Organosilane-modified biological denitrification filler, and preparation method and application thereof

Abstract

This invention discloses an organosilane-modified biological denitrification packing material, its preparation method, and its application, belonging to the field of water treatment. The invention involves mixing hydroxyethyl methacrylate, sulfur, and vinyltrimethoxysilane in a solvent, adding a catalyst, and heating the mixture to allow vinyltrimethoxysilane to simultaneously combine with hydroxyethyl methacrylate and sulfur, forming a stable cross-linked structure. After cooling and drying, a preliminary product is obtained, which is then granulated with a binder to obtain the final product. This invention utilizes the addition reaction between the vinyl group of vinyltrimethoxysilane and the sulfur free radical generated from the decomposition of sulfur, where the methoxy group reacts with the hydroxyl group of hydroxyethyl methacrylate to form a siloxane bond, forming a polymer. The prepared denitrification biological composite packing material can achieve sulfur autotrophic and heterotrophic coupled denitrification, possessing excellent mechanical strength, hydrophilicity, and carbon source slow-release function.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to an organosilane-modified biological denitrification packing material, its preparation method, and its application. Background Technology

[0002] Among current ecological and environmental issues, nitrogen pollution in water bodies is a significant challenge facing my country. Nitrogen pollutants, such as ammonia nitrogen and nitrates, are widely present in domestic sewage, agricultural wastewater, and industrial wastewater. If left untreated, these pollutants can lead to eutrophication, causing algal blooms, disrupting the balance of aquatic ecosystems, and even posing a threat to human health. Therefore, effectively removing nitrogen pollutants from wastewater is crucial for protecting water quality and safeguarding human health.

[0003] Biological nitrogen removal is widely used in practical engineering due to its advantages of low cost, simple operation, and stable results. Through the metabolic activities of microorganisms, biological methods can convert nitrogen pollutants into harmless nitrogen gas. Currently, biological nitrogen removal technologies mainly include two aspects: heterotrophic denitrification and autotrophic denitrification.

[0004] Heterotrophic denitrification relies on organic carbon sources to reduce nitrate nitrogen to nitrogen gas through heterotrophic bacteria. This method is widely used and has advantages including rapid microbial growth, high denitrification efficiency, and good performance when sufficient carbon sources are available. However, this method also has significant drawbacks: when carbon sources are insufficient, denitrification efficiency decreases significantly, requiring the addition of external organic carbon sources, increasing treatment costs, and potentially leading to secondary pollution.

[0005] Autotrophic denitrification utilizes reducing elements such as sulfur or iron as electron donors, with autotrophic denitrifying bacteria converting nitrate nitrogen into nitrogen gas. Its advantages include the ability to achieve maximal nitrogen removal without the need for external organic carbon sources. However, autotrophic denitrification also has limitations: slow microbial proliferation and poor adaptability to environmental changes affect its practical application. Sulfate accumulation during sulfur-autotrophic denitrification limits its widespread application. Heterotrophic-autotrophic coupled denitrification combines the advantages of both, achieving synergistic effects by adding various organic carbon sources to electron donors such as sulfur or iron. This technology compensates for the slow proliferation and poor shock resistance of autotrophic bacteria. Nevertheless, this coupled process also presents challenges: the need to manage two different types of denitrification processes simultaneously increases operational complexity. Balancing the growth and efficiency of heterotrophic and autotrophic bacteria is difficult during the competition for substrate among microbial communities.

[0006] To address these challenges, patent CN117865340A provides a denitrification biocomposite packing material, its preparation method, and its application. Employing a reverse sulfurization polymerization reaction, the prepared denitrification biocomposite packing material significantly improves sulfur bioavailability, maintains the stable structure of sulfur chains and organic matter, and exhibits good slow-release performance. Utilizing a sulfur autotrophic and heterotrophic coupling system for denitrification, it achieves efficient denitrification of low-carbon wastewater. However, this method requires sophisticated equipment and is complex to operate, increasing the difficulty and uncertainty of the process. Furthermore, the energy consumption during preparation is high, and operation under vacuum or nitrogen atmosphere increases equipment and operating costs. Patent CN117326689A discloses a method for preparing a mixed-nutrient denitrification packing material. It utilizes a sulfur-carbon composite carbon source generated after the reaction of acidic substances, combined with nano-ferrous sulfide to form a mixed nutrient system. This system synergistically maintains the abundance of autotrophic and heterotrophic denitrifying microorganisms and can enrich mixed-nutrient functional microorganisms with both autotrophic and heterotrophic electron utilization pathways, significantly enhancing the load resistance of acclimated sludge and achieving efficient and stable nitrogen removal. However, the composite carbon source and nano-ferrous sulfide used in this method may lack sufficient chemical and physical stability in actual wastewater treatment environments, and are easily decomposed or precipitated during operation, thus affecting its long-term effectiveness. Summary of the Invention

[0007] This invention provides an organosilane-modified biological denitrification filler, its preparation method, and its application. By optimizing the combination of hydroxyethyl methacrylate, sulfur, and vinyltrimethoxysilane, a stable cross-linked structure is formed, providing an ideal growth environment for sulfur autotrophic and heterotrophic denitrifying bacteria. When applied to the sulfur autotrophic and heterotrophic denitrification coupling process, it can effectively solve the problems in the coupling process in the prior art.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for preparing an organosilane-modified biological denitrification packing material includes the following steps:

[0010] S1 Heat the reaction solvent xylene to dissolve sulfur in the reaction solvent. Stir until completely dissolved, then add vinyltrimethoxysilane, stir well, and continue stirring.

[0011] Add catalyst S2, continue heating the mixed solution to maintain a constant temperature, and keep stirring continuously;

[0012] S3 is added to the mixed solution along with hydroxyethyl methacrylate, and the mixture is kept heated and stirred continuously.

[0013] After the S4 reaction is complete, stop heating and allow the solution to cool to room temperature. The reaction product will precipitate from the solvent. Add anhydrous ethanol or methanol to precipitate the product, filter, wash, and dry in a vacuum oven.

[0014] S5 mixes the dried reaction product with an appropriate amount of binder evenly, and then performs hot melt granulation in a granulator to obtain uniform granular filler.

[0015] In the steps described above, the solvent heating temperature in S1 is maintained at 120-130℃, the stirring speed is 80-120 rpm, and the stirring time is 20-40 minutes;

[0016] In S2, the stirring speed is 150-200 rpm, the heating temperature is maintained at 120-130℃, and the stirring time is 2-4 hours;

[0017] Heat in S3 and maintain at 70-90℃, stirring at 150-200 rpm for 1-2 hours;

[0018] The drying temperature described in S4 is 60-80℃, and the drying time is 6-10h;

[0019] The temperature for hot melt granulation in S5 is 150-200℃, and the stirring speed is 120-300rpm;

[0020] The components are composed of the following parts by weight: 30-60 parts sulfur, 140-150 parts vinyltrimethoxysilane, 150-300 parts hydroxyethyl methacrylate, 2-5 parts catalyst, and 5-10 parts binder.

[0021] The catalyst is one or more of nitrogen diisobutyronitrile (AIBN), dicumyl peroxide (DCP), and platinum-chromium complex; the binder is one or more of polyvinyl alcohol and polyacrylamide.

[0022] In the organosilane-modified biological denitrification filler prepared above, vinyltrimethoxysilane is simultaneously combined with hydroxyethyl methacrylate and sulfur to form a cross-linked network; the particle size of the filler is 2-5 mm.

[0023] The organosilane-modified biological denitrification packing material can be used for denitrification of wastewater coupled with sulfur autotrophic and heterotrophic denitrification.

[0024] Beneficial effects: This invention provides an organosilane-modified biological denitrification packing material, its preparation method, and its application, which has the following advantages compared with the prior art:

[0025] 1. This invention optimizes the combination of hydroxyethyl methacrylate (HEMA), sulfur, and vinyltrimethoxysilane (VTMS) to form a stable cross-linked structure, providing an ideal growth environment for sulfur-autotrophic and heterotrophic denitrifying bacteria. The sulfur in the packing material can act as an electron donor, utilized by sulfur-autotrophic denitrifying bacteria under anaerobic conditions to reduce nitrates to nitrogen. The organic matter in the packing material (such as hydroxyethyl methacrylate) provides an additional organic carbon source, promoting the growth and activity of heterotrophic denitrifying bacteria. These bacteria can utilize organic matter as an electron donor to reduce nitrates to nitrogen. The two bacterial groups can coexist and synergistically work on the same packing material, significantly improving denitrification efficiency.

[0026] 2. The packing design of this invention can precisely control the slow release rate of carbon source, avoiding the problem of microbial inhibition caused by excessive release of sulfur and carbon source; at the same time, it ensures that heterotrophic denitrifying bacteria can obtain a continuous and stable carbon source supply, maintain their growth and denitrification function, thereby achieving an efficient and stable nitrogen removal process.

[0027] 3. The silicon-oxygen bonds and silicon center structure in the filler of this invention provide high chemical stability and heat resistance, which enables the filler to maintain its physical and chemical properties under various harsh environments, thus extending its service life and reducing maintenance costs.

[0028] 4. The abundant carbon chains in the packing material of this invention not only provide the carbon source required for heterotrophic denitrifying bacteria, supporting their growth and denitrification, but also ensure that sulfur atoms participate efficiently in the sulfur autotrophic denitrification reaction, converting nitrate nitrogen into nitrogen gas, and significantly improving the overall denitrification effect.

[0029] 5. The presence of carbon chains and ether bonds in the packing material of this invention endows it with good mechanical strength and elasticity, making it less prone to breakage or deformation during use, thus extending its service life and reducing the frequency of replacement and maintenance. 6. The carboxyl groups and ether bonds in the packing material of this invention increase its hydrophilicity and water contact area, promoting the reaction. Simultaneously, the carboxyl groups provide good ion exchange capacity, helping to regulate the pH value of the reaction environment and optimize the growth conditions for microorganisms. Furthermore, the carbonyl groups in the packing material increase its polarity, giving it good solubility and dispersibility in water, further promoting the reaction and the attachment of microorganisms.

[0030] 7. The carbon-carbon double bonds in the filler of this invention provide active centers for the filler in free radical polymerization reactions, enabling it to undergo further chemical modification and cross-linking during processing and application, thereby improving the functionality and applicability of the material and meeting the needs of different application scenarios. Attached Figure Description

[0031] Figure 1 The NO3 in the effluent from bioreactors R1, R2, and R3 at each stage in this embodiment of the invention.- -N concentration.

[0032] Figure 2 This invention illustrates the effect of bioreactors R1, R2, and R3 on NO3 at each stage in embodiments of the invention. - -N removal rate.

[0033] Figure 3 The pH changes of bioreactors R1, R2, and R3 at each stage in this embodiment of the invention are shown.

[0034] Figure 4 This is a reaction mechanism diagram from an embodiment of the present invention. Detailed Implementation

[0035] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments:

[0036] Example 1

[0037] A method for preparing an organosilane-modified biological denitrification packing material includes the following steps:

[0038] Sulfur and vinyltrimethoxysilane in a mass ratio of 40:140 were added sequentially to xylene heated to 120°C, and stirred continuously for at least 30 minutes until completely dissolved. One part (by mass) of nitrogen diisobutyronitrile was added to the mixture, and heating and stirring were maintained for 2 hours. 150 parts of hydroxyethyl methacrylate were added to the mixture, the heating temperature was adjusted to 60°C, and stirring was continued for 1 hour. The mixture was then cooled to room temperature, and a preliminary product was precipitated using anhydrous ethanol. The preliminary product was dried in a vacuum oven at 60°C for 6 hours to obtain a crude product. The crude product was mixed with polyvinyl alcohol powder and granulated in a granulator at 150°C and 120 rpm to obtain an organosilane-modified biological denitrification filler with a stable cross-linked structure. Figure 4 As shown, by heating the mixture, the vinyl group of vinyltrimethoxysilane undergoes an addition reaction with the sulfur free radical generated from the decomposition of sulfur, and the methoxy group then reacts with the hydroxyl group of hydroxyethyl methacrylate to form a siloxane bond, thus forming a polymer. This allows vinyltrimethoxysilane to simultaneously combine with hydroxyethyl methacrylate and sulfur to form a stable cross-linked structure.

[0039] Example 2

[0040] A method for preparing an organosilane-modified biological denitrification packing material includes the following steps:

[0041] Sulfur and vinyltrimethoxysilane in a mass ratio of 60:140 were added sequentially to xylene heated to 125°C and stirred continuously for at least 30 minutes until completely dissolved. Two parts by mass fraction of nitrogen diisobutyronitrile were added to the mixture, and the mixture was heated and stirred continuously for 3 hours. 150 parts by mass fraction of hydroxyethyl methacrylate were added to the mixture, the heating temperature was adjusted to 75°C, and the mixture was stirred continuously for 2 hours. After cooling to room temperature, a preliminary product was precipitated using anhydrous ethanol. The preliminary product was dried in a vacuum oven at 70°C for 8 hours to obtain a crude product. The crude product was mixed with polyvinyl alcohol powder and granulated in a granulator at 180°C and 200 rpm to obtain an organosilane-modified biological denitrification filler with a stable cross-linked structure.

[0042] Example 3

[0043] A method for preparing an organosilane-modified biological denitrification packing material includes the following steps:

[0044] Sulfur and vinyltrimethoxysilane in a mass ratio of 30:150 were added sequentially to xylene heated to 130°C and stirred continuously for at least 30 minutes until completely dissolved. Three parts by mass fraction of nitrogen diisobutyronitrile were added to the mixture, and the mixture was heated and stirred continuously for 4 hours. 300 parts by mass fraction of hydroxyethyl methacrylate were added to the mixture, the heating temperature was adjusted to 90°C, and the mixture was stirred continuously for 2 hours. After cooling to room temperature, the preliminary product was precipitated using anhydrous ethanol. The preliminary product was dried in a vacuum oven at 80°C for 10 hours to obtain a crude product. The crude product was mixed with polyvinyl alcohol powder and granulated in a granulator at 200°C and 300 rpm to obtain an organosilane-modified biological denitrification filler with a stable cross-linked structure.

[0045] This invention provides the application of the prepared biological composite packing material in wastewater treatment.

[0046] The packing materials prepared in Examples 1, 2, and 3 were placed in a 5L UASB reactor in the laboratory, with a packing material filling rate of 60%. Activated sludge from an anaerobic tank of a wastewater treatment plant was inoculated with biofilm-forming sludge every five days. After three cycles, water quality indicators, i.e., culture medium utilization, were monitored daily. Biofilm formation was considered successful when water quality indicators remained stable and culture medium utilization was good for three consecutive cycles. The three reactors were designated R1, R2, and R3. A continuous flow experiment was conducted under the same conditions to verify the denitrification effect. The reactor influent was laboratory-simulated wastewater, prepared using laboratory tap water. Potassium nitrate (KNO3) was added as the sole nitrogen source to each reactor.

[0047] The operating parameters, such as the nitrogen concentration in the influent, are shown in Table 1. The hydraulic retention time is 6 hours, the temperature is 15-20℃, and the pH is 7.8.

[0048] Table 1. Specific influent water quality at each stage

[0049]

[0050] Figure 1-3 The diagram shows the treatment effect of reactors R1, R2, and R3 on the simulated wastewater. From this, we can see that:

[0051] (1) The sulfur content in the packing material of reactor R2 is relatively high compared with the carbon source content, which can easily lead to water acidification. Although the removal efficiency is close to that of R1 in the early stage, the pH decreases in the later stage, resulting in a decrease in the removal rate compared with R1.

[0052] (2) The carbon source content in reactor R3 is relatively high. Its treatment efficiency in the early stage is close to that of R1, but in the later stage, heterotrophic denitrifying bacteria inhibit sulfur autotrophic denitrifying bacteria, resulting in poor removal effect.

[0053] (3) Overall, reactor R1 performed best, maintaining stable and sustained removal capacity even under high nitrogen loads.

[0054] In summary, although reactors R1, R2, and R3 exhibit different performance characteristics, they all demonstrate superior nitrogen removal performance compared to conventional sulfur autotrophic denitrification reactors. The sulfur, vinyltrimethoxysilane, and hydroxyethyl methacrylate of this invention can all be used to prepare the aforementioned packing material within the specified dosage range. However, excessively high or low proportions can lead to performance degradation similar to that of reactors R2 and R3 under high loads; the optimal mass ratio should be close to 40:140:150.

[0055] Reactor R1 has the most stable nitrogen removal efficiency. By rationally proportioning the content of each component in the packing, the packing can maintain a low nitrate concentration in the effluent during long-term operation. It can also maintain good performance even when facing high concentrations of nitrate shock, which has great economic value and practical engineering application value. It also promotes the development of sulfur autotrophic coupled heterotrophic denitrification process.

[0056] The above are merely preferred embodiments of the present invention, which will help those skilled in the art to further understand the present invention, but do not limit the present invention in any way. It should be noted that for those skilled in the art, any modifications and improvements made without departing from the concept of the present invention are protected by the present invention.

Claims

1. A process for the preparation of an organosilane-modified biological denitrification filler, characterized in that, It comprises the following steps: S1: Heat the reaction solvent, dissolve sulfur in the reaction solvent, and stir until completely dissolved. Then add vinyltrimethoxysilane and stir evenly. Continue stirring; S2: Add catalyst, continue heating the mixed solution to maintain constant temperature, and continue stirring; S3: Add hydroxyethyl methacrylate to the mixed solution, keep heating, and continuously stir. The vinyl group of vinyltrimethoxysilane reacts with sulfur radicals generated by the decomposition of sulfur to form a siloxane bond, and the methoxy group reacts with the hydroxyl group of hydroxyethyl methacrylate to form a polymer. This allows vinyltrimethoxysilane to simultaneously bind with hydroxyethyl methacrylate and sulfur, forming a cross-linked structure; S4: After the reaction is complete, stop heating and let the solution cool to room temperature. The reaction product precipitates from the solvent and is precipitated by adding anhydrous ethanol or methanol. Filter, wash, and dry; S5: Mix the dried reaction product with an appropriate amount of binder and heat-melt granulate to obtain uniform granular filler.

2. The method for preparing an organosilane-modified biological denitrification filler according to claim 1, characterized in that, The heating temperature of the solvent in S1 is 120-130℃; the stirring speed is 80-120rpm, and the stirring time is 20-40 minutes.

3. The method for preparing the organosilane-modified biological denitrification packing material according to claim 1, characterized in that, The heating temperature in S2 is 120-130℃, the stirring speed is 150-200rpm, and the stirring time is 2-4 hours.

4. The method of claim 1, wherein the organosilane-modified biological denitrification filler is prepared by the steps of: (a) mixing a biological denitrification filler and a silane coupling agent; (b) drying the mixture; (c) calcining the dried mixture; and (d) washing the calcined mixture with water. The heating temperature in S3 is maintained at 70-90℃; the stirring speed is 150-200rpm, and the stirring time is 1-2 hours.

5. The method of claim 1, wherein the organosilane-modified biological denitrification filler is prepared by the steps of: (a) mixing a biological denitrification filler and a silane coupling agent; (b) drying the mixture; (c) calcining the dried mixture; and (d) washing the calcined mixture. The drying temperature in S4 is 60-80℃, and the time is 6-10h.

6. The method of claim 1, wherein the organosilane-modified biological denitrification filler is prepared by the steps of: (a) mixing a biological denitrification filler and a silane coupling agent; (b) drying the mixture; (c) calcining the dried mixture; and (d) washing the calcined mixture. The temperature for heat-melt granulation in S5 is 150-200℃, and the stirring speed is 120-300rpm.

7. The method of claim 1, wherein the organosilane-modified biological denitrification filler is prepared by the steps of: (a) mixing a biological denitrification filler and a silane coupling agent; (b) drying the mixture; (c) calcining the dried mixture; and (d) washing the calcined mixture. The components are as follows: sulfur 30-60 parts, vinyltrimethoxysilane 140-150 parts, hydroxyethyl methacrylate 150-300 parts, catalyst 2-5 parts, and binder 5-10 parts.

8. The organosilane-modified biological denitrification filler produced by the method according to any one of claims 1 to 7, characterized by, The vinyl group of vinyltrimethoxysilane reacts with sulfur radicals generated by the decomposition of sulfur to form a siloxane bond, and the methoxy group reacts with the hydroxyl group of hydroxyethyl methacrylate to form a polymer. This allows vinyltrimethoxysilane to simultaneously bind with hydroxyethyl methacrylate and sulfur, forming a cross-linked structure.

9. The organosilane-modified biological denitrification filler according to claim 8, characterized in that, The particle size of the filler is 2-5mm.

10. Use of the organosilane-modified biological denitrification filler according to any one of claims 8 to 9, characterized in that, The filler is used for sulfur autotrophic and heterotrophic denitrification coupling process wastewater denitrification.

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