Some issues in using the hydrolysis-acidification + A/O process for treating wastewater with high COD and high ammonia nitrogen levels
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The above process is used to treat electrodialysis sludge wastewater; the quality of this wastewater features a COD level of 1000–2000 mg/L, ammonia nitrogen at 200–300 mg/L, TP at 1 mg/L, and a B/C ratio of around 0.4, indicating good biodegradability. My control conditions are hydrolytic acidification with an HRT of 24 hours for A, 24 hours for H, and 32 hours for O; the sludge concentration remains at around 4000–5000 mg/L. There is a 1:1 ratio of sludge to supernatant in the recirculation process. The required treatment standards are COD < 100 and ammonia nitrogen < 25. The ammonia nitrogen level is now within the specified range, but the COD level fails to decrease and remains around 100–200. Increasing the recirculation of sludge and supernatant does not help either. Could it be that the C:N ratio of the raw water is imbalanced? Is it possible to reduce COD again without using C code? Also, could the experts help me check if there are any issues with the retention time in each pool? What other conditions am I not meeting fully?
The addition of a carbon source here is primarily intended to ensure that the C/TN ratio for denitrification is greater than 4; it also helps in the removal of COD, though the effect is not very significant.
Adding carbon sources such as methanol or glucose ensures the concentration of MLSS, thereby improving COD removal through sludge discharge.
For the A/O process, achieving a removal rate of over 90% for COD is already a very good result; it is quite difficult to improve upon that. Under optimal conditions, it is possible to meet an emission standard of 100, but it is hard to maintain such levels.
It is recommended to add a fixed amount of activated carbon daily to the biological unit, which yields good results in removing COD.
It is recommended to add supplementary methods, such as enhanced hydrolysis acidification, to improve the biodegradability of organic matter； Increasing the MBR membrane can improve the COD removal rate by over 20% ； Add sand filtration and carbon filtration at the outlet, etc
Your COD removal efficiency is already at 90%; what remains are likely substances that are difficult to degrade. Use physical and chemical methods for treatment, such as coagulation and sedimentation or other physical and chemical techniques.
Conditionally measure the BOD5 of the effluent, and we’ll decide based on the data
If the BOD5 of the effluent is around 20, it generally indicates that the biological unit has reached an optimal level of treatment, and there is no room for further improvement
What is the level of SS in the effluent? If it exceeds 60 mg/L, something can be done to address this issue, with a COD removal rate of around 20% generally achieved.
Another drawback of the A2/O process is that excessive aeration occurs when a high removal rate of ammonia nitrogen is to be achieved; this leads to a decline in the flocculation properties of the activated sludge due to sludge aging, thereby deteriorating the quality of the effluent water.