METHOD FOR TREATING NITROGEN-CONTAINING WASTEWATER

摘要

PROBLEM TO BE SOLVED: To provide a method for treating nitrogen-containing wastewater capable of reducing the addition amount of organic matter, capable of efficiently reducing the formation amount of excess sludge and capable of stably obtaining treated water of high water quality. SOLUTION: Raw water, return sludge 11 and the ozone treated sludge 12 from an ozone treatment tank 6 are introduced into a first denitrification tank 1 to be subjected to denitrification treatment. The amount of introduced ozone treated sludge is regulated in the first denitrification tank to control the concentration of NOx-N of the liquid sent to a second denitrification tank 2 to 5 mg-N/l or more. The liquid in the first denitrification tank 1 is introduced into the second denitrification tank 2 and methanol 16 is injected to almost perfectly denitrify residual NOx-N. The denitrified liquid of the second denitrification tank is aerated and subsequently introduced into a sedimentation tank 4 to be subjected to solid-liquid separation treatment and a part of separated sludge is returned to the first denitrification tank as return sludge and the separated liquid is discharged as treated water. The separated sludge of which the pH is adjusted in a pH adjusting tank 5 is introduced into an ozone treatment tank 6 to be treated with ozone before introduced into the first denitrification tank.