CN114456816A

CN114456816A - Reagent for reducing soil methane emission and method for reducing soil methane emission

Info

Publication number: CN114456816A
Application number: CN202210148486.8A
Authority: CN
Inventors: 李田; 张晓林; 王鑫; 宋金童
Original assignee: Nankai University
Current assignee: Nankai University
Priority date: 2022-02-18
Filing date: 2022-02-18
Publication date: 2022-05-10
Anticipated expiration: 2042-02-18
Also published as: CN114456816B

Abstract

The invention belongs to the technical field of environmental management, and particularly relates to a reagent and a method for reducing soil methane emission. The reagent for reducing the methane emission of the soil comprises a graphite rod, magnetite and biochar. The graphite rod is used for collecting electrons and transferring the electrons to the surface layer of the soil to generate water under the action of oxygen; magnetite induces the electrogenesis bacteria and dissimilatory iron reducing bacteria of the soil system to enrich and promote the direct electronic transmission among the species; the biochar is used for enhancing the mass transfer efficiency of soil and promoting the long-distance transmission of electrons in the soil. According to the invention, the graphite rod, the magnetite and the biochar are utilized to construct the biochar-magnetite-graphite rod electronic transfer network, so that a continuous electron acceptor is provided for electrogenic bacteria in soil, the electrogenic bacteria and a substrate of functional bacteria and methanogenic bacteria cooperating with the electrogenic bacteria are formed to compete for reducing a carbon source available for the methanogenic bacteria, thus a path of carbon dioxide reduction and methyl compound reduction in a methanogenic process is inhibited, and the aim of reducing the emission of soil methane is finally realized.

Description

Reagent for reducing soil methane emission and method for reducing soil methane emission

Technical Field

The invention belongs to the technical field of environmental management, and particularly relates to a reagent for reducing soil methane emission and a method for reducing soil methane emission.

Background

The greenhouse effect is becoming more severe with the development of socioeconomic performance, which gradually affects the quality of ecological environment and the development of human survival. As the largest carbon reservoir of the earth's surface ecosystem, the carbon cycle and conversion processes of soil have important effects on global climate change. Research on improving the carbon sequestration capacity of soil and reducing the emission of greenhouse gases has become a hotspot. The existing research shows that effective farmland control management measures such as straw returning, organic fertilizer application and the like can promote the carbon sequestration capacity of soil to offset the emission of greenhouse gases in the production process.

Compared with dry farming soil, rice soil is covered by accumulated water all year round and is in an anaerobic environment, and methanogens metabolize organic carbon in the soil and generate methane. The studies reported by IPCC (Interactive Panel on simulation Change) indicate that equal mass methane contributes 21 times more greenhouse gas than carbon dioxide within 100 years. Rice soil is an important source of methane emission, and the emission amount of the rice soil accounts for about 17.5% of the total global methane emission amount. Therefore, it is very important to find a scientific and effective method for reducing the soil methane emission of the rice.

Disclosure of Invention

In view of the above, the present invention provides a reagent for reducing soil methane emission and a method for reducing soil methane emission, and the reagent provided by the present invention can change an electron transfer path for soil carbon conversion, thereby inhibiting the activity of methanogens, and further reducing the amount of methane emission in soil.

In order to solve the technical problem, the invention provides a reagent for reducing soil methane emission, which comprises a graphite rod, magnetite and biochar.

Preferably, the mass ratio of the graphite rod to the magnetite to the biochar is 1: 0.1-0.3: 01-0.2.

Preferably, the diameter of the graphite rod is 0.5-10 cm, and the length of the graphite rod is 10-100 cm.

Preferably, the mean particle size of the magnetite is 0.1-50 μm; the average particle size of the biochar is 0.02-5 mm.

The invention provides a method for reducing soil methane emission, which comprises the following steps:

inserting a graphite rod into soil, wherein the graphite rod is communicated with air on the surface of the soil, an aerobic layer of the soil and an anaerobic layer of the soil in sequence;

taking a graphite rod as a center, and adding magnetite and biochar into soil in a region within 100cm from the center.

Preferably, the length of the graphite rod inserted into the soil exposed in the air is 2-20 cm, and the insertion depth of the graphite rod inserted into the soil is 8-80 cm;

the density of the graphite rods inserted into the soil is 8-120 pieces/m²。

Preferably, the mass percentage of the magnetite added in the soil within 5cm from the center accounts for 40-60% of the total mass of the magnetite.

Preferably, the doping depth of the doped magnetite is 20-100 cm.

Preferably, the doping depth of the doped biochar is 5-100 cm.

Preferably, the soil comprises flooded soil.

The invention provides a reagent for reducing soil methane emission, which comprises a graphite rod, magnetite and biochar. In the invention, the graphite rod is used for collecting electrons and transferring the electrons to the surface layer of soil, and generates water with hydrogen ions in the soil under the action of oxygen; magnetite induces the electrogenesis bacteria and dissimilatory iron reducing bacteria of the soil system to enrich and promote the direct electronic transmission among the species; the biochar is used for enhancing the soil mass transfer efficiency and promoting the long-distance transmission of electrons in the soil. According to the invention, the graphite rod, the magnetite and the biochar are utilized to construct the biochar-magnetite-graphite rod electron transfer network, and a continuous electron acceptor is provided for the electrogenic bacteria in the soil, so that the consumption of the electrogenic bacteria and the functional bacteria (such as dissimilatory iron reducing bacteria) cooperating with the electrogenic bacteria on organic substrates in the soil is accelerated, carbon sources available for methanogenic bacteria are reduced by competing with the substrates of the methanogenic bacteria, the paths of carbon dioxide reduction and methyl compound reduction in the methanogenic process are inhibited, and the aim of reducing the emission of the soil methane is finally realized.

The invention provides a method for reducing soil methane emission, which comprises the following steps: inserting a graphite rod into soil, wherein the graphite rod is communicated with air on the surface of the soil, an aerobic layer of the soil and an anaerobic layer of the soil in sequence; taking a graphite rod as a center, and adding magnetite and biochar into soil in a region within 100cm from the center. According to the invention, the biochar-magnetite-graphite rod electron transfer network is constructed to transfer electrons in soil to air on the surface of the soil and react with oxygen in the air to generate water, so that the water and methanogen form an electron donor competition, and the formation of methane is reduced; meanwhile, the invention changes the oxidation-reduction potential of the soil under the action of the biochar-magnetite-graphite rod electron transfer network, strengthens the methane oxidation process and further reduces the methane emission. The method for reducing the soil methane emission is simple, convenient to operate, free of negative effects on the environment and capable of being popularized and applied in a large area.

Drawings

Fig. 1 is a schematic diagram of a soil mitigation system of example 1;

FIG. 2 is a bar graph comparing the average gas collection rates of the gas collection pockets of example 1 and comparative examples 1-3;

FIG. 3 is a bar graph comparing the methane production rates in example 1 and comparative examples 1-3;

FIG. 4 is a histogram comparing the total organic carbon content in the pore water of the soil in example 1 and comparative examples 1 to 3;

FIG. 5 is a bar graph comparing the total inorganic carbon content in the pore water of the soil in example 1 and comparative examples 1 to 3.

Detailed Description

The invention provides a reagent for reducing soil methane emission, which comprises a graphite rod, magnetite and biochar.

In the invention, the diameter of the graphite rod is preferably 0.5-10 cm, and more preferably 1-5 cm; the length of the graphite rod is preferably 10-100 cm, and more preferably 20-50 cm. In the present invention, the purity of the graphite rod is preferably 99% or more, and more preferably 99.9% or more. In the invention, the graphite rod has good electron enrichment capacity and higher electron transfer efficiency. In the invention, the graphite rod can transmit electrons of an anaerobic layer in soil to an aerobic layer and consume oxygen above the aerobic layer. In the invention, the aerobic layer in the soil is a soil layer with the depth of 1cm from the surface layer of the soil, and the soil layer with the depth of more than 1cm from the surface layer of the soil is an anaerobic layer.

In the present invention, the mean particle diameter of the magnetite is preferably 0.1 to 50 μm, and more preferably 5 to 20 μm. In the invention, the magnetite is a conventional commercially available product; the present invention is particularly required for the source of the magnetite as long as the above particle size range can be satisfied. The magnetite with the particle size range does not generate toxicity to microorganisms, and has high electron transfer efficiency. In the invention, the magnetite can induce the enrichment of electrogenic bacteria and dissimilatory iron reducing bacteria in soil, promote the direct electron transfer between the electrogenic bacteria and dissimilatory iron reducing bacteria to form electron competition with methanogenic bacteria, and reduce the formation of methane.

In the invention, the average particle size of the biochar is preferably 0.02-5 mm, and more preferably 1-3 mm. In the present invention, the biochar is preferably prepared according to the following method: decomposing the plant residue under the anaerobic condition to obtain the biochar. In the present invention, the plant residue preferably comprises rice hulls or plant straw, more preferably rice hulls; the plant straw preferably comprises corn straw or wheat straw. In the present invention, the oxygen-free condition is preferably prepared by introducing an inert gas into a container, and the inert gas preferably includes nitrogen or argon, and more preferably nitrogen. In the invention, the decomposition temperature is preferably 400-700 ℃, and more preferably 500-600 ℃; the time for decomposition is preferably 3-8 h, and more preferably 4-5 h. The preparation method of the biochar is simple, the biochar has excellent conductivity, meanwhile, the biochar prepared by taking the plant residues as the raw materials inhibits the process of discharging greenhouse gases into the atmosphere after the plant residues are biologically decomposed, and the inert biochar is reserved in soil, so that the soil carbon sequestration capacity is enhanced. In the invention, the biochar can enhance the soil mass transfer efficiency and promote the long-distance transmission of electrons.

In the invention, the mass ratio of the graphite rod, the magnetite and the biochar is preferably 1: 0.1-0.3: 01-0.2, and more preferably 1: 0.15-0.2: 0.15-0.17.

According to the invention, a graphite rod is inserted into soil, and the graphite rod is sequentially communicated with air on the surface of the soil, an aerobic layer of the soil and an anaerobic layer of the soil. In the present invention, the soil preferably includes flooded soil, and more preferably, paddy soil. In the invention, the aerobic layer in the soil is a soil layer with the depth of 1cm from the surface layer of the soil, and the soil layer with the depth of more than 1cm from the surface layer of the soil is an anaerobic layer. In the invention, the length of the graphite rod inserted into the soil exposed in the air is preferably 1-20 cm, and more preferably 2-10 cm; the length of the graphite rod exposed to the air when the soil surface has a water layer is a length higher than the surface of the water layer based on the surface of the water layer. In the invention, the graphite rod can transmit electrons of an anaerobic layer in soil to an aerobic layer and the electrons above the aerobic layer are consumed by oxygen in the air to generate water.

In the invention, the insertion depth of the graphite rod into the soil is preferably 8-80 cm, and more preferably 10-30 cm; the density of the graphite rods inserted into the soil is preferably 8-120/m²More preferably 36 to 100 roots/m²。

After the graphite rod is inserted into soil, the invention takes the graphite rod as the center, and magnetite and biochar are doped into the soil in the area within 100cm away from the center. In the present invention, the magnetite added to the soil within a distance of 5cm from the center is preferably 40 to 60% by mass based on the total mass of the magnetite, and the magnetite added to the soil within a distance of 5cm from the center is more preferably 50 to 58% by mass based on the total mass of the magnetite. In the present invention, the surplus magnetite is preferably incorporated in a soil region having a length of more than 5cm and 100cm, more preferably more than 5cm and 50cm, and still more preferably more than 5cm and 10 cm.

In the invention, the doping depth of the doped magnetite is preferably 20-100 cm, and more preferably 30-50 cm. The invention has no special requirement on the doping mode, as long as the magnetite and the soil can be uniformly mixed.

According to the invention, more magnetite is added in the area close to the graphite rod part, so that enrichment of electrogenic bacteria and dissimilatory iron reducing bacteria on and around the graphite rod can be induced, and less magnetite is added in the area far away from the graphite rod, so that cost is reduced and inter-species electron transfer can be enhanced.

In the invention, the area doped with the biochar is a soil area with the distance from the center preferably being 5-60 cm, and more preferably being 10-30 cm. In the invention, the doping depth of the doped biochar is preferably 5-100 cm, and more preferably 10-60 cm. The doping of the invention is not particularly limited as long as the biochar and the soil can be uniformly mixed.

The invention has no special requirement on the sequence of adding the magnetite and the biochar, and can be added according to any sequence.

In the invention, the graphite rod, the magnetite and the biochar construct a graphite rod-biochar-magnetite soil electron transfer network; the graphite rod is used as an electron current collector and a 'cable' which penetrates through an anaerobic zone and an aerobic layer at the bottom of the soil to transmit electrons in the soil to the aerobic layer and enable the electrons to react with oxygen in the air to generate water. The invention utilizes the graphite rod-biochar-magnetite soil electron transfer network to change the electron transfer path of soil carbon conversion, thereby inhibiting the activity of methanogens and reducing the generation of methane in the soil; meanwhile, the oxidation-reduction potential of the soil is changed to strengthen the oxidation process of methane, so that the emission of methane in the soil is reduced.

In the invention, the biochar, the magnetite and the graphite rod are all green and environment-friendly natural materials, so that secondary pollution or threat to the ecological environment can not be caused; the method for reducing the soil methane emission is simple and convenient to operate and has the potential of large-area farmland popularization and application.

In order to further illustrate the present invention, the following embodiments are described in detail, but they should not be construed as limiting the scope of the present invention.

Example 1

Decomposing the rice hull at 500 ℃ for 5h to obtain biochar with the average particle size of 2 mm;

the method comprises the steps of filling 10 cm-deep soil (50kg of soil obtained from a paddy field in the county of the mouth of a shouyang city in Hunan province) into an organic glass box body with the length of 100cm, the width of 100cm and the height of 20cm, adding 1L of water into the soil to form a water covering layer with the depth of 1cm on the surface of the soil layer, and simulating a paddy field to perform a test; uniformly inserting 36 graphite rods (each graphite rod is 17g in mass) with the diameter of 1cm, the length of 10cm and the purity of 99.9% into soil, wherein the height of the graphite rods exposed out of the water surface is 1cm, and the depth of the graphite rods inserted into the soil is 8 cm;

uniformly doping 200g of biochar into a soil area which takes a graphite rod as a center and is 10cm away from the center;

70g of magnetite having an average particle size of 10 μm was incorporated into a soil region centered on a graphite rod and 5cm in length from the center; 50g of magnetite with the average grain diameter of 10 mu m is doped into a soil area which takes a graphite rod as a center and has the length more than 5cm and less than or equal to 10cm away from the center; a cover is arranged above the organic glass box body, a small hole with the diameter of 3cm is distilled off, the small hole is used for collecting gas and sampling, and the soil emission reduction system is abbreviated as GCFe.

A schematic diagram of the soil emission reduction system of example 1 is shown in fig. 1, where a is a general schematic diagram, and b is a longitudinal sectional schematic diagram of a graphite rod and distribution of magnetite and biochar around the graphite rod, where 1 is the graphite rod, 2 is the magnetite, and 3 is the biochar.

Comparative example 1

A soil emission reduction system was set up as in example 1, except that biochar, magnetite and graphite rod were not incorporated as blank controls, abbreviated as CK.

Comparative example 2

A soil emission reduction system was set up as in example 1, except that no biochar or magnetite, abbreviated as GCK, was added.

Comparative example 3

The soil emission reduction system was set up as in example 1, except that only biochar, magnetite and no graphite rod, CFeCK for short, were incorporated.

Test example

After the soil emission reduction system constructed in the embodiment 1 and the comparative examples 1 to 3 is constructed, the air collecting bag is kept sealed and connected through the small holes, the operation is carried out under the conditions that the temperature is 22-25 ℃ and the relative humidity is 40-50% RH, the illumination of 12h every day is guaranteed, the operation period is 15 days, the air collecting bag is replaced after each period is finished, the gas collection is carried out again, pore water samples on the surface layer and the deep layer of the soil are collected, and the operation lasts for three periods.

The gas collection pocket volume was measured by the drainage method and the gas collection rate was calculated, and the results are shown in table 1. The histogram is plotted according to table 1, as shown in fig. 2.

TABLE 1 gas collection rates for example 1 and comparative examples 1-3 over three cycles

As can be seen from table 1 and fig. 2, the gas rates collected during the operation of CK group, GCK group, CFeCK group, and GCFe group all showed a tendency to decrease, which may be related to the consumption of available organic carbon in the system. The GCFe group has the lowest gas collection rate in the first period; the GCFe group still exhibited the lowest gas collection rate during the second and third cycles and no more gas was produced during the third cycle. The existence of the graphite rod, the biochar and the magnetite changes the electron transfer in the biological methanogenesis path, thereby inhibiting the gas collection speed, and the graphite rod, the biochar and the magnetite can also play a certain methane production inhibiting role by being added independently.

The total volume of the collected gas of the CK group, the GCK group, the CFeCK group and the GCFe group in three periods is 242mL, 210mL, 192mL and 62mL respectively, and under the combined action of the graphite rod, the biochar and the magnetite, the total volume of the gas collected by the gas collection bag is reduced by 74 percent relative to the CK group. The components of each group of collected gas are analyzed by a gas chromatograph, and the content of methane in the CK group of collected gas in the first period, the second period and the third period is 68%, 66% and 60% respectively; the content of methane in the GCK group collected gas in the first period, the second period and the third period is 58%, 57% and 55% respectively; the content of methane in the CFeCK group collecting gas in the first period, the second period and the third period is respectively 55%, 52% and 52%; the content of methane in the GCFe group collected gas in the first period, the second period and the third period was 48%, 46% and 0%, respectively.

The volume of air above the soil mass of the soil emission reduction device used in the experiment was 36000mL, and the methane emission rate was obtained by conversion, and the results are shown in table 2. A histogram is plotted according to table 2 as shown in fig. 3.

TABLE 2 methane production rates for example 1 and comparative examples 1-3 over three cycles

As can be seen from Table 2 and FIG. 3, the rate of methane production in the GCFe group was 1153mL/d in the first cycle, which is a 30%, 17% and 13% reduction in the CK group, the GCK group and the CFeCK group, respectively. The same rule is shown in the second period and the third period, which shows that the method for reducing the emission of the soil methane has good emission reduction effect on the emission of the methane.

The Total Organic Carbon (TOC) and total Inorganic Carbon (IC) content changes of the soil pore water sample, the related carbon conversion process in the reaction system, were measured using a TOC analyzer, and the results thereof are shown in tables 3 and 4. Plotting a histogram according to table 3, as shown in fig. 4; the histogram is plotted according to table 4, as shown in fig. 5.

TABLE 3 TOC content in three cycles for example 1 and comparative examples 1 to 3

TABLE 4 IC content of example 1 and comparative examples 1 to 3 in three cycles

As can be seen from tables 3 and 4 and FIGS. 4 and 5, in the first cycle, the TOC content of the soil pore water of CK group, GCK group, CFeCK group and GCFe group showed a trend of decreasing, 210mg/kg, 182mg/kg, 161mg/kg and 100mg/kg, respectively, but the IC content showed a trend of increasing. This indicates that the presence of graphite rods, biochar and magnetite can accelerate the consumption of organic carbon in the system, especially at the highest rate in the GCFe group. In the constructed soil carbon emission reduction system, the biochar and the magnetite accelerate electron transfer in substrate consumption, and the graphite rod serves as a 'cable' to communicate an aerobic area on the surface layer of the soil and an anaerobic area on the deep layer of the soil, so that the consumption of organic carbon is accelerated and carbon dioxide is generated. In the second and third periods, the TOC content of the soil pore water in the GCFe group is respectively reduced by 48 percent and 18 percent relative to the CK group. It is noted that the variation in TOC content in the pore water of each group of soils has gradually decreased by the late stage, because the organic carbon available to the microorganisms in the soil is limited. According to the method for reducing the emission of the methane in the soil, the graphite rod-biochar-magnetite is used for constructing the soil electron transfer network to accelerate the consumption of the organic carbon in the soil and produce water, so that the emission of the methane gas is effectively inhibited.

Although the present invention has been described in detail with reference to the above embodiments, it is only a part of the embodiments of the present invention, not all of the embodiments, and other embodiments can be obtained without inventive step according to the embodiments, and all of the embodiments are included in the scope of the present invention.

Claims

1. A reagent for reducing methane emission from soil comprises graphite rod, magnetite and biochar.

2. The agent for reducing soil methane emission according to claim 1, wherein the mass ratio of the graphite rod, the magnetite and the biochar is 1: 0.1-0.3: 01-0.2.

3. The agent for reducing the emission of methane from soil according to claim 1 or 2, wherein the graphite rod has a diameter of 0.5-10 cm and a length of 10-100 cm.

4. The agent for reducing soil methane emission according to claim 1 or 2, wherein the magnetite has an average particle size of 0.1 to 50 μm; the average particle size of the biochar is 0.02-5 mm.

5. A method for reducing methane emissions from soil comprising the steps of:

6. The method for reducing the emission of methane from soil according to claim 5, wherein the length of the graphite rod inserted into the soil exposed in the air is 2-20 cm, and the insertion depth of the graphite rod inserted into the soil is 8-80 cm;

the density of the graphite rods inserted into the soil is 8-120 pieces/m²。

7. The method for reducing soil methane emission according to claim 5, wherein the magnetite added to the soil in an area within 5cm from the center accounts for 40-60% by mass of the total mass of the magnetite.

8. The method for reducing the methane emission from the soil according to claim 5 or 7, wherein the magnetite is added at a depth of 20-100 cm.

9. The method for reducing the methane emission from the soil according to claim 5, wherein the doping depth of the doped biochar is 5-100 cm.

10. The method of reducing methane emissions from soil according to claim 5, wherein said soil comprises flooded soil.