60 inches application_number US 45219489 A description according to the present invention substances are removed from a liquid by directing the liquid through a filter bed comprising flocculated active particulate material in the average size range of from about 5 0 to about 100 microns most preferably from about 30 microns to about 100 microns and having a depth in the range of from about 3 0 inches to about 60 inches most preferably from about 10 inches to about 40 inches it is unexpected that the pressure drops through beds of finally divided materials of such depths are quite similar to those exhibited by beds of normal size bead resins the active particulate material may be flocculated by mixing same with a filter aid material having an opposite surface charge the desired surface charge may be imparted to the filter aid material in the manner as described in u s pat no 4 238 334 which patent is assigned to the assignee of the present invention and is incorporated herein by reference the flow rates through the bed are preferably greater than about 0 02 gm ft 2 most preferably greater than about 0 2 gpm ft 2 and the pressure differential therethrough is generally less than about 3 0 psi in at 5 gpm ft 2 most preferably less than about 1 0 psi in at 5 gpm ft 2 the filter bed includes an active particulate material that is selected dependent upon the specific application in a well known manner the active particulate material preferably comprises from about 5 0 percent to about 99 percent by weight in accordance with presently considered preferred embodiments of the invention.