Method for reducing greenhouse gas emission in freezing and thawing period of constructed wetland in cold region

Abstract

The invention belongs to the technical field of constructed wetlands, and provides a method for reducing greenhouse gas emission in a freezing and thawing period of a constructed wetland in a cold region. Before the constructed wetland enters the freezing and thawing period, the surface of the constructed wetland is covered with the snow quilt with the thickness of 20-30 cm, the water content of a matrix in the freezing and thawing period can be increased, the oxidation-reduction potential (ORP) can be reduced, the anaerobic environment can be created, microbial metabolism can be regulated and controlled, aerobic respiration and nitrogen circulation can be inhibited, anaerobic fermentation and a methanogenesis pathway can be promoted, emission of CO2 and N2O and the global warming potential (GWP) can be reduced, and the constructed wetland has the advantages of being capable of improving the water content of the matrix in the freezing and thawing period. The greenhouse effect can be relieved. Meanwhile, accumulation of fungus residues is promoted through the arrangement of the snow quilt, accumulation of bacterial residues is reduced, and the stability of matrix organic carbon and the carbon sequestration function of the constructed wetland are enhanced. Finally, the method provided by the invention makes up the vacancy in the artificial wetland management in the freezing and thawing period in the prior art, and expands the management and application range of the artificial wetland.

Description

Technical Field

[0001] The present invention relates to the technical field of artificial wetlands, and in particular to a method for reducing greenhouse gas emissions from artificial wetlands in cold regions during freeze-thaw periods. Background Art

[0002] As an ecological sewage treatment system, artificial wetlands have been widely used in the treatment of urban sewage, agricultural runoff and industrial wastewater due to their efficient water purification and ecological restoration functions. Globally, artificial wetlands in cold regions account for a considerable proportion. Compared with tropical regions, artificial wetlands in cold regions are dormant for nearly half of the year due to lower winter temperatures. Although the operation of artificial wetlands stops during the dormant period, the biogeochemical processes in the matrix continue. When the temperature of the matrix layer in the artificial wetland reaches 0°C for the first time, it can be considered to have entered the freeze-thaw period. The freeze-thaw period is an important greenhouse gas emission period for artificial wetlands.

[0003] At present, the main research and technical means for greenhouse gas emissions from artificial wetlands are concentrated in the following aspects: 1. Operation management: During the operation period of artificial wetlands, the treatment effect of artificial wetlands is enhanced and greenhouse gas emissions are reduced by adjusting hydraulic loads, optimizing plant configurations, adding fillers, etc. 2. Substrate improvement: Adding modifiers such as biochar and zeolite to the substrate aims to improve the adsorption capacity and biological activity of the substrate, thereby reducing the production of greenhouse gases. 3. Microbial regulation: By introducing microbial flora with specific functions, the growth of beneficial microorganisms is promoted and the microbial metabolic pathways that produce greenhouse gases are inhibited.

[0004] However, these technical means are mainly aimed at the operation period of artificial wetlands, and do not involve greenhouse gas emissions from artificial wetlands during the freeze-thaw period. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a method for reducing greenhouse gas emissions from artificial wetlands in cold regions during the freeze-thaw period. The method of the present invention can reduce greenhouse gas emissions from artificial wetlands during the freeze-thaw period.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The invention provides a method for reducing greenhouse gas emissions from artificial wetlands in cold regions during the freeze-thaw period. Before entering the freeze-thaw period, the artificial wetlands are covered with a snow blanket, wherein the thickness of the snow blanket is 20 to 30 cm.

[0008] Preferably, the artificial wetland is a vertical submerged flow artificial wetland.

[0009] Preferably, the artificial wetland comprises a support layer and a matrix layer from bottom to top, and the matrix of the matrix layer is a mixed filler of lignite and steel slag.

[0010] Preferably, the particle size of the lignite is 2 to 3 mm, and the particle size of the steel slag is 5 to 10 mm.

[0011] Preferably, the volume ratio of lignite to steel slag in the lignite and steel slag mixed filler is 1:1.

[0012] Preferably, the filler of the support layer is crushed stone, and the particle size of the crushed stone is 10-15 mm.

[0013] Preferably, the thickness of the support layer is 0.2-0.3 m, and the thickness of the matrix layer is 0.6-0.7 m.

[0014] Preferably, the artificial wetland further comprises plants planted in the substrate layer, wherein the plants comprise reeds and oriental irises.

[0015] Preferably, the hydraulic load of the artificial wetland is 0.2 to 0.5 m 3 ·m -2 ·d -1 .

[0016] Preferably, the artificial wetland further comprises a water inlet pipe, which is arranged on the surface of the matrix layer and is a "F"-shaped pipe.

[0017] The invention provides a method for reducing greenhouse gas emissions during the freeze-thaw period of artificial wetlands in cold regions.

[0018] The present invention covers the surface of the artificial wetland with a snow blanket with a thickness of 20 to 30 cm before entering the freeze-thaw period, which can increase the moisture content and temperature of the matrix in the matrix layer during the freeze-thaw period, reduce the redox potential (ORP), create an anaerobic environment, regulate microbial metabolism, inhibit aerobic respiration and nitrogen cycle, promote anaerobic fermentation and methanogenesis, and thus reduce CO2 and N2O emissions and global warming potential (GWP), which helps to alleviate the greenhouse effect. At the same time, the provision of the snow blanket promotes the accumulation of fungal residues, reduces the accumulation of bacterial residues, enhances the stability of matrix organic carbon and the carbon sink function of the artificial wetland. Finally, the method of the present invention fills the gap in the management of artificial wetlands in the freeze-thaw period in the prior art and expands the management and application scope of artificial wetlands. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A top view of an artificial wetland in a specific embodiment of the present invention;

[0020] Figure 2 It is a side view of an artificial wetland in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0021] The invention provides a method for reducing greenhouse gas emissions from artificial wetlands in cold regions during the freeze-thaw period. Before entering the freeze-thaw period, the artificial wetlands are covered with a snow blanket, wherein the thickness of the snow blanket is 20 to 30 cm.

[0022] Unless otherwise specified, the raw materials used in the present invention are preferably commercially available products.

[0023] In the present invention, the thickness of the snow blanket is 20 to 30 cm, and is preferably 20 cm, 22 cm, 24 cm, 26 cm, 28 cm or 30 cm. In the present invention, the snow blanket is preferably formed by natural snowfall or artificial snowfall, and is further preferably formed by natural snowfall. The present invention uses natural snowfall to form a snow blanket, which is easy to operate, does not require complex equipment and high investment, and has high practical value; at the same time, after entering the freeze-thaw period, the snow blanket changes with the temperature and melts automatically. After the snow blanket melts, it is converted into water, so that the snow blanket can regulate the redox conditions of the artificial wetland matrix while not introducing foreign substances, has no negative impact on the ecosystem, and has good environmental benefits.

[0024] In the present invention, the artificial wetland is preferably a vertical submerged flow artificial wetland.

[0025] In the present invention, the artificial wetland preferably includes a support layer, the filler of the support layer is preferably crushed stone, and the particle size of the crushed stone is preferably 10-15 mm. In the present invention, the thickness of the support layer is preferably 0.2-0.3 m, and specifically preferably 0.2 m, 0.25 m or 0.3 m. In the present invention, the support layer plays a supporting and filtering role.

[0026] In the present invention, the artificial wetland preferably includes a matrix layer, and the matrix of the matrix layer is preferably a mixed filler of lignite and steel slag, and the volume ratio of lignite and steel slag in the mixed filler of lignite and steel slag is preferably 1:1. In the present invention, the particle size of the lignite is preferably 2-3 mm. In the present invention, the particle size of the steel slag is preferably 5-10 mm. In the present invention, the thickness of the matrix layer is preferably 0.6-0.7 m, specifically preferably 0.6 m, 0.65 m or 0.7 m. In the present invention, the matrix layer can provide a growth medium for microorganisms and plants, and at the same time, it can also adsorb and remove pollutants. In particular, the matrix layer of the mixed filler of lignite and steel slag in the present invention can further improve the efficiency of nitrogen removal and phosphorus removal.

[0027] In the present invention, a temperature sensor is preferably arranged in the matrix layer to monitor the temperature of the matrix in the matrix layer. In the present invention, the temperature sensor is preferably arranged at a position 20 cm below the upper surface of the matrix layer.

[0028] In the present invention, the artificial wetland preferably further comprises a water inlet pipe, and the water inlet pipe is preferably arranged on the surface of the substrate layer. In the present invention, the water inlet pipe is preferably a Feng-shaped pipe. In the present invention, the water inlet of the artificial wetland is preferably surface runoff or rural sewage.

[0029] In the present invention, a static box is preferably further provided on the artificial wetland, and the static box can observe the greenhouse gas emission in situ.

[0030] In the present invention, the artificial wetland preferably includes plants planted in the substrate layer, and the plants preferably include reeds and oriental irises. In the present invention, the plants exist in their natural state during the freeze-thaw period, that is, during the freeze-thaw period, the plants are in a withered state. In the present invention, the plants can increase the ecological function and landscape effect of the artificial wetland.

[0031] In the present invention, the hydraulic load of the artificial wetland is preferably 0.2 to 0.5 m 3 ·m -2 ·d -1 .

[0032] In a specific embodiment of the present invention, the top view and the side view of the artificial wetland are respectively as follows: Figure 1 and Figure 2 In a specific embodiment of the present invention, the size of the artificial wetland is preferably: 10m in length, 3m in width, and 1m in depth; the thickness of the support layer is 0.25m, the filler of the support layer is crushed stone, and the particle size of the crushed stone is 10-15mm; the matrix of the matrix layer is a mixed filler formed by lignite with a particle size of 2-3mm and steel slag with a particle size of 5-10mm, wherein the volume ratio of lignite to steel slag is 1:1, the thickness of the matrix layer is 0.65m, and the plants planted in the matrix layer are reeds and oriental irises.

[0033] In the present invention, the provision of snow blankets can increase the moisture content of the substrate during the freeze-thaw period, reduce the redox potential (ORP), create an anaerobic environment, regulate microbial metabolism, inhibit aerobic respiration and nitrogen cycle, promote anaerobic fermentation and methanogenesis, and thus reduce CO2 and N2O emissions and the global warming potential (GWP), which helps to alleviate the greenhouse effect. At the same time, the provision of snow blankets promotes the accumulation of fungal residues, reduces the accumulation of bacterial residues, enhances the stability of organic carbon in the substrate and the carbon sink function of artificial wetlands. Finally, the method of the present invention fills the gap in the prior art in the management of artificial wetlands during the freeze-thaw period and expands the management and application scope of artificial wetlands.

[0034] The method for reducing greenhouse gas emissions from artificial wetlands in cold regions during freeze-thaw periods provided by the present invention is described in detail below in conjunction with the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0035] Example

[0036] Step 1: Construction of artificial wetlands

[0037] according to Figure 1 and Figure 2 Two pilot-scale vertical subsurface artificial wetlands were built in the Xingkai Lake area of ​​Heilongjiang Province. The dimensions of each artificial wetland are: 10 meters long, 3 meters wide, and 1 meter deep. In the artificial wetland, the matrix of the matrix layer is a mixture of lignite (particle size 2-3mm) and steel slag (particle size 5-10mm). The lignite and steel slag in the mixture are mixed in a volume ratio of 1:1, and are filled from top to bottom with a 0.65-meter-thick matrix layer and a 0.25-meter-thick support layer (the support layer is filled with gravel, and the particle size of the gravel is 10-15mm). The support layer plays a filtering and supporting role. During operation, the plant community was a mixed community of reeds and oriental irises.

[0038] The water inflow of the artificial wetland is surface runoff and rural sewage. The hydraulic load of the artificial wetland is 0.2m 3 ·m -2 ·d -1 .

[0039] Step 2: Setting up the snow quilt

[0040] In winter, natural snowfall was collected so that before the freeze-thaw period, the surface of one artificial wetland was covered with a snow blanket with a thickness of 20 to 24 cm, which served as the experimental group; the surface of another artificial wetland was covered with a snow blanket with a thickness of 10 to 12 cm, which served as the control group. After entering the freeze-thaw period, the snow blanket changed automatically with the temperature and no excessive treatment was performed on the snow blanket.

[0041] Step 3: Monitoring of environmental parameters

[0042] Temperature monitoring of the matrix layer: A temperature sensor was buried 20 cm below the upper surface of the matrix layer to record the temperature of the matrix in the matrix layer during the entire freeze-thaw period (March to April) in real time. The data recording interval was 30 minutes. By obtaining the temperature curve, the average temperature of the matrix layer during the entire freeze-thaw period was calculated.

[0043] Monitoring of moisture content of substrate layer: When all the snow on the artificial wetland is melted, substrate samples in the substrate layer are collected and the moisture content of the substrate samples is determined by drying method.

[0044] Oxidation-reduction potential monitoring: After all the snow on the artificial wetland was melted, the oxidation-reduction potential (ORP) at a position 20 cm below the upper surface of the substrate layer was measured using a multi-channel soil ORP test system to reflect the oxidation or reduction state of the substrate layer.

[0045] Greenhouse gas emissions: The greenhouse gas emissions of the artificial wetland during the entire freeze-thaw period (March to April) were obtained through a static chamber.

[0046] Monitoring of microbial communities in the matrix layer: After the freeze-thaw period ends, which means that the temperature of the matrix layer in the artificial wetland is no longer lower than 0°C, the microorganisms in the matrix layer are collected for metagenomic sequencing.

[0047] Monitoring of microbial residues in the matrix layer: After the freeze-thaw period ends, which means that the temperature of the matrix layer in the artificial wetland is no longer lower than 0°C, the amino sugar content in the matrix is ​​determined by high performance liquid chromatography, and the carbon of microbial residues in the matrix layer is obtained after calculation.

[0048] Step 4: Result Analysis

[0049] In the experimental group artificial wetland, the moisture content of the matrix in the matrix layer was 90-95%, and in the control group artificial wetland, the moisture content of the matrix in the matrix layer was 80-85%.

[0050] The average temperature of the matrix layer in the experimental group artificial wetland was 0.27℃, and the average temperature of the matrix layer in the control group artificial wetland was 0.18℃.

[0051] In the experimental group artificial wetland, the redox potential of the matrix layer was -200mV, and in the control group artificial wetland, the redox potential of the matrix layer was -50mV.

[0052] Greenhouse gas emissions: During the freeze-thaw period, the cumulative CO2 emissions in the artificial wetland of the experimental group were 15913.92 mg / m 2 The cumulative emission of CH4 is 60.25 mg / m 2 The cumulative emission of N2O is 8.43 mg / m 2 In the artificial wetland of the control group, the cumulative CO2 emission was 20997.83 mg / m 2 The cumulative emission of CH4 is 16.60 mg / m 2 The cumulative emission of N2O is 22.99 mg / m 2 .

[0053] Compared with the artificial wetlands in the control group, the artificial wetlands in the experimental group reduced the cumulative emissions of CO2 and N2O during the freeze-thaw period, with CO2 reduced by about 24.21% and N2O reduced by about 63.33%. The increase in snow thickness significantly increased the cumulative emissions of CH4, which increased by 262.91% compared with the artificial wetlands in the control group. The experimental group overall reduced the global warming potential (GWP) of the artificial wetlands during the freeze-thaw period by about 29.47%.

[0054] Changes in microbial communities and metabolic functions in the substrate layer: The setting of snow cover of reasonable thickness changed the relative abundance of microorganisms in the substrate layer, with an increase in the relative abundance of anaerobic bacteria such as Firmicutes and Bacteroidetes, and a decrease in the relative abundance of aerobic bacteria. The setting of snow cover inhibited the aerobic respiration and nitrogen cycle pathways of microorganisms, and promoted anaerobic fermentation and methane production pathways.

[0055] Accumulation of microbial residue carbon in the matrix layer: The carbon content of fungal residues in the matrix layer of the artificial wetland in the experimental group was 0.34 mg / kg, and the carbon content of fungal residues in the matrix layer of the artificial wetland in the control group was 0.23 mg / kg. It can be seen that compared with the carbon content of fungal residues in the matrix layer of the artificial wetland in the control group, the carbon content of fungal residues in the matrix layer of the artificial wetland in the experimental group increased by 47.83%.

[0056] The carbon content of bacterial residues in the matrix layer of the artificial wetland in the experimental group was 0.77 mg / kg, and the carbon content of bacterial residues in the matrix layer of the artificial wetland in the control group was 1.44 mg / kg. It can be seen that compared with the carbon content of bacterial residues in the matrix layer of the artificial wetland in the control group, the carbon content of bacterial residues in the matrix layer of the artificial wetland in the experimental group was reduced by 46.53%.

[0057] In summary, the setting of a reasonable thickness of snow cover is more conducive to the stable accumulation of fungal residues due to strong anaerobic conditions, while bacterial residues are more easily decomposed. This change enhances the long-term stability of microbial residue carbon in the substrate layer.

[0058] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for reducing greenhouse gas emissions during freeze-thaw periods of artificial wetlands in cold regions, characterized in that: Before entering the freeze-thaw period, the artificial wetland is covered with a snow blanket, wherein the thickness of the snow blanket is 20 to 30 cm.

2. The method for reducing greenhouse gas emissions during freeze-thaw period of artificial wetlands in cold regions according to claim 1, characterized in that: The artificial wetland is a vertical subsurface flow artificial wetland.

3. The method for reducing greenhouse gas emissions during freeze-thaw period of artificial wetlands in cold regions according to claim 2, characterized in that: The artificial wetland comprises a support layer and a matrix layer from bottom to top, and the matrix of the matrix layer is a mixed filler of lignite and steel slag.

4. The method for reducing greenhouse gas emissions during freeze-thaw period of artificial wetlands in cold regions according to claim 3, characterized in that: The particle size of the lignite is 2 to 3 mm, and the particle size of the steel slag is 5 to 10 mm.

5. The method for reducing greenhouse gas emissions during freeze-thaw period of artificial wetlands in cold regions according to claim 4, characterized in that: The volume ratio of lignite to steel slag in the lignite and steel slag mixed filler is 1:

1.

6. The method for reducing greenhouse gas emissions during freeze-thaw period of artificial wetlands in cold regions according to claim 3, characterized in that: The filler of the support layer is crushed stone, and the particle size of the crushed stone is 10-15 mm.

7. The method for reducing greenhouse gas emissions from artificial wetlands in cold regions during freeze-thaw periods according to claim 3, 4, 5 or 6, characterized in that: The thickness of the support layer is 0.2-0.3 m, and the thickness of the matrix layer is 0.6-0.7 m.

8. The method for reducing greenhouse gas emissions during freeze-thaw period of artificial wetlands in cold regions according to claim 3, characterized in that: The artificial wetland further comprises plants planted in the substrate layer, wherein the plants comprise reeds and oriental irises.

9. The method for reducing greenhouse gas emissions during freeze-thaw period of artificial wetlands in cold regions according to claim 1, 2 or 3, characterized in that: The hydraulic load of the artificial wetland is 0.2 to 0.5 m 3 ·m -2 ·d -1 .

10. The method for reducing greenhouse gas emissions during freeze-thaw period of artificial wetlands in cold regions according to claim 1, 2 or 3, characterized in that: The artificial wetland also includes a water inlet pipe, which is arranged on the surface of the substrate layer and is a "F"-shaped pipe.

Images