A high-rate degradation of 4-chloroaniline (4-CIA) was achieved by developing mixed-culture microbial granules under aerobic conditions in a sequencing airlift bioreactor (SABR). An essential step in this process was the enrichment of the biomass with improved setting characteristics and high 4-CIA degradation activity by manipulating combined hydraulic and microbial selection pressures via stepwise increases in 4-CIA loading. The seed sludge was conditioned over a 15-day acclimation period to allow the biomass to adapt to the presence of 4-CIA and the preferred short-settling time. Over the subsequent two months, aerobic granular sludge was developed by decreasing the settling time and gradually increasing the 4-CIA loading, and glucose/CH3COONa was used to facilitate the growth of the 4-CIA-fed biomass. High specific degradation rates of more than 0.27 g gVSS(-1) d(-1) were sustained for 4-CIA concentrations above 400 mg L-1. At concentrations as high as (8.18 +/- 0.06)g L-1, 4-CIA was completely removed, and the biomass concentration was maintained. Degradation kinetics for all tests was described well by the typical substrate-inhibition pattern predicted by the Haldane equation. The aerobic granule primarily degraded 4-CIA via the meta-cleavage pathway. (c) 2011 Elsevier Ltd. All rights reserved.