DEVICE FOR TREATING DIFFICULT-TO-DECOMPOSE SUBSTANCE

PURPOSE:To enhance the efficiency in utilizing ozone and to reduce the ozone treatment cost in the device in which a water contg. difficult-to-decompose substances is treated with ozone and then biologically treated by measuring the biogradability of the ozone-treated water and adjusting the ozone supply based on the measured value. CONSTITUTION:The device for treating a waste water contg. difficult-to- decompose substances such as the waste water contg. acrylonitrile from the chemical plant and the waste fiber scouring water contg. poval is formed by a pretreating device consisting of an ozonizer 1 and an ozone oxidation tower, an ozone-treated water tank 3 and a biological treating device 4 such as an activated-sludge treating device. In this case, a part of the ozone-treated water discharged from the ozone oxidation tower is drawn off, the remainng ozone is removed in an ozone removing tank 5, the BOD is automatically measured by a BOD meter 6 (biogradability meter), and the ozone output of the ozonizer 1 is automatically adjusted by an adjuster 7 based on the measured value so that the BOD/CODcr for example, is controlled to about 20%.