Total Nitrogen Exceeding the Standard and Its Impact on Sewage Treatment Systems

1. Decreased Process Efficiency

- Impeded Denitrification
Excessive total nitrogen often accompanies reduced denitrification efficiency. High dissolved oxygen (DO) levels in the anoxic zone (＞0.5 mg/L) disrupt the anoxic environment, inhibiting denitrifying bacteria activity and preventing effective conversion of nitrate nitrogen to nitrogen gas. Additionally, insufficient carbon-to-nitrogen ratio (C/N＜4) restricts the denitrification process, preventing complete nitrogen removal.

- Restricted Nitrification
Accumulation of ammonia nitrogen may suppress nitrifying bacteria activity, especially when influent ammonia nitrogen concentration fluctuates or pH deviates from the suitable range (6.5-8.0), significantly reducing nitrification rates. Low temperatures (＜15℃) also decrease both nitrification and denitrification efficiency.

2. Imbalanced Microbial System

- Inhibition of Bacterial Communities
High concentrations of free ammonia (FA＞60 mg/L) directly inhibit the activity of nitrifying bacteria (AOB and NOB), leading to system collapse. Additionally, insufficient carbon sources may cause heterotrophic bacteria to proliferate excessively, reducing space for denitrifying bacteria.

- Abnormal Sludge Activity
Short sludge age (SRT) or excessive sludge wasting prevents nitrifying bacteria from completing their reproductive cycles. High sludge loading (＞0.15 kgBOD/kgMLSS·d) may cause non-filamentous bulking, reducing sludge settleability.

3. Uncontrolled Operating Parameters

- Malfunctioning Recirculation Ratios
Insufficient internal recirculation ratio (＜300%) prevents adequate return of nitrate nitrogen to the anoxic zone, affecting denitrification efficiency. Excessive external recirculation ratio (＞50%) may introduce dissolved oxygen into the anoxic zone, disrupting denitrification conditions.

- DO and pH Fluctuations
Insufficient dissolved oxygen (DO＜2 mg/L) in the aeration tank limits nitrification, while excessive DO disrupts anoxic zone denitrification. Deviations in pH from the optimal range (7.2-8.0 for nitrification, 6.5-8.0 for denitrification) inhibit key enzyme activity.

4. Effluent Quality and Ecological Risks

- Worsened Eutrophication
Excessive total nitrogen in effluent (＞1.0 mg/L) directly causes water eutrophication, leading to algal blooms, dissolved oxygen depletion, and ecological chain collapse.

- Accumulation of Toxic Substances
Excessive nitrate and nitrite may accumulate through the food chain, posing health risks (e.g., carcinogenic risks).

1. Process Optimization

- Supplement carbon sources (e.g., sodium acetate) to adjust C/N to 4-6.

- Control internal recirculation ratio (300-500%) and external recirculation ratio (30-50%).

- Install pre-denitrification tanks or MBR processes to extend sludge age.

2. Parameter Regulation

- Maintain anoxic zone DO＜0.5 mg/L and aerobic zone DO=2-4 mg/L.

- Add alkalinity (e.g., sodium carbonate) to stabilize pH at 7.0-8.0.

3. Emergency Measures

- Add denitrifying bacterial agents to accelerate system recovery.

- Use chemical methods (e.g., breakpoint chlorination) for rapid nitrogen reduction in the short term.