Method for enhancing denitrification of nano-iron adaptive microorganisms

Abstract

The invention discloses a method for enhancing denitrification of nano-iron adaptive microorganisms, and belongs to the technical field of water pollution control. The method comprises the following steps: preparing extracellular polymeric substance (EPS) and iron sulfide co-doped modified nano-iron (E (at) SnZVI) through a mechanical ball milling method or a liquid phase chemical reduction-co-precipitation method; the method comprises the following steps: adjusting the pH value of nitrate-containing wastewater to be treated to 5.0-7.0; (2) adding the E (at) SnZVI prepared in the step (1) into the wastewater according to the adding amount of 150 mg / L, inoculating domesticated denitrifying bacteria mixed liquor (MLSS is 3000 mg / L), and controlling the C / N ratio of the system to be 2-5; reacting under an anoxic condition, and monitoring the concentration change of nitrate, nitrite, ammonia nitrogen and nitrogen in the system until the reaction is balanced. In the wastewater with low carbon-nitrogen ratio (C / N = 2), the reaction period is shortened from more than 24 hours to 4-8 hours, and the method is suitable for a continuous flow treatment process. EPS is natural secreta of microorganisms, FeSx is low in toxicity, reaction products are iron oxide and nitrogen, and secondary pollution is avoided; no additional carbon source is needed, and the policy requirements of pollution reduction and carbon reduction are met.

Description

Technical Field

[0001] This invention belongs to the field of water pollution control technology and relates to a method for enhancing microbial targeted denitrification. It improves the compatibility between nano-iron and microorganisms by co-doping extracellular polymeric substances (EPS) and iron sulfide (FeSx), thereby achieving targeted denitrification of wastewater with a low carbon-to-nitrogen ratio. Background Technology

[0002] With the acceleration of industrialization and urbanization, nitrate pollution in water bodies has become an urgent environmental problem. Nitrates not only cause eutrophication and disrupt the aquatic ecological balance, but they can also enter the human body through drinking water. In the acidic environment of the stomach, they are converted into nitrites, which then combine with amines to form highly carcinogenic nitrosamines, inducing diseases such as liver cancer and stomach cancer. Infants who ingest high concentrations of nitrates may also develop methemoglobinemia, which can be life-threatening in severe cases.

[0003] For nitrate removal, microbial denitrification is the mainstream treatment process. Its principle is that denitrifying bacteria use nitrate as an electron acceptor, gradually reducing it to nitrogen gas under anaerobic conditions. However, in wastewater with low carbon-to-nitrogen ratios or low biodegradability, insufficient carbon sources lead to a lack of electron donors, hindering the metabolism of denitrifying bacteria and ultimately resulting in low nitrate removal rates, nitrite accumulation, and long reaction cycles. Traditional solutions involve adding carbon sources such as sodium acetate and glucose to the wastewater to maintain microbial activity and promote nitrate reduction. However, this method has drawbacks such as high reagent consumption, unstable effluent quality, and increased carbon emissions. Nano-iron (nZVI), with its high specific surface area, excellent electron density, and environmental compatibility, can serve as an electron donor in the auxiliary microbial denitrification process. Compared with the traditional carbon source-microbial denitrification process, nano-iron-microbial denitrification technology can reduce nitrate content in water and save on carbon source usage, which aligns perfectly with my country's policy requirements for carbon reduction and nitrogen removal.

[0004] However, there are limitations to the synergistic effect of nano-iron with microorganisms. Nano-iron readily undergoes a corrosion reaction with hydrogen ions in water, leading to the easy competitive consumption of nano-iron electrons by non-target reactive species, which greatly reduces the utilization efficiency of nano-iron electrons by microorganisms. At the same time, the iron ions produced by the corrosion reaction hydrolyze and form a dense iron (hydroxyl) oxide film, which hinders the transfer rate of nano-iron electrons to microorganisms. In addition, nano-iron may cause microbial poisoning or inactivation through cell invasion and membrane damage, which can further impact the microbial water treatment system.

[0005] In the reference (Sci. Total Environ. 2020, 708: 135063), the authors found that introducing the noble metal Pd into the interface of nano-iron increased the removal rate of nitrate by microorganisms by 31.5% and reduced nitrite accumulation by 18.1%. However, it should be emphasized that although this enhancement method can improve the conductivity of nano-iron and accelerate the removal rate of nitrate, the improvement in nitrogen selectivity is still relatively limited. In the reference (J. Am. Chem. Soc. 2024, 146(47):32785—32794), the authors proposed introducing oxalic acid into the surface of nano-iron to improve the electron transfer efficiency of nano-iron by adjusting the surface proton concentration. However, this method will cause excessive hydrogen generation, resulting in a waste of electron source, and may also disrupt the reduction pathway of nitrate (i.e., generate ammonia nitrogen). Therefore, in order to enhance the denitrification performance of the nano-iron-microbial system for wastewater with low carbon-nitrogen ratio, it is urgent to develop a method that can both increase the rate of electron transfer from nano-iron to microorganisms and improve the targeting of nano-iron electron transfer to microorganisms. Summary of the Invention

[0006] To overcome the problems of low electron transfer rate and poor targeting in existing nano-iron systems, this invention provides a method to enhance the adaptation of nano-iron to microbial denitrification. This method optimizes the electron transfer rate and electron donor targeting of nano-iron by introducing iron sulfide (FeSx) and extracellular polymeric substances (EPS) at the nano-iron interface. This allows for precise regulation of electron transfer from nano-iron to microorganisms, achieving a match between the electrons released by nano-iron and the electron supply and demand required for the denitrification process of denitrifying bacteria. This method can improve the removal rate of nitrates from low C / N ratio wastewater by the nano-iron-microbial system, reduce ammonia nitrogen formation, and ensure the effective utilization of the nano-iron electron source by microorganisms.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for enhancing denitrification of nano-iron-adapted microorganisms, the method comprising:

[0009] Step 1: Modified iron nanoparticles (E@SnZVI) co-doped with extracellular polymeric material (EPS) and iron sulfide (FeSx) are prepared by mechanical ball milling or liquid-phase chemical reduction-coprecipitation method, with the mass ratio of EPS to Fe controlled at 0.1~0.5:1 and the molar ratio of S / Fe controlled at 0.1~0.5:1.

[0010] Step 2: Adjust the pH of the nitrate-containing wastewater to 5.0~7.0 using hydrochloric acid or sodium hydroxide. This pH range can prevent the functional groups in EPS from being protonated and deactivated, while ensuring the activity of denitrifying bacteria.

[0011] Step 3: Add E@SnZVI prepared in step (1) to the wastewater at a dosage of 150 mg / L, and simultaneously introduce the acclimatized denitrifying bacteria mixture (MLSS of 3000 mg / L), controlling the C / N ratio of the system to 2~5 (the carbon source is the original organic matter in the wastewater, and no additional addition is required).

[0012] Step 4: React under anaerobic conditions, monitor the changes in the concentrations of nitrate, nitrite, ammonia nitrogen, and nitrogen in the system until the nitrate concentration stabilizes (change rate < 5% / h), indicating that the reaction has reached equilibrium.

[0013] Further, in step one, the mechanical ball milling method specifically involves: placing micron-sized iron powder and steel balls into a ball mill jar at a mass ratio of 1:10~50, adding FeSx and EPS, and grinding at 300~500 rpm for 20~24 h under nitrogen protection (to prevent oxidation). Particle refinement and doping are achieved through the impact and friction between the steel balls and the iron powder. The product E@SnZVI is collected by magnetic separation and then vacuum dried. EPS is extracted by ethanol precipitation: the supernatant containing EPS is mixed with anhydrous ethanol at a volume ratio of 1:3, allowed to stand at 4℃, and then centrifuged at 12000 rpm for 20 min. The precipitate is purified by ultrafiltration and then freeze-dried into powder.

[0014] Furthermore, in step one, the liquid-phase chemical reduction-coprecipitation method specifically refers to:

[0015] (1) Dissolve FeCl3 in deionized water to prepare a solution with a concentration of 0.02 mol / L, and aerate with nitrogen gas (0.1~0.5L / min) for 10~15 min to remove dissolved oxygen;

[0016] (2) Mix NaBH4 with EPS was dissolved in deionized water to prepare a mixed reducing agent solution, which was then added to the solution from step (1) at a rate of 5-15 mL / min using a peristaltic pump. The reaction was allowed to proceed for 5-10 min to generate E@SnZVI nanoparticles (reaction formula: Fe 3+ + +S 2- →FeSx↓+ Centrifuge at 3000~6000 rpm for 1~5 min, wash with ethanol 2~4 times to remove impurities, and obtain E@SnZVI, which is stored in ethanol for later use.

[0017] Furthermore, in step two, the concentration of nitrate in the wastewater to be treated is 100~500 mg / L. Other indicators such as COD and trace elements should be as compatible as possible with the survival requirements of denitrifying bacteria.

[0018] Furthermore, in step three, the denitrifying bacteria are acclimatized with a culture medium containing 1.0 g / L KNO3, and the nitrate concentration is gradually increased to 1000 mg / L during the acclimatization process.

[0019] Furthermore, in step four, the anoxic conditions are maintained by sealing the reactor and introducing nitrogen gas (0.1~0.5 L / min), and the dissolved oxygen concentration is controlled at 1~3 mg / L (strict anoxic conditions will inhibit the respiratory metabolism of some denitrifying bacteria).

[0020] Furthermore, in step four, the reaction temperature is controlled at 30~35℃ and the oscillation rate is 120~150 rpm.

[0021] The advantages of this invention over the prior art are as follows:

[0022] (1) Improved denitrification efficiency and directionality: Nitrate removal rate increased from below 50% to above 98%, nitrogen production rate increased from <60% to above 80%, and ammonia nitrogen generation rate decreased to below 8%, solving the problem of excessive by-products.

[0023] (2) Optimization of electron utilization: The electron efficiency of nZVI is significantly improved, more than 50% higher than that of unmodified nZVI. Under the same processing volume, the consumption of nZVI is reduced by 50%, and the operating cost is reduced by 30%~40%.

[0024] (3) Shortened reaction cycle: In wastewater with low carbon-to-nitrogen ratio (C / N=2), the reaction cycle is shortened from more than 24 hours to 4-8 hours, which is suitable for continuous flow treatment processes.

[0025] (4) Enhanced environmental compatibility: EPS is a natural secretion of microorganisms, FeSx has low toxicity, and the reaction products are iron oxide and nitrogen gas, with no secondary pollution; and no additional carbon source is required, which meets the requirements of the "pollution reduction and carbon reduction" policy.

[0026] (5) Wide applicability: It can treat low carbon-to-nitrogen ratio wastewater (C / N = 2~5) from industries such as chemical, electronics, and food, and still maintains stable performance for wastewater containing complex organic matter (such as aromatics and heterocyclic compounds). Attached Figure Description

[0027] Figure 1 The image shows the effect of FeSx and EPS doping on the synergistic microbial denitrification of nano-iron in Example 1.

[0028] Figure 2 This is a diagram illustrating the effect of FeSx and EPS doping on the synergistic microbial denitrification of nano-iron in Example 2.

[0029] Figure 3 This is a diagram illustrating the effect of FeSx and EPS doping on the synergistic microbial denitrification of nano-iron in Example 3.

[0030] Figure 4 This is a diagram illustrating the effect of FeSx and EPS doping on the synergistic microbial denitrification of nano-iron in Example 4.

[0031] Figure 5 This is a diagram illustrating the effect of FeSx and EPS doping on the synergistic microbial denitrification of nano-iron in Example 5.

[0032] Figure 6 This is a diagram illustrating the effect of FeSx and EPS doping on the synergistic microbial denitrification of nano-iron in Example 6.

[0033] Figure 7 This is a diagram illustrating the effect of FeSx and EPS doping on the synergistic microbial denitrification of nano-iron in Example 7.

[0034] Figure 8 This is a diagram illustrating the effect of FeSx and EPS doping on the synergistic microbial denitrification of nano-iron in Example 8.

[0035] Figure 9 This is a graph showing the effect of FeSx and EPS doping on the selective nitrogen removal of nano-iron by microorganisms in Example 9.

[0036] Figure 10 The graph shows the effect of FeSx and EPS doping on the synergistic effect of nano-iron on the removal rate of nitrate by microbial denitrification. Detailed Implementation

[0037] The technical solution of the present invention will be further described below with reference to specific embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0038] This invention addresses the problems of slow reaction rate, low electron utilization, ammonia nitrogen accumulation as a byproduct, and insufficient microbial adaptability in existing nZVI-assisted microbial denitrification technologies. It provides a method for enhanced microbial targeted denitrification based on EPS and FeSx co-doped nano-iron, improving the targeted denitrification of low C / N ratio wastewater by the nano-iron-microbial system. The core of this invention lies in utilizing the synergistic effect of EPS and FeSx to regulate the balance between electrons donated by nano-iron and electrons required by the microorganisms, ultimately achieving targeted denitrification in the denitrification system.

[0039] This invention achieves synergistic effects through co-doping of EPS and FeSx. The core mechanism is as follows: Enhanced electron transfer rate of nano-iron: FeSx forms a highly conductive network on the surface of nano-iron. Simultaneously, the carboxyl groups (-COOH) and phosphate groups (-PO3H2) in EPS can replenish the H+ consumed on the surface through proton transfer. + Inhibit Fe 2+Hydrolysis and passivation film formation prevent the formation of non-conductive passivation films, ultimately synergistically promoting the rate of electron transfer from the nano-iron core to microorganisms. Enhanced electron targeting of nano-iron: FeSx effectively inhibits corrosion side reactions of nano-iron, avoiding electron waste and ammonia nitrogen generation. Simultaneously, the quinone groups of EPS can act as electron shuttles, further improving the targeted electron transfer between microorganisms and nano-iron. Furthermore, as a natural extracellular component of microorganisms, EPS can reduce the toxicity of nano-iron to bacteria, ultimately improving the compatibility between nano-iron and microorganisms.

[0040] Example 1

[0041] Step 1: Modified nano-iron (E@SnZVI) co-doped with extracellular polymeric material (EPS) and iron sulfide (FeSx) was prepared by mechanical ball milling. The mass ratio of EPS to Fe was controlled at 0.1~0.5:1, and the molar ratio of S / Fe was controlled at 0.1~0.5:1. The mechanical ball milling method was as follows: micron-sized iron powder and steel balls were loaded into a ball mill jar at a mass ratio of 1:10. FeSx and EPS were added, and the mixture was ground at 500 rpm for 24 h under nitrogen protection (to prevent oxidation). The particles were refined and doped by the impact and friction between the steel balls and the iron powder. The product E@SnZVI was collected by magnetic separation and then vacuum dried.

[0042] Step 2: Adjust the pH of the nitrate-containing wastewater to 6.5 using hydrochloric acid or sodium hydroxide. This pH range can prevent the functional groups in EPS from being protonated and deactivated, while ensuring the activity of denitrifying bacteria. The wastewater contains 300 mg / L nitrate, 600 mg / L COD (C / N=2), and 1 g / L NaCl.

[0043] Step 3: Reaction system: Add 300 mL of wastewater to a 500 mL serum bottle, add E@SnZVI (preparation) to a concentration of 150 mg / L, inoculate with 10% (v / v) acclimatization bacterial solution (M LSS=3000 mg / L), seal with butyl rubber stopper, purge with nitrogen (0.2 L / min) for 10 min to remove oxygen, and place in a 30℃ constant temperature water bath for shaking reaction at 150 rpm.

[0044] Monitoring results: Sampling was conducted periodically from 0 to 6 hours. Nitrate concentration decreased from 300 mg / L to 5.8 mg / L (removal rate 98%), and the maximum nitrite accumulation was 12 mg / L (4 hours), eventually decreasing to 0.5 mg / L. Nitrogen production in the gas phase was 42.6 ml (82% of theoretical production), and ammonia nitrogen concentration was 5.3 mg / L. Compared to the unmodified nZVI group (under the same conditions), nitrate removal rate and nitrogen production were significantly increased, while ammonia nitrogen concentration was significantly decreased. See details below. Figure 1 .

[0045] Example 2

[0046] Step 1: Modified nano-iron (E@SnZVI) co-doped with extracellular polymeric material (EPS) and iron sulfide (FeSx) is prepared by liquid-phase chemical reduction-coprecipitation method, controlling the mass ratio of EPS to Fe to be 0.1~0.5:1 and the molar ratio of S / Fe to be 0.1~0.5:1; the liquid-phase chemical reduction-coprecipitation method is as follows: (1) FeCl3 is dissolved in deionized water to prepare a solution with a concentration of 0.02mol / L, and nitrogen gas (0.2 L / min) is introduced for aeration for 10 min to remove dissolved oxygen; (2) NaBH4 and EPS was dissolved in deionized water to prepare a mixed reducing agent solution, which was added to the solution in step (1) at a rate of 10 mL / min using a peristaltic pump. After reacting for 5 min, E@SnZVI nanoparticles were generated (reaction formula: Fe 3+ + +S 2- →FeSx↓+ +H2↑); Centrifuge at 4500 rpm for 1 min, wash three times with ethanol to remove impurities, and obtain E@SnZVI, which is stored in ethanol for later use.

[0047] Step 2: Adjust the pH of the nitrate-containing wastewater to 6.5 using hydrochloric acid or sodium hydroxide. This pH range can prevent the functional groups in EPS from being protonated and deactivated, while ensuring the activity of denitrifying bacteria. The wastewater contains 300 mg / L nitrate, 300 mg / L COD (C / N = 3), and 1 g / L NaCl. The suspended solids are removed through pretreatment.

[0048] Step 3: Reaction System: Add 300 mL of wastewater to a 500 mL serum bottle, add E@SnZVI (prepared) to achieve a concentration of 150 mg / L, and inoculate with 10% (v / v) acclimated denitrifying bacteria solution (M LSS = 3000 mg / L). Control the reaction temperature at 30-35℃ and the shaking rate at 120-150 rpm, maintaining an anaerobic environment (DO 1-3 mg / L) with nitrogen. Monitoring after reaction equilibrium showed that this system achieved a nitrate removal rate >90%, a nitrogen yield >75%, and ammonia nitrogen generation <10 mg / L in actual wastewater. Furthermore, the biodegradability of the wastewater (BOD5 / COD) was improved compared to before treatment, and no secondary pollution occurred. See details below. Figure 2 .

[0049] Example 3

[0050] Step 1: Modified nano-iron (E@SnZVI) co-doped with extracellular polymeric material (EPS) and iron sulfide (FeSx) was prepared by mechanical ball milling. The mass ratio of EPS to Fe was controlled at 0.1~0.5:1, and the molar ratio of S / Fe was controlled at 0.1~0.5:1. The mechanical ball milling method was as follows: micron-sized iron powder and steel balls were loaded into a ball mill jar at a mass ratio of 1:10. FeSx and EPS were added, and the mixture was ground at 500 rpm for 24 h under nitrogen protection (to prevent oxidation). The particles were refined and doped by the impact and friction between the steel balls and the iron powder. The product E@SnZVI was collected by magnetic separation and then vacuum dried.

[0051] Step 2: Adjust the pH of the nitrate-containing wastewater to 6.5 using hydrochloric acid or sodium hydroxide. This pH range can prevent the functional groups in EPS from being protonated and deactivated, while ensuring the activity of denitrifying bacteria. The wastewater to be treated is low biodegradability wastewater containing 280 mg / L nitrate, 520 mg / L COD (C / N = 1.88), 12 mg / L benzene series compounds, and BOD5 / COD = 0.22. Two experimental groups were set up: nZVI+ bacteria and E@SnZVI+ bacteria, with simulated wastewater as a control. The dosage of both types of nano-iron was 150 mg / L, and the bacterial solution dosage was 10% (v / v). The reaction was carried out at 30℃, 150 rpm shaking, and nitrogen was maintained at DO = 1~3 mg / L for 8 hours. The results showed that the E@SnZVI+ bacteria group achieved a nitrate removal rate of 92.7%, a nitrogen yield of 75.3%, and ammonia nitrogen of 7.8 mg / L. Simultaneously, the BOD5 / COD ratio increased to 0.38 (due to improved biodegradability), and the benzene series removal rate reached 68.3%. In contrast, the nZVI+ bacteria group had a removal rate below 60%, demonstrating that this technology can stably and efficiently remove nitrogen even in actual wastewater containing complex organic matter. (See details below.) Figure 3 .

[0052] Example 4

[0053] Step 1: Modified nano-iron (E@SnZVI) co-doped with extracellular polymeric material (EPS) and iron sulfide (FeSx) was prepared by mechanical ball milling. The mass ratio of EPS to Fe was controlled at 0.1~0.5:1, and the molar ratio of S / Fe was controlled at 0.1~0.5:1. The mechanical ball milling method was as follows: micron-sized iron powder and steel balls were loaded into a ball mill jar at a mass ratio of 1:10. FeSx and EPS were added, and the mixture was ground at 500 rpm for 24 h under nitrogen protection (to prevent oxidation). The particles were refined and doped by the impact and friction between the steel balls and the iron powder. The product E@SnZVI was collected by magnetic separation and then vacuum dried.

[0054] Step 2: Adjust the pH of the nitrate-containing wastewater to 6.5 using hydrochloric acid or sodium hydroxide. This pH range can prevent the functional groups in EPS from being protonated and deactivated, while ensuring the activity of denitrifying bacteria. The wastewater to be treated is the discharge wastewater from the Jinmaoyuan Electroplating Industrial Park in Huizhou, Guangdong (derived from a mixture of pretreatment, copper plating, zinc alkali wastewater, and RO concentrate). Its COD is 135 mg / L (containing benzotriazole 8 mg / L and sodium m-nitrobenzenesulfonate 5 mg / L), TN is 64.5 mg / L (nitrate nitrogen 8.7 mg / L and organic nitrogen 55 mg / L), C / N ratio is 2.1, and pH is 6.5.

[0055] Step 3: Take 300 mL of wastewater into a serum bottle, add E@SnZVI to 150 mg / L, add 10% (v / v) acclimation denitrifying bacteria solution (MLSS 3000 mg / L), fine-tune the pH to 6.2, purge with nitrogen (0.2 L / min) to control DO 1.5~2.5 mg / L, and react in a 32℃ constant temperature water bath with shaking at 140 rpm. After 6 h, COD drops to 45 mg / L (benzotriazole degradation rate 85%), TN drops to 12.3 mg / L (removal rate 80.9%), nitrate nitrogen drops to 0.4 mg / L (removal rate 95.4%), and ammonia nitrogen generation is <8%. The reaction cycle is shortened to 6 h compared to the traditional process, no additional carbon source is required, and the operating cost is reduced by 35%. See details. Figure 4 .

[0056] Example 5

[0057] Step 1: Modified nano-iron (E@SnZVI) co-doped with extracellular polymeric material (EPS) and iron sulfide (FeSx) is prepared by liquid-phase chemical reduction-coprecipitation method, controlling the mass ratio of EPS to Fe to be 0.1~0.5:1 and the molar ratio of S / Fe to be 0.1~0.5:1; the liquid-phase chemical reduction-coprecipitation method is as follows: (1) FeCl3 is dissolved in deionized water to prepare a solution with a concentration of 0.02mol / L, and nitrogen gas (0.2 L / min) is introduced for aeration for 10 min to remove dissolved oxygen; (2) NaBH4 and EPS was dissolved in deionized water to prepare a mixed reducing agent solution, which was added to the solution in step (1) at a rate of 10 mL / min using a peristaltic pump. After reacting for 5 min, E@SnZVI nanoparticles were generated (reaction formula: Fe 3+ + +S 2- →FeSx↓+ +H2↑); Centrifuge at 4500 rpm for 1 min, wash three times with ethanol to remove impurities, and obtain E@SnZVI, which is stored in ethanol for later use.

[0058] Step 2: Adjust the pH of the nitrate-containing wastewater to 6.2 using hydrochloric acid or sodium hydroxide. This pH range can prevent the functional groups in EPS from being protonated and deactivated, while ensuring the activity of denitrifying bacteria. The wastewater to be treated is the tailwater after anoxic + aerobic treatment in the Taixing Economic Development Zone Chemical Industrial Park (TN < 15 mg / L for upgrading), with COD 150 mg / L (containing anthraquinone 3 mg / L, lignin 5 mg / L, BOD5 / COD = 0.12), TN 35 mg / L (nitrate nitrogen 18 mg / L, organic nitrogen 14 mg / L), C / N 1.8, and pH 6.2.

[0059] Step 3: Take 800 mL of effluent into the reactor, add E@SnZVI to 150 mg / L, and inoculate with 12% (v / v) acclimation denitrifying bacteria solution (MLSS 3000 mg / L). Purge nitrogen to control DO at 1.2~2.0 mg / L. Incubate at 34℃ with shaking in a water bath at 130 rpm. After 8 h, COD decreased to 68 mg / L (BOD5 / COD increased to 0.35), TN decreased to 11.2 mg / L (removal rate 68.0%), nitrate nitrogen decreased to 0.8 mg / L (removal rate 95.6%), and organic nitrogen decreased to 3.5 mg / L (degradation rate 75.0%). Ammonia nitrogen generation was <6%, and the electron utilization rate of nano-iron reached 62% (55% higher than unmodified nZVI). After 15 days of continuous operation, no obvious passivation film was observed, and the viable bacteria rate remained above 85%. See details... Figure 5 .

[0060] Example 6

[0061] Step 1: Modified nano-iron (E@SnZVI) co-doped with extracellular polymeric material (EPS) and iron sulfide (FeSx) was prepared by mechanical ball milling. The mass ratio of EPS to Fe was controlled at 0.1~0.5:1, and the molar ratio of S / Fe was controlled at 0.1~0.5:1. The mechanical ball milling method was as follows: micron-sized iron powder and steel balls were loaded into a ball mill jar at a mass ratio of 1:10. FeSx and EPS were added, and the mixture was ground at 500 rpm for 24 h under nitrogen protection (to prevent oxidation). The particles were refined and doped by the impact and friction between the steel balls and the iron powder. The product E@SnZVI was collected by magnetic separation and then vacuum dried.

[0062] Step 2: Adjust the pH of the nitrate-containing wastewater to 6.5 using hydrochloric acid or sodium hydroxide. This pH range can prevent the functional groups in EPS from being protonated and deactivated, while ensuring the activity of denitrifying bacteria. The wastewater to be treated is collected from an electronics factory with a low carbon-to-nitrogen ratio (C / N=2~5) and nitrate content. Add 150 mg / L of prepared E@SnZVI and inoculate with acclimatized denitrifying bacteria solution (MLSS about 3000 mg / L). Control the reaction temperature at 30~35 ℃ and the oscillation rate at 120~150 rpm. Maintain an anaerobic environment (DO 1~3 mg / L) using nitrogen. Post-equilibrium monitoring showed that the system achieved a nitrate removal rate >90%, a nitrogen yield >75%, and ammonia nitrogen generation <10 mg / L in wastewater from the electronics industry. Furthermore, no new pollutants were added after wastewater treatment, meeting the requirements of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB18918-2002). This confirms the suitability of the E@SnZVI-microbial system for low C / N ratio wastewater from the electronics industry. See details below. Figure 6 .

[0063] Example 7

[0064] Step 1: Modified nano-iron (E@SnZVI) co-doped with extracellular polymeric material (EPS) and iron sulfide (FeSx) is prepared by liquid-phase chemical reduction-coprecipitation method, controlling the mass ratio of EPS to Fe to be 0.1~0.5:1 and the molar ratio of S / Fe to be 0.1~0.5:1; the liquid-phase chemical reduction-coprecipitation method is as follows: (1) FeCl3 is dissolved in deionized water to prepare a solution with a concentration of 0.02mol / L, and nitrogen gas (0.2 L / min) is introduced for aeration for 10 min to remove dissolved oxygen; (2) NaBH4 and EPS was dissolved in deionized water to prepare a mixed reducing agent solution, which was added to the solution in step (1) at a rate of 10 mL / min using a peristaltic pump. After reacting for 5 min, E@SnZVI nanoparticles were generated (reaction formula: Fe 3+ + +S 2- →FeSx↓+ +H2↑); Centrifuge at 4500 rpm for 1 min, wash three times with ethanol to remove impurities, and obtain E@SnZVI, which is stored in ethanol for later use.

[0065] Step 2: Adjust the pH of the nitrate-containing wastewater to 6.2 using hydrochloric acid or sodium hydroxide. This pH range can prevent the functional groups in EPS from being protonated and deactivated, while ensuring the activity of denitrifying bacteria. The wastewater to be treated was collected from the secondary effluent of a municipal sewage treatment plant (nitrate 80 mg / L, COD 160 mg / L, C / N=2, pH=7.2).

[0066] Step 3: Take 500 mL of the solution in a reaction flask, add 150 mg / L LE@SnZVI, and inoculate with 10% (v / v) acclimation denitrifying bacteria solution (MLSS = 3000 mg / L). Fine-tune the pH to 6.8, and control the DO to 1.5~2.5 mg / L by purging with nitrogen. React at 32℃ and 140 rpm for 6 h. The results show that the nitrate concentration decreased to 2.4 mg / L (removal rate 97%), ammonia nitrogen was 7.2 mg / L, nitrogen production was 78%, and effluent COD < 50 mg / L. The water quality is superior to the Class A standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB 18918—2002). See details below. Figure 7 .

[0067] Example 8

[0068] Step 1: Modified nano-iron (E@SnZVI) co-doped with extracellular polymeric material (EPS) and iron sulfide (FeSx) was prepared by mechanical ball milling. The mass ratio of EPS to Fe was controlled at 0.1~0.5:1, and the molar ratio of S / Fe was controlled at 0.1~0.5:1. The mechanical ball milling method was as follows: micron-sized iron powder and steel balls were loaded into a ball mill jar at a mass ratio of 1:10. FeSx and EPS were added, and the mixture was ground at 500 rpm for 24 h under nitrogen protection (to prevent oxidation). The particles were refined and doped by the impact and friction between the steel balls and the iron powder. The product E@SnZVI was collected by magnetic separation and then vacuum dried.

[0069] Step 2: The pH of the nitrate-containing wastewater to be treated was adjusted to 6.5 using hydrochloric acid or sodium hydroxide. This pH range can prevent the functional groups in EPS from being protonated and deactivated, while ensuring the activity of denitrifying bacteria. The wastewater to be treated was designed for a specific agricultural area with groundwater (nitrate 120 mg / L, COD 60 mg / L, C / N=0.5, pH=6.8) lacking carbon sources. 150 mg / L of LE@SnZVI was added, along with 12% (v / v) of highly active acclimation bacteria solution (MLSS=3000 mg / L). The pH was adjusted to 6.5, and nitrogen was purged to maintain DO=1.0~2.0 mg / L. The reaction was carried out at 30℃ and 120 rpm for 8 h. The results showed that the nitrate removal rate reached 96% (reduced to 4.8 mg / L), the nitrogen yield was 76%, and the ammonia nitrogen was <6 mg / L. This confirms that this method can still efficiently drive denitrification and maintain stable bacterial activity under extremely low C / N ratio conditions. See details below. Figure 8 .

[0070] Example 9

[0071] Step 1: Modified nano-iron (E@SnZVI) co-doped with extracellular polymeric material (EPS) and iron sulfide (FeSx) was prepared by mechanical ball milling. The mass ratio of EPS to Fe was controlled at 0.1~0.5:1, and the molar ratio of S / Fe was controlled at 0.1~0.5:1. The mechanical ball milling method was as follows: micron-sized iron powder and steel balls were loaded into a ball mill jar at a mass ratio of 1:10. FeSx and EPS were added, and the mixture was ground at 500 rpm for 24 h under nitrogen protection (to prevent oxidation). The particles were refined and doped by the impact and friction between the steel balls and the iron powder. The product E@SnZVI was collected by magnetic separation and then vacuum dried.

[0072] Step 2: Adjust the pH of the nitrate-containing wastewater to 6.5 using hydrochloric acid or sodium hydroxide. This pH range can prevent the functional groups in EPS from being protonated and deactivated, while ensuring the activity of denitrifying bacteria. The wastewater to be treated is selected from a eutrophic lake (nitrate 60 mg / L, COD 100 mg / L, C / N=1.67, pH=7.5, containing algal secretions).

[0073] Step 3: Take 300 mL of water sample, add 150 mg / L LE@SnZVI, and inoculate with 10% (v / v) denitrifying bacteria solution (MLSS = 3000 mg / L). Adjust the pH to 7.0, control the DO = 1.5~2.5 mg / L, and react at 30℃ and 150 rpm for 6 h. The results show that the nitrate removal rate is 97% (reduced to 1.8 mg / L), ammonia nitrogen <5 mg / L, nitrogen production rate is 80%, algal toxin degradation rate is >50%, and effluent transparency is improved. This indicates that the technology has a synergistic purification effect on nitrate and organic micropollutants in natural water bodies. See details below. Figure 9 and Figure 10 .

Claims

1. A method for enhancing denitrification of nano-iron-adapted microorganisms, characterized in that: The method is as follows: Step 1: Modified iron nanoparticles (E@SnZVI) co-doped with extracellular polymeric material (EPS) and iron sulfide (FeSx) are prepared by mechanical ball milling or liquid-phase chemical reduction-coprecipitation method, with the mass ratio of EPS to Fe controlled at 0.1~0.5:1 and the molar ratio of S / Fe controlled at 0.1~0.5:

1. Step 2: Adjust the pH of the nitrate-containing wastewater to 5.0~7.0; Step 3: Add E@SnZVI prepared in step (1) to the wastewater at a dosage of 150 mg / L, and simultaneously introduce the acclimatized denitrifying bacteria mixture (MLSS of 3000 mg / L) to control the C / N ratio of the system to 2~5; Step 4: React under anaerobic conditions, and monitor the changes in the concentrations of nitrate, nitrite, ammonia nitrogen, and nitrogen in the system until the reaction reaches equilibrium.

2. The method according to claim 1, characterized in that: In step one, the mechanical ball milling method is specifically as follows: micron-sized iron powder and steel balls are loaded into a ball mill jar at a mass ratio of 1:10~50, FeSx and EPS are added, and the mixture is ground at a speed of 300~500 rpm for 20~24 h under nitrogen protection. The product E@SnZVI is collected by magnetic separation and then vacuum dried.

3. The method according to claim 1, characterized in that: In step one, the liquid-phase chemical reduction-coprecipitation method specifically refers to: (1) Dissolve FeCl3 in deionized water to prepare a solution with a concentration of 0.02 mol / L, and aerate with nitrogen gas (0.1~0.5 L / min) for 10~15 min to remove dissolved oxygen; (2) Mix NaBH4 with EPS was dissolved in deionized water to prepare a mixed reducing agent solution, which was then added to the solution from step (1) at a rate of 5-15 mL / min using a peristaltic pump. The reaction was allowed to proceed for 5-10 min to generate E@SnZVI nanoparticles (reaction formula: Fe 3+ + +S 2- →FeSx↓+ Centrifuge at 3000~6000 rpm for 1~5 min, wash with ethanol 2~4 times to remove impurities, and obtain E@SnZVI, which is stored in ethanol for later use.

4. The method according to claim 1, characterized in that: In step two, the concentration of nitrate in the wastewater to be treated is 100~500 mg / L.

5. The method according to claim 1, characterized in that: In step three, the denitrifying bacteria are acclimatized in a culture medium containing 1.0 g / L KNO3, and the nitrate concentration is gradually increased to 1000 mg / L during the acclimatization process.

6. The method according to claim 1, characterized in that: In step four, the anoxic conditions are maintained by sealing the reactor and introducing nitrogen gas (0.1~0.5 L / min), and the dissolved oxygen concentration is controlled at 1~3 mg / L.

7. The method according to claim 1, characterized in that: In step four, the reaction temperature is controlled at 30~35℃ and the oscillation rate is 120~150 rpm.

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