CN1958471A - Method for treating ammonia nitrogen wastewater - Google Patents

Abstract

This invention relates to a method for treating ammonia nitrogen wastewater, especially high-concentration ammonia nitrogen wastewater produced during manufacture of oil-refinery catalyst. The method comprises: (1) adjusting the pH value of the wastewater, and solid-liquid separating to remove suspended matters and dissolved Si2+, Al3+ and their compounds; (2) adding Ca2+ to form CaSO4 precipitate, and solid-liquid separating to reduce acidic matters in the wastewater; (3) adding CO32- to form CaCO3 precipitate, and solid-liquid separating to remove Ca2+ in the wastewater; (4) steam-stripping for deamination, and performing biochemical treatment so that wastewater reaches state discharge standards. The method can solve the problems of low effect on removing suspended matters and dissolved Si2+, Al3+ and their compounds, scaling and column blockage during steam-stripping process, and the need for a large amount of alkali added, and can improve wastewater treatment effect.

Description

A kind of treatment method of ammonia nitrogen wastewater

technical field

The invention relates to a treatment method for industrial wastewater, in particular to a treatment method for high-concentration ammonia nitrogen wastewater.

Background technique

Ammonia nitrogen is a pollutant that has a serious impact on the water environment. Its main manifestations are: eutrophication of water body, promotion of algae reproduction, large consumption of dissolved oxygen in water, death of aquatic organisms, and water odor. All countries in the world strictly limit the concentration of ammonia nitrogen in wastewater. The discharge standard currently adopted in my country is the "Comprehensive Discharge Standard for Wastewater" (GB8978-1996). The standard ammonia nitrogen discharge concentration is less than or equal to 15mg/l, and the secondary standard ammonia nitrogen discharge concentration is less than or equal to 25mg/l.

At present, there are many methods for treating ammonia nitrogen wastewater, mainly including: air stripping method, resin exchange method, breakpoint chlorination method, membrane filtration method, chemical precipitation method and biological method.

The air stripping method firstly adjusts the wastewater to be alkaline, so that the NH ₄ ⁺ ions in it are converted into ammonia molecules, and then the ammonia is removed by stripping; because the concentration of ammonia in the stripping gas is low, it is not easy to recycle, and direct discharge will cause secondary pollution. secondary pollution. Resin exchange method, breakpoint chlorination method and membrane filtration method, because they are easily interfered by other pollutants in wastewater, have poor treatment effect and high treatment cost. The chemical precipitation method uses ammonia to react with phosphate and magnesium oxide to generate insoluble magnesium ammonium phosphate (MgNH ₄ PO ₄ ) to remove ammonia nitrogen in wastewater; magnesium ammonium phosphate can be used as fertilizer for crops, but the ammonium phosphate obtained by this method Magnesium often contains substances that are harmful to crops and cannot be utilized.

Biological method is currently the main method for treating low-concentration ammonia-nitrogen wastewater. For low-concentration wastewater with an ammonia nitrogen concentration below 300mg/l, biological methods are generally used for direct treatment (anaerobic denitrification-aerobic nitrification); for medium-concentration wastewater with an ammonia nitrogen concentration of 300-1000mg/l, because of its ammonia nitrogen The concentration has already produced toxicity and inhibitory effect on microorganisms. Generally, the ammonia nitrogen concentration of the wastewater is diluted to below 300mg/l, and then treated by biological methods; for high-concentration ammonia nitrogen wastewater with an ammonia nitrogen concentration above 1000mg/l, steam stripping is generally used recovery of ammonia from wastewater.

The ammonia nitrogen wastewater treatment method of the invention mainly treats the high concentration ammonia nitrogen wastewater produced in the production of oil refining catalysts. Refining catalysts are used in the petroleum refining process, usually using rare earth NaY type and rare earth NaX type zeolites as raw materials, using (NH ₄ ) ₂ SO ₄ or NH ₄ Cl to exchange Na ⁺ in the zeolite to generate NH ₄ Y or NH ₄ X-type refining catalyst. In the production process of oil refining catalysts, a large amount of production wastewater will be produced, which is characterized by: in addition to ammonia nitrogen, the wastewater also contains a large number of fine suspended solids and dissolved ions and colloidal compounds containing silicon and aluminum.

In the prior art, Chinese patent CN1367147A discloses a method for treating high-concentration ammonia-nitrogen wastewater. In the method, quicklime and calcium peroxide are first added to the wastewater, and after stirring and aeration, sodium hydroxide and calcium perborate are added. After stirring, Aeration, adding aluminum salt or iron salt flocculant, stirring and aeration, and finally adding polymer flocculant, stirring evenly and then settling and separating. In this method, the ammonia nitrogen in the waste water is directly discharged into the atmosphere, which not only wastes resources, but also causes secondary pollution.

In the prior art, Chinese patent CN1078872C discloses a method for recycling suspended solids in catalyst production wastewater. This method uses microporous filtration technology to recover solid materials in ammonia nitrogen wastewater, but does not recover ammonia nitrogen dissolved in wastewater. High concentration The ammonia nitrogen wastewater cannot be discharged directly.

Combining the above existing technologies, there are currently two main treatment methods for this type of wastewater: one method is that the wastewater first removes suspended solids through precipitation, then adds sodium hydroxide, and recovers ammonia through stripping; the other method is, first Remove suspended matter by membrane filtration, then add sodium hydroxide, and recover ammonia by stripping.

The above method has the following problems:

1. The precipitation method removes suspended solids. Due to the fine particles, the sedimentation effect of suspended solids is poor, and the silicon-aluminum substances dissolved in wastewater cannot be precipitated and removed. Suspended solids and silicon-aluminum substances that are easy to scale enter the stripping tower, and fillers are prone to occur Fouling and blockage.

2. Membrane filtration removes suspended solids. Due to the fine particles of suspended solids and the viscous nature of colloidal compounds in wastewater, the filter membrane is easily blocked, and microfiltration and ultrafiltration membranes cannot remove dissolved silicon-aluminum ions and their compounds. Packing fouling and tower plugging are prone to occur during stripping.

3. In order to convert ammonia nitrogen into ammonium hydroxide and ammonia that can be separated by stripping, the wastewater needs to be adjusted to alkalinity before stripping. Generally, 20-25g of sodium hydroxide needs to be added for stripping 1 ton of the above wastewater. higher cost.

Contents of the invention

In order to solve the problems existing in the prior art: poor removal of suspended solids, dissolved silicon-aluminum substances brought into the stripping process to cause fouling and tower blockage, high cost of stripping deamination and alkali addition, etc., the treatment method of the present invention is as follows Achieved:

The ammonia nitrogen wastewater treated by the invention is mainly composed of catalyst wastewater and molecular sieve wastewater in oil refining catalyst production. Among them, the catalyst wastewater comes from the catalyst production unit, and its suspended solids are 500-3000 mg/l, and ammonia nitrogen is 50-500 mg/l; the molecular sieve alkaline wastewater comes from the NaY crystallization mother liquor and washing water of the molecular sieve device, and its suspended solids are 300-500 mg/l. l; Molecular sieve acid wastewater comes from the exchange and washing filtrate of the molecular sieve device, the suspended matter is 1000-1200mg/l, and the ammonia nitrogen is 5000-10000mg/l. The above wastewater is generally acidic after mixing. The soluble substances in the wastewater include: ammonia nitrogen, SO ₄ ^2- , SiO ₂ , Al ³⁺ and Na ⁺ , etc. The main components of the suspended matter are: SiO ₂ and Al(OH) ₃ , etc. .

The processing method includes the following steps in sequence:

a. Removing silicon and aluminum: adding alkali to the waste water to make the pH 5.0-10.5; and then separating the solid and liquid to obtain the separation liquid.

The added alkali is preferably calcium oxide, calcium hydroxide or sodium hydroxide; the pH of the waste water is preferably 6.5-9.0. Adjust the appropriate pH value, and the soluble silicon-aluminum ions and their compounds in the wastewater are decomposed to form suspended solids; generally, the suspended solids concentration of the wastewater before adjusting the pH value is 500-2000 mg/l, and the wastewater after adjusting the pH value The concentration of suspended solids reaches 1000-3000mg/l.

There are many methods of solid-liquid separation, and the method of flocculation and precipitation is preferred; the flocculant can be selected from known products in the industry, and the polymer flocculant-polyacrylamide or/and polyaluminum chloride is preferably used; among them, polyacrylamide The concentration of polyaluminum chloride is 2-30 mg/l, preferably 4-10 mg/l, the concentration of polyaluminium chloride is 10-100 mg/l, and the preferred concentration is 20-60 mg/l; the flocculation temperature is 10-40 °C, The preferred flocculation temperature is 15-35°C.

Add a flocculant to the wastewater, stir evenly at an appropriate temperature, and let it stand still, so that the fine particles precipitated in the wastewater and the original suspended matter condense into larger particles, and after being removed by precipitation, the silicon aluminum ions and their The total concentration of compounds was reduced to 0.5-60 mg/l.

b. Removal of SO ₄ ^2- : Add Ca ²⁺ to the separation liquid, and the molar ratio of the added Ca ²⁺ to SO ₄ ^2- in the separation liquid is 0.5:1~3:1; then undergo solid-liquid separation to obtain separation liquid.

Preferably, calcium oxide or calcium hydroxide is added to the separation liquid; the molar ratio of the added Ca ²⁺ to the SO ₄ ^2- in the separation liquid is preferably 0.5:1 to 1.5:1; there are many methods for solid-liquid separation, preferably using the precipitation method.

The reaction formula for removing SO ₄ ^2- is:

After the above reaction, SO ₄ ^2- and Ca ²⁺ form water-insoluble calcium sulfate precipitation, and the ammonium sulfate salt in the wastewater is converted into ammonium hydroxide and ammonia that can be stripped and separated. Precipitation removes the acidic substance SO ₄ ^2- in wastewater, which is equivalent to adding sodium hydroxide before stripping (removing one mole of SO ₄ ^2- is equivalent to adding one mole of sodium hydroxide), which reduces the cost of stripping and deamination in the subsequent steps. Alkali cost. However, too much Ca ²⁺ added will increase the cost of Ca ²⁺ removal if it is brought into the subsequent process. Considering the cost of adding Ca ²⁺ , the cost of removing Ca ²⁺ and reducing the amount of alkali used in the stripping process, choose the appropriate molar ratio of Ca ²⁺ to SO ₄ ^2- . After precipitation, the SO ₄ ^2- in the separated liquid is reduced from 10,000 to 60,000 mg/l to 1,000 to 20,000 mg/l.

c. Removal of Ca ²⁺ : add CO ₃ ^2- to the separation liquid, and the molar ratio of the added CO ₃ ^2- to Ca ²⁺ in the separation liquid is 1:1~10:1; then undergo solid-liquid separation to obtain separation liquid.

Preferably, sodium carbonate is added to the separation liquid; the molar ratio of the added CO ₃ ^2- to Ca ²⁺ in the separation liquid is preferably 2:1 to 6:1; there are many methods for solid-liquid separation, preferably flocculation and precipitation Method; the flocculant can be selected from known products in the industry, preferably polymer flocculant--polyacrylamide or/and polyaluminum chloride; wherein, the concentration of polyacrylamide is 2-30mg/l, and the preferred concentration is 4-10mg/l, the concentration of polyaluminum chloride is 10-100mg/l, preferably 20-60mg/l; the flocculation temperature is 10-40°C, preferably 15-35°C.

The separation liquid for removing SO ₄ ^2- contains 200-1000mg/l Ca ²⁺ , and Ca ²⁺ will also cause fouling and tower blockage during stripping and deamination, and is formed by the reaction of CO ₃ ^2- and Ca ²⁺ Calcium carbonate precipitates to remove Ca ²⁺ in the separation solution. After flocculation and precipitation, the concentration of Ca ²⁺ in the separated liquid is reduced to 5-100 mg/l.

d. Stripping and deamination: add alkali to the separation liquid to make the pH 9.5 to 13.0; then carry out stripping treatment to obtain the stripping liquid and recover ammonia.

The added base is preferably sodium hydroxide. Preferably, a stripping tower is used to carry out stripping treatment, and a demister and foam section is arranged above the waste water inlet of the stripper; the distance between the demist and foam section and the waste water inlet is preferably 0.1 to 0.5 meters; the demist and foam section of the stripper and The stripping section is a packing section, and the packing is preferably a structured packing.

The reaction formula of the deamination process is:

There are many ways to remove NH ₃ , among which stripping NH ₃ is simple and efficient. Adjust the pH of the separation liquid to be alkaline so that the ammonia nitrogen can be converted into ammonium hydroxide and ammonia that can be stripped and separated.

The stripping process is usually carried out in the stripping tower. The stripping tower has a stripping section and a rectifying section. The rectifying section also plays the role of removing mist. The form of the stripper can be varied, such as plate tower and packed tower; the packing can use bulk packing or structured packing, and the use of high-efficiency structured packing is beneficial to improve the separation effect of the stripping section and the bottom of the tower, and reduce the stripping liquid. concentration of ammonia nitrogen. Recovered ammonia is obtained from the top of the stripping tower, which can be reused in the catalyst preparation system; the ammonia nitrogen wastewater treated by the present invention contains Na ⁺ , and substances containing Na ⁺ are added in the wastewater treatment process. If Na ⁺ is contained in the recovered ammonia, it will affect Its reuse; in the stripping process, the ^Na in the waste water mainly enters the recovered ammonia through the mist entrainment phenomenon, and the mist removal section is set on the upper part of the stripping tower, which can reduce the occurrence of the mist entrainment phenomenon and reduce the recovery of ammonia. ^Na concentration.

After stripping, the ammonia nitrogen concentration of the stripping liquid in the bottom of the tower is 10-300 mg/l, and the Na ⁺ concentration of ammonia recovered at the top of the tower is 1-20 mg/l.

e. adding carbon-containing compounds to the stripping liquid in step d, so that the nitrogen-to-carbon molar ratio of the stripping liquid is 1:1 to 1:10, and then performing aerobic biochemical treatment.

The added carbon-containing compound is preferably sodium carbonate or/and sodium bicarbonate, so that the nitrogen-to-carbon molar ratio of the stripping liquid is preferably 1:3-1:7.

The concentration of ammonia nitrogen in the stripping liquid is 10-300mg/l, and the biochemical treatment can further reduce the concentration of ammonia nitrogen in the waste water, so as to realize the standard discharge of waste water. The biochemical method can adopt the biological anaerobic denitrification-aerobic nitrification process, and the carbon source of the biochemical reaction can use inorganic carbon compounds, such as sodium carbonate and sodium bicarbonate, instead of the organic carbon source to reduce the cost of biochemical treatment. After biochemical treatment, the concentration of ammonia nitrogen in the wastewater is less than 15mg/l, meeting the national discharge standard.

A more preferred embodiment of the processing method of the present invention is:

The waste water contains ammonia nitrogen and SO ₄ ^2- , Al ³⁺ , SiO ₂ , and the treatment method includes the following steps in sequence:

a. Removing silicon and aluminum: adding at least one of calcium oxide, calcium hydroxide and sodium hydroxide to the wastewater to make the pH 6.5 to 9.0; ; Wherein, the flocculant is polyacrylamide or/and polyaluminum chloride, the concentration of the flocculant is 4-70mg/l, and the flocculation temperature is 15-35°C;

b. Removal of SO ₄ ^2- : add calcium oxide or calcium hydroxide to the separation liquid, and the molar ratio of the added Ca ²⁺ to SO ₄ ^2- in the separation liquid is 0.5:1~1.5:1; then use the method of precipitation Carry out solid-liquid separation to obtain separation liquid;

c. Removal of Ca ²⁺ : add sodium carbonate to the separation liquid, and the molar ratio of the added CO ₃ ^2- to Ca ²⁺ in the separation liquid is 2:1~6:1; then use the method of flocculation and precipitation for solid-liquid separation , to obtain a separation liquid; wherein, the flocculant is polyacrylamide or/and polyaluminum chloride, the concentration of the flocculant is 4-70mg/l, and the flocculation temperature is 15-35°C;

d. Stripping and deamination: Add sodium hydroxide to the separation liquid to make the pH 9.5 to 13.0; then use a stripping tower to carry out stripping treatment to obtain stripping liquid and recover ammonia; The demister section is set above, and the distance between the wastewater inlet and the demist section is 0.1 to 0.5 meters; the demist section and stripping section of the stripper are packing sections, and the packing adopts structured packing;

e. adding sodium carbonate or/and sodium bicarbonate to the stripping liquid in step d, so that the nitrogen-to-carbon molar ratio of the stripping liquid is 1:3 to 1:7, and then carry out aerobic biochemical treatment.

In the treatment method of the present invention, by adjusting the pH of the wastewater, the soluble silicon-aluminum ions and their compounds are precipitated from the wastewater, and after flocculation and precipitation, the suspended solids and soluble silicon-aluminum ions and their compounds in the wastewater are basically removed, avoiding steam Problems such as scaling and tower blockage during stripping and deamination; use Ca ²⁺ to react with SO ₄ ^2- in wastewater to form solid calcium sulfate precipitation, which reduces the cost of adding alkali for stripping deamination; after biochemical treatment, the wastewater meets national standards Emission Standards.

Description of drawings

Figure 1 is a schematic flow chart of the ammonia nitrogen wastewater treatment method.

Fig. 2 is a structural schematic diagram of a stripping tower.

Detailed ways

The technical solutions of the present invention will be further described in detail below in conjunction with the examples, and the protection scope of the present invention is not limited to the following specific embodiments.

Example 1

Remove suspended solids and soluble silicon-aluminum substances.

A kind of oil refining catalyst production wastewater, the wastewater contains dissolved SiO ₂ and Al ³⁺ and suspended solids, the main components of the suspended solids are SiO ₂ and Al(OH) ₃ , the concentration of Al ³⁺ in the wastewater is 323.4mg/l, The concentration of SiO ₂ was 124.4 mg/l.

Add sodium hydroxide to the wastewater to make the pH value 6.0; then add the flocculant polyacrylamide, the concentration is 10mg/l; after flocculation and precipitation, the concentration of Al ³⁺ in the wastewater is 0.49mg/l, SiO ₂ The concentration is 40.5 mg/l.

Examples 2-14

Remove suspended solids and soluble silicon-aluminum substances.

The type of alkali, adjusted pH, concentration of flocculant, and flocculation temperature were changed, and others were the same as in Example 1. The results of wastewater treatment are shown in Table 1.

Table 1 Raw water quality (unit mg/l) Add flocculant (unit mg/l) Flocculation temperature (℃) add alkali adjust pH Water quality after treatment (unit mg/l) Al ³⁺ SiO ₂ polyacrylamide PAC Al ³⁺ SiO ₂ Example 2 323.4 124.4 2 10 10 sodium hydroxide 5.0 1.30 36.7 Example 3 4 20 40 6.6 0.42 15.4 Example 4 6 40 15 7.0 0.29 9.0 Example 5 8 50 35 7.4 0.21 3.9 Example 6 10 60 25 8.2 0.46 1.3 Example 7 30 100 25 9.0 0.45 0.6 Example 8 2 10 10 Calcium hydroxide 6.0 0.42 39.5 Example 9 4 20 40 6.5 0.39 15.1 Example 10 6 40 15 7.0 0.28 8.9 Example 11 8 40 35 7.6 0.19 3.2 Example 12 8 50 30 8.1 0.40 1.1 Example 13 10 60 25 9.0 0.46 0.5 Example 14 30 100 25 10.5 1.20 0.6

Example 15

Removal of acidic substances SO ₄ ^2- .

A refinery catalyst production waste water, after removing suspended solids and soluble silicon-aluminum substances, the SO ₄ ^2- concentration of the waste water is 43200mg/l.

Calcium hydroxide is added to the wastewater, and the molar ratio of Ca ²⁺ and SO ₄ ^2- added is 0.5:1. After precipitation, the concentration of SO ₄ ^2- in the wastewater is 19150 mg/l.

Examples 16-21

Removal of acidic substances SO ₄ ^2- .

The added Ca ²⁺ -containing substances, the molar ratio of Ca ²⁺ to SO ₄ ^2- were changed, and the others were the same as in Example 15. See Table 2 for the wastewater treatment results.

Table 2 SO ₄ ^2- concentration before treatment (unit mg/l) join in Molar ratio of Ca ²⁺ to SO ₄ ^2- SO ₄ ^2- concentration after treatment (unit mg/l) Example 16 43200 Calcium hydroxide 0.75:1 15900 Example 17 1.0:1 11200 Example 18 1.25:1 5690 Example 19 Calcium Oxide 1.5:1 3770 Example 20 2.0:1 3240 Example 21 3.0:1 1670

Example 22

Removal of Ca ²⁺ .

A refinery catalyst produces waste water. After removing acidic substance SO ₄ ^2- , the concentration of Ca ²⁺ in the waste water is 458.7mg/l.

Sodium carbonate is added to waste water to form calcium carbonate precipitation; the molar ratio of added CO ₃ ^2- to Ca ²⁺ is 1:1; polyacrylamide 8 mg/l and polyaluminum chloride 20 mg/l are added to waste water, and the Flocculation and precipitation, the concentration of Ca ²⁺ in the wastewater is 99.6mg/l.

Examples 23-26

Removal of Ca ²⁺ .

The concentration of flocculant, flocculation temperature, and the molar ratio of CO ₃ ^2- to Ca ²⁺ were changed, and the others were the same as in Example 22. See Table 3 for the wastewater treatment results.

table 3 Ca ²⁺ concentration before treatment (mg/l) Add flocculant (unit mg/l) Flocculation temperature (℃) Molar ratio of sodium carbonate to Ca2 ⁺ Ca ²⁺ concentration after treatment (mg/l) polyacrylamide PAC Example 23 458.7 2 10 10 1.5:1 77.6 Example 24 4 20 15 2:1 62.4 Example 25 10 60 35 6:1 26.3 Example 26 30 100 30 10:1 16.5

Example 27

Stripping deamination.

A refinery catalyst produces waste water. After removing Ca ²⁺ , the concentration of ammonia nitrogen in the waste water is 5379mg/l.

The stripping tower is used to strip and remove ammonia; the stripping tower has a stripping section [2] and a mist-removing section [1], and the stripping section [2] and the mist-removing section [1] use structured packing; the waste water pipe [ 4] The inlet is located under the mist removal section [1], the inlet of the steam pipe [5] is located under the liquid level [3] of the tower kettle, and its opening direction is downward.

The diameter of the stripper is 0.20 meters, the height of the stripping section [2] is 1.00 meters, the height of the mist removal section [1] is 0.15 meters, the depth of the tower still liquid is 0.30 meters, and the inlet of the steam pipe [5] is located in the tower still 1/2 place of the liquid depth, the distance of the waste water pipe [4] inlet and the defogging foam section [1] is 0.30 meters.

Add sodium hydroxide to the wastewater to make its pH 9.5. After stripping, the ammonia nitrogen concentration of the stripping liquid at the bottom of the tower is 86 mg/l, and the Na ⁺ concentration of ammonia recovered at the top of the tower is 2.2 mg/l.

Example 28

Stripping deamination.

The structure of the stripper is the same as in Example 27. The ammonia nitrogen concentration of the waste water is 3651 mg/l, and sodium hydroxide is added to make the pH of the waste water 13.0. After stripping, the ammonia nitrogen concentration of the stripping liquid at the bottom of the tower is 69 mg/l, and the Na ⁺ concentration of ammonia recovered at the top of the tower is 1.4 mg/l.

Example 29

biochemical treatment.

A kind of refinery catalyst production wastewater, after stripping and deammonification, the ammonia nitrogen concentration of the stripping liquid is 135mg/l.

Sodium carbonate and sodium bicarbonate are added to the wastewater to make the nitrogen-to-carbon molar ratio of the wastewater 1:4; an aerobic process is used for biochemical treatment, and the treatment time is 8 hours.

The ammonia nitrogen concentration of the biochemical effluent after treatment is 13mg/l, which meets the national discharge standard.

Examples 30-33

biochemical treatment.

The ammonia nitrogen concentration, nitrogen-to-carbon molar ratio, and biochemical treatment time of the stripping liquid were changed, and the others were the same as in Example 27. The wastewater treatment results are shown in Table 4.

Table 4 Biochemical treatment time (hours) Nitrogen to carbon molar ratio Ammonia nitrogen concentration in biochemical influent (mg/l) Ammonia nitrogen concentration in biochemical effluent (mg/l) Example 30 8 1:1 135 10.5 Example 31 6 1:6 96 9.0 Example 32 6 1:8 127 11.3 Example 33 6 1:10 173 13.8

Claims (13)

1. A treatment method for ammonia nitrogen waste water, containing ammonia nitrogen and SO ₄ ^2- , Al ³⁺ , SiO ₂ in the waste water, the treatment method comprises the following steps in turn: a. Removing silicon and aluminum: adding alkali to the wastewater to make the pH 5.0 to 10.5; and then undergoing solid-liquid separation to obtain a separation liquid; b. Removal of SO ₄ ^2- : Add Ca ²⁺ to the separation liquid, and the molar ratio of the added Ca ²⁺ to SO ₄ ^2- in the separation liquid is 0.5:1~3:1; then undergo solid-liquid separation to obtain separation liquid; c. Removal of Ca ²⁺ : add CO ₃ ^2- to the separation liquid, and the molar ratio of the added CO ₃ ^2- to Ca ²⁺ in the separation liquid is 1:1~10:1; then undergo solid-liquid separation to obtain separation liquid; d. Stripping and deamination: add alkali to the separation liquid to make the pH 9.5 to 13.0; then carry out stripping treatment to obtain the stripping liquid and recover ammonia. 2. The method for treating ammonia nitrogen wastewater according to claim 1, characterized in that: In step a, the alkali added is at least one of calcium oxide, calcium hydroxide and sodium hydroxide; the pH of the waste water is 6.5-9.0; the solid-liquid separation adopts the method of flocculation and precipitation. 3. The method for treating ammonia nitrogen wastewater according to claim 2, characterized in that: The flocculant for flocculation and precipitation is polyacrylamide or/and polyaluminum chloride, the concentration of the flocculant is 2-130mg/l, and the flocculation temperature is 10-40°C. 4. The method for treating ammonia nitrogen wastewater according to claim 3, characterized in that: The concentration of the flocculant is 4-70mg/l, and the flocculation temperature is 15-35°C. 5. The method for treating ammonia nitrogen wastewater according to claim 1, characterized in that: In step b, calcium oxide or calcium hydroxide is added to the separation liquid; the molar ratio of the added Ca ²⁺ to SO ₄ ^2- in the separation liquid is 0.5:1-1.5:1; the solid-liquid separation adopts the method of precipitation. 6. The method for treating ammonia nitrogen wastewater according to claim 1, characterized in that: In step c, sodium carbonate is added to the separation liquid; the molar ratio of the added CO ₃ ^2- to Ca ²⁺ in the separation liquid is 2:1-6:1; the solid-liquid separation adopts the method of flocculation and precipitation. 7. The method for treating ammonia nitrogen wastewater according to claim 6, characterized in that: The flocculant for flocculation and precipitation is polyacrylamide or/and polyaluminium chloride, the total concentration of the flocculant is 2-130mg/l, and the flocculation temperature is 10-40°C. 8. The method for treating ammonia nitrogen wastewater according to claim 7, characterized in that: The total concentration of the flocculant is 4-70mg/l, and the flocculation temperature is 15-35°C. 9. The method for treating ammonia nitrogen wastewater according to claim 1, characterized in that: In step d, the alkali is sodium hydroxide; a stripping tower is used for stripping treatment, and a mist removal section is set above the waste water inlet of the stripping tower. 10. The method for treating ammonia nitrogen wastewater according to claim 9, characterized in that: The distance between the demister section and the waste water inlet is 0.1-0.5 meters; the demist section and the stripping section of the stripping tower are packing sections, and the packing adopts structured packing. 11. The method for treating ammonia nitrogen wastewater according to any one of claims 1-10, characterized in that: Carbon-containing compounds are added to the stripping liquid in step d, so that the nitrogen-to-carbon molar ratio of the stripping liquid is 1:1 to 1:10, and then aerobic biochemical treatment is performed. 12. The treatment method of ammonia nitrogen wastewater according to claim 11, characterized in that: The carbon-containing compound is sodium carbonate or/and sodium bicarbonate, and the nitrogen-to-carbon molar ratio is 1:3˜1:7. 13. A treatment method for ammonia nitrogen wastewater, the wastewater contains ammonia nitrogen and SO ₄ ^2- , Al ³⁺ , SiO ₂ , the treatment method includes the following steps in sequence: a. Removing silicon and aluminum: adding at least one of calcium oxide, calcium hydroxide and sodium hydroxide to the wastewater to make the pH 6.5 to 9.0; ; Wherein, the flocculant is polyacrylamide or/and polyaluminum chloride, the concentration of the flocculant is 4-70mg/l, and the flocculation temperature is 15-35°C; b. Removal of SO ₄ ^2- : add calcium oxide or calcium hydroxide to the separation liquid, and the molar ratio of the added Ca ²⁺ to SO ₄ ^2- in the separation liquid is 0.5:1~1.5:1; then use the method of precipitation Carry out solid-liquid separation to obtain separation liquid; c. Removal of Ca ²⁺ : add sodium carbonate to the separation liquid, and the molar ratio of the added CO ₃ ^2- to Ca ²⁺ in the separation liquid is 2:1~6:1; then use the method of flocculation and precipitation for solid-liquid separation , to obtain a separation liquid; wherein, the flocculant is polyacrylamide or/and polyaluminum chloride, the concentration of the flocculant is 4-70mg/l, and the flocculation temperature is 15-35°C; d. Stripping and deamination: Add sodium hydroxide to the separation liquid to make the pH 9.5 to 13.0; then use a stripping tower to carry out stripping treatment to obtain stripping liquid and recover ammonia; The demister section is set above, and the distance between the wastewater inlet and the demist section is 0.1 to 0.5 meters; the demist section and stripping section of the stripper are packing sections, and the packing adopts structured packing; e. adding sodium carbonate or/and sodium bicarbonate to the stripping liquid in step d, so that the nitrogen-to-carbon molar ratio of the stripping liquid is 1:3 to 1:7, and then carry out aerobic biochemical treatment.

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