An MXene-enhanced sulfur-iron autotrophic denitrification composite packing, its preparation method, and its application.

Abstract

This invention belongs to the technical field of water pollution control materials, specifically relating to an enhanced pyrite-iron autotrophic denitrification composite packing and its preparation and application. The invention involves mixing sulfur, pyrite, less-layer MXene, clay, and a binder in a certain proportion, then mixing and extruding the mixture with a sodium thiosulfate aqueous solution to form granules. Sulfur, Fe... 2+ S ‑ As an electron donor and electron transport bridge, MXene confines electrons within its two-dimensional structure, accelerating electron transfer. This enhances the activity of denitrifying bacteria and thiobacilli, strengthening microbial activity. Simultaneously, the surface of MXene contains numerous hydroxyl functional groups and other active terminals, enabling it to adsorb pollutants and improve nitrate nitrogen removal efficiency. This packing material exhibits stable performance, high mechanical strength, and a large specific surface area, making it a suitable replacement for traditional organic carbon sources in simulated reaction devices for treating target wastewater. It is applicable to rural sewage, industrial wastewater with an imbalanced carbon-to-nitrogen ratio, and municipal wastewater.

Description

Technical Field

[0001] This invention belongs to the field of sulfur autotrophic denitrification technology, specifically relating to an MXene-enhanced sulfur-iron autotrophic denitrification composite packing, its preparation method, and its application. Background Technology

[0002] Sulfur autotrophic denitrification technology: Nitrogen in water causes severe pollution, with ammonia nitrogen and nitrates widely present in domestic sewage, rural sewage, and industrial wastewater. Nitrogen removal mainly relies on anaerobic denitrification. Heterotrophic denitrifying bacteria use methanol, ethanol, sodium acetate, glucose, and organic matter as carbon sources. However, in practical applications, this method suffers from drawbacks such as organic matter residue and high costs. Autotrophic denitrification, using iron, sulfur, ammonia, and hydrogen as electron donors, does not require the addition of organic substrates and has broad application prospects. Sulfur autotrophic denitrification is the primary method, using elemental sulfur, sulfur, thiosulfate, and sulfides as electron donors and carbonate as the inorganic carbon source, achieving denitrification under the action of desulfurizing bacteria. This technology still faces some technical bottlenecks, such as sulfur oxidation loss, anaerobic microenvironment acid-base imbalance, and the inhibition of microorganisms by excessive hydrogen sulfide. However, these can be addressed through methods such as adding reducing substances during preparation and hydroxylation modification of the packing surface. The rapid release rate of sulfur from packing materials significantly impacts the growth and denitrification of autotrophic nitrifying bacteria, particularly its transfer efficiency within the microenvironment. Excessive sulfur release can be mitigated by adding polyvinyl alcohol or sodium alginate to the sulfur-based autotrophic denitrification packing material. To improve the reaction rate, Chinese patent publication CN111072132A discloses a sulfur-iron mixed packing material preparation technology. This technology improves the microenvironment of the microbial action medium through alkalinity complementarity, thereby enhancing the autotrophic denitrification rate. Chinese patent publication CN115028261A discloses a sulfur-based autotrophic denitrification packing material and its preparation method, which incorporates calcium ions to neutralize the acid generated, regulating the microenvironment. However, calcium deposition on the sulfur surface inhibits active sites and weakens electron transfer efficiency. Currently, no method has been found to modify sulfur-based autotrophic packing materials that significantly improves electron transfer efficiency or overcomes the low redox reaction potential. Summary of the Invention

[0003] To overcome the above drawbacks, this invention uses sulfur and pyrite as electron donors and MXene as an electron transfer bridge to enhance electron transfer between microorganisms. The resulting packing material has well-developed pores, high mechanical strength, large specific surface area, and enhanced denitrification efficiency, thus achieving efficient and deep denitrification.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing an MXene-enhanced sulfur-iron autotrophic denitrification composite packing, comprising the following steps:

[0005] 1) Weigh the following materials by weight: 20-60 parts sulfur, 20-60 parts pyrite, 4-10 parts clay, 1-5 parts binder, 0.5-2 parts less-layer MXene powder, and 0.5-5 parts reducing agent. Put them into a mixer and mix them evenly to obtain a mixed powder.

[0006] 2) Prepare a 20-30 wt% sodium thiosulfate aqueous solution and add it to the above mixed powder at an amount of 20-40 mL / 100 g. After stirring, granulation, and drying, the MXene-enhanced sulfur-iron autotrophic denitrification composite packing is obtained.

[0007] Further improvements to the preparation method of MXene-enhanced sulfur-iron autotrophic denitrification composite packing:

[0008] Preferably, the preparation method of the few-layer MXene powder is as follows: MAX phase powder is added to hydrofluoric acid at a concentration of 25-50 g / L, and subjected to liquid nitrogen freezing treatment and ultrasonic dispersion and exfoliation. The liquid nitrogen freezing treatment is carried out at a temperature of -196℃ for 30-60 min, and the ultrasonic dispersion and exfoliation is carried out for 30-60 min, with 2-5 cycles to obtain a suspension. The upper suspension is then filtered, washed, and dried to obtain few-layer MXene powder.

[0009] Preferably, the clay is one of illite powder, sodium bentonite, and kaolin.

[0010] Preferably, the binder is one of starch, carboxymethyl cellulose, or hydroxypropyl methyl cellulose.

[0011] Preferably, the reducing protective agent is one or more of sodium bisulfite, potassium bisulfite, and sodium sulfite, or two of them.

[0012] Preferably, the sulfur has a sieve particle size of 100-300 mesh, and the pyrite has a sieve particle size of 50-200 mesh.

[0013] Preferably, the drying of the granulated pellets in step 2) is divided into three steps: drying at 10-30℃ for 1-2 hours, drying at 60-80℃ for 1-2 hours, and drying at 150-160℃ for 0.5-1 hours, and then cooling to room temperature and sealing for later use.

[0014] Preferably, the bulk density of the MXene-enhanced ferrous sulfate autotrophic denitrification composite packing is 0.8-1.5 g / cm³. 3 Porosity 10-20%.

[0015] The second objective of this invention is to provide an MXene-enhanced sulfur-iron autotrophic denitrification composite packing material prepared by any of the above-described preparation methods.

[0016] The third objective of this invention is to provide an application of the above-mentioned MXene-enhanced sulfur-iron autotrophic denitrification composite packing material in anaerobic reactors for wastewater treatment.

[0017] The advantages of this invention compared to the prior art are as follows:

[0018] 1) This invention uses sulfur and pyrite as the main functional materials, and mixes MXene powder, a reducing agent, and a binder to prepare a sulfur-autotrophic denitrification filler. The preparation method of this invention includes the steps of preparing single-layer MXene sheets, granulation and pelletizing, and gradient drying. By etching with lithium fluoride and hydrochloric acid, and under repeated freezing and ultrasonic treatment, the interlayer bonding force of titanium carbide is reduced to prepare a few-layer MXene. Clay and a binder are used to uniformly mix elemental sulfur and MXene materials and granulate them to form a composite filler. Gradual drying of the filler ensures a uniform increase in the internal strength of the material. The final temperature is raised to the melting point of elemental sulfur, and the surface temperature is controlled at a critical state to prevent the excessive oxidation of the internal MXene. MXene has a large specific surface area and a strong interlayer confinement effect, thus improving redox capacity and facilitating electron transfer. The method of adding MXene in this invention can enhance electron transfer between sulfur and microorganisms and improve microbial activity.

[0019] 2) The MXene-enhanced sulfur-iron autotrophic denitrification composite packing material prepared in this invention can convert nitrate nitrogen and nitrite nitrogen into N2 under the action of sulfur bacteria and denitrifying bacteria. The surface of the MXene packing material is rich in hydroxyl functional groups, which easily form covalent bonds with the surface groups of pollutant molecules. MXene has excellent conductivity and interlayer structure, which enhances electron transfer between sulfur and microorganisms, improves electron transfer efficiency, and increases denitrification efficiency. Attached Figure Description

[0020] Figure 1 This is an electron microscope image of the few-layer MXene powder prepared in Example 1 of the present invention;

[0021] Figure 2 This is the XRD pattern of the few-layer MXene powder obtained in Example 1 of the present invention.

[0022] Figure 3 This is a CV comparison curve of the composite filler prepared by adding few-layer MXene and the composite filler prepared without adding few-layer MXene in Example 1 of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0024] Example 1:

[0025] This embodiment provides a method for preparing MXene-enhanced sulfur-iron autotrophic denitrification composite packing, which specifically includes the following steps:

[0026] (1) Preparation of few-layer MXene: 10 g of MAX was dissolved in 300 mL of hydrofluoric acid, frozen in liquid nitrogen at -196 °C for 30 min, and then placed under an ultrasonic machine for 30 min. The liquid nitrogen freezing treatment and ultrasonic dispersion and peeling were repeated 3 times to obtain a suspension. The upper mixture was filtered, washed and dried to obtain few-layer MXene.

[0027] (2) Preparation of composite filler: Weigh 400g of sulfur (sieve particle size of 200 mesh), 400g of pyrite (sieve particle size of 50 mesh), 100g of clay (sodium bentonite), 50g of binder (carboxymethyl cellulose), 5g of MXene powder, and 40g of reducing protectant (sodium bisulfite), and mix them evenly in a ball mill to obtain a mixed powder.

[0028] (3) Prepare a 20wt% sodium thiosulfate aqueous solution and add it to the above mixed powder at a ratio of 25mL / 100g. After stirring and granulation, obtain small balls with a size of 30mm. Dry them at 15℃ for 1h to harden the filler, and then place them in a drying oven and heat at 60℃ for 1h, followed by holding at 150℃ for 0.5h. The bulk density of the resulting material is 1.0g / m³. 3 With a porosity of 15%, MXene-reinforced sulfur-iron autotrophic denitrification composite packing was prepared.

[0029] As a control, no "5g of MXene powder" was added in step (2), and all other steps were the same, to obtain a composite filler without the addition of a few layers of MXene.

[0030] The composite packing material prepared above was placed in a column-type anaerobic reactor with a filling ratio of 10% and an effective reactor volume of 10.5 L. 1.2 L of desulfurization bacteria solution was inoculated, with a desulfurization bacteria concentration of 20%, and the inoculated anaerobic sludge concentration was 3000 mg / L. The influent was rural wastewater with a hydraulic retention time of 3 h. The average nitrate nitrogen content in the raw water was 60-65 mg / L, and the average nitrate nitrogen content in the effluent was 3.2 mg / L, resulting in a removal rate of 90.8%.

[0031] The scanning electron microscope (SEM) images of the few-layer MXene powder obtained in step (1) are as follows: Figure 1 As shown. By Figure 1 The morphology can be seen to be flake-like, showing as few-layered MXene flakes, composed of... Figure 2 XRD analysis revealed a significant leftward shift of the 002 peak, which is attributed to the few-layer MXene obtained from the exfoliation of the MAX phase powder.

[0032] The few-layer MXene powder obtained in step (1) was subjected to XRD scanning, and the results are as follows: Figure 2 As shown, by Figure 2 It can be seen that the (002) peak is significantly shifted to the left of the multilayer, thus a few-layer MXene material was synthesized.

[0033] Figure 3 The CV curves of composite fillers prepared with and without few-layer MXene were compared. The addition of few-layer MXene significantly enhanced the current effect of the material and improved the electron transfer efficiency at the interface and in the medium microenvironment.

[0034] Example 2:

[0035] This embodiment provides a method for preparing MXene-enhanced sulfur-iron autotrophic denitrification composite packing, which specifically includes the following steps:

[0036] (1) Preparation of few-layer MXene: 10 g of MAX was dissolved in 400 mL of hydrofluoric acid, frozen in liquid nitrogen at -196 °C for 60 min, and then placed in an ultrasonic machine for dispersion and peeling for 60 min. The liquid nitrogen freezing treatment and ultrasonic dispersion and peeling treatment were repeated 3 times to obtain a suspension. The upper mixture was filtered and dried to obtain few-layer MXene.

[0037] (2) Preparation of composite filler: Weigh 500g of sulfur (sieve particle size of 200 mesh), 300g of pyrite (sieve particle size of 100 mesh), 100g of clay (illite powder), 50g of binder (hydroxypropyl methylcellulose), 10g of MXene powder, and 40g of reducing protectant (sodium bisulfite), and mix them evenly in a ball mill to obtain a mixed powder.

[0038] (3) Prepare a 25wt% sodium thiosulfate aqueous solution and add it to the above mixed powder at a ratio of 30mL / 100g. After stirring and granulation, obtain small balls with a size of 50mm. Dry them at 15℃ for 1h to harden the filler, and then place them in a drying oven and heat them at 70℃ for 1h, and then keep them at 155℃ for 1h. The bulk density of the obtained material is 1.1g / m³. 3 With a porosity of 15%, MXene-reinforced sulfur-iron autotrophic denitrification composite packing was prepared.

[0039] The composite packing material prepared above was placed in a column-type anaerobic reactor with a filling ratio of 10% and an effective reactor volume of 10.5 L. 1.2 L of desulfurization bacteria solution was inoculated, with a desulfurization bacteria concentration of 20%, and the inoculated anaerobic sludge concentration was 3000 mg / L. This solution was used to treat municipal wastewater with a hydraulic retention time of 3 h. The average nitrate nitrogen content in the raw wastewater was 18-22 mg / L, and the average nitrate nitrogen content in the effluent was 0.87 mg / L, achieving a removal rate of 95.7%.

[0040] Example 3:

[0041] This embodiment provides a method for preparing MXene-enhanced sulfur-iron autotrophic denitrification composite packing, which specifically includes the following steps:

[0042] (1) Preparation of few-layer MXene: 10 g of MAX was dissolved in 350 mL of hydrofluoric acid, frozen in liquid nitrogen at -196 °C for 45 min, and then placed under an ultrasonic machine for 45 min. The liquid nitrogen freezing treatment and ultrasonic dispersion and peeling treatment were repeated 3 times to obtain a suspension. The upper mixture was filtered and dried to obtain few-layer MXene.

[0043] (2) Preparation of composite filler: Weigh 600g of sulfur powder (sieve particle size of 250 mesh), 200g of pyrite (sieve particle size of 200 mesh), 100g of clay (kaolin), 50g of binder (hydroxypropyl methylcellulose), 20g of MXene powder, and 30g of reducing protectant (sodium bisulfite), and mix them evenly in a ball mill to obtain a mixed powder.

[0044] (3) Prepare a 30wt% sodium thiosulfate aqueous solution and add it to the above mixed powder at a ratio of 30mL / 100g. After stirring and granulation, obtain small balls with a size of 80mm. Dry them at 15℃ for 2h to harden the filler, and then place them in a drying oven and heat at 80℃ for 2h, followed by holding at 160℃ for 1h. The bulk density of the obtained material is 1.2g / m³. 3 With a porosity of 15%, MXene-reinforced sulfur-iron autotrophic denitrification composite packing was prepared.

[0045] The composite packing material prepared above was placed in a column-type anaerobic reactor with a filling ratio of 10%. The effective volume of the reactor was 10.5 L. 1.2 L of desulfurization bacteria solution was inoculated, with a desulfurization bacteria concentration of 20%, and the inoculated anaerobic sludge concentration was 3000 mg / L. The influent was wastewater from a service area, with a hydraulic retention time of 3 h. The average nitrate nitrogen content in the raw water was 60-65 mg / L, and the average nitrate nitrogen content in the effluent was 3.2 mg / L, resulting in a removal rate of 94.84%. Nitrate nitrogen removal in water can only occur through denitrification, which is also the only way denitrification generates nitrogen gas. Therefore, the nitrate nitrogen removal rate confirms the efficiency of denitrification.

[0046] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments. It should be noted that many modifications and improvements can be made by those skilled in the art, and all modifications or improvements not exceeding the scope of the claims should be considered within the protection scope of the present invention.

Claims

1. A method for preparing an MXene-enhanced sulfur-iron autotrophic denitrification composite packing, characterized in that, Includes the following steps: 1) Weigh the following materials by weight: 20-60 parts sulfur, 20-60 parts pyrite, 4-10 parts clay, 1-5 parts binder, 0.5-2 parts less-layer MXene powder, and 0.5-5 parts reducing agent. Put them into a mixer and mix them evenly to obtain a mixed powder. 2) Prepare a 20-30 wt% sodium thiosulfate aqueous solution and add it to the above mixed powder at an addition amount of 20-40 mL / 100 g. After stirring, granulate it into small balls with a diameter of 30-80 mm and perform gradient drying. The gradient drying is divided into three steps: drying at 10-30℃ for 1-2 h, drying at 60-80℃ for 1-2 h, and drying at 150-160℃ for 0.5-1 h. After that, cool it to room temperature and seal it for later use. This yields the MXene-enhanced sulfur-iron autotrophic denitrification composite packing.

2. The preparation method of the MXene-enhanced sulfur-iron autotrophic denitrification composite packing according to claim 1, characterized in that, The preparation method of the few-layer MXene powder is as follows: MAX phase powder is added to hydrofluoric acid at a concentration of 25-50 g / L, and subjected to liquid nitrogen freezing treatment and ultrasonic dispersion and exfoliation. The liquid nitrogen freezing treatment is carried out at a temperature of -196℃ for 30-60 min, and the ultrasonic dispersion and exfoliation is carried out for 30-60 min. The number of cycles is 2-5, and a suspension is obtained. The upper suspension is filtered, washed, and dried to obtain few-layer MXene powder.

3. The preparation method of the MXene-enhanced sulfur-iron autotrophic denitrification composite packing according to claim 1, characterized in that, The clay is one of illite powder, sodium bentonite, or kaolin.

4. The preparation method of the MXene-enhanced sulfur-iron autotrophic denitrification composite packing according to claim 1, characterized in that, The binder is one of starch, carboxymethyl cellulose, or hydroxypropyl methyl cellulose.

5. The preparation method of the MXene-enhanced sulfur-iron autotrophic denitrification composite packing according to claim 1, characterized in that, The reducing protective agent is one or more of sodium bisulfite, potassium bisulfite, and sodium sulfite.

6. The preparation method of the MXene-enhanced sulfur-iron autotrophic denitrification composite packing according to claim 1, characterized in that, The sulfur has a sieve particle size of 100-300 mesh, and the pyrite has a sieve particle size of 50-200 mesh.

7. The preparation method of the MXene-enhanced sulfur-iron autotrophic denitrification composite packing according to claim 1, characterized in that, The bulk density of the MXene-enhanced ferrous sulfate autotrophic denitrification composite packing is 0.8-1.5 g / cm³. 3 Porosity 10-20%.

8. An MXene-enhanced sulfur-iron autotrophic denitrification composite packing prepared by the preparation method according to any one of claims 1-7.

9. The application of the MXene-enhanced sulfur-iron autotrophic denitrification composite packing material as described in claim 8 in the treatment of wastewater in an anaerobic reactor.

Images