Short-cut nitrification, as one of the core processes for efficient nitrogen removal in wastewater treatment, operates on the principle of selectively enriching ammonia-oxidizing bacteria (AOB) while inhibiting the activity of nitrite-oxidizing bacteria (NOB) through controlled environmental conditions and operational parameters. This process achieves directed conversion of ammonia nitrogen into nitrite. With advantages such as low energy consumption, short reaction cycles, and minimal alkalinity requirements, standardized cultivation is crucial for ensuring stable and efficient process operation. The key technical points are as follows:
1. Screening and Acclimation of Inoculation Sludge
The quality of the inoculated sludge directly determines the startup efficiency of short-cut nitrification. Municipal wastewater treatment plant aeration tank activated sludge or acclimated short-cut nitrifying sludge should be prioritized, with the sludge settling ratio (SV30) maintained at 20%-30% and MLSS concentration between 3000-5000 mg/L, ensuring no significant odor and good settling performance. The inoculation volume should be controlled at 15%-20% of the reactor's effective volume. After inoculation, initiate the acclimation phase: set the initial influent ammonia nitrogen concentration at 50-80 mg/L, maintain a volumetric loading rate of 0.1-0.2 kg NH4+-N/(m³·d). Once the ammonia nitrogen removal rate stabilizes above 70%, gradually increase the influent ammonia nitrogen concentration by 20%-30% weekly until reaching the design load, thereby enhancing the environmental adaptability and metabolic activity of AOB through gradient adaptation.
2. Parameter Control
(1) Temperature Control
The optimal growth temperature for AOB is 25-35°C, where its ammonia oxidation rate is significantly higher than that of NOB. During cultivation, the reactor temperature fluctuation should be controlled within ±1°C, which can be maintained using equipment such as a constant-temperature water bath or heating jacket. When the temperature falls below 15°C, the influent load should be appropriately reduced to prevent process failure due to inhibited AOB activity.
(2) Dissolved Oxygen (DO) Regulation
One of the core control points for short-cut nitrification is maintaining a low-oxygen environment, with dissolved oxygen (DO) concentration strictly controlled at 0.5-1.0 mg/L. Precise DO regulation is achieved by adjusting aeration intensity (using low-intensity continuous or intermittent aeration modes). The low-oxygen environment significantly inhibits the proliferation of aerobic nitrifying bacteria (NOB) while meeting the micro-aerobic metabolic requirements of ammonia-oxidizing bacteria (AOB). If a biofilm reactor is employed, the anoxic microenvironment within the biofilm can further enhance the selective enrichment of AOB.
(4) Nutrient Proportioning
The influent must meet the nutritional requirements for AOB growth, with a nitrogen-to-phosphorus (N:P) ratio controlled at 10:1. Additionally, trace elements such as magnesium, iron, and manganese should be supplemented (with concentrations preferably ranging from 0.1 to 1.0 mg/L) to provide essential cofactor support for AOB metabolism. High concentrations of toxic or harmful substances (e.g., heavy metals, antibiotics, etc.) in the influent should be avoided to prevent irreversible inhibition of microbial activity.
III. Monitoring and Regulation of the Cultivation Process
During the cultivation period, a routine monitoring mechanism must be established to measure the concentrations of ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen in the influent and effluent daily, while simultaneously monitoring pH, dissolved oxygen (DO), temperature, alkalinity, and other parameters.
In the initial phase (1-2 weeks), the focus should be on the ammonia nitrogen removal rate and sludge settling performance. If the ammonia nitrogen removal rate is below 50%, the current load should be maintained until the microbial community adapts.
During the transition phase (2-4 weeks), the primary concern is monitoring the nitrite accumulation rate (NO2--N/(NO2--N+NO3--N)). When the accumulation rate stabilizes at 80% or higher, the load can be gradually increased.
In the stable phase (4-6 weeks), it is essential to ensure that the nitrite accumulation rate is ≥90% and the ammonia nitrogen removal rate is ≥85%, indicating that the shortcut nitrification system has reached a mature state.
If excessive proliferation of NOB (continuous increase in nitrate nitrogen concentration) occurs during the cultivation process, measures such as raising the temperature (to 30-35°C), shortening the aeration time, or implementing short-term starvation (stopping influent for 1-2 days) can be taken to inhibit NOB activity. If AOB activity declines, it is necessary to investigate whether parameters such as pH, DO, and temperature deviate from the optimal range, promptly adjust them, and supplement nutrients.
IV. Measures to Ensure Stable Process Operation
Once the short-cut nitrification system matures, it is essential to maintain stable operational parameters and avoid drastic fluctuations in influent load, temperature, pH, and other factors. Regular sludge discharge should be implemented to keep MLSS concentration within the range of 3000-6000 mg/L, preventing sludge aging. When there are significant changes in influent quality, a stepwise load adjustment approach should be adopted to allow microbial communities time to adapt. Through standardized cultivation procedures and precise operational control, stable and efficient operation of the short-cut nitrification process can be achieved, laying the foundation for subsequent denitrification or anammox process integration.
