Optimization Plan for Ammonia Nitrogen and Total Nitrogen Exceedance in Wastewater Treatment Systems

In-depth Analysis and Process Optimization Plan for Ammonia Nitrogen and Total Nitrogen Exceedance in Wastewater Treatment Systems

Under increasingly stringent environmental discharge standards, nitrogen removal efficiency has become a core indicator for evaluating the operational level of wastewater treatment plants (WWTP). However, in actual operation, ammonia nitrogen (NH4+-N) and total nitrogen (TN) frequently fluctuate and exceed standards, seriously affecting compliance. As a professional brand in environmental monitoring and process control, NiuBoL combines engineering experience to provide comprehensive logical analysis and response strategies for common denitrification abnormalities in biochemical systems.

Part 1: In-depth Causes and Countermeasures for Ammonia Nitrogen Exceedance

The removal of ammonia nitrogen mainly relies on autotrophic nitrifying bacteria in the aerobic tank. Nitrifying bacteria are extremely sensitive to environmental changes, and any imbalance in physical or chemical parameters can cause a sharp decline in nitrification rates.

1. Organic Load Shock (Abnormal High C/N Ratio)
When a large amount of carbon sources (such as methanol leakage or high-concentration industrial wastewater) enters the aerobic tank, heterotrophic bacteria rapidly proliferate and compete for dissolved oxygen (DO) and trace elements.
Mechanism: As autotrophic bacteria, nitrifying bacteria have much weaker metabolic competitiveness than heterotrophic bacteria. Under sufficient substrate conditions, the aerobic metabolism of heterotrophic bacteria prevents nitrifying bacteria from forming dominant populations, leading to stagnation of nitrification.
NiuBoL Expert Recommendation: Immediately stop influent and perform “idle aeration,” maintain sludge concentration through recirculation, and add PAC if necessary to improve sludge flocculation.

2. Internal Reflux System Failure
Internal reflux (Nitrate Recycle) is critical for returning nitrified liquid to the anoxic tank. If the internal reflux pump fails electrically or mechanically, or runs in reverse, the A tank will lose nitrate nitrogen.
Analysis: Without nitrate return, the A tank becomes purely anaerobic, where carbon sources can only undergo hydrolysis and acidification, causing large amounts of organics to enter the O tank and indirectly increase ammonia nitrogen.
Identification Signal: Abnormally high nitrate nitrogen at the O tank outlet, while nitrate in the A tank approaches zero.

3. pH Imbalance
For every 1g of ammonia nitrogen converted, nitrification consumes 7.14g of alkalinity. If alkalinity is insufficient and pH drops below 6.0, nitrifying bacteria activity is strongly inhibited.
Interference Factor: Excess dissolved oxygen carried by internal reflux disrupts the anoxic environment, preventing effective alkalinity recovery through denitrification.
Solution: Monitor pH in real time, supplement alkalinity when necessary, and adjust aeration intensity to maintain true anoxic conditions.

4. Insufficient Dissolved Oxygen (DO)
Nitrification is an aerobic process, requiring DO levels above 2.0 mg/L.
Hidden Risk: High-hardness wastewater can cause scaling and blockage of microporous diffusers.
Hardware Optimization: Replace with coarse bubble diffusers or jet aerators, and deploy NiuBoL fluorescence DO sensors for precise closed-loop aeration control.

5. Insufficient Sludge Retention Time (SRT)
Nitrifying bacteria have long generation cycles. Excessive sludge discharge or uneven return reduces SRT below their growth cycle, causing washout.
Principle: Maintain SRT at 3–4 times the nitrifying bacteria generation cycle.

6. Temperature and Free Ammonia (FA) Inhibition
Low Temperature: In winter, low water temperatures can cause microbial dormancy. Increase MLSS or heat influent to compensate.
Free Ammonia: High ammonia shocks produce FA, inhibiting ammonia-oxidizing bacteria (AOB) and more sensitive nitrite-oxidizing bacteria (NOB), leading to nitrification collapse.

Part 2: Core Mechanisms of Total Nitrogen (TN) Exceedance

TN removal depends on the synergy of nitrification and denitrification. Even if ammonia nitrogen meets standards, TN may still exceed limits.

1. Carbon Source Deficiency
Denitrification requires carbon as an electron donor. The theoretical C/N ratio is 2.86, but in practice it should be controlled at 4.0–6.0.
Current Situation: Many municipal wastewater influents lack sufficient carbon, requiring precise dosing of methanol, sodium acetate, or composite carbon sources.

2. Improper Internal Reflux Ratio (r)
Denitrification efficiency is proportional to the internal reflux ratio. If pump capacity is insufficient, nitrate cannot effectively return to the anoxic zone.
Optimization: Maintain internal reflux ratio at 200%–400%.

3. Damaged Anoxic Environment in Denitrification Tank
If internal reflux carries excessive DO or influent aeration occurs, DO > 0.5 mg/L in the anoxic tank, facultative heterotrophic bacteria will prioritize aerobic metabolism over denitrification.

4. Refractory Organic Nitrogen
Industrial wastewater containing nitrogen heterocycles is difficult to degrade biologically and requires pretreatment such as hydrolysis-acidification or advanced oxidation (Fenton, O3).

Part 3: Monitoring Hardware for Precise Control

To prevent ammonia and TN exceedance, establishing a real-time warning and data-driven monitoring system is essential.

FAQ:

Q1: Why does pH decrease when ammonia nitrogen increases?
This is because nitrification is an acid-producing process. When ammonia nitrogen is converted, alkalinity is consumed. If alkalinity is already low, pH will drop rapidly, further inhibiting nitrification.

Q2: The internal reflux pump is running, why is denitrification still poor?
Check whether the impeller has detached or reversed, and inspect for air blockages in pipelines. The most scientific method is measuring nitrate differences between A tank inlet and outlet.

Q3: Why does excessive foam in the aeration tank affect ammonia nitrogen?
Foam often indicates overgrowth of heterotrophic or filamentous bacteria, which interferes with oxygen transfer efficiency and limits oxygen availability for nitrifiers.

Q4: Why stop sludge dewatering when ammonia nitrogen exceeds limits?
To quickly increase MLSS and extend SRT, allowing slow-growing nitrifying bacteria sufficient time to accumulate and reproduce.

Q5: What is simultaneous nitrification-denitrification (SND)?
It refers to nitrification and denitrification occurring simultaneously within the same space (e.g., inside sludge flocs), typically under low DO and high MLSS conditions, saving carbon sources and improving efficiency.

Q6: How to quickly recover a shocked nitrification system?
The fastest way is seeding—introducing activated sludge from a well-functioning system, combined with idle aeration and low-load influent, typically recovering within 3–7 days.

Conclusion

Ammonia nitrogen and total nitrogen exceedance is usually caused by multiple factors including carbon source, DO, sludge age, and pH. Establishing a data-driven preventive system is far more effective than reactive measures.

By deploying NiuBoL industrial-grade online monitoring solutions, system integrators and operators can monitor the “health pulse” of biochemical systems in real time. Our RS485 digital solutions not only reduce maintenance costs but also provide precise data support for automated process control. On the path to compliant discharge, NiuBoL is committed to being your most reliable technical partner.

Water Quality Sensor Data Sheet

NBL-WQ-CL Water Quality Sensor Online Residual Chlorine Sensor.pdf    

NBL-WQ-DO Online Fluorescence Dissolved Oxygen Sensor.pdf    

NBL-WQ-NHN Ammonia Nitrogen Water Quality Sensor.pdf    

NBL-WQ-COD Online Water Quality COD Sensor.pdf    

NBL-WQ-PH Online pH Water Quality Sensor.pdf    

NBL-WQ-EC water quality conductivity sensor.pdf    

NBL-WQ-BOD-4A Online BOD Sensor.pdf    

NBL-WQ-TH-4S online total hardness sensor.pdf