A study was conducted to investigate the utilization of mature compost as a biofilter media for the removal of ammonia from the exhaust gases of the composting process. Source-selected organic fraction of municipal solid wastes, digested wastewater sludge and animal byproducts were composted in a pilot-scale reactor and the exhaust gas was treated in a biofilter. Due to the high ammonia adsorption and absorption capacity of the compost media, no delay or start-up phase was observed and high removal efficiencies were achieved from the beginning of the experiments. A global ammonia removal efficiency of 95.9% was obtained in the biofilter for a loading rate range of 846-67, 100 mg NH3 m(-3) biotilter h(-1). However, an important reduction of ammonia removal was observed when the waste gas contained high NH3 concentration (more than 2000 mg NH3 m(-3)), which corresponded with the case of animal by-products composting. (c) 2005 Elsevier B.V. All rights reserved.