Abstract: A unit is disclosed for removal of impurities present in liquids such as waste water effluent. The unit comprises a vessel containing a loose quantity of particulate treating material for absorption or reaction with the impurities in the liquid. A wall of the unit has multiple small openings therein, each of the openings filled with a finely-divided, compacted, particulate filter material such as diatomaceous earth which is retained in the openings by one or more layers of a woven inert material such as nylon or polyester having mesh openings sufficiently small to prevent passage of the particulate filter material therethrough. The woven material is secured over the outer surface of the openings in the wall of the vessel.