June 14, 2024 Longchang Chemical

What is the cause analysis and solution for ammonia nitrogen exceeding the standard?

Nitrogen is the main nutrient causing eutrophication of water bodies, nitrogen source pollution causes many environmental hazardous problems, the content of the relevant emission standards and numerical indicators are constantly improving.
Nitrogen removal mechanism

Nitrogen removal is not removed by cellular over-absorption removal, the main mechanism is:
1. Particulate non-biodegradable organic nitrogen becomes an activated sludge component through bioflocculation and is removed from the system by excluding the remaining activated sludge;
2. Particulate biodegradable organic nitrogen is converted to soluble biodegradable organic nitrogen through hydrolysis. Dissolved non-biodegradable organic nitrogen, which is discharged with the treated effluent, determines the organic nitrogen concentration of the effluent;
3. Dissolved biodegradable organic nitrogen is converted into ammonia nitrogen through the ammonification of heterotrophic bacteria, in which urea can be rapidly hydrolysed into ammonium carbonate. Nitrifying bacteria oxidise ammonia nitrogen to nitrate nitrogen under aerobic conditions, and denitrifying bacteria heterotrophically reduce nitrate to gaseous nitrogen under anoxic conditions, which is removed from the water.
Due to the anoxic area denitrification requires a large amount of carbon source, so the general anoxic area are placed in the front end of the biological treatment (intake end), but the intake water is mostly ammonia nitrogen, less nitrate nitrogen, can not be denitrification, so the need for internal reflux.
The total nitrogen concentration in the effluent of the biochemical tank and the internal reflux is the same, therefore, even in the theoretical state, the maximum nitrogen removal rate can only reach (r+R)/(1+r+R), of which, r is the ratio of internal reflux, R is the ratio of sludge reflux.
Nitrogen biochemical removal process

Nitrogen biochemical removal process mainly contains ammonification process, nitrification process, denitrification process, which denitrification process contains the whole process of denitrification and short-range denitrification, nitrifying bacteria generation cycle of 5~8 days, denitrifying bacteria generation cycle of about 15 days.
1. Ammonification process:
Ammonification process is the microbial decomposition of organic nitrogen compounds to produce ammonia, generally can be divided into two steps. The first step is the degradation of nitrogenous organic compounds (proteins, nucleic acids, etc.) into simple nitrogenous compounds such as peptides, amino acids, amino sugars, etc. The second step is the degradation of simple nitrogenous compounds produced in the deamidation process into NH₃.
2. Nitrification process:
The principle of nitrification reaction process is: under aerobic conditions, ammonia and nitrogen are oxidised by nitrifying bacteria into nitrite and nitrate.
Including two basic reaction steps: the nitrite bacteria involved in the conversion of ammonia nitrogen into nitrite reaction; nitrate bacteria involved in the conversion of nitrite into nitrate reaction.
3. Denitrification process:
The principle of denitrification reaction process is: in anoxic conditions, the use of denitrifying bacteria will nitrite and nitrate reduction to nitrogen and escape from the sewage, so as to achieve the purpose of nitrogen removal.
Denitrification is the nitrification reaction process of nitrate and nitrite reduced to nitrogen, denitrifying bacteria is a class of chemical energy heterotrophic parthenogenetic anoxic microorganisms. Nitrite bacteria and nitrate bacteria are chemoenergetic autotrophs, which use CO₂, CO₃²ˉ, HCO₃-, etc., as a carbon source, and obtain energy through the redox reaction of NH₃, NH⁴﹢, or NO²ˉ. The nitrification reaction process needs to be carried out under aerobic conditions and uses oxygen as the electron acceptor and elemental nitrogen as the electron donor.
When there is molecular oxygen, denitrifying bacteria oxidative decomposition of organic matter, the use of molecular oxygen as the final electron acceptor, when there is no molecular oxygen, denitrifying bacteria use nitrate and nitrite in the N ³ ﹢ and N ⁵ ﹢ as an electron acceptor, the organic matter is used as a carbon source to provide the electron donor to provide energy and oxidative stabilisation, which can be seen that denitrifying reaction must be carried out under anoxic conditions. This means that denitrification must be carried out under anoxic conditions.
During denitrification, denitrifying bacteria need organic carbon sources (e.g., carbohydrates, alcohols, organic acids) as electron donors and use nitrogen in NO³ˉ for anoxic respiration. The nitrification reaction consumes 4.57g of oxygen and 7.14g of alkalinity per 1g of ammonia nitrogen oxidised, which is manifested as a decrease in pH. During denitrification, the removal of nitrate nitrogen is accompanied by the removal of the carbon source, which is discounted to DO2.6g, and additionally, the denitrification process compensates for the alkalinity of 3.57g.
Picture of the whole process of denitrification and short process of denitrification biochemical principle diagrams

Ammonia nitrogen exceeds the standard reason and solution

1. High concentration of organic matter
Reason for analysis: operation and management is not in place, poor pretreatment effect, SS is more, so that the concentration of organic matter in the biochemical feed water of wastewater treatment is too high, which has exceeded the processing capacity of biochemical, thus leading to the removal of COD and ammonia nitrogen is inefficient.COD is high, which will inhibit the activity of nitrifying bacteria and help to give play to the activity of anaerobic bacteria, which will lead to the hydrolysis of organic nitrogen into ammonia, which will cause the ammonia nitrogen content of wastewater to be higher. higher.
Solution: immediately stop water intake for mulled aeration, internal and external reflux continuous opening; stop sludge discharge to ensure sludge concentration; if the organic matter has caused non-filamentous bacteria expansion can be added PAC to increase sludge flocculation, add defoamer to eliminate the impact of foam. Follow-up to improve the management level, do a good job of front-end pretreatment, reduce biochemical load.
2. Internal reflux abnormality
Reason for analysis: abnormal internal reflux due to electrical failure, mechanical failure or man-made reasons. Internal reflux caused by ammonia nitrogen exceeds the standard can also be attributed to the impact of organic matter, because there is no nitrification liquid reflux, resulting in aerobic pool only a small amount of nitrate nitrogen carried by the external reflux, the overall anaerobic environment, the carbon source will only be hydrolysed and acidified and will not be metabolised into carbon dioxide escape, so a large number of organic matter into the aeration tank, resulting in an increase in ammonia nitrogen.
Solution: internal reflux has led to elevated ammonia nitrogen, overhaul the internal reflux pump, stop or reduce the water intake for mulled aeration; nitrification system has collapsed, stop the water intake for mulled aeration, if there are conditions, the situation is more urgent can be added to a similar denitrification system biochemical sludge, to speed up the recovery of the system. Follow-up regularly check the return pump, timely detection and resolution of the problem.
3. pH is too low
Analyse the reason: general microorganisms should be in the pH=6-9 range is more appropriate, generally low pH caused by ammonia nitrogen exceeds the standard there are three cases:
a. Within the reflux is too large or within the reflux at the aeration open too large, resulting in carrying a large amount of oxygen into the anoxic pool, damage to the anoxic environment, denitrifying bacteria aerobic metabolism, part of the organic matter is aerobically metabolised, which seriously affects the completeness of the denitrification, because denitrification can be compensated for the nitrification reaction metabolism off the alkalinity of half, so because of the destruction of the anoxic environment leads to a reduction in the alkalinity generated by the reduction of pH below the appropriate pH of the nitrification bacterium. After the pH of nitrification reaction is inhibited, ammonia nitrogen rises.
b. Inlet water CN ratio is insufficient, the reason is also denitrification is incomplete, the alkalinity produced is less, resulting in a decrease in pH.
c. The pH decreases continuously due to the decrease of alkalinity of feed water.
Solution: found that the pH continuous decline should start adding alkali to maintain pH, and then analyse to find the cause; if the pH is too low has led to the collapse of the system, first of all, to add up the pH of the system, and then boring aeration or adding the same type of sludge.
4.DO is too low
Reason analysis: aerator aging and intermittent aeration can easily lead to aerator clogging, pool aeration oxygenation and mixing is blocked, while the nitrification reaction is aerobic metabolism, need to ensure that the aeration pool of dissolved oxygen suitable environment (anoxic pool DO = 0.2 ~ 0.5mg / L, aerobic pool DO ≥ 2mg / L) can be carried out normally, and DO is too low will result in nitrification is blocked, the ammonia nitrogen exceeds the standard.
Solution: replace the aeration head; increase the frequency conversion power of the fan, increase the air volume.
5. Mud age is too low
Reason analysis: too much sludge discharge and too little sludge reflux will lead to sludge age reduction, because bacteria have generation period, SRT is lower than generation period, it will lead to the bacteria can not be gathered in the system, the formation of dominant strains, so the corresponding metabolites can not be removed. Generally the sludge age is 3-4 times of the bacterial generation period. In multi-series, the sludge return is not balanced, and the difference between the sludge return of each series is too big, which leads to the rise of ammonia nitrogen in the series with less sludge return.
Solution: reduce the water intake or muffled aeration; add the same type of sludge; if the problem is caused by unbalanced sludge reflux, reduce the problem series of water intake or muffled aeration, to ensure that the normal series of operation will be part of the sludge reflux to the problem series, each series of flow measurement devices set up to facilitate observation.
6. Water quality fluctuations impact
Reason analysis: water quality and quantity fluctuations, regulating pool treatment is not in place, resulting in a sudden rise in ammonia nitrogen water, nitrogen removal system collapse, water ammonia nitrogen exceeds the standard.
Solution: Ensure that the pH of the case, add the same type of sludge, bored aeration recovery system; the end of the process to add ammonia nitrogen remover dosing and reaction device for emergency management.
7. Low temperature
Reason analysis: winter water temperature is very low, especially the temperature difference between day and night, often lower than the temperature needed for bacterial metabolism, making the bacteria dormant, nitrification system abnormal.
Solution: make the pool buried at the design stage; increase the sludge concentration in advance; heat the influent water to the appropriate temperature (the optimal temperature of nitrification reaction is generally 20-30℃, the nitrification reaction rate decreases below 15℃, and stops below 5℃; the optimal temperature of denitrification is 20-40℃, and the activity of denitrifying bacteria decreases below 15℃; the optimal temperature of common aerobic bacteria is generally 15-30℃).
8. Problem of process selection
Reason analysis: denitrification process chosen is simple aeration tank, contact oxidation, SBR and so on these processes, in fact, to ensure that HRT (hydraulic retention time) and SRT (mud age) is long enough, these processes can be de-ammonia nitrogen, but not economic.
Solution: Extend HRT and SRT, such as transforming into MBR to improve the age of mud, etc.; increase denitrification tank in front.

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