A biofilter inoculated with Arthrobacter sp. was applied to the simultaneous elimination of trimethylamine (TMA) and ammonia (NH3) from the exhaust air of swine waste storage pits. The results showed that the biofilter achieved average removal efficiencies of 96.8 +/- 2.5% and 97.2 +/- 2.3% for TMA and NH3, respectively. A near-neutral pH (7.3-7.4) was maintained due to the accumulation of acid metabolites and the adsorption of alkaline NH3. Low moisture demand, low pressure drop and high biofilm stability in the system were other advantages. After long-term operation, the bacterial community structure showed that at least twenty-five bands were explicitly detected by a denaturing gradient gel electrophoresis (DGGE) method. However, the inoculated Arthrobacter sp. still maintained a dominant population (> 50%). Paracoccus denitrificans' presence in the biofilter could play an important role in oxidizing NH3 and reducing nitrite by heterotrophic nitrification and anaerobic denitrification. (c) 2007 Published by Elsevier Ltd.