FILTHY WATER DISPOSAL PLANT

PURPOSE:To effectively remove BOD, nitrogen components, etc., by providing a denitrification tank for anaerobic treatment, an anaerobic tank, a plurality of nitrification tanks for aerobic treatment, a solid-liquid separation means and a channel for returning sludge and a nitrified liquid to the denitrification tank. CONSTITUTION:Raw water (a) is mixed with returned sludge and let stay in a denitrification tank 1 under an agitated condition for a predetermined time. Hence, nitric ion, etc. are denitrified by denitrifying bacteria in the sludge while consuming BOD components. Outflow water from the denitrification tank 1 is introduced into an anaerobic tank 2, wherein microbes take up BOD components and discharge orthophosphoric acid instead. The mixed liquid effluent is transferred to a nitrification tank 3, wherein ammonia is converted into nitric or nitrous acid by microbes. The same treatment is repeated in another nitrification tank 4. The mixed liquid effluent from the nitrification tank 4 is introduced into a precipitate separation tank 5 to separate it into sludge composed of microbes having taken up phosphorus in their bodies and treated water (b) from which BOD, nitrogen and phosphorus components have been removed.