a single bioscrubber. The reactor was consisted of a bubble column (gas absorption) and a packed bed (nitrification) which contained polyurethane foams with immobilized nitrifying activated sludge. The entering gas and scrubbing liquid were contacted countercurrently. The bubble column elimination capacity (EC) was 26.74 g NH3/m(3) h at >99% ammonia gas removal and effluent gas concentration lower than 2 ppm(v). Without ammonium supplement, EC can reach 35.66 g NH3/m(3) h which is equivalently the highest tolerable ammonia loading rate of 700 g N/m(3) day (1650 mg N/L) at the packed bed. At this level, 593 g N/m(3)-day ammonia removal rate was achieved via nitrification, dominated by ammonia oxidation. Partial recycling (R/Q=0.5) of scrubbing solution reduced the secondary wastewater volume by producing 233% more concentrated nitrified products. Hydraulic retention time (HRT) of 24 h was found optimal for both processes (gas absorption and nitrification). (C) 2008 Elsevier Ltd. All rights reserved.