A method for applying red mud iron selection residue to rice field wetland to purify nitrogen in nitrogen-containing water body

Abstract

The application discloses a method for applying red mud iron separation residue to purify nitrogen in nitrogen-containing water bodies in rice field wetlands, and belongs to the technical field of water pollution ecological restoration in environmental engineering. The red mud iron separation residue is washed with clean water to remove the impurities adhered to the surface until the washed water is clear and transparent; the washed red mud iron separation residue is naturally dried, the dried red mud iron separation residue is ground to a particle size of 0.1-1 mm by using a ball mill, the nitrogen-exceeding river water is used to irrigate by using the artificial irrigation mode, the irrigation is performed until the flowerpot is filled, and then sampling is performed after standing for 1 day, 2 days, 4 days and 6 days of the hydraulic retention time set in the fourth step; the experimental variables are whether the rice is planted and whether the red mud iron separation residue is used, and the rest of the variables are guaranteed to be consistent. By applying the red mud iron separation residue in the rice field wetland, the nitrogen-containing water bodies can be effectively purified, the nitrogen loss can be reduced, and the pollution risk of surrounding water bodies and soil can be reduced.

Description

Technical Field

[0001] This invention belongs to the field of water pollution ecological restoration technology in environmental engineering, specifically involving a method for applying iron-removing residue from red mud to purify nitrogen in nitrogen-containing water bodies in paddy wetlands. Background Technology

[0002] With the rapid development of urbanization, environmental problems brought about by urbanization have gradually become prominent, including pollution of small and medium-sized rivers. According to surface water statistics... [1] The proportion of surface water sections with excellent (Class I-III) water quality reached 89.4%, an increase of 1.5 percentage points year-on-year, while the proportion of sections with inferior (Class V) water quality was 0.7%, unchanged year-on-year. However, the total nitrogen concentration in some rivers flowing into the sea remains high, and total nitrogen pollution has become an important factor affecting the water quality of nearshore sea areas. The water quality along the entire main stream remained stable at Class II, and the water quality in the Haihe River Basin improved from slightly polluted to good. However, in some areas with severe agricultural non-point source pollution, the seasonal variation in total nitrogen concentration was significant. Significant progress has been made in pollution control in key river basins, and the surface water environmental quality has continued to improve, but nitrogen pollution in some rivers still requires attention. In the process of urbanization, the proportion of hardened urban surfaces has increased, and the natural vegetation coverage has decreased, leading to increased rainwater runoff and a faster rate of pollutant inflow into rivers. Researchers have used isotope methods to study the long-term accumulation of nitrogen pollution in groundwater and rivers in some areas, especially in densely agricultural areas and rivers surrounding cities, where nitrogen levels are high. [2] Based on Wang Mengru's research, she identified the sources of nitrates in groundwater and rivers in complex urban environments through isotopic and hydrochemical analysis, pointing out that nitrogen levels in urban rivers are significantly affected by the discharge of domestic sewage and industrial wastewater. [3] Human activities impact the environment, and despite significant efforts to control pollution and improve environmental conditions, some pollution is unavoidable. From 2021 to 2022, an in-depth survey and analysis of surface water quality in a specific region was conducted. This region has a unique geographical location, situated at the intersection of farmland, industrial areas, and coal mining subsidence areas, facing a serious problem of excessive total nitrogen (TN) levels. According to relevant investigation reports, the TN content in this area not only exceeds the standard limit, but its forms are also quite complex, encompassing various forms such as ammonia nitrogen, nitrite nitrogen, and organic nitrogen. Excessive TN in rivers poses a risk of eutrophication.

[0003] Treatment methods for nitrogen in water vary depending on the type of wastewater. For wastewater with high ammonia nitrogen levels, alkaline substances can be added to change the pH value, thereby converting ammonia nitrogen into ammonia gas, which can then be removed via stripping. [4] Membrane separation method that utilizes the high efficiency and selectivity of membrane technology to separate nitrogen. [5] The inflection point chlorination method involves adding chlorine to water to convert ammonia nitrogen into nitrogen gas.[6] A biological method that removes nitrogen by utilizing substances in water through nitrification and denitrification via the action of microorganisms. [7] Constructing artificial wetlands is an ecological restoration method that utilizes the synergistic effects of wetland plants and microorganisms to remove substances from water bodies. [8] And so on. Among the technologies mentioned above, stripping may only remove a portion of ammonia nitrogen and consumes a large amount of alkali, while the nitrogen-contaminated river water introduces new problems; membrane separation can separate nitrogen, but the large volume of surface water discharge makes the membrane prone to clogging and damage, thus increasing operating costs; breakpoint chlorination is costly and may produce harmful byproducts; biological methods utilizing microbial nitrification and denitrification have low treatment efficiency for low-pollution water due to insufficient carbon sources; constructing artificial wetlands requires consideration of the land area and whether the water body can meet the growth needs of wetland plants. For river water with large amounts of nitrogen exceeding standards, directly using traditional methods cannot achieve ideal treatment results.

[0004] [1] Ministry of Ecology and Environment of the People's Republic of China. 2023 China Ecological and Environmental Status Bulletin [M]. Beijing: Ministry of Ecology and Environment, 2024.

[0005] [2]CHEN W,ZHANG

[0006] [3]Wang M, Bodirsky BL, Rijneveld R, et al. A triple increase in global river basins with water scarcity due to future pollution [J]. Nature Communications, 2024, 15(1):880.

[0007] [4] Zhang Yuyue, Xu Xiangdong, Wang Kaichong, et al. Research progress on resource utilization technology of nitrogen in wastewater [J]. Water Purification Technology, 2024, 43(12):18-26+159.

[0008] [5] Zhang Bianyang, Zhu Xinhua, Zhou Jing, et al. Research progress on the application of membrane separation technology in industrial wastewater treatment [J]. Modern Chemical Industry Research, 2024, (15):30-32.

[0009] [6] Yu Xinlong, Wan Qiang, Gao Zhen, et al. Application of breakpoint chlorination in wastewater treatment plants [J]. Journal of Tianjin University of Science and Technology, 2021, 36(04):47-50.

[0010] [7] Lin Hongjian, Liu Wei, Chen Yibin. Research progress on biological treatment technology for ammonia nitrogen wastewater [J]. Guangzhou Chemical Industry, 2016, 44(11):16-18.

[0011] [8] Ran Qiaoling, Yang Juan, Xu Haitao. Application and exploration of water ecological restoration technology in river pollution control [J]. Leather Manufacturing and Environmental Protection Technology, 2024, 5(18):131-133. Summary of the Invention

[0012] Technical problems to be solved:

[0013] To address the shortcomings of existing technologies, this application solves the problems of stripping methods removing only a portion of ammonia nitrogen and consuming large amounts of alkali, membrane separation methods being prone to membrane clogging and damage, which inevitably increases operating costs, breakpoint chlorination methods being costly and potentially producing harmful byproducts, biological methods having low treatment efficiency for low-pollution water due to insufficient carbon sources, and the inability to achieve ideal treatment results by directly using traditional methods for river water with large amounts of nitrogen exceeding standards. The proposed method is to apply iron residue from red mud to paddy wetlands to purify nitrogen in nitrogen-containing water bodies.

[0014] Technical solution:

[0015] To achieve the above objectives, this application provides the following technical solution:

[0016] A method for applying iron-removing residue from red mud to purify nitrogen in nitrogen-containing water bodies in paddy wetlands, comprising the following steps:

[0017] The first step is the pretreatment of red mud iron ore beneficiation residue: Rinse the red mud iron ore beneficiation residue with clean water to remove impurities attached to the surface. After rinsing, continue washing by stirring and filtering until the water is clear and transparent. Place the washed red mud iron ore beneficiation residue in a well-ventilated environment to air dry naturally. Use a ball mill to grind the dried red mud iron ore beneficiation residue to a particle size between 0.1-1mm. Remove particles that do not meet the particle size requirements through a sieving device.

[0018] The second step is to prepare potted plants to simulate a paddy field wetland system: prepare a set of potted plants with a radius of 20cm, and fill them with 14kg of natural soil; evenly spread red mud and iron residue at the bottom of the pots, with a thickness of 2-3cm.

[0019] The third step is rice transplanting: Place the rice seeds in a dry, sunny environment to dry for 2-3 days. Then, completely immerse the seeds in clean water, stirring to remove any unripe or empty grains, selecting only the plump seeds. Continue soaking, changing the water every 4-6 hours, until the seeds germinate and develop white roots. Afterward, transfer them to cultivated soil and natural soil, with a soil layer 5cm thick, and add fertilizer to meet the rice's nutritional needs before transplanting. Once the seeds are in the soil cultivation stage, cover them with a thin layer of soil. During the transplanting process, the relative humidity of the soil was maintained at 70%–80%, and the temperature was kept between 25–35℃. A plastic film was used to cover the soil at night to stabilize the temperature. When the rice reached the three-leaf stage, plants with consistent growth and vigor were selected for transplanting. These plants were then placed in pots within a simulated paddy field wetland system, with three holes per pot and one plant per hole. After transplanting, the rice needed a 5–7 day acclimatization period to adapt to the new environment. Subsequently, monitoring of the water quality and the rice plants within the paddy field wetland system began. Water quality monitoring included the concentration of ammonium nitrogen (NH4) in the water samples. + -N, Nitrate Nitrogen NO3 - -N and total nitrogen TN;

[0020] Step 4: The application rate of phosphate fertilizer (P2O5) is 37.5 kg / hm². 2 The potassium fertilizer (K2O) application rate is 60 kg / hm². 2 TN was 9.40 mg / L, NH4 + -N is 2.30 mg / L, NO3 - The river water with nitrogen exceeding the standard (3.54 mg / L) was used to artificially flood irrigate rice plants in pots, with 10 t / hm² of zeolite added. 2 The equivalent dry soil was 20g / kg. Four different hydraulic retention times were set: 1d, 2d, 4d and 6d. After each irrigation, the soil was left to stand for one day before adding fresh river water with excessive nitrogen. Two groups of potted plants without plants were set up as controls. Each treatment was repeated three times at the same retention time.

[0021] Step 5: Four different treatments were set up for the pot experiment: natural soil CK, natural soil treatment SA with rice planted, natural soil treatment SA-IRF with rice planted and red mud iron residue added, and natural soil treatment IRF with red mud iron residue added without rice planted.

[0022] Step 6, simulated paddy field wetland experiment: artificial irrigation was used, with river water exceeding the nitrogen standard for irrigation until the flowerpots were full. After that, the water was left to stand for 1 day, 2 days, 4 days and 6 days as set in Step 4 before water samples were taken. The experimental variables were whether rice was used and whether red mud and iron residue were used. All other variables were kept consistent.

[0023] Step 7: Test the water quality at each of the rice's vegetative growth stage, parallel growth stage, and reproductive growth stage, with hydraulic retention times of 1 day, 2 days, 4 days, and 6 days, and repeat three times.

[0024] Step 8: After the rice matures and is harvested, measure the relevant growth indicators of the plants, including root length, plant height, dry and fresh weight, number of effective panicles, rice panicle length, seed setting rate, number of tillers determined by manual counting method, and weight of 100 grains.

[0025] Furthermore, in the seventh step, the vegetative growth stage of rice is characterized by the development of vegetative organs, before the formation of reproductive organs; the vegetative organs of rice are one or more of the following: roots, stems and leaves, and tillers; the reproductive organ of rice is the young panicle.

[0026] Furthermore, the parallel development stage of rice in the seventh step is a transitional stage in which rice undergoes both vegetative and reproductive growth simultaneously, with the stems elongating rapidly and the young panicles beginning to differentiate.

[0027] Furthermore, in the seventh step, the reproductive growth stage of rice is mainly characterized by the development of reproductive organs, which includes heading, flowering, grain filling, and maturity.

[0028] Furthermore, in the eighth step, the plant was tested for related growth indicators such as root length, plant height, number of tillers, and weight per 100 seeds. The specific testing method was as follows:

[0029] Plant height measurement: After the rice is fully mature, the plants are removed and thoroughly cleaned to remove any attached soil and water. Then, the plant height is accurately measured using a measuring tape in an indoor environment.

[0030] Root length measurement: After washing the plant, use a measuring tape to measure the root length of the plant in an indoor environment;

[0031] Dry and fresh weight determination: After measuring plant height and root length, remove soil from the plant roots, use absorbent paper to dry the plant surface, and use a balance with an accuracy of 0.01% to measure the fresh weight of the plant. After the fresh weight measurement, place the plant in an oven and perform blanching treatment at 105℃ for 0.5 hours. Then adjust the temperature to 80℃ and dry to constant weight. Measure the dry weight of the plant again using a balance.

[0032] Effective panicle count: Before rice harvest, record the number of panicles produced by each rice plant in each treatment group;

[0033] Rice panicle length measurement: After the last irrigation and the rice matures, the tail of the rice panicle is cut off with scissors, and the length of the rice panicle is measured in an indoor environment;

[0034] Calculation of grain setting rate: For rice in each treatment group, the number of plump grains and shriveled grains were counted separately, and the following formula was used to calculate the grain setting rate: Grain setting rate = Number of plump grains / (Number of plump grains + Number of shriveled grains) × 100%;

[0035] Weight determination of 100 kernels: The weight of 100 plump kernels was accurately weighed using a balance with an accuracy of 1 / 10,000.

[0036] Chlorophyll fluorescence parameter determination: Before the experimental system was stopped, the fluorescence parameters of rice leaves were measured using a chlorophyll fluorometer. For each treatment group, one leaf was selected from each rice plant for measurement to ensure the representativeness and consistency of the data.

[0037] Tiller number: Select representative sample plants, such as single-planted areas, mark the leaf age of the main stem, and regularly record the node position, number and changes of tillering.56; investigate every 3-5 days during the tillering period until heading, and count the number of effective ears at maturity.

[0038] Beneficial effects:

[0039] This application provides a method for applying iron ore residue from red mud to purify nitrogen in nitrogen-containing water bodies in paddy wetlands, which has the following advantages compared with the prior art:

[0040] 1. This application can both utilize nitrogen-exceeding water bodies (the nitrogen-exceeding river water has a TN of 10.53 mg / L, and the nitrogen removal rate of paddy wetland with added red mud iron residue is 78% when the hydraulic retention time is 6 days) and also have certain economic benefits (paddy field grain rate (91.14%) and 100-grain weight (2.89 g)).

[0041] 2. As a special ecosystem, paddy field wetlands play an important role in the prevention and control of agricultural non-point source pollution. By applying red mud to remove iron residue in paddy field wetlands, nitrogen-containing water bodies can be effectively purified, nitrogen loss can be reduced, and the risk of pollution to surrounding water bodies and soil can be lowered. Attached Figure Description

[0042] Figure 1 This is a graph showing the ammonia nitrogen removal rate at different hydraulic retention times in the paddy field wetland of this application.

[0043] Figure 2 This is a graph showing the ammonia nitrogen removal rate at different growth stages in the paddy field wetland of this application.

[0044] Figure 3 This is a graph showing the nitrate nitrogen removal rate at different hydraulic retention times in the paddy field wetland of this application.

[0045] Figure 4 This is a graph showing the nitrate nitrogen removal rate at different growth stages in the paddy field wetland of this application.

[0046] Figure 5 This is a graph showing the total nitrogen removal rate at different hydraulic retention times in the paddy field wetlands of this application;

[0047] Figure 6 This is a graph showing the total nitrogen removal rate at different growth stages in the paddy field wetland of this application. Detailed Implementation

[0048] The present invention will be further described below with reference to embodiments. The following description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make equivalent modifications to the disclosed technical content to create equivalent embodiments. Any simple modifications or equivalent changes made to the following embodiments based on the technical essence of the present invention without departing from the scope of the invention are all within the protection scope of the present invention.

[0049] Example 1:

[0050] The method for applying iron residue from red mud to purify nitrogen in nitrogen-containing water bodies in paddy field wetlands involves the following steps:

[0051] The first step is the pretreatment of red mud iron ore beneficiation residue: Rinse the red mud iron ore beneficiation residue with clean water to remove impurities attached to the surface. After rinsing, continue washing by stirring and filtering until the water is clear and transparent. Place the washed red mud iron ore beneficiation residue in a well-ventilated environment to air dry naturally. Use a ball mill to grind the dried red mud iron ore beneficiation residue to a particle size between 0.1-1mm. Remove particles that do not meet the particle size requirements through a sieving device.

[0052] The second step is to prepare potted plants to simulate a paddy field wetland system: prepare a set of potted plants with a radius of 20cm, and fill them with 14kg of natural soil; evenly spread red mud and iron residue at the bottom of the pots, with a thickness of 2-3cm.

[0053] The third step is rice transplanting: Place the rice seeds in a dry, sunny environment to dry for 2-3 days. Then, completely immerse the seeds in clean water, stirring to remove any unripe or empty grains, selecting only the plump seeds. Continue soaking, changing the water every 4-6 hours, until the seeds germinate and develop white roots. Afterward, transfer them to cultivated soil and natural soil, with a soil layer 5cm thick, and add fertilizer to meet the rice's nutritional needs before transplanting. Once the seeds are in the soil cultivation stage, cover them with a thin layer of soil. During the transplanting process, the relative humidity of the soil was maintained at 70%–80%, and the temperature was kept between 25–35℃. A plastic film was used to cover the soil at night to stabilize the temperature. When the rice reached the three-leaf stage, plants with consistent growth and vigor were selected for transplanting. These plants were then placed in pots within a simulated paddy field wetland system, with three holes per pot and one plant per hole. After transplanting, the rice needed a 5–7 day acclimatization period to adapt to the new environment. Subsequently, monitoring of the water quality and the rice plants within the paddy field wetland system began. Water quality monitoring included the concentration of ammonium nitrogen (NH4) in the water samples. + -N, Nitrate Nitrogen NO3 - -N and total nitrogen TN;

[0054] Step 4: The application rate of phosphate fertilizer (P2O5) is 37.5 kg / hm². 2 The potassium fertilizer (K2O) application rate is 60 kg / hm². 2 Using river water with excessive nitrogen (

[0055] TN was 9.40 mg / L, NH4+ + -N is 2.30 mg / L, NO3 - Artificial flooding irrigation was carried out on potted rice (N = 3.54 mg / L), with zeolite added at a rate of 10 t / hm². 2 Equivalent to 20g / kg dry soil, four different hydraulic retention times were set: 1 day, 2 days, etc.

[0056] After each irrigation (4 days and 6 days), the plants were left to stand for one day before being added with fresh river water containing excessive nitrogen. Two groups of potted plants without plants were set up as a control.

[0057] Each treatment was irrigated three times at the same residence time;

[0058] Step 5: Four different treatments were set up in the pot experiment: natural soil (CK), natural soil treatment with rice plants (SA).

[0059] Natural soil treatment SA-IRF with rice cultivation and the addition of red mud iron ore residue, and natural soil treatment IRF with red mud iron ore residue without rice cultivation.

[0060] Step 6, simulated paddy field wetland experiment: artificial irrigation was used, with river water exceeding nitrogen standards, until the flowerpots were full. After that, the water was left to stand for the hydraulic retention time set in Step 6 for 1 day, 2 days, 4 days, and 6 days before water samples were taken. The experimental variables were whether rice was used and whether red mud and iron residue were used; all other variables were kept consistent.

[0061] Step 7: Test water quality at each of the rice's vegetative growth, concurrent growth, and reproductive growth stages, with hydraulic retention times of 1, 2, 4, and 6 days, repeated three times. The vegetative growth stage is characterized by the development of vegetative organs, before the formation of reproductive organs. The vegetative organs of rice include one or more of the roots, stems, leaves, and tillers. The reproductive organ is the young panicle. The concurrent growth stage is a transitional phase where vegetative and reproductive growth occur simultaneously, with rapid stem elongation and the beginning of panicle differentiation. The reproductive growth stage is characterized by the development of reproductive organs, including heading, flowering, grain filling, and maturity. The specific water quality test involves measuring the ammonium nitrogen (NH4) in the water sample. + -N, nitrate nitrogen NO3 - -N and total nitrogen TN;

[0062] Step 8: After the rice matures and is harvested, measure the relevant growth indicators of the plants, including root length, plant height, dry and fresh weight, number of effective panicles, rice panicle length, seed setting rate, number of tillers determined by manual counting method, and weight of 100 grains.

[0063] Furthermore, in the eighth step, the plant was tested for related growth indicators such as root length, plant height, number of tillers, and weight per 100 seeds. The specific testing method was as follows:

[0064] Plant height measurement: After the rice is fully mature, the plants are removed and thoroughly cleaned to remove any attached soil and water. Then, the plant height is accurately measured using a measuring tape in an indoor environment.

[0065] Root length measurement: After washing the plant, use a measuring tape to measure the root length of the plant in an indoor environment;

[0066] Dry and fresh weight determination: After measuring plant height and root length, remove soil from the plant roots, use absorbent paper to dry the plant surface, and use a balance with an accuracy of 0.01% to measure the fresh weight of the plant. After the fresh weight measurement, place the plant in an oven and perform blanching treatment at 105℃ for 0.5 hours. Then adjust the temperature to 80℃ and dry to constant weight. Measure the dry weight of the plant again using a balance.

[0067] Effective panicle count: Before rice harvest, record the number of panicles produced by each rice plant in each treatment group;

[0068] Rice panicle length measurement: After the last irrigation and the rice matures, the tail of the rice panicle is cut off with scissors, and the length of the rice panicle is measured in an indoor environment;

[0069] Calculation of grain setting rate: For rice in each treatment group, the number of plump grains and shriveled grains were counted separately, and the following formula was used to calculate the grain setting rate: Grain setting rate = Number of plump grains / (Number of plump grains + Number of shriveled grains) × 100%;

[0070] 100-grain weight determination: The weight of 100 plump grains was accurately weighed using a balance with an accuracy of 0.01%. Chlorophyll fluorescence parameter determination: Before the experimental system stopped running, the fluorescence parameters of rice leaves were measured using a chlorophyll fluorometer. For each treatment group, one leaf was selected from each rice plant for measurement to ensure the representativeness and consistency of the data.

[0071] Tiller number: Select representative sample plants, such as single-planted areas, mark the leaf age of the main stem, and regularly record the node position, number, and changes in tillering.56. During the tillering period, conduct surveys every 3-5 days until heading, and count the number of effective ears at maturity.

[0072] The nitrogen removal efficiency of paddy field wetland systems on surface water, such as... Figure 1 and Figure 2 The graph shows the removal efficiency of ammonia nitrogen in paddy field wetlands under different hydraulic retention times and different growth stages. The removal efficiency of ammonia nitrogen increases with the increase of hydraulic retention time.

[0073] The removal rate was higher during the vegetative growth stage than in other stages. With a hydraulic retention time of 6 days, the ammonia nitrogen removal rate was 71.2% for CK, 83.2% for SA, 88.7% for SA-IRF, and 77.2% for IRF.

[0074] like Figure 3 and Figure 4 As shown in the figure, the removal efficiency of nitrate nitrogen in paddy field wetlands at different hydraulic retention times and different growth stages is as follows: when the hydraulic retention time is 6 days, the ammonia nitrogen removal rate of CK reaches 29.4%, the ammonia nitrogen removal rate of SA is 54.2%, the removal rate of SA-IRF is 70.4%, and the removal rate of IRF is 63.2%.

[0075] like Figure 5 and Figure 6As shown in the figure, the total nitrogen removal efficiency of paddy field wetlands at different hydraulic retention times and growth stages shows that the total nitrogen removal rate increases with increasing hydraulic retention time. There is no significant difference between HRT=1d and HRT=2d, but both show an increasing trend. HRT=4d shows a significant difference compared to other hydraulic retention time groups. HRT=6d shows the highest removal efficiency, and this difference is also significant. The total nitrogen removal efficiency of paddy field wetland experimental groups at different growth stages within the same growth period is also shown.

[0076] The results showed that the total nitrogen removal rate was significantly higher during the vegetative growth stage of rice than in other stages. With a hydraulic retention time of 6 days, the ammonia nitrogen removal rate was 55.5% for the control group (CK), 68.8% for the ammonia nitrogen removal group (SA), 82.1% for the SA-IRF group, and 71.0% for the IRF group.

[0077] Table 1. Relevant indicators for rice harvesting in this application.

[0078] Group Plant height / cm Root length / cm Number of tillers / plant Fresh weight / g Dry weight / g SA 80.00±1.93b 23.30±0.92b 6.53±0.34b 210.70±21.64b 120.01±22.03b SA-IRF 95.00±1.91a 30.87±0.99a 7.67±0.19a 299.27±20.29a 155.00±36.29a

[0079] These physiological indicators can reflect the growth status of rice plants. In the SA-IRF experimental group, the physiological indicators of rice plants, including plant height, number of tillers, fresh weight, dry weight, and root length, were significantly higher than those of the conventional rice treatment.

[0080] Table 2 Rice yield and related indicators after harvest

[0081] Group ear length / cm 100-grain weight / g Seed yield / % Ear count Estimated yield (kg / a) SA 23.13±0.45a 2.19±0.14b 73.65±1.23b 33 342.15 SA-IRF 24.00±2.02a 2.81±0.10a 83.64±1.11a 30 462.46

[0082] In summary, paddy field wetlands exhibit the best nitrogen removal efficiency at an HRT of 6 days. SA-IRF achieves highly efficient nitrogen removal, with an effluent NH4 removal rate of [missing information]. + -N, NO3 - -N and TN reached 77.3%, 63.3%, and 71.0%, respectively. The seed setting rate of 83.64% and the 100-grain weight of 2.81g indicate that the addition of red mud iron ore residue has a synergistic effect with paddy field wetlands, positively impacting rice yield. Red mud iron ore residue reduces the concentration of nitrate nitrogen in the water through adsorption, providing a more suitable growth environment for rice; while rice further removes nitrogen from the water through biological absorption, and its root exudates may also promote the adsorption performance of red mud iron ore residue.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the spirit and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A method for applying iron-removing residue from red mud to purify nitrogen in nitrogen-containing water bodies in paddy field wetlands, characterized in that, The steps are as follows: The first step is the pretreatment of red mud iron ore beneficiation residue: Rinse the red mud iron ore beneficiation residue with clean water to remove impurities attached to the surface. After rinsing, continue washing by stirring and filtering until the water is clear and transparent. Place the washed red mud iron ore beneficiation residue in a well-ventilated environment to air dry naturally. Use a ball mill to grind the dried red mud iron ore beneficiation residue to a particle size between 0.1-1mm. Remove particles that do not meet the particle size requirements through a sieving device. The second step is to prepare potted plants to simulate a paddy field wetland system: prepare a set of potted plants with a radius of 20cm, and fill them with 14kg of natural soil; evenly spread red mud and iron residue at the bottom of the pots, with a thickness of 2-3cm. The third step is rice transplanting: Place the rice seeds in a dry, sunny environment to dry for 2-3 days. Then, completely immerse the seeds in clean water, stirring to remove any unripe or empty grains, selecting only the plump seeds. Continue soaking, changing the water every 4-6 hours, until the seeds germinate and develop white roots. Afterward, transfer them to cultivated soil and natural soil, with a soil layer 5cm thick, and add fertilizer to meet the rice's nutritional needs before transplanting. Once the seeds are in the soil cultivation stage, cover them with a thin layer of soil. During the transplanting process, the relative humidity of the soil was maintained at 70%–80%, and the temperature was kept between 25–35℃. A plastic film was used to cover the soil at night to stabilize the temperature. When the rice reached the three-leaf stage, plants with consistent growth and vigor were selected for transplanting. These plants were then placed in pots within a simulated paddy field wetland system, with three holes per pot and one plant per hole. After transplanting, the rice needed a 5–7 day acclimatization period to adapt to the new environment. Subsequently, monitoring of the water quality and the rice plants within the paddy field wetland system was initiated. Water quality monitoring included the concentration of ammonium nitrogen (NH4) in the water samples. + -N, nitrate nitrogen NO3 - -N and total nitrogen TN; Step 4: The application rate of phosphate fertilizer (P2O5) is 37.5 kg / hm². 2 The potassium fertilizer (K2O) application rate is 60 kg / hm². 2 TN was 9.40 mg / L, NH4 + -N is 2.30 mg / L, NO3 - The river water with nitrogen exceeding the standard (3.54 mg / L) was used to artificially flood and irrigate rice plants in pots, with 10 t / hm² of zeolite added. 2 The equivalent dry soil was 20g / kg. Four different hydraulic retention times were set: 1d, 2d, 4d and 6d. After each irrigation, the soil was left to stand for one day before adding fresh river water with excessive nitrogen. Two groups of potted plants without plants were set up as controls. Each treatment was repeated three times at the same retention time. Step 5: Four different treatments were set up for the pot experiment: natural soil CK, natural soil treatment SA with rice planted, natural soil treatment SA-IRF with rice planted and red mud iron residue added, and natural soil treatment IRF with red mud iron residue added without rice planted. Step 6, simulated paddy field wetland experiment: artificial irrigation was used, with river water exceeding the nitrogen standard for irrigation until the flowerpots were full. After that, the water was left to stand for 1 day, 2 days, 4 days and 6 days as set in Step 4 before water samples were taken. The experimental variables were whether rice was used and whether red mud and iron residue were used. All other variables were kept consistent. Step 7: Test the water quality at each of the rice's vegetative growth stage, parallel growth stage, and reproductive growth stage, with hydraulic retention times of 1 day, 2 days, 4 days, and 6 days, and repeat three times. Step 8: After the rice matures and is harvested, measure the relevant growth indicators of the plants, including root length, plant height, dry and fresh weight, number of effective panicles, rice panicle length, seed setting rate, number of tillers determined by manual counting method, and weight of 100 grains.

2. The method for applying iron-removing residue from red mud to purify nitrogen in nitrogen-containing water bodies in paddy wetlands according to claim 1, characterized in that: In the seventh step, the vegetative growth stage of rice refers to the development of vegetative organs before the formation of reproductive organs; the vegetative organs of rice are one or more of the roots, stems and leaves, and tillers; the reproductive organ of rice is the young panicle.

3. The method for applying iron-removing residue from red mud to purify nitrogen in nitrogen-containing water bodies in paddy wetlands according to claim 1, characterized in that: The seventh step, the parallel development stage of rice, is a transitional stage in which rice undergoes both vegetative and reproductive growth simultaneously, during which the stems elongate rapidly and the young panicles begin to differentiate.

4. The method for applying iron-removing residue from red mud to purify nitrogen in nitrogen-containing water bodies in paddy wetlands according to claim 1, characterized in that: The seventh step refers to the reproductive growth stage of rice, which involves the development of reproductive organs, including heading, flowering, grain filling, and maturity.

5. The method for applying iron-removing residue from red mud to purify nitrogen in nitrogen-containing water bodies in paddy wetlands according to claim 1, characterized in that: The water quality test in the seventh step specifically involves testing the ammonium nitrogen (NH4) in the water sample. + -N, nitrate nitrogen NO3 - -N and total nitrogen TN.

6. The method for applying iron-removing residue from red mud to purify nitrogen in nitrogen-containing water bodies in paddy wetlands according to claim 1, characterized in that: In the eighth step, the plant was tested for growth indicators such as root length, plant height, number of tillers, and weight per 100 seeds. The specific testing method was as follows: Plant height measurement: After the rice is fully mature, the plants are removed and thoroughly cleaned to remove any attached soil and water. Then, the plant height is accurately measured using a measuring tape in an indoor environment. Root length measurement: After washing the plant, use a measuring tape to measure the root length of the plant in an indoor environment; Dry and fresh weight determination: After measuring plant height and root length, remove soil from the plant roots, use absorbent paper to dry the plant surface, and use a balance with an accuracy of 0.01% to measure the fresh weight of the plant. After the fresh weight measurement, place the plant in an oven and perform blanching treatment at 105℃ for 0.5 hours. Then adjust the temperature to 80℃ and dry to constant weight. Measure the dry weight of the plant again using a balance. Effective panicle count: Before rice harvest, record the number of panicles produced by each rice plant in each treatment group; Rice panicle length measurement: After the last irrigation and the rice matures, the tail of the rice panicle is cut off with scissors, and the length of the rice panicle is measured in an indoor environment; Seed setting rate calculation: For rice in each treatment group, the number of plump grains and shriveled grains were counted separately, and the seed setting rate was calculated using the following formula: Seed setting rate = Number of plump grains / (Number of plump grains + Number of shriveled grains) × 100%; Weight determination of 100 kernels: The weight of 100 plump kernels was accurately weighed using a balance with an accuracy of 1 / 10,000. Chlorophyll fluorescence parameter determination: Before the experimental system was stopped, the fluorescence parameters of rice leaves were measured using a chlorophyll fluorometer. For each treatment group, one leaf was selected from each rice plant for measurement to ensure the representativeness and consistency of the data. Tiller number: Select representative sample plants, mark the leaf age of the main stem, and record the node position, number and changes of tillering regularly. During the tillering period, investigate every 3-5 days until heading, and count the number of effective ears at maturity.

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