Moving bed (MBBR)
Fluidized beds are three-phase (gas-liquid-solid) reactors formed by an ensemble of small-sized materials (generally plastic rings with different forms, as BIOFILL® type C), on which the biomass remains attached the filling floats and through flows constantly wastewater at a sufficient speed to cause all the mass in the bed to move, as shown in the attached video. In a fluidized bed, most of the biomass is stuck onto the filling material’s surface, in comparison to the small proportion in suspention.
In order to achieve the flow speeds needed, a recirculation is done with part of the effluent and a complementary agitation. The liquid current generated by the recirculation, the feeding and the aeration goes through the inferior part of the reactor.
The fluidized bed system has been proved as extremely efficient, much more than suspended biomass and anaerobic systems, which show a very slow growing of the biomass. The fluidized bed reactors allow to work with very high volume charges, surpassing every type of digester used in wastewater anaerobic treatment.
Advantages of the fluidized bed reactors are:
- Adhesion of the microorganisms to the support elements, thus creating what is known as biofilm, which allows to reach high concentrations of active biomass with the consequent intensification of the process and reduction of the reactor’s physical volume.
- Biomass retention onto the supporting material prevents it from being easily removed from the reactor.
- Matter transfer speed between the particles and the fluid is high compared with other contact methods.
- Few operating personnel is required to maintain these systems in good operating conditions.