WASTE WATER TREATMENT

PURPOSE:To increase the speed of a waste water treatment by hermetically communicating the waste water-microorganism mixture in a bioreaction vessel to a centrifugal separator, separating the mixture to a thickened liquid and clean liquid and hermetically returning the thickened liquid from the centrifugal separator to the bioreaction vessel. CONSTITUTION:The treated water in the liquid mixture 3 in the centrifugal separator 23 shifts to the clean liquid 25 and the greater part of the bacteria therein remain in the thickened liquid 24 and, therefore, the liquid 24 contains the bacteria at a high concn. The bacteria in the liquid 3 sent first to the centrifugal separator 23 by a circulation pump 22 are thickened and are returned to the bioreaction vessel 20 when the liquid 24 is returned to the vessel 20. The clean liquid 25 is discharged as treated water 6 through a water sealing device 26 in an ordinary operation. However, the liquid 25 is fed into the vessel 20 through a liquid level control valve 27 when the water level L in the vessel 20 is lowered by a decrease in the inflow rate of the waste water 1, etc.