Design and Construction Plan for Flocculation Tanks in Water Plant Water Supply and Drainage Systems

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Design and construction plan for the flocculation tank in water treatment plants: The flocculation tank should be constructed together with the sedimentation tank. The selection of the flocculation tank type and the determination of the flocculation time should be based on the quality of the raw water, operational experience under similar conditions, or through testing. When designing a partitioned flocculation tank, the following requirements should be met: 1. The flocculation time is generally preferably 20–30 minutes ； 2 The flow velocity in the channels of the coagulation tank should be designed to decrease gradually from one end to the other; the flow velocity at the starting end should be 0.5–0.6 m/s, while it should be 0.2–0.3 m/s at the ending end ； 3 The clear distance between partitions should be greater than 0.5 m. When designing mechanical flocculation tanks, the following requirements should be met: 1 The flocculation time should be between 15 and 20 minutes ； 2 The tank is equipped with a mixer featuring 3–4 speed settings ； 3 The speed of the mixer should be determined through calculation based on the linear velocity at the edge of the pulp board; this linear velocity should gradually decrease from 0.5 m/s in the first gear to 0.2 m/s in the final gear ； 4 Facilities to prevent short-circuiting of water flow should be installed in the pool. When designing a folded-plate flocculation tank, the following requirements should be met: 1. The flocculation time is generally recommended to be between 12 and 20 minutes ； 2. The velocity during the flocculation process should be reduced in stages, with no fewer than three stages; the flow velocities for each stage can be as follows: First stage: 0.25–0.35 m/s ； Second paragraph: 0.15～0.25 m/s ； Third paragraph: 0.10～0.15 m/s ； The angle of the 3-fold clamping plate should be between 90° and 120° ； 4 The third paragraph should use a straight format. When designing grid-type coagulation tanks, the following requirements should be met: 1. The coagulation tank should be designed as a multi-chamber vertical flow type ； 2 The flocculation time is generally recommended to be 12–20 minutes; when treating water with low temperature and low turbidity, this time can be appropriately extended. 3 The flow velocities in the vertical shafts of the flocculation tank, as well as the flow velocities through the grids and holes, should decrease gradually from one section to another. It is advisable to divide this into three sections; the respective flow velocities are as follows: the average flow velocity in the vertical shafts is 0.14–0.12 m/s in the first and middle sections, and 0.14–0.10 m/s in the last section ； Flow velocity through the grid: 0.30–0.25 m/s in the upstream section, 0.25–0.22 m/s in the middle section ； Volumetric flow rate through the holes between shafts: 0.30–0.20 m/s in the upstream section, 0.20–0.15 m/s in the middle section, and 0.14–0.10 m/s in the downstream section. 4 The flocculation tanks should be arranged in 2 or more parallel groups. 5 The flocculation tank should be equipped with sludge discharge facilities.