CN117069264A - A system and method based on nitrosation-anammonia oxidation coupled magnesium and phosphorus crystallization to achieve denitrification of anaerobic digestion liquid and simultaneous phosphorus recovery - Google Patents

Abstract

The invention belongs to the field of sewage biological treatment technology and resource recovery. It discloses a system and method for realizing denitrification of anaerobic digestion liquid and simultaneous phosphorus recovery based on nitrosation-anaerobic ammonium oxidation coupled magnesium and phosphorus crystallization. The system of the present invention includes: a raw water tank, a nitrification reactor, an intermediate tank, an anaerobic ammonium oxidation reactor, and a magnesium salt solution storage tank; The anaerobic ammonium oxidation reactor contains a reflux device composed of a return pipe and a reflux water pump. The magnesium salt solution storage tank is connected to the bottom of the anaerobic ammonium oxidation reactor through a water pump and pipes. After the sewage enters the system of the present invention, it undergoes nitrification reaction and anaerobic ammonium oxidation reaction coupled with magnesium salt precipitation in sequence, which solves the problem that sludge in the anaerobic ammonium oxidation reactor is easy to float and lose with the bubbles, and at the same time realizes the removal of nitrogen and phosphorus in the sewage. The effects are respectively over 85% and 75%.

Description

An anaerobic digestion solution based on nitrosation-anaerobic ammonium oxidation coupled magnesium and phosphorus crystallization System and method for nitrogen removal and simultaneous phosphorus recovery

Technical field

The invention belongs to the field of sewage biological treatment technology and resource recovery, and particularly relates to a system and method for realizing denitrification of anaerobic digestion liquid and simultaneous phosphorus recovery based on nitrosation-anaerobic ammonium oxidation coupled magnesium and phosphorus crystallization.

Background technique

The activated sludge method is currently the most widely used sewage treatment method, with significant advantages such as high efficiency and small footprint. However, a large amount of residual sludge will also be produced during the sewage treatment process. Anaerobic digestion of the residual sludge is a feasible and mature method for sludge reduction and resource utilization.

However, the sludge anaerobic digestion produced by anaerobic digestion contains a large amount of nitrogen, phosphorus and other pollutants, which can easily cause eutrophication of water bodies. As a non-renewable resource, phosphorus plays a key role in food production and industrial applications. Therefore, the development of a high-efficiency, low-energy consumption and resource recovery technology for sewage nitrogen and phosphorus removal is of great significance in water pollution control.

Since the anaerobic digestion liquid is a typical wastewater with a low carbon-to-nitrogen ratio (C/N), there is a lack of carbon sources required for denitrification biological denitrification, and the traditional biological denitrification and phosphorus removal processes have long process flows to varying degrees, and the aeration energy There are many problems such as high consumption, insufficient carbon sources, difficulty in meeting standards, and high construction and operation costs.

Anaerobic ammonium oxidizing bacteria use NH ₄ ⁺ -N as the electron donor and NO ₂ ^- -N as the electron acceptor. The reaction generates N ₂ and a small amount of NO ₃ ^- -N, thereby achieving total nitrogen removal without the need for additional additions during the process. Carbon source, theoretically can achieve more than 85% TN removal effect. However, anaerobic ammonium oxidizing bacteria grow and reproduce slowly, have a long generation cycle, and easily flow out of the reactor with the water flow, resulting in a decrease in reactor treatment efficiency.

Contents of the invention

In order to overcome the shortcomings and shortcomings of the above-mentioned prior art, the primary purpose of the present invention is to provide a system based on nitrosation-anaerobic ammonium oxidation coupled magnesium and phosphorus crystallization to achieve denitrification of anaerobic digestion liquid and simultaneous phosphorus recovery.

Another object of the present invention is to provide a method for achieving denitrification of anaerobic digestion liquid and simultaneous phosphorus recovery based on nitrosation-anaerobic ammonium oxidation coupled magnesium and phosphorus crystallization using the above system.

This invention aims at the outstanding problems of traditional denitrification technology such as limited denitrification efficiency and lack of phosphorus recovery when treating low C/N, high nitrogen and phosphorus wastewater. Based on the reaction characteristics of anaerobic ammonium oxidizing bacteria, this invention proposes a method based on nitrification-anaerobic ammonia. Oxidation and high-efficiency denitrification reaction, coupling magnesium and phosphorus mineralization to form crystallized anaerobic digestion liquid denitrification and phosphorus removal systems and methods, based on limited carbon sources, can not only achieve the removal of nitrogen and phosphorus, but also realize the recovery of phosphorus resources. It is a new anaerobic digestion liquid treatment process with low-carbon denitrification and simultaneous phosphorus resource recovery. At the same time, magnesium and phosphorus crystals can also become attachment points for microorganisms, promoting the enrichment and stable persistence of anaerobic ammonium oxidizing bacteria.

The object of the present invention is achieved through the following solutions:

A system based on nitrosation-anaerobic ammonium oxidation coupled magnesium and phosphorus crystallization to achieve denitrification of anaerobic digestion liquid and simultaneous phosphorus recovery, including: raw tank, nitrification reactor, intermediate tank, anaerobic ammonium oxidation reactor, magnesium salt solution Reserve tank; among them, the original pool, nitrification reactor, intermediate pool, and anaerobic ammonium oxidation reactor are connected in sequence through water pumps and pipelines. The anaerobic ammonium oxidation reactor includes a reflux device composed of a reflux pipe and a reflux water pump. Magnesium The salt solution storage tank is connected to the bottom of the anaerobic ammonium oxidation reactor through a water pump and pipeline.

The nitrification reactor is equipped with an aeration device and a stirring device; the anaerobic ammonium oxidation reactor and the magnesium salt solution storage tank are equipped with a stirring device; the original pool and the intermediate pool are optionally equipped with stirring devices.

The nitrification reactor is a sequencing batch reactor (SBR); the anaerobic ammonia oxidation reactor is an upflow anaerobic sludge bed reactor (UASB).

The nitrification reactor is equipped with a stirring and aeration device; the top of the anaerobic ammonia oxidation reactor is equipped with a reflux pipe, a three-phase separator and an overflow weir; the anaerobic ammonia oxidation reactor is a bottom inlet. Water flows out from the top after passing through the overflow weir.

A method for denitrification and phosphorus removal of anaerobic digestion liquid based on nitrosation-anammonia oxidation coupled magnesium and phosphorus crystallization using the above system, including:

(1) Inoculate sludge 1 in the nitrification reactor and inoculate sludge 2 in the anaerobic ammonium oxidation reactor;

(2) The sewage in the original pool enters the nitrification reactor for nitrification reaction;

(3) The effluent from the nitrification reactor enters the anaerobic ammonium oxidation reactor for anaerobic ammonium oxidation treatment;

(4) The magnesium salt solution in the magnesium salt solution storage tank is pumped into the anaerobic ammonium oxidation reactor from the bottom of the anaerobic ammonium oxidation reactor through water pumps and pipelines, providing a magnesium source for phosphate crystallization in sewage to achieve phosphorus removal;

(5) The sewage at the top of the anaerobic ammonium oxidation reactor flows back to the water inlet at the bottom of the reactor through the return pipe and the return water pump to achieve reflux in the reactor.

The sludge 1 in step (1) is sludge containing ammonia oxidizing bacteria, preferably at least one of nitrification sludge and secondary sedimentation tank sludge; sludge 2 is sludge containing anaerobic ammonium oxidizing bacteria, preferably Sludge in the anaerobic ammonium oxidation reactor for engineering operation.

The ammonia nitrogen concentration of the sewage in step (2) is 800-2000 mg/L; the total nitrogen concentration is 800-2500 mg/L; and the phosphorus concentration is 60-150 mg/L.

The nitrification reactor described in step (2) adopts sequential batch operation, and a single cycle includes water inlet-reaction (aeration plus stirring)-precipitation-water outlet.

The conditions for the nitrification reaction in step (2) are: the concentration of sludge 1 in the nitrification reactor is 4000-6000mg/L; the hydraulic retention time (HRT) in the nitrification reactor is 12-30h; the nitrification reaction The drainage ratio of the reactor is 20 to 50%; the aeration volume of the nitrification reactor is such that the dissolved oxygen concentration in the nitrification reactor is maintained at 0.5 to 3 mg/L.

The nitrification reaction in step (2) is that under the action of ammonia oxidizing bacteria (AOB) in the sludge, the ammonia nitrogen in the sewage is converted into nitrite nitrogen. By controlling the aeration amount and hydraulic retention time in the nitrification reactor, the ammonia nitrogen in the sewage is converted into nitrite nitrogen. After the reaction, the ratio of nitrite nitrogen concentration to ammonia nitrogen concentration in the effluent is 1.32:1~1:1.

The conditions for the anaerobic ammonium oxidation treatment in step (3) are: the concentration of sludge 2 in the anaerobic ammonium oxidation reactor is 5000~8000 mg/L; the hydraulic retention time in the anaerobic ammonium oxidation reactor is 12~24h, The reaction temperature is 28-33°C; appropriate anaerobic ammonium oxidation sludge concentration and hydraulic retention time are conducive to the progress of the anaerobic ammonium oxidation reaction.

The anaerobic ammonium oxidation treatment in step (3) is in the anaerobic ammonium oxidation reactor. The anaerobic ammonium oxidizing bacteria use NH ₄ ⁺ -N as the electron donor and NO ₂ ^- -N as the electron acceptor. Through biochemistry The reaction generates nitrogen to achieve the removal of nitrogen in sewage.

The amount of magnesium salt solution in step (4) is such that the molar ratio of magnesium ions and phosphate entering the anaerobic ammonium oxidation reactor is 1.5 to 2:1.

The dosage of the magnesium salt solution in step (4) satisfies: the molar ratio of the magnesium ion concentration of the magnesium salt solution to the phosphate concentration in the sewage is 150 to 200, and the ratio of the flow rate of the magnesium salt solution to the inlet water flow rate of the anaerobic ammonium oxidation reactor is 1:100, which is equivalent to a molar ratio of magnesium ions to phosphate entering the anaerobic ammonium oxidation reactor of 1.5 to 2:1.

The phosphorus removal described in step (4) is specifically: after the anaerobic ammonium oxidation reaction, the pH in the water environment is increased, causing magnesium ions to combine with phosphate ions to form magnesium phosphorus crystal precipitation, thereby achieving the removal and recovery of phosphorus; magnesium phosphorus The crystal is mainly composed of hydrated magnesium phosphate (Mg ₃ (PO ₄ ) ₂ ·xH ₂ O).

The magnesium salt in step (4) is at least one of magnesium chloride and magnesium sulfate.

The reflux ratio of the reflux in step (5) is 100% to 500%, preferably 300% to 500%.

The mechanism of the present invention is:

Anaerobic ammonium oxidizing bacteria are autotrophic microorganisms with a long generation cycle. They grow slowly, and the anaerobic ammonium oxidation reaction they occur generates nitrogen. Nitrogen bubbles easily adhere to the anaerobic ammonium oxidation sludge floc, causing sludge formation. Floating phenomenon. Part of the floating sludge bypasses the three-phase separator and flows out of the reactor with water flow, which can easily cause sludge loss and reduce the reactor's sewage treatment performance. In view of the above shortcomings, the present invention proposes a system and method for denitrification and phosphorus removal of anaerobic digestion liquid based on nitrosation-anaerobic ammonium oxidation coupled magnesium and phosphorus crystallization using the above system: the system consists of a nitrification reactor, anaerobic ammonia The oxidation reactor and magnesium salt solution provide equipment components; the nitrification reactor converts part of the ammonia nitrogen in the sewage into nitrite nitrogen, and at the same time uses the organic matter in the sewage to achieve denitrification; the anaerobic ammonium oxidation reactor uses the nitrite produced by the nitrification reactor Nitrogen is used as an electron acceptor, and ammonia nitrogen is used as an electron donor to produce nitrogen gas through anaerobic ammonium oxidation reaction, thereby achieving the removal of nitrogen in sewage. At the same time, the magnesium salt solution is added to the anaerobic ammonium oxidation reactor, using the characteristics of the anaerobic ammonium oxidation reaction to consume system hydrogen ions and improve the system pH, as well as the adsorption and release characteristics of ions by the sludge in the reactor, to improve the efficiency of magnesium phosphorus compounds. Saturation index (SI). At the same time, the adsorption of ions by sludge provides nucleation sites for the generation of magnesium phosphorus crystals and promotes magnesium phosphorus crystallization. The generation of magnesium phosphorus crystals realizes the removal and recovery of phosphorus in sewage, provides attachment sites for microorganisms, promotes the formation of granular sludge, improves sludge sedimentation performance and retention capacity in the reactor, and ensures efficient denitrification of the reactor. performance.

Anaerobic ammonium oxidizing bacteria and other microorganisms in the anaerobic ammonium oxidation reactor can attach and grow on the surface of magnesium phosphorus crystals. Under the action of extracellular polymers and water flow shear force, flocculation occurs between anaerobic ammonium oxidizing micro-colonies to form bacterial colony flocculation. With the growth of magnesium phosphorus crystals and the expansion and coverage of bacterial colony flocs, granular sludge with magnesium phosphorus crystals as the core and microorganisms covering the outer layer is gradually formed. The sludge is discharged regularly, and the sludge is crushed and centrifuged. The sludge containing microorganisms is replenished back to the reactor, and the inorganic matter (magnesium phosphorus crystals) is further processed and recovered.

The setting of the intermediate pool can adjust the incoming water properties and chemical dosage according to the actual situation, such as adjusting pH and adding alkalinity.

Compared with the existing technology, the present invention has the following advantages and beneficial effects:

1) Realize the simultaneous removal of nitrogen and phosphorus in the anaerobic digestion liquid, and achieve the removal effect of nitrogen and phosphorus in the sewage reaching more than 85% and 75% respectively;

2) Solve the problem that sludge in the anaerobic ammonium oxidation reactor is easy to float and lose with the bubbles;

3) Anaerobic ammonium oxidation is a typical autotrophic reaction process. The nitrification reactor can consume most of the bioavailable organic matter in the sewage, realize synchronous nitrification and denitrification, remove part of the nitrogen in the sewage, and also provide subsequent anaerobic ammonia Oxidizing bacteria provide good growth conditions and avoid excessive competition with other heterotrophic bacteria;

4) Compared with traditional precipitation methods to recover phosphorus, such as struvite crystallization and hydroxyapatite crystallization, which require the addition of alkaline chemicals to adjust the pH of wastewater, the alkalinity brought by the anaerobic ammonium oxidation reaction can reduce or even eliminate the need for additional chemicals;

5) The sludge containing magnesium and phosphorus crystals formed in the anaerobic ammonium oxidation reactor can be recycled and sold as magnesium and phosphorus-containing composite sludge organic fertilizer; the sludge and magnesium and phosphorus crystals can also be separated and recycled, and used as fertilizer Or sell industrial raw materials to increase income from the sewage treatment process;

6) The entire system integrates pollutant removal and resource recovery, especially the integrated anaerobic ammonium oxidation coupled magnesium and phosphorus crystallization reactor, which can reduce the area occupied by sewage treatment facilities and is suitable for the upgrading and reconstruction of current and future sewage treatment plants.

Description of the drawings

Figure 1 is a schematic structural diagram of the system of the present invention:

(1)—raw pool, (2)—nitrification reactor, (2-1)—aerator, (2-2)—aeration head, (2-3)—stirring device, (3)—middle Pool, (4)—anammonia oxidation reactor, (4-1)—overflow weir, (4-2)—three-phase separator, (5)—magnesium salt solution storage tank, (6)—nitrification Reactor water inlet pump, (7) - anaerobic ammonium oxidation reactor water inlet pump, (8) - magnesium salt solution feed pump, (9) - anaerobic ammonium oxidation reactor reflux pump, (10) anaerobic ammonium oxidation reaction device return line.

Detailed ways

The present invention will be described in further detail below with reference to the examples and drawings, but the implementation of the present invention is not limited thereto. If the specific conditions are not specified in the examples, the conditions should be carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not indicated, they are all conventional products that can be purchased commercially.

The reagents used in the examples can all be purchased from the market unless otherwise specified.

A system based on nitrification-anaerobic ammonium oxidation coupled magnesium and phosphorus crystallization to achieve simultaneous denitrification and phosphorus recovery of anaerobic digestion liquid, including (1)-raw pool, (2)-nitrification reactor, (2-1)-aeration machine, (2-2)—aeration head, (2-3)—stirring device, (3)—intermediate tank, (4)—anammonia oxidation reactor, (4-1)—overflow weir, ( 4-2)—three-phase separator, (5)—magnesium salt solution storage tank, (6)—nitrification reactor water inlet pump, (7)—anaerobic ammonium oxidation reactor water inlet pump, (8)—magnesium salt Solution feed pump, (9) - anaerobic ammonium oxidation reactor reflux pump, (10) - anaerobic ammonium oxidation reactor reflux pipeline.

The nitrification reactor (2) contains an aerator (2-1), an aeration head (2-2) and a stirring device (2-3), and the anaerobic ammonium oxidation reactor (4) contains an overflow weir (4- 1) and three-phase separator (4-2). The original pool (1) is used to store anaerobic digestion liquid, and the intermediate pool (3) is used to store the nitrification reactor effluent. The magnesium salt solution storage tank (5) is used to store the magnesium salt solution. A nitrification reactor water inlet pump (6) is provided on the pipeline connecting the original pool (1) to the nitrification reactor. The water outlet of the nitrification reactor (2) and the intermediate pool (3) are connected through pipelines. An anaerobic ammonium oxidation reactor water inlet pump (7) is provided on the pipeline connecting the intermediate pool (3) and the bottom water inlet of the anaerobic ammonium oxidation reactor (4). A magnesium salt solution feed pump (8) is provided on the pipeline connecting the magnesium salt solution storage tank (5) and the water inlet at the bottom of the anaerobic ammonium oxidation reactor (4). The anaerobic ammonium oxidation reactor reflux pipeline (10) connects the top water outlet and the bottom water inlet of the reactor, and the anaerobic ammonium oxidation reactor reflux pipeline (10) is provided with an anaerobic ammonium oxidation reactor reflux pump (9).

Sludge 1 was inoculated in the nitrification reactor, and sludge 2 was inoculated in the anaerobic ammonium oxidation reactor. During sewage treatment, the sewage in the original pool (1) enters the nitrification reactor (2) through the nitrification reactor water inlet pump (6). The nitrification reactor operates in sequential batch mode, including water inlet-reaction (aeration plus stirring)-precipitation-water outlet in a single cycle. The average concentration of sludge 1 in the nitrification reactor is 4000~6000mg/L, the drainage ratio of the nitrification reactor is 20~50%, the hydraulic retention time in the nitrification reactor is 12~30h, and the aeration of the nitrification reactor The amount is sufficient: the dissolved oxygen concentration in the nitrification reactor is maintained at 0.5~3mg/L. Under the action of ammonia-oxidizing bacteria (AOB) in the sludge, the ammonia nitrogen in the sewage is partially converted into nitrite nitrogen. By controlling the aeration volume and hydraulic retention time in the reactor, the ratio of nitrite nitrogen concentration and ammonia nitrogen concentration in the effluent after the reaction is controlled between 1.32:1 and 1:1.

The effluent from the nitrification reactor enters the intermediate tank (3), and the sewage in the intermediate tank is then fed into the anaerobic ammonium oxidation reactor (4) through the anaerobic ammonium oxidation inlet pump (7). The concentration of sludge 2 in the anaerobic ammonium oxidation reactor is 5000-8000 mg/L; the hydraulic retention time in the anaerobic ammonium oxidation reactor is 12-24 hours. In the anaerobic ammonium oxidation reactor, anaerobic ammonium oxidizing bacteria use NH ₄ ⁺ -N as the electron donor and NO ₂ ^- -N as the electron acceptor to generate nitrogen through biochemical reactions to achieve the removal of nitrogen in sewage. The sewage passes through the three-phase separator (4-2) to separate mud, water and gas, and then is discharged from the top overflow weir (4-1). The anaerobic ammonium oxidation reactor realizes internal reflux through the reflux pipeline (10), and the reflux ratio is 100% to 500%.

The magnesium salt solution in the magnesium salt solution storage tank (5) enters the anaerobic ammonium oxidation reactor (4) through the magnesium salt solution feed pump (8). The molar ratio between the magnesium ion concentration of the magnesium salt solution and the phosphate concentration in the sewage is 150 to 200. The ratio of the flow rate of the magnesium salt solution to the inlet water flow rate of the anaerobic ammonium oxidation reactor is 1:100, which is equivalent to the amount of water entering the anaerobic ammonium oxidation reactor. The molar ratio of magnesium ions to phosphate is 1.5~2:1. The anaerobic ammonium oxidation reaction will increase the pH in the surrounding water environment. At a suitable pH, magnesium ions combine with phosphate ions to form magnesium phosphorus crystal precipitation, thereby achieving the removal and recovery of phosphorus. Magnesium phosphorus crystals are mainly hydrated magnesium phosphate (Mg ₃ (PO ₄ ) ₂ ·xH ₂ O).

Optionally, the magnesium salt solution may be magnesium chloride or magnesium sulfate.

Example

Using simulated anaerobic digestion liquid as raw water, its water quality characteristics are shown in the table below:

Experimental conditions:

Sludge 1 comes from: sludge from the secondary sedimentation tank of the sewage treatment plant of Guangzhou Water Purification Co., Ltd.;

Sludge 2 comes from: anaerobic ammonium oxidation sludge (red bacteria) in the anaerobic ammonium oxidation engineering unit of Foshan Huer ammonium Biotechnology Co., Ltd.

The sludge 1 concentration in the nitrification reactor is 5500mg/L, the drainage ratio is 50%, HTR=24h, and the aeration amount of the nitrification reactor is adjusted to keep the dissolved oxygen concentration in the nitrification reactor at 1~1.5mg/L. L, the ratio of nitrite nitrogen concentration and ammonia nitrogen concentration in the effluent after the reaction is 1.1~1.3; the sludge 2 concentration in the anaerobic ammonium oxidation reactor is 7500mg/L, HRT=19h, the reflux ratio is 500%, and the temperature is 32±1℃ , the concentration of the magnesium chloride solution in the magnesium salt solution storage tank is 400mM, the ratio of the flow rate of the magnesium salt solution to the inlet water flow rate of the anaerobic ammonium oxidation reactor is 1:100, that is, the Mg/P molar ratio in the anaerobic ammonium oxidation reactor is 1.6: 1.

The experimental results show that the average ammonia nitrogen, total nitrogen, and P concentrations in the system effluent are 4.5, 132.8, and 18 mg/L respectively. The system can achieve a total nitrogen removal rate of about 87% and a phosphorus removal rate of about 77%.

The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, etc. may be made without departing from the spirit and principles of the present invention. All simplifications should be equivalent substitutions, and are all included in the protection scope of the present invention.

Claims (10)

1. A system for realizing denitrification and synchronous phosphorus recovery of anaerobic digestion liquid based on nitrosation-anaerobic ammonia oxidation coupling magnesium phosphorus crystallization is characterized by comprising: a raw water tank, a nitrosation reactor, an intermediate tank, an anaerobic ammonia oxidation reactor and a magnesium salt solution storage tank; wherein, the raw water tank, the nitrosation reactor, the middle tank and the anaerobic ammonia oxidation reactor are sequentially connected with a pipeline through a water pump, the anaerobic ammonia oxidation reactor comprises a reflux device consisting of a reflux pipe and a reflux water pump, and the magnesium salt solution storage tank is connected with the bottom of the anaerobic ammonia oxidation reactor through the water pump and the pipeline.

2. The system for realizing denitrification and synchronous phosphorus recovery of anaerobic digestion liquid based on nitrosation-anaerobic ammonia oxidation coupled magnesium phosphorus crystallization according to claim 1, which is characterized in that:

the nitrosation reactor is a sequencing batch reactor; the anaerobic ammonia oxidation reactor is an up-flow anaerobic sludge blanket reactor;

a stirring and aerating device is arranged in the nitrosation reactor; a reflux pipe, a three-phase separator and an overflow weir are arranged at the inner top of the anaerobic ammonia oxidation reactor; the anaerobic ammonia oxidation reactor is characterized in that water enters from the bottom and water flows out from the top after passing through an overflow weir.

3. A method for implementing denitrification and dephosphorization of anaerobic digestion liquid based on nitrosation-anaerobic ammoxidation coupling magnesium phosphorus crystallization by using the system as claimed in claim 1 or 2, which is characterized by comprising the following steps:

(1) Inoculating sludge 1 in the nitrosation reactor, and inoculating sludge 2 in the anaerobic ammoxidation reactor;

(2) Sewage in the raw water tank enters a nitrosation reactor to perform nitrosation reaction;

(3) The effluent from the nitrosation reactor enters an anaerobic ammoxidation reactor for anaerobic ammoxidation treatment;

(4) Pumping the magnesium salt solution in the magnesium salt solution storage tank into the anaerobic ammonia oxidation reactor from the bottom of the anaerobic ammonia oxidation reactor through a water pump and a pipeline to provide a magnesium source for phosphate crystallization in sewage, so as to realize dephosphorization;

(5) Sewage at the top of the anaerobic ammoxidation reactor is refluxed to a water inlet at the bottom of the reactor through a reflux pipe and a reflux water pump, so that the internal reflux of the reactor is realized.

4. The method for realizing denitrification and dephosphorization of anaerobic digestion liquid based on nitrosation-anaerobic ammonia oxidation coupled magnesium-phosphorus crystallization according to claim 3, which is characterized in that: the sludge 1 in the step (1) is sludge containing ammonia oxidizing bacteria; the sludge 2 is sludge containing anaerobic ammonia oxidizing bacteria.

5. The method for realizing denitrification and dephosphorization of anaerobic digestion liquid based on nitrosation-anaerobic ammonia oxidation coupled magnesium-phosphorus crystallization according to claim 3, which is characterized in that: the ammonia nitrogen concentration of the sewage in the step (2) is 800-2000 mg/L; the total nitrogen concentration is 800-2500 mg/L; the phosphorus concentration is 60-150 mg/L.

6. The method for realizing denitrification and dephosphorization of anaerobic digestion liquid based on nitrosation-anaerobic ammonia oxidation coupled magnesium-phosphorus crystallization according to claim 3, which is characterized in that: the nitrosation reaction conditions in step (2) are: the concentration of the sludge 1 in the nitrosation reactor is 4000-6000 mg/L; the hydraulic retention time in the nitrosation reactor is 12-30 h; the drainage ratio of the nitrosation reactor is 20-50%; the aeration amount of the nitrosation reactor satisfies the following conditions: so that the concentration of dissolved oxygen in the nitrosation reactor is kept between 0.5 and 3mg/L.

7. The method for realizing denitrification and dephosphorization of anaerobic digestion liquid based on nitrosation-anaerobic ammonia oxidation coupled magnesium-phosphorus crystallization, which is characterized in that: and adjusting the aeration quantity and the hydraulic retention time in the nitrosation reactor to ensure that the ratio of the nitrosamine concentration and the ammonia nitrogen concentration of the effluent after the reaction is 1.32:1-1:1.

8. The method for realizing denitrification and dephosphorization of anaerobic digestion liquid based on nitrosation-anaerobic ammonia oxidation coupled magnesium-phosphorus crystallization according to claim 3, which is characterized in that: the anaerobic ammonia oxidation treatment conditions in the step (3) are as follows: the concentration of the sludge 2 in the anaerobic ammoxidation reactor is 5000-8000 mg/L; the hydraulic retention time in the anaerobic ammonia oxidation reactor is 12-24 h, and the reaction temperature is 28-33 ℃.

9. The method for realizing denitrification and dephosphorization of anaerobic digestion liquid based on nitrosation-anaerobic ammonia oxidation coupled magnesium-phosphorus crystallization according to claim 3, which is characterized in that:

the dosage of the magnesium salt solution in the step (4) is as follows: so that the molar ratio of magnesium ions to phosphate entering the anaerobic ammonia oxidation reactor is 1.5-2:1;

the magnesium salt in the step (4) is at least one of magnesium chloride and magnesium sulfate.

10. The method for realizing denitrification and dephosphorization of anaerobic digestion liquid based on nitrosation-anaerobic ammonia oxidation coupled magnesium-phosphorus crystallization according to claim 3, which is characterized in that: and (5) the reflux ratio of the reflux in the step (5) is 100-500%.