Activated sewage plant and process

A filter especially designed for use in filtering the effluent flowing from the settling tank of an activated sewage plant to a clearwell and chlorinating vessel having an effluent discharge comprising:

• a. a vessel having a bottom and side walls and having a perforate false bottom spaced above the bottom,
• b. a filter bed not less than 6 feet in depth supported on said false bottom and comprised of hard gravel-like quartz sand, the particles of which are rounded and non-angular and in the general size ranging between 1 mm and 3 mm in the greatest dimension and with the particles in the bed predominantly varying from one another but not substantially more than 1 mm, said filter having a valved discharge outlet from the space below the false bottom for the collection of filtered water, said filter having means for forcing air under pressure into the space under the false bottom when said valved outlet is closed, said filter having means for forcing backwash water into the space under the false bottom when air is also being forced into said space, said filter having a head space above the filter bed for receiving water to be filtered and having an overflow weir into which water flows when the water is being backwashed.