Dual-pore iron-carbon composite filler for enhancing Feammox-NDFO autotrophic denitrification and preparation method thereof

Abstract

The application provides a double-pore iron-carbon composite filler for strengthening Feammox-NDFO autotrophic denitrification and a preparation method thereof, relates to the technical field of biological autotrophic denitrification of sewage, and raw material composition comprises 30-45 parts of iron-containing powder, 15-30 parts of biochar powder, 20-30 parts of a binder and 10-15 parts of a pore-forming agent according to weight percentage. The iron-containing powder is one or a combination of Fe2O3, FePO4, FeO(OH) and Fe(C6H5O7). The pore-forming agent is NaHCO3. The preparation method of the double-pore iron-carbon composite filler for strengthening Feammox-NDFO autotrophic denitrification specifically comprises the following steps: 1, raw material pretreatment; 2, mixing and granulation; 3, steam curing for pore formation, curing temperature is 60-80 DEG C, humidity is 80-90% RH; 4, ultrasonic wave assisted deionized water immersion for pore formation, immersion temperature is 30-50 DEG C, time is 6-12 h, ultrasonic wave frequency is 20-40 kHz; 5, finished product screening. The filler is mainly applied to low-carbon sewage with C / N less than or equal to 0.5, and can still maintain high-efficiency denitrification under the low-carbon condition, and the TN removal rate can reach 91.6-97.8%.

Description

Technical Field

[0001] This invention relates to the field of biological autotrophic denitrification technology for wastewater, specifically to a dual-pore iron-carbon composite packing material for enhancing Feammox-NDFO autotrophic denitrification and its preparation method. Background Technology

[0002] Biological nitrogen removal from wastewater remains a significant need in water environment management. Traditional biological nitrogen removal processes rely on two stages: aerobic nitrification and anoxic denitrification. This process involves temporal and spatial separation and requires continuous aeration and the addition of external carbon sources to maintain nitrogen removal efficiency. However, this method is poorly applicable to wastewater with low C / N ratios, as the scarcity of carbon sources limits the denitrification process and affects overall nitrogen removal efficiency. In recent years, Feammox (ferric ammonia oxidation) coupled with NDFO (nitrate-dependent ferrous oxidation) has attracted widespread attention and become a research hotspot due to its unique autotrophic nitrogen removal mechanism, gradually demonstrating its feasibility for engineering applications.

[0003] Feammox (ferric ammonium oxidation) and NDFO (nitrate-dependent ferrous oxidation) are two important autotrophic nitrogen removal processes that utilize Fe(III) and Fe(II) as electron acceptors and donors, respectively, to achieve nitrogen conversion. In the Feammox process, Fe(III) acts as the electron acceptor, reacting with NH4+ under anaerobic conditions. + The reaction will cause NH4 to... + Oxidized to NO2 - Or NO3 - Simultaneously, Fe(III) is reduced to Fe(II). However, as the Feammox reaction continues, Fe(III) is gradually consumed. If it cannot be effectively replenished, the Feammox process will be limited, affecting nitrogen removal efficiency. The NDFO process, in the presence of nitrates, uses Fe(II) as an electron donor to remove NO3-. - The NO3 produced by Feammox is reduced to N2, while Fe(II) is oxidized back to Fe(III). If the Feammox and NDFO processes can be coupled, the NO3 produced by Feammox can be reduced... - As an electron acceptor in the NDFO reaction, Fe(III) generated in the NDFO process is also resupplyed for use in the Feammox process, thereby realizing the recycling of Fe(III) / Fe(II). This allows for the construction of a stable Feammox-NDFO autotrophic denitrification system, achieving efficient iron recycling and continuous nitrogen removal. Therefore, this dual-pore-forming iron-carbon composite packing for enhanced Feammox-NDFO autotrophic denitrification and its preparation method were developed. Summary of the Invention

[0004] This invention provides a dual-pore iron-carbon composite packing material for enhanced Feammox-coupled NDFO autotrophic denitrification based on iron cycling and its preparation method. By constructing a high specific surface area packing material with a multi-level pore structure, the adhesion ability and mass transfer efficiency of microorganisms are improved, further enhancing the stability and denitrification efficiency of the Feammox-NDFO system.

[0005] A dual-pore-forming iron-carbon composite filler, the raw material composition of which includes the following components in parts by weight: 30-45 parts of iron powder, 15-30 parts of biochar powder, 20-30 parts of binder, and 10-15 parts of pore-forming agent.

[0006] In a preferred embodiment, the iron-containing powder is one or a combination of ferric oxide (Fe2O3), ferric phosphate (FePO4), goethite (FeO(OH)), and ferric citrate;

[0007] In a preferred embodiment, the iron-containing powder has a particle size of 1–10 μm;

[0008] In a preferred embodiment, the biochar powder is prepared from one or a combination of corn stalks, wheat stalks, and rice stalks, with a particle size between 75 and 150 μm.

[0009] In a preferred embodiment, the adhesive is silicate cement;

[0010] In a preferred embodiment, the pore-forming agent is sodium bicarbonate with a particle size of 50–100 μm;

[0011] In a preferred embodiment, the dual-pore iron-carbon composite filler consists of spherical particles of 5–8 mm in size to ensure optimal mass transfer performance and microbial adhesion.

[0012] A method for preparing a dual-pore-forming iron-carbon composite filler with enhanced Feammox-NDFO autotrophic denitrification specifically includes the following steps:

[0013] Step 1: Raw material pretreatment

[0014] After drying, the iron-containing powder, biochar powder, binder, and pore-forming agent are weighed according to the weight proportions for later use.

[0015] Preferably, an electric heating forced-air drying oven is used to dry the iron-containing powder, biochar powder, adhesive, and pore-forming agent, and the moisture content is controlled to be ≤1%.

[0016] Step 2, Mixing and Granulation

[0017] The iron-containing powder, biochar powder, binder and pore-forming agent in step 1 are mixed evenly in the above proportions to obtain a mixed powder.

[0018] The mixed powder is placed in a granulator, sprayed with water and granulated to produce iron-carbon composite particles with a diameter of 6-8 mm.

[0019] Furthermore, the granulator has a rotation speed of 30-40 rpm, an inclination angle of 25-35°, and a granulation time of 40-60 min; the water is added by spraying to ensure uniform particle formation.

[0020] Step 3: Steam curing and hole making

[0021] The iron-carbon composite particles granulated in step 2 are placed in a constant temperature and humidity chamber for wet heat curing, so that they release CO2 in the steam environment, forming large pores of 50-500μm, enhancing the specific surface area of ​​the filler, and ensuring the normal hardening of the cement-based adhesive.

[0022] Furthermore, the conditions for curing and creating the holes are: temperature 60-80℃; humidity 80-90%RH; curing time 2-4 days.

[0023] Steam source: Deionized water, heated to form steam;

[0024] Step 4: Ultrasonic-assisted deionized water soaking to create pores

[0025] After steam curing, some Na2CO3 remains inside the iron-carbon composite particles. The iron-carbon composite particles are then dissolved by immersing them in deionized water with ultrasonic assistance. The immersion conditions for pore formation are: temperature 30-50℃; time 6-12h; ultrasonic frequency 20-40kHz, forming micropores of 1-10μm.

[0026] Furthermore, stirring ensures that Na2CO3 is fully dissolved, optimizes the pore structure of the iron-carbon composite particles, and promotes the attachment and growth of microorganisms.

[0027] Step 5: Finished product screening

[0028] After drying by ventilation at room temperature, the iron-carbon composite particles with a particle size between 5-8 mm are screened as the finished product of dual-pore-forming iron-carbon composite filler.

[0029] Furthermore, allow the filler to air dry naturally at room temperature (20-25℃) for 24-48 hours to ensure complete evaporation of moisture and prevent structural deformation and cracking. Use only after the filler is completely dry.

[0030] Preferably, the iron-carbon composite particles are screened using 5mm and 8mm standard sieves to remove particles with a diameter less than 5mm and greater than 8mm, ensuring that the particle size of the finished product is between 5-8mm.

[0031] A dual-pore iron-carbon composite packing material is applied to wastewater treatment processes.

[0032] Furthermore, the double-pore iron-carbon composite packing is introduced into the sewage treatment device, and the double-pore iron-carbon composite packing occupies 28-45% of the internal volume of the sewage treatment device.

[0033] The beneficial effects of this invention are:

[0034] (1) In this invention, Fe(III) is fixed in the packing as an electron acceptor to ensure that the ammonia oxidation and Fe(III) reduction in the Feammox process are carried out simultaneously, and Fe(III) / Fe(II) is efficiently circulated through the NDFO process, so that the Feammox and NDFO processes can operate stably for a long time, improve the denitrification efficiency and reduce the need for additional iron sources.

[0035] (2) This invention adopts a dual pore-forming mechanism of steam curing and ultrasonic-assisted soaking to form a multi-level pore structure in the packing material where 50-500μm macropores and 1-10μm micropores coexist. The macropores provide sufficient attachment space for microorganisms, while the micropores optimize the mass transfer efficiency between water and microorganisms. Through the combination of the above two types of pores, the porosity of the packing material is increased by 15-20%, and the specific surface area is increased by 10-15%, which significantly enhances the growth carrier capacity of microorganisms in the Feammox-NDFO system and improves nitrogen removal efficiency. The packing material of this invention is mainly used in low-carbon wastewater conditions with C / N≤0.5, and it can still maintain high-efficiency denitrification under such low-carbon conditions without the need for additional organic carbon sources. After 60 days of long-term operation, the TN removal rate can reach 91.6-97.8%, which is suitable for the treatment of low-carbon, high-ammonia nitrogen wastewater and expands the application scope of autotrophic denitrification technology.

[0036] (3) The packing material of the present invention is doped with biochar powder, which on the one hand increases the NH4 content of the packing material. + The adsorption capacity makes the matrix for the ammonia oxidation reaction in the Feammox process more concentrated, promoting Fe(III) reduction; on the other hand, the oxygen-containing functional groups (such as carbonyl, hydroxyl, and quinone groups) on the surface of biochar powder promote extracellular electron transfer in the Feammox and NDFO processes, increasing the Fe(III) reduction rate and NO3- reduction. - This improves reduction efficiency, thereby enhancing denitrification performance. Attached Figure Description

[0037] The accompanying drawings are provided to further understand the technical solutions of the present invention and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of the present invention and do not constitute a limitation on the technical solutions of the present invention.

[0038] Figure 1 This is a schematic diagram illustrating the mechanism of the dual-pore-forming iron-carbon composite packing material of the present invention in the Feammox-NDFO coupled autotrophic denitrification process;

[0039] Figure 2 The image shows the surface microstructure and pore structure of the dual-pore iron-carbon composite filler of the present invention under a scanning electron microscope (SEM) at Mag=200X.

[0040] Figure 3 The image shows the surface microstructure and pore structure of the dual-pore iron-carbon composite filler of the present invention under scanning electron microscope (SEM) conditions of Mag = 1.00 KX.

[0041] Figure 4 The embodiments and comparative examples of this invention demonstrate the denitrification effect on wastewater with a low carbon-to-nitrogen ratio (artificially prepared water, no added organic carbon source, C / N≈0). Detailed Implementation

[0042] This invention innovatively combines the Feammox and NDFO processes, optimizes the packing structure, and enhances microbial activity and electron transfer capabilities. Compared to traditional iron-carbon packing and sulfur autotrophic packing, it exhibits significant advantages in denitrification efficiency, long-term stability, adaptability, and economy. The packing material of this invention is primarily used in low-carbon wastewater conditions with a C / N ratio ≤ 0.5. To better illustrate the purpose, technical solution, and advantages of this invention, the following detailed description of embodiments is provided in conjunction with the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The embodiments of this invention are for illustrative purposes only and are not intended to limit its scope.

[0043] In an embodiment of the present invention, a dual-pore-forming iron-carbon composite filler is provided, which comprises the following components in parts by weight: 30-45 parts of iron powder, 15-30 parts of biochar powder, 20-30 parts of binder, and 10-15 parts of pore-forming agent.

[0044] In this embodiment of the invention, the iron-containing powder is selected from one or a combination of ferric oxide (Fe2O3), ferric phosphate (FePO4), goethite (FeO(OH)), and ferric citrate.

[0045] In a preferred embodiment, the iron-containing powder has a particle size of 1–10 μm;

[0046] In a preferred embodiment, the biochar powder is prepared from one or a combination of corn stalks, wheat stalks, and rice stalks, with a particle size between 75 and 150 μm.

[0047] In a preferred embodiment, the adhesive is silicate cement;

[0048] In a preferred embodiment, the pore-forming agent is sodium bicarbonate;

[0049] The dual-pore iron-carbon composite filler is controlled within the range of 5-8 mm to ensure optimal mass transfer performance and microbial adhesion ability.

[0050] Example 1

[0051] In this embodiment, the preparation steps of the dual-pore-forming iron-carbon composite filler used to enhance the autotrophic denitrification of Feammox-NDFO are as follows:

[0052] 1) Raw material selection and pretreatment:

[0053] The iron-containing powder selected was ferric oxide (Fe₂O₃) with a particle size of 1–10 μm; the biochar powder, derived from carbonized corn stalks, had a particle size of 100 μm; the binder was silicate cement; and the pore-forming agent was sodium bicarbonate with a particle size of 50–100 μm. The ferric oxide (Fe₂O₃), biochar powder, silicate cement, and sodium bicarbonate were dried to constant weight in an electrically heated forced-air drying oven at 40℃, with the moisture content controlled to ≤1%.

[0054] 2) Packing material preparation, molding, and curing:

[0055] Weigh out 45 parts by weight of ferric oxide (Fe2O3), 15 parts by weight of biochar powder, 25 parts by weight of silicate cement, and 15 parts by weight of sodium bicarbonate. Mix them in a mixer for 10 minutes to ensure uniformity. The mixing process involves placing the mixed powder into a disc granulator, adjusting the rotation speed to 35 rpm and the inclination angle to 30°, and spraying water (10-15% by weight) to granulate, obtaining spherical particles. The granulated iron-carbon composite particles are then placed in a constant temperature and humidity chamber at 70°C and 85% RH, and cured with deionized water vapor for 3 days. This process decomposes the NaHCO3 in the filler to generate Na2CO3 and releases CO2 to form macropores of 50-100 μm. This process constitutes the first stage of pore formation.

[0056] After the first stage of pore formation is completed, the iron-carbon composite particles are placed in deionized water at 40°C and treated with ultrasound at 30kHz for 12 hours to dissolve residual Na2CO3 and further form micropores of 1-10μm. The above process is the second stage of pore formation.

[0057] Finally, the material was allowed to air dry naturally at 25°C for 36 hours. It was then sieved using 5mm and 8mm standard sieves to remove excess particles, resulting in a double-pore iron-carbon composite filler with a particle size of 5-8mm. Its porosity, specific surface area, pore size range, and ammonia nitrogen adsorption capacity are shown in Table 1.

[0058] 3) The enhancing effect of the dual-pore-forming iron-carbon composite filler on the Feammox-NDFO autotrophic denitrification system.

[0059] A Feammox-NDFO autotrophic denitrification system was constructed in a 2L UASB reactor to investigate the enhancing effect of the prepared packing material on the autotrophic denitrification system. A was selected. 2 The activated sludge from the anoxic section of the O process was used as inoculum sludge at a concentration of 5000 mg / L. The double-porous iron-carbon composite packing material prepared in the above steps filled 30% of the reactor volume. The influent was artificially synthesized simulated wastewater, the composition of which is shown in Table 2, including NH4+. + With a nitrogen concentration of 75.2 ± 2.3 mg / L, a COD concentration of 23 ± 1.4 mg / L, a pH of 7.0, and a C / N ratio of 0.32, a Feammox-NDFO autotrophic denitrification system was constructed under the conditions of a hydraulic retention time (HRT) of 8 h and a reflux ratio of 10:1. The system reached a steady state after 10 days, and the effluent NH4+... + -N concentration is 2.7-4.1 mg / L, effluent NO3 - With a nitrogen concentration of 3.9-6.6 mg / L, and continuous operation for 60 days, the total nitrogen removal rate was 85.7-91.2%.

[0060] Example 2

[0061] In this embodiment, the preparation steps of the dual-pore-forming iron-carbon composite filler used to enhance the autotrophic denitrification of Feammox-NDFO are as follows:

[0062] 1) Raw material selection and pretreatment:

[0063] The iron-containing powder selected was goethite FeO(OH), with a particle size of 1–10 μm; biochar powder, derived from carbonized wheat straw, with a particle size of 80 μm; silicate cement as the binder; and sodium bicarbonate as the pore-forming agent, with a particle size of 50–100 μm. Goethite FeO(OH), biochar powder, silicate cement, and sodium bicarbonate were dried to constant weight in an electrically heated forced-air drying oven at 40℃, with the moisture content controlled to ≤1%.

[0064] 2) Packing material preparation, molding, and curing:

[0065] Weigh out 40 parts by weight of goethite FeO(OH), 20 parts by weight of biochar, 30 parts by weight of silicate cement, and 10 parts by weight of sodium bicarbonate. Mix them in a mixer for 10 minutes to ensure uniformity. Place the mixed powder into a disc granulator, adjust the rotation speed to 35 rpm and the tilt angle to 30°, spray water (10-15% by weight) to granulate, and obtain spherical particles.

[0066] The granulated packing was placed in a constant temperature and humidity chamber at 70℃ and 85%RH and cured with deionized water vapor for 3 days to decompose NaHCO3 in the packing to generate Na2CO3 and release CO2 to form macropores of 50-100μm.

[0067] After curing, the packing material is placed in deionized water at 40℃ and treated with ultrasound at 30kHz for 12 hours to dissolve residual Na2CO3 and further form micropores of 1-10μm.

[0068] The material was allowed to air dry naturally at 25°C for 36 hours. Excess particles were removed by sieving using 5mm and 8mm standard sieves, yielding a double-porous iron-carbon composite filler with a particle size of 5-8mm. Its porosity, specific surface area, pore size range, and ammonia nitrogen adsorption capacity are shown in Table 1.

[0069] 3) The enhancing effect of dual-pore-forming iron-carbon composite filler on the Feammox-NDFO autotrophic denitrification system

[0070] A Feammox-NDFO autotrophic denitrification system was constructed in a 2L UASB reactor to investigate the enhancing effect of the prepared packing material on the autotrophic denitrification system. A was selected. 2 The activated sludge from the anoxic section of the O process was used as inoculum sludge at a concentration of 5000 mg / L. The double-porous iron-carbon composite packing material prepared in the above steps filled 30% of the reactor volume. The influent was artificially synthesized simulated wastewater, the composition of which is shown in Table 2, including NH4+. + With a nitrogen concentration of 75.2 ± 2.3 mg / L, a COD concentration of 23 ± 1.4 mg / L, a pH of 7.0, and a C / N ratio of 0.32, a Feammox-NDFO autotrophic denitrification system was constructed under the conditions of a hydraulic retention time (HRT) of 8 h and a reflux ratio of 10:1. The system reached a steady state after 10 days, and the effluent NH4+... + -N concentration is 0.6-2.6 mg / L, effluent NO3 - With a nitrogen concentration of 1.0-3.7 mg / L, and continuous operation for 60 days, the total nitrogen removal rate was 91.6-97.8%.

[0071] Example 3

[0072] In this embodiment, the preparation steps of the dual-pore-forming iron-carbon composite filler used to enhance the autotrophic denitrification of Feammox-NDFO are as follows:

[0073] 1) Raw material selection and pretreatment:

[0074] The selected iron-containing powder was ferric oxide (Fe₂O₃) with a particle size of 1–10 μm; biochar powder, derived from carbonized wheat straw, had a particle size of 80 μm; the binder was silicate cement; and the pore-forming agent was sodium bicarbonate with a particle size of 50–100 μm. The ferric oxide (Fe₂O₃), biochar powder, silicate cement, and sodium bicarbonate were dried to constant weight in an electrically heated forced-air drying oven at 40℃, with the moisture content controlled to ≤1%.

[0075] 2) Packing material preparation, molding, and curing:

[0076] Weigh out 38 parts by weight of ferric oxide (Fe2O3), 22 parts by weight of biochar powder, 30 parts by weight of silicate cement, and 10 parts by weight of sodium bicarbonate. Mix them in a mixer for 10 minutes to ensure uniformity. Place the mixed powder into a disc granulator, adjust the rotation speed to 40 rpm and the inclination angle to 30°, spray water (10-15% by weight) to granulate, and obtain spherical particles.

[0077] The granulated packing was placed in a constant temperature and humidity chamber at 80℃ and 90%RH and cured with deionized water vapor for 3 days to decompose NaHCO3 in the packing to generate Na2CO3 and release CO2 to form macropores of 50-100μm.

[0078] After curing, the packing material is placed in deionized water at 50℃ and treated with ultrasound at 30kHz for 12 hours to dissolve residual Na2CO3 and further form micropores of 1-10μm.

[0079] The material was allowed to air dry naturally at 25°C for 36 hours. Excess particles were removed by sieving using 5mm and 8mm standard sieves, yielding a double-porous iron-carbon composite filler with a particle size of 5-8mm. Its porosity, specific surface area, pore size range, and ammonia nitrogen adsorption capacity are shown in Table 1.

[0080] 3) The enhancing effect of dual-pore-forming iron-carbon composite filler on the Feammox-NDFO autotrophic denitrification system

[0081] A Feammox-NDFO autotrophic denitrification system was constructed in a 2L UASB reactor to investigate the enhancing effect of the prepared packing material on the autotrophic denitrification system. A was selected. 2 The activated sludge from the anoxic section of the O process was used as inoculum sludge at a concentration of 5000 mg / L. The double-porous iron-carbon composite packing material prepared in the above steps filled 30% of the reactor volume. The influent was artificially synthesized simulated wastewater, the composition of which is shown in Table 2, including NH4+. + With a nitrogen concentration of 75.2 ± 2.3 mg / L, a COD concentration of 23 ± 1.4 mg / L, a pH of 7.0, and a C / N ratio of 0.32, a Feammox-NDFO autotrophic denitrification system was constructed under the conditions of a hydraulic retention time (HRT) of 8 h and a reflux ratio of 10:1. The system reached a steady state after 10 days, and the effluent NH4+... + -N concentration is 3.5-5.8 mg / L, effluent NO3 - With a nitrogen concentration of 5.8-8.2 mg / L, and after 60 days of continuous operation, the total nitrogen removal rate was 81.4-87.6%.

[0082] Comparative Example 1

[0083] Sodium chloride is used instead of sodium bicarbonate, while other conditions remain unchanged, to demonstrate the beneficial effect of using sodium bicarbonate as a pore-forming agent in this invention patent.

[0084] 1) Raw material selection and pretreatment:

[0085] The following materials were selected: ferric oxide (Fe₂O₃) powder with a particle size of 1–10 μm; biochar derived from carbonized corn stalks with a particle size of 100 μm; silicate cement as the binder; and sodium chloride as the pore-forming agent with a particle size of 50–100 μm. The ferric oxide (Fe₂O₃), biochar powder, silicate cement, and sodium chloride were dried to constant weight in an electrically heated forced-air drying oven at 40℃, with the moisture content controlled to ≤1%.

[0086] 2) Packing material preparation, molding, and curing:

[0087] Weigh out each component according to the following proportions: 45 parts ferric oxide (Fe2O3), 15 parts biochar powder, 25 parts silicate cement, and 15 parts sodium chloride. Place them in a mixer and mix for 10 minutes to ensure uniformity. The mixing process is as follows: put the above powder mixture into a disc granulator, adjust the rotation speed to 35 rpm and the tilt angle to 30°, spray water (10-15% by mass) to granulate into iron-carbon composite particles, and obtain spherical iron-carbon composite particles.

[0088] The granulated iron-carbon composite particles were placed in a constant temperature and humidity chamber at 70°C and 85% RH and cured with deionized water vapor for 3 days. After curing, the filler was placed in deionized water at 40°C and treated with ultrasound at 30kHz for 12 hours.

[0089] The material was allowed to air dry naturally at 25℃ for 36 hours. Excess particles were removed by sieving using 5mm and 8mm standard sieves, yielding sodium chloride pore-forming iron-carbon composite filler with a particle size of 5-8mm. Its porosity, specific surface area, pore size range, and ammonia nitrogen adsorption capacity are shown in Table 1.

[0090] 3) The enhancing effect of sodium chloride pore-forming iron-carbon composite filler on the Feammox-NDFO autotrophic denitrification system

[0091] A Feammox-NDFO autotrophic denitrification system was constructed in a 2L UASB reactor to investigate the enhancing effect of the prepared packing material on the autotrophic denitrification system. A was selected. 2 The activated sludge from the anoxic section of the O process was used as inoculum sludge at a concentration of 5000 mg / L. The sodium chloride porous iron-carbon composite packing material prepared in the above steps filled 30% of the reactor volume. The influent was artificially synthesized simulated wastewater, the composition of which is shown in Table 2, including NH4+. +With a nitrogen concentration of 75.2 ± 2.3 mg / L, a COD concentration of 23 ± 1.4 mg / L, a pH of 7.0, and a C / N ratio of 0.32, a Feammox-NDFO autotrophic denitrification system was constructed under the conditions of a hydraulic retention time (HRT) of 8 h and a reflux ratio of 10:1. The system reached a steady state after 10 days, and the effluent NH4+... + -N concentration is 6.6-9.8 mg / L, effluent NO3 - With a nitrogen concentration of 10.9-14.1 mg / L, and continuous operation for 60 days, the total nitrogen removal rate was 68.2-76.7%.

[0092] Comparative Example 2

[0093] Based on Example 1, steam curing for pore formation was omitted, while other parameters remained unchanged. The porosity, specific surface area, pore size range, and ammonia nitrogen adsorption capacity are shown in Table 1.

[0094] 1) Raw material selection and pretreatment:

[0095] The following materials were selected: ferric oxide (Fe₂O₃) powder with a particle size of 1–10 μm; biochar powder derived from carbonized corn stalks with a particle size of 100 μm; silicate cement as the binder; and sodium bicarbonate as the pore-forming agent with a particle size of 50–100 μm. The ferric oxide (Fe₂O₃), biochar powder, silicate cement, and sodium bicarbonate were dried to constant weight in an electrically heated forced-air drying oven at 40°C, with the moisture content controlled to ≤1%.

[0096] 2) Packing material preparation, molding, and curing:

[0097] Weigh out the components according to the following proportions: 45 parts ferric oxide (Fe2O3), 15 parts biochar powder, 25 parts silicate cement, and 15 parts sodium bicarbonate. Mix them in a mixer for 10 minutes to ensure uniformity. Place the mixed powder into a disc granulator, adjust the speed to 35 rpm and the inclination angle to 30°, and spray water to granulate into iron-carbon composite particles. The amount of water added is 10-15% by weight, resulting in spherical iron-carbon composite particles.

[0098] The granulated spherical iron-carbon composite particles were placed in a constant temperature and humidity chamber at 40°C and 85% RH and cured with deionized water for 3 days. After curing, the filler was placed in deionized water at 40°C and treated with ultrasound at 30kHz for 12 hours to form micropores.

[0099] The material was allowed to air dry naturally at 25℃ for 36 hours. Excess particles were removed by sieving using 5mm and 8mm standard sieves, yielding a single-layer impregnated pore-forming iron-carbon composite filler with a particle size of 5-8mm. Its porosity, specific surface area, pore size range, and ammonia nitrogen adsorption capacity are shown in Table 1.

[0100] 3) The strengthening effect of single-immersion pore-forming iron-carbon composite filler on the Feammox-NDFO autotrophic denitrification system

[0101] A Feammox-NDFO autotrophic denitrification system was constructed in a 2L UASB reactor to investigate the enhancing effect of the prepared packing material on the autotrophic denitrification system. A was selected. 2 The activated sludge from the anoxic section of the O process was used as inoculum sludge at a concentration of 5000 mg / L. The single-layer soaked porous iron-carbon composite packing material prepared in the above steps filled 30% of the reactor volume. The influent was artificially synthesized simulated wastewater, the composition of which is shown in Table 2, including NH4+. + With a nitrogen concentration of 75.2 ± 2.3 mg / L, a COD concentration of 23 ± 1.4 mg / L, a pH of 7.0, and a C / N ratio of 0.32, a Feammox-NDFO autotrophic denitrification system was constructed under the conditions of a hydraulic retention time (HRT) of 8 h and a reflux ratio of 10:1. The system reached a steady state after 10 days, and the effluent NH4+... + -N concentration is 5.8-12 mg / L, effluent NO3 - With a nitrogen concentration of 9.7-17.2 mg / L, and after 60 days of continuous operation, the total nitrogen removal rate was 71.2-79.4%.

[0102] Comparative Example 3

[0103] Without granulation or pore formation, ferric oxide (Fe2O3) and biochar powder were directly added to the system to investigate the beneficial effects of pore formation and granulation. Specifically, A was selected... 2 The activated sludge from the anoxic section of the O process was used as inoculum sludge at a concentration of 5000 mg / L. The mass of ferric oxide and biochar powder to be added was calculated based on the packing volume as described in Example 1. The two were mixed thoroughly and added to a 2L UASB reactor. The influent was artificially synthesized simulated wastewater, the composition of which is shown in Table 2, including NH4+. + A Feammox-NDFO autotrophic denitrification system was constructed with a nitrogen concentration of 75.2 ± 2.3 mg / L, a COD concentration of 23 ± 1.4 mg / L, a pH of 7.0, and a C / N ratio of 0.32, under conditions of a hydraulic retention time (HRT) of 8 h and a reflux ratio of 10:1. With continuous operation of the system, the NH4+ effluent from the reactor increased... + The concentration of -N varied from 5.3 to 19.9 mg / L, and the effluent NO3 - The concentration of -N varied from 8.9 to 28.4 mg / L, and the total nitrogen removal rate ranged from 35.8% to 81.1%. With the increase of time, the total nitrogen removal effect gradually deteriorated.

[0104] Comparative Example 4

[0105] Based on Example 1, ultrasonic-assisted deionized water soaking for pore formation was omitted, while other parameters remained unchanged. The porosity, specific surface area, pore size range, and ammonia nitrogen adsorption capacity are shown in Table 1.

[0106] 1) Raw material selection and pretreatment:

[0107] The iron-containing powder selected was ferric oxide (Fe₂O₃) with a particle size of 1–10 μm; the biochar powder, derived from carbonized corn stalks, had a particle size of 100 μm; the binder was silicate cement; and the pore-forming agent was sodium bicarbonate with a particle size of 50–100 μm. The ferric oxide (Fe₂O₃), biochar powder, silicate cement, and sodium bicarbonate were dried to constant weight in an electrically heated forced-air drying oven at 40℃, with the moisture content controlled to ≤1%.

[0108] 2) Packing material preparation, molding, and curing:

[0109] Weigh out 45 parts of ferric oxide (Fe2O3), 15 parts of biochar powder, 25 parts of silicate cement, and 15 parts of sodium bicarbonate according to the specified weight ratio. Place them in a mixer and mix for 10 minutes to ensure uniformity. The mixing process is as follows: put the above-mentioned powder mixture into a disc granulator, adjust the rotation speed to 35 rpm and the inclination angle to 30°, spray water (10-15% by mass) to granulate, and obtain spherical particles.

[0110] The granulated iron-carbon composite particles are placed in a constant temperature and humidity chamber at 70°C and 85% RH and cured with deionized water vapor for 3 days to decompose NaHCO3 in the filler to generate Na2CO3 and release CO2 to form macropores of 50-100μm. The above process is the first stage of pore formation.

[0111] After the first stage of pore formation, the iron-carbon composite particles were placed in deionized water at 40℃ and soaked for 12 hours to dissolve residual Na2CO3, further forming micropores. This process constitutes the second stage of pore formation. Finally, the particles were allowed to air dry naturally at 25℃ for 36 hours. They were then sieved using 5mm and 8mm standard sieves to remove excess particles, yielding a double-pore-forming iron-carbon composite filler with a particle size of 5-8mm. Its porosity, specific surface area, pore size range, and ammonia nitrogen adsorption capacity are shown in Table 1.

[0112] 3) The enhancing effect of the dual-pore-forming iron-carbon composite filler on the Feammox-NDFO autotrophic denitrification system.

[0113] A Feammox-NDFO autotrophic denitrification system was constructed in a 2L UASB reactor to investigate the enhancing effect of the prepared packing material on the autotrophic denitrification system. A was selected. 2The activated sludge from the anoxic section of the O process was used as inoculum sludge at a concentration of 5000 mg / L. The double-porous iron-carbon composite packing material prepared in the above steps filled 30% of the reactor volume. The influent was artificially synthesized simulated wastewater, the composition of which is shown in Table 2, including NH4+. + With a nitrogen concentration of 75.2 ± 2.3 mg / L, a COD concentration of 23 ± 1.4 mg / L, a pH of 7.0, and a C / N ratio of 0.32, a Feammox-NDFO autotrophic denitrification system was constructed under the conditions of a hydraulic retention time (HRT) of 8 h and a reflux ratio of 10:1. The system reached a steady state after 10 days, and the effluent NH4+... + -N concentration is 5.6-8.5 mg / L, effluent NO3 - With a nitrogen concentration of 9.4-12.2 mg / L, and continuous operation for 60 days, the total nitrogen removal rate was 72.5-80.1%.

[0114] Comparative Example 5

[0115] Based on Example 1, the addition ratio was changed.

[0116] 1) Raw material selection and pretreatment:

[0117] The iron-containing powder selected was ferric oxide (Fe₂O₃) with a particle size of 1–10 μm; biochar, derived from carbonized corn stalks, with a particle size of 100 μm; silicate cement as the binder; and sodium bicarbonate as the pore-forming agent with a particle size of 50–100 μm. The ferric oxide (Fe₂O₃), biochar powder, silicate cement, and sodium bicarbonate were dried to constant weight in an electrically heated forced-air drying oven at 40℃, with the moisture content controlled to ≤1%.

[0118] 2) Packing material preparation, molding, and curing:

[0119] Weigh out 45 parts by weight of ferric oxide (Fe2O3), 30 parts by weight of biochar powder, 20 parts by weight of silicate cement, and 5 parts by weight of sodium bicarbonate. Mix these components in a mixer for 10 minutes to ensure uniformity. The mixing process involves placing the mixed powder into a disc granulator, adjusting the rotation speed to 35 rpm and the inclination angle to 30°, and spraying water (10-15% by weight) to granulate, obtaining spherical particles. The granulated iron-carbon composite particles are then placed in a constant temperature and humidity chamber at 70°C and 85% RH, and cured with deionized steam for 3 days. This process decomposes the NaHCO3 in the filler to generate Na2CO3 and releases CO2, forming macropores of 50-100 μm. This is the first stage of pore formation. After the first stage of pore formation, the iron-carbon composite particles are placed in deionized water at 40°C and treated with ultrasound at 30 kHz for 12 hours to dissolve residual Na2CO3, further forming micropores of 1-10 μm. This is the second stage of pore formation. Finally, the material was allowed to air dry naturally at 25°C for 36 hours. It was then sieved using 5mm and 8mm standard sieves to remove excess particles, resulting in a double-pore iron-carbon composite filler with a particle size of 5-8mm. Its porosity, specific surface area, pore size range, and ammonia nitrogen adsorption capacity are shown in Table 1.

[0120] 3) The enhancing effect of the dual-pore-forming iron-carbon composite filler on the Feammox-NDFO autotrophic denitrification system.

[0121] A Feammox-NDFO autotrophic denitrification system was constructed in a 2L UASB reactor to investigate the enhancing effect of the prepared packing material on the autotrophic denitrification system. A was selected. 2 The activated sludge from the anoxic section of the O process was used as inoculum sludge at a concentration of 5000 mg / L. The double-porous iron-carbon composite packing material prepared in the above steps filled 30% of the reactor volume. The influent was artificially synthesized simulated wastewater, the composition of which is shown in Table 2, including NH4+. + With a nitrogen concentration of 75.2 ± 2.3 mg / L, a COD concentration of 23 ± 1.4 mg / L, a pH of 7.0, and a C / N ratio of 0.32, a Feammox-NDFO autotrophic denitrification system was constructed under the conditions of a hydraulic retention time (HRT) of 8 h and a reflux ratio of 10:1. The system reached a steady state after 10 days, and the effluent NH4+... + -N concentration is 7.0-9.4 mg / L, effluent NO3 - With a nitrogen concentration of 11.6-13.5 mg / L, and continuous operation for 60 days, the total nitrogen removal rate was 69.5-75.3%.

[0122] Comparative Example 6

[0123] Based on Example 1, the addition ratio was changed.

[0124] 1) Raw material selection and pretreatment:

[0125] The iron-containing powder selected was ferric oxide (Fe₂O₃) with a particle size of 1–10 μm; the biochar powder, derived from carbonized corn stalks, had a particle size of 100 μm; the binder was silicate cement; and the pore-forming agent was sodium bicarbonate with a particle size of 50–100 μm. The ferric oxide (Fe₂O₃), biochar powder, silicate cement, and sodium bicarbonate were dried to constant weight in an electrically heated forced-air drying oven at 40℃, with the moisture content controlled to ≤1%.

[0126] 2) Packing material preparation, molding, and curing:

[0127] Weigh out 40 parts by weight of ferric oxide (Fe2O3), 25 parts by weight of biochar powder, 15 parts by weight of silicate cement, and 20 parts by weight of sodium bicarbonate. Mix these components in a mixer for 10 minutes to ensure uniformity. The mixing process involves placing the mixed powder into a disc granulator, adjusting the rotation speed to 35 rpm and the inclination angle to 30°, and spraying water (10-15% by weight) to granulate, obtaining spherical particles. The granulated iron-carbon composite particles are then placed in a constant temperature and humidity chamber at 70°C and 85% RH, and cured with deionized steam for 3 days. This process decomposes the NaHCO3 in the filler to generate Na2CO3 and releases CO2, forming macropores of 50-100 μm. This is the first stage of pore formation. After the first stage of pore formation, the iron-carbon composite particles are placed in deionized water at 40°C and treated with ultrasound at 30 kHz for 12 hours to dissolve residual Na2CO3, further forming micropores of 1-10 μm. This is the second stage of pore formation. Finally, the material was allowed to air dry naturally at 25°C for 36 hours. It was then sieved using 5mm and 8mm standard sieves to remove excess particles, resulting in a double-pore iron-carbon composite filler with a particle size of 5-8mm. Its porosity, specific surface area, pore size range, and ammonia nitrogen adsorption capacity are shown in Table 1.

[0128] 3) The enhancing effect of the dual-pore-forming iron-carbon composite filler on the Feammox-NDFO autotrophic denitrification system.

[0129] A Feammox-NDFO autotrophic denitrification system was constructed in a 2L UASB reactor to investigate the enhancing effect of the prepared packing material on the autotrophic denitrification system. A was selected. 2 The activated sludge from the anoxic section of the O process was used as inoculum sludge at a concentration of 5000 mg / L. The double-porous iron-carbon composite packing material prepared in the above steps filled 30% of the reactor volume. The influent was artificially synthesized simulated wastewater, the composition of which is shown in Table 2, including NH4+. +With a nitrogen concentration of 75.2 ± 2.3 mg / L, a COD concentration of 23 ± 1.4 mg / L, a pH of 7.0, and a C / N ratio of 0.32, a Feammox-NDFO autotrophic denitrification system was constructed under the conditions of a hydraulic retention time (HRT) of 8 h and a reflux ratio of 10:1. The system reached a steady state after 10 days, and the effluent NH4+... + -N concentration 4.3-7.2 mg / L, effluent NO3 - With a nitrogen concentration of 6.3-9.0 mg / L, and continuous operation for 60 days, the total nitrogen removal rate was 79.6-84.7%.

[0130] Comparative Example 7

[0131] Based on Example 2, the addition ratio was changed.

[0132] 1) Raw material selection and pretreatment:

[0133] The iron-containing powder selected was goethite FeO(OH), with a particle size of 1–10 μm; biochar powder, derived from carbonized wheat straw, with a particle size of 100 μm; silicate cement as the binder; and sodium bicarbonate as the pore-forming agent, with a particle size of 50–100 μm. Goethite FeO(OH), biochar powder, silicate cement, and sodium bicarbonate were dried to constant weight in an electrically heated forced-air drying oven at 40℃, with the moisture content controlled to ≤1%.

[0134] 2) Packing material preparation, molding, and curing:

[0135] Weigh out 35 parts by weight of goethite FeO(OH), 35 parts by weight of biochar powder, 15 parts by weight of silicate cement, and 15 parts by weight of sodium bicarbonate. Mix these components in a mixer for 10 minutes to ensure uniformity. The mixing process involves placing the mixed powder into a disc granulator, adjusting the rotation speed to 35 rpm and the inclination angle to 30°, and spraying water (10-15% by weight) to granulate, obtaining spherical particles. The granulated iron-carbon composite particles are then placed in a constant temperature and humidity chamber at 70°C and 85% RH, and cured with deionized steam for 3 days. This process decomposes the NaHCO3 in the filler to generate Na2CO3 and releases CO2, forming macropores of 50-100 μm. This is the first stage of pore formation. After the first stage of pore formation, the iron-carbon composite particles are placed in deionized water at 40°C and treated with ultrasound at 30 kHz for 12 hours to dissolve residual Na2CO3, further forming micropores of 1-10 μm. This is the second stage of pore formation. Finally, the material was allowed to air dry naturally at 25°C for 36 hours. It was then sieved using 5mm and 8mm standard sieves to remove excess particles, resulting in a double-pore iron-carbon composite filler with a particle size of 5-8mm. Its porosity, specific surface area, pore size range, and ammonia nitrogen adsorption capacity are shown in Table 1.

[0136] 3) The enhancing effect of the dual-pore-forming iron-carbon composite filler on the Feammox-NDFO autotrophic denitrification system.

[0137] A Feammox-NDFO autotrophic denitrification system was constructed in a 2L UASB reactor to investigate the enhancing effect of the prepared packing material on the autotrophic denitrification system. A was selected. 2 The activated sludge from the anoxic section of the O process was used as inoculum sludge at a concentration of 5000 mg / L. The double-porous iron-carbon composite packing material prepared in the above steps filled 30% of the reactor volume. The influent was artificially synthesized simulated wastewater, the composition of which is shown in Table 2, including NH4+. + With a nitrogen concentration of 75.2 ± 2.3 mg / L, a COD concentration of 23 ± 1.4 mg / L, a pH of 7.0, and a C / N ratio of 0.32, a Feammox-NDFO autotrophic denitrification system was constructed under the conditions of a hydraulic retention time (HRT) of 8 h and a reflux ratio of 10:1. The system reached a steady state after 10 days, and the effluent NH4+... + -N concentration is 3.8-6.6 mg / L, effluent NO3 - With a nitrogen concentration of 6.2-9.5 mg / L, and continuous operation for 60 days, the total nitrogen removal rate was 78.6-86.7%.

[0138] Table 1. Physicochemical properties of the packings used in the examples and comparative examples.

[0139]

[0140] Table 2. Composition of artificially simulated wastewater

[0141] Concentration (mg / L) 287 10 100 600 600 1ml / L

[0142] Table 1 shows that the porosities of the fillers in Examples 1 and 2 were 56.5% and 53.9%, respectively, and their specific surface areas were 25.74 m². 2 / g and 27.43m 2 The porosity / g of Comparative Examples 2 and 4 was significantly higher than that of Comparative Examples 2 and 4. This indicates that the dual-pore-forming process improved the pore structure of the packing material, enhanced its adsorption performance, and was beneficial for the construction of the Feammox-NDFO system. In contrast, Comparative Examples 2 and 4 had lower porosity and smaller specific surface area, limiting their adsorption capacity and hindering efficient nitrogen removal. Comparative Example 3 was not granulated, and the packing material was prone to agglomeration or loss, making it difficult to measure the specific surface area and porosity, thus affecting the stability of the system.

[0143] Figure 4The results showed that the total nitrogen removal rates of Examples 1 and 2 increased rapidly within 10 days and stabilized above 85%, demonstrating excellent denitrification effects. Comparative Examples 1 and 2 had lower removal rates, with a significant downward trend after long-term operation, indicating limited enhancement effects on the Feammox-NDFO system. The total nitrogen removal rate of Comparative Example 3 initially increased, but decreased significantly after 30 days, falling below 40% after 50 days, indicating that ungranulated packing material is detrimental to the long-term stable operation of the system.

[0144] This invention develops a dual-pore-forming iron-carbon composite packing material to construct a Feammox-NDFO coupled system and enhance its nitrogen removal efficiency. First, the Fe(III) fixed in the packing material acts as an electron acceptor in the Feammox process and is gradually reduced to Fe(II) during the reaction. Subsequently, Fe(II) acts as an electron donor in the NDFO process, driving a nitrate-dependent ferrous oxidation reaction, thus removing nitrogen from the water. Simultaneously, Fe(II) is oxidized back to Fe(III), ensuring the sustainable operation of the Feammox-NDFO system. Second, the biochar powder doped in the packing material participates in redox reactions through its oxygen-containing functional groups, promoting electron transfer in both the Feammox and NDFO processes, thereby increasing the ammonia oxidation rate in the Feammox process and the nitrate reduction efficiency in the NDFO process. Finally, the packing material employs a dual-pore-forming mechanism. During the molding and curing stage, steam is generated by heating deionized water, allowing the packing material to gradually release CO2 in a humid and hot environment, forming a macroporous structure. Subsequently, during the deionized water soaking stage, the residual Na2CO3 inside the packing gradually dissolves, further forming micropores, thereby constructing a high specific surface area packing with a multi-level pore structure, improving the adhesion ability and mass transfer efficiency of microorganisms, and further enhancing the stability and denitrification efficiency of the Feammox-NDFO system.

[0145] This invention provides a dual-pore iron-carbon composite packing and its preparation method. This packing can be used to construct a Feammox-NDFO coupled system based on iron cycling and enhance its autotrophic denitrification efficiency. The Fe(III) fixed in the packing acts as the electron acceptor in the Feammox process, gradually reducing to Fe(II) during the reaction. Fe(II), acting as the electron donor in the NDFO process, is oxidized back to Fe(III), forming a Fe(III) / Fe(II) cycle supply, maintaining the continuous operation of the Feammox-NDFO system. The biochar powder doped in the packing can improve the extracellular electron transfer efficiency of nitrogen-converting microorganisms. Simultaneously, its large specific surface area and abundant functional groups have a certain adsorption effect on ammonia nitrogen, allowing NH4+ to be absorbed. +Enriched on the surface of the packing material, it enhances the mass transfer efficiency of the Feammox-NDFO system. The packing material employs a dual pore-forming mechanism to form a multi-level pore structure and provide a large specific surface area, providing a stable carrier for microbial attachment and growth, and improving the denitrification efficiency and long-term stability of the system.

[0146] The packing material of this invention is mainly used in low-carbon wastewater conditions with C / N ≤ 0.5. Moreover, it can still maintain high-efficiency denitrification under such low-carbon conditions without the need for additional organic carbon sources. After 60 days of long-term operation, the TN removal rate can reach 91.2-97.8%. It is suitable for the treatment of low-carbon, high-ammonia nitrogen wastewater, thus expanding the application scope of autotrophic denitrification technology.

[0147] It should be noted that the above embodiments are merely preferred embodiments of the present invention. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described above. Various improvements, adjustments, or combinations can be made without departing from the basic concept of the present invention, and these modifications and improvements are also within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A method for preparing a dual-pore-forming iron-carbon composite packing material with enhanced Feammox-NDFO autotrophic denitrification, characterized in that: Specifically, the following steps are included: Step 1, Raw material pretreatment: Dry the iron powder, biochar powder, binder and pore-forming agent to a moisture content of ≤1%, and weigh each component according to the weight proportions for later use; The pore-forming agent is sodium bicarbonate; the adhesive is silicate cement. Step 2, Mixing and Granulation: Mix the components weighed in Step 1 evenly into a mixed powder, and put it into a disc granulator. Spray water to granulate and make iron-carbon composite particles. The rotation speed of the disc granulator is 30-40 rpm, the tilt angle is controlled at 25-35°, and the granulation time is 40-60 min. Step 3, Steam curing and pore formation: The iron-carbon composite particles granulated in Step 2 are placed in a constant temperature and humidity chamber for moist heat curing, which decomposes sodium bicarbonate to generate sodium carbonate and releases carbon dioxide, forming macropores of 50-500μm; the curing and pore formation conditions are: temperature 60-80℃; humidity 80-90%RH; curing time 2-4 days; the steam source is steam generated by heating deionized water. Step 4, Ultrasonic-assisted deionized water soaking to create pores: The iron-carbon composite particles cured in step 3 are soaked in ultrasonic-assisted deionized water to dissolve the residual sodium carbonate and form micropores of 1-10 μm; the soaking conditions are: temperature 30-50℃; time 6-12h; ultrasonic frequency 20-40kHz. Step 5, Finished product screening: Dry the iron-carbon composite particles after step 4 by ventilation at room temperature, and screen the iron-carbon composite particles with a particle size between 5-8 mm as the finished product of double-pore iron-carbon composite filler.

2. The preparation method of the enhanced Feammox-NDFO autotrophic denitrification dual-pore-forming iron-carbon composite packing according to claim 1, characterized in that: In step 1, during the raw material pretreatment process, an electric heating forced-air drying oven is specifically used to dry the iron-containing powder, biochar powder, adhesive, and pore-forming agent. In step 2, during the mixing and granulation process, the raw materials from step 1 are granulated with water, wherein the amount of water added is 10-15%, to produce iron-carbon composite particles with a diameter of 6-8 mm. In step 5, the finished product screening process is carried out under controlled ambient temperature of 20-25℃ and allowed to stand for 24-48 hours with ventilation.

3. The method for preparing a dual-pore-forming iron-carbon composite packing material with enhanced Feammox-NDFO autotrophic denitrification according to claim 1 or 2, characterized in that: The raw materials used in step 1 are proportioned by weight as follows: 30-45 parts iron powder, 15-30 parts biochar powder, 20-30 parts binder, and 10-15 parts pore-forming agent. The iron-containing powder is one or more of ferric oxide (Fe2O3), ferric phosphate (FePO4), goethite (FeO(OH)), and ferric citrate; The biochar powder is selected from one or more of corn stalks, wheat stalks, and rice stalks.

4. The preparation method of a dual-pore-forming iron-carbon composite packing material for enhanced Feammox-NDFO autotrophic denitrification according to claim 3, characterized in that: The iron-containing powder has a particle size of 1–10 μm; The biochar powder has a particle size of 75–150 μm; The pore-forming agent has a particle size of 50–100 μm.

5. The preparation method of a dual-pore-forming iron-carbon composite packing material for enhanced Feammox-NDFO autotrophic denitrification according to claim 4, characterized in that: 40 parts iron powder, 20 parts biochar powder, 30 parts binder, and 10 parts pore-forming agent; The iron-containing powder is goethite FeO(OH), with a particle size of 1–10 μm; the biochar powder is derived from the carbonization of wheat straw, with a particle size of 80 μm; the binder is silicate cement; and the pore-forming agent is sodium bicarbonate, with a particle size of 50–100 μm.

6. The method for preparing a dual-pore-forming iron-carbon composite packing material with enhanced Feammox-NDFO autotrophic denitrification according to claim 5, characterized in that: Step 1, Raw material pretreatment: Select goethite FeO(OH) powder with a particle size of 1-10 μm; biochar powder, derived from wheat straw carbonization, with a particle size of 80 μm; binder, silicate cement; pore-forming agent, sodium bicarbonate with a particle size of 50-100 μm; use an electric heating forced-air drying oven at 40℃ to dry goethite FeO(OH), biochar powder, silicate cement, and sodium bicarbonate to constant weight, controlling the moisture content to ≤1%; Step 2, Mixing and Granulation: According to the weight proportions, place 40 parts of goethite FeO(OH), 20 parts of biochar powder, 30 parts of silicate cement, and 10 parts of sodium bicarbonate into a mixer and mix for 10 minutes to ensure uniformity; put the mixed powder into a disc granulator, adjust the speed to 35 rpm and the inclination angle to 30°, spray with 10-15% water to granulate, and obtain spherical particles; Step 3, Steam curing and pore formation: The granulated packing is placed in a constant temperature and humidity chamber at 70℃ and 85%RH, and cured with deionized water steam for 3 days to decompose NaHCO3 in the packing to generate Na2CO3 and release CO2 to form macropores of 50-100μm. Step 4: Ultrasonic-assisted deionized water soaking to create pores: The cured filler is placed in deionized water at 40℃ and treated with ultrasound at 30kHz for 12 hours to form micropores of 1-10μm. Step 5, Finished product screening: Allow the product to air dry naturally at 25℃ for 36 hours, then screen it using 5mm and 8mm standard sieves to remove excessive particles and obtain double-pore iron-carbon composite filler with a particle size of 5-8mm.

7. The application of a dual-pore iron-carbon composite packing in a wastewater treatment process, wherein the dual-pore iron-carbon composite packing is prepared by the preparation method of the enhanced Feammox-NDFO autotrophic denitrification dual-pore iron-carbon composite packing as described in any one of claims 1-6.

8. The application of the dual-pore iron-carbon composite packing material according to claim 7 in wastewater treatment process, characterized in that: The double-pore iron-carbon composite packing is put into the sewage treatment device, and the double-pore iron-carbon composite packing occupies 28-45% of the internal volume of the sewage treatment device.

9. The application of the dual-pore iron-carbon composite packing material according to claim 8 in wastewater treatment process, characterized in that: Dual-pore iron-carbon composite packing material is used in low-carbon wastewater conditions with C / N ≤ 0.

5. Specifically, a Feammox-NDFO autotrophic denitrification system is constructed in a UASB reactor: A... 2 Activated sludge from the anoxic section of the O process was used as inoculum sludge at a concentration of 5000 mg / L, and the double-porous iron-carbon composite packing material occupied 30% of the reactor volume; the influent NH4... + The system was constructed under the following conditions: N concentration 75.2±2.3 mg / L, COD concentration 23±1.4 mg / L, pH=7.0, C / N=0.32, hydraulic retention time HRT=8h, and reflux ratio=10:

1. The system reached a stable state after 10 days.

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