| 摘要 |
<p>PROBLEM TO BE SOLVED: To simply and automatically extract excessive sludge and to hold the concn. of sludge in an aeration tank to a predetermined sludge concn. range by controlling a pump operating time from preset upper and lower limit concns. of activated sludge, change quantity and a pump operating time so as to increase or decrease the same. SOLUTION: Raw water is weighed by the weighing device 3 within a flow rate adjusting tank 1 and a proper amt. of raw water is supplied to an aeration tank 4 to be subjected to activated sludge treatment and the treated raw water is transferred to a sedimentation tank 6 to be subjected to solid-liquid separation treatment. The supernatant liquid stored in the upper part of the sedimentation tank 6 is discharged out of the system and sedimented sludge is returned to the aeration tank 4 by an air lift pump 7 through sludge mass 8 and excessive sludge is sent to a sludge concentrating and storing tank 9 by an air lift pump 14. At this time, the difference between the measured concn. of activated sludge and predetermined upper and lower limit concns. of activated sludge or concn. change quantity is calculated by a control unit 16 to increase and decrease the extracting time of excessive sludge. For example, when the concn. of activated sludge is equal to or more than the upper limit concn. of activated sludge, a pump operating time is increased.</p> |
