Multi-level rhizopore wetland system for removing nitrogen pollution from water bodies by slow-release biocarbon from plant solid phase

Abstract

The present invention provides a multi-stage root hole wetland system of plant solid phase slow-release biochar for removing nitrogen pollution from water bodies, comprising a sleeved inner ring and outer ring filtration system, wherein the inner and outer ring filtration systems are annular soil columns surrounded by a protective net, filled with a matrix and plant solid phase slow-release biochar, and planted with plants, and nano aeration tubes are provided in the matrix, the inner ring is higher than the outer ring, and the plant solid phase slow-release biochar is a biochar material activated by an improver, and the improver includes clay minerals and a heat preservation agent. First, sewage enters the core area of the inner ring, and the biochar is used as the matrix material of the annular soil column to fill the artificial wetland system, thereby increasing the denitrification rate without reducing the effective carbon source supply. The water level difference is used to solve the problem of hydraulic flow path connectivity, and the water ecological filtration is achieved through the stepped water level difference. The present invention can achieve the purpose of efficient resource utilization of aquatic plant waste in water bodies and simultaneous treatment of excessive nitrogen pollutants in water bodies.

Description

Technical Field

[0001] The present invention belongs to the field of environmental protection technology and relates to a multi-stage rhizopore wetland system that utilizes a continuous and efficient supply of effective biochar and an enhanced plant solid-phase slow-release biochar. In particular, it relates to a wetland system constructed using slow-release carbon source materials for enhanced denitrification and denitrification in lakeside and riparian wetlands or artificial vertical flow wetlands. Background Art

[0002] Biological denitrification is the process of converting nitrate nitrogen into nitrogen gas through denitrification in the presence of denitrifying bacteria. Denitrification in water, particularly in vertical flow constructed wetlands, is a primary nitrogen removal process. Sufficient electron donors are essential for successful denitrification, and organic matter in wastewater can provide electron donors for denitrifying bacteria. In actual wetland denitrification, a COD / TN ratio of 4 to 15 is generally required to ensure successful denitrification. However, the C / N ratio in typical wastewater is less than 3. This clearly indicates that deep denitrification of tailwater requires insufficient carbon sources, necessitating continuous external carbon addition. Therefore, research on the supply of external carbon sources (electron donors) has become a critical and pressing issue in deep denitrification of urban reclaimed water.

[0003] If a soluble carbon source is added directly, as the nitrate concentration in the treated water fluctuates, it is easy to cause problems such as insufficient carbon source, incomplete denitrification, excessive carbon source waste and secondary pollution. The difficulty in controlling the amount of addition becomes the biggest difficulty, which is very disadvantageous in terms of economic cost and operation management. The sustainable supply of sufficient effective carbon source is the main means to improve microbial activity. In addition, combining the characteristics of the "multi-media" active interface of the micropores of the rhizopore wetland, a rich aerobic and anaerobic microporous environment is constructed in the wetland matrix environment to continuously supply effective carbon sources for denitrification, thereby improving the coupled denitrification process of nitrification-denitrification, which can accelerate the removal efficiency of nitrogen in the water. Summary of the Invention

[0004] To address the above problems, the present invention adopts enhanced plant solid phase slow-release biochar and takes the rhizopore wetland microporous "multi-media" active interface as the core to construct a ring-shaped rhizopore wetland system with plant solid phase slow-release biochar and multi-stage ecological filtration to remove nitrogen pollution in water bodies.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A multi-stage root hole wetland system for removing nitrogen pollution from water bodies by slow-release biochar from plant solid phase comprises a sheathed inner ring filtration system and an outer ring filtration system. The water inlet of the wetland system is located inside the inner ring filtration system.

[0007] The inner ring filtration system is a ring column surrounded by a protective net, wherein the inner ring matrix, plant solid phase slow-release biochar and nano aeration tubes are arranged inside the protective net and plants are planted.

[0008] The outer ring filtration system is an annular column surrounded by a protective net. The protective net is provided with an outer ring matrix, plant solid phase slow-release biochar and nano aeration tubes and is planted with plants. The height of the outer ring filtration system is lower than that of the inner ring filtration system.

[0009] The plant solid phase slow-release biochar is a biochar material activated by an improver, wherein the improver comprises clay minerals and a heat preservation agent.

[0010] Preferably, the nano aeration tube is placed horizontally in the inner ring matrix or the outer ring matrix, and the plant solid phase slow-release biochar surrounds the nano aeration tube in the form of a plant solid phase slow-release biochar module.

[0011] Preferably, the total volume ratio of the plant solid phase slow-release biochar module to the inner ring matrix or the outer ring matrix is 1:3.

[0012] Preferably, the inner ring filtration system or the outer ring filtration system comprises an upper layer of nano aeration tubes and a lower layer of nano aeration tubes, and the lower layer of nano aeration tubes is arranged in the middle and lower layer of the inner ring filtration system or the outer ring filtration system.

[0013] Preferably, the lower nano-aeration tube is 15 to 25 cm away from the bottom of the inner ring filtration system or the outer ring filtration system.

[0014] Preferably, the lower layer nano-aeration tubes are surrounded by the lower layer plant solid phase slow-release biochar modules, and the upper layer nano-aeration tubes are surrounded by the upper layer plant solid phase slow-release biochar modules.

[0015] The upper layer plant solid phase slow-release biochar module is prepared by the following steps (0-1) to (0-3), and the lower layer plant solid phase slow-release biochar module is prepared by the following steps (0-1) to (0-2):

[0016] (0-1) Aquatic plant straw and corn cobs are crushed and mixed, and then anaerobically matured in an inert gas to obtain biochar material;

[0017] (0-2) adding an improver uniformly to the biochar material to activate it, filling it into a three-dimensional plant net, and then spreading the activation agent on the surface of the three-dimensional plant net, and air-drying and solidifying it;

[0018] (0-3) Planting the underground stems of plants with spore roots into the modules obtained in step (0-2).

[0019] Preferably, the density of the plants planted in steps (0-3) is 8 to 12 plants per square meter.

[0020] Preferably, the aquatic plant straws in step (0-1) are straws of submerged plants, floating-leaf plants, and emergent plants. Preferably, the submerged plants are mainly water chestnuts, and the floating plants are water nymphs, water peanuts, or green foxtails; the emergent plants are reeds or water chestnuts; and preferably, the above-ground portion of the emergent plant straws.

[0021] Preferably, the mixing mass ratio of the aquatic plant straw and corn cob in step (0-1) is: submerged plant: floating plant: emergent plant: corn cob = 25~35:25~35:15~30:5~15.

[0022] Preferably, the aquatic plant straw in step (0-1) is dried and ground.

[0023] Preferably, the length of the aquatic plant straw in step (0-1) is 1-2 cm; and the corn cob is a particle with a particle size of 1-2 cm.

[0024] Preferably, the inert gas in step (0-1) is N2.

[0025] Preferably, the temperature of the anaerobic maturation in step (0-1) is 25-40°C, preferably 30-35°C.

[0026] Preferably, the activation temperature in step (0-2) is 30-35°C.

[0027] Preferably, the spreading activation in step (0-2) is activation by spraying a Ca(OH)2 or Mg(OH)2 suspension.

[0028] Preferably, the spore burial depth of the plant in step (0-3) is 5 to 10 cm.

[0029] Preferably, the clay mineral is diatomaceous earth, attapulgite or kaolin.

[0030] Preferably, the clay mineral is diatomaceous earth, and the dosage is 25-160 g / L.

[0031] Preferably, the heat preservation agent is a 10-20% slaked lime suspension.

[0032] Preferably, the three-dimensional plant net is made of plant fiber; preferably, the plant fiber is coconut shell fiber or flax fiber.

[0033] Preferably, the inner ring matrix is a mixture of clay, iron oxide and limestone. Preferably, the mass ratio of clay, iron oxide and limestone is 80-90:2-5:5-10.

[0034] Preferably, the outer ring matrix is a mixture of gravel, limestone and iron oxide. Preferably, the mass ratio of gravel, limestone and iron oxide is 85-90:2-5:5-15.

[0035] Preferably, the protective net is a galvanized wire mesh.

[0036] Preferably, the plants grown are reeds and cattails.

[0037] Preferably, to effectively control the ratio of live root pores to dead root pores and improve the denitrification efficiency of the root pore wetland, the porosity ratio of live root pores to dead root pores within the multi-stage root pore wetland system is 1:0.5-0.9. The porosity ratio is specifically adjusted by adjusting the clay ratio and aeration rate in the matrix layer. Plant roots are interspersed in the matrix, and live root pores form around the roots. Root secretions form functional microbial communities. The effective range of the root pores is within 1-2 cm of the root surface. Dead root pores are the gaps left behind after the plant roots rot and die.

[0038] The rhizopore wetland system is equipped with nano-aeration tubes in the matrix and plant solid-phase slow-release biochar to form an aerobic-anaerobic multi-microporous interface denitrification enhanced treatment mixed matrix system. An active biofilm layer is formed 1-2 cm around the root surface. The well-developed root system of the plant, the microbial film attached to the surface of the matrix layer and the aeration pipes are used together as the basic plant active rhizopore system.

[0039] The inner and outer rings form a two-stage filtration system. The inner ring is the core area, where wastewater is piped into the inner ring. Nano-aeration tubes enhance local water reoxygenation. The inner ring is higher than the outer ring, and the water flow between the inner and outer rings is achieved by gravity due to the height difference.

[0040] After the solid phase slow-release biochar module containing underground stems of plants with spore roots is laid out, after 2 to 3 months, the plant roots will fill the three-dimensional plant net and the inner and outer ring filtration systems.

[0041] The plant solid phase slow-release biocarbon multi-level rhizopore wetland system is composed of a multi-level ecological filtration mesh rhizopore wetland, which uses the water level drop to solve the problem of hydraulic flow path connectivity and realizes water ecological filtration through the stepped water level drop.

[0042] Preferably, the water head difference between the inner ring filtration system and the outer ring filtration system is controlled within the range of 0.2 to 0.4 m, and the height of the inner ring or outer ring is 50 to 120 cm.

[0043] At present, artificial wetlands have the following technical difficulties: slow-release carbon sources have problems with the sustainable supply of effective carbon sources during the carbon supply stage; denitrification materials require thermal insulation properties under low temperature conditions during the carbon source supply process; and there are problems with the control of toxic substances in the carbon source supply, and the toxic and harmful substances released by anaerobic degradation have an inhibitory effect on the denitrification process.

[0044] In view of the above technical difficulties, the technical advancement of the solution provided by the present invention lies in:

[0045] (1) In order to solve the technical difficulty of sustainable supply of effective carbon source in the carbon supply stage with slow-release carbon source, the technical solution provided by the present invention is realized by optimizing the internal component structure of the wetland system. Specifically, the degradation characteristics and proportion configuration of different solid-phase plant materials are utilized, and the excess plant materials in the wetland are recycled and reused, which fully exploits the advantages of wetland plant solid-phase carbon sources in strengthening the denitrification process without introducing new pollution sources to form secondary pollution.

[0046] (2) In order to solve the technical difficulties of excessive release of nitrogen and phosphorus nutrients during the carbon source supply process, while utilizing plant carbon, the excessive release of other plant secondary biomass such as nitrogen and phosphorus was effectively controlled. The slow-release characteristics of carbon were used to effectively control the carbon and nitrogen decay and decomposition process. At the same time, the small amount of released soluble nitrogen and phosphorus was effectively fixed to prevent them from entering the water body and causing serious secondary pollution.

[0047] (3) Regarding the control of toxic substances in carbon source supply, the technical difficulty of the inhibitory effect of toxic and harmful substances released by anaerobic degradation on the denitrification process: In order to solve the problem of biological toxicity in the process of plant carbon source supply, excessive biocarbon supply causes anaerobic and toxic organic matter accumulation in the water body, inhibiting the physiological ecology and enzyme activity of active microorganisms in the nitrification-denitrification process. The slow release process of the present invention simultaneously reoxygenates the system, forming a rich anaerobic reoxygenation microenvironment, avoiding the inhibitory effect of toxic substances on the denitrification process, and providing a strong habitat condition for the coupled denitrification process.

[0048] (4) Improve the performance of biochar that can be utilized, forming a rich aerobic and anaerobic microporous environment, providing a good habitat for the high efficiency of biochar, maintaining a high reaction temperature for carbon participation in the biochemical process, and continuously and efficiently utilizing carbon, which to some extent solves the technical difficulty of low efficiency in winter wetlands. Under the joint coupling of the two, the carbon supply in the denitrification process involving plant carbon sources is effectively utilized, thereby improving the efficiency of coupled denitrification and denitrification in water bodies.

[0049] Beneficial effects of the present invention:

[0050] (1) The invention involves a relatively simplified engineering implementation technology process and has strong technical operability. It can be implemented simultaneously during the construction of general artificial wetlands, thereby improving the restoration effect of ecological projects.

[0051] (2) The restoration materials involved in the present invention, such as plant straw, reed, cattail, etc., as well as slaked lime, diatomaceous earth, and attapulgite, are all eco-friendly materials with low prices and wide sources, and are suitable for application and promotion in the practice of artificial wetland ecological engineering.

[0052] (3) The technical solution provided by the present invention fully utilizes the self-regulating function of river and lake ecosystems to reduce the frequency and intensity of human interference. By adjusting the internal component structure of the ecosystem, the quantity and quality of the carbon source supply of plant materials are improved, and the goal of sustainable and efficient carbon source supply is ultimately achieved. After pre-treating the supplied carbon source, the secondary overflow of major pollutants in the process of carbon synchronous release is removed or reduced, and the safe disposal and thermal insulation properties of eco-friendly modifiers are utilized to a certain extent to solve the technical difficulties of low wetland efficiency in winter. The carbon source is used in oxidation ponds and vertical flow artificial wetland systems to increase the denitrification rate without reducing the effective carbon source supply.

[0053] The present invention focuses on the wetland carbon source supply system, develops a method for preparing a water body with a continuous and efficient supply of effective carbon, and uses biochar to construct an enhanced multi-level rhizopore wetland system with slow-release biochar in the plant solid phase, providing a new solution for the treatment of nitrogen pollution in polluted water bodies and sediments in my country. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a schematic diagram of the top view of the multi-stage root hole wetland system described in the present invention.

[0055] Figure 2 It is a schematic diagram of the semi-sectional structure of the multi-stage root hole wetland system described in the present invention.

[0056] 1 is the inlet tank, 2 is the inner ring matrix, 3 is the primary outlet tank, 4 is the secondary outlet tank, 5 is the outer ring filtration system, 6 is the outer ring matrix, 7 is the lower layer plant solid phase slow-release carbon module, 8 is the nano aeration pipe, 9 is the plant, and 10 is the upper layer plant solid phase slow-release carbon module. Arrows in the diagram indicate the direction of water flow.

[0057] Figure 3 This is a comparison chart of the dynamic changes of TOC in the water body in Example 1 before and after the addition of plant solid phase slow-release biochar.

[0058] Figure 4 This is a comparison chart of the dynamic changes of N2O in the water body in Example 1 before and after the addition of plant solid phase slow-release biochar.

[0059] Figure 5 This is a comparison chart of the dynamic changes of TOC in the water body in Example 2 before and after the addition of plant solid phase slow-release biochar.

[0060] Figure 6This is a comparison chart of the dynamic changes of N2O in the water body in Example 2 before and after the addition of plant solid phase slow-release biochar.

[0061] Figure 7 This is a comparison chart of the dynamic changes of TOC in the water body in Example 3 before and after the addition of plant solid phase slow-release biochar.

[0062] Figure 8 This is a comparison chart of the dynamic changes of N2O in the water body in Example 3 before and after the addition of plant solid phase slow-release biochar.

[0063] Figure 9 This is a comparison chart of the dynamic changes of TOC in the water body in Example 4 before and after the addition of plant solid phase slow-release biochar.

[0064] Figure 10 This is a comparison chart of the dynamic changes of N2O in the water body in Example 4 before and after the addition of plant solid phase slow-release biochar.

[0065] Figure 11 This is a comparison chart of the dynamic changes of TOC in the water body in Example 5 before and after the addition of plant solid phase slow-release biochar.

[0066] Figure 12 This is a comparison chart of the dynamic changes of N2O in the water body in Example 5 before and after the addition of plant solid phase slow-release biochar. DETAILED DESCRIPTION

[0067] The technical solution of the present invention is described in detail below with reference to specific embodiments and accompanying drawings. The scope of protection of the present invention is not limited to the specific embodiments, but is defined by the claims.

[0068] Example 1

[0069] According to the present invention, to address the issue of nitrogen pollution in water bodies, and to enhance the denitrification process in an oxidation pond at a river bypass wetland in Anhui Province, the plant solid-phase slow-release biochar described in the present invention is used to supplement carbon, enhance microbial activity, and improve nitrogen removal efficiency. The specific implementation plan is as follows:

[0070] (1) Preparation of plant solid phase slow-release biochar: The aboveground plant materials of water chestnut, water hyacinth, reed and water chestnut straw were collected, and then dried and crushed into 1 cm small segments respectively. At the same time, corn cobs were collected and dried and crushed into small particles with a particle size of about 1 cm. Then, the plant carbon source was obtained by mixing water chestnut: water chestnut: reed and water chestnut mixture: corn cob in a mass ratio of 35:25:30:5, which was used as a reserve for the modification of biochar using mixed amendments in the next step. The plant carbon source was then anaerobically fermented in a closed container under N2 atmosphere at 30~35℃ to obtain biochar material. The mixed amendment 25g / L diatomaceous earth and 10% slaked lime suspension were added by broadcasting. After the above-mentioned material components were mixed and aged for 24h, fermentation began for 3 days, and the fermentation temperature was controlled at 30℃. Then, a secondary fermentation treatment was performed, in which 50 g / L zeolite suspension and 2 mol / L H2SO4 were added for spraying. After the above-mentioned components were mixed and aged for 24 hours, fermentation was started for 5 days at a controlled fermentation temperature of 32° C. After the fermentation was completed, an activated solid-phase plant carbon source was obtained.

[0071] (2) A three-dimensional plant net was prepared using coconut shell materials. The obtained plant-based carbon source was filled into the three-dimensional plant net to a filling volume of 60%. Then, a 20 g / L Ca(OH)2 suspension was sprayed on the net. After a secondary activation treatment, the upper layer of the plant solid phase slow-release biochar module was obtained.

[0072] (3) Preparation of the lower layer plant solid phase slow-release biochar module: Planting of underground stems of reed and cattail with spore roots in the three-dimensional net of the upper layer plant solid phase slow-release biochar module was carried out at a rate of 8 plants / m2. The spore burial depth was 5 cm.

[0073] (4) Constructing a multi-level rhizopore wetland system with slow-release biocarbon from plant solid phase to remove nitrogen pollution from water bodies:

[0074] An inner ring filtration system and an outer ring filtration system are constructed, and the water inlet of the wetland system is located inside the inner ring filtration system. The inner ring filtration system and the outer ring filtration system are annular columns surrounded by galvanized wire mesh, and the height of the outer ring filtration system is lower than that of the inner ring filtration system.

[0075] The inner ring matrix is made of an auxiliary filler mixture consisting of clay, iron oxide and limestone. The mass ratio of clay, iron oxide and limestone is 80:2:10. Two horizontal nano-aeration tubes are set in the matrix, one above and one below. The lower nano-aeration tube is surrounded by the lower plant solid-phase slow-release biochar module, 15 to 25 cm away from the bottom, and the upper nano-aeration tube is surrounded by the plant solid-phase slow-release biochar module.

[0076] The total volume ratio of the plant solid phase slow-release biochar module in the inner ring to the inner ring matrix is 1:3.

[0077] The structure of the outer ring is the same as that of the inner ring, with the only difference being that the matrix of the outer ring is gravel, limestone and iron oxide, and the mass ratio of gravel, limestone and iron oxide is 90:5:5.

[0078] After two months, the plant roots are filled with the three-dimensional network and annular matrix, and the multi-level root hole wetland system is basically completed.

[0079] (5) After the system has been running for a period of time and stabilized, the high-nitrogen sewage is introduced into the wetland system and is retained and treated in the multi-stage ecological filtration ring root hole wetland before being discharged. The water body is continuously monitored for 6 months, and the data are as follows: Figure 3 and Figure 4 As shown in the figure, the total dissolved organic carbon (TOC) and NO levels in the water were significantly higher than the control, reaching 2.28 and 3.74 times higher, respectively. The number of nitrifying bacteria and denitrifying bacteria increased by 95% and 120%, respectively. The removal rates of ammonia nitrogen and nitrate nitrogen in the water decreased significantly by 45% and 76% compared to the control. The results were significant, and water quality was significantly improved.

[0080] Example 2

[0081] According to the present invention, to address the issue of nitrogen pollution in water bodies and enhance the denitrification process in a vertical flow wetland at a river bypass water purification wetland in Anhui Province, the plant-based solid-phase slow-release biochar described in the present invention is used to replenish carbon and enhance microbial activity. The specific implementation plan is as follows:

[0082] (1) Preparation of plant solid phase slow-release biochar: The aboveground plant materials of water chestnut, green foxtail algae, water chestnut, and water chestnut straw were collected, and then dried and crushed into 2 cm small segments. At the same time, corn cobs were collected and dried and crushed into particles with a particle size of about 2 cm. Then, the mixture of water chestnut: green foxtail algae and water chestnut: water chestnut: corn cob was mixed in a mass ratio of 25:30:30:15 to obtain a plant-based carbon source, which was used as a reserve for the next step of modifying the biochar using a mixed amendment. The plant-based carbon source was then anaerobically fermented in a sealed container under an N2 atmosphere at 25-30°C to obtain a biochar material. The mixed amendment 60g / L attapulgite and 12% slaked lime suspension were added by broadcasting. After the above-mentioned material components were mixed and aged for 24 hours, fermentation began for 3 days, and the fermentation temperature was controlled at 30°C. Then, a secondary fermentation treatment was performed, and 60 g / L zeolite suspension and 2 mol / L H2SO4 were added for spraying. After the above-mentioned material components were mixed and aged for 24 hours, fermentation was started for 5 days at a controlled fermentation temperature of 32° C. After the fermentation was completed, an activated solid-phase plant carbon source was obtained.

[0083] (2) A three-dimensional plant net was prepared using flax fibers. The obtained plant-based carbon source was filled into the three-dimensional plant net to a filling volume of 60%. Then, a 20 g / L Ca(OH)2 and 10% Mg(OH)2 suspension was sprayed on the net. After a secondary activation treatment, an upper layer plant solid phase slow-release biochar module was obtained.

[0084] (3) Preparation of the lower layer plant solid phase slow-release biochar module: Planting of underground stems of reed and cattail with spore roots in the three-dimensional net of the upper layer plant solid phase slow-release biochar module was carried out at a rate of 10 plants / m2. The spore burial depth was 10 cm.

[0085] (4) Constructing a multi-level rhizopore wetland system with slow-release biocarbon from plant solid phase to remove nitrogen pollution from water bodies:

[0086] An inner ring filtration system and an outer ring filtration system are constructed, and the water inlet of the wetland system is located inside the inner ring filtration system. The inner ring filtration system and the outer ring filtration system are annular columns surrounded by galvanized wire mesh, and the height of the outer ring filtration system is lower than that of the inner ring filtration system.

[0087] The inner ring matrix is composed of an auxiliary filler mixture of clay, iron oxide and limestone, with a mass ratio of clay, iron oxide and limestone of 90:5:5. Two horizontal nano-aeration tubes are set in the matrix, one above and one below. The lower nano-aeration tube is surrounded by the lower plant solid-phase slow-release biochar module, 15 to 25 cm away from the bottom, and the upper nano-aeration tube is surrounded by the plant solid-phase slow-release biochar module.

[0088] The total volume ratio of the plant solid phase slow-release biochar module in the inner ring to the inner ring matrix is 1:3.

[0089] The structure of the outer ring is the same as that of the inner ring, with the only difference being that the matrix of the outer ring is gravel, limestone and iron oxide, and the mass ratio of gravel, limestone and iron oxide is 85:2:15.

[0090] After two months, the plant roots are filled with the three-dimensional network and annular matrix, and the multi-level root hole wetland system is basically completed.

[0091] (5) After the system has been running for a period of time and stabilized, the high-nitrogen sewage is introduced into the wetland system and is retained and treated in the multi-stage ecological filtration ring root hole wetland before being discharged. The water body is continuously monitored for 6 months, and the data are as follows: Figure 5 and Figure 6 As shown in the figure, the water's total dissolved organic carbon (TOC) and nitrogen dioxide (NO) levels were significantly higher than the control. The TOC and denitrification product, NO, were 1.64 and 3.28 times higher than the control, respectively. The number of nitrifying and denitrifying bacteria increased by 85% and 140%, respectively. Ammonia nitrogen and nitrate nitrogen levels in the water were 52% and 68% lower than the control, respectively. The results were significant, with noticeable improvements in water quality.

[0092] Example 3

[0093] According to the present invention, to address the issue of nitrogen pollution in water bodies and enhance the denitrification process in a vertical flow wetland at a river bypass water purification wetland in Anhui Province, the plant-based solid-phase slow-release biochar described in the present invention is used to replenish carbon and enhance microbial activity. The specific implementation plan is as follows:

[0094] (1) Preparation of plant solid phase slow-release biochar: The aboveground plant materials of water chestnut, water chestnut, elodea, and water peanut straw were collected, and then dried and crushed into 1 cm small segments respectively. At the same time, corn cobs were collected and dried and crushed into particles with a particle size of about 1 cm. Then, the plant carbon source was obtained by mixing water chestnut: green water peanut and elodea mixture: water chestnut: corn cob in a mass ratio of 35:35:15:15, which was used as a reserve for the next step of modifying the biochar with a mixed amendment. The plant carbon source was then anaerobically fermented in a sealed container at 35-40°C in an N2 atmosphere to obtain biochar material. The mixed amendment 150g / L attapulgite and 20% slaked lime suspension were added by broadcasting. After the above-mentioned material components were mixed and aged for 24 hours, fermentation began for 3 days, and the fermentation temperature was controlled at 30°C. Then, a secondary fermentation treatment was performed, in which 20 g / L zeolite suspension and 2 mol / L H2SO4 were added for spraying. After the above-mentioned components were mixed and aged for 24 hours, fermentation was started for 5 days at a controlled fermentation temperature of 35° C. After the fermentation was completed, an activated solid-phase plant carbon source was obtained.

[0095] (2) A three-dimensional plant net was prepared using coconut shell materials. The obtained plant-based carbon source was filled into the three-dimensional plant net to a filling volume of 65%. Then, a 10g / L Ca(OH)2 and 10% Mg(OH)2 suspension was sprayed on the net. After a secondary activation treatment, the upper layer plant solid phase slow-release biochar module was obtained.

[0096] (3) Preparation of the lower layer plant solid phase slow-release biochar module: Planting of underground stems of reed and cattail with spore roots in the three-dimensional net of the upper layer plant solid phase slow-release biochar module was carried out at a rate of 8 plants / m2. The spore burial depth was 5 cm.

[0097] (4) Constructing a multi-level rhizopore wetland system with slow-release biocarbon from plant solid phase to remove nitrogen pollution from water bodies:

[0098] An inner ring filtration system and an outer ring filtration system are constructed, and the water inlet of the wetland system is located inside the inner ring filtration system. The inner ring filtration system and the outer ring filtration system are annular columns surrounded by galvanized wire mesh, and the height of the outer ring filtration system is lower than that of the inner ring filtration system.

[0099] The inner ring matrix is made of an auxiliary filler mixture consisting of clay, iron oxide and limestone. The mass ratio of clay, iron oxide and limestone is 80:2:10. Two horizontal nano-aeration tubes are set in the matrix, one above and one below. The lower nano-aeration tube is surrounded by the lower plant solid-phase slow-release biochar module, 15 to 25 cm away from the bottom, and the upper nano-aeration tube is surrounded by the plant solid-phase slow-release biochar module.

[0100] The total volume ratio of the plant solid phase slow-release biochar module in the inner ring to the inner ring matrix is 1:3.

[0101] The structure of the outer ring is the same as that of the inner ring, with the only difference being that the matrix of the outer ring is gravel, limestone and iron oxide, and the mass ratio of gravel, limestone and iron oxide is 90:5:5.

[0102] After two months, the plant roots are filled with the three-dimensional network and annular matrix, and the multi-level root hole wetland system is basically completed.

[0103] (5) After the system has been running for a period of time and stabilized, the high-nitrogen sewage is introduced into the wetland system and is retained and treated in the multi-stage ecological filtration ring root hole wetland before being discharged. The water body is continuously monitored for 6 months, and the data are as follows: Figure 7 and Figure 8 As shown in the figure, the total dissolved organic carbon (TOC) and NO in the water were significantly higher than those in the control. The TOC and denitrification product NO in the water were 1.70 and 2.70, respectively, compared to the control. The number of nitrifying bacteria and denitrifying bacteria increased by 75% and 160%, respectively. Ammonia nitrogen and nitrate nitrogen in the water were 55% and 71% lower than those in the control. The results were significant, and water quality improved significantly.

[0104] Example 4

[0105] According to the present invention, to address the issue of nitrogen pollution in water bodies and enhance the denitrification process in a vertical flow wetland at a river bypass water purification wetland in Anhui Province, the plant solid phase slow-release biochar described in the present invention is used to replenish carbon and enhance microbial activity. The specific implementation plan is as follows:

[0106] (1) Preparation of plant solid phase slow-release biochar: The above-ground plant materials of water chestnut, water chestnut and green foxtail algae straw were collected, and then dried and crushed into 1 cm small segments respectively. At the same time, corn cobs were collected and dried and crushed into particles with a particle size of about 1 cm. Then, the plant carbon source was obtained by mixing water chestnut: green foxtail algae: water chestnut: corn cob in a mass ratio of 25:35:30:10 to obtain a plant carbon source, which was used as a reserve for the modification of biochar using a mixed amendment in the next step. The plant carbon source was then anaerobically fermented in a sealed container at 30-35°C in an N2 atmosphere to obtain biochar material. The mixed amendment 160g / L diatomaceous earth and 15% slaked lime suspension were added by broadcasting. After the above-mentioned material components were mixed and aged for 24 hours, fermentation began for 3 days, and the fermentation temperature was controlled at 30°C. Then, a secondary fermentation treatment was performed, in which 10 g / L zeolite suspension and 2 mol / L H2SO4 were added for spraying. After the above-mentioned components were mixed and aged for 24 hours, fermentation was started for 5 days at a controlled fermentation temperature of 35° C. After the fermentation was completed, an activated solid-phase plant carbon source was obtained.

[0107] (2) A three-dimensional plant net was prepared using coconut shell materials. The obtained plant-based carbon source was filled into the three-dimensional plant net to a filling volume of 70%. Then, a 15g / L Ca(OH)2 and 10% Mg(OH)2 suspension was sprayed on the net. After a secondary activation treatment, the upper layer of the plant solid phase slow-release biochar module was obtained.

[0108] (3) Preparation of the lower layer plant solid phase slow-release biochar module: Planting of underground stems of reed and cattail with spore roots in the three-dimensional net of the upper layer plant solid phase slow-release biochar module was carried out at a rate of 8 plants / m2. The spore burial depth was 5 cm.

[0109] (4) Constructing a multi-level rhizopore wetland system with slow-release biocarbon from plant solid phase to remove nitrogen pollution from water bodies:

[0110] An inner ring filtration system and an outer ring filtration system are constructed, and the water inlet of the wetland system is located inside the inner ring filtration system. The inner ring filtration system and the outer ring filtration system are annular columns surrounded by galvanized wire mesh, and the height of the outer ring filtration system is lower than that of the inner ring filtration system.

[0111] The inner ring matrix is made of an auxiliary filler mixture consisting of clay, iron oxide and limestone. The mass ratio of clay, iron oxide and limestone is 80:2:10. Two horizontal nano-aeration tubes are set in the matrix, one above and one below. The lower nano-aeration tube is surrounded by the lower plant solid-phase slow-release biochar module, 15 to 25 cm away from the bottom, and the upper nano-aeration tube is surrounded by the plant solid-phase slow-release biochar module.

[0112] The total volume ratio of the plant solid phase slow-release biochar module in the inner ring to the inner ring matrix is 1:3.

[0113] The structure of the outer ring is the same as that of the inner ring, with the only difference being that the matrix of the outer ring is gravel, limestone and iron oxide, and the mass ratio of gravel, limestone and iron oxide is 90:5:5.

[0114] After two months, the plant roots are filled with the three-dimensional network and annular matrix, and the multi-level root hole wetland system is basically completed.

[0115] (5) After the system has been running for a period of time and stabilized, the high-nitrogen sewage is introduced into the wetland system and is retained and treated in the multi-stage ecological filtration ring root hole wetland before being discharged. The water body is continuously monitored for 6 months, and the data are as follows: Figure 9 and Figure 10 As shown in the figure, the total dissolved organic carbon (TOC) and NO in the water were significantly higher than those in the control. The TOC and denitrification product NO in the water were 1.70 and 2.70, respectively, compared to the control. The number of nitrifying bacteria and denitrifying bacteria increased by 85% and 180%, respectively. Ammonia nitrogen and nitrate nitrogen in the water were 65% and 77% lower than those in the control. The results were significant, and water quality improved significantly.

[0116] Example 5

[0117] According to the present invention, to address the issue of nitrogen pollution in water bodies and enhance the denitrification process in a vertical flow wetland at a river bypass water purification wetland in Anhui Province, the plant solid phase slow-release biochar described in the present invention is used to replenish carbon and enhance microbial activity. The specific implementation plan is as follows:

[0118] (1) Preparation of plant solid phase slow-release biochar: The aboveground plant materials of water chestnuts, foxtail algae, water chestnuts, and green foxtail algae straw were collected, and then dried and crushed into 1 cm small segments. At the same time, corn cobs were collected and dried and crushed into particles with a particle size of about 1 cm. Then, the plant carbon source was obtained by mixing water chestnuts: green foxtail algae: water chestnuts: corn cobs in a mass ratio of 30:30:25:15 to obtain a plant carbon source, which was used as a reserve for the next step of modifying the biochar using a mixed amendment. The plant carbon source was then anaerobically fermented in a sealed container under an N2 atmosphere at 30-35°C to obtain a biochar material. The mixed amendment 120 g / L kaolin and 10% slaked lime suspension were added by broadcasting. After the above-mentioned material components were mixed and aged for 24 hours, fermentation began for 3 days, and the fermentation temperature was controlled at 30°C. Then, a secondary fermentation treatment was performed, in which 15 g / L zeolite suspension and 2 mol / L H2SO4 were added for spraying. After the above-mentioned components were mixed and aged for 24 hours, fermentation was started for 5 days at a controlled fermentation temperature of 35° C. After the fermentation was completed, an activated solid-phase plant carbon source was obtained.

[0119] (2) A three-dimensional plant net was prepared using coconut shell materials. The obtained plant-based carbon source was filled into the three-dimensional plant net to a filling volume of 60%. Then, a 20g / L Ca(OH)2 and 12% Mg(OH)2 suspension was sprayed on the net. After a secondary activation treatment, the upper layer plant solid phase slow-release biochar module was obtained.

[0120] (3) Preparation of the lower layer plant solid phase slow-release biochar module: Planting of underground stems with spore roots of reed and cattail in the three-dimensional net of the upper layer plant solid phase slow-release biochar module at a rate of 8 plants / m2. The spore burial depth was 5 cm.

[0121] (4) Constructing a multi-level rhizopore wetland system with slow-release biocarbon from plant solid phase to remove nitrogen pollution from water bodies:

[0122] An inner ring filtration system and an outer ring filtration system are constructed, and the water inlet of the wetland system is located inside the inner ring filtration system. The inner ring filtration system and the outer ring filtration system are annular columns surrounded by galvanized wire mesh, and the height of the outer ring filtration system is lower than that of the inner ring filtration system.

[0123] The inner ring matrix is made of an auxiliary filler mixture consisting of clay, iron oxide and limestone. The mass ratio of clay, iron oxide and limestone is 80:2:10. Two horizontal nano-aeration tubes are set in the matrix, one above and one below. The lower nano-aeration tube is surrounded by the lower plant solid-phase slow-release biochar module, 15 to 25 cm away from the bottom, and the upper nano-aeration tube is surrounded by the plant solid-phase slow-release biochar module.

[0124] The total volume ratio of the plant solid phase slow-release biochar module in the inner ring to the inner ring matrix is 1:3.

[0125] The structure of the outer ring is the same as that of the inner ring, with the only difference being that the matrix of the outer ring is gravel, limestone and iron oxide, and the mass ratio of gravel, limestone and iron oxide is 90:5:5.

[0126] After two months, the plant roots are filled with the three-dimensional network and annular matrix, and the multi-level root hole wetland system is basically completed.

[0127] (5) After the system has been running for a period of time and stabilized, the high-nitrogen sewage is introduced into the wetland system and is retained and treated in the multi-stage ecological filtration ring root hole wetland before being discharged. The water body is continuously monitored for 6 months, and the data are as follows: Figure 11 and Figure 12 As shown in the figure, the total dissolved organic carbon (TOC) and NO in the water were significantly higher than those in the control. The TOC and denitrification product NO in the water were 1.81 and 3.14, respectively, compared to the control. The number of nitrifying bacteria and denitrifying bacteria increased by 85% and 120%, respectively. Ammonia nitrogen and nitrate nitrogen in the water were 40% and 70% lower than those in the control. The effect was significant, and water quality was significantly improved.

Claims

1. A plant solid phase slow-release biochar multi-level rhizopore wetland system for removing nitrogen pollution from water bodies, characterized in that: It includes an inner ring filtration system and an outer ring filtration system, and the water inlet of the wetland system is located inside the inner ring filtration system. The inner ring filtration system is an annular column surrounded by a protective net. The protective net is provided with an inner ring matrix, plant solid phase slow-release biochar and nano aeration tubes and is planted with plants. The nano aeration tubes are placed horizontally in the inner ring matrix. The plant solid phase slow-release biochar surrounds the nano aeration tubes in the form of plant solid phase slow-release biochar modules. The outer ring filtration system is an annular column surrounded by a protective net. The protective net is provided with an outer ring matrix, plant solid phase slow-release biochar and nano aeration tubes and is planted with plants. The nano aeration tubes are placed horizontally in the outer ring matrix. The plant solid phase slow-release biochar surrounds the nano aeration tubes in the form of plant solid phase slow-release biochar modules. The height of the outer ring filtration system is lower than that of the inner ring filtration system. The plant solid phase slow-release biochar is a biochar material activated by an improver, wherein the improver includes clay minerals and a heat preservation agent; The ratio of the porosity of live root pores to that of dead root pores in the multi-level root hole wetland system is 1:0.5-0.9; The inner ring filtration system or the outer ring filtration system comprises an upper layer of nano aeration tubes and a lower layer of nano aeration tubes, and the lower layer of nano aeration tubes is arranged in the middle and lower layers of the inner ring filtration system or the outer ring filtration system; The lower layer nano-aeration tube is surrounded by the lower layer plant solid phase slow-release biochar module, and the upper layer nano-aeration tube is surrounded by the upper layer plant solid phase slow-release biochar module. The upper layer plant solid phase slow-release biochar module is prepared by the following steps (0-1) to (0-3), and the lower layer plant solid phase slow-release biochar module is prepared by the following steps (0-1) to (0-2): (0-1) Aquatic plant straw and corn cobs are crushed and mixed, and then anaerobically matured in an inert gas to obtain a biochar material; the anaerobic maturation temperature is stabilized at 25-40°C; (0-2) adding an improver uniformly to the biochar material to activate it, filling it into a three-dimensional plant net, and then spreading the activation agent on the surface of the three-dimensional plant net, and air-drying and solidifying it; (0-3) Planting the underground stems of plants with spore roots into the modules obtained in step (0-2).

2. The multi-stage root hole wetland system according to claim 1, characterized in that: The total volume ratio of the plant solid phase slow-release biochar module to the inner ring matrix or the outer ring matrix is 1:

3.

3. The multi-stage root hole wetland system according to claim 1, characterized in that: The density of the plants planted in steps (0-3) is 8 to 12 plants per square meter.

4. The multi-stage root hole wetland system according to claim 1, characterized in that: The aquatic plant straws described in step (0-1) are straws of submerged plants, floating-leaf plants and emergent plants.

5. The multi-stage root hole wetland system according to claim 4, characterized in that: The submerged plant is water chestnut, the floating plant is water nymph, water peanut or green foxtail algae; the emergent plant is reed or water grass.

6. The multi-stage root hole wetland system according to claim 4 or 5, characterized in that: The aquatic plant straw described in step (0-1) is the above-ground part of the emergent plant straw.

7. The multi-stage root hole wetland system according to claim 1, characterized in that: The temperature of the anaerobic maturation in step (0-1) is 30-35°C.

8. The multi-stage root hole wetland system according to claim 1, characterized in that: The spore burial depth of the plant in steps (0-3) is 5~10cm.

9. The multi-stage root hole wetland system according to claim 1, characterized in that: The inner ring matrix is a mixture of clay, iron oxide and limestone; the outer ring matrix is a mixture of gravel, limestone and iron oxide.

10. The multi-stage root hole wetland system according to claim 9, characterized in that: The mass ratio of the clay, iron oxide and limestone is 80-90:2-5:5-10; the mass ratio of the gravel, limestone and iron oxide is 85-90:2-5:5-15.

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