Sludge carbon-based bioelectrochemical constructed wetland for enhancing sewage denitrification

Abstract

The invention provides a sludge carbon-based bioelectrochemical constructed wetland for enhancing sewage denitrification. The sludge carbon-based bioelectrochemical constructed wetland comprises a wetland reactor and a circuit connecting device, the wetland reactor comprises a wetland pool as well as a water distribution layer, a lower filter material layer, an anode layer, an upper filter material layer and a cathode layer which are sequentially arranged in the wetland pool from bottom to top; the circuit connecting device comprises a power supply device and an adjustable resistor electrically connected with the power supply device; the adjustable resistor is respectively and electrically connected with the anode layer and the cathode layer through conductive wires; wherein the anode layer and the cathode layer are sludge biochar coated by a conductive metal net; the adjustable resistor is electrically connected with the conductive metal nets in the anode layer and the cathode layer through conductive wires respectively; the bioelectrochemistry-constructed wetland is coupled with the sludge biochar, and the biocompatibility and catalytic characteristics of the sludge biochar are utilized, so that the diversity and activity of microorganisms in an anode region are effectively improved, and the reduction effect of a cathode region on anions is promoted, thereby improving the removal effect on total nitrogen.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and more specifically, to a sludge-based bioelectrochemical constructed wetland for enhanced wastewater denitrification. Background Technology

[0002] Using reclaimed water from wastewater treatment plants for replenishment is an effective way to solve the problem of water shortage. Constructed wetlands can purify wastewater, and their natural wastewater treatment process is environmentally friendly, easy to operate, and economical.

[0003] However, the low carbon / nitrogen ratio (C / N) in wastewater makes complete denitrification difficult to achieve during advanced treatment in constructed wetlands, leading to eutrophication of the receiving water body. Furthermore, wastewater treatment typically includes a final disinfection stage to control the spread of pathogens and ensure public health safety. Chlorine dioxide (ClO2), with its high bactericidal properties and low levels of disinfection byproducts (DBPs), has gradually become the preferred disinfectant for wastewater treatment systems. However, during disinfection, as the dosage of ClO2 increases, chlorate will be produced. and chlorite Byproducts.

[0004] and It can disrupt the cell membrane structure of microorganisms, induce oxidative stress by generating reactive oxygen species, and significantly inhibit microbial activity. Furthermore, With nitrite Similar chemical structures will affect the complete denitrification process, leading to incomplete nitrogen removal by constructed wetland microorganisms. Excessive accumulation will harm the environment. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a sludge-based bioelectrochemical constructed wetland that enhances wastewater denitrification, so as to solve the above problems.

[0006] The present invention adopts the following solution:

[0007] This application provides a sludge-based bioelectrochemical constructed wetland for enhanced wastewater denitrification, comprising a wetland reactor and a circuit connection device; the wetland reactor includes a wetland pool, and a water distribution layer, a lower filter layer, an anode layer, an upper filter layer, and a cathode layer arranged sequentially from bottom to top within the wetland pool; the circuit connection device includes a power supply device and an adjustable resistor electrically connected to the power supply device; the adjustable resistor is electrically connected to the anode layer and the cathode layer respectively through conductive wires;

[0008] The anode layer and the cathode layer are sludge biochar covered by a conductive metal mesh; the adjustable resistor is electrically connected to the conductive metal mesh in the anode layer and the cathode layer respectively through conductive wires; the bottom side of the water distribution layer is provided with an inlet pipe for wastewater to enter, and the top side of the cathode layer is provided with an outlet pipe.

[0009] Furthermore, the sludge biochar is obtained by recovering the residual sludge from the biological treatment tank, drying it at 105℃ for 24 hours to remove moisture, then crushing and screening it to a particle size of 2-5mm; after further screening, it is sealed with aluminum foil and placed in a muffle furnace, where the sludge is pyrolyzed for 2 hours in a nitrogen atmosphere and at a pyrolysis temperature of 600℃ at a heating rate of 10℃ / min; finally, after natural cooling, it is screened again to a particle size of 1-3mm, and then washed with pure water and soaked for 4 days to obtain the sludge biochar for use.

[0010] Furthermore, the wastewater is pretreated artificially prepared water, with specific concentrations including 40 mg / L COD, 15 mg / L total nitrogen, and 0.5-1 mg / L chlorite; the water intake is controlled by a water pump, and the hydraulic retention time is 3 days.

[0011] Furthermore, the adjustable resistor is set to a resistance of 1000Ω, and the power supply is set to a voltage of 0.1V.

[0012] Furthermore, the water distribution layer is formed by laying pebbles with a particle size of 40-60mm.

[0013] Furthermore, the lower filter layer is formed by laying gravel with a particle size of 2-4 mm.

[0014] Furthermore, the upper filter layer is formed by laying gravel with a particle size of 2-4 mm.

[0015] Furthermore, the wetland pool is a hollow cylinder with a height of 750 mm and a diameter of 180 mm; the total height of the water distribution layer is 100 mm; the total height of the lower filter layer is 200 mm; the total height of the anode layer is 100 mm; the total height of the upper filter layer is 200 mm; the total height of the cathode layer is 50 mm; and sampling pipes are provided on the upper side of the water distribution layer, the lower filter layer, the anode layer, and the upper filter layer.

[0016] Furthermore, the conductive metal mesh is a stainless steel mesh, and the connection between it and the conductive wire is wrapped with epoxy resin.

[0017] Furthermore, the wetland reactor is wrapped with aluminum foil.

[0018] By adopting the above technical solution, the present invention can achieve the following technical effects:

[0019] 1. By coupling bioelectrochemistry—constructed wetlands—with sludge biochar, the biocompatibility and catalytic properties of sludge biochar are utilized to effectively enhance microbial diversity and activity in the anodic region and promote anion absorption in the cathode region. The reducing effect enhances the removal of total nitrogen;

[0020] 2. Effective use of sludge biochar as an electrode matrix effectively recovers solid waste and realizes resource reuse;

[0021] 3. No additional aeration or carbon source is required, and only 0.1V of external power is needed to enhance total nitrogen removal under chlorite stress. It boasts advantages such as low initial investment cost, low operating cost, simple and easy operation, wide applicability, and environmental friendliness.

[0022] 4. By utilizing the surface properties of materials to improve the microbial community structure, expand denitrification pathways, enhance autotrophic denitrification and anaerobic ammonia oxidation processes, and improve the denitrification capacity of constructed wetlands for low C / N ratio wastewater under chlorite stress. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the structure of a sludge-based bioelectrochemical constructed wetland for enhanced wastewater denitrification according to an embodiment of the present invention;

[0025] Figure 2 These are actual photos of the sludge biochar used in the embodiments of the present invention;

[0026] Figure 3 The total nitrogen concentration in the effluent of Examples 1, 2, 3, 4, and 5 of this invention;

[0027] Figure 4 The effluent nitrate nitrogen concentrations in Examples 1, 2, 3, 4, and 5 of this invention;

[0028] Figure 5 The effluent nitrite nitrogen concentrations in Examples 1, 2, 3, 4, and 5 of this invention;

[0029] Figure 6 Cyclic voltammetry curves of sludge biochar and granular activated carbon, the electrode materials used in this invention;

[0030] Figure 7 The N1s spectrum of the X-ray energy spectrum of the electrode materials used in this invention, namely sludge biochar and granular activated carbon.

[0031] Figure 8 The Fe2p spectra of the X-ray energy spectra of sludge biochar and granular activated carbon used as electrode materials in this invention;

[0032] Figure 9 The horizontal distribution of microbial genera after the addition of chlorite in Examples 1, 2, 3, 4, and 5 of the present invention;

[0033] Icons: 1. Wetland pond; 2. Circuit connection device; 3. Water distribution layer; 4. Lower filter layer; 5. Anode layer; 6. Upper filter layer; 7. Cathode layer; 8. Conductive wire; 9. Adjustable resistor; 10. Power supply device; 11. Inlet pipe; 12. Pebbles; 13. Sampling pipe; 14. Gravel; 15. Sludge biochar; 16. Conductive metal mesh; 17. Outlet pipe; 18. Peristaltic pump. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to represent selected embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Example

[0036] Combination Figure 1 As shown, this embodiment provides a sludge-based bioelectrochemical constructed wetland for enhanced wastewater denitrification, comprising a wetland reactor and a circuit connection device 2; the wetland reactor includes a wetland pool 1, and, from bottom to top, a water distribution layer 3, a lower filter layer 4, an anode layer 5, an upper filter layer 6, and a cathode layer 7 arranged within the wetland pool 1; the circuit connection device 2 includes a power supply device 10 and an adjustable resistor electrically connected to the power supply device 10; the adjustable resistor is electrically connected to the anode layer 5 and the cathode layer 7 respectively via conductive lines 8;

[0037] The anode layer 5 and the cathode layer 7 are sludge biochar 15 covered by a conductive metal mesh 16; the adjustable resistor is electrically connected to the conductive metal mesh 16 in the anode layer 5 and the cathode layer 7 respectively through a conductive wire 8; the bottom side of the water distribution layer 3 is provided with an inlet pipe 11 for wastewater to enter, and the top side of the cathode layer 7 is provided with an outlet pipe 17.

[0038] In one feasible embodiment of this scheme, the wetland pool 1 is specifically a hollow cylinder with a height of 750mm and a diameter of 180mm. It should be noted that it only serves as a support structure and can have other shapes; this is not specifically limited here. This embodiment only describes a cylindrical wetland. In this embodiment, the total height of the water distribution layer 3 is 100mm, formed by laying pebbles 12 with a particle size of 40-60mm; the total height of the lower filter layer 4 is 200mm, formed by laying gravel 14 with a particle size of 2-4mm; the total height of the anode layer 5 is 100mm, formed by covering sludge biochar 15 with a particle size of 1-3mm with a conductive metal mesh 16; the total height of the upper filter layer 6 is 200mm, formed by laying gravel 14 with a particle size of 2-4mm; and the total height of the cathode layer 7 is 50mm, formed by covering sludge biochar 15 with a particle size of 1-3mm with a conductive metal mesh 16. The bottom side of the water distribution layer 3 is provided with an inlet pipe 11 with a diameter of 6mm for wastewater to enter, and the top side of the cathode layer 7 is provided with an outlet pipe 17 with a diameter of 6mm; and sampling pipes 13 with a diameter of 6mm are provided on the top side of the water distribution layer 3, the lower filter layer 4, the anode layer 5, and the upper filter layer 6.

[0039] Specifically, the sludge biochar 15 is prepared by the following method:

[0040] S1. Recover the remaining sludge from the biological treatment tank and dry it at 105℃ for 24 hours to remove moisture.

[0041] S2. Crush and screen the sludge until the particle size is 2-5mm;

[0042] S3. After screening, the sludge is sealed with aluminum foil and placed in a muffle furnace. The heating rate is 10℃ / min. The sludge is pyrolyzed under a nitrogen atmosphere at a temperature of 600℃ for 2 hours.

[0043] S4. After natural cooling, screen again to a particle size of 1-3mm.

[0044] S5. After washing and soaking in pure water for 4 days, the sludge biochar is prepared as 15.

[0045] like Figure 2 The prepared sludge biochar 15 shown is a black solid granular form.

[0046] After the sludge biochar 15 prepared by the above method is compacted, it is wrapped with the conductive metal mesh 16 and placed in the wetland pond 1. It is then electrically connected to the adjustable resistor via conductive wire 8. In this embodiment, the conductive metal mesh 16 is a stainless steel mesh with a 1mm aperture and a 0.5mm wire diameter. The conductive wire 8 is a conductive copper wire, and the connection between the conductive copper wire and the stainless steel mesh is wrapped with epoxy resin to prevent corrosion.

[0047] The sludge biochar 15 is a low-cost conductive material with good biocompatibility and oxygen reduction catalytic activity, effectively enhancing microbial diversity and activity in the anode region and promoting anion absorption in the cathode region. The reducing effect enhances the removal of total nitrogen. Sludge biochar 15 possesses advantages such as a rough surface, richer functional groups, suitable porosity, and high specific surface area, promoting higher biodiversity, slow-release carbon source, and providing good electronic conductivity, thereby facilitating the anaerobic heterotrophic denitrification process. Effectively utilizing sludge biochar 15 as an electrode matrix effectively recovers solid waste and achieves resource reuse.

[0048] In this embodiment, the wastewater is pretreated artificially prepared water with a specific concentration including 40 mg / L COD, 15 mg / L total nitrogen, and 0.5-1 mg / L chlorite. The water intake is controlled by a peristaltic pump 18, and the hydraulic retention time (HRT) is 3 days, which is the average reaction time of the artificially prepared water with microorganisms within the wetland reactor. An appropriate HRT ensures that the microorganisms fully purify the intake water. HRT = V / Q, where V is the effective volume of the reactor and Q is the influent flow rate. After determining the overall effective volume of the wetland reactor, adjusting the influent flow rate of the peristaltic pump 18 adjusts the hydraulic retention time.

[0049] The adjustable resistor 9 has an adjustable resistance value of 0.1-10000Ω; the power supply device 10 provides a stable DC voltage. In this embodiment, the adjustable resistor 9 is set to a resistance value of 1000Ω, and the power supply device 10 is set to a voltage of 0.1V. It requires no additional aeration or carbon source, and only needs an external power supply of 0.1V to enhance the removal of total nitrogen under chlorite stress. It has advantages such as low initial investment cost, low operating cost, simple and easy operation, wide applicability, and environmental friendliness.

[0050] Furthermore, in this embodiment, the wetland reactor is wrapped with aluminum foil to reduce external light exposure and algae growth.

[0051] The features and performance of this application (Example 1) will be further described in detail below with reference to other embodiments.

[0052] Example 2:

[0053] The main difference from Example 1 is that it lacks conductive copper wires connecting the cathode and anode, making it an open-circuit artificial wetland.

[0054] Example 3:

[0055] The main difference from Example 1 is that no external power source is provided; instead, it is a microbial fuel cell-constructed wetland.

[0056] Example 4:

[0057] The main difference from Example 1 is that the cathode and anode electrode materials are replaced with commercially available granular activated carbon of the same size.

[0058] Example 5:

[0059] The main difference from Example 1 is that the cathode and anode electrode materials are replaced with commercially available granular activated carbon of the same size, and no external power source is provided; it is a microbial fuel cell-constructed wetland.

[0060] like Figure 3 As shown, at 0 mg / L chlorite ( During the period, Example 1 (0.51±0.10 mg / L) and Example 4 (0.43±0.11 mg / L) showed the lowest average TN concentration (average total nitrogen content in the effluent). The average TN concentrations in the effluents of Examples 2, 3, and 5 were 2.82±0.19, 1.41±0.11, and 2.30±0.24 mg / L, respectively. At the 0.5 mg / L level, the average TN concentration in the effluent of all examples showed a slight increase. At the 1.0 mg / L level, the average TN concentration in the effluents of Examples 2, 3, and 5 increased significantly, with concentrations of 4.03±0.28, 2.61±0.14, and 3.29±0.22 mg / L, respectively. Example 4 (1.84±0.11 mg / L) showed a slight increase in the average TN concentration in the effluent. Example 1 (1.10±0.22 mg / L) had the lowest TN concentration in the effluent.

[0061] The above results indicate that the presence of chlorite negatively impacts the denitrification effect in each embodiment. Furthermore, Example 1 effectively reduces this negative impact, thus enabling normal denitrification.

[0062] like Figure 4As shown, the addition of chlorite did not significantly affect the removal of nitrate nitrogen (NO3-N) in the constructed wetland system. The average effluent concentration in Example 2 was 2.27 ± 0.19 mg / L, achieving an average removal rate of 82.63%; the average effluent concentration in Example 3 was 0.34 ± 0.07 mg / L, with a removal rate of 97.39%; the average effluent concentration in Example 1 was 0.24 ± 0.10 mg / L, corresponding to a removal rate as high as 98.16%; the average effluent concentration in Example 5 was 1.33 ± 0.14 mg / L, with a removal rate of 89.82%; and the average effluent concentration in Example 4 was 0.75 ± 0.11 mg / L, with a removal rate of 94.26%.

[0063] The above results indicate that all the examples performed well in nitrate nitrogen removal, with Example 1 showing the best overall removal effect. This is attributed to the fact that the micro-electric field can promote microbial activity and the excellent surface characteristics of sludge biochar 15.

[0064] like Figure 5 As shown, nitrite (NO2-N) is a toxic substance that can adversely affect the aquatic environment. No chlorite was added. The residual concentrations in all embodiments were low, ranging from 0.022 to 0.091 mg / L. Example 1 exhibited the lowest residual concentration, which is related to the ability of the bioelectrochemical wetland cathode region to reduce anions. After adding 0.5 mg / L, the residual concentrations in all embodiments increased, with the residual concentrations ranked as follows: Example 2 (1.28 ± 0.052 mg / L) > Example 5 (0.81 ± 0.013 mg / L) > Example 3 (0.58 ± 0.070 mg / L) > Example 4 (0.44 ± 0.022 mg / L) > Example 1 (0.15 ± 0.043 mg / L). Furthermore, under stress of 1.0 mg / L, the residues in each group of examples further increased, with the specific residue concentration ranking as follows: Example 2 (1.79±0.050 mg / L) > Example 5 (0.92±0.057 mg / L) > Example 3 (0.86±0.054 mg / L) > Example 4 (0.60±0.035 mg / L) > Example 1 (0.18±0.043 mg / L). The results indicate that... The removal of each embodiment was affected, with Example 1 showing less increase in residual concentration, indicating that it can effectively alleviate the stress effect.

[0065] like Figure 6As shown, cyclic voltammetry (CV) curves were performed on the electrode materials sludge biochar 15 and granular activated carbon used in each embodiment under an oxygen-saturated solution environment. The CV curve of sludge biochar 15 showed a significant reduction current as the potential changed, while granular activated carbon showed almost no reduction current. This indicates that sludge biochar 15 has higher oxygen reduction (ORR) catalytic activity than granular activated carbon. ORR is a key reaction in the cathode region of a bioelectrochemical wetland system; high ORR activity can accelerate the reaction rate, improve the energy conversion efficiency of the entire system, and increase electrical output. Higher ORR catalytic activity can effectively promote the growth of autotrophic denitrifying bacteria and effectively reduce anions. The above results indicate that sludge biochar 15, as the electrode in this example, can effectively promote the denitrification process under chlorite stress.

[0066] like Figure 7 As shown, X-ray photoelectron spectroscopy (XPS) can accurately determine the types, contents, and chemical states of elements on the material surface, providing important evidence for revealing the microstructure and properties of materials. The characteristic peaks of the N 1s spectrum were deconvolved into pyridine-N (398.1 eV), pyrrole-N (399.5 eV), and graphite-N (400.8 eV). The sludge biochar 15 material exhibits higher contents of pyridine-N and graphite-N. Pyridine-N and graphite-N play a crucial role in the oxygen reduction reaction (ORR), providing active sites and reducing mass transfer resistance. Pyridine-N accelerates the oxygen reduction process by weakening the OO bond, while graphite-N enhances electrocatalytic performance by increasing conductivity in the high-energy band region. These results indicate that the pyridine-N and graphite-N on the surface of sludge biochar 15 contribute to its high ORR catalytic activity.

[0067] like Figure 8 As shown, the X-ray photoelectron spectroscopy (XPS) Fe 2p spectra of the two electrode materials reveal the presence and formation of iron compounds on the surface of sludge biochar 15. Iron compounds play important catalytic roles in various chemical reactions, such as serving as electron donors for iron-autotrophic denitrifying bacteria, promoting the growth of energy-producing bacteria, and enhancing oxygen reduction catalytic activity. These results indicate that the surface Fe element of sludge biochar 15 can effectively promote microbial denitrification and bioelectrochemical processes.

[0068] like Figure 9As shown, Example 1 exhibits the highest abundance of dechlorinating bacteria (Dechloromonas, 18.10%), which can anaerobically degrade chlorite and synergistically promote nitrogen cycling with anaerobic ammonia oxidizing bacteria, indicating that Example 1 can more effectively alleviate chlorite stress. Furthermore, Example 1 shows the highest relative abundance of anaerobic ammonia oxidizing bacteria (Candidatus Brocadia, 7.86%) and autotrophic denitrifying bacteria (Hydrogenophaga, 6.18%). These results demonstrate that sludge biochar 15 and bioelectrochemical wetlands can be effectively coupled to enhance total nitrogen removal under chlorite stress through autotrophic denitrification and anaerobic ammonia oxidation processes.

[0069] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions that fall within the scope of the present invention are within the scope of protection of the present invention.

[0070] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0071] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0072] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0073] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

Claims

1. A sludge-based bioelectrochemical constructed wetland for enhanced wastewater denitrification, characterized in that, It includes a wetland reactor and an electrical connection device (2); the wetland reactor includes a wetland pool (1), and a water distribution layer (3), a lower filter layer (4), an anode layer (5), an upper filter layer (6), and a cathode layer (7) arranged sequentially from bottom to top in the wetland pool (1); the electrical connection device (2) includes a power supply device (10) and an adjustable resistor electrically connected to the power supply device (10); the adjustable resistor is electrically connected to the anode layer (5) and the cathode layer (7) respectively through a conductive wire (8); The anode layer (5) and the cathode layer (7) are sludge biochar (15) covered by a conductive metal mesh (16); the adjustable resistor is electrically connected to the conductive metal mesh (16) in the anode layer (5) and the cathode layer (7) respectively through a conductive wire (8); the bottom side of the water distribution layer (3) is provided with an inlet pipe (11) for wastewater to enter, and the top side of the cathode layer (7) is provided with an outlet pipe (17).

2. The sludge-based bioelectrochemical constructed wetland for enhanced wastewater denitrification according to claim 1, characterized in that, The sludge biochar (15) is made by recovering the residual sludge from the biological treatment tank, drying it at 105℃ for 24 hours to remove moisture, then crushing and screening it to a particle size of 2-5 mm, further screening it, sealing it with aluminum foil and placing it in a muffle furnace, using a heating rate of 10℃ / min, pyrolyzing the sludge in a nitrogen atmosphere and at a pyrolysis temperature of 600℃ for 2 hours, and finally cooling it naturally and screening it again to a particle size of 1-3 mm, then washing it with pure water and soaking it for 4 days to obtain the sludge biochar (15) used.

3. The sludge-based bioelectrochemical constructed wetland for enhanced wastewater denitrification according to claim 1 or 2, characterized in that, The wastewater is pretreated artificially prepared water with specific concentrations including 40 mg / L COD, 15 mg / L total nitrogen, and 0.5-1 mg / L chlorite. The water intake is controlled by a water pump, and the hydraulic retention time is 3 days.

4. The sludge-based bioelectrochemical constructed wetland for enhanced wastewater denitrification according to claim 3, characterized in that, The adjustable resistor (9) is set to a resistance of 1000Ω, and the power supply device (10) is set to a voltage of 0.1V.

5. The sludge-based bioelectrochemical constructed wetland for enhanced wastewater denitrification according to claim 3, characterized in that, The water distribution layer (3) is formed by laying pebbles (12) with a particle size of 40-60mm.

6. The sludge-based bioelectrochemical constructed wetland for enhanced wastewater denitrification according to claim 5, characterized in that, The lower filter layer (4) is formed by laying gravel (14) with a particle size of 2-4 mm.

7. The sludge-based bioelectrochemical constructed wetland for enhanced wastewater denitrification according to claim 6, characterized in that, The upper filter layer (6) is formed by laying gravel (14) with a particle size of 2-4 mm.

8. The sludge-based bioelectrochemical constructed wetland for enhanced wastewater denitrification according to claim 7, characterized in that, The wetland pool (1) is a hollow column with a height of 750 mm and a diameter of 180 mm; the total height of the water distribution layer (3) is 100 mm; the total height of the lower filter layer (4) is 200 mm; the total height of the anode layer (5) is 100 mm; the total height of the upper filter layer (6) is 200 mm; the total height of the cathode layer (7) is 50 mm; and sampling pipes (13) are provided on the upper side of the water distribution layer (3), the lower filter layer (4), the anode layer (5), and the upper filter layer (6).

9. The sludge-based bioelectrochemical constructed wetland for enhanced wastewater denitrification according to claim 1, characterized in that, The conductive metal mesh (16) is a stainless steel mesh, and its connection with the conductive wire (8) is wrapped with epoxy resin.

10. The sludge-based bioelectrochemical constructed wetland for enhanced wastewater denitrification according to claim 1, characterized in that, The wetland reactor is wrapped with aluminum foil.

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