Preparation method and application of modified salicornia biochar

Abstract

The invention discloses a preparation method of modified salicornia biochar, and belongs to the technical field of environmental protection. The preparation method comprises the following steps: washing, drying and crushing salicornia europaea serving as a raw material, mixing the salicornia europaea with a nitrogen source modifier according to a certain mass ratio, adding water, uniformly stirring, dipping and drying; the nitrogen source modifier is one or more of urea, melamine or thiourea; then carrying out pyrolysis and carbonization, grinding, washing and drying the obtained carbon material, and finally preparing the modified salicornia biochar. The prepared modified salicornia biochar is used for adsorbing organic matters in sewage or wastewater, can effectively remove dissolved organic carbon (DOC, 86.34%), UV254 (89.33%) and chromaticity (CN, 94.74%) in an adsorption experiment of livestock and poultry biogas slurry, and shows excellent adsorption performance. The method follows the principle of treating waste with waste, the salicornia europaea waste is effectively treated, the obtained biochar has good application potential in the aspect of sewage and wastewater treatment, and high-value utilization of the waste is achieved.

Description

Technical Field

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

[0002] With the expansion of halophyte cultivation and the significant increase in their biomass, a large amount of biomass residues (stems, leaves, etc.) are generated. Disposal using traditional methods such as open-air incineration or landfill not only exacerbates air pollution and increases carbon emissions but also wastes valuable biomass resources. Pyrolysis of these residues into biochar provides a circular economy approach for reducing and recycling agricultural waste. Biochar, a carbonaceous material prepared by the pyrolysis of biomass under oxygen-limited conditions, possesses a high specific surface area, well-developed porosity, and excellent pollutant adsorption capacity. It can not only promote the circular development of saline-alkali agriculture but also serve as a low-cost adsorbent for the treatment of wastewater, such as domestic sewage, industrial wastewater, livestock and poultry wastewater, or anaerobic fermentation slurry.

[0003] *Salvia splendens* is a typical halophyte widely distributed in Northwest my country and saline-alkali regions. It is not only an important species for saline-alkali land management and ecological restoration, but also a biochar precursor with great development potential. In terms of material composition, *Salvia splendens* stems are rich in inorganic elements such as potassium, calcium, magnesium, sodium, and chlorine, which act as natural biochar modifiers. Structurally, its unique salt tolerance mechanism allows a large number of ions to be isolated within cell vacuoles. This special salt-isolated structure can act as a natural template during pyrolysis, inducing a unique pore configuration different from traditional biochar, thus endowing it with superior adsorption potential. However, systematic research is currently lacking on the impact of *Salvia splendens*'s special properties on the pore evolution, surface chemical properties, and removal efficiency and mechanisms of biochar.

[0004] Therefore, developing a high-performance Salicornia glutinosa biochar based on nitrogen source modification technology is of great scientific significance and application value for solving the environmental burden of waste, enhancing the deep purification of sewage, and promoting the recycling of resources in saline-alkali land. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the existing technology, the purpose of this invention is to provide a method for preparing nitrogen-modified Salicornia glutinosa biochar and its application. By introducing a nitrogen source modifier to optimize the pore structure and surface activity of the biochar, a high-performance adsorbent material with both high specific surface area and abundant active sites is developed, which has a significant effect on the adsorption of organic matter in sewage or wastewater treatment.

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

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

[0008] S1. Using the stems of Salicornia glutinosa as raw material, wash, dry, cut into small sections, crush and sieve to obtain Salicornia glutinosa powder;

[0009] S2. Mix the Salicornia glutinosa powder with a nitrogen source modifier at a certain mass ratio, add water and stir evenly, and finally soak and dry to obtain Salicornia glutinosa powder with modifier.

[0010] S3. The modified Salicornia glutinosa powder was pyrolyzed under an inert gas atmosphere, cooled, ground, sieved, washed and dried to obtain modified Salicornia glutinosa biochar.

[0011] Furthermore, in step S1, the particle size of the Salicornia salsa powder is 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 nitrogen source modifier in step S2 is one or more of urea, melamine, or thiourea; the mass ratio of the *Salvia splendens* powder to the nitrogen source modifier is 1:(0.5-2). Urea, melamine, and thiourea can all provide a stable nitrogen source and form nitrogen-containing functional groups during pyrolysis. Appropriate proportions of these substances with *Salvia splendens* powder ensure a moderate and uniform nitrogen source loading. Adding an appropriate amount of water allows for the full dissolution of the modifier and effective dispersion of the *Salvia splendens* powder, thereby promoting the efficient generation of nitrogen-containing functional groups and significantly improving the surface activity and adsorption performance of biochar.

[0013] Furthermore, in step S3, the inert gas is high-purity N2, with a flow rate controlled between 0.5 and 1 L / min. N2 provides inert protection, effectively preventing oxidation reactions during pyrolysis and improving the structural stability of the biochar. This flow rate range effectively removes volatile gases generated during pyrolysis, preventing secondary condensation and blockage of the biochar pores, while also avoiding excessive flow leading to powder dispersion or rapid heat loss.

[0014] Furthermore, the pyrolysis conditions in step S3 are specifically as follows: the temperature is increased to 300℃ to 800℃ at a rate of 10℃ / min, and the pyrolysis reaction is carried out for 1.5 to 2.5 hours. Using a heating rate of 10℃ / min avoids the collapse of the carbon skeleton due to excessively rapid heating or increased energy consumption due to excessively slow heating; the temperature range of 300℃ to 800℃ covers the key stages of biomass carbonization and functional group reconstruction, and the holding time of 1.5 to 2.5 hours ensures complete carbonization of biomass and the formation of a stable structure, while maximizing the preservation of the activity of nitrogen-containing functional groups.

[0015] This invention also provides modified Salicornia glutinosa biochar prepared by the above method, and its applications. The modified Salicornia glutinosa biochar is used in wastewater or sewage treatment to remove dissolved organic carbon (DOC) and ultraviolet absorbance (UVA). 254 It has significant effects on color (CN) and fluorescent organic compounds.

[0016] The wastewater includes domestic sewage, industrial wastewater, livestock and poultry breeding wastewater, or anaerobic fermentation biogas slurry. The dosage of the modified Salicornia glutinosa biochar is 0.1–5 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 Salicornia glutinosa as raw material. The plant is rich in inorganic salts and possesses a unique salt compartment structure within its cells, which can act as a natural modifier, inducing the rapid formation of a special porous structure different from traditional biochar. Based on this, this invention introduces a nitrogen source modifier for synergistic effect. The gas generated during its pyrolysis enhances the activation of the carbon skeleton, opening up more micropore channels. Simultaneously, highly active nitrogen-containing functional groups are in-situ doped into the carbon lattice, thereby inducing the formation of a special structure with both well-developed hierarchical pores and abundant surface active sites, endowing it with adsorption performance far superior to traditional biochar.

[0019] 2. The modified Salicornia biochar prepared by this invention has a large specific surface area and porosity, which is conducive to the physical adsorption of organic matter and thus has a high adsorption capacity; and it has a large number of active adsorption sites such as oxygen-containing, nitrogen-containing functional groups and cations, which is conducive to the chemical adsorption of organic matter and thus has a high adsorption capacity.

[0020] 3. The process for preparing modified Salicornia glutinosa biochar according to this invention is simple and environmentally friendly, overcoming the problems of high energy consumption and secondary pollution in traditional modified biochar preparation processes. Furthermore, the Salicornia glutinosa biochar prepared by this invention exhibits good recyclability, with its adsorption performance decreasing by less than 10% after multiple regenerations, demonstrating excellent potential for sustainable application and contributing to resource conservation and sustainable ecological development. Attached Figure Description

[0021] Figure 1 This is a schematic diagram illustrating the preparation process and application of modified Salicornia glutinosa biochar.

[0022] Figure 2 This is a scanning electron microscope image of Salthorn biochar.

[0023] Figure 3 Nitrogen adsorption-desorption isotherms, specific surface area, and pore size diagrams for Salicornia glutinosa biochar.

[0024] Figure 4X-ray photoelectron spectrum of Salicornia glutinosa biochar.

[0025] Figure 5 This is a fitting diagram of the C1s peaks of Salicornia glutinosa biochar.

[0026] Figure 6 This is the Fourier transform infrared spectrum of Salicornia salina biochar.

[0027] Figure 7 The contact angle and zeta potential diagrams for Salicornia glutinosa biochar are shown.

[0028] Figure 8 This is a graph showing the adsorption efficiency of Salicornia glutinosa biochar on organic matter in wastewater.

[0029] Figure 9 This is a diagram showing the adsorption kinetics of organic matter in wastewater by Salicornia glutinosa biochar.

[0030] Figure 10 This is an isotherm diagram showing the adsorption of organic matter in wastewater by Salicornia glutinosa biochar.

[0031] Figure 11 This diagram illustrates the regeneration and recycling of Salicornia glutinosa biochar.

[0032] Figure 12 The figure shows the effect of different types and proportions of modifiers on the adsorption of Salicornia glutinosa biochar. Detailed Implementation

[0033] 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 test materials used in the following embodiments are commercially available products.

[0034] This invention provides a method for preparing modified Salicornia glutinosa biochar, comprising the following steps:

[0035] S1. Using the stems of Salicornia glutinosa as raw material, wash, dry, cut into small sections, crush and sieve to obtain Salicornia glutinosa powder with a particle size of less than 100 mesh.

[0036] S2. Mix the *Salvia splendens* powder with a nitrogen source modifier at a certain mass ratio, add water and stir evenly, and finally soak and dry; the nitrogen source modifier is one or more of urea, melamine or thiourea; the mass ratio of *Salvia splendens* powder to nitrogen source modifier is 1:(0.5-2), and add water and stir evenly to dissolve the modifier and disperse the *Salvia splendens* powder, so that the modifier can be evenly loaded on the powder surface to obtain *Salvia splendens* powder with modifier.

[0037] S3. The modified *Salix babylonica* powder was pyrolyzed under an inert gas atmosphere. After cooling, it was ground, sieved, washed, and dried to obtain modified *Salix babylonica* biochar. The inert gas was high-purity N2, with a flow rate controlled at 0.5 to 1 L / min. The pyrolysis specifically involved heating at a rate of 10 °C / min to 300 °C, 400 °C, 500 °C, 600 °C, 700 °C, and 800 °C for 1.5–2 h.

[0038] The modified Salicornia biochar has a porous surface with numerous mesopores and micropores and a large specific surface area, and contains high ion content and active functional groups.

[0039] This invention also provides an application of modified Salicornia glutinosa biochar in the treatment of livestock and poultry biogas slurry wastewater. The application in the treatment of livestock and poultry biogas slurry wastewater includes the reduction of dissolved organic carbon (DOC) and ultraviolet absorbance (UVA) of the wastewater. 254 Removal of organic compounds, including color (CN) and fluorescent organic compounds.

[0040] This invention utilizes modified Salicornia glutinosa biochar as an adsorbent to conduct adsorption experiments on livestock and poultry biogas slurry. After adsorption equilibrium, the removal rate of DOC from the biogas slurry was 86.34%, and the UV removal rate was [missing data]. 254 The removal rate was 89.33%, and the CN removal rate was 94.74%. Therefore, the adsorption performance of the Salicornia glutinosa biochar adsorbent was significantly improved compared with that of traditional biochar.

[0041] Example

[0042] I. Preparation method of modified Salicornia glutinosa biochar, the specific steps are as follows:

[0043] S1. Collect discarded Salicornia stems, rinse the stems with tap water to remove the soil, then rinse again with deionized water, air dry, cut into 3 to 5 cm pieces, and dry at 60℃ for 24 hours. Grind the dried sample using a universal grinder, pass through a 100-mesh sieve, and obtain Salicornia powder.

[0044] S2. Mix the *Salix babylonica* powder with a nitrogen source modifier at a certain mass ratio, add deionized water and stir evenly, then impregnate and dry, and place in a tube furnace for pyrolysis. First, purge the air in 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. The specific types of nitrogen source modifiers, mass ratios, and final pyrolysis temperatures are shown in Table 1. Maintain for 2 hours.

[0045] S3. After pyrolysis, the sample was cooled to room temperature in a nitrogen atmosphere, and the biochar was removed. The obtained biochar was ground and sieved, washed multiple times with deionized water, and then dried overnight in a 60°C drying oven to finally obtain modified Salicornia glutinosa biochar.

[0046] Example 1

[0047] Following the preparation method in step S1, the mass ratio of Salicornia glutinosa powder to nitrogen source modifier was adjusted to 1:0, and the pyrolysis temperature was set to 300℃, in order to investigate the effect of different temperatures on the adsorption performance of biochar materials on biogas slurry.

[0048] Example 2

[0049] Following the preparation method of Example 1, the pyrolysis temperature in step S1 of Example 1 was adjusted to 400℃, while the remaining conditions were 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.

[0050] Example 3

[0051] Following the preparation method of Example 1, the pyrolysis temperature in step S1 of Example 1 was adjusted to 500℃, while the remaining conditions were 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.

[0052] Example 4

[0053] Following the preparation method of Example 1, the pyrolysis temperature in step S1 of Example 1 was adjusted to 600℃, while the remaining conditions were 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.

[0054] Example 5

[0055] Following the preparation method of Example 1, the pyrolysis temperature in step S1 of Example 1 was adjusted to 700℃, while the remaining conditions were 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.

[0056] Example 6

[0057] Following the preparation method of Example 1, the pyrolysis temperature in step S1 of Example 1 was adjusted to 800℃, while the remaining conditions were 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.

[0058] Example 7

[0059] Referring to the preparation method in Example 1, the mass ratio of Salicornia glutinosa powder to urea was adjusted to 1:0.5, and the pyrolysis temperature was set to 700℃, in order to investigate the effect of different mass ratios of urea-modified biochar materials on the adsorption performance of biogas slurry.

[0060] Example 8

[0061] Referring to the preparation method in Example 1, the mass ratio of Salicornia glutinosa powder to urea was adjusted to 1:1, and the pyrolysis temperature was set to 700℃, in order to investigate the effect of different mass ratios of urea-modified biochar materials on the adsorption performance of biogas slurry.

[0062] Example 9

[0063] Referring to the preparation method of Example 1, the mass ratio of Salicornia glutinosa powder to urea was adjusted to 1:2, and the pyrolysis temperature was set to 700℃, in order to investigate the effect of different mass ratios of urea-modified biochar materials on the adsorption performance of biogas slurry.

[0064] Example 10

[0065] Referring to the preparation method in Example 1, the mass ratio of Salicornia glutinosa powder to thiourea was adjusted to 1:0.5, and the pyrolysis temperature was set to 700℃, in order to investigate the effect of different mass ratios of thiourea-modified biochar materials on the adsorption performance of biogas slurry.

[0066] Example 11

[0067] Referring to the preparation method in Example 1, the mass ratio of Salicornia glutinosa powder to thiourea was adjusted to 1:1, and the pyrolysis temperature was set to 700℃, in order to investigate the effect of different mass ratios of thiourea-modified biochar materials on the adsorption performance of biogas slurry.

[0068] Example 12

[0069] Referring to the preparation method in Example 1, the mass ratio of Salicornia glutinosa powder to thiourea was adjusted to 1:2, and the pyrolysis temperature was set to 700℃, in order to investigate the effect of different mass ratios of thiourea-modified biochar materials on the adsorption performance of biogas slurry.

[0070] Example 13

[0071] Referring to the preparation method in Example 1, the mass ratio of Salicornia glutinosa powder to melamine was adjusted to 1:0.5, and the pyrolysis temperature was set to 700℃, in order to investigate the effect of different mass ratios of melamine-modified biochar materials on the adsorption performance of biogas slurry.

[0072] Example 14

[0073] Referring to the preparation method in Example 1, the mass ratio of Salicornia glutinosa powder to melamine was adjusted to 1:1, and the pyrolysis temperature was set to 700℃, in order to investigate the effect of different mass ratios of melamine-modified biochar materials on the adsorption performance of biogas slurry.

[0074] Example 15

[0075] Referring to the preparation method in Example 1, the mass ratio of Salicornia glutinosa powder to melamine was adjusted to 1:2, and the pyrolysis temperature was set to 700℃, in order to investigate the effect of different mass ratios of melamine-modified biochar materials on the adsorption performance of biogas slurry.

[0076] II. Performance Characterization of Salicornia glutinosa Biochar

[0077] Figure 1 This diagram illustrates the preparation process and application of Salicornia glutinosa biochar. First, Salicornia glutinosa raw material is uniformly mixed with a nitrogen source modifier and then subjected to a pyrolysis process at 300–800℃ to generate Salicornia glutinosa biochar. Subsequently, the obtained biochar is used for the adsorption treatment of various types of wastewater to remove organic pollutants.

[0078] Figure 2 The images shown are scanning electron microscope (SEM) images of *Salix salicifolia* biochar from Examples 1-6. 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℃.

[0079] Figure 3 Nitrogen adsorption-desorption isotherms, specific surface area, and pore size diagrams for *Salvia splendens* biochar. Figure 3 It was found that all *Salix salina* biochar exhibited typical type IV adsorption isotherms and significant hysteresis loops, indicating that mesoporous structures (2-50 nm) were dominant. At pyrolysis temperatures of 300℃ and 400℃, the narrower H3-type hysteresis loops indicated that the porosity mainly originated from slit-like pores formed by the aggregation of plate-like particles, resulting in a low specific surface area (SSA), only 4.42-6.67 m². 2 / g, total pore volume (Vt) less than 0.021cm³ 3 / g. As the pyrolysis temperature increases to 500℃, the H3-type hysteresis ring gradually widens, and the specific surface area increases to 38.35m². 2 / g indicates 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 formation of a large number of micropores (<2nm), while the hysteresis loop transforms into a mixed H3 / H4 type, indicating the coexistence of slit-like mesopores and narrow micropores. At this time, the specific surface area (SSA) increases significantly (>500m²). 2 / g), total pore volume (V t (More than 0.300cm) 3 / g, micropore volume (V) m (More than 0.180cm) 3 / g, thereby significantly enhancing the pore-filling adsorption sites for organic pollutants.

[0080] Figure 4 This is an X-ray photoelectron spectrum of *Salix babylonica* biochar. Figure 4It can be seen that the inorganic salt content in *Salix triangularis* biochar increases with increasing pyrolysis temperature, mainly including Ca, Mg, Na, and Cl, indicating that its inherent salt content is relatively high. *Salix triangularis* biochar exhibits relatively high O / C and (O+N) / C ratios at pyrolysis temperatures of 600℃ and 700℃, indicating that its elemental changes are not monotonic.

[0081] Figure 5 This is a C1s peak fitting diagram of Salicornia glutinosa biochar. (From...) Figure 5 It is evident that *Salix salina* biochar exhibits a high proportion of CC / C=C / CH (78.98%) at a pyrolysis temperature of 300℃, while the proportions of nitrogen- and oxygen-containing functional groups are relatively low, indicating that it underwent a rapid and high-level carbonization process at a lower temperature. This may be attributed to the catalytic effect of abundant inorganic salts on deoxygenation and the formation of aromatic carbon structures during pyrolysis. When the pyrolysis temperature increases to 600℃ and 700℃, the proportions of CO / CN and C=O functional groups increase significantly, while the π-π* domains are enhanced. These oxygen- and nitrogen-containing functional groups can promote the adsorption of organic matter through hydrogen bonding and electrostatic attraction, while the enhanced π-π* domains provide a conjugated electron system conducive to π-π electron donor-acceptor interactions. However, at 800℃, these functional groups decrease again due to decarboxylation, condensation, and further aromatization reactions, leading to a reduction in the number of active sites.

[0082] Figure 6 This is the Fourier transform infrared spectrum of *Salvia splendens* biochar. Figure 6 It can be seen that the spectral changes of Salicornia biochar are relatively gradual across all pyrolysis temperature ranges. Although the intensity of the -OH and C=O absorption peaks is weakened, it indicates that the carbon matrix of Salicornia biochar can achieve a rapid and stable structural stabilization process at lower pyrolysis temperatures.

[0083] Figure 7 This is a diagram showing the contact angle and zeta potential of *Salvia splendens* biochar. (From...) Figure 7 It is observed that the contact angle (CA) continuously decreases with increasing pyrolysis temperature, while the Zeta potential initially decreases and then significantly increases above 600℃. This is because *Salix elegans* biochar retains abundant oxygen- and nitrogen-containing functional groups at high temperatures, thereby enhancing its surface hydrophilicity and negative charge density. Furthermore, when the pyrolysis temperature exceeds 600℃, the endogenous salt content (Na₂O₃) increases. + K + Ca 2+ Mg 2+ (e.g., ) migrate and crystallize on the surface, leading to a significant increase in the Zeta potential. The exposed mineral phases have good hydrophilicity, further enhancing the overall hydrophilicity.

[0084] III. Adsorption of Organic Matter in Wastewater by Salicornia glutinosa Biochar

[0085] This invention uses dissolved organic carbon (DOC) 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 TOC analyzer. The absorbance of the wastewater under 254 nm ultraviolet light (UV) was used as the analytical measure. 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.

[0086]

[0087] (1) Determination of adsorption capacity: The adsorbent was actual biogas slurry without pH adjustment (pH 7.0–8.9), 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.

[0088] (2) Determination of adsorption kinetics: The adsorbent was actual biogas slurry without pH adjustment (pH 7.0–8.9). 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, 30, 45, 60, 90, 120, 240, 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.

[0089] (3) Determination of adsorption isotherms: The adsorption target was actual biogas slurry without pH adjustment (pH 7.0–8.9), 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 the biogas slurry were fitted using the Langmuir and Fruendlich models. The average value of two repeated experiments was used to avoid errors.

[0090] Figure 8 This is a graph showing the adsorption efficiency of *Salvia splendens* biochar on 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 a maximum at 700℃: the DOC removal rate is 47.54%, and the UV removal efficiency is... 254 The removal rate was 59.98%, and the CN removal rate was 58.28%, which then decreased slightly at a pyrolysis temperature of 800℃.

[0091] Figure 9 This is a diagram showing the adsorption kinetics of organic matter in wastewater by *Salvia splendens* biochar. Figure 9 It was observed that when the pyrolysis temperature exceeded 600℃, the adsorption process of DOC proceeded rapidly within the first 30 minutes and reached 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 no kinetic analysis was conducted. Kinetic fitting results showed that *Salix matsudana* biochar at pyrolysis temperatures above 600℃ better conformed to the pseudo-second-order kinetic model (PSO), indicating that chemisorption was the dominant mechanism, accompanied by strong affinity between organic molecules and the biochar surface and rapid mass transfer. This behavior can be attributed to its high abundance of oxygen / nitrogen functional groups, increased salt content, and enhanced π-π* structure, which collectively promote hydrogen bonding, electrostatic attraction to negatively charged organic matter, and π-π electron donor-acceptor interactions. In contrast, biochar with pyrolysis temperatures of 400℃ and 500℃ better conformed to the pseudo-first-order kinetic model (PFO), indicating that physical pore filling played a dominant role in its adsorption process.

[0092] Figure 10 This is an isotherm diagram showing the adsorption of organic matter from wastewater by *Salvia splendens* biochar. Figure 10 It can be seen that the Langmuir and Freundlich models for all samples showed high correlation coefficients (R²). 2 The results indicate a good fit. Biochar with a pyrolysis temperature of 400℃ better fits the Langmuir model, suggesting that its adsorption process is mainly monolayer adsorption. However, when the pyrolysis temperature exceeds 500℃, the adsorption behavior gradually transforms into multilayer adsorption characteristics that conform to the Freundlich model, indicating enhanced surface heterogeneity and a more diverse range of active sites.

[0093] IV. Recyclability of Salicornia biochar

[0094] The *Salix triangularis* biochar that had adsorbed organic matter was regenerated by pyrolysis. Nitrogen flow was adjusted to 0.5 L / min, and the temperature was increased to 700 °C at a rate of 10 °C / min, held for 2 hours. After cooling, it was washed with deionized water and vacuum dried overnight at 60 °C to obtain the regenerated *Salix triangularis* biochar.

[0095] Figure 11 This diagram illustrates the regeneration and recycling of Salicornia glutinosa biochar. (Source: [Insert Source Here] Figure 11 It can be seen that after three independent pyrolysis regenerations, the adsorption capacity of Salicornia biochar for organic matter decreased by less than 10%, indicating good reusability.

[0096] V. Optimization of Modifier Ratio

[0097] Figure 12 The graph shows the effect of different types and proportions of modifiers on the adsorption of *Salix babylonica* biochar. Under a fixed pyrolysis temperature of 700℃, the effect of different mass ratios (1:0.5, 1:1, 1:2) of nitrogen source modifiers on the material properties was investigated. Figure 12 It is evident that the addition ratio of the modifier has a significant impact on the pore development and surface active site density of biochar. All nitrogen source modifiers reached their peak performance when the mass ratio with *Salix babylonica* powder was 1:1. At lower addition ratios (1:0.5), although the DOC removal rate increased to 68.15%, the active sites were not yet saturated due to the limited introduction of nitrogen source. When the mass ratio was optimized to 1:1, the modification effect was significantly improved. At this point, the nitrogen source modifier and the biomass matrix achieved the best synergistic effect, not only constructing a high specific surface area framework but also introducing a large number of highly active nitrogen- and oxygen-containing functional groups. This enabled the modified biochar to effectively remove DOC and UV radiation from the biogas slurry. 254 The removal rates increased to 86.34% and 89.33% respectively, demonstrating excellent adsorption efficiency. When the ratio was further increased to 1:2, the excessive decomposition products of the modifier clogged some micropores, causing the removal rate to decline. In summary, a 1:1 addition ratio maximizes the synergistic effect of the modifier.

[0098] VI. Effects of Different Nitrogen Source Modifiers on the Performance of Modified Biochar

[0099] Figure 12 Different types and proportions of modifiers for Salicornia biochar affect DOC, CN, and UV. 254 Adsorption diagram. To screen for the most efficient modifying component, this invention compared the modification effects of urea, thiourea, and melamine under the same conditions. Experimental results show that different nitrogen sources significantly improve biochar performance, with melamine exhibiting the best modification advantage. While urea and thiourea modifications can increase DOC removal rates to the 63%–69% range and improve the original char performance, melamine modification achieves a breakthrough improvement in adsorption performance. This is due to the abundant amino and triazine ring structures in melamine, which can incorporate more highly active nitrogen sites into the biochar lattice during pyrolysis. This unique surface chemical modification significantly increases the affinity of biochar for organic pollutants, achieving a DOC removal rate as high as 86.34% and UV... 254The removal rate reached 89.33%, and the CN removal rate reached 94.74%. In summary, this invention preferentially uses melamine as the best modifier, and the prepared modified biochar has extremely high application value and can achieve deep purification of wastewater.

[0100] Table 1 shows the performance comparison of the examples.

[0101]

[0102]

[0103]

[0104]

[0105] The *Salix triangularis* biochar prepared by this invention is used to adsorb organic matter in sewage or wastewater. In adsorption experiments on biogas slurry, its removal rate of dissolved organic carbon (DOC) was 86.34%, and UV... 254 The removal rate was 89.33%, and the color (CN) removal rate was 94.74%, demonstrating good adsorption performance. This invention follows the principle of "treating waste with waste," effectively disposing of *Salix babylonica* waste and demonstrating that the resulting biochar has good application potential in treating wastewater, thus achieving high-value utilization of waste.

[0106] 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 Salicornia glutinosa biochar, characterized in that, Includes the following steps: S1. Using the stems of Salicornia glutinosa as raw material, wash, dry, cut into small sections, crush and sieve to obtain Salicornia glutinosa powder; S2. Mix the Salicornia glutinosa powder with the nitrogen source modifier according to a preset mass ratio, add water and stir evenly, and finally soak and dry to obtain Salicornia glutinosa powder with modifier. S3. The modified Salicornia glutinosa powder is pyrolyzed under an inert gas atmosphere, cooled, ground, sieved, washed and dried to obtain modified Salicornia glutinosa biochar.

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

3. The preparation method according to claim 1, characterized in that, In step S2, the nitrogen source modifier is one or more of urea, melamine, or thiourea; the preset mass ratio of the Salicornia glutinosa powder to the nitrogen source modifier is 1:(0.5~2). Add an appropriate amount of water to dissolve the modifier and disperse the Salicornia glutinosa powder so that the modifier can be uniformly loaded on the powder surface.

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

6. A modified Salicornia glutinosa biochar, characterized in that, It is prepared by the method described in any one of claims 1 to 5.

7. An application of modified Salicornia glutinosa biochar, characterized in that, The modified Salicornia glutinosa biochar of claim 6 is applied in sewage or wastewater treatment to remove dissolved organic carbon (DOC) and ultraviolet absorbance (UVA). 254 ), color (CN) and fluorescent organic compounds.

8. The application of the modified Salicornia biochar 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 of the modified Salicornia biochar according to claim 7 or 8, characterized in that, The dosage of the modified Salicornia biochar is 0.1 ~ 5 g / L, and the adsorption equilibrium time is 120 min.

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