Application of biochar in simultaneously reducing cadmium content and methane emissions in cadmium-containing paddy fields

Abstract

The present invention belongs to the field of soil environmental remediation technology, and specifically relates to the application of biochar in simultaneously reducing the cadmium content and methane emissions in cadmium-containing paddy fields. The application of biochar in the treatment of soil cadmium pollution and methane emission reduction, wherein the specific surface area of ​​the biochar is greater than 200m 2 g ‑1 . The biochar of the present invention has the advantages of rich pore structure, large specific surface area, small pore size, etc., and can adsorb DOC in the soil that can be absorbed and utilized by methanogenic microorganisms. The H / C and O / C of biochar are low, and the ash content is increased, which changes the physical and chemical properties of the soil and plays the role of a soil conditioner; at the same time, the number and types of hydroxyl, carboxyl and carbonyl oxygen-containing functional groups are reduced, the stability is increased, and the adsorption capacity is strong, which can increase the content of residual cadmium in the soil that is not easily absorbed and utilized by plants, and reduce the content of exchangeable cadmium in the soil.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil environmental remediation, and particularly relates to the application of biochar in simultaneously reducing the cadmium content and methane emissions in cadmium-containing paddy fields. Background Art

[0002] The methods for treating cadmium-contaminated rice fields currently mainly include engineering physics, agronomic regulation, and in-situ passivation remediation. Engineering physics methods mainly include soil leaching, surface clean soil covering, and imported soil methods. These treatment methods require large engineering workloads and high treatment costs, and may also damage the soil structure of the paddy field, reduce soil fertility, and be detrimental to the reduction of greenhouse gas methane emissions. Agronomic regulation methods mainly refer to water and fertilizer management, adjusting crop varieties, and fertilization regulation. For example, patent CN115160065A prepares a cadmium-reducing foliar barrier that can effectively reduce the ability of rice roots and leaves to absorb cadmium, thereby reducing the accumulation of cadmium in rice. However, the remediation effect of this method is limited and it is only applicable to slightly contaminated paddy soil. In-situ passivation remediation technology refers to the addition of inorganic passivators (such as phosphates, clay minerals, etc.) and organic passivators (farmyard manure, grass ash, etc.) to the soil to cause a series of reactions such as adsorption, ion exchange, precipitation, and oxidation-reduction in the soil to fix heavy metals. Invention patent CN106512945A, although biochar prepared from crop straw can reduce the cadmium content in the solution, has not been applied in actual soil with the participation of microorganisms, and there is a lack of verification of the effectiveness of the actual application of biochar materials. Patent CN202111503737A, coupling iron-carbon materials with biological enzymes can enhance sludge methane production, and it is believed that iron-carbon materials can promote the growth of anaerobic microorganisms and promote methane production. However, the above-mentioned cadmium pollution control technology mainly focuses on the stabilization performance and application of heavy metal cadmium, and does not involve the impact on greenhouse gas emissions.

[0003] In summary, how to effectively reduce the bioavailability of heavy metal cadmium in soil and achieve multi-target coordinated management of methane emissions remains a major technical challenge. Summary of the Invention

[0004] The present invention aims to address at least one of the technical problems existing in the aforementioned prior art. To this end, the present invention proposes the use of biochar to simultaneously reduce cadmium content and methane emissions in cadmium-containing paddy fields. The biochar disclosed in the present invention can be applied to soil pollution control, deactivating cadmium while simultaneously reducing methane emissions.

[0005] The concept of the present invention is as follows:

[0006] Rice paddy methanogenesis occurs when methanogenic archaea in the soil decompose and utilize simple organic matter, such as dissolved organic carbon (DOC), to produce methane. Soil DOC content reflects the substrate availability for methanogenic archaea and directly influences soil methane production. High soil DOC levels increase the availability of carbon sources for microorganisms, leading to higher expression of methanogenic genes and higher methane production. Low soil DOC levels reduce methane production. Therefore, reducing soil DOC levels can be a key approach to achieving methane reduction.

[0007] Biochar is a carbonaceous material formed by pyrolysis of biomass residues under anoxic conditions and at a certain temperature. It possesses a highly aromatic carbonized structure and exhibits exceptional stability. The higher the pyrolysis temperature, the larger and more robust the micropores within the biochar, enhancing its adsorption capacity, capable of absorbing and fixing heavy metal cadmium and DOC in the soil. High-temperature pyrolysis also fully carbonizes the biochar, reducing its O / C and H / C ratios and increasing its ash content, making it alkaline. This can be used to improve acidic soils, particularly those contaminated with cadmium.

[0008] Based on the above reasons, the present invention adopts a biochar material with large pores, large specific surface area and strong adsorption capacity, which can fully adsorb and fix cadmium in the soil, reduce the biological effectiveness of cadmium in the soil, and at the same time adsorb and reduce DOC in the soil to reduce methane emissions.

[0009] The technical solutions of the present invention are as follows:

[0010] The present invention proposes the use of biochar in reducing the cadmium content and methane emissions in cadmium-containing paddy fields at the same time, wherein the specific surface area of ​​the biochar is greater than 200m 2 g -1 .

[0011] In the present invention, biochar has a rich pore structure and a large specific surface area, and is used for soil remediation to achieve cadmium passivation while significantly reducing methane emissions.

[0012] In some embodiments of the present invention, the specific surface area of ​​the biochar is greater than 250 m 2 g -1 , preferably with a specific surface area of ​​>270m 2 g -1 ; The pore volume of the biochar is ≥0.05cm 3 g -1 , preferably pore volume ≥ 0.10cm 3 g -1 , more preferably pore volume ≥ 0.14cm 3 g -1The pore size of the biochar is 1 to 5 nm, preferably 1 to 3 nm, and more preferably about 2.0473 nm; the pH value of the biochar is 10 to 12, preferably 10 to 11.

[0013] In some embodiments of the present invention, the carbon content of the biochar is 40-50wt%, preferably 45-50wt%; the hydrogen content of the biochar is 0.5-2wt%, preferably 0.5-1wt%; the oxygen content of the biochar is 1-10wt%, preferably 5-10wt%; the hydrogen / carbon ratio (H / C) of the biochar is 0.1-0.5, preferably the hydrogen / carbon ratio (H / C) is 0.2-0.3; the oxygen / carbon ratio (O / C) of the biochar is 0.01-0.15, preferably the hydrogen / carbon ratio (H / C) is 0.05-0.09.

[0014] In some embodiments of the present invention, the particle size of the biochar is 300-500 nm, preferably 400-450 nm, and more preferably about 421.9 nm.

[0015] In some embodiments of the present invention, the biochar is obtained by pyrolysis and reduction of biomass materials under an inert atmosphere at 600-1000°C.

[0016] In some embodiments of the present invention, the temperature of the thermal reduction is 700-1000°C, preferably 700-900°C, including but not limited to 700°C, 750°C, 800°C, 850°C, 900°C, etc., and the heating rate is 2-20°C / min, preferably 5-10°C / min; the time of the thermal reduction is 1-4h, preferably 1-3h, and more preferably about 2h.

[0017] In some embodiments of the present invention, the inert atmosphere is an inert gas protection, including but not limited to nitrogen, argon, helium, etc.; the gas flow rate of the inert gas is controlled at 100-150 mL / min, preferably around 125 mL / min.

[0018] In some embodiments of the present invention, the biochar production method further comprises pre-treatment of the biomass material, specifically removing impurities from the biomass material surface, shredding, sun exposure, and drying. The sun exposure is performed in sunlight for 24 to 48 hours, preferably about 36 hours; the drying temperature is 50 to 80°C, preferably 60 to 80°C; and the drying time is 36 to 60 hours, more preferably about 48 hours.

[0019] In some embodiments of the present invention, the method for preparing biochar further comprises sieving the biochar after pyrolysis and reduction, wherein the aperture of the sieve is 0.1 to 0.2 mm, preferably 0.15 mm.

[0020] In some embodiments of the present invention, the biomass material includes at least one of rice straw, wheat straw, corn straw, waste wood, nut shells, rice husks, peanut shells, and coconut shells.

[0021] In some embodiments of the present invention, the cadmium-containing paddy field includes flooded rice fields, ponds, swamps, etc.; the cadmium content of the cadmium-containing paddy field is 0-10 mg / kg, preferably 0-5.0 mg / kg, and more preferably 4.0-5.0 mg / kg; the pH value of the cadmium-containing paddy field is 4.0-7.0, preferably acidic soil with a pH value of 5.0-7.0; the methane emission of the cadmium-containing paddy field is 5-70 mg / m 2 h, preferably 7.8 to 60 mg / m 2 ·h.

[0022] The second aspect of the present invention provides a method for simultaneously reducing the cadmium content and methane emissions in cadmium-containing paddy fields, comprising the following steps: applying 0.1-2% of the soil mass of the biochar to the cadmium-containing paddy fields before flooding, wherein the specific surface area of ​​the biochar is greater than 200m 2 g -1 The biochar used in this method is similar to that used in applications to simultaneously reduce cadmium levels and methane emissions from cadmium-containing paddy fields.

[0023] In some embodiments of the present invention, the amount of biochar added is 0.5-1% of the soil mass, preferably about 1%.

[0024] In some embodiments of the present invention, the method further includes an activation process, specifically, mixing the biochar with the soil, adding water to submerge the soil to a depth of 2 to 3 cm, and submerging the soil for 3 to 6 days to activate the microorganisms in the soil; the soil is soil from a 0 to 20 cm plow layer of a cadmium-contaminated rice field, the pH of the soil is 6 to 7; and the cadmium content of the soil is 4 to 5 mg / kg.

[0025] In some embodiments of the present invention, the biochar can be applied directly to rice paddies. Specifically, the biochar is mixed with soil, activated, and rice is transplanted into the activated soil for cultivation. Except for the mature soil, which is dry, the soil is flooded at all other stages. The biochar of the present invention can be directly applied to rice-growing soil to reduce methane emissions and passivate cadmium. It is adaptable to all stages of rice cultivation without affecting normal crop production.

[0026] In some embodiments of the present invention, the transplanted rice is rice seedlings that have been grown for 20 to 25 days from rice seeds; the seedling growing process is to sterilize the surface of the rice seeds with a 30 to 40% hydrogen peroxide solution for 10 to 20 minutes, wash them, and then place them in a constant temperature culture room for seedling growing. The rice variety is Huanghuazhan (Yue Shen Rice 2002010).

[0027] In some embodiments of the present invention, fertilizer is added to the soil before transplanting the rice; and topdressing is performed again during the tillering period of the rice; the fertilizer includes at least one of dipotassium hydrogen phosphate trihydrate (K2HPO4·3H2O), potassium dihydrogen phosphate (KH2PO4), and urea; 0.2-0.4 g of K2HPO4·3H2O, preferably 0.3-0.4 g of K2HPO4·3H2O, is added to each kilogram of soil; 0.01-0.05 g of KH2PO4, preferably 0.03-0.04 g of KH2PO4, is added to each kilogram of soil; and 0.05-0.3 g of urea, preferably 0.1-0.2 g of urea, is added to each kilogram of soil.

[0028] In some embodiments of the present invention, the cultivation time is 100 to 120 days, preferably 100 to 110 days, and more preferably about 105 days.

[0029] Compared with the prior art, the present invention has at least the following beneficial effects:

[0030] 1) The biochar of the present invention has the advantages of rich pore structure, large specific surface area, small pore size, etc., and can absorb DOC in the soil that can be absorbed and utilized by methanogenic microorganisms.

[0031] 2) Biochar has low H / C and O / C, and its ash content is increased, which changes the physical and chemical properties of the soil and acts as a soil conditioner. At the same time, the number and types of hydroxyl, carboxyl and carbonyl oxygen-containing functional groups are reduced, the stability is increased, and the adsorption capacity is strong. It can increase the content of residual cadmium in the soil that is not easily absorbed and utilized by plants, and reduce the content of exchangeable cadmium in the soil.

[0032] 3) In general, the biomass-based porous biochar material of the present invention is simple to prepare and can effectively reduce soil methane emissions and reduce the bioavailability of heavy metal cadmium. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0034] Figure 1 SEM images of rice straw biochar prepared in Example 1 and Comparative Examples 1-2 of the present invention;

[0035] Figure 2 FTIR images of rice straw biochar prepared in Example 1 and Comparative Examples 1-2 of the present invention;

[0036] Figure 3 This is the methane accumulation dynamics of different treatment groups in the microcosm incubation experiment of Example 2 of the present invention;

[0037] Figure 4The dissolved organic carbon content of different treatment groups on the 25th day of the microcosm incubation experiment in Example 2 of the present invention;

[0038] Figure 5 The water-soluble cadmium content of different treatment groups on the 25th day of the microcosm incubation experiment in Example 2 of the present invention;

[0039] Figure 6 The distribution of soil cadmium species in different treatment groups on day 0 and day 25 of the microcosm incubation experiment in Example 2 of the present invention;

[0040] Figure 7 The copy number of the mcrA gene abundance in the CK, BC300, and BC800 treatment groups at 25 days after the microcosm incubation experiment in Example 2 of the present invention;

[0041] Figure 8 The methane emission flux of rice in different treatment groups during the entire growth period in the pot experiment of Example 3 of the present invention;

[0042] Figure 9 The cadmium content as extracted by calcium chloride in the rhizosphere soil of rice in different treatment groups in the pot experiment of Example 3 of the present invention is shown. DETAILED DESCRIPTION

[0043] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0044] Unless otherwise specified, the raw materials used in the following examples can be obtained from conventional commercial sources; the processes used, unless otherwise specified, are conventional processes in the art; and the operating temperatures used, unless otherwise specified, are room temperature (20±5°C).

[0045] Example 1

[0046] In this example, rice straw biochar was prepared. The specific process was as follows:

[0047] Step 1): Collect 5 kg of rice straw biomass from a pollutant-free rice field. Rinse the straw with deionized water for 30 minutes to clean the surface of the straw from dirt and impurities. Use ceramic scissors to remove excess stem from the straw and chop it into 1 cm pellets. Place the pellets in a clean, dry container and expose them to sunlight for 36 hours. To fully remove moisture from the straw pellets, dry them in a 60°C oven for 48 hours and collect them in a dry glass container.

[0048] Step 2): Weigh 60g of the straw pellets and evenly distribute them between three high-temperature-resistant ceramic boats for later use. Place the boats containing the straw pellets in a vacuum tube furnace protected by nitrogen (airflow rate of 125mL / min) and pyrolyze at 800°C for 2 hours at a pyrolysis heating rate of 10°C / min. After the pyrolysis is complete, stop heating and remove the material after the temperature drops to room temperature to obtain straw biochar.

[0049] Step 3) The biochar prepared in step 2 was ground into a fine powder using an agate mortar and sieve, and passed through a 0.15 mm mesh sieve to prepare homogeneous biochar particles (BC800) with a mesoporous pore size. The particles were mixed and placed in a dry brown sealed vial for storage.

[0050] Comparative Example 1

[0051] In this comparative example, a rice straw biochar (BC300) was prepared. The difference from Example 1 was that the pyrolysis temperature in step 2) was 300° C. The other experimental processes were similar to those in Example 1.

[0052] Comparative Example 2

[0053] In this comparative example, a rice straw biochar (BC500) was prepared. The difference from Example 1 was that the pyrolysis temperature in step 2) was 500° C. The other experimental processes were similar to those in Example 1.

[0054] Biochar performance test:

[0055] The properties of the biochar prepared in Example 1 and Comparative Examples 1-2 were tested. According to different preparation conditions, three biomass-based carbon materials at different temperatures were obtained. The pH, element content, specific surface area and pore volume and pore size of the biochar were measured. The results are shown in Table 1 below.

[0056] Table 1 Properties of biochar prepared in Example 1 and Comparative Examples 1-2

[0057]

[0058] As shown in Table 1, BC300, BC500, and BC800 exhibit significant differences in properties such as pH, elemental content, and specific surface area. Furthermore, as the anaerobic pyrolysis temperature increases, the H and O content, H / C ratio, and O / C ratio of the biochar decrease, while the pH, specific surface area, and pore volume increase. BC800 has a specific surface area and pore volume 55.6 and 14 times those of BC300, respectively, indicating a greater adsorption capacity. The biochar adsorption pore sizes shown in Table 1 indicate that the pyrolysis preparation method successfully produced biomass-based carbon materials with mesoporous pores. Furthermore, higher temperatures lead to smaller adsorption pores and improved adsorption performance.

[0059] SEM images of rice straw biochar BC300, BC500 and BC800 Figure 1 .Depend on Figure 1 It can be seen that the overall surface of BC300 and BC500 is smooth, with a dense and regular tubular structure, small pores and a small number; the surface of biochar BC800 is rough, with a richer honeycomb microporous structure, many pores and a large number. This feature makes BC800 have a stronger ability to adsorb heavy metals and organic matter.

[0060] Fourier transform infrared (FTIR) spectra of rice straw biochar BC300, BC500 and BC800 are as follows: Figure 2 The FTIR and element content results in Table 1 show that with the increase of pyrolysis temperature, the H / C and O / C ratios of biochar decrease, and the number and types of hydroxyl, carboxyl and carbonyl oxygen-containing functional groups decrease, indicating that the aromaticity and stability of BC800 biochar increase.

[0061] Example 2

[0062] This example uses the biochar prepared in Example 1 and Comparative Examples 1-2 to study its carbon sequestration and emission reduction and cadmium passivation effects and specific mechanisms through microcosm incubation experiments. The specific process is as follows:

[0063] Step 1) Soil pretreatment: Soil samples were collected from the 0-25 cm cadmium-contaminated paddy field in Dongtang Town, Shaoguan City, Guangdong Province (soil pH 5.8, cadmium content 4.6 mg / kg, average methane emission flux 7.8-60 mg / m 2 h), collect 5 kg of soil sample, spread it flat in a dry, ventilated, and cool place, and allow it to air dry at room temperature. After removing plant residues and gravel from the soil, grind it through a 100-mesh sieve, and store it in a sealed desiccator for later use.

[0064] Step 2) Weigh 5.0g of air-dried soil sample into a 50mL transparent vial, add 0.1g of BC300, BC500 or BC800, mix the soil sample and material, and add 25mL of ultrapure water to make the soil-water ratio of the whole system 1:5; then use high-purity nitrogen to aerate at a flow rate of 200mL / min for 45min to remove oxygen from the vial. After sealing with a bromobutyl rubber stopper and a perforated aluminum cap, use a 6cm long gas needle with nitrogen to purge and replace the headspace of the vial, so that the oxygen in the vial is fully drained. The simulated microcosm incubation bottle is placed in a constant temperature shaking box at 180rpm and 30℃ for 2h to mix the sample. Finally, the mixed incubation bottle is placed in a constant temperature, dark incubator at 30℃ and cultured for 25d.

[0065] Step 3) Determination of greenhouse gases and dissolved organic carbon: Gas sampling was performed on the 2nd, 5th, 11th, 17th, and 25th day after incubation, and the concentration of the corresponding methane in the incubation bottle was measured using a GC gas chromatograph. The results are shown in Figure 3. Figure 3 As shown, the supernatants of different treatments on the 25th day of culture were taken, acidified with 6 mol / L hydrochloric acid and then measured for dissolved organic carbon on an organic carbon analyzer. The results are shown in Figure 4 shown.

[0066] Step 4) Water-soluble cadmium and cadmium forms: The supernatant of different treatments on the 25th day of incubation was taken, acidified with 1 mol / L nitric acid, and then the water-soluble cadmium concentration was determined by graphite furnace atomic absorption spectrometry; 2 g of soil samples of different treatments on the 25th day of incubation were taken, and five different forms of cadmium, namely, exchangeable state, carbonate-bound state, iron-manganese-bound state, organic-bound state, and residual state, were extracted in sequence according to the Tessier five-step extraction method for cadmium. The cadmium content of different forms was then measured by inductively coupled plasma mass spectrometry. The results were as follows: Figure 5 、 Figure 6 shown.

[0067] Step 5) Soil DNA extraction and mcrA methane gene quantification: Soil from the CK, BC300, and BC800 treatment groups was collected on the 25th day after anaerobic incubation. The total soil DNA was extracted using the Pro Kit (refer to the kit instructions for operation); the extracted DNA was quantified using a real-time fluorescence quantitative PCR instrument for the specific methanogenic functional gene mcrA, where the primer sequences are:

[0068] Upstream primer mcrA-F: 5'-GGTGGTGTMGGATTCACACARTAYGCWACAGC-3' (SEQ ID NO: 1); downstream primer mcrA-R: 5'-TTCATTGCRTAGTTWGGRTAGTT-3' (SEQ ID NO: 2). The qPCR amplification reaction was a 10 μL reaction system, including: 4.4 μL sterile ultrapure water, 0.2 μL (10 μM) downstream primer, 0.2 μL (10 μM) upstream primer, 0.2 μL DNA template (i.e., total DNA extracted by the kit), 5 μL TB Premix Ex TaqTMII enzyme, reaction parameters are as follows: 95℃ pre-denaturation for 5 min; 95℃ denaturation for 60 s, 55℃ annealing for 45 s, 72℃ extension for 60 s, 35 cycles; final extension at 72℃ for 5 min. Figure 7 shown.

[0069] The carbon materials BC300, BC500, and BC800 were tested for their carbon fixation, emission reduction, and cadmium passivation performance in a microcosm incubation experiment. The test results are as follows:

[0070] Figure 3 The effects of three carbon materials prepared at different temperatures on soil methane production were compared. Figure 3 It can be seen that during the entire anaerobic incubation period, BC800 has an inhibitory effect on the production of soil methane, and the inhibitory effect on methane is 15%. This is related to the fact that BC800 adsorbs and reduces the DOC used by methanogenic microorganisms in the soil. The reduction rate of DOC is 18.13% ( Figure 4 ), while BC300 had a tendency to promote soil methane accumulation, and BC500 had no significant effect.

[0071] Figure 5 The passivation effects of the three materials on water-soluble cadmium in flooded soil environment were compared: the passivation rates of BC300, BC500 and BC800 on water-soluble cadmium in soil were 22.7%, 43.1% and 50.1%, respectively. Figure 6 The researchers compared the effects of three materials on the distribution of cadmium forms in flooded soils: BC300, BC500, and BC800 deactivate the most active exchangeable cadmium in the soil at rates of 10.7%, 20.4%, and 54.5%, respectively. Compared to BC300 and BC500, BC800 significantly reduces the available cadmium in the soil, increases the residual cadmium, and improves its stability.

[0072] Figure 7 The copy number of the soil methanogenic functional gene mcrA was compared in the CK, BC300, and BC800 treatment groups on the 25th day of incubation. Figure 7 It can be seen that compared with the control group, BC300 treatment increased the abundance of soil methanogenic functional genes, while BC800 treatment reduced the abundance of soil methanogenic functional genes, indicating that BC800 can inhibit the expression of soil microbial methanogenic functional genes, thereby inhibiting methane production.

[0073] It can be seen that compared with other materials, BC800 can effectively passivate heavy metal cadmium while achieving the purpose of carbon fixation and emission reduction in the microcosm incubation experiment.

[0074] Example 3

[0075] This example uses the biochar prepared in Example 1 (BC800) and Comparative Example 1 (BC300) for carbon sequestration and cadmium passivation pot experiments to study the role of biochar in rice growth. The specific process is as follows:

[0076] Step 1) Soil sample collection and pretreatment: Soil samples were collected from the 0-20 cm tillage layer of cadmium-contaminated rice fields in Shaoguan City, Guangdong Province (soil pH 6.5, cadmium content 4.0 mg / kg, average methane emission flux 7.8-60 mg / m 2 h), collect 60 kg of soil sample, spread it flat in a dry, ventilated, and cool place, and allow it to air dry at room temperature. Remove plant residues and gravel from the soil, grind it through a 10-mesh nylon mesh, mix it thoroughly, and bag it for later use.

[0077] Step 2) Experimental Pot Preparation: For the potted experiments, plastic buckets 24 cm high and 21.3 cm in inner diameter were used, with each pot containing 3 kg of soil. For the BC300 and BC800 treatments, 30 g of the corresponding biochar was added to each pot. After thorough mixing, water was added to cover the soil by 2–3 cm. The soil was submerged for 5 days to activate soil microorganisms.

[0078] Step 3) Seedling cultivation: The rice seeds were surface sterilized in a 30% hydrogen peroxide solution for 15 minutes, washed repeatedly with deionized water, and then placed in a constant temperature culture room for seedling cultivation. The seedling cultivation time was about 21 days. The rice variety used in this experiment was Huanghuazhan (Yue Shen Rice 2005010).

[0079] Step 4) Transplanting: One day before transplanting rice seedlings, add 0.344 g / kg of K₂HPO₄·3H₂O, 0.038 g / kg of KH₂PO₄, and 0.1 g / kg of urea. Apply a topdressing fertilizer once during the tillering stage. After raising rice seedlings, select seedlings of equal height and transplant them into experimental pots, planting four plants per pot, pairing them together. After transplanting, all pots were moved to a greenhouse for 105 days. The pots were flooded except during the maturation phase, when drainage was required. Three pots of rice were used for each treatment (CK, BC300, BC800).

[0080] Step 5) Greenhouse gas monitoring: During the rice growth cycle, the methane emission flux of the rice pot was measured every 7 days between 9:30 am and 12:30 pm using a fully automatic multi-channel long-term soil greenhouse gas flux measurement system. The results are as follows: Figure 8 The closed-circuit flux is calculated using the following formula:

[0081]

[0082] Where: Fc is the measured gas flux in soil, in μmol / (m 2 ·s); V is the total volume of the system, in cm 3 ; P0 is the initial pressure of the air chamber, in kPa; W0 is the initial water vapor concentration of the air chamber, in mmol / mol; R is Planck's constant, in 8.314 Pa·m 3 / (k·mol); S is the soil measurement area, unit is cm 2; T0 is the initial temperature of the air chamber, in °C; It is the emission rate of the measured gas after water correction, and its unit is 1 / μmol·s.

[0083] Step 6) Determination of available cadmium in calcium chloride: After the rice matures, 10 g of rice rhizosphere soil from different treatment groups is taken and freeze-dried. After grinding through a 100 sieve, it is stored for later use. 2 g of dry soil is added to 20 mL of 0.1 mol / L CaCl2 solution and placed in a constant temperature shaking box at 25 ° C and 180 rpm for continuous shaking for 2 hours. After the end, the extract is taken out and centrifuged at 7500 rpm for 6 minutes. The supernatant is filtered through a 0.22 mm filter membrane. The concentration of Cd in the extract is determined by ICP-OES method. The results are as follows: Figure 9 shown.

[0084] The carbon materials BC300 and BC800 were tested for their carbon sequestration, emission reduction, and cadmium passivation performance in a rice pot experiment. The test results are as follows:

[0085] from Figure 8 It can be seen that during the entire rice growth process, the trend of rice methane emission flux after biochar application in the control group CK and the BC300 and BC800 treatment groups generally showed an increase first and then a decrease, and finally tended to zero emission flux when the water was drained in the late maturity period. Moreover, the peak methane emission flux of the control group CK and the BC300 and BC800 treatment groups appeared on the 42nd day after transplanting, which were 28.3, 20.6 and 16.06 nmol / (m 2 ·s), at this time, the methane flux reduction rate of BC800 was 43.25%. The methane emission flux of rice in the BC800 treatment group was lower than that of the control group throughout the cultivation period, showing the effect of methane emission reduction. Figure 9 BC800 treatment also reduced the available cadmium content in soil calcium chloride, with a cadmium passivation rate of 37.3%. This suggests that BC800 also has the ability to reduce methane emissions and passivate heavy metal cadmium in rice pot experiments.

[0086] While the embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above. Various modifications may be made within the scope of knowledge possessed by a person skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof may be combined with one another unless there is a conflict.

Claims

1. The application of biochar in simultaneously reducing cadmium content and methane emissions in cadmium-containing paddy fields, characterized in that: The specific surface area of ​​the biochar is greater than 200 m 2 g -1 ; The pore size of the biochar is 1 to 5 nm; the biochar is obtained by pyrolysis and reduction of biomass materials in an inert atmosphere at 600 to 1000°C.

2. The use according to claim 1, characterized in that The pore volume of the biochar is ≥0.05cm 3 g -1 .

3. The use according to claim 1, characterized in that The time of the thermal reduction is 1 to 4 hours.

4. The use according to claim 1, characterized in that The biomass material includes at least one of rice straw, wheat straw, corn straw, waste wood, nut shells, rice husks, peanut shells, and coconut shells.

5. The use according to claim 1, characterized in that The cadmium-containing paddy field includes at least one of a flooded rice field, a pond, and a swamp.

6. The use according to claim 1, characterized in that The cadmium content of the cadmium-containing paddy field is 0-10 mg / kg.

7. The use according to claim 1, characterized in that The average methane emission flux of the cadmium-containing paddy field is 5-70 mg / m 2 ·h.

8. A method for simultaneously reducing the cadmium content and methane emissions in cadmium-containing paddy fields, characterized in that: The method comprises the following steps: applying 0.1-2% of the soil mass of biochar to the cadmium-containing paddy field before flooding, wherein the specific surface area of ​​the biochar is greater than 200m 2 g -1 .

Images