Abstract: In the filtration cycle, a fluid such as water containing suspended solid waste matter is treated with a coagulating agent and gravity-fed through a plurality of individual filter cells, or modules, containing a particulate, coarse, granular filter media. Backwashing is effected by injecting water into the filter media at the bottom center of the cell, causing the filter media to well upwardly and to form on the surface a series of polarly oriented ridges and troughs, the troughs serving to guide "mudballs" and coagulant particles on the media into an inlet port connected to the injector pipe where the high pressure water breaks up the mudballs into manageable particle sizes and scours the media. Solid particles suspended in the water overlying the media are drawn off through a backwash overflow and are fed into a clarifier where separation is effected and clarified water is provided for re-injection into the media.