Deep denitrification method for eutrophic water bodies

Abstract

The present invention relates to a method for deep denitrification of eutrophic water bodies, comprising the following steps: (1) pre-treating a resin with a sodium chloride solution, a dilute hydrochloric acid solution, and a sodium hydroxide solution in sequence to remove impurities; (2) subjecting the resin obtained after the pre-treatment in step (1) to adsorption on a slightly polluted water body; (3) backwashing the resin after adsorption in step (2) with a 10% (w / w) sodium chloride solution to regeneration, thereby obtaining a backwash liquid; and (4) recovering the sodium chloride in the backwash liquid obtained in step (3); wherein the resin is an anionic resin. The method for deep denitrification of eutrophic water bodies of the present invention can ensure that the total nitrogen content of the effluent is less than 1 mg / L, can achieve surface water quality Class III, and can enable the treated wastewater to be directly discharged into a lake.

Description

Technical Field

[0001] The present invention relates to the technical field of micro-polluted water treatment, in particular to a method for deep denitrification of eutrophic water. Background Art

[0002] Currently, sewage treatment plants treat wastewater that meets the Class A surface water quality standard and then discharges it directly into rivers and then into lakes. According to lake water quality indicators, this treated wastewater still exacerbates eutrophication. There is an urgent need to deeply denitrify water bodies that remain eutrophic even after sewage treatment plants meet discharge standards, ensuring that the effluent nitrogen content meets the Class III water discharge standard.

[0003] Among the numerous effluent standards required by wastewater treatment plants, organic matter can be achieved through advanced oxidation or simply adjusting operating parameters, while total phosphorus can be nearly completely removed through chemical precipitation. However, nitrogen removal is the most challenging. First, nitrogen concentrations are extremely low. The total nitrogen levels for Class IV and Class III water are 1.5 and 1.0 mg / L, respectively, representing 90% and 93% improvements over the Class A standards. Traditional biological processes, such as the A / O water treatment process, can effectively reduce nitrogen and phosphorus in slightly polluted waters. However, the effectiveness of existing biological processes has reached its limits. Typical biochemical processes are generally considered to have an effluent TN level of approximately 10 mg / L. Even with post-denitrification filters, effluent TN can only be reduced to 2 mg / L, still failing to meet Class III water requirements. Therefore, more advanced treatment methods are needed to achieve an effluent TN level of ≤1 mg / L.

[0004] In addition, after the process of deep denitrification of water bodies, the products have the characteristics of high salinity and high nitrogen content. Therefore, how to reuse and utilize the products after deep denitrification is also an urgent problem to be solved. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the prior art, the object of the present invention is to provide a method for deep denitrification of eutrophic water bodies to solve one or more problems in the prior art.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] The deep denitrification method for eutrophic water bodies comprises the following steps:

[0008] (1) The resin is pretreated with sodium chloride solution, dilute hydrochloric acid solution, and sodium hydroxide solution in sequence to remove impurities;

[0009] (2) using the resin obtained after the pretreatment in step (1) to adsorb slightly polluted water;

[0010] (3) The resin after adsorption in step (2) is backwashed and regenerated using a 10% (w) sodium chloride solution to obtain a backwash solution;

[0011] (4) recovering sodium chloride from the backwash solution of step (3);

[0012] Wherein, the resin is an anionic resin.

[0013] Furthermore, the resin is pretreated sequentially with a sodium chloride solution, a dilute hydrochloric acid solution, and a sodium hydroxide solution, comprising:

[0014] Add twice the volume of 10% (w) sodium chloride solution to the container containing the resin. After soaking for 20 h, pour out the upper layer of sodium chloride solution and rinse the resin repeatedly with deionized water until the rinse water is no longer yellow.

[0015] Add twice the volume of 2 mol / L hydrochloric acid solution to the container containing the resin, soak for 3 hours, pour out the solution, and rinse repeatedly with deionized water until the pH of the solution reaches neutral;

[0016] Add twice the volume of 1 mol / L sodium hydroxide solution to the container containing the resin, soak for 3 hours, and then rinse repeatedly with deionized water until the pH of the solution reaches neutral.

[0017] Furthermore, the step of adsorbing slightly polluted water with the resin obtained after the pretreatment in step (1) includes:

[0018] The resin performs static adsorption on slightly polluted water, and the static adsorption capacity of the resin is 12.4 mg / mL to 13.2 mg / mL.

[0019] Furthermore, the step of adsorbing slightly polluted water with the resin obtained after the pretreatment in step (1) includes:

[0020] The resin dynamically adsorbs slightly polluted water, and the dynamic adsorption capacity of the resin is 4 mg / mL to 6.2 mg / mL.

[0021] Furthermore, the step of backwashing and regenerating the resin after adsorption in step (2) using a 10% (w) sodium chloride solution comprises:

[0022] The resin was backwashed for 10 minutes using 1~6BV of 10% (w) sodium chloride solution, and the resin regeneration rate was 78%~90%.

[0023] Furthermore, the step of backwashing and regenerating the resin after adsorption in step (2) using a 10% (w) sodium chloride solution comprises:

[0024] The backwashing was carried out by using a double wash method. In the first batch of backwashing, 20 BV of 10% sodium chloride solution was prepared. The backwashing was repeated several times until the volume of sodium chloride solution in the backwashing liquid was 5-12 BV. The 5-12 BV sodium chloride solution was reconfigured into 20 BV of 10% sodium chloride solution. The second batch of backwashing was carried out. Each time the backwashing liquid was backwashed with a volume of 1-4 BV of sodium chloride solution, it was recycled in step (4). The above steps were repeated until all the backwashing liquid was processed. The resin regeneration rate was greater than 95%.

[0025] Furthermore, the step of recovering sodium chloride in the backwash liquid of step (3) comprises:

[0026] The backwash liquid is evaporated and crystallized using an MVR evaporator or a double-effect evaporator to concentrate the backwash liquid by 20 to 40 times, with a sodium chloride recovery rate of 80 to 90%.

[0027] Furthermore, the MVR device consumes 50 kWh of electricity and 60-80 kg of steam per ton of backwash liquid evaporated.

[0028] Furthermore, the step of recovering sodium chloride in the backwash liquid of step (3) comprises:

[0029] A denitrification filter tank is used to remove nitrate nitrogen from the backwash liquid. The nitrate nitrogen concentration in the backwash liquid is 50~150 mg / L, the sodium chloride concentration is 1~6 g / L, and the nitrate nitrogen removal amount is 30~35 mg / L.

[0030] Furthermore, the resin is any one or more of Kohis T-42H, Kohis A-62MP, and Ningbo Zhengguang D890.

[0031] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0032] (1) The method for deep denitrification of eutrophic water bodies of the present invention comprises pre-treating an anion resin with a sodium chloride solution, a dilute hydrochloric acid solution, and a sodium hydroxide solution in sequence to remove impurities; applying the pre-treated resin to slightly polluted water for adsorption; and backwashing the adsorbed resin with a 10% (w / w) sodium chloride solution to regenerate the resin, thereby obtaining a backwash solution. This ensures that the total nitrogen content of the effluent is less than 1 mg / L, achieving Class III surface water quality, and enabling the treated wastewater to be directly discharged into the lake.

[0033] (2) Furthermore, the deep denitrification method for eutrophic water bodies of the present invention uses an MVR evaporator and a two-effect evaporator to evaporate and crystallize the backwash liquid, concentrating the backwash liquid by 20 to 40 times, with a sodium chloride recovery rate of 80 to 90%. The remaining liquid can be used as a bio-fertilizer auxiliary material, thereby realizing resource recycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The static adsorption capacity of three resins in the deep denitrification method for eutrophic water provided by the present invention is shown.

[0035] Figure 2 The figure shows the nitrate nitrogen concentration of the static backwash effluent in the deep denitrification method for eutrophic water provided by the present invention.

[0036] Figure 3 The flowchart of the backwashing method in the deep denitrification method for eutrophic water provided by the present invention is shown.

[0037] Figure 4 The figure shows the nitrate nitrogen concentration of the washout liquid from the backwashing in the deep denitrification method for eutrophic water provided by the present invention.

[0038] Figure 5 The figure shows the nitrate nitrogen removal rate of the backwashing and overwashing in the deep denitrification method for eutrophic water provided by the present invention.

[0039] Figure 6 A photograph of the backwash liquid when the concentration ratio is 1 in the deep denitrification method for eutrophic water provided by the present invention is shown.

[0040] Figure 7 The figure shows a photo of the backwash liquid when the concentration ratio is 20 times in the deep denitrification method for eutrophic water provided by the present invention.

[0041] Figure 8 A photograph of the backwash liquid when the concentration ratio is 41 times in the deep denitrification method for eutrophic water provided by the present invention is shown.

[0042] Figure 9 The figure shows the nitrate nitrogen concentration in the effluent of the denitrification filter during operation in the deep denitrification method for eutrophic water provided by the present invention.

[0043] Figure 10 The figure shows the amount of nitrate nitrogen removed when the denitrification filter is in operation in the deep denitrification method for eutrophic water provided by the present invention. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solutions and advantages of the present invention clearer, the device proposed in the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. According to the following description, the advantages and features of the present invention will be clearer. It should be noted that the drawings are in a very simplified form and use non-precise proportions, which are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention. In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, please refer to the drawings. It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention, so they have no technical substantive significance. Any structural modification, change in proportional relationship or adjustment of size, without affecting the efficacy and purpose that can be achieved by the present invention, should still fall within the scope of the technical content disclosed by the present invention.

[0045] In the description of the present invention, the orientations or positional relationships indicated by terms such as "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "top", "bottom", "inside", "outside", "axial", "radial", and "circumferential" are defined as orientations or positional relationships based on those shown in the accompanying drawings. These are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, they should not be understood as limitations on the present invention.

[0046] Example 1

[0047] The deep denitrification method for eutrophic water bodies comprises the following steps:

[0048] (1) The resin is pretreated with sodium chloride solution, dilute hydrochloric acid solution, and sodium hydroxide solution in sequence to remove impurities;

[0049] (2) using the resin obtained after the pretreatment in step (1) to adsorb slightly polluted water;

[0050] (3) The resin after adsorption in step (2) is backwashed and regenerated using a 10% (w) sodium chloride solution to obtain a backwash solution;

[0051] (4) recovering sodium chloride from the backwash solution of step (3);

[0052] Wherein, the resin is an anionic resin.

[0053] Specifically, the slightly polluted water body refers to a water body that is polluted by organic matter, whose water quality reaches the surface water level A standard or above, and some water quality indicators exceed the Class III water body standard of the "Surface Water Environmental Quality Standards".

[0054] The steps of resin pretreatment are described in detail below:

[0055] The pretreatment is used to remove some impurity ions and oligomers on the resin surface. The resin is pretreated with sodium chloride solution, dilute hydrochloric acid solution, and sodium hydroxide solution in sequence, including the following steps:

[0056] Add twice the volume of 10% (w) sodium chloride solution to the container containing the resin. After soaking for 20 h, pour out the upper layer of sodium chloride solution and rinse the resin repeatedly with deionized water until the rinse water is no longer yellow.

[0057] Add twice the volume of 2 mol / L hydrochloric acid solution to the container containing the resin, soak for 3 hours, pour out the solution, and rinse repeatedly with deionized water until the pH of the solution reaches neutral;

[0058] Add twice the volume of 1 mol / L sodium hydroxide solution to the container containing the resin, soak for 3 hours, and then rinse repeatedly with deionized water until the pH of the solution reaches neutral.

[0059] The steps of resin adsorption are described in detail below:

[0060] Furthermore, the step of adsorbing slightly polluted water with the resin obtained after the pretreatment in step (1) includes:

[0061] The resin performs static adsorption on slightly polluted water, and the static adsorption capacity of the resin is 12.4 mg / mL to 13.2 mg / mL.

[0062] Static adsorption capacity test method: artificially prepare 1 L of potassium nitrate solution with concentrations of 15, 30, and 50 mg / L, take 250 mL of each solution into a conical flask, add 1 mL of resin into the conical flask, stir on a magnetic stirrer for 90 min, take samples at regular intervals, detect the nitrate nitrogen concentration, and calculate the adsorption capacity of the resin.

[0063] The static adsorption capacity of the three resins is shown in Figure 1 . Figure 1 The results showed that the adsorption capacity of nitrate nitrogen by the Kehaisi T-42H was 0, the adsorption capacity of nitrate nitrogen by the Kehaisi A-62MP was 12.48 mg / mL, and the adsorption capacity of nitrate nitrogen by the Ningbo Zhengguang D890 was 13.18 mg / mL. This indicates that the ammonia nitrogen adsorption resin has no adsorption capacity for nitrate nitrogen, indicating that the resin has strong selectivity.

[0064] Water quality analysis revealed that the primary nitrogen form in this slightly polluted water body was nitrate nitrogen. To meet Class III water discharge standards, a suitable nitrate nitrogen adsorption resin was required for deep denitrification. Ningbo Zhengguang D890 resin exhibits stronger adsorption capacity and selectivity for nitrate nitrogen than Kohis A-62MP resin, and is unaffected by anions in the slightly polluted water. Therefore, in subsequent dynamic adsorption experiments, Ningbo Zhengguang D890 resin was selected to adsorb nitrate nitrogen, while Kohis T-42H resin was used to adsorb ammonia nitrogen to analyze dynamic adsorption capacity.

[0065] Furthermore, the step of adsorbing slightly polluted water with the resin obtained after the pretreatment in step (1) includes:

[0066] The resin dynamically adsorbs slightly polluted water, and the dynamic adsorption capacity of the resin is 4 mg / mL to 6.2 mg / mL.

[0067] Dynamic adsorption capacity test method:

[0068] A. Artificially prepare 110 L of 7.88 mg / L potassium nitrate solution. The resin filling volume in the plexiglass tube is 100 mL. The water inlet flow rate is controlled at 100 mL / min, that is, the linear velocity is 12.22 m / h. The experiment is conducted in a top-in, bottom-out manner. Sampling is performed at regular intervals to detect the nitrate nitrogen concentration in the outlet water.

[0069] Table 1 Dynamic adsorption capacity of Ningbo Zhengguang D890 resin

[0070] Outlet nitrate nitrogen concentration (mg / L) Adsorption capacity (mgNO3--N / mL resin) Adsorption time (h) Processing volume multiple (BV) 0.05 4.02 8.5 510 ＜1 4.90 10.5 630 ≈7.88 (influent concentration) 6.18 17.5 1050

[0071] Where BV represents the resin loading. At the start of adsorption, no nitrate nitrogen was detected in the effluent. It wasn't until around 8.5 hours that nitrate nitrogen began to be detected, reaching a concentration of 0.05 mg / L. Between 10 and 11 hours, the effluent nitrate nitrogen concentration exceeded 1 mg / L, reaching 0.79 mg / L at 10.5 hours and 1.34 mg / L at 11 hours. Around 17.5 hours, the effluent concentration was essentially the same as the inlet concentration.

[0072] B. Artificially prepare 90 L of 3.88 mg / L ammonium chloride solution, fill 50 mL of resin, control the water inlet flow rate at 100 mL / min, or a linear velocity of 12.22 m / h, and conduct the experiment in a top-in, bottom-out manner. Take samples at regular intervals to detect the ammonia nitrogen concentration in the effluent.

[0073] Table 2 Dynamic adsorption capacity of Kehaisi T-42H resin

[0074] Effluent ammonia nitrogen concentration (mg / L) Adsorption capacity (mg-NH3-N / mL resin) Adsorption time (h) Processing volume multiple (BV) Not detected 0.47 1 120 ＜1 1.24 2.75 165 ≈3.88 (influent concentration) 1.51 4 480

[0075] The resin backwash regeneration method is described below:

[0076] Backwashing begins when the nitrate nitrogen concentration in the resin effluent is >1 mg / L.

[0077] Furthermore, the step of backwashing and regenerating the resin after adsorption in step (2) using a 10% (w) sodium chloride solution comprises:

[0078] The resin was backwashed for 10 minutes using 1~6BV of 10% (w) sodium chloride solution, and the resin regeneration rate was 78%~90%.

[0079] Static backwash method: Use 6BV of 10% (w) sodium chloride solution for backwashing, control the peristaltic pump flow rate at 100mL / min, first pump in 1BV of sodium chloride solution, then pause the peristaltic pump, let the sodium chloride solution in the chromatography column stand for 10 minutes, then pump in 1BV of sodium chloride solution again to replace the sodium chloride solution in the chromatography column, and then let it stand for 10 minutes, and so on. The nitrate nitrogen concentration of the backwash effluent is shown in Figure 2 .

[0080] Furthermore, the step of backwashing and regenerating the resin after adsorption in step (2) using a 10% (w) sodium chloride solution comprises:

[0081] The backwashing was carried out by using a double wash method. In the first batch of backwashing, 20 BV of 10% sodium chloride solution was prepared. The backwashing was repeated several times until the volume of sodium chloride solution in the backwashing liquid was 5-12 BV. The 5-12 BV sodium chloride solution was reconfigured into 20 BV of 10% sodium chloride solution. The second batch of backwashing was carried out. Each time the backwashing liquid was backwashed with a volume of 1-4 BV of sodium chloride solution, it was recycled in step (4). The above steps were repeated until all the backwashing liquid was processed. The resin regeneration rate was greater than 95%.

[0082] Washing and backwashing method: please refer to Figure 3 For the first wash, use 20BV of 10% (w) sodium chloride solution. For the second and subsequent washes, only 4BV of new backwash solution is needed. The backwash method can reuse the backwash solution, thereby reducing the consumption of sodium chloride solution during backwashing and significantly saving costs. The nitrate nitrogen concentration of the backwash effluent can be seen in Figure 4 .

[0083] Depend on Figure 4 It can be seen that the nitrate nitrogen concentration of the 1~4 BV eluate is very high, and the nitrate nitrogen concentration of the 5~20 BV eluate decreases in sequence, indicating that it is feasible to use the 5~20 BV eluate for the next backwash, and Figure 5The nitrate removal results also show that backwashing does not reduce nitrate removal. As the number of backwashes increases, the nitrate concentration in the wash solution also increases, indicating that when the number of backwashes is high enough, the effectiveness of backwashing decreases. In this case, the first 8 or 12 BV of backwash solution should be used for denitrification treatment, and a new 8-12 BV of backwash solution should be prepared for backwashing to maintain a high nitrate removal rate.

[0084] The backwash flow rate during the overwash is 50 mL / min, which can achieve a higher backwash effect with a shorter backwash time of 40 minutes, that is, the nitrate nitrogen removal rate is >95%.

[0085] The method for concentrating the backwash liquid is described below:

[0086] Furthermore, the step of recovering sodium chloride in the backwash liquid of step (3) comprises:

[0087] The backwash liquid is evaporated and crystallized using an MVR evaporator or a double-effect evaporator to concentrate the backwash liquid by 20 to 40 times, with a sodium chloride recovery rate of 80 to 90%.

[0088] MVR evaporators and double-effect evaporators can be commercially available, such as Jiangsu Shijie's MVR forced circulation evaporation crystallization device or multi-effect evaporator. The main components of the backwash liquid are sodium chloride, sodium nitrate, and a small amount of COD. During the evaporation and concentration process, the solubility of sodium chloride is 35-39g / 100mL, and it will be the first to precipitate crystals. Since the solubility of sodium nitrate is 140-180g / 100mL, when the concentration ratio is less than 50 times, sodium nitrate will not precipitate as crystals. Therefore, evaporation and crystallization can be used to recover sodium chloride and separate it from sodium nitrate. If MVR concentration is used, the energy consumption required in the evaporation and crystallization process can be significantly reduced. The MVR evaporator consumes 50kWh of electricity and 60-80kg of steam for every ton of backwash liquid evaporated.

[0089] Please refer to Figure 6 and Figure 7 When the concentration ratio reaches 20 times, the color of the backwash solution becomes obviously darker, brown-red, but the backwash solution remains clear. Figure 8 When the concentration ratio reaches 41 times, in addition to sodium chloride precipitated at the bottom, a thin film of substance precipitated on the surface of the concentrate, which may be the precipitation of COD substances. Excessive precipitation of COD substances will affect the scaling of the MVR concentration equipment and the purity and morphology of sodium chloride crystals.

[0090] Furthermore, the step of recovering sodium chloride in the backwash liquid of step (3) comprises:

[0091] A denitrification filter tank is used to remove nitrate nitrogen from the backwash liquid. The nitrate nitrogen concentration in the backwash liquid is 50~150 mg / L, the sodium chloride concentration is 1~6 g / L, and the nitrate nitrogen removal amount is 30~35 mg / L.

[0092] Denitrification filter elution method:

[0093] 1) Take the aerobic sludge of Wuxi Huilian landfill leachate as the inoculated sludge of the denitrification filter and inoculate it.

[0094] 2) Prepare water: Weigh 0.361g potassium nitrate, 1g glucose, and 1mL trace elements to make 1L of nutrient solution. The nitrate nitrogen concentration of this solution should be 50mg / L.

[0095] 3) Hydraulic retention time: 6h, artificial water distribution, daily sampling to measure water quality indicators such as COD and total nitrogen, and gradually increase the influent nitrate nitrogen concentration and influent sodium chloride concentration.

[0096] The operation status of denitrification filter is shown in Figure 9 In stages one and two, the influent nitrate nitrogen concentration was 50 mg / L, and the effluent concentration was around 2-3 mg / L, with the filter operating well. In stage three, the influent nitrate nitrogen concentration was increased to 150 mg / L, and the effluent nitrate nitrogen concentration was around 50 mg / L. In stage four, the influent nitrate nitrogen concentration was restored to around 50 mg / L, and after it operated well, it was increased to around 100 mg / L (stage five).

[0097] Please refer to Figure 10 In the process of increasing the influent sodium chloride concentration from 1g / L to 6g / L, the nitrate nitrogen removal content of the denitrification filter fluctuated in the range of 30~35 mg / L. In the process of increasing the NaCl concentration from 1g / L to 6g / L, the denitrification process was not significantly inhibited.

[0098] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0099] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for deep denitrification of eutrophic water bodies, characterized in that: The following steps are involved: (1) The resin is pretreated with sodium chloride solution, dilute hydrochloric acid solution, and sodium hydroxide solution in sequence to remove impurities; (2) using the resin obtained after the pretreatment in step (1) to adsorb slightly polluted water; (3) The resin after adsorption in step (2) is backwashed and regenerated using a 10% (w) sodium chloride solution to obtain a backwash solution; (4) recovering sodium chloride from the backwash solution of step (3); Wherein, the resin is an anionic resin; The step of backwashing and regenerating the resin after adsorption in step (2) with a 10% (w) sodium chloride solution comprises: The backwashing was performed by using a double wash method. In the first batch of backwashing, 20 BV of 10% sodium chloride solution was prepared. The backwashing was repeated several times until the volume of sodium chloride solution in the backwash liquid was 5-12 BV. The 5-12 BV sodium chloride solution was reconfigured into 20 BV of 10% sodium chloride solution. The second batch of backwashing was performed. Each time the backwash liquid with a volume of 1-4 BV of sodium chloride solution was recycled in step (4). The above steps were repeated until all the backwash liquid was processed. The backwash flow rate during double wash was 50 mL / min, the backwash time was 40 min, and the resin regeneration rate was greater than 95%.

2. The deep denitrification method for eutrophic water according to claim 1, characterized in that: The resin is pretreated sequentially with a sodium chloride solution, a dilute hydrochloric acid solution, and a sodium hydroxide solution, comprising: Add twice the volume of 10% (w) sodium chloride solution to the container containing the resin. After soaking for 20 h, pour out the upper layer of sodium chloride solution and rinse the resin repeatedly with deionized water until the rinse water is no longer yellow. Add twice the volume of 2 mol / L hydrochloric acid solution to the container containing the resin, soak for 3 hours, pour out the solution, and rinse repeatedly with deionized water until the pH of the solution reaches neutral; Add twice the volume of 1 mol / L sodium hydroxide solution to the container containing the resin, soak for 3 hours, and then rinse repeatedly with deionized water until the pH of the solution reaches neutral.

3. The deep denitrification method for eutrophic water according to claim 1, characterized in that: The step of using the resin obtained after the pretreatment in step (1) to adsorb slightly polluted water comprises: The resin performs static adsorption on slightly polluted water, and the static adsorption capacity of the resin is 12.4 mg / mL to 13.2 mg / mL.

4. The deep denitrification method for eutrophic water according to claim 1, characterized in that: The step of using the resin obtained after the pretreatment in step (1) to adsorb slightly polluted water comprises: The resin dynamically adsorbs slightly polluted water, and the dynamic adsorption capacity of the resin is 4 mg / mL to 6.2 mg / mL.

5. The deep denitrification method for eutrophic water according to claim 1, characterized in that: The step of recovering sodium chloride in the backwash liquid of step (3) comprises: The backwash liquid is evaporated and crystallized using an MVR evaporator or a double-effect evaporator to concentrate the backwash liquid by 20 to 40 times, with a sodium chloride recovery rate of 80 to 90%.

6. The deep denitrification method for eutrophic water according to claim 1, characterized in that: The step of recovering sodium chloride in the backwash liquid of step (3) comprises: A denitrification filter tank is used to remove nitrate nitrogen from the backwash liquid. The nitrate nitrogen concentration in the backwash liquid is 50~150 mg / L, the sodium chloride concentration is 1~6 g / L, and the nitrate nitrogen removal amount is 30~35 mg / L.

7. The method for deep denitrification of eutrophic water according to claim 1, wherein: The resin is any one or more of Kehaisi A-62MP and Ningbo Zhengguang D890.

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