METHOD FOR TREATING WASTE WATER

摘要

PROBLEM TO BE SOLVED: To obtain satisfactory reduction effect on sludge in volume without deteriorating COD of processing water to be treated in a biological treating tank. SOLUTION: In such a waste water treating system 10 that organic waste water is treated biologically in the biological treating tank 1 by using activated sludge, a sludge-mixed liquid discharged from the tank 1 is separated in a solid-liquid separating tank 2 and the separated activated sludge is returned to the tank 1 again, at least a part of the sludge to be returned is introduced into a sludge treating unit 5 and subjected to WJ treatment. The amount of the activated sludge to be subjected to WJ treatment is adjusted according to a sludge treating ratio shown as the ratio of the amount of the activated sludge to be subjected to WJ treatment to that of the activated sludge to be held in the tank 1.