A municipal sludge-based biochar material and a preparation method and application thereof

Abstract

The application belongs to the technical field of biochar material preparation, and discloses a kind of municipal sludge-based biochar material and its preparation method and application.The preparation method comprises the following steps: municipal sludge is mixed with organic solid waste and then dried to obtain a mixture; the obtained mixture is heated to a heat treatment temperature, mixed steam is introduced for reaction at the heat treatment temperature, and then cooling and drying are sequentially performed to obtain a biochar material; the mixed steam is a mixture of sodium hydroxide steam and water vapor.The obtained municipal sludge-based biochar has a high specific surface area (120-300 m 2 / g) and can cyclically adsorb organic dyes, and the removal rate of the biochar material to organic dyes can still be maintained at more than 90% after multiple cycles.

Description

Technical Field

[0001] This invention relates to the field of biochar material preparation technology, and in particular to a municipal sludge-based biochar material, its preparation method, and its application. Background Technology

[0002] Currently, commonly used materials for adsorbing organic dyes include activated carbon, diatomaceous earth, chitosan, resin, and cellulose. Activated carbon is a very common adsorbent material with a high specific surface area and abundant pore structure, effectively adsorbing organic dyes. However, its production cost is high, and its regeneration process after dye adsorption is complex and time-consuming, affecting its long-term efficiency. Diatomaceous earth is a natural material with a porous structure, capable of adsorbing organic dyes. However, its adsorption capacity is relatively low, requiring large quantities to achieve ideal adsorption effects. Furthermore, its mechanical strength is insufficient to withstand the pressure in practical applications. Chitosan is a natural polymer with good biocompatibility and adsorption performance. However, chitosan is easily soluble under acidic conditions, limiting its application in acidic environments. This chitosan is mainly derived from crustaceans, and its source is limited by season and region. Resin is a synthetic material with high adsorption performance, commonly used in water treatment and dye recovery. However, resin has demanding operating conditions, and its chemical stability is affected by specific environmental conditions. Cellulose is a natural polymer with excellent adsorption properties, commonly used in wastewater treatment and dye adsorption. To improve its adsorption performance, cellulose may require chemical modification, which increases production costs and complexity. Cellulose exhibits good adsorption properties for certain dyes but is less effective for others.

[0003] In addition, there are some novel materials, such as metal-organic framework nanomaterials (MOF), Keggin-type polyacid nanomaterials, and MXene nanomaterials, which are used for the efficient adsorption of organic dyes. However, due to the biotoxicity of these materials, their high preparation costs, and extremely low yields, they cannot play an effective role in practical engineering.

[0004] Therefore, it is of great significance to study a municipal sludge-based biochar material with excellent adsorption performance, no biotoxicity, and renewability, as well as a preparation method with low production cost, simple preparation process, and high yield. Summary of the Invention

[0005] In view of this, the present invention provides a municipal sludge-based biochar material, its preparation method and application, the purpose of which is to solve the problems of high cost, low mechanical strength, poor chemical stability and poor regeneration capacity of existing biochar materials.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention provides a method for preparing municipal sludge-based biochar material, comprising the following steps:

[0008] 1) The municipal sludge and organic solid waste are mixed and then dried to obtain a mixture;

[0009] 2) The resulting mixture is heated to the heat treatment temperature, and mixed steam is introduced at the heat treatment temperature to carry out the reaction. Then, the mixture is cooled and dried sequentially to obtain biochar material.

[0010] The mixed steam is a mixture of sodium hydroxide steam and water steam.

[0011] Preferably, in step 1), the organic solid waste includes one or more of plant straw, livestock and poultry manure, and kitchen waste.

[0012] Preferably, in step 1), the mass ratio of municipal sludge to organic solid waste is 2 to 7:1; the drying temperature is 40 to 80°C, and the drying time is 20 to 25 hours.

[0013] Preferably, in step 2), an inert gas is introduced during the process of heating to the heat treatment temperature, introducing mixed steam, and cooling. The inert gas is nitrogen, and the flow rate of the inert gas is 50-200 mL / min.

[0014] Preferably, in step 2), the heating rate to the heat treatment temperature is 2-10℃ / min, the heat treatment temperature is 600-900℃, the heat treatment time is 10-120min, and the flow rate of the mixed steam is 10-1000mL / min.

[0015] Preferably, in step 2), the cooling temperature is 20–30°C; the drying temperature is 30–60°C; and the drying time is 20–26 hours.

[0016] Preferably, the ratio of sodium hydroxide vapor to water vapor is 0.1 to 1 mol: 1 L.

[0017] The present invention also provides a municipal sludge-based biochar material prepared by the aforementioned method.

[0018] The present invention also provides the application of the aforementioned municipal sludge-based biochar material in the adsorption of organic dyes.

[0019] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0020] This invention prepares a renewable municipal sludge-based biochar material for adsorbing organic dyes using a one-step carbonization-activation method. The prepared biochar material can sustainably adsorb and remove organic dyes, while using municipal sludge and other organic solid wastes as raw materials, which is in line with the environmental protection concept of "treating waste with waste".

[0021] The municipal sludge-based biochar obtained by this invention has a high specific surface area (120-300 m²). 2 It can circulate and adsorb organic dyes, and the removal rate of organic dyes by biochar material can still be maintained at over 90% after multiple cycles. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0023] Figure 1 The image shows a scanning electron microscope image of the biochar material obtained in Example 1.

[0024] Figure 2 The image shows a scanning electron microscope image of the biochar material obtained in Example 2.

[0025] Figure 3 This is a scanning electron microscope image of the biochar material obtained in Example 3;

[0026] Figure 4 The Fourier transform infrared spectrum of the biochar material obtained in Example 1 is shown below.

[0027] Figure 5 Fourier transform infrared spectra of the biochar materials obtained in Example 2 and Comparative Example 1;

[0028] Figure 6 Fourier transform infrared spectra of the biochar materials obtained in Example 3 and Comparative Example 2;

[0029] Figure 7 The image shows the Raman spectrum of the biochar material obtained in Example 1.

[0030] Figure 8 The images show the Raman spectra of the biochar materials obtained in Example 2 and Comparative Example 1.

[0031] Figure 9 The images show the Raman spectra of the biochar materials obtained in Example 3 and Comparative Example 2.

[0032] Figure 10The diagram shows the cyclic adsorption of the biochar material obtained in Example 1.

[0033] Figure 11 The diagram shows the cyclic adsorption of the biochar materials obtained in Example 2 and Comparative Example 1.

[0034] Figure 12 The diagram shows the cyclic adsorption of the biochar materials obtained in Example 3 and Comparative Example 2. Detailed Implementation

[0035] This invention provides a method for preparing municipal sludge-based biochar material, comprising the following steps:

[0036] 1) The municipal sludge and organic solid waste are mixed and then dried to obtain a mixture;

[0037] 2) The resulting mixture is heated to the heat treatment temperature, and mixed steam is introduced at the heat treatment temperature to carry out the reaction. Then, the mixture is cooled and dried sequentially to obtain biochar material.

[0038] The mixed steam is a mixture of sodium hydroxide steam and water steam.

[0039] In this invention, in step 1), the organic solid waste preferably includes one or more of plant straw, livestock and poultry manure, and kitchen waste.

[0040] In this invention, in step 1), the mass ratio of municipal sludge to organic solid waste is preferably 2-7:1, more preferably 3-6:1, and even more preferably 4-5:1; the drying temperature is preferably 40-80℃, more preferably 50-70℃, and even more preferably 60-65℃; the drying time is preferably 20-25h, more preferably 21-24h, and even more preferably 22-23h.

[0041] In this invention, during step 2), an inert gas is introduced during the process of heating to the heat treatment temperature, introducing mixed steam, and cooling. The inert gas is preferably nitrogen, and the flow rate of the inert gas is preferably 50-200 mL / min, more preferably 80-150 mL / min, and even more preferably 100-120 mL / min.

[0042] In this invention, in step 2), the heating rate to the heat treatment temperature is preferably 2-10℃ / min, more preferably 4-8℃ / min, and even more preferably 5-6℃ / min; the heat treatment temperature is preferably 600-900℃, more preferably 650-850℃, and even more preferably 700-800℃; the heat treatment time is preferably 10-120min, more preferably 40-90min, and even more preferably 60-80min; and the flow rate of the mixed steam is preferably 10-1000mL / min, more preferably 100-800mL / min, and even more preferably 300-500mL / min.

[0043] In this invention, in step 2), the cooling temperature is preferably 20-30°C, more preferably 22-28°C, and even more preferably 24-26°C; the drying temperature is preferably 30-60°C, more preferably 35-55°C, and even more preferably 40-50°C; and the drying time is preferably 20-26 hours, more preferably 21-25 hours, and even more preferably 22-24 hours.

[0044] In this invention, the washing is performed after cooling, and the washing reagent is preferably water. The number of washings is preferably 5 to 10 times, more preferably 6 to 9 times, and even more preferably 7 to 8 times.

[0045] In this invention, the preferred ratio of sodium hydroxide vapor to water vapor is 0.1–1 mol:1 L, more preferably 0.3–0.8 mol:1 L, and even more preferably 0.5–0.6 mol:1 L.

[0046] The present invention also provides a municipal sludge-based biochar material prepared by the aforementioned method.

[0047] The present invention also provides the application of the aforementioned municipal sludge-based biochar material in the adsorption of organic dyes.

[0048] In this invention, the biochar material can be regenerated after adsorbing organic dyes. The regeneration process involves: heat-treating the biochar material after adsorbing organic dyes and then cooling it to obtain regenerated biochar material.

[0049] An inert gas is introduced during the heat treatment process, preferably nitrogen. The flow rate of the inert gas is preferably 50–200 mL / min, more preferably 80–150 mL / min, and even more preferably 100–120 mL / min. The heating rate of the heat treatment is preferably 2–10 °C / min, more preferably 4–8 °C / min, and even more preferably 5–6 °C / min. The heat treatment temperature is preferably 300–500 °C, more preferably 350–450 °C, and even more preferably 400–420 °C. The heat treatment time is preferably 0.5–2 h, more preferably 1–1.5 h. The cooling temperature is preferably 20–30 °C, more preferably 22–28 °C, and even more preferably 24–26 °C.

[0050] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0051] In the embodiments and comparative examples of this invention, the municipal sludge comes from the thickening tank of a municipal wastewater treatment plant, which uses an anaerobic-anoxic-aerobic process. The municipal sludge needs to be treated with polyacrylamide flocculant before entering the thickening tank.

[0052] Example 1

[0053] Municipal sewage sludge and wheat straw were mixed at a mass ratio of 2:1 and dried at 60°C for 24 hours to obtain a mixture.

[0054] The mixture was placed in a high-temperature tube furnace and heated to 800°C at a rate of 5°C / min under continuous nitrogen flow (100 mL / min). Then, at 800°C, a mixture of sodium hydroxide vapor and water vapor was continuously introduced into the high-temperature tube furnace through a steam generator at a rate of 100 mL / min for 1 hour (nitrogen was still introduced at a flow rate of 100 mL / min during this process, and the ratio of sodium hydroxide vapor to water vapor was 0.1 mol: 1 L). After the introduction of the sodium hydroxide vapor and water vapor mixture was stopped, nitrogen was continued to be introduced and the mixture was allowed to cool naturally to 25°C. The cooled product was washed with water 8 times and then dried at 55°C for 24 hours to obtain the biochar material.

[0055] Example 2

[0056] Municipal sewage sludge and rice husks were mixed at a mass ratio of 3:1 and dried at 80°C for 24 hours to obtain a mixture.

[0057] The mixture was placed in a high-temperature tube furnace and heated to 850°C at a rate of 10°C / min under continuous nitrogen flow (150 mL / min). Then, at 850°C, a mixture of sodium hydroxide vapor and water vapor was continuously introduced into the high-temperature tube furnace through a steam generator at a rate of 1000 mL / min for 1.5 h (nitrogen was still introduced at a flow rate of 150 mL / min during this process, and the ratio of sodium hydroxide vapor to water vapor was 1 mol: 1 L). After the introduction of the sodium hydroxide vapor and water vapor mixture was stopped, nitrogen was continued to be introduced and the mixture was naturally cooled to 25°C. The cooled product was washed with water 5 times and then dried at 60°C for 24 h to obtain the biochar material.

[0058] Example 3

[0059] Municipal sewage sludge and cow manure were mixed at a mass ratio of 2:1 and dried at 60°C for 24 hours to obtain a mixture.

[0060] The mixture was placed in a high-temperature tube furnace and heated to 600°C at a rate of 5°C / min under continuous nitrogen flow (50 mL / min). Then, at 600°C, a mixture of sodium hydroxide vapor and water vapor was continuously introduced into the high-temperature tube furnace at a rate of 500 mL / min for 1 hour through a steam generator (nitrogen was still introduced at a flow rate of 50 mL / min during this process, and the ratio of sodium hydroxide vapor to water vapor was 0.5 mol: 1 L). After the introduction of the sodium hydroxide vapor and water vapor mixture was stopped, nitrogen was continued to be introduced and the mixture was allowed to cool naturally to 25°C. The cooled product was washed with water 5 times and then dried at 60°C for 24 hours to obtain the biochar material.

[0061] Comparative Example 1

[0062] Municipal sewage sludge and rice husks were mixed at a mass ratio of 3:1 and dried at 80°C for 24 hours to obtain a mixture.

[0063] The mixture was placed in a high-temperature tube furnace and heated to 850°C at a rate of 10°C / min under continuous nitrogen flow (150 mL / min). Then, at 850°C, steam was continuously introduced into the high-temperature tube furnace through a steam generator at a rate of 1000 mL / min for 1.5 h (nitrogen was still introduced at a flow rate of 150 mL / min during this process). After the steam introduction was stopped, nitrogen was continued to be introduced and the mixture was allowed to cool naturally to 25°C to obtain primary biochar material.

[0064] Primary biochar material was mixed with 1M sodium hydroxide solution at a ratio of 1g:10mL and stirred at 400rpm for 4h. Then it was dried at 80℃ for 24h and placed in a high-temperature tube furnace. Under continuous nitrogen gas (flow rate of 150mL / min), the temperature was increased to 850℃ at a rate of 10℃ / min and held for 1h. The mixture was then naturally cooled to 25℃ under nitrogen gas. The cooled product was washed with water 8 times and then dried at 80℃ for 24h to obtain the biochar material.

[0065] Comparative Example 2

[0066] Municipal sewage sludge and cow manure were mixed at a mass ratio of 2:1 and dried at 60°C for 24 hours to obtain a mixture.

[0067] The mixture was placed in a high-temperature tube furnace and heated to 600°C at a rate of 5°C / min under continuous nitrogen flow (50 mL / min). Then, at 600°C, steam was continuously introduced into the high-temperature tube furnace through a steam generator at a rate of 500 mL / min for 1 hour (nitrogen was still introduced at a rate of 50 mL / min during this process). After the steam introduction was stopped, nitrogen was continued to be introduced and the mixture was allowed to cool naturally to 25°C to obtain primary biochar material.

[0068] Primary biochar material was mixed with 0.5M sodium hydroxide solution at a ratio of 1g:20mL and stirred at 600rpm for 4h. Then it was dried at 60℃ for 24h and placed in a high-temperature tube furnace. Under continuous nitrogen gas (flow rate of 50mL / min), the temperature was increased to 600℃ at a rate of 5℃ / min and held for 1h. The mixture was then naturally cooled to 25℃ under nitrogen gas. The cooled product was washed with water 8 times and then dried at 60℃ for 24h to obtain the biochar material.

[0069] The cyclic adsorption performance of organic dyes on the biochar materials obtained in Examples 1-3 and Comparative Examples 1-2 was tested. The organic dyes could be Rhodamine B or methylene blue.

[0070] The specific testing steps are as follows:

[0071] Isothermal adsorption experiment: 1L of organic dye aqueous solutions of different concentrations (40mg / L, 80mg / L, 100mg / L, 250mg / L, 500mg / L, 700mg / L and 1000mg / L) were added to 1g of biochar material. After adsorption was fully carried out for 24h under magnetic stirring, the supernatant solution was taken to measure and calculate the adsorption amount.

[0072] Adsorption kinetics experiment: 1g of biochar material was added to 1L of organic dye aqueous solution (100mg / L). Under the assistance of magnetic stirring, the supernatant solution was taken at different time periods (0min, 20min, 40min, 60min, 90min, 120min, 180min, 240min and 300min) and the adsorption amount was measured and calculated.

[0073] Adsorption thermodynamics experiment: 1 g of biochar material was added to 1 L of organic dye aqueous solution (100 mg / L), and the adsorption environment temperature of the material was maintained at specific values ​​(293 K, 303 K, and 313 K) using a constant temperature water bath. After sufficient adsorption for 24 h under magnetic stirring, the supernatant solution was taken for measurement and the adsorption amount was calculated.

[0074] After adsorption, the biochar material was placed in a high-temperature tube furnace and heated to 300°C at a rate of 5°C / min under continuous nitrogen flow (flow rate of 100 mL / min). The temperature was maintained in this environment for 0.5 h and then naturally cooled to 25°C, thus completing the recovery of the biochar material.

[0075] The above operation was repeated 3 times for the biochar materials obtained in Examples 1-3 and Comparative Examples 1-2, and the adsorption amount and adsorption removal rate of the biochar materials were recorded.

[0076] Scanning electron microscope image of the biochar material obtained in Example 1 is shown below. Figure 1 As shown. By Figure 1 It is evident that after mixing and pyrolyzing, straw and municipal sludge form a tight "insertion" structure, which makes the strip-shaped channels in straw biochar interconnected with the channels in municipal sludge biochar, thus changing the pore structure of single-component biochar.

[0077] Scanning electron microscope image of the biochar material obtained in Example 2 is shown below. Figure 2 As shown. By Figure 2 It is evident that after activation by alkali and steam, numerous pores appear on the surface of the biochar, indicating that the material's interior is effectively connected to the external environment. Furthermore, the municipal sludge and rice husks undergo fusion and rearrangement under heat treatment, becoming a whole. This further supplements the original pore structure of the municipal sludge, which is beneficial for improving the relevant adsorption performance.

[0078] Scanning electron microscope image of the biochar material obtained in Example 3 is shown below. Figure 3 As shown. By Figure 3 It is evident that, since cow dung itself does not exhibit significant regularity in its microstructure, the product obtained by mixing and carbonizing and activating it with municipal sludge exhibits a blocky overall microstructure. After co-activation with alkali and water, the microscopic surface of the material becomes non-smooth, which provides a large number of active sites for the adsorption of organic dyes.

[0079] The Fourier transform infrared spectrum of the biochar material obtained in Example 1 is shown below. Figure 4 As shown. By Figure 4 It can be seen that the absorption peak caused by the -OH stretching vibration appears at 3432 cm⁻¹. -1 The changes at this point were used to determine the contribution of hydrogen bonding to the adsorption process. At 2914 cm⁻¹ -1 and 2975cm -1 The absorption peak is caused by the stretching vibration of C and H functional groups, which are common functional groups in biochar. (1625 cm⁻¹) -1 The absorption peak indicates the stretching vibration of the C=C functional group, which originates from the aromatic structure formed during the pyrolysis of straw and municipal sludge. This can positively evaluate the chemical stability of biochar in environmental applications. The absorption peak formed by the stretching vibration of the CO functional group appears at 1045 cm⁻¹. -1 Accompanied by stretching vibrations of a small number of Si-O functional groups. CO mainly originates from cellulose, hemicellulose, and lignin. 400–800 cm⁻¹ -1 The series of absorption peaks that appeared in the range are attributed to the bending vibrations of Si-O and Si-O-Si bridging oxygen.

[0080] The Fourier transform infrared spectra of the biochar materials obtained in Example 2 and Comparative Example 1 are as follows: Figure 5 As shown. By Figure 5 As can be seen, compared with the biochar material obtained in Comparative Example 1, the biochar material obtained in Example 2 exhibits a red shift in its spectral composition. This phenomenon indicates that the one-step method shown in Example 2 and the two-step method shown in Comparative Example 1 have a significant impact on the functional groups of the final product, effectively altering the electron transport mechanism. This change in electron transport mechanism is beneficial to improving the material's adsorption capacity for organic dyes.

[0081] The Fourier transform infrared spectra of the biochar materials obtained in Example 3 and Comparative Example 2 are as follows: Figure 6 As shown. By Figure 6 As can be seen, the transmittance of -CH2 and -CH3 in the biochar material obtained in Example 3 is significantly enhanced, indicating that the content and intensity of carbon components in the one-step biochar material shown in Example 3 are higher than those in the two-step biochar material shown in Comparative Example 2. The same signal enhancement phenomenon also appears in CO and Si-O, proving that the biochar material prepared by the one-step method has more adsorption active sites, which is beneficial for improving the adsorption performance of the material for organic dyes.

[0082] The Raman spectrum of the biochar material obtained in Example 1 is shown below. Figure 7 As shown. By Figure 7 It can be seen that it is located at approximately 1580cm -1 The G peak and E in graphite 2gVibration mode correlation, i.e., sp 2 The stretching vibrations of hybrid carbon atoms within the graphite plane make the G peak an important indicator for evaluating the degree of graphitization of biochar. (Approximately 1350 cm⁻¹) -1 The D peak at that location is related to defects, disordered structures, or sp in biochar. 3 The correlation between hybridized carbon atoms can be used to evaluate the degree of defects in biochar and the state of edge carbon atoms. The intensity ratio of the D peak to the G peak (I D / I G ) is commonly used to describe the graphitization and defect degree of biochar. After calculation, I D / I G The value is 0.89, a lower I D / I G The value indicates that the graphitization process in biochar is significant, and that biochar possesses a relatively high sp value. 2 Hybridized carbon atoms and a relatively complete graphite layer structure.

[0083] The Raman spectra of the biochar materials obtained in Example 2 and Comparative Example 1 are as follows: Figure 8 As shown. By Figure 8 As can be seen, compared with the biochar material obtained by the two-step method shown in Comparative Example 1, the biochar material obtained by the one-step method shown in Example 2 has a stronger Raman signal, especially in the range of 2500–3000 cm⁻¹. -1 The presence of the 2D peak indicates the existence of a distinct layered graphite structure in the biochar material. In the adsorption experiment, this structure ensures maximum contact between the biochar and the organic dye. Furthermore, the spectral noise of the biochar material obtained in Example 2 is lower than that of the biochar material obtained in Comparative Example 1, indicating that the biochar material obtained in Example 2 has a lower impurity content and a higher biochar content and degree of graphitization.

[0084] The Raman spectra of the biochar materials obtained in Example 3 and Comparative Example 2 are as follows: Figure 9 As shown. By Figure 9 As can be seen, the biochar material obtained by the one-step method in Example 3 shows higher signals at both the G and D peaks than the biochar material obtained by the two-step method in Comparative Example 2. This indicates that the biochar material obtained in Example 3 has a more complete internal structure and more surface defects, suggesting that both channel adsorption and active site adsorption jointly enhance the material's adsorption capacity. Furthermore, the lower Raman shift (0-800 cm⁻¹) is also observed. -1 At the location shown, the biochar material obtained in Example 3 has a more regular Si-O bond signal, while the biochar material obtained in Comparative Example 2 also has other burr peaks, indicating that the latter has more inorganic impurities.

[0085] The cyclic adsorption diagram of the biochar material obtained in Example 1 is shown below. Figure 10 As shown. By Figure 10It is evident that cyclic adsorption is a crucial indicator for evaluating the adsorption and recycling capacity of biochar. After three rounds of adsorption experiments, the biochar material maintained a high adsorption removal rate (over 90%) for methylene blue, with an adsorption capacity of approximately 45 mg / g. The activation process not only improved the pore structure of the biochar but also effectively increased its thermal shock resistance due to the generated SiO2, reducing functional losses caused by recycling. Furthermore, the addition and activation of organic solid waste during the initial preparation of biochar introduced a large number of active sites and surface functional groups. Although some active sites lost their activity and the types of functional groups changed during recycling, the remaining original active sites and functional groups still ensured that the biochar's adsorption performance remained at a high level and stable.

[0086] The cyclic adsorption diagrams of the biochar materials obtained in Example 2 and Comparative Example 1 are shown below. Figure 11 As shown. By Figure 11 As can be seen, the methylene blue removal rates of the biochar material obtained in Example 2 were 97.75%, 94.24%, and 92.11% for the three adsorption cycles, respectively; while the methylene blue removal rates of the biochar material obtained in Comparative Example 1 were 90.31%, 85.21%, and 83.19% for the three adsorption cycles, respectively. The comparison revealed that within the same batch of adsorption experiments, the methylene blue removal rate of the biochar material obtained in Example 2 was consistently higher than that of the biochar material obtained in Comparative Example 1. Furthermore, after three adsorption experiments, the methylene blue removal rate of the biochar material obtained in Example 2 remained above 90%, while the methylene blue removal rate of the biochar material obtained in Comparative Example 1 was close to 80%. Therefore, it can be seen that although the methylene blue removal rate of the biochar material obtained in Comparative Example 1 exhibited excellent and stable removal efficiency, the adsorption performance of the biochar material obtained in Example 2 was superior.

[0087] The cyclic adsorption diagrams of the biochar materials obtained in Example 3 and Comparative Example 2 are shown below. Figure 12 As shown. By Figure 12 As can be seen, the removal rates of the biochar material obtained in Example 3 after three adsorption cycles were 97.58%, 93.13%, and 90.95%, respectively, while the removal rates of the biochar material obtained in Comparative Example 2 were 91.37%, 87.83%, and 82.14%, respectively. In any adsorption removal experiment for Rhodamine B, the removal effect of the biochar material obtained in Example 3 was consistently better than that of the biochar material obtained in Comparative Example 2. With the increase of the number of adsorption experiments, the adsorption removal rate of Rhodamine B by the biochar material obtained in Example 3 decreased by 6.79%, while the adsorption removal rate of Rhodamine B by the biochar material obtained in Comparative Example 2 decreased by 9.68%. Therefore, it can be seen that the adsorption removal effect of the biochar material obtained in Example 3 for Rhodamine B is better than that of the biochar material obtained in Comparative Example 2.

[0088] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing municipal sludge-based biochar material, characterized in that, Includes the following steps: 1) The municipal sludge and organic solid waste are mixed and then dried to obtain a mixture; 2) The resulting mixture is heated to the heat treatment temperature, and mixed steam is introduced at the heat treatment temperature to carry out the reaction. Then, the mixture is cooled and dried sequentially to obtain biochar material. The mixed steam is a mixture of sodium hydroxide steam and water steam.

2. The method for preparing municipal sludge-based biochar material according to claim 1, characterized in that, In step 1), organic solid waste includes one or more of plant straw, livestock and poultry manure, and kitchen waste.

3. The method for preparing municipal sludge-based biochar material according to claim 2, characterized in that, In step 1), the mass ratio of municipal sludge to organic solid waste is 2 to 7:1; the drying temperature is 40 to 80°C, and the drying time is 20 to 25 hours.

4. The method for preparing municipal sludge-based biochar material according to claim 3, characterized in that, In step 2), an inert gas is introduced during the process of heating to the heat treatment temperature, introducing mixed steam, and cooling. The inert gas is nitrogen, and the flow rate of the inert gas is 50-200 mL / min.

5. The method for preparing a municipal sludge-based biochar material according to claim 4, characterized in that, In step 2), the heating rate to the heat treatment temperature is 2-10℃ / min, the heat treatment temperature is 600-900℃, the heat treatment time is 10-120min, and the flow rate of the mixed steam is 10-1000mL / min.

6. A method for preparing municipal sludge-based biochar material according to claim 4 or 5, characterized in that, In step 2), the cooling temperature is 20–30°C; the drying temperature is 30–60°C; and the drying time is 20–26 hours.

7. The method for preparing municipal sludge-based biochar material according to claim 6, characterized in that, The ratio of sodium hydroxide vapor to water vapor is 0.1–1 mol:1 L.

8. The municipal sludge-based biochar material prepared by the method for preparing a municipal sludge-based biochar material according to any one of claims 1 to 7.

9. The application of the municipal sludge-based biochar material according to claim 8 in the adsorption of organic dyes.

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