Method for preparing waste-based biochar co-pyrolysis ceramsite and application thereof

Abstract

The application belongs to the field of adsorbing materials, and relates to a preparation method and application of waste-based biochar co-pyrolysis ceramsite, including preparation of magnesium modified peanut shell and preparation of waste-based biochar co-pyrolysis ceramsite. The application applies waste to the preparation of ceramsite, and prepares ceramsite products with large porosity, high consolidation, good durability and outstanding blocking effect through process improvement and addition of key components.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of adsorption materials, and relates to a preparation method of waste-based biochar co-pyrolysis ceramsite and application thereof. BACKGROUND

[0002] Nitrogen and phosphorus are the most important limiting factors for the growth of plants and crops. At the same time, a large amount of nitrogen and phosphorus-containing wastewater is generated from point source and non-point source pollution such as agricultural fertilization, industrial production, livestock and poultry breeding, and residents' life, part of which is directly or indirectly discharged into rivers, lakes, reservoirs and seawater without treatment, which is an important growth limiting factor for algae in rivers and lakes and an important inducement for water eutrophication, and can further cause ecological disasters such as water bloom and blue-green algae outbreak. A typical case is the blue-green algae event in Taihu Lake in 2007. Therefore, the water quality standards of ammonia nitrogen, total nitrogen and total phosphorus are set as 2.0, 2.0 and 0.4 mg / L (V class water) respectively in the Surface Water Environmental Quality Standard of China to control the input of nitrogen and phosphorus nutrients in surface water bodies. Therefore, controlling nitrogen and phosphorus in water has important practical significance for controlling water environment, controlling water eutrophication and water ecological system health.

[0003] Resource utilization of agricultural waste is an important task of ecological civilization construction in China, and the traditional resource utilization methods such as natural decomposition and incineration will produce greenhouse gas emissions and water and soil environmental pollution. Therefore, reasonable and efficient resource utilization of agricultural waste has important practical significance for energy saving and emission reduction and environmental pollution control.

[0004] Coal gangue is a common solid waste screened in the process of coal mining and washing, mainly including aluminum oxide, silicon oxide and carbon, and has a certain combustion value. The annual emission amount in China is huge, accounting for about 10% of the total amount of coal according to statistics. The production of coal gangue can cause a large number of accompanying environmental problems, such as large occupation of land resources, health hazards caused by dust, leakage or leaching of harmful substances, etc. Therefore, effective utilization of coal gangue also has important significance for resource efficient and reasonable utilization.

[0005] At present, the interception fillers for pollutants in water bodies mainly include zeolite, aerated concrete and volcanic rock, which mainly rely on their rich pore structure and adsorption sites to realize physical or chemical adsorption of nitrogen and phosphorus. However, the interception effect of the above-mentioned interception fillers is general, and the main reasons are that the surface pore structure of the above-mentioned fillers is not outstanding, and another important reason is that there are fewer adsorption sites combined with pollutants.

[0006] Ceramsite is one of the environmental protection materials that is developing rapidly in China at present, which has the characteristics of small volume, rich pore size and high adsorption efficiency. The ceramsite material in the field of water treatment is mainly formed by crushing, balling, drying and high-temperature calcination of some industrial waste (slag, fly ash and mineral materials), which plays an important role in intercepting pollutants in water pollution treatment. SUMMARY

[0007] The purpose of the present application is to provide a preparation method of waste-based biochar co-pyrolysis ceramsite and its application. The waste is applied to the preparation of ceramsite, and through process improvement and the addition of key components, a ceramsite product with high porosity, high consolidation, good durability and outstanding blocking effect is prepared.

[0008] The first aspect of the present application is to provide a preparation method of waste-based biochar co-pyrolysis ceramsite, which comprises the following steps:

[0009] Preparation of magnesium modified peanut shell: the crushed peanut shell is sprayed with magnesium salt solution for modification, and then treated with KOH solution to obtain magnesium modified peanut shell;

[0010] Preparation of waste-based biochar co-pyrolysis ceramsite: magnesium modified peanut shell, potassium bicarbonate and water are mixed, and bauxite and coal gangue are added for granulation and balling. After balling, aging is performed, and preheating is performed at 300-400℃ for 0.5-1.5h. After preheating, calcination is continuously performed at 500-700℃ for 0.5-1.5h, and then cooling is performed to form waste-based biochar co-pyrolysis ceramsite;

[0011] The mass ratio of magnesium modified peanut shell, bauxite, coal gangue, potassium bicarbonate and water is 0.1:(0.5-1.5):(1.5-2.5):(0.04-0.06):(0.3-0.4);

[0012] The total molar ratio of magnesium ions in the magnesium salt solution and hydroxide ions in the KOH solution is 1:(2.3-2.7).

[0013] In a preferred embodiment, in the preparation process of magnesium modified peanut shell, the crushed peanut shell is sieved, and 0.2-1.5mol / L magnesium salt solution is sprayed on the peanut shell to uniformly wet the surface of the peanut shell. After standing for 18-28h (preferably 24h), 1-2mol / L KOH solution is uniformly sprayed on the peanut shell, and then stirred and mixed uniformly.

[0014] Further, the total molar ratio of magnesium ions in the magnesium salt solution and hydroxide ions in the KOH solution is 1:2.5; and the magnesium salt is MgCl2.

[0015] In a preferred embodiment, the nanoscale magnesium oxide MgO is formed by magnesium modification and pyrolysis of the swelling in the pores of the peanut shell.

[0016] In a preferred embodiment, when preheated, the decomposition of potassium bicarbonate generates a large amount of CO2 to form a pore structure, and the magnesium modified peanut shell begins to gradually pyrolyze to form biochar; when calcined, the coal gangue pyrolysis forms a pore structure, the bauxite recrystallizes to form a hard skeleton, the peanut shell pyrolysis forms a biochar with abundant pore sizes, and the Mg(OH)2 formed by coprecipitation pyrolyzes to form abundant MgO binding sites.

[0017] Further, the ball diameter is 2-3 cm; the ball forming time is 20-40 min. The specific surface area is >5.0 m 2 / g, and the porosity is >53%.

[0018] The second aspect of the present application is to disclose the waste-based biochar copyrolysis ceramsite prepared by the preparation method.

[0019] The third aspect of the present application is to provide an interception dam filled with the waste-based biochar copyrolysis ceramsite.

[0020] Further, the interception dam is used for intercepting or adsorbing nitrogen and phosphorus in farmland return water during the fertilization period and / or the rainstorm period.

[0021] The fourth aspect of the present application is to disclose the application of the preparation method or the waste-based biochar copyrolysis ceramsite in intercepting or adsorbing nitrogen and phosphorus in farmland return water.

[0022] Compared with the prior art, the present application has the following obvious advantages:

[0023] The biochar copyrolysis ceramsite production process of the present application is simple and convenient, and the reagents such as MgCl2 and KOH are low in price. Preferably, KOH and MgCl2 are used as the sprayed reagents. Compared with alkaline reagents such as NaOH, the purpose of selecting KOH is mainly that the residual K can promote the growth of crops as a main essential element for crops; compared with Mg(NO3)2, the main purpose of selecting MgCl2 is that it has a significant price advantage, and on the other hand, the residual metal chloride is more prone to decomposition than oxides and sulfides.

[0024] More importantly, the spraying and wetting process can effectively save the use of chemical reagents, reduce the waste of reagents caused by solution impregnation or solution coprecipitation, and reduce the environmental problems and manufacturing costs caused by reagent treatment.

[0025] According to the spraying ratio of 1:2.5, Mg 2+ and OH -The reaction is not complete, and therefore, a sufficient amount of OH 2+ The reaction is not complete, and therefore, a sufficient amount of OH - The reaction is not complete, and therefore, a sufficient amount of OH

[0026] The metal load, agricultural waste material and its additive amount of the product are determined through a large number of experiments. After analyzing different metal loads (Mg, Fe, Ca, La) and agricultural wastes such as wheat straw, rice straw, peanut shells, corn cobs, yellow canna, water hyacinth, poplar sawdust and coffee grounds, and through cross-validation analysis, it is found that peanut shells loaded with Mg can achieve the maximum nitrogen and phosphorus adsorption capacity. The peanut shells buried in the ground have the characteristics of loose and breathable, rich in pore size, and have the interconnected pore structure that other biological wastes cannot have. Through the modification of Mg, the Mg oxide components formed in the pore channel during the pyrolysis process can also be proved to form a nano-level MgO structure through the swelling effect, thereby expanding the original pore channel of the peanut shells (i.e. MgO formed by pyrolysis of Mg(OH)2 and water vapor can expand the channel of biochar and promote the cross-linking structure of the pore channel). Mg oxide is an important adsorption site in the water environment, which can adsorb pollutants such as nitrate nitrogen and phosphate. After preheating and high-temperature pyrolysis, the network structure formed by peanut shell biochar, MgO, coal gangue and potassium bicarbonate has higher nitrogen and phosphorus binding capacity than traditional ceramsite.

[0027] China has abundant bauxite resources, with outstanding price advantage, in addition, Al2O3 in bauxite can form crystalline components under high temperature conditions, which can improve the compressive strength and durability of ceramsite, provide the basic rigid characteristics of ceramsite, and avoid the material from being washed away in water. Coal gangue has a certain combustion value, with a carbon content of about 14.07%, which can effectively save energy and realize efficient utilization of coal mining waste. The organic matter component after combustion can form a cross-linked pore structure, which can also increase the pollutant interception capacity of ceramsite, and the calcium-silicon-aluminum-magnesium structure in coal gangue can become an effective structure for building the skeleton of ceramsite. The combination of bauxite and coal gangue can increase the hardness of ceramsite, and the modified peanut shell and coal gangue can increase the pore structure of ceramsite. The ratio of bauxite, coal gangue and modified peanut shell should be controlled. Too high content of coal gangue may lead to difficulty in meeting the standard of ceramsite hardness, too low content may not be enough for porosity, and too high content of bauxite may lead to high cost, and too high content of modified peanut shell may also lead to high cost, and too low content may not be enough for porosity.

[0028] Potassium bicarbonate as a foaming agent, a large amount of CO2 and H2O(gas) is generated in the preheating stage, which can effectively produce pore structure, thereby improving the specific surface area of ceramsite. The preheating process is 300-400 DEG C preheating for 0.5-1.5 h, which can promote the decomposition of potassium bicarbonate to form CO2 and H2O(gas), and the formation process and release of CO2 and water vapor can promote the formation of rich pore structure, and can also help to promote the network cross-linked structure formed by the pyrolysis of coal gangue and modified biochar during calcination; too high preheating temperature will increase the preparation cost of ceramsite.

[0029] The calcination temperature of ceramsite is 500-700 DEG C, bauxite starts to decompose and recrystallize at this temperature stage to form a hard ceramsite skeleton, and biochar completes high pyrolysis to form a rich MgO structure. However, too high temperature may cause the cross-linked pore structure of biochar to collapse, but too low pyrolysis temperature may cause bauxite to be difficult to decompose and weaken its rigid characteristics.

[0030] The ceramsite of the present application has a nitrogen and phosphorus interception effect not lower than that of similar ceramsite, while the cost is only about 1 / 3-1 / 2 of that of similar products. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 Adsorption isotherm curves of ceramsite prepared by different strategies for (a) nitrate and (b) phosphate;

[0032] Figure 2 SEM electron microscope images of ceramsite 8 and ceramsite 1;

[0033] Figure 3 BET specific surface area distribution graph, A, ceramsite without magnesium loading, B, ceramsite with magnesium loading;

[0034] Figure 4 Ceramicite pore volume and specific surface area, a, b correspond to example 1, c, d correspond to example 2, e, f correspond to example 9;

[0035] Figure 5 Intercepted rate of different intercepting fillers for (a) nitrate, (b) phosphate (where 1-5 are ordinary zeolite, ordinary ceramicite, example 8, example 9, example 1 respectively). DETAILED DESCRIPTION

[0036] The application will be further described below in connection with the drawings and specific examples.

[0037] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, instruments, etc. used in the following examples can be obtained from commercial channels unless otherwise specified.

[0038] Example 1

[0039] The broken peanut shell is passed through a 60-mesh sieve, and a 0.5 mol / L MgCl2 solution is sprayed on the peanut shell at a spraying speed of 0.1 L / (h*kg) (i.e. 0.1 L of MgCl2 solution is sprayed per kg of broken peanut shell per hour), and the spraying time is 10 min. Mixing and stirring are performed at the same time using a stirring device (200 rpm). The spraying method depends on the actual preparation scene, and the surface of the peanut shell is wetted. After standing overnight, a 1.25 mol / L KOH solution is uniformly sprayed according to the same steps as spraying MgCl2, and the stirring speed, spraying speed and spraying time are consistent with the steps of spraying MgCl2. The two reagents are alternately sprayed twice, and the mixer is used for stirring (200 rpm) to mix uniformly for 1-2 h. The magnesium-modified peanut shell is taken out and dried for standby use.

[0040] Preparation of waste-based biochar co-pyrolysis ceramicite:

[0041] After the different components are broken, the magnesium-modified peanut shell and potassium bicarbonate are mixed first, and then mixed with bauxite and coal gangue. The mass ratio of bauxite, coal gangue, magnesium-modified peanut shell and potassium bicarbonate is 1:2:0.1:0.05. After grinding and mixing with water (10%, which refers to the mass percentage of water in the mixture of bauxite, coal gangue, magnesium-modified peanut shell and potassium bicarbonate), a disc-type ball making machine is used to make balls with a diameter of about 2-3 cm. The ball making time is 30 min, and the standing aging time is 24 h. Then, the mixture is preheated at a preheating temperature of 350℃ for 1 h, calcined (600℃ for 1 h), and cooled to obtain the desired ceramicite 1 (PS-600-C-Mg).

[0042] Example 2:

[0043] The preparation method was similar to Example 1, except that the raw material was rice straw, and the product was noted as RS-600-C-Mg.

[0044] Example 3:

[0045] The preparation method was similar to Example 1, except that the calcination temperature was 400 degrees Celsius, and the product was noted as PS-400-C-Mg.

[0046] Example 4:

[0047] The preparation method was similar to Example 1, except that there was no spraying process with KOH, and the product was noted as PS-600-I-Mg.

[0048] Example 5:

[0049] The preparation method was similar to Example 1, except that the sprayed metal salt solution was iron chloride, and the product was noted as PS-600-C-Fe.

[0050] Example 6:

[0051] The preparation method was similar to Example 1, except that the sprayed metal salt solution was lanthanum chloride, and the product was noted as PS-600-C-La.

[0052] Example 7

[0053] The preparation method was similar to Example 1, except that the related modified Mg biochar was prepared using an impregnation method.

[0054] Example 8:

[0055] The preparation method was similar to Example 1, except that there was no surface modification process with magnesium oxide (i.e., the peanut shells were not modified with magnesium chloride and KOH), and the product was noted as Ceramsite 8.

[0056] Example 9:

[0057] The preparation method was similar to Example 1, except that there was no addition of potassium bicarbonate, and the product was noted as Ceramsite 9.

[0058] Example 10:

[0059] The preparation method was similar to Example 1, except that there was no preheating process, and the product was noted as Ceramsite 10.

[0060] By analyzing the adsorption effect of different preparation strategies of ceramsite on typical nitrate and phosphate, it can be found that the theoretical maximum adsorption capacity of ceramsite PS-600-C-Mg is 49.63 mg / g and 59.84 mg / g, respectively, which is significantly better than that of other preparation conditions (raw materials, pyrolysis temperature, modification method, and modification metal type) (Table 1 and Figure 1 ).

[0061] Table 1 Nitrogen and phosphorus removal efficiency of different ceramsite powders

[0062]

[0063]

[0064] The loading of metal Mg significantly improves the purification effect of ceramsite on total phosphorus and total nitrogen, which is mainly due to the fact that the main components (phosphate and nitrate) are in anionic form, and the MgO component formed during the sintering process can form effective adsorption sites, and the positive charge surface characteristics have very high adsorption efficiency for phosphate and nitrate.

[0065] Compared with the ceramsite prepared from rice straw, the nitrogen and phosphorus removal effect of the ceramsite prepared from peanut shells shows more prominent purification effect, which is mainly due to the fact that compared with other agricultural wastes, peanut shells have interconnected pore structure, and the sintered ceramsite has higher nitrogen and phosphorus interception capacity.

[0066] The calcination temperature can significantly affect the hardening degree of ceramsite, and the applicant found that other calcination temperatures (400℃) cannot significantly increase the nitrogen and phosphorus interception and purification capacity of ceramsite, therefore, the present application uses 600℃ as the final preferred calcination temperature.

[0067] The nitrogen and phosphorus interception capacity of ceramsite products loaded with iron chloride and lanthanum chloride is lower than that of the ceramsite prepared in the present application, the main reason is that the particles of iron / lanthanum oxides produced by the two are large, which is difficult to enter the pores of peanut shells, so as to be difficult to build a network of pore structure, thereby leading to the decrease of purification capacity.

[0068] Figure 2 From the SEM electron microscope images of the ceramsite 8 (a, b, corresponding to Example 8) without loading magnesium and the ceramsite 1 (c, d, corresponding to Example 1) sintered with magnesium loading, it can be found that the loading process of magnesium effectively increases the pore structure, and the swelling process of magnesium oxide is beneficial to the expansion process of micropores, which can increase the adsorption capacity of nitrogen and phosphorus. Figure 3 ) also further verifies the results of the swelling process of magnesium oxide, and after the loading of magnesium, the mesopore and macropore volume is further increased, which is beneficial to the interception and consumption of pollutants.

[0069] Figure 4It is illustrated that the replacement of magnesium modified peanut shell biochar with magnesium modified rice straw biochar (Example 2) or without the addition of potassium bicarbonate greatly weakens the specific surface area and pore volume of the ceramsite. In Example 1, the combined use of peanut shell and potassium bicarbonate can greatly increase the specific surface area of the ceramsite, thereby improving the ceramsite's ability to reduce pollutants. This is mainly due to the fact that potassium bicarbonate enters the loose and porous structure of the peanut shell, and during the preheating stage, potassium bicarbonate functions as a foaming agent, producing a large amount of carbon dioxide gas and water vapor, which promotes the generation of pores in the ceramsite. Therefore, in the invention, the combination of the "foaming agent" function of potassium bicarbonate in the porous structure of the peanut shell can effectively improve the pore structure of the ceramsite and achieve a synergistic effect of adsorption and interception.

[0070] Application Example 1

[0071] The market-sold ordinary zeolite (green zeolite, diameter 2-3 cm) and ordinary ceramsite (bauxite ceramsite, made of bauxite and manganese powder after crushing, ball making, and calcination with coal powder to 1100 degrees Celsius for 1 hour), as well as the co-pyrolyzed ceramsite 1 (corresponding to Example 1) prepared in Examples 8 and 9, and the biochar prepared in the invention, were placed in parallel ditches to test their interception ability for runoff nitrogen and phosphorus. The pollutant concentration levels in the farmland runoff in the ditches were: total nitrogen 1.32-9.18 mg / L, total phosphorus 0.05-0.13 mg / L, ammonia nitrogen 0.25-2.58 mg / L, and COD 5.5-42.1 mg / L. The ceramsite filler was filled at a volume of 0.03 cubic meters per mu. The pollutant content changes in the water before and after the interception dam were measured every 30 minutes or until the runoff ended. The final average interception rates are shown in Table 1, where the ceramsite of the application examples can achieve total nitrogen and total phosphorus reduction rates of 46.25±10.72% and 29.96±8.80%, which are much higher than those of other interception fillers (-2.96%-13.23% and -9.41-3.88%) (Example 1). Figure 5 Figure 5 ).

[0072] Application Example 2

[0073] Laboratory interception and purification experiment:

[0074] The experimental water was artificially configured simulated polluted water: COD 30 mg / L, total nitrogen 8 mg / L, ammonia nitrogen (NH4 + -N) 5 mg / L, and total phosphorus 1 mg / L.

[0075] ​The adsorption device test was constructed in the laboratory. 5 g of the different test fillers in Examples 1, 8-10 was added in 5 L simulated wastewater, the pH was set at 7.5±0.2 at room temperature, the content change of different pollutants in supernatant before and after adsorption was detected after stirring (10 r / min) adsorption for 24 h, and the adsorption removal rate was calculated according to the content change, and the results are shown in Table 2.

[0076] Table 2 removal capacity of different ceramsites for nitrogen and phosphorus

[0077]

[0078]

[0079] The addition of magnesium oxide and potassium bicarbonate in Examples 8 and 9 respectively led to the reduction of surface adsorption sites and pore structure, thereby causing the decline of the purification capacity for nitrogen and phosphorus. In Example 10, the preheating process led to incomplete reaction of MgO and water vapor, so that the pore crosslinking structure of the ceramsite was not perfect, thereby greatly affecting the interception effect.

[0080] Application Example 3

[0081] Actual ditch interception and purification experiment:

[0082] The interception dam filled with the above ceramsite (Example 1) was set in the actual ditch, and the interception effect of nitrogen and phosphorus in farmland runoff during the fertilization period and the rainstorm period was monitored and analyzed. The specific location was in the farmland interception ditch in Zhaojiatang area of Xin Kang village, Wujin district, Changzhou, China, and the filling amount of the ceramsite filler was 0.03 cubic meters per mu. The content change of pollutants in water before and after the interception dam was determined every 30 min or until no rainfall runoff, and the final average interception efficiency was calculated. The results are as follows:

[0083] Table 3 actual rainfall runoff interception experiment

[0084]

[0085]

[0086] The interception effect shows that with the increase of the number of interceptions, the interception effect of total nitrogen and total phosphorus gradually decreases, but the interception effect of the ceramsite of the present application for total phosphorus is more than 50%, and the interception effect for total nitrogen is more than 30%.

[0087] The above shows and describes the basic principles, main features and advantages of the present application. It should be understood by those skilled in the art that the above examples do not limit the present application in any form, and any technical solution obtained by equivalent substitution or equivalent transformation falls within the protection scope of the present application.

Claims

1. The application of waste-based biochar co-pyrolysis ceramsite in intercepting or adsorbing nitrogen and phosphorus in farmland runoff water, characterized in that, The waste-based biochar co-pyrolysis ceramsite is prepared by a preparation method comprising the following steps: Preparation of magnesium-modified peanut shells: the broken peanut shells are sprayed with a magnesium salt solution for modification, and then treated with a KOH solution to obtain magnesium-modified peanut shells; Preparation of the waste-based biochar co-pyrolysis ceramsite: the magnesium-modified peanut shells, potassium bicarbonate and water are mixed, granulated into balls by adding bauxite and coal gangue, aged after balling, preheated at 300-400 DEG C for 0.5-1.5 h, calcined at 500-700 DEG C for 0.5-1.5 h after preheating, and cooled to form the waste-based biochar co-pyrolysis ceramsite; The mass ratio of the magnesium-modified peanut shells, bauxite, coal gangue, potassium bicarbonate and water is 0.1:(0.5-1.5):(1.5-2.5):(0.04-0.06):(0.3-0.4); The total molar ratio of magnesium ions in the magnesium salt solution and hydroxide ions in the KOH solution is 1:(2.3-2.7); During preheating, the magnesium-modified peanut shells begin to pyrolyze to form biochar, and the potassium bicarbonate decomposes and dehydrates to form a pore structure; during calcination, the coal gangue decomposes and dehydrates to form a pore structure, the bauxite decomposes and dehydrates to form a hard skeleton, the peanut shells pyrolyze to form biochar with rich pore diameters, and the co-precipitated Mg(OH)2 pyrolyzes to form a rich MgO structure.

2. The use of the waste-based biochar-copyrolyzed haydite according to claim 1 for intercepting or adsorbing nitrogen and phosphorus in farmland runoff water, characterized in that, During the preparation of the magnesium-modified peanut shells, the broken peanut shells are sieved, and the peanut shells are sprayed with a magnesium salt solution of 0.2-1.5 mol / L to uniformly wet the surface of the peanut shells, and then uniformly sprayed with a KOH solution of 1-2 mol / L after standing for 18-28 h, and then stirred and mixed uniformly.

3. The use of waste-based biochar-coprocessed haydite for interception or adsorption of nitrogen and phosphorus in farmland runoff water according to claim 1, characterized in that, The total molar ratio of magnesium ions in the magnesium salt solution and hydroxide ions in the KOH solution is 1:2.5; the magnesium salt is MgCl2.

4. The use of the waste-based biochar-coprocessed haydite of claim 1 for intercepting or adsorbing nitrogen and phosphorus in farmland runoff water, characterized in that, The magnesium oxide MgO of nanoscale is formed in the pores of the peanut shells through magnesium modification and pyrolysis.

5. The use of the waste-based biochar-coprocessed haydite of claim 1 for interception or adsorption of nitrogen and phosphorus in farmland runoff water, characterized in that, Pellets of 2-3 cm in diameter are formed in 20-40 min; specific surface area > 5.0 m 2 / g, porosity > 53 %.

6. The waste-based biochar co-pyrolysis ceramsite prepared by the preparation method of the waste-based biochar co-pyrolysis ceramsite in the application of any one of claims 1-5.

7. A barrier dam, characterized in that The intercepting dam is filled with the waste-based biochar co-pyrolysis ceramsite of claim 6.

8. The intercepting dam according to claim 7, characterized in that, The intercepting dam is used for intercepting or adsorbing nitrogen and phosphorus in farmland return water during fertilization and / or storm periods.

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