In recent years, several brand-new denitrogenation processes have emerged both domestically and internationally, providing new avenues for the treatment of high-concentration ammonia nitrogen wastewater. These primarily include short-cut nitrification and denitrification, aerobic denitrification, and Anaerobic Ammonia Oxidation (ANAMMOX).

1. Short-cut Nitrification and Denitrification

In 1975, Voets and others discovered the phenomenon of NO2--N accumulation during the nitrification process while studying the treatment of high-concentration ammonia nitrogen wastewater, first proposing the concept of short-cut nitrification and denitrification.

Since the oxidation of ammonia nitrogen requires a large amount of oxygen, aeration costs become the primary expenditure for this denitrogenation method. Short-cut nitrification and denitrification (oxidizing ammonia nitrogen only to nitrite nitrogen before denitrification) can save not only the oxygen required for ammonia oxidation but also the carbon source needed for denitrification. Ruiza and others used synthetic wastewater (simulating industrial wastewater containing high concentrations of ammonia nitrogen) to determine the conditions for achieving nitrite accumulation. To achieve nitrite accumulation, pH is not a critical control parameter, because when the pH is between 6.45 and 8.95, total nitrification occurs to form nitrate; when pH < 6.45 or pH > 8.95, nitrification is inhibited and ammonia nitrogen accumulates. When DO = 0.7 mg/L, 65% of the ammonia nitrogen can be accumulated in the form of nitrite, with an ammonia nitrogen conversion rate of over 98%. When DO < 0.5 mg/L, ammonia nitrogen accumulation occurs; when DO > 1.7 mg/L, total nitrification occurs to form nitrate. Liu Junxin and others conducted a comparative analysis of the effects of nitrite-type and nitrate-type denitrogenation for high-concentration ammonia nitrogen wastewater with a low carbon-to-nitrogen ratio. Experimental results show that nitrite-type denitrogenation can significantly improve total nitrogen removal efficiency, and the ammonia nitrogen and nitrate nitrogen loads can be nearly doubled. In addition, factors such as pH and ammonia nitrogen concentration have an important influence on the type of denitrogenation.

Pilot scale results for treating coking wastewater via short-cut nitrification and denitrification show that when influent concentrations of COD, ammonia nitrogen, TN, and phenol are 1201.6, 510.4, 540.1, and 110.4 mg/L respectively, the average effluent concentrations are 197.1, 14.2, 181.5, and 0.4 mg/L. The corresponding removal rates are 83.6%, 97.2%, 66.4%, and 99.6% respectively. Compared with conventional biological denitrogenation processes, this process has a higher ammonia nitrogen load and can increase the TN removal rate under conditions of lower C/N values.

2. Anaerobic Ammonia Oxidation (ANAMMOX)

Anaerobic Ammonia Oxidation (ANAMMOX) refers to the process where ammonia nitrogen is directly oxidized into nitrogen gas using nitrite as an electron acceptor under anaerobic conditions.

The biochemical reaction equation for ANAMMOX is:
NH₄⁺ + NO₂⁻ → N₂↑ + 2H₂O

ANAMMOX bacteria are obligate anaerobic autotrophs, making them highly suitable for treating ammonia nitrogen wastewater containing NO₂⁻ and low C/N ratios. Compared with traditional processes, denitrogenation based on anaerobic ammonia oxidation has a simple process flow, does not require an external organic carbon source, prevents secondary pollution, and has great application prospects. There are two main applications of anaerobic ammonia oxidation: the CANON process and integration with Single reactor High activity Ammonia Removal Over Nitrite (SHARON) to form the SHARON-ANAMMOX combined process.

3. Completely Autotrophic Nitrogen-removal Over Nitrite (CANON)

The CANON process is a method that utilizes completely autotrophic microorganisms to simultaneously remove ammonia nitrogen and nitrite under oxygen-limited conditions. In terms of reaction form, it is a combination of the SHARON and ANAMMOX processes carried out in the same reactor. Meng Liao and others found at the Shenzhen Xiaping Solid Waste Landfill Leachate Treatment Plant that when dissolved oxygen is controlled at around 1 mg/L, influent ammonia nitrogen < 800 mg/L, and ammonia nitrogen load < 0.46 kg NH₄⁺/(m³•d), the CANON process can be achieved using an SBR reactor, with an ammonia nitrogen removal rate > 95% and a total nitrogen removal rate > 90%.

Research by Sliekers and others shows that both ANAMMOX and CANON processes can operate well in gas-lift reactors and achieve very high nitrogen conversion rates. Controlling dissolved oxygen at around 0.5 mg/L in a gas-lift reactor, the denitrogenation rate of the ANAMMOX process reached 8.9 kg N/(m³•d), while the CANON process reached 1.5 kg N/(m³•d).

4. Simultaneous Nitrification and Denitrification (SND)

According to traditional biological denitrogenation theory, the denitrogenation pathway generally includes two stages: nitrification and denitrification. These two processes need to be carried out in two isolated reactors, or in the same reactor with alternating anoxic and aerobic environments created in time or space. In fact, as early as years ago, in some activated sludge processes without obvious anoxic and anaerobic stages, the phenomenon of non-assimilative loss of nitrogen was observed multiple times, and the disappearance of nitrogen was also frequently observed in aeration systems.

In these treatment systems, nitrification and denitrification reactions often occur under the same treatment conditions and in the same treatment space; therefore, these phenomena are called Simultaneous Nitrification/Denitrification (SND). Currently, the representative process for simultaneous nitrification and denitrification is MBBR.

5. Aerobic Denitrification

Traditional denitrogenation theory holds that denitrifying bacteria are facultative, and their respiratory chain uses oxygen as the terminal electron acceptor under aerobic conditions and nitrate as the terminal electron acceptor under anoxic conditions. Therefore, if a denitrification reaction is to occur, it must be in an anoxic environment. In recent years, the phenomenon of aerobic denitrification has been continuously discovered and reported, gradually gaining attention. Some aerobic denitrifying bacteria have been isolated, some of which can simultaneously perform aerobic denitrification and heterotrophic nitrification (such as T. pantotropha LMD82.5 isolated and screened by Robertson and others). This allows for simultaneous nitrification and denitrification in the true sense within the same reactor, simplifying the process flow and saving energy.

Experimental results from an SBR reactor treating ammonia nitrogen wastewater verified the existence of aerobic denitrification. The aerobic denitrification capacity decreases as the dissolved oxygen concentration of the mixed liquor increases. When the dissolved oxygen concentration is 0.5 mg/L, the total nitrogen removal rate can reach 66.0%.

Continuous dynamic experimental research shows that for high-concentration ammonia nitrogen leachate, the total nitrogen removal rate of the aerobic denitrification process with common activated sludge can reach more than 10%. The nitrification reaction rate decreases as the dissolved oxygen concentration decreases, while the denitrification reaction rate increases as the dissolved oxygen concentration decreases. Kinetic analysis of nitrification and denitrification shows that when the dissolved oxygen is around 0.14 mg/L, simultaneous nitrification and denitrification will occur where the nitrification rate and denitrification rate are equal. The rate is 4.7 mg/(L•h), with a nitrification reaction constant KN = 0.37 mg/L and a denitrification reaction constant KD = 0.48 mg/L.

N2O, a greenhouse gas, is produced during the denitrification process, causing new pollution. Research on its related mechanisms is not yet deep enough, and many processes are still in the laboratory stage, requiring further study before they can be effectively applied in practical engineering. In addition, processes such as the completely autotrophic denitrogenation process and simultaneous nitrification and denitrification are still in the experimental research stage, all of which have great application prospects.

YexSensor Core Monitoring Matrix for System Integration

Frequently Asked Questions (FAQ)

Q1: Why is dissolved oxygen (DO) control so critical in short-cut nitrification?
   A: Precise DO control allows for the survival of Ammonia-Oxidizing Bacteria (AOB) while inhibiting Nitrite-Oxidizing Bacteria (NOB). Maintaining DO at approximately 0.7 mg/L ensures that ammonia is only oxidized to nitrite, which is the cornerstone of the short-cut process.

Q2: What are the primary advantages of the ANAMMOX process for system integrators?
   A: For large-scale projects, ANAMMOX eliminates the need for external carbon sources and reduces oxygen requirements by 60%, significantly lowering the operational expenditure (OPEX) and footprint of the plant.

Q3: How does YexSensor ensure data stability in high-concentration ammonia environments?
   A: Our YEX-NHN-206 uses an advanced Ion Selective Electrode with integrated interference compensation algorithms, specifically designed to resist the "poisoning" effects commonly found in industrial-strength wastewater.

Q4: Can the CANON process be implemented in a single reactor?
   A: Yes. CANON combines partial nitritation and ANAMMOX in a single reactor by controlling oxygen levels to allow both autotrophic aerobic and anaerobic bacteria to coexist in different layers of the biofilm or floc.

Q5: What is the benefit of RS485 Modbus RTU communication for wastewater projects?
   A: It facilitates seamless integration into PLC and SCADA systems, allowing for long-distance data transmission (up to 1200m) and the daisy-chaining of multiple sensors on a single cable, reducing installation complexity.

Q6: Does temperature affect the accuracy of ammonia nitrogen monitoring?
   A: Yes, temperature significantly impacts ion activity. Therefore, the YEX-NHN-206 includes a high-precision internal temperature sensor for real-time automatic compensation to ensure data integrity across varying seasonal temperatures.

Q7: Why is pH monitoring essential for achieving nitrite accumulation?
   A: While DO is the primary driver, pH outside the 6.45–8.95 range can inhibit nitrification altogether. For short-cut processes, maintaining an optimal pH ensures that AOB remains active while helping to suppress NOB growth.

Q8: Is Simultaneous Nitrification and Denitrification (SND) suitable for high-load industrial wastewater?
   A: SND is highly effective when used with biofilm carriers like MBBR, which create the necessary aerobic/anoxic micro-zones. It is particularly useful for projects with limited space and requires precise DO control at around 0.1-0.5 mg/L.

Summary: Driving the Future of Nitrogen Removal

The transition from traditional nitrogen removal to advanced autotrophic and short-cut processes represents a significant leap in environmental engineering efficiency. By integrating high-performance sensing technology like the YexSensor YEX-206 series with innovative processes like ANAMMOX and CANON, system integrators can deliver solutions that are not only compliant but also highly sustainable.

As global standards for Total Nitrogen (TN) continue to tighten, the ability to monitor and control these sensitive biological processes in real-time will be the defining factor in the success of modern industrial wastewater treatment projects.

Project Support & Integration:
       For detailed Modbus register maps, custom flow cell designs, or integration support for large-scale nitrogen removal projects, please contact the YexSensor technical engineering team.