A device for the treatment of an influent with a nonbonded media, and when
the media becomes spent, the media is fluidized with a backwash fluid.
Concentric inner and outer perforated cylinders contain a column of media
therebetween. The influent is passed radially inwardly through the column
of media and into the lower portion of the inner perforated cylinder,
where the effluent is removed from the device. During a backwash
operation, a backwash fluid is forced into the lower portion of the inner
perforated cylinder, radially outwardly into the column of media to
provide an upwardly directed drag force. When the drag force exceeds the
buoyant weight of the media, the media is fluidized so that the
contaminants can be removed therefrom by the backwash fluid.