An airlift inner-loop bioreactor packed with honeycomb-like ceramic as the carrier was developed and its capacity to immobilize microorganism was studied through adding bacteria, Achromobacter sp., capable of degrading 2,4-dichlorophenol (2,4-DCP), directly to the reactor under continuous operation. Effects of phenol in the feed with 2,4-DCP on 2,4-DCP removal were investigated under fed-batch and continuous operations. The results showed that the pure strain could be easily immobilized on the carrier and proliferated using 2,4-DCP as the sole carbon source. In the process of fed-batch operation, removal rate of 2,4-DCP decreased with the increase in run number, while that of phenol was just to the contrary. In the continuous operation, 2.4-DCP loading rate was kept at 29.72-32.23 mg/(1 day), but phenol loading rate was increased stepwise from 325.56 to 602.79 mg/(1 day). The results showed that with the increase of phenol loading rates, the removal efficiency of 2,4-DCP declined from 100 to 87.9%. while that of phenol remained at about 99.6%. Presence of phenol in feed inhibited the biodegradation of 2,4-DCP and caused the major carbon source shift from 2,4-DCP to phenol. (C) 2003 Elsevier B.V. All rights reserved.