Novel sulfur autotrophic denitrification filter material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of sewage treatment, and discloses a novel sulfur autotrophic denitrification filter material and a preparation method and application thereof.The particle size of the filter material is 3.0-4.0 mm, and the filter material is prepared from 40%-45% of a composite sulfur source, 70 + / -2% of sulfur and 30 + / -2% of sodium thiosulfate, 30%-35% of modified ceramsite, 50-100 [mu] m / 200-300 [mu] m of bimodal pore size and 8%-10% of a conducting medium. The ratio of graphene to biochar is 3: 1), a buffer medium (5%-7%, Fe2O3 (52% + / -2%), CaCO3 (31% + / -2%) and MgO (17% + / -2%), a binder and an inert filler. The preparation method comprises the steps of raw material pretreatment, mixing granulation, stepped calcination, gradient impregnation, buffer medium directional loading, post-treatment and the like. The filter material solves the problems of by-product accumulation, insufficient microbial adhesion, large pH fluctuation and blockage of a traditional filter material through gradient sulfur release, a three-dimensional electron transfer network, a multistage pore anti-blockage design and a composite pH buffer system, is suitable for sewage denitrification treatment, and is high in denitrification efficiency and good in stability.

Description

Technical Field

[0001] The present invention relates to the field of sewage treatment, and particularly to a novel sulfur autotrophic denitrification filter material, a preparation method thereof, and an application thereof. Background Art

[0002] Sulfur autotrophic denitrification (SAD) is an autotrophic denitrification technology that uses sulfide or reduced sulfur as an electron donor for sewage denitrification. Its core is to reduce nitrate to nitrogen under anoxic conditions through the metabolic activities of specific autotrophic microorganisms, while using sulfide as an electron donor and inorganic carbon source as a carbon source to synthesize bacterial community cell tissues. The main functional bacteria include Thiobacillus denitrificans (a typical sulfur autotrophic denitrifying bacterium, with an optimum growth temperature of 30 °C and a pH of 6.8 - 7.0, obtaining energy by oxidizing sulfur), and sulfur-oxidizing bacteria (in the pyrite system, collaborating to complete the oxidation of sulfur and iron and denitrification). Since no additional organic carbon source needs to be added, it has great potential in the field of sewage treatment.

[0003] However, the current filter materials for sulfur autotrophic denitrification have the following defects, which limit their practical applications:

[0004] (1) Sulfur + calcium carbonate composite filter material has the problem of by-product sulfate accumulation;

[0005] (2) Sulfur and biochar composite filter material has insufficient microbial adhesion;

[0006] (3) Sulfur-iron composite filter material has large pH fluctuations and a risk of blockage. Summary of the Invention

[0007] To solve the technical problems such as by-product sulfate accumulation, insufficient microbial adhesion, large pH fluctuations, and blockage risk existing in the existing sulfur autotrophic denitrification filter materials in the background art, the present invention provides a novel sulfur autotrophic denitrification filter material, a preparation method thereof, and an application thereof, achieving an efficient and stable sewage denitrification effect by optimizing the filter material composition and preparation process.

[0008] The novel sulfur autotrophic denitrification filter material of the present invention has a particle size of 3.0 mm - 4.0 mm and is composed of a composite sulfur source, modified ceramsite, conductive medium, buffer medium, binder, and inert filler. The mass percentage and characteristics of each component are as follows:

[0009] Composite sulfur source: accounting for 40% - 45% of the total mass, consisting of 70 ± 2% sulfur and 30 ± 2% sodium thiosulfate, forming a core-shell structure with sulfur-coated sodium thiosulfate by dry mixing in a three-dimensional mixer, constituting a gradient release sulfur source, and continuously providing an electron donor for the denitrification process.

[0010] Modified ceramsite: accounting for 30%-35% of the total mass, after ultrasonic pickling with 5% HCl solution, 3% carboxymethyl cellulose is added as a pore-forming agent to form a bimodal pore size distribution (main pore 100μm ± 10%, secondary pore 200μm ± 15%), which is beneficial to the mass transfer between sewage and filter media and reduces the risk of blockage.

[0011] Conductive medium: accounting for 8%-10% of the total mass, where the ratio of graphene to biochar is 3:1. It is formulated into a 2mg / mL dispersion with water and ethanol (7:3) as solvents and 0.1% SDBS as a dispersant, and is loaded onto the filter media in a honeycomb shape through gradient vacuum impregnation (primary impregnation, secondary impregnation, tertiary impregnation), enhancing the electron exchange between the filter media and nitrogen and improving the microbial adhesion.

[0012] Buffer medium: accounting for 5%-7% of the total mass, consisting of 52% ± 2% of Fe2O3, 31% ± 2% of CaCO3, and 17% ± 2% of MgO. Through the chemical precipitation method, under the conditions of pH = 8.5 ± 0.2 and 45℃ ± 2℃, Fe 3+ and Mg 2+ react with OH - etc. to form hydroxide precipitates respectively, and then heat-treat at 200℃ for 2h to control the conversion rate of Fe(OH)3 ≥ 90% to generate Fe2O3, and 10% of Mg(OH)2 remains in the untransformed state, playing a role in stabilizing the pH.

[0013] The preparation method includes the following steps:

[0014] Raw material pretreatment: Crush sulfur to 150-180 mesh, ball-mill sodium thiosulfate to 200-300 mesh and mix to form a core-shell structure; carry out pickling and pore-forming modification on the ceramsite.

[0015] Mixing and granulation: Use 12% sodium-based bentonite and 3% polyvinyl alcohol as binders, granulate under the conditions of a granulator rotation speed of 450rpm ± 10rpm and a spraying rate of 8mL / min ± 0.5mL, control the formed particle size to be 3.5mm ± 0.2mm, screen through a double-layer vibrating screen to ensure that the particle size qualification rate is ≥ 95%, and then dry in a hot air circulation at 50℃ until the moisture content ≤ 2%.

[0016] Stepwise calcination: In a tubular atmosphere furnace, use N2 with a purity ≥ 99.99% as a protective gas (flow rate 1.5L / min, oxygen content in the furnace < 50ppm). In the first stage, heat from room temperature to 300℃ at a rate of 5℃ / min and hold for 1h to remove organic substances. In the second stage, heat from 300℃ to 600℃ at a rate of 3℃ / min and hold for 1h to form a stable pore structure.

[0017] Gradient impregnation: First, perform primary impregnation (maintain a vacuum of -0.1 MPa for 30 min and then soak at atmospheric pressure for 1 h) to load the conductive medium on the inner layer of the pores. Then, perform secondary impregnation (maintain a vacuum of -0.08 MPa for 20 min and then impregnate under a pressure of 0.3 MPa for 30 min) to achieve middle-layer penetration. Finally, perform rotary impregnation at atmospheric pressure (rotation speed of 15 rpm, impregnation for 2 h) to uniformly coat the conductive medium on the surface.

[0018] Directional loading of buffer medium: Load metal hydroxide by chemical precipitation method and then convert it into oxide by heat treatment to achieve directional loading of the buffer medium.

[0019] Post-treatment: First, dry in a vacuum drying oven at -0.09 MPa and 40 °C until the moisture content ≤ 1%. Then, electrostatically spray a 1 wt% polydopamine solution (dissolved in 10 mM Tris-HCl buffer) to form a bioaffinity layer with a thickness of 50 - 80 μm, further enhancing the microbial attachment ability.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1. The present invention adopts gradient sulfur source sulfur release and denitrification: sulfur (fast release phase) and sodium thiosulfate (slow release phase) are compounded at a ratio of 7:3, with gradient release, small fluctuation coefficient of denitrification efficiency, and high sulfur utilization rate;

[0022] 2. The present invention has a three-dimensional electron transfer network: a graphene-biochar honeycomb conductive network, which improves the electron transfer efficiency and increases the abundance of denitrifying bacteria;

[0023] 3. The present invention adopts a multi-stage pore anti-blocking design: a bimodal pore size design (main pore 100 μm ± 10%, secondary pore 200 μm ± 15%), which improves the hydraulic permeability coefficient and reduces the backwashing frequency;

[0024] 4. The present invention has a composite pH buffer system: CaO / MgO releases alkalinity slowly at a ratio of 3:1, and Fe2O3 inhibits the excessive accumulation of H + , and the pH is automatically stabilized at 7.0 ± 0.5 (without adding an external alkalinity regulator)

[0025] In summary, the present invention adopts four key solutions:

[0026] Key point 1: Stepwise calcination, slow heating with a two-temperature zone to avoid sintering of ceramsite, and the porosity is increased by 35%;

[0027] Key point 2: Gradient impregnation, three-stage pressure alternating impregnation, and the loading rate of the conductive material is increased to 92%;

[0028] Key point 3: Directional loading, pH-controlled stepwise precipitation, and the uniformity of the distribution of Fe-Ca-Mg oxides > 90%;

[0029] Key point 4: Surface modification, electrostatic spraying of polydopamine, the biofilm formation rate is increased by 2.3 times; Description of the Drawings

[0030] Figure 1 This is a schematic diagram of the preparation process of the present invention. Detailed Embodiments

[0031] Next, in combination with the drawings and specific embodiments, the present invention will be further described. It should be noted that on the premise of non-conflict, the following-described embodiments or technical features can be arbitrarily combined to form new embodiments.

[0032] Example 1: Preparation and Application of a Novel Sulfur Autotrophic Denitrification Filter Media

[0033] I. Filter Media Composition

[0034] Particle size: 3.5 mm (controlled by screening to be within 3.0 mm - 4.0 mm, with a qualification rate ≥ 95%).

[0035] Composition and mass ratio:

[0036] Composite sulfur source (45%): Sulfur (70%) + sodium thiosulfate (30%), forming a gradient-release sulfur source.

[0037] Modified ceramsite (35%): Bimodal pore size distribution, main pore 100 μm ± 10%, secondary pore 200 μm ± 15%, promoting mass transfer.

[0038] Conductive medium (10%): Graphene: Biochar = 3:1, honeycomb-like loading, enhancing electron exchange.

[0039] Buffer medium (7%): Fe2O3 (52%), CaCO3 (31%), MgO (17%), adjusting the pH.

[0040] Remaining components: Binder (sodium-based bentonite + polyvinyl alcohol) and inert filler.

[0041] II. Preparation Method

[0042] As Figure 1 shown, the specific method includes the following steps:

[0043] Step 1: Pretreatment of raw materials

[0044] Treatment of sulfur source:

[0045] Sulfur (industrial grade, purity ≥ 99%) is pulverized by an air-flow pulverizer to 150 - 180 meshes (D50 = 85 μm).

[0046] Sodium thiosulfate (Na2S2O3·5H2O) is ball-milled with zirconia balls (ball-to-material ratio of 5:1) to 200 - 300 mesh.

[0047] The three-dimensional mixer is used for dry mixing for 30 min (rotation speed of 25 rpm) to form a core-shell structure with sulfur-coated sodium thiosulfate.

[0048] Ceramsite modification:

[0049] Pickling: The 5% HCl solution (liquid-to-solid ratio of 5:1) is ultrasonically treated for 2 h.

[0050] Pore formation: 3% carboxymethyl cellulose is added as a pore-forming agent to form a bimodal pore size (main pore of 100 μm ± 10%, secondary pore of 200 μm ± 15%).

[0051] Step 2: Mixing and granulation

[0052] Binder system: 12% sodium-based bentonite + 3% polyvinyl alcohol.

[0053] Granulation parameters:

[0054] The rotation speed of the granulator is 450 rpm (accuracy of ±10 rpm), and the spraying rate is 8 mL / min (accuracy of ±0.5 mL).

[0055] The formed particle size is 3.5 mm, and it is screened by a double-layer vibrating screen (pore size of 3.0 mm - 4.0 mm), with a qualified rate of ≥95%.

[0056] Drying conditions: Hot air circulation drying at 50°C until the moisture content ≤2%.

[0057] Step 3: Stepwise calcination

[0058] Equipment: Tube-type atmosphere furnace (N2 purity ≥99.99%, flow rate of 1.5 L / min, oxygen content <50 ppm).

[0059] Temperature program:

[0060] The first stage: Room temperature → 300°C (heating rate of 5°C / min), keep warm for 1 h to eliminate organic substances.

[0061] The second stage: 300°C → 600°C (heating rate of 3°C / min), keep warm for 1 h to form a stable pore structure.

[0062] Step 4: Gradient impregnation

[0063] Preparation of impregnation solution:

[0064] Graphene / biochar dispersion: 2 mg / mL (graphene:biochar = 3:1, solvent is water:ethanol = 7:3, dispersant SDBS 0.1%).

[0065] Polydopamine precursor: 0.5 g / L Tris-HCl buffer (pH = 8.5).

[0066] Vacuum impregnation procedure:

[0067] Initial impregnation: Maintain a vacuum of -0.1 MPa for 30 min → Immerse under normal pressure for 1 h (load the inner layer of pores).

[0068] Secondary impregnation: Maintain a vacuum of -0.08 MPa for 20 min → Impregnate under a pressure of 0.3 MPa for 30 min (middle layer penetration).

[0069] Tertiary impregnation: Rotate and impregnate under normal pressure (rotation speed 15 rpm, impregnation for 2 h), with uniform surface coating.

[0070] Step Five: Directionally load the buffer medium

[0071] Chemical precipitation method:

[0072] Impregnation solution: Fe(NO3)3·9H2O (0.2 mol / L) + CaCl2 (0.15 mol / L) + MgSO4 (0.1 mol / L);

[0073] Precipitation conditions: pH = 8.5 ± 0.2 (adjusted with NH3·H2O), temperature 45°C ± 2°C, stirring rate 200 rpm;

[0074] Reaction formula:

[0075] Chemical equation

[0076] Fe 3+ + 3OH - → Fe(OH)3↓ (main reaction)

[0077] Ca 2+ + CO2 + H2O → CaCO3↓ + 2H + (CO2 in the air participates)

[0078] Mg 2+ + 2OH - → Mg(OH)2↓

[0079] Heat treatment conversion:

[0080] Heat treatment at 200°C for 2 h, Fe(OH)3 → FeO(OH) → Fe2O3, control the conversion rate ≥ 90%;, part of Mg(OH)2 is converted to MgO (10% of the unconverted state is retained).

[0081] Step Six: Post-treatment

[0082] Drying: Vacuum drying oven (-0.09 MPa, 40°C) until the moisture content ≤ 1%.

[0083] Surface modification: Electrostatic spraying of 1 wt% polydopamine solution (dissolved in 10 mM Tris-HCl buffer) to form a bioaffinity layer with a thickness of 50 - 80 μm.

[0084] III. Application

[0085] The prepared filter material is applied to the sewage treatment system for sulfur autotrophic denitrification nitrogen removal process. Under anoxic conditions, the filter material provides electrons by gradually releasing sulfur sources, the conductive medium promotes electron exchange, and the buffer medium stabilizes the pH, achieving efficient nitrogen removal while avoiding problems such as sulfate accumulation, insufficient microbial attachment, and pH fluctuations of traditional filter materials.

[0086] Example 2: Preparation of filter material with optimized parameters

[0087] Based on Example 1, some parameters are adjusted to optimize the performance:

[0088] Proportion of composite sulfur source: Adjusted to 40%, sulfur: sodium thiosulfate = 72%:28%.

[0089] Proportion of conductive medium: Adjusted to 8%, graphene: biochar = 2:1.

[0090] Proportion of buffer medium: Adjusted to 5%, Fe2O3:CaCO3:MgO = 50%:32%:18%.

[0091] Granulation parameters: Spray rate adjusted to 7 mL / min, and the formed particle size is controlled to be 3.0 mm.

[0092] The remaining preparation steps and application scenarios are the same as those in Example 1, and the denitrification efficiency and stability of the filter material are further improved by optimizing the composition ratio.

[0093] The above embodiments are only the preferred embodiments of the present invention, and the scope of protection of the present invention cannot be limited by these. Any non-substantive changes and substitutions made by those skilled in the art based on the present invention fall within the scope of protection required by the present invention.

Claims

1. A novel sulfur autotrophic denitrification filter material, characterized in that, The filter media has a particle size of 3.0 mm - 4.0 mm and is composed of a composite sulfur source, modified ceramsite, a conductive medium, and a buffer medium; (1) Filter media ratio: Composite sulfur source: accounting for 40% - 45% of the total mass percentage; the composite sulfur source consists of sulfur: 70 ± 2% and sodium thiosulfate: 30 ± 2% to form a gradient-release sulfur source; Modified ceramsite: accounting for 30 - 35% of the total mass percentage; showing a bimodal pore size distribution with pore sizes of 50 - 100 μm / 200 - 300 μm, used for mass transfer between sewage and the filter media; Conductive medium: accounting for 8 - 10% of the total mass percentage; the ratio of graphene to biochar in the conductive medium is 3:1, showing a honeycomb-like loading to enhance the electron exchange between the filter media and nitrogen; Buffer medium: accounting for 5 - 7% of the total mass percentage; among which, Fe2O3: 52% ± 2%, CaCO3: 31% ± 2%, MgO: 17% ± 2%, playing a role in pH buffering; The remaining components are binders and inert fillers.

2. A preparation method of a novel sulfur autotrophic denitrification filter material, which is used to prepare the novel sulfur autotrophic denitrification filter material described in claim 1, and is characterized in that, The preparation method includes the following steps: Step 1: Raw material pretreatment 1.1 Sulfur source treatment Sulfur is of industrial grade with a purity ≥ 99%; it is pulverized to 150 - 180 mesh by an air-flow pulverizer, and the particle size: D50 = 85 μm; Sodium thiosulfate: ball-milled using zirconia balls with a ball-to-material ratio of 5:1 and ball-milled to 200 - 300 mesh; Mixing method: using a three-dimensional mixer, rotating at 25 rpm for dry mixing for 30 min to form a core-shell structure with sulfur coating sodium thiosulfate; 1.2 Ceramsite modification Pickling: 5% HCl solution with a liquid-to-solid ratio of 5:1, and ultrasonic treatment for 2 h; Pore formation: adding a pore-forming agent, the pore-forming agent is carboxymethyl cellulose, with an addition amount of 3%, to form a bimodal pore size inside the ceramsite; Step 2: Mixing and granulation 2.1 Binder system: 12% sodium-based bentonite + 3% polyvinyl alcohol; 2.2 Granulation parameters: The rotation speed of the granulator is controlled at 450 rpm, with a control accuracy of ±10 rpm; The spraying rate is controlled at 8 mL / min, with a control accuracy of ±0.5 mL; The formed particle size is controlled at 3.5 mm, and the control accuracy is ±0.2 mm through screening; 2.3 Drying conditions: Drying with hot air circulation at 50°C until the moisture content ≤ 2%; Step 3: Stepwise calcination 3.1 The equipment uses a tube-type atmosphere furnace with N2 purity ≥ 99.99%; 3.2 Temperature program: The first stage: room temperature → 300°C → hold for 1 h; The second stage: 300°C → 600°C → hold for 1 h; 3.3 Gas control: N2 flow rate of 1.5 L / min, and the oxygen content in the furnace < 50 ppm; Step 4: Gradient impregnation 4.1 Preparation of the impregnation solution: Graphene / biochar dispersion: 2 mg / mL; Polydopamine precursor: 0.5 g / L Tris-HCl buffer solution, pH = 8.5 4.2 Vacuum impregnation procedure: Initial impregnation: maintaining a vacuum of -0.1 MPa for 30 min → soaking at atmospheric pressure for 1 h; Secondary impregnation: maintaining a vacuum of -0.08 MPa for 20 min → impregnating under a pressure of 0.3 Mpa for 30 min; Tertiary impregnation: rotating impregnation at atmospheric pressure, controlling the rotation speed at 15 rpm, and impregnating for 2 h; Step 5: Directionally loading the buffer medium 5.1 Chemical precipitation method: Impregnating solution: Fe(NO3)3·9H2O (0.2 mol / L) + CaCl2 (0.15 mol / L) + MgSO4 (0.1 mol / L); Precipitation conditions: pH = 8.5 ± 0.2, temperature 45°C ± 2°C, stirring rate 200 rpm; 5.2 Heat treatment conversion: Procedure: Heat treatment at 200°C for 2 h to convert metal hydroxides into oxides; Phase change control: Fe(OH)3 → FeO(OH) → Fe2O3, controlling the conversion rate ≥ 90%; Mg(OH)2 → MgO, retaining 10% of the unconverted state as a pH buffer; Step Six: Post-treatment 6.1 Drying: Vacuum drying oven, internal control of the box at -0.09 MPa, 40°C, until the moisture content ≤ 1% 6.2 Surface modification: Spraying solution: 1 wt% polydopamine, dissolved in 10 mM Tris-HCl buffer solution; Spraying parameters: Electrostatic spraying to form a bioaffinity layer with a thickness of 50 - 80 μm.

3. The preparation method of a novel sulfur autotrophic denitrification filter material according to claim 2, wherein, The particle size distribution control in Step Two: A double-layer vibrating screen is used in the granulation stage, with pore sizes of 3.0 mm - 4.0 mm, ensuring that the particle size qualification rate ≥ 95%.

4. The preparation method of a novel sulfur autotrophic denitrification filter material according to claim 2, characterized in that, In the first stage of the temperature program in Step Three, from room temperature to 300°C, the heating rate is controlled at 5°C / min and held for 1 h to remove organic substances.

5. The preparation method of a novel sulfur autotrophic denitrification filter material according to claim 2, characterized in that, In the second stage of the temperature program in Step Three, from 300°C to 600°C, the heating rate is controlled at 3°C / min and held for 1 h to form a stable pore structure.

6. The preparation method of a novel sulfur autotrophic denitrification filter material according to claim 2, characterized in that, The solid solute of the graphene / biochar dispersion liquid in Step Four is a mixture of graphene and biochar, and the solvent of the dispersion liquid is composed of a mixture of water and ethanol, water / ethanol = 7:3, and the dispersant is SDBS 0.1%.

7. The preparation method of a novel sulfur autotrophic denitrification filter material according to claim 2, characterized in that, The bimodal pore sizes of the pore formation in Step 1 are: the main pore is 100 μm ± 10%, and the secondary pore is 200 μm ± 15%.

8. Application of a novel sulfur autotrophic denitrification filter material, characterized in that, Using the filter material prepared by the method according to any one of claims 2 - 7 in the treatment of sewage.

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