Some problems encountered during the pilot tests!
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My project deals with electrodialysis sludge wastewater. The parameters of this wastewater are as follows: COD is around 1000–2000, ammonia nitrogen is around 200–300, TP is about 1, the pH is 11, and the B/C ratio is 0.4; thus, its biodegradability is relatively good. The process being used for debugging at the moment is a treatment system that includes a regulating tank, hydrolysis-acidification, and an A/O stage. During normal operation, the HRT for the hydrolysis-acidification stage is kept at 12 hours, with a sludge concentration of 5000 mg/L. The pH in the A/O stage is maintained around 8, and there is a sludge return ratio of 2:1. However, the levels of COD and ammonia nitrogen do not decrease over time. I have set the sludge concentration in both the A-stage and O-stage to between 4000 and 5000 mg/L, with a retention time of around 20 hours each. Is this too long? Also, isn’t the C/N ratio of the raw water too low? Should an additional carbon source be used? Moreover, after running for some time, the nitrification capacity of pool O is almost gone. Could it be that the heterotrophic bacteria from pool A have entered pool O? Did it cause the death of the nitrifying bacteria in Pool O? Also, during the testing phase, are there any other areas where I haven’t done well? I would really appreciate some guidance from those who are more experienced!
Is a sludge return ratio of 2:1 internal return or external return?
I keep the sludge concentration in tanks A and O at 4000–5000 mg/L, with a retention time of around 20 hours. A longer retention time is beneficial for removing organic matter and carrying out denitrification; retention times of up to 80 hours are no problem.
For denitrification, a longer sludge age is required; generally, more than 20 days is preferable.
Additionally, water temperature has a significant impact on denitrification; 20–35 degrees is the optimal temperature. When the temperature is below 20 degrees, the nitrification efficiency drops by half for every 5-degree decrease, and below 10 degrees, nitrification becomes very poor or even stops altogether.
An indicator that denitrification is proceeding normally is a C/TN ratio greater than 4; this ratio is usually kept above 6. Based on your data, the BOD is around 400 mg/L, the ammonia nitrogen level is 200 mg/L, and the total nitrogen level is even higher； With a C/N ratio of around 2, denitrification cannot take place due to insufficient driving force. Suggestions: 1. Reduce ammonia nitrogen in the water ； 2. Add a carbon source to make the C/TN ratio greater than 4.
This post was last edited by zhaolijun on 2015-10-28 at 15:41. Indeed, there is an imbalance in the ratio between carbon sources and ammonia nitrogen, but the reflux ratio is also an important factor affecting the removal of ammonia nitrogen. It is recommended that the poster try increasing the reflux ratio first.