Reason 1: The sudden increase in water inflow shortens the residence time of the secondary sedimentation tank, causing activated sludge to flow out of the tank before settling, resulting in sludge leakage. At the same time, an increase in influent concentration can lead to enhanced activity of activated sludge, which is unfavorable for sedimentation, resulting in turbid effluent with sludge running phenomenon. Solution: During the design phase of the sewage treatment plant, control wells and regulating tanks should be installed. By controlling the opening angle of valves, the amount of water entering the sewage treatment system should be relatively stable to avoid significant impact on the system.
Reason 2: As the temperature rises, nitrogen gas in the secondary sedimentation tank is generated along with denitrification, and the denitrification rate is related to factors such as nitrate concentration, temperature, carbon source, and sludge concentration in the wastewater. Especially in the cold northern regions, the temperature rise directly accelerates the denitrification process, resulting in large pieces of sludge in the secondary sedimentation tank floating up with N2. Solution: In low temperature weather, especially at minus 10 ℃, microbial activity will be affected to some extent, leading to sludge expansion. Therefore, in cold northern regions, measures such as controlling dissolved oxygen (DO), adjusting sludge concentration, sludge reflux rate, and sludge age should be taken to prevent sludge swelling.
Reason 3: pH values that are too high or too low are not conducive to the survival of microorganisms, especially when the pH value is below 5, which has a greater impact on the expansion of sludge in the secondary sedimentation tank and accelerates the upward movement of activated sludge, leading to the loss of activated sludge and directly affecting the standard of effluent water quality. Solution: The pH value at the sewage inlet is generally between 7 and 8, which is beneficial for microbial treatment of organic matter. If the pH value of the incoming water from the sewage treatment plant is too low, it is necessary to adjust the pH value by adding alkali (caustic soda, lime). Reason 4: Insufficient dissolved oxygen, low dissolved oxygen is very easy to cause sludge expansion. The reason is that the oxygen in the sewage can inhibit the nitrogen produced by denitrification, delay the denitrification rate, and the dissolved oxygen is too low
Solution: Strengthen aeration, increase the concentration of dissolved oxygen (DO) in the mixed solution, and control DO above 2mg/L.
Reason 5: Activated sludge stays in the secondary sedimentation tank for too long, and the sludge decomposes due to hypoxia and overflows with the water flow.
Solution: Increase the amount of returned sludge and shorten the residence time in the secondary sedimentation tank.
Reason 6: The disintegration of activated sludge causes a decrease or disappearance of its flocculation, and sludge fragments flow out with water.
Solution: Find the cause of sludge disintegration, eliminate and solve it one by one.
