BIOLOGICAL DENITRIFICATION APPARATUS

PURPOSE:To efficiently treat sewage, by providing an oxygen-containing gas supply means at the intermediate position in the up-and-down direction of a sludge bed and setting the lower part of said sludge bed to a denitrification part while setting the upper part thereof to an oxidizing part. CONSTITUTION:Raw sewage having an org. substance (methanol) injected therein through an org. substance injection line 5 is supplied to the lower part of a reaction tank 51 through a sewage inflow line 4. Air is introduced into the granular sludge bed 7 formed in the reaction tank 51 at the intermediate position thereof in the form of fine air bubbles from an air diffuser 53 through an air pipe 52 to supply oxygen to the granular sludge bed 7. The raw sewage denitrified herein by the action of denitrifying bacteria undergoes the oxidative decomposition treatment of the excessive org. substance. Further, the sewage reaches the gas-liquid-solid separation part 8 above the sludge bed to be separated into treated water, gas and sludge. By this method, the capacity of the tank can be miniaturized.