Cu (II) gradient regulation-based CH4 and N2O collaborative emission reduction constructed wetland system

Abstract

The invention discloses a Cu (II) gradient regulation-based CH4 and N2O collaborative emission reduction constructed wetland system, which comprises a system main body, the top end of the system main body is open, the bottom end of the system main body is closed, and the system main body sequentially comprises an anaerobic zone, a transition zone and an aerobic zone from bottom to top; the anaerobic zone, the transition zone and the aerobic zone are filled with gravels and Cu (II)-loaded sludge biochar, and the volume ratio of the Cu (II)-loaded sludge biochar in the transition zone is the largest, the volume ratio of the Cu (II)-loaded sludge biochar in the aerobic zone is the second, and the volume ratio of the Cu (II)-loaded sludge biochar in the anaerobic zone is the smallest. According to the constructed wetland system, the problem that emission reduction of CH4 and N2O in a traditional constructed wetland is difficult to consider at the same time is solved, and cooperative emission reduction of greenhouse gas is achieved through precise regulation and control of microbial enzyme activity. By integrating the regulation and control mechanism of Cu (II) on microbial functional genes (such as nosZ and pMMO), the transformation of the constructed wetland from pollution treatment to greenhouse gas cooperative control is promoted.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater treatment, and in particular relates to an artificial wetland system. Background Art

[0002] Constructed wetlands are an environmentally friendly, low-energy, and highly efficient ecological wastewater treatment technology widely used worldwide. While this technology offers significant advantages in pollutant removal, it also releases greenhouse gases such as CO2, CH4, and N2O into the atmosphere. Although wetlands occupy only 5-8% of Earth's land surface, they contribute 20-30% of the world's major greenhouse gas emissions. It is estimated that greenhouse gas emissions from constructed wetlands are 2-10 times greater than those from natural wetlands, making them a significant contributor to global greenhouse gas emissions. Of these three greenhouse gases, CH4 and N2O have the most significant greenhouse effects, with global warming potentials 25 and 298 times that of CO2, respectively. Therefore, effectively achieving synergistic reductions in CH4 and N2O emissions is a key approach to promoting the sustainable development of constructed wetland technology.

[0003] During the denitrification process in traditional constructed wetlands, insufficient nitrification and denitrification activity in denitrifying bacteria prevents complete nitrification and denitrification, leading to the accumulation and release of NO. Fluctuating dissolved oxygen levels in the anaerobic zone of the system can disrupt the competitive balance between methanogens and methanotrophs, causing CH4 to escape. Cu(II) is the active site of both denitrifying nitrous oxide reductase and methanotrophic methane monooxygenase, and both compete for Cu(II) in the biological process. Studies have shown that 1 μM Cu(II) can triple the number of methanotrophs. By effectively competing for Cu(II), these bacteria reduce their contact with NO-reducing bacteria, thereby increasing NO emissions. Conversely, NO inhibits methylation and methanogenesis, resulting in a 50% increase in CH4 emissions when ambient NO concentration decreases. Therefore, CH4 and NO have an antagonistic effect on emission reduction in traditional constructed wetland systems.

[0004] CN 119175073 A discloses a method for preparing a sludge biochar material and its application in municipal sewage treatment. The method comprises: 1. mixing sludge discharged from an aerobic tank with fly ash and then subjecting the mixture to anaerobic carbonization to obtain sludge biochar; 2. modifying the sludge biochar by loading it with manganese using a chemical precipitation method; 3. conditioning the sludge, adding cationic polyacrylamide and potassium ferrate for secondary stirring, and then pyrolyzing the sludge; 4. adding aluminum hydroxide and carborane for staged heat treatment, and subjecting the mixture to high-temperature heat treatment with copper hydroxide to further improve the pore structure; and 5. activating the sludge biochar material with ozone. The patent's shortcomings are:

[0005] 1. Manganese-loaded sludge biochar is added with fly ash, aluminum hydroxide, potassium ferrate, cationic polyacrylamide, carborane, copper hydroxide and other materials. Among them, potassium ferrate, carborane and copper hydroxide are relatively expensive. Compared with the Cu(II)-loaded sludge biochar patent, copper sulfate and gravel are relatively cheap. In addition, manganese-loaded sludge biochar is loaded with manganese through a chemical precipitation method (manganese sulfate + sodium carbonate), which is cumbersome and may introduce impurities. It improves the pore structure through ozone activation, but ozone equipment is expensive and ozone activation may leave residual ozone, which may cause secondary pollution.

[0006] 2. Manganese is easily dissolved under acidic or oxidizing conditions, which may cause excessive manganese in water bodies. The release concentration of Cu(Ⅱ) is precisely controlled through a layered design (48-96 μg / L), which has a lower risk.

[0007] 3. Manganese-loaded sludge biochar lacks a synergistic effect on greenhouse gas emission reduction. In terms of greenhouse gas (such as CH4 and N2O) emission reduction, the activation effect of Cu(Ⅱ) on methane monooxidase and N2O reductase is more obvious.

[0008] Based on the above analysis, there is an urgent need to develop an artificial wetland system that can regulate the function of microbial communities through the Cu(Ⅱ) concentration gradient to achieve synergistic reduction of CH4 and N2O emissions. Summary of the Invention

[0009] In view of the antagonistic effect between CH4 and N2O in the emission reduction of traditional artificial wetland systems, the present invention provides an artificial wetland system for the synergistic reduction of CH4 and N2O emissions based on Cu(II) gradient regulation. The copper ion concentration is regulated by vertical partition gradient to achieve the synchronous reduction of CH4 and N2O emissions.

[0010] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0011] A constructed wetland system for synergistic reduction of CH4 and N2O emissions based on Cu(II) gradient regulation includes a system main body, which is open at the top and closed at the bottom. The system main body is composed of an anaerobic zone, a transition zone, and an aerobic zone from bottom to top. The anaerobic zone, the transition zone, and the aerobic zone are filled with gravel and Cu(II)-loaded sludge biochar, wherein the volume proportion of the Cu(II)-loaded sludge biochar is the largest in the transition zone, the second largest in the aerobic zone, and the smallest in the anaerobic zone.

[0012] As a preferred technical solution of the present invention, the anaerobic zone is a first gravel layer, which is filled with gravel and Cu (II) loaded sludge biochar, wherein the Cu (II) loaded sludge biochar is evenly distributed in the first gravel layer at a volume ratio of 5-10%; the transition zone is a second gravel layer, which is filled with gravel and Cu (II) loaded sludge biochar, wherein the Cu (II) loaded sludge biochar is evenly distributed in the second gravel layer at a volume ratio of 25-30%; the aerobic zone is a third gravel layer, which is filled with gravel and Cu (II) loaded sludge biochar, wherein the Cu (II) loaded sludge biochar is evenly distributed in the third gravel layer at a volume ratio of 15-20%.

[0013] As a preferred technical solution of the present invention, the particle size of the Cu(II)-loaded sludge organisms is 8-15 mm, the particle size of the first gravel layer is 20-40 mm, and the particle sizes of the second and third gravel layers are 8-15 mm.

[0014] As a preferred technical solution of the present invention, the method for preparing Cu(II)-loaded sludge biochar comprises the following steps:

[0015] The residual sludge from a wastewater plant is used as a matrix, immersed in a copper sulfate solution, stirred, air-dried, shaped, and pyrolyzed under a protective gas atmosphere to obtain Cu(II)-loaded sludge biochar, with a Cu(II) loading mass fraction of 0.2-0.3%.

[0016] As a preferred technical solution of the present invention, the water content of the excess sludge is 90%, the mass ratio of the excess sludge to the copper sulfate solution is 1:1, the concentration of the copper sulfate solution is 0.6-0.7 g / L, and the paddle-type mechanical stirrer is used at a speed of 90-110 rpm at room temperature for 15-28 hours.

[0017] As a preferred technical solution of the present invention, the protective gas is nitrogen or inert gas, the heating rate during the pyrolysis process is 8-12°C / min, the pyrolysis temperature is 600-900°C, and the pyrolysis time is 2.1-2.5h.

[0018] As a preferred technical solution of the present invention, the artificial wetland system further includes:

[0019] A water distribution tank connected to the bottom end of the system body via a water inlet pipe, wherein the water inlet pipe is provided with a power mechanism;

[0020] The wetland plant is arranged at the top of the system body. The top side wall of the system body is provided with a wastewater outlet, and the bottom side wall is provided with a wastewater inlet. The wastewater inlet is connected to the water inlet pipe through an inlet valve, and an outlet valve is provided on the water outlet; the monitoring pipe, the lower end of which is arranged in the system body, and the upper end part passes through the wetland plant.

[0021] The present invention also provides a method for synergistically reducing CH4 and N2O emissions, which is performed using the Cu(II)-loaded sludge biochar constructed wetland system, while simultaneously strengthening the complete denitrification process and methane oxidation process, comprising the following steps:

[0022] Sludge from a wastewater aeration tank is used as bacterial strain in the aerobic zone, and is domesticated to obtain aerobic activated sludge. Sludge from a wastewater upflow anaerobic sludge bed is used as bacterial strain in the anaerobic zone, and is domesticated to obtain anaerobic activated sludge.

[0023] The main body of the system is equipped with an anaerobic zone, a transition zone, and an aerobic zone. Along the height direction of the main body of the system, the anaerobic zone is located below the transition zone, and the transition zone is located at the lower end of the aerobic zone. A continuous flow operation mode of bottom-in and top-out is adopted. First, the anaerobic activated sludge and wastewater are mixed and added to the anaerobic zone of the main body of the system to form biofilms to form an anaerobic activated sludge layer. Then, the aerobic activated sludge and wastewater are mixed and added to the aerobic zone of the main body of the system to form biofilms to form an aerobic activated sludge layer.

[0024] The wastewater to be treated is injected into the main body of the system in a continuous upstream flow mode to enhance the complete denitrification process and methane oxidation process.

[0025] As a preferred technical solution of the present invention, in the process of enhanced complete denitrification, the gradient distribution of Cu(II)-loaded sludge biochar and the setting of hydraulic load are as follows: in the aerobic zone, the volume ratio of Cu(II)-loaded sludge biochar is 15-20%, so that Cu(II) is released into the water body with the water flow and maintained at 48-64 μg / L, activating the methane monooxygenase of methanotrophic bacteria; in the transition zone (3), the volume ratio of Cu(II)-loaded sludge biochar is 25-30%, so that Cu(II) is maintained at 80-96 μg / L, and the activity of N2O reductase is simultaneously improved; the hydraulic retention time is 24-72 hours, and the dissolved oxygen levels in the aerobic zone and the transition zone are maintained at 1.5-2.0 mg / L and 1.0-1.5 mg / L, respectively.

[0026] As a preferred technical solution of the present invention, during the methane oxidation process, the volume ratio of Cu(II)-loaded sludge biochar and the hydraulic load are set as follows: the volume ratio of Cu(II)-loaded sludge biochar in the anaerobic zone is 5-10%, so that Cu(II) is slowly released with the water flow and maintained at less than 15 μg / L, the hydraulic retention time is 24 to 72 hours, and the dissolved oxygen concentration in the anaerobic zone is maintained at a level of <0.5 mg / L, thereby inhibiting the activity of methanogens.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The present invention achieves simultaneous reduction of CH4 and N2O emissions by regulating the Cu(II) concentration through vertical partition gradient.

[0029] CH4 oxidation: In the upper aerobic zone, medium concentration (48-64 μg / L) of Cu(Ⅱ) activates the active center (containing copper ions) of methane monooxygenase and pMMO gene expression, thereby promoting the oxidation of CH4 to CO2.

[0030] N2O reduction: In the middle transition zone, high concentrations (80-96 μg / L) of Cu(Ⅱ) enhance the gene expression of nitrous oxide reductase (NosZ) (containing a copper-zinc active center), inhibit nitrite reductase (NirK), and promote complete denitrification.

[0031] CH4 control: In the bottom anaerobic zone, low concentrations (<15μg / L) of Cu(Ⅱ) can inhibit the gene expression of methyl coenzyme M reductase (McrA), thereby controlling CH4 production.

[0032] This mechanism solves the problem of simultaneous reduction of CH4 and N2O emissions in traditional artificial wetlands, and achieves coordinated reduction of greenhouse gas emissions through precise regulation of microbial enzyme activity.

[0033] (2) The present invention is based on the slow-release carrier technology of Cu(II)-loaded sludge biochar to ensure the operational reliability of the artificial wetland system.

[0034] Slow-release carrier design: Sludge biochar-CuSO4 (loading 0.2% to 0.3%) has a half-life of ≥4 years, providing continuous Cu(II) release and reducing the need for frequent dosing. Furthermore, as a constructed wetland matrix, sludge biochar provides an effective microenvironment for microbial attachment, facilitating the close interaction between biological factors (functional microorganisms, key enzymes, functional genes, etc.) and Cu(II), reducing Cu(II) loss during transmission and ensuring system stability.

[0035] (3) Based on the principles of environmental microbiology, the present invention enhances ecological compatibility.

[0036] Sustainable regulation: Cu(Ⅱ) dosage is controlled by different zones to reduce the risk of metal ion residue (low concentration at the bottom layer inhibits the McrA gene of methanogens) and avoid secondary pollution.

[0037] Technological innovation: Integrate the regulatory mechanism of Cu(Ⅱ) on microbial functional genes (such as nosZ and pMMO) to promote the transformation of artificial wetlands from pollution control to coordinated control of greenhouse gases. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0039] Figure 1 This is a schematic structural diagram of the artificial wetland system for synergistic CH4 and N2O emission reduction based on Cu(II) gradient regulation of the present invention, wherein 1-system body, 2-anaerobic zone, 3-transition zone, 4-aerobic zone, 5-water distribution tank, 6-water inlet pipe, 7-power mechanism, 8-wetland plants, and 9-monitoring pipe.

[0040] Figure 2 This is a scanning electron microscope image of the Cu(II)-loaded sludge biochar prepared in Example 1 of the present invention.

[0041] Figure 3 This is the Cu element mapping diagram of the Cu(II)-loaded sludge biochar prepared in Example 1 of the present invention.

[0042] Figure 4 This is the metal element energy spectrum of Cu(II) loaded sludge biochar prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0043] The present invention will be further described below with reference to specific examples. It should be understood that the following examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention, and that those skilled in the art may make non-essential improvements and adjustments based on the contents of the above invention.

[0044] The present invention provides a constructed wetland system for synergistic reduction of CH4 and N2O emissions based on Cu(II) gradient regulation, such as Figure 1 As shown, the system includes a main body 1, which is open at the top and closed at the bottom. The main body 1 is composed of an anaerobic zone 2, a transition zone 3 and an aerobic zone 4 from bottom to top. The anaerobic zone 2, the transition zone 3 and the aerobic zone 4 are filled with gravel and Cu(II)-loaded sludge biochar. Among them, the volume proportion of Cu(II)-loaded sludge biochar is the largest in the transition zone 3, the second largest in the aerobic zone 4, and the smallest in the anaerobic zone 2.

[0045] In some specific embodiments, the anaerobic zone 2 is a first gravel layer, which is filled with gravel and Cu(II)-loaded sludge biochar, wherein the Cu(II)-loaded sludge biochar is uniformly distributed in the first gravel layer at a volume ratio of 5-10%; the transition zone 3 is a second gravel layer, which is filled with gravel and Cu(II)-loaded sludge biochar, wherein the Cu(II)-loaded sludge biochar is uniformly distributed in the second gravel layer at a volume ratio of 25-30%; the aerobic zone 4 is a third gravel layer, which is filled with gravel and Cu(II)-loaded sludge biochar, wherein the Cu(II)-loaded sludge biochar is uniformly distributed in the third gravel layer at a volume ratio of 15-20%.

[0046] In some specific embodiments, the particle size of the Cu(II)-loaded sludge organisms is 8-15 mm, the particle size of the first gravel layer is 20-40 mm, and the particle sizes of the second gravel layer and the third gravel layer are 8-15 mm.

[0047] In some specific embodiments, the method for preparing Cu(II)-loaded sludge biochar comprises the following steps:

[0048] The residual sludge from a wastewater plant is used as a matrix, immersed in a copper sulfate solution, stirred, air-dried, shaped, and pyrolyzed under a protective gas atmosphere to obtain Cu(II)-loaded sludge biochar, with a Cu(II) loading mass fraction of 0.2-0.3%.

[0049] In some specific embodiments, the water content of the excess sludge is 90%, the mass ratio of the excess sludge to the copper sulfate solution is 1:1, the concentration of the copper sulfate solution is 0.6-0.7 g / L, and the paddle-type mechanical stirrer is used at a speed of 90-110 rpm at room temperature for 15-28 hours.

[0050] In some specific embodiments, the protective gas is nitrogen or an inert gas, the heating rate during the pyrolysis process is 8-12° C. / min, the pyrolysis temperature is 600-900° C., and the pyrolysis time is 2.1-2.5 h.

[0051] In some specific embodiments, the artificial wetland system further comprises:

[0052] A water distribution tank (5) is connected to the bottom end of the system body (1) via a water inlet pipe (6), wherein a power mechanism (7) is provided on the water inlet pipe (6);

[0053] A wetland plant (8) is arranged at the top of a system body (1); a wastewater outlet is provided on the top side wall of the system body (1); a wastewater inlet is provided on the bottom side wall; the wastewater inlet is connected to the water inlet pipe (6) through an inlet valve; and an outlet valve is provided on the water outlet; a monitoring pipe (9) is arranged at its lower end in the system body (1) and its upper end partially passes through the wetland plant (8).

[0054] The present invention also provides a method for synergistically reducing CH4 and N2O emissions, which is performed using the Cu(II)-loaded sludge biochar constructed wetland system, while simultaneously strengthening the complete denitrification process and methane oxidation process, comprising the following steps:

[0055] Sludge from a wastewater aeration tank is used as bacterial strain in the aerobic zone, and is domesticated to obtain aerobic activated sludge. Sludge from a wastewater upflow anaerobic sludge bed is used as bacterial strain in the anaerobic zone, and is domesticated to obtain anaerobic activated sludge.

[0056] The system body (1) is provided with an anaerobic zone, a transition zone and an aerobic zone. Along the height direction of the system body (1), the anaerobic zone is located below the transition zone, and the transition zone is located at the lower end of the aerobic zone. A continuous flow operation mode of bottom-in and top-out is adopted. First, the anaerobic activated sludge and wastewater are mixed and then added to the anaerobic zone of the system body (1) to form an anaerobic activated sludge layer. Then, the aerobic activated sludge and wastewater are mixed and added to the aerobic zone of the system body (1) to form an aerobic activated sludge layer.

[0057] The wastewater to be treated is injected into the main body of the system (1) in a continuous flow manner in an upstream manner to enhance the complete denitrification process and the methane oxidation process.

[0058] In some specific embodiments, during the enhanced complete denitrification process, the gradient distribution of Cu(II)-loaded sludge biochar and the setting of hydraulic load are as follows: in the aerobic zone (4), the volume ratio of Cu(II)-loaded sludge biochar is 15-20%, so that Cu(II) is released into the water body with the water flow and maintained at 48-64 μg / L, activating the methane monooxygenase of methanotrophic bacteria; in the transition zone (3), the volume ratio of Cu(II)-loaded sludge biochar is 25-30%, so that Cu(II) is maintained at 80-96 μg / L, and the activity of N2O reductase is simultaneously improved; the hydraulic retention time is 24-72 h, and the dissolved oxygen levels in the aerobic zone (4) and the transition zone (3) are maintained at 1.5-2.0 mg / L and 1.0-1.5 mg / L, respectively.

[0059] In some specific embodiments, during the methane oxidation process, the volume ratio of Cu(II)-loaded sludge biochar and the hydraulic load are set as follows: the volume ratio of Cu(II)-loaded sludge biochar in the anaerobic zone (2) is 5-10%, so that Cu(II) is slowly released with the water flow and maintained at less than 15 μg / L, the hydraulic retention time is 24 to 72 hours, and the dissolved oxygen concentration in the bottom layer is maintained at a level of <0.5 mg / L, thereby inhibiting the activity of methanogens.

[0060] The following is further described through specific examples.

[0061] Example 1

[0062] like Figure 1As shown, this embodiment discloses a constructed wetland system for synergistic CH4 and N2O emission reduction based on Cu(II) gradient regulation. The system includes a system body 1, which is a cylindrical cavity with an open top and a closed bottom. The system body is 300 mm tall and 140 mm in diameter, with a cylindrical volume of approximately 4.62 L and an effective volume of approximately 1.74 L. The system body is made of organic glass and is wrapped with tin-platinum foil to prevent algae growth. Along the height direction of the system body, a bottom anaerobic zone 2, a middle transition zone 3, and an upper aerobic zone 4 are stacked within the system body, wherein the height ratio of the bottom anaerobic zone 2, the middle transition zone 3, and the upper aerobic zone 4 is 1:1:1.

[0063] The anaerobic zone 2 is the first gravel layer, which is filled with gravel and Cu(Ⅱ)-loaded sludge biochar, wherein the Cu(Ⅱ)-loaded sludge biochar is evenly distributed in the first gravel layer at a volume ratio of 8%, that is, the volume ratio of Cu(Ⅱ)-loaded sludge biochar to gravel is 8:92; the transition zone 3 is the second gravel layer, which is filled with gravel and Cu(Ⅱ)-loaded sludge biochar, wherein the Cu(Ⅱ)-loaded sludge biochar is evenly distributed in the second gravel layer at a volume ratio of 27%, that is, the volume ratio of Cu(Ⅱ)-loaded sludge biochar to gravel is 27:73; the aerobic zone 4 is the third gravel layer, which is filled with gravel and Cu(Ⅱ)-loaded sludge biochar, wherein the Cu(Ⅱ)-loaded sludge biochar is evenly distributed in the third gravel layer at a volume ratio of 18%, that is, the volume ratio of Cu(Ⅱ)-loaded sludge biochar to gravel is 18:82.

[0064] The gravel particle size of the first gravel layer is 20-40 mm, the gravel particle size of the second gravel layer and the third gravel layer is 8-15 mm, and the particle size of the Cu(Ⅱ) loaded sludge biochar is 8-15 mm.

[0065] The artificial wetland system of this embodiment further includes: a water distribution tank 5, which is connected to the bottom end of the system body 1 through a water inlet pipe 6, and a power device 7 is provided on the water inlet pipe 6;

[0066] Wetland plants 8 are arranged at the top of the system body 1. The top side wall of the system body 1 is provided with a wastewater outlet, and the bottom side wall is provided with a wastewater inlet. The wastewater inlet is connected to the water inlet pipe 6 through an inlet valve, and an outlet valve is provided on the water outlet;

[0067] The monitoring pipe 9 has its lower end disposed in the system body 1 and its upper end partially passing through the wetland plants 8 .

[0068] The preparation method of Cu(II)-loaded sludge biochar in this embodiment is as follows:

[0069] The residual sludge with a moisture content of 90% from the wastewater plant was used as the matrix, and was immersed in a 0.6 g / L copper sulfate solution at a mass ratio of 1:1. It was stirred with a paddle mechanical stirrer at a speed of 100 rpm and room temperature for 24 hours. After air-drying and shaping, it was pyrolyzed at 700°C for 2 hours to obtain Cu(Ⅱ)-loaded sludge biochar with a Cu(Ⅱ) loading mass fraction of 0.2%.

[0070] Figure 2 This is a scanning electron microscope image of the Cu(II)-loaded sludge biochar prepared in Example 1 of the present invention. Figure 3 This is the Cu element mapping diagram of Cu(Ⅱ) loaded sludge biochar. It can be seen that the Cu element is densely distributed in the sludge biochar; Figure 4 This is the metal element spectrum of Cu(Ⅱ) loaded sludge biochar. It can be seen from the figure that the Cu(Ⅱ) loading mass fraction is 0.2%.

[0071] This embodiment utilizes the Cu(II)-loaded sludge biochar constructed wetland system to perform a method for synergistic reduction of CH4 and N2O emissions, while simultaneously enhancing the complete denitrification process and methane oxidation process, including the following steps:

[0072] Sludge from a wastewater aeration tank is used as bacterial strain in the aerobic zone, and is domesticated to obtain aerobic activated sludge. Sludge from a wastewater upflow anaerobic sludge bed is used as bacterial strain in the anaerobic zone, and is domesticated to obtain anaerobic activated sludge.

[0073] The system body 1 is provided with an anaerobic zone, a transition zone and an aerobic zone. Along the height direction of the system body (1), the anaerobic zone is located below the transition zone, and the transition zone is located at the lower end of the aerobic zone. A continuous flow operation mode of bottom-in and top-out is adopted. First, the anaerobic activated sludge and wastewater are mixed and then added to the anaerobic zone of the system body 1 to form an anaerobic activated sludge layer. Then, the aerobic activated sludge and wastewater are mixed and added to the aerobic zone of the system body 1 to form an aerobic activated sludge layer.

[0074] The wastewater to be treated is injected into the main body of the system 1 by adopting the continuous flow mode of the above upstream flow to strengthen the complete denitrification process and methane oxidation process. The hydraulic retention time is 72h and the hydraulic load is 36.4L / (m 2 d) Strengthening the complete denitrification process and methane oxidation process. In the aerobic zone (4), Cu(II) was loaded with sludge biochar at an 18% volume ratio, allowing Cu(II) to be released into the water body with the water flow and maintained at 58μg / L, activating the methane monooxygenase of methanotrophic bacteria. In the transition zone (3), Cu(II) was loaded with sludge biochar at a 27% volume ratio, maintaining Cu(II) at 90μg / L and simultaneously improving the activity of N2O reductase. The dissolved oxygen levels in the aerobic zone (4) and transition zone (3) were maintained at approximately 1.7mg / L and 1.2mg / L, respectively.

[0075] In the anaerobic zone (2), the Cu(II)-loaded sludge biochar with a volume ratio of 8% causes the Cu(II) to be released slowly with the water flow and maintained at about 9 μg / L, and the dissolved oxygen concentration in the bottom layer is maintained at a level of <0.5 mg / L, thereby inhibiting the activity of methanogens.

[0076] Wastewater quality: COD 302mg / L, NH4 + -N 36mg / L, TN 37mg / L, PO4 3- -P 5mg / L.

[0077] Emission Reduction Effect: The system operated stably for 80 days, and its pollutant removal and greenhouse gas reduction effects remained stable. The pollutant removal efficiencies are shown in Table 1, demonstrating that the constructed wetland system achieved a high simultaneous nitrogen and phosphorus removal rate. More importantly, the gradient distribution of Cu(II)-loaded sludge biochar throughout the system promoted complete nitrification and denitrification, significantly reducing the average CH4 flux while simultaneously reducing N2O emissions.

[0078] Table 1 Pollutant treatment efficiency of the artificial wetland system in Example 1 of the present invention

[0079]

[0080] Example 2

[0081] like Figure 1 As shown, this embodiment discloses a constructed wetland system for synergistic CH4 and N2O emission reduction based on Cu(II) gradient regulation. The system includes a system body 1, which is a cylindrical cavity with an open top and a closed bottom. The system body is 300 mm tall and 140 mm in diameter, with a cylindrical volume of approximately 4.62 L and an effective volume of approximately 1.74 L. The system body is made of organic glass and is wrapped with tin-platinum foil to prevent algae growth. Along the height direction of the system body, a bottom anaerobic zone 2, a middle transition zone 3, and an upper aerobic zone 4 are stacked within the system body, wherein the height ratio of the bottom anaerobic zone 2, the middle transition zone 3, and the upper aerobic zone 4 is 1:1:1.

[0082] The anaerobic zone 2 is the first gravel layer, which is filled with gravel and Cu(Ⅱ)-loaded sludge biochar, wherein the Cu(Ⅱ)-loaded sludge biochar is evenly distributed in the first gravel layer at a volume ratio of 5%, that is, the volume ratio of Cu(Ⅱ)-loaded sludge biochar to gravel is 5:95; the transition zone 3 is the second gravel layer, which is filled with gravel and Cu(Ⅱ)-loaded sludge biochar, wherein the Cu(Ⅱ)-loaded sludge biochar is evenly distributed in the second gravel layer at a volume ratio of 25%, that is, the volume ratio of Cu(Ⅱ)-loaded sludge biochar to gravel is 25:75; the aerobic zone 4 is the third gravel layer, which is filled with gravel and Cu(Ⅱ)-loaded sludge biochar, wherein the Cu(Ⅱ)-loaded sludge biochar is evenly distributed in the third gravel layer at a volume ratio of 15%, that is, the volume ratio of Cu(Ⅱ)-loaded sludge biochar to gravel is 15:85.

[0083] The gravel particle size of the first gravel layer is 20-40 mm, the gravel particle size of the second gravel layer and the third gravel layer is 8-15 mm, and the particle size of the Cu(Ⅱ) loaded sludge biochar is 8-15 mm.

[0084] The artificial wetland system of this embodiment further comprises: a water distribution tank 5 connected to the bottom end of the system body 1 via a water inlet pipe 6, wherein the water inlet pipe 6 is provided with a power mechanism 7;

[0085] Wetland plants 8 are arranged at the top of the system body 1. The top side wall of the system body 1 is provided with a wastewater outlet, and the bottom side wall is provided with a wastewater inlet. The wastewater inlet is connected to the water inlet pipe 6 through an inlet valve, and an outlet valve is provided on the water outlet;

[0086] The monitoring pipe 9 has its lower end disposed in the system body 1 and its upper end partially passing through the wetland plants 8 .

[0087] The preparation method of Cu(II)-loaded sludge biochar in this embodiment is as follows:

[0088] The residual sludge with a moisture content of 90% from the wastewater plant was used as the matrix, and was immersed in a 0.6 g / L copper sulfate solution at a mass ratio of 1:1. It was stirred with a paddle mechanical stirrer at a speed of 100 rpm and room temperature for 24 hours. After air-drying and shaping, it was pyrolyzed at 900°C for 2 hours to obtain Cu(Ⅱ)-loaded sludge biochar with a Cu(Ⅱ) loading mass fraction of 0.3%.

[0089] This embodiment utilizes the Cu(II)-loaded sludge biochar constructed wetland system to perform a method for synergistic reduction of CH4 and N2O emissions, while simultaneously enhancing the complete denitrification process and methane oxidation process, including the following steps:

[0090] Sludge from a wastewater aeration tank is used as bacterial strain in the aerobic zone, and is domesticated to obtain aerobic activated sludge. Sludge from a wastewater upflow anaerobic sludge bed is used as bacterial strain in the anaerobic zone, and is domesticated to obtain anaerobic activated sludge.

[0091] The system body 1 is provided with an anaerobic zone, a transition zone and an aerobic zone. Along the height direction of the system body (1), the anaerobic zone is located below the transition zone, and the transition zone is located at the lower end of the aerobic zone. A continuous flow operation mode of bottom-in and top-out is adopted. First, the anaerobic activated sludge and wastewater are mixed and then added to the anaerobic zone of the system body 1 to form an anaerobic activated sludge layer. Then, the aerobic activated sludge and wastewater are mixed and added to the aerobic zone of the system body 1 to form an aerobic activated sludge layer.

[0092] The wastewater to be treated is injected into the main body of the system 1 by adopting the continuous flow mode of the above upstream flow to strengthen the complete denitrification process and methane oxidation process. The hydraulic retention time is 72h and the hydraulic load is 36.4L / (m 2 d) Strengthening the complete denitrification process and methane oxidation process. In the aerobic zone (4), Cu(II) was loaded with sludge biochar at a volume ratio of 15%, so that Cu(II) was released into the water body with the water flow and maintained at 49μg / L, activating the methane monooxygenase of methanotrophic bacteria. In the transition zone (3), Cu(II) was loaded with sludge biochar at a volume ratio of 25%, so that Cu(II) was maintained at 82μg / L, and the activity of N2O reductase was simultaneously improved. The dissolved oxygen levels in the aerobic zone (4) and the transition zone (3) were maintained at approximately 1.5mg / L and 1.0mg / L, respectively.

[0093] In the anaerobic zone (2), the Cu(II)-loaded sludge biochar with a volume ratio of 5% causes the Cu(II) to be released slowly with the water flow and maintained at about 7 μg / L, and the dissolved oxygen concentration in the bottom layer is maintained at a level of <0.5 mg / L, thereby inhibiting the activity of methanogens.

[0094] Example 3

[0095] like Figure 1 As shown, this embodiment discloses a constructed wetland system for synergistic CH4 and N2O emission reduction based on Cu(II) gradient regulation. The system includes a system body 1, which is a cylindrical cavity with an open top and a closed bottom. The system body is 300 mm tall and 140 mm in diameter, with a cylindrical volume of approximately 4.62 L and an effective volume of approximately 1.74 L. The system body is made of organic glass and is wrapped with tin-platinum foil to prevent algae growth. Along the height direction of the system body, a bottom anaerobic zone 2, a middle transition zone 3, and an upper aerobic zone 4 are stacked within the system body, wherein the height ratio of the bottom anaerobic zone 2, the middle transition zone 3, and the upper aerobic zone 4 is 1:1:1.

[0096] The anaerobic zone 2 is the first gravel layer, which is filled with gravel and Cu(II)-loaded sludge biochar, wherein the Cu(II)-loaded sludge biochar is evenly distributed in the first gravel layer at a volume ratio of 10%, that is, the volume ratio of Cu(II)-loaded sludge biochar to gravel is 10:90; the transition zone 3 is the second gravel layer, which is filled with gravel and Cu(II)-loaded sludge biochar, wherein the Cu(II)-loaded sludge biochar is evenly distributed in the second gravel layer at a volume ratio of 30%, that is, the volume ratio of Cu(II)-loaded sludge biochar to gravel is 30:70; the aerobic zone 4 is the third gravel layer, which is filled with gravel and Cu(II)-loaded sludge biochar, wherein the Cu(II)-loaded sludge biochar is evenly distributed in the third gravel layer at a volume ratio of 20%, that is, the volume ratio of Cu(II)-loaded sludge biochar to gravel is 20:80.

[0097] The gravel particle size of the first gravel layer is 20-40 mm, the gravel particle size of the second gravel layer and the third gravel layer is 8-15 mm, and the particle size of the Cu(Ⅱ) loaded sludge biochar is 8-15 mm.

[0098] The artificial wetland system of this embodiment further comprises: a water distribution tank 5 connected to the bottom end of the system body 1 via a water inlet pipe 6, wherein the water inlet pipe 6 is provided with a power mechanism 7;

[0099] Wetland plants 8 are arranged at the top of the system body 1. The top side wall of the system body 1 is provided with a wastewater outlet, and the bottom side wall is provided with a wastewater inlet. The wastewater inlet is connected to the water inlet pipe 6 through an inlet valve, and an outlet valve is provided on the water outlet;

[0100] The monitoring pipe 9 has its lower end disposed in the system body 1 and its upper end partially passing through the wetland plants 8 .

[0101] The preparation method of Cu(II)-loaded sludge biochar in this embodiment is as follows:

[0102] The residual sludge with a moisture content of 90% from the wastewater plant was used as the matrix, and was immersed in a 0.6 g / L copper sulfate solution at a mass ratio of 1:1. It was stirred with a paddle mechanical stirrer at a speed of 100 rpm and room temperature for 24 hours. After air-drying and shaping, it was pyrolyzed at 800°C for 2 hours to obtain Cu(Ⅱ)-loaded sludge biochar with a Cu(Ⅱ) loading mass fraction of 0.25%.

[0103] This embodiment utilizes the Cu(II)-loaded sludge biochar constructed wetland system to perform a method for synergistic reduction of CH4 and N2O emissions, while simultaneously enhancing the complete denitrification process and methane oxidation process, including the following steps:

[0104] Sludge from a wastewater aeration tank is used as bacterial strain in the aerobic zone, and is domesticated to obtain aerobic activated sludge. Sludge from a wastewater upflow anaerobic sludge bed is used as bacterial strain in the anaerobic zone, and is domesticated to obtain anaerobic activated sludge.

[0105] The system body 1 is provided with an anaerobic zone, a transition zone and an aerobic zone. Along the height direction of the system body (1), the anaerobic zone is located below the transition zone, and the transition zone is located at the lower end of the aerobic zone. A continuous flow operation mode of bottom-in and top-out is adopted. First, the anaerobic activated sludge and wastewater are mixed and then added to the anaerobic zone of the system body 1 to form an anaerobic activated sludge layer. Then, the aerobic activated sludge and wastewater are mixed and added to the aerobic zone of the system body 1 to form an aerobic activated sludge layer.

[0106] The wastewater to be treated is injected into the main body of the system 1 by adopting the continuous flow mode of the above upstream flow to strengthen the complete denitrification process and methane oxidation process. The hydraulic retention time is 72h and the hydraulic load is 36.4L / (m 2 d) Strengthening the complete denitrification process and methane oxidation process. In the aerobic zone (4), Cu(II) was loaded with sludge biochar at a volume ratio of 20%, so that Cu(II) was released into the water body with the water flow and maintained at 62μg / L, activating the methane monooxygenase of methanotrophic bacteria. In the transition zone (3), Cu(II) was loaded with sludge biochar at a volume ratio of 30%, so that Cu(II) was maintained at 95μg / L, and the activity of N2O reductase was simultaneously improved. The dissolved oxygen levels in the aerobic zone (4) and the transition zone (3) were maintained at approximately 1.5mg / L and 1.0mg / L, respectively.

[0107] In the anaerobic zone (2), the Cu(II)-loaded sludge biochar with a volume ratio of 10% causes the Cu(II) to be released slowly with the water flow and maintained at about 14 μg / L, and the dissolved oxygen concentration in the bottom layer is maintained at a level of <0.5 mg / L, thereby inhibiting the activity of methanogens.

[0108] Comparative Example 1

[0109] Comparative Example 1 is a sludge biochar constructed wetland system without a Cu(II) gradient, comprising a system body 1, which is a cylindrical cavity with an open top and a closed bottom. The system body has a height of 300 mm and a diameter of 140 mm, a cylindrical volume of approximately 4.62 L, and an effective volume of approximately 1.74 L. The system body is made of organic glass and wrapped with tin foil to prevent algae growth. A bottom anaerobic zone 2, a middle transition zone 3, and an upper aerobic zone 4 are stacked within the system body along its height, with the height ratio of the bottom anaerobic zone 2, the middle transition zone 3, and the upper aerobic zone 4 being 1:1:1.

[0110] Anaerobic zone 2 consisted of the first gravel layer, transition zone 3 consisted of the second gravel layer, and aerobic zone 4 consisted of the third gravel layer. The first, second, and third gravel layers were filled with gravel and Cu(II)-loaded sludge biochar. The Cu(II)-loaded sludge biochar was evenly distributed throughout the gravel layers at a volume ratio of 27%, meaning the Cu(II)-loaded sludge biochar and gravel were arranged in a volume ratio of 27:73. The gravel particle size in the first gravel layer ranged from 20 to 40 mm, while the gravel particle sizes in the second and third gravel layers ranged from 8 to 15 mm. The Cu(II)-loaded sludge biochar had a particle size of 8 to 15 mm.

[0111] The artificial wetland system of this embodiment further comprises: a water distribution tank 5 connected to the bottom end of the system body 1 via a water inlet pipe 6, wherein the water inlet pipe 6 is provided with a power mechanism 7;

[0112] Wetland plants 8 are arranged at the top of the system body 1. The top side wall of the system body 1 is provided with a wastewater outlet, and the bottom side wall is provided with a wastewater inlet. The wastewater inlet is connected to the water inlet pipe 6 through an inlet valve, and an outlet valve is provided on the water outlet;

[0113] The monitoring pipe 9 has its lower end disposed in the system body 1 and its upper end partially passing through the wetland plants 8 .

[0114] The preparation method of Cu(II)-loaded sludge biochar in this comparative example is as follows:

[0115] The residual sludge with a moisture content of 90% from the wastewater plant was used as the matrix, and was immersed in a 0.6 g / L copper sulfate solution at a mass ratio of 1:1. It was stirred with a paddle mechanical stirrer at a speed of 100 rpm and room temperature for 24 hours. After air-drying and shaping, it was pyrolyzed at 700°C for 2 hours to obtain Cu(Ⅱ)-loaded sludge biochar with a Cu(Ⅱ) loading mass fraction of 0.2%.

[0116] The method for synergistically reducing CH4 and N2O emissions using the Cu(II)-loaded sludge biochar constructed wetland system described above, while simultaneously enhancing the complete denitrification process and methane oxidation process, includes the following steps:

[0117] Sludge from a wastewater aeration tank is used as bacterial strain in the aerobic zone, and is domesticated to obtain aerobic activated sludge. Sludge from a wastewater upflow anaerobic sludge bed is used as bacterial strain in the anaerobic zone, and is domesticated to obtain anaerobic activated sludge.

[0118] The system body 1 is provided with an anaerobic zone, a transition zone and an aerobic zone. Along the height direction of the system body (1), the anaerobic zone is located below the transition zone, and the transition zone is located at the lower end of the aerobic zone. A continuous flow operation mode of bottom-in and top-out is adopted. First, the anaerobic activated sludge and wastewater are mixed and then added to the anaerobic zone of the system body 1 to form an anaerobic activated sludge layer. Then, the aerobic activated sludge and wastewater are mixed and added to the aerobic zone of the system body 1 to form an aerobic activated sludge layer.

[0119] The wastewater to be treated is injected into the main body of the system 1 by adopting the continuous flow mode of the above upstream flow to strengthen the complete denitrification process and methane oxidation process. The hydraulic retention time is 72h and the hydraulic load is 36.4L / (m 2 d). The volume ratio of Cu(Ⅱ)-loaded sludge biochar in the aerobic zone (4), transition zone (3), and anaerobic zone (2) was 27%. Although the dissolved oxygen levels were different, namely 2.0 mg / L, 1.7 mg / L, and 0.9 mg / L, respectively, since the volume ratio of Cu(Ⅱ)-loaded biochar did not change in each zone, the concentration of Cu(Ⅱ) released into the water body with the water flow was maintained at 89-91 μg / L, with no obvious gradient difference between the zones.

[0120] Wastewater quality: COD 302mg / L, NH4 + -N 36mg / L, TN 37mg / L, PO4 3- -P 5mg / L. The CH4 and N2O emission effects are shown in Table 2.

[0121] Comparative Example 2

[0122] Comparative Example 1 presents a sludge biochar constructed wetland system with two Cu(II) gradients. The system comprises a main body 1, which is a cylindrical chamber with an open top and a closed bottom. The main body is 300 mm tall and 140 mm in diameter, with a cylindrical volume of approximately 4.62 L and an effective volume of approximately 1.74 L. The main body is constructed of plexiglass and wrapped with tin foil to prevent algae growth. A lower anaerobic zone, a middle transition zone, and an upper aerobic zone are arranged along the main body's height. The height ratio of the lower anaerobic zone, the middle transition zone, and the upper aerobic zone is 1:1:1.

[0123] The anaerobic zone is filled with gravel and Cu(Ⅱ)-loaded sludge biochar, in which the Cu(Ⅱ)-loaded sludge biochar is evenly distributed in the gravel layer at a volume ratio of 8%, that is, the Cu(Ⅱ)-loaded sludge biochar and gravel are arranged at a volume ratio of 8:92, and the gravel particle size in the anaerobic zone is 20-40 mm. The transition zone is filled with gravel and Cu(Ⅱ)-loaded sludge biochar, in which the Cu(Ⅱ)-loaded sludge biochar is evenly distributed in the gravel layer at a volume ratio of 27%, that is, the Cu(Ⅱ)-loaded sludge biochar and gravel are arranged at a volume ratio of 27:73, and the gravel particle size in the aerobic zone is 8-15 mm; the aerobic zone is filled with gravel and Cu(Ⅱ)-loaded sludge biochar, in which the Cu(Ⅱ)-loaded sludge biochar is evenly distributed in the gravel layer at a volume ratio of 27%, that is, the Cu(Ⅱ)-loaded sludge biochar and gravel are arranged at a volume ratio of 27:73, and the gravel particle size in the aerobic zone is 8-15 mm; the particle size of Cu(Ⅱ)-loaded sludge biochar is 8-15 mm.

[0124] The artificial wetland system of this embodiment further comprises: a water distribution tank 5 connected to the bottom end of the system body 1 via a water inlet pipe 6, wherein the water inlet pipe 6 is provided with a power mechanism 7;

[0125] Wetland plants 8 are arranged at the top of the system body 1. The top side wall of the system body 1 is provided with a wastewater outlet, and the bottom side wall is provided with a wastewater inlet. The wastewater inlet is connected to the water inlet pipe 6 through an inlet valve, and an outlet valve is provided on the water outlet;

[0126] The monitoring pipe 9 has its lower end disposed in the system body 1 and its upper end partially passing through the wetland plants 8 .

[0127] The preparation method of Cu(II)-loaded sludge biochar in this comparative example is as follows:

[0128] The residual sludge with a moisture content of 90% from the wastewater plant was used as the matrix, and was immersed in a 0.6 g / L copper sulfate solution at a mass ratio of 1:1. It was stirred with a paddle mechanical stirrer at a speed of 100 rpm and room temperature for 24 hours. After air-drying and shaping, it was pyrolyzed at 700°C for 2 hours to obtain Cu(Ⅱ)-loaded sludge biochar with a Cu(Ⅱ) loading mass fraction of 0.2%.

[0129] The method for synergistically reducing CH4 and N2O emissions using the Cu(II)-loaded sludge biochar constructed wetland system described above, while simultaneously enhancing the complete denitrification process and methane oxidation process, includes the following steps:

[0130] Sludge from a wastewater aeration tank is used as bacterial strain in the aerobic zone, and is domesticated to obtain aerobic activated sludge. Sludge from a wastewater upflow anaerobic sludge bed is used as bacterial strain in the anaerobic zone, and is domesticated to obtain anaerobic activated sludge.

[0131] The system body 1 is provided with an upper aerobic zone, a middle transition zone and a lower anaerobic zone. Along the height direction of the system body (1), a continuous flow operation mode of bottom-in and top-out is adopted. First, the anaerobic activated sludge and wastewater are mixed and then added to the anaerobic zone of the system body 1 to form an anaerobic activated sludge layer. Then, the aerobic activated sludge and wastewater are mixed and added to the aerobic zone of the system body 1 to form an aerobic activated sludge layer.

[0132] The wastewater to be treated is injected into the main body of the system 1 by adopting the continuous flow mode of the above upstream flow to strengthen the complete denitrification process and methane oxidation process. The hydraulic retention time is 72h and the hydraulic load is 36.4L / (m 2d). In the upper layers (aerobic and transition zones), the Cu(II)-loaded sludge biochar volume ratio was 27%, and the dissolved oxygen level was 1.9 mg / L. However, due to the same volume ratio of Cu(II)-loaded biochar, the concentration of Cu(II) released into the water with the flow was maintained at 85-90 μg / L. In the lower layer (anaerobic zone), the Cu(II)-loaded sludge biochar volume ratio was 8%, the dissolved oxygen concentration was maintained at 0.6 mg / L, and Cu(II) was released into the water with the flow and maintained at 6-20 μg / L.

[0133] Wastewater quality: COD 302mg / L, NH4 + -N 36mg / L, TN 37mg / L, PO4 3- -P 5mg / L. The CH4 and N2O emission effects are shown in Table 2.

[0134] Table 2 Comparison of CH4 and N2O emissions from sludge biochar constructed wetland systems in Example 1 and Comparative Examples 1-2

[0135]

[0136] As can be seen from Table 2, the present invention achieves a synergistic reduction in emissions of two greenhouse gases, and the effect is significant. Since the Cu(II)-loaded sludge biochar in the comparative example 1 system is evenly distributed in the upper, middle, and lower layers, and the aerobic and anaerobic zones have a higher proportion of sludge biochar, the Cu(II) concentration is high, maintained at 89-91 μg / L. This range inhibits the monooxygenase activity of methanotrophic bacteria, thereby ultimately making the methane emission flux higher than that of the embodiment. In addition, the evenly distributed biochar provides the system with a lower dissolved oxygen difference, making it impossible for the transition zone to create the anaerobic environment required for a complete denitrification reaction, thereby significantly increasing the N2O emission energy.

[0137] Comparative Example 2 is a sludge biochar artificial wetland system with two Cu(II) gradients. The system has exactly the same volume ratio and influent concentration as the Cu(II)-loaded sludge biochar of the present invention, but the system only has two Cu(II) concentration gradients. Although the nitrification and denitrification processes can be carried out more fully and a better N2O emission flux can be achieved, the Cu(II) concentration in the aerobic zone and the transition zone is relatively high, maintained at 85-90 μg / L. This concentration range has a significant inhibitory effect on the monooxygenase activity of methanotrophic bacteria in the water treatment system, and cannot effectively oxidize the methane produced in the anaerobic zone, thereby causing the methane emission flux to be higher than that of the embodiment.

[0138] It should be noted that when numerical ranges are mentioned in the present invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints may be selected. Since the steps and methods used are the same as those in the embodiments, in order to avoid redundancy, the present invention describes preferred embodiments. Although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they understand the basic inventive concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0139] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A constructed wetland system for synergistic reduction of CH4 and N2O emissions based on Cu(II) gradient regulation, characterized in that: The system comprises a main body (1), the top of the main body (1) is open and the bottom is closed, and the main body (1) is composed of an anaerobic zone (2), a transition zone (3) and an aerobic zone (4) from bottom to top; the anaerobic zone (2), the transition zone (3) and the aerobic zone (4) are filled with gravel and Cu (II)-loaded sludge biochar, wherein the volume proportion of the Cu (II)-loaded sludge biochar is the largest in the transition zone (3), the second largest in the aerobic zone (4), and the smallest in the anaerobic zone (2).

2. The constructed wetland system for synergistic reduction of CH4 and N2O emissions based on Cu(II) gradient regulation according to claim 1, characterized in that: The anaerobic zone (2) is the first gravel layer, which is filled with gravel and Cu (II) loaded sludge biochar, wherein the Cu (II) loaded sludge biochar is evenly distributed in the first gravel layer at a volume ratio of 5-10%; the transition zone (3) is the second gravel layer, which is filled with gravel and Cu (II) loaded sludge biochar, wherein the Cu (II) loaded sludge biochar is evenly distributed in the second gravel layer at a volume ratio of 25-30%; the aerobic zone (4) is the third gravel layer, which is filled with gravel and Cu (II) loaded sludge biochar, wherein the Cu (II) loaded sludge biochar is evenly distributed in the third gravel layer at a volume ratio of 15-20%.

3. The constructed wetland system for synergistic reduction of CH4 and N2O emissions based on Cu(II) gradient regulation according to claim 2, characterized in that: The particle size of the Cu (II) loaded sludge organisms is 8-15 mm, the particle size of the first gravel layer is 20-40 mm, and the particle sizes of the second gravel layer and the third gravel layer are 8-15 mm.

4. The artificial wetland system for synergistic reduction of CH4 and N2O emissions based on Cu(II) gradient regulation according to any one of claims 1-3, characterized in that: The method for preparing Cu(II)-loaded sludge biochar comprises the following steps: The residual sludge from a wastewater plant was used as the matrix, immersed in a copper sulfate solution, stirred, air-dried, shaped, and pyrolyzed under a protective gas atmosphere to obtain Cu (II)-loaded sludge biochar, with a Cu (II) loading mass fraction of 0.2-0.3%.

5. The constructed wetland system for synergistic reduction of CH4 and N2O emissions based on Cu(II) gradient regulation according to claim 4, characterized in that: The water content of the residual sludge is 90%, the mass ratio of the residual sludge to the copper sulfate solution is 1:1, the concentration of the copper sulfate solution is 0.6-0.7 g / L, and the paddle-type mechanical stirrer is used at a speed of 90-110 rpm at room temperature for 15-28 h.

6. The constructed wetland system for synergistic reduction of CH4 and N2O emissions based on Cu(II) gradient regulation according to claim 4, characterized in that: The protective gas is nitrogen or inert gas, the heating rate during the pyrolysis process is 8-12°C / min, the pyrolysis temperature is 600-900°C, and the pyrolysis time is 2.1-2.5 h.

7. The constructed wetland system for synergistic reduction of CH4 and N2O emissions based on Cu(II) gradient regulation according to claim 1, characterized in that: The artificial wetland system also includes: A water distribution tank (5) is connected to the bottom end of the system body (1) via a water inlet pipe (6), wherein a power mechanism (7) is provided on the water inlet pipe (6); A wetland plant (8) is provided at the top of the system body (1); a wastewater outlet is provided on the top side wall of the system body (1); a wastewater inlet is provided on the bottom side wall; the wastewater inlet is connected to the water inlet pipe (6) via an inlet valve; and an outlet valve is provided on the water outlet; a monitoring pipe (9) has its lower end provided in the system body (1) and its upper end partially passes through the wetland plant (8).

8. A method for synergistically reducing CH4 and N2O emissions, characterized in that: The method comprises the following steps: utilizing the Cu(II)-loaded sludge biochar artificial wetland system according to any one of claims 1 to 3 to simultaneously enhance the complete denitrification process and the methane oxidation process: Sludge from a wastewater aeration tank is used as bacterial strain in the aerobic zone, and is domesticated to obtain aerobic activated sludge. Sludge from a wastewater upflow anaerobic sludge bed is used as bacterial strain in the anaerobic zone, and is domesticated to obtain anaerobic activated sludge. The system body (1) is provided with an anaerobic zone, a transition zone and an aerobic zone. Along the height direction of the system body (1), the anaerobic zone is located below the transition zone, and the transition zone is located at the lower end of the aerobic zone. A bottom-in-top-out continuous flow operation mode is adopted. The anaerobic activated sludge and wastewater are first mixed and then added to the anaerobic zone of the system body (1) to form an anaerobic activated sludge layer. Then, the aerobic activated sludge and wastewater are mixed and added to the aerobic zone of the system body (1) to form an aerobic activated sludge layer. The wastewater to be treated is injected into the main body of the system (1) in a continuous flow manner in the upward flow, thereby enhancing the complete denitrification process and the methane oxidation process.

9. The method for synergistically reducing CH4 and N2O emissions according to claim 7, characterized in that: During the enhanced complete denitrification process, the gradient distribution of Cu (II)-loaded sludge biochar and the setting of hydraulic load were as follows: in the aerobic zone (4), the volume ratio of Cu (II)-loaded sludge biochar was 15-20%, so that Cu (II) was released into the water body with the water flow and maintained at 48-64 μg / L, activating the methane monooxygenase of methanotrophic bacteria; in the transition zone (3), the volume ratio of Cu (II)-loaded sludge biochar was 25-30%, so that Cu (II) was maintained at 80-96 μg / L, and the activity of N2O reductase was simultaneously improved; the hydraulic retention time was 24-72 h, and the dissolved oxygen levels in the aerobic zone (4) and the transition zone (3) were maintained at 1.5-2.0 mg / L and 1.0-1.5 mg / L, respectively.

10. The method for synergistically reducing CH4 and N2O emissions according to claim 7, characterized in that: During the methane oxidation process, the volume ratio of Cu (II) loaded sludge biochar and the hydraulic load were set as follows: in the anaerobic zone (2), the volume ratio of Cu (II) loaded sludge biochar was 5-10%, so that Cu (II) was released slowly with the water flow and maintained at <15 μg / L, the hydraulic retention time was 24-72 h, and the dissolved oxygen concentration was maintained at <0.5 mg / L, inhibiting the activity of methanogens.

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