Multi-layer composite filler for nitrogen conversion as well as preparation method and application of multi-layer composite filler

Abstract

The invention belongs to the field of environmental material preparation, and discloses a multi-layer composite filler for nitrogen conversion and a preparation method and application thereof. The composite filler comprises an inner core layer, a middle layer and an outer layer which are sequentially connected from inside to outside, the inner core layer contains a mixture formed by denitrifying bacteria, agricultural and forestry waste biomass and soil; the middle layer is a biological membrane loaded with nitrifying bacteria and wraps the inner core layer; the outer layer is a zeolite layer and wraps the middle layer. The multi-layer composite filler can efficiently remove dissolvable nitrogen which is not completely converted due to rainfall in agricultural non-point source treatment, the adsorption effect is rapid and stable, and desorption is not prone to occurring.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of environmental material preparation, and particularly relates to a multi-layer composite filler for nitrogen conversion and a preparation method and application thereof. BACKGROUND

[0002] Nitrogen and phosphorus in farmland soil can enter rivers and lakes with surface runoff under rainfall scouring, leading to water eutrophication, which is a typical agricultural non-point source pollutant. Interception and removal of the nitrogen and phosphorus from the runoff before entering the river can effectively prevent and control the pollution of downstream water bodies. Ammonia nitrogen and other dissolved nitrogen are the main forms of nitrogen in farmland, especially in paddy fields. Zeolite is a silicate mineral with a special crystal structure, which has a large number of pores and a large specific surface area, and has a strong adsorption performance for ammonia nitrogen. Existing treatment technologies usually select zeolite as the filler of drainage ditches or retention ponds to retain ammonia nitrogen in the ditches or ponds by using its adsorption function, and then the ammonia nitrogen is consumed by nitrification and denitrification. However, the nitrification rate is fast and the denitrification rate is slow, which leads to the release of the adsorbed nitrogen in the form of nitrate nitrogen into the water. In areas with frequent rainfall, such as southern China, the dissolved nitrogen in the ditches cannot be effectively consumed during the interval between two rainfall events, and will become a secondary output source. The lack of carbon source and anoxic environment are the two limiting factors of denitrification in farmland ditches and other water bodies. SUMMARY

[0003] The primary purpose of the present application is to overcome the deficiencies in the prior art and provide a multi-layer composite filler for nitrogen conversion.

[0004] Another purpose of the present application is to provide a preparation method of the multi-layer composite filler for nitrogen conversion.

[0005] Still another purpose of the present application is to provide an application of the multi-layer composite filler for nitrogen conversion.

[0006] The present application is achieved by the following technical solutions:

[0007] A multi-layer composite filler for nitrogen conversion, which comprises an inner core layer, an intermediate layer and an outer layer connected in sequence from inside to outside. The inner core layer contains a mixture of denitrifying bacteria, agricultural and forestry waste biomass and soil. The intermediate layer is a biofilm loaded with nitrifying bacteria, which wraps the inner core layer. The outer layer is a zeolite layer, which wraps the intermediate layer.

[0008] The denitrifying bacteria are preferably derived from activated sludge.

[0009] The agricultural and forestry waste biomass is preferably straw, and more preferably rice straw.

[0010] The soil is preferably red soil.

[0011] The inner core layer is limited by oxygen diffusion and affected by the release of dissolved organic matter degradation, and the layer can maintain anaerobic state.

[0012] The carrier of the biofilm is a soft sheet medium; preferably at least one of woven cloth, non-woven fabric and polyurethane sponge.

[0013] The nitrifying bacteria are derived from activated sludge.

[0014] The zeolite is preferably a modified zeolite; more preferably a soluble sodium salt modified zeolite.

[0015] The soluble sodium salt is preferably sodium chloride.

[0016] The outer layer can adsorb ammonia nitrogen, which is converted to nitrate nitrogen by nitrifying bacteria in the middle layer, which diffuses to the inner layer and can rapidly denitrify under the action of sufficient carbon source provided by the agricultural and forestry waste biomass.

[0017] The shape of the multi-layer composite filler for nitrogen conversion is preferably spherical or elliptical.

[0018] The multi-layer composite filler for nitrogen conversion not only has ammonia nitrogen adsorption and interception capacity, but also has denitrification and nitrogen removal capacity. When it is arranged in an ecological ditch, it can greatly improve the capacity of the ditch to absorb dissolved nitrogen.

[0019] The preparation method of the multi-layer composite filler for nitrogen conversion comprises the following steps:

[0020] (1) modifying the zeolite in a soluble sodium salt solution to obtain a modified zeolite;

[0021] (2) incubating the carrier in a solution containing nitrifying bacteria until the nitrifying bacteria are loaded on the carrier to obtain a biofilm loaded with nitrifying bacteria;

[0022] (3) drying and crushing the agricultural and forestry waste biomass to obtain biomass powder; grinding the soil to obtain soil powder; mixing the biomass powder, soil powder and water to obtain a slurry-like state, then adding denitrifying bacteria or activated sludge containing denitrifying bacteria, and carrying out anaerobic culture to obtain a fermented mud sample;

[0023] (4) placing the fermented mud sample in a container with holes, coating the biofilm loaded with nitrifying bacteria obtained in step (2) to obtain a two-layer structure product; finally, wrapping the two-layer structure product with the modified zeolite obtained in step (1) to obtain a multi-layer composite filler for nitrogen conversion.

[0024] The zeolite in step (1) is a natural zeolite, and the particle size is preferably 0.5-1 mm.

[0025] The soluble sodium salt in step (1) is preferably sodium chloride.

[0026] The concentration of the soluble sodium salt solution in step (1) is preferably 0.5-1 mol / L; more preferably 0.8 mol / L.

[0027] The ratio of the zeolite to the soluble sodium salt solution in step (1) is preferably 1 g: 8-12 mL; more preferably 1 g: 10 mL.

[0028] The modification in step (1) is preferably carried out as follows: the soluble sodium salt solution is allowed to act on the zeolite in a non-stationary state.

[0029] The non-stationary state is preferably achieved by stirring the soluble sodium salt solution, or by allowing the soluble sodium salt solution to flow.

[0030] The time for the modification in step (1) is preferably 5-10 h; more preferably 8 h.

[0031] The carrier in step (2) is a soft sheet medium; preferably at least one of woven cloth, non-woven cloth and polyurethane sponge.

[0032] The nitrifying bacteria in step (2) are preferably derived from activated sludge.

[0033] The solution containing nitrifying bacteria in step (2) is obtained by inoculating activated sludge or nitrifying bacteria into an ammonia nitrogen solution.

[0034] The concentration of ammonia nitrogen in the ammonia nitrogen solution is preferably 10-20 mg / L; more preferably 15 mg / L.

[0035] The composition of the ammonia nitrogen solution is preferably as follows: ammonium chloride 0.0573 g / L, sodium bicarbonate 0.1146 g / L, 0.3125 mL of mineral salt medium solution / L, 0.0625 mL of trace elements / L and 14 mL of 1x PBS solution / L.

[0036] The composition of the mineral salt medium solution is as follows: per liter contains calcium chloride 2H20 0.65 g, magnesium chloride 6H20 0.65 g, sodium chloride 4.6 g, sodium sulfate 2.3 g, potassium dihydrogen phosphate 2.8 g, potassium chloride 1.6 g.

[0037] The trace element solution contains per liter ferrous sulfate 7H20 172 mg, zinc chloride 20 mg, manganese chloride 4H20 47 mg, boric acid 6 mg, copper sulfate 1H20 3 mg, sodium molybdate 2H20 2 mg, sodium chloride 584 mg, potassium chloride 746 mg, magnesium sulfate 7H20 2465 mg, calcium chloride 2H20 1470 mg.

[0038] The incubation in step (2) is carried out at room temperature.

[0039] The room temperature is 20-35 DEG C.

[0040] The agricultural and forestry waste in step (3) is preferably straw; more preferably rice straw.

[0041] The biomass powder and the soil powder in step (3) are preferably mixed at a mass ratio of 1:1.

[0042] The water in step (3) is used in an amount such that the biomass powder and the soil powder form a mud-like state.

[0043] The temperature of the anaerobic culture in step (3) is preferably 30±2 DEG C.

[0044] The perforated container in step (4) is preferably a perforated plastic hollow sphere, preferably having the following structure: the pore size is 1-2 mm, the number of pores is not less than 6, the pores are uniformly distributed on the surface of the sphere, one open-ended hard plastic tube is inserted into each pore, the tube diameter is 1-2 mm, the thickness is 0.5-1 mm, and the length is determined according to the ability to enter the interior of the fermentation mud.

[0045] The modified zeolite obtained in step (1) is wrapped around the two-layer structure product in step (4), which is preferably achieved by the following steps: placing the modified zeolite and the two-layer structure product in a net, fixing the positions of the modified zeolite and the two-layer structure product by the net, and wrapping the modified zeolite around the two-layer structure product.

[0046] The above multi-layer composite filler for nitrogen conversion is used in the prevention and control of agricultural non-point source pollution, preferably comprising the following steps: placing the above multi-layer composite filler for nitrogen conversion in an environment where agricultural runoff passes through or reaches, to remove ammonia nitrogen and nitrate nitrogen, thereby improving the conversion rate of dissolved nitrogen in the field runoff.

[0047] The environment is preferably a ditch or a pond.

[0048] The present application has the following advantages and effects relative to the prior art:

[0049] (1) The present application provides a kind of multilayer composite filler for nitrogen conversion.The outermost layer of the multilayer composite filler is zeolite layer, and the ammonia nitrogen adsorption removal rate of the modified zeolite layer can reach more than 90%, which is much higher than that of the original zeolite without strengthening;The middle layer is a biofilm loaded with nitrifying bacteria, so that the ammonia nitrogen adsorbed by the modified zeolite layer can be quickly converted into nitrate nitrogen;The inner core is an anaerobic denitrification system constructed by agricultural and forestry waste biomass, soil and denitrifying bacteria, and the nitrate nitrogen can be quickly denitrified after entering the inner core, and the agricultural and forestry waste biomass can continuously supply carbon source to ensure the activity of denitrifying bacteria, thereby improving the conversion rate of dissolved nitrogen.

[0050] (2) In the prior art, due to the surface runoff of farmland, there is no anaerobic denitrification environment.The multilayer composite filler provided by the present application ingeniously constructs an anaerobic denitrification environment, integrates ammonia nitrogen enrichment, nitrification and denitrification, and improves the conversion rate of dissolved nitrogen. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 is the ammonia nitrogen adsorption change graph of zeolite under different dynamic modification times.

[0052] Figure 2 is the ammonia nitrogen removal rate change graph of two kinds of fabrics respectively domesticated.

[0053] Figure 3 is the structure device schematic diagram of the multilayer composite filler of the present application; wherein, 1 is zeolite layer, 2 is fabric layer, and 3 is inner core layer.

[0054] Figure 4 is the total nitrogen concentration removal change graph of different materials in simulated detention pond filter.

[0055] Figure 5 is the actual application schematic diagram of the present application in farmland; wherein, 4 is foam board, 5 is multilayer composite filler, and 6 is net. DETAILED DESCRIPTION

[0056] The present application will be further described in detail below in conjunction with examples and drawings, but the embodiments of the present application are not limited thereto.

[0057] Rice straw can be obtained from the field, and after being dried in an oven at 105℃ for 2h, it is crushed to a size of 50 mesh and used.

[0058] Red soil can be obtained from forest or river bank, and after being dried and ground to 50 mesh, it is used.

[0059] Fabric, any fabric with adhesion effect on the surface can be selected.

[0060] The simulated domestic wastewater, the phosphorus and ammonia nitrogen solution with certain pH buffering capacity, can be prepared by using ammonium chloride, sodium bicarbonate, potassium dihydrogen phosphate, or can use wastewater with corresponding elements. The specific composition of the simulated domestic wastewater used in this embodiment is as follows: ammonium chloride 0.0573 g / L, sodium bicarbonate 0.1146 g / L, 0.3125 mL of mineral salt medium solution / L, 0.0625 mL of trace elements / L, and 14 mL of 1x PBS solution / L.

[0061] The composition of the mineral salt medium solution is as follows: 0.65 g of calcium chloride dihydrate, 0.65 g of magnesium chloride hexahydrate, 4.6 g of sodium chloride, 2.3 g of sodium sulfate, 2.8 g of potassium phosphate dibasic, and 1.6 g of potassium chloride per liter.

[0062] The trace element solution contains 172 mg of ferrous sulfate heptahydrate, 20 mg of zinc chloride, 47 mg of manganese chloride tetrahydrate, 6 mg of boric acid, 3 mg of copper sulfate dihydrate, 2 mg of sodium molybdate dihydrate, 584 mg of sodium chloride, 746 mg of potassium chloride, 2465 mg of magnesium sulfate heptahydrate, and 1470 mg of calcium chloride dihydrate per liter.

[0063] The total nitrogen is determined by alkaline potassium persulfate digestion ultraviolet spectrophotometry (HJ 636-2012), and the ammonia nitrogen is determined by Nessler's reagent spectrophotometry (HJ 535-2009).

[0064] Example 1 Construction of dynamic modification device

[0065] (1) Construction of device: a plastic measuring cylinder with a height of about 35 cm is selected, a 10 L water bucket is used to modify the sodium chloride solution with a concentration of 0.8 mol / L, and the measuring cylinder is used to modify the natural zeolite with a particle size of 0.5-1 cm; wherein the liquid-solid ratio of the sodium chloride solution and the zeolite is 10 mL:1 g.

[0066] The measuring cylinder is provided with a lower water inlet and an upper water outlet at positions 4 cm and 30 cm from the bottom on the side, respectively, wherein the lower water inlet is used to input the sodium chloride solution with a concentration of 0.8 mol / L into the measuring cylinder through a peristaltic pump, and the upper water outlet is used to output the sodium chloride solution to the water bucket for recycling; a large-particle-size gravel is laid as a supporting layer at the bottom of the measuring cylinder, with a height of 5 cm, and the upper part is the zeolite to be modified.

[0067] (2) Monitoring of dynamic modification device: during operation, the flow rate is controlled by the peristaltic pump to be 1.25, 2.5, 5, and 10 L / h, respectively, and the operation is 8 h; when the sodium chloride solution appears large-area turbidity, the solution and the zeolite in the measuring cylinder can be replaced to ensure that the zeolite has sufficient sodium chloride solution input. Repeat multiple batches to obtain enough dynamic modified zeolite.

[0068] Meanwhile, the natural zeolite is placed in a sodium chloride solution with a concentration of 0.8 mol / L, a solid-liquid ratio of 1 g:10 mL, and is shaken in a shaking bed at 150 r / min for 8 h to obtain the shaking modified zeolite.

[0069] The adsorption performance of the modified zeolite and the dynamic modified zeolite on ammonia nitrogen in water is determined by static adsorption experiments. 200 mL conical bottles are used as adsorption devices, and simulated domestic wastewater with an ammonia nitrogen concentration of 15 mg / L is prepared according to the field rainfall interception. The shaking modified zeolite and the dynamic modified zeolite are respectively tested for their adsorption and removal performance, wherein the modified zeolite and the simulated domestic wastewater are mixed at a mass ratio of 1:5, and the residual ammonia nitrogen in the solution is determined after oscillation at a constant temperature of 25°C and a speed of 150 r / min for 2 h. The ammonia nitrogen is determined by the Nash reagent colorimetric method. The experimental results are shown in Table 1. Figure 1 As shown in Table 1, the removal amount of ammonia nitrogen by the shaking modified zeolite is 11.75±0.65 mg / L, and the removal amount of ammonia nitrogen by the dynamic modified zeolite (obtained by a flow rate of 5 L / h) is 13.36±1.24 mg / L, which indicates that the adsorption and removal rate of ammonia nitrogen by the dynamic modified zeolite is increased by more than 15% in a short time (30 min).

[0070] (3) Collection of the modified zeolite: after the dynamic modification system is stopped, the zeolite in the graduated cylinder is taken out, which is the modified zeolite with improved adsorption performance. The modified zeolite is placed in a tray lined with tin paper and dried in an oven at 100°C for 2 h before being stored.

[0071] (4) Preparation of simulated domestic wastewater: 4.5 L of simulated domestic wastewater with an ammonia nitrogen concentration of 15 mg / L is prepared for testing the biofilm formation of the non-woven fabric and the polyurethane sponge. Sodium bicarbonate in the simulated domestic wastewater is used to buffer the abnormal pH of the solution to affect the activity of nitrifying bacteria, and potassium dihydrogen phosphate is used to provide trace elements required for the normal growth of nitrifying bacteria.

[0072] (5) Prepare a 5L plastic measuring cylinder, pour 1L of activated sludge containing nitrifying bacteria (activated sludge taken from the aerobic tank of the Foshan Shunde Sewage Treatment Plant) into it, cultivate the nitrifying bacteria by acclimation, the specific steps are as follows: pour 4.5L of simulated domestic wastewater into it and add an aeration pump, cut the non-woven fabric and polyurethane sponge to the appropriate length, then fix them with chopsticks and put them into the solution for normal temperature acclimation, and take samples every 1h (measure pH and dissolved oxygen at the same time), and measure the ammonia nitrogen concentration at regular intervals; after the ammonia nitrogen concentration of the solution decreases to 0, record the time point t, pour out the supernatant, add newly configured simulated domestic wastewater, continue to detect the ammonia nitrogen concentration at regular intervals, repeat for 20 batches, then remove the sludge. Then only put in non-woven fabric and polyurethane sponge, continue to add newly configured simulated domestic wastewater, take samples at time point t to measure ammonia nitrogen concentration, when the solution ammonia nitrogen concentration can be continuously removed for at least 80% in multiple batches, at this time the non-woven fabric and polyurethane sponge are inoculated, take out for standby, at this time the biofilm formation process is completed, the test results of the treatment process are shown in Figure 2 .

[0073] Figure 2 The 1st-11th and 16th batches in Table 1 are samples taken after 4h of treatment, and the 12th-15th batches are samples taken after 3h of treatment. It can be seen that the ammonia nitrogen removal rate can be stabilized at more than 80% after 4h of treatment, and both non-woven fabric and polyurethane sponge as carriers can load nitrifying bacteria.

[0074] (6) Mix rice straw powder and red soil at a mass ratio of 1:1, add water to mix evenly to form a slurry state, add 1mL of activated sludge (activated sludge taken from the sewage ditch in Shantou, Guangdong) to 20g of the mixture of straw and red soil, cultivate denitrifying bacteria by acclimation, i.e. anaerobic culture at 30℃ in the dark for 54 days.

[0075] (7) The fermented material obtained in step (6) is made into a mud ball with a diameter of about 3cm, 10g of the mud ball is placed in a transparent plastic spherical shell, 8 holes with a diameter of 1.5mm are evenly drilled on the shell, small plastic tubes with a tube diameter of 1mm and a length of 1.5cm are inserted into each hole, the non-woven fabric for nitrifying bacteria biofilm formation is wrapped around the transparent plastic spherical shell to obtain a two-layer structure small ball. 67.5g of modified zeolite obtained in step (3) is wrapped with a cut nylon filter screen and fixed with a ribbon, so that the modified zeolite wraps the two-layer structure small ball to obtain a multi-layer composite filler for nitrogen conversion, the structure of which is shown in Figure 3 , from outside to inside, it is zeolite layer 1, fabric layer 2 and inner core layer 3.

[0076] In actual operation, the multi-layer composite filler for nitrogen conversion is hung below the ditch runoff liquid surface with wear-resistant high molecular braided rope.

[0077] Example 2 titration device in simulated detention pond filter

[0078] Prepare 2L measuring cylinder, respectively, into 20 multi-layer composite filler (of which the modified zeolite is a dynamic modified zeolite obtained by a flow rate of 5L / h) and only dynamic modified zeolite filler (control group) to form a conversion pile (the amount of zeolite in the composite filler group and the control group is consistent), through the titrator to control 15mg / L of ammonia nitrogen solution (i.e. simulate domestic wastewater) to 250mL / h rate of uninterrupted drop into the measuring cylinder, when the solution from the measuring cylinder overflow, continue to drop the simulated domestic wastewater and start every 8h sampling monitoring of each nitrogen index. This experiment is carried out in a water bath at 25℃.

[0079] The results are shown in Figure 4 As shown, at 32h, the total nitrogen removal amount of the filler group is 9.81±0.20mg / L, and the total nitrogen removal amount of the control group is 5.43±0.11mg / L, the total nitrogen removal rate of the filler group has reached more than 65%, far exceeding the 35% of the control group.

[0080] Example 3 Practical application of multi-layer composite filler in farmland

[0081] Figure 5 For the practical application of the present application in farmland, a foam board 4 slightly smaller than the ditch is placed in the ditch, both ends are connected with hooks fixed on both sides of the ditch with small ropes that can be stretched enough, and a net 6 is tied on the small rope, and a plurality of multi-layer composite fillers 5 are placed in it. When the amount of drainage is small, the foam board 4 will press under the ditch to make the multi-layer composite fillers 5 in the net 6 accumulate, so as to fully adsorb and convert the dissolved nitrogen in the drainage, when the rainfall is large, the foam board 4 will rise due to the water level and increase the gap between the multi-layer composite fillers 5 in the net 6, so as to not only adsorb and convert the dissolved nitrogen, but also reduce the water flow blockage caused by accumulation.

[0082] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited by the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application are equivalent replacement methods, which are all included in the protection scope of the present application.

Claims

1. A multilayer composite packing material for nitrogen conversion, characterized in that: The multi-layer composite packing material for nitrogen conversion consists of an inner core layer, a middle layer, and an outer layer connected sequentially from the inside out. The inner core layer contains a mixture of denitrifying bacteria, agricultural and forestry waste biomass, and soil. The middle layer is a biofilm loaded with nitrifying bacteria, which wraps around the inner core layer. The outer layer is a zeolite layer, which wraps around the middle layer.

2. The multilayer composite packing material for nitrogen conversion according to claim 1, characterized in that: The denitrifying bacteria mentioned above are derived from activated sludge; The aforementioned agricultural and forestry waste biomass is straw; The soil in question is red soil; The carrier of the biofilm is at least one of woven fabric, nonwoven fabric and polyurethane foam; The nitrifying bacteria mentioned above are derived from activated sludge; The zeolite mentioned is a zeolite modified with soluble sodium salt.

3. The multilayer composite packing material for nitrogen conversion according to claim 2, characterized in that: The straw mentioned is rice straw; The soluble sodium salt mentioned is sodium chloride; The multilayer composite packing material used for nitrogen conversion has spherical or elliptical shapes.

4. The method for preparing the multilayer composite packing material for nitrogen conversion according to any one of claims 1 to 3, characterized in that... Includes the following steps: (1) The zeolite was modified by placing it in a soluble sodium salt solution to obtain modified zeolite; (2) The carrier is placed in a solution containing nitrifying bacteria and incubated until the nitrifying bacteria are loaded onto the carrier to obtain a biofilm loaded with nitrifying bacteria; (3) Dry and crush agricultural and forestry waste biomass to obtain biomass powder; grind soil to obtain soil powder; mix biomass powder, soil powder and water to obtain mud-like state, add denitrifying bacteria or activated sludge containing denitrifying bacteria, carry out anaerobic culture, and obtain fermented mud sample. (4) Selectively place the fermented mud sample inside a perforated container and cover it with the biofilm of nitrifying bacteria obtained in step (2) to obtain a two-layer structure product; finally, wrap the two-layer structure product with the modified zeolite obtained in step (1) to obtain a multi-layer composite filler for nitrogen conversion.

5. The method for preparing the multilayer composite packing material for nitrogen conversion according to claim 4, characterized in that: The zeolite mentioned in step (1) is natural zeolite; The soluble sodium salt mentioned in step (1) is sodium chloride; The carrier mentioned in step (2) is a soft sheet-like medium; The nitrifying bacteria mentioned in step (2) are derived from activated sludge; The nitrifying bacteria solution mentioned in step (2) is obtained by inoculating activated sludge or nitrifying bacteria into an ammonia nitrogen solution; The agricultural and forestry waste mentioned in step (3) is straw; The perforated container mentioned in step (4) is a perforated hollow plastic sphere.

6. The method for preparing the multilayer composite packing material for nitrogen conversion according to claim 5, characterized in that: The particle size of the zeolite mentioned in step (1) is 0.5 to 1 mm; The concentration of the soluble sodium salt solution mentioned in step (1) is 0.5–1 mol / L; The zeolite and the soluble sodium salt solution mentioned in step (1) are mixed in a ratio of 1 g: 8-12 mL; The carrier mentioned in step (2) is at least one of woven fabric, nonwoven fabric and polyurethane foam; The concentration of ammonia nitrogen in the ammonia nitrogen solution is 10–20 mg / L; The straw mentioned is rice straw; The biomass powder and the soil powder mentioned in step (3) are mixed in a mass ratio of 1:1; The amount of water used in step (3) is such that the biomass powder and soil powder form a mud-like state; The perforated hollow plastic sphere has the following structure: the pore diameter is 1-2 mm, the number of pores is not less than 6, and they are evenly distributed on the surface of the sphere. A hard plastic tube with a diameter of 1-2 mm and a thickness of 0.5 mm-1 mm is inserted into each pore, and the length of the tube depends on whether it can enter the interior of the fermented mud sample.

7. The method for preparing the multilayer composite packing material for nitrogen conversion according to claim 4, characterized in that: The specific steps of the modification described in step (1) are as follows: the soluble sodium salt solution reacts with the zeolite in a non-static state; The anaerobic culture temperature described in step (3) is 30±2 ℃; The modification of the zeolite obtained in step (1) to encapsulate the two-layer structure product in step (4) is achieved by the following steps: placing the modification of the zeolite and the two-layer structure product in a net, fixing the positions of the modification of the zeolite and the two-layer structure product in the net, and encapsulating the two-layer structure product with the modification of the zeolite.

8. The method for preparing the multilayer composite packing material for nitrogen conversion according to claim 7, characterized in that: The non-static state is achieved by stirring the soluble sodium salt solution or by making the soluble sodium salt solution flow. The modification time described in step (1) is 5 to 10 hours.

9. The application of the multilayer composite packing material for nitrogen conversion as described in any one of claims 1 to 3 in the prevention and control of agricultural non-point source pollution.

10. The application according to claim 9, characterized in that... The method includes the following steps: placing the multilayer composite packing material for nitrogen conversion as described in any one of claims 1 to 3 in the environment through which farmland runoff passes or reaches, to remove ammonia nitrogen and nitrate nitrogen, thereby increasing the conversion rate of dissolved nitrogen in field runoff.

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