Changes in microbial metabolic characteristics of a thermophilic biofilter (TBF) and a mesophilic biofilter (MBF) were studied using the Biolog plates technique in this study. The results showed that the TBF exhibited lower metabolic activities (0.006h(-1)) than the MBF (0.011 h(-1)) did during the early phase, and both showed similar metabolic activities after a long-term operation (181 days). The substrate utilization profiles and the dominant substrate in the Biolog ECO-plates and its molar fraction in both biofilters indicated different behaviors in the early phase and displayed a similar trend after a long-term operation. The principal component analysis showed that the samples in the TBF and MBF initially clustered separately and then moved into another similar cluster. The plot of the mole fraction of the dominant substrate and the diversity index (DQ +/- f(d) plot) also clearly showed the similar variation trend in the microbial community structures. (C) 2013 Elsevier B.V. All rights reserved.