What to do about the mushroom cloud-shaped sludge in the secondary sedimentation tank?
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In the secondary sedimentation tank, mushroom cloud-shaped sludge suspension occurs. This phenomenon starts with the appearance of such suspended sludge in the area around the center of the tank; from above, it appears to cover a small area. Over time, as the water flows, this sludge moves towards the triangular area at the edge of the tank, where it then flows out in large quantities, resulting in localized sludge loss in the tank. This situation lasts for 1–4 hours, without any regular pattern. Increasing the rate of sludge removal and controlling the DO level can help reduce the duration of sludge loss, but it is not possible to completely eliminate it. After continuous heavy sludge removal, the sludge concentration drops to around 2000. Last week, efforts were made to reduce sludge discharge; initially, there was a noticeable reduction in the amount of suspended sludge. However, starting on Saturday, sludge loss occurred repeatedly, with the affected area increasing significantly, and this happened regularly around 7:00 am, when the sludge began to float to the surface and flow out. Our process uses the A2O method; the water volume is around 22,000, the BOD level is 150–180, and the COD is above 300. Currently, the MLSS level is around 2200, with a sedimentation rate of about 22% (the supernatant after sedimentation contains fine suspended particles, along with a large amount of flocs on its surface). The approach currently adopted is to control the DO level
This post was last edited by Gorō Bagua Stick on 2015-7-23 at 15:31. It might be worth considering whether the bubbles are caused by anaerobic conditions resulting from an excess of organic matter; if the retention time in the secondary sedimentation tank is over 2 hours yet the dissolved oxygen level is low, it could be due to excessive aeration
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There are local dead zones in the sedimentation tank where sludge accumulates; it’s necessary to find a way to disperse that sludge. It is also necessary to speed up the sludge pumping cycle to minimize the accumulation of dead sludge. Sludge scum is a product of nitrification and denitrification in sludge.