The activated sludge is entrained with fine air bubbles

In addition to denitrification, bubbles are mainly caused by aeration residue, which has little to do with how big the fan you drive, and a small fan will also lead to a reduction in pollutant treatment capacity. As far as I can speculate, your sewage is estimated to contain high molecular weight in organic matter, or the relative organic matter content is too high (relatively inorganic), which makes it easy for air bubbles to remain in the sludge. So the solution starts with two aspects:

Increasing the aeration rate to improve the removal of organic matter may also be important by increasing the inorganic matter in the aeration tank (e.g., adding sodium hydroxide or hydrochloric acid to adjust the pH value to deviate from 7, and adding inorganic salts, etc.). Hehe, I don't know if you're satisfied.

In addition, there are simple ways to eliminate this phenomenon.

Our company has also done a lot of contact oxidation pool, I feel that your DO is not big but small, generally we control it at 4 8mg L. It is recommended that you understand the pressure that the aeration head can bear, and then turn on the aeration volume for a period of time (about two months) (half a day is enough), which can not only blow off the aging biofilm, but also make the sludge deposited in the dead corner run out, and then increase the sludge discharge.

We have encountered similar problems twice, once because of the blockage of the local aeration pipe, caused by the deposition of sludge at the bottom of the contact oxidation tank, and once the corrosion of part of the sludge discharge pipe of the secondary sedimentation tank, caused by the poor local sludge discharge, it is recommended that you check these two aspects again.

Produced by denitrification.

Because your TN is 10 and the ammonia nitrogen is 4, in the case of hypoxia in the secondary sedimentation tank, denitrification will occur and nitrogen will be produced. Bring the sludge out.

If the sludge is a normal color, it is nitrogen, and if the sludge is black, it is anaerobic biogas, and the sludge should be discharged frequently.

In fact, your suspicion may not be wrong, it may still be over-aeration, after all, your tn is not very high, it may not be denitrifying floating mud.

Specifically, you can observe your own operation, whether the residence time of the secondary sedimentation tank is too long, if it is too long, it may be denitrification with mud, the bubbles are generally not very fine, and the color of the sludge may be black; If the sludge contains a lot of fine air bubbles, it is still likely that the aeration is excessive.

In addition, it can be observed whether there will be other conditions, and the sludge aging will often be full of mud, but there will be no bubbles in the sludge.

It can't be denitrification.

Regardless of the process of biochemical systems, the causes of foam or floating mud are similar.

1.The observation of foam focuses on the observation and summary of the production cycle, foam color, viscosity, brittleness, etc. Of course, changes in influent water quality and changes in other operating indicators also need to be observed and understood.

2.The production of floating sludge should also observe the color, viscosity and whether there are bubbles, etc., and if necessary, microscopic observation and comparison of normal sludge and floating sludge should be carried out to understand the properties of sludge.

3.Through the above main observation methods and points, find out the cause of foam or floating mud, and solve it in a targeted manner, I think the system can return to normal operation!

If you can explain your process a little bit more clearly, the parameters of the inlet water, the design of the pool, and so on, I might be able to give you some advice.