| 摘要 |
PURPOSE:To maintain the quality of treated water at satisfactory level by extracting specified amt. of sludge from a precipitation tank depending on a detected signal of anaerobic state of a sludge layer in the precipitation tank and returning the sludge to the precipitation tank. CONSTITUTION:An oxidation reduction potential sensing element 25 is provided to near the bottom of a precipitation tank 10 as a means for sensing that the inside of a sludge layer 3 of the precipitation tank 10 has changed to anaerobic state. And the flow rate of the sludge is performed by inputting the data concerning the oxidation- reduction potential in the sludge layer 3 into a controlling device 27 and adjusting the degree of opening of an electromotive valve 17 of a sludge transfer pipe 16 and an electromotive valve 21 of a return pipe 22 in accordance with the inputted signal. In this stage of separating precipitate, the settled sludge inside of the precipitation tank 10 is held at slowly moving condition in the inside of the sludge layer 3. Therefore, the anaerobic part in the inside of the sludge layer 3 is removed and denitrification reaction is retarded, moreover, formation of scum is prevented due to acceleration of defoaming. By this process, the quality of treated water is held at satisfactory level without causing mixing of sludge in the supernatant water.
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