Some fluidization characteristics of biological beds.

The free-fall terminal velocity of particles coated with a nitrifying biofilm was investigated. The drag force exerted by the liquid on a biocoated particle was found larger than that for an uncoated particle. A new formula for the drag coefficient was proposed. The wet density of biofilm was estimated as 1.14 g/cm(3). A proposed modification of the Zaki-Richardson method was successfully used for calculations of the porosity of a fluidized bed.