What Is a Sedimentation Tank?

Sedimentation tank is a structure that removes suspended matter in water by sedimentation and purifies water. Use the natural precipitation or coagulation of water to remove suspended matter in water. The sedimentation tank is divided into horizontal sedimentation tank and vertical sedimentation tank according to the direction of water flow. The precipitation effect is determined by the water flow rate and the residence time of the water in the sedimentation tank. In order to improve the sedimentation effect and reduce the area of land, honeycomb inclined tube countercurrent sedimentation tanks, accelerated clarification tanks and pulse clarification tanks are currently used. Sedimentation tanks are widely used in wastewater treatment. Considering the flocculation factors in the process of particle sedimentation, it is assumed that the sedimentation speed of the particles changes with constant acceleration, and the initial sedimentation speed is set to zero. Considering the flow velocity distribution in the tube, the length of the inclined tube is: -d * tg where a is the acceleration of the particle sedimentation velocity change, that is, a = du / dt. The above three methods each have disadvantages. ^[1]

The surface of the sedimentation tank is rectangular, and the inlet is set at the end of the tank. Generally, the water inlet is submerged. The ground is distributed across the width of the pool. The outlet of the sedimentation tank is located at the other end of the tank.

The sedimentation tank is generally a structure for the separation of mud and water before or after the biochemical process, and most of them are sludge with finer particles. Before biochemical

Inclined tube onclick = "g (sedimentation tank); The design principle of the sedimentation tank creates ideal laminar flow conditions and improves the removal rate. It is necessary to control the thunder number Re =. Due to the wet p of the inclined tube, Re can be controlled below 200 Is much smaller than the laminar flow limit of 500. From the Froude number Fr =, we know that

The basic requirements for the operation and management of the sedimentation tank are to ensure that the equipment is safe and intact, to timely adjust various operating control parameters to ensure that the quality of the effluent water reaches the specified indicators. To this end, we should focus on the following areas.

Avoid short flow in sedimentation tank

The flow of water entering the sedimentation tank usually stays in the pool for a different time. The retention time of a part of the water is shorter than the design retention time and flows out quickly.

Liugang swirling sedimentation tank

Outside the pool; the other part of the residence time is longer than the design residence time. This phenomenon of different residence time is called short flow. The short flow shortens the residence time of some water and does not get sufficient sedimentation, which reduces the sedimentation efficiency. The residence time of other water may be very long, even in the dead water area where the water flow is basically stagnant, reducing the effective volume of the sedimentation tank. In short, short flow is one of the main reasons affecting the effluent quality of the sedimentation tank. There are many reasons for the short-flow phenomenon, such as the excessively high flow velocity into the sedimentation tank; the unit weir length of the outlet weir is too large; the distance between the inlet and outlet areas of the sedimentation tank is too close; the water surface of the sedimentation tank is affected by strong winds; the pool water is exposed to sunlight Causes changes in water temperature; the difference between the density of the incoming water and the water in the pool; and the presence of pillars, diversion walls, and mud scraping facilities in the sedimentation tank can form a short-flow image.

Sedimentation tank with coagulant

When the sedimentation tank is used for liquid-solid separation of the coagulation process, the correct addition of coagulant is one of the keys to the operation management of the sedimentation tank. To achieve the correct addition of coagulant, it is necessary to grasp the changes in the quality and volume of the incoming water. Taking drinking water purification as an example, the turbidity, pH, water temperature, and alkalinity of raw water are usually measured once every 2-4 hours. In frequent seasons of water quality, a measurement is required every 1-2 hours to understand the start and stop status of the inlet pump room and adjust the dosage in time according to the changes in water quality and water volume. In particular, we should prevent drug withdrawal accidents, because even if the dosing is stopped for a short period of time, the quality of the effluent water will deteriorate.

Settling sludge in a timely manner

The timely discharge of sludge is an extremely important task in the operation and management of the sedimentation tank. The sedimentation tank in sewage treatment contains a large amount of sludge, most of which are organic matter. If the sludge is not discharged in time, anaerobic fermentation will occur, causing the sludge to float, which not only disrupts the normal work of the sedimentation tank, but also The effluent quality is deteriorated, such as the increase of soluble BOD value in the effluent water and the decrease of pH value. The sludge drainage period of the primary sedimentation tank should generally not exceed 2 days, and the drainage period of the secondary sedimentation tank should generally not exceed 2 hours. When the sludge drainage is not complete, the pond should be stopped (emptied) and the mud should be cleaned manually. The sedimentation tank for mechanical sludge drainage should strengthen the maintenance and management of the sludge drainage equipment. Once the mechanical sludge drainage equipment fails, it should be repaired in time to avoid excessive sediment accumulation at the bottom of the pond and affect the water quality.

Sedimentation pond prevents algae

In the sedimentation tank in the water supply treatment, when the raw water algae content is high, it will cause algae to breed in the pond, especially in areas with high temperature, when the inclined tank is installed in the sedimentation tank, this phenomenon may be more prominent. Although algae breeding will not seriously affect the operation of the sedimentation tank, it is not good for the water quality of the effluent. Preventive measures are: add chlorine to the raw water to prevent algae growth. The use of ferric chloride coagulant also has an inhibitory effect on algae.