What is a sedimentation tank? What is the principle of a sedimentation tank?

What is a sedimentation tank? What is the principle of a sedimentation tank?

1、 What is a sedimentation tank?

A sedimentation tank is a treatment structure that uses gravity sedimentation to remove suspended particles with a higher density than water from water. It is one of the most widely used treatment units in wastewater treatment and can be used for wastewater treatment, post-treatment of biological treatment, and deep treatment. The application of sedimentation principle in the sedimentation tank can remove inorganic impurities in water, the application of sedimentation principle in the initial sedimentation tank can remove suspended solids and other solid substances in water, the application of sedimentation principle in the secondary sedimentation tank can remove activated sludge in biological treatment effluent, and the application of sedimentation principle in the concentration tank can separate the water in sludge and concentrate the sludge, In the field of advanced treatment, the application of sedimentation principle can remove suspended solids in water after adding coagulants to the effluent of secondary sedimentation tanks for coagulation reaction.

The sedimentation tank consists of five parts: inlet area, sedimentation area, buffer area, sludge area, and outlet area. The function of the inlet and outlet zones is to evenly flow water through the sedimentation tank, avoiding the adverse effects of short flow and reduced turbulence on sedimentation cattle production, while reducing dead water zones and improving the volume utilization rate of the sedimentation tank; The sedimentation zone, also known as the clarification zone, refers to the working area of the sedimentation tank, which is a sufficient area for separating precipitated particles from wastewater; The sludge area is the area where sludge is stored, concentrated, and discharged; The buffer zone is the water layer area that separates the sedimentation zone and the sludge zone, ensuring that the settled particles do not float again due to water flow agitation.

2、 What is the principle of a sedimentation tank?

A sedimentation tank is a water purification system that utilizes the principle that suspended impurity particles in the water flow can separate from the water flow when the settling speed is greater than the flow speed of the water flow, or the settling time is less than the time when the water flows out of the sedimentation tank.

The treatment efficiency of an ideal sedimentation tank is only related to surface load, that is, to the surface area of the sedimentation tank, and is not related to the depth of the sedimentation tank. The depth of the tank is only related to factors such as the time and quantity of sludge storage and the prevention of sludge erosion. In actual continuous operation sedimentation tanks, due to the overflow of water from the top of the outlet weir, particles with a sedimentation rate lower than the rising flow rate will follow the water flow, particles with a sedimentation rate equal to the rising flow rate will be suspended in the tank, and only particles with a sedimentation rate greater than the rising flow rate will settle in the tank. The time for settling particles to settle at the bottom of the sedimentation tank is related to the hydraulic retention time of the water flow in the sedimentation tank, that is, it is related to the depth of the tank body.

In theory, the shallower the tank, the easier it is for particles to reach the bottom of the tank, which is the theoretical basis for shallow sedimentation tanks such as inclined tube or inclined plate sedimentation tanks. In order to allow particles slightly larger than the rising flow rate in the sedimentation tank to settle and prevent sludge that has already settled from being disturbed by the incoming water flow and resurfacing, a buffer zone is left between the sedimentation area and sludge storage area, allowing particles slightly larger than the rising flow rate or resurfacing particles in these sedimentation tanks to come into contact with each other and settle again.

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