By maintaining the same operational conditions of one conventional¯uidized-bed bioreactor (CFB) and two tapered¯uidized-bed bioreactors (TFBs), the performance of the TFBs with taper angles of 5°and 2.5°were found to be superior to that of the CFB with a taper angle of 0°. Experimental results together with statistical analyses showed that the bioparticle and hydrodynamic characteristics of the TFBs were signi®cantly different from those of the CFB. Also, bioparticle strati®cation occurred in the three bioreactors. The bio®lm thickness (d) and the speci®c biomass (b) of the three bioreactors varied in the following decreasing order 5°b 2.5°b 0°under the same volumetric loading. Meanwhile, the speci®c energy dissipation rate (v) and the bioparticle washout rates (W = 0.214 AE 0.219; 0.537 AE 0.493 g BAC dm

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