PURIFIER

PROBLEM TO BE SOLVED: To effectively reduce the amt. of sludge by activating a microorganism in a first treating tank to allow it to contribute to the adsorption of org. matter, reactivating the microorganism in a second treating tank and returning the starved microorganism to the first treating tank to allow it again to contribute to the adsorption of org. matter. SOLUTION: A sewage supplied to a treating tank 12 is agitated by the air from a diffuser pipe 14 and supplied with oxygen, and the microorganism is activated. The sewage in the tank 12 is then discharged into a separation tank 56 by a pump 42 and provided with a pressurized water from a tank 60, and the solid material is supplied to the treating chamber 20a of a treating tank 20, agitated with the air from a diffuer pipe 22, replenished with oxygen and reactivated, and an activated sludge is generated in the treating tank 20. However, the microroganism in the tank 20 is starved and self-oxidized, and the sludge is decreased. A part of the sewage in the tank 20 is returned to the treating tank 12 by a sludge discharge pump 82.