Two reactor types, a fluidized bed reactor and a RotoTorque reactor, were tested for their suitability as model systems for immobilization studies of pure cultures of T. pantotropha. T. pantotropha is a very interesting organism for waste water treatment, because of its ability of simultaneous aerobic denitrification and heterotrophic nitrification. Results indicate that the RotoTorque reactor is a more attractive model system for immobilization studies of T. pantotropha than the fluidized bed reactor used in this study. Using the RotoTorque reactor, studies on immobilized growth of T. pantotropha are currently being performed under anaerobic conditions. At a dilution rate of 1.2 h-1 (about four-fold higher than mu(max) under the experimental conditions) rapid attachment of T. pantotropha can be reproducibly observed. Within a couple of days, the cultures reach a 'steady state', where growth of the attached biomass is balanced by erosion. Microscopic investigations of the attached biomass indicated that T. pantotropha forms microcolonies rather than homogeneous biofilms.
