Analysis and Countermeasures of Ammonia Nitrogen Exceeding Standard in Wastewater Treatment Plant

2020/10/21

I. Methods for Treating Ammonia Nitrogen in Sewage Plants

At present, the main ammonia nitrogen reduction methods include biological nitrification and denitrification, break point chlorination, stripping and ion exchange. The application of the above methods will be limited due to ammonia nitrogen concentration, regeneration problems, treatment cost and other reasons. At present, large-scale sewage plants still adopt traditional biological denitrification technologies, mainly including A/O process, A2/O process, oxidation ditch, various improved SBR and other biological treatment methods. In the treatment process, denitrification is mainly realized through nitrification and denitrification processes.

Second, factors leading to excessive ammonia nitrogen in sewage plants

With the increasingly strict environmental protection, the stable operation of sewage treatment plants is particularly important. At present, nitrogen removal in sewage plants is mainly realized through nitrification and denitrification processes. Nitrifying bacteria are mostly autotrophic bacteria with slow proliferation, long generation period, sensitivity to external factors and easy impact of water quality and quantity. Once the influent quality and quantity of biochemical system change greatly, it will impact the biological system, and nitrifying bacteria will disappear in large quantities, which is difficult to recover naturally. The factors that usually lead to excessive ammonia nitrogen in sewage treatment plants include the following aspects:

1. The influent concentration is too high

High concentration of influent COD, ammonia nitrogen and organic nitrogen all affect the ammonia nitrogen treatment effect of nitrification system. The effect of COD on nitrification stage is mainly reflected in the competition for oxygen between heterotrophic bacteria and nitrifying bacteria. When COD is high, it is beneficial to the growth of heterotrophic bacteria. Heterotrophic bacteria dominate and nitrifying bacteria are few, resulting in poor nitrification effect. After hydrolysis and acidification, organic nitrogen can be converted into ammonia nitrogen, which indirectly leads to the increase of ammonia nitrogen in influent. Excessive ammonia nitrogen load has a great impact on activated sludge system. In addition, too high ammonia nitrogen will lead to an increase in the concentration of free ammonia, which will lead to the accumulation of nitrite.

2. The ratio of COD to SS is out of balance

Influenced by the influent quality and system design, the initial sedimentation tank is not fully precipitated and inorganic substances cannot be fully removed, resulting in low effective components of activated sludge and high actual organic sludge load. Even if SV30 is within the normal range, the content of inorganic substances is high, the content of MLSS is high, and the content of MLVSS/MLSS is low. In this case, the calculation load is deviated and the sludge discharge is too large. In addition, inorganic particles settle in the aerobic zone, which is easy to block the aeration head and affect the aeration effect. 

3. Effect of temperature

At low temperature, the reproduction rate of nitrifying bacteria decreases, the enzyme activity in the body is inhibited, and the metabolic speed is slow. The nitrification rate is generally lower than 15 , and the activity begins to decrease when the temperature is lower than 12 . When the sewage temperature is lower than 8 , the nitrification and denitrification activities of microbial micelles are obviously inhibited or even stopped. Therefore, it is easy to reduce ammonia nitrogen treatment capacity in winter.

4. Other factors

In addition, there are many factors affecting nitrification. For example, high pH value will affect the normal growth of microorganisms, increase the concentration of free ammonia in water and inhibit nitrifying bacteria. Nitrifying bacteria are also particularly sensitive to toxic substances such as heavy metals, phenols and cyanide. Therefore, the toxicity test of nitrifying bacteria to water samples can be used to determine whether wastewater has inhibitory effect on nitrification.

III. Control Measures When Ammonia Nitrogen Abnormality is Found

If ammonia nitrogen in effluent shows an upward trend, the following emergency measures can be selected to prevent further deterioration of water quality.

1. Reduce influent ammonia nitrogen load

Reduce the intake of ammonia nitrogen. When high concentration ammonia nitrogen is found to enter, it is necessary to start the emergency regulating tank in time and increase sampling and monitoring of influent water. Control ammonia nitrogen concentration from the source. Reducing the intake of water is an effective means to promote the recovery of nitrifying bacteria, but in actual operation, due to the limitation of residence time of the regulating tank, it can only be realized for several hours. 

2. Reduce the discharge of oxygen sludge 

Due to the long reproduction cycle of nitrifying bacteria, appropriate extension of SRT is beneficial to the growth of nitrifying bacteria. Secondly, when nitrification decreases, a large number of nitrifying bacteria will be lost, and mud discharge will accelerate the loss of nitrifying bacteria.

3. Increase internal and external reflux of that biochemical system

On the one hand, this can maintain a high sludge concentration and improve the impact resistance of the system; On the other hand, it can reduce the concentration of ammonia nitrogen entering the biochemical system, thus reducing the inhibitory effect of high concentration ammonia nitrogen or free ammonia on nitrifying bacteria.

4. Adding nitrifying bacteria to rapidly promote the recovery of nitrification system

Nitrifying bacteria are microbial inoculants after artificial enrichment and culture, which have better biological activity than conventional bacteria and solve the problem of slow natural growth of nitrifying bacteria. According to the microbial nutrition and physiological principles of sewage treatment, the addition can significantly improve the growth and reproduction rate of nitrifying bacteria in the system and promote the rapid recovery of nitrifying system. Nitrifying bacteria can not only be used for system recovery, but also improve the ammonia nitrogen treatment capacity of the original system without increasing the tank capacity. After addition, the load can be gradually increased and the ammonia nitrogen in the influent can be increased, with remarkable effect.

Especially in the near future, pneumonia caused by Novel Coronavirus has enhanced the disinfection awareness of families and enterprises across the country, and the use of chlorine-containing disinfectants has increased, which may lead to an increase in residual chlorine in the influent. The bactericidal effect of disinfectant has an impact on the biochemical system. Adding microbial inoculum to quickly restore the processing capacity of biochemical system is the best choice.