As a microbial-environmental-control-type deodorizing system, we have developed a compact biotrickling filter system for small-scale livestock farms. The performance of the compact co-current biotrickling filter operated at high recycle liquid flow rates was systematically examined. In particular, we studied improvements in the nitrification ability of the system due to the resultant enhancement of absorption and dissolution of NH3 and absorption of O-2 with the high flow rates of recycle liquid flowing downward co-currently with gas flow. At the empty bed residence time of 50s, almost complete removal of NH3 was obtained with recycle liquid flow rates of 103 and 205 L m(-3) day(-1) for 20 days while the inlet NH3 concentration was increased from 200 to 500 ppm. With a recycle liquid flow rate of 411 L m(-3) day(-1) the removal efficiency remained above 95% for 57 days while the inlet NH3 concentration was increased from 200 to 700 ppm. The biodegradation kinetics for NH3 removal was successfully analyzed using the Haldane substrate inhibition kinetics. The present data and kinetic analyses showed that the substrate inhibition was suppressed and the biodegradation of ammonia in the compact biotrickling filter could be improved by the high recycle liquid flow rate. (C) 2014 Elsevier Ltd. All rights reserved.