PURPOSE: To prevent the carry over of dissolved oxygen into an anaeration tank by the endogenous denitrification and endogeneous respipration in a mixing tank and to improve the efficiency of denitrification and dephosphorization by injecting a circulating nitrifying liquid into the mixing tank and mixing this liquid with return sludge, then returning the sludge to the anaeration tank.
CONSTITUTION: The nitrifying liquid delivered from an aeration tank 6 by a pump P2, is injected from a circulating path 3 into the mixing tank 7 interposed in a return sludge path 4. The sludge settled in a final settling tank 2 is put into the mixing tank 7. The nitrifying liquid is also injected via the circulating path 3 by a pump P2. into the mixing tank 7 and is mixed with the sludge. The sludge mixed with the nitrifying liquid in the mixing tank 7 is intermittently returned by a pump P1, to the anaeration tank 5 in the front stage of the aeration tank 1. Since the nitrifying liquid is incorporated into the sludge in the mixing tank 7, the nitrate nitrogen in this nitrifying liquid is partly removed by the endogeneous denitrification. The dissolved oxygen is consumed by the endogeneous respiration.
KUSUMI MIYOKO
WADA NOBUYUKI
