| 摘要 |
<p>PROBLEM TO BE SOLVED: To keep a high water permeating rate and low turbidity of permeated water over a long period by equipping a turbidimeter for measuring the turbidity after permeation in a permeated liquid line further arranging a switching valve and a return line for returning the permeated liquid to a biologically treating vessel when the turbidity of the permeated liquid becomes equal to or above a specific value. SOLUTION: At the time of normal filtration, a biologically treated liquid in a biologically treating vessel 2 is filtered and treated by a filtration body 1 by operating a suction pump 8 and the permeated liquid is sent through a permeated liquid line 5. At this time, a valve 7a in the permeated liquid line 5 is opened and a valve 7b in a washing line 3 and a valve 7c in a return line 6 are closed. Then, when the measured value of a turbidimeter 4 disposed in the permeated line 5 is >=50, each of the valve 7a and 7b is closed and the valve 7c is opened to return the permeated liquid to the biological reaction vessel 2 through the return line 6. As a result, the permeated liquid increased in the turbidity is filtered again in the biologically treating vessel 2 to keep the turbidity of the permeated liquid constantly low and to prevent the lowering of a water permeation rate.</p> |
