A polysulfide-achieving deep denitrification biological composite filler and a preparation method thereof

Abstract

The application discloses a preparation method of a biological composite filler capable of generating polysulfides to realize deep denitrification, and belongs to the technical field of sewage biological treatment. The filler takes sulfur and limestone as a matrix, adds cysteine and mixes uniformly, simultaneously supplements trace elements, is subjected to bonding and foaming treatment, and is finally shaped to obtain the biological composite filler capable of generating polysulfides to realize deep denitrification. The absorption and utilization of elemental sulfur by sulfur autotrophic bacteria are mediated by extracellular substances. Under the condition of elemental sulfur, substances containing mercapto groups are highly expressed and differentially expressed. They activate elemental sulfur and biologically modify sulfur to generate polysulfides as soluble intermediates for bacteria to utilize. The biological composite filler prepared by the application has the advantages that a small amount of cysteine is added to promote the formation of organic polysulfides, improve the solubility of sulfur in sewage, be beneficial to the absorption of sulfur source by sulfur-oxidizing bacteria and the formation of EPS, shorten the domestication time of microorganisms, and improve the denitrification capacity.

Description

Technical Field

[0001] This invention belongs to the field of wastewater denitrification treatment, specifically relating to a biological composite packing material that generates polysulfides to achieve deep denitrification and its preparation method. Background Technology

[0002] Elemental sulfur is frequently used in wastewater treatment due to its low cost, availability, non-toxicity, and harmlessness. Utilizing elemental sulfur as an inorganic electron donor for advanced denitrification of oligotrophic nitrogen-containing wastewater, such as drinking water, groundwater, and secondary effluent from municipal wastewater treatment plants, has become a research hotspot in recent years. Compared to heterotrophic denitrification processes using organic carbon sources as electron donors, sulfur autotrophic denitrification (SADN) offers advantages such as lower sludge production and lower operating costs. However, the low solubility of elemental sulfur leads to poor bioavailability, thus limiting the rate of SADN and hindering its widespread application.

[0003] Currently, many studies are dedicated to exploring how to improve the electron's ability to escape from S. 0 The transfer rate of sulfur-oxidizing denitrifying bacteria to nitrate reduction increases the rate of SADN, polysulfides (S... n 2- (Formula 1) is generated by the chemical reaction of elemental sulfur and sulfides under neutral to alkaline conditions. As a transfer carrier of dissolved zero-valent sulfur in water, its bioavailability is much higher than that of sulfur. 0 S n 2- Once produced, it can be rapidly utilized by sulfur-oxidizing denitrifying bacteria to achieve rapid nitrate reduction (Equation 2). Therefore, S n 2- It can be used as sulfur-oxidizing and denitrifying bacteria and S 0 It acts as a medium for electron conduction between the two, accelerating the rate of electron transfer between them.

[0004]

[0005]

[0006] However, polysulfide chemicals are extremely expensive and difficult to store for long periods, making direct addition to wastewater treatment processes unsuitable. Using sulfides (such as sodium sulfide and sodium hydrosulfide) as precursors can promote the growth of polysulfides. n 2- Naturally formed, but the transportation, use and storage of sulfides pose safety risks.

[0007] Adding an organic carbon source to a sulfur autotrophic reactor allows for the conversion of elemental sulfur or sulfate into sulfur through heterotrophic sulfur-reducing bacteria. n 2-The goal is to increase the denitrification rate. However, the difficulty lies in precisely controlling the amount of organic carbon. Too much organic carbon can lead to the proliferation of heterotrophic bacteria, which occupy the ecological niche of sulfur autotrophic bacteria and disrupt the reactor's balance. Furthermore, sulfur autotrophic bacteria inevitably produce some organic matter during their proliferation. Small amounts of non-corresponding organic matter do not promote reactor growth but instead lead to higher effluent COD. In previous studies and practices, trace amounts of COD have always been detected in the effluent of sulfur autotrophic reactors without external organic carbon sources. This is generally considered to be endogenous organic matter produced during the cell proliferation of sulfur autotrophic bacteria. Externally added high-quality organic carbon sources such as sodium acetate and ethanol are mainly absorbed and utilized by heterotrophic bacteria for heterotrophic denitrification or heterotrophic sulfur reduction activities. Only a small number of sulfur autotrophic bacteria can absorb and utilize these organic carbon sources. Summary of the Invention

[0008] This invention provides a biological composite packing material for generating polysulfides to achieve deep denitrification and its preparation method. The prepared biological composite packing material can shorten the acclimatization time of sulfur autotrophic reactors, improve the bioavailability of elemental sulfur, and achieve efficient and deep denitrification.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] A method for preparing a bio-composite packing material that generates polysulfides to achieve deep denitrification includes the following steps:

[0011] S1: Mix polyvinyl acetate with glycerol to obtain mixture A;

[0012] S2: Mix sulfur and calcium carbonate thoroughly and add them to mixture A to make the first mixture to obtain mixture B;

[0013] S3: Cysteine, trace elements and sodium alginate aqueous solution are mixed in a second process to dissolve them and obtain mixture C;

[0014] S4: Add the mixtures B and C obtained in S2 and sodium dodecylbenzenesulfonate into a container for the third mixing. Add a foaming agent and mix thoroughly to obtain a uniform mixture. Heat and melt the mixture, feed it into the container, and then injection mold it into granules to obtain the desired filler.

[0015] In the steps described above, the mass ratio of polyvinyl acetate to glycerol in S1 is (15-20):(30-35);

[0016] The sulfur and calcium carbonate in S2 are stirred until they turn grayish-yellow and are uniform; the sulfur and calcium carbonate are in powder form; the mass ratio of sulfur to calcium carbonate is (20-40):(15-20); the mass ratio of sulfur to mixture A is (20-40):(3-6).

[0017] The mass ratio of sulfur to cysteine ​​is (20-40):(0.5-2); the mass fraction of the sodium alginate aqueous solution is 2-5 wt%; the mass ratio of sulfur to sodium alginate solution is (20-40):(1-3); the composition of trace elements (based on sodium alginate solution: g) L-1): Disodium EDTA-Na 5, Ferrous sulfate (FeSO4) 5, Disodium EDTA-Na 15, Boric acid (H3BO4) 0.0014, Manganese chloride tetrahydrate (MnCl2·4H2O) 0.99, Copper sulfate pentahydrate (CuSO4·5H2O) 0.25, Zinc sulfate heptahydrate (ZnSO4·7H2O) 0.43, Nickel chloride hexahydrate (NiCl2·6H2O) 0.19, Sodium selenate decahydrate (NaSeO4·10H2O) 0.21, Sodium molybdate dihydrate (NaMoO4·2H2O) 0.22;

[0018] The second mixing method in S3 is heating and stirring, with a temperature of 45-55℃ and a time of 10-20 minutes;

[0019] The mass ratio of sulfur to sodium dodecylbenzenesulfonate is (20-40):(4-7);

[0020] The mass ratio of sulfur to foaming agent is (20-40):(5-8); the foaming agent is sodium bicarbonate solution, and the mass fraction of sodium bicarbonate solution is 0.5-2 wt%.

[0021] The melt granulation described in S4 is carried out under a protective atmosphere and stirring conditions; the temperature of the melt granulation is 240-280℃, the stirring speed is 120-150rpm, and the specific time depends on the quality of the raw materials; the vacuum feeding can be carried out using either an electric vacuum feeder or a pneumatic vacuum feeder.

[0022] The biological composite packing material prepared by the above method, which generates polysulfides to achieve deep denitrification, has a particle size of 8–15 mm.

[0023] Beneficial effects: This invention provides a bio-composite packing material for deep denitrification by generating polysulfides and its preparation method. Compared with the prior art, this invention has the following advantages:

[0024] This invention provides a biocomposite packing material for deep denitrification by generating polysulfides. Using sulfur and limestone as a matrix, cysteine ​​is added and mixed uniformly, while trace elements are supplemented. After bonding and foaming, the final product is a biocomposite packing material capable of generating polysulfides for deep denitrification. Sodium alginate, as a natural anionic polysaccharide, is non-toxic and has good biocompatibility. It can effectively protect microorganisms from the effects of harmful environmental media and is an ideal material for immobilizing microbial cells. Sodium dodecylbenzenesulfonate, as a solid surfactant, improves the hydrophilicity of the packing surface, increasing the enrichment of microorganisms and significantly enhancing their activity. Its utilization rate of sulfur sources, carbon sources, and nutrients also improves the denitrification effect of microorganisms on nitrogen-containing pollutants. The absorption and utilization of elemental sulfur by sulfur-autotrophic bacteria is mediated by extracellular substances. Under elemental sulfur conditions, substances containing thiol groups are highly and differentially expressed. These substances activate elemental sulfur, biomodify it, and generate polysulfides as soluble intermediates, altering the chemical form of sulfur and changing its hydrophobicity to hydrophilicity for bacterial utilization. The biocomposite packing material prepared in this invention activates elemental sulfur by adding a small amount of cysteine, thereby converting elemental sulfur into a soluble polysulfide form that enters the cell. n 2- Once generated, it can be rapidly utilized by sulfur-oxidizing denitrifying bacteria to achieve rapid reduction of nitrates. A small amount of cysteine ​​acts as a primer for sulfur-autotrophic denitrifying bacteria to activate elemental sulfur, making it easier for them to absorb. This promotes the formation of organic polysulfides, increases the solubility of sulfur in wastewater, and, combined with trace elements, promotes the proliferation and growth of microorganisms. This is beneficial for sulfur-oxidizing bacteria to absorb sulfur sources and for the formation of EPS, shortens the acclimatization time of microorganisms, and improves denitrification capacity. No additional organic matter and sulfide chemicals are required. The biological treatment unit is simple, has low operating costs, good denitrification effect, stable system performance, and high denitrification rate. Attached Figure Description

[0025] Figure 1 This is a diagram showing the effluent output of the reactor in Embodiment 1 of the present invention;

[0026] Figure 2 This is a diagram showing the effluent output of the reactor in Embodiment 2 of the present invention;

[0027] Figure 3 This is a diagram showing the effluent output of the reactor in Embodiment 3 of the present invention. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments:

[0029] A method for preparing a bio-composite packing material that generates polysulfides to achieve deep denitrification includes the following steps:

[0030] Polyvinyl acetate and glycerol are mixed to obtain mixture A; the mass ratio of polyvinyl acetate to glycerol is preferably (15-20):(30-35), more preferably 20:30;

[0031] Sulfur and calcium carbonate are mixed and stirred until evenly distributed, then added to mixture A for a first mixing to obtain mixture B. The sulfur and calcium carbonate are in powder form, and the mass ratio of sulfur to calcium carbonate is (20-40):(15-20), more preferably 30:20; the mass ratio of sulfur to mixture A is (20-40):(3-6), more preferably 30:5. The sulfur can be used as a sulfur source by sulfur autotrophic denitrifying bacteria to form sulfur autotrophic denitrification; the calcium carbonate is a buffer to resist the influence of adverse pH from the outside environment; mixture A acts as a binder for sulfur and calcium carbonate, providing toughness, strength and plasticity to the filler. The first mixing method is preferably stirring, the stirring speed is preferably 10000-20000 rpm, more preferably 15000 rpm, and the time is preferably 0.5-1 h, more preferably 0.75 h.

[0032] Cysteine, trace elements, and sodium alginate aqueous solution are mixed in a second step to dissolve them and obtain mixture C. The sodium alginate aqueous solution preferably has a mass fraction of 2-5 wt%, more preferably 4 wt%, and can be a self-made solution or a purchased product. The mass ratio of sulfur to cysteine ​​is preferably (20-40):(0.5-2), more preferably 30:1, and the mass ratio of sulfur to sodium alginate solution is (20-40):(1-3), more preferably 30:2. Cysteine ​​and trace elements are added to the sodium alginate solution, and there is no requirement for the order of mixing. The second mixing method is heating and stirring. The stirring speed is preferably 200-600 rpm, more preferably 300 rpm, the stirring time is preferably 20-50 min, more preferably 40 min, and the temperature is preferably 45-55℃, more preferably 50℃.

[0033] Mixtures B and C are added to a container for a third mixing process. A foaming agent is added, and the mixture is thoroughly stirred and mixed to obtain a homogeneous mixture. This mixture is then heated and melted, vacuum-fed, and injection-molded to obtain the desired filler. The second mixing process is preferably a process where mixtures B and C are initially mixed, and the resulting initial mixture is then mixed with sodium dodecylbenzenesulfonate. The initial mixing method is preferably stirring, with a stirring speed preferably of 8000–15000 rpm, more preferably 12000 rpm, and a stirring time preferably of 40–60 min, more preferably 50 min. The remixing method is preferably the same as the initial mixing method and will not be described in detail here. In this invention, the mass ratio of sulfur to sodium dodecylbenzenesulfonate is (20-40):(4-7), and the mass ratio of sulfur to foaming agent is preferably (20-40):(5-8), more preferably 30:6-7; the foaming agent is a sodium bicarbonate solution, with a mass fraction preferably 0.5-2 wt%, more preferably 1-2 wt%, and the foaming agent is added uniformly during the third mixing; the melt granulation is carried out under a protective atmosphere and stirring conditions, the melt granulation temperature is preferably 240-280℃, more preferably 270℃, and the stirring speed is 120-150 rpm. This invention does not specifically limit the specific operation steps of the granulation, as long as granules with a particle size of 8-15 mm are obtained; in the embodiments of this invention, the equipment used for granulation is preferably a granulator, specifically, the composite material obtained after heat treatment is transported to the granulator for granulation. This invention preferably uses granulation to give the biocomposite filler greater mechanical strength, smaller particle size, and larger specific surface area.

[0034] Example 1

[0035] Mixture A was prepared with a polyvinyl acetate to glycerol mass ratio of 20:30. Then, 35 parts by mass of sulfur, 15 parts by mass of calcium carbonate, and 5 parts by mass of mixture A were weighed and stirred at 15,000 rpm for 1 hour until homogeneous to obtain mixture B. 2 parts by mass of cysteine ​​and 3 parts by mass of sodium alginate solution were weighed and added to a 4 wt% sodium alginate solution. The mixture was heated and stirred at 300 rpm and 45–55 °C for 50 minutes to obtain mixture B. Material C; 7 parts by mass of sodium dodecylbenzenesulfonate were weighed and added to mixture B and mixture C after initial mixing. The mixture was stirred at 12000 rpm for 50 min. 5 parts by mass of 1wt% sodium bicarbonate solution were weighed and added evenly during stirring to obtain the filler raw material. The raw material was transported to the injection molding machine through a vacuum feeder. The filling was carried out under a protective atmosphere and stirring conditions at 240-280℃. After cooling, the bio-composite filler was obtained.

[0036] Example 2

[0037] Mixture A was prepared with polyvinyl acetate and glycerol in a mass ratio of 20:30. Then, 30 parts by mass of sulfur, 20 parts by mass of calcium carbonate, and 5 parts by mass of mixture A were weighed and stirred at 15000 rpm for 0.75 h until homogeneous, yielding mixture B. One part by mass of cysteine ​​and two parts by mass of sodium alginate solution were weighed and added to a 4 wt% sodium alginate solution. The mixture was heated and stirred at 300 rpm and 45–55 °C for 40 min to obtain mixture B. Compound C; 5 parts by mass of sodium dodecylbenzenesulfonate were weighed and added to mixture B and mixture C after initial mixing. The mixture was stirred at 12000 rpm for 50 min. 3 parts by mass of 2wt% sodium bicarbonate solution were weighed and added evenly during stirring to obtain the filler raw material. The raw material was transported to the injection molding machine through a vacuum feeder. The filling was carried out under a protective atmosphere and stirring conditions, maintaining a temperature of 240-280℃. After cooling, the bio-composite filler was obtained.

[0038] Example 3

[0039] Mixture A was prepared with a polyvinyl acetate to glycerol mass ratio of 20:30. Then, 25 parts by mass of sulfur, 25 parts by mass of calcium carbonate, and 3 parts by mass of mixture A were weighed and stirred at 15000 rpm for 0.5 h until homogeneous, yielding mixture B. 0.5 parts by mass of cysteine ​​and 1 part by mass of sodium alginate solution were weighed and added to a 4 wt% sodium alginate solution. The mixture was heated and stirred at 300 rpm and 45–55 °C for 45 min to obtain mixture B. Compound C; 4 parts by mass of sodium dodecylbenzenesulfonate were weighed and added to mixture B and mixture C after initial mixing. The mixture was stirred at 12000 rpm for 50 min. 5 parts by mass of 0.5 wt% sodium bicarbonate solution were weighed and added evenly during stirring to obtain the filler raw material. The raw material was transported to the injection molding machine through a vacuum feeder and carried out under a protective atmosphere and stirring conditions at 240-280℃ to produce the filler. After cooling, the bio-composite filler was obtained.

[0040] The biocomposite packing particles prepared in Examples 1-3 were respectively packed into fixed-bed biocolumn reactors, inoculated with nitrate-dependent sulfur autotrophic denitrifying bacteria and anaerobic sludge for biofilm formation. After biofilm formation, simulated nitrogen-containing wastewater, prepared from sodium nitrate and tap water, was introduced into the reactor using a peristaltic pump. The nitrate nitrogen concentration in the simulated nitrogen-containing wastewater was 40 mg / L. The reactors were operated for a period of time in three stages: Stage I (0-30 days), Stage II (30-60 days), and Stage III (60-90 days), with hydraulic retention times of 9 h, 6 h, and 3 h for each stage, respectively. The effluent conditions were observed. The reactor corresponding to the biocomposite packing particles prepared in Example 1 was designated as reactor E1, the reactor corresponding to the biocomposite packing particles prepared in Example 2 as reactor E2, and the reactor corresponding to the biocomposite packing particles prepared in Example 3 as reactor E3. The results are as follows: Figures 1-3 As shown. By Figures 1-3 It can be seen that the effluent effect of reactor E2 is relatively excellent, with an average nitrate nitrogen removal rate of 91.7% in stage III, while the removal rates of other reactors are basically around 88%. This proves that the biological composite packing particles provided by this invention can achieve a relatively excellent denitrification effect in wastewater treatment and have high practical application value.

[0041] 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 method for preparing a biological composite filler for achieving deep denitrification by polysulfide, characterized in that, The method comprises the following steps: S1: mixing polyvinyl acetate and glycerol to obtain mixture A; S2: mixing sulfur and calcium carbonate, and then adding the mixture A into the mixture of sulfur and calcium carbonate to obtain mixture B; S3: mixing cysteine and trace elements with sodium alginate solution, and dissolving the mixture to obtain mixture C, wherein the mass ratio of sulfur to cysteine is (20-40):(0.5-2), and the composition of the trace elements is as follows: 20 g / L of disodium ethylenediaminetetraacetate, 5 g / L of ferrous sulfate, 0.0014 g / L of boric acid, 0.99 g / L of manganese chloride tetrahydrate, 0.25 g / L of copper sulfate pentahydrate, 0.43 g / L of zinc sulfate heptahydrate, 0.19 g / L of nickel chloride hexahydrate, 0.21 g / L of sodium selenate decahydrate, and 0.22 g / L of sodium molybdate dihydrate; S4: adding mixture B, mixture C and sodium dodecylbenzenesulfonate into a container to obtain a mixture, adding a foaming agent, and then fully stirring and mixing the mixture to obtain a mixture, and then heating, melting, feeding and injection molding to obtain the composite filler.

2. The method of claim 1, wherein the method is characterized by: The mass ratio of polyvinyl acetate to glycerol is (15-20):(30-35).

3. The method of claim 1, wherein the method is characterized by: The mass ratio of sulfur to calcium carbonate is (20-40):(15-20), the mass ratio of sulfur to mixture A is (20-40):(3-6), and the mass ratio of sulfur to sodium alginate solution is (20-40):(1-3).

4. The method of claim 1, wherein the method is characterized by: The second mixing method in S3 is heating and stirring, the temperature is 45-55 DEG C, and the time is 10-20 min.

5. The method for preparing the biological composite filler for achieving deep denitrification by polysulfide according to claim 1 or 3, characterized in that, The mass ratio of sulfur to sodium dodecylbenzenesulfonate in S4 is (20-40):(4-7), and the mass ratio of sulfur to the foaming agent is (20-40):(5-8).

6. The method of claim 1, wherein the method further comprises the step of: 6.

1. mixing the bio-composite filler with a poly-sulphide solution to form a bio- composite filler with poly-sulphide. The melting and granulation in S4 is carried out in a protective atmosphere and under stirring, the temperature is 240-280 DEG C, and the stirring speed is 120-150 rpm.

7. The bio-composite filler for deep denitrification by polysulfide generation prepared by the method according to any one of claims 1 to 6, characterized in that, The cysteine in the composite filler is a substance containing a sulfhydryl structure, which activates elemental sulfur, modifies the sulfur to generate polysulfides as a soluble intermediate, combines with trace elements to promote the proliferation and growth of microorganisms, and is beneficial to the absorption of sulfur source by sulfur-oxidizing bacteria and the formation of EPS.

8. The bio-composite packing material for achieving deep denitrification through polysulfide generation as claimed in claim 7, wherein, The particle size of the composite filler is 8-15 mm.

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