Pyrite-activated carbon composite constructed wetland filler based on agricultural waste, and preparation method and application thereof

Abstract

The application discloses a kind of pyrite-activated carbon composite artificial wetland fillings based on agricultural waste and its preparation method and application, belong to water treatment technical field.The filler is composed of three-layer composite structure: the bottom layer is nano pyrite loaded hydrothermal carbon skeleton, middle layer is Fe3O4 modified activated carbon-pyrite complex, surface layer is biochar regulation filter layer.The above composite layer structure is respectively by hydrothermal carbonization agricultural waste and form porous skeleton in situ load nano pyrite to obtain bottom layer;KOH activation preparation microporous activated carbon and load Fe3O4 to obtain middle layer;With agricultural waste pyrolysis steam as carbon source, by chemical vapor deposition to obtain surface layer.The filler is through the multi-component synergistic effect of three-layer structure, realizes denitrification and phosphorus removal, adsorbs heavy metal and inhibits malodor, porosity>60% effectively relieves the filling blockage, suitable for as artificial wetland filling to low carbon nitrogen ratio wastewater, heavy metal and nano plastic pollution wastewater treatment.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a pyrite-activated carbon composite artificial wetland filler based on agricultural waste, its preparation method, and its application. Background Technology

[0002] Constructed wetlands are a wastewater treatment and ecological restoration technology that simulates natural wetland ecosystems. They purify water through the synergistic effects of physical, chemical, and biological processes, while also providing ecosystem services. However, traditional constructed wetlands face numerous challenges in practical applications. For example, the filling and replacement of the packing material is difficult, easily leading to hydraulic short circuits due to blockage, resulting in high maintenance costs; the substrate has limited adsorption capacity, easily becoming saturated and ineffective, requiring frequent replacement or replenishment of the packing material; it has weak resistance to shock loads, is sensitive to fluctuations in water quality and quantity, and exhibits unstable treatment efficiency; it has poor adaptability to wastewater with low carbon-to-nitrogen ratios (C / N), and insufficient carbon sources lead to a sharp drop in denitrification efficiency; chemical precipitation is lacking, such as insufficient replenishment of iron and aluminum salts, resulting in phosphorus removal relying on physical adsorption, which is easily saturated and irreversible; and it easily generates malodorous gases such as H2S and CH4, impacting the surrounding environment. These problems limit the efficiency, stability, and large-scale promotion of constructed wetland treatment technology.

[0003] Pyrite is a sulfide mineral, mainly composed of FeS2, and possesses unique redox activity, conductivity, and microbial affinity. Currently, constructed wetlands using pyrite alone have achieved significant optimization compared to traditional constructed wetlands: they simultaneously drive autotrophic denitrification (adapting to low C / N ratio wastewater) and chemical phosphorus removal (generating stable iron phosphate precipitates) through synergistic iron-sulfur redox reactions, and accelerate microbial electron transfer using the conductivity of pyrite, significantly improving nitrogen and phosphorus removal efficiency. Simultaneously, the slow-release effect and anti-clogging properties of the mineral packing improve the long-term stability of the system, reduce carbon source dependence and odor emissions, making it particularly suitable for complex scenarios involving heavy metals, high salinity, or sulfate wastewater. However, it still has shortcomings such as limited adsorption capacity due to its small specific surface area, susceptibility to pH fluctuations in phosphorus removal, excessive reliance of the microbial community on sulfur / iron metabolic bacteria, and the potential for localized acidification and sulfate accumulation during long-term operation. Therefore, further optimization through material modification or composite system construction is needed.

[0004] In recent years, pyrite has significantly improved its efficiency and application potential in removing pollutants from water through multi-strategy optimization and modification. For example, mechanochemical modification (such as ball milling) introduces sulfur vacancies to narrow the band gap, accelerates electron transfer, and enhances stability; thermal modification (such as pyrolysis at 600℃) induces a phase transformation of pyrite into pyrrhotite through high-temperature calcination, increasing phosphorus adsorption capacity to 10 times that of natural minerals. Although modified pyrite exhibits excellent performance in heavy metal adsorption, antibiotic degradation, and nitrogen and phosphorus removal, it still faces challenges such as high economic costs, processes that do not conform to green chemistry principles, limited specific surface area, long-term passivation risks, and insufficient microbial community stability. Therefore, its large-scale application needs to be promoted through green modification processes and multi-material synergistic systems. Summary of the Invention

[0005] The purpose of this invention is to provide a pyrite-activated carbon composite constructed wetland filler based on agricultural waste, its preparation method, and its application. Utilizing the redox activity of pyrite, the adsorption capacity of activated carbon, and the carbon source function of agricultural waste, the constructed wetland is suitable for treating various types of wastewater, including rural sewage, industrial wastewater, heavy metal pollution, low carbon-to-nitrogen ratio wastewater, and nanoplastic pollution wastewater. This invention solves the problems of traditional fillers in the background art, such as single function, easy saturation and clogging, unstable operation, and acidification of the pyrite system, achieving low-carbon and efficient simultaneous removal of multiple pollutants.

[0006] To achieve the above objectives, the present invention provides a pyrite-activated carbon composite constructed wetland filler based on agricultural waste, comprising:

[0007] The slow-release driven bottom layer of pyrite-agricultural waste-based hydrothermal carbon consists of a porous hydrothermal carbon framework and a pyrite hydrothermal carbon composite formed by nano-pyrite particles loaded in its pores.

[0008] The middle layer of the pyrite-activated carbon adsorption catalysis is composed of Fe3O4 / activated carbon-pyrite complex, which is formed by physically intercalating microporous activated carbon and the bottom layer of pyrite hydrothermal carbon composite and then loading Fe3O4 nanocrystals.

[0009] The activated carbon-agricultural waste-based biochar regulates the filter surface. It is composed of a middle layer of Fe3O4 / activated carbon-pyrite complex and mesoporous activated carbon physically intercalated to form a mesoporous activated carbon-Fe3O4 / activated carbon-pyrite complex. Then, it is combined with a layer of pyrolysis biochar particles obtained by chemical vapor deposition (CVD) of agricultural waste pyrolysis steam.

[0010] This invention also provides a method for preparing the above-mentioned pyrite-activated carbon composite constructed wetland filler based on agricultural waste, comprising the following steps:

[0011] Preparation of S1, Pyrite-Agricultural Waste-Based Hydrothermal Carbon Slow-Release Driven Substrates

[0012] Agricultural waste powder was mixed with deionized water and placed in a high-pressure reactor for hydrothermal carbonization. After cooling and acid washing with hydrochloric acid solution to remove ash, the mixture was dried to obtain a porous hydrothermal carbon skeleton with a pore size of 10-50 μm.

[0013] Natural pyrite ore powder was mixed with NaBH4 solution and subjected to hydrothermal reduction reaction under nitrogen protection to generate nano-pyrite particles with a particle size of 50-100nm in situ. These nano-pyrite particles were then confined and loaded into the pores of a porous hydrothermal carbon framework and vacuum dried to obtain a pyrite hydrothermal carbon composite.

[0014] Preparation of S2, Pyrite-Activated Carbon Adsorption Catalytic Middle Layer

[0015] Agricultural waste is placed in a tubular furnace and pyrolyzed under the protection of inert gas to obtain biochar. After mixing with KOH solution, it is activated and washed with deionized water until the solution is neutral and then dried to obtain microporous activated carbon. It is then physically integrated with the pyrite-hydrothermal carbon composite obtained in step S1 to obtain a pyrite-hydrothermal carbon-activated carbon composite.

[0016] Natural pyrite ore powder was oxidized in an acidic solution to obtain pyrite oxidation solution. Then, NH4OH was added to adjust the pH to 8.0-9.0, and the reaction was stirred to generate a suspension containing Fe3O4 nanocrystal particles. The suspension was mixed with a pyrite-hydrothermal carbon-activated carbon composite and ultrasonically impregnated. After drying, Fe3O4 was uniformly attached to the surface of the pyrite-hydrothermal carbon-activated carbon composite to obtain the Fe3O4 / activated carbon-pyrite composite.

[0017] S3, Activated Carbon - Agricultural Waste-Based Biochar for Filter Surface Regulation

[0018] Agricultural waste is placed in a tubular furnace and pre-carbonized under the protection of inert gas to obtain biochar. The biochar is then activated by impregnation with H3PO4 solution to obtain mesoporous activated carbon. This activated carbon is then physically intercalated with the Fe3O4 / activated carbon-pyrite composite obtained in step S2 to obtain mesoporous activated carbon-Fe3O4 / activated carbon-pyrite composite.

[0019] Agricultural waste is converted into pure pyrolysis steam using a two-stage pyrolysis device. Then, a mesoporous activated carbon-Fe3O4 / activated carbon-pyrite composite is placed in a fluidized bed CVD reactor. Nitrogen and pyrolysis steam are introduced into the reactor in stages. In the first stage, nitrogen is introduced to remove air. In the second stage, a mixture of nitrogen and pyrolysis steam is introduced. Using the pyrolysis steam of agricultural waste as a carbon source, under the catalysis of Fe3O4 in the composite, the pyrolysis steam is deposited on the middle layer surface to form a biochar-regulated filtration layer.

[0020] S4, Composite filler inert treatment molding

[0021] The carbon source supply was stopped, and nitrogen gas was continuously purged to cool the mixture to room temperature, resulting in a composite artificial wetland filler with a three-layer coupled structure consisting of a "slow-release driven bottom layer, an adsorption-catalytic middle layer, and a regulated filtration surface layer".

[0022] Preferably, in step S1, the agricultural waste is corn cob or corn stalk, and the particle size of the agricultural waste powder is 2-5 mm; the solid-liquid mass ratio of the agricultural waste powder and deionized water is 1:(4-6); the pressure range of the reactor is 1.8-5.2 MPa; the temperature of hydrothermal carbonization is 150-180℃, and the time of hydrothermal carbonization is 5-6 h; the concentration of the hydrochloric acid solution is 1.0 mol / L; the drying temperature is 100-110℃, and the drying time is 12 h.

[0023] Preferably, in step S1, the particle size of the natural pyrite ore powder is 230-830 μm, the concentration of the NaBH4 solution is 0.5 mol / L, and the solid-liquid mass ratio of the pyrite ore powder to the NaBH4 solution is 1:(2.5-4); the temperature of the hydrothermal reduction reaction is 150-180℃, and the time of the hydrothermal reduction reaction is 4-6 h; the temperature of the vacuum drying is 60℃, and the time of the vacuum drying is 6 h.

[0024] Preferably, in step S2, the inert gas is nitrogen, the pyrolysis temperature is 700℃, and the pyrolysis time is 1.5-2.5h; the concentration of KOH solution is 1.0mol / L; the mass ratio of KOH solution to biochar is 1:5; the activation temperature is 800-900℃, and the activation time is 1-2h.

[0025] Preferably, in step S2, the acidic solution is an H2SO4 solution with a pH of 3.0, and the oxidation time is 18-30 h; the stirring rate is 300-400 r / min, the stirring time is 1.5-2.5 h, the reaction temperature is 80-90 ℃, and the Fe3O4 nanocrystalline particles have a particle size of 20-50 nm; the solid-liquid mass ratio of the pyrite-hydrothermal carbon-activated carbon composite and the suspension containing Fe3O4 nanocrystalline particles is 1:(9-11), the ultrasonic impregnation power is 200-300 W, the ultrasonic impregnation time is 1 h, the drying temperature is 70-80 ℃, and the drying time is 6-8 h.

[0026] Preferably, in step S3, the inert gas is nitrogen, the pre-carbonization temperature is 250-350℃, the pre-carbonization time is 1h-2h, the mass fraction of H3PO4 solution is 78%, the solid-liquid mass ratio of biochar to H3PO4 solution is 3:1, the impregnation activation temperature is 650-750℃, and the impregnation activation time is 2-3h.

[0027] Preferably, in step S3, the pyrolysis temperature of the pyrolysis device is 200-300℃, the pyrolysis time is 30-60min, and the temperature of the insulated pipe for conveying pyrolysis steam and nitrogen is 100-200℃.

[0028] Preferably, in step S3, the temperature of the fluidized bed CVD reactor is 380℃ and the pressure is 0.1-0.2MPa; the nitrogen gas introduction time in the first stage is 2-3h and the flow rate is 400-700mL / min; the mixed gas introduction time in the second stage is 4-5h and the flow rate is 200-300mL / min; wherein, the volume flow ratio of pyrolysis steam and nitrogen gas is 1:(4-6); the deposition time is 1.5-2h; and the thickness of the biochar-controlled filter layer is 50-100nm.

[0029] The present invention also provides the application of the above-mentioned pyrite-activated carbon composite constructed wetland filler based on agricultural waste in wastewater treatment.

[0030] The principle behind the holistic construction and functional integration of the multi-component synergistic system of the pyrite-activated carbon composite constructed wetland filler based on agricultural waste, which possesses a three-layer structure of "slow-release driven bottom layer - adsorption-catalytic middle layer - regulation-filtering surface layer", is as follows:

[0031] 1. Design of a three-layer multi-component synergistic system

[0032] The packing material used in constructing a novel multi-interface coupled artificial wetland treatment system, which uses pyrite as the reaction-driven core, agricultural waste-based biochar as the carbon source framework, and activated carbon as the adsorption and catalysis platform, is as follows:

[0033] (1) Functional Collaboration Chain

[0034] Using pyrite (FeS2) as the core driving material, Fe is released under specific conditions. 2+ and S 2- These reducing substances act as effective electron donors, driving the denitrification removal of nitrate nitrogen from wastewater. Combined with biochar prepared from agricultural waste, which continuously releases usable organic carbon, the carbon-to-nitrogen ratio (C / N) of the wastewater can be precisely adjusted, providing crucial metabolic support for the microbial community, stimulating its metabolic activity, and enhancing the system's ability to remove nitrate nitrogen (NO3). - -N) and ammonia nitrogen (NH4) + The biochar exhibits high biological removal capacity and overall efficiency. Further activation of the biochar to form activated carbon allows for the efficient adsorption and removal of volatile organic compounds (VOCs) generated during wastewater treatment, while simultaneously achieving deep oxidation, decomposition, and control of residual odorous substances.

[0035] (2) Cyclical efficiency enhancement mechanism

[0036] Fe released by the oxidation of pyrite (FeS2) 3+ With phosphate (PO4) 3- The combination of these molecules forms an iron phosphate precipitate (FePO4), achieving primary fixation of inorganic phosphorus; humic acid (HA) produced from the degradation of agricultural waste further combines with Fe... 3+ A colloidal complex (Fe-HA) is formed, which, through surface complexation and co-precipitation, deeply captures residual inorganic phosphorus, forming a stable ternary colloidal precipitate (Fe-HA-PO4). Simultaneously, the organic phosphorus portion in the system can be degraded and mineralized by microorganisms to form inorganic phosphorus, which is then fixed via the aforementioned pathway. Another portion can be directly adsorbed and co-precipitated by the Fe-HA colloid. Together, these factors ensure the system's significant removal efficiency of total phosphorus (TP).

[0037] 2. A "regenerative sustained-release stabilization" cycle mechanism based on the synergistic effect of three components.

[0038] (1) Activated carbon regeneration: Utilizing Fe generated from the oxidation of pyrite 3+ The catalytic thermal regeneration process of activated carbon efficiently decomposes organic matter that clogs pores, and simultaneously generates magnetic Fe3O4 loaded on the surface of activated carbon, significantly enhancing its porosity and adsorption capacity.

[0039] (2) Long-term carbon source: Fully utilize SiO2 in the pyrolysis ash of agricultural waste, and construct a silica nano-coating layer on the surface of biochar in situ through the sol-gel method to precisely control the carbon source release rate, avoid the explosive release of microbial available carbon, and maintain the stability of community structure.

[0040] (3) Pyrite stability: During the processing, a carbonate buffer (such as CaCO3 or Na2CO3) is added to utilize the slightly soluble properties of carbonates to establish a CO2-HCO3 buffer. - -CO3 2- The buffer system maintains a neutral pH range of 6.5–7.5, inhibiting excessive oxidation of pyrite and effectively controlling SO42-. 2- Accumulation and system acidification.

[0041] Through the above design, the three-component synergistic system not only achieves the superposition of technical indicators, but also forms a novel pyrite-activated carbon composite constructed wetland filler based on agricultural waste through the deep interweaving of chemical, biological, and physical interactions between components, resulting in a synergistic effect of "1+1+1>3". On the one hand, it utilizes the adsorption properties of pyrite for nitrogen, phosphorus, organic matter, and heavy metal ions in wastewater, while the biochar made from agricultural waste slowly releases natural carbon sources, supporting the activity of heterotrophic denitrifying bacteria and reducing dependence on external carbon sources. On the other hand, it utilizes the lightweight, porous characteristics, and good mechanical properties of activated carbon made from agricultural waste-based biochar to develop a novel composite filler, clarifying its removal efficiency for various pollutants in constructed wetland systems. Through the complementary functions of multiple materials, it solves the problems of low efficiency, easy clogging, acid pollution, and poor stability of traditional wetland systems, as well as single pyrite systems. At the same time, it achieves low-carbon and low-cost operation, suitable for industrial wastewater treatment scenarios with high heavy metal pollution loads and agricultural wastewater with low carbon-to-nitrogen ratios.

[0042] Specifically, the present invention provides a method for preparing and applying a pyrite-activated carbon composite constructed wetland filler based on agricultural waste, which has the following beneficial effects:

[0043] (1) The filler material made by combining agricultural waste-based biochar with pyrite has a lower density (porosity > 60%), improved air permeability and hydraulic conductivity, avoids clogging, and extends hydraulic retention time (HRT); the biochar made from agricultural waste such as corn cobs has a porous structure (specific surface area 200-500 m²). 2 / g) binding to pyrite active sites enhances the activity against NH4+. + PO4 3- It also has the ability to adsorb heavy metals, solving the problems of poor matrix permeability, weak hydraulic conductivity, easy clogging and low pollutant contact efficiency caused by the high density and low porosity of traditional fillers such as gravel and ceramsite.

[0044] (2) Using agricultural waste (such as corn stalks and corn cobs) to replace gravel / ceramsite avoids the problems of mining damage and sintering energy consumption; pyrite is a natural mineral, avoiding dependence on chemical raw materials; biochar prepared from agricultural waste degrades slowly, has a long carbon release life, the dissolution rate of pyrite is controllable, and the replacement frequency of filler is reduced by more than 50%, which solves the problems of high energy consumption and large carbon emissions of traditional filler relying on gravel mining or ceramsite firing, and the high cost and non-renewable nature of chemical synthetic fillers (such as activated carbon).

[0045] (3) Activated carbon prepared from agricultural waste has a specific surface area of ​​1000-3000 m² after activation of biochar with KOH and other agents. 2 / g, with a microporous / mesoporous structure, it efficiently adsorbs VOCs, H2S, NH3 and heavy metals; after the saturated packing is treated to be harmless, it can be recycled for soil improvement (replenishing Fe / S elements) or incineration power generation (carbon resource reuse), avoiding secondary pollution. It solves the problems of low adsorption capacity, easy saturation, frequent replacement and soil / groundwater pollution caused by landfill after disposal of traditional packing materials such as gravel.

[0046] (4) Gas adsorption enhancement-chemical degradation mechanism: Pyrite-modified activated carbon enhances the adsorption capacity of VOCs by 15%-20% through Fe3O4 catalysis. The enhanced hydrophobicity allows it to preferentially adsorb non-polar pollutants (such as halogenated hydrocarbons). The oxidation-reduction reaction on the Fe3O4 surface degrades VOCs into CO2 / H2O, avoiding secondary pollution. This solves the problems of malodorous gases such as H2S and NH3 released during traditional wetland treatment and the weak adsorption capacity of VOCs (such as benzene compounds), which are harmful to the environment and human health.

[0047] (5) Pyrite-derived Fe3O4 enhances the synergistic effect between microorganisms and chemicals: the electron transfer function of Fe3O4 can enrich bacterial communities such as Thiobacillus, and enhance the stability of the sulfur / iron cycle; the acid resistance and system tolerance are enhanced. Under the condition of pH=2, the oxidation rate of pyrite in the composite packing increases by 2-3 times, which solves the problems of traditional packings that only rely on physical interception and have a single function, and the small specific surface area and low reactivity of pyrite when used alone (such as phosphorus removal relying on precipitation rather than adsorption), and the H released by the oxidation of pyrite. + This leads to system acidification and instability.

[0048] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0049] Figure 1 A schematic diagram of the process for preparing a pyrite-activated carbon composite artificial wetland filler based on agricultural waste in an embodiment of the present invention;

[0050] Figure 2 This is a schematic diagram of the structure of a pyrite-activated carbon composite artificial wetland filler based on agricultural waste prepared according to an embodiment of the present invention;

[0051] Figure 3 This invention provides an example of a pyrite-activated carbon composite constructed wetland filler based on agricultural waste, compared to a single pyrite constructed wetland filler. The results demonstrate the effectiveness of different treatment times for organic matter (using COD as an indicator) and NH4 in complex polluted wastewater with a low carbon-to-nitrogen ratio and containing heavy metals. + A comparison chart of -N removal rates;

[0052] Figure 4This is a comparison chart showing the removal rates of TN and TP in a composite polluted wastewater containing heavy metals and with a pyrite-activated carbon composite constructed wetland filler based on agricultural waste and a single pyrite constructed wetland filler prepared according to an embodiment of the present invention, under different treatment times.

[0053] Figure 5 This invention relates to a composite constructed wetland filler based on agricultural waste (pyrite-activated carbon) and a single pyrite constructed wetland filler, and compares their effects on heavy metals (Cu) in complex polluted wastewater with low carbon-to-nitrogen ratio and containing heavy metals under different treatment times. 2+ Cr 6+ A comparison chart of removal rates;

[0054] Figure 6 This invention provides an example of a pyrite-activated carbon composite constructed wetland filler based on agricultural waste, compared to a single pyrite constructed wetland filler, for different treatment times to reduce NO3 in complex polluted wastewater with low carbon-to-nitrogen ratio and heavy metal content. - A comparison chart of -N removal rates. Detailed Implementation

[0055] This invention uses agricultural waste (corn stalks / cores) as raw material. A porous hydrothermal carbon skeleton is prepared by hydrothermal carbonization at 150-180℃ (solid-liquid mass ratio 1:(4-6)). After ash removal with 1.0mol / L HCl and drying at 100-110℃ for 12h, pyrite powder and 0.5mol / L NaBH4 are reacted at 160-180℃ for 4-6h under nitrogen protection at a solid-liquid mass ratio of 1:(2-4). 50-100nm nano-pyrite is generated in situ and confined for loading. Vacuum drying at 60℃ for 6h forms a pyrite hydrothermal carbon composite, which is used to construct a pyrite-agricultural waste-based hydrothermal carbon slow-release driven bottom layer.

[0056] Subsequently, agricultural waste was carbonized in a nitrogen-protected tubular furnace at 700℃ for 1.5-2.5h to obtain biochar, which was then mixed with 1.0mol / L KOH solution at an alkali-to-carbon mass ratio of 1:5 and activated at 800-900℃ for 1-2h. After washing and drying, microporous activated carbon was obtained. Mechanical extrusion was achieved through the strong shear force and bidirectional stirring of the propeller of a twin-shaft mixer to premix and embed the microporous activated carbon and the pyrite-hydrothermal carbon composite obtained in step S1. Then, the mixture was pressurized stepwise by a hydraulic tablet press in stages of "low pressure → medium pressure → high pressure" to gradually expel air and strengthen the embedding. Finally, low-temperature curing was used to strengthen the bonding force between particles to achieve physical embedding, and the pyrite-hydrothermal carbon-activated carbon composite was finally obtained. Specifically, the pyrite-hydrothermal-carbon composite obtained from the bottom layer is mechanically premixed with the pyrite-hydrothermal-carbon composite obtained from the bottom layer using a biaxial mixer (100-200 r / min, 40-60 min). Then, it is subjected to a hydraulic tablet press with gradient pressure increases at low pressure (0.5-1 MPa) for 5-10 min, medium pressure (5-10 MPa) for 10-15 min, and high pressure (15-20 MPa) for 20-30 min, followed by low-temperature curing at 60-100℃ for 2-3 h to achieve physical integration, resulting in a pyrite-hydrothermal-carbon-activated carbon composite. Separately, pyrite powder is oxidized in H2SO4 solution at pH 3.0 for 18-30 h, and the pH is adjusted to 8.0-9.0 with NH4OH. The mixture is then stirred at 80-90℃ and 300-400 r / min for 1.5-2.5 h to generate a product containing 20-50 nm... A suspension of Fe3O4 particles was prepared. The above composite was impregnated with the solid-liquid mass ratio of 1:(9-11) and loaded onto a composite substrate by ultrasonic impregnation at 200-300W for 1 hour. The composite was then dried at 70-80℃ for 6-8 hours to form a Fe3O4 / activated carbon-pyrite composite, which was used to construct the pyrite-activated carbon adsorption catalytic middle layer.

[0057] Agricultural waste is pre-carbonized in a tube furnace at 250-350℃ for 1-2 hours under a nitrogen atmosphere to obtain biochar. This biochar is then impregnated with a 2mol / L H3PO4 solution at a solid-liquid mass ratio of 3:1 and activated at 650-750℃ for 2-3 hours to obtain mesoporous activated carbon. The mesoporous activated carbon and the Fe3O4 / activated carbon-pyrite composite obtained in step S2 are pre-mixed and intercalated using a biaxial mixer. The mixture is then pressurized stepwise using a hydraulic tablet press with "low pressure → medium pressure → high pressure" to gradually expel air and strengthen the intercalation. Finally, low-temperature curing strengthens the bonding force between particles to achieve physical intercalation, ultimately yielding the mesoporous activated carbon-Fe3O4 / activated carbon-pyrite composite. Then, a two-stage pyrolysis device is used. The pyrolysis stage is carried out in a tubular furnace to convert agricultural waste into pyrolysis steam. The purification stage is carried out in a filter to finally obtain transportable pure pyrolysis steam. Then, the mesoporous activated carbon-Fe3O4 / activated carbon-pyrite composite is placed in a fluidized bed CVD reactor. Nitrogen and pyrolysis steam are introduced into the reactor in stages. In the first stage, nitrogen is introduced to remove air. In the second stage, a mixture of nitrogen and pyrolysis steam is introduced through an insulated pipe. Using the pyrolysis steam of agricultural waste as a carbon source, under the catalysis of Fe3O4 in the composite, the pyrolysis steam is deposited on the middle surface to form a biochar-regulated filter layer. Specifically, the Fe3O4 / activated carbon-pyrite composite obtained in the middle layer is premixed in a biaxial mixer (150-200 r / min, 20-40 min), and then subjected to a hydraulic tablet press with gradient pressure increases of 1-2 MPa for 10-15 min, 5-10 MPa for 10-20 min, and 15-20 MPa for 15-20 min, respectively, and cured at 50-100℃ for 3-4 h to obtain a mesoporous activated carbon-Fe3O4 / activated carbon-pyrite composite. A two-stage pyrolysis device is then used (pyrolysis section: tubular furnace 200-300℃ / 30-60 min; purification section: filter with 15-20 μm pore size) to further process the composite. Agricultural waste is converted into pure pyrolysis steam (the conveying pipeline is insulated at 100-200℃); the mesoporous activated carbon-Fe3O4 / activated carbon-pyrite composite is placed in a fluidized bed CVD reactor (380℃, 0.1-0.2MPa), nitrogen gas is first introduced (400-700mL / min, 2-3h) to remove air, and then a mixture of nitrogen gas and pyrolysis steam is introduced (volume flow ratio 1:(4-6), total flow rate 200-300mL / min, 4-5h). The pyrolysis steam is deposited for 1.5-2h using Fe3O4 catalysis to form a 50-100nm thick biochar control layer, thus constructing an activated carbon-agricultural waste-based biochar control filter surface.

[0058] Finally, after stopping the carbon source supply and cooling the nitrogen to room temperature, a composite artificial wetland packing material with a three-layer coupled structure of "slow-release driven bottom layer - adsorption catalytic middle layer - regulation filtration surface layer" is obtained.

[0059] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention should be considered equivalent substitutions and are included within the protection scope of the present invention. Furthermore, it should be understood that after reading the contents of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims and are all within the protection scope of the present invention.

[0060] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0061] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0062] Unless otherwise specified, the reagents, instruments, equipment, and performance testing methods used in this invention are all commonly used by those skilled in the art.

[0063] Example

[0064] like Figure 1 As shown, this embodiment provides a method for preparing a pyrite-activated carbon composite constructed wetland filler based on agricultural waste, specifically including the following steps:

[0065] 1. Substrate preparation: Pyrite-agricultural waste-based hydrothermal carbon slow-release driving layer

[0066] Constructing a hydrothermal carbonization framework: Agricultural waste corn cob powder pulverized to 3 mm was mixed with deionized water at a solid-liquid mass ratio of 1:5 and placed in a high-pressure reactor with a pressure of 3.5 MPa. The mixture was subjected to hydrothermal carbonization at 165 °C for 5.5 h. After cooling, the solid product was removed and washed twice with 1.0 mol / L HCl solution to remove ash. The product was then dried at 105 °C for 12 h to obtain a porous hydrothermal carbon framework with a pore size of 30 μm.

[0067] Nano-pyrite loading: Natural pyrite ore powder crushed to a particle size of 500 μm was mixed with a 0.5 mol / L NaBH3 solution at a solid-liquid mass ratio of 1:3 and reacted at 180℃ for 5 h under nitrogen protection. After the reaction, centrifugation was performed to generate nano-pyrite particles with a particle size of 75 nm. These particles were then uniformly confined and loaded into the pores of a hydrothermal carbon framework and vacuum dried at 60℃ for 6 h to form a pyrite hydrothermal carbon composite. In this process, NaBH4 acts as a reducing agent in the hydrothermal reduction method, generating nano-pyrite in situ on the straw carbon framework, and utilizing the carbon-based pore confinement effect to prevent particle agglomeration.

[0068] 2. Preparation of the middle layer: Pyrite-activated carbon adsorption catalytic layer

[0069] Preparation of microporous activated carbon: Corn cobs were placed in a tubular furnace that could be purged with inert gas. Under the protection of inert gas (nitrogen), the corn cobs were carbonized at 700℃ for 2 hours to obtain biochar. The biochar was mixed with a 1.0 mol / L KOH solution at a carbon-alkali mass ratio of 5:1 and activated at 700℃ for 2 hours to construct a micro-mesoporous synergistic structure. After washing with deionized water until neutral and drying, microporous activated carbon with a pore size of 1-10 nm accounting for >75% was obtained. The microporous activated carbon was mixed at a speed of 150 r / min for 50 min using a biaxial mixer to achieve mechanical extrusion and premix and embed the microporous activated carbon with the pyrite hydrothermal carbon composite obtained at the bottom layer. Then, the mixture was pressed into shape by a pressure gradient press at low pressure of 0.75 MPa for 7 min, medium pressure of 5-10 MPa for 13 min, and high pressure of 18 MPa for 25 min. Finally, it was cured at 80℃ for 2.5 hours to form a pyrite-hydrothermal carbon-activated carbon composite.

[0070] Fe3O4 nanocrystal loading: Natural pyrite ore was oxidized in an acidic H2SO4 solution (pH 3.0) for 24 h to obtain Fe3O4 nanocrystals. 3+ The pyrite oxidation solution was adjusted to pH 8.5 by adding NH4OH, and stirred at 85℃ and 350 r / min for 2 h to generate a suspension containing Fe3O4 nanocrystals; the Fe3O4 nanocrystals had a particle size of 35 nm. The pyrite-hydrothermal carbon-activated carbon composite was mixed with the Fe3O4 suspension at a solid-liquid mass ratio of 1:10, ultrasonically impregnated at 250 W for 1 h, and then dried at 75℃ for 7 h to allow Fe3O4 to uniformly adhere to the surface of the activated carbon, thus obtaining the Fe3O4 / activated carbon-pyrite composite.

[0071] 3. Surface preparation: Activated carbon-agricultural waste-based biochar regulating filtration layer

[0072] Preparation of mesoporous activated carbon: Corn cobs are first pre-carbonized at 300℃ for 1.5h, and then activated at 700℃ for 2.5h to generate biochar (specific surface area of ​​3200-3300 m²). 2 / g), possessing both slow-release carbon source (C / N = 8-12) and microbial attachment functions, is then impregnated and activated with 78% H3PO4 solution and biochar at a solid-liquid mass ratio of 3:1 to form mesoporous activated carbon (introducing oxygen-containing functional groups -COOH, -OH, enhancing the resistance to NH4+). + and PO4 3- The ion exchange capacity of the activated carbon was measured. The mixture was stirred in a biaxial mixer at a speed of 175 r / min for 30 min to achieve mechanical extrusion. The mesoporous activated carbon was then premixed and intercalated with the Fe3O4 / activated carbon-pyrite composite obtained in the middle layer. The mixture was then pressed into shape by a pressure gradient press at a pressure of 1.5 MPa for 13 min, 8 MPa for 15 min, and 17 MPa for 18 min. Finally, the mixture was cured at 75℃ for 3.5 h to obtain the mesoporous activated carbon-Fe3O4 / activated carbon-pyrite composite.

[0073] Low-temperature catalytic CVD deposition: A two-stage pyrolysis device was used, in which the pyrolysis stage was carried out in a tubular furnace at 250℃ for 45 min, and the purification stage was carried out in a filter with a pore size of 18 μm to obtain transportable pure pyrolysis steam. The temperature of the transport pipeline was 150℃. The mesoporous activated carbon-Fe3O4 / activated carbon-pyrite composite was placed in a fluidized bed CVD reactor. Under the conditions of 380℃ and 0.13 MPa, nitrogen gas was first introduced at a flow rate of 550 mL / min for 2.5 h to remove air. Then, a mixed gas composed of nitrogen and pyrolysis steam at a volume flow rate ratio of 1:5 was introduced, with the total flow rate controlled at 250 mL / min and the introduction time at 4.5 h. Using pyrolysis steam as the carbon source, under the catalysis of Fe3O4, the reaction pressure was maintained at 0.15 MPa. The pyrolysis steam was deposited on the surface of the composite for 1.8 h to form a biochar control layer with a thickness of 80 nm.

[0074] 4. Preparation of composite fillers

[0075] Stop the carbon source supply, continue to purge nitrogen and cool to room temperature, and obtain as follows: Figure 2 The composite artificial wetland packing shown has a three-layer coupled structure of "slow-release driven bottom layer - adsorption catalytic middle layer - regulation filtration surface layer".

[0076] Application examples

[0077] This application example provides an experimental method for applying the pyrite-activated carbon composite constructed wetland packing material based on agricultural waste prepared in the above embodiments to simulated wastewater treatment, specifically including the following steps:

[0078] 1. Preparation of experimental setup

[0079] This experiment used a vertical subsurface flow constructed wetland pilot device, which mainly consisted of two sets of PVC cylinders with an inner diameter of 50 mm and a height of 800 mm and a bottom. They were a single pyrite constructed wetland system (CW-1) and a pyrite-activated carbon constructed wetland system based on agricultural waste (CW-2).

[0080] The constructed wetland system consists of three main layers: the bottom layer is the support layer of the wetland system, covered with 100mm thick quartz sand (particle size 5-10mm); the middle layer is the wetland bed matrix layer, with different functional fillers for different wetland systems: CW-1 is pyrite filler; CW-2 is pyrite-activated carbon composite filler based on agricultural waste (both with the same particle size of 5mm, and porosity of 30%-40% for CW1 and 60%-70% for CW2); and the top layer is covered with 50mm thick quartz sand (particle size 2-5mm) as a water distribution layer.

[0081] An electromagnetic variable frequency air compressor (flow rate 0.8-3L / min, pressure 0.15-0.25MPa) is connected to an annular microporous aeration tube (inner diameter 10mm, pore size 0.5mm), and a pulse aeration mode is used to achieve controlled oxygen transfer to ensure the oxygen supply in the system.

[0082] The core microorganisms of the pyrite-biochar constructed wetland are inoculated and domesticated using a natural enrichment culture method (autotrophic denitrification driven by sulfur / iron cycling bacteria, carbon-dependent pathway supplemented by heterotrophic denitrifying bacteria, and phosphorus and heavy metal fixation synergistically by iron oxide generating bacteria and heavy metal resistant bacteria), forming a sustainable pollutant removal mechanism to ensure that the microorganisms adapt to the new environment and grow and reproduce effectively; the device is equipped with a constant temperature water bath sleeve to maintain the reaction temperature at 25±1℃.

[0083] 2. Pretreatment of experimental wastewater

[0084] Based on the common pollutant components and concentration ranges in agricultural and industrial wastewater, the wastewater used in the experiment was artificially prepared. The specific water quality indicators of the experimental wastewater are shown in Table 1.

[0085] Table 1 Water quality indicators of experimental wastewater

[0086]

[0087] 3. Continuous operation treatment of constructed wetlands

[0088] A continuous flow influent method was adopted, with peristaltic pumps used to pump experimental wastewater from the bottom of the constructed wetland to the top. The influent flow rate was adjusted to control the hydraulic retention time at 1 day, and the total operating time of the constructed wetland was 45 days. After the reactor was started up, formal operation to treat wastewater began on the 5th day, and water quality was sampled and measured to ensure data representativeness.

[0089] 4. Pollutant Sampling and Determination Methods

[0090] Sampling points were set up at the water outlet, and samples were taken once daily for testing. Chemical oxygen demand (COD) was determined using the potassium dichromate method, and heavy metals (Cu) were determined using atomic absorption spectrometry (AAS). 2+ Cr 6+ Concentration and spectrophotometric determination of TN and NH4 + -N, NO3 - -N and TP concentrations were used to calculate organic matter removal rate, heavy metal removal rate, and nitrogen and phosphorus removal rate.

[0091] 5. Analysis of the treatment performance results of constructed wetlands

[0092] Depend on Figures 3 to 6 It is evident that the pyrite-activated carbon composite constructed wetland packing material prepared in this invention, based on agricultural waste, exhibits significant advantages in wastewater purification due to its unique three-layer structure and functional synergistic mechanism. The packing material achieves a peak COD removal rate of 85.6% after 30 days of operation, exceeding CW-1 by 13.3%, demonstrating its highly efficient degradation capacity for organic matter. After 20 and 25 days of operation, the removal rate of Cu... 2+ The removal rates of Cr and TN reached as high as 95.4% and 92.1% respectively, far exceeding the bottleneck of traditional packing materials in terms of treatment efficiency, with particularly outstanding performance in treating heavy metals; for TN and NO3... - -N removal rates reached peak values ​​of 85.5% and 82.3%, and NH4... + The nitrogen removal rate steadily increased with the passage of time in the early stages, reaching 94.3% after 30 days. TP maintained a continuous removal efficiency of over 70% throughout the entire operation, confirming the high efficiency and stability of the packing material's decarburization and phosphorus removal performance. After reaching the aforementioned peak values, the system continued to operate for another 15 days, and the removal efficiency of all pollutants remained stable near their respective peak levels without significant decline.

[0093] Furthermore, the pyrite-activated carbon composite constructed wetland filler prepared by this invention, based on agricultural waste, also plays an important role in the treatment process due to its high porosity. By comparing the changes in pollutant concentrations of CW-1 and CW-2 within the same treatment time, the CW-2 constructed wetland, which is mainly composed of composite filler, far surpasses the CW-1 constructed wetland, which is mainly composed of pyrite, in terms of both peak removal rate and treatment performance stability. The high porosity structural design effectively solves the clogging problem of traditional constructed wetland fillers. Combined with the slow release of biochar made from agricultural waste and the adsorption function of activated carbon, it achieves multiple objectives of nitrogen and phosphorus removal, heavy metal adsorption, and odor suppression. It is especially suitable for the treatment of wastewater with low carbon-to-nitrogen ratio, heavy metal, and nanoplastic pollutants, providing an innovative solution for efficient and low-cost water environment management.

[0094] In summary, the pyrite-activated carbon composite constructed wetland filler prepared by this invention, through resource synergy and physical-chemical-biological coupling, achieves multiple functions such as nitrogen and phosphorus removal, heavy metal adsorption, and odor suppression compared to traditional constructed wetland technology and constructed wetlands using pyrite alone. It also features low cost, high efficiency, and environmental friendliness.

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A pyrite-activated carbon composite constructed wetland filler based on agricultural waste, characterized in that, include: The slow-release driven bottom layer of pyrite-agricultural waste-based hydrothermal carbon consists of a porous hydrothermal carbon framework and a pyrite hydrothermal carbon composite formed by nano-pyrite particles loaded in its pores. The middle layer of the pyrite-activated carbon adsorption catalysis is composed of Fe3O4 / activated carbon-pyrite complex, which is formed by physically intercalating microporous activated carbon and the bottom layer of pyrite hydrothermal carbon composite and then loading Fe3O4 nanocrystals. The activated carbon-agricultural waste-based biochar regulates the filter surface. It is composed of a middle layer of Fe3O4 / activated carbon-pyrite complex and mesoporous activated carbon physically intercalated to form a mesoporous activated carbon-Fe3O4 / activated carbon-pyrite complex. Then, it is combined with a layer of pyrolysis biochar particles obtained by chemical vapor deposition of agricultural waste pyrolysis steam.

2. The preparation method of a pyrite-activated carbon composite constructed wetland filler based on agricultural waste as described in claim 1, characterized in that, Includes the following steps: Preparation of S1, Pyrite-Agricultural Waste-Based Hydrothermal Carbon Slow-Release Driven Substrates Agricultural waste powder was mixed with deionized water and placed in a high-pressure reactor for hydrothermal carbonization. After cooling and acid washing with hydrochloric acid solution to remove ash, the mixture was dried to obtain a porous hydrothermal carbon skeleton with a pore size of 10-50 μm. Natural pyrite ore powder was mixed with NaBH4 solution and subjected to hydrothermal reduction reaction under nitrogen protection to generate nano-pyrite particles with a particle size of 50-100nm in situ. These nano-pyrite particles were then confined and loaded into the pores of a porous hydrothermal carbon framework and vacuum dried to obtain a pyrite hydrothermal carbon composite. Preparation of S2, Pyrite-Activated Carbon Adsorption Catalytic Middle Layer Agricultural waste is placed in a tubular furnace and pyrolyzed under the protection of inert gas to obtain biochar. After mixing with KOH solution, it is activated and washed with deionized water until the solution is neutral and then dried to obtain microporous activated carbon. It is then physically integrated with the pyrite-hydrothermal carbon composite obtained in step S1 to obtain a pyrite-hydrothermal carbon-activated carbon composite. Natural pyrite ore powder was oxidized in an acidic solution to obtain pyrite oxidation solution. Then, NH4OH was added to adjust the pH to 8.0-9.0, and the reaction was stirred to generate a suspension containing Fe3O4 nanocrystal particles. The suspension was mixed with a pyrite-hydrothermal carbon-activated carbon composite and ultrasonically impregnated. After drying, Fe3O4 was uniformly attached to the surface of the pyrite-hydrothermal carbon-activated carbon composite to obtain the Fe3O4 / activated carbon-pyrite composite. S3, Activated Carbon - Agricultural Waste-Based Biochar for Filter Surface Regulation Agricultural waste is placed in a tubular furnace and pre-carbonized under the protection of inert gas to obtain biochar. The biochar is then activated by impregnation with H3PO4 solution to obtain mesoporous activated carbon. This activated carbon is then physically intercalated with the Fe3O4 / activated carbon-pyrite composite obtained in step S2 to obtain mesoporous activated carbon-Fe3O4 / activated carbon-pyrite composite. Agricultural waste is converted into pure pyrolysis steam using a two-stage pyrolysis device. Then, a mesoporous activated carbon-Fe3O4 / activated carbon-pyrite composite is placed in a fluidized bed CVD reactor. Nitrogen and pyrolysis steam are introduced into the reactor in stages. In the first stage, nitrogen is introduced to remove air. In the second stage, a mixture of nitrogen and pyrolysis steam is introduced. Using the pyrolysis steam of agricultural waste as a carbon source, under the catalysis of Fe3O4 in the composite, the pyrolysis steam is deposited on the middle layer surface to form a biochar-regulated filter surface. S4, Composite filler inert treatment molding The carbon source supply was stopped, and nitrogen gas was continuously purged to cool the mixture to room temperature, resulting in a composite artificial wetland filler with a three-layer coupled structure consisting of a "slow-release driven bottom layer, an adsorption-catalytic middle layer, and a regulated filtration surface layer".

3. The preparation method of a pyrite-activated carbon composite artificial wetland filler based on agricultural waste according to claim 2, characterized in that: In step S1, the agricultural waste is corn cob or corn stalk, and the particle size of the agricultural waste powder is 2-5 mm; the solid-liquid mass ratio of the agricultural waste powder and deionized water is 1:(4-6); the pressure range of the reactor is 1.8-5.2 MPa; the temperature of hydrothermal carbonization is 150-180℃, and the time of hydrothermal carbonization is 5-6 h; the concentration of hydrochloric acid solution is 1.0 mol / L; the drying temperature is 100-110℃, and the drying time is 12 h.

4. The preparation method of a pyrite-activated carbon composite artificial wetland filler based on agricultural waste according to claim 2, characterized in that: In step S1, the particle size of the natural pyrite ore powder is 230-830 μm, the concentration of the NaBH4 solution is 0.5 mol / L, and the solid-liquid mass ratio of the pyrite ore powder to the NaBH4 solution is 1:(2.5-4); the temperature of the hydrothermal reduction reaction is 150-180℃, and the time of the hydrothermal reduction reaction is 4-6 h; the temperature of the vacuum drying is 60℃, and the time of the vacuum drying is 6 h.

5. The preparation method of a pyrite-activated carbon composite artificial wetland filler based on agricultural waste according to claim 2, characterized in that: In step S2, the inert gas is nitrogen, the pyrolysis temperature is 700℃, and the pyrolysis time is 1.5-2.5h; the concentration of KOH solution is 1.0mol / L; the mass ratio of KOH solution to biochar is 1:5; the activation temperature is 800-900℃, and the activation time is 1-2h.

6. The preparation method of a pyrite-activated carbon composite artificial wetland filler based on agricultural waste according to claim 2, characterized in that: In step S2, the acidic solution is H2SO4 solution with a pH of 3.0, and the oxidation time is 18-30 h; the stirring rate is 300-400 r / min, the stirring time is 1.5-2.5 h, the reaction temperature is 80-90 ℃, and the Fe3O4 nanocrystal particles have a particle size of 20-50 nm; the solid-liquid mass ratio of the pyrite-hydrothermal carbon-activated carbon composite and the suspension containing Fe3O4 nanocrystal particles is 1:(9-11), the ultrasonic impregnation power is 200-300 W, the ultrasonic impregnation time is 1 h, the drying temperature is 70-80 ℃, and the drying time is 6-8 h.

7. The preparation method of a pyrite-activated carbon composite constructed wetland filler based on agricultural waste according to claim 2, characterized in that, In step S3, the inert gas is nitrogen, the pre-carbonization temperature is 250-350℃, the pre-carbonization time is 1-2h, the mass fraction of H3PO4 solution is 78%, the solid-liquid mass ratio of biochar to H3PO4 solution is 3:1, the impregnation activation temperature is 650-750℃, and the impregnation activation time is 2-3h.

8. The preparation method of a pyrite-activated carbon composite artificial wetland filler based on agricultural waste according to claim 2, characterized in that: In step S3, the pyrolysis temperature of the pyrolysis device is 200-300℃, and the pyrolysis time is 30-60 min; the temperature of the insulated pipeline for conveying pyrolysis steam and nitrogen is 100-200℃.

9. The preparation method of a pyrite-activated carbon composite artificial wetland filler based on agricultural waste according to claim 2, characterized in that: In step S3, the temperature of the fluidized bed CVD reactor is 380℃ and the pressure is 0.1-0.2MPa; the nitrogen gas introduction time in the first stage is 2-3h and the flow rate is 400-700mL / min; the mixed gas introduction time in the second stage is 4-5h and the flow rate is 200-300mL / min; the volume flow ratio of pyrolysis steam to nitrogen is 1:(4-6); the deposition time is 1.5-2h; and the thickness of the biochar-controlled filter surface layer is 50-100nm.

10. The application of the pyrite-activated carbon composite constructed wetland filler based on agricultural waste as described in claim 1, characterized in that: The packing material is used in wastewater treatment.

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