Tandem modular constructed wetland and accurate methane emission reduction method thereof

Abstract

The invention discloses a tandem type modular constructed wetland and a precise methane emission reduction method thereof, and relates to the technical field of sewage treatment.The constructed wetland comprises a pool body, the pool body is composed of a plurality of liftable modules which are sequentially communicated and form an up-down circulation communication channel, and matrix purification modules are arranged in the liftable modules; a water through hole convenient for water flow to pass through is formed in the matrix purification module, a plant purification module is arranged at the top of the tank body, a backwashing module is arranged at the bottom of the liftable module, an aeration module is arranged between the matrix purification module and the backwashing module, and a water inlet pipe and a water outlet pipe are respectively arranged at two ends of the tank body. The emission reduction method sequentially comprises the following steps: collecting methane concentration, and adjusting the working state of the aeration module according to inlet water quality and methane concentration. The sewage purification efficiency is high, the methane emission amount is small, the construction cost is low, the system can be widely applied to rural non-point-source sewage treatment, and accurate emission reduction of methane is achieved in an accurate aeration mode.

Description

Technical Field

[0001] The invention relates to the technical field of sewage treatment, and in particular to a series-type modular artificial wetland and a method for accurately reducing methane emissions thereof. Background Art

[0002] In recent years, the concentration of methane in the atmosphere has increased significantly. According to the Sixth Assessment Report (AR6) of the Intergovernmental Panel on Climate Change (IPCC), the concentration of greenhouse gases in the atmosphere and the annual emissions of anthropogenic greenhouse gases continue to grow. In 2019, the concentration of CO2 was the highest in 2 million years, and the concentration of CH4 was the highest in 800,000 years. As the global climate warms, the activity of wetland microorganisms has further increased, causing wetland methane emissions to continue to increase rapidly, currently accounting for about 30% of the global annual methane emissions. In the past 20 years, wetland methane emissions have increased by an average of 1.3 million to 1.4 million tons per year. Since 2007, the concentration of methane in the atmosphere has begun to rise rapidly, setting historical highs for two consecutive years in 2020 and 2021, increasing by 14 million tons to 26 million tons and 13 million tons to 23 million tons, respectively.

[0003] As an ecological water treatment system, artificial wetlands have the advantages of good treatment effect, low construction and maintenance cost, and ecological landscape, and are widely used in various wastewater treatment. Nowadays, the issue of global warming has received more and more attention. With the widespread use of artificial wetlands in water treatment, greenhouse gas emissions from artificial wetlands have also received attention. As a traditional ecological treatment technology, artificial wetlands have great potential in reducing greenhouse gas emissions.

[0004] Traditional artificial wetlands have low sewage purification efficiency, large methane emissions, and high construction costs, and cannot be widely used in rural non-point source sewage treatment. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and propose a series modular artificial wetland and a method for precise methane emission reduction thereof, which has high sewage purification efficiency and low methane emissions, low construction cost, can be widely used in rural non-point source sewage treatment, and achieves precise methane emission reduction through precise aeration methods.

[0006] The objective of the present invention is achieved through the following technical solutions: a serial modular artificial wetland, comprising a pool body, wherein the pool body is composed of a plurality of extractable modules which are connected in sequence to form an upper and lower circulation connecting channel, wherein a matrix purification module and a plant purification module arranged on the top of the matrix purification module are arranged in the extractable module, wherein water holes for facilitating the passage of water are opened on the matrix purification module, wherein a plurality of the plant purification modules are located on the top of the pool body, a backwash module is arranged at the bottom of the extractable module, an aeration module is arranged between the matrix purification module and the backwash module, and an inlet pipe and an outlet pipe are arranged at both ends of the pool body respectively.

[0007] The matrix purification module includes a placement frame, which is filled with a sand layer, a coarse sand layer, a gravel layer, a pebble layer and a large pebble layer. Gaps are set between the multiple placement frames, and the plant purification modules are stacked on the upper end of the placement frame. The gaps between the placement frames make the hydraulic flow smoother, which prevents and controls dead water, thereby reducing methane emissions in anaerobic environments. The placement frame can be made of porous medium materials (good adsorption effect, convenient water degradation) or nanomaterial frames. The plant purification module can be stacked on the placement frame. Thereby, modular series or parallel replacement can be achieved. But the general principle is that the particle size below should be larger than that above, which is intended to facilitate methane emission reduction. The particles in the placement frame can be arranged from large to small in medium particle size from bottom to top, or they can be staggered.

[0008] The aeration module comprises a plurality of microporous aeration disks mounted on the substrate purification module and an aeration pipe penetrating the tank body. One end of the aeration pipe is connected to an aerator and the other end is connected to the microporous aeration disk.

[0009] The backwash module includes a backwash air pipe arranged at the bottom of the pool body, a plurality of backwash water distribution pipes are arranged on the backwash air pipe, an air pump is connected to the backwash air pipe, and a backwash valve is arranged on the backwash air pipe. The backwash valve can effectively prevent the blockage of the artificial wetland, thereby solving the blockage problem of the artificial wetland after long-term operation.

[0010] The plant purification module comprises an isolation plate arranged on the substrate purification module, a plurality of root control pots arranged on the isolation plate, and aquatic plants planted in the root control pots, wherein the roots of the aquatic plants penetrate deeply into the substrate purification module.

[0011] The water inlet pipe and the water outlet pipe are provided with water quality monitoring probes.

[0012] A grid supporting frame is arranged in the pool body, and the substrate purification module and the aeration module are arranged on the grid supporting frame.

[0013] A method for accurately reducing methane emissions based on the artificial wetland comprises the following steps: S1. Monitor the methane concentration and obtain the average value of the methane flux during the monitoring period; S2. Adjust the aeration time and aeration intensity of the aeration module according to the collected methane flux average value data.

[0014] In step S1, within the time period from 15:00 to 8:00, every 3 hours is a monitoring time period, within the time period from 8:00 to 10:00, every 1 hour is a monitoring time period, within the time period from 10:00 to 12:00, every 2 hours is a monitoring time period; within the time period from 12:00 to 15:00, every 1 hour is a monitoring time period.

[0015] According to the formula Determining the aeration time and aeration intensity of the aeration module (6); Where S is the average methane flux during the monitoring period, in mol / m 2 / day -1 ; t is the monitoring time, in h; T is the aeration time, in h; q is the aeration intensity (m 3 / h).

[0016] The beneficial effects of the present invention are: (1) The present invention is a unique wetland system with multiple groups of downstream-upstream composite water flow modes, which is composed of multiple groups of matrix purification modules. Usually, one group is used as a downstream pool and the other group is used as an upstream pool. The two groups are connected at the bottom and a partition wall is provided in the middle. Sewage flows vertically downward (upward) from one group of matrix purification modules into another group of matrix purification modules and then flows vertically upward (downward) out.

[0017] (2) The flow of sewage in the present invention relies on the water level difference between the two pools to provide power to push the water forward, and no other power is required.

[0018] (3) Compared with the traditional vertical flow artificial wetland, the present invention has the following characteristics: the water flows through multiple groups of matrix purification modules, so that the hydraulic retention time of sewage in the system is prolonged and the treatment is more complete; the entire artificial wetland adopts a reasonable aeration scheme, which makes the artificial wetland system reoxygenated more rapidly, and the oxygen mass transfer efficiency can reach 3.9m³ / h; at the same time, by controlling the position of the aeration pipe section, the realization of the aerobic-anoxic-aerobic mechanism can be promoted, and the simultaneous nitrification-denitrification of aerobic and anaerobic microorganisms can be combined to deeply degrade pollutants.

[0019] (4) The aeration module intermittently creates an oxygen environment, thereby killing methanogens. The aeration volume of the aeration module is controlled according to the methane production, and the aeration interval is determined according to the methane generation cycle, thereby achieving precise methane emission reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the present invention; Figure 2 This is the plan layout of the aeration head; Figure 3 It is a transverse cross-sectional view of the present invention; Figure 4 It is a first vertical cross-sectional view of the present invention; Figure 5 It is a second vertical cross-sectional view of the present invention; Figure numerals: 1. Tank body; 11. Water inlet pipe; 12. Water outlet pipe; 13. Water quality monitoring probe; 14. Grid support frame; 16. Methane monitoring point; 2. Extractable test module; 3. Matrix purification module; 4. Plant purification module; 41. Isolation plate; 42. Root control pot; 43. Aquatic plants; 5. Backwash module; 51. Backwash gas pipe; 52. Backwash water distribution pipe; 6. Aeration module; 61. Microporous aeration disk; 62. Aeration pipe. DETAILED DESCRIPTION

[0021] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0022] It is to be noted that the concepts of directions “left”, “right”, “up”, “down”, “front”, “back”, “inside” and “outside” in the following schemes are all relative directions and will not be listed one by one here.

[0023] A series of modular artificial wetlands, reference Figure 1-Figure 5 , including a tank body 1. A water inlet pipe 11 and a water outlet pipe 12 are respectively provided at both ends of the tank body 1. A water quality monitoring probe 13 is provided on the water inlet pipe 1 and the water outlet pipe 2. Four portable modules 2 are provided in the tank body 1. The upper end of one side of the portable module 2 is connected to the portable module 2, and the lower end of the other side is connected to the portable module 2, thereby forming a channel that bends up and down. Two methane monitoring points 16 are provided on the tank body 1. The top of the portable module 2 is provided with a plant purification module 4, and the lower middle part is provided with a grid support frame 14. The grid support frame 14 is provided with a substrate purification module 3 and an aeration module 6. The substrate purification module 3 is provided with a water hole for facilitating the passage of water. A backwash module 5 is provided between the bottom wall of the portable module 2 and the grid support frame 14.

[0024] The matrix purification module 3 includes a placement frame. A sand layer, a coarse sand layer, a gravel layer, a pebble layer and a large pebble layer are arranged in the placement frame. The fine sand layer uses a micro-mineral composite filter material with a particle size of 1-2mm, the middle sand layer uses a micro-mineral composite filter material with a particle size of 2-4mm, and the coarse sand layer uses a micro-mineral composite filter material with a particle size of 4-5mm. The composite filter material used in this example has good adsorption performance and specific surface area, has a good purification effect on sewage, and has great economic benefits. Gravel is cheap and easy to obtain. There is a gap between two adjacent placement frames, and the hydraulic flow is relatively smooth, which prevents and controls dead water, thereby reducing methane emissions in anaerobic environments. The placement frame can consider using porous medium materials (good adsorption effect, convenient water degradation) or nanomaterial frames. The plant purification module 4 can be stacked with the placement frame. Thereby realizing modular series or parallel replacement at will. But the general principle is that the particle size below is larger than that above, which is intended to facilitate methane emission reduction. The particles in the placement frame can be arranged from large to small in particle size from bottom to top, or can be arranged in a staggered manner.

[0025] The plant purification module 4 includes an isolation plate 41 arranged on the substrate purification module 3. A root control basin 42 is arranged on the isolation plate 41. Aquatic plants 43 are arranged on the root control basin 42. The roots of the aquatic plants 43 penetrate into the substrate purification module 3. The roots of the aquatic plants 43 are sealed with plastic film, the plant stems are sealed with plastic film and foam glue, the stems and leaves are also sealed with plastic film, and the built-in wooden strips support the seal. The root water and the top of the stems and leaves are set with a slope to ensure that the middle gas collection point is the highest position, which is convenient for collecting methane gas with a lighter density. A thermometer, a hygrometer and a fan are installed in the plant purification module 4.

[0026] The backwash module 5 includes a backwash air pipe 51 passing through the bottom of the pool body 1. A backwash valve is arranged on the backwash air pipe 51, and an air pump is arranged at one end of the backwash air pipe 51 outside the pool body 1. A plurality of backwash water distribution pipes 52 are arranged on the backwash air pipe 51.

[0027] The aeration module 6 includes an aeration pipe 62 that passes through the tank body 1 from front to back. The aeration pipe 62 is located outside the tank body 1 and is connected to an aerator. The aeration pipe 62 is connected to a plurality of microporous aeration disks 61. The microporous aeration disks 61 are installed in the middle, sides and corners of the substrate purification module 3. Aeration is performed using an electromagnetic compressor. The aeration machine model is AL-60, with a power of 60w, a voltage / frequency of 220v / 50Hz, an exhaust volume of 60L / min, a pressure of 0.015mPa, and an aeration volume of 3.6m 3 / h, the aeration range is a cone area, the bottom range of the cone area is 0.2m 2 .

[0028] A method for accurately reducing methane emissions based on artificial wetlands comprises the following steps: S1. Monitor the methane concentration and obtain the average methane flux during the monitoring time; in which, within the time period of 15:00-8:00, every 3 hours is a monitoring time period, within the time period of 8:00-10:00, every 1 hour is a monitoring time period, within the time period of 10:00-12:00, every 2 hours is a monitoring time period; within the time period of 12:00-15:00, every 1 hour is a monitoring time period.

[0029] S2. After collecting the average value of methane flux, according to the formula Adjust the aeration time and aeration intensity of the aeration module (6); where S is the average value of the methane flux during the monitoring period, in mol / m 2 / day -1 ; t is the monitoring time, in h; T is the aeration time, in h; q is the aeration intensity (m 3 / h).

[0030] The methane measurement instrument uses a portable soil gas flux measurement system or an online methane monitoring instrument for measurement. The roots of the 43 aquatic plants are sealed with plastic film, the stems of the 43 aquatic plants are sealed with plastic film and foam glue, and the stems and leaves of the 43 aquatic plants are also sealed with plastic film, with built-in wooden strips to support the seal. The roots and the tops of the stems and leaves are set with slopes to ensure that the middle gas collection point is the highest position, which is convenient for collecting methane gas with a lighter density. The system is equipped with a thermometer, a hygrometer and a fan.

[0031] The method is used to automatically control the aeration of the artificial wetland in this embodiment. Since the aeration intensity of the aeration module 6 in the artificial wetland is 3.6m 3 / h, therefore, the average value of methane flux in each monitoring period and each aeration time can be found in Table 1. The average value of methane flux is 0.099115 mol / m 2 / day -1 , the emission range is 0.03122~0.18746 mol / m 2 / day -1 The average methane reduction rate is 60.7%, and the average methane reduction rate ranges from 50% to 71.7%. The precise aeration time is 0.1 to 0.6 hours, with an average of 0.3125 hours.

[0032] Table 1 Average methane emission flux and precise aeration time distribution of serial modular constructed wetlands The above is only a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the concept described herein through the above description or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art shall not deviate from the spirit and scope of the present invention, and shall be within the scope of protection of the claims attached to the present invention.

Claims

1. A series modular artificial wetland, characterized in that: The invention comprises a tank body (1), wherein the tank body (1) is composed of a plurality of extractable test modules (2) which are connected in sequence to form an upper and lower circulation communication channel, wherein a matrix purification module (3) and a plant purification module (4) arranged on the top of the matrix purification module (3) are arranged in the extractable test module (2), wherein a water hole for facilitating water flow is provided on the matrix purification module (3), wherein a plurality of the plant purification modules (4) are located on the top of the tank body (1), wherein a backwash module (5) is arranged at the bottom of the extractable test module (2), wherein an aeration module (6) is arranged between the matrix purification module (3) and the backwash module (5), and wherein a water inlet pipe (11) and a water outlet pipe (12) are arranged at both ends of the tank body (1).

2. A serial modular artificial wetland according to claim 1, characterized in that: The substrate purification module (3) comprises a placement frame, the placement frame is filled with a sand layer, a coarse sand layer, a crushed stone layer, a pebble layer and a large pebble layer, gaps are provided between the plurality of placement frames, and the plant purification modules (4) are stacked on the upper ends of the placement frames.

3. The serial modular artificial wetland according to claim 1, characterized in that: The aeration module (6) comprises a plurality of microporous aeration disks (61) mounted on the substrate purification module (3) and an aeration pipe (62) penetrating the tank body; one end of the aeration pipe (62) is connected to an aerator, and the other end is connected to the microporous aeration disk (61).

4. The serial modular artificial wetland according to claim 1, characterized in that: The backwashing module (5) comprises a backwashing air supply pipe (51) arranged at the bottom of the pool body, a plurality of backwashing water distribution pipes (52) are arranged on the backwashing air supply pipe (51), an air pump is arranged in communication with the backwashing air supply pipe (51), and a backwashing valve for preventing blockage is arranged on the backwashing air supply pipe (51).

5. The serial modular artificial wetland according to claim 1, characterized in that: The plant purification module (4) comprises an isolation plate (41) arranged on the substrate purification module (3), a plurality of root control pots (42) arranged on the isolation plate (41), and aquatic plants (43) planted in the root control pots (42), wherein the roots of the aquatic plants (43) penetrate deeply into the substrate purification module (3).

6. The serial modular artificial wetland according to claim 1, characterized in that: The water inlet pipe (11) and the water outlet pipe (12) are provided with water quality monitoring probes (13), and the pool body (1) is provided with at least one methane monitoring point (16).

7. The serial modular artificial wetland according to claim 1, characterized in that: A grid support frame (14) is provided in the pool body (1), and the substrate purification module (3) and the aeration module (6) are arranged on the grid support frame (14).

8. A method for accurately reducing methane emissions based on the serial modular artificial wetland described in any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Monitor the methane concentration and obtain the average value of the methane flux during the monitoring period; S2. According to the collected methane flux average value data, adjust the aeration time and aeration intensity of the aeration module (6).

9. A method for accurate methane emission reduction according to claim 8, characterized in that: In step S1, within the time period from 15:00 to 8:00, every 3 hours is a monitoring time period, within the time period from 8:00 to 10:00, every 1 hour is a monitoring time period, and within the time period from 10:00 to 12:00, every 2 hours is a monitoring time period; During the time period from 12:00 to 15:00, every 1 hour is a monitoring period.

10. A method for accurate methane emission reduction according to claim 8, characterized in that: According to the formula Determining the aeration time and aeration intensity of the aeration module (6); Where S is the average methane flux during the monitoring period, in mol / m 2 / day -1 ; t is the monitoring time, in h; T is the aeration time, in h; q is the aeration intensity (m 3 / h).

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