PURPOSE: To keep a constant value of dissolved oxygen content (DO) in an aeration tank by a method wherein the measured results of DO in the tank is used so that when sewage flow rate is reduced, the quantity of air to the tank is decreased below the limit value of surging (vibration of blower and blast tube caused by reduced blow rate of air).
CONSTITUTION: Dissolved oxygen meter 7 measures DO and obtains deviation value ΔDO from the target value DO*. The proportion integration regulator 11, in accordance with ΔDO, provides the quantity of air Q*A necessary for compensating for it. The Q*A enters the comparator 14 and is compared with surging limit value QAL. If Q*A is smaller than QAL and therefore surging is likely to occur, relay 15 receives command from the comparator 14 and connect loop of the air-quantity controller 16 from the proportional integration regulator 11, so that air blast valve is controlled. That is, based on the measured air blast quantity QA from the valve opening-degree meter 8, targer valve opening-degree value V*A1 of flow control valve 5 is calculated and operagion/stop at valve motor 6 is controlled.
TANUMA MASAYA
KAWANO SHIGEYOSHI
KASHIWAGI MASAHIKO
SUGIURA MOTOHIRO
KATO NAOJI
HITACHI ENG CO LTD