Restoration method for moderately and severely cadmium-polluted rice field

Abstract

The remediation method for the moderately and severely cadmium-polluted rice field aims at strictly controlled cadmium-polluted rice fields, and is divided into two stages of strict control and safe utilization for remediation. In the strict management and control stage, an activating agent is applied to the soil in spring, then microalgae are inoculated, cadmium-enriched plants are planted, the plants are collected after being full of the microalgae, the plants are harvested when the plants grow to the enrichment extreme value, stubbles are reserved for growth, and the steps are repeated till winter; applying an activating agent in winter, planting green manure, and harvesting in spring in the next year; the process is cyclically carried out until the cadmium content of the soil is reduced to a safe utilization level. Entering a safe utilization stage, applying an activating agent in spring, inoculating nitrogen-fixing cyanobacteria, collecting the cyanobacteria after the cyanobacteria overgrow, and repeating the steps until the rice seedlings are transplanted; applying nitrogen-fixing blue-green algae, and planting rice; applying an activating agent after rice harvesting, planting winter green manure, and harvesting in next spring; the process is cyclically carried out until the cadmium content of the soil is reduced to a preferential protection level. The method is low in cost, high in remediation efficiency and good in effect, and a new way is provided for cadmium-polluted rice field remediation.

Description

Technical Field

[0001] The invention relates to a method for repairing a paddy field with moderate to severe cadmium pollution, and specifically belongs to the technical field of repairing heavy metals in paddy field soil. Background Art

[0002] In recent years, cadmium pollution in paddy soil has become a serious problem that threatens rice safety and the agricultural ecological environment. The presence of cadmium not only affects the quality of rice, but also poses a threat to human health. In the Soil Pollution Prevention and Control Law, according to the degree of soil pollution and relevant standards, my country divides agricultural land into priority protection, safe utilization and strict control categories. Among them, the strict control category has the heaviest pollution, generally medium to severe pollution. There is no mature technology to ensure the safe production of rice in this type of rice field, and the risk of cadmium pollution in rice is high. In view of this, rice planting is generally prohibited. Usually, the risk is strictly controlled by adjusting the planting structure, prohibiting the planting of edible agricultural products, or even leaving the land fallow, but this will make it difficult to maximize the use of limited arable land resources. For strictly controlled rice fields, to ensure the safe production of rice, the cadmium content in the paddy soil must be reduced first.

[0003] At present, the research hotspots of cadmium reduction technology for paddy field soil include electric remediation technology, leaching technology, plant extraction technology and microalgae remediation technology. Electric remediation technology can remove heavy metals and organic pollutants at the same time, does not stir the soil layer, is simple to operate, and has high processing efficiency, but it is easy to cause changes in the physical and chemical properties of the soil and is still in the exploratory stage. Leaching technology is fast and efficient, but it has poor remediation effects on soils with heavy geological viscosity and poor permeability, and there are problems of damaging soil fertility and causing secondary pollution of soil and groundwater. Plant extraction technology can effectively avoid the disadvantages of electric remediation technology and leaching technology, but plants have the problem of slow growth, and the remediation cycle generally takes more than 5 years. In addition, the plant's ability to enrich cadmium is unstable. Large-scale planting of enriched plants occupying arable land does not conform to my country's national conditions of a large population and limited land, so large-scale applications are rare.

[0004] Microalgae restoration technology has become a promising alternative in recent years due to its low cost, environmental friendliness, and the fact that it does not occupy arable land. Soil microalgae include prokaryotic cyanobacteria and eukaryotic microalgae, and are an important part of the soil microecological community. Microalgae have a high surface-to-volume ratio and rich functional groups, such as carboxyl and hydroxyl groups, which enable them to firmly bind to cadmium ions in the soil to form a stable complex. Both living and dead algae have a strong adsorption capacity for heavy metals. Microalgae can remove heavy metals to reduce the cadmium content in the soil and improve soil quality. Microalgae can also adsorb and passivate heavy metals to further reduce the cadmium content in rice. In addition, microalgae play an important role in nitrogen fixation, carbon fixation, oxygen supply, secretion of substances that promote plant growth, and promotion of the formation of soil aggregate structure. They help reduce cadmium oxidative damage to rice, enhance rice's resistance to cadmium, reduce rice's absorption of cadmium, and promote the improvement of rice quality, thus ensuring food security in many aspects.

[0005] At present, the microalgae commonly used for heavy metals are mainly some algae of Chlorophyta, Cyanobacteria, Rhodophyta and Phaeophyta. These microalgae have been widely studied in the treatment of heavy metal wastewater, but less in the remediation of paddy field soil. Some microalgae contain algae toxins, some only grow in static water bodies such as lakes, and some grow scattered in water bodies, making them difficult to use in paddy fields. Therefore, most of the research on soil heavy metal remediation remains in the pot experiment or small-scale trial experiment stage. Invention patent ZL202010093994.1 discloses a method for repairing cadmium contamination in paddy field soil by using an activator in conjunction with nitrogen-fixing cyanobacteria. This method uses nitrogen-fixing cyanobacteria to adsorb cadmium, reduce the cadmium content in the soil, and reduce the absorption and accumulation of heavy metal cadmium by rice, thereby ensuring the safe production of rice. However, this method is mainly aimed at safe utilization of paddy fields. For strictly controlled paddy fields, due to the high degree of soil pollution, longer treatment time may be required.

[0006] In order to shorten the restoration time and improve the restoration efficiency, it is necessary to explore an optimized combination of microalgae combined with different methods and measures for strictly controlled rice fields. At the same time, considering that cadmium pollution in paddy field soil will also inhibit the transformation process of nitrogen in the soil and reduce the nitrogen supply capacity of the soil; and nitrogen fertilizer application will aggravate soil acidification and further aggravate cadmium pollution, we will integrate nitrogen management strategies into the restoration system to build a more complete paddy field soil cadmium pollution restoration system. Summary of the invention

[0007] In view of the above situation, the present invention provides a method for repairing moderately and severely cadmium-contaminated rice fields. The present invention provides a method for repairing moderately and severely cadmium-contaminated rice fields. The method aims to reduce the cadmium content in the soil, enhance soil fertility, improve the repair efficiency, and reduce the absorption of cadmium by rice in many aspects, thereby ensuring the safe production of rice, by combining the synergistic effect of activators, the joint reduction of cadmium by algae and plants, and the reduction of green manure and nitrogen-fixing cyanobacteria. The specific process is as follows: Phase 1: Strict control phase soil remediation Step 1: In spring, apply activators to the strictly controlled cadmium-contaminated paddy field soil and plow the cultivated layer soil to promote the dissolution of heavy metal cadmium from the soil solid phase; one day after the cadmium in the soil is activated, irrigate to establish the paddy field water layer, control the paddy field water layer height to 8-10 cm, and evenly plow to migrate the cadmium to the paddy field water layer; then inoculate microalgae and plant cadmium-enriching plants to jointly reduce cadmium; collect the microalgae after they fill the paddy field water layer, leave 1 / 3 of the microalgae to continue growing, harvest the cadmium-enriching plants when they grow to the enrichment extreme, and leave the stubble to continue growing; repeat the above steps until the temperature drops in winter, collect all the microalgae, and harvest all the cadmium-enriching plants; Step 2: In winter, apply the activator to the soil again and plow the cultivated layer soil to plant winter green manure until all the green manure is harvested in spring, and the underground part of the green manure is turned over and returned to the field; the activator is applied once a month; Step 3: Repeat steps 1 and 2 to reduce the cadmium content in the moderately and severely cadmium-contaminated paddy soil from the strictly controlled soil level to the safe utilization soil level, thus ending the soil remediation in the strict control stage; Phase 2: Safe Utilization Phase Soil Remediation Step 4: In spring, an activator is applied to the soil of the paddy field contaminated by safe utilization of cadmium, and the cultivated layer soil is evenly plowed to activate the insoluble heavy metal cadmium; after cadmium in the soil is activated for 1 day, water is irrigated to establish the paddy field water layer, and the height of the paddy field water layer is controlled to be 8-10 cm, and the soil is evenly plowed; nitrogen-fixing cyanobacteria are inoculated in the paddy field water layer, and after 5-7 days when the nitrogen-fixing cyanobacteria cover the water surface of the paddy field, 2 / 3 of the nitrogen-fixing cyanobacteria in the paddy field are collected using a 80-120 mesh gauze, and the remaining nitrogen-fixing cyanobacteria continue to grow in the paddy field; the application of the activator, the inoculation of nitrogen-fixing cyanobacteria and the collection of nitrogen-fixing cyanobacteria are repeated until all the nitrogen-fixing cyanobacteria are collected before rice transplanting; Step 5: Planting rice in the paddy field soil treated in step 4, and inoculating nitrogen-fixing microalgae as nitrogen fertilizer and cadmium passivator; Step 6: After rice is harvested, apply activators to the cadmium-contaminated paddy field soil, evenly plow the cultivated layer soil, plant winter green manure, harvest the above-ground part in spring, and press the underground part of the green manure back into the field. Apply the activator once a month; Step 7: Repeat steps 4 to 6 until the cadmium content in the paddy soil drops to the level of priority protected soil, thus ending soil remediation in the safe utilization stage.

[0008] The activator is obtained by diluting a tetrasodium glutamate diacetate GLDA solution, with a mass concentration of 0.02-0.05%, and a single application amount of 0.001-0.01 mL of activator / g of paddy soil.

[0009] The microalgae is Anabaena Anabaena、 Hydrodictyum Hydrodictyon , Nostoc Nostoc , and Spirogyra Spirogyra A mixture of various algae selected from the sample.

[0010] The cadmium-accumulating plants are one or more plants selected from barnyard grass, wild rice, canna, cattail, calamus, pickerel grass, iris and Azolla.

[0011] The green manure is one or more plants selected from rape, alfalfa, broad bean, astragalus, and ryegrass.

[0012] The nitrogen-fixing cyanobacteria are Anabaena Anabeana and Siphonaptera Aulosira A mixture of various algae selected from the sample.

[0013] The microalgae, nitrogen-fixing cyanobacteria, cadmium-enriching plants and green manure are collected, dried and then incinerated, and the incineration residues are sent to a hazardous waste treatment plant for treatment.

[0014] Beneficial effects of the present invention: 1. The method of the present invention overcomes the time and space limitations of biological remediation and greatly improves the remediation efficiency. In terms of time, the combined remediation using microalgae, cadmium-enriching plants and winter green manure that meet the climatic conditions and geographical environment of the remediation area overcomes the seasonal limitations of a single remediation technology; in terms of space, the use of microalgae and cadmium-enriching plants simultaneously reduces the heavy metal cadmium in the water layer and soil layer of the paddy field; 2. The method of the present invention integrates nitrogen management strategies into the restoration system. Based on the characteristics of nitrogen fixation by cyanobacteria and nitrogen fixation by underground nodules of green manure, the algae and underground parts of green manure are turned over and returned to the field to achieve weight reduction and efficiency improvement. By reducing the amount of nitrogen fertilizer, alleviating soil acidification, and reducing cadmium pollution; while increasing the nitrogen content in the soil, it effectively inhibits the absorption and transport of cadmium by rice, further improving soil restoration efficiency, and ensuring the safe growth of rice. This strategy actively responds to the national action to reduce the amount of chemical fertilizers, promotes soil health, improves restoration efficiency, and provides a green solution for the sustainable development of agriculture.

[0015] 3. The method of the present invention adopts a method of improving the species richness of the microalgae rice field artificial ecosystem, and mixedly adds cadmium-tolerant microalgae and cadmium-sensitive microalgae, which can improve the cadmium removal efficiency of the microalgae rice field artificial ecosystem at a low cost.

[0016] 4. The method of the present invention is environmentally friendly, follows the laws of nature, and does not damage the quality of farmland soil; after the algae and green manure are turned over and returned to the field, they can increase the soil porosity, improve the soil organic matter and nitrogen content, increase the soil pH value, optimize the rhizosphere microbial community structure, increase rice yield, and improve rice quality.

[0017] 5. The method of the present invention uses the biodegradable chelating agent GLDA, which can enhance the repair effect of microalgae and plants without causing damage to the physical and chemical properties and biological structure of the soil.

[0018] 6. The present invention has low cost, high remediation efficiency, good effect and good benefits. It can effectively solve the problem of severe cadmium pollution in the soil, improve soil type, ensure safe rice production, and provide a new way for heavy metal treatment in paddy field soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 : The technical roadmap of a method for repairing moderately to severely cadmium-contaminated rice fields of the present invention. DETAILED DESCRIPTION

[0020] Example 1 This example is located in a cadmium-contaminated area in Jiangxi Province, with an area of ​​10 mu. The average total cadmium concentration in the soil is 1.7 mg / kg, and the soil pH is 5.45, which belongs to the strictly controlled soil. The method of the present invention is used to repair cadmium-contaminated rice fields.

[0021] Activator: Dilute the 47% GLDA solution 1500 times to a mass concentration of 0.03%, and the single application amount is 0.007 mL activator / g paddy soil.

[0022] Phase 1: Strict control phase soil remediation (1) After the Spring Waking of Insects, apply activators to the cadmium-contaminated paddy soil and evenly plow the tillage layer to a thickness of 20 cm; (2) One day after the cadmium in the soil was activated, water was irrigated to establish the paddy field water layer, and the height of the paddy field water layer was controlled to be 5-8 cm. The activated soil was evenly plowed, and then the cadmium-enriching plant barnyard grass was planted in rows with a spacing of 20 cm between plants and 2 m between rows. Anabaena and Spirogyra were inoculated in the paddy field water layer between rows of barnyard grass. (3) When the Anabaena and Spirogyra have grown all over the paddy field, collect 2 / 3 of the Anabaena and Spirogyra in the paddy field, and leave the rest to grow in the paddy field. Repeat this process until all the Anabaena and Spirogyra are collected after the Cold Dew and before the Frost Descent.

[0023] (4) Barnyard grass should be harvested every 50 days, leaving 15 cm of stubble, and allowed to continue growing. After the Cold Dew, before the Frost, all barnyard grass should be removed by the roots. Apply an activator once after each harvest.

[0024] (5) After harvesting barnyard grass, plant alfalfa and apply activator once every 10 days. After application, evenly plow the soil of the cultivated layer of the rice field and continue to apply for 1 month.

[0025] (6) Before the Spring Waking of Insects, all alfalfa should be harvested and the roots of alfalfa should be turned over and returned to the field.

[0026] (7) The collected Anabaena, Spirogyra, Echinochloa crus-galli and alfalfa are dried and incinerated, and the incineration residues are sent to a hazardous waste treatment plant for disposal.

[0027] (8) Detect soil pH and total cadmium content monthly.

[0028] In just one year, the cadmium content in paddy field soil dropped to a safe level, the soil pH was 5.65, and the total cadmium content dropped from 1.7 mg / kg to 1.47 mg / kg.

[0029] Phase II: Soil remediation during safe utilization phase (1) After the Spring Waking of Insects, add activators to the cadmium-contaminated rice fields and evenly plow the soil in the cultivated layer of the rice fields; (2) Water was irrigated to establish a water layer in the paddy field, and Anabaena was inoculated into the water layer. After 7 days, the Anabaena covered the entire water surface of the paddy field. After 10 days, 2 / 3 of the Anabaena was collected, and the remaining part was allowed to continue growing in the paddy field. This process was repeated 3 times, and the remaining part was collected once before rice seedlings were transplanted. After all the Anabaena were collected, the total cadmium content in the soil, the effective cadmium content, and the cadmium content in the algae were tested.

[0030] (3) Three days after rice seedlings were transplanted, the inoculated Anabaena was not collected. During its continuous growth, the Anabaena adsorbed and fixed heavy metals in the water. At the same time, the Anabaena secreted amino acids, plant growth hormones and other substances outside the cells to promote rice growth.

[0031] (4) After rice is harvested, the cadmium content in brown rice is tested; (5) After rice is harvested, alfalfa is planted and the activator is applied once every 10 days for one month.

[0032] (6) Before the Spring Waking of Insects, all alfalfa should be harvested and the roots of alfalfa should be turned over and returned to the field.

[0033] (7) The collected anabaena and alfalfa are dried and incinerated, and the incineration residues are sent to a hazardous waste treatment plant for disposal.

[0034] The results showed that in the first year, the cadmium content in brown rice was 0.19 mg / kg, which was lower than the limit of 0.2 mg / kg in the "National Food Safety Standard Limit of Contaminants in Food" (GB2762-2017).

[0035] The above steps are repeated until the cadmium content in the paddy soil drops to the priority protection level.

[0036] The results of this example show that the method of combining microalgae with phytoremediation can effectively remove heavy metal cadmium in rice fields and ensure the safe production of rice.

[0037] Example 2 This example is located in a cadmium-contaminated area in Jiangxi Province, covering an area of ​​1 mu. The average total cadmium concentration in the soil is 2.3 mg / kg, and the soil pH is 5.75, which belongs to the strictly controlled soil. The method of the present invention is used to repair cadmium-contaminated rice fields.

[0038] Activator: Dilute the 47% GLDA solution 1200 times to a mass concentration of 0.04%, and apply 0.01 mL activator / g paddy soil at a single application.

[0039] Phase 1: Strict control phase soil remediation (1) After the Spring Waking of Insects, apply activators to the cadmium-contaminated paddy soil and evenly plow the cultivated layer of soil; (2) One day after the cadmium in the soil was activated, water was irrigated to establish the water layer in the paddy field. The height of the water layer in the paddy field was controlled to be 10-20 cm. The activated soil was evenly plowed and then canna was planted in rows with a spacing of 60 cm between plants and 2 m between rows. Hydrophora and Spirogyra were inoculated between the rows of canna. (3) When the water hyacinth and water sponge have grown all over the paddy field, collect 2 / 3 of the water hyacinth and water sponge from the paddy field, and leave the rest to grow in the paddy field. Repeat this process until all of the water hyacinth and water sponge are collected after the Cold Dew and before the Frost Descent.

[0040] (4) Cannas are harvested every 50 days. Cannas that are beyond the growth range are removed. Cannas within the area are harvested in a sparse manner, leaving stubble of 7 to 10 cm and continue to grow. After the Cold Dew and before the Frost, all cannas are removed by the roots. Apply an activator once after each harvest.

[0041] (5) After the canna is removed, plant ryegrass and apply activator once every 10 days for one month.

[0042] (6) Before the Spring Waking of Insects, harvest all the ryegrass and turn over the ryegrass roots and return them to the field.

[0043] (7) The collected hydrophytes, Spirogyra, Canna and ryegrass are dried and incinerated, and the incineration residues are sent to a hazardous waste treatment plant for disposal.

[0044] (8) Detect soil pH and total cadmium content monthly.

[0045] By repeating the above steps in a cycle, in just 18 months, the cadmium content in the paddy soil dropped to a safe level for utilization, the soil pH was 5.85, and the average concentration of total cadmium in the soil dropped from 2.3 mg / kg to 1.43 mg / kg.

[0046] Phase II: Soil remediation during safe utilization phase (1) After the Spring Waking of Insects, add activators to the cadmium-contaminated rice fields and evenly plow the soil in the cultivated layer of the rice fields; (2) Water was irrigated to establish a water layer in the paddy field, and Anabaena was inoculated into the water layer. After 7 days, the Anabaena covered the entire water surface of the paddy field. After 10 days, 2 / 3 of the Anabaena was collected, and the remaining part was allowed to continue growing in the paddy field. This process was repeated 3 times, and the remaining part was collected once before rice seedlings were transplanted. After all the Anabaena were collected, the total cadmium content in the soil, the effective cadmium content, and the cadmium content in the algae were tested.

[0047] (3) Three days after rice seedlings were transplanted, the inoculated Anabaena was not collected. During its continuous growth, the Anabaena adsorbed and fixed heavy metals in the water. At the same time, the Anabaena secreted amino acids, plant growth hormones and other substances outside the cells to promote rice growth.

[0048] (4) After rice is harvested, the cadmium content in brown rice is tested; (5) After rice is harvested, plant astragalus. Apply activator once every 10 days, and evenly plow the soil in the rice field after application. Continue to apply for 1 month.

[0049] (6) Before the Spring Waking of Insects, harvest all the astragalus and turn over the roots of the astragalus and return them to the field.

[0050] (7) The collected Anabaena and Astragalus are dried and incinerated, and the incineration residues are sent to a hazardous waste treatment plant for disposal.

[0051] The results showed that in the first year, the cadmium content in brown rice was 0.18 mg / kg, which was lower than the limit of 0.2 mg / kg in the "National Food Safety Standard Limit of Contaminants in Food" (GB2762-2017).

[0052] The above steps are repeated until the cadmium content in the paddy soil drops to the priority protection level.

[0053] The results of this example show that the method of combining microalgae with phytoremediation can effectively remove heavy metal cadmium in rice fields and ensure the safe production of rice.

[0054] The above embodiments are further detailed descriptions of the present invention in combination with specific preferred embodiments, and the descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the attached claims.

Claims

1. A method for repairing moderately or severely cadmium-contaminated rice fields, characterized in that: The remediation method is aimed at strictly controlled cadmium-contaminated rice fields. It combines activator synergy, algae and plants to reduce cadmium, and green manure and nitrogen-fixing cyanobacteria to reduce weight and increase efficiency. It aims to reduce the cadmium content in the soil, enhance soil fertility, improve remediation efficiency, and reduce the absorption of cadmium by rice in many aspects, thereby ensuring the safe growth of rice. The specific process is as follows: Phase 1: Strict control phase soil remediation Step 1: In spring, apply activators to the strictly controlled cadmium-contaminated paddy field soil and plow the cultivated layer soil to promote the dissolution of heavy metal cadmium from the soil solid phase; one day after the cadmium in the soil is activated, irrigate to establish the paddy field water layer, control the paddy field water layer height to 8-10 cm, and evenly plow to migrate the cadmium to the paddy field water layer; then inoculate microalgae and plant cadmium-enriching plants to jointly reduce cadmium; collect the microalgae after they fill the paddy field water layer, leave 1 / 3 of the microalgae to continue growing, harvest the cadmium-enriching plants when they grow to the enrichment extreme, and leave the stubble to continue growing; repeat the above steps until the temperature drops in winter, collect all the microalgae, and harvest all the cadmium-enriching plants; Step 2: In winter, apply the activator to the soil again and plow the cultivated layer soil to plant winter green manure until all the green manure is harvested in spring, and the underground part of the green manure is turned over and returned to the field; the activator is applied once a month; Step 3: Repeat steps 1 and 2 to reduce the cadmium content in the moderately and severely cadmium-contaminated paddy soil from the strictly controlled soil level to the safe utilization soil level, thus ending the soil remediation in the strict control stage; Phase 2: Safe Utilization Phase Soil Remediation Step 4: In spring, an activator is applied to the soil of the paddy field contaminated by safe utilization of cadmium, and the cultivated layer soil is evenly plowed to activate the insoluble heavy metal cadmium; after cadmium in the soil is activated for 1 day, water is irrigated to establish the paddy field water layer, and the height of the paddy field water layer is controlled to be 8-10 cm, and the soil is evenly plowed; nitrogen-fixing cyanobacteria are inoculated in the paddy field water layer, and after 5-7 days when the nitrogen-fixing cyanobacteria cover the water surface of the paddy field, 2 / 3 of the nitrogen-fixing cyanobacteria in the paddy field are collected using a 80-120 mesh gauze, and the remaining nitrogen-fixing cyanobacteria continue to grow in the paddy field; the application of the activator, the inoculation of nitrogen-fixing cyanobacteria and the collection of nitrogen-fixing cyanobacteria are repeated until all the nitrogen-fixing cyanobacteria are collected before rice transplanting; Step 5: Planting rice in the paddy field soil treated in step 4, and inoculating nitrogen-fixing microalgae as nitrogen fertilizer and cadmium passivator; Step 6: After rice is harvested, apply activators to the cadmium-contaminated paddy field soil, evenly plow the cultivated layer soil, plant winter green manure, harvest the above-ground part in spring, and press the underground part of the green manure back into the field. Apply the activator once a month; Step 7: Repeat steps 4 to 6 until the cadmium content in the paddy soil drops to the level of priority protected soil, thus ending the soil remediation in the safe utilization stage.

2. The method for repairing moderately or severely cadmium-contaminated rice fields according to claim 1, characterized in that: The activator is obtained by diluting a tetrasodium glutamate diacetate solution, with a mass concentration of 0.02-0.05%, and a single application amount of 0.001-0.01 mL of activator / g of paddy soil.

3. The method for repairing moderately or severely cadmium-contaminated rice fields according to claim 1, characterized in that: The microalgae is Anabaena Anabaena, Hydrodictyum Hydrodictyon , Nostoc Nostoc , and Spirogyra Spirogyra A mixture of various algae selected from the sample.

4. The method for repairing moderately or severely cadmium-contaminated rice fields according to claim 1, characterized in that: The cadmium-accumulating plants are one or more plants selected from barnyard grass, wild rice, canna, cattail, calamus, pickerel grass, iris and Azolla.

5. The method for repairing moderately or severely cadmium-contaminated rice fields according to claim 1, characterized in that: The green manure is one or more plants selected from rape, alfalfa, broad bean, astragalus, and ryegrass.

6. The method for treating moderately or severely cadmium-contaminated paddy soil according to claim 1, characterized in that: The nitrogen-fixing cyanobacteria are Anabaena Anabeana and Siphonaptera Aulosira A mixture of various algae selected from the sample.

7. The method for repairing moderately or severely cadmium-contaminated rice fields according to claim 1, characterized in that: The microalgae, nitrogen-fixing cyanobacteria, cadmium-enriching plants and green manure are collected, dried and then incinerated, and the incineration residues are sent to a hazardous waste treatment plant for treatment.

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