A hydrodynamic characteristic performance of a three phase fluidised bed bioreactor has been studied with brewery wastewater. The influence of operating parameters, such as phase hold up, phase mixing, aspect ratio and superficial gas velocity, on an aerobic biodegradation in a bioreactor of 0.16 m i.d. and 2.7 m in height, was analysed. A low-density (960 kg/m(3)) Support particle with an internal interstice was employed. The particle and liquid loading were varied in order to determine the effect of phase hold up on bed homogeneity. The ranges in which particle loading and bed height affect fluidisation, and consequently chemical oxygen demand (COD) reduction, were determined. The distributor used in this work was designed such that fluid flow pattern similar to that of a draft tube was induced in the reactor. The low-density particles enabled cost effective operation at a relatively low gas superficial velocity (2.5 cm/s). Aspect ratio significantly influenced the overall bed homogeneity, and the optimum aspect ratio was 10, with volume of the support particles being 21% of the reactor volume. (C) 2002 Elsevier Science B.V. All rights reserved.