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High efficiency sedimentation tank of sewage treatment plant is one of the links of advanced treatment process, which is very important in sewage treatment process. It is just like a defender in football. Under the condition of very good operation, it can completely replace the goalkeeper. Recently, the performance of this "defender" has made me have to take special care of him, because the players with the best ability also have poor performance.


High efficiency sedimentation tank is developed from the theory of shallow tank, which is widely used in the field of urban water supply and drainage. It is mainly composed of fast coagulation area, flocculation area and inclined tube sedimentation area. By adding polyaluminium and polyacrylamide anion, most of the colloidal suspended matter, organic matter, phosphorus and some oil in the raw water can be removed. The mixed addition of the two agents can improve the sedimentation rate of alum. Abnormal conditions will also occur during operation:


(1) A small amount of sludge flocs floating up in the effluent


In a short period of time, the water load is large, resulting in shortened flocculation time. It can be operated by small pump or low liquid level. It can also reduce the mud surface in the sedimentation area, increase the sludge discharge, increase the effective volume and depth of the tank body, and reduce the short flow phenomenon.


(2) A large number of algae grow in the outlet channel, resulting in uneven outlet water


Due to a small amount of sludge attached to the outlet weir, green algae can be grown under the long-term sunlight. It can be cleaned manually regularly to increase the sludge discharge in the sedimentation area, or it can be covered on the tank body to reduce direct sunlight so as to prevent the growth of algae.


(3) Sludge floating up in the sedimentation area


Sludge retention time is long, organic matter is putrefactive, bottom sludge is anaerobic denitrification, so sludge discharge shall be increased, retention time of sludge and sewage shall be reduced, nitrification degree of biochemical system shall be reduced, dissolved oxygen of sedimentation tank shall be increased, and sludge concentration can be sampled and tested in part of bottom layer of the tank to confirm sludge discharge amount; in addition, dosage of polyaluminium and polyacrylamide anion shall be controlled, and polyaluminium dosage shall be short-term In the room, the turbidity of effluent will be reduced, but the sludge production will also be increased. The excess agent will destroy the sludge quality of the precipitated sludge, still cause the sludge to float up, which is not conducive to sludge concentration and sludge discharge. The excess polyacrylamide will also lead to the increase of COD of effluent.


The key to the operation of high efficiency sedimentation tank is to control the dosage of agent and sludge discharge. The correct dosage can be controlled by configuring the appropriate concentration of agent and adjusting the appropriate flow of the dosing pump. First of all, the normal operation of all the chemical dissolving equipment and dosing equipment must be ensured. Under the condition that a certain amount of reflux sludge concentration is ensured, proper sludge discharge and reflux sludge can reduce the dosage of agent, and ensure the quality of effluent under the condition of energy saving and consumption reduction.