| 摘要 |
<p>PROBLEM TO BE SOLVED: To prevent clogging of a membrane module and flux deterioration and smoothly carry out treatment by turning back treated water after membrane separation to a raw water tank and keeping the liquid level at a prescribed level or higher when the liquid level of the raw water tank is lowered to the prescribed level. SOLUTION: A turning back circuit 6A is installed in the outlet side of a membrane separation apparatus 2 to turn back treated water to a raw water tank 4. A separated water turning back valve 6 whose opening and closing is controlled by a controller 3A based on the detection signal of the liquid level detection apparatus 3 is installed in the middle of the circuit. Consequently, when the liquid level of the raw water tank 4 is lowered to an optionally set lower limit level L, the controller 3A opens the separated water-turning back valve 6 based on the detection signal of the liquid level detection apparatus 3. As a result, the treated water after the membrane separation is turned back to the raw water tank 4 through the turning back circuit 6A and the liquid level in the raw water tank 4 is recovered to the prescribed level or higher. The prescribed level is the same as the lower limit level L and may be determined in consideration of time lag. In this way, the liquid level in the raw water tank is kept constant and the MLSS concentration is made even and clogging of a membrane module can be prevented.</p> |
