Device and method for removing nitrogen and phosphorus from liquid

Abstract

The invention belongs to the technical field of environmental protection, and discloses a device and a method for removing nitrogen and phosphorus from liquid. The device comprises a struvite reaction tank, a pressure gas dissolving device and an ammonia nitrogen stripping tank which are connected in sequence, the struvite reaction tank is configured as follows: liquid and a precipitation agent are subjected to struvite precipitation reaction, and nitrogen and phosphorus are removed; the pressure gas dissolving device is configured to partially or completely pressurize and dissolve gas in reaction liquid after struvite reaction; and the ammonia nitrogen stripping tank is configured to release the reaction liquid containing the dissolved gas under reduced pressure, and stripping to remove ammonia nitrogen. According to the method, struvite precipitation and pressurized dissolved gas denitrification are combined, the problem that the sludge filtrate generated after sludge hydrolytic acidification cannot be directly used as a carbon source to be reused for sewage treatment is solved, the treatment cost is low, and the method is suitable for engineering application.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental protection, and in particular relates to a device and a method for removing nitrogen and phosphorus from liquid. Background Art

[0002] As my country's sewage treatment technology has been gradually improved and put into use, the output of sludge as a by-product of sewage treatment has also increased significantly. Sludge is mainly composed of microorganisms. It contains relatively rich organic matter and nitrogen and phosphorus elements, which lays a good foundation for its resource utilization. In recent years, the academic community has proposed a new idea to control the anaerobic digestion of sludge in the hydrolysis and acidification stage to obtain digestion products mainly containing volatile fatty acids (Volatile Fatty Acids, referred to as VFAs) such as acetic acid, propionic acid, butyric acid, and valeric acid, which can produce greater economic benefits than methane. Laboratory studies have shown that VFAs, as a high-quality carbon source, have a significantly better denitrification effect than methanol or ethanol as a carbon source, and can greatly improve the phosphorus removal effect under the action of denitrifying phosphorus removal bacteria. Therefore, anaerobic hydrolysis and acidification of sludge to produce VFAs as a carbon source for denitrification and phosphorus removal is expected to fundamentally solve the two major problems of insufficient carbon source for sewage treatment plant influent and sludge disposal.

[0003] However, a large amount of ammonia nitrogen and orthophosphate will be released during the hydrolysis and acidification process of sludge. If not treated, it will increase the load of the sewage treatment process. Therefore, the sludge filtrate produced after sludge hydrolysis and acidification cannot be directly reused as a carbon source for sewage treatment.

[0004] At present, in actual engineering, ammonia nitrogen and orthophosphate in the fermentation broth are mostly recovered in the form of magnesium ammonium phosphate precipitation (struvite precipitation), which is a method that can simultaneously recover nitrogen and phosphorus. However, the sludge filtrate produced after sludge hydrolysis and acidification usually contains n(NH3) and n(PO4 3- ) is about 5:1, and n(NH3) and n(PO4 3- ) is 1:1, when the PO4 3- After the reaction is complete, 80% of NH3 still remains in the sludge filtrate because it does not participate in the reaction, affecting the sludge filtrate's reuse as a carbon source in the sewage treatment system. If a large amount of magnesium chloride and phosphate are required to completely remove the residual NH3, the cost of the reagent will inevitably increase.

[0005] How to provide a low-cost device and method for removing nitrogen and phosphorus from waste liquid, effectively remove ammonia nitrogen and orthophosphate in sludge filtrate, and use it as a carbon source for sewage treatment, is of great significance to fundamentally solve the two major problems of insufficient carbon source for sewage plant influent and sludge disposal. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a device and method for removing nitrogen and phosphorus from liquid.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A device for removing nitrogen and phosphorus from liquid, comprising a struvite reaction tank, a pressure gas dissolving device and an ammonia nitrogen stripping tank connected in sequence;

[0009] The struvite reaction tank is configured to: the liquid reacts with the precipitation agent to produce struvite precipitation to remove PO4 in the liquid. 3- and ammonia nitrogen; the struvite reaction tank is provided with a dosing port, a No. 1 liquid inlet, a No. 1 liquid outlet and a No. 1 discharge port;

[0010] The ammonia nitrogen stripping tank is configured to: release the reaction liquid containing dissolved gas under reduced pressure and remove ammonia nitrogen by stripping; the ammonia nitrogen stripping tank is provided with a No. 2 liquid inlet, a No. 2 liquid outlet and a No. 2 discharge port;

[0011] The pressure gas dissolving device is configured to: pressurize and dissolve part or all of the reaction liquid after the struvite reaction; the liquid inlet of the pressure gas dissolving device is connected to the No. 1 liquid outlet of the struvite reaction tank through a water outlet pump, and the liquid outlet of the pressure gas dissolving device is connected to the No. 2 liquid inlet of the ammonia nitrogen stripping tank through a pipeline.

[0012] Preferably, the struvite reaction tank is provided with a reflux device, which is configured to: reflux part of the liquid in the struvite reaction tank to the struvite reaction tank, achieve disturbance and stirring of the liquid in the tank, and accelerate the formation of struvite precipitation; the reflux device includes a reflux pump and a reflux pipe.

[0013] Preferably, the struvite reaction tank is provided with a No. 1 tail gas recovery port, and the ammonia nitrogen stripping tank is provided with a No. 2 tail gas recovery port, and the No. 1 tail gas recovery port and / or the No. 2 tail gas recovery port are configured to: recover the ammonia in the tank; further preferably, the No. 1 tail gas recovery port and / or the No. 2 tail gas recovery port are connected to the air inlet of the pressure gas dissolution device through a pipeline.

[0014] Preferably, the struvite reaction tank is provided with a No. 1 backwashing device, and the No. 1 backwashing device comprises the No. 1 discharge port and the No. 1 liquid inlet;

[0015] The ammonia nitrogen stripping tank is provided with a No. 2 backwashing device, and the No. 2 backwashing device comprises a No. 2 discharge port and a No. 2 liquid inlet;

[0016] The No. 1 backwash device and the No. 2 backwash device are configured to remove sediment in the tank.

[0017] Preferably, the struvite reaction tank is provided with a No. 1 breathing valve, and the ammonia nitrogen stripping tank is provided with a No. 2 breathing valve; the No. 1 breathing valve and the No. 2 breathing valve are configured to: empty the gas in the tank body.

[0018] The present invention also provides a method for removing nitrogen and phosphorus from waste liquid using the above-mentioned device, comprising the following steps:

[0019] (1) Add precipitation reagents to the liquid to produce struvite precipitation reaction and remove PO4 in the liquid 3- and ammonia nitrogen to obtain a reaction solution;

[0020] (2) pressurizing part or all of the reaction liquid obtained in step (1) to dissolve gas, dissolving the gas in the reaction liquid to obtain a reaction liquid containing dissolved gas;

[0021] (3) The reaction liquid containing dissolved gas obtained in step (2) is decompressed to release the dissolved gas, and ammonia nitrogen is blown off to obtain denitrified and dephosphorized water.

[0022] Preferably, the liquid in step (1) contains ammonia nitrogen and phosphate; more preferably, the molar ratio of ammonia nitrogen to phosphate ions in the liquid is greater than 1; more preferably, it is greater than 2. Most preferably, the liquid is sludge filtrate produced after sludge hydrolysis and acidification, wherein the molar ratio of ammonia nitrogen to phosphate ions is 5.

[0023] Preferably, the pressure of the pressurized dissolved gas in step (2) is 1-5 kg / cm 2 The gas is air and / or recycled ammonia. Further preferably, the pressure of the pressurized dissolved gas is 3-5 kg / cm 2 .

[0024] Preferably, the stripping conditions in step (3) are: temperature 60-70°C, pH 9-10.5; more preferably, the stripping temperature is 60-65°C.

[0025] The beneficial effects of the present invention are:

[0026] (1) Pressurized dissolved gas can dissolve air in liquid, or the ammonia nitrogen gas after stripping can be refluxed and dissolved in liquid. The liquid containing dissolved gas is rapidly decompressed to normal pressure in the ammonia nitrogen stripping tank, and the gas dissolved in the water escapes in the form of fine bubbles, stripping the ammonia nitrogen in the liquid and removing it. The present invention unexpectedly found that in a high-temperature alkaline environment, ammonia nitrogen in the liquid containing dissolved gas is more likely to overflow with the gas, and the ammonia nitrogen removal rate is higher.

[0027] (2) The present invention utilizes a method combining struvite precipitation and pressurized dissolved air denitrification to solve the problem of safe reuse of sludge filtrate produced after sludge hydrolysis and acidification in the sewage treatment system due to ammonia nitrogen and as a carbon source. It is low-cost and suitable for engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A schematic diagram of a device for removing nitrogen and phosphorus from a liquid according to the present invention;

[0029] Among them, 1. struvite reaction tank, 2. pressure dissolving gas device, 3. ammonia nitrogen stripping tank, 4. dosing port, 5. tail gas recovery port No. 1, 6. liquid inlet No. 1, 7. liquid outlet No. 1, 8. discharge port No. 1, 9. tail gas recovery port No. 2, 10. liquid inlet No. 2, 11. liquid outlet No. 2, 12. discharge port No. 2, 13. water outlet pump, 14. reflux device, 14-1, reflux pump, 14-2, reflux pipe, 15. breathing valve No. 1, 16. breathing valve No. 2. DETAILED DESCRIPTION

[0030] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0031] Before further describing the specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terms used in the examples of the present invention are for describing specific embodiments rather than for limiting the scope of protection of the present invention.

[0032] When the embodiment gives a numerical range, it should be understood that, unless otherwise specified in the present invention, the two endpoints of each numerical range and any numerical value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those of ordinary skill in the art to which the present invention belongs.

[0033] Example 1 A device and method for removing nitrogen and phosphorus from a liquid

[0034] A device for removing nitrogen and phosphorus from a liquid, such as Figure 1 As shown, it includes a struvite reaction tank 2, a pressure gas dissolving device 2 and an ammonia nitrogen stripping tank 3 which are connected in sequence;

[0035] The struvite reaction tank 1 is configured to: the liquid reacts with the precipitation agent to produce struvite precipitation to remove PO4 in the liquid. 3- and NH4 + -N; the struvite reaction tank 1 is provided with a dosing port 4, a No. 1 liquid inlet 7, a No. 1 liquid outlet 6 and a No. 1 discharge port 8;

[0036] The ammonia nitrogen stripping tank 3 is configured to: strip the reaction liquid containing dissolved gas under reduced pressure to remove ammonia nitrogen; the ammonia nitrogen stripping tank 3 is provided with a No. 2 liquid inlet 10, a No. 2 liquid outlet 11 and a No. 2 discharge port 12;

[0037] The pressure gas dissolving device 2 is configured to: pressurize and dissolve all the reaction liquid after the struvite reaction; the liquid inlet of the pressure gas dissolving device 2 is connected to the No. 1 liquid outlet 7 of the struvite reaction tank through a water outlet pump 13, and the liquid outlet of the pressure gas dissolving device 2 is connected to the No. 2 liquid inlet 10 of the ammonia nitrogen stripping tank through a pipeline.

[0038] A method for removing nitrogen and phosphorus from a liquid comprises the following steps:

[0039] (1) adding a precipitation agent to the liquid to cause a struvite precipitation reaction, thereby removing phosphate and ammonia nitrogen in the liquid to obtain a reaction liquid;

[0040] (2) pressurizing the entire reaction solution obtained in step (1) to dissolve air, dissolving air in the reaction solution to obtain a reaction solution containing dissolved air;

[0041] (3) The reaction liquid containing dissolved gas obtained in step (3) is decompressed to release the dissolved gas, and ammonia nitrogen is blown off to obtain denitrified and dephosphorized water.

[0042] Example 2 A device and method for removing nitrogen and phosphorus from a liquid

[0043] A device for removing nitrogen and phosphorus from a liquid, such as Figure 1 As shown, it includes a struvite reaction tank 2, a pressure gas dissolving device 2 and an ammonia nitrogen stripping tank 3 which are connected in sequence;

[0044] The struvite reaction tank 1 is configured to: the liquid reacts with the precipitation agent to produce struvite precipitation to remove PO4 in the liquid. 3- and NH4 + -N; the struvite reaction tank 1 is provided with a dosing port 4, a No. 1 liquid inlet 7, a No. 1 liquid outlet 6 and a No. 1 discharge port 8;

[0045] The ammonia nitrogen stripping tank 3 is configured to: release the reaction liquid containing dissolved gas by decompression, and remove the ammonia nitrogen by stripping; the ammonia nitrogen stripping tank 3 is provided with a No. 2 liquid inlet 10, a No. 2 liquid outlet 11 and a No. 2 discharge port 12;

[0046] The pressure gas dissolving device 2 is configured to: pressurize and dissolve gas in part of the reaction liquid after the struvite reaction; the liquid inlet of the pressure gas dissolving device 2 is connected to the No. 1 liquid outlet 7 of the struvite reaction tank through a water outlet pump 13, and the liquid outlet of the pressure gas dissolving device 2 is connected to the No. 2 liquid inlet 10 of the ammonia nitrogen stripping tank through a pipeline.

[0047] A method for removing nitrogen and phosphorus from a liquid comprises the following steps:

[0048] (1) adding a precipitation agent to the liquid to cause a struvite precipitation reaction, thereby removing phosphate and ammonia nitrogen in the liquid to obtain a reaction liquid;

[0049] (2) pressurizing a portion of the reaction solution obtained in step (1) to dissolve air, dissolving air in the reaction solution to obtain a reaction solution containing dissolved air;

[0050] (3) The reaction liquid containing dissolved gas obtained in step (3) and the remaining reaction liquid not subjected to pressurized dissolved gas are decompressed and released, and ammonia nitrogen is blown off to obtain denitrified and dephosphorized water.

[0051] Example 3 A device for removing nitrogen and phosphorus from liquid and its application

[0052] In some preferred embodiments, the present invention provides a device for removing nitrogen and phosphorus from a liquid, such as Figure 1 As shown, the struvite reaction tank 1 is provided with a reflux device 14, which is configured to: reflux part of the liquid in the struvite reaction tank 1 to the struvite reaction tank 1, to achieve disturbance and stirring of the liquid in the tank body, and to accelerate the formation of struvite precipitation. The reflux device 14 includes a reflux pump 14-1 and a reflux pipe 14-2.

[0053] A method for removing nitrogen and phosphorus from a liquid comprises the following steps: to ensure that a sufficient struvite precipitation reaction can be carried out, a portion of the liquid in a struvite reaction tank 1 is extracted by a reflux pump 14-1 and refluxed to the struvite reaction tank 1 through a reflux pipe 14-2, thereby ensuring the disturbance and stirring of the liquid in the struvite reaction tank.

[0054] Example 4: A device for removing nitrogen and phosphorus from liquid and its application

[0055] In some preferred embodiments, the present invention provides a device for removing nitrogen and phosphorus from a liquid, such as Figure 1 As shown, the struvite reaction tank 1 is provided with a No. 1 tail gas recovery port 5, and the ammonia nitrogen stripping tank 3 is provided with a No. 2 tail gas recovery port 9; the No. 1 tail gas recovery port 5 and / or the No. 2 tail gas recovery port 9 are configured to: recover the ammonia in the tank; the No. 1 tail gas recovery port 5 and / or the No. 2 tail gas recovery port 9 are connected to the air inlet of the pressure gas dissolving device 2 through a pipeline, and the ammonia nitrogen after stripping is refluxed and dissolved in the reaction liquid under pressure.

[0056] A method for removing nitrogen and phosphorus from liquid comprises the following steps: pressurizing part or all of the reaction liquid to dissolve gas, dissolving the recovered ammonia nitrogen in the reaction liquid to obtain the reaction liquid containing dissolved gas.

[0057] Example 5: A device and method for removing nitrogen and phosphorus from a liquid

[0058] In some preferred embodiments, the present invention provides a device for removing nitrogen and phosphorus from a liquid, such as Figure 1 As shown, it also includes a backwashing device for removing the deposited sediment in the tank; specifically, the struvite reaction tank 1 is provided with a No. 1 backwashing device, and the No. 1 backwashing device includes the No. 1 discharge port 8 and the No. 1 liquid inlet 6; the ammonia nitrogen stripping tank 3 is provided with a No. 2 backwashing device, and the No. 2 backwashing device includes the No. 2 discharge port 12 and the No. 2 liquid inlet 10.

[0059] A method for removing nitrogen and phosphorus from liquid, comprising the following steps: backwashing liquid enters from discharge port No. 1 and flows out through liquid inlet No. 1, and backwashing is used to solve the sediment deposition problem in the struvite reaction tank; or / and

[0060] The backwash liquid enters from the No. 2 discharge port and flows out through the No. 2 liquid inlet. Backwashing is used to solve the sediment deposition problem in the ammonia nitrogen stripping tank.

[0061] Example 6: A device and method for removing nitrogen and phosphorus from a liquid

[0062] In some preferred embodiments, the present invention provides a device for removing nitrogen and phosphorus from a liquid, such as Figure 1 As shown, the struvite reaction tank 1 is provided with a No. 1 breathing valve 15, and the ammonia nitrogen stripping tank 3 is provided with a No. 2 breathing valve 16; the No. 1 breathing valve 15 and the No. 2 breathing valve 16 are configured to: empty the gas in the tank body.

[0063] A method for removing nitrogen and phosphorus from liquid comprises the following steps: using a breathing valve to evacuate the gas in a tank, specifically, using a No. 1 breathing valve to evacuate the gas in a struvite reaction tank, and using a No. 2 breathing valve to evacuate the gas in an ammonia nitrogen stripping tank.

[0064] The liquid described in the present invention contains ammonia nitrogen and phosphate; more preferably, the molar ratio of ammonia nitrogen to phosphate ions in the liquid is greater than 1; more preferably, it is greater than 2. Most preferably, the liquid is sludge filtrate produced after sludge hydrolysis and acidification, wherein the molar ratio of ammonia nitrogen to phosphate ions is 5.

[0065] The pressure of the pressurized dissolved gas in the present invention is 1-5 kg / cm 2 ; More preferably 3-5kg / cm 2 .

[0066] The stripping conditions in the present invention are: temperature 60-70°C, pH 9-10.5; more preferably, the stripping temperature is 60-65°C.

[0067] The following is a detailed description of the technical solution and corresponding technical effects of the present invention in combination with the device of the present invention and its application in the removal of nitrogen and phosphorus. The liquid to be treated is sludge filtrate (filtrate after sludge hydrolysis and acidification), which is taken from the sludge carbon source extraction project of the self-owned water plant, wherein the sludge soluble COD (SCOD) is 20140 mg / L, NH4 + -N is 274mg / L, PO4 3- -P is 238.6 mg / L.

[0068] Example 7 A device for removing nitrogen and phosphorus from a liquid

[0069] like Figure 1 As shown, a device for removing nitrogen and phosphorus from a liquid comprises a struvite reaction tank 1, a pressure gas dissolving device 2 and an ammonia nitrogen stripping tank 3 which are connected in sequence;

[0070] The struvite reaction tank 1 is configured to: the liquid reacts with the precipitation agent to produce struvite precipitation to remove PO4 in the liquid. 3- and ammonia nitrogen;

[0071] The top of the struvite reaction tank 1 is provided with a dosing port 4 and a No. 1 tail gas recovery port 5, the side wall of the struvite reaction tank 1 is provided with a No. 1 liquid inlet 6 and a No. 1 liquid outlet 7, and the bottom of the struvite reaction tank 1 is provided with a No. 1 discharge port 8;

[0072] The top of the ammonia nitrogen stripping tank 3 is provided with a No. 2 tail gas recovery port 9, the side wall of the ammonia nitrogen stripping tank 3 is provided with a No. 2 liquid inlet 10 and a No. 2 liquid outlet 11, and the bottom of the ammonia nitrogen stripping tank 3 is provided with a No. 2 discharge port 12;

[0073] The inlet of the pressure gas dissolving device 2 is connected to the No. 1 liquid outlet 7 of the struvite reaction tank 1 through a water outlet pump 13, and the outlet of the pressure gas dissolving device 2 is connected to the No. 2 liquid inlet 10 of the ammonia nitrogen stripping tank 4 through a pipeline;

[0074] The struvite reaction tank 1 is provided with a reflux device 14, which includes a reflux pump 14-1 and a reflux pipe 14-2; the reflux of the liquid in the struvite reaction tank 1 is utilized to achieve disturbance and stirring of the liquid in the tank, thereby accelerating the formation of struvite precipitation;

[0075] The No. 1 tail gas recovery port 5 and / or the No. 2 tail gas recovery port 9 are connected to the air inlet of the pressure gas dissolving device 2 through a pipeline, and the ammonia nitrogen after the blow-off is refluxed and dissolved in the reaction liquid under pressure;

[0076] The No. 1 discharge port 8 of the struvite reaction tank 1 and the No. 2 discharge port 12 of the ammonia nitrogen stripping tank 3 are used to discharge the precipitation in the tank, and the device also includes a backwashing device, which can be used to remove the sediment (sediment) in the tank; specifically, the struvite reaction tank 1 is provided with a No. 1 backwashing device, and the No. 1 backwashing device includes the No. 1 discharge port 8 and the No. 1 liquid inlet 6; the ammonia nitrogen stripping tank 3 is provided with a No. 2 backwashing device, and the No. 2 backwashing device includes the No. 2 discharge port 12 and the No. 2 liquid inlet 10; the backwashing liquid enters from the No. 1 discharge port and flows out through the No. 1 liquid inlet, and the backwashing is used to solve the sediment deposition problem in the struvite reaction tank; or / and the backwashing liquid enters from the No. 2 discharge port and flows out through the No. 2 liquid inlet, and the backwashing is used to solve the sediment deposition problem in the ammonia nitrogen stripping tank;

[0077] A No. 1 breathing valve 15 is provided on the top of the struvite reaction tank 1, and a No. 2 breathing valve 16 is provided on the top of the ammonia nitrogen stripping tank 3. The No. 1 breathing valve 15 and the No. 2 breathing valve 16 are used to exhaust the gas in the tank.

[0078] The method of removing nitrogen and phosphorus from waste liquid using the above device has the following results:

[0079] Example 7-1

[0080] The sludge filtrate enters the struvite reaction tank through the No. 1 liquid inlet of the struvite reaction tank. At the same time, the precipitation drug magnesium chloride is added from the dosing port to make n(Mg 2+ ): n(NH4 + ): n(PO4 3- ) is 1.2:1:1, and the pH is 9-10.5. In order to ensure the full progress of the struvite precipitation reaction, the sludge filtrate in the struvite reaction tank is extracted by the reflux pump for reflux to ensure the disturbance and stirring of the sludge filtrate in the struvite reaction tank. The generated struvite precipitation is discharged from the No. 1 and No. 2 discharge ports; the reaction liquid in the tank is pumped from the No. 1 liquid outlet by the water outlet pump to the pressure gas dissolving device, which pressurizes the reaction liquid (3kg / cm 2 ), dissolve the ammonia recovered from the tail gas recovery port in the reaction liquid; the reaction liquid containing dissolved gas is discharged into the ammonia nitrogen stripping tank through the No. 2 liquid inlet of the ammonia nitrogen stripping tank, and is rapidly decompressed to normal pressure at 65°C to remove ammonia nitrogen; the liquid after stripping is discharged from the No. 2 liquid outlet to obtain recycled water, which is used as a carbon source in the sewage treatment system.

[0081] The water quality indicators of the recycled water are as follows: SCOD: 28940mg / L, NH4 + -N is 24mg / L, PO4 3- -P is 12mg / L.

[0082] Example 7-2

[0083] The sludge filtrate enters the struvite reaction tank through the No. 1 liquid inlet of the struvite reaction tank. At the same time, the precipitation drug magnesium chloride is added from the dosing port to make n(Mg 2+ ): n(NH4 + ): n(PO4 3- ) is 1.2:1:1. In order to ensure the full progress of the struvite precipitation reaction, the sludge filtrate in the struvite reaction tank is extracted by the reflux pump for reflux to ensure the disturbance and stirring of the sludge filtrate in the struvite reaction tank. The generated struvite precipitation is discharged from the No. 1 and No. 2 discharge ports; the reaction liquid in the tank is pumped from the No. 1 liquid outlet by the water outlet pump to the pressure gas dissolving device, which pressurizes the reaction liquid (1kg / cm 2 ), dissolve the ammonia recovered from the tail gas recovery port in the reaction liquid; the reaction liquid containing dissolved gas is discharged into the ammonia nitrogen stripping tank through the No. 2 liquid inlet of the ammonia nitrogen stripping tank, and is rapidly decompressed to normal pressure at 70°C to remove ammonia nitrogen; the liquid after stripping is discharged from the No. 2 liquid outlet to obtain recycled water, which is used as a carbon source in the sewage treatment system.

[0084] The water quality indicators of the recycled water are as follows: SCOD: 29830mg / L, NH4 + -N is 38mg / L, PO4 3- -P is 76mg / L.

[0085] Example 7-3

[0086] The sludge filtrate enters the struvite reaction tank through the No. 1 liquid inlet of the struvite reaction tank. At the same time, the precipitation drug magnesium chloride is added from the dosing port to make n(Mg 2+ ): n(NH4 + ): n(PO4 3- ) is 1.2:1:1. In order to ensure the full progress of the struvite precipitation reaction, the sludge filtrate in the struvite reaction tank is extracted by the reflux pump for reflux to ensure the disturbance and stirring of the sludge filtrate in the struvite reaction tank. The generated struvite precipitation is discharged from the No. 1 and No. 2 discharge ports; the reaction liquid in the tank is pumped from the No. 1 liquid outlet by the water outlet pump to the pressure gas dissolving device, which pressurizes the reaction liquid (5kg / cm 2 ), dissolve the ammonia recovered from the tail gas recovery port in the reaction liquid; the reaction liquid containing dissolved gas is discharged into the ammonia nitrogen stripping tank through the No. 2 liquid inlet of the ammonia nitrogen stripping tank, and is rapidly decompressed to normal pressure at 60°C to remove ammonia nitrogen; the liquid after stripping is discharged from the No. 2 liquid outlet to obtain recycled water, which is used as a carbon source in the sewage treatment system.

[0087] The water quality indicators of the recycled water are as follows: SCOD: 28450mg / L, NH4 + -N is 26mg / L, PO4 3--P is 15mg / L.

[0088] Comparative Example 7-4

[0089] The sludge filtrate enters the struvite reaction tank through the No. 1 liquid inlet of the struvite reaction tank. At the same time, the precipitation drug magnesium chloride is added from the dosing port to make n(Mg 2+ ): n(NH4 + ): n(PO4 3- ) is 1.2:1:1. In order to ensure the full progress of the struvite precipitation reaction, the sludge filtrate in the struvite reaction tank is extracted by the reflux pump for reflux to ensure the disturbance and stirring of the sludge filtrate in the struvite reaction tank. The generated struvite precipitation is discharged from the No. 1 and No. 2 discharge ports; the reaction liquid in the tank is pumped from the No. 1 liquid outlet by the water outlet pump to the pressure gas dissolving device, which pressurizes the reaction liquid (6kg / cm 2 ), dissolve the ammonia recovered from the tail gas recovery port in the reaction liquid; the reaction liquid containing dissolved gas is discharged into the ammonia nitrogen stripping tank through the No. 2 liquid inlet of the ammonia nitrogen stripping tank, and is rapidly decompressed to normal pressure at 50°C to remove ammonia nitrogen; the liquid after stripping is discharged from the No. 2 liquid outlet to obtain recycled water, which is used as a carbon source in the sewage treatment system.

[0090] The water quality indicators of the recycled water are as follows: SCOD: 30010mg / L, NH4 + -N is 76mg / L, PO4 3- -P is 112mg / L.

[0091] Comparative Example 7-5

[0092] The sludge filtrate was treated by the method of Example 2 in the urea hydrolysis wastewater resource treatment system and method disclosed in CN116282688A, specifically: (1) the sludge filtrate was heated to 50°C and then entered into a stripping tower for stripping treatment, and the air-water ratio in the stripping tower was 4500m / s. 3 / m 3 , hydraulic load is 3m 3 / m 2 ·h, the stripping treatment time is 60min; (2) After the stripping treatment, the sludge filtrate enters the reaction tank, and magnesium chloride is added to the sludge filtrate to make n(Mg 2+ ): n(NH4 + ): n(PO4 3- ) is in a molar ratio of 1.2:1:1, and struvite is precipitated and discharged to obtain recycled water.

[0093] The water quality indicators of the recycled water are as follows: SCOD: 29800mg / L, NH4 + -N is 40.1mg / L, PO4 3--P is 78mg / L.

[0094] The above is a further description of the present invention in conjunction with specific embodiments, but these embodiments are merely exemplary and do not constitute any limitation on the scope of the present invention. It should be understood by those skilled in the art that the details and forms of the technical solution of the present invention may be modified or replaced without departing from the spirit and scope of the present invention, but these modifications and replacements all fall within the scope of protection of the present invention.

Claims

1. A device for removing nitrogen and phosphorus from a liquid, characterized in that: It includes a struvite reaction tank, a pressure gas dissolving device and an ammonia nitrogen stripping tank which are connected in sequence; The struvite reaction tank is configured to: the liquid reacts with the precipitation agent to produce struvite precipitation to remove PO4 in the liquid. 3- and ammonia nitrogen; the struvite reaction tank is provided with a dosing port, a No. 1 liquid inlet, a No. 1 liquid outlet and a No. 1 discharge port; The ammonia nitrogen stripping tank is configured to: release the reaction liquid containing dissolved gas under reduced pressure and remove ammonia nitrogen by stripping; the ammonia nitrogen stripping tank is provided with a No. 2 liquid inlet, a No. 2 liquid outlet and a No. 2 discharge port; The pressure gas dissolving device is configured to: pressurize and dissolve part or all of the reaction liquid after the struvite reaction; the liquid inlet of the pressure gas dissolving device is connected to the No. 1 liquid outlet of the struvite reaction tank through a water outlet pump, and the liquid outlet of the pressure gas dissolving device is connected to the No. 2 liquid inlet of the ammonia nitrogen stripping tank through a pipeline.

2. The device according to claim 1, characterized in that The struvite reaction tank is provided with a reflux device, which is configured to: reflux part of the liquid in the struvite reaction tank to the struvite reaction tank, realize disturbance and stirring of the liquid in the tank, and accelerate the formation of struvite precipitation; the reflux device includes a reflux pump and a reflux pipeline.

3. The device according to claim 1, characterized in that The struvite reaction tank is provided with a No. 1 tail gas recovery port, and the ammonia nitrogen stripping tank is provided with a No. 2 tail gas recovery port; the No. 1 tail gas recovery port and / or the No. 2 tail gas recovery port are connected to the air inlet of the pressure gas dissolution device through a pipeline.

4. The device according to claim 1, characterized in that The struvite reaction tank is provided with a No. 1 backwashing device, and the No. 1 backwashing device comprises the No. 1 discharge port and the No. 1 liquid inlet; The ammonia nitrogen stripping tank is provided with a No. 2 backwashing device, and the No. 2 backwashing device comprises a No. 2 discharge port and a No. 2 liquid inlet; The No. 1 backwash device and the No. 2 backwash device are configured to remove sediment in the tank.

5. The device according to claim 1, characterized in that The struvite reaction tank is provided with a No. 1 breathing valve, and the ammonia nitrogen stripping tank is provided with a No. 2 breathing valve; the No. 1 breathing valve and the No. 2 breathing valve are configured to: empty the gas in the tank body.

6. A method for removing nitrogen and phosphorus from a liquid, characterized in that: The following steps are involved: (1) Add precipitation reagents to the liquid to produce struvite precipitation reaction and remove PO4 in the liquid 3- and ammonia nitrogen to obtain a reaction solution; (2) pressurizing part or all of the reaction liquid obtained in step (1) to dissolve gas, dissolving the gas in the reaction liquid to obtain a reaction liquid containing dissolved gas; (3) The reaction liquid containing dissolved gas obtained in step (3) is decompressed to release the dissolved gas, and ammonia nitrogen is blown off to obtain denitrified and dephosphorized water.

7. The method according to claim 6, characterized in that The pressure of the pressurized dissolved gas in step (2) is 1-5 kg / cm 2 , the gas is air and / or recovered ammonia.

8. The method according to claim 7, characterized in that The pressure of the pressurized dissolved gas is 3-5 kg / cm 2 .

9. The method according to claim 6, characterized in that The stripping conditions in step (3) are: temperature 60-70° C., pH 9-10.

5.

10. The method according to claim 9, characterized in that The stripping temperature is 60-65°C.

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