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What factors will cause the total nitrogen to exceed the standard?

Time : 2020-04-15

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What factors will cause the total nitrogen to exceed the standard?
The total nitrogen exceeds the standard in the current environmental protection industry is no stranger, then do you know what causes the total nitrogen to exceed the standard? After years of research, Making Green Environmental Protection has summarized the factors that caused the total nitrogen to exceed the standard. Let's understand it.
1) Sludge load and sludge age

Since biological nitrification is the prerequisite for biological denitrification, only good nitrification can obtain stable denitrification. Therefore, the nitrogen removal system must also use low load or ultra-low load, and use high sludge age.


(2) Internal and external reflux ratio

The external reflux of the biological denitrification system is smaller than that of the simple biological nitrification system. This is mainly because most of the nitrogen in the influent sewage has been removed, and the concentration of NO3--N in the secondary sedimentation tank is not high. Relatively speaking, the risk of sludge floating in the secondary sedimentation tank due to denitrification is very small. On the other hand, the sludge settling speed of the denitrification system is relatively fast. Under the premise of ensuring the required sludge concentration, the reflux ratio can be reduced to extend the residence time of sewage in the aeration tank.
For well-operated sewage treatment plants, the external reflux ratio can be controlled below 50%. The internal reflux ratio is generally controlled between 300 and 500%.

(3) Denitrification rate

Denitrification rate refers to the amount of nitrate denitrified per unit of activated sludge per day. Denitrification rate is related to temperature and other factors, and the typical value is 0.06 ~ 0.07gNO3--N / gMLVSS × d.

(4) Dissolved oxygen in anoxic area
For denitrification, it is hoped that the DO is as low as possible, preferably zero, so that denitrifying bacteria can "fully" denitrify and improve the efficiency of denitrification. However, from the perspective of the actual operation of the sewage treatment plant, it is still difficult to control the DO in the anoxic zone below 0.5 mg / L. Therefore, it affects the process of biological denitrification and thus affects the total nitrogen index of the effluent.

(5) BOD5 / TKN‍

Because denitrifying bacteria denitrify and denitrify in the process of decomposing organic matter, there must be sufficient organic matter in the sewage entering the anoxic zone to ensure the smooth progress of denitrification. Due to the lag in the construction of supporting pipeline networks in many sewage treatment plants, the BOD5 of the incoming plant is lower than the design value, while the indicators of nitrogen and phosphorus are equal to or higher than the design value, making the influent carbon source unable to meet the demand of denitrification carbon source It also led to the situation that the total nitrogen in the effluent exceeded the standard.

(6) pH‍
Denitrifying bacteria are not as sensitive to pH changes as nitrifying bacteria. They can perform normal physiological metabolism in the pH range of 6-9, but the preferred pH range for biological denitrification is 6.5-8.0.

(7) Temperature

Although denitrifying bacteria are not as sensitive to temperature changes as nitrifying bacteria, the denitrifying effect will also change with temperature changes. The higher the temperature, the higher the denitrification rate. At 30 ~ 35 ℃, the denitrification rate increases. When it is lower than 15 ℃, the denitrification rate will be significantly reduced, to 5 ℃, denitrification will tend to stop. Therefore, in order to ensure the denitrification effect in winter, it is necessary to increase the SRT, increase the sludge concentration or increase the number of operational pools.

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