The high efficiency sedimentation tank is a kind of structure which uses sedimentation to remove suspended matters in the water and it is an equipment to purify the water quality. The suspended matter in water can be removed by natural sedimentation or coagulation sedimentation. The sedimentation tank is divided into horizontal sedimentation tank and vertical sedimentation tank according to the flow direction. The sedimentation effect depends on the flow rate of water and the residence time of water in the high efficiency sedimentation tank.

The high-efficiency sedimentation tank is generally a structure for separation of sludge and water before or after biochemical treatment, and most of them are the sludge with fine particles. Before biochemical treatment, it is called primary sedimentation tank, which has more inorganic components and lower water content than secondary sedimentation tank. The sedimentation tank after biochemical treatment is generally called secondary sedimentation tank, which is mostly organic sludge with high moisture content.

Clarifier: the coagulation process of water and wastewater includes three stages: mixing of water and agent, reaction and separation of flocculent and water. The clarifier is a special equipment to complete the above three processes.

In the clarifier, the medium that can intercept and separate the impurity particles is suspended sludge. In the clarifier, the sludge is lifted up and placed in a suspension state of uniform distribution. A stable active sludge layer with high concentration is formed in the clarifier. The concentration of suspended solids in this layer is about 3-10g / L. The raw water in the clarifier is from bottom to top, and the sludge layer can be in a dynamic equilibrium state in the rising water flow due to the gravity effect. When the raw water passes through the sludge suspension layer, based on the contact flocculation principle, the suspended solids in the raw water will be blocked by the sludge suspension layer to make the water clear. Clear water is collected in the upper part of the clarifier.

The rising velocity of the sludge suspension layer is related to the volume and concentration of the sludge. Therefore, the correct selection of the rising velocity and the maintenance of a good sludge suspension layer are the basic conditions for a better treatment effect of the clarifier.

At present, the commonly used clarifiers in wastewater treatment are: mechanical accelerated clarifier, hydraulic circulating clarifier, suspended clarifier and pulse clarifier.

The traditional water supply treatment process includes four parts: coagulation, sedimentation, filtration and disinfection. Generally, when we compare the sedimentation tank with the clarifier, we refer to the four parts of the water supply process, because the clarifier is more common in the water supply process (that is, the water plant and the China Water plant).

In fact, generally speaking, the clarifier is also one of the sedimentation tanks, but it is different from the sedimentation tank. Because the sedimentation tank generally only includes the process of particles (masses) sinking in the water due to the gravity greater than the buoyancy, and then separating from the incoming water.

However, clarification is actually equivalent to two parts of "coagulation" + "precipitation" (among which there are also filter components). Because in the clarifier, it is generally necessary to add chemicals to generate alum flowers (this is the process of coagulation), and then suspend alum flowers through mechanical or hydraulic agitation to play a certain role in filtration, and then separate the solid and liquid through the principle of sedimentation, so the effluent is relatively clear.