The effluent from the secondary sedimentation tank in the A/O process is turbid
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In the A/O process, the discharge standard for COD is 500 mg/L. The effluent from the secondary sedimentation tank has been a bit turbid recently; very fine particles can be seen suspended in the water, resulting in a decrease in transparency. However, the SS level has not increased and remains around 40 ppm. Recently, due to the drop in water temperature, the biochemical water temperature is 22°C; dissolved oxygen was deliberately increased from 1.5 to 2.5 mg/L, and MLSS was raised from 3.5 to around 4 g/L. There were no significant changes in the removal efficiency or the COD level of the effluent. Was it over-aeration?
Although I have only been working on sewage treatment for half a year, it can be determined that this is caused by over-aeration; moreover, over-aeration increases the hydraulic load. The amount of flocculant can be increased appropriately.
It increases the hydraulic load. The amount of flocculant can be increased appropriately. I didn’t understand what you mean. Could you explain it again?
That is, when aeration increases, the water is stirred more vigorously, which hinders sedimentation and allows suspended solids to enter the secondary sedimentation tank. Adding a flocculant can accelerate sedimentation.
Personally, I think it is the drop in temperature that leads to poor performance during the hydrolytic acidification stage, which in turn results in low aerobic efficiency.
Previously, the secondary sedimentation tank also had excessive sludge, with COD levels exceeding the limits. The reason is low dissolved oxygen; it has now become relatively stable since jet aerators were installed.
The biochemical water temperature is 22°C, which is too low; it should be above 25 degrees
There is no way to adjust the water temperature in the biochemical process; during winter, the temperature drops to as low as 16°C, yet the quality of the effluent still remains satisfactory even in the absence of anaerobic conditions.
Personally, I think 2.5 mg/l of dissolved oxygen is not high; let’s calculate the sludge load to see.