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Questions of Sludge in the Secondary Sedimentation Tank
2022-11-21 14:28:49

Questions of Sludge in the Secondary Sedimentation Tank

 

The secondary sedimentation tank is an important part of wastewater treatment, which is mainly used to separate the sludge, make the mixed liquor clear, concentrate and return the activated sludge. Once the secondary sedimentation tank has mud running, mud floating, turbidity and other phenomena, its working effect can directly affect the effluent quality and return sludge concentration of the activated sludge system.

 

QUESTION:Sludge Floating in Secondary Sedimentation Tank   

Sludge floating in the secondary sedimentation tank refers to the phenomenon that sludge floats to the surface of the secondary sedimentation tank due to acidification or denitrification of sludge in the secondary sedimentation tank. The floating sludge itself has no quality problem, and its biological activity and sedimentation performance are normal.

REASON:

The main reason for floating is that these normal sludge stay in the secondary sedimentation tank for a long time, and the dissolved oxygen is gradually consumed, leading to acidification. The gas produced, such as H2S, attaches to the sludge floc, reducing its density and causing the sludge to float up.

When the SRT of the system is long, after nitrification, the mixed liquor entering the secondary sedimentation tank will contain a large amount of nitrate. The sludge in the secondary sedimentation tank will undergo denitrification due to the lack of sufficient dissolved oxygen (DD<0.5 mg/L). The N2 generated by denitrification will also attach to the sludge floc, reducing its density and causing the sludge to float up.

SOLUTION:

The measures to control the floating of sludge are: first, discharge the surplus sludge in time and increase the amount of returned sludge to prevent the sludge from staying in the secondary sedimentation tank for too long; The second is to strengthen the oxygen charging capacity at the end of the aeration tank, increase the dissolved oxygen content in the mixed solution entering the secondary sedimentation tank, and ensure that the sludge in the secondary sedimentation tank is not under anaerobic or anoxic conditions.

For the sludge floating caused by denitrification, it can also increase the discharge of excess sludge, reduce SRT, and control denitrification by controlling the degree of nitrification.

 

QUESTION:The Black Lump Sludge in Secondary Sedimentation Tank   

Black lump sludge on the surface of secondary sedimentation tank is usually caused by sludge decay.

REASON:

If the aeration amount is too small, the sludge will be anoxic in the secondary sedimentation tank, or if the amount of sludge generated in the aeration tank is large and the discharge amount of excess sludge is small, the sludge will stay in the secondary sedimentation tank for a long time, or if the sludge hopper is unreasonable during gravity sludge discharge, which makes it difficult for the sludge to slide, or if some of the suction pipes of the sludge scraper and suction machine are not smooth and there is a blind corner that cannot be scraped, the sludge will be stored locally in the secondary sedimentation tank for a long time and anaerobic metabolism will occur, generating a lot of H2S C} {4 and other gases are wrapped on the mud lump to promote the sludge to float up in a large block, and the color is black.

The sludge will rot and become black when it is decomposed and floated, which is different from the ordinary sludge.

SOLUTION:

The solutions are to ensure the timely discharge of excess sludge, eliminate the failure of sludge discharge equipment, remove the sludge on the inner wall of sedimentation tank or some dead corners, reduce the nitrification degree of sludge in aerobic treatment system, increase the sludge return flow, and prevent the entry of putrid sludge from other treatment structures.

 

In wastewater treatment process,after biological treatment, the sewage must enter the secondary sedimentation tank for sludge water separation, and the clarified qualified treated water can be discharged. At the same time, a certain concentration of returned sludge or a certain amount of treated water must be provided for biological treatment facilities. Therefore, the working performance of the secondary sedimentation tank has a direct relationship with the operating effect of the activated sludge system.

 

#QDEVU #WASTEWATERTREATMENT #SEWAGETREATMENT #WATERTREATMENT

 

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