Preparation method of sulfur-iron compound autotrophic denitrification filler free of high-temperature sintering

Abstract

The invention belongs to the technical field of sewage denitrification, and provides a preparation method of a high-temperature-sintering-free sulfur-iron compound autotrophic denitrification filler, which comprises the following steps: mixing pyrite, sulfur powder, limestone, cement, quicklime, calcium sulfate and dry sludge as raw materials according to a mass ratio of 50: 30: 6: 8: 2: 3: 1, granulating to obtain particles of 5-8 mm, drying at room temperature for 12-24 hours, and crushing to obtain the high-temperature-sintering-free sulfur-iron compound autotrophic denitrification filler. Spraying clear water under a ventilation condition every day, and curing for 48 hours to obtain a finished product, wherein high-temperature sintering is not needed in the whole preparation process; preferably, the mass ratio of the pyrite to the sulfur is 1: 1-2: 1. The obtained filler has stable mechanical properties and adaptive bulk density, and realizes autotrophic denitrification nitrogen removal under the condition of no additional organic carbon source. The method is simple in process, low in energy consumption and material cost, and suitable for upgrading and reconstruction scenes of upflow anaerobic biofilters and constructed wetlands.

Description

Technical Field

[0001] This invention relates to the field of wastewater denitrification technology, and more specifically, to a method for preparing a sulfur-iron composite autotrophic denitrification packing material that does not require high-temperature sintering. Background Technology

[0002] With the acceleration of industrialization, the control of total nitrogen emissions in wastewater is becoming stricter. Traditional heterotrophic denitrification relies on external carbon sources and produces a large amount of sludge with high operating costs. Sulfide-iron autotrophic denitrification has attracted attention because it does not require external organic carbon sources, produces low sludge, and has high efficiency.

[0003] To meet the requirements of upgrading and deep denitrification of low C / N effluent, there is an urgent need for a non-sintering, self-trophic denitrification packing material of sulfur iron that does not require high-temperature sintering and its simple preparation process, which can reduce preparation costs and maintain good denitrification performance. Summary of the Invention

[0004] To overcome the aforementioned deficiencies of the prior art, this invention provides a method for preparing a sulfur-iron composite autotrophic denitrification packing material without high-temperature sintering. The method involves feeding a mixture of proportions into a granulator to obtain particles with a diameter of 5-8 mm, allowing them to dry at room temperature, and then spraying the particles with clean water daily under ventilated conditions to maintain their curing properties. This yields a sulfur-iron autotrophic denitrification packing material that does not undergo high-temperature sintering, thus avoiding energy consumption and material phase changes, and facilitating the maintenance of the packing material's microbial compatibility, thereby solving the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: The objective of this invention can be achieved through the following technical solutions: A method for preparing a sulfur-iron composite autotrophic denitrification packing material without high-temperature sintering includes the following steps: S1. Mix the materials according to the mass ratio of pyrite: sulfur powder: limestone: cement: quicklime: calcium sulfate: dry sludge = 50:30:6:8:2:3:1.

[0006] S2, the mixture is fed into a granulator to obtain particles with a diameter of 5-8 mm, and then dried at room temperature for 12-24 hours.

[0007] S3, the particles are sprayed with clean water daily under ventilated conditions for 48 hours to obtain a non-fired sulfur-iron self-trophic denitrification filler. The entire preparation process does not involve high-temperature sintering.

[0008] Preferably, the mass ratio of pyrite to sulfur powder is between 1:1 and 2:1.

[0009] Preferably, the high-temperature sinter-free pyrite-iron composite autotrophic denitrification packing comprises pyrite, sulfur powder, limestone, dried sludge, cement, calcium sulfate, and quicklime; the pyrite is crushed and sieved to a particle size of 100-200 mesh; the sulfur powder has a purity of ≥99.7%; the limestone is crushed and sieved to a particle size of 100-200 mesh; the cement is ordinary 425# silicate cement; the dried sludge is taken from a wastewater treatment plant, and the dewatered sludge is dried and ground; the quicklime, calcium sulfate, and other conventional reagents used in the experiment are all of analytical grade.

[0010] Preferably, the proportion of particles with a diameter of 5-8 mm obtained by granulation is not less than 95%.

[0011] Preferably, the cement, calcium sulfate and quicklime are used as a cementing system, and their mass parts in the formula are 8, 3 and 2, respectively.

[0012] Preferably, the S3 maintenance step involves spraying the surface with clean water in a ventilated environment, with a spraying frequency of at least once a day, and a total maintenance time of 48 hours.

[0013] Preferably, the compressive strength of a single particle is ≥0.60MPa.

[0014] Preferably, the high-temperature sintering-free sulfur iron self-trophic denitrification packing is used in the denitrification process for treating municipal sewage containing nitrate nitrogen or low C / N industrial wastewater, without the addition of external organic carbon sources during operation.

[0015] Preferably, the autotrophic denitrification reactor is an upflow anaerobic biological filter. The reactor has a cylindrical structure with a total height of 600 mm and an inner diameter of 50 mm. A pebble support layer with a thickness of 100 mm is set at the bottom, and the packing material is filled with 500 g.

[0016] Preferably, an autotrophic denitrification device includes an autotrophic denitrification reactor body, inlet and outlet water pipes, and a support layer. The autotrophic denitrification reactor body is filled with high-temperature sintering-free ferrous sulfate autotrophic denitrification packing material, and the support layer is located at the bottom of the reactor and has a thickness of 100 mm.

[0017] The technical effects and advantages of this invention's method for preparing a high-temperature sinter-free pyrite-iron composite autotrophic denitrification packing are as follows: This invention involves granulating pyrite, sulfur powder, limestone, cement, quicklime, calcium sulfate, and dry sludge in a mass ratio of 50:30:6:8:2:3:1 (5–8 mm), drying at room temperature, and curing with clean water spray under ventilated conditions for 48 days. The non-sintering process of h forms an autotrophic denitrification packing material with sulfur / iron as electron donors: it avoids high-temperature sintering, reduces energy consumption and material costs, and has a simple process. It obtains stable mechanical properties (single particle compressive strength ≥0.60MPa) and suitable bulk density by means of cement-calcium sulfate-quicklime cementing system, and the proportion of 5-8mm particle size ≥95% facilitates engineering filling and stable operation; the mass ratio of pyrite to sulfur in the formula is 1:1 to 2:1, which enables the packing material to achieve autotrophic denitrification without the addition of external organic carbon source and with low sludge production. It is suitable for deep denitrification of low C / N municipal and industrial wastewater; at the same time, it uses dry sludge to participate in the preparation to achieve resource utilization. Overall, it is suitable for upgrading and renovation scenarios such as upflow anaerobic biological filters and constructed wetlands. Attached Figure Description

[0018] Figure 1 This is a flowchart of a method for preparing a sulfur-iron composite autotrophic denitrification filler without high-temperature sintering according to the present invention.

[0019] Figure 2 This is a schematic diagram of the upflow anaerobic biological filter reactor structure of the present invention.

[0020] Figure 3 This is a comparison chart of the physical properties of the high-temperature sintering-free sulfur-iron self-growing filler and the sulfur self-growing filler of this invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1

[0023] like Figure 1 As shown, a method for preparing a sulfur-iron composite autotrophic denitrification packing material without high-temperature sintering includes the following steps: S1. Mix the materials according to the mass ratio of pyrite: sulfur powder: limestone: cement: quicklime: calcium sulfate: dry sludge = 50:30:6:8:2:3:1.

[0024] S2, the mixture is fed into a granulator to obtain particles with a diameter of 5-8 mm, and then dried at room temperature for 12-24 hours.

[0025] S3, the particles are sprayed with clean water daily under ventilated conditions for 48 hours to obtain a non-fired sulfur-iron self-trophic denitrification filler. The entire preparation process does not involve high-temperature sintering.

[0026] In this embodiment, the preferred mass ratio of pyrite to sulfur powder is between 1:1 and 2:1. To verify that the overall denitrification performance is optimal when the mass ratio of pyrite to sulfur powder is controlled between 1:1 and 2:1 in the autotrophic denitrification packing, three parallel experiments were conducted under the same equipment conditions: pyrite:sulfur powder = 2:1, 1:1, and 1:2. Combined with the high-load operation results of the continuous flow engineering unit and the system comparison results, the following data were obtained: Table 1. Start-up and steady-state performance of different ratios of pyrite:sulfur powder in parallel operation of the same unit.

[0027] Table 1 shows that, under the same equipment and influent conditions, the start-up and steady-state performance of three pyrite-sulfur powder ratios (2:1, 1:1, 1:2) were compared: The 1:1 group had the fastest start-up and the highest NO3⁻-N removal rate during the start-up period, with removal rates of 94.2% and 81.3% at HRT=24h and 12h, respectively, and the smallest pH fluctuation in the effluent, indicating the most stable operation; The 2:1 group had a start-up time of 10.4 days and a start-up rate of 1.25 mg·L⁻¹·h⁻¹, with a removal rate of 94.2% at HRT=24h and 78.5% at HRT=12h, similar to the 1:1 group, and a pH fluctuation of ±1.2, placing it in the middle; The 1:2 group had the slowest start-up and the lowest start-up rate (0.98 mg·L⁻¹·h⁻¹), with removal rates of 84.2% and 65.2% at HRT=24h and 12h, respectively, and the largest pH fluctuation (±1.8). Therefore, under the same conditions, a 1:1 ratio offers the fastest start-up, a high removal rate with a short HRT, and optimal pH stability, while a 2:1 ratio maintains a high removal rate even when the HRT is shortened to 12 hours. Thus, a pyrite:sulfur powder ratio of 1:1 results in the shortest start-up time and is suitable for rapid start-up; a pyrite:sulfur powder ratio of 2:1 is suitable for high-load scenarios.

[0028] Table 2 High Load and High Speed ​​Conditions

[0029] Table 2 summarizes the engineered high-load performance of continuous flow iron-sulfur coupled autotrophic denitrification (ISAD): with FeS and S 0 In a biofilter with a mass ratio of approximately 2:1 as a composite electron donor, the system can maintain a stable total nitrogen and total phosphorus removal rate of approximately 90–100% during long-term operation within a wide HRT range of 1–12 h, and the highest nitrogen removal volume rate of 960 mg·L⁻¹·d⁻¹ was measured, demonstrating the upper limit of flux and deep nitrogen removal capability.

[0030] Table 3. System Comparison: Comparison between the pyrite and sulfur powder coupled system (PSAD) and the single electron-donating system (pyrite only or sulfur powder only).

[0031] Table 3 shows the representative "capability boundaries" of the three systems in comparable scenarios: PSAD (FeS2+S 0 When treating actual secondary sedimentation effluent, the iron-sulfur coupling method (PSAD) reduced TN to 1.40±0.03 mg / L and TP to 0.19±0.02 mg / L within 3 hours of heating time (HRT). PSAD was superior in simultaneous nitrogen and phosphorus removal. This indicates that iron-sulfur coupling can maintain deep denitrification and phosphorus removal simultaneously with a short residence time. In contrast, PAD required 18 hours of HRT in a fluidized bed reactor with contaminated groundwater (influent NO3⁻≈178 mg / L) to achieve 79% nitrate removal and an average denitrification rate of approximately 171 mg NO3⁻·L⁻¹·d⁻¹, demonstrating stable adaptability to high-concentration influent. However, obtaining deep effluent typically requires a longer HRT. In sulfur-limestone upflow biological filters, SAD achieves approximately 90% removal of low-concentration influent (10 or 40 mg N / L) at an HRT of 3 h and 20–25 °C, suggesting that pure sulfur systems can be highly efficient even with short HRTs. However, in engineering practice, limestone is often used to provide alkalinity and pH buffering. In summary, when the goal is to achieve deep TN / TP targets with a short HRT, PSAD shows the most significant advantage. PAD and SAD are valuable for reference in terms of robustness at high concentrations and rapid removal at low concentrations, but under the same short HRT conditions, they cannot simultaneously achieve the same synergistic nitrogen and phosphorus removal and effluent depth as PSAD.

[0032] Example 2

[0033] In this embodiment, an upflow anaerobic biological filter reactor made of plexiglass is selected, such as... Figure 2 As shown, its geometry is cylindrical, with a total reactor height of 600mm and an inner diameter of 50mm. Two sets of parallel devices are set up, filled with non-fired sulfur-iron autotrophic packing (SUF) and sulfur autotrophic packing (CF) respectively. The loading amount of both sets of devices is 500g, with the SUF bed height being 200mm and the CF bed height being 150mm. The bottom of both sets of devices is laid with a pebble support layer with a cushion layer height of 100mm for uniform water distribution and load bearing.

[0034] During parallel operation, the sulfur-iron composite system provides alkalinity supplementation to the reaction solution through alkali-supplying components such as limestone / quicklime, keeping the pH of the reaction system stable in the ideal range of about 7.2 to 7.5. This effectively avoids the risk of autotrophic denitrification activity decay and by-product (such as excess sulfate) accumulation caused by acidification. At the same time, it exhibits a wider range of temperature and reaction condition adaptability compared to the single sulfur autotrophic system.

[0035] Material cost calculations were performed based on the condition of complete treatment of nitrate nitrogen concentration of 44 mg / L. The results showed that the material cost of the SUF reactor was 0.027 yuan / t, which was lower than the 0.037 yuan / t of the control CF reactor, demonstrating the cost advantage of the non-burning sulfur-iron self-growth packing material.

[0036] Example 3

[0037] In this embodiment, using the same preparation and drying / wet curing processes, the high-temperature sintering-free sulfur-iron self-trophic denitrification filler (SUF) of this invention and the control sulfur self-trophic filler (CF) were selected for testing of single-particle compressive strength, 1-hour water absorption, bulk density, apparent density, and particle breakage rate. The results are as follows: Figure 3 As shown: The single-particle compressive strength of SUF / CF is 0.64 / 0.71 MPa, the 1-hour water absorption is 5.30% / 3.62%, and the bulk density is 1.12 / 1.09. The apparent densities are 2.0 / 2.5 g·cm⁻³ and 4.73% / 4.04%, respectively. Considering the aforementioned particle size of 5–8 mm and the bed filling conditions (the reactor is a cylindrical upflow anaerobic biological filter, with a 100 mm pebble support layer, 500 g each of SUF / CF, and bed heights of 200 mm and 150 mm), it is evident that SUF meets the basic requirements for filter filling and operation in terms of mechanics and physical properties: its single-particle compressive strength ≥ 0.60 MPa provides sufficient anti-breakage protection for conventional filling, operation, and maintenance; its moderate water absorption rate (5.30%) facilitates rapid wetting and biofilm adhesion without significantly reducing the particle skeleton strength; and its bulk density is close to that of CF (1.12 vs. 1.09). The apparent density (g·cm⁻³) is beneficial for maintaining a similar bed pressure drop and hydraulic distribution as the control packing material; the lower apparent density (2.0 vs. 2.5 g·cm⁻³) reflects the lightweight characteristics of the non-fired composite skeleton, which helps to obtain a uniform flow state under upflow conditions; the particle breakage rate is controlled within about 5% (4.73%), indicating that excessive fine powder is not easily generated during filling and long-term operation, reducing the risk of clogging and short-circuiting. Based on the above test data and filling conditions, SUF meets the key requirements of upflow filters for packing materials in terms of pressure stability, wetting and biofilm support, bed pressure drop and mass transfer channel maintenance, thus supporting its long-term stable operation and hydraulic adaptability under the device and operating conditions of this invention.

[0038] Example 4

[0039] In this embodiment, after the device was running stably, high-throughput sequencing analysis was performed on biofilm samples from the high-temperature sintering-free sulfur-iron autotrophic packing (SUF) and sulfur autotrophic packing (CF) reactors. The results showed that both devices were enriched with functional bacterial communities closely related to autotrophic denitrification, mainly including Ferritrophicum, Sulfurimonas, Thiobacillus, Thiomonas, Geothhrix, and Thiotrix. Among them, Thiobacillus and Sulfurimonas use reduced sulfur / sulfides as electron donors to reduce NO3⁻-N to N2 and oxidize sulfur to sulfate, and are typical core genera of sulfur autotrophic denitrification. In the high-temperature sintering-free sulfur-iron autotrophic packing (SUF) reactor, the relative abundances of Thiobacillus and Sulfurimonas were 17.65% and 10.65%, respectively; in the sulfur autotrophic packing (CF) reactor, the relative abundances of Thiobacillus and Sulfurimonas were 20.44% and 24.31%, respectively, indicating that the SUF system maintains a moderate proportion of sulfur-oxidizing autotrophic communities without excessive sulfur bias, which is beneficial for synergistic interaction with iron-related metabolism (see below). Meanwhile, Ferritrophicum accounted for as much as 32.84% in the SUF reactor. This genus can oxidize Fe²⁺ to Fe³⁺ under anaerobic conditions using NO⁻-N as an electron acceptor to complete autotrophic denitrification, and can utilize various electron donors such as Fe²⁺ / H₂ / sulfides for metabolism. This microbiologically confirms that the packing material of this invention achieves the synergistic effect of two autotrophic denitrification pathways: sulfur and iron.

[0040] Example 5

[0041] The suitability and stability of the high-temperature sintering-free sulfur-iron self-growth packing (SUF) were verified in two scenarios: engineered filter beds and constructed wetlands. (1) Equipment and filling: The filter adopts an upflow structure (bottom pebble support layer, upper SUF particle layer, particle size 5-8mm). In the constructed wetland, SUF is placed near the root zone according to the functional layer to enhance denitrification; no external organic carbon source is added in either scenario.

[0042] (2) Operation and control: Relying on the alkali supply effect of limestone / quicklime in the formula, the pH of the effluent is stable at about 7.2–7.5 during operation, avoiding the decline of sulfur oxidizing bacteria activity caused by acidification, and inhibiting the accumulation of by-products caused by excessive sulfur oxidation; Under the same equipment, the control sulfur autotrophic packing (CF) is more prone to pH fluctuation and insufficient alkalinity.

[0043] (3) Performance and load: In typical low C / N secondary effluent deep denitrification conditions, SUF increases the denitrification load per unit volume to 1.05 kg / (m³·d), and achieves effluent total nitrogen <5mg / L after stable operation; the above indicators meet the requirements of upgrading and deep purification, and remain stable under conditions such as influent temperature, dissolved oxygen disturbance, and instantaneous load fluctuation.

[0044] (4) Economic and environmental benefits: Based on the calculation of 44 mg / L of nitrate nitrogen after complete treatment, the cost of SUF material is RMB 0.027 / t, which is lower than RMB 0.037 / t of CF. Since no external carbon source is required and the production of autotrophic denitrification sludge is low, the overall operating cost and carbon emissions will decrease accordingly.

[0045] (5) Maintenance and hydraulics: The single particle strength, water absorption rate and bulk density of SUF meet the requirements of filter filling and long-term operation. The particle breakage rate is low and the pressure drop of the bed increases slowly. In constructed wetlands, the SUF layer and the substrate form a stable hydraulic channel. Routine maintenance only requires setting the backwash / tillage cycle according to the pressure drop or changes in effluent sulfate.

[0046] (6) Applicable scenarios: SUF is suitable for low C / N scenarios such as dyeing and printing wastewater, municipal sewage effluent upgrading, landscape water and decentralized treatment in villages and towns; in projects that need to reduce land occupation or shorten retention time, it can be combined with the modular layout of upflow filter to maintain high volumetric load and low effluent TN. In the above two types of applications, SUF demonstrates the comprehensive advantages of "no external carbon addition - pH self-buffering - high efficiency denitrification - controllable cost", proving that it has replicable engineering adaptability and promotion value in multiple working conditions and scenarios.

[0047] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0048] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a sulfur-iron composite autotrophic denitrification packing material without high-temperature sintering, characterized in that, Includes the following steps: S1. Mix the materials according to the mass ratio of pyrite: sulfur powder: limestone: cement: quicklime: calcium sulfate: dry sludge = 50:30:6:8:2:3:

1. S2, feed the mixture into a granulator to obtain particles with a particle size of 5-8 mm, and let it stand and dry at room temperature for 12-24 hours; S3, the particles are sprayed with clean water daily under ventilation conditions for 48 hours to obtain a non-fired sulfur-iron self-trophic denitrification filler. The entire preparation process does not involve high-temperature sintering. The mass ratio of pyrite to sulfur powder is between 1:1 and 2:

1.

2. The method for preparing the high-temperature sinter-free sulfur-iron composite autotrophic denitrification packing according to claim 1, characterized in that... The non-fired pyrite-iron autotrophic denitrification packing material comprises pyrite, sulfur powder, limestone, dried sludge, cement, calcium sulfate, and quicklime; the pyrite is crushed and sieved to a particle size of 100-200 mesh; the sulfur powder has a purity of ≥99.7%; the limestone is crushed and sieved to a particle size of 100-200 mesh; the cement is ordinary 425# silicate cement; the dried sludge is taken from a sewage treatment plant, and the dewatered sludge is dried and ground; the quicklime, calcium sulfate, and other conventional reagents used in the experiment are all of analytical grade.

3. The method for preparing the high-temperature sinter-free sulfur-iron composite autotrophic denitrification packing according to claim 1, characterized in that... The proportion of particles with a diameter of 5-8 mm obtained by granulation is not less than 95%.

4. The method for preparing the high-temperature sinter-free sulfur-iron composite autotrophic denitrification packing according to claim 1, characterized in that, The cement, calcium sulfate, and quicklime form a binding system, with mass fractions of 8, 3, and 2, respectively, in the formula.

5. The method for preparing the high-temperature sinter-free sulfur-iron composite autotrophic denitrification packing according to claim 1, characterized in that, The maintenance steps involve spraying the surface with clean water in a well-ventilated environment at least once a day, for a total maintenance time of 48 hours.

6. The method for preparing the high-temperature sinter-free sulfur-iron composite autotrophic denitrification packing according to claim 1, characterized in that, The compressive strength of a single particle is ≥0.60MPa.

7. The use of the high-temperature sintering-free sulfur-iron composite autotrophic denitrification packing material according to claim 2 in autotrophic denitrification denitrification, characterized in that, A denitrification process for treating municipal wastewater containing nitrate nitrogen or low C / N industrial wastewater, without the addition of external organic carbon sources during operation.

8. The use in autotrophic denitrification nitrogen removal according to claim 7, characterized in that, The autotrophic denitrification reactor is an upflow anaerobic biological filter. The reactor has a cylindrical structure with a total height of 600 mm and an inner diameter of 50 mm. A pebble support layer with a thickness of 100 mm is set at the bottom, and the packing material is filled with 500 g.

9. An autotrophic denitrification device, characterized in that, The reactor includes an autotrophic denitrification reactor body, inlet and outlet water pipes, and a support layer. The autotrophic denitrification reactor body is filled with the non-burning sulfur-iron autotrophic denitrification packing material as described in claim 2. The support layer is located at the bottom of the reactor and has a thickness of 100 mm.

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