Method and system for treating biogas slurry through electrochemical membrane ammonia stripping

Abstract

The invention relates to the technical field of agricultural waste treatment and utilization, and discloses a method and system for treating biogas slurry through electrochemical membrane ammonia stripping. The method comprises the following steps: (1) adding a flocculating agent into the biogas slurry for flocculation treatment; (2) inputting the flocculated biogas liquid supernatant into a cathode chamber of an electrolytic bath, separating the cathode chamber from an anode chamber of the electrolytic bath by a cation exchange membrane, carrying out water electrolysis reaction in the electrolytic bath, and carrying out aeration stripping on the biogas liquid supernatant in the cathode chamber while carrying out water electrolysis reaction, the obtained ammonia gas is blown off from the biogas slurry supernatant under the disturbance of aeration. According to the method disclosed by the invention, the electrolytic bath is modified, and a specific electrochemical method is combined, so that relatively high ammonia nitrogen removal and recovery efficiency can be achieved under the conditions of no addition of an alkaline agent and no heating, and the problems of high cost and low ammonia removal efficiency of a biogas liquid ammonia recovery process are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of agricultural waste treatment and utilization, and particularly relates to a method and system for treating biogas slurry by electrochemical membrane ammonia stripping. Background Art

[0002] Anaerobic digestion is a technology that converts various organic wastes into renewable energy and is widely used in research and practical applications, which has led to the generation of a large amount of biogas slurry with a high ammonia nitrogen concentration. If directly discharged or used, it will cause serious non-point source pollution and water eutrophication. At the same time, ammonia is also the most critical element in fertilizers. Therefore, removing and recovering nitrogen sources from biogas slurry is of great significance for circular economy and social sustainable development. Currently, nitrogen sources can be recovered from wastewater through various technologies, such as ammonia stripping, struvite precipitation, etc. Chinese Patent Application CN119219191A discloses a method for phosphorus enrichment and struvite recovery from anaerobic fermentation liquid of sludge by a combined biological membrane method, in which Mg 2+ , NH 4+ , PO4 3- ions react in a molar ratio of 1:1:1 to form magnesium ammonium phosphate (Mg(NH4)PO4·6H2O), but this method requires the addition of a large amount of magnesium salts (MgCl2·6H2O), and a large amount of scale is likely to accumulate on the equipment, significantly increasing the treatment and maintenance costs.

[0003] Compared with the struvite precipitation technology, the research on the combination of ammonia stripping and acid-base absorption technology is more extensive. By introducing air into the biogas slurry with adjusted pH, ammonia nitrogen is transferred from the liquid phase to the gas phase, and then the ammonia gas is absorbed by acid solution. The nitrogen source in the biogas slurry is finally recovered as ammonium salts (such as (NH4)2SO4) and used as fertilizers, which can effectively balance the biogas slurry treatment cost.

[0004] Chinese Patent Application CN118684389A designs a new type of high-efficiency, low-carbon and intelligent high-concentration ammonia nitrogen wastewater treatment system. To make the ammonia nitrogen concentration of the effluent meet the standard, a large amount of alkali needs to be added through an alkali addition system to adjust the pH of the wastewater ≥ 12. The addition of alkali agents greatly increases the biogas slurry treatment cost. At the same time, the heating consumption of the biogas slurry is also a key factor that significantly increases the treatment cost. Chinese Patent Application CN117361597A discloses a method for ammonia recovery and biogas purification from biogas slurry. This method requires controlling the temperature of the ammonia stripping tower at 50 - 70 °C, greatly increasing the biogas slurry treatment cost. Therefore, seeking cheap pH adjustment and heating means to replace traditional methods is the key to cost reduction, high efficiency and sustainable development of the biogas slurry ammonia stripping technology. Summary of the Invention

[0005] The object of the present invention is to overcome the problems existing in the prior art that a large amount of alkali needs to be added to adjust the pH value for ammonia nitrogen treatment, or heating is required during the ammonia stripping process, resulting in high cost of biogas slurry treatment and low ammonia removal efficiency. A method and system for treating biogas slurry by electrochemical membrane ammonia stripping are provided. The method of the present invention achieves high ammonia nitrogen removal and recovery efficiency without adding alkali agents and without heating by modifying the electrolytic cell and combining with a specific electrochemical method, solving the problems of high cost and low ammonia removal efficiency in the biogas slurry ammonia recovery process.

[0006] To achieve the above object, on the one hand, the present invention provides a method for treating biogas slurry by electrochemical membrane ammonia stripping, the method comprising the following steps:

[0007] (1) Adding a flocculant to the biogas slurry for flocculation treatment;

[0008] (2) Inputting the supernatant of the flocculation-treated biogas slurry into the cathode chamber of the electrolytic cell. The cathode chamber and the anode chamber of the electrolytic cell are separated by a cation exchange membrane. The electrolytic cell conducts an electrolytic water reaction. Under the action of the cation exchange membrane, OH in the supernatant of the biogas slurry - accumulates in the cathode chamber to create an alkaline environment required for generating ammonia gas. While conducting the electrolytic water reaction, the supernatant of the biogas slurry in the cathode chamber is aerated and stripped to obtain ammonia gas.

[0009] Preferably, in step (1), the content of ammonia nitrogen in the biogas slurry is 1400 - 1500 mg / L, and the content of suspended solids is 0.5 - 1 g / L.

[0010] Preferably, in step (1), the flocculant is polyacrylamide.

[0011] Preferably, in step (1), relative to 1 L of biogas slurry, the dosage of the flocculant is 3 - 5 g.

[0012] Preferably, in step (1), the time of the flocculation treatment is 10 - 30 min.

[0013] Preferably, in step (1), the flocculation treatment is carried out under stirring conditions, and the stirring rate is 800 - 1200 rpm.

[0014] Preferably, in step (2), the cation exchange membrane is FKS - PET - 130 membrane.

[0015] Preferably, in step (2), the electrolyte in the anode chamber is a 0.2 - 0.4 M disodium hydrogen phosphate solution.

[0016] Preferably, in step (2), the constant current intensity of the electrolytic water reaction is 30 - 40 mA / cm 2 .

[0017] Preferably, in step (2), the process of aeration stripping of the supernatant of biogas slurry in the cathode chamber includes: introducing air into the bottom of the cathode chamber, and the air flow rate is 0.5-1.1 L / min.

[0018] Preferably, in step (2), the anode of the electrolytic cell is a ruthenium-iridium-titanium plate, and the cathode of the electrolytic cell is a titanium plate.

[0019] Preferably, the process of the electrolytic cell for electrolyzing water includes: when an electric current is applied to the electrolytic cell, the electrolytic cell undergoes an electrolytic water reaction. Among them, the reaction occurring in the anode chamber is: 2H2O → O2↑ + 4H + + 4e - , and the reaction occurring in the cathode chamber is: 2H2O + 2e - → H2↑ + 2OH - , the cation exchange membrane allows cations to transfer between the anode chamber and the cathode chamber, and prevents the OH - generated in the cathode chamber from entering the anode chamber through the cation exchange membrane. Furthermore, the OH - in the supernatant of biogas slurry accumulates in the cathode chamber to create an alkaline environment required for the generation of ammonia gas, so that the OH - generated in the cathode chamber reacts with the ammonia nitrogen in the supernatant of biogas slurry to obtain ammonia gas.

[0020] Preferably, the method further includes: absorbing the ammonia gas stripped from the supernatant of biogas slurry in the cathode chamber with an acidic solution.

[0021] Preferably, the acidic solution is a 20-40 vol% concentrated sulfuric acid solution.

[0022] The second aspect of the present invention provides a system for electrochemically membrane ammonia stripping treatment of biogas slurry, and the system includes:

[0023] A flocculation tank, and the biogas slurry from the biogas slurry tank enters the flocculation tank for flocculation treatment;

[0024] An electrolytic cell, the cathode chamber and the anode chamber of the electrolytic cell are separated by a cation exchange membrane, the supernatant of biogas slurry from the flocculation tank enters the cathode chamber, the electrolytic cell undergoes an electrolytic water reaction, and under the action of the cation exchange membrane, the OH - in the supernatant of biogas slurry accumulates in the cathode chamber to create an alkaline environment required for the generation of ammonia gas;

[0025] An air pump, which is used to aerate and strip the supernatant of biogas slurry in the cathode chamber while the electrolytic water reaction is taking place to obtain ammonia gas.

[0026] Preferably, in the electrolytic cell, the electrolytic water reaction is carried out under the condition of applying an electric current. Among them, electrolytic water in the anode chamber generates H+ , electrolyzed water in the cathode chamber generates OH - , the cation exchange membrane allows cations to transfer between the anode chamber and the cathode chamber, while the OH - generated in the cathode chamber cannot pass through the cation exchange membrane and thus accumulates in the cathode chamber to create the alkaline environment required for ammonia production, enabling the OH - generated in the cathode chamber to react with the ammonia nitrogen in the supernatant of the biogas slurry to obtain ammonia.

[0027] Preferably, the electrolytic cell further includes a cathode, an anode, and a DC power supply. The cathode is disposed in the cathode chamber, the anode is disposed in the anode chamber, the anode is connected to the positive pole of the DC power supply by a wire, and the cathode is connected to the negative pole of the DC power supply by a wire;

[0028] A first peristaltic pump is provided on the connecting pipeline between the biogas slurry tank and the flocculation tank. A stirrer is provided in the flocculation tank, and the stirring paddle of the stirrer is located at the center of the biogas slurry in the flocculation tank. A second peristaltic pump is provided on the connecting pipeline between the flocculation tank and the cathode chamber. The bottom of the cathode chamber has an air inlet, and the air pumped in by the air pump enters the cathode chamber through the air inlet. The top of the cathode chamber has an air outlet, and the air outlet is connected to the ammonia recovery tank through an air pipe.

[0029] Compared with the prior art, the present invention has at least the following beneficial effects:

[0030] (1) Using a flocculant to flocculate the biogas slurry can effectively remove the suspended solids in the biogas slurry, reduce the blockage of the cation exchange membrane in the electrolytic cell during subsequent treatment, and reduce the damage to the membrane; at the same time, it can also enable the cation NH4 + in the anode chamber to smoothly pass through the cation exchange membrane and transfer to the cathode chamber to be converted into NH3, improving the ammonia nitrogen removal rate;

[0031] (2) A cation exchange membrane is provided between the cathode chamber and the anode chamber of the electrolytic cell of the present invention. This cation exchange membrane only allows cations to pass through. When a DC current is applied to the electrolytic cell, an electrolyzed water reaction occurs in the electrolytic cell (2H2O → O2↑ + 4H + + 4e - (anode), 2H2O + 2e - → H2↑ + 2OH - (cathode)). Due to the generation of OH - , the pH value of the liquid in the cathode significantly increases. At the same time, to ensure the electrical neutrality of the system, the cations in the anode chamber will also transfer to the cathode chamber through the cation exchange membrane. Almost all the NH4 + in the system accumulates in the cathode chamber and then reacts with the OH - in the cathode chamber to be converted into NH3 NH3 is stripped out under the agitation of aeration. Therefore, in the method of the present invention, OH generated in the cathode chamber by electrolyzing water - replaces the addition of traditional alkaline agents, and can achieve efficient ammonia nitrogen removal without the addition of alkaline agents, with high economic benefits. Compared with using the traditional alkaline agent NaOH to adjust the pH value of biogas slurry, the cost of adding alkaline agents can be saved by 25 yuan / t. In addition, in the present invention, air is introduced from the bottom of the cathode chamber for aeration stripping while electrolyzing water, and high ammonia nitrogen removal efficiency can be achieved without heating. Description of the Drawings

[0032] Figure 1 is a schematic diagram of the electrolytic cell of the present invention;

[0033] Figure 2 is a schematic diagram of the system for treating biogas slurry by electrochemical membrane ammonia stripping of the present invention.

[0034] Description of the Reference Numerals

[0035] 100 Electrolytic cell; 101 Cathode chamber; 102 Anode chamber; 103 Cation exchange membrane; 104 Anode; 105 Cathode; 106 DC power supply; 200 Flocculation tank; 300 Biogas slurry tank; 400 Air pump; 500 Ammonia recovery tank; 600 First peristaltic pump; 700 Stirrer; 800 Second peristaltic pump; Air pump 900. Detailed Embodiments

[0036] The following details the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only for explaining and illustrating the present invention, and are not used to limit the present invention.

[0037] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0038] As described above, the first aspect of the present invention provides a method for treating biogas slurry by electrochemical membrane ammonia stripping, and the method includes the following steps:

[0039] (1) Adding a flocculant to the biogas slurry for flocculation treatment;

[0040] (2) Inputting the supernatant of the flocculated biogas slurry into the cathode chamber 101 of the electrolytic cell 100. The cathode chamber 101 and the anode chamber 102 of the electrolytic cell 100 are separated by a cation exchange membrane 103. The electrolytic cell 100 performs an electrolytic water reaction. Under the action of the cation exchange membrane 103, OH in the supernatant of the biogas slurry- Accumulate in the cathode chamber 101 to create an alkaline environment required for ammonia production. While electrolyzing water, aerate and strip the supernatant of biogas slurry in the cathode chamber 101 to obtain ammonia.

[0041] As Figure 1 shown, the electrolytic cell 100 of the present invention has a similar structure to a conventional electrolytic cell. The difference is that the cathode chamber 101 and the anode chamber 102 of the electrolytic cell 100 of the present invention are separated by a cation exchange membrane 103. Further, the cathode 105 and the anode 104 are respectively arranged in the cathode chamber 101 and the anode chamber 102, and are respectively connected to the negative electrode and the positive electrode of a DC power supply 106 by wires.

[0042] In the method of the present invention, in step (1), the biogas slurry is flocculated by a flocculant to effectively remove suspended solids in the biogas slurry. The content of suspended solids in the supernatant of the flocculated biogas slurry is greatly reduced, reducing the blockage of the cation exchange membrane 103 in the electrolytic cell 100 in the later treatment and reducing the damage to the membrane. The content of ammonia nitrogen in the supernatant of the flocculated biogas slurry hardly changes; in step (2), by arranging a cation exchange membrane 103 between the cathode chamber 101 and the anode chamber 102 of the electrolytic cell 100, the cation exchange membrane 103 only allows cations to pass through. When a DC current is applied to the electrolytic cell 100, the electrolytic cell 100 undergoes an electrolytic water reaction (2H2O → O2↑ + 4H + + 4e - (anode), 2H2O + 2e - → H2↑ + 2OH - (cathode)). Due to the generation of OH - , the pH value of the liquid in the cathode 106 increases significantly. At the same time, to ensure the electrical neutrality of the system, cations in the anode chamber 102 (such as H + , NH4 + ) will also transfer to the cathode chamber 101 through the cation exchange membrane 103. The supernatant of the biogas slurry containing a large amount of ammonia nitrogen also exists in the cathode chamber 101. Eventually, almost all NH4 + in the system accumulates in the cathode chamber 101, and then reacts with OH - in the cathode chamber 101 to be converted into NH3 is stripped out under the disturbance of aeration. Therefore, in the method of the present invention, the OH - generated by electrolyzing water in the cathode chamber 101 replaces the addition of traditional alkaline agents, and high-efficiency ammonia nitrogen removal can be achieved without adding alkaline agents, with high economic benefits. Compared with using the traditional alkaline agent NaOH to adjust the pH value of the biogas slurry, the cost of adding alkaline agents can be saved by 25 yuan / t. In addition, in the present invention, by introducing air from the bottom of the cathode chamber for aeration and stripping while electrolyzing water, high ammonia nitrogen removal efficiency can be achieved without heating.

[0043] In some embodiments, the content of ammonia nitrogen and suspended solids in the biogas slurry is relatively high; specifically, in step (1), the content of ammonia nitrogen in the biogas slurry is 1400 - 1500 mg / L, and the content of suspended solids is 0.5 - 1 g / L. In the present invention, the suspended solids can be of common types in the art, such as undecomposed organic matters (such as lignin), inorganic particles (such as sediment), and colloidal substances (such as proteins), etc.

[0044] In the present invention, the flocculant can be a conventional choice in the art. In a preferred embodiment, the flocculant in step (1) is polyacrylamide (PAM). Polyacrylamide not only has a high removal effect on suspended solids, but also the obtained flocs can be used for planting, which can provide nutrients for the soil while realizing soil improvement.

[0045] In some preferred embodiments, in step (1), relative to 1 L of biogas slurry, the dosage of the flocculant is 3 - 5 g, that is to say, to treat 1 L of biogas slurry, 3 - 5 g of the flocculant needs to be added, that is, the addition concentration of the flocculant is 3 - 5 g / L. When the addition concentration of the polyacrylamide flocculant is too low (<3 g / L), the electro-neutralization effect is insufficient, the electrostatic repulsion between particles is still large, it is difficult for particles to approach and aggregate, and at the same time, the degree of interweaving between molecular chains is insufficient, the formed flocs are relatively loose, and are easily broken under the disturbance of water flow, resulting in the re-dispersion of particles, and the flocculation effect will decline; while when the concentration of the polyacrylamide flocculant is too high (>5 g / L), the viscosity of the solution will increase significantly, and the high-viscosity solution will hinder the free movement and collision of particles, reducing the contact opportunity between particles, which is not conducive to the effective aggregation and flocculation of particles, and will also cause the formed flocs to be too compact, reducing the voids between particles, resulting in a decrease in the strength and stability of the flocs. Under the disturbance of water flow, the too-compact flocs are easily broken, and the particles are re-dispersed into the water, thus affecting the flocculation effect. Therefore, controlling the dosage of the flocculant within the aforementioned range can further improve the flocculation effect and further improve the removal effect of suspended solids.

[0046] In some preferred embodiments, in step (1), the time for the flocculation treatment is 10 - 30 min. The flocculation reaction requires a certain amount of time to complete. If the stirring time is too short (<10 min), the reaction between the flocculant and the particles will be insufficient, resulting in incomplete interaction between the particles and the inability to form stable large particles. If the stirring time is too long (>30 min), a large shear force will be continuously generated, causing the already formed larger flocs to be excessively sheared and broken. The flocs will be degraded or structurally damaged under the action of mechanical shear force, and finally the flocculation efficiency will be poor. Therefore, controlling the time for the flocculation treatment within the aforementioned range can further improve the flocculation effect and further improve the removal effect of suspended solids.

[0047] In a more preferred embodiment, the flocculation treatment is carried out under stirring conditions, and the stirring rate is 800 - 1200 rpm. When the stirring rate is too low (<800 rpm), the contact between the flocculant and the suspended particles and colloidal particles in the water will be insufficient. This is because the collision chance between the particles decreases, and the flocculant cannot be effectively adsorbed on the particle surface, thereby reducing the adsorption bridging effect between the particles and making it difficult for the particles to aggregate together to form larger flocs, affecting the flocculation effect. When the stirring speed is too high (>1200 rpm), a large shear force will be generated, causing the particles in the water body to be over-dispersed, reducing the effective collision chance between the particles. If the particles cannot effectively collide, it is difficult to form larger flocs through adsorption and aggregation. At the same time, it will also lead to insufficient contact time between the flocculant and the particles, making the flocculant unable to fully exert its adsorption and bridging effects, and the adsorption of the flocculant molecules on the particle surface is not firm, thereby affecting the flocculation efficiency. Therefore, controlling the stirring rate within the aforementioned range can further improve the flocculation effect and further improve the removal effect of suspended solids.

[0048] In the present invention, after the biogas slurry undergoes flocculation treatment, the concentration of suspended solids in the supernatant of the biogas slurry is reduced to 0.15 - 0.4 g / L, and the flocculation treatment has no effect on the concentration of ammonia nitrogen.

[0049] In some embodiments, in step (2), the cation exchange membrane 103 is an FKS - PET - 130 membrane. Due to electrolysis, the pH values of the liquids at the anode and cathode of the electrolytic cell are relatively extreme. The FKS - PET - 130 membrane can withstand such extreme conditions and is therefore suitable for the electrolysis process of the present invention.

[0050] In step (2) of the present invention, the electrolyte in the anode chamber 102 is not particularly limited as long as it ensures that the aforementioned electrolysis of water reaction can occur in the electrolytic cell 100, that is, 2H2O → O2↑ + 4H + +4e - (anode), 2H2O + 2e- →H2↑ + 2OH - (Cathode). In some embodiments, in step (2), the electrolyte solution in the anode chamber 102 is a disodium hydrogen phosphate solution with a concentration of 0.2 - 0.4 M. Here, M is the concentration unit mol / L. When the concentration of the disodium hydrogen phosphate solution is lower than this range, the current intensity cannot reach the required current intensity; when the concentration of the disodium hydrogen phosphate solution is higher than this range, the reagent cost is too high and the economic efficiency is low.

[0051] In the method of the present invention, the constant current intensity is provided by the DC power supply 106. In some preferred embodiments, the constant current intensity of the electrolytic water reaction can be 30 - 40 mA / cm 2 . When the current intensity is too low, the cathode chamber 101 cannot generate enough OH - to react with NH4 + , and there are fewer bubbles generated on the electrode surface. The generation of bubbles can play a role in stirring and mass transfer. At the same time, due to the too low current intensity, NH4 in the cathode chamber 101 + may diffuse reversely into the anode chamber 102, ultimately resulting in a lower ammonia nitrogen removal rate; the ammonia nitrogen removal rate increases with the increase of the current intensity. When the current intensity increases to a certain level, the ammonia nitrogen removal rate will no longer increase significantly. And when the current intensity is too high, it will also accelerate the corrosion of the electrode material, shorten the service life of the electrode, and thus reduce the economic efficiency of the system treatment. Therefore, controlling the constant current intensity within the aforementioned range can not only further improve the ammonia nitrogen removal rate but also increase the service life of the electrode.

[0052] In the method of the present invention, the function of aeration stripping the supernatant of the biogas slurry in the cathode chamber 101 during the electrolytic water reaction is to strip out the NH3 generated in the cathode chamber 101 under the disturbance of aeration, promote the generation of NH3, and improve the ammonia nitrogen removal rate.

[0053] In some preferred embodiments, in step (2), the process of aeration stripping of the supernatant of biogas slurry in the cathode chamber 101 includes: introducing air into the bottom of the cathode chamber 101, and the air flow rate is 0.5 - 1.1 L / min. When the air flow rate is too low, the contact area between the gas and the supernatant of biogas slurry will decrease, reducing the mass transfer driving force of ammonia stripping, and the stirring effect on the supernatant of biogas slurry is weak, resulting in uneven distribution of ammonia nitrogen in the supernatant of biogas slurry, making it difficult to fully contact and exchange with the gas phase, thus reducing the ammonia nitrogen removal rate; while when the air flow rate is too high, the residence time of the gas in the supernatant of biogas slurry will decrease, resulting in insufficient contact time between ammonia nitrogen and the gas, unable to fully carry out the gas-liquid mass transfer process, and may also cause too violent turbulence at the gas-liquid mass transfer interface, increasing the mass transfer resistance, reducing the transfer efficiency of ammonia nitrogen from the liquid phase to the gas phase, thus reducing the ammonia nitrogen removal efficiency. Therefore, controlling the air flow rate within the aforementioned range can further improve the ammonia nitrogen removal rate.

[0054] In the present invention, there are no particular limitations on the anode 104 and the cathode 105 of the electrolytic cell 100, as long as the object of the present invention can be achieved. In one embodiment, in step (2), the anode 104 of the electrolytic cell 100 is a ruthenium-iridium-titanium plate, that is, ruthenium-iridium is coated on the titanium plate, and the cathode 105 of the electrolytic cell 100 is a titanium plate. The ruthenium-iridium-titanium plate and the titanium plate have good corrosion resistance and are suitable for the electrolysis process of the present invention.

[0055] In the present invention, the process of the electrolytic cell 100 for electrolyzing water includes: when an electric current is applied to the electrolytic cell 100, the electrolytic cell 100 undergoes an electrolytic water reaction. Among them, the reaction occurring in the anode chamber 102 is: 2H2O → O2↑ + 4H + + 4e - , and the reaction occurring in the cathode chamber 101 is: 2H2O + 2e - → H2↑ + 2OH - , the cation exchange membrane 103 allows cations to transfer between the anode chamber 102 and the cathode chamber 101, while preventing the OH - generated in the cathode chamber 101 from entering the anode chamber 102 through the cation exchange membrane 103. Furthermore, the OH - in the supernatant of biogas slurry accumulates in the cathode chamber 101 to create an alkaline environment required for the generation of ammonia gas, enabling the OH - generated in the cathode chamber 101 to react with the ammonia nitrogen in the supernatant of biogas slurry to obtain ammonia gas.

[0056] In one embodiment, the method further includes: absorbing the ammonia gas stripped from the supernatant of biogas slurry in the cathode chamber 101 with an acidic solution to generate ammonium sulfate liquid for use as a fertilizer, thereby improving the nitrogen source recovery rate.

[0057] In some preferred embodiments, the acidic solution may be a concentrated sulfuric acid solution of 20-40% by volume. When the concentration of the sulfuric acid solution is too low, the solution cannot provide enough SO4 2- to absorb NH3, resulting in low absorption efficiency; while when the sulfuric acid concentration is too high, there will be excess SO4 2- , making the reagent cost too high and the economic efficiency low.

[0058] When the method of the present invention is used to treat biogas slurry, the removal rate of suspended solids in the biogas slurry can reach more than 50%. Specifically, the removal rate of suspended solids in the biogas slurry can reach 50%-70%; the removal rate of ammonia nitrogen can reach 70%-93%; and the recovery rate of nitrogen source > 99%.

[0059] The second aspect of the present invention provides a system for electrochemically membrane ammonia stripping treatment of biogas slurry, as Figure 2 shown. This system includes:

[0060] A flocculation tank 200, into which the biogas slurry from the biogas slurry tank 300 enters for flocculation treatment;

[0061] An electrolytic cell 100, the cathode chamber 101 and the anode chamber 102 of the electrolytic cell 100 are separated by a cation exchange membrane 103. The supernatant of the biogas slurry from the flocculation tank 200 enters the cathode chamber 101, and the electrolytic cell 100 undergoes an electrolytic water reaction. Under the action of the cation exchange membrane 103, OH in the supernatant of the biogas slurry - accumulates in the cathode chamber 101 to create an alkaline environment required for the generation of ammonia gas;

[0062] An air pump 400, which is used to aerate and strip the supernatant of the biogas slurry in the cathode chamber 101 during the electrolytic water reaction to obtain ammonia gas.

[0063] In one embodiment, a first peristaltic pump 600 is provided on the connecting pipeline between the biogas slurry tank 300 and the flocculation tank 200, and the biogas slurry in the biogas slurry tank 300 is transported to the flocculation tank 200 by the first peristaltic pump 600 for flocculation treatment.

[0064] The system of the present invention further includes a stirrer 700 provided in the biogas slurry tank 300, which is used to stir and flocculate the biogas slurry during the flocculation treatment. Among them, the stirring paddle of the stirrer 700 is located at the center of the biogas slurry in the flocculation tank 200.

[0065] As Figure 1 and Figure 2As shown in the figure, the electrolytic cell 100 of the present invention includes a cathode chamber 101 and an anode chamber 102, and the cathode chamber 101 and the anode chamber 102 are separated by a cation exchange membrane 103. More specifically, the electrolytic cell 100 further includes a cathode 105, an anode 104, and a DC power supply 106. The cathode 105 is disposed in the cathode chamber 101, the anode 104 is disposed in the anode chamber 102, the cathode 105 is connected to the negative electrode of the DC power supply 106 by a wire, and the anode 104 is connected to the positive electrode of the DC power supply 106 by a wire.

[0066] In one embodiment, a second peristaltic pump 800 is provided on the communication pipeline between the flocculation tank 200 and the cathode chamber 101. The supernatant of the biogas slurry in the flocculation tank 200 is transported to the cathode chamber 101 by the second peristaltic pump 800. The supernatant of the biogas slurry contains a large amount of ammonia nitrogen, and the NH4 + aggregated in the cathode chamber 101 reacts with the OH - electrolyzed in the cathode chamber 101 and is converted into

[0067] In the present invention, the bottom of the cathode chamber 101 has an air inlet, and the air blown into the bottom of the cathode chamber 101 by the air pump 400 enters the cathode chamber 101 through the air inlet.

[0068] In the present invention, in the electrolytic cell 100, the electrolytic water reaction is carried out under the condition of applying an electric current. Among them, H + is generated by electrolyzing water in the anode chamber 102, and the reaction occurring in the anode chamber 102 is: 2H2O → O2↑ + 4H + + 4e - OH - is generated by electrolyzing water in the cathode chamber 101, and the reaction occurring in the cathode chamber 101 is: 2H2O + 2e - → H2↑ + 2OH - , the cation exchange membrane 103 allows cations to transfer between the anode chamber 102 and the cathode chamber 101, while the OH - generated in the cathode chamber 101 cannot pass through the cation exchange membrane 103, thus aggregating in the cathode chamber 101 to create an alkaline environment required for generating ammonia gas, so that the OH - generated in the cathode chamber 101 reacts with the ammonia nitrogen in the supernatant of the biogas slurry to obtain ammonia gas.

[0069] In the present invention, the system further includes an ammonia recovery tank 500 filled with an acidic solution for absorbing the ammonia gas blown out from the cathode chamber 101, and the acidic solution absorbs the ammonia gas to form ammonium sulfate liquid.

[0070] In one embodiment, the top of the cathode chamber 101 has an air outlet, and the ammonia gas generated in the cathode chamber 101 flows out through the air outlet and enters the ammonia recovery tank 500 through a gas pipe, so that the ammonia gas blown out from the cathode chamber 101 enters the ammonia recovery tank 500 for absorption.

[0071] In a more specific embodiment, as Figure 2 shown, the system includes an electrolytic cell 100, a flocculation tank 200, a biogas slurry tank 300, an air pump 400, and an ammonia recovery tank 500. The electrolytic cell 100 includes a cathode chamber 101 and an anode chamber 102. The cathode chamber 101 and the anode chamber 102 are separated by a cation exchange membrane 103. A cathode 105 and an anode 104 are respectively arranged in the cathode chamber 101 and the anode chamber 102, and are respectively connected to the negative and positive poles of a DC power supply 106 by wires. A first peristaltic pump 600 is arranged on the connecting pipe between the biogas slurry tank 300 and the flocculation tank 200. A stirrer 700 is arranged in the flocculation tank 200, and the stirring paddle of the stirrer 700 is located at the center of the biogas slurry in the flocculation tank 200. A second peristaltic pump 800 is arranged on the connecting pipe between the flocculation tank 200 and the cathode chamber 101. The bottom of the cathode chamber 101 has an air inlet, and the air blown in by the air pump 400 enters the cathode chamber 101 through the air inlet. The top of the cathode chamber 101 has an air outlet, and the air outlet is communicated with the ammonia recovery tank 500 through a gas pipe.

[0072] The working process of the system of the present invention includes: the biogas slurry from the biogas slurry tank 300 is transported to the flocculation tank 200 by the first peristaltic pump 600 and is subjected to flocculation treatment by the stirrer 700. The supernatant of the biogas slurry after flocculation treatment is transported from the flocculation tank 200 to the cathode chamber 101 by the second peristaltic pump 800. The anode chamber 102 is filled with an electrolyte solution (disodium hydrogen phosphate), and the positive and negative poles of the DC power supply 106 are respectively connected to the anode 104 and the cathode 105 to provide current. The electrolytic cell 100 undergoes an electrolytic water reaction (2H2O → O2↑ + 4H + + 4e - (anode), 2H2O + 2e - → H2↑ + 2OH - (cathode)), at the same time, the air blown in by the air pump 400 enters the cathode chamber 101 through the air inlet for aeration and stripping. A large amount of ammonia nitrogen is contained in the supernatant of the biogas slurry, and the NH4 + aggregated in the cathode chamber 101 reacts with the OH - electrolytically generated in the cathode chamber 101 to be converted into NH3. NH3 is stripped out under the disturbance of aeration, and the ammonia gas blown out from the cathode chamber 101 enters the ammonia recovery tank 500 and is absorbed by an acidic solution (sulfuric acid solution).

[0073] The method and system for treating biogas slurry by electrochemical membrane ammonia stripping of the present invention will be further described below through embodiments. The embodiments are implemented on the premise of the technical solution of the present invention, and the detailed implementation manners and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0074] In the experimental methods in the following embodiments, unless otherwise specified, they are all conventional methods in the art. The experimental materials used in the following embodiments can be commercially obtained unless otherwise specified.

[0075] The following embodiments are all implemented in the system for treating biogas slurry by electrochemical membrane ammonia stripping of the present invention. As Figure 2 shown, the system includes an electrolytic cell 100, a flocculation tank 200, a biogas slurry tank 300, an air pump 400, and an ammonia recovery tank 500. The electrolytic cell 100 includes a cathode chamber 101 and an anode chamber 102. The cathode chamber 101 and the anode chamber 102 are separated by a cation exchange membrane 103. A cathode 105 and an anode 104 are respectively arranged in the cathode chamber 101 and the anode chamber 102, and are respectively connected to the negative electrode and the positive electrode of a DC power supply 106 by wires. A first peristaltic pump 600 is arranged on the connecting pipeline between the biogas slurry tank 300 and the flocculation tank 200. A stirrer 700 is arranged in the flocculation tank 200, and the stirring paddle of the stirrer 700 is located at the center of the biogas slurry in the flocculation tank 200. A second peristaltic pump 800 is arranged on the connecting pipeline between the flocculation tank 200 and the cathode chamber 101. The bottom of the cathode chamber 101 has an air inlet, and the air blown by the air pump 400 enters the cathode chamber 101 through the air inlet. The top of the cathode chamber 101 has an air outlet, and the air outlet is communicated with the ammonia recovery tank 500 through an air pipe;

[0076] The anode 104 of the electrolytic cell 100 is a ruthenium-iridium-titanium plate, and the cathode 105 of the electrolytic cell 100 is a titanium plate;

[0077] The cation exchange membrane 103 is an FKS-PET-130 membrane.

[0078] Among them, the specific parameters of the FKS-PET-130 membrane are shown in Table 1.

[0079] Table 1

[0080]

[0081] Examples 1-1 to 1-3 are used to illustrate the flocculation treatment process of biogas slurry.

[0082] Example 1-1

[0083] The biogas slurry with an ammonia nitrogen concentration of 1444 mg / L and a suspended solid concentration of 0.74 g / L in the biogas slurry tank 300 is transported to the flocculation tank 200 through the first peristaltic pump 600. The flocculant PAM is added to the flocculation tank 200, and the addition concentration of the flocculant PAM is 4 g / L. The stirring paddle of the stirrer 700 is adjusted to the center of the biogas slurry, the stirring rate of the stirrer 700 is set to 800 rpm, and the stirring time is 30 min. After flocculation, the suspended solid concentration in the biogas slurry is reduced from 0.74 g / L to 0.34 g / L, and the removal rate of suspended solids is 54.1%.

[0084] Example 1-2

[0085] The biogas slurry with an ammonia nitrogen concentration of 1444 mg / L and a suspended solid concentration of 0.74 g / L in the biogas slurry tank 300 is transported to the flocculation tank 200 through the first peristaltic pump 600. The flocculant PAM is added to the flocculation tank 200, and the addition concentration of the flocculant PAM is 4 g / L. The stirring paddle of the stirrer 700 is adjusted to the center of the biogas slurry, the stirring rate of the stirrer 700 is set to 1000 rpm, and the stirring time is 30 min. After flocculation, the suspended solid concentration in the biogas slurry is reduced from 0.74 g / L to 0.25 g / L, and the removal rate of suspended solids is 66.2%.

[0086] Example 1-3

[0087] The biogas slurry with an ammonia nitrogen concentration of 1444 mg / L and a suspended solid concentration of 0.74 g / L in the biogas slurry tank 300 is transported to the flocculation tank 200 through the first peristaltic pump 600. The flocculant PAM is added to the flocculation tank 200, and the addition concentration of the flocculant PAM is 4 g / L. The stirring paddle of the stirrer 700 is adjusted to the center of the biogas slurry, the stirring rate of the stirrer 700 is set to 1000 rpm, and the stirring time is 20 min. After flocculation, the suspended solid concentration in the biogas slurry is reduced from 0.74 g / L to 0.23 g / L, and the removal rate of suspended solids is 68.9%.

[0088] Examples 2-1 to 2-5 are used to illustrate the removal process of ammonia nitrogen in biogas slurry.

[0089] Example 2-1

[0090] After the biogas slurry flocculated under the optimal conditions obtained in Example 1-3, the supernatant of the biogas slurry in Example 1-3 is transported from the flocculation tank 200 to the cathode chamber 101 through the second peristaltic pump 800. The electrolyte in the anode chamber 102 is a 0.3 M disodium hydrogen phosphate solution, and the constant current intensity provided by the DC power supply 106 is set to 30 mA / cm 2 , the electrolytic cell 100 undergoes an electrolytic water reaction, and the OH generated by the electrolytic water reaction -The pH value of the biogas slurry in the cathode chamber 101 is made to exceed 12. Meanwhile, the air pumped in by the air pump 400 enters the cathode chamber 101 through the air inlet for aeration stripping. The air flow rate of the air pump 400 is set to 0.5 L / min, and the NH4 in the cathode chamber 101 + reacts with the OH generated by electrolyzing water in the cathode chamber 101 - to be converted into NH3. NH3 is stripped out under the disturbance of aeration. Finally, the ammonia nitrogen concentration in the biogas slurry drops from the initial 1444 mg / L to 397 mg / L, and the removal rate reaches 72.5%; the absorbent liquid in the ammonia recovery tank 500 uses concentrated sulfuric acid with a volume concentration of 30% to absorb ammonia gas, and 1040 mg of nitrogen source can be recovered (NH4 in the biogas slurry in the biogas slurry tank + ), and the nitrogen source recovery rate reaches 99.3%.

[0091] In the present invention, the removal rate of ammonia nitrogen = (the concentration of ammonia nitrogen in the biogas slurry in the biogas slurry tank - the concentration of ammonia nitrogen in the biogas slurry in the cathode after electrolysis) / the concentration of ammonia nitrogen in the biogas slurry in the biogas slurry tank × 100%; in this embodiment, the removal rate of ammonia nitrogen = (1444 - 397) / 1444 × 100%.

[0092] In the present invention, the recovery rate of nitrogen source = the recovered nitrogen source / (the concentration of ammonia nitrogen in the biogas slurry in the biogas slurry tank - the concentration of ammonia nitrogen in the biogas slurry in the cathode after electrolysis) × 100%; in this embodiment, the recovery rate of nitrogen source = 1040 / (1444 - 397) × 100%.

[0093] Example 2 - 2

[0094] The biogas slurry flocculated under the optimal conditions obtained in Examples 1 - 3 is taken. The supernatant of the biogas slurry in Examples 1 - 3 is transported from the flocculation tank 200 to the cathode chamber 101 by the second peristaltic pump 800. The electrolyte in the anode chamber 102 is a 0.3 M disodium hydrogen phosphate solution. The constant current intensity provided by the DC power supply 106 is set to 40 mA / cm 2 , and the electrolytic cell 100 undergoes an electrolytic water reaction. The OH generated by the electrolytic water reaction - makes the pH value of the biogas slurry in the cathode chamber 101 exceed 12. Meanwhile, the air pumped in by the air pump 400 enters the cathode chamber 101 through the air inlet for aeration stripping. The air flow rate of the air pump 400 is set to 0.5 L / min, and the NH4 in the cathode chamber 101 + reacts with the OH generated by electrolyzing water in the cathode chamber 101 - to be converted into NH3. NH3 is stripped out under the disturbance of aeration. Finally, the ammonia nitrogen concentration in the biogas slurry drops from the initial 1444 mg / L to 173 mg / L, and the removal rate reaches 88%; the absorbent liquid in the ammonia recovery tank 500 uses concentrated sulfuric acid with a volume concentration of 30% to absorb ammonia gas, and 1260 mg of nitrogen source can be recovered, and the nitrogen source recovery rate reaches 99.1%.

[0095] Example 2-3

[0096] The biogas slurry flocculated under the optimal conditions obtained in Examples 1-3 was taken. The supernatant of the biogas slurry in Examples 1-3 was transported from the flocculation tank 200 to the cathode chamber 101 by the second peristaltic pump 800. The electrolyte in the anode chamber 102 was a 0.3 M disodium hydrogen phosphate solution. The constant current intensity provided by the DC power supply 106 was set to 35 mA / cm 2 , and the electrolytic cell 100 underwent an electrolytic water reaction. The OH generated by the electrolytic water reaction - caused the pH value of the biogas slurry in the cathode chamber 101 to exceed 12. At the same time, the air pumped in by the air pump 400 entered the cathode chamber 101 through the air inlet for aeration stripping. The air flow rate of the air pump 400 was set to 0.5 L / min. The NH4 in the cathode chamber 101 + reacted with the OH generated by the electrolytic water in the cathode chamber 101 - to be converted into NH3. NH3 was stripped out under the disturbance of aeration. Finally, the ammonia nitrogen concentration in the biogas slurry decreased from the initial 1444 mg / L to 210 mg / L, and the removal rate reached 85.5%; the absorbent in the ammonia recovery tank 500 was concentrated sulfuric acid with a volume concentration of 30%. Ammonia was absorbed, and 1225 mg of nitrogen source could be recovered, and the nitrogen source recovery rate reached 99.3%.

[0097] Example 2-4

[0098] The biogas slurry flocculated under the optimal conditions obtained in Examples 1-3 was taken. The supernatant of the biogas slurry in Examples 1-3 was transported from the flocculation tank 200 to the cathode chamber 101 by the second peristaltic pump 800. The electrolyte in the anode chamber 102 was a 0.3 M disodium hydrogen phosphate solution. The constant current intensity provided by the DC power supply 106 was set to 35 mA / cm 2 , and the electrolytic cell 100 underwent an electrolytic water reaction. The OH generated by the electrolytic water reaction - caused the pH value of the biogas slurry in the cathode chamber 101 to exceed 12. At the same time, the air pumped in by the air pump 400 entered the cathode chamber 101 through the air inlet for aeration stripping. The air flow rate of the air pump 400 was set to 0.7 L / min. The NH4 in the cathode chamber 101 + reacted with the OH generated by the electrolytic water in the cathode chamber 101 - to be converted into NH3. NH3 was stripped out under the disturbance of aeration. Finally, the ammonia nitrogen concentration in the biogas slurry decreased from the initial 1444 mg / L to 308 mg / L, and the removal rate reached 79%; the absorbent in the ammonia recovery tank 500 was concentrated sulfuric acid with a volume concentration of 30%. Ammonia was absorbed, and 1128 mg of nitrogen source could be recovered, and the nitrogen source recovery rate reached 99.3%.

[0099] Example 2-5

[0100] After the biogas slurry is flocculated under the optimal conditions obtained in Examples 1-3, the supernatant of the biogas slurry in Examples 1-3 is transported from the flocculation tank 200 to the cathode chamber 101 by the second peristaltic pump 800. The electrolyte in the anode chamber 102 is a 0.3M disodium hydrogen phosphate solution, and the constant current intensity provided by the DC power supply 106 is set to 35 mA / cm 2 , the electrolytic cell 100 undergoes an electrolytic water reaction, and the OH generated by the electrolytic water reaction - makes the pH value of the biogas slurry in the cathode chamber 101 exceed 12. At the same time, the air blown in by the air pump 400 enters the cathode chamber 101 through the air inlet for aeration stripping. The air flow rate of the air pump 400 is set to 1.1 L / min, and the NH4 in the cathode chamber 101 + reacts with the OH generated by the electrolytic water in the cathode chamber 101 - to be converted into NH3. NH3 is stripped out under the disturbance of aeration. Finally, the ammonia nitrogen concentration in the biogas slurry drops from the initial 1444 mg / L to 103 mg / L, and the removal rate is as high as 93%; the absorbent in the ammonia recovery tank 500 uses concentrated sulfuric acid with a volume concentration of 30% to absorb ammonia gas, and 1330 mg of nitrogen source can be recovered, and the nitrogen source recovery rate reaches 99.2%.

[0101] Comparative Example 1

[0102] Implemented according to the methods of Examples 2-3, except that the supernatant of the biogas slurry in Examples 1-3 is transported from the flocculation tank 200 to the anode chamber 102 by the second peristaltic pump 800, and the electrolyte in the cathode chamber 101 is a 0.3M disodium hydrogen phosphate solution. Finally, the ammonia nitrogen concentration in the biogas slurry drops from the initial 1444 mg / L to 622 mg / L, and the removal rate drops to 56.9%; the absorbent in the ammonia recovery tank 500 uses concentrated sulfuric acid with a volume concentration of 30% to absorb ammonia gas, and 815 mg of nitrogen source can be recovered, and the nitrogen source recovery rate reaches 99.1%.

[0103] It can be seen from the examples and comparative examples that when the biogas slurry is treated by the method of the present invention, the treatment rate of ammonia nitrogen > 70%, and the nitrogen source recovery rate > 99%.

[0104] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for treating biogas slurry by electrochemical membrane ammonia stripping, characterized in that: The method comprises the following steps: (1) adding a flocculant to the biogas slurry for flocculation treatment; (2) the supernatant of the biogas slurry after flocculation treatment is input into the cathode chamber (101) of the electrolytic cell (100), wherein the cathode chamber (101) and the anode chamber (102) of the electrolytic cell (100) are separated by a cation exchange membrane (103), and the electrolytic cell (100) performs a water electrolysis reaction, and OH in the supernatant of the biogas slurry is converted into water under the action of the cation exchange membrane (103). - The ammonia is accumulated in the cathode chamber (101) to create an alkaline environment required for the production of ammonia. During the water electrolysis reaction, the supernatant of the biogas slurry in the cathode chamber (101) is aerated and stripped to obtain ammonia.

2. The method according to claim 1, characterized in that In step (1), the content of ammonia nitrogen in the biogas slurry is 1400-1500 mg / L, and the content of suspended solids is 0.5-1 g / L.

3. The method according to claim 1 or 2, characterized in that: In step (1), the flocculant is polyacrylamide; In step (1), the amount of the flocculant is 3-5 g relative to 1 L of biogas slurry; In step (1), the flocculation treatment time is 10-30 min; In step (1), the flocculation treatment is carried out under stirring conditions, and the stirring rate is 800-1200 rpm.

4. The method according to claim 1, characterized in that: In step (2), the cation exchange membrane (103) is a FKS-PET-130 membrane; In step (2), the electrolyte in the anode chamber (102) is a 0.2-0.4 M disodium hydrogen phosphate solution.

5. The method according to claim 1, characterized in that In step (2), the constant current intensity of the water electrolysis reaction is 30-40 mA / cm 2 ; In step (2), the process of aerating and stripping the supernatant of the biogas slurry in the cathode chamber (101) comprises: introducing air into the bottom of the cathode chamber (101) at a flow rate of 0.5-1.1 L / min; In step (2), the anode (104) of the electrolytic cell (100) is a ruthenium-iridium-titanium plate, and the cathode (105) of the electrolytic cell (100) is a titanium plate.

6. The method according to claim 1, characterized in that The process of the electrolytic cell (100) performing a water electrolysis reaction comprises: when a current is applied to the electrolytic cell (100), the electrolytic cell (100) performs a water electrolysis reaction, wherein the reaction occurring in the anode chamber (102) is: 2H2O→O2↑+4H + +4e - The reaction in the cathode chamber (101) is: 2H2O+2e - →H2↑+2OH - The cation exchange membrane (103) allows cations to transfer between the anode chamber (102) and the cathode chamber (101), while preventing OH generated in the cathode chamber (101). - The cation exchange membrane (103) enters the anode chamber (102), and the OH in the supernatant of the biogas slurry is - The alkaline environment required for the production of ammonia is created by the accumulation of OH in the cathode chamber (101), so that the OH produced in the cathode chamber (101) - It reacts with ammonia nitrogen in the supernatant of biogas slurry to produce ammonia gas.

7. The method according to claim 1, characterized in that The method further comprises: absorbing ammonia gas blown off from the supernatant of the biogas slurry in the cathode chamber (101) with an acidic solution; The acidic solution is a 20-40 volume % concentrated sulfuric acid solution.

8. A system for treating biogas slurry by electrochemical membrane ammonia stripping, characterized in that: The system includes: A flocculation tank (200), wherein the biogas slurry from the biogas slurry tank (300) enters the flocculation tank (200) for flocculation treatment; An electrolytic cell (100), wherein the cathode chamber (101) and the anode chamber (102) of the electrolytic cell (100) are separated by a cation exchange membrane (103), the supernatant liquid of the biogas slurry from the flocculation tank (200) enters the cathode chamber (101), the electrolytic cell (100) undergoes a water electrolysis reaction, and under the action of the cation exchange membrane (103), OH in the supernatant liquid of the biogas slurry is - Gathering in the cathode chamber (101) to create an alkaline environment required for the production of ammonia; The air pump (400) is used to aerate and blow off the supernatant of the biogas slurry in the cathode chamber (101) during the water electrolysis reaction to obtain ammonia gas.

9. The system according to claim 8, characterized in that In the electrolytic cell (100), the water electrolysis reaction is carried out under the condition of applying current, wherein water is electrolyzed in the anode chamber (102) to generate H + , water is electrolyzed in the cathode chamber (101) to produce OH - The cation exchange membrane (103) allows cations to transfer between the anode chamber (102) and the cathode chamber (101), while the OH generated in the cathode chamber (101) - The cation exchange membrane (103) cannot pass through the cation exchange membrane (103) and thus gathers in the cathode chamber (101) to create an alkaline environment required for the production of ammonia, so that the OH produced in the cathode chamber (101) - It reacts with ammonia nitrogen in the supernatant of biogas slurry to produce ammonia gas.

10. The system according to claim 8 or 9, characterized in that The electrolytic cell (100) further comprises a cathode (105), an anode (104) and a DC power supply (106), wherein the cathode (105) is arranged in the cathode chamber (101), the anode (104) is arranged in the anode chamber (102), the anode (104) is connected to the positive electrode of the DC power supply (106) by a wire, and the cathode (105) is connected to the negative electrode of the DC power supply (106) by a wire; A first peristaltic pump (600) is arranged on the connecting pipe between the biogas slurry tank (300) and the flocculation tank (200), a stirrer (700) is arranged in the flocculation tank (200), a stirring paddle of the stirrer (700) is located at the center of the biogas slurry in the flocculation tank (200), a second peristaltic pump (800) is arranged on the connecting pipe between the flocculation tank (200) and the cathode chamber (101), the bottom of the cathode chamber (101) has an air inlet, air blown in by the air pump (400) enters the cathode chamber (101) through the air inlet, and the top of the cathode chamber (101) has an air outlet, and the air outlet is connected to the ammonia recovery tank (500) through an air pipe.

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