Effects of biofilm growth, gas and liquid velocities on the expansion of an anaerobic fluidized bed reactor (AFBR)

An anaerobic fluidized bed reactor, with 30 1 sepiolite particles as support material was used to study the influence of biofilm growth and biogas production over hydrodynamic behaviour. It was verified that although gas production transforms the AFBR from a two-phase fluidized bed to a three-phase gas-liquid-solid system, the formation of a gas phase has little effect over hydrodynamic behaviour, and therefore it is possible to describe the bed as like a two-phase solid-liquid system. However biofilm development has a more important effect on the hydrodynamic behaviour, so it is necessary to reduce the recirculation ratio to maintain a set expansion, when the attached volatile solids increase. The superficial velocity necessary to maintain a 20% bed expansion, decreased from 11.5 m/h for clean particles, to 9.0 m/h for 20 g/l attached volatile solids concentration. The growth of the biofilm varies throughout the reactor, increasing the natural variation in the size of the particles in the bed.