| 摘要 |
PROBLEM TO BE SOLVED: To prevent deterioration of water quality caused by adhesion of huge flocs of flocculated microorganism and flowing-in soil to bottom of a floc formation tank 6 and their putrefaction in the case the bottom is formed in the tank 6. SOLUTION: A floc formation tank has a shape formed by joining a cylinder and a right cone having a head and the shape satisfies the following: A2/B2=50-280 wherein A denotes the diameter of the cylinder and B denotes the diameter of the head of the (right) cone having the head. Even if water discharge amount is greatly fluctuated owing to a holiday or the like, the supernatant liquid 25 in a precipitation tank 29 is supplied to the (right) cone having the head from a fluidizing and circulating pump 19 through a blowing-up pipe 18 with the diameter (B) connected to the head 17 of the cone having the head. If the supply is performed at lowest a supply speed which is the minimum fluidizing speed in a circle surface area equivalent to B2×20 as the surface area of the circle formed by cutting the (right) cone having the head in a round slice, the flocs are moved fiercely in the section lower than the position of the cutting in a round slice and the flocs thus do not adhere to improve the water quality and operation control is made easy.
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