Questions of Suspended Solids in the Secondary Sedimentation Tank

In sewage treatment process,the function of the secondary sedimentation tank is to separate sludge and water to clarify the biologically treated mixed liquor, and to concentrate the sludge in the mixed liquor.

QUESTION:High content of suspended solids in the effluent of the secondary sedimentation tank

The reasons for the increase of suspended solids content in the effluent of the secondary sedimentation tank and the corresponding solutions are as follows:

REASON 1:

The activated sludge bulking makes the sludge settling performance worse, the sludge water interface is close to the water surface, and some sludge fragments overflow through the effluent weir.

The countermeasure is to eliminate sludge bulking one by one by analyzing the causes.

REASON 2:

The sudden increase of water inflow will increase the hydraulic load on the surface of the secondary sedimentation tank, leading to the increase of the rising flow rate, affecting the normal sedimentation of activated sludge, and the water flow carrying sludge debris overflows through the outlet weir.

The countermeasure is to give full play to the role of the regulating tank and make the inflow as balanced as possible.

REASON 3:

There are too many algae in the outlet weir or the outlet sump.

The countermeasure is that operators should remove these algae in time.

REASON 4:

The concentration of activated sludge in the aeration tank is high, the sludge water interface of the secondary sedimentation tank is close to the water surface, and some sludge fragments overflow through the effluent weir.

The countermeasure is to increase the discharge of excess sludge.

REASON 5:

The disintegration of activated sludge causes the reduction or disappearance of sludge flocculation, and sludge fragments flow out with water.

The countermeasure is to find out the causes of sludge disintegration, eliminate and solve them one by one.

REASON 6:

The working condition of the suction (scraper) sludge machine is not good, resulting in short flow of sludge or water in the secondary sedimentation tank. Local sludge can not return in time. Some sludge stays in the secondary sedimentation tank for a long time, and the sludge will overflow with the water flow after anaerobic decomposition.

The countermeasure is to repair the mud suction (scraping) machine in time to restore it to normal working condition.

REASON 7:

The activated sludge stays in the secondary sedimentation tank for a long time, and the sludge will overflow with the water after disintegration due to anoxic decay.

The countermeasure is to increase the amount of returned sludge and shorten the retention time in the secondary sedimentation tank.

REASON 8:

When the water temperature is high and the nitrate content in the water is high, the secondary sedimentation tank will experience denitrification and denitrification of sludge, and the large sludge wrapped in nitrogen will float to the water surface and overflow with the water flow.

The countermeasure is to increase the amount of returned sludge and shorten the retention time of sludge in the secondary sedimentation tank.

The secondary sedimentation tank is the last link of biological treatment in sewage treatment process, which plays a decisive role in ensuring that the suspended solids content in the effluent quality is qualified.

#QDEVU #SEWAGETREATMENT #WASTEWATERTREATMENT #WATERTREATMENT