This study employed a newly developed treatment biofilter to remove high nitrogen (N) concentration from synthetic livestock wastewater combined with media containing neutralized used acid (NUA) and dewatered alum sludge (DAS). This biofilter was also utilized to investigate the spatial and temporal distributions of ammonia-oxidizing bacterial (AOB) and nitrite-oxidizing bacterial (NOB) communities and their active responses to effluent characteristics. Data were obtained from 210 days of operations. Results showed that N removal was robust, with ammonia N and total N removal efficiencies of 59.8-82.1% and 57.5-74.9%, respectively. Denaturing gradient gel electrophoresis and sequence analyses revealed that the shift of AOB and NOB community structures in DAS was time dependent. These structures did not exhibit distinct differences in both media as depth varied. The retrieved AOB and NOB sequences from both media primarily belonged to Nitrosomonas, Nitrosovibrio, and Nitrobacter. The nitrification rates indicated that the change in AOB activity corresponded to the AOB community structure variation in the system. The peak was observed in DAS at the final time. By contrast, the NOB activity was inconsistent with the trend of its community structure. The AOB rate was positively related to the NOB rate. This finding suggested that AOB and NOB mutually promoted each other. The AOB and NOB activities of DAS rather than those of NUA appeared dependent on available nitrate from the effluent. Overall, these findings on AOB and. NOB helped enhance further understanding on the efficient N removal of the NUA-DAS system. (C) 2016 Elsevier B.V. All rights reserved.