Dual-pore-forming iron-carbon composite filler for strengthening Feammox-NDFO autotrophic nitrogen removal and preparation method of dual-pore-forming iron-carbon composite filler

Abstract

The invention provides a dual-pore-forming iron-carbon composite filler for strengthening Feammox-NDFO autotrophic nitrogen removal and a preparation method thereof, and relates to the technical field of sewage organism autotrophic nitrogen removal, the dual-pore-forming iron-carbon composite filler comprises the following raw materials by weight: 30-45 parts of iron-containing powder, 15-30 parts of charcoal powder, 20-30 parts of an adhesive, and 10-15 parts of a pore-forming agent. The iron-containing powder is one or a combination of iron sesquioxide (Fe2O3), iron phosphate (FePO4), goethite (FeO (OH)) and ferric citrate; the pore-forming agent is sodium bicarbonate; the invention relates to a preparation method of a dual-pore-forming iron-carbon composite filler for strengthening Feammox-NDFO autotrophic nitrogen removal. The preparation method specifically comprises the following steps: 1, pretreating raw materials; 2, mixing and granulating; 3, steam curing and pore forming are carried out, wherein the curing temperature is 60-80 DEG C; the humidity is 80-90% RH; 4, ultrasonic-assisted deionized water soaking and pore forming are carried out, and the soaking temperature is 30-50 DEG C; the time is 6-12 hours; the ultrasonic frequency is 20-40 kHz. And 5, screening a finished product. The filler disclosed by the invention has the beneficial effects that the filler is mainly applied to a low-carbon sewage condition that C / N is less than or equal to 0.5, efficient denitrification can still be kept under the low-carbon condition, and the TN removal rate can reach 91.6-97.8%.

Description

Technical Field

[0001] The present invention relates to the technical field of biological autotrophic nitrogen removal from sewage, and particularly to a double-porous iron-carbon composite filler for enhancing Feammox-NDFO autotrophic nitrogen removal and a preparation method thereof. Background Art

[0002] Biological nitrogen removal from sewage has always been a major requirement for water environment treatment. Traditional biological nitrogen removal processes rely on two stages: aerobic nitrification and anoxic denitrification. There are time and space disconnections in the reaction process, and continuous aeration and external carbon source supplementation are required to maintain the nitrogen removal effect. However, this method has poor applicability in the treatment of wastewater with a low C / N ratio. The lack of carbon source limits the denitrification process and affects the overall nitrogen removal efficiency. In recent years, Feammox (ferroammonium oxidation) coupled with NDFO (nitrate-dependent ferrous oxidation) has received extensive attention due to its unique autotrophic nitrogen removal mechanism, becoming a research hotspot and gradually showing the feasibility of engineering applications.

[0003] Feammox (ferroammonium oxidation) and NDFO (nitrate-dependent ferrous oxidation) are two important autotrophic nitrogen removal processes. They use Fe(III) and Fe(II) as electron acceptors and electron donors respectively to achieve nitrogen transformation. In the Feammox process, Fe(III) acts as an electron acceptor and reacts with NH4 + under anaerobic conditions to oxidize NH4 + to NO2 - or NO3 - , while 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 the nitrogen removal efficiency. The NDFO process, in the presence of nitrate, uses Fe(II) as an electron donor to reduce NO3 - to N2, while Fe(II) is oxidized back to Fe(III). If the Feammox and NDFO processes can be coupled, making the NO3 - produced by Feammox serve as the electron acceptor for the NDFO reaction, and the Fe(III) generated in the NDFO process is reused for the Feammox process, thus realizing the recycling of Fe(III) / Fe(II), a stable Feammox-NDFO autotrophic nitrogen removal system can be constructed to achieve efficient iron recycling and continuous nitrogen removal. Therefore, the present double-porous iron-carbon composite filler for enhancing Feammox-NDFO autotrophic nitrogen removal and its preparation method are developed. Summary of the Invention

[0004] The present invention provides a dual-porous iron-carbon composite filler for enhancing Feammox-coupled NDFO autotrophic denitrification based on iron cycle and a preparation method thereof. By constructing a high-specific-surface-area filler with a multi-level pore structure, the attachment ability of microorganisms and the mass transfer efficiency are improved, and the stability and denitrification performance of the Feammox-NDFO system are further enhanced.

[0005] A dual-porous iron-carbon composite filler, the raw material composition of which includes the following components by weight: 30-45 parts of iron-containing 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 iron(III) oxide (Fe2O3), iron phosphate (FePO4), goethite (FeO(OH)), and iron citrate;

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

[0008] In a preferred embodiment, the biochar powder is selected from one or a combination of corn straw, wheat straw, and rice straw to prepare biochar powder, and the particle size is between 75-150 μm;

[0009] In a preferred embodiment, the binder is portland cement;

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

[0011] In a preferred embodiment, the dual-porous iron-carbon composite filler is spherical particles with a diameter of 5-8 mm to ensure the best mass transfer performance and microorganism attachment ability.

[0012] A preparation method of a dual-porous iron-carbon composite filler for enhancing Feammox-NDFO autotrophic denitrification, specifically including the following steps:

[0013] Step 1. Raw material pretreatment

[0014] After drying the iron-containing powder, biochar powder, binder, and pore-forming agent, weigh each component according to the weight parts for standby;

[0015] Preferably, use an electrothermal blast drying oven to dry the iron-containing powder, biochar powder, binder, and pore-forming agent, and control the moisture content ≤ 1%;

[0016] Step 2. Mixing and granulation

[0017] Mix the iron-containing powder, biochar powder, binder, and pore-forming agent in step 1 evenly according to the above ratio to obtain a mixed powder;

[0018] Put the mixed powder into a granulator, spray water for granulation to produce iron-carbon composite particles with a diameter of 6-8 mm;

[0019] Furthermore, the rotation speed of the granulator is 30-40 revolutions per minute, the inclination angle is controlled at 25-35°, and the granulation time is 40-60 minutes; the water addition method is spray water addition to ensure uniform formation of particles.

[0020] Step 3: Steam curing for pore formation

[0021] Put the iron-carbon composite particles after granulation in step 2 into a constant temperature and humidity box for wet heat curing, so that CO2 is released in a steam environment to form macropores with a size of 50-500 μm, enhance the specific surface area of the filler, and ensure the normal hardening of the cement-based binder;

[0022] Furthermore, the conditions for curing and pore formation are: temperature 60-80 °C; 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 immersion for pore formation

[0025] After steam curing, part of Na2CO3 still remains inside the iron-carbon composite particles. The iron-carbon composite particles are soaked in deionized water assisted by ultrasonic waves to dissolve it. The conditions for immersion pore formation are: temperature 30-50 °C; time 6-12 h; ultrasonic frequency 20-40 kHz, forming micropores with a size of 1-10 μm.

[0026] Furthermore, stirring is carried out to ensure the full dissolution of Na2CO3, optimize the pore structure of the iron-carbon composite particles, and promote the attachment and growth of microorganisms.

[0027] Step 5: Finished product screening

[0028] At room temperature, ventilate it to dry, and screen the iron-carbon composite particles with a particle size between 5-8 mm as the finished product of the double-pore-forming iron-carbon composite filler;

[0029] Furthermore, ventilate and let it stand at room temperature of 20-25 °C for 24-48 h, and air dry naturally to ensure that the moisture of the filler is fully evaporated, avoiding structural deformation and cracking. Use it after the filler is completely dry;

[0030] Preferably, 5 mm and 8 mm standard sieves are used to screen the iron-carbon composite particles, removing particles with a particle size less than 5 mm and greater than 8 mm to ensure that the particle size of the finished product particles is between 5-8 mm.

[0031] A double-pore-forming iron-carbon composite filler is applied to the sewage treatment process.

[0032] Furthermore, the dual-porous iron-carbon composite filler is put into the sewage treatment device, and the dual-porous iron-carbon composite filler accounts for 28-45% of the internal volume of the sewage treatment device.

[0033] Advantages of the present invention:

[0034] (1) In the present invention, Fe(III) is fixed as an electron acceptor in the filler to ensure the synchronous progress of ammonia oxidation and Fe(III) reduction in the Feammox process, and the efficient cycle of Fe(III) / Fe(II) is realized through the NDFO process, enabling the Feammox and NDFO processes to operate stably for a long time, improving the denitrification efficiency and reducing the dosing requirement of additional iron sources.

[0035] (2) The present invention adopts a dual-porous formation mechanism of steam curing and ultrasonic-assisted soaking to form a multi-level pore structure with coexisting macropores of 50-500 μm and micropores of 1-10 μm inside the filler. The macropores provide sufficient attachment space for microorganisms, and the micropores optimize the mass transfer efficiency between water and microorganisms. Through the cooperation of the above two types of pores, the porosity of the filler is increased by 15-20%, and the specific surface area is increased by 10-15%, significantly enhancing the growth carrier capacity of microorganisms in the Feammox-NDFO system and improving the nitrogen removal efficiency. The filler of the present invention is mainly applied to the condition of low-carbon sewage with C / N ≤ 0.5, and still can maintain high-efficiency denitrification under such low-carbon conditions without the additional dosing of 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 source and high-ammonia-nitrogen wastewater, expanding the application range of autotrophic denitrification technology.

[0036] (3) Biochar powder is doped in the filler of the present invention. On the one hand, it improves the NH4 + adsorption capacity of the filler, making the ammonia oxidation reaction substrate in the Feammox process more concentrated and promoting the reduction of Fe(III); on the other hand, the surface oxygen-containing functional groups (such as carbonyl, hydroxyl, and quinone groups) of the biochar powder promote the extracellular electron transfer in the Feammox and NDFO processes, improving the Fe(III) reduction rate and the NO3 - reduction efficiency, thereby improving the denitrification performance. Description of the drawings

[0037] The drawings are used to provide a further understanding of the technical solutions of the present invention, and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solutions of the present invention, and do not constitute a limitation to the technical solutions of the present invention.

[0038] Figure 1 It is a schematic diagram of the mechanism of the dual-porous iron-carbon composite filler of the present invention in the Feammox-NDFO coupled autotrophic denitrification process;

[0039] Figure 2 This is the scanning electron microscope (SEM) image of the dual-porous iron-carbon composite filler of the present invention. When Mag = 200X, it shows the surface microtopography and pore structure of the filler.

[0040] Figure 3 This is the scanning electron microscope (SEM) image of the dual-porous iron-carbon composite filler of the present invention. When Mag = 1.00KX, it shows the surface microtopography and pore structure of the filler.

[0041] Figure 4 This shows the denitrification effect of the examples and comparative examples of the present invention on wastewater with a low carbon-nitrogen ratio (artificially prepared water, without added organic carbon source, C / N ≈ 0). Detailed implementation manners

[0042] The present invention innovatively combines the Feammox and NDFO processes, optimizes the filler structure, and enhances the microbial activity and electron transfer ability. Compared with traditional iron-carbon fillers and sulfur autotrophic fillers, it has significant advantages in terms of denitrification efficiency, long-term stability, adaptability, and economy. The filler of the present invention is mainly applied under the condition of low-carbon sewage with C / N ≤ 0.5. In order to better illustrate the purpose, technical solution, and its advantages of the present invention, the following will describe the examples in detail with reference to the accompanying drawings. It should be noted that, without conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The embodiments of the present invention are only used to illustrate the present invention, rather than limiting its scope.

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

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

[0045] In a preferred embodiment, the particle size of the iron-containing powder is 1 - 10 μm.

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

[0047] In a preferred embodiment, the binder is portland cement.

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

[0049] The double-porous iron-carbon composite filler is controlled within the range of 5-8 mm to ensure the best mass transfer performance and microbial attachment ability.

[0050] Example 1

[0051] In this example, the preparation steps of the double-porous iron-carbon composite filler for strengthening Feammox-NDFO autotrophic denitrification are as follows:

[0052] 1) Raw material selection and pretreatment:

[0053] The iron-containing powder selected is ferric oxide (Fe2O3) with a particle size of 1-10 μm; the biochar powder is derived from the carbonization of corn straw with a particle size of 100 μm; the binder is Portland cement; the pore-forming agent is sodium bicarbonate with a particle size of 50-100 μm. The ferric oxide (Fe2O3), biochar powder, Portland cement, and sodium bicarbonate are dried to a constant weight in an electrothermal blast drying oven at 40°C, and the moisture content is controlled to be ≤1%.

[0054] 2) Filler preparation, forming, and curing:

[0055] By weight, 45 parts of ferric oxide (Fe2O3), 15 parts of biochar powder, 25 parts of Portland cement, and 15 parts of sodium bicarbonate are weighed and placed in a mixer and mixed for 10 min to ensure uniformity. The mixing process is as follows: the above-mentioned powders are put into a pan granulator, the rotation speed is adjusted to 35 rpm, the inclination angle is 30°, and water is sprayed (10-15% by mass) to granulate to obtain spherical particles. The iron-carbon composite particles after granulation are placed in a constant temperature and humidity box at 70°C and a humidity of 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 50-100 μm. The above process is the first-stage pore formation.

[0056] The iron-carbon composite particles after the first-stage pore formation are put into deionized water at a temperature of 40°C and treated with ultrasonic waves at 30 kHz for 12 h to dissolve the residual Na2CO3 and further form micropores of 1-10 μm. The above process is the second-stage pore formation.

[0057] Finally, it is left to air dry naturally at room temperature of 25°C for 36 h, and screened with standard sieves of 5 mm and 8 mm to remove oversized particles, and a double-porous iron-carbon composite filler with a particle size of 5-8 mm is obtained. Its porosity, specific surface area, pore size range, and ammonia nitrogen adsorption capacity are shown in Table 1.

[0058] 3) The strengthening effect of the double-porous iron-carbon composite filler on the Feammox-NDFO autotrophic denitrification system

[0059] Construct a Feammox-NDFO autotrophic denitrification system in a 2L UASB reactor to investigate the strengthening effect of the prepared packing in the autotrophic denitrification system. Select the activated sludge from the anoxic section of the A 2 O process as the inoculated sludge with an inoculation concentration of 5000 mg / L, and fill the dual-porous iron-carbon composite packing prepared in the above steps, accounting for 30% of the reactor volume. The influent uses synthetic simulated wastewater, and the composition is shown in Table 2. Among them, the concentration of NH4 + -N is 75.2 ± 2.3 mg / L, the COD concentration is 23 ± 1.4 mg / L, pH = 7.0, C / N = 0.32. Construct a Feammox-NDFO autotrophic denitrification system under the conditions of hydraulic retention time HRT = 8 h and reflux ratio = 10:1. After 10 d, the system reaches a stable state, and the concentration of NH4 + -N in the effluent is 2.7 - 4.1 mg / L, and the concentration of NO3 - -N in the effluent is 3.9 - 6.6 mg / L. Continuously operate for 60 d, and the total nitrogen removal rate is 85.7 - 91.2%.

[0060] Example 2

[0061] In this example, the preparation steps of the dual-porous iron-carbon composite packing for strengthening Feammox-NDFO autotrophic denitrification are as follows:

[0062] 1) Raw material selection and pretreatment:

[0063] Select iron-containing powder as goethite FeO(OH) with a particle size of 1 - 10 μm; biochar powder, derived from the carbonization of wheat straw, with a particle size of 80 μm; the binder is Portland cement; the pore-forming agent is sodium bicarbonate with a particle size of 50 - 100 μm. Use an electrothermal blast drying oven to dry goethite FeO(OH), biochar powder, Portland cement, and sodium bicarbonate to a constant weight at 40 °C, and control the moisture content ≤ 1%.

[0064] 2) Packing preparation, forming and curing:

[0065] Weigh each component according to the weight ratio of 40 parts of goethite FeO(OH), 20 parts of biochar, 30 parts of Portland cement, and 10 parts of sodium bicarbonate, and place them in a mixer and mix for 10 min to ensure uniformity. Put the mixed powder into a disk granulator, adjust the rotation speed to 35 rpm and the inclination angle to 30°, and spray water (10 - 15% by mass) for granulation to obtain spherical particles.

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

[0067] The cured filler was placed in deionized water at 40°C and treated with ultrasound at 30kHz for 12h to dissolve the residual Na2CO3 and further form micropores of 1-10μm.

[0068] The mixture was ventilated and allowed to stand for 36 hours at room temperature of 25°C to dry naturally, and then sieved with standard sieves of 5 mm and 8 mm to remove particles exceeding the standard, thereby obtaining a double-pored iron-carbon composite filler with a particle size of 5-8 mm. The porosity, specific surface area, pore size range, and ammonia nitrogen adsorption capacity are shown in Table 1.

[0069] 3) Enhancement effect of double-pored iron-carbon composite filler on Feammox-NDFO autotrophic denitrification system

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

[0071] Example 3

[0072] In this embodiment, the double-pored iron-carbon composite filler used to strengthen Feammox-NDFO autotrophic denitrification is prepared in the following steps:

[0073] 1) Raw material selection and pretreatment:

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

[0075] 2) Filler preparation, molding and curing:

[0076] Weigh each component according to the proportion of 38 parts of iron oxide (Fe2O3), 22 parts of biochar powder, 30 parts of portland cement, and 10 parts of sodium bicarbonate by weight, and place them in a mixer to mix for 10 minutes to ensure uniformity. Put the mixed powder into a disk granulator, adjust the rotation speed to 40 rpm and the inclination angle to 30°, and spray water (10 - 15% by mass) to granulate to obtain spherical particles.

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

[0078] The cured filler is put into deionized water at 50 °C and treated with ultrasonic waves at 30 kHz for 12 h to dissolve the residual Na2CO3 and further form micropores with a size of 1 - 10 μm.

[0079] It is left to air dry naturally at room temperature of 25 °C for 36 h, screened with standard sieves of 5 mm and 8 mm, and the oversized particles are removed to obtain a dual-porous iron-carbon composite filler with a particle size of 5 - 8 mm. Its porosity, specific surface area, pore size range, and ammonia nitrogen adsorption capacity are shown in Table 1.

[0080] 3) Enhancement effect of the dual-porous iron-carbon composite filler on the Feammox-NDFO autotrophic denitrification system

[0081] Construct a Feammox-NDFO autotrophic denitrification system in a 2 L UASB reactor to investigate the enhancement effect of the prepared filler in the autotrophic denitrification system. Select the activated sludge in the anoxic section of the AO process as the inoculated sludge, with an inoculation concentration of 5000 mg / L, and fill the dual-porous iron-carbon composite filler prepared in the above steps, accounting for 30% of the reactor volume. The influent uses synthetic simulated wastewater, and the composition is shown in Table 2, where the NH4 2 -N concentration is 75.2 ± 2.3 mg / L, the COD concentration is 23 ± 1.4 mg / L, pH = 7.0, C / N = 0.32. Construct a Feammox-NDFO autotrophic denitrification system under the conditions of a hydraulic retention time HRT = 8 h and a reflux ratio = 10:1. After 10 days, the system reaches a stable state, and the effluent NH4 + -N concentration is 3.5 - 5.8 mg / L, the effluent NO3 + -N concentration is 5.8 - 8.2 mg / L. Continuously operate for 60 days, and the total nitrogen removal rate is 81.4 - 87.6%. - -N concentration is 5.8 - 8.2 mg / L. Continuously operate for 60 days, and the total nitrogen removal rate is 81.4 - 87.6%.

[0082] Comparative Example 1

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

[0084] 1) Raw material selection and pretreatment:

[0085] Select iron powder as iron oxide (Fe2O3) with a particle size of 1 - 10 μm; biochar, derived from the carbonization of corn straw, with a particle size of 100 μm; the binder is Portland cement; the pore-forming agent is sodium chloride with a particle size of 50 - 100 μm. Use an electrothermal blast drying oven to dry iron oxide (Fe2O3), biochar powder, Portland cement, and sodium chloride to constant weight at 40 °C, and control the moisture content ≤ 1%.

[0086] 2) Filler preparation, forming and curing:

[0087] Weigh each component according to the proportion of 45 parts of iron oxide (Fe2O3), 15 parts of biochar powder, 25 parts of Portland cement, and 15 parts of sodium chloride by weight, and place them in a mixer to mix for 10 min to ensure uniformity. The mixing process is as follows: put the above-mentioned mixed powder into a pan granulator, adjust the rotation speed to 35 rpm, the inclination angle to 30°, and 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 are placed in a constant temperature and humidity box at 70 °C and a humidity of 85% RH, and cured with deionized water vapor for 3 days. The cured filler is put into deionized water at 40 °C and treated with ultrasonic waves at 30 kHz for 12 h.

[0089] Ventilate and let it stand at room temperature of 25 °C for 36 h to air-dry naturally, and screen with standard sieves of 5 mm and 8 mm to remove oversized particles, and obtain sodium chloride pore-forming iron-carbon composite filler with a particle size of 5 - 8 mm. Its porosity, specific surface area, pore size range, and ammonia nitrogen adsorption capacity are shown in Table 1.

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

[0091] Construct a Feammox-NDFO autotrophic denitrification system in a 2L UASB reactor to investigate the strengthening effect of the prepared filler in the autotrophic denitrification system. Select the activated sludge in the anoxic section of the A 2 O process as the inoculated sludge with an inoculation concentration of 5000 mg / L, and the sodium chloride pore-forming iron-carbon composite filler prepared in the above steps is filled accounting for 30% of the reactor volume. The influent uses synthetic simulated wastewater, and the composition is shown in Table 2, where NH4 +The concentration of -N is 75.2 ± 2.3 mg / L, the concentration of COD is 23 ± 1.4 mg / L, pH = 7.0, C / N = 0.32. Under the conditions of hydraulic retention time HRT = 8 h and reflux ratio = 10:1, a Feammox-NDFO autotrophic denitrification system was constructed. After 10 days, the system reached a stable state, and the effluent NH4 + -N concentration is 6.6 - 9.8 mg / L, and the effluent NO3 - -N concentration is 10.9 - 14.1 mg / L. After continuous operation for 60 days, the total nitrogen removal rate is 68.2 - 76.7%.

[0092] Comparative Example 2

[0093] On the basis of Example 1, steam curing for pore formation was cancelled, and other parameters remained unchanged. Its 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 selected iron-containing powder is iron oxide (Fe2O3) with a particle size of 1 - 10 μm; the biochar powder is derived from the carbonization of corn straw with a particle size of 100 μm; the binder is Portland cement; the pore-forming agent is sodium bicarbonate with a particle size of 50 - 100 μm. The iron oxide Fe2O3, biochar powder, Portland cement, and sodium bicarbonate were dried to constant weight in an electrothermal blast drying oven at 40°C, and the moisture content was controlled to be ≤ 1%.

[0096] 2) Packing preparation, forming and curing:

[0097] Weigh each component according to the proportion of 45 parts of iron oxide (Fe2O3), 15 parts of biochar powder, 25 parts of Portland cement, and 15 parts of sodium bicarbonate by weight, and place them in a mixer and mix for 10 minutes to ensure uniformity. Put the mixed powder into a disk granulator, adjust the rotation speed to 35 rpm and the inclination angle to 30°, and spray water to granulate into iron-carbon composite particles. The added amount of water is 10 - 15% by mass to obtain spherical iron-carbon composite particles.

[0098] The spherical iron-carbon composite particles after granulation were placed in a constant temperature and humidity box at a temperature of 40°C and a humidity of 85% RH, and cured with deionized water for 3 days. The cured packing was put into deionized water at 40°C and treated with ultrasonic waves at 30 kHz for 12 h to form micropores.

[0099] At room temperature of 25°C, it was left to stand in ventilation for 36 h to air dry naturally, and screened with standard sieves of 5 mm and 8 mm to remove oversized particles, and a single immersion pore-forming iron-carbon composite packing with a particle size of 5 - 8 mm was obtained. Its porosity, specific surface area, pore size range, and ammonia nitrogen adsorption capacity are shown in Table 1.

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

[0101] A Feammox-NDFO autotrophic denitrification system was constructed in a 2L UASB reactor to investigate the strengthening effect of the prepared filler in the autotrophic denitrification system. 2 The activated sludge from the anoxic stage of the O process was used as the inoculated sludge, with an inoculation concentration of 5000 mg / L, and the single immersion pore-forming iron-carbon composite filler prepared in the above steps accounted for 30% of the reactor volume. The influent used artificially synthesized simulated wastewater, the composition of which is shown in Table 2, among which NH4 + -N concentration was 75.2±2.3mg / L, COD concentration was 23±1.4mg / L, pH=7.0, C / N=0.32, and the Feammox-NDFO autotrophic denitrification system was constructed under the conditions of hydraulic retention time HRT=8h and reflux ratio=10:1. After 10 days, the system reached a stable state and the effluent NH4 + -N concentration is 5.8-12mg / L, effluent NO3 - -N concentration was 9.7-17.2 mg / L, and the total nitrogen removal rate was 71.2-79.4% after 60 days of continuous operation.

[0102] Comparative Example 3

[0103] Without granulation or pore formation, ferric oxide (Fe2O3) and biochar powder were directly added into the system to investigate the beneficial effects of pore formation and granulation. 2 The activated sludge from the anoxic stage of the O process was used as the inoculated sludge with an inoculation concentration of 5000 mg / L. The mass of the added ferric oxide and biochar powder was calculated according to the volume of the filler filled in Example 1. The two were mixed and added to a 2L UASB reactor. The influent was artificially synthesized simulated wastewater with the composition shown in Table 2, where NH4 + -N concentration was 75.2±2.3mg / L, COD concentration was 23±1.4mg / L, pH=7.0, C / N=0.32, and the Feammox-NDFO autotrophic denitrification system was constructed under the conditions of hydraulic retention time HRT=8h and reflux ratio=10:1. With the continuous operation of the system, the effluent NH4 + -N concentration ranges from 5.3 to 19.9 mg / L, and the effluent NO3 - The concentration of -N varied between 8.9 and 28.4 mg / L, and the removal rate of total nitrogen ranged from 35.8 to 81.1%. As time went by, the removal effect of total nitrogen gradually deteriorated.

[0104] Comparative Example 4

[0105] On the basis of Example 1, ultrasonic-assisted deionized water immersion for pore formation was cancelled, and 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 selected iron powder is ferric oxide (Fe2O3) with a particle size of 1 - 10 μm; the biochar powder is derived from the carbonization of corn straw with a particle size of 100 μm; the binder is portland cement; the pore former is sodium bicarbonate with a particle size of 50 - 100 μm. Use an electrothermal blast drying oven to dry ferric oxide (Fe2O3), biochar powder, portland cement, and sodium bicarbonate to constant weight at 40 °C, and control the moisture content ≤ 1%.

[0108] 2) Filler preparation, forming, and curing:

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

[0110] The granulated iron-carbon composite particles are placed in a constant temperature and humidity box at 70 °C and a humidity of 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 with a size of 50 - 100 μm. The above process is the first-stage pore formation.

[0111] After the first-stage pore formation is completed, the iron-carbon composite particles are put into deionized water at a temperature of 40 °C and soaked for 12 h to dissolve the residual Na2CO3 and further form micropores. The above process is the second-stage pore formation. Finally, it is left to stand naturally in a ventilated place at room temperature of 25 °C for 36 h and air-dried, and screened with standard sieves of 5 mm and 8 mm to remove oversized particles, obtaining a double-pore-formed iron-carbon composite filler with a particle size of 5 - 8 mm. The porosity, specific surface area, pore size range, and ammonia nitrogen adsorption capacity are shown in Table 1.

[0112] 3) The strengthening effect of the double-pore-formed iron-carbon composite filler on the Feammox-NDFO autotrophic denitrification system

[0113] Construct a Feammox-NDFO autotrophic denitrification system in a 2L UASB reactor to investigate the strengthening effect of the prepared filler in the autotrophic denitrification system. Select A 2The activated sludge in the anoxic section of the O process was used as the inoculated sludge, and the inoculation concentration was 5000 mg / L. The dual-porous iron-carbon composite filler prepared in the above steps was filled, accounting for 30% of the reactor volume. The influent was artificial synthetic simulated wastewater, and the composition was shown in Table 2, in which the concentration of NH4 + -N was 75.2 ± 2.3 mg / L, the COD concentration was 23 ± 1.4 mg / L, pH = 7.0, C / N = 0.32. Under the conditions of hydraulic retention time HRT = 8 h and reflux ratio = 10:1, a Feammox-NDFO autotrophic denitrification system was constructed. After 10 d, the system reached a stable state, and the effluent NH4 + -N concentration was 5.6 - 8.5 mg / L, and the effluent NO3 - -N concentration was 9.4 - 12.2 mg / L. The system was continuously operated for 60 d, and the total nitrogen removal rate was 72.5 - 80.1%.

[0114] Comparative Example 5

[0115] On the basis of Example 1, the addition ratio was changed.

[0116] 1) Raw material selection and pretreatment:

[0117] The selected iron powder was ferric oxide (Fe2O3) with a particle size of 1 - 10 μm; the biochar was derived from the carbonization of corn straw with a particle size of 100 μm; the binder was Portland cement; the pore-forming agent was sodium bicarbonate with a particle size of 50 - 100 μm. The ferric oxide (Fe2O3), biochar powder, Portland cement, and sodium bicarbonate were dried to a constant weight in an electrothermal blast drying oven at 40 °C, and the moisture content was controlled ≤ 1%.

[0118] 2) Filler preparation, forming and curing:

[0119] By weight, 45 parts of iron oxide (Fe2O3), 30 parts of biochar powder, 20 parts of portland cement, and 5 parts of sodium bicarbonate are weighed and placed in a mixer and mixed for 10 min to ensure uniformity. The mixing process is as follows: the above-mentioned powders are put into a disk granulator, the rotation speed is adjusted to 35 rpm, the inclination angle is 30°, and water is sprayed and added (10 - 15% by mass) for granulation to obtain spherical particles. The iron-carbon composite particles after granulation are placed in a constant temperature and humidity chamber at 70 °C and a humidity of 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 - 100 μm. The above process is the first-stage pore formation. The iron-carbon composite particles after the first-stage pore formation are put into deionized water at a temperature of 40 °C and treated with ultrasonic waves at 30 kHz for 12 h to dissolve the residual Na2CO3 and further form micropores of 1 - 10 μm. The above process is the second-stage pore formation. Finally, it is left to stand naturally at room temperature of 25 °C for 36 h for natural air drying, and screened with standard sieves of 5 mm and 8 mm to remove oversized particles, and a double-pore-formed iron-carbon composite filler with a particle size of 5 - 8 mm is obtained. Its porosity, specific surface area, pore size range, and ammonia nitrogen adsorption capacity are shown in Table 1.

[0120] 3) The strengthening effect of the double-pore-formed iron-carbon composite filler on the Feammox-NDFO autotrophic denitrification system

[0121] An Feammox-NDFO autotrophic denitrification system is constructed in a 2 L UASB reactor to investigate the strengthening effect of the prepared filler in the autotrophic denitrification system. Anaerobic activated sludge from the anoxic section of the AO process is selected as the inoculated sludge, and the inoculation concentration is 5000 mg / L. The double-pore-formed iron-carbon composite filler prepared in the above steps is filled, accounting for 30% of the reactor volume. The influent uses synthetic simulated wastewater, and the composition is shown in Table 2, where the NH4 2 -N concentration is 75.2 ± 2.3 mg / L, the COD concentration is 23 ± 1.4 mg / L, pH = 7.0, C / N = 0.32. An Feammox-NDFO autotrophic denitrification system is constructed under the conditions of a hydraulic retention time HRT = 8 h and a reflux ratio = 10:1. After 10 d, the system reaches a stable state, and the effluent NH4 + -N concentration is 7.0 - 9.4 mg / L, the effluent NO3 + -N concentration is 11.6 - 13.5 mg / L, and it is continuously operated for 60 d, and the total nitrogen removal rate is 69.5 - 75.3%. - -N concentration is 11.6 - 13.5 mg / L, and it is continuously operated for 60 d, and the total nitrogen removal rate is 69.5 - 75.3%.

[0122] Comparative Example 6

[0123] On the basis of Example 1, the addition ratio is changed.

[0124] 1) Raw material selection and pretreatment:

[0125] The iron-containing powder selected is iron(III) oxide (Fe2O3) with a particle size of 1 - 10 μm; the biochar powder is derived from the carbonization of corn straw with a particle size of 100 μm; the binder is Portland cement; the pore former is sodium bicarbonate with a particle size of 50 - 100 μm. The iron(III) oxide (Fe2O3), biochar powder, Portland cement, and sodium bicarbonate are dried to a constant weight in an electrothermal blast drying oven at 40 °C, and the moisture content is controlled to be ≤1%.

[0126] 2) Preparation, molding and curing of the filler:

[0127] By weight, 40 parts of iron(III) oxide (Fe2O3), 25 parts of biochar powder, 15 parts of Portland cement, and 20 parts of sodium bicarbonate are weighed for each component, placed in a mixer and mixed for 10 min to ensure uniformity. The mixing process is as follows: the above-mentioned mixed powders are put into a disk granulator, the rotation speed is adjusted to 35 rpm, the inclination angle is 30°, and granulation is carried out by spraying water (10 - 15% by mass) to obtain spherical particles. The iron-carbon composite particles after granulation are placed in a constant temperature and humidity box at 70 °C and a humidity of 85% RH, and cured with deionized water vapor for 3 days, so that NaHCO3 in the filler decomposes to form Na2CO3 and releases CO2 to form macropores with a size of 50 - 100 μm. The above process is the first-stage pore formation. The iron-carbon composite particles after the first-stage pore formation are put into deionized water at a temperature of 40 °C and treated with ultrasonic waves at 30 kHz for 12 h to dissolve the residual Na2CO3 and further form micropores with a size of 1 - 10 μm. The above process is the second-stage pore formation. Finally, it is naturally air-dried by ventilation and static placement at room temperature of 25 °C for 36 h, and screened with standard sieves of 5 mm and 8 mm to remove oversized particles, and a double-pore-formed iron-carbon composite filler with a particle size of 5 - 8 mm is obtained. Its porosity, specific surface area, pore size range, and ammonia nitrogen adsorption capacity are shown in Table 1.

[0128] 3) The strengthening effect of the double-pore-formed iron-carbon composite filler on the Feammox-NDFO autotrophic denitrification system

[0129] An Feammox-NDFO autotrophic denitrification system is constructed in a 2-L UASB reactor to investigate the strengthening effect of the prepared filler in the autotrophic denitrification system. The activated sludge in the anoxic section of the AO process is selected as the inoculated sludge, with an inoculation concentration of 5000 mg / L, and the double-pore-formed iron-carbon composite filler prepared in the above steps is filled, accounting for 30% of the reactor volume. The influent uses synthetic simulated wastewater, and the composition is shown in Table 2, where NH4 2 O process anoxic section activated sludge as the inoculated sludge, inoculation concentration 5000mg / L, filling the double-pore-formed iron-carbon composite filler prepared in the above steps accounting for 30% of the reactor volume. The influent uses synthetic simulated wastewater, the composition of which is shown in Table 2, where NH4 +The concentration of -N is 75.2 ± 2.3 mg / L, the concentration of COD is 23 ± 1.4 mg / L, pH = 7.0, C / N = 0.32. Under the conditions of hydraulic retention time HRT = 8 h and reflux ratio = 10:1, a Feammox-NDFO autotrophic denitrification system was constructed. After 10 days, the system reached a stable state, and the effluent NH4 + -N concentration was 4.3 - 7.2 mg / L, and the effluent NO3 - -N concentration was 6.3 - 9.0 mg / L. It was continuously operated for 60 days, and 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 selected iron-containing powder was goethite FeO(OH) with a particle size of 1 - 10 μm; the biochar powder was derived from the carbonization of wheat straw with a particle size of 100 μm; the binder was Portland cement; the pore-forming agent was sodium bicarbonate with a particle size of 50 - 100 μm. The goethite FeO(OH), biochar powder, Portland cement, and sodium bicarbonate were dried to a constant weight in an electrothermal blast drying oven at 40°C, and the moisture content was controlled to be ≤ 1%.

[0134] 2) Filler preparation, forming and curing:

[0135] By weight, 35 parts of goethite FeO(OH), 35 parts of biochar powder, 15 parts of Portland cement, and 15 parts of sodium bicarbonate were weighed and placed in a mixer and mixed for 10 min to ensure uniformity. The mixing process was as follows: the above-mentioned powders were put into a pan granulator, the rotation speed was adjusted to 35 rpm, the inclination angle was 30°, and water was sprayed (10 - 15% by mass) for granulation to obtain spherical particles. The granulated iron-carbon composite particles were placed in a constant temperature and humidity box at 70°C and a humidity of 85% RH, and cured with deionized water vapor for 3 days to decompose NaHCO3 in the filler to form Na2CO3 and release CO2 to form macropores of 50 - 100 μm. The above process was the first-stage pore formation. The iron-carbon composite particles after the first-stage pore formation were put into deionized water at a temperature of 40°C and treated with ultrasonic waves at 30 kHz for 12 h to dissolve the residual Na2CO3 and further form micropores of 1 - 10 μm. The above process was the second-stage pore formation. Finally, it was left to stand naturally at room temperature of 25°C for 36 h and air-dried, and screened with standard sieves of 5 mm and 8 mm to remove oversized particles, and a double-pore-formed iron-carbon composite filler with a particle size of 5 - 8 mm was obtained. Its porosity, specific surface area, pore size range, and ammonia nitrogen adsorption capacity are shown in Table 1.

[0136] 3) Enhancement effect of the dual-porous iron-carbon composite filler on the Feammox-NDFO autotrophic denitrification system

[0137] An Feammox-NDFO autotrophic denitrification system was constructed in a 2L UASB reactor to investigate the enhancement effect of the prepared filler in the autotrophic denitrification system. Anaerobic activated sludge from the anoxic section of the A 2 / O process was selected as the inoculated sludge with an inoculation concentration of 5000 mg / L. The dual-porous iron-carbon composite filler prepared in the above steps was filled, accounting for 30% of the reactor volume. The influent used synthetic simulated wastewater, and the composition is shown in Table 2. Among them, the concentration of NH4 + -N was 75.2 ± 2.3 mg / L, the COD concentration was 23 ± 1.4 mg / L, pH = 7.0, C / N = 0.32. An Feammox-NDFO autotrophic denitrification system was constructed under the conditions of hydraulic retention time HRT = 8 h and reflux ratio = 10:1. After 10 days, the system reached a stable state. The concentration of NH4 + -N in the effluent was 3.8 - 6.6 mg / L, and the concentration of NO3 - -N in the effluent was 6.2 - 9.5 mg / L. After continuous operation for 60 days, the total nitrogen removal rate was 78.6 - 86.7%.

[0138] Table 1 Physicochemical properties of the fillers in the examples and comparative examples

[0139]

[0140] Table 2 Composition table of artificial simulated wastewater

[0141] Component <![CDATA[NH4Cl]]> <![CDATA[Calcium chloride]]> <![CDATA[MgCl2]]> <![CDATA[KHCO3]]> <![CDATA[KH2PO4]]> Trace element Concentration (mg / L) 287 10 100 600 600 1 ml / L

[0142] Table 1 shows that the porosity of the fillers in Examples 1 and 2 was 56.5% and 53.9% respectively, and the specific surface areas were 25.74 m 2 / g and 27.43 m 2 / g respectively, which were significantly higher than those of Comparative Examples 2 and 4. This indicates that the dual-porous process improved the pore structure of the filler, enhanced the adsorption performance, and was beneficial to the construction of the Feammox-NDFO system. In contrast, the porosity of Comparative Examples 2 and 4 was low, the specific surface area was small, and the adsorption capacity was limited, which was not conducive to the efficient denitrification of the system. In Comparative Example 3, granulation was not carried out, and the filler was prone to agglomeration or loss, resulting in difficulty in measuring the specific surface area and porosity, which affected 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%, indicating excellent denitrification performance. The removal rates of Comparative Examples 1 and 2 were relatively low, and showed an obvious downward trend after long-term operation, indicating that their strengthening effects on the Feammox-NDFO system were limited. The total nitrogen removal rate of Comparative Example 3 increased initially, but decreased significantly after 30 days and was lower than 40% after 50 days, indicating that the ungranulated packing was not conducive to the long-term stable operation of the system.

[0144] The present invention develops a dual-porous iron-carbon composite packing to construct a Feammox-NDFO coupling system and enhance its denitrification efficiency. First, the immobilized Fe(III) in the packing serves as the electron acceptor for the Feammox process and is gradually reduced to Fe(II) during the reaction. Subsequently, Fe(II) serves as the electron donor for the NDFO process, driving the nitrate-dependent ferrous oxidation reaction to remove nitrogen in the water body. At the same time, Fe(II) is oxidized back to Fe(III) to ensure the sustainable operation of the Feammox-NDFO system. Second, the doped biochar powder in the packing can participate in the redox reaction through the oxygen-containing functional groups on its surface, promoting electron transfer in the Feammox and NDFO processes, thereby increasing the ammonia oxidation rate of the Feammox process and the nitrate reduction efficiency of the NDFO process. Finally, the packing adopts a dual-porous mechanism. During the forming and curing stage, steam is formed by heating deionized water, causing the packing to gradually release CO2 in a humid and hot environment to form a macroporous structure. Subsequently, during the deionized water soaking stage, the residual Na2CO3 inside the packing is gradually dissolved to further form micropores, thereby constructing a packing with a multi-level pore structure and a high specific surface area, improving the attachment ability of microorganisms and the mass transfer efficiency, and further enhancing the stability and denitrification efficiency of the Feammox-NDFO system.

[0145] The present invention provides a dual-porous iron-carbon composite packing and its preparation method. The packing can be used to construct a Feammox-NDFO coupling system based on the iron cycle and enhance its autotrophic denitrification efficiency. The immobilized Fe(III) in the packing serves as the electron acceptor for the Feammox process and is gradually reduced to Fe(II) during the reaction. Fe(II) serves as the electron donor for the NDFO process and is oxidized back to Fe(III), forming a cyclic supply of Fe(III) / Fe(II) to maintain the continuous operation of the Feammox-NDFO system. The doped biochar powder in the packing can improve the extracellular electron transfer efficiency of nitrogen-converting functional microorganisms. At the same time, its large specific surface area and rich functional groups have a certain adsorption effect on ammonia nitrogen, making NH4 +Enriched on the surface of the packing, enhancing the mass transfer efficiency of the Feammox-NDFO system. The packing adopts a dual pore-forming mechanism to form a multi-level pore structure and provides a large specific surface area, providing a stable carrier for the attachment and growth of microorganisms, and improving the denitrification efficiency and long-term stability of the system.

[0146] The packing of the present invention is mainly applied under the condition of low-carbon sewage with C / N ≤ 0.5, and still can maintain high-efficiency denitrification under such low-carbon conditions without the need for additional organic carbon source addition. After 60 days of long-term operation, the TN removal rate can reach 91.2 - 97.8%, which is suitable for the treatment of low-carbon source and high-ammonia-nitrogen wastewater, expanding the application range of autotrophic denitrification technology.

[0147] It should be noted that the above embodiments are only the preferred implementation schemes of the present invention. Those skilled in the art can understand that the present invention is not limited to the above specific embodiments. Without departing from the basic concept of the present invention, various improvements, adjustments or combinations can be made, and these deformations and improvements are also within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.

Claims

1. A preparation method of a dual-porous iron-carbon composite filler for enhancing Feammox-NDFO autotrophic denitrification, characterized in that: Specifically, it includes the following steps: Step 1: Raw material pretreatment After drying the double-porous iron-carbon composite filler, weigh each component according to the weight parts for standby; The double-porous iron-carbon composite filler includes iron powder, biochar powder, binder, and pore-forming agent; Step 2: Mixing and granulation Mix the double-porous iron-carbon composite filler in Step 1 in proportion to form a mixed powder, and put it into a granulator to spray water for granulation; The rotation speed of the granulator is 30 - 40 r / min, the inclination angle is controlled at 25 - 35°, and the granulation time is 40 - 60 min; Step 3: Steam curing for pore formation Put the iron-carbon composite particles granulated in Step 2 into a constant temperature and humidity box for hydrothermal curing to form macropores of 50 - 500 μm; The conditions for curing and pore formation are temperature 60 - 80°C; humidity 80 - 90%RH, and the curing time is 2 - 4 days; Steam source: deionized water; Step 4: Ultrasonic-assisted deionized water soaking for pore formation Soak the iron-carbon composite particles with ultrasonic-assisted deionized water. The conditions for soaking and pore formation are temperature 30 - 50°C; time 6 - 12 h; ultrasonic frequency 20 - 40 kHz, to form micropores of 1 - 10 μm; Step 5: Finished product screening After drying it by ventilation at room temperature, screen the iron-carbon composite particles with a particle size between 5 - 8 mm as the finished product of the double-porous iron-carbon composite filler.

2. The preparation method of a double-porous iron-carbon composite filler for enhancing Feammox-NDFO autotrophic denitrification according to claim 1, characterized in that: In Step 1, during the raw material pretreatment process, the water content of the raw materials is controlled ≤1%. Specifically, use an electric heating blast drying oven to dry the iron powder, biochar powder, binder, and pore-forming agent; In Step 2, during the mixing and granulation process, add water to the raw materials in Step 1 for granulation, where the addition amount of water is 10 - 15% by weight parts, and make iron-carbon composite particles with a diameter of 6 - 8 mm; In Step 3, during the steam curing for pore formation process, the steam source is formed by heating deionized water; In Step 4, during the ultrasonic-assisted deionized water soaking for pore formation process, dissolve Na2CO3 by stirring; In Step 5, during the finished product screening process, control the ventilation and static placement at room temperature of 20 - 25°C for 24 - 48 h.

3. The preparation method of a double-porous iron-carbon composite filler for enhancing Feammox-NDFO autotrophic denitrification according to claim 1 or 2, characterized in that: In Step 1, the double-porous iron-carbon composite filler includes the following components according to the weight parts: 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; The iron powder is one or a combination of iron oxide (Fe2O3), iron phosphate (FePO4), goethite (FeO(OH)), and iron citrate; The biochar powder is selected from one or a combination of corn straw, wheat straw, and rice straw; The binder is Portland cement; The pore-forming agent is sodium bicarbonate.

4. The preparation method of a dual-porous iron-carbon composite filler for enhancing Feammox-NDFO autotrophic denitrification according to claim 3, characterized in that: The particle size of the iron powder is 1 - 10 μm; The particle size of the biochar powder is between 75 - 150 μm; The particle size of the pore former is 50 - 100 μm.

5. The preparation method of a dual-porous iron-carbon composite filler for enhancing Feammox-NDFO autotrophic denitrification according to claim 4, characterized in that: 40 parts of iron-containing powder, 20 parts of biochar powder, 30 parts of binder, and 10 parts of pore former; 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 portland cement; the pore former is sodium bicarbonate with a particle size of 50 - 100 μm.

6. A preparation method of a dual-porous iron-carbon composite filler for enhancing Feammox-NDFO autotrophic denitrification according to any one of claim 5, characterized in that: Step 1, Raw material pretreatment Select goethite FeO(OH) as the iron-containing powder 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 portland cement; the pore former is sodium bicarbonate with a particle size of 50 - 100 μm; use an electric heating blast drying oven to dry goethite FeO(OH), biochar powder, portland cement, and sodium bicarbonate to constant weight at 40 °C, and control the moisture content ≤ 1%; Step 2, Mixing and granulation Weigh each component according to the weight ratio of 40 parts of goethite FeO(OH), 20 parts of biochar powder, 30 parts of portland cement, and 10 parts of sodium bicarbonate, place them in a mixer and mix for 10 min to ensure uniformity; put the mixed powder into a disk granulator, adjust the rotation speed to 35 rpm, the inclination angle to 30°, and spray 10 - 15% by mass of water for granulation to obtain spherical particles; Step 3, Steam curing for pore formation The granulated filler is placed in a constant temperature and humidity box at 70 °C and a humidity of 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 with a size of 50 - 100 μm; Step 4, Ultrasonic-assisted deionized water immersion for pore formation The cured filler is put into deionized water at 40 °C and treated with ultrasonic waves at 30 kHz for 12 h to form micropores with a size of 1 - 10 μm; Step 5, Finished product screening Air-dry naturally at room temperature of 25 °C for 36 h, and screen with standard sieves of 5 mm and 8 mm to remove oversized particles to obtain a dual-porous iron-carbon composite filler with a particle size of 5 - 8 mm.

7. Application of the dual-porous iron-carbon composite filler prepared by the preparation method of the dual-porous iron-carbon composite filler for enhancing Feammox-NDFO autotrophic denitrification according to any one of 1 - 6 in the sewage treatment process.

8. The application of a dual-porosity iron-carbon composite filler according to claim 7 in a sewage treatment process, characterized in that: The dual-porous iron-carbon composite filler is put into the sewage treatment device, and the dual-porous iron-carbon composite filler accounts for 28 - 45% of the internal volume of the sewage treatment device.

9. The application of a double-pore-forming iron-carbon composite filler in a sewage treatment process according to claim 8, wherein: The dual-porosity iron-carbon composite filler is applied under the condition of low-carbon sewage with C / N ≤ 0.

5. Specifically, a Feammox-NDFO autotrophic denitrification system is constructed in the UASB reactor: Select the activated sludge in the anoxic section of the A 2 O process as the inoculated sludge, with an inoculation concentration of 5000 mg / L, and the dual-porosity iron-carbon composite filler prepared in the above steps is filled to account for 30% of the reactor volume; the influent NH4 + -N concentration is 75.2 ± 2.3 mg / L, the COD concentration is 23 ± 1.4 mg / L, pH = 7.0, C / N = 0.32, and it is constructed under the conditions of a hydraulic retention time HRT = 8 h and a reflux ratio = 10:

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

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