A method for purifying nitrogen from a nitrogen-containing water body using a combined farmland ecosystem

Abstract

The application discloses a method for purifying nitrogen in nitrogen-containing water bodies by using a combined farmland ecological system and relates to the technical field of water treatment. The combined farmland ecological system is composed of a paddy field wetland and an ecological floating bed, can realize efficient biological repair of nitrogen-containing water bodies, and can achieve the effects of purifying water quality and solving water body eutrophication. The combined farmland ecological system can not only enhance the removal effect of nitrogen in surface water, but also can generate certain economic benefits, and is a new type of in-situ repair technology which is in line with the actual situation.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a method for purifying nitrogen in nitrogen-containing water bodies using a combined farmland ecosystem. Background Technology

[0002] While industrial and agricultural levels continue to develop, water pollution and shortage remain major development issues that urgently need to be addressed, and eutrophication of water bodies is also a significant challenge to green development.

[0003] Nitrogen (N) in water is one of the important factors leading to eutrophication. Currently, there are various methods for removing N from water, such as adsorption, ion exchange, electrochemical reduction, reverse osmosis, and biological methods. Each of these methods has its own advantages and disadvantages.

[0004] Constructed wetland technology boasts the advantages of wide applicability and low cost, even finding its place in the field of environmental beautification and ecological landscape construction. Constructed wetland systems purify various pollutants in water through physicochemical and biological processes, including plant absorption, microbial degradation, and matrix adsorption. It is currently widely used in the advanced treatment of low-concentration nitrogen (N) wastewater. While nitrogen is a pollutant that can lead to eutrophication, it is also an essential nutrient for plant growth. Therefore, it can be utilized; special paddy field wetlands within constructed wetlands can achieve a win-win situation for agricultural production and environmental protection.

[0005] However, the effluent from paddy field wetlands has not yet achieved excellent technical results. How to effectively purify nitrogen in surface water and efficiently utilize nitrogen in wastewater remains an important technical problem that needs to be solved. Summary of the Invention

[0006] The purpose of this invention is to provide a method for purifying nitrogen in nitrogen-containing water bodies using a combined farmland ecosystem, in order to solve the problems existing in the prior art.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] This invention provides an application of a combined paddy field wetland-ecological floating bed ecosystem in purifying nitrogen from nitrogen-containing water bodies: the paddy field wetland system is connected to the ecological floating bed system, and the nitrogen-containing water body flows through the paddy field wetland system and the ecological floating bed system in sequence;

[0009] The plants in the paddy field wetland system are japonica rice, salt-tolerant rice, or bamboo rice; the substrate of the paddy field wetland system is a mixture of paddy field soil and zeolite or paddy field soil.

[0010] The plant in the ecological floating bed system is water spinach.

[0011] This invention also provides a method for purifying nitrogen in nitrogen-containing water bodies using a combined paddy field wetland-ecological floating bed ecosystem, comprising the following steps:

[0012] The paddy field wetland system is connected to the ecological floating bed system. Nitrogen-containing water is introduced into the paddy field wetland system, and then the tailwater discharged from the paddy field wetland system is introduced into the ecological floating bed system to purify the nitrogen in the nitrogen-containing water.

[0013] The plants in the paddy field wetland system are japonica rice, salt-tolerant rice, or bamboo rice; the substrate of the paddy field wetland system is a mixture of paddy field soil and zeolite or paddy field soil.

[0014] The plant in the ecological floating bed system is water spinach.

[0015] As a further preferred embodiment of the present invention, the hydraulic retention time of the paddy field wetland system is set to 2-6 days; the hydraulic retention time of the ecological floating bed system is set to 1-7 days.

[0016] As a further preferred embodiment of the present invention, the hydraulic residence time of the paddy field wetland system is set to 6 days; the hydraulic residence time of the ecological floating bed system is set to 5 days.

[0017] As a further preferred embodiment of the present invention, when a mixture of paddy soil and zeolite is used as the substrate of the paddy wetland system, the amount of zeolite added to the dry paddy soil is 10-20 g / kg.

[0018] As a further preferred embodiment of the present invention, the phosphorus application rate in the paddy field wetland system is 100-150 kg / hm². 2 The potassium application rate is 80-100 kg / hm². 2 .

[0019] As a further preferred embodiment of the present invention, the total nitrogen concentration in the nitrogen-containing water body is 8-10 mg / L.

[0020] As a further preferred embodiment of the present invention, the pH of the nitrogen-containing water body is 7-9, and the NH4+ content is... + -N concentration is 1-3 mg / L, NO3 - -N concentration is 2-3 mg / L.

[0021] The present invention discloses the following technical effects:

[0022] This invention combines paddy field wetlands with ecological floating beds to form an in-situ remediation farmland ecosystem, enabling highly efficient bioremediation of nitrogen-containing water bodies, thereby purifying water quality and addressing eutrophication. This combined farmland ecosystem enhances nitrogen removal from surface water and generates economic benefits, representing a novel and practical in-situ remediation technology.

[0023] This invention explores the feasibility of this ecological combination system and the mechanism of nitrogen removal from aspects such as rice, substrate and microorganisms, and makes a new step in exploring the in-situ remediation technology of low-pollution surface water. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a diagram of the simulated paddy field wetland rice device in Embodiment 1 of the present invention;

[0026] Figure 2 The COD of each treatment group under different HRTs in paddy field wetlands in Example 1 of this invention is shown. Mn Average removal rate;

[0027] Figure 3 The NH4+ of the different treatment groups under different HRT in the paddy field wetland in Example 1 of this invention. + -N average removal rate;

[0028] Figure 4 NO3 in different treatment groups under different HRT in paddy field wetlands in Example 1 of this invention - -N average removal rate;

[0029] Figure 5 The average TN removal rate of each treatment group under different HRT in paddy field wetlands in Example 1 of this invention;

[0030] Figure 6 The COD of different treatment groups at different growth stages in paddy field wetlands in Example 1 of this invention is shown. Mn Average removal rate;

[0031] Figure 7 The NH4 in the different growth stages of the paddy field wetland in Example 1 of this invention is NH4. + -N average removal rate;

[0032] Figure 8 NO3 in different treatment groups at different growth stages of paddy field wetlands in Example 1 of this invention - -N average removal rate;

[0033] Figure 9 The average TN removal rate of each treatment group at different growth stages in the paddy field wetland in Example 1 of this invention;

[0034] Figure 10Images of harvested rice from each treatment group in Example 1 of this invention;

[0035] Figure 11 Images of different varieties of rice grains from Example 1 of this invention;

[0036] Figure 12 The images show the PCoA principal coordinate analysis (a) and NMDS plot (b) at the bacterial OUT level in Example 1 of this invention.

[0037] Figure 13 This is the bacterial colony composition at the level of the microbial phylum in paddy field wetlands in Example 1 of the present invention;

[0038] Figure 14 This is a pie chart showing the relative abundance of microorganisms in paddy field wetlands in Example 1 of the present invention;

[0039] Figure 15 This refers to the hierarchical cluster analysis of paddy field wetland microorganisms in Example 1 of the present invention;

[0040] Figure 16 This is a schematic diagram of the hydroponic device used in Embodiment 1 of the present invention;

[0041] Figure 17 This invention relates to the COD of paddy field tailwater under different HRTs in the hydroponic water spinach system of Embodiment 1 of the present invention. Mn Average removal rate;

[0042] Figure 18 This invention relates to the effects of different HRTs on NH4 in paddy field tailwater of the hydroponic water spinach system in Embodiment 1 of the present invention. + -N average removal rate;

[0043] Figure 19 This invention relates to the NO3 content in paddy field tailwater under different HRT levels in the hydroponic water spinach system of Example 1 of the present invention. - -N average removal rate;

[0044] Figure 20 The average TN removal rate of paddy field tailwater under different HRTs in the hydroponic water spinach system of Embodiment 1 of the present invention;

[0045] Figure 21 This is a schematic diagram of the growth of hydroponically grown water spinach in Embodiment 1 of the present invention. Detailed Implementation

[0046] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0047] Example 1

[0048] Experimental materials:

[0049] This invention uses three different rice varieties: the salt-tolerant rice variety Shuangliangyou 138, provided by the Taobao store Beimeng Seed Industry; the local Xuzhou rice variety Xudao 9, provided by the Xuzhou Agricultural Science Research Institute; and the bamboo rice variety Taoxiu Youmeizhen, provided by Hunan Taohuayuan Agricultural Technology Co., Ltd. The water spinach used is hydroponically grown willow-leaf water spinach, provided by the Taobao store Huizhili Horticulture.

[0050] The wetland filler material is paddy soil, which is taken from Xuzhou and air-dried before being sieved through a 10-mesh sieve.

[0051] The soil physicochemical properties are as follows:

[0052] Table 1 Basic physical and chemical properties of soil

[0053]

[0054]

[0055] The wastewater to be treated was selected from the confluence of a river, and the specific water quality indicators are as follows:

[0056] Table 2 Water quality indicators of the tested wastewater

[0057]

[0058] The soil conditioner zeolite is made of 80-120 mesh natural zeolite powder provided by Huizhi Water Treatment, and its adsorption capacity for ammonia nitrogen is 3.12 mg / g.

[0059] I. Paddy Wetland Simulation Device

[0060] This invention employs pot experiments. Pots are 20cm in diameter and 50cm high, with sealed bottoms to prevent water leakage. Three different rice varieties were germinated and seedlings transplanted into the pots, with three holes per pot and one seedling per hole. The rice in the pots was irrigated with the aforementioned wastewater (low-pollution surface water), maintaining a water depth of 10-15cm. The application rates of phosphorus and potassium fertilizers were kept consistent across all treatments, with 0.03g / kg and 0.02g / kg of phosphorus and potassium in dry soil, equivalent to 150kg / hm² in field application. 2 and 100kg / hm 2 This ensures the supply of phosphorus and potassium nutrients to paddy wetlands. Studies have shown that adding 10 t / hm² of phosphorus and potassium to paddy fields... 2 The optimal effect on plant growth is achieved by applying 10 t / hm². 2 This is equivalent to 20g / kg of dry soil. The typical flooding time for paddy field wetlands is 4-6 days. Therefore, this invention sets three different hydraulic retention times: 2 days, 4 days, and 6 days. To ensure alternating wet and dry conditions for rice management, new low-pollution water is added one day after each drainage.

[0061] Each device was designed with four water outlets. The lowest outlet was located 3 cm from the bottom, and the other outlets were spaced 10 cm upwards. Water was only drawn from the lowest outlet in this experiment. To prevent soil from clogging the outlets, a 5 cm layer of coarse quartz sand was laid at the bottom, followed by a 2 cm layer of fine quartz sand. Three different rice varieties were selected as the research subjects for this experiment: Japonica rice, salt-tolerant rice (sea rice), and bamboo rice. The varieties selected were Xu Dao 9 (XD), Shuang Liang You 138 (SA), and Tao Xiu You Mei Zhen (BR). This experiment included eight different treatments: CK1 (no plants and no zeolite), XD1 (planted Xudao 9 but no zeolite), SA1 (planted salt-tolerant rice (Shuangliangyou 138) but no zeolite), BR1 (planted bamboo rice (Taoxiu Youmeizhen) but no zeolite), CK2 (no rice but zeolite), XD2 (planted Xudao 9 and zeolite), SA2 (planted salt-tolerant rice (Shuangliangyou 138) and zeolite), and BR2 (planted bamboo rice (Taoxiu Youmeizhen) and zeolite). After germination and planting, the rice was transplanted into soil columns at the tillering stage to investigate its effect on pollutant removal.

[0062] This paddy field simulation device simulates paddy field irrigation. After irrigation, the paddy field is left to stand, and water is then introduced manually. Since this invention explores the purification of the raw water, no other substances are added except for the substrate fertilizer and low-pollution water, ensuring that other variables remain unchanged.

[0063] Figure 1 This is a diagram of the simulated paddy field wetland rice device in Embodiment 1 of the present invention.

[0064] Soak rice seeds in tap water for 24 hours, then place them in a sterilized petri dish wrapped in gauze. Spray the gauze with tap water daily to keep it moist. After germination, transfer the seeds to flowerpots for seedling cultivation. When the seedlings have three leaves and a central bud, transplant them into soil columns. After acclimatization for 7 days, begin monitoring the pH, conductivity, and COD of the effluent. Mn NH4 + -N, NO3 - -N and TN were measured.

[0065] After the rice matures, the rice ears from each device are harvested, followed by further harvesting of rice. The yield of rice grains and physiological indicators of the roots, stems, and leaves are measured, and high-throughput sequencing of the microorganisms in the substrate is performed. The positive effects of zeolite addition on plant growth and yield increase are verified by analyzing different biomass levels. The influence, purification effect, and purification mechanism of different HRTs on rice paddy wetland desiccation are investigated.

[0066] (1) Changes in water quality indicators of paddy field wetlands under different HRTs

[0067] This invention divides rice growth into three stages: vegetative growth, simultaneous vegetative and reproductive growth, and reproductive growth. Since the water quality indicators change similarly under different HRTs (Heat-Resistance Testing) during these three growth stages, this invention uses the vegetative growth stage as an example to illustrate the effects of different HRTs on the effluent water quality indicators of a simulated paddy field wetland system.

[0068] a. pH changes under different HRTs

[0069] Table 3 pH of influent and effluent for different treatments under different HRTs

[0070]

[0071] Note: Different lowercase letters after the data in the same column indicate significant differences between wetland systems under the same HRT (P<0.05); different uppercase letters after the data in the same row indicate significant differences between the same wetland system under different HRTs (P<0.05).

[0072] As shown in Table 3, under the condition that the influent pH was basically the same, the pH of the effluent water in all treatment groups decreased to varying degrees. When the HRT was 2 days, the highest pH of CK2 was 7.92±0.10Ba, and the lowest pH of SA1 was 7.35±0.09Bc. When the HRT was 4 days, the highest pH of CK2 was 7.73±0.09Aa, and the lowest pH of XD1 was 7.05±0.11Ab. When the HRT was 6 days, the highest pH of CK2 was 7.54±0.10Ab, and the lowest pH of XD1 was 6.41±0.12Ac. Significant differences were observed between the rice-planted treatment group and the non-rice-planted treatment group. This is likely because rice roots secrete organic acids (malic acid, tartaric acid, succinic acid, citric acid, and lactic acid, etc.), leading to a decrease in effluent pH. The pH of the non-rice-planted treatment group also decreased slightly, possibly related to the alkalinity consumption during nitrification. Significant differences were also observed between the zeolite-added treatment group and the non-zeolite-added treatment group. This is likely because zeolite is slightly alkaline, and its addition to the soil releases some ions, resulting in a slight increase in pH. No significant differences were found between different rice varieties regardless of the addition of zeolite. Significant differences were observed between the treatment groups at different hydraulic retention times (HRTs), possibly due to the continuous secretion of organic acids by plant roots and the alkalinity consumption during nitrification. Overall, the pH of the rice-planted paddy system was generally lower than that of the non-rice-planted system. The pH of the zeolite-added treatment group was slightly higher at each hydraulic retention time than that of the non-zeolite-added treatment group. Planting different rice varieties had little impact on the final effluent pH of the paddy wetland system.

[0073] b. Changes in conductivity under different HRTs

[0074] Table 4. Conductivity of influent and effluent at different HRT levels

[0075]

[0076] Note: Different lowercase letters after the data in the same column indicate significant differences between wetland systems under the same HRT (P<0.05); different uppercase letters after the data in the same row indicate significant differences between the same wetland system under different HRTs (P<0.05). Further details will not be elaborated upon hereafter.

[0077] As shown in Table 4, with essentially the same influent conductivity, the effluent conductivity of all treatment groups varied to different degrees. At an HRT of 2 days, CK2 had the highest conductivity at 894.08 ± 3.87 Ab, while BR1 had the lowest at 820.93 ± 4.52 Ad. At an HRT of 4 days, CK2 had the highest conductivity at 864.50 ± 3.56 Ba, while XD2 had the lowest at 707.14 ± 4.23 Bb. At an HRT of 6 days, CK2 had the highest conductivity at 837.57 ± 3.67 Ca, while BR2 had the lowest at 654.19 ± 4.23 Ce. The effluent conductivity of the treatment groups without zeolite gradually decreased with increasing HRT. In some treatment groups with zeolite, the conductivity slightly increased at HRT = 2 days, and then gradually decreased with further increases in HRT. It is possible that zeolite dissolves some ions, leading to an increase in electrical conductivity. As HRT increases, plants absorb some nutrients, resulting in a decrease in electrical conductivity.

[0078] c. COD under different HRTs Mn Concentration changes and removal effect

[0079] like Figure 2 As shown, during the vegetative growth stage of rice, all treatment groups showed varying effects on COD levels in low-pollution water. Mn The removal rate increased with the extension of HRT. At HRT = 6 days, the COD of each treatment group... Mn The removal rate reached its maximum. When HRT = 2 days, SA2 significantly reduced COD levels in low-pollution surface water. Mn The removal effect was the best, with an average removal rate of 56.44%, for COD in low-pollution surface water. Mn The worst removal effect was achieved by CK1, with an average removal rate of only 17.56%. The effluent from CK1, CK2, XD1, and XD2 met the Class III surface water quality standard, while the effluent from the remaining treatment groups met the Class II surface water quality standard. When HRT = 4 days, BR2 effectively removed COD from low-pollution surface water. Mn The removal effect was the best, with an average removal rate of 74.57%, for COD in low-pollution surface water. MnThe worst removal effect was observed in CK1, with an average removal rate of only 21.48%. The effluent from BR2 met the Class I surface water quality standard, while the effluent from CK1 and CK2 met the Class III standard. The effluent from the remaining treatment groups met the Class II standard. When HRT = 6 days, SA2 effectively removed COD from low-pollution surface water. Mn The removal effect was the best, with an average removal rate of 83.3%, for COD in low-pollution surface water. Mn The treatment group with the worst removal efficiency was CK1, with an average removal rate of only 25.11%. The effluent from CK1 and CK2 met the Class III surface water quality standard, while the effluent from the other treatment groups met the Class I standard. There was a significant difference between the rice-planted treatment group and the non-rice-planted treatment group. This may be because the rice-planted treatment group had a richer root microbial community, with Acidobacteria and Firmicutes playing a role in the decomposition of organic matter. The synthesis of microbial substances within the microorganisms themselves also contributes to COD reduction. Mn During heterotrophic denitrification, microorganisms also consume some of the carbon source in the water. The treatment efficiency of the bamboo rice (Taoxiu Youmeizhen) and salt-tolerant rice (Shuangliangyou 138) was better than that of the treatment of Xu rice (Xudao 9). This may be because the former two are indica rice, while the latter is japonica rice, and the rhizosphere microorganisms of indica rice are richer than those of japonica rice.

[0080] d. NH4 under different HRTs + -N concentration change and removal rate

[0081] like Figure 3 As shown, during the vegetative growth stage of rice, all treatment groups showed the effect of NH4 in low-pollution water. + -N removal rate increased with increasing HRT; at HRT=6d, NH4+ removal rate increased in each treatment group. + -N removal rate reaches its maximum when HRT = 2d. SA2 effectively removes NH4+ from low-pollution surface water. + -N showed the best removal effect, with an average removal rate of 73.74%, for NH4+ in low-pollution surface water. + The treatment group with the worst removal efficiency for NH4+ was CK1, with an average removal rate of only 54.17%. The effluent from CK1, CK2, XD1, and SA1 met the Class III surface water quality standard, while the effluent from the other treatment groups met the Class II surface water quality standard. When HRT = 4 days, SA2 showed the best removal efficiency for NH4+ in low-pollution surface water. + -N showed the best removal effect, with an average removal rate of 88.91%, for NH4+ in low-pollution surface water. + The worst removal efficiency for NH4+ was observed in CK1, with an average removal rate of only 73.41%. All treatment groups produced effluent that met the Class II surface water quality standard. When HRT = 6 days, SA2 effectively removed NH4+ from low-pollution surface water. +-N showed the best removal effect, with an average removal rate of 96.67%, for NH4+ in low-pollution surface water. + The treatment group with the worst removal efficiency for -N was CK1, with an average removal rate of only 79.81%. The effluent from CK1, XD1, and XD2 met the Class II surface water quality standard, while the effluent from the other treatment groups met the Class I standard. There was a significant difference between the rice-grown treatment group and the non-rice-grown treatment group. This is likely because rice requires nitrogen for growth and preferentially absorbs NH4+ from the water. + -N, the treatment group for rice cultivation NH4 + -N concentration further decreased, leading to a decrease in NH4 in this treatment group. + -N removal rate increased. There was a significant difference between the treatment group with added zeolite and the treatment group without added zeolite, which may be due to the increased NH4+ removal efficiency of zeolite. + The adsorption capacity of -N is equivalent to 9 times that of ordinary soil, and some of the NH4+ in the water... + -N is adsorbed by zeolite in the soil, thus leading to the addition of zeolite to the treatment group NH4. + -N removal rate further increased. Different rice varieties showed different effects on NH4+ removal. + The removal rate of -N did not differ significantly under the same HRT. In terms of removal effectiveness, Shuangliangyou 138 > Taoxiu Youmeizhen > Xudao 9. There was no significant difference between CK1 and CK2, possibly because the zeolite in the soil absorbed some of the NH4+. + -N, thus leading to NH4+ in the water + -N concentration decreases, influent NH4+ + -N concentration is low, NO3 - High N-N concentration limits the system's nitration capacity, leading to NH4+ ions being released. + -N removal rate could not be improved further.

[0082] e. NO3 under different HRT - -N concentration change and removal rate

[0083] like Figure 4 As shown, during the vegetative growth stage of rice, all treatment groups showed an effect on NO3 in low-pollution water. - -N removal rate increased with increasing HRT; at HRT=6d, NO3 removal rate was highest in each treatment group. - -N removal rate reaches its maximum when HRT = 2d. - -N concentration was not significantly different from the influent; NO3 concentrations in other treatment groups were similar. - The concentration of -N will increase, possibly because the nitration reaction converts other forms of N into NO3. - -N; When HRT = 4d, BR2 has a lower effect on NO3 in low-pollution surface water. --N showed the best removal effect, with an average removal rate of 54.93%, for NO3 in low-pollution surface water. - The worst removal efficiency for NO3- was observed in CK1, with an average removal rate of only 25.84%. When HRT = 6 days, SA2 showed the best removal efficiency for NO3- in low-pollution surface water. - -N showed the best removal effect, with an average removal rate of 73.68%, for NO3 in low-pollution surface water. - The CK1 sample showed poor removal of -N, with an average removal rate of only 36.50%.

[0084] The treatment group with rice cultivation showed significant differences from the treatment group without rice cultivation. This may be partly due to the richer rhizosphere microorganisms in rice, which facilitate denitrification and reduce NO3- content. - -N is converted into gases such as N2, and another part may be absorbed by rice because rice needs N for growth. Significant differences were found in the treatment groups under different HRTs, mainly because nitrification and denitrification initially rely on microorganisms. As the concentrations of various forms of N and organic matter decrease, the C / N ratio decreases, leading to a decrease in the nitrification and denitrification rate.

[0085] f. Changes in TN concentration and removal rate under different HRTs

[0086] like Figure 5 As shown, during the vegetative growth stage of rice, the TN removal rate of all treatment groups in low-pollution water increased with the extension of HRT, and the TN removal rate of each treatment group reached its highest value when HRT = 6 days. When HRT = 2 days, SA2 showed the best removal effect of TN in low-pollution surface water, with an average removal rate of 53.96%, while CK1 showed the worst removal effect, with an average removal rate of only 17.58%. When HRT = 4 days, BR2 showed the best removal effect of TN in low-pollution surface water, with an average removal rate of 74.57%, while CK1 showed the worst removal effect, with an average removal rate of only 45.01%. The effluent from all treatment groups met the Class II surface water quality standard. When HRT = 6 days, SA2 showed the best removal effect of TN in low-pollution surface water, with an average removal rate of 83.24%, while CK1 showed the worst removal effect, with an average removal rate of only 55.02%. The effluent from SA1, BR1, XD2, SA2, and BR2 met the Class IV surface water quality standard, while the effluent from the remaining treatment groups remained at the Class V surface water quality standard at each HRT. TN in water includes NH4+. + -N, NO3 - The decrease in total nitrogen (TN) in water, including nitrogen (N) and organic nitrogen, is related to the nitrification and denitrification of various forms of nitrogen by rice rhizosphere microorganisms and the absorption by plants.

[0087] Significant differences were observed between the rice-planted treatment group and the unplanted treatment group, primarily due to the high microbial abundance in the rice-planted system and the absorption of various forms of nitrogen (N) from the water by the plants. Significant differences also existed among the treatment groups under different HRTs (Heat Retention Periods). In the first few days, microbial nitrification and denitrification were dominant, while in the later days, plant absorption of N from the water became the primary method. Under low load conditions, plant absorption became even more crucial in wetlands. Rice is an extremely important factor in this wetland system. It not only absorbs inorganic nitrogen directly from the water through its roots, but its root exudates are also a vital carbon source for microbial denitrification. The exudative function of rice roots can also divide the substrate into aerobic, facultative anaerobic, and anaerobic zones, promoting the growth and reproduction of wetland microorganisms and indirectly improving the effluent quality of the wetland system. Generally, plants absorb 36-74% of the total N removed by the entire system.

[0088] (2) Changes in the final effluent water quality indicators at different growth stages of rice

[0089] Since the variation patterns of various water quality indicators with respect to HRT are similar across the three growth stages of rice, and the effluent water quality is optimal when HRT = 6 days, the following study in this invention uses the effluent water quality at HRT = 6 days to represent the surface water removal effect of the paddy field simulation device at different growth stages.

[0090] a. pH changes in effluent at different growth stages

[0091] Table 5 pH of influent and effluent at different growth stages for each treatment

[0092]

[0093] Table 5 shows that the differences between the treatment groups at each stage are consistent with the vegetative growth stage. The pH of each treatment group was lowest during the vegetative growth stage, possibly because rice roots grow and secrete more organic acids and other substances during this stage. Overall, the effluent pH of the simulated paddy field wetland system decreased to varying degrees in all three stages. Because rice roots secrete organic acids to lower the pH of the water, and because zeolite filler is slightly alkaline, XD1, SA1, and BR1 showed the largest decreases. Ultimately, the effluent from all treatment groups became neutral, meeting the surface water environmental quality standards.

[0094] b. Changes in effluent conductivity concentration at different growth stages

[0095] Table 6. Conductivity of influent and effluent at different growth stages for each treatment

[0096]

[0097] Table 6 shows that the differences in conductivity among the treatment groups at different stages are basically consistent with those in the vegetative growth stage. The conductivity of each treatment group is lowest during the vegetative growth stage, which may be due to the rapid growth of rice during this stage, resulting in a greater absorption of ions and thus a decrease in water conductivity. Overall, the effluent conductivity of the simulated paddy field wetland system decreased to varying degrees in all three stages, and the salinity in the water was lower than that of the original water.

[0098] c. COD of effluent at different growth stages Mn Concentration changes and removal effect

[0099] Depend on Figure 6 It can be seen that CK1 and CK2 differ in COD across the three stages. Mn There was no significant difference in removal rates, and the removal rates were generally low. This may be because the soil microorganisms were not as abundant as those in rice root systems, resulting in poor removal efficiency in both treatment groups. XD1, SA1, BR1, XD2, SA2, and BR2 showed the best removal efficiency during the vegetative growth stage, and the COD in the effluent from these simulated paddy field wetland treatment groups was [data missing]. Mn The concentrations were all below 2 mg / L, meeting the Class I surface water quality standard; however, during the parallel growth and reproductive growth stages, the COD in the effluent from these treatment groups was... Mn With a concentration between 2-4 mg / L, the removal rate is slightly lower than that during the vegetative growth stage, but it still meets the Class II surface water quality standard.

[0100] During the rice growth process, a small number of ineffective tillers die and fall off during the paratactic and reproductive growth stages. These fallen leaves decompose in the system and may contribute to COD in the water. Mn An increase in concentration.

[0101] Overall, rice cultivation with the addition of zeolite has a positive effect on COD. Mn The removal effect was the best during the vegetative growth stage, and the COD in the effluent from these treatment groups was highest. Mn The concentration reached the Class I standard for surface water, and in the parallel growth and reproductive growth stages, it reached the Class II standard for surface water. The treatment group with added zeolite showed a reduction in COD in the water at all three stages. Mn The treatment effect was not good, but the quality of the effluent basically met the Class III standard for surface water.

[0102] d. Effluent NH4 at different growth stages + -N concentration changes and removal efficiency

[0103] Depend on Figure 7 It can be seen that the vegetative growth stage and the parallel development stage have different effects on the NH4 content of the effluent from each treatment group. + There was no significant difference in NH4+ concentration, and the final effluent concentration in some treatment groups could meet the Class I surface water standard; however, during the reproductive growth stage, the effluent NH4+ concentration in all treatment groups was significantly different. +The -N concentration should be slightly higher than in the other two stages, and the NH4 concentration in the effluent of each treatment group should be higher. + The -N concentration only meets the Class II and III surface water standards. This may be due to two reasons: firstly, the lower temperature may affect the activity of nitrifying bacteria; secondly, the reduced N requirement after rice matures may lead to a decrease in NH4+ in the effluent of each treatment group during the reproductive growth stage. + -N concentration is high.

[0104] Overall, the treatment group that grew rice and added zeolite showed better control of NH4. + -N removal is most effective during the nutrient growth and concurrent growth stages, resulting in the highest NH4 removal efficiency in the effluent. + The concentrations of NH4+ and NH4+ in the treatment group with added zeolite all met the Class I standard for surface water. + The removal effect of -N was slightly better than that of the treatment group without zeolite, and for NH4+... + The treatment group with the best NH4+ removal effect was the one that planted indica rice and added zeolite, which reduced NH4+ in the effluent during both the vegetative growth and development stages. + -N concentration meets Class I surface water standards, and the reproductive growth stage meets Class II surface water standards.

[0105] e. NO3 in water during different reproductive stages - -N concentration changes and removal efficiency

[0106] Depend on Figure 8 It can be seen that CK1 and CK2, during the vegetative growth stage and the parallel growth stage, significantly affected the NO3 levels in the effluent of each treatment group. - -N concentrations did not differ significantly from those in the reproductive growth stage, possibly due to decreased soil microbial activity caused by lower temperatures. Other treatment groups underwent the same NO3- concentration phase. - -N removal rate was highest during the vegetative growth stage, followed by the reproductive growth stage, while it was lowest during the reproductive growth stage. This may be related to the decrease in N requirement after the plant matures, in addition to microbial activity.

[0107] Overall, the treatment group that grew rice and added zeolite showed better control of NO3. - The removal effect of NO3- was relatively good, while the removal effect in the treatment group without rice cultivation may be less significant due to insufficient abundance of denitrifying bacteria. During the vegetative growth and parallel growth stages, NO3- in the water may increase due to plant uptake and higher temperatures. - -N removal rate is high, NO3- during reproductive growth stage - -N removal effect is worse than the other two periods.

[0108] f. Changes in TN concentration and removal efficiency in effluent at different growth stages

[0109] Depend on Figure 9It can be seen that the TN removal rate of each treatment group at each growth stage generally follows the order: vegetative growth stage > parallel growth stage > reproductive growth stage. During the vegetative growth stage, SA2 and BR2 effluent TN concentrations were <1.5 mg / L, meeting the Class IV surface water standard; XD1, SA1, BR1, and XD2 effluent TN concentrations were <2 mg / L, meeting the Class V surface water standard; CK1 and CK2 effluent concentrations were >2 mg / L, classifying them as worse than Class V surface water. During the parallel growth stage, SA2 met the Class IV surface water standard, SA1 and BR1 were Class V, and the remaining treatment groups produced worse than Class V effluent. During the reproductive growth stage, only SA2 effluent total nitrogen met the Class V surface water standard, while the remaining treatment groups produced worse than Class V effluent. This may be due to the reduced nitrogen demand during the reproductive growth stage and the increase in organic nitrogen in the water caused by plant decomposition.

[0110] (3) The impact of the tandem paddy field system on water quality

[0111] To further utilize nitrogen in low-pollution water, this invention connects three paddy field wetland systems in series. After the rice paddies have been planted in parallel, water flows sequentially through SA2, BR2, and XD2. The hydraulic retention time (HRT) in each system is controlled to be 2 days, and the total HRT in the three simulated systems is 6 days. Relevant water quality indicators of the effluent from each system are then measured.

[0112] Table 7 Water quality indicators at different stages of the tandem paddy field system

[0113]

[0114]

[0115] As shown in Table 7, the final effluent quality of this series system is not significantly different from that of the paddy field wetland system with an HRT of 6 days. The pH and conductivity of the final effluent from this series system are both lower than the raw water, while the conductivity is slightly higher than that of SA2, BR2, and XD2 systems with an HRT of 6 days. This may be due to the dissolution of some ions as the system flows through more substrate. The COD of the final effluent from this system... Mn Its concentration is not significantly different from SA2, BR2, and XD2, and meets the Class II standard for surface water; its NH4 + The concentrations of -N and TN are not significantly different from those of SA2, BR2, and XD2, and meet the Class I and IV standards for surface water, respectively.

[0116] Growth status and quality of different rice varieties:

[0117] Before rice harvest, chlorophyll fluorescence tests were conducted on rice from each treatment group. This invention references the Fv / Fm value; a higher Fv / Fm value indicates a higher light energy conversion efficiency in the plant. Test results showed that the average Fv / Fm for XD1 rice was 0.774, and for XD2 it was 0.759, increasing by 2.02% after adding zeolite; the average Fv / Fm for SA1 rice was 0.758, and for XD2 it was 0.774, increasing by 2.11% after adding zeolite; the average Fv / Fm for BR1 rice was 0.758, and for XD2 it was 0.762, increasing by 0.53% after adding zeolite. Overall, adding zeolite had a certain promoting effect on chlorophyll fluorescence in all three rice varieties, but the increase was relatively small.

[0118] Table 8. Some physiological indicators of rice under different treatments

[0119]

[0120] Depend on Figure 10 As shown in Table 8, the plant height and biomass of the zeolite-added treatment groups (XD2, SA2, and BR2) were significantly better than those of the zeolite-free treatment groups. There were significant differences in plant height and root length between the zeolite-added treatment groups (XD2, SA2, and BR2) and the zeolite-free treatment groups (XD1, SA1, and BR1). The plant height of the zeolite-added Xudao (Xudao 9), salt-tolerant rice (Shuangliangyou 138), and bamboo rice (Taoxiu Youmeizhen) increased by 7.72%, 5.52%, and 13.17%, respectively; the root length increased by 13.92%, 7.00%, and 12.31%, respectively; the fresh weight of stems and leaves increased by 65.09%, 99.19%, and 66.77%, respectively; and the dry weight of stems and leaves increased by 62.79%, 140.04%, and 50.48%, respectively. This may be because zeolite can adsorb nitrogen in the water, and 60% of it can be released and absorbed by rice, thus promoting rice growth.

[0121] Depend on Figure 11 As shown in Table 9, the number of effective panicles in the zeolite-added treatment group was significantly better than that in the zeolite-free treatment group. The number of effective panicles in Xudao (Xudao 9) and Zhudao (Taoxiu Youmeizhen) increased significantly after zeolite addition, while the number of panicles in salt-tolerant rice (Shuangliangyou 138) remained unchanged. The average panicle length of rice increased slightly after zeolite addition, but the difference was not significant. Regarding the grain setting rate, zeolite addition had no effect on salt-tolerant rice (Shuangliangyou 138), increasing it by only 0.52%, while the grain setting rate of Xudao (Xudao 9) and Zhudao (Taoxiu Youmeizhen) decreased. This is because the number of tillers in salt-tolerant rice (Shuangliangyou 138) did not increase after zeolite addition, while the new panicles of Xudao (Xudao 9) and Zhudao (Taoxiu Youmeizhen) contained a large number of shriveled grains, resulting in a lower grain setting rate compared to the zeolite-free treatment group.

[0122] Table 9. Rice yield and grain quality under different treatments

[0123]

[0124] The addition of zeolite also had a certain impact on the total grain yield per plant, with Xu Dao (Xu Dao 9), salt-tolerant rice (Shuang Liang You 138), and bamboo rice (Tao Xiu You Mei Zhen) showing increases of 157.71%, 74.32%, and 100%, respectively. This may be because zeolite can adsorb nitrogen in the water, and 60% of it can be released and absorbed by the rice, thereby promoting rice growth.

[0125] (4) Changes in soil physicochemical properties

[0126] After the rice harvest, the physicochemical properties of the paddy field wetland soil were measured, and the specific values ​​are shown in the table below:

[0127] Table 10 Changes in the physicochemical properties of paddy field wetland soil

[0128]

[0129]

[0130] Table 10 shows that the original soil was slightly alkaline. After one round of rice planting, the pH of the soil matrix in the untreated group decreased compared to the original soil, while the pH of the soil matrix in the zeolite-treated group increased slightly compared to the original soil. The electrical conductivity of all treatment groups increased to varying degrees compared to the original soil, with the zeolite-treated group showing a greater increase. The changes in available nitrogen and phosphorus in the soil followed a similar pattern to electrical conductivity, while available potassium showed little change, and was even lower than the original soil. The organic matter in the soil significantly increased compared to the original soil, especially in the zeolite-treated group.

[0131] (5) Analysis of biological characteristics of different treatment groups in paddy field wetlands

[0132] This invention uses high-throughput sequencing of microorganisms in paddy field wetland soils where rice is grown. By studying the differences in microbial species and structural and functional characteristics of different treatment groups, it explores the mechanistic effect of adding zeolite on the pollutant removal effect of the system.

[0133] a. Microbial community diversity analysis

[0134] Table 11 Microbial diversity and richness of paddy field wetlands

[0135]

[0136] Table 11 shows that the number of OUTs detected in the treatment groups without zeolite (XD1, SA1, and BR1) were 3083, 3252, and 2803, respectively; while the number of OUTs detected in the treatment groups with zeolite (XD2, SA2, and BR2) were 2863, 2709, and 3527, respectively. The higher the values ​​of Ace and Chao1, the more community species they correspond to. The table shows that the trends for these two values ​​are generally consistent across the six treatment groups. The addition of zeolite slightly reduced substrate species in the treatment groups planting *Xu* rice and salt-tolerant rice, while it increased in the treatment groups planting *Bamboo* rice. Overall, the ranking of these two values ​​across the six groups is BR2>SA1>XD1>XD2>BR1>SA2. The Shannon index also represents microbial diversity; the lower the value, the lower the community diversity in the sample, following the same pattern as the indices mentioned above.

[0137] Beta diversity can reflect the differences in microbial communities among different samples. This invention analyzes the microbial community from two aspects: PCoA analysis and NMDS analysis.

[0138] PCoA plots can be used to analyze the differences between various paddy field wetland samples. The closer the points corresponding to different samples are in the plot, the more similar their microbial communities are. Figure 12 It can be seen that all sample points are in the negative value region and the sample points are relatively close to each other, indicating that the community composition of XD1, XD2, SA1, SA2, BR1 and BR2 is highly similar, proving that the microbial community in the soil matrix of different rice varieties has little difference and the community structure composition is highly similar.

[0139] Nonmetric multidimensional scaling (NMDS) is a data analysis method that simplifies multidimensional research objects to a lower-dimensional space, and then classifies, locates, and analyzes them. Its basic characteristics are similar to principal coordinate analysis; the distance between sample points indirectly reflects the degree of difference in community structure among the sample points.

[0140] Depend on Figure 13 It can be seen that SA1 and SA2 are very close, as are XD1 and XD2, while BR1 and BR2 are relatively far apart. This indicates that the addition of zeolite has a relatively small impact on the soil microbial community structure of rice planted with salt-tolerant rice (Shuangliangyou 138) and Xudao rice (Xudao 9), but a slightly larger impact on the soil microbial community structure of rice planted with bamboo rice (Taoxiu Youmeizhen). Overall, the microbial community structures of the six rice-planting treatment groups showed little difference and high similarity.

[0141] b. Analysis of differences in matrix microbial composition

[0142] Species with an abundance percentage of less than 1% in all samples were classified as "Others," while the rest were analyzed as dominant species. A total of 14 phyla were obtained from the 6 matrix samples: Proteobacteria, Actinobacteria, Bacteroidota, Verrucomicrobia, Acidobacteria, Planctomycetes, Cyanobacteria / Chloroplast, Firmicutes, Chloroflexi, Gemmatimonadota, Patescibactiota, Nitrospirota, Desulfobacterota, and Myxococcota. The dominant bacterial phyla in wetland substrates are mostly Proteobacteria, Bacteroides, Actinomycetes, Firmicutes, and Green Curvatures, indicating that the dominant bacterial phyla in paddy field wetlands and general artificial wetlands are similar.

[0143] The most prevalent phylum among the soil substrate microorganisms in all treatment groups was Proteobacteria, which contains a large number of nitrifying and denitrifying bacteria, enhancing the nitrification and denitrification capacity of the paddy field wetland system to a certain extent. Bacteroides is also an important phylum among soil microorganisms; these are chemoheterotrophic bacteria, primarily responsible for CO2 degradation. Some denitrifying and nitrogen-fixing bacteria also belong to this phylum, contributing positively to substrate denitrification. Acidobacteria degrade organic matter and participate in carbon cycling, playing a crucial role in constructing complex bacterial communities in artificial wetlands. The Green Bay phylum also has potential applications in carbon cycling. Among the Cyanobacteria, some nitrogen-fixing cyanobacteria exhibit good nitrogen-fixing effects, playing an important role in denitrification. Bacillus in the Firmicutes phylum effectively promotes NH4+ ionization in water. + The degradation of -N promotes digestion and also plays a role in the decomposition of organic matter. Some microorganisms in Firmicutes and Bacteroidetes also participate in anaerobic methanogenesis. Verrucous microbes have a certain nitrogen-fixing potential, diazotrophic nutrition function, and the ability to reduce nitrates. Planctomycetes mainly play a role in anaerobic ammonium oxidation, which can reduce NH4+. + -N and NO2 - -N is reduced to N2 without producing greenhouse gases such as N2O.

[0144] Depend on Figure 14It is known that the three dominant phyla are Proteobacteria, Acidobacteria, and Bacteroidetes, accounting for 43.57%, 14.18%, and 13.83% of the total, respectively. These microorganisms play an important role in substrate nitrogen fixation and denitrification, nitrification and denitrification, and the degradation of organic matter. Verrucous Microbes, Bacillus, Patellae Bacteria, and Chlorophylloidea also account for a significant proportion, accounting for 4.35%, 4.25%, 3.55%, and 3.25% of the total, respectively, and play an important role in nitrogen fixation, nitrate reduction, and the carbon cycle. The phyla Planicillium, Actinobacteria, Nitrifying Spirogyra, Desulfurizing Bacteria, and Firmicutes accounted for 2.21%, 1.76%, 1.49%, 1.21%, and 1.09% of the total, respectively, playing important roles in organic matter degradation, nitrogen fixation, methanogenesis, and anaerobic ammonia oxidation in the substrate. Other non-dominant bacterial groups accounted for 5.25% of the total, playing an important role in the structure and composition of the microbial community.

[0145] Figure 15 Hierarchical clustering analysis was performed on the distance matrix to construct a tree structure, which was then used for visualization analysis. The similarity between samples was measured by the distance between clusters and the length of branches. It can be seen that the bacterial community structure of SA2 is similar to that of SA1, followed by BR1 and BR2. XD1 and XD2 were grouped together and showed significant differences from the other four groups. Therefore, it can be concluded that the differences between treatment groups of the same rice variety are small, while the differences between different rice treatment groups are large. Differences exist between japonica rice (Xu rice) and indica rice (Zhu rice and Hai rice).

[0146] II. Artificial Ecological Floating Bed Simulation Device

[0147] The simulated artificial ecological floating bed device consists of a box body and a planting board. The box body measures 25.7cm × 18.2cm × 7.4cm and is made of polyethylene, purchased from the Taobao store Shunxingda Plastics. The planting basket is a cylinder with a diameter of 4cm and a height of 5cm, purchased from the Taobao store Awen Vegetable Garden. It contains planting cotton with a diameter of 4.2cm and a height of 3cm, purchased from the Taobao store Yunchuang Sponge Encyclopedia Enterprise Store. The acrylic board measures 28cm × 20cm × 2mm and was purchased from the Taobao store Jumeng Flagship Store. The opening positions are as follows... Figure 16 As shown.

[0148] This invention uses water spinach (Water Spinach) as the experimental plant. The seeds were first disinfected with 30% hydrogen peroxide, then soaked in tap water for 12 hours. After removing any shriveled or impurities floating on the surface, the seeds were wrapped in sterile gauze and placed in a high-temperature sterilized petri dish. The gauze was watered daily to keep it moist. After germination, the seeds were transferred to flowerpots for cultivation. When the plants reached approximately 5cm in height, they were transplanted into a hydroponic system. After acclimatization for 3 days, the water quality indicators of the effluent from each system were measured. This invention uses artificial watering, with wastewater left to settle in the hydroponic system. Four hydraulic retention times were set: 1 day, 3 days, 5 days, and 7 days. The pH, conductivity, and COD of the effluent from each system were measured. Mn NH4 + -N, NO3 - -N and TN were determined. Each treatment was repeated three times.

[0149] The experiment included four treatments: the apparatus for treating the effluent from the XD2 system was named XD-SP, the apparatus for treating the effluent from the SA2 system was named SA-SP, the apparatus for treating the effluent from the BR2 system was named BR-SP, and the apparatus for treating the effluent from the series system was named SA-BR-XD-SP. Hydraulic retention times were set at 1 day, 3 days, 5 days, and 7 days. The pH, conductivity, and COD of the effluent from each system were measured. Mn NH4 + -N, NO3 - -N and TN were determined. Each treatment was repeated three times.

[0150] About one month after the end of the water spinach growing season, the water spinach was harvested, and its biological indicators such as root length, plant height, dry weight, and fresh weight were measured to explore the effects of different HRTs on the purification of the tailwater of the paddy field wetland system by the hydroponic water spinach system, as well as the growth of water spinach under this condition and the possible economic benefits.

[0151] a. Effects of different HRTs on pH of paddy field tailwater

[0152] Table 12 Effects of different HRTs on pH of paddy field tailwater

[0153]

[0154] As shown in Table 12, the pH of each treatment group at each HRT increased to varying degrees compared to the original water. Because the influent pH of the SA-BR-XD-SP system was higher, the effluent pH was also slightly higher than other treatment groups. In the hydroponic water spinach system, complex biochemical reactions occur continuously. The digestive action of some nitrifying bacteria attached to the water spinach roots may lead to the depletion of alkalinity in the water, resulting in a decrease in pH, while the denitrification reaction of denitrifying bacteria can increase the pH. Water spinach absorbs NH4 from the water.+ -N causes a decrease in pH, while absorbing NO3 in the water - -N can also cause the pH to rise. This is because NH4+ is present in rice paddy wetland simulation systems. + Due to factors such as the easier absorption and adsorption of -N, NH4 enters the water of hydroponic water spinach systems. + -N concentration is low, NO3 - The higher NO3- concentration makes denitrification easier than nitrification, while producing more NO3- - -N is absorbed, leading to an increase in pH. There were no significant differences in pH across treatment groups at different HRTs; the pH fluctuated at different HRTs, ranging from 7.21 to 7.71, indicating weakly alkaline water.

[0155] b. Effects of different HRTs on the electrical conductivity of paddy field tailwater

[0156] Table 13 Effect of different HRTs on the conductivity of paddy field tailwater

[0157]

[0158] As shown in Table 13, with the continuous increase of HRT, the conductivity of the effluent from the hydroponic water spinach system gradually decreased, but the rate of decrease gradually slowed down. Significant differences were observed among the treatment groups at different HRTs. At HRT = 7 days, the conductivity of each treatment group reached its lowest point. The BR-SP system had the lowest conductivity (511.64 ± 4.32 μs / cm) due to its lower influent conductivity, while the SA-BR-XD-SP system had the highest effluent conductivity (690.06 ± 5.67 μs / cm) due to its higher influent concentration. The higher effluent conductivity of the SA-BR-XD-SP system at each HRT compared to the other three systems is likely because the tailwater from the series system flows through multiple paddy field wetland systems, dissolving more ions from the soil during the flow, thus increasing the influent conductivity and ultimately leading to a higher effluent conductivity for the entire system. This may be because the plant roots continuously absorb nutrients from the water, causing the salinity of the water to gradually decrease. As the HRT increases, the water spinach roots may secrete some substances, and the death of water spinach root microorganisms increases the electrical conductivity of the water. Therefore, the rate of decrease in electrical conductivity gradually slows down in the later stages.

[0159] c. Effects of different HRTs on CODMn removal efficiency in paddy field tailwater

[0160] like Figure 17 As shown, the final effluent COD of each treatment group Mn All levels were slightly above 2 mg / L, meeting the Class II surface water quality standard. With increasing HRT, the final effluent from each treatment group showed a slight decrease compared to the influent, but the degree was limited. The combined systems affected the COD levels in the surface water.Mn The average total removal rate was between 60-70%, simulating the COD removal rate in the paddy field wetland system. Mn The removal effect accounts for more than 90% of the total removal effect; the hydroponic water spinach system effectively removes COD from paddy field tailwater. Mn The purification effect did not differ significantly across different HRTs, proving that COD Mn Most of the removal is done in paddy field wetland systems.

[0161] Hydroponic water spinach system reduces COD in water Mn The poor removal effect may be due to several factors. Firstly, the paddy field wetland simulation system is rich in rice root microorganisms, and the thick substrate easily forms an anaerobic zone. Most readily biodegradable organic matter may be degraded in the paddy field wetland, and denitrification also consumes some carbon sources, thus reducing the COD removal efficiency of the hydroponic water spinach system in the paddy field wetland effluent. Mn The purification effect is not particularly ideal.

[0162] In summary, this ecological combination system of simulated paddy field wetlands and floating bed hydroponic water spinach has a significant impact on COD levels in this type of surface water. Mn The removal effect is acceptable, and the final treatment effect can reach 60%-70%. The degradation process of organic matter mainly occurs in the paddy field wetland system, and the final effluent water quality index can reach Class II surface water quality standard.

[0163] d. Effects of different HRTs on NH4 in paddy field tailwater + The impact of -N removal efficiency

[0164] like Figure 18 As shown, when HRT = 1 day, the NH4 content of each treatment group... + -N concentration reached its highest level, compared to the original water NH4. + The concentration of NH4+ in the water increased slightly, with the highest concentration in the XD-SP system reaching 0.14 ± 0.02 mg / L; subsequently, with the increase of HRT, when HRT = 3 days and HRT = 5 days, the concentration of NH4+ in the water... + -N concentration gradually decreased, with the lowest effluent concentrations in the SA-BR-XD-SP system being 0.07±0.02 mg / L and 0.05±0.02 mg / L, respectively. When HRT=7d, the effluent quality of each treatment group slightly improved, with the lowest concentration in the SA-BR-XD-SP system being 0.07±0.03 mg / L.

[0165] Each system controls NH4 in surface water + The removal efficiency of NH4+ reached over 90% in all systems. With the increase of HRT, the removal efficiency of each system for NH4+ increased. +The average removal rate of -N showed a trend of first increasing and then decreasing, reaching its highest point at HRT=5d, with the SA-BR-XD-SP system achieving the highest average removal rate of 96.53%. The effluent NH4 from each system... + The -N concentrations are all below 0.15 mg / L, meeting the Class I surface water quality standard.

[0166] This may be due to NH4 in the tailwater of paddy field wetlands + The concentration of -N is low, so water spinach does not absorb it effectively; however, the content of organic nitrogen in the water is not low, so some organic nitrogen is converted into NH4. + -N, thus causing NH4 + -N concentration increases; with the absorption of water spinach and the consumption of organic nitrogen, NH4+ concentration decreases at HRT=3d and HRT=5d. + -N concentration decreases, and finally, when HRT = 7 days, organic nitrogen concentration increases, possibly due to bacterial death and microbial assimilation, followed by NH4+. + -N concentration increased slightly.

[0167] In summary, this ecological combination system of simulated paddy field wetlands and floating bed hydroponic water spinach effectively controls NH4 in such surface water. + The removal efficiency of NH4+ is high, with a final treatment rate of over 90%. The final effluent water quality meets the Class I surface water quality standard. The removal effect is optimal when the hRT (water retention time) in paddy wetlands is 6 days and the hRT for hydroponic water spinach is 5 days. The series system is particularly effective for removing NH4+. + -N removal is most effective, likely because as it flows through the system, more ions that are beneficial for plant absorption and growth are dissolved from the substrate, thus increasing the water spinach's NH4+ uptake. + -N absorption capacity.

[0168] e. NO3 in paddy field tailwater under different HRT conditions - The impact of -N removal efficiency

[0169] like Figure 19 As shown, with the increase of HRT, at HRT = 1, 3, and 5 days, NO3 in water... - The concentration of -N gradually decreased; when HRT = 7d, the NO3 concentration in the effluent decreased. - The concentration of -N has rebounded somewhat. The lowest concentration was observed at 5 days (HRT) in the effluent from the BR-SP and SA-BR-XD-SP systems. - The lowest concentrations of -N were 0.23 ± 0.06 mg / L and 0.23 ± 0.04 mg / L, respectively. The systems' response to NO3- in water was assessed at HRT = 3 days and HRT = 7 days. - The removal efficiency of -N showed no significant difference, but was significantly different from the other two different HRTs; effluent NO3- The concentration of -N initially decreased and then increased with increasing HRT. The decrease was due to the nitrification-denitrification process carried out by the microorganisms attached to the water spinach, as well as the increase in NH4+ concentration. + -N concentrations are low, and water spinach requires N for growth, while NO3 in the water is not. - -N is absorbed, ultimately leading to NO3 in the water. - -N concentration decreases, and overall removal rate increases. When HRT=7, the TN concentration in the water may increase due to the death of bacteria and plant root cells, as well as the assimilation by microorganisms, and then be converted into NO3 under the action of microorganisms. - -N, which leads to a decrease in its average removal rate.

[0170] In summary, this ecological combination system of simulated paddy field wetlands and floating bed hydroponic water spinach effectively controls NO3 in this type of surface water. - The removal effect of NO3- is relatively good, with a final treatment rate of 75%-90%. The removal effect is best when the HRT in paddy wetland is 6 days and the HRT in hydroponic water spinach is 5 days. Among them, the series system and the BR-SP system are effective in removing NO3-. - -N has the best removal effect.

[0171] f. Effects of different HRTs on TN removal efficiency in paddy field tailwater

[0172] like Figure 20 As shown, with the increase of HRT, the concentration of TN in the water gradually decreased at HRT = 1, 3, and 5 days; when HRT = 7 days, the concentration of TN in the effluent rebounded. The lowest concentration was observed at HRT 5 days, with the lowest effluent TN concentrations of 0.96±0.11 mg / L and 0.95±0.12 mg / L for the SA-SP system and SA-BR-XD-SP system, respectively, both <1.0 mg / L, meeting the Class III surface water quality standard. Except for XD-SP, which was Class V at HRT = 1 day, the effluent TN concentrations of the other treatment groups were between 1.0 mg / L and 1.5 mg / L, meeting the Class IV surface water quality standard. The effluent TN concentration showed a trend of first decreasing and then increasing with increasing HRT. The decrease was due to the nitrification and denitrification of N by microorganisms attached to the roots of water spinach and the absorption of different forms of N by plants, leading to a decrease in effluent TN concentration and an increase in overall removal rate. When HRT=7, the concentration of TN in the water may increase due to the death of bacteria and plant root cells and the assimilation of microorganisms, which may lead to a decrease in its average removal rate.

[0173] In summary, the simulated paddy field wetland-floating bed hydroponic water spinach ecological combination system showed good TN removal efficiency in this type of surface water, with a final treatment rate of 80%-90%. Specifically, at a water retention time (HRT) of 5 days, the effluent quality of the SA-SP and SA-BR-XD-SP systems met the Class III surface water quality standards. The above study indicates that the removal effect was optimal when the paddy field wetland HRT was 6 days and the hydroponic water spinach HRT was 5 days. The series system showed better TN removal efficiency, possibly because the flow through the system dissolves more ions from the substrate that are beneficial for plant growth, thus increasing the water spinach's nitrogen absorption capacity. The SA-SP system showed good removal efficiency because the SA2 system had a low TN influent concentration, and the paddy field wetland planted with salt-tolerant rice (Shuangliangyou 138) showed good TN purification effect.

[0174] Water spinach growth status and quality:

[0175] Table 14 Indicators of Water Spinach Growth

[0176]

[0177] Depend on Figure 21 As shown in Table 14, the water spinach in the XD-SP system had the best growth. This was because the higher N concentration in the paddy field wetland water provided more abundant nutrients, resulting in more vigorous plant growth and an extremely developed root system. The plant height reached 17.81±0.63cm, and the dry and fresh weight of the roots was significantly higher than that of other treatment groups. The SA-BR-XD-SP system was the second best. Due to its better absorption of N from the water, its plant height, root length, and dry and fresh weight were second only to XD-SP. The other two groups had poor growth.

[0178] This invention employs a small-scale experimental setup to simulate paddy field wetlands and ecological floating beds. Three different rice varieties were selected as wetland plants, with soil as the primary substrate. Water spinach (Ipomoea aquatica) was selected as the floating bed plant. The simulated paddy field wetland had eight treatment groups: four with zeolite added and four without zeolite as a control. The simulated ecological floating bed had four treatment groups, treating the wastewater from the paddy field wetland with added zeolite. The simulated paddy field wetland had three hydraulic retention times (2 days, 4 days, and 6 days), while the simulated ecological floating bed had four hydraulic retention times (1 day, 3 days, 5 days, and 7 days). The simulated paddy field wetland was operated from June 30, 2023 to November 7, 2023, and the simulated ecological floating bed was operated from July 20, 2023 to November 7, 2023. During system operation, the removal efficiency of each system for various pollutants under different HRTs was analyzed and compared. After system operation, the growth of three types of rice and water spinach was measured, and the characteristics of soil matrix microorganisms were studied using high-throughput sequencing technology. The study found that:

[0179] (1) When the HRT of the paddy field wetland was 6 days and the HRT of the ecological floating bed was 5 days, the removal effects of each treatment group on various pollutants in the surface water were relatively good. Regarding the paddy field wetlands, the wetland system planted with indica rice had a slightly higher wastewater treatment efficiency than the wetland system planted with japonica rice, and this was also true for their growth. However, the lower concentration of paddy field effluent was not conducive to the growth of water spinach; therefore, the overall effluent quality of XD-SP was better, with lower NH4 content. + The TN concentration meets the Class I surface water quality standard, and the effluent TN concentration basically meets the Class III surface water quality standard.

[0180] (2) The addition of zeolite has a promoting effect on the growth of rice, including a significant increase in the yield of rice grains; the growth status of the three types of rice is basically in the order of salt-tolerant rice (Shuangliangyou 138) > bamboo rice (Taoxiuyoumeizhen) > Xu rice (Xudao 9); the chlorophyll fluorescence parameters of each type of rice also increased slightly after the addition of zeolite, indicating that the addition of zeolite can promote the plant's utilization of light energy.

[0181] (3) Based on the Ace and Chao1 indices, the number of microorganisms in the substrate of each paddy field wetland basically followed the order BR2>SA1>XD1>XD2>BR1>SA2. PCoA principal coordinate analysis and NMDS plot analysis showed that the microbial community structure of each treatment group was quite similar. High-throughput sequencing analysis indicated that the most dominant bacteria in the paddy field wetland were Proteobacteria, which play an important role in nitrification and denitrification. Other dominant bacteria, such as Bacteroidetes, Acidobacteria, Verrucous Microbes, Planctomyces, and Firmicutes, play important roles in nitrogen fixation, carbon cycling, and organic matter degradation. Cluster analysis at the phylum level revealed that the differences in rice root microbial communities were largely related to rice varieties.

[0182] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for purifying nitrogen in a nitrogen-containing water body using a paddy field wetland-ecological floating bed combined ecosystem, characterized in that, The method comprises the following steps: The rice field wetland system is connected with the ecological floating bed system, nitrogen-containing water is introduced into the rice field wetland system, and tail water discharged from the rice field wetland system is introduced into the ecological floating bed system, so as to purify nitrogen in the nitrogen-containing water; The plants in the rice field wetland system are japonica rice, salt-tolerant rice or bamboo rice; the substrate in the rice field wetland system is a mixture of rice field soil and zeolite or rice field soil; The plants in the ecological floating bed system are water spinach; The hydraulic retention time of the rice field wetland system is set to 2-6 days; the hydraulic retention time of the ecological floating bed system is set to 1-7 days; When the mixture of rice field soil and zeolite is used as the substrate of the rice field wetland system, the addition amount of zeolite in dry rice field soil is 10-20 g / kg; The phosphorus application amount in the rice field wetland system is 100-150 kg / hm 2 , and the potassium application amount is 80-100 kg / hm 2 ; The total nitrogen concentration in the nitrogen-containing water is 8-10 mg / L; pH of the nitrogen-containing water body is 7-9, NH4 + - N concentration is 1-3 mg / L, NO3 - - N concentration is 2-3 mg / L.

2. The method of claim 1, wherein, The hydraulic retention time of the rice field wetland system is set to 6 days; the hydraulic retention time of the ecological floating bed system is set to 5 days.

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