A method has been presented for modelling a three-phase fluidized-bed microbiological process. An algorithm was proposed for determining the steady states of such a continuous bioreactor and quantitative analysis of the basic properties of these states was performed. It was assumed that the process occurs according to dual-substrate kinetics with inhibition by carbon substrate. A comparison between basic properties of the three-phase fluidized-bed reactor and the reactor operating without immobilisation of microorganisms was accomplished.