The total nitrogen remains high, hovering at the critical point of exceeding the standard, and there is no way to start. The inflow of more than 7000 water does not exceed the standard, the sludge concentration is around 4500, the internal and external reflux is 100%, other equipment is normal, and the outlet dissolved oxygen is just over 2 points, but the total nitrogen cannot go down. What is the reason?
In fact, the problem of ammonia nitrogen reaching the standard and total nitrogen remaining high is not complicated. Sometimes adjusting the parameters can achieve the standard!
1. Lack of carbon source
In the process of nitrification and denitrification, the theoretical CN ratio required for removing TN is 2.86, but in actual operation, the CN (COD: TN) ratio is generally controlled at 4-6, and the lack of carbon sources is one of the most common reasons why many friends encounter TN non-compliance!
Solution: Add carbon source according to CN ratio of 4-6.
2. Internal reflux r is too small
The full name of AO process is inverted nitrification denitrification process, and the denitrification efficiency of AO process is directly proportional to the internal reflux ratio! According to the denitrification efficiency formula, the higher the internal reflux ratio r, the higher the denitrification efficiency. Some sewage treatment internal reflux pumps are partially damaged or selected too small, which can lead to low denitrification efficiency!
Solution: Increase the internal reflux ratio r to 200-400% (some denitrification processes combine internal and external reflux, and the internal and external reflux ratio should also be controlled within this range, which ensures both sludge reflux and nitrification liquid reflux, ensuring denitrification efficiency)
3. Environmental damage in denitrification tank
The sign of this situation is that the dissolved oxygen (DO) in the denitrification tank is greater than 0.5, which destroys the anaerobic environment and allows facultative heterotrophic bacteria to preferentially utilize oxygen for metabolism. Nitrate nitrogen cannot be removed, resulting in an overall increase in TN. The anaerobic environment in the denitrification tank is destroyed, which often leads to excessive ammonia nitrogen. The reason is that nitrifying bacteria cannot form dominant strains, but the aeration tank is large enough, so there is still no problem!
terms of settlement:
1. If the internal reflux is too large and carries too much DO, adjust the internal reflux ratio or turn off the aeration at the internal reflux point.
2. The high DO caused by other issues, such as the high distance between the inflow and the water surface, leading to a drop and oxygenation, requires reducing the height difference.
3. Containing n-heterocyclic organic nitrogen
Some nitrogen-containing organic compounds cannot be broken down by ordinary biochemistry, resulting in their inability to be removed. This situation is relatively rare, mainly in a certain type of wastewater. In this case, it is mainly a problem of process selection, without considering the process of organic nitrogen ammonification (conversion of organic nitrogen into ammonia nitrogen).
terms of settlement:
1. Increase pre-treatment for hydrolysis and acidification;
2. For those that cannot be broken by hydrolysis acidification, advanced oxidation pretreatment should be added.
