Hydrodynamics of a gas–liquid–solid fluidised bed bioreactor with a low density biomass support

Abstract

The hydrodynamics of a gas–liquid–solid fluidised bed bioreactor with a low density biomass support (matrix density smaller than that of water) was investigated. In particular, a minimum fluidisation air velocity U gf and an air holdup ϵ g were measured in a bioreactor with KMT ® (Kaldnes Miljotechnologi AS) particles used as biomass support. It was found that values of U gf depended on the ratio of bed (settled) volume to bioreactor volume ( V b/ V r) and the mass M bp of cells grown on the particles. For a given mass M bp, the values of U gf increased with an increase in the ratio of ( V b/ V r). The values of U gf were strongly affected by the mass M bp and decreased with an increase in M bp. There was a critical ratio ( V b/ V r) cr above which movement of the whole bed was impossible: the particles either remained at the top of the bioreactor or settled at its bottom. The values of ( V b/ V r) cr for which this was happening depended on the mass M bp and decreased with an increase in M bp. It was established that the air holdup ϵ g depended on the air velocity U g, the ratio ( V b/ V r) and the mass M bp. For a given ratio ( V b/ V r) and mass M bp, the values of ϵ g increased with an increase in the air velocity U g. The optimal ratios ( V b/ V r) o for which the largest values of ϵ g were obtained depended on the mass M bp. The values of ( V b/ V r) o decreased with an increase in M bp. It was also established that the values of ϵ g obtained in a bioreactor with the KMT ® particles were approximately 40% larger than those reported in the literature for bioreactors with other low density support media such as spheres and toroids. It was therefore concluded that the large values of the air holdup achieved with the KMT ® particles merit their application as a biomass support for high-rate aerobic biological treatment of industrial and municipal wastewaters.