Abstract: A filter including a combination bypass valve and anti-drain valve is disclosed herein. The filter includes an annular valve support which supports an annular valve member disposed between the support and a filter cartridge. The valve support has an inner sleeve portion which seats against an end plate and an outer sleeve portion including bypass louvers therethrough. The valve member has an expandable collar portion which normally seals the bypass louvers and a skirt portion which normally seals inlet openings extending through the end plate. The skirt permits flow through the inlet openings into the filter but prevents out of the filter through the inlet openings. Excessive pressure caused by a clogged filter element deflects the expandable collar away from the bypass louvers thereby permitting flow to bypass the filter element.

Abstract: To desludge the final settlement tank of a waste water treatment plant which includes a bio zone equipped with slowly rotating rotors on which biomass deposited from the waste water is digested by microorganisms as the biomass is periodically exposed to air, the level of liquid in the final settlement tank is raised above that in the bio zone so that gravity induced desludging can occur. One of the rotating rotors can be equipped with water lifting means to generate the required hydraulic head for desludging.Skimming off of scum from the surface of the water in the final settlement tank can also be effected using the hydraulic head between the tank and the bio zone.