Hydrodynamics analysis of biological reactors for effluent treatment is an essential step towards
reactor optimization. This is even more important for fluidized bed reactors, which have characteristic flow
patterns. The present chapter provides some background on the hydrodynamics of biological fluidized bed
reactors. The basic principles concerning the operation of this type of reactor are presented along with the
definition of some important parameters, such as, minimum fluidization velocity and the transition between
fluidized and fixed bed modes. At the end of the chapter, two case studies on the influence of adhered
biomass over the reactor hydrodynamics are analyzed. It is noteworthy that fundamental studies are still
required for a more comprehensive approach on this subject.
Keywords: Fixed bed, anaerobic fluidized bed reactors, holdup, pressure gradient, wastewater.
