An artificial wetland system and method for enhancing iron-based carbon release, nitrogen removal, and greenhouse gas emission reduction.

Abstract

An artificial wetland system and method for enhancing iron-based denitrification and greenhouse gas emission reduction includes: an inlet module, a purification module, and an outlet module connected in sequence; the outlet of the outlet module is connected to a drain pipe or a return pipe, and the other end of the return pipe is connected to the inlet module; the return pipe is located between the inlet module and the outlet module; the purification module includes several wetlands, and each wetland is equipped with a valve for inlet water between itself and the inlet channel, and between the wetlands; the other end of each wetland is equipped with a valve for outlet water; the wetlands are connected in parallel or in series by controlling the opening and closing of the valves. This invention flexibly adjusts the artificial wetland system according to different water quality purification needs, targeting water bodies with varying degrees of pollution. It uses iron-based materials and biochar as a combined matrix to form an iron-carbon micro-electrolysis system, promoting nitrogen conversion and improving denitrification efficiency while synergistically reducing greenhouse gas emissions by 20%-40%, enabling the device to simultaneously achieve wastewater treatment and greenhouse gas emission reduction.

Description

Technical Field

[0001] This invention belongs to the fields of wastewater denitrification treatment, water purification and constructed wetlands, and relates to a constructed wetland system and method for enhancing iron-based carbon release and denitrification and greenhouse gas emission reduction. Background Technology

[0002] In recent years, rapid industrial development has led to a surge in wastewater discharge, resulting in severe eutrophication due to nitrogen and phosphorus accumulation, which has impacted the water quality of rivers and lakes. At the same time, global warming is becoming increasingly severe with industrial development, making the effective control and reduction of greenhouse gas emissions crucial for mitigating global warming.

[0003] Constructed wetlands, as an environmentally friendly ecological technology, offer advantages such as low investment costs, high treatment efficiency, and low maintenance costs, and are commonly used to treat domestic sewage, mine wastewater, and landfill leachate. The substrate, as the main carrier of constructed wetlands, plays a crucial role, such as facilitating biofilm attachment, anchoring plant growth, and acting as an adsorbent for pollutants. Different types of substrates exhibit different pollutant removal mechanisms, and their unique physicochemical properties lead to variations in pollutant removal efficiencies.

[0004] The Chinese patent application CN202110903100.5, entitled "An Artificial Wetland System with Enhanced Denitrification," discloses a system that uses biochar prepared from wetland plants as a wetland substrate to enhance denitrification, improve nitrate nitrogen removal, and achieve the reuse of wetland plants, thereby reducing the land area required. However, this patent does not address iron-based materials or the reduction of carbon emissions.

[0005] The Chinese patent application CN201920949145.4, entitled "A Biochar-Based Sequencing Batch Constructed Wetland Wastewater Treatment System," discloses a system that uses an alternating saturation-drying operation mode to create aerobic-anoxic environmental conditions, achieving efficient wastewater removal and alleviating wetland clogging with a small footprint and without increasing costs. However, this patent does not address iron-based materials or the reduction of carbon emissions.

[0006] Studies have shown that composite substrates of different types have a stronger denitrification capacity than single substrates. However, constructed wetlands currently generally use single substrates, which limits the ability of substrates with different characteristics to exert different physicochemical properties to adsorb or transform nitrogen, thus hindering the improvement of denitrification efficiency. Furthermore, the operation mode of wetland systems is singular and cannot be adjusted according to different water quality conditions. Summary of the Invention

[0007] To overcome the above-mentioned shortcomings of the prior art, the present invention provides an artificial wetland system and method for enhancing iron-based carbon release, denitrification, and greenhouse gas emission reduction. The artificial wetland system is flexibly adjusted according to different water quality purification needs for water bodies with different levels of pollution. Iron-based materials and biochar are used as a combined matrix to promote nitrogen conversion and improve denitrification efficiency while synergistically reducing greenhouse gas emissions, so that the device can simultaneously achieve wastewater treatment and greenhouse gas emission reduction.

[0008] The constructed wetland system of this invention uses iron-based materials and biochar as the constructed wetland substrate:

[0009] (1) The iron autotrophic denitrification reactions (②, ③) that occur inside the system greatly reduce the emission flux of greenhouse gas CO2 compared with the ordinary denitrification reaction (①), and can reduce CO2 emissions by 70-85%.

[0010] Ordinary denitrification: 5CH3COOH+8NO3 - →6H₂O + 10CO₂ + 4N₂ + 8OH⁻ - +ATP ①

[0011] Iron autotrophic denitrification: 4Fe(0) + NO3 - +7H₂O→4Fe 3+ +NH4 + +10OH - ②(Zero-priced iron)

[0012] 5Fe 2+ +NO3 - +7H₂O→5FeOOH+1 / 2N₂+9H + ③ (Divalent iron)

[0013] (2) 1 molar unit of Fe 0 Converted to Fe 3+ It can provide 3 moles of electron donors, while 1 mole of NO3... - It takes 5 moles of electron donors to convert it into N2.

[0014] 1 molar unit of Fe 2+ Converted to Fe 3+ It can provide 1 mole of electron donor, while 1 mole of NO3... - It takes 5 moles of electron donors to convert it into N2.

[0015] The formula for calculating the mass of iron-based matrix in an constructed wetland system is as follows:

[0016] M Fe总 =M Fe1 +M Fe2

[0017]

[0018]

[0019] x+y=1

[0020] M Fe总 —Total mass of iron required for an constructed wetland system, in kg;

[0021] M Fe1 —The mass of elemental iron required for an constructed wetland system, in kg;

[0022] M Fe2 —The mass of ferrous iron required for the constructed wetland system, in kg;

[0023] —The required reduction in nitrate concentration for constructed wetland systems, in units (kg / L);

[0024] —The volume of water that the constructed wetland system needs to treat, in units (L);

[0025] α – the electron donor availability rate in elemental iron, which can be taken as 0.5-0.7;

[0026] β—the electron donor rate in divalent iron, which can be taken as 0.6-0.8;

[0027] x — The ratio of nitrate to nitrogen required to be treated by elemental iron, which can be taken as 0-1;

[0028] y—The percentage of nitrate and nitrogen that needs to be treated by divalent iron, which can be taken as 0-1;

[0029] (3) When Fe 2+ The concentration exceeds the electrons required for N2O. N2O can accept the excess electrons and be further reduced to N2. 4.2g Fe 2+ It can reduce the emission of 1g of N2O greenhouse gas (④), and can reduce N2O emissions by 30%-45%.

[0030] 2Fe 2+ +2H + +N₂O→2Fe 3+ +N2+H2O ④

[0031] (4) The addition of iron will also change the microbial community structure in wetlands, affecting nitrogen removal and N2O emissions at the micro level. Iron can improve nitrogen removal efficiency through biological pathways such as autotrophic denitrification and anaerobic ammonia oxidation.

[0032] (5) Adding biochar to wetland systems can slowly release carbon sources and provide electron donors to alleviate the low-carbon problem in wastewater treatment. On the other hand, it can form an iron-carbon micro-electrolysis system with iron. The many micro-current electric fields formed between iron and carbon have a galvanic cell effect, which enhances the adsorption, reduction and microbial degradation effects.

[0033] (6) The total nitrogen concentration in the water is 0-50 mg / L, and the volume ratio of iron-based to biochar is 2:1; the total nitrogen concentration in the water is 51-100 mg / L, and the volume ratio of iron-based to biochar is 1:1.

[0034] The objective of this invention is achieved through the following technical solution:

[0035] An artificial wetland system for enhancing iron-based carbon release, nitrogen removal, and greenhouse gas emission reduction includes:

[0036] The system consists of an inlet module, a purification module, and an outlet module connected in sequence; wherein the outlet module's outlet is connected to a drain pipe or a return pipe, and the other end of the return pipe is connected to the inlet module.

[0037] The return pipe is installed between the inlet module and the outlet module;

[0038] The water purification module includes several wetlands, and each wetland is equipped with a valve for water intake between itself and the water inlet channel, as well as between the wetlands; at least one wetland is equipped with a valve for water outlet at its other end; the wetlands are connected in parallel or in series by controlling the opening and closing of the valves.

[0039] The aforementioned constructed wetland system for enhanced iron-based carbon release, denitrification, and greenhouse gas emission reduction has an inlet channel as the water intake module and an outlet channel as the water outlet module.

[0040] The aforementioned constructed wetland system for enhanced iron-based carbon release, denitrification, and greenhouse gas emission reduction includes a water purification module comprising a first wetland and a second wetland.

[0041] The aforementioned constructed wetland system for enhanced iron-based carbon release, denitrification, and greenhouse emission reduction is equipped with water quality testing instruments at the bottom of the inlet channel and the bottom of the outlet channel.

[0042] The aforementioned constructed wetland system for enhanced iron-based carbon release, nitrogen removal, and greenhouse gas emission reduction comprises a first wetland that is a conventional aerated wetland, and a second wetland containing a water purification substrate layer, including a lower substrate layer and an upper substrate layer. The upper substrate layer is planted with aquatic plants, specifically one or more of the following: yellow iris, canna lily, iris, and canna lily, at a planting density of 20-40 plants / m². 2 .

[0043] The aforementioned constructed wetland system for enhanced iron-based carbon release, nitrogen removal, and greenhouse gas emission reduction comprises an upper substrate layer filled with ordinary gravel with a particle size range of 10-20 mm; and a lower substrate layer filled with a composite matrix of iron-based and biochar, wherein the iron-based particles range in size from 5-10 mm, the biochar particles range in size from 5-10 mm, and the biochar has a specific surface area of ​​10-1000 m². 2 / g.

[0044] The aforementioned constructed wetland system for enhanced iron-based carbon release, denitrification, and greenhouse emission reduction has a lower substrate layer with a height of h1 (10-20 cm) and an upper substrate layer with a height of h2 (20-30 cm).

[0045] The usage methods of the above-mentioned constructed wetland system for enhanced iron-based carbon release, nitrogen removal, and greenhouse gas emission reduction are as follows:

[0046] Step 1: The wastewater to be treated enters the inlet channel through the inlet;

[0047] Step 2: The incoming water is tested by the first water quality analyzer at the bottom of the inlet channel. The first water quality analyzer judges the transmitted data C1:

[0048] a. If C1>C 进 The valves between the first wetland and the inlet canal, and between the first wetland and the second wetland, are opened. The first wetland and the second wetland are connected in series, and the sewage passes through the first wetland and the second wetland in sequence.

[0049] b. If C1≤C 进 In this case, only the valve between the second wetland and the inlet canal is opened, and the sewage flows through the second wetland;

[0050] Step 3: Wastewater flows into the first wetland through the inlet channel, where ammonia nitrogen removal is enhanced by the aeration system, and dissolved oxygen content is monitored.

[0051] Step 4: Wastewater enters the second wetland through a valve between the first and second wetlands, where it undergoes enhanced denitrification and greenhouse gas emission reduction using iron-based methods.

[0052] Step 5: The treated water is discharged into the drainage ditch;

[0053] Step 6: The effluent is then tested by a second water quality analyzer at the bottom of the effluent channel. The second water quality analyzer interprets the transmitted data C2.

[0054] a. If C2>C 出 Then the valve between the outlet channel and the return pipe is opened, and the water flows back to the inlet channel through the return pipe for further purification.

[0055] b. If C2≤C 出 The water is discharged from the outlet channel;

[0056] c. If the NO3-N data is abnormal, the water purification substrate layer of the second wetland needs to be replenished or replaced.

[0057] Optionally, the volume ratio of the lower substrate layer of the water purification substrate in the second wetland is adjusted according to the concentration of pollutants in the treated water: when the total nitrogen concentration is 0-50 mg / L, the volume ratio of iron-based substrate to biochar is 2:1; when the total nitrogen concentration is 51-100 mg / L, the volume ratio of iron-based substrate to biochar is 1:1.

[0058] The aforementioned enhanced iron-based carbon release, denitrification, and greenhouse emission reduction constructed wetland system has a vertical downflow constructed wetland structure, an intermittent water inlet method, an optional hydraulic retention time of 66-70 hours, and an emptying time of 2-6 hours. An aeration device is installed in the first wetland.

[0059] The dissolved oxygen content in the first wetland is collected by sensors and monitored in real time by a monitoring system. The monitoring system monitors the current dissolved oxygen concentration (DO). n The criteria are determined by n = 0, 1, 2... When the content is below the lower limit, i.e., DO... n <DO L When the concentration exceeds the upper limit, start the aeration equipment for aeration; when the concentration exceeds the upper limit, DO... n >DO U When the concentration is within the upper or lower limit, turn off the aeration equipment; when the concentration is within the upper or lower limit, i.e., DO L ≤DO n ≤DO U At this point, the aeration intensity remains unchanged, and then the operation continues at n = n + 1.

[0060] Optionally, the lower limit of dissolved oxygen concentration (DO) L The upper limit of dissolved oxygen concentration (DO) is 2 mg / L. U The concentration is 6 mg / L; when the concentration is within the upper and lower limits, the aeration intensity is 1.0-2.0 L / min.

[0061] The beneficial effects obtained by adopting the above technical solution include:

[0062] (1) The wetland of this invention comprises a first wetland, which is a conventional aerated wetland, and a second wetland, which employs a double-layer purification base layer: a layer of ordinary gravel and a layer of composite matrix composed of a mixture of iron-based materials and biochar. Utilizing the inherent properties of the different matrices, the iron-based materials provide inorganic electron donors to enhance the autotrophic denitrification of the system, while the biochar serves as a slow-release carbon denitrification source for denitrifying microorganisms. The mixture of these two materials forms an iron-carbon micro-electrolysis system, further promoting simultaneous nitrification and denitrification, strengthening microbial autotrophic and heterotrophic denitrification, promoting nitrogen conversion, and improving denitrification efficiency while reducing greenhouse gas emissions. After operation, the artificial wetland denitrification device provided by this invention can achieve a denitrification efficiency of 90%-98% and reduce greenhouse gas emissions by 20%-40%.

[0063] (2) The artificial wetland system of the present invention selectively operates two sets of wetland devices according to the water purification needs, flexibly adjusts the artificial wetland system, improves purification efficiency, and avoids waste of resources. Attached Figure Description

[0064] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following accompanying drawings are provided:

[0065] Figure 1 This is a plan view of the artificial wetland system described in this invention;

[0066] Figure 2 For along Figure 1 Cross-sectional view of line AA in the middle;

[0067] Figure 3 For along Figure 1 Cross-sectional view of the middle BB line;

[0068] Figure 4 This is a schematic diagram of the layered structure of the second wetland according to the present invention;

[0069] Figure 5 This is a schematic diagram illustrating the operating principle of the constructed wetland system described in this invention.

[0070] Figure 6 This is a schematic diagram showing the connection relationship between the various functional modules of the present invention;

[0071] Figure 7 This is a schematic diagram of the aeration system operation principle of the present invention.

[0072] Explanation of reference numerals in the attached drawings: 1-1. Inlet channel; 2-1. First wetland; 2-2. Second wetland; 2-3. Lower substrate layer; 2-4. Upper substrate layer; 2-5. Aquatic plants; 3-1. Outlet channel; 4. Return pipe; 5-1. First valve; 5-2. Second valve; 5-3. Third valve; 5-4. Fourth valve; 5-5. Fifth valve; 5-6. Sixth valve; 6. Sensor; 7-1. First water quality analyzer; 7-2. Second water quality analyzer; 8. Aeration equipment; 9. Monitoring system;

[0073] 10. Water inlet module, 20. Water purification module, 30. Water outlet module.

[0074] It should be noted that the above figures only show some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained from these figures without any creative effort. Detailed Implementation

[0075] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0076] For ease of description, spatial relative terms such as "below," "below," "down," "above," "upper," etc., will be used where necessary to describe the relationship of one element or feature shown in the figures relative to another element or feature. These spatial relative terms are intended to include different orientations of the device in use or operation, in addition to those shown in the figures. For example, if the devices in the figures are flipped, an element described as "below" or "below" other elements or features would be oriented as "above" other elements or features.

[0077] Unless otherwise specified, the terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains, and are to be understood as having the meaning consistent with the meaning in the context of the relevant art, and should not be interpreted in an idealized or over-formalized manner, except as expressly defined in this invention.

[0078] In this invention, the first wetland is a common aerated wetland, and there are no special requirements for the substrate layer filler; commonly used materials such as gravel, zeolite, coal, river sand, and pebbles can all be used. The filler is selected and cleaned before use. This invention does not have special requirements for the cleaning method; impurities can be removed according to processes well-known in the art.

[0079] In this invention, the material of the lower substrate layer laid in the second wetland is ordinary gravel, preferably with a particle size of 10-20 mm. This invention does not have special requirements regarding the source of the gravel; commercially available gravel is sufficient. The gravel is preferably washed before use. This invention does not have special requirements regarding the washing method; impurities can be removed according to processes well-known in the art.

[0080] In this invention, the lower substrate layer of the second wetland is a composite substrate layer made of iron-based materials and biochar mixed in a volume ratio. The preferred particle size of the biochar is 5-10 mm. The preferred particle size of the iron-based materials is also 5-10 mm. This invention does not have special requirements regarding the source of the biochar; commercially available biochar or self-prepared biochar can be used. Before use, the biochar is selected based on its particle size and cleaned. This invention does not have special requirements regarding the cleaning method; impurities can be removed according to processes well-known in the art. For the source of the iron-based materials, this invention can use commercially available iron-based materials (zero-valent iron, iron (hydrogen) oxides, iron sulfides). Before use, the iron-based materials are selected based on their particle size and cleaned. This invention does not have special requirements regarding the cleaning method; impurities can be removed according to processes well-known in the art.

[0081] Example 1

[0082] An artificial wetland system for enhancing iron-based carbon release, denitrification, and greenhouse gas emission reduction includes: an inlet module 10, a purification module 20, and an outlet module 30 connected in sequence; wherein the outlet of the outlet module 30 is connected to a drain pipe or a return pipe 4, and the other end of the return pipe 4 is connected to the inlet module 10.

[0083] The water inlet module 10 adopts an inlet channel 1-1, the water outlet module 30 adopts an outlet channel 3-1, and the return pipe 4 is set between the outlet channel 3-1 and the inlet channel 1-1. A first water quality detector 7-1 and a second water quality detector 7-2 are installed at the bottom of the inlet channel 1-1 and the bottom of the outlet channel 3-1, respectively, to measure the water quality of the inlet and outlet water.

[0084] The water purification module 20 includes a first wetland 2-1 and a second wetland 2-2. The structure of the first wetland 2-1 and the second wetland 2-2 is a vertical downflow constructed wetland. An aeration device is installed inside the first wetland 2-1 (not shown in the figure for simplicity).

[0085] A first valve 5-1 for water intake is provided between the first wetland 2-1 and the inlet channel 1-1; a second valve 5-2 for water intake is provided between the second wetland 2-2 and the inlet channel 1-1; a third valve 5-3 is provided between the first wetland 2-1 and the second wetland 2-2; a fourth valve 5-4 for water outlet is provided at the other end of the second wetland 2-2; the first wetland 2-1 and the second wetland 2-2 are connected in parallel or in series by controlling the opening and closing of the above valves; the two ends of the return pipe 4 are connected to the two ends of the outlet channel 3-1 through a fifth valve 5-5 and a sixth valve 5-6, respectively.

[0086] A water purification substrate layer is laid within the second wetland 2-2 of the water purification module 20. The lower substrate layer 2-3 is made of ordinary gravel with a particle size range of 10-20 mm and a laying height of 15 cm. The upper substrate layer 2-4 is a composite substrate layer composed of pyrite and biochar mixed in a volume ratio of 2:1, with a particle size range of 5-10 mm and a laying height of 25 cm. In this invention, wastewater flows sequentially through the pyrite-biochar layer of the upper substrate layer 2-4 and the gravel layer of the lower substrate layer 2-3. Nitrogen is adsorbed on the substrate surface or transformed through electron donors provided by pyrite and biochar.

[0087] Aquatic plants 2-5 are planted in the upper substrate layer of the artificial wetland, with *Iris tectorum* (yellow iris) being the preferred aquatic plant, at a planting density of 30 plants / m². 2 The preferred method for water inflow into the constructed wetland is intermittent water inflow; the preferred hydraulic retention time for this intermittent water inflow method is 68 hours, and the preferred emptying time is 4 hours. The dissolved oxygen content within the first wetland 2-1 is collected by sensor 6 and monitored in real-time by monitoring system 9. Monitoring system 9 monitors the current dissolved oxygen concentration (DO). n (n = 0, 1, 2...) is used for judgment, and when the content is lower than the lower limit (DO) n <DO L When the concentration is 2 mg / L, start aeration equipment 8 for aeration. When the concentration is higher than the upper limit (DO), n >DO U When the concentration is 6 mg / L, turn off aeration equipment 8. When the concentration is within the upper and lower limits (DO), L ≤DO n ≤DO U When the aeration intensity remains constant at 1.0-2.0 L / min, it continues to run at n = n+1.

[0088] The operation mode of the above-mentioned constructed wetland system is as follows:

[0089] Step 1: The wastewater to be treated enters the inlet channel 1-1 through the inlet;

[0090] Step 2: Wastewater is tested by the first water quality analyzer 7-1 at the bottom of the inlet channel 1-1. The first water quality analyzer 7-1 judges the transmitted data C1:

[0091] Wherein, C1 is the ammonia nitrogen concentration before wastewater treatment; C1 = 28 mg / L;

[0092] C 进 It is the ammonia nitrogen concentration entering the wetland, C 进 =20mg / L;

[0093] C1>C 进 Valves 5-1, 5-3, and 5-4 are opened, and the sewage flows through the first wetland 2-1 and the second wetland 2-2 in sequence.

[0094] Step 3: Wastewater flows into the first wetland 2-1 through the inlet channel 1-1. Ammonia nitrogen removal is enhanced through the aeration system. The dissolved oxygen content is 3 mg / L. The aeration system is turned on and the aeration intensity is 2.0 L / min.

[0095] Step 4: Wastewater enters the second wetland 2-2 through valve 5-3 between the first wetland 2-1 and the second wetland 2-2, where it undergoes enhanced denitrification and greenhouse gas emission reduction through iron-based methods.

[0096] Step 5: The treated effluent is discharged into the effluent channel 3-1;

[0097] Step 6: The effluent is tested by the second water quality analyzer 7-2 at the bottom of the effluent channel 3-1. The second water quality analyzer 7-2 judges the transmitted data C2: C2 < C 出 The water is discharged from the outlet channel 3-1.

[0098] Where C2 is the total nitrogen concentration after wastewater purification; C2 = 3.6 mg / L;

[0099] C 出 It is the total nitrogen concentration (C) at the wetland. 出 =5mg / L.

[0100] Example 2

[0101] The constructed wetland system described in Example 1 operates as follows:

[0102] Step 1: The wastewater to be treated enters the inlet channel 1-1 through the inlet;

[0103] Step 2: Wastewater is tested by the first water quality analyzer 7-1 at the bottom of the inlet channel 1-1. The first water quality analyzer 7-1 judges the transmitted data C1:

[0104] Wherein, C1 is the ammonia nitrogen concentration before wastewater treatment; C1 = 15 mg / L;

[0105] C 进 It is the ammonia nitrogen concentration entering the wetland, C 进 =20mg / L;

[0106] C1 < C 进 Valves 5-2 and 5-4 are opened, and sewage flows through the second wetland 2-2;

[0107] Step 3: After being treated in the second wetland 2-2, the wastewater is discharged into the effluent channel 3-1;

[0108] Step 4: The effluent is tested by the second water quality analyzer 7-2 at the bottom of the effluent channel 3-1. The second water quality analyzer 7-2 judges the transmitted data C2: C2 < C 出 The water is discharged from the outlet channel 3-1.

[0109] Where C2 is the total nitrogen concentration after wastewater purification; C2 = 2.8 mg / L;

[0110] C 出 It is the total nitrogen concentration (C) at the wetland. 出 =5mg / L.

[0111] Example 3

[0112] The difference from Example 1 is that:

[0113] A water purification substrate layer is laid in the second wetland 2-2 of the water purification module. The upper substrate layer 2-4 is a composite substrate layer made of pyrite and biochar mixed in a volume ratio of 1:1, with a particle size range of 5-10mm and a laying height of 25cm.

[0114] The operation mode of the above-mentioned constructed wetland system is as follows:

[0115] Step 1: The wastewater to be treated enters the inlet channel 1-1 through the inlet;

[0116] Step 2: Wastewater is tested by the first water quality analyzer 7-1 at the bottom of the inlet channel 1-1. The first water quality analyzer 7-1 judges the transmitted data C1:

[0117] Wherein, C1 is the ammonia nitrogen concentration before wastewater treatment; C1 = 90 mg / L;

[0118] C 进 It is the ammonia nitrogen concentration entering the wetland, C 进 =20mg / L;

[0119] C1>C 进 With valves 5-1, 5-3, and 5-4 opened, sewage flows sequentially through wetland 2-1 and wetland 2-2.

[0120] Step 3: Wastewater flows into the first wetland 2-1 through the inlet channel 1-1. Ammonia nitrogen removal is enhanced by the aeration system. Dissolved oxygen content = 7 mg / L. The aeration system is then shut down.

[0121] Step 4: Wastewater enters the second wetland 2-2 through valve 5-3 between the first wetland 2-1 and the second wetland 2-2, where it undergoes enhanced denitrification and greenhouse gas emission reduction through iron-based methods.

[0122] Step 5: The treated effluent is discharged into the effluent channel 3-1;

[0123] Step 6: The effluent is tested by the second water quality analyzer 7-2 at the bottom of the effluent channel 3-1. The second water quality analyzer 7-2 judges the transmitted data C2: C2 > C 出 When valves 5-5 and 5-6 are opened, the effluent flows back to the inlet channel 1-1 via return pipe 4 for further purification.

[0124] Wherein, C2 is the total nitrogen concentration after wastewater purification; C2 = 10 mg / L;

[0125] C 出 It is the total nitrogen concentration (C) at the wetland. 出 =5mg / L.

[0126] Step 7: Wastewater is tested by the first water quality analyzer 7-1 at the bottom of the inlet channel 1-1. The first water quality analyzer 7-1 judges the transmitted data C3:

[0127] Wherein, C3 is the ammonia nitrogen concentration before wastewater treatment; C3 = 6 mg / L;

[0128] C 进 It is the ammonia nitrogen concentration entering the wetland, C 进 =20mg / L;

[0129] C3 < C 进 Valves 5-2 and 5-4 are opened, and sewage flows through the second wetland 2-2;

[0130] Step 8: After being treated in the second wetland 2-2, the wastewater is discharged into the effluent channel 3-1;

[0131] Step 9: The effluent is tested by the second water quality analyzer 7-2 at the bottom of the effluent channel 3-1. The second water quality analyzer 7-2 judges the transmitted data C4: C4 < C 出 The water is discharged from the outlet channel 3-1.

[0132] Wherein, C4 is the total nitrogen concentration after wastewater purification; C4 = 1 mg / L;

[0133] C 出 It is the total nitrogen concentration (C) at the wetland. 出=5mg / L.

[0134] Example 4

[0135] The difference from Example 1 is that:

[0136] The total nitrogen concentration after wastewater purification is C2 = 40 mg / L.

[0137] The NO3-N concentration was 30 mg / L.

[0138] The NO3-N data in the effluent is abnormal, and the water purification substrate in the second wetland 2-2 needs to be replenished or replaced.

[0139] The above description of the embodiments is provided to enable those skilled in the art to understand and use the present invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. An artificial wetland system for enhanced iron-based denitrification and greenhouse gas emission reduction, characterized in that, include: The system comprises an inlet module, a purification module, and an outlet module connected in sequence; wherein the outlet module's outlet is connected to a drain pipe or a return pipe, and the other end of the return pipe is connected to the inlet module; the inlet module is an inlet channel, and the outlet module is an outlet channel; the return pipe is located between the inlet module and the outlet module. The water purification module includes several wetlands, each with a valve for water intake between itself and the inlet channel, and between the wetlands themselves; at least one wetland has a valve for water outlet at its other end; the wetlands can be connected in parallel or in series by controlling the opening and closing of these valves; the water purification module includes a first wetland and a second wetland; the dissolved oxygen content in the first wetland is collected by sensors and monitored in real time by a monitoring system, which monitors the current dissolved oxygen concentration (DO). n The criteria are determined by n=0,1,2... When the content is below the lower limit, i.e., DO n <DO L When the concentration exceeds the upper limit, start the aeration equipment for aeration; when the concentration exceeds the upper limit, DO... n >DO U When the concentration is within the upper or lower limit, turn off the aeration equipment; when the concentration is within the upper or lower limit, i.e., DO L ≤DO n ≤DO U At this point, the aeration intensity remains unchanged, and then the operation continues at n=n+1; The second wetland is covered with a water purification substrate layer, including a lower substrate layer and an upper substrate layer. Aquatic plants are planted in the upper substrate layer. The upper substrate layer is filled with ordinary gravel. The lower substrate layer is filled with an iron-based and biochar composite substrate. The formula for calculating the mass of the iron-based matrix is ​​as follows: M Fe总= M Fe1+ M Fe2 M Fe1 =xC NO3 - - N* V NO3 - - N / 14*5 / 3*56 / α=6.67x C NO3 - - N* V NO3 - - N / α M Fe2 =yC NO3 - - N* V NO3 - - N / 14*5*56 / β=20y C NO3 - - N* V NO3 - - N / β x+y=1 M Fe总 —Total mass of iron required for the constructed wetland system, in kg. M Fe1 —The mass of elemental iron required for an artificial wetland system, in kg. M Fe2 —The mass of ferrous iron required for the constructed wetland system, in kg. C NO3 - -N —The required reduction in nitrate concentration for constructed wetland systems, in units of (kg / L). V NO3 - -N —The volume of water that the constructed wetland system needs to treat, in units (L); α – the electron donor availability rate in elemental iron, which can be taken as 0.5-0.7; β—the electron donor rate in divalent iron, which can be taken as 0.6-0.8; x — The ratio of nitrate to nitrogen required to be treated by elemental iron, which can be taken as 0-1; y – The percentage of nitrate and nitrogen that needs to be treated by ferrous iron, which can be taken as 0-1.

2. The constructed wetland system for enhanced iron-based denitrification and greenhouse gas emission reduction according to claim 1, characterized in that: Water quality testing instruments are installed at the bottom of the inlet channel and the bottom of the outlet channel, respectively.

3. The constructed wetland system for enhanced iron-based denitrification and greenhouse gas emission reduction according to claim 1, characterized in that: The first wetland mentioned is a typical aerated wetland.

4. The constructed wetland system for enhanced iron-based denitrification and greenhouse gas emission reduction according to claim 3, characterized in that: The aquatic plants mentioned are one or more of the following: yellow iris, canna lily, iris, and canna lily.

5. The constructed wetland system for enhanced iron-based denitrification and greenhouse gas emission reduction according to claim 3, characterized in that: The planting density of the aquatic plants is 20-40 plants / m². 2 .

6. The constructed wetland system for enhanced iron-based denitrification and greenhouse gas emission reduction according to claim 1, characterized in that: The ordinary gravel has a particle size range of 10-20 mm; the iron-based gravel has a particle size range of 5-10 mm; the biochar has a particle size range of 5-10 mm; and the biochar has a specific surface area of ​​10-1000 m². 2 / g.

7. The constructed wetland system for enhanced iron-based denitrification and greenhouse gas emission reduction according to claim 3, characterized in that: The height of the lower matrix layer is h1, 10~20 cm; the height of the upper matrix layer is h2, 20~30 cm.

8. The method of using the constructed wetland system for enhanced iron-based denitrification and greenhouse emission reduction according to claim 1, characterized in that, Includes the following steps: Step 1: The wastewater to be treated enters the inlet channel through the inlet; Step 2: The incoming water is tested by the first water quality analyzer at the bottom of the inlet channel. The first water quality analyzer judges the transmitted data C1: a. If C1>C 进 The valves between the first wetland and the inlet canal, and between the first wetland and the second wetland, are opened. The first wetland and the second wetland are connected in series, and the sewage passes through the first wetland and the second wetland in sequence. b. If C1≤C 进 In this case, only the valve between the second wetland and the inlet canal is opened, and the sewage flows through the second wetland; Step 3: Wastewater flows into the first wetland through the inlet channel, where ammonia nitrogen removal is enhanced by the aeration system, and dissolved oxygen content is monitored. Step 4: Wastewater enters the second wetland through a valve between the first and second wetlands, where it undergoes enhanced denitrification and greenhouse gas emission reduction using iron-based methods. Step 5: The treated water is discharged into the drainage ditch; Step 6: The effluent is then tested by a second water quality analyzer at the bottom of the effluent channel. The second water quality analyzer interprets the transmitted data C2. a. If C2>C 出 Then the valve between the outlet channel and the return pipe is opened, and the water flows back to the inlet channel through the return pipe for further purification. b. If C2≤C 出 The water is discharged from the outlet channel; c. If the NO3-N data is abnormal, the water purification substrate layer of the second wetland needs to be replenished or replaced; Where C1 is the ammonia nitrogen concentration before wastewater treatment; C 进 C1 is the ammonia nitrogen concentration entering the wetland; C2 is the total nitrogen concentration after wastewater treatment; C 出 It is the total nitrogen concentration outside the wetland.

9. The method of using the constructed wetland system for enhanced iron-based denitrification and greenhouse emission reduction according to claim 8, characterized in that; The volume ratio of the lower substrate layer of the water purification substrate in the second wetland is adjusted according to the concentration of pollutants in the treated water: when the total nitrogen concentration is 0-50 mg / L, the volume ratio of iron-based and biochar is 2:1; when the total nitrogen concentration is 51-100 mg / L, the volume ratio of iron-based and biochar is 1:

1.

10. The method of using the constructed wetland system for enhanced iron-based denitrification and greenhouse emission reduction according to claim 8, characterized in that: The wetland is a vertical downflow constructed wetland with intermittent water intake.

11. The method of using the constructed wetland system for enhanced iron-based denitrification and greenhouse emission reduction according to claim 10, characterized in that: The hydraulic retention time of the wetland is 66-70 h, and the drainage time is 2-6 h. An aeration device is installed in the first wetland.

12. The method of using the constructed wetland system for enhanced iron-based denitrification and greenhouse emission reduction according to claim 8, characterized in that: The lower limit of dissolved oxygen concentration (DO) L The upper limit of dissolved oxygen concentration (DO) is 2 mg / L. U The concentration is 6 mg / L; when the concentration is within the upper and lower limits, the aeration intensity is 1.0-2.0 L / min.

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