In this work, limits and capacities of biotrickling filtration as a technique to compete with chemical scrubbing for the treatment of ammonia loads above 40 g N m(-3) h(-1) are investigated. Long-term operation of a lab-scale biotrickling filter under different inlet NH3 concentrations (100-1400 ppm(v)) and gas contact times (2-46 s) was performed to study the influence of operating parameters such as the make-up water flowrate and to assess biological and mass transfer limitations. The effect of the ammonia load over nitritation and nitratation rates was analyzed. At the same ammonia load, nitrification rates at gas velocities of 38.4 m h(-1) (large gas contact times) were 2-fold higher compared to those at gas velocities of 844 m h(-1) (short gas contact time) due to a better distribution of the NH3 along the packed bed, thus reducing the inhibitory effect of free ammonia (FA) and free nitrous acid (FNA) accumulation. Microbial diversity was compared between low and high-ammonia load conditions through tag encoded FLX amplicon pyrosequencing showing that accumulation of FA and FNA promoted the growth of nitrifiers. Also, a large fraction of denitrifying species was found demonstrating that denitrification occurs also in aerobic biotrickling filters. (C) 2016 Elsevier B.V. All rights reserved.