Sludge Problems in Secondary Sedimentation Tank
PROBLEM:Sludge Floating
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.
The main reasons for floating are: normal sludge stays in the secondary sedimentation tank for a long time, acidification occurs due to the gradual consumption of dissolved oxygen, H2S and other gases are generated and attached 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 (DO<0.5mg/L). The N2 generated by denitrification will also attach to the sludge floc, reducing its density and causing the sludge to float up.
Measures to control sludge floating: First, timely discharge the surplus sludge 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.
PROBLEM:Black Lumpy Sludge On The Surface
The black lumpy sludge on the surface of the secondary sedimentation tank is usually caused by sludge decay. Too little aeration makes the sludge anoxic in the secondary sedimentation tank, or the large amount of sludge generated in the aeration tank and the small amount of residual sludge discharge make the sludge stay in the secondary sedimentation tank for too long, or the unreasonable sludge bucket during the gravity sludge discharge makes it difficult for the sludge to slide, or part of the sludge suction pipe of the sludge scraper and suction machine is not smooth and there is a dead angle that cannot be scraped, which will cause the sludge to stay and deposit in the secondary sedimentation tank for a long time, resulting in anaerobic metabolism, producing a large amount of H2S, CH4 and other gases, Wrapped on the mud block, the sludge floats up in large pieces, and the color is black. The sludge is different from the general sludge. When the sludge is decayed and floating, it will become black and produce a bad smell.
The solutions include ensuring the timely discharge of excess sludge, removing the fault of sludge discharge equipment, removing the sludge from the inner wall of sedimentation tank or some dead corners, reducing the nitrification degree of sludge in aerobic treatment system, increasing the sludge return flow, preventing the entry of decayed sludge from other treatment structures, etc.
PROBLEM:Foam Scum On The Surface
After the scum appears on the surface of the secondary sedimentation tank, first check whether the scum scraper, scum bucket and scum washing water are normal, and whether the scum pump has problems. If it is the fault of the scum scraping system itself, it should be repaired immediately.
The sewage contains surfactants, lipid compounds and other organic substances that can cause rapid proliferation of actinomycetes, resulting in biological foam scum on the surface of the secondary sedimentation tank. The countermeasures are to spray with water, reduce aeration time, and add oxidation disinfectant or coagulant.
The sludge in the secondary sedimentation tank is partially anoxic for a short time, and the denitrification phenomenon occurs, which causes the sludge to float up and form scum. The sludge in the secondary sedimentation tank will decay and deteriorate if it stays for a long time, and part of the sludge will float under the wrapping of H2S, CH4 and other gases, which will also form scum. The fundamental measure to solve these two kinds of scum is to find out the causes of sludge denitrification and degradation and adjust them respectively.
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