A nano zero-valent iron composite sponge filler, a preparation method thereof and a nitrate wastewater denitrification method

Abstract

The application discloses a kind of nano zero-valent iron composite sponge fillers and preparation method and nitrate wastewater denitrification method thereof, and relates to wastewater treatment material technical field.Polyurethane sponge is used as matrix, and nano zero-valent iron composite sponge filler is prepared by sequentially dipping PVA-PQ-10 / water-based polyurethane modified adhesive, FeCl3 solution crosslinking, NaBH4 solution reduction and other steps.The application utilizes modified adhesive to give the surface of carrier positive electricity and hydrophilicity, significantly enhances its biological affinity;And by in-situ reduction method, nano zero-valent iron is stably loaded in the three-dimensional network structure of sponge.The nano zero-valent iron composite sponge filler prepared by the application has high reactivity, excellent denitrification effect and good sludge granulation capacity, and is suitable for wastewater treatment.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment materials technology, specifically to a nano-zero-valent iron composite sponge filler, its preparation method, and a method for denitrifying nitrate wastewater. Background Technology

[0002] With the acceleration of industrialization and urbanization, eutrophication and health risks caused by nitrate pollution have become a global environmental challenge. Biological denitrification technology, due to its advantages such as low cost, high efficiency, and environmental friendliness, has become an important research direction in the field of wastewater treatment. Among them, biological denitrification, as the core process for removing nitrates from wastewater, relies on microorganisms to denitrate (NO3) into nitrogen dioxide. - The carbon-to-nitrogen ratio of wastewater is gradually reduced to nitrogen (N2), and its efficiency is comprehensively regulated by electron donors, microbial communities, and environmental factors. However, domestic wastewater generally has a low carbon-to-nitrogen ratio, which often leads to a lack of electron donors in the denitrification process. To ensure effluent quality, most wastewater treatment plants choose organic carbon sources as external carbon sources, which greatly increases operating costs and the risk of organic matter concentration exceeding standards.

[0003] To overcome carbon source limitations, many studies have focused on exploring autotrophic denitrification biological nitrogen removal technologies. Among them, nano-zero-valent iron (nZVI) has attracted widespread attention due to its strong reducing properties, high electron donation capacity, and environmentally friendly characteristics. nZVI mainly promotes the nitrogen removal process through three pathways: First, its surface electrons can directly chemically reduce NO3. - -N is N2; secondly, Fe produced by corrosion 2+It can participate in the microbial electron transport chain as an electron shuttle; third, the H2 generated in the reaction can serve as a high-quality electron donor. Theoretically, the addition of nZVI can achieve highly efficient denitrification without an external carbon source. However, nZVI also has many drawbacks in its application. Due to its high surface energy, nZVI easily forms micron-sized aggregates, leading to a reduction in active sites, which lowers electron utilization and reusability. At the same time, nZVI exposed to air will quickly form an oxide layer, which will severely hinder electron transport efficiency, limit the electron supply to the target pollutants, and reduce removal efficiency. In order to ensure the continuous high activity of nZVI in the system and its continuous enhancement effect on microbial metabolism, the dosage is often increased or continuously added. Studies have shown that intermittent addition of nZVI in anaerobic ammonia oxidation systems can shorten the acclimatization time of anaerobic ammonia oxidizing bacteria by 76 days and increase the denitrification efficiency to 91.07%. However, in practical applications, direct addition of nZVI will result in high operating costs, and the dosage needs to be precisely controlled. When the concentration of nZVI is too high, it will inhibit microbial activity. To overcome the problem of limited effective active sites caused by nZVI aggregation, common methods for modifying nZVI include sulfidation, carbon coating, and polymer coating to improve its stability. Studies have shown that activated carbon-coated nZVI, after high-temperature calcination, achieves more than three times the nitrate removal efficiency of pure nZVI in water. This demonstrates that dispersing nZVI on a suitable carrier material to reduce aggregation is an effective method. However, most modified nZVI composites have small particle sizes (typically between 50-500 nm), making direct recycling of nZVI composites from aqueous solutions difficult. Therefore, developing an nZVI composite material that can be prepared easily, possesses high performance, recyclability, and good biocompatibility has become a current research hotspot. Furthermore, enhancing the role of denitrifying microorganisms in nitrate wastewater treatment is also a key step in achieving efficient denitrification. Summary of the Invention

[0004] The purpose of this invention is to provide a nano-zero-valent iron composite sponge packing material, its preparation method, and a method for denitrifying nitrate wastewater, aiming to solve the technical problems of easy agglomeration, difficult recovery, and poor biocompatibility of existing nano-zero-valent iron materials. By using polyurethane sponge as a carrier, combined with impregnation modification and in-situ reduction processes, uniform loading of nano-zero-valent iron is achieved within the sponge skeleton. When this packing material is applied to the denitrification treatment of low C / N ratio nitrate wastewater, it stably provides electron donors for denitrifying bacteria and provides numerous attachment sites for functional microorganisms, forming a highly efficient "chemical-biological" synergistic denitrification pathway, thus maintaining a high denitrification effect even under low C / N ratio conditions.

[0005] In a first aspect, the present invention provides a method for preparing a nano-zero-valent iron composite sponge filler, the specific steps of which are as follows:

[0006] S1. Mix the polyvinyl alcohol solution with the polyquaternium-10 solution to obtain the PVA-PQ-10 mixture;

[0007] S2. Mix the aqueous polyurethane emulsion, deionized water and the PVA-PQ-10 mixture prepared in step S1, and homogenize for 0.5-1.5 h to obtain the modified adhesive.

[0008] S3. Immerse the polyurethane sponge in the modified adhesive until fully impregnated, and sonicate at 40 kHz for 10-20 min, then impregnate for 20-40 min to obtain the modified polyurethane sponge.

[0009] S4. Immerse the modified polyurethane sponge in a FeCl3 mixed solution for crosslinking treatment for 1.5-3 hours to obtain Fe... 3+ - Polyurethane foam;

[0010] S5, Fe 3+ Polyurethane sponge was immersed in 0.4-1.2 mol / L NaBH4 solution for 0.5-1.5 h for reduction treatment, washed 3 times with anhydrous ethanol, washed 3 times with deionized water, and then freeze-dried under vacuum to obtain nano-zero valent iron composite sponge filler.

[0011] As a preferred embodiment of the present invention, in step S1, the mass fraction of the polyvinyl alcohol solution is 8%-10%.

[0012] As a preferred embodiment of the present invention, in step S1, the mass fraction of the polyquaternium-10 solution is 3%-5%.

[0013] As a preferred embodiment of the present invention, in step S1, the volume ratio of the polyvinyl alcohol solution to the polyquaternary ammonium salt-10 solution is (10-20):1.

[0014] It should be noted that polyvinyl alcohol (PVA) molecules are rich in hydroxyl groups and hydrogen bonds, exhibiting excellent film-forming properties and water solubility. This allows it to form a uniform gel film on the surface of polyurethane (PU), which constitutes the basic framework of the modified adhesive. Polyquaternium-10 (PQ-10) is a key cationic modifier and biocompatibility enhancer. It binds to PVA molecules through ionic bonds, introducing its own quaternary ammonium cationic groups into the modified layer. This makes the carrier surface positively charged, while most bacterial cell membranes are negatively charged. The introduction of quaternary ammonium groups promotes initial adhesion to microorganisms. Simultaneously, the hydrophilicity of the quaternary ammonium groups improves the relatively hydrophobic surface of PU, making it easier for microorganisms to adhere. While PVA provides a robust framework and crosslinking sites, its surface is electrically neutral and has limited hydrophilicity. The introduction of PQ-10, without damaging the PVA framework, grafts positively charged and hydrophilic groups onto the PVA framework, improving the biocompatibility of the carrier surface.

[0015] As a preferred embodiment of the present invention, in step S2, the volume ratio of the aqueous polyurethane emulsion, deionized water and PVA-PQ-10 mixture is 5:15:2.

[0016] As a preferred embodiment of the present invention, in step S3, the ratio of the amount of polyurethane sponge to the modified adhesive is (12-18) g: 500 mL.

[0017] It should be noted that the polyurethane foam and the waterborne polyurethane emulsion (WPU) in the composition are "homogeneous but different in form." The polyurethane foam is a fully reacted cross-linked network polymer, while WPU is a linear polymer particle dispersion capable of forming a film. The PU foam has a highly cross-linked, inert surface and relatively weak adhesion to modifiers such as PVA and PQ-10. The waterborne polyurethane (WPU) has a similar chemical structure to the PU foam and good compatibility. Its addition can further enhance the interfacial bonding strength between the PVA-PQ-10 modified layer and the PU matrix, jointly constructing a uniform, robust, multifunctional polymer network with PVA and PQ-10, improving the material's mechanical strength and wear resistance, and ensuring its durability and long-term service stability.

[0018] As a preferred embodiment of the present invention, in step S4, the concentration of FeCl3 in the FeCl3 mixed solution is 0.1-0.3 mol / L, the mass fraction of ethanol is 30%, and the concentration of hydrochloric acid is 0.01 mol / L.

[0019] As a preferred embodiment of the present invention, in step S4, the ratio of the amount of modified polyurethane sponge to FeCl3 mixed solution is (25-35) g: 500 mL.

[0020] It should be noted that Fe3+ The ions can coordinate with the hydroxyl groups on the PVA molecular chain to form PVA-Fe 3+ The complexation process achieves cross-linking, significantly enhancing the stability of the modified layer. Ethanol in the mixed solution reduces the surface tension of the solution, promoting the penetration of FeCl3 solution into the porous structure inside the sponge, ensuring the stability of the Fe... 3+ The ions are uniformly distributed within the support, laying the foundation for subsequent uniform loading of nano-sized zero-valent iron. A 0.01 mol / L hydrochloric acid solution maintains an acidic environment, preventing Fe from being trapped. 3+ Premature hydrolysis of ions to form Fe(OH)3 precipitate ensures the effectiveness and uniformity of the cross-linking reaction.

[0021] As a preferred embodiment of the present invention, in step S5, the concentration of the NaBH4 solution is 0.4-1.2 mol / L.

[0022] As a preferred embodiment of the present invention, in step S5, the Fe 3+ - The ratio of polyurethane sponge to NaBH4 solution is (50-70) g: 500 mL.

[0023] It should be noted that the Fe in the modified sponge three-dimensional network 3+ The ions undergo a reduction reaction with the strong reducing agent NaBH4, producing Fe. 0 Atoms immediately nucleate and grow into nanoscale zero-valent iron particles. Due to Fe... 3+ Ions are pre-fixed in the PVA / WPU / PQ-10 polymer network through cross-linking, so the nZVI particles generated by reduction can be effectively anchored and dispersed on the surface and in the internal pores of the carrier, avoiding the aggregation and loss of nZVI particles. The prepared nZVI composite sponge filler has both high reactivity and good physical stability.

[0024] As a preferred technical solution of the present invention, the entire preparation process, namely steps S1-S5, is carried out under a nitrogen atmosphere.

[0025] In a second aspect, the present invention provides a nano-zero-valent iron composite sponge filler prepared by the method described above.

[0026] A third aspect of the present invention provides an application of nano-zero-valent iron composite sponge packing in nitrate wastewater denitrification, the specific method of use being as follows:

[0027] The prepared nano-zero-valent iron composite sponge filler was added to the activated sludge system at a ratio of 25%-35%, with a 12-hour operating cycle and two cycles per day.

[0028] As a preferred technical solution of the present invention, the operation mode of each cycle is as follows: 5 min water inlet, 680 min anoxic stirring, 30 min sedimentation, 5 min drainage, and the water exchange rate is 35%.

[0029] It should be noted that the nano-zero-valent iron composite sponge filler in this invention reacts with water within the system, and the generated active hydrogen, together with the nano-zero-valent iron composite sponge filler, participates in the production of NO3 within the system. - -N reduction reaction, part of NO3 - -N is reduced to generate NO2 - -N (formula ①, ②), NO2 - -N is further reduced to N2 or NH4+. 4+ -N (Formulas ③ and ④), another part NO3 - -N is then affected by Fe 0 Active hydrogen is directly reduced to N2 or NH. 4+ -N (Formulas ⑤ and ⑥). The electrons released by the nano-zero-valent iron composite sponge filler can be utilized as direct electron donors by denitrifying microorganisms. Simultaneously, during a series of chemical reduction processes, the Fe released by the nano-zero-valent iron composite sponge filler... 2+ H2 can also be utilized by microorganisms as electron shuttles. Nano-zero-valent iron composite sponge fillers, by directly and indirectly providing electron donors to microorganisms, complete the biological removal of NO3--N under conditions of reduced dependence on external carbon sources. The reactions involved in the chemical reduction process are as follows:

[0030] ①

[0031] ②

[0032] ③

[0033] ④

[0034] ⑤

[0035] ⑥

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) The preparation process of nano-zero valent iron composite sponge filler is simple. The preparation process combines impregnation method and in-situ reduction method to load nZVI on sponge skeleton, which significantly improves the dispersibility of nZVI and enhances the recyclability of the material.

[0038] (2) The nano-zero-valent iron composite sponge filler has excellent hydrophilicity and biofilm adhesion performance, which can effectively promote the initial adhesion of microorganisms in the system. The three-dimensional porous structure of the material provides abundant pores and a large specific surface area, creating ideal conditions for the formation and stability of biofilm.

[0039] (3) Within the biological system coupled with nano-zero-valent iron composite sponge filler, there exists an efficient "chemical-biological" synergistic denitrification pathway. The chemical reduction of nZVI removes NO3. - Reduced to NO2 - Microorganisms simultaneously convert NO2 - It is converted into N2, forming a complete short-range denitrification pathway.

[0040] (4) The settling performance of activated sludge in the biological system coupled with nano-zero-valent iron composite sponge filler is effectively improved, which is conducive to sludge granulation.

[0041] (5) Nano-zero valent iron composite sponge filler utilizes the oxidation-reduction products of nZVI (Fe) 2+ and Fe 3+ Using electron donors, NO3 is converted into nitrogen through autotrophic denitrification. - It is converted into N2, realizing the full cycle of iron ions in the coupling system, enhancing the activity of the electron transport system while saving carbon source and making it more efficient.

[0042] (6) Functional microorganisms can be successfully enriched on nano-zero-valent iron composite sponge packing. The oxidized iron ions on the surface of the packing can act as molecular bridges and participate in nitrogen cycling in synergy with microorganisms, which is beneficial to improving the denitrification efficiency of the system. Attached Figure Description

[0043] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0044] Figure 1 a is a SEM image of the nano-zero-valent iron composite sponge filler prepared in Example 1 of the present invention.

[0045] Figure 1 b represents the EDS result of the nano-zero-valent iron composite sponge filler prepared in Example 1 of this invention.

[0046] Figure 2 a is the XPS iron element spectrum of the nano-zero-valent iron composite sponge filler prepared in Example 1 of this invention.

[0047] Figure 2 b represents the XRD phase composition analysis of the nano-zero-valent iron composite sponge filler prepared in Example 1 of this invention.

[0048] Figure 3a, 3b, 3c, and 3d represent the denitrification effects of the nano-zero-valent iron composite sponge filler (R2) prepared in Example 1 of this invention and the control group (R1).

[0049] Figure 4 a represents the removal characteristics and removal effect of typical periodic pollutants of the nano-zero-valent iron composite sponge filler (R2) prepared in Example 1 of this invention and the control group (R1).

[0050] Figure 4 b represents the iron concentration detection of the nano-zero-valent iron composite sponge filler (R2) prepared in Example 1 of this invention and the control group (R1).

[0051] Figure 5 a, 5b, and 5c represent the effects of the nano-zero-valent iron composite sponge filler (R2) prepared in Example 1 of this invention and the control group (R1) on sludge characteristics. Detailed Implementation

[0052] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] The sources of some components in the examples and comparative examples are as follows:

[0054] Table 1

[0055]

[0056] Example 1

[0057] A method for preparing a nano-zero-valent iron composite sponge filler, the specific steps of which are as follows:

[0058] S1. Weigh 10g of PVA and add it to 100mL of deionized water. Dissolve the PVA solution by stirring in a 90℃ water bath to obtain a polyvinyl alcohol solution. Cool the solution for later use. Weigh 0.5g of polyquaternium-10 and dissolve it in 10mL of deionized water to obtain a polyquaternium-10 solution. Cool the solution for later use. Mix 100mL of polyvinyl alcohol solution with 10mL of polyquaternium-10 solution evenly to obtain a PVA-PQ-10 mixture.

[0059] S2. Take 25 mL of waterborne polyurethane emulsion, 75 mL of deionized water and 10 mL of the PVA-PQ-10 mixture obtained in step S1, and mix the above solutions evenly for 1 h to obtain the modified adhesive.

[0060] S3. Impregnate 15g of polyurethane sponge in 500mL of the modified adhesive obtained in step S2, sonicate at 40kHz for 15min, and impregnate for 30min to obtain the modified polyurethane sponge.

[0061] S4. Weigh 16.22g of FeCl3 and dissolve it in 500mL of acidic ethanol solution to obtain a FeCl3 mixed solution. Nitrogen gas is bubbled through the solution to remove oxygen during preparation. 30g of modified polyurethane sponge is impregnated in the 500mL FeCl3 mixed solution for crosslinking for 2 hours to obtain Fe... 3+ - Polyurethane foam;

[0062] The acidic ethanol solution contains 30% ethanol by mass and 0.01 mol / L hydrochloric acid by concentration.

[0063] S5. Weigh 15.2g of NaBH4 and dissolve it in 500mL of deionized water to obtain a NaBH4 solution. Nitrogen gas is bubbled through the solution to remove oxygen during preparation. 60g of the Fe obtained in step S4 is then added... 3+ - Polyurethane sponge was impregnated with 500 mL NaBH4 solution, stirred for 30 min, allowed to stand for 30 min, drained, washed three times with deoxygenated water and anhydrous ethanol respectively, and then freeze-dried under vacuum at -60℃ for 24 h to obtain nano-zero valent iron composite sponge filler.

[0064] Example 2

[0065] A method for preparing a nano-zero-valent iron composite sponge filler, the specific steps of which are as follows:

[0066] S1. Weigh 10g of PVA and add it to 100mL of deionized water. Dissolve the PVA solution by stirring in a 90℃ water bath to obtain a polyvinyl alcohol solution. Cool the solution for later use. Weigh 0.5g of polyquaternium-10 and dissolve it in 10mL of deionized water to obtain a polyquaternium-10 solution. Cool the solution for later use. Mix 150mL of polyvinyl alcohol solution with 10mL of polyquaternium-10 solution to obtain a PVA-PQ-10 mixture.

[0067] S2. Take 25 mL of waterborne polyurethane emulsion, 75 mL of deionized water and 10 mL of the PVA-PQ-10 mixture obtained in step S1, and mix the above solutions evenly for 1 h to obtain the modified adhesive.

[0068] S3. Impregnate 15g of polyurethane sponge in 500mL of the modified adhesive obtained in step S2, sonicate at 40kHz for 15min, and impregnate for 30min to obtain the modified polyurethane sponge.

[0069] S4. Weigh 16.22g of FeCl3 and dissolve it in 500mL of acidic ethanol solution to obtain a FeCl3 mixed solution. Nitrogen gas is bubbled through the solution to remove oxygen during preparation. 30g of modified polyurethane sponge is impregnated in the 500mL FeCl3 mixed solution for crosslinking for 2 hours to obtain Fe... 3+ - Polyurethane foam;

[0070] The acidic ethanol solution contains 30% ethanol by mass and 0.01 mol / L hydrochloric acid by concentration.

[0071] S5. Weigh 15.2g of NaBH4 and dissolve it in 500mL of deionized water to obtain a NaBH4 solution. Nitrogen gas is bubbled through the solution to remove oxygen during preparation. 60g of the Fe obtained in step S4 is then added... 3+ - Polyurethane sponge was impregnated with 500 mL NaBH4 solution, stirred for 30 min, allowed to stand for 30 min, drained, washed three times with deoxygenated water and anhydrous ethanol respectively, and then freeze-dried under vacuum at -60℃ for 24 h to obtain nano-zero valent iron composite sponge filler.

[0072] The difference between this embodiment and Embodiment 1 is that, in step S1, the volume ratio of polyvinyl alcohol solution to polyquaternium-10 solution in this embodiment is 15:1.

[0073] Example 3

[0074] A method for preparing a nano-zero-valent iron composite sponge filler, the specific steps of which are as follows:

[0075] S1. Weigh 10g of PVA and add it to 100mL of deionized water. Dissolve the PVA solution by stirring in a 90℃ water bath to obtain a polyvinyl alcohol solution. Cool the solution for later use. Weigh 0.5g of polyquaternium-10 and dissolve it in 10mL of deionized water to obtain a polyquaternium-10 solution. Cool the solution for later use. Mix 200mL of polyvinyl alcohol solution with 10mL of polyquaternium-10 solution to obtain a PVA-PQ-10 mixture.

[0076] S2. Take 25 mL of waterborne polyurethane emulsion, 75 mL of deionized water and 10 mL of the PVA-PQ-10 mixture obtained in step S1, and mix the above solutions evenly for 1 h to obtain the modified adhesive.

[0077] S3. Impregnate 15g of polyurethane sponge in 500mL of the modified adhesive obtained in step S2, sonicate at 40kHz for 15min, and impregnate for 30min to obtain the modified polyurethane sponge.

[0078] S4. Weigh 16.22g of FeCl3 and dissolve it in 500mL of acidic ethanol solution to obtain a FeCl3 mixed solution. Nitrogen gas is bubbled through the solution to remove oxygen during preparation. 30g of modified polyurethane sponge is impregnated in the 500mL FeCl3 mixed solution for crosslinking for 2 hours to obtain Fe... 3+ - Polyurethane foam;

[0079] The acidic ethanol solution contains 30% ethanol by mass and 0.01 mol / L hydrochloric acid by concentration.

[0080] S5. Weigh 15.2g of NaBH4 and dissolve it in 500mL of deionized water to obtain a NaBH4 solution. Nitrogen gas is bubbled through the solution to remove oxygen during preparation. 60g of the Fe obtained in step S4 is then added... 3+ - Polyurethane sponge was impregnated with 500 mL NaBH4 solution, stirred for 30 min, allowed to stand for 30 min, drained, washed three times with deoxygenated water and anhydrous ethanol respectively, and then freeze-dried under vacuum at -60℃ for 24 h to obtain nano-zero valent iron composite sponge filler.

[0081] The difference between this embodiment and Embodiment 1 is that, in step S1, the volume ratio of polyvinyl alcohol solution to polyquaternium-10 solution in this embodiment is 20:1.

[0082] Example 4

[0083] A method for preparing a nano-zero-valent iron composite sponge filler, the specific steps of which are as follows:

[0084] S1. Weigh 10g of PVA and add it to 100mL of deionized water. Dissolve the PVA solution by stirring in a 90℃ water bath to obtain a polyvinyl alcohol solution. Cool the solution for later use. Weigh 0.5g of polyquaternium-10 and dissolve it in 10mL of deionized water to obtain a polyquaternium-10 solution. Cool the solution for later use. Mix 100mL of polyvinyl alcohol solution with 10mL of polyquaternium-10 solution evenly to obtain a PVA-PQ-10 mixture.

[0085] S2. Take 25 mL of waterborne polyurethane emulsion, 75 mL of deionized water and 10 mL of the PVA-PQ-10 mixture obtained in step S1, and mix the above solutions evenly for 1 h to obtain the modified adhesive.

[0086] S3. Impregnate 15g of polyurethane sponge in 500mL of the modified adhesive obtained in step S2, sonicate at 40kHz for 15min, and impregnate for 30min to obtain the modified polyurethane sponge.

[0087] S4. Weigh 24.33g of FeCl3 and dissolve it in 500mL of acidic ethanol solution to obtain a FeCl3 mixed solution. Nitrogen gas is bubbled through the solution to remove oxygen during preparation. 30g of modified polyurethane sponge is impregnated in the 500mL FeCl3 mixed solution for crosslinking for 2 hours to obtain Fe... 3+ - Polyurethane foam;

[0088] The acidic ethanol solution contains 30% ethanol by mass and 0.01 mol / L hydrochloric acid by concentration.

[0089] S5. Weigh 15.2g of NaBH4 and dissolve it in 500mL of deionized water to obtain a NaBH4 solution. Nitrogen gas is bubbled through the solution to remove oxygen during preparation. 60g of the Fe obtained in step S4 is then added... 3+ - Polyurethane sponge was impregnated with 500 mL NaBH4 solution, stirred for 30 min, allowed to stand for 30 min, drained, washed three times with deoxygenated water and anhydrous ethanol respectively, and then freeze-dried under vacuum at -60℃ for 24 h to obtain nano-zero valent iron composite sponge filler.

[0090] The difference between this embodiment and Embodiment 1 is that, in step S4, the concentration of FeCl3 in the FeCl3 mixed solution in this embodiment is 0.3 mol / L.

[0091] Example 5

[0092] A method for preparing a nano-zero-valent iron composite sponge filler, the specific steps of which are as follows:

[0093] S1. Weigh 10g of PVA and add it to 100mL of deionized water. Dissolve the PVA solution by stirring in a 90℃ water bath to obtain a polyvinyl alcohol solution. Cool the solution for later use. Weigh 0.5g of polyquaternium-10 and dissolve it in 10mL of deionized water to obtain a polyquaternium-10 solution. Cool the solution for later use. Mix 100mL of polyvinyl alcohol solution with 10mL of polyquaternium-10 solution evenly to obtain a PVA-PQ-10 mixture.

[0094] S2. Take 25 mL of waterborne polyurethane emulsion, 75 mL of deionized water and 10 mL of the PVA-PQ-10 mixture obtained in step S1, and mix the above solutions evenly for 1 h to obtain the modified adhesive.

[0095] S3. Impregnate 15g of polyurethane sponge in 500mL of the modified adhesive obtained in step S2, sonicate at 40kHz for 15min, and impregnate for 30min to obtain the modified polyurethane sponge.

[0096] S4. Weigh 16.22g of FeCl3 and dissolve it in 500mL of acidic ethanol solution to obtain a FeCl3 mixed solution. Nitrogen gas is bubbled through the solution to remove oxygen during preparation. 30g of modified polyurethane sponge is impregnated in the 500mL FeCl3 mixed solution for crosslinking for 2 hours to obtain Fe... 3+ - Polyurethane foam;

[0097] The acidic ethanol solution contains 30% ethanol by mass and 0.01 mol / L hydrochloric acid by concentration.

[0098] S5. Weigh 32.44g of NaBH4 and dissolve it in 500mL of deionized water to obtain a NaBH4 solution. Nitrogen gas is bubbled through the solution to remove oxygen during preparation. 60g of the Fe obtained in step S4 is then added... 3+ - Polyurethane sponge was impregnated with 500 mL NaBH4 solution, stirred for 30 min, allowed to stand for 30 min, drained, washed three times with deoxygenated water and anhydrous ethanol respectively, and then freeze-dried under vacuum at -60℃ for 24 h to obtain nano-zero valent iron composite sponge filler.

[0099] The difference between this embodiment and Embodiment 1 is that, in step S4, the concentration of FeCl3 in the FeCl3 mixed solution in this embodiment is 0.4 mol / L.

[0100] Comparative Example

[0101] Commercially available polyurethane foam.

[0102] Tests were conducted on Example 1 and the comparative example, as follows:

[0103] I. Physicochemical Properties Characterization

[0104] (1) The nano-zero-valent iron composite sponge filler prepared in Example 1 was tested by scanning electron microscopy (SEM).

[0105] Figure 1 The results show that the sponge skeleton of the nano-zero-valent iron composite sponge filler changed from a smooth polyurethane structure to a rough polyurethane structure support loaded with a large number of particles, indicating that nZVI successfully adhered to the carrier surface.

[0106] (2) Energy dispersive X-ray spectroscopy (EDS) was performed on the nano-zero-valent iron composite sponge filler prepared in Example 1.

[0107] Figure 1 The results showed that Fe accounted for 19.31% of the material by mass, and the distribution of Fe was consistent with the morphology of the sponge skeleton, confirming that nZVI was uniformly dispersed on the carrier surface and in the micro-gaps.

[0108] (3) X-ray photoelectron spectroscopy (XPS) was performed on the nano-zero-valent iron composite sponge filler prepared in Example 1 to analyze the valence state of Fe element.

[0109] Figure 2 The results showed that Fe was detected at 705.7 eV. 0 Characteristic peaks, with Fe present simultaneously 2+ (709.6eV) and Fe 3+ The characteristic peak (711.7eV) indicates the dominance of nZVI and the presence of some oxidized iron in the material.

[0110] (4) X-ray diffraction (XRD) was performed on the nano-zero-valent iron composite sponge filler prepared in Example 1 to analyze its phase composition.

[0111] Figure 2 The results showed that the XRD pattern of the nano-zero-valent iron composite sponge filler exhibited a broad peak at 2θ≈22°, which is a characteristic peak of polyurethane sponge. The peak at 2θ≈45° was due to Fe. 0 The characteristic peaks confirmed the successful synthesis of nZVI on the sponge framework. The peak appearing near 2θ≈33.15° is consistent with the characteristic peaks of α-Fe₂O₃, and the Fe 2p spectrum in XPS also shows Fe... 2+ and Fe 3+ The presence of this indicates the presence of iron oxide on the surface of the composite carrier. This iron oxide material coats the surface of nZVI, giving nZVI a unique core-shell structure.

[0112] II. Denitrification effect test and pollutant removal effect

[0113] Two activated sludge control systems (R1 and R2) with an effective volume of 3L were constructed. The nano-zero-valent iron composite sponge packing material prepared in Example 1 was added to R2, while R1 served as a control group, with an equal mass of commercially available polyurethane sponge added to R1. The filling rate of both R1 and R2 was 35%. Except for the packing material, the operation of the two reactors was identical. The activated sludge was obtained from the anoxic tank of a wastewater treatment plant in Qingdao. The system operating temperature was room temperature (22.5℃), and the influent was synthetic wastewater. The HRT was 12h, and the operating mode was: 5min influent, 680min anoxic stirring, 30min sedimentation, and 5min effluent, with a water exchange rate of 35%. Samples were collected daily from both systems, filtered through a 0.45µm filter membrane, and analyzed to investigate the long-term nitrogen removal effect.

[0114] Typical periodic in-situ experiments were conducted during the operation of both systems, with the operation mode being the same as the daily operating conditions. Water samples were collected at regular intervals to observe the pollutant removal within one cycle.

[0115] Figure 3 The results showed that, compared with group R1, the total nitrogen removal rate of R2 increased by an average of 47%; the COD concentration of the effluent was maintained below 35 mg / L; carbon source consumption was reduced by an average of 32%; and nZVI could serve as an electron donor for microorganisms, reducing their dependence on external carbon sources.

[0116] Figure 4 The results showed that within 1 hour of reaction, the nitrate concentration in the system decreased by 50%, and nZVI dominated the rapid NO3-growth in the initial 1 hour. - -N to NO2 - -N conversion, NO2 in R2 system at 1 hour - -N accumulation reached 11.14 mg / L, NO2 in system R1 - The highest accumulation of -N was only 4.16 mg / L, and NO2 was observed in both subsequent systems. - The concentration of -N continues to decrease. This is accompanied by a decrease in NO2 concentration within the R2 system. - The generation of -N triggers microorganisms to simultaneously initiate the production of NO2. - The reduction of -N to N2 forms a short-range denitrification pathway that seamlessly connects "chemical and biological" processes, avoiding the problem of ammonia nitrogen accumulation in traditional processes.

[0117] Figure 4 The results showed that the total iron concentration in reactor R2 was consistently higher than that in reactor R1, indicating a continuous iron ion cycle within the reactor. nZVI continuously released electron donors, promoting microbial metabolic activity.

[0118] III. Impact on sludge characteristics

[0119] Depend on Figure 5 As shown in Figure a, the sludge biomass data indicates that the MLSS and MLVSS concentrations of R2 consistently remained higher than those of R1. This result suggests that the addition of the nano-zero-valent iron composite sponge packing provided a more suitable growth environment for microorganisms. Its porous structure not only provided a carrier for microbial attachment but also, through the slow release of iron ions, served as an essential trace element for microbial metabolism, promoting sludge proliferation within the system.

[0120] Figure 5 b shows that the SVI5 of R2 is significantly lower than that of R1, and the SVI... 30 The same trend is also observed; among them, SVI at the end of R2 30 The SVI5 / R ratio reached 0.85, far exceeding the corresponding value of R1. This data indicates that the introduction of nano-zero-valent iron composite sponge filler enhances the sludge's aggregation capacity, making the sludge floc structure more compact, significantly improving settling performance, and making it easier to form granular sludge.

[0121] Figure 5The results showed that the final average electron transport system activity (ETSA) of R1 was 10.2 µgO2 / g / h, while the final average ETSA of R2 reached 13.98 µgO2 / g / h. This increase in ETSA indicates that the nano-zero-valent iron composite sponge packing enhances the respiratory enzyme activity and electron transport efficiency of microorganisms within the system by providing iron electron donors, accelerating electron transport during microbial metabolism. This effect directly promotes the degradation and transformation of pollutants by activated sludge, especially providing highly efficient biological support for denitrification reactions under low carbon-to-nitrogen ratio conditions.

Claims

1. A method for preparing a nano-zero-valent iron composite sponge filler, characterized in that: Specifically, the following steps are included: S1. Mix the polyvinyl alcohol solution with the polyquaternium-10 solution to obtain the PVA-PQ-10 mixture; S2. Mix the aqueous polyurethane emulsion, deionized water and the PVA-PQ-10 mixture prepared in step S1, and homogenize for 0.5-1.5 h to obtain the modified adhesive. S3. Immerse the polyurethane sponge in the modified adhesive until fully impregnated, and sonicate at 40 kHz for 10-20 min, then impregnate for 20-40 min to obtain the modified polyurethane sponge. S4. Immerse the modified polyurethane sponge in a FeCl3 mixed solution for crosslinking treatment for 1.5-3 hours to obtain Fe... 3+ - Polyurethane foam; S5, Fe 3+ Polyurethane sponge was immersed in 0.4-1.2 mol / L NaBH4 solution for 0.5-1.5 h for reduction treatment, washed 3 times with anhydrous ethanol, washed 3 times with deionized water, and then freeze-dried under vacuum to obtain nano-zero valent iron composite sponge filler.

2. The method for preparing a nano-zero-valent iron composite sponge filler according to claim 1, characterized in that: In step S1, the polyvinyl alcohol solution has a mass fraction of 8%-10%, and the polyquaternium-10 solution has a mass fraction of 3%-5%.

3. The method for preparing a nano-zero-valent iron composite sponge filler according to claim 1, characterized in that: In step S1, the volume ratio of the polyvinyl alcohol solution to the polyquaternium-10 solution is (10-20):

1.

4. The method for preparing a nano-zero-valent iron composite sponge filler according to claim 1, characterized in that: In step S2, the volume ratio of the aqueous polyurethane emulsion, deionized water, and PVA-PQ-10 mixture is 5:15:

2.

5. The method for preparing a nano-zero-valent iron composite sponge filler according to claim 1, characterized in that: In step S3, the ratio of the polyurethane sponge to the modified adhesive is (12-18) g: 500 mL.

6. The method for preparing a nano-zero-valent iron composite sponge filler according to claim 1, characterized in that: In step S4, the FeCl3 mixed solution has a FeCl3 concentration of 0.1-0.3 mol / L, an ethanol mass fraction of 30%, and a hydrochloric acid concentration of 0.01 mol / L.

7. The method for preparing a nano-zero-valent iron composite sponge filler according to claim 1, characterized in that: In step S4, the ratio of the modified polyurethane sponge to the FeCl3 mixed solution is (25-35) g: 500 mL.

8. The method for preparing a nano-zero-valent iron composite sponge filler according to claim 1, characterized in that: In step S5, the concentration of the NaBH4 solution is 0.4-1.2 mol / L, and the Fe... 3+ - The ratio of polyurethane sponge to NaBH4 solution is (50-70) g: 500 mL.

9. A nano-zero-valent iron composite sponge filler prepared by the preparation method of a nano-zero-valent iron composite sponge filler as described in any one of claims 1-8.

10. The application of the nano-zero-valent iron composite sponge packing according to claim 9 in nitrate wastewater denitrification, characterized in that, The specific usage method is as follows: Add the prepared nano-zero-valent iron composite sponge filler to the activated sludge system at a ratio of 25%-35%, with a 12-hour operating cycle and 2 cycles per day. The operating mode of each cycle is: 5 min water inlet, 680 min anoxic stirring, 30 min sedimentation, and 5 min drainage, with a water exchange rate of 35%.

Images