As a sewage treatment worker, facing the problem of rising total nitrogen (TN) data, we need to take a series of scientifically effective measures as soon as possible to cope with it. The following are some commonly used operational techniques. And a simple analysis was conducted on corresponding practical cases, aiming to provide practical reference and guidance for environmental wastewater practitioners. 1. TN exceedance caused by excessive ammonia nitrogen 1.1 Ammonia nitrogen exceedance index parameters caused by organic matter - influent ammonia nitrogen (NH4-N): usually should be controlled below 30 mg/L- Dissolved oxygen (DO) in the aeration tank should be maintained at 2-4 mg/L- PH value: The suitable pH range is 6.5-8.5. Reason for debugging: A large amount of carbon source enters tank A, which cannot be utilized for denitrification and enters the aeration tank, resulting in limited nitrification reaction and increased ammonia nitrogen. This is because nitrifying bacteria are autotrophic and have poor metabolic capacity. Oxygen is contested and cannot form a dominant bacterial community, which limits the nitrification reaction and increases ammonia nitrogen. Operation technique: Immediately stop the water inlet for suffocation and continuous opening of internal and external reflux- Stop pressing the sludge to ensure its concentration- Add PAC to increase sludge flocculability, and add defoamer to eliminate impact foam. For example, in a wastewater treatment plant of a food processing plant, a large amount of carbon containing wastewater is generated during the production process, resulting in an excess of carbon source in tank A and an increase in ammonia nitrogen concentration to 50 mg/L. By stopping the water inlet and activating the explosion mode, adjusting the reflux ratio to 200%, and adding PAC and defoamer, the ammonia nitrogen concentration was reduced to below 30 mg/L after 24 hours of treatment. 1.2 Parameters of ammonia nitrogen exceeding the standard caused by internal reflux: - Internal reflux ratio (r): The ideal value is 200-400%- DO in hypoxic zone: should be controlled below 0.5 mg/L. Reason for debugging: Internal reflux pump malfunction or improper selection, resulting in a decrease in nitrate nitrogen in tank A, a large amount of organic matter entering the aeration tank, and an increase in ammonia nitrogen. This is because the excessive ammonia nitrogen caused by internal reflux can also be attributed to organic matter impact, as there is no reflux of nitrification solution, resulting in only a small amount of nitrifying bacteria in tank A, which cannot effectively nitrify. Operation skills: - Inspect and repair the internal reflux pump- Reduce the inflow rate and conduct a suffocating explosion- If necessary, add the same type of sludge to accelerate system recovery. For example, a textile factory's sewage treatment station experienced a malfunction in the reflux pump, resulting in an increase in ammonia nitrogen concentration to 70 mg/L. Timely maintenance was carried out to reduce the inflow rate, and the same type of sludge was urgently transported from nearby sewage treatment plants. After 48 hours of treatment, the ammonia nitrogen concentration returned to normal levels. 2. Lack of carbon source leads to TN exceeding the standard parameters:- CN ratio: The ideal value is 4-6- Inlet COD: It should be maintained in an appropriate proportion with TN to support the denitrification process. Reason for debugging: In the process of nitrification and denitrification, the theoretical CN ratio required for TN removal is 2.86, but in actual operation, the CN (COD: TN) ratio is generally controlled at 4-6, and the lack of carbon source is one of the most common reasons why many of my friends' TN does not meet the standard. Operation skills: Add carbon source in a CN ratio of 4-6.
For example, in winter, a city's sewage treatment plant experiences a decrease in denitrification efficiency and an increase in TN concentration due to low inlet water temperature. Laboratory analysis found that the CN ratio was only 2. Operators added methanol as a carbon source according to the CN ratio standard of 4-6, gradually controlling the TN concentration below 15 mg/L. 3. The internal reflux r is too small, resulting in TN exceeding the standard parameter: - Internal reflux ratio (r): The ideal value should be between 200-400%. Debugging reason: 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. Operation skills: - Increase the internal reflux ratio r to 200-400%. For example, the sewage treatment plant of a certain petrochemical enterprise has low TN removal efficiency due to the low internal reflux ratio. By increasing the flow rate of the internal reflux pump, the reflux ratio was increased to 300%, and the TN concentration was reduced from 30 mg/L to below 20 mg/L. 4. Environmental damage in the denitrification tank leads to TN exceeding the standard parameter: - Denitrification tank DO: should be lower than 0.5 mg/L- Denitrification tank pH: The suitable range is 6.5-8.0. Debugging reason: The DO of the denitrification tank is greater than 0.5, which destroys the anoxic environment and allows facultative heterotrophic bacteria to preferentially utilize oxygen for metabolism. Nitrate nitrogen cannot be removed, resulting in an overall increase in TN. Operation skills: - Adjust the internal reflux ratio or turn down the aeration at the internal reflux point- Reduce the height difference between the inflow and the water surface to avoid falling and oxygenation. For example, a meat processing wastewater treatment plant experienced a decrease in TN removal efficiency due to excessive DO in the denitrification tank. The operator reduced DO to 0.3 mg/L and TN concentration by adjusting the internal reflux ratio and reducing the difference in inlet water height. 5. The inflow contains n-heterocyclic organic nitrogen, leading to TN exceeding the standard parameter: - Organic nitrogen concentration: should be reduced to a biodegradable level through pretreatment. Reason for debugging: Some nitrogen-containing organic compounds cannot be removed by ordinary biochemical methods, which is relatively rare. This is mainly due to a certain type of wastewater, and 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). Operation skills: - Increase hydrolysis acidification pretreatment- For organic compounds that cannot be broken by hydrolysis and acidification, advanced oxidation pretreatment should be added. For example, the wastewater from a pharmaceutical factory contains a large amount of heterocyclic organic nitrogen, which makes it difficult to meet the TN standard. By increasing hydrolysis acidification and advanced oxidation pretreatment, the organic nitrogen concentration was effectively reduced, resulting in TN emissions meeting standards. Conclusion: Faced with the increase in total nitrogen data, technical personnel of sewage treatment plants need to comprehensively consider multiple factors and take scientifically reasonable measures when debugging. Through the above operational techniques and practical cases, we hope to provide practical reference and guidance for environmental wastewater practitioners. In practical operation, it is necessary to flexibly adjust strategies based on specific situations to achieve the best processing effect.
