Nostoc sphaeroids kutz acetylation modified flocculant as well as preparation method and application thereof

Abstract

The invention provides a nostoc sphaeroids kutz acetylation modified flocculant as well as a preparation method and application thereof, and belongs to the field of water treatment. The flocculating agent is an acetylated derivative of nostoc sphaeroids kutz polysaccharide and protein, the acetyl content in each gram of the flocculating agent is 12%-28%, and the total substitution degree is 0.2-0.5. The preparation method comprises the following steps: mixing nostoc sphaeroids kutz powder with acetic anhydride, glacial acetic acid and concentrated sulfuric acid for acetylation, and then neutralizing, washing, drying and crushing to finally obtain the modified flocculant. Compared with unmodified nostoc sphaeroids kutz, the modified flocculant has higher flocculation efficiency and stability, impurities in water can be more quickly gathered to form flocs, and the flocs are not easy to disperse. The flocculant is free of harmful by-products, does not cause secondary pollution, and is suitable for treating various types of wastewater. The problems that an existing natural nostoc sphaeroids kutz flocculant is unstable in performance, poor in adaptability, insufficient in efficiency and incapable of meeting the complex water quality treatment requirement are effectively solved.

Description

Technical Field

[0001] The invention belongs to the field of water treatment and relates to an acetylated modified flocculant of kudzu vine and a preparation method and application thereof. Background Art

[0002] With the rapid development of global industrialization and urbanization, water pollution has become one of the most severe environmental challenges facing the world today. The large-scale discharge of various industrial wastewaters, domestic sewage, and agricultural non-point source pollution not only severely damages aquatic ecosystems but also directly threatens human health and the living environment. In the process of water pollution control, flocculants, as a key water treatment agent, are widely used in various water purification and sewage treatment processes. The main function of flocculants is to aggregate suspended solid particles, colloids, and dissolved pollutants in water through chemical or physical effects to form larger flocs, thereby facilitating subsequent separation operations such as sedimentation and filtration, thereby removing pollutants and purifying water quality.

[0003] At present, the common flocculants on the market mainly include two categories: inorganic flocculants and organic flocculants. Inorganic flocculants such as aluminum salts and iron salts have the advantages of low cost and wide application, but they have obvious limitations. For example, aluminum salt flocculants may cause aluminum ion residues in water bodies, and long-term use may cause harm to the environment and human health. Organic flocculants can be further divided into synthetic organic polymer flocculants, natural organic polymer flocculants and microbial flocculants. Synthetic organic polymer flocculants such as polyacrylamide have the advantages of good flocculation effect and low dosage, but the residues of this type of polymer have "three-hazard" effects (teratogenicity, carcinogenicity, and mutagenicity), which pose a serious threat to human health. At the same time, they are difficult to degrade in the natural environment and are prone to secondary pollution. Natural organic polymer flocculants and microbial flocculants have received increasing attention due to their natural sources and environmental friendliness. However, natural organic polymer flocculants often have problems such as unstable flocculation performance and limited scope of application; although microbial flocculants have the advantages of high efficiency, non-toxicity and no secondary pollution, the production process is relatively complex and the cost is high, which limits their large-scale application.

[0004] Nostoc sphaeroides, a pseudo-globose algae belonging to the Nostocaceae family of the Cyanobacteria class, secretes large amounts of exopolysaccharides and proteins, which give it certain flocculating activity. Studies have shown that, under natural conditions, Nostoc sphaeroides can flocculate some suspended particles and colloidal substances in water. However, its original flocculation performance may not meet the increasingly complex demands of water pollution control. For example, when treating high-concentration, highly polluted industrial wastewater, Nostoc sphaeroides' flocculation effect may be less than ideal, and the stability and selectivity of its flocculation effect also need to be improved. Summary of the invention

[0005] The technical problem to be solved by the present invention is the problems existing in the existing natural Nostoc flagelliforme flocculant, such as unstable flocculation performance, poor adaptability to high-concentration pollutants, insufficient flocculation efficiency, and inability to meet the requirements of complex water quality treatment. In order to overcome the problems existing in the existing flocculant and make full use of the potential value of the biological resource of Nostoc flagelliforme, it is necessary to chemically modify Nostoc flagelliforme to improve its flocculation performance. Acetylation modification is a commonly used chemical modification method. By introducing acetyl groups into the polysaccharide molecules of Nostoc flagelliforme, the hydrophobicity and charge density of its molecules can be enhanced, thereby enhancing its adsorption and flocculation ability to impurities in water. This modified Nostoc flagelliforme flocculant is expected to improve the flocculation effect and expand the scope of application on the basis of maintaining natural characteristics, providing a new and effective solution for water pollution treatment.

[0006] To achieve the above application purpose, the technical solutions adopted in this application are as follows:

[0007] In the first aspect, the present invention provides a Nostoc flagelliforme acetylated modified flocculant, which is an acetylated derivative of polysaccharide and protein in Nostoc flagelliforme, and its elemental composition includes 40% - 45% carbon by mass percentage.

[0008] In the above Nostoc flagelliforme acetylated modified flocculant, the acetyl group content per gram of the Nostoc flagelliforme acetylated modified flocculant is 12% - 28%, and the total substitution degree of the acetyl group is 0.2 - 0.5.

[0009] In the above Nostoc flagelliforme acetylated modified flocculant, the hydroxyl groups on the polysaccharide molecular chain are connected to the acetyl group -O-COCH3 through ester bonds, and the hydroxyl substitution degree is 30% - 55%.

[0010] In the above Nostoc flagelliforme acetylated modified flocculant, the amino groups on the protein molecular chain are connected to the acetyl group -NH-COCH3 through amide bonds, and the substitution rate of the amino group is 15% - 30%.

[0011] The zeta potential of the above Nostoc flagelliforme acetylated modified flocculant is -25 mV to -35 mV.

[0012] In the second aspect, the present invention provides a preparation method of a Nostoc flagelliforme acetylated modified flocculant, which specifically includes the following steps:

[0013] S1. Weigh the Nostoc flagelliforme powder and measure its hydroxyl content;

[0014] S2. Mix the Nostoc flagelliforme powder with acetic anhydride, glacial acetic acid and concentrated sulfuric acid for acetylation reaction to obtain a reaction solution, which specifically includes:

[0015] S2-1. Mix acetic anhydride and glacial acetic acid to prepare an acetic anhydride solution;

[0016] S2-2. Add concentrated sulfuric acid to the acetic anhydride solution and mix evenly to obtain a mixed solution;

[0017] S2-3. After mixing the Nostoc commune powder with the mixed solution, heat and stir at a constant temperature to complete the acetylation reaction;

[0018] S3. Neutralize, wash, dry and pulverize the reaction solution to obtain the Nostoc commune acetylation-modified flocculant described in any one of claims 1 to 3.

[0019] In the above step S1, the particle size of the Nostoc commune powder is the powder obtained by passing through a 200-mesh sieve.

[0020] Furthermore, the preparation method of the Nostoc commune powder is: select Nostoc commune raw materials, and successively carry out soaking, rinsing for impurity removal, draining and drying treatments. After drying, pulverize and screen through a 200-mesh sieve to obtain Nostoc commune powder.

[0021] Even further, the selected Nostoc commune raw materials are high-quality Nostoc commune manually selected without obvious impurities.

[0022] Even further, the impurity removal is: soak the Nostoc commune in deionized water for 2 to 3 hours, and stir once every 30 minutes during this period; after soaking, rinse repeatedly with deionized water until the rinsing water is clear and transparent without impurity residue.

[0023] Even further, the drying is: drain the surface moisture of the Nostoc commune on a clean filter paper, and then put it into an oven for drying at 40 to 45 °C for 10 to 12 hours; during the drying process, regularly check the drying degree of the Nostoc commune to avoid deterioration of the Nostoc commune caused by local overheating.

[0024] In the above step S1, the measurement method of the hydroxyl content is: use the acetic anhydride-pyridine method to measure the hydroxyl value, and calculate the hydroxyl molar amount according to the formula n OH =(OH × m)÷(56.1×1000);

[0025] Where: n OH is the hydroxyl molar amount, mol; OH is the hydroxyl value, mg KOH / g; m is the mass of the Nostoc commune powder, g; 56.1 is the molar mass of KOH, g / mol.

[0026] In the above step S2-2, the addition amount of concentrated sulfuric acid is 0.5 to 1.5 mL / g of Nostoc commune powder, and its mass concentration ≥ 98%.

[0027] In the above step S2-2, the concentrated sulfuric acid is added in a slow dropping manner and continuously stirred, and continue to stir for 5 to 10 minutes after dropping until it is mixed evenly.

[0028] In the above step S2-3, the solid-liquid ratio of Nostoc commune powder to acetic anhydride solution is 1:10 - 1:15 (w / v), and the molar amount of acetic anhydride is 1.2 - 1.5 times the molar amount of hydroxyl groups.

[0029] In the above step S2-3, the Nostoc commune powder and the mixed solution are magnetically stirred and mixed at a speed of 150 - 250 rpm, and react for 2 - 4 hours under the constant temperature condition of 40 - 50 °C.

[0030] In the above step S3, the neutralization, washing, drying and pulverization include:

[0031] S3-1. Ice water is added to the reaction solution to terminate the reaction, and then it is neutralized with sodium hydroxide solution.

[0032] S3-2. The neutralized reaction solution is diluted, and the precipitate is obtained by centrifugal separation.

[0033] S3-3. After the precipitate is washed, dried and pulverized, it is sieved through a 300-mesh sieve to obtain the Nostoc commune acetylated modified flocculant.

[0034] Furthermore, in the above step S3-1, the reaction solution is neutralized with 1 - 2 mol / L sodium hydroxide solution to a pH of 7 ± 0.5.

[0035] Furthermore, in the above step S3-2, the reaction solution is diluted to 3 - 5 times the original volume with deionized water and centrifuged at a speed of 3000 - 4000 rpm for 15 - 25 minutes.

[0036] Furthermore, in the above step S3-3, after the precipitate is washed with deionized water, it is centrifugally separated at a speed of 3000 - 4000 rpm / min, and the washing and centrifugation operations are repeated 3 - 5 times; the drying is carried out at 50 - 55 °C for 6 - 8 hours.

[0037] In the third aspect, the present invention provides the application of the above Nostoc commune acetylated modified flocculant, or the Nostoc commune acetylated modified flocculant prepared by the above preparation method, in the technical field of wastewater and sewage treatment.

[0038] Advantages of the present invention: The present invention uses natural Nostoc commune as a raw material to prepare a flocculant through a green chemical modification process. No toxic by-products are generated during the preparation process. The product is easily degraded in the natural environment after use, will not cause secondary pollution, and is environmentally friendly. The present invention precisely regulates the molecular structures of Nostoc commune polysaccharides and proteins through acetylation reactions. On the basis of retaining the environmental compatibility of natural products, the hydrophobic properties and charge density of the molecular chains are significantly enhanced, enabling better interaction with impurity particles in water. Through adsorption, bridging and other action mechanisms, suspended particles, colloids, etc. in water are rapidly aggregated and precipitated, showing good flocculation effects. This flocculant can maintain a certain flocculation activity under different pH values and temperature conditions, with a fast floc formation rate, a dense structure and excellent sedimentation performance, and is applicable to the treatment of various types of wastewater, including industrial wastewater, domestic sewage, etc. Compared with the unmodified Nostoc commune flocculant, the broad-spectrum treatment ability of this product for pollutants is significantly improved, with stronger flocculation efficiency and stability, while avoiding the risk of secondary pollution caused by residues of traditional flocculants. Brief Description of the Drawings

[0039] Figure 1 It is a schematic process flow diagram of the preparation method of the Nostoc commune acetylation-modified flocculant. Detailed Embodiments

[0040] In order to make the technical problems to be solved, technical solutions and beneficial effects of the present application clearer and more understandable, the present application will be further described in detail below in conjunction with the embodiments. Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those of ordinary skill in the art.

[0041] The present invention discloses a preparation method of a Nostoc commune acetylation-modified flocculant, and its process flow is as Figure 1 shown, and specifically includes the following steps.

[0042] (1) Preparation of Nostoc commune powder

[0043] Manually select high-quality Nostoc commune without obvious impurities. Carefully check the Nostoc commune and remove the sand, soil, plant residues and other foreign matters mixed therein. The selected Nostoc commune is placed in sufficient deionized water and soaked for 2 - 3 hours, during which it is gently stirred every 30 minutes to fully remove the impurities attached to the surface of the Nostoc commune. After the soaking is over, the Nostoc commune is repeatedly rinsed with deionized water until the rinsing water is clear and transparent without impurity residues, and then the Nostoc commune is fished out and placed on a clean filter paper to drain the surface moisture.

[0044] Evenly spread the drained Nostoc flagelliforme on a clean tray and place it in an oven for drying at 40 - 45°C for 10 - 12 hours. During this process, regularly check the drying degree of Nostoc flagelliforme to avoid deterioration of Nostoc flagelliforme caused by local overheating and ensure that Nostoc flagelliforme is completely dry and has a crispy texture. Take out the dried Nostoc flagelliforme and put it into a pulverizer for crushing. First, use the coarse crushing mode to preliminarily crush Nostoc flagelliforme into smaller particles, and then switch to the fine crushing mode to further crush it into fine powder. The crushed Nostoc flagelliforme powder is screened through a 200-mesh sieve, and the Nostoc flagelliforme powder passing through the sieve is collected for standby, and the part that does not pass through the sieve can be crushed and screened again.

[0045] (2) Preparation of materials and reagents

[0046] Weigh an appropriate amount of Nostoc flagelliforme powder and determine the hydroxyl value by the acetic anhydride - pyridine method. Calculate the molar amount of hydroxyl groups by titration. The calculation formula is: n OH =(OH × m)÷(56.1×1000) to calculate the molar amount of hydroxyl groups; where: n OH is the molar amount of hydroxyl groups, mol; OH is the hydroxyl value, mg KOH / g; m is the mass of Nostoc flagelliforme powder, g; 56.1 is the molar mass of KOH, g / mol.

[0047] According to the mass of Nostoc flagelliforme powder, its molar amount of hydroxyl groups, and the following limiting conditions, calculate the dosages of acetic anhydride, glacial acetic acid, and concentrated sulfuric acid to be added. Weigh / measure the corresponding materials or reagents for standby to ensure sufficient reaction and avoid waste.

[0048] 1) The solid - liquid ratio of Nostoc flagelliforme powder to acetic anhydride solution is 1:10 - 1:15 (w / v);

[0049] 2) The molar amount of acetic anhydride is 1.2 - 1.5 times the molar amount of hydroxyl groups;

[0050] 3) For each gram of Nostoc flagelliforme powder, it corresponds to 0.5 - 1.5 milliliters of concentrated sulfuric acid.

[0051] (3) Acetylation reaction

[0052] Slowly add acetic anhydride to glacial acetic acid while stirring to ensure complete dissolution of acetic anhydride and obtain an acetic anhydride solution for later use. Select concentrated sulfuric acid as the catalyst for the acetylation reaction. Slowly add concentrated sulfuric acid dropwise to the acetic anhydride solution while stirring. After the addition is complete, continue stirring for 5 - 10 minutes to ensure the solution is homogeneous. Slowly add Nostoc commune powder to the prepared acetic anhydride solution containing the catalyst, and at the same time turn on the magnetic stirrer and stir evenly at a speed of 150 - 250 rpm / min to form a Nostoc commune - acetylation reagent mixed solution. Place the reaction system (Nostoc commune - acetylation reagent mixed solution) in a constant temperature water bath, set the temperature to 40 - 50 °C, and react for 2 - 4 hours under stirring conditions. During the reaction process, closely observe the temperature and stirring condition of the reaction system to ensure the reaction proceeds under stable conditions, enabling the active functional groups such as hydroxyl groups in the Nostoc commune polysaccharide molecules to fully react with the acetylation reagent and introducing acetyl groups onto the Nostoc commune molecules to complete the acetylation reaction. After the reaction is completed, use pH test paper to detect the pH value of the reaction solution to ensure the reaction is complete.

[0053] (4) Post - treatment

[0054] After the acetylation reaction is completed, slowly pour the reaction solution into a large amount of ice water while stirring to terminate the reaction. Then use a sodium hydroxide solution with a concentration of 1 - 2 mol / L to neutralize the reaction solution to a pH value of 7 ± 0.5. Add sufficient deionized water to dilute the neutralized reaction solution to increase the total volume to 3 - 5 times the volume of the original reaction solution. After stirring evenly, pour the mixed solution into a special centrifuge tube for the centrifuge, set the centrifuge speed to 3000 - 4000 rpm / min, and the centrifugation time to 15 - 25 minutes for centrifugal separation. After centrifugation, pour off the supernatant and leave the precipitate at the bottom.

[0055] Wash the precipitate with deionized water, and after washing, centrifuge at a speed of 3000 - 4000 rpm / min. Repeat the washing and centrifugation steps 3 - 5 times to remove unreacted reagents and by - products. Take out the precipitate after multiple washing and centrifugation, evenly spread it on a clean tray, put it into an oven, set the temperature to 50 - 55 °C for drying, and the drying time is 6 - 8 hours until the precipitate is completely dry. Take out the dried product, crush it again with a pulverizer, and screen it through a 300 - mesh sieve. Collect the powder passing through the sieve, which is the prepared Nostoc commune acetylated modified flocculant.

[0056] The present invention also provides a Nostoc flagelliforme acetylated modified flocculant prepared by the above preparation method. The flocculant is an acetylated derivative of Nostoc flagelliforme polysaccharide and protein. Among them: the hydroxyl groups on the polysaccharide molecular chain are connected to the acetyl group -O-COCH3 through an ester bond, and the amino groups on the protein molecular chain are connected to the acetyl group -NH-COCH3 through an amide bond. The total substitution degree of the acetyl group is 0.2 - 0.5 (that is, the acetyl group content per gram of the flocculant is 12% - 28%). Among them, the substitution rate of hydroxyl groups in the polysaccharide molecule is 30% - 55%, and the substitution rate of amino groups in the protein molecule is 15% - 30%. In the elemental composition of the modified flocculant, the carbon content is increased to 40% - 45% (35% - 38% for unmodified Nostoc flagelliforme), which proves that the acetyl group is successfully introduced; its zeta potential is -25 mV to -35 mV, indicating that the surface negative charge density is significantly enhanced, which is beneficial to adsorbing positively charged pollutant particles through electrostatic interaction.

[0057] Nostoc flagelliforme is rich in biological macromolecules such as polysaccharides and proteins. The polysaccharide molecule contains a large number of hydroxyl groups (-OH), and the protein molecule has various active functional groups such as amino groups (-NH2), carboxyl groups (-COOH), etc. These functional groups provide reaction sites for subsequent chemical modification. In the present invention, through the acetylation reaction, the hydrogen atoms of the hydroxyl groups in Nostoc flagelliforme polysaccharide are replaced by acetyl groups to form an ester bond (-O-COCH3); the hydrogen atoms of the amino groups in Nostoc flagelliforme protein molecules are replaced by acetyl groups to generate an amide structure (-NH-COCH3). The present invention introduces acetyl groups onto Nostoc flagelliforme polysaccharide and protein molecules through a series of reactions to complete the acetylation reaction. After acetylation modification, the structure of Nostoc flagelliforme molecules has changed. Due to the introduction of acetyl groups, the spatial structure of the molecules becomes more extended or has a specific conformation, which is beneficial to the dispersion of the molecules in water and the contact with impurity particles. At the same time, the presence of acetyl groups may affect the charge distribution of the molecules, thereby affecting the electrostatic interaction between the molecules and impurity particles. Compared with unmodified Nostoc flagelliforme, the acetylated modified flocculant can make the impurities in water aggregate to form flocs faster, and the flocs are more stable and not easily dispersed, improving the efficiency and effect of the flocculation process. At the same time, this modified flocculant may also improve the adaptability to different types of pollutants to a certain extent and expand its application range in water treatment.

[0058] Specific examples will be listed below to explain the solution of the present invention. Those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those not specified in the examples regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the field or according to the product instructions. For the reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0059] Example

[0060] 1. Preparation of acetylated modified flocculant from Nostoc commune

[0061] The Nostoc commune acetylated modified flocculant was prepared according to the preparation method described in the specific implementation mode, as follows:

[0062] (1) Select high-quality Nostoc commune, soak it in deionized water for 2 hours, and stir it every 30 minutes during the soaking period; rinse to remove impurities, drain the water, and dry it at 40 °C for 10 hours to ensure that the Nostoc commune is completely dry and crispy; crush the dried Nostoc commune and pass it through a 200-mesh sieve to obtain Nostoc commune powder.

[0063] (2) Weigh the Nostoc commune powder, measure its hydroxyl value and calculate the molar amount of hydroxyl groups. According to the limiting conditions shown in Table 1, further determine the dosages of acetic anhydride, glacial acetic acid, and concentrated sulfuric acid, and weigh / measure the corresponding materials or reagents for standby.

[0064] Table 1 Preparation of raw materials and reagents

[0065] Example 1 Example 2 Example 3 Mass of Nostoc commune powder / g 10 12 15 Hydroxyl value / mgKOH / g 320 310 300 Amount of hydroxyl in moles / mol 0.057 0.066 0.080 Solid-liquid ratio of Nostoc commune powder to acetic anhydride solution 1:12 1:12 1:10 Molar ratio of acetic anhydride to hydroxyl 1.2 1.3 1.5 Dropwise addition amount of concentrated sulfuric acid / mL / g 0.5 0.8 1.2

[0066] (3) Slowly add acetic anhydride to glacial acetic acid, and fully dissolve it to obtain an acetic anhydride solution; slowly drip concentrated sulfuric acid into the acetic anhydride solution and continuously stir, and continue to stir for 5 minutes after dripping to obtain a mixed solution; slowly add the Nostoc commune powder to the mixed solution, turn on the magnetic stirrer and stir evenly at a speed of 150 rpm / min; place the reaction system in a constant temperature water bath and stir and react at a constant temperature of 40 °C for 2 hours to complete acetylation.

[0067] (4) After the acetylation reaction is completed, add ice water to terminate the reaction, and then add 1 mol / L sodium hydroxide solution to neutralize the reaction solution to a pH value of 7 ± 0.5; dilute the reaction solution with deionized water to 3 times the original volume, stir evenly, and centrifuge at 3000 rpm / min for 15 minutes to obtain a precipitate.

[0068] (4) Wash the precipitate with deionized water, centrifuge and separate it at a speed of 3000 rpm / min, and repeat the washing and centrifugation steps 3 times; after the precipitate is washed clean, dry it at 50 °C for 6 hours; pass the dried product through a 300-mesh sieve to obtain the Nostoc commune acetylated modified flocculant.

[0069] 2. Performance detection of Nostoc commune acetylated modified flocculant

[0070] The degree of acetylation substitution is a key index for evaluating the performance of the flocculant, which directly affects the charge density and hydrophobicity of the molecular chain; in this invention, the total substitution degree is determined by acid-base titration, and the calculation formula is: DS = [(V0 - V) × C NaOH × M acetyl )] ÷ (W sample×1000); where V0 and V are the volumes of NaOH consumed by the blank and the sample (mL), C NaOH is the concentration of NaOH (mol / L), M acetyl is the molar mass of the acetyl group (43 g / mol), W sample is the mass of the sample (g).

[0071] The substitution rate of polysaccharide hydroxyl groups was determined by 1H NMR. Based on glucose units, the substitution rate was calculated from the proportion of the peak area of the acetyl group; the substitution rate of protein amino groups was determined by the TNBS method (trinitrobenzenesulfonic acid colorimetric method) to measure the content of free amino groups, and the substitution rate was calculated by comparison with the unmodified sample; elemental analysis was used to detect the contents of C, H, N, and S with an elemental analyzer Vario EL III; the Zeta potential was measured using a nanoparticle size and potential analyzer Malvern Zetasizer. The sample concentration was 1 mg / mL and the pH was 7.0.

[0072] At the same dosage, the turbidity removal rate was determined by treating simulated industrial wastewater (containing various suspended particles and colloidal substances, with an initial turbidity of 500 NTU); its flocculation activity was detected within different pH values and temperature ranges; and its natural degradation rate within 28 days was measured.

[0073] Taking the unmodified Nostoc flagelliforme flocculant as a comparative example, the performance of the Nostoc flagelliforme acetylated modified flocculants prepared in Examples 1 - 3 was tested according to the above method, and the results are as follows.

[0074] Unmodified Nostoc flagelliforme flocculant: The results of elemental analysis were: C = 36.5%, H = 6.0%, N = 2.2%, S = 0.03%; Zeta potential: -12 mV; the turbidity removal rate of simulated industrial wastewater was 65%, and within the pH range of 4 - 10 and temperature range of 10 - 40 °C, the flocculation activity ≥ 75%; the natural degradation rate within 28 days was 85%.

[0075] Example 1: The total degree of substitution DS of acetyl groups = 0.42 (acetyl group content 23%); the substitution rate of polysaccharide hydroxyl groups = 48%; the substitution rate of protein amino groups = 18%; the results of elemental analysis were: C = 42.3%, H = 6.1%, N = 2.5%, S = 0.05%; Zeta potential: -28 mV. Compared with the unmodified flocculant, the electrostatic adsorption capacity increased by 130%; the turbidity removal rate of simulated industrial wastewater was 85%; within the pH range of 4 - 10 and temperature range of 10 - 40 °C, the flocculation activity ≥ 85%; the natural degradation rate within 28 days was 95%.

[0076] Example 2: The total degree of substitution DS of acetyl groups = 0.47 (acetyl group content 25.8%); polysaccharide hydroxyl substitution rate = 52%; protein amino substitution rate = 22%; elemental analysis results are: C = 43.1%, H = 6.3%, N = 2.7%, S = 0.06%; Zeta potential = -32 mV, compared with the unmodified flocculant, the electrostatic adsorption capacity is increased by 167%; the turbidity removal rate of simulated industrial wastewater is 90%; at pH 4 - 10 and temperature conditions of 10 - 40 °C, the flocculation activity ≥ 88%; the 28-day natural degradation rate is 93%.

[0077] Example 3: The total degree of substitution DS of acetyl groups = 0.52 (acetyl group content 28.6%); polysaccharide hydroxyl substitution rate = 55%; protein amino substitution rate = 28%; elemental analysis: C = 44.5%, H = 6.5%, N = 2.9%, S = 0.08%; Zeta potential = -35 mV, compared with the unmodified flocculant, the electrostatic adsorption capacity is increased by 192%; the turbidity removal rate of simulated industrial wastewater is 92%; at pH 4 - 10 and temperature conditions of 10 - 40 °C, the flocculation activity ≥ 90%; the 28-day natural degradation rate is 90%.

[0078] The results show that: when treating simulated industrial wastewater (containing various suspended particles and colloidal substances), compared with the unmodified Nostoc flagelliforme flocculant, the acetylated modified flocculant prepared by the present invention has a significantly improved removal rate of suspended particles and colloids at the same dosage. The total degree of substitution (DS) in the acetylated modified flocculants prepared in Examples 1 - 3 increased from 0.42 to 0.52, and the turbidity removal rate increased significantly from 85% to 92%, proving that the introduction amount of acetyl groups is positively correlated with the flocculation performance. When DS ≥ 0.4, the removal rate of the flocculant for wastewater with a turbidity of 500 NTU is stably ≥ 85%; the Zeta potential decreased from -28 mV to -35 mV, the surface negative charge density increased, and the electrostatic adsorption capacity improved, especially suitable for the treatment of wastewater containing metal ions or positively charged colloids. In the elemental analysis, the carbon content showed a linear increase with DS (R 2 = 0.98), verifying the successful grafting of acetyl groups; the polysaccharide hydroxyl substitution rate and the protein amino substitution rate jointly contributed to the synergistic improvement of hydrophobicity and charge density. At the same time, within different pH values (4 - 10) and temperature ranges (10 - 40 °C), the acetylated modified flocculant can maintain a high flocculation activity, indicating its good adaptability and stability, suitable for the treatment of wastewater under various complex water quality conditions, and the 28-day natural degradation rate is ≥ 90% in all cases, far superior to synthetic flocculants. The present invention realizes the dual goals of efficient flocculation and green degradation by precisely controlling the degree of acetylation substitution, charge density and molecular structure, providing a reliable technical solution for the modification and application of natural bio-based flocculants.

Claims

1. Nostoc flagelliforme acetylated modified flocculant, characterized in that: The flocculant is an acetylated derivative of polysaccharide and protein in Nostoc sphaeroides, and its elemental composition includes 40% - 45% carbon by mass percentage; The acetyl group content per gram of the flocculant is 12% - 28%, and the total degree of substitution of acetyl groups is 0.2 - 0.

5.

2. The Nostoc flagelliforme acetylation modified flocculant according to claim 1, characterized in that: The hydroxyl groups on the polysaccharide molecular chain are connected to the acetyl group -O-COCH3 through ester bonds, and the degree of substitution of hydroxyl groups is 30% - 55%; the amino groups on the protein molecular chain are connected to the acetyl group -NH-COCH3 through amide bonds, and the substitution rate of amino groups is 15% - 30%.

3. The Nostoc flagelliforme acetylation modified flocculant according to claim 1, characterized in that: The zeta potential of the flocculant is -25 mV to -35 mV.

4. Preparation method of acetylated modified flocculant of Nostoc commune, characterized in that, It includes the following steps: S1. Weigh the Nostoc sphaeroides powder and measure its hydroxyl group content; S2. Mix the Nostoc sphaeroides powder with acetic anhydride, glacial acetic acid and concentrated sulfuric acid for acetylation reaction to obtain a reaction solution, specifically including: S2-1. Mix acetic anhydride and glacial acetic acid to prepare an acetic anhydride solution; S2-2. Add concentrated sulfuric acid to the acetic anhydride solution and mix evenly to obtain a mixed solution; S2-3. After mixing the Nostoc sphaeroides powder with the mixed solution, heat and stir at a constant temperature to complete the acetylation reaction; S3. Neutralize, wash, dry and crush the reaction solution to obtain the Nostoc sphaeroides acetylated modified flocculant according to any one of claims 1 - 3.

5. The preparation method of the Nostoc sphaeroides acetylated modified flocculant according to claim 4, characterized in that: In step S1, the particle size of the Nostoc sphaeroides powder is the powder obtained by passing through a 200-mesh sieve; In step S1, the method for determining the hydroxyl content is: using the acetic anhydride-pyridine method to determine the hydroxyl value, according to the formula n OH =(OH×m)÷(56.1×1000) to calculate the molar amount of hydroxyl groups; Where: n OH is the molar amount of hydroxyl groups, mol; OH is the hydroxyl value, mg KOH / g; m is the mass of kudzu vine powder, g; 56.1 is the molar mass of KOH, g / mol.

6. The preparation method of the Nostoc sphaeroides acetylated modified flocculant according to claim 4, characterized in that: In step S2-2, the addition amount of concentrated sulfuric acid is 0.5 - 1.5 mL / g of Nostoc sphaeroides powder; In step S2-3, the solid-liquid ratio of Nostoc sphaeroides powder to acetic anhydride solution is 1:10 - 1:15 (w / v), and the molar amount of acetic anhydride is 1.2 - 1.5 times the molar amount of hydroxyl groups.

7. The preparation method of the Nostoc sphaeroides acetylated modified flocculant according to claim 4, characterized in that: In step S2-2, concentrated sulfuric acid is added in a slow dropping manner and continuously stirred, and continue to stir for 5 - 10 minutes after dropping to mix evenly; In step S2-3, the Nostoc sphaeroides powder and the mixed solution are magnetically stirred and mixed at a speed of 150 - 250 rpm, and react at a constant temperature of 40 - 50 °C for 2 - 4 hours.

8. The preparation method of the Nostoc sphaeroides acetylated modified flocculant according to claim 4, characterized in that: In step S3, the neutralization, washing, drying and crushing include: S3-1. Add ice water to the reaction solution to terminate the reaction, and then neutralize it with sodium hydroxide solution; S3-2. Dilute the neutralized reaction solution and centrifuge to obtain a precipitate; S3-3. The precipitate is washed, dried and crushed, and then passed through a 300-mesh sieve to obtain the Nostoc sphaeroides acetylated modified flocculant.

9. The preparation method of the Nostoc sphaeroides acetylated modified flocculant according to claim 8, characterized in that: In step S3-1, the reaction solution is neutralized to pH 7 ± 0.5 with 1 - 2 mol / L sodium hydroxide solution; In step S3-2, the reaction solution is diluted to 3 to 5 times its original volume with deionized water and centrifuged at 3000 to 4000 rpm for 15 to 25 minutes; In step S3-3, after the precipitate is washed with deionized water, it is centrifuged at 3000 to 4000 rpm / min, and the washing and centrifugation operations are repeated 3 to 5 times; the drying is carried out at 50 to 55 °C for 6 to 8 hours.

10. Application of Nostoc flagelliforme acetylated modified flocculant in the technical field of wastewater and sewage treatment.

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