New technology for biological denitrification of sewage-short-cut nitrification-denitrification process (1)

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1 New technology for biological denitrification of sewage

The traditional biological treatment method of nitrogen removal mainly relies on the assimilation of microbial cells to convert nitrogen into cell protoplasm components, so the traditional biological treatment method can only remove about 40% of the nitrogen in the domestic sewage
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The new biological denitrification technology is mainly aimed at the traditional biological denitrification theory, which is to oxidize ammonia nitrogen into nitrate through the action of nitrifying bacteria under aerobic and low substrate concentration conditions .

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1 Short-cut nitrification-denitrification process

Short-cut nitrification-denitrification biological denitrification can also be called nitrous acid type biological denitrification technology
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The principle is to control the nitrification process in NO ₂ ^- stage is terminated, followed by denitrification

(1) Sharon process According to the principle of short-cut nitrification and denitrification, in 1997, Helling, Delft University of Technology in the Netherlands, developed a new type of process—Sharon process
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Sharon process is a new process for treating ammonia-containing wastewater with high concentration and low carbon to nitrogen mass ratio.

In the Sharon process, firstly, based on the fact that the growth rate of nitrosating bacteria at higher temperatures (30～35℃) is significantly higher than that of nitrifying bacteria, the rapid proliferation of nitrosating bacteria is used to make nitrifying bacteria compete Failed
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High temperature is beneficial to increase the specific growth rate of bacteria, so that the reactor can maintain a sufficient concentration of nitrosating bacteria without sludge retention, that is, the sludge age in the Sharon process is completely equal to the hydraulic retention time (SRT=HRT)

The Sharon process has the following characteristics
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① Developed a new process for biological denitrification treatment of high-concentration wastewater via the nitrite route, which has a fast denitrification rate and low investment and operating costs
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②Due to the high temperature (30～35℃), the microorganisms proliferate rapidly during the reaction period and the aerobic residence time is short, which is limited to 1d
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③ high microbial activity, and K
.

The value is also quite high.

④Because nitrosating bacteria grow faster than nitrifying bacteria under high temperature, the oxidation of nitrite is blocked, and there is no organism (sludge) in the system (because SRT=HRT), so simply restrict SRT to achieve ammonia oxidation and nitrous acid Salt does not oxidize
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⑤The influent concentration is high and a lot of heat is generated.
This should be considered in the design
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⑥Because the process has no sludge retention, the suspended solids in the discharged water will not affect the process operation
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⑦ Only a single reactor is needed, which simplifies the processing system
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(2) Anammox process In 1990, the Kluyver Biotechnology Laboratory of Delft University of Technology in the Netherlands developed the Anammox process, that is, under anaerobic conditions, microorganisms directly use NH4+ as electron donors and NO ₂ ^-Is the electron acceptor, the biological oxidation process of converting NH ₄ ⁺ or NO ₂ ^- into N ₂ , the reaction formula is:

NH2 _.
4 ⁺ + NO ₂ ^- → N ₂ ↑ + 2H ₂ O

Since NO ₂ ^- is a key electron acceptor, the Anammox process is also classified as a nitrous acid type biological denitrification technology
.

Because the bacteria involved in anammox are autotrophic bacteria, there is no need to add COD to support denitrification, which can save 100% of the carbon source compared with conventional denitrification processes

The anammox bacteria found so far are Brocadia anam moxidans, Kuenenia stuttgartiensis, Scindua sorokinii, Scindua brodae and Scindua wagneri
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In addition to their wide distribution, these anammox bacteria also have the characteristics of multiple metabolic pathways

Anammox bacteria realize the short-range conversion of ammonia nitrogen, shorten the conversion process of nitrogen, and rely less on energy consumption and carbon sources, and have great advantages
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The synergistic coupling effect of anammox bacteria, methanogens and aerobic ammonia oxidizing bacteria provides the possibility for a new type of denitrification process

The main factors affecting the Anammox process are: matrix inhibition.
The matrix of the anammox process is ammonia and nitrite .
If the concentration of both is too high, it will also inhibit the anammox process; pH value, due to ammonia And NO ₂ ^- will dissociate in the aqueous solution, so the pH value has an effect on anammox.
Its suitable pH range is 6.
7～8.
3, and the most suitable pH value is 8
.