METHOD FOR CONTROLLING INTERMITTENT AERATION TYPE ACTIVATED SLUDGE METHOD

PROBLEM TO BE SOLVED: To prevent secondary discharge of phosphorus in a final sedimentation basin by arranging an ORP meter to the final sedimentation basin and providing a lower limit threshold value to the ORP value and increasing the flow rate of return sludge from the final sedimentation basin to an aeration tank when the ORP measured value becomes this lower limit value or less. SOLUTION: In an intermittent aeration type activated sludge method constituted of first and second aeration tanks 2a, 2b removing phosphorus in sewage 1 by activated sludge, a final sedimentation basin 4 separating activated sludge to obtain treated water 3 and a return pump 5 returning sedimented activated sludge to the first aeration tank 2a, an ORP meter is provided to the final sedimentation basin and a return sludge flowmeter 11 is provided on the way of a sludge return route. The preset lower limit of ORP is set to RL with respect to the measured value R of ORP sent from the ORP meter 10 to a control unit 9 and, when R