Nitrate nitrogen aqueous solution concentration system and method

Abstract

This invention provides a nitrate nitrogen aqueous solution concentration system and method, which uses a reverse osmosis process to concentrate nitrate nitrogen, solving the problems of low efficiency and space and energy consumption limitations in traditional low-concentration wastewater treatment. The system includes an oxidation reaction and solid-liquid separation section, an organic and solid impurity filtration section, and a multi-stage reverse osmosis concentration section. Through oxidation reaction steps, solid-liquid separation steps, solid impurity filtration steps, organic pollutant filtration steps, and reverse osmosis concentration steps, the system concentrates low-concentration nitrate nitrogen-containing wastewater into a high-concentration nitrate nitrogen aqueous solution. It also allows for concentrate reflux and pH adjustment to improve treatment efficiency and membrane lifespan. The system offers advantages of high efficiency, energy saving, and modularity, making it suitable for various industrial wastewater treatment needs.

Description

Technical Field

[0001] This invention relates to a treatment system and method for aqueous solutions containing nitrate nitrogen (NO3--N), and particularly to a treatment system and method for concentrating low-concentration nitrate nitrogen aqueous solutions by forming a series and parallel process using multiple reverse osmosis devices. Prior Technology

[0002] Nitrate nitrogen is widely present in wastewater generated from various industrial processes, with common sources including semiconductor manufacturing, metal surface treatment, explosives manufacturing, fertilizer production, electroplating, and nitrogen-containing chemical processes. If nitrate nitrogen pollutants in these wastewaters are discharged without proper treatment, they will cause eutrophication of water bodies, thereby affecting water quality and ecological balance.

[0003] According to regulations from Taiwan's Environmental Protection Administration, the nitrate nitrogen content (nitrogen content in nitrates) in wastewater must be below 50 ppm, prompting various industrial units to seek effective nitrate nitrogen removal technologies. While traditional technologies for treating nitrate nitrogen wastewater have some effectiveness, they still face several limitations and problems in practical application. For example, the common biological denitrification method requires the construction of numerous aeration tanks and the maintenance of a microbial culture environment, occupying a large processing space and demanding high operational and maintenance requirements, making it inflexible for factories with limited space. Chemical treatment methods such as metal displacement or electrolysis are also problematic. While metal displacement reacts rapidly, it often faces issues of byproduct control and reagent costs. Electrolysis requires a longer processing time and is not conducive to the degradation of low-concentration nitrate nitrogen. Furthermore, some systems use mechanical evaporation (such as mechanical vapor recompression, MVR) for concentration. Although this achieves the concentration goal, the system needs to operate under vacuum, resulting in high energy consumption, large equipment investment costs, and operational complexity and instability.

[0004] More importantly, traditional technologies such as MVR are generally designed for treating wastewater containing high concentrations (greater than 6000 ppm) of nitrate nitrogen. When faced with wastewater containing low concentrations (less than or equal to 6000 ppm) of nitrate nitrogen, not only is the concentration efficiency poor, but it also cannot effectively balance resource recovery and treatment timeliness, resulting in a trade-off between overall operating costs and environmental benefits. In addition, MVR also faces the problem of not being able to solve the problems of Chemical Oxygen Demand (COD) and Suspended Solids (SS). MVR cannot reduce COD to below 50 ppm or SS to below 1 ppm. Thus, the concentrated wastewater containing nitrate nitrogen actually contains higher concentrations of COD and SS than the original wastewater, which only increases the trouble and cost of subsequent use.

[0005] Therefore, developing a technology that can concentrate low-concentration nitrate nitrogen solutions while taking into account energy saving, processing efficiency and space flexibility, and avoiding the concentration of COD and SS, has become an urgent issue for the industry. Summary of the Invention

[0006] In view of the aforementioned technical problems, the inventors of this invention have conceived and designed a reverse osmosis concentration system and method for nitrate nitrogen. This system utilizes multiple reverse osmosis (RO) devices arranged in series and parallel to form a primary and secondary cycle for the concentration and purification of nitrate nitrogen aqueous solution, thereby improving the efficiency of subsequent resource recovery and wastewater reduction. This overcomes the problems of space limitations, high energy consumption, and low efficiency faced by existing technologies in treating low-concentration (less than or equal to 6000 ppm) nitrate nitrogen wastewater.

[0007] To achieve the above objectives, the present invention provides a nitrate nitrogen aqueous solution concentration system, comprising: An organic pollutant degradation section includes a reaction tank connected to a solid-liquid separation device. The reaction tank is fed with nitrate nitrogen-containing wastewater, ferrous salt, and hydrogen peroxide for reaction to form a mixed liquid which is then output to the solid-liquid separation device, whereby a first nitrate nitrogen aqueous solution and a ferric hydroxide are separated. A filtration section includes a solid impurity filtration device connected to an organic pollutant filtration device, the solid impurity filtration device being connected to a solid-liquid separation device; a first nitrate nitrogen aqueous solution is input into the solid impurity filtration device to remove the contained solid impurities, forming a second nitrate nitrogen aqueous solution which is output to the organic pollutant filtration device for organic pollutant filtration, and the organic pollutant filtration device outputs a third nitrate nitrogen aqueous solution; A reverse osmosis concentration section includes a first reverse osmosis water purifier and a second reverse osmosis water purifier. One of the concentrated water outlets of the first reverse osmosis water purifier is connected to one of the inlets of the second reverse osmosis water purifier. The first reverse osmosis water purifier is connected to the organic pollutant filtration device, so that the third nitrate nitrogen aqueous solution output from the filtration section flows sequentially through the first reverse osmosis water purifier and the second reverse osmosis water purifier. One of the concentrated water outlets of the second reverse osmosis water purifier outputs a high-concentration nitrate nitrogen aqueous solution to increase the nitrate nitrogen concentration in the nitrate nitrogen-containing waste liquid.

[0008] According to an embodiment of the present invention, the nitrate nitrogen aqueous solution concentration system further includes a third reverse osmosis water purifier and a fourth reverse osmosis water purifier; wherein, one inlet of the first reverse osmosis water purifier is used to input the third nitrate nitrogen aqueous solution, and one freshwater outlet of the first reverse osmosis water purifier is connected to one inlet of the third reverse osmosis water purifier; one concentrated water outlet of the third reverse osmosis water purifier and one freshwater outlet of the second reverse osmosis water purifier are connected and converged to one inlet of the fourth reverse osmosis water purifier; one freshwater outlet of the third reverse osmosis water purifier and one freshwater outlet of the fourth reverse osmosis water purifier are connected and converged to output a low-concentration nitrate nitrogen aqueous solution; one concentrated water outlet of the fourth reverse osmosis water purifier is recirculated and connected to the inlet of the first reverse osmosis water purifier to form a circulating concentration loop.

[0009] According to an embodiment of the present invention, the organic pollutant filtration device is provided with a return pipeline; thereby, when the concentration of organic pollutants in the third nitrate nitrogen aqueous solution is greater than or equal to a concentration threshold, the third nitrate nitrogen aqueous solution is returned through the return pipeline and merged with the second nitrate nitrogen aqueous solution, and then input into the organic pollutant filtration device for further filtration; until the concentration of organic pollutants in the third nitrate nitrogen aqueous solution is less than the concentration threshold, the third nitrate nitrogen aqueous solution is output to the first reverse osmosis water purifier for concentration. Specifically, the concentration threshold is 50ppm ± 10ppm, but is not limited to this.

[0010] According to an embodiment of the present invention, the organic pollutant degradation section further includes an aeration device that supplies gas to the bottom of the reaction tank for aeration of the mixture. The air flow rate supplied by the aeration device to the reaction tank is 40 to 80 liters per minute, and the bubble size is approximately 3 to 7 mm. Specifically, the air flow rate supplied by the aeration device to the bottom of the reaction tank is 40, 50, 60, 70, or 80 liters per minute, but is not limited to these values; each of these specific values ​​can be considered as the endpoint of another range. Specifically, the bubble size supplied by the aeration device to the reaction tank is approximately 3 mm, 4 mm, 5 mm, 6 mm, or 7 mm, but is not limited to these values; each of these specific values ​​can be considered as the endpoint of another range.

[0011] This invention also provides a method for concentrating nitrate nitrogen in an aqueous solution, the method comprising the following steps: Oxidation reaction steps: Nitrate-containing nitrogen waste liquid, ferrous salt (Fe2+), and hydrogen peroxide (H2O2) are introduced into a reaction tank for oxidation reaction to generate a mixed liquid; Solid-liquid separation step: The mixture is fed into a solid-liquid separation device for separation to obtain a first nitrate nitrogen aqueous solution and an iron hydroxide solution; Solid impurity filtration step: The first nitrate nitrogen aqueous solution is fed into a solid impurity filtration device to filter out solid impurities and form a second nitrate nitrogen aqueous solution; Organic pollutant filtration step: The second nitrate nitrogen aqueous solution is fed into an organic pollutant filtration device to filter out organic pollutants and form a third nitrate nitrogen aqueous solution; Reverse osmosis concentration step: The third nitrate nitrogen aqueous solution is sequentially introduced into a first reverse osmosis water purifier and a second reverse osmosis water purifier to concentrate the nitrate nitrogen concentration of the nitrate nitrogen-containing waste liquid and output a high-concentration nitrate nitrogen aqueous solution.

[0012] According to an embodiment of the present invention, the method for concentrating nitrate nitrogen aqueous solution further includes an advanced reverse osmosis circulation step; the advanced reverse osmosis circulation step involves introducing one of the freshwater outputs from the first reverse osmosis water purifier into a third reverse osmosis water purifier, and then converging the concentrated water from the third reverse osmosis water purifier with one of the freshwater outputs from the second reverse osmosis water purifier and sending it to a fourth reverse osmosis water purifier, whereby the concentrated water from the fourth reverse osmosis water purifier flows back to the first reverse osmosis water purifier, forming a circulating concentration loop; the freshwater from the third reverse osmosis water purifier and the freshwater from the fourth reverse osmosis water purifier converge to form a low-concentration nitrate nitrogen aqueous solution output.

[0013] According to embodiments of the present invention, the aforementioned ferrous salt can be specifically selected from ferrous sulfate, ferrous salt complex salt, or ferrous chloride. Preferably, the ferrous salt is ferrous sulfate (FeSO4). In embodiments of the present invention, based on 100 wt% of the total weight of organic pollutants, the amount of the aforementioned ferrous sulfate added is 0.1 wt% to 1.2 wt%. Specifically, based on 100 wt% of the total weight of organic pollutants, the amount of the aforementioned ferrous sulfate added is 0.1 wt%, 0.14 wt%, 0.28 wt%, 0.3 wt%, 0.5 wt%, 0.56 wt%, 0.7 wt%, 0.9 wt%, 1.1 wt%, 1.12 wt%, or 1.2 wt%.

[0014] In this embodiment of the invention, based on a total weight of 100 wt% of ferrous salts, the amount of hydrogen peroxide (H2O2) added is 0.1 wt% to 0.5 wt%. Specifically, based on a total weight of 100 wt% of ferrous salts, the amount of hydrogen peroxide added is 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, or 0.5 wt%.

[0015] According to an embodiment of the present invention, an alkali adjustment step is included before the solid-liquid separation step. This alkali adjustment step involves adding an alkali agent to the mixed liquid output from the reaction tank to adjust the pH value to a range of 6 to 8 before inputting it into the solid-liquid separation device. Preferably, adjusting the pH to 7 stabilizes the chemical environment, preventing iron precipitation from clogging the filter membrane, improving plate pressure filtration efficiency and device lifespan, and achieving the purpose of facilitating the precipitation of ferric hydroxide and improving separation efficiency. The alkali agent is sodium hydroxide. Specifically, the pH value of the mixed liquid is adjusted to 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, or 8.0, but is not limited to these values; each of these specific values ​​can be used as an endpoint of another range.

[0016] According to an embodiment of the present invention, an acidification step is included before the organic pollutant filtration step. This acidification step involves adding an acid to the second nitrate nitrogen aqueous solution output from the solid impurity filtration device to adjust the pH value to a range of 3 to 4 before it is input into the organic pollutant filtration device. This pre-filtration acidification treatment effectively improves the removal efficiency of organic pollutants, thereby increasing the nitrate nitrogen rejection rate, inhibiting scaling, extending membrane life, and maintaining system operational stability during subsequent reverse osmosis filtration. The acid is selected from sulfuric acid, nitric acid, or hydrochloric acid. Specifically, the pH value of the second nitrate nitrogen aqueous solution is adjusted to 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, or 4.0, but is not limited to these values; each of these specific values ​​can be considered an endpoint of another range.

[0017] According to an embodiment of the present invention, when the concentration of organic pollutants in the third nitrate nitrogen aqueous solution is greater than or equal to a concentration threshold, the third nitrate nitrogen aqueous solution is refluxed and mixed into the second nitrate nitrogen aqueous solution, and then filtered until the concentration of organic pollutants is less than the concentration threshold. Specifically, the concentration threshold is 50 ppm ± 10 ppm, but is not limited thereto; preferably, the concentration threshold is 50 ppm.

[0018] According to an embodiment of the present invention, in the oxidation reaction step, gas aeration is performed at the bottom of the reaction tank to promote the oxidation reaction and increase the decomposition rate of pollutants in the mixture.

[0019] According to an embodiment of the present invention, the initial organic pollutant concentration of the nitrate nitrogen-containing waste liquid is 100 ppm to 500 ppm, and the initial nitrate nitrogen concentration is 1000 ppm to 6000 ppm.

[0020] Specifically, the initial organic pollutant concentration of the nitrate-containing nitrogen waste liquid is 100ppm, 150ppm, 200ppm, 250ppm, 300ppm, 350ppm, 400ppm, 450ppm or 500ppm, but is not limited to these; each of the above specific values ​​can be used as the endpoint of another range.

[0021] Specifically, the initial nitrate nitrogen concentration of the nitrate-containing waste liquid is 1000ppm, 1500ppm, 2000ppm, 2500ppm, 3000ppm, 3500ppm, 4000ppm, 4500ppm, 5000ppm, 5500ppm, or 6000ppm, but is not limited to these; each of the above specific values ​​can be used as the endpoint of another range.

[0022] According to an embodiment of the present invention, when the initial nitrate nitrogen concentration of the nitrate nitrogen-containing waste liquid is 4000 ppm, the concentration of organic pollutants in the first nitrate nitrogen aqueous solution output by the solid-liquid separation device is less than 100 ppm; after the first nitrate nitrogen aqueous solution is filtered by the solid impurity filtration device to remove solid impurities to a concentration of less than 1 ppm, the second nitrate nitrogen aqueous solution is formed and then filtered by the organic pollutant filtration device to remove organic pollutants to a concentration of less than 50 ppm, thereby forming the third nitrate nitrogen aqueous solution.

[0023] According to an embodiment of the present invention, the organic pollutant filtration device is a nanofiltration device with a nanofiltration membrane, and the material of the nanofiltration membrane is selected from polyamide (PA) or polyether amide (PEI) composite material. Preferably, the material of the nanofiltration membrane is PA.

[0024] According to an embodiment of the present invention, the solid impurity filtration device is an ultrafiltration device, which has an ultrafiltration membrane made of cellulose acetate.

[0025] According to an embodiment of the present invention, the reverse osmosis membrane of the aforementioned reverse osmosis water purifier (the first reverse osmosis water purifier, the second reverse osmosis water purifier, the third reverse osmosis water purifier, or the fourth reverse osmosis water purifier) ​​is made of polyamide (PA) or polyether amide (PEI) composite material. Preferably, the reverse osmosis membrane is made of PA.

[0026] According to an embodiment of the present invention, in the method for concentrating nitrate nitrogen aqueous solution, the concentration of organic pollutants in the liquid in the pipeline is determined by means of an online organic pollutant sensing device or manual detection.

[0027] According to an embodiment of the present invention, in the method for concentrating nitrate nitrogen aqueous solution, the concentration of solid impurities in the liquid in the pipeline is determined by means of an online solid impurity (i.e., suspended solid) sensing device or by manual detection.

[0028] According to an embodiment of the present invention, in the alkali adjustment step or the acid adjustment step, the pH value of the liquid in the pipeline is determined by an online pH sensing device or by manual detection.

[0029] The nitrate nitrogen aqueous solution concentration system and method proposed in this invention effectively overcomes the problems of traditional treatment technologies, such as large space requirements, high energy consumption, complex operation, and poor treatment efficiency for low-concentration wastewater, by combining oxidation reaction, solid-liquid separation, filtration of solid impurities and organic pollutants, and a multi-stage reverse osmosis concentration process. Compared with biological methods that require a large number of aeration tanks or energy-intensive evaporation concentration methods (such as MVR), this invention can operate at atmospheric pressure and be combined with a modular reverse osmosis water purifier, reducing the system's energy burden and operating costs. In particular, for low-concentration nitrate nitrogen aqueous solutions with an initial concentration of 1000ppm to 6000ppm, the reverse osmosis series and circulation concentration mechanism can effectively concentrate the solution to a high-concentration liquid product, improving recovery efficiency. At the same time, the system also integrates pH control and reflux concentration control design, which can extend the membrane element life and maintain overall operational stability while stabilizing the chemical environment and preventing membrane fouling, demonstrating excellent treatment performance and industrial application potential.

[0030] In summary, the nitrate nitrogen aqueous solution concentration system and method of the present invention take into account treatment efficiency, energy efficiency, equipment life and resource recovery. It is particularly suitable for the treatment of high volume, low concentration polluted wastewater and can be widely used in various industrial fields such as semiconductor manufacturing, fertilizer synthesis, metal processing and electroplating. It has high practicality and industrial application value. Simple Explanation of the Diagram

[0031] Figure 1 is a schematic diagram of the implementation architecture of the nitrate nitrogen aqueous solution concentration system of the present invention. Figure 2 is a schematic diagram of the implementation scheme of the method for concentrating nitrate nitrogen aqueous solution of the present invention. Implementation

[0032] To facilitate understanding of the technical features, content, advantages, and effects of this invention, the invention is described in detail below with reference to the accompanying drawings. The drawings used are for illustrative purposes and to assist in the description only, and may not represent the actual proportions and precise configurations of the invention after implementation. Therefore, the proportions and configurations of the accompanying drawings should not be used to interpret or limit the scope of the invention in actual implementation. This should be stated in advance.

[0033] As shown in Figures 1 and 2, the present invention provides a system and method for concentrating nitrate nitrogen aqueous solution.

[0034] Nitrate Nitrogen Aqueous Solution Concentration System

[0035] As shown in Figure 1, the nitrate nitrogen aqueous solution concentration system of the present invention includes an organic pollutant degradation section A, a filtration section B, and a reverse osmosis concentration section C. The organic pollutant degradation section A has a reaction tank 10 connected to a solid-liquid separation device 20. The reaction tank 10 has a waste liquid input device, a ferrous salt input device, and a hydrogen peroxide input device for respectively inputting nitrate nitrogen-containing waste liquid A1, ferrous salt A2, and hydrogen peroxide A3 to react and form a mixed liquid A4. The mixed liquid A4 is then fed into an alkali input device with an alkali agent A7 to adjust the pH to 7 before being fed into the solid-liquid separation device 20, thereby separating out a first nitrate nitrogen aqueous solution A51 which flows out from an outlet of the solid-liquid separation device 20, and a solid ferric hydroxide A6 which can be separated and cleaned.

[0036] The organic pollutant degradation section A may also be equipped with an aeration device 11, which includes an air source 111 connected to the bottom of the reaction tank 10 through an air supply pipe 112 to aerate the mixture A4; the air source 111 may also be monitored by a flow meter 113 to measure the flow rate; in this embodiment of the invention, the air flow rate delivered by the aeration device 11 to the reaction tank 10 is about 60 liters per minute, and the bubble size is about 5 mm.

[0037] The filtration section B includes a solid impurity filtration device 30 connected to an organic pollutant filtration device 40. The solid impurity filtration device 30 is connected to the outlet of the solid-liquid separation device 20. The first nitrate nitrogen aqueous solution A51 is fed into the solid impurity filtration device 30 to filter out the solid impurities contained therein, so as to form a second nitrate nitrogen aqueous solution A52. The second nitrate nitrogen aqueous solution A52 is fed into the organic pollutant filtration device 40 after the pH value is adjusted to 4 by an acid B1, so as to filter the organic pollutants. Then, the organic pollutant filtration device 40 outputs a third nitrate nitrogen aqueous solution A53.

[0038] Further, as shown in Figure 1, the organic pollutant filtration device 40 may be provided with a return pipe 41; thereby, when the concentration of organic pollutants in the third nitrate nitrogen aqueous solution A53 is greater than or equal to a concentration threshold (e.g., 50 ppm), the third nitrate nitrogen aqueous solution A53 is returned through the return pipe 41 and merged with the second nitrate nitrogen aqueous solution A52, and then input into the organic pollutant filtration device 40 for further filtration; until the concentration of organic pollutants in the third nitrate nitrogen aqueous solution A53 is less than the concentration threshold, the third nitrate nitrogen aqueous solution A53 is output to the first reverse osmosis water purifier 51 for concentration. In one embodiment, after the second nitrate nitrogen aqueous solution A52 is input into the organic pollutant filtration device 40, the third nitrate nitrogen aqueous solution A53 and a return water are output, and the return water enters the return pipe 41 and merges with the second nitrate nitrogen aqueous solution A52.

[0039] In this embodiment of the invention, the solid impurity filtration device 30 is an ultrafiltration device, and its filter membrane material is cellulose acetate, purchased from SIZIKI, model UF2012, with a pore size of 0.01 micrometers to 0.1 micrometers; the organic pollutant filtration device 40 is a nanofiltration device, and its filter membrane material is polyamide (PA), purchased from SIZIKI, model NF3013, with a pore size of 0.001 micrometers to 0.01 micrometers.

[0040] The reverse osmosis concentration section C includes a first reverse osmosis water purifier 51, a second reverse osmosis water purifier 52, a third reverse osmosis water purifier 53, and a fourth reverse osmosis water purifier 54. Each reverse osmosis water purifier has an inlet, a concentrated water outlet for supplying a high-concentration solution (hereinafter referred to as concentrated water), and a fresh water outlet for supplying a low-concentration solution (hereinafter referred to as fresh water). In this embodiment of the invention, the filter membrane material of each reverse osmosis water purifier is polyamide-based, purchased from SIZIKI, model RO3013, and the pore size of the filter membrane is 0.0001 micrometers.

[0041] As shown in Figure 1, the concentrated water outlet 512 of the first reverse osmosis water purifier 51 is connected to the inlet 521 of the second reverse osmosis water purifier 52; the third nitrate nitrogen aqueous solution A53 output from the filter section B flows sequentially through the first reverse osmosis water purifier 51 and the second reverse osmosis water purifier 52, and the concentrated water outlet 522 of the second reverse osmosis water purifier 52 outputs a high-concentration nitrate nitrogen aqueous solution C1 to concentrate the nitrate nitrogen concentration in the nitrate nitrogen-containing waste liquid A1. Furthermore, the inlet 511 of the first reverse osmosis water purifier 51 is used to input the third nitrate nitrogen aqueous solution A53, and the freshwater outlet 513 of the first reverse osmosis water purifier 51 is connected to the inlet 531 of the third reverse osmosis water purifier 53; the concentrated water outlet 532 of the third reverse osmosis water purifier 53 and the freshwater outlet 523 of the second reverse osmosis water purifier 52 are connected to the inlet 541 of the fourth reverse osmosis water purifier 54; the freshwater outlet 533 of the third reverse osmosis water purifier 53 and the freshwater outlet 543 of the fourth reverse osmosis water purifier 54 are connected to output a low-concentration nitrate nitrogen aqueous solution C2; the concentrated water outlet 542 of the fourth reverse osmosis water purifier 54 is connected back to the inlet 511 of the first reverse osmosis water purifier 51 to form a circulating concentration loop. The first reverse osmosis water purifier 51 and the second reverse osmosis water purifier 52 are arranged in series, the third nitrate nitrogen solution A53 and the fourth reverse osmosis water purifier 54 are also arranged in series, and the two are arranged in parallel.

[0042] In an embodiment of the present invention, as shown in Figure 1, the interconnected or connected segments and devices are connected or connected by a system pipeline P, and the system pipeline P is equipped with a gate valve P1 and / or a booster pump P2 to effectively adjust the fluid delivery rate and pressure conditions between the segments and devices, thereby realizing the control of the fluid flow direction and flow rate of the overall system.

[0043] Method for Concentrating Nitrate Nitrogen Aqueous Solution

[0044] The present invention is based on the aforementioned system for the concentration of nitrate nitrogen aqueous solution, as shown in Figure 2. It combines a pretreatment step (including an oxidation reaction step S1, an alkali adjustment step S11, and a solid-liquid separation step S2) with a separation membrane treatment technology (including a solid impurity filtration step S3, an acid adjustment step S31, an organic pollutant filtration step S4, a reverse osmosis concentration step S5, and an advanced reverse osmosis circulation step S6) to effectively solve the treatment difficulties caused by the coexistence of organic pollutants (represented by chemical oxygen demand (COD)) and solid impurities (represented by suspended solids (SS)) in nitrate nitrogen wastewater A1.

[0045] In this embodiment of the invention, the water sample containing nitrate nitrogen undergoes chemical oxidation treatment in the pretreatment step. This is achieved through the co-reaction of ferrous sulfate (Fe2+) and hydrogen peroxide (H2O2) to generate highly oxidizing hydroxyl radicals (‧OH), which then decompose organic pollutants in the water sample. This reaction mechanism can be simplified as follows:

[0046] Fe2++H2O2→Fe3++OH-+‧OH Equation (1)

[0047] In this step, ferrous ions (Fe2+) react with hydrogen peroxide to generate ferric ions (Fe3+), hydroxide ions (OH-), and hydroxyl radicals (‧OH). Among these, the hydroxyl radicals are the main oxidizing agents in the reaction and can react with organic pollutants (RH) in the water sample to further produce oxidation products (ROH) and hydrogen ions (H+).

[0048] RH+‧OH→ROH+H+ Equation (2)

[0049] The above reaction has a highly efficient and non-selective oxidation capability, effectively breaking down functional groups such as CH bonds and C=C bonds in the organic molecule structure, converting them into smaller oxidation products, thereby reducing the overall chemical oxygen demand (COD). This technology can be applied to the pretreatment process before reverse osmosis, helping to improve the operational stability and service life of membrane modules.

[0050] As shown in Figures 1 and 2, and in conjunction with Tables 1 and 2 below, the method steps for concentrating nitrate nitrogen aqueous solution according to the present invention are as follows:

[0051] The oxidation reaction step S1 involves introducing nitrate-containing nitrogen wastewater A1, ferrous sulfate (i.e., ferrous salt A2), and hydrogen peroxide A3 into a reaction tank 10 for oxidation to generate a mixed liquid A4. Optionally, gas aeration is performed on the mixed liquid A4 at the bottom of the reaction tank 10 to promote the oxidation reaction and increase the decomposition rate of pollutants in the mixed liquid. In this embodiment of the invention, the nitrate-containing nitrogen wastewater A1 with a nitrate nitrogen (NO3--N) concentration of approximately 4000 ppm and a COD concentration of approximately less than or equal to 500 ppm and greater than or equal to 100 ppm is used as the starting water sample for concentration. The amount of ferrous sulfate added is 0.14 wt% to 1.12 wt% based on an organic pollutant COD of 100 wt%. The amount of hydrogen peroxide added is 0.2 wt% to 0.4 wt% based on a total weight of ferrous salts of 100 wt%.

[0052] The alkali adjustment step S11 involves adding an alkali agent A7 to the mixture A4 to adjust the pH value to approximately 7, which facilitates the precipitation of ferric hydroxide and improves the separation efficiency; the alkali agent A7 is sodium hydroxide.

[0053] The solid-liquid separation step S2 involves feeding the mixture A4 into a plate press (i.e., solid-liquid separation device 20) for separation to obtain a first nitrate nitrogen aqueous solution A51 and an iron hydroxide solution A6. The nitrate nitrogen (NO3--N) concentration of the mixture A4 is approximately 4000 ppm, and the COD concentration is approximately equal to or less than 500 ppm and greater than or equal to 100 ppm.

[0054] The solid impurity filtration step S3 involves feeding the first nitrate nitrogen aqueous solution A51 into an ultrafiltration device (i.e., solid impurity filtration device 30) to remove solid impurities and form a second nitrate nitrogen aqueous solution A52. The first nitrate nitrogen aqueous solution A51 has a nitrate nitrogen (NO3--N) concentration of approximately 4000 ppm, a COD concentration of approximately less than or equal to 100 ppm, and an SS concentration of approximately 2 ppm to 10 ppm.

[0055] The acidification step S31 involves adding an acidic agent B1 to the second nitrate nitrogen aqueous solution A52 to adjust the pH value to 4, thereby improving the removal efficiency of organic pollutants; the acidic agent B1 is sulfuric acid.

[0056] The organic pollutant filtration step S4 involves feeding the second nitrate nitrogen aqueous solution A52 into an organic pollutant filtration device 40 to remove organic pollutants and form a third nitrate nitrogen aqueous solution A53. The acidified second nitrate nitrogen aqueous solution A52 has a nitrate nitrogen (NO3--N) concentration of approximately 4000 ppm, a COD concentration of approximately less than or equal to 100 ppm, and an SS concentration of approximately less than 1 ppm.

[0057] The reverse osmosis concentration step S5 involves sequentially introducing the third nitrate nitrogen aqueous solution A53 into a first reverse osmosis water purifier 51 and a second reverse osmosis water purifier 52 to concentrate the nitrate nitrogen concentration of the nitrate nitrogen-containing waste liquid A1 and output a high-concentration nitrate nitrogen aqueous solution C1. The third nitrate nitrogen aqueous solution A53 has a nitrate nitrogen (NO3--N) concentration of approximately 4000 ppm, a COD concentration of approximately less than 50 ppm, and an SS concentration of approximately less than 1 ppm; the high-concentration nitrate nitrogen aqueous solution C1 has a nitrate nitrogen (NO3--N) concentration of approximately 10500 ppm, a COD concentration of approximately less than 50 ppm, and an SS concentration of approximately less than 1 ppm.

[0058] The advanced reverse osmosis cycle step S6 involves introducing one of the freshwater outputs from the first reverse osmosis water purifier 51 into a third reverse osmosis water purifier 53, and then combining the concentrated water from the third reverse osmosis water purifier 53 with the freshwater from the second reverse osmosis water purifier 52 before sending it to a fourth reverse osmosis water purifier 54. The concentrated water from the fourth reverse osmosis water purifier 54 then flows back to the first reverse osmosis water purifier 51, forming a circulating concentration loop. The freshwater from the third reverse osmosis water purifier 53 and the freshwater from the fourth reverse osmosis water purifier 54 combine to form a low-concentration nitrate nitrogen aqueous solution C2 output. The composition and concentration conditions of the solutions introduced into the second reverse osmosis water purifier 52, the third reverse osmosis water purifier 53, and the fourth reverse osmosis water purifier 54 are shown in Table 1 below.

[0059] Table 1: Composition and concentration conditions of the introductory solution in each processing device of the method of the present invention Nitrate nitrogen aqueous solution treatment stage Import solution Concentration conditions of the imported solution reaction tank (Reaction Tank 10) Nitrate-containing nitrogen waste liquid NO3--N approximately 4000ppm COD less than or equal to 500 ppm Plate press (Solid-liquid separation device 20) Mixture NO3--N approximately 4000ppm COD less than or equal to 500 ppm Ultrafiltration device (Solid impurity filtration device 30) First nitrate nitrogen aqueous solution NO3--N approximately 4000ppm COD less than or equal to 100 ppm SS approximately 2~10ppm Filter unit (Organic pollutant filtration device 40) Second nitrate nitrogen aqueous solution NO3--N approximately 4000ppm COD less than or equal to 100 ppm SS < 1ppm First Reverse Osmosis Water Purifier 51 (abbreviated as RO1) Third nitrate nitrogen aqueous solution NO3--N approximately 4000ppm COD <50ppm SS < 1ppm Second reverse osmosis water purifier 52 (abbreviated as RO2) Concentrate from RO1 NO3--N approximately 6500ppm COD <50ppm SS < 1ppm Third Reverse Osmosis Water Purifier 53 (abbreviated as RO3) Freshwater from RO1 NO3--N approximately 1500ppm COD <50ppm SS < 1ppm Fourth Reverse Osmosis Water Purifier 54 (abbreviated as RO4) Freshwater from RO2 and Concentrate from RO3 NO3--N approximately 2500ppm COD <50ppm SS < 1ppm Note: NO3--N refers to nitrate nitrogen concentration; COD refers to organic pollutant concentration; SS refers to solid impurity concentration.

[0060] In this embodiment of the invention, in order to reduce the content of organic pollutants (COD) and avoid RO membrane (reverse osmosis membrane) fouling and scaling, and to ensure the stability and efficiency of the subsequent reverse osmosis treatment, Table 2 below shows the effect analysis of the pretreatment (oxidation reaction step S1) before reverse osmosis concentration in this invention. Specifically, it uses nitrate-containing nitrogen wastewater as the treatment target, and performs oxidation treatment with hydrogen peroxide and ferrous sulfate, and observes the removal effect of COD (chemical oxygen demand) under different conditions.

[0061] As shown in Table 2 below, the experiment used industrial wastewater containing nitrate nitrogen (nitrate nitrogen concentration approximately 4000 ppm; COD concentration 500 ppm) as the starting water sample, and 250 mL was taken for treatment. The test conditions are as follows: The hydrogen peroxide concentration was set to 0.2 wt% or 0.4 wt%. The ferrous sulfate concentration was set at 0.14 wt%, 0.28 wt%, 0.56 wt%, or 1.12 wt%. Whether or not aeration is performed is a variable (air is introduced into the bottom of the reaction tank); The reaction time is fixed at 30 minutes.

[0062] Table 2: Operating conditions, residual COD concentration, COD removal amount, and removal efficiency of Examples E1 to E14 of the method of the present invention Example code name hydrogen peroxide concentration (wt%) Ferrous sulfate concentration (wt%) Aeration Remaining COD (ppm) COD Removal amount (mg) efficiency (%) E1 0.2 0.14 yes 245 63.75 51.0 E2 0.28 yes 75 106.25 85.2 E3 0.56 yes 119 95.25 76.2 E4 1.12 yes 112 97.00 77.6 E5 0.4 0.14 yes 213 71.75 57.4 E6 0.28 yes 228 68.00 54.4 E7 0.56 yes 130 92.50 74.0 E8 0.2 0.14 no 300 49.85 39.9 E9 0.28 no 130 92.43 73.9 E10 0.56 no 157 85.67 68.5 E11 1.12 no 156 85.92 68.7 E12 0.4 0.14 no 268 57.73 46.2 E13 0.28 no 275 55.97 44.8 E14 0.56 no 181 79.57 63.7 When calculating based on an initial water sample (containing nitrate nitrogen waste liquid) of 250 mL, the concentration of nitrate nitrogen aqueous solution is 4000 ppm; the COD concentration is 500 ppm (i.e., the COD content in the 250 mL initial water sample is 125 mg).

[0063] The experimental results are shown in Table 2 above. The COD removal efficiency of Examples 1 to 14 (E1 to E14) varied significantly with changes in reagent concentration and aeration conditions. At the same concentrations of hydrogen peroxide and ferrous sulfate, the aerated group was significantly better than the non-aerated group (e.g., the removal efficiency increased from 73.9% to 85.2% in E2 compared to E9). When the hydrogen peroxide concentration was 0.2 wt%, the ferrous sulfate concentration was 0.28 wt%, and aeration was performed (E2), the COD removal efficiency reached 85.2%, which was the optimal combination of conditions in this experiment.

[0064] Based on the above, this experiment shows that the organic pollutant degradation section A of the present invention can effectively reduce the COD concentration in the water sample to 75 ppm (see E2) by aeration with an appropriate ratio of hydrogen peroxide and ferrous sulfate, without the need for high temperature or vacuum conditions, thus meeting the feed water conditions of the reverse osmosis module, thereby improving the subsequent concentration efficiency and extending the service life of the membrane element.

[0065] In this embodiment of the invention, in order to further verify the concentration and volume change effect of the reverse osmosis system of the present invention under continuous circulation operation, a single circulation and a double circulation process were implemented respectively, and the volume and nitrate nitrogen concentration changes of the water sample at each stage were recorded. The specific results are shown in Tables 3 and 4 below.

[0066] Table 3: Total Volume Distribution of the Reverse Osmosis Concentration Section in the Nitrate Nitrogen Aqueous Solution Concentration Method of the Present Invention Total volume of one cycle Enter RO1 Nitrate nitrogen aqueous solution 4000ppm (10L) RO1 input RO2 Nitrate nitrogen aqueous solution 6500ppm (5L) RO2 output Nitrate nitrogen aqueous solution 10500ppm (2.5L) RO2 and RO3 combiner input to RO4 Nitrate nitrogen aqueous solution 2500ppm (5L) RO4 reflux input RO1 Nitrate nitrogen aqueous solution 4000ppm (2.5L) RO1 input RO3 Nitrate nitrogen aqueous solution 1500ppm (5L) RO4 output Nitrate nitrogen aqueous solution 950ppm (2.5L) RO3 output Nitrate nitrogen aqueous solution 550ppm (2.5L)

[0067] Table 4: Total Volume Distribution of Secondary Circulation in the Reverse Osmosis Concentration Section of the Nitrate Nitrogen Aqueous Solution Concentration Method of the Present Invention Total volume of the second cycle RO4 reflux input RO1 Nitrate nitrogen aqueous solution 4000ppm (2.5L) RO1 input RO2 Nitrate nitrogen aqueous solution 6500ppm (1.25L) RO2 output Nitrate nitrogen aqueous solution 10500ppm (0.625L) RO2 and RO3 combiner input to RO4 Nitrate nitrogen aqueous solution 2500ppm (1.25L) RO4 reflux input RO1 Nitrate nitrogen aqueous solution 4000ppm (0.625L) RO1 input RO3 Nitrate nitrogen aqueous solution 1500ppm (1.25L) RO4 output Nitrate nitrogen aqueous solution 950ppm (0.625L) RO3 output Nitrate nitrogen aqueous solution 550ppm (0.625L)

[0068] In one cycle, the initial input is a 10-liter water sample with a nitrate nitrogen concentration of 4000 ppm. This water sample first enters the first reverse osmosis water purifier 51 (RO1) for separation, producing 5 liters of concentrated water with a concentration of 6500 ppm, which is then introduced into the second reverse osmosis water purifier 52 (RO2) for further concentration. RO1 simultaneously produces 5 liters of fresh water with a concentration of 1500 ppm, which is then introduced into the third reverse osmosis water purifier 53 (RO3). After treatment by RO2, the concentration of the concentrate increases to 10500 ppm, with a volume of 2.5 liters. RO3 further produces 2.5 liters of fresh water with a concentration of 550 ppm and 2.5 liters of concentrated water with a concentration of 2500 ppm. The concentrate from RO3 and the desalinated water from RO2 are then combined and introduced into the fourth reverse osmosis water purifier 54 (RO4) for further separation, producing 2.5 liters of low-concentration desalinated water (950 ppm) and 2.5 liters of medium-concentration concentrate (4000 ppm). The 4000 ppm water sample (medium-concentration concentrate) can be recycled as raw water for the next cycle.

[0069] In the secondary cycle, the total volume of the reflux liquid is 2.5 liters, with a concentration of 4000 ppm. Following the same treatment process, RO1 produces 1.25 liters of concentrate with a concentration of 6500 ppm and 1.25 liters of desalinated water with a concentration of 1500 ppm; RO2 concentrates the concentrate to 0.625 liters with a concentration of 10500 ppm; RO3 desalinates the desalinated water to 0.625 liters of desalinated water with a concentration of 550 ppm and 0.625 liters of concentrate with a concentration of 2500 ppm; RO4 produces 0.625 liters of desalinated water with a concentration of 950 ppm and 0.625 liters of concentrate with a concentration of 4000 ppm, which are then refluxed for the next cycle.

[0070] The results of this embodiment confirm that the reverse osmosis circulation system of the present invention can gradually increase the concentration of the concentrate and reduce the total volume under continuous circulation conditions, and stably separate low-concentration clear liquid and high-concentration concentrate. It has good dynamic volume management and resource recovery efficiency, and is suitable for the reduction treatment and concentration recovery of low-concentration nitrate nitrogen water samples. In addition, the obtained high-concentration nitrate nitrogen aqueous solution C1 can be further treated by, for example, electrolytic reduction when the nitrate nitrogen concentration is higher than 10,000 ppm; the obtained low-concentration nitrate nitrogen aqueous solution C2 can be further treated by, for example, iron powder replacement when the nitrate nitrogen concentration is lower than 1,000 ppm.

[0071] After treatment with the nitrate nitrogen aqueous solution concentration system and method proposed in this invention, organic pollutants and solid impurities in nitrate nitrogen-containing wastewater can be effectively removed, and the nitrate nitrogen concentration can be further increased to a high concentration level. Specifically, after the oxidation reaction step, the chemical oxygen demand (COD) in the initial water sample can be reduced from 500 ppm to 75 ppm (Example 2, E2). Subsequently, the pH value of the water sample is adjusted to promote the formation of ferric hydroxide precipitate, and filtration is performed to remove the precipitate. Then, ultrafiltration is used to remove suspended solids (SS) in the water, so that the SS content before the nanofiltration membrane (nanofiltration) feed water is controlled below 1 ppm. Through nanofiltration, residual organic pollutants in the water can be further removed, reducing the COD concentration to below 50 ppm, while reducing the SS concentration to below 1 ppm, which helps to improve the operational stability and extend the lifespan of the subsequent reverse osmosis system.

[0072] In the first cycle of the reverse osmosis concentration section of the nitrate nitrogen aqueous solution concentration system of the present invention, a water sample with an initial nitrate nitrogen concentration of 4000 ppm and a volume of 10 liters can be concentrated by this system to obtain a high-concentration concentrate with a concentration of 10500 ppm and a volume of 2.5 liters, and produce fresh water with a concentration of less than 1000 ppm, for a total volume of 5 liters. After a second cycle, further concentration can obtain a high-concentration liquid with a volume of 3.125 liters and a concentration of 10500 ppm, and a clear liquid with a total volume of 6.25 liters and a concentration of less than 1000 ppm.

[0073] Experimental results also confirm that the polyamide reverse osmosis membrane (RO membrane) can effectively retain more than 80% of nitrate nitrogen, with a significant concentration effect. For example, compared with the original 10 liters of 4000 ppm solution, the retention efficiency of 5 liters of RO concentrate (6500ppm) is more than 80% (6500ppm×5L / 4000ppm×10L). Further calculation of the concentration effect shows that 10500ppm×(2.5L+0.625L) / (4000ppm×10L) yields a concentration efficiency of approximately 82%, demonstrating that this system has a high-efficiency capacity for nitrate nitrogen concentration and supernatant reduction.

[0074] The embodiments described above are merely for illustrating the technical ideas and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the patent scope of the present invention. That is, all equivalent changes or modifications made in accordance with the spirit disclosed in the present invention should still be covered within the patent scope of the present invention.

[0075] A: Organic pollutant degradation section A1: Nitrate-containing nitrogen waste liquid A2: Ferrous salt A3: Hydrogen peroxide A4: Mixture A51: Nitrate Nitrogen Aqueous Solution A52: Nitrate Nitrogen Aqueous Solution A53: Nitrate nitrogen aqueous solution A6: Ferric hydroxide A7: Alkali B: Filtering section B1: Acid C: Reverse Osmosis Concentration Section C1: High-concentration nitrate nitrogen aqueous solution C2: Low-concentration nitrate nitrogen aqueous solution 10: Reaction tank 11: Aeration device 111: Air source 112: Gas pipeline 113: Flow meter 20: Solid-liquid separation device 30: Solid impurity filtration device 40: Organic pollutant filtration device 41: Return pipe 51: First Reverse Osmosis Water Purifier 511: Inlet 512: Concentrate outlet 513: Freshwater Export 52: Second Reverse Osmosis Water Purifier 521: Inlet 522: Concentrate outlet 523: Freshwater Export 53: Third Reverse Osmosis Water Purifier 531: Inlet 532: Concentrate outlet 533: Freshwater Export 54: Fourth Reverse Osmosis Water Purifier 541: Inlet 542: Concentrate outlet 543: Freshwater Export P: System piping P1: Gate valve P2: Pressure pump S1: Oxidation reaction steps S11: Alkali Adjustment Steps S2: Solid-liquid separation step S3: Solid impurity filtration steps S31: Acid Adjustment Steps S4: Organic Pollutant Filtration Steps S5: Reverse Osmosis Concentration Step S6: Advanced Reverse Osmosis Cycle Steps

Claims

1. A system for concentrating nitrate nitrogen in an aqueous solution, comprising: An organic pollutant degradation section (A) includes a reaction tank (10) connected to a solid-liquid separation device (20); the reaction tank (10) has a waste liquid input device, a ferrous salt input device and a hydrogen peroxide input device for respectively inputting nitrate nitrogen waste liquid (A1), ferrous salt (A2) and hydrogen peroxide (A3) to react and form a mixed liquid (A4) which is output to the solid-liquid separation device (20), thereby separating out a first nitrate nitrogen aqueous solution (A51) which flows out from an outlet of the solid-liquid separation device (20), and separating out ferric hydroxide (A6); A filtration section (B) includes a solid impurity filtration device (30) connected to an organic pollutant filtration device (40), the solid impurity filtration device (30) being connected to the outlet of the solid-liquid separation device (20); the first nitrate nitrogen aqueous solution (A51) is fed into the solid impurity filtration device (30) to remove the contained solid impurities, forming a second nitrate nitrogen aqueous solution (A52) which is output to the organic pollutant filtration device (40) for organic pollutant filtration, the organic pollutant filtration device (40) outputting a third nitrate nitrogen aqueous solution (A53); and a reverse osmosis concentration section (C) including a first reverse osmosis water purifier (51) and a second reverse osmosis water purifier (52). A third reverse osmosis water purifier (53) and a fourth reverse osmosis water purifier (54) are provided. One of the concentrated water outlets (512) of the first reverse osmosis water purifier (51) is connected to one of the inlets (521) of the second reverse osmosis water purifier (52). The first reverse osmosis water purifier (51) is connected to the organic pollutant filtration device (40), so that the third nitrate nitrogen aqueous solution (A53) output from the filtration section (B) flows sequentially through the first reverse osmosis water purifier (51) and the second reverse osmosis water purifier (52). One of the concentrated water outlets (522) of the second reverse osmosis water purifier (52) is used to output a high-concentration nitrate nitrogen aqueous solution (C1) to concentrate the nitrate nitrogen concentration in the nitrate nitrogen-containing waste liquid (A1). The first reverse osmosis water purifier (51) has an inlet (511) for receiving the third nitrate nitrogen solution (A53), and a freshwater outlet (513) of the first reverse osmosis water purifier (51) is connected to an inlet (531) of the third reverse osmosis water purifier (53). A concentrated water outlet (532) of the third reverse osmosis water purifier (53) is connected to a freshwater outlet (523) of the second reverse osmosis water purifier (52), which then flows into the fourth reverse osmosis water purifier. The inlet (541) of the reverse osmosis water purifier (54); the fresh water outlet (533) of the third reverse osmosis water purifier (53) and the fresh water outlet (543) of the fourth reverse osmosis water purifier (54) are connected to each other to output a low concentration nitrate nitrogen aqueous solution (C2); and the concentrated water outlet (542) of the fourth reverse osmosis water purifier (54) is connected back to the inlet (511) of the first reverse osmosis water purifier (51) to form a circulating concentration loop;The mixture (A4) is fed into the solid-liquid separation device (20) after the pH value is adjusted to 6 to 8 by an alkali agent (A7); the second nitrate nitrogen aqueous solution (A52) is fed into the organic pollutant filtration device (40) after the pH value is adjusted to 3 to 4 by an acid agent (B1); the organic pollutant filtration device (40) is equipped with a return pipe (41). When the organic pollutant concentration of the third nitrate nitrogen aqueous solution (A53) is greater than or equal to a concentration threshold, the third nitrate nitrogen aqueous solution (A53) is returned through the return pipe (41) and merged with the second nitrate nitrogen aqueous solution (A52) to be fed into the organic pollutant filtration device (40) for further filtration; and until the organic pollutant concentration of the third nitrate nitrogen aqueous solution (A53) is less than the concentration threshold, the third nitrate nitrogen aqueous solution (A53) is output to the first reverse osmosis water purifier (51) for concentration.

2. The nitrate nitrogen aqueous solution concentration system as described in claim 1, wherein, The organic pollutant degradation section (A) also includes an aeration device (11) that supplies output gas to the bottom of the reaction tank (10) to aerate the mixture (A4); the organic pollutant filtration device (40) is a nanofiltration device with a nanofiltration membrane made of polyamide (PA) or polyether amide (PEI); the solid impurity filtration device (30) is an ultrafiltration device with an ultrafiltration membrane made of cellulose acetate; and the reverse osmosis membranes of the first reverse osmosis water purifier, the second reverse osmosis water purifier, the third reverse osmosis water purifier, or the fourth reverse osmosis water purifier are made of polyamide (PA) or polyether amide (PEI).

3. The nitrate nitrogen aqueous solution concentration system as described in claim 2, wherein, The initial organic pollutant concentration of the nitrate nitrogen waste liquid (A1) is 100 ppm to 500 ppm, and the initial nitrate nitrogen concentration is 1000 ppm to 6000 ppm; the organic pollutant concentration of the first nitrate nitrogen aqueous solution (A51) output by the solid-liquid separation device (20) is less than 100 ppm; and the first nitrate nitrogen aqueous solution (A51) is filtered by the solid impurity filtration device (30) to remove the solid impurities to a concentration of less than 1 ppm to form the second nitrate nitrogen aqueous solution (A52), which is then filtered by the organic pollutant filtration device (40) to remove the organic pollutants to a concentration of less than 50 ppm to form the third nitrate nitrogen aqueous solution (A53).

4. A method for concentrating nitrate nitrogen in an aqueous solution, the method comprising the following steps: Oxidation reaction step (S1): Nitrate nitrogen waste liquid (A1), ferrous salt (A2), and hydrogen peroxide (A3) are introduced into a reaction tank (10) for oxidation reaction to generate a mixed liquid (A4); Solid-liquid separation step (S2): The mixed liquid (A4) is fed into a solid-liquid separation device (20) for separation to obtain a first nitrate nitrogen aqueous solution (A51) and an iron hydroxide (A6); Solid impurity filtration step (S3): The first nitrate nitrogen aqueous solution (A51) is fed into a solid impurity filtration device (30) to filter out solid impurities and form a second nitrate nitrogen aqueous solution (A52); Organic pollutant filtration step (S4): The second nitrate nitrogen aqueous solution (A52) is fed into an organic pollutant filtration device (40) to filter out organic pollutants and form a third nitrate nitrogen aqueous solution (A53); Reverse osmosis concentration step (S5): The third nitrate nitrogen aqueous solution (A53) is sequentially introduced into a first reverse osmosis water purifier (51) and a second reverse osmosis water purifier (52) to concentrate the nitrate nitrogen concentration of the nitrate nitrogen-containing waste liquid (A1) and output a high-concentration nitrate nitrogen aqueous solution (C1); and advanced reverse osmosis circulation step (S6): One of the fresh water outputs from the first reverse osmosis water purifier (51) is introduced into a third reverse osmosis water purifier (53), and one of the concentrated waters from the third reverse osmosis water purifier (53) and one of the fresh waters from the second reverse osmosis water purifier (52) are combined and then transported to a fourth reverse osmosis water purifier (54). One of the concentrated waters from the fourth reverse osmosis water purifier (54) is then returned to the first reverse osmosis water purifier (51) to form a circulating concentration cycle. The fresh water from one of the third reverse osmosis water purifiers (53) and one of the fresh water from the fourth reverse osmosis water purifier (54) are combined to form a low-concentration nitrate nitrogen aqueous solution (C2) for output; and, before the solid-liquid separation step (S2), an alkali adjustment step (S11) is included, in which an alkali agent (A7) is added to the mixture (A4) to adjust the pH value to the range of 6 to 8, and the alkali agent (A7) is sodium hydroxide; and, before the organic pollutant filtration step (S4), an acid adjustment step (S31) is included, in which an acid agent (B1) is added to the second nitrate nitrogen aqueous solution (A52) to adjust the pH value to the range of 3 to 4, and the acid agent (B1) is selected from sulfuric acid, nitric acid or hydrochloric acid.

5. The method for concentrating nitrate nitrogen aqueous solution as described in claim 4, wherein, When the concentration of organic pollutants in the third nitrate nitrogen aqueous solution (A53) is greater than or equal to a concentration threshold, the third nitrate nitrogen aqueous solution (A53) is refluxed and mixed into the second nitrate nitrogen aqueous solution (A52), and then filtered until the concentration of organic pollutants is less than the concentration threshold.

6. The method for concentrating nitrate nitrogen aqueous solution as described in claim 5, wherein, The organic pollutant filtration device (40) is a nanofiltration device with a nanofiltration membrane, and the material of the nanofiltration membrane is selected from polyamide (PA) or polyether amide (PEI) composite material; the solid impurity filtration device (30) is an ultrafiltration device with an ultrafiltration membrane, and the material of the ultrafiltration membrane is cellulose acetate; and the reverse osmosis membrane of the first reverse osmosis water purifier, the second reverse osmosis water purifier, the third reverse osmosis water purifier or the fourth reverse osmosis water purifier is made of polyamide (PA) or polyether amide (PEI).

7. The method for concentrating nitrate nitrogen aqueous solution as described in claim 6, wherein, In the oxidation reaction step (S1), gas aeration is performed at the bottom of the reaction tank (10); the initial organic pollutant concentration of the nitrate nitrogen waste liquid (A1) is 100 ppm to 500 ppm, and the initial nitrate nitrogen concentration is 1000 ppm to 6000 ppm; and the organic pollutant concentration in the first nitrate nitrogen aqueous solution (A51) is less than 100 ppm, the solid impurity concentration in the second nitrate nitrogen aqueous solution (A52) is less than 1 ppm, and the organic pollutant concentration in the third nitrate nitrogen aqueous solution (A53) is less than 50 ppm.

Images