Method for improving wastewater treatment efficiency of constructed wetland by manganese-bacteria coupling peroxodisulfate advanced oxidation

Abstract

The application discloses a method for improving the wastewater treatment efficiency of a constructed wetland by coupling manganese bacteria with peroxodisulfate advanced oxidation, which comprises the following steps: firstly, biochar and gravel particles are filled into the front end (main reaction zone 1) of the constructed wetland, and the gravel particles are filled into the rear end (main reaction zone 2) of the constructed wetland; an iron-plated graphite rod and a graphite rod are respectively inserted into the filler layer at the front end of the wetland, the iron-plated graphite rod is connected with the positive electrode of an external direct-current power supply, and the graphite rod is connected with the negative electrode of the external direct-current power supply; after power-on, the iron-plated graphite rod releases O2 and Fe 2+ ; and then, a mixture of urban domestic sewage and an equal volume of peroxodisulfate + manganese chloride solution is used as the wetland device inflow, and the pollutants in the wastewater are degraded through the action of microorganisms, catalysis, electrolysis, advanced oxidation and adsorption. The application aims to form an electrochemical and manganese bacteria, peroxodisulfate advanced oxidation coupling principle, and improve the wastewater treatment efficiency of the constructed wetland.

Description

Technical Field

[0001] This invention belongs to the field of constructed wetland wastewater treatment technology, specifically relating to a method for improving the wastewater treatment efficiency of constructed wetlands by coupling manganese bacteria with persulfate advanced oxidation. Background Technology

[0002] Constructed wetland technology is a promising wastewater treatment technology due to its environmental friendliness, low energy consumption, simple management, and effective nitrogen and phosphorus removal. However, problems such as easy clogging, large land area requirements, low pollutant load, and low treatment efficiency are the main factors restricting its engineering application.

[0003] To enhance the wastewater degradation capacity of constructed wetlands, the applicant employs a coupling of principles including electrolysis, biocatalysis, persulfate advanced oxidation, manganese bacteria, and manganese oxide adsorption to strengthen the wastewater treatment efficiency of constructed wetlands. Iron-plated graphite rods and biochar particles that form the anode after conducting electricity serve as the anode, generating O2 and Fe... 2+ And the oxidized organic matter, and the Fe dissolved by electrolysis 2+ It can catalyze the formation of SO4 from persulfate in water. - ·, SO4 - Both the · and its hydrolysis product (·OH) have strong oxidizing properties, which can enhance the removal efficiency of organic pollutants in wetlands. The dissolved oxygen content near the anode electrode in the wetland is high, while the area away from the anode electrode is an anaerobic zone. The aerobic-anaerobic alternation zone / interface and the addition of a manganese ion-containing solution to the influent are conducive to accelerating the enrichment of manganese bacteria. Biochar in the wetland provides a good carrier for manganese bacteria. Manganese elements are present in the wetland influent and soil layer, and under the mediation of manganese bacteria, manganese oxides with strong adsorption and catalytic oxidation capabilities are generated, which can enhance the removal efficiency of heavy metals and organic pollutants in the wetland. Therefore, this invention proposes a method for improving the wastewater treatment efficiency of constructed wetlands by coupling manganese bacteria with persulfate advanced oxidation: the wetland influent is first treated by coagulation and sedimentation, and then an equal volume of persulfate (concentration of 100-200 mg / L) + manganese chloride (2-10 mg / L) solution is added. Through the main reaction zone, multiple principles are coupled to improve the wastewater treatment efficiency of constructed wetlands. Summary of the Invention

[0004] This invention addresses the problem of low efficiency in treating urban domestic sewage using constructed wetlands by proposing a method to improve the sewage treatment efficiency of constructed wetlands through manganese bacteria coupled with persulfate advanced oxidation.

[0005] To address the aforementioned technical problems, this invention proposes a method for improving the wastewater treatment efficiency of constructed wetlands through manganese bacteria coupled with persulfate advanced oxidation. A pair of electrodes is inserted into the main reaction zone 1 of the wetland and connected to an external DC power supply. When the output voltage of the external DC power supply is 2-8V, an electrolysis reaction occurs. One of the electrolysis products at the anode is O2, which makes the area near the anode aerobic (main reaction zone 1) and the area away from the anode anaerobic (main reaction zone 2). Through aerobic / anaerobic (O / A)... n The two-stage spatial design and the addition of manganese ion solution to the influent facilitate the rapid accumulation of manganese bacteria within the wetland. The main reaction zone 1 of the wetland device is filled with a mixture of biochar and gravel particles. The biochar, with its large porous structure, provides an excellent carrier for microorganisms, including manganese bacteria, promoting their growth. Simultaneously, under the stimulation of an external electric field, the microbial community composition becomes richer, with electrogenic bacteria and manganese bacteria effectively increasing the stability and hierarchy of the microbial community structure and the metabolic activity of pollutants. Manganese bacteria convert manganese ions in the influent into manganese oxides. These manganese oxides, loaded onto the surfaces of the biochar and gravel, not only effectively increase the specific surface area, adsorption capacity, and microbial carrier capacity of the wetland packing material but also effectively catalyze microbial biochemical reactions, accelerating the biodegradation rate of pollutants in the water. Under an applied electric field, the mixed particles of biochar and gravel can serve as an extension of the traditional two-dimensional electrode, forming a three-dimensional electrode structure. This not only achieves higher current efficiency and lower internal resistance compared to two-dimensional electrodes, but also allows microorganisms to be fully exposed to a large-area electric field environment. This enhances the stimulating effect of the applied electric field on wetland microbial communities, electrode reactions, and the removal of pollutants (especially organic matter). Another product of anodic electrolysis is Fe. 2+ The dissolved Fe 2+ Adsorption / loading onto the surface of biochar forms iron-based biochar, which can effectively catalyze persulfate (S2O8) in water. 2- This improved the stability, dispersibility, and rapid precipitation of iron, and slowed the release of Fe. 2+ Catalyst S2O8 2- Sulfate free radicals (SO4) are continuously formed - Sulfate radicals and their hydrolysis products (hydroxyl radicals) have strong oxidizing properties and can oxidize most organic matter in water, thus improving the removal efficiency of organic matter in wetlands.

[0006] To achieve the above objectives, the technical solution adopted by this invention is:

[0007] A method for improving the wastewater treatment efficiency of constructed wetlands by coupling manganese bacteria with persulfate advanced oxidation, characterized by comprising the following steps:

[0008] Step 1: Pretreatment of the graphite rod with iron plating. The graphite rod is cleaned sequentially with acetone, anhydrous ethanol and pure water. Each cleaning solution is used for ultrasonic cleaning for 20 minutes. Then it is dried at room temperature. Finally, an iron metal plating layer is formed on the surface of the anodic graphite rod by electroplating.

[0009] Step 2: Pretreatment of the packing material. Biochar and gravel are used as the packing material for the wetland device, and pebbles are used as the support layer. The packing material is washed with tap water 5 times and then air-dried.

[0010] Step 3: Construction of the Constructed Wetland Device. The wetland device dimensions are: 1.2m long × 0.4m wide × 0.6m high. The device is made of plexiglass and is divided into a water distribution zone, a main reaction zone, and an effluent zone according to the wastewater flow direction. Each zone is separated by perforated plexiglass panels. The main reaction zone is further divided into Main Reaction Zone 1 and Main Reaction Zone 2. The constructed wetland device uses horizontal subsurface flow. The main reaction zone vertically consists of a plant layer, a soil layer, a filler layer, and a support layer. The filler layer in Main Reaction Zone 1 is a mixture of biochar particles and gravel particles, while Main Reaction Zone 2 consists of gravel particles. The device is constructed according to the following process: First, gravel particles are filled into the bottom of the device to form a 15cm thick support layer. Next, one iron-plated graphite rod and one graphite rod (400mm long, 5mm in diameter) are placed in the mixed packing layer of biochar and gravel in the main reaction zone 1, positioned centrally. The iron-plated graphite rods are spaced 20cm apart. The iron-plated graphite rods are connected to the positive terminal of an external DC power supply via wires, and the graphite rods are connected to the negative terminal of the external DC power supply via wires (with an external resistor in series, 10-20Ω). The biochar particles and gravel particles are mixed evenly and naturally stacked on top of the support layer to form a 20cm thick packing layer. The non-conductive particles (gravel) prevent the biochar particles from connecting and forming short circuits after becoming conductive. As conductors, the biochar particles can be polarized under the electric field of the anode and cathode iron-plated graphite rods, making each biochar particle an independent three-dimensional electrode particle. The positive electrode particles and the positive iron-plated graphite rod undergo an oxidation reaction, i.e., the oxidation of organic matter in the wastewater or the dissolution of iron ions from the iron plating layer (such as Fe). 2+ Or remove hydroxide ions (OH) from the water - The oxygen is oxidized into oxygen (O2). Finally, soil is filled on top of the filler layer to form a soil layer with a thickness of 15cm; wetland plants are planted on top of the soil layer, with reeds, calamus, and black sedges selected as wetland plants to form a plant layer.

[0011] Step Four: Operation of the Constructed Wetland System. Urban domestic sewage (pretreated by coagulation to ensure SS < 120 mg / L to prevent wetland clogging) and an equal volume of persulfate (100–200 mg / L) + manganese chloride solution (2–10 mg / L) are used as the influent to the wetland system. This influent is introduced into the wetland distribution zone (formed by filling the front end of the wetland with large-diameter gravel) through the influent pipe, and sequentially passes through the main reaction zone 1, main reaction zone 2, and effluent zone of the horizontal subsurface flow constructed wetland. Under an applied voltage of 2–8V, the hydraulic retention time of the wetland is 2 days. The addition of manganese ion solution to the wetland influent stimulates the rapid accumulation of manganese bacteria within the wetland system.

[0012] Preferably, in step one, there is one pair of electrodes, namely one iron-plated graphite rod and one graphite rod. The electrode material is graphite rod, wherein the surface of the anode graphite rod is electroplated to form an iron metal layer. The specific operation steps are as follows: the graphite rod is placed in an electrolyte at 80°C to form an oxide film on its surface; the FeSO4 plating solution is poured into the electroplating tank, and the graphite rod is placed in the electroplating tank as the cathode. An iron metal coating is formed on the surface of the graphite rod through an electroplating reaction at a voltage of 8-10V; after electroplating is completed, the graphite rod is removed from the electroplating tank, rinsed with pure water, and dried at room temperature.

[0013] Preferably, in step two, the biochar particles have a diameter of 4–8 mm, the gravel particles have a diameter of 4–10 mm, and the pebble particles have a diameter of 40–80 mm. Furthermore, in step three, the filler layer of the main reaction zone 1 is a mixture of biochar and gravel particles with a volume ratio of 1:4 (biochar:gravel) to prevent excessive biochar addition, which could reduce the permeability of the filler matrix.

[0014] Preferably, in step three, the perforated acrylic sheet has a hole diameter of 2mm, a hole center-to-center spacing of 4mm, and is orthogonally arranged, with the edges utilizing... Figure 2 The tenon joints shown are fixed in pre-drilled slots to separate different areas of the wetland. Examples include the water distribution area and the main reaction area, main reaction area 1 and main reaction area 2, and the main reaction area and the effluent area. Simultaneously, the perforated plexiglass panels prevent the packing material in main reaction area 1 and main reaction area 2 from mixing and facilitate the formation of an aerobic-anaerobic interface, promoting the rapid accumulation of manganese bacteria in the constructed wetland system.

[0015] Preferably, in step three, the electrolysis-constructed wetland coupling system adopts a two-stage aerobic / anaerobic (O / An) spatial design. A pair of electrodes is inserted into the main reaction zone 1, and an external resistor (10-20Ω) and a DC power supply (2-8V) are connected in series between the anode (iron-plated graphite rod) and the cathode (graphite rod). At the anode (iron-plated graphite rod and biochar particles that form the anode after conduction), O2, one of the electrolysis products, facilitates the formation of the aerobic (O) stage. Conversely, in the main reaction zone 2, since there are no electrodes, the organic matter in the wastewater is degraded during the aerobic microbial biochemical reaction, consuming dissolved oxygen in the water and forming the anaerobic (An) stage. During wetland operation, an external power source continuously supplies power to the electrodes, ensuring the formation of both aerobic and anaerobic zones within the wetland system. The applicant's research found that the existence of the boundary zone between aerobic and anaerobic zones is conducive to the enrichment of manganese bacteria. It should be noted that there is a transition zone between the aerobic and anaerobic zones in the wetland, namely the anoxic zone. Due to the presence of anoxic-aerobic environmental conditions, the wetland device can achieve biological denitrification efficiency. That is, in the main reaction zone 1 (aerobic section), organic matter degradation and nitrification reactions occur simultaneously, and nitrifying bacteria convert nitrogenous substances into nitrates. In the transition zone from the main reaction zone 1 to the main reaction zone 2 (anaerobic section), due to the presence of anoxic conditions, denitrification reactions occur, and denitrifying bacteria reduce nitrates to gaseous nitrogen, thereby realizing the biological denitrification function of the wetland.

[0016] Preferably, in step four, the influent is a mixture of urban domestic sewage and an equal volume of persulfate (concentration 100-200 mg / L) + manganese chloride solution (2-10 mg / L). The typical components and concentrations of this mixture are: C6H... 12 O6 (80 mg / L), CH3COONa (50 mg / L), KNO3 (100 mg / L), NH4Cl (80 mg / L), MgSO4·7H2O (30 mg / L), KH2PO4 (15 mg / L), anhydrous CaCl2 (5 mg / L), Na2S2O8 (100-200) mg / L, MnCl2 (2-10 mg / L).

[0017] The main beneficial effects of this invention are as follows:

[0018] 1) Compared with traditional constructed wetland technology, this invention couples principles such as microorganisms, biocatalysis, electrolysis, advanced oxidation, and adsorption with constructed wetland technology. Based on the coupling of multiple reaction principles, it enhances the purification efficiency of the constructed wetland system, mainly in the following aspects: The electrolysis of the anode (iron-plated graphite rod and biochar particles forming the anode after conduction) generates O2, creating an aerobic environment near the anode and an anaerobic environment further away. This alternating aerobic-anaerobic environment is conducive to the rapid accumulation of manganese bacteria. Furthermore, the addition of manganese ions to the influent stimulates the growth of manganese bacteria, which convert the manganese ions in the influent into manganese oxides. These oxides are loaded onto the surface of biochar and gravel, effectively increasing the specific surface area, pollutant adsorption performance, and microbial carrier capacity of the wetland filler. They also effectively catalyze microbial biochemical reactions, accelerating the biodegradation rate of pollutants in the water. Another product of anodic electrolysis within the wetland is Fe. 2+ Its functions are numerous, including: promoting the expression of functional iron complex transport genes in microorganisms, thereby enhancing the biotransformation and catalytic activity of manganese oxides; Fe 2+ It reacts with phosphates in water to form sparingly soluble salts, accompanied by Fe... 2+ Vigorous hydrolysis and various polymerization reactions occur, generating a variety of polynuclear hydroxyl complexes. These complexes, through double-layer compression, charge neutralization, adsorption bridging, and the entrapment effect of flocs, cause colloids in the water to coagulate and precipitate, i.e., through Fe... 2+ The complexing and coagulation processes achieve phosphorus removal from wastewater; Fe produced by anodic electrolysis 2+ Adsorption / loading on the surface of biochar forms iron-based biochar, which can effectively catalyze persulfate (S2O8). 2- The high specific surface area and porous structure of biochar help to immobilize Fe. 2+ And disperse it evenly on its surface; otherwise, if Fe is added directly... 2+ Solution (not the Fe produced by the electrolytic anode used in this invention) 2+ (Method) Complete activation of persulfate requires the addition of excess Fe. 2+ The solution, and the anions introduced by the addition of ferrous salts, will inhibit Fe 2+ It catalyzes the reaction of persulfate. Therefore, it is evident that direct addition of Fe... 2+ The solution is added in a single dosing method, which requires the addition of an excess of Fe. 2+ The solution, and also led to the introduction of anions and excess Fe by the ferrous salt. 2+ Problems such as sulfate radicals generated in competition with pollutants in water, and the Fe produced by the electrolytic anode in this invention. 2+ The approach combines biochar adsorption / loading of Fe. 2+ The technology not only enabled Fe in the system 2+ Concentration control, and also has slow-release Fe2+ The effect is to continuously catalyze the reaction of persulfate; therefore, the technical method adopted in this application improves the stability, dispersibility, and rapid precipitation of iron, preventing Fe... 2+ Too rapid loss, slow-release Fe 2+ Catalyst for S2O8 in water 2- Sulfate free radicals (SO4) are continuously formed - ·), SO4 - Both the sulfur dioxide (·) and its hydrolysis product (·OH) possess strong oxidizing properties, and together they enhance the degradation efficiency of organic pollutants in the wetland system. Under the stimulation of an applied electric field, the microbial community within the wetland becomes richer, with electrogenic bacteria and manganese bacteria effectively increasing the stability, hierarchy, symbiotic relationships, and pollutant metabolic activity of the microbial community structure. Combining these effects, a method for improving the wastewater treatment efficiency of constructed wetlands by coupling manganese bacteria with persulfate advanced oxidation enhances the effectiveness of wetland wastewater treatment and effectively solves the bottleneck problem of recalcitrant organic matter removal in constructed wetland systems.

[0019] 2) Traditional constructed wetlands use biochar as a filler, which adsorbs pollutants in the water and provides a carrier for microorganisms. This invention improves the function of biochar, not only through manganese oxides and Fe... 2+ Loading manganese oxides onto biochar effectively increases the specific surface area of ​​the biochar and enhances its function as a microbial carrier. Manganese oxides and Fe... 2+ The loading of manganese oxide / biochar formed a multi-layered heterogeneous catalytic reaction system within the wetland system, namely, manganese oxide / biochar acted as a heterogeneous catalyst to catalyze the biochemical reactions of microbial degradation of pollutants within the wetland system, and Fe... 2+ Biochar as a heterogeneous catalyst for S2O8 in wetland systems 2- Sulfate free radicals are continuously formed. Furthermore, biochar plays a crucial role as a three-dimensional electrode in the wetland electrolysis system. Under the influence of an applied electric field, each working electrode particle (biochar particle) within the wetland packing layer becomes an independent three-dimensional electrode, forming a micro-electrolysis cell with an anode at one end and a cathode at the other. This provides more active reaction sites, resulting in better proton diffusion performance, improving the efficiency and speed of electrochemical reactions, and thus enhancing the removal efficiency of organic pollutants. On the other hand, the surface of the biochar particles generates highly oxidizing hydroxyl radicals (·OH), achieving the oxidation of recalcitrant organic matter in the water. By mixing biochar particles with gravel particles in an appropriate ratio as packing material, the hydraulic effect of the wetland can be improved when biochar particles are used alone, ensuring good hydraulic permeability of the wetland packing layer. Simultaneously, the non-conductive particles (gravel particles) maintain the stable structure and shape of the three-dimensional electrode system, preventing short circuits caused by electrical conductivity between biochar particles.

[0020] 3) This invention enhances the wastewater treatment efficiency of constructed wetlands by adding an equal volume of persulfate (100-200 mg / L) and manganese chloride solution (2-10 mg / L) to the wetland influent. This is achieved through the synergistic effect of multiple catalytic mechanisms, including the activation of persulfate by biochar-loaded iron and the promotion of manganese bacteria accumulation and manganese oxide generation by manganese ion addition to the influent, thus catalyzing microbial biochemical reactions. In the wetland system, an iron-coated graphite rod serves as the anode; when an external voltage is applied, electrolysis produces Fe. 2+ Or O2. Fe 2+ Fe is adsorbed by the biochar in the wetland filler layer, forming biochar-loaded Fe. 2+ Slowly release Fe into the wetland water environment 2 + Fe released into the water 2+ An electron can be donated to persulfate in water, causing the O-O bond of the persulfate to break, resulting in the following reaction and the formation of SO4. - · Fe 2+ +S2O8 2- →Fe 3+ +SO4 ·- +SO4 2- The above reaction product SO4 - • It can non-selectively oxidize the vast majority of organic pollutants; in addition, SO4 - • Reacts with water molecules or other reducing substances in water to produce ·OH, which also has the function of oxidizing and decomposing organic matter; when Fe 2+ When coexisting with other heteroatoms (such as N and S) in biochar, it can alter the electronic structure of the carbon material, induce electron transfer, and promote the non-radical activation of persulfate. Simultaneously, in the presence of SO4... - During the hydrolysis to generate OH, Fe 2+ As a catalyst, Fe participates in the reaction, making Fe 2+ With S2O8 2- The reaction system can continuously and effectively degrade organic pollutants.

[0021] 4) The constructed wetland device is spatially divided into two sections: the front section is the aerobic (O) section, and the rear section is the anaerobic (A) section. n )part. O / A n Under the two-stage structure, organic matter degradation, nitrification, and phosphorus uptake occur simultaneously in main reaction zone 1 (section O). Nitrification utilizes nitrifying bacteria to convert nitrogenous substances into nitrates. Main reaction zone 2 (section A...) nIn this constructed wetland, organic matter degradation and phosphorus release occur simultaneously. The alternating environment and interface between the aerobic and anaerobic sections are conducive to the rapid proliferation of manganese bacteria. Furthermore, the transition zone between the aerobic and anaerobic sections contains anoxic areas where denitrification occurs, utilizing denitrifying bacteria to reduce nitrates to gaseous nitrogen. Therefore, constructed wetlands possess nitrogen and phosphorus removal functions. Attached Figure Description

[0022] Figure 1 This is a cross-sectional view of the process structure of a method for improving the wastewater treatment efficiency of constructed wetlands by coupling manganese bacteria with persulfate advanced oxidation, as described in this invention.

[0023] Figure 2 This is a top view of the process structure described in this invention.

[0024] Figure labels: 1-Inlet pipe, 2-Iron-plated graphite rod (anode), 3-Resistor (10-20Ω), 4-External DC power supply (2-8V), 5-Graphite rod (cathode), 6-Porous plexiglass baffle, 7-Main reaction zone (horizontal subsurface flow constructed wetland), 8-Soil layer, 9-Gravel filler layer, 10-Pebble support layer, 11-Outlet pipe, 12-Water distribution area, 13-Outlet area, 14-Porous plexiglass baffle, 15-Biochar and gravel mixed filler layer, 16-Main reaction zone 1, 17-Main reaction zone 2 Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments.

[0026] Step 1: Pretreatment of the graphite rod with iron plating. The graphite rod is cleaned sequentially with acetone, anhydrous ethanol and pure water. Each cleaning solution is used for ultrasonic cleaning for 20 minutes. Then it is dried at room temperature. Finally, an iron metal plating layer is formed on the surface of the anodic graphite rod by electroplating.

[0027] Step 2: Pretreatment of the packing material. Biochar and gravel are used as the packing material for the wetland device, and pebbles are used as the support layer. The packing material is washed with tap water 5 times and then air-dried.

[0028] Step 3: Construction of the Constructed Wetland Device. The wetland device dimensions are: 1.2m long × 0.4m wide × 0.6m high. The device is made of plexiglass and is divided into a water distribution zone, a main reaction zone, and an effluent zone according to the wastewater flow direction. Each zone is separated by perforated plexiglass panels. The main reaction zone is further divided into Main Reaction Zone 1 and Main Reaction Zone 2. The constructed wetland device uses horizontal subsurface flow. The main reaction zone vertically consists of a plant layer, a soil layer, a filler layer, and a support layer. The filler layer in Main Reaction Zone 1 is a mixture of biochar particles and gravel particles, while Main Reaction Zone 2 consists of gravel particles. The device is constructed according to the following process: First, gravel particles are filled into the bottom of the device to form a 15cm thick support layer. Next, one iron-plated graphite rod and one graphite rod (400mm long, 5mm in diameter) are placed in the mixed packing layer of biochar and gravel in the main reaction zone 1, positioned centrally. The iron-plated graphite rods are spaced 20cm apart. The iron-plated graphite rods are connected to the positive terminal of an external DC power supply via wires, and the graphite rods are connected to the negative terminal of the external DC power supply via wires (with an external resistor in series, 10-20Ω). The biochar particles and gravel particles are mixed evenly and naturally stacked on top of the support layer to form a 20cm thick packing layer. The non-conductive particles (gravel) prevent the biochar particles from connecting and forming short circuits after becoming conductive. As conductors, the biochar particles can be polarized under the electric field of the anode and cathode iron-plated graphite rods, making each biochar particle an independent three-dimensional electrode particle. The positive electrode particles and the positive iron-plated graphite rod undergo an oxidation reaction, i.e., the oxidation of organic matter in the wastewater or the dissolution of iron ions from the iron plating layer (such as Fe). 2+ Or remove hydroxide ions (OH) from the water - The oxygen is oxidized into oxygen (O2). Finally, soil is filled on top of the filler layer to form a soil layer with a thickness of 15cm; wetland plants are planted on top of the soil layer, with reeds, calamus, and black sedges selected as wetland plants to form a plant layer.

[0029] Step Four: Operation of the Constructed Wetland System. Urban domestic sewage (pretreated by coagulation to ensure SS < 120 mg / L to prevent wetland clogging) and an equal volume of persulfate (100–200 mg / L) + manganese chloride solution (2–10 mg / L) are used as the influent to the wetland system. This influent is introduced into the wetland distribution zone (formed by filling the front end of the wetland with large-diameter gravel) through the influent pipe, and sequentially passes through the main reaction zone 1, main reaction zone 2, and effluent zone of the horizontal subsurface flow constructed wetland. Under an applied voltage of 2–8V, the hydraulic retention time of the wetland is 2 days. The addition of manganese ion solution to the wetland influent stimulates the rapid accumulation of manganese bacteria within the wetland system.

[0030] Preferably, in step one, there is one pair of electrodes, namely one iron-plated graphite rod and one graphite rod. The electrode material is graphite rod, wherein the surface of the anode graphite rod is electroplated to form an iron metal layer. The specific operation steps are as follows: the graphite rod is placed in an electrolyte at 80°C to form an oxide film on its surface; the FeSO4 plating solution is poured into the electroplating tank, and the graphite rod is placed in the electroplating tank as the cathode. An iron metal coating is formed on the surface of the graphite rod through an electroplating reaction at a voltage of 8-10V; after electroplating is completed, the graphite rod is removed from the electroplating tank, rinsed with pure water, and dried at room temperature.

[0031] Preferably, in step two, the biochar particles have a diameter of 4–8 mm, the gravel particles have a diameter of 4–10 mm, and the pebble particles have a diameter of 40–80 mm. Furthermore, in step three, the filler layer of the main reaction zone 1 is a mixture of biochar and gravel particles with a volume ratio of 1:4 (biochar:gravel) to prevent excessive biochar addition, which could reduce the permeability of the filler matrix.

[0032] Preferably, in step three, the perforated acrylic sheet has a hole diameter of 2mm, a hole center-to-center spacing of 4mm, and is orthogonally arranged, with the edges utilizing... Figure 2 The tenon joints shown are fixed in pre-drilled slots to separate different areas of the wetland. Examples include the water distribution area and the main reaction area, main reaction area 1 and main reaction area 2, and the main reaction area and the effluent area. Simultaneously, the perforated plexiglass panels prevent the packing material in main reaction area 1 and main reaction area 2 from mixing and facilitate the formation of an aerobic-anaerobic interface, promoting the rapid accumulation of manganese bacteria in the constructed wetland system.

[0033] Preferably, the electrolysis-artificial wetland coupling system in step three adopts an aerobic / anaerobic (O / A) system. n The two-stage spatial design involves inserting a pair of electrodes into the main reaction zone 1, with an external resistor (10-20Ω) and a DC power supply (2-8V) connected in series between the anode (iron-plated graphite rod) and the cathode (graphite rod). At the anode (iron-plated graphite rod and biochar particles that form the anode after conduction), O2, one of the electrolysis products, favors the formation of the aerobic (O) stage. Conversely, in the main reaction zone 2, lacking electrodes, the organic matter in the wastewater is degraded during the aerobic microbial biochemical reaction, consuming dissolved oxygen in the water and forming an anaerobic (A) stage. n(Section 1) During wetland operation, an external power source continuously supplies power to the electrodes, ensuring the formation of both aerobic and anaerobic zones within the wetland system. The applicant's research found that the existence of the boundary zone between aerobic and anaerobic areas is conducive to the enrichment of manganese bacteria. It should be noted that there is a transition zone between the aerobic and anaerobic zones in the wetland, namely the anoxic zone. Due to the presence of anoxic-aerobic environmental conditions, the wetland device can achieve biological denitrification efficiency. That is, in the main reaction zone 1 (aerobic section), organic matter degradation and nitrification reactions occur simultaneously, and nitrifying bacteria convert nitrogenous substances into nitrates. In the transition zone from main reaction zone 1 to main reaction zone 2 (anaerobic section), due to the presence of anoxic conditions, denitrification reactions occur, and denitrifying bacteria reduce nitrates to gaseous nitrogen, thereby realizing the biological denitrification function of the wetland.

[0034] Preferably, in step four, the influent is a mixture of urban domestic sewage and an equal volume of persulfate (concentration 100-200 mg / L) + manganese chloride solution (2-10 mg / L). The typical components and concentrations of this mixture are: C6H... 12 O6 (80 mg / L), CH3COONa (50 mg / L), KNO3 (100 mg / L), NH4Cl (80 mg / L), MgSO4·7H2O (30 mg / L), KH2PO4 (15 mg / L), anhydrous CaCl2 (5 mg / L), Na2S2O8 (100-200) mg / L, MnCl2 (2-10 mg / L).

[0035] Example 1:

[0036] The aforementioned method of enhancing the wastewater treatment efficiency of constructed wetlands by coupling manganese bacteria with persulfate advanced oxidation was used to treat urban domestic sewage. In step three, a 20Ω resistor and a 6V DC regulated power supply were connected in series between the graphite rod with an iron-plated anode layer and the graphite rod at the cathode of the wetland device. The heating time (HRT) was 48 hours, and the power supply was continuous. In step four, the COD concentration of the urban domestic sewage was 176.24 mg / L, the total nitrogen concentration was 31.70 mg / L, the total phosphorus concentration was 3.26 mg / L, and the added Na₂S₂O₈ concentration was 100 mg / L. After the process system operated stably for 20 days, the effluent quality was tested. Considering that the constructed wetland system consists of a complex microbial community and has strong ecological characteristics, sampling times were set at 7:00, 15:00, and 21:00 on the same day, with each sampling interval of 5 days. Water quality analysis of 12 samples obtained from 4 sampling days revealed that the average COD concentration in the wetland effluent was 16.85 mg / L, with a removal rate of 90.44%; the total nitrogen concentration was 6.52 mg / L, with a removal rate of 79.43%; and the total phosphorus concentration was 0.97 mg / L, with a removal rate of 70.25%.

[0037] Example 2:

[0038] The above-mentioned method of enhancing the wastewater treatment efficiency of constructed wetlands by coupling manganese bacteria with persulfate advanced oxidation was used to treat urban domestic sewage. In step three, a 10Ω resistor and an 8V DC regulated power supply were connected in series between the graphite rod with an iron-plated anode layer and the graphite rod with the cathode in the wetland device. The heating time (HRT) was 48 hours, and the power supply was continuous. In step four, the COD concentration of the urban domestic sewage was 340.38 mg / L, the total nitrogen concentration was 60.24 mg / L, the total phosphorus concentration was 5.86 mg / L, and the added Na₂S₂O₈ concentration was 200 mg / L. After the process system operated stably for 30 days, the effluent quality was tested. Sampling times were set at 9:00, 14:00, and 20:00 on the same day, with each sampling interval of 7 days. Water quality analysis of 15 samples obtained from 5 sampling days revealed that the average COD concentration in the wetland effluent was 32.57 mg / L, with a removal rate of 90.43%; the total nitrogen concentration was 11.54 mg / L, with a removal rate of 80.84%; and the total phosphorus concentration was 1.72 mg / L, with a removal rate of 70.65%.

[0039] The above results indicate that the method for improving the wastewater treatment efficiency of constructed wetlands by coupling manganese bacteria with persulfate advanced oxidation effectively improves the removal efficiency of organic matter and nitrogen and phosphorus pollutants in constructed wetlands and can be widely applied in the field of domestic wastewater treatment in small and medium-sized towns or rural areas.

[0040] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for improving the wastewater treatment efficiency of constructed wetlands by coupling manganese bacteria with persulfate advanced oxidation, characterized in that, Includes the following steps: Step 1: Pretreatment of graphite rods with iron plating: The graphite rods are cleaned in sequence with acetone, anhydrous ethanol and pure water. Each cleaning solution is cleaned under ultrasonic conditions for 20 minutes. Then, they are dried at room temperature. Finally, an iron metal plating layer is formed on the surface of the anodic graphite rods by electroplating. Step 2: Pretreatment of packing material: Biochar and gravel are used as packing material for the wetland device, and pebbles are used as the support layer for the wetland device. The packing material is washed with tap water 5 times and then air-dried. Step 3: Construction of the Constructed Wetland Device: The wetland device dimensions are 1.2 m long × 0.4 m wide × 0.6 m high. The device is made of plexiglass. Following the wastewater flow direction, the device is divided into a water distribution zone, a main reaction zone, and an effluent zone, separated by perforated plexiglass panels. The main reaction zone is further divided into Main Reaction Zone 1 and Main Reaction Zone 2. The constructed wetland device uses horizontal subsurface flow. The main reaction zone vertically consists of a plant layer, a soil layer, a filler layer, and a support layer. The filler layer in Main Reaction Zone 1 is a mixture of biochar particles and gravel particles, while Main Reaction Zone 2 uses gravel particles. The device is constructed according to the following process: First, fill the bottom of the device with gravel particles to form a 15 cm thick support layer. Next, place one iron-plated graphite rod and one graphite rod with a length of 400 mm and a diameter of 5 mm into the mixed biochar and gravel filler layer in Main Reaction Zone 1, centered, with a 20 mm spacing between the iron-plated graphite rod and the graphite rod. A graphite rod with an iron plating layer is connected to the positive terminal of an external DC power supply via a wire, and the graphite rod is connected to the negative terminal of the external DC power supply via a wire, with an external resistor of 10~20 Ω connected in series. Biochar particles and gravel particles are mixed evenly and naturally packed onto the support layer to form a 20 cm thick filler layer. The gravel, as a non-conductive particle, prevents the biochar particles from short-circuiting due to conductivity. The biochar particles, as conductors, are polarized under the electric field of the anode and cathode graphite rods, making each biochar particle an independent three-dimensional electrode particle. The electrode particles acting as the anode and the anode graphite rod undergo an oxidation reaction, i.e., oxidation of the organic matter in the wastewater or oxidation of the iron plating layer. 2+ The solution dissolves or oxidizes hydroxide ions in the water into oxygen; finally, the soil is filled on top of the filler layer to form a soil layer with a thickness of 15 cm; wetland plants are planted on top of the soil layer, and reeds, calamus, and black sedge are selected as wetland plants to form a plant layer. Step 4: Operation of the constructed wetland device: After coagulation pretreatment to achieve SS < 120 mg / L, urban domestic sewage is mixed with an equal volume of persulfate solution at a concentration of 100 ~ 200 mg / L and manganese chloride solution at a concentration of 2 ~ 10 mg / L as the influent to the wetland device. This mixture is introduced into the wetland distribution zone through the wetland inlet pipe. The wetland distribution zone is formed by filling the front end of the wetland with large-diameter gravel and passes sequentially through the main reaction zone one, main reaction zone two, and effluent zone of the horizontal subsurface flow constructed wetland. Under an applied voltage of 2 ~ 8 V, the hydraulic retention time of the wetland is 2 days. Due to the addition of manganese ion solution to the wetland influent, the rapid accumulation of manganese bacteria in the wetland device is stimulated.

2. The method for improving the wastewater treatment efficiency of constructed wetlands by coupling manganese bacteria with persulfate advanced oxidation according to claim 1, characterized in that, In step two, the biochar particles have a diameter of 4-8 mm, the gravel particles have a diameter of 4-10 mm, and the pebble particles have a diameter of 40-80 mm.

3. The method for improving the wastewater treatment efficiency of constructed wetlands by coupling manganese bacteria with persulfate advanced oxidation according to claim 1, characterized in that, In step three, the perforated acrylic sheet has a hole diameter of 2 mm and a hole center-to-center spacing of 4 mm. The holes are arranged orthogonally and the edges are fixed in the reserved slots using tenon joints to separate different areas of the wetland.

4. The method for improving the wastewater treatment efficiency of constructed wetlands by coupling manganese bacteria with persulfate advanced oxidation according to claim 1, characterized in that, In step three, the packing layer of the main reaction zone one uses a mixture of biochar and gravel particles, with a volume ratio of biochar to gravel of 1:

4.

5. The method for improving the wastewater treatment efficiency of constructed wetlands by coupling manganese bacteria with persulfate advanced oxidation according to claim 1, characterized in that, In step three, the electrolysis-constructed wetland coupling system adopts a two-stage aerobic / anaerobic design. In the main reaction zone one, a pair of electrodes are inserted: the iron-plated graphite rod at the anode and the O2, one of the electrolysis products of the biochar particles that form the anode after conduction, facilitate the formation of the aerobic section. In the main reaction zone two, since there are no electrodes, the organic matter in the sewage is degraded and the dissolved oxygen in the water is consumed during the aerobic microbial biochemical reaction, forming the anaerobic section. During the operation of the wetland, the external power supply continuously supplies power to the electrodes to ensure that an aerobic and anaerobic interface area is formed in the wetland system. The existence of the aerobic and anaerobic interface area is conducive to the enrichment of manganese bacteria.

6. The method for improving the wastewater treatment efficiency of constructed wetlands by coupling manganese bacteria with persulfate advanced oxidation according to claim 1, characterized in that, In step four, the influent is a mixture of urban domestic sewage and an equal volume of persulfate solution with a concentration of 100-200 mg / L and a manganese chloride solution with a concentration of 2-10 mg / L. The typical components and concentrations of this mixture are: C6H... 12 O680 mg / L, CH3COONa 50 mg / L, KNO3 100 mg / L, NH4Cl 80 mg / L, MgSO4·7H2O 30 mg / L, KH2PO4 15 mg / L, anhydrous CaCl2 5 mg / L, Na2S2O8 100 ~ 200 mg / L, MnCl2 2 ~ 10 mg / L.

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