Preparation method and application of modified apocynum venetum charcoal

Abstract

The invention discloses a preparation method of modified apocynum venetum charcoal. The preparation method comprises the following steps: flushing apocynum venetum, drying, crushing and sieving; adding water, uniformly mixing the apocynum venetum powder with a composite modifier, and drying, wherein the composite modifier comprises a urea, sodium carbonate and ferric salt ternary system; and then carrying out pyrolysis. The obtained modified apocynum venetum charcoal is applied to adsorption of organic matters in sewage or wastewater treatment. Adsorption experiments are carried out on livestock and poultry biogas slurry, after 48 hours, the removal rate of the modified apocynum venetum charcoal adsorbent on soluble organic carbon in biogas slurry wastewater is 57.42%, the removal rate of UV254 is 75.90%, the removal rate of chromaticity is 78.64%, and the modified apocynum venetum charcoal adsorbent shows excellent adsorption performance and can be used as a good adsorbent for removing organic pollutants in water treatment. According to the method, circular economy and the idea of treating waste with waste are taken as basic principles, so that the apocynum venetum waste is treated, and the obtained apocynum venetum biochar can effectively treat organic matters in wastewater and meet the treatment requirements of various types of wastewater.

Description

Technical Field

[0001] This invention relates to the field of environmental protection technology, specifically to a method for preparing and applying modified Apocynum venetum biochar. Background Technology

[0002] With the acceleration of industrialization and urbanization, large amounts of sewage and wastewater containing dissolved organic pollutants are discharged into the environment, causing serious impacts on aquatic ecosystems. Traditional physicochemical or biological treatment technologies have limited efficiency in removing recalcitrant organic matter and suffer from problems such as high operating costs, high energy consumption, and secondary pollution. Biochar, as a widely available carbon material with a large specific surface area and rich pore structure, has become an important material in the field of wastewater treatment due to its excellent adsorption performance and sustainable preparation process. However, existing biochar generally suffers from problems such as low specific surface area and insufficient active sites, resulting in poor adsorption efficiency in complex organic wastewater, which restricts its market promotion.

[0003] Apocynum venetum is a typical halophyte, characterized by its salt and alkali tolerance and strong resilience. Widely distributed in Northwest my country and saline-alkali regions, it is an important species for saline-alkali land management and ecological restoration. The extraction and processing of Apocynum venetum fiber generates a large amount of stem waste, which, if not utilized, will cause environmental pollution. These stems are rich in cellulose, hemicellulose, and lignin, and contain inorganic elements such as potassium, calcium, magnesium, and sodium. They possess excellent carbonization properties and potential for pore structure formation, making them suitable as raw materials for high-performance biochar. Therefore, developing a biochar material prepared from Apocynum venetum stems can improve adsorption performance and application efficiency while achieving high-value utilization of Apocynum venetum waste resources, which is of great significance for sewage and wastewater purification, saline-alkali land resource recycling, and environmental protection. Summary of the Invention

[0004] To address the aforementioned shortcomings of existing technologies, the present invention aims to provide a method for preparing modified Apocynum venetum biochar and its application, thereby solving the problems of low specific surface area and insufficient active sites commonly found in existing biochar; and simultaneously addressing the environmental pollution caused by the large amount of stem waste generated during the extraction and processing of Apocynum venetum fiber.

[0005] Furthermore, the present invention also provides the application of the modified Apocynum venetum biochar in the treatment of livestock and poultry biogas slurry wastewater.

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

[0007] A method for preparing modified Apocynum venetum biochar, characterized by comprising the following steps:

[0008] S1. Using Apocynum venetum stems as raw material, wash, dry, cut into small sections, pulverize and sieve to obtain Apocynum venetum powder;

[0009] S2. Mix the Apocynum venetum powder and the ternary composite modifier according to the preset ratio, add water and mix evenly, then dry to obtain Apocynum venetum powder loaded with modifier;

[0010] S3. Pyrolysis of Apocynum venetum powder loaded with modifier under an inert gas atmosphere, followed by cooling, grinding, sieving, washing, and drying to obtain modified Apocynum venetum biochar.

[0011] Furthermore, the Apocynum venetum powder obtained in step S1 has a particle size of less than 100 mesh. Powder particles smaller than 100 mesh are fine and have good dispersibility, which is conducive to the uniform loading of the modifier and the full pyrolysis reaction, thereby increasing the specific surface area and adsorption active sites of the final biochar.

[0012] Furthermore, the ternary composite modifier in step S2 is urea, sodium carbonate, and iron salt; the preset ratio is a mass ratio of Apocynum venetum powder to urea of ​​1:(1-9), the amount of sodium carbonate is 2%-8% of the mass of Apocynum venetum powder, and the amount of iron salt is 1%-5% of the mass of Apocynum venetum powder. An appropriate amount of water is added to dissolve the ternary composite modifier and disperse the Apocynum venetum powder, so that the modifier can be uniformly loaded on the powder surface, thereby achieving the synergistic effect of nitrogen doping, alkali activation, and metal promotion during pyrolysis, significantly improving the pore structure and surface activity of the final biochar.

[0013] Furthermore, the inert gas in step S3 is high-purity N2, with a flow rate controlled between 0.5 and 1 L / min. A stable N2 flow provides inert protection, which can effectively prevent oxidation reactions during pyrolysis and improve the structural stability of biochar.

[0014] Furthermore, the pyrolysis conditions in step S3 are as follows: the temperature is increased to 300-800℃ at a rate of 10℃ / min, and the pyrolysis reaction time is 1.5h-2.5h. The appropriate pyrolysis temperature can promote the carbonization of the Apocynum venetum matrix and stimulate the nitrogen doping and activation reaction of the ternary composite modifier, while the sufficient pyrolysis time ensures that these structural reconstruction processes are fully carried out.

[0015] This invention also provides a modified Apocynum venetum biochar and its application. The modified Apocynum venetum biochar prepared by the method described above is used in wastewater or sewage treatment to remove dissolved organic carbon (DOC) and UV radiation. 254 Color (CN) and fluorescent organic compounds.

[0016] The wastewater or sewage includes domestic sewage, industrial wastewater, livestock and poultry breeding wastewater, or anaerobic fermentation biogas slurry. The dosage of the modified Apocynum venetum biochar is 0.5–5 g / L, and the adsorption equilibrium time is 120 min.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. This invention uses Apocynum venetum stems as the main raw material. As a typical halophyte, Apocynum venetum is characterized by high cellulose, hemicellulose, and lignin content, and stable char formation rate. It is also rich in inorganic salts such as potassium, sodium, magnesium, and calcium, which can promote the natural development of pore structure during pyrolysis. The main raw material of this invention is green and renewable, possessing significant resource and ecological advantages. Furthermore, Apocynum venetum generates a large amount of byproducts during saline-alkali land management and ecological restoration; its waste stems can be used for biochar preparation, achieving resource utilization and combining environmental benefits with economic value.

[0019] 2. This invention employs a ternary composite modifier to synergistically improve the structure and surface chemical properties of biochar. Specifically, it utilizes a ternary composite modification system composed of urea, sodium carbonate, and iron salts to achieve a synergistic effect of "nitrogen doping—alkali activation—metal promotion" during pyrolysis. Urea provides the nitrogen source, which is beneficial for the formation of nitrogen-containing functional groups; sodium carbonate releases CO2 during pyrolysis, which generates micro-gasification activation, significantly increasing the specific surface area and micropore volume of biochar; iron salts promote aromatization and nitrogen-carbon bond stabilization, enhancing the thermal stability of surface cation active sites and functional groups. This multi-component synergistic modification method is superior to single-component modification methods in both structure and chemical activity.

[0020] 3. The modified Apocynum venetum biochar prepared by this invention exhibits enhanced pore structure and surface functional groups, resulting in significantly improved adsorption performance. The specific surface area of ​​the ternary composite-modified Apocynum venetum biochar is significantly increased, with micropores and mesopores developing synergistically, and the number of active sites increasing. The introduction of nitrogen-containing functional groups enhances the adsorption capacity for polar organic compounds, while micropore filling and π-π interactions enhance the removal effect on aromatic and color substances. The modified biochar of this invention effectively removes DOC and UV... 254 The removal rates of 57.42%, 75.90%, and 78.64% of CN were achieved, respectively, which is 15% to 40% higher than that of unmodified Apocynum venetum biochar, showing significant performance gains and achieving unexpected technical effects.

[0021] 4. The process of this invention is green, simple, and energy-efficient, making it suitable for engineering-scale preparation. The ternary composite modified system does not require highly corrosive chemicals, has mild pyrolysis conditions, simple process steps, is environmentally friendly, and has controllable costs, making it suitable for large-scale production and widespread application. Furthermore, the resulting biochar has a stable structure, good recyclability, and its adsorption performance decreases by less than 10% after multiple regenerations, demonstrating excellent potential for sustainable application. Attached Figure Description

[0022] Figure 1 This is a picture of the modified Apocynum venetum biochar.

[0023] Figure 2 This is a scanning electron microscope image of Apocynum venetum biochar.

[0024] Figure 3 The nitrogen-adsorption-desorption isotherm, specific surface area, and pore size diagrams for Apocynum venetum biochar are shown.

[0025] Figure 4 This is the X-ray photoelectron spectrum of Apocynum venetum biochar.

[0026] Figure 5 The image shows the C1s peak of the X-ray photoelectron spectrum of Apocynum venetum biochar.

[0027] Figure 6 This is the Fourier transform infrared spectrum of Apocynum venetum biochar.

[0028] Figure 7 The diagram shows the contact angle and zeta potential of Apocynum venetum biochar.

[0029] Figure 8 This is a graph showing the adsorption efficiency of Apocynum venetum biochar on organic matter in wastewater.

[0030] Figure 9 The graph shows the adsorption efficiency of modified Apocynum venetum biochar on organic matter in wastewater.

[0031] Figure 10 This is a diagram showing the adsorption kinetics of organic matter in wastewater by Apocynum venetum biochar.

[0032] Figure 11 This is an isotherm diagram of the adsorption of organic matter in wastewater by Apocynum venetum biochar.

[0033] Figure 12 This diagram illustrates the regeneration and recycling of modified Apocynum venetum biochar. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, specific examples are provided below to illustrate the implementation of this invention. Those skilled in the art can easily understand other advantages and effects of this invention from the content disclosed in this specification. This invention can also be implemented or applied through other different specific embodiments. Unless otherwise specified, the experimental methods in the following embodiments are conventional methods. Unless otherwise specified, the experimental materials involved are commercially available products.

[0035] This invention uses Apocynum venetum stems as the main raw material and employs a composite modifier to prepare modified Apocynum venetum biochar via pyrolysis. The effects of pyrolysis temperature and urea content in the composite modifier on the physicochemical properties and organic matter adsorption performance of the biochar are systematically studied. Pyrolytic biochar possesses a series of functional structures, but due to the small specific surface area and low porosity of the original biochar, a composite modifier is used to modify the original biochar, increasing the specific surface area and enriching the functional groups on the biochar. This provides active sites for the reaction system and improves the treatment capacity of biogas slurry.

[0036] Example

[0037] I. A method for preparing modified Apocynum venetum biochar, comprising the following steps:

[0038] S1. Collect discarded Apocynum venetum stems, wash off the soil with tap water, rinse again with pure water, air dry, cut into 3 to 5 cm pieces, and dry at 60℃ for 24 hours. Grind the dried sample using a universal pulverizer, pass through a 100-mesh sieve, and obtain Apocynum venetum powder.

[0039] S2. Mix the Apocynum venetum powder and the composite modifier according to a preset ratio. The preset ratio is that the mass ratio of Apocynum venetum powder to urea is 1:1, 1:3, 1:5, 1:7, and 1:9, respectively. The amount of sodium carbonate is 5% of the mass of Apocynum venetum powder, and the amount of iron salt is 2% of the mass of Apocynum venetum powder. Add an appropriate amount of pure water, stir, and then dry to obtain Apocynum venetum powder loaded with modifier.

[0040] S3. Take an appropriate amount of modified Apocynum venetum powder and place it in a tube furnace for pyrolysis. First, purge the air from the tube furnace with nitrogen at a flow rate of 1 L / min. Then, adjust the nitrogen flow rate to 0.5 L / min and heat to the final temperature (300℃, 400℃, 500℃, 600℃, 700℃, 800℃) at a heating rate of 10℃ / min, and maintain for 1.5–2 hours. After pyrolysis, cool the sample to room temperature in a nitrogen atmosphere and remove the biochar. Grind and sieve the obtained biochar, wash it several times with pure water, and then dry it overnight in a 60℃ drying oven to finally obtain modified Apocynum venetum biochar.

[0041] Example 1

[0042] Following the preparation method described above, the mass ratio of Apocynum venetum powder, urea, sodium carbonate, and iron salt was 1:0:0:0, and the pyrolysis temperature was set to 300℃ to investigate the effect of different temperatures on the adsorption performance of biochar materials on biogas slurry.

[0043] Example 2

[0044] Following the preparation method of Example 1, the pyrolysis temperature in Example 1 was adjusted to 400℃, while the other conditions remained the same as in Example 1. This was to investigate the effect of different temperatures on the adsorption performance of biochar materials on biogas slurry.

[0045] Example 3

[0046] Following the preparation method of Example 1, the pyrolysis temperature in Example 1 was adjusted to 500℃, while the other conditions remained the same as in Example 1. This was to investigate the effect of different temperatures on the adsorption performance of biochar materials on biogas slurry.

[0047] Example 4

[0048] Following the preparation method of Example 1, the pyrolysis temperature in Example 1 was adjusted to 600℃, while the other conditions remained the same as in Example 1. This was to investigate the effect of different temperatures on the adsorption performance of biochar materials on biogas slurry.

[0049] Example 5

[0050] Following the preparation method of Example 1, the pyrolysis temperature in Example 1 was adjusted to 700℃, while the other conditions remained the same as in Example 1. This was to investigate the effect of different temperatures on the adsorption performance of biochar materials on biogas slurry.

[0051] Example 6

[0052] Following the preparation method of Example 1, the pyrolysis temperature in Example 1 was adjusted to 800℃, while the other conditions remained the same as in Example 1. This was to investigate the effect of different temperatures on the adsorption performance of biochar materials on biogas slurry.

[0053] Example 7

[0054] Referring to the preparation method in Example 1, the mass ratio of Apocynum venetum powder: urea: sodium carbonate: iron salt was 1:1:0.05:0.02, and the pyrolysis temperature was set to 700℃, in order to investigate the effect of different mass ratios of composite modifier on the adsorption performance of biochar materials modified with biochar materials to biogas slurry.

[0055] Example 8

[0056] Referring to the preparation method in Example 1, the mass ratio of Apocynum venetum powder: urea: sodium carbonate: iron salt was 1:3:0.05:0.02, and the pyrolysis temperature was set to 700℃, in order to investigate the effect of different mass ratios of composite modifier on the adsorption performance of biochar materials modified with biochar materials to biogas slurry.

[0057] Example 9

[0058] Referring to the preparation method in Example 1, the mass ratio of Apocynum venetum powder: urea: sodium carbonate: iron salt was 1:5:0.05:0.02, and the pyrolysis temperature was set to 700℃, in order to investigate the effect of different mass ratios of composite modifier on the adsorption performance of biochar materials modified with biochar materials to biogas slurry.

[0059] Example 10

[0060] Following the preparation method of Example 1, the mass ratio of Apocynum venetum powder: urea: sodium carbonate: iron salt was 1:7:0.05:0.02, and the pyrolysis temperature was set to 700℃ to investigate the effect of different mass ratios of the composite modifier on the adsorption performance of biochar material modified with biochar material of biogas slurry. After adsorption, a cycle experiment was conducted according to step 3 to investigate the reusability of the biochar material modified with composite modifier adsorbed with biogas slurry.

[0061] Example 11

[0062] Referring to the preparation method in Example 1, the mass ratio of Apocynum venetum powder: urea: sodium carbonate: iron salt was 1:9:0.05:0.02, and the pyrolysis temperature was set to 700℃, in order to investigate the effect of different mass ratios of composite modifier on the adsorption performance of biochar materials modified with biochar materials to biogas slurry.

[0063] II. Performance Characterization of Apocynum Venetum Biochar

[0064] Figure 1 This is a photograph of the modified Apocynum venetum biochar. The sample is dark black, powdery, with a rough surface, loose structure, and low bulk density, exhibiting typical characteristics of pyrolytic biochar.

[0065] Figure 2 This is a scanning electron microscope image of Apocynum venetum biochar. (Source: [Original Text]) Figure 2 It is known that the higher the pyrolysis temperature, the rougher the surface of biochar and the more pore structures it has, reaching a peak at a pyrolysis temperature of 700℃. However, the surface becomes denser at a pyrolysis temperature of 800℃.

[0066] Figure 3 The nitrogen adsorption-desorption isotherm, specific surface area, and pore size diagrams for Apocynum venetum biochar are shown. Figure 3 It can be seen that all Apocynum venetum biochar exhibited typical type IV adsorption isotherms and significant hysteresis loops, indicating that mesopores (2-50 nm) are dominant. At pyrolysis temperatures of 300℃ and 400℃, the narrower H3-type hysteresis loops indicate that the porosity mainly originates from slit-like pores formed by the aggregation of plate-like particles. Their specific surface area (SSA) and total pore volume (V) are also significant. t The specific surface area (SSA) is relatively low. With increasing pyrolysis temperature, the H3-type hysteresis loop gradually widens, and the specific surface area increases, indicating the formation of more slit-like mesopores and the onset of capillary condensation. When the pyrolysis temperature exceeds 600℃, the adsorption capacity increases sharply at low relative pressure (P / P0 < 0.1), indicating the large-scale formation of micropores (< 2 nm). Simultaneously, the hysteresis loop transforms into a mixed H3 / H4 type, indicating the coexistence of slit-like mesopores and narrow micropores. At this point, the SSA significantly increases (> 300 nm). 2 / g), total pore volume (V t (More than 0.160cm) 3 / g, micropore volume (V) m (More than 0.129cm) 3 / g, thereby significantly enhancing the pore-filling adsorption sites for organic pollutants.

[0067] Figure 4 This is the X-ray photoelectron spectrum of Apocynum venetum biochar. (Source: [Insert source here]) Figure 4It can be seen that the inorganic salt content in Apocynum venetum biochar increases with increasing pyrolysis temperature, mainly including Ca, Mg, Na, and K, indicating that its inherent salt content is relatively high. With increasing pyrolysis temperature, the O / C and (O+N) / C ratios decrease, indicating a reduction in hydrophilicity and polarity.

[0068] Figure 5 This is a C1s peak fitting diagram of Apocynum venetum biochar. (Source: [Insert source here]) Figure 5 It can be seen that when the pyrolysis temperature increases from 300℃ to 500℃, the CC / C=C / CH ratio increases significantly from 39.93% to 76.05%, while the oxygen-containing / nitrogen-containing functional groups decrease significantly. These changes indicate that with increasing temperature, thermally unstable functional groups such as hydroxyl, carbonyl, and carboxyl groups are continuously broken down and removed. However, when the temperature reaches 500℃, the carbon structure tends to stabilize, and a π-π* vibrational peak appears.

[0069] Figure 6 This is the Fourier transform infrared spectrum of Apocynum venetum biochar. Figure 6 It can be seen that oxygen-containing functional groups (including 3335cm) -1 A broad -OH absorption band at 1700 cm⁻¹ -1 The C=O absorption peak at 1056 cm⁻¹ and the absorption peak at 1056 cm⁻¹ -1 The CO stretching vibration at [location] gradually weakens or even disappears with increasing pyrolysis temperature. Meanwhile, the stretching vibration peak of aliphatic CH [at 2987 cm⁻¹] gradually decreases. -1 2901cm -1 ) and bending vibration peak (1394cm) -1 The absorption band of aromatic C=C molecules is significantly reduced, while the absorption band of aromatic molecules (1599 cm⁻¹) is significantly reduced. -1 The O / C and (O+N) / C ratios gradually increase. These changes indicate that the carbon matrix has undergone a continuous deoxygenation and aromatization process, which is consistent with the decreasing trend of the O / C and (O+N) / C ratios.

[0070] Figure 7 This is a diagram showing the contact angle and zeta potential of Apocynum venetum biochar. (Source: [Insert source here]) Figure 7 It can be seen that both the contact angle (CA) and the Zeta potential show a consistent trend with the pyrolysis temperature, reflecting the evolution of surface chemical properties during pyrolysis. As the temperature increases from 300℃ to 800℃, the CA- increases from 132.12° to nearly 150°, while the Zeta potential increases from -9.62mV to -1.19mV. The decrease in hydrophilicity and the reduction in surface negative charge indicate that polar oxygen- and nitrogen-containing functional groups (such as -COOH, -OH, and -NH2) are gradually lost, and aromatic carbon structures are gradually formed, thereby weakening the electrostatic repulsion of organic matter and enhancing hydrophobic interactions and π-π interactions.

[0071] III. Adsorption of Organic Matter in Wastewater by Apocynum Venetum Biochar

[0072] Dissolved organic carbon (DOC) was used to reflect the total dissolved organic pollutant concentration in biogas slurry. All samples were filtered through a 0.45 μm microporous membrane and then analyzed using a total organic carbon analyzer. The absorbance of the wastewater under ultraviolet light at a wavelength of 254 nm was used for measurement. 254 The concentration of dissolved organic pollutants with unsaturated bonds in the water samples was characterized using a UV spectrophotometer. All samples were filtered through a 0.45 μm microporous membrane and then analyzed using a UV spectrophotometer. The color (CN) of the water samples was characterized using the absorbance of the wastewater under UV light at wavelengths of 436, 525, and 620 nm.

[0073]

[0074] (1) Determination of adsorption capacity: The adsorbent was actual biogas slurry without pH adjustment (pH 7.8–8.5), the adsorption temperature was room temperature (25℃), and the biochar dosage was 5 g / L. 40 ml of biogas slurry was added to an Erlenmeyer flask, and the mixture was shaken on a shaker for 48 h at 180 rpm. Further analysis was performed after filtration through a 0.45 μm microporous membrane. The adsorption kinetics of DOC in biogas slurry by biochar were fitted using pseudo-first-order and pseudo-second-order kinetic models. The average value of two repeated experiments was used to avoid errors.

[0075] (2) Determination of adsorption kinetics: The adsorbent was actual biogas slurry without pH adjustment (pH 7.8–8.5). The adsorption temperature was room temperature (25℃). 5 g / L biochar was added to an Erlenmeyer flask. The mixture containing the adsorbent was placed on a shaker at 180 rpm. Adsorption times were 15 min, 30 min, 45 min, 60 min, 90 min, 120 min, 240 min, and 480 min. Samples were taken with a syringe, filtered through a 0.45 μm microporous membrane, and then further analyzed. Two repeated experiments were performed, and the average value was used to avoid errors.

[0076] (3) Determination of adsorption isotherms: The adsorption target was actual biogas slurry without pH adjustment (pH 7.8–8.5), and the adsorption temperature was room temperature (25℃). The biogas slurry was diluted 2, 4, 6, and 8 times, respectively. The biochar dosage was 2 g / L. 0.06 g of biochar was added to an Erlenmeyer flask, followed by 30 ml of biogas slurry. The mixture was shaken for 48 h at 180 rpm and then filtered through a 0.45 μm microporous membrane for further analysis. The isothermal adsorption curves of DOC in biogas slurry by the biochar material were fitted using the Langmuir and Fruendlich models. The average value of two repeated experiments was used to avoid errors.

[0077] Figure 8 This is a graph showing the adsorption efficiency of Apocynum venetum biochar for organic matter in wastewater. Figure 8 It can be seen that DOC and UV 254The removal efficiency of both DOC and UVC increases monotonically with increasing pyrolysis temperature, reaching its maximum at 700℃: DOC removal rate is approximately 40%, and UV removal efficiency is... 254 The removal rate of CN was approximately 20%, which then decreased slightly at a pyrolysis temperature of 800℃.

[0078] Figure 10 This is a diagram showing the adsorption kinetics of organic matter in wastewater by Apocynum venetum biochar. Figure 10 It was observed that the adsorption process of DOC proceeded rapidly within the first 30 minutes, reaching equilibrium at approximately 120 minutes. In contrast, the adsorption rate of low-temperature biochar was slower. Biochar with a pyrolysis temperature of 300℃ had too low an adsorption capacity for reliable model fitting, therefore kinetic analysis was not conducted. Kinetic fitting results indicated that the adsorption process of *Apocynum venetum* biochar was primarily dominated by a physical pore-filling mechanism, which better conforms to a pseudo-first-order kinetic model (PFO). Biochar pyrolyzed at 400℃ exhibited certain chemisorption characteristics due to its rich content of oxygen / nitrogen functional groups. With increasing pyrolysis temperature, these functional groups rapidly decreased, while the number of π-π* domains and pores significantly increased, enhancing the pore-filling effect.

[0079] Figure 11 This is an adsorption isotherm diagram of organic matter in wastewater by Apocynum venetum biochar. Figure 11 It can be seen that when the pyrolysis temperature is below 700℃, the adsorption behavior consistently shows the best fit with the Langmuir model, indicating that adsorption mainly occurs on a relatively homogeneous surface, primarily as monolayer adsorption. However, at a pyrolysis temperature of 800℃, the adsorption characteristics shift to multilayer adsorption behavior consistent with the Freundlich model, which may be attributed to the formation of microcracks and increased surface heterogeneity at high temperatures. For all biochar samples, the Freundlich constant 1 / n ranges from 0.1 to 1, indicating that DOC has a relatively easy adsorption characteristic in the system.

[0080] IV. Adsorption of Organic Matter in Wastewater by Modified Apocynum Venetum Biochar

[0081] Following the preparation method of Example 1, the mass ratio of Apocynum venetum powder to urea was adjusted to 1:1, 1:3, 1:5, 1:7, and 1:9, respectively, and the amounts of sodium carbonate and iron salt added were 5% and 2% of the Apocynum venetum powder, respectively. The pyrolysis temperature was set to 700℃ to investigate the effect of the composite modifier on the adsorption performance of biochar material on biogas slurry.

[0082] Figure 9 This is a graph showing the adsorption efficiency of modified Apocynum venetum biochar on organic matter in livestock and poultry biogas slurry wastewater. Figure 9 It can be seen that DOC and UV 254The removal efficiency of both DOC and UVC increased with increasing urea content, reaching its maximum at a ratio of 1:7 (Apocynum venetum:urea). The removal efficiency was 57.42%. 254 The removal rate was 75.90%, and the CN removal rate was 78.64%, which then slightly decreased at a ratio of 1:9 for Apocynum venetum and urea. Modification with a composite modifier provides biochar with more nitrogen-containing functional groups, cations, and π-π* structure adsorption sites, improves pore structure, increases specific surface area, and enhances adsorption efficiency. Compared with unmodified Apocynum venetum biochar, the biochar treated with the ternary composite modifier showed a significant increase in the removal rate of organic matter. The CN removal rate of modified Apocynum venetum biochar is typically 15%–40% higher than that of unmodified samples, and this improvement is even more pronounced in the treatment of livestock and poultry biogas slurry wastewater, fully demonstrating the optimizing effect of the modification process on the removal performance of organic pollutants by Apocynum venetum biochar.

[0083] V. Recyclability of Apocynum venetum biochar

[0084] Modified Apocynum venetum biochar with adsorbed organic matter was regenerated by pyrolysis. Nitrogen flow was adjusted to 0.5 L / min, and the temperature was increased to 700℃ at a rate of 10℃ / min, held for 2 hours. After cooling, it was washed with pure water and vacuum dried overnight at 60℃ to obtain regenerated Apocynum venetum biochar.

[0085] Figure 12 This diagram illustrates the regeneration and recycling of modified Apocynum venetum biochar. (Source: [Insert Source Here]) Figure 12 It can be seen that after three independent thermal regenerations, the adsorption capacity of Apocynum venetum biochar for organic matter decreased by less than 10%, indicating good reusability.

[0086] As described above, although the invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the invention itself. Various changes in form and detail may be made without departing from the spirit and scope of the invention as defined in the appended claims.

[0087] Table 1 shows the comparison of various embodiments and their performance.

[0088]

[0089]

[0090] Therefore, this invention utilizes modified Apocynum venetum biochar adsorbent to conduct adsorption experiments on biogas slurry. Apocynum venetum, a halophyte, is widely available and low-cost; utilizing its waste stems as a resource can achieve the dual environmental benefits of ecological restoration of saline-alkali land and waste reduction. Apocynum venetum is rich in salt, acting as a natural modifier that promotes the development of biochar pore structure. By introducing the modifier, nitrogen doping—alkali activation—metal promotion are achieved during pyrolysis, significantly increasing the content of nitrogen-containing functional groups on the biochar surface, enhancing surface polarity and hydrophilicity, improving electron distribution and chemical reactivity, and resulting in biochar with good structural stability and pore development. After 48 hours, the modified Apocynum venetum biochar adsorbent achieved a removal rate of 57.42% of dissolved organic carbon in biogas slurry, with UV... 254 The removal rate is 75.90%, and the color removal rate is 78.64%, demonstrating excellent adsorption performance. The process employs inert atmosphere pyrolysis combined with doping modification, requiring no complex chemical reagents. The process is simple, environmentally friendly, and low-cost, suitable for large-scale preparation and engineering applications. It maintains good adsorption stability and regeneration performance even in complex wastewater systems, making it a good adsorbent for controlling organic pollutants. This invention is based on the principles of circular economy and waste-to-waste treatment, not only disposing of Apocynum venetum waste, but also providing Apocynum venetum biochar that effectively treats organic matter in wastewater, meeting the requirements for treating various types of wastewater.

[0091] This invention combines a multi-component synergistic modification approach, introducing composite modifiers such as nitrogen sources, alkali activators, and metal ions. During pyrolysis, this simultaneously promotes multiple reactions including nitrogen doping, micropore activation, and functional group stabilization, achieving concurrent optimization of structure and surface chemistry. Compared to single-modification methods, this ternary composite modification system significantly enhances the specific surface area, micropore and mesopore development, and nitrogen-containing functional group density of biochar, thereby further strengthening its adsorption capacity for dissolved organic carbon, aromatic substances, and color pollutants. This provides a more promising technical approach for the efficient preparation of Apocynum venetum-based functional biochar.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications and substitutions should be covered within the scope of the claims of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments. More other equivalent embodiments may be included without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A method for preparing modified Apocynum venetum biochar, characterized in that, Includes the following steps: S1. Using Apocynum venetum stems as raw material, wash, dry, cut into small sections, pulverize and sieve to obtain Apocynum venetum powder; S2. Mix the Apocynum venetum powder and the ternary composite modifier according to the preset ratio, add water and mix evenly, then dry to obtain Apocynum venetum powder loaded with modifier; S3. Pyrolysis of Apocynum venetum powder loaded with modifier under an inert gas atmosphere, followed by cooling, grinding, sieving, washing, and drying to obtain modified Apocynum venetum biochar.

2. The preparation method according to claim 1, characterized in that, The particle size of the Apocynum venetum powder obtained in step S1 is less than 100 mesh.

3. The preparation method according to claim 1, characterized in that, The ternary composite modifier in step S2 is urea, sodium carbonate, and iron salt; the preset ratio is a mass ratio of Apocynum venetum powder to urea of ​​1:(1-9), the amount of sodium carbonate is 2%-8% of the mass of Apocynum venetum powder, and the amount of iron salt is 1%-5% of the mass of Apocynum venetum powder. Water is added to dissolve the ternary composite modifier and disperse the Apocynum venetum powder so that the modifier can be uniformly loaded on the powder surface.

4. The preparation method according to claim 1, characterized in that, The inert gas in step S3 is high-purity N2, and the flow rate is controlled between 0.5 and 1 L / min.

5. The preparation method according to claim 1, characterized in that, The pyrolysis conditions for step S3 are as follows: the temperature is increased to 300~800℃ at a rate of 10℃ / min, and the pyrolysis reaction time is 1.5h~2.5h.

6. A modified Apocynum venetum biochar, characterized in that, It is obtained by any of the preparation methods described in claims 1 to 5.

7. An application of modified Apocynum venetum biochar, characterized in that, The modified Apocynum venetum biochar according to claim 6 is used in sewage or wastewater treatment to remove dissolved organic carbon (DOC) and UV radiation. 254 Colorimetric (CN) or fluorescent organic compounds.

8. The application according to claim 7, characterized in that, The sewage or wastewater includes domestic sewage, industrial wastewater, livestock and poultry breeding wastewater, or anaerobic fermentation biogas slurry.

9. The application according to claim 7 or 8, characterized in that, The dosage of the modified Apocynum venetum biochar is 0.5~5 g / L, and the adsorption equilibrium time is 120 min.

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