Magnetized hydrophobic chitosan-alum composite flocculant, preparation method and application thereof

Abstract

The application discloses a preparation method of a magnetized hydrophobic chitosan-alum composite flocculant, which comprises the following steps: mixing chitosan, lauric acid, N-hydroxysuccinimide (NHS) and 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) to obtain hydrophobic chitosan; mixing the hydrophobic chitosan with Fe3O4 magnetic particles to obtain magnetized hydrophobic chitosan; and then reacting the magnetized hydrophobic chitosan with Al2(SO4)3.18H2O and K2SO4 to obtain the magnetized hydrophobic chitosan-alum composite flocculant. The magnetized hydrophobic chitosan-alum composite flocculant prepared by the method has good stability in sewage, is small in dosage, high in removal rate, good in sedimentation, and can be recycled and removed through an external magnetic field, so that the residual amount of the flocculant in treated wastewater is small, and there is no secondary pollution.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of water treatment, in particular to a magnetized hydrophobic chitosan-alum composite flocculant and its preparation method and application. BACKGROUND

[0002] Plastics are widely used in modern life due to their good performance and low cost. Plastic waste will gradually degrade into microplastics (MPs) in the natural environment. Microplastics are plastic particles with a size of less than 5 mm. Microplastics have a large specific surface area, and the aged and broken microplastics have abundant functional groups. During the migration and transformation process, microplastics can enrich heavy metals, organic pollutants, pathogenic bacteria and other pollutants, thus forming a complex pollution. Therefore, the pollution control of microplastics in water bodies is imminent.

[0003] The commonly used treatment method for removing microplastics in wastewater is chemical coagulation, which involves adding a flocculant to wastewater to make the suspended particles or colloids in the water coagulate and form flocs, and then separating the flocs from the wastewater to remove pollutants and purify the wastewater. Chemical coagulation is an economical and practical wastewater treatment technology with simple operation and obvious effect, and is widely used in the water treatment industry and plays an important role in wastewater treatment.

[0004] The key to chemical coagulation for treating wastewater is to select a suitable flocculant. Studies have shown that the use of natural flocculants shows good results in MP removal, and has many advantages compared with traditional flocculants (inorganic and organic flocculants).

[0005] Chitosan is a natural flocculant with many active functional groups on its molecular chain that can undergo hydrophobic association and complexation with pollutants in water. Chitosan also has good biocompatibility and biodegradability, and has been proven to be one of the most effective and environmentally friendly products in the coagulation process. However, chitosan is hydrophilic, while microplastics are hydrophobic. Simply using chitosan as a flocculant has poor removal capacity.

[0006] Currently, in related technologies, CS is modified into hydrophobic chitosan to improve the removal capacity of hydrophobic microplastic pollutants. However, the overall removal effect is not obvious, the removal rate is not high, and the hydrophobic chitosan is in powder form, which has high solubility in acidic environments, low mechanical strength, poor reusability, and weak separation capacity. Therefore, in order to solve these problems, a new type of composite flocculant is designed for hydrophobic microplastic pollutants to better adapt to water bodies containing hydrophobic microplastic pollutants and improve the removal rate of microplastics. SUMMARY

[0007] Therefore, the present application aims to provide a magnetized hydrophobic chitosan-alum composite flocculant and its preparation method and application, so as to solve the problems of the current hydrophobic chitosan in treating the micro-plastic pollutants in wastewater, such as low overall removal rate, high solubility, low mechanical strength, poor reusability, strong separation capacity and the like.

[0008] The first aspect of the present application is to provide a preparation method of a magnetized hydrophobic chitosan-alum composite flocculant, which comprises the following steps:

[0009] (1) Dissolve chitosan in acetic acid to obtain a chitosan solution, add methanol to the chitosan solution, stir, and adjust the pH of the solution to obtain an acidified chitosan solution;

[0010] (2) Prepare lauric acid, N-hydroxysuccinimide (NHS), and 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) mother liquor respectively, add lauric acid, N-hydroxysuccinimide (NHS), and 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) solutions into ethanol respectively and stir, add the acidified chitosan solution during stirring to react, adjust the pH of the reaction solution after reaction, centrifuge, wash, dry, and grind to obtain hydrophobic chitosan powder;

[0011] (3) Add the hydrophobic chitosan powder into water, stir, and then add Fe3O4 magnetic particles to mix to obtain a mixed solution, first add cyclohexane, an emulsifier, and a surfactant into the mixed solution and stir, then add glutaraldehyde to cross-link to obtain a magnetized hydrophobic chitosan solution, collect the magnetized hydrophobic chitosan solution through an external magnetic field, wash, dry, and grind to obtain magnetized hydrophobic chitosan powder;

[0012] (4) Dissolve the obtained magnetized hydrophobic chitosan powder in acetic acid solution or hydrochloric acid solution to obtain a magnetized hydrophobic chitosan solution, add Al2(SO4)3·18H2O and K2SO4 into the magnetized hydrophobic chitosan solution to react, and then stand and mature to obtain a magnetized hydrophobic chitosan-alum composite flocculant.

[0013] In an alternative embodiment, in the above-mentioned step (2), the molar ratio of chitosan to lauric acid is 1:(0.2-2).

[0014] In an alternative embodiment, in the above-mentioned step (2), the molar ratio of lauric acid, N-hydroxysuccinimide (NHS), and 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) is 1:2:2.

[0015] In an alternative embodiment, in the step (3), the mass ratio of the hydrophobic chitosan powder to the Fe3O4 magnetic particles is 1:(0.5-3).

[0016] In an alternative embodiment, in the step (3), the volume ratio of the cyclohexane, the emulsifier and the surfactant is 150:1:30.

[0017] In an alternative embodiment, in the step (4), the mass ratio of the Al2(SO4)3·18H2O to the K2SO4 is 1:(1-4).

[0018] In an alternative embodiment, in the step (1), before the methanol is added into the chitosan solution, the chitosan solution is first stored in a storage box at 2-6℃ for 24-28h, the pH of the chitosan solution is adjusted by 1% acetic acid, and the pH of the acidified chitosan solution is 4.

[0019] In the step (2), the lauric acid, the N-hydroxysuccinimide (NHS) and the 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) are stirred in ethanol for 2-4h, the acidified chitosan solution is added for reaction for 24-28h, the reaction solution is first ultrasonically treated for 10-15min, then the pH of the reaction solution is adjusted to 9, and then the reaction solution is stored in a storage box at 2-6℃ for 24-28h, and then the hydrophobic chitosan powder is obtained by centrifugation, washing, drying and grinding.

[0020] In an alternative embodiment, in the step (3), the mixing time of the hydrophobic chitosan and the Fe3O4 magnetic particles is 12-15h, the mixing and stirring time of the cyclohexane, the emulsifier and the surfactant added into the mixed solution is 3-5h, the cross-linking reaction time of the glutaraldehyde added under the condition of stirring at 50℃ is 3-5h, and the drying time is 24-26h.

[0021] In the step (4), the Al2(SO4)3·18H2O and the K2SO4 are added into the magnetized hydrophobic chitosan solution under the condition of a temperature of 50-80℃ and a rotation speed of 600-750r / min for reaction for 3-5h, and the standing and curing time is 24-28h.

[0022] The second aspect of the present application is to provide a magnetized hydrophobic chitosan-alum composite flocculant prepared by the preparation method.

[0023] The third aspect of the present application is to provide an application of the magnetized hydrophobic chitosan-alum composite flocculant in the treatment of wastewater containing microplastics.

[0024] Compared with the prior art, the technical scheme of the present application has the following advantages:

[0025] (1) The removal rates of different types of microplastics, polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), and polylactic acid (PLA), reach 99.85%, 99.55%, 99.05%, and 99.60%, respectively, and the removal effect is good.

[0026] (2) The removal effect of the present application on different types of microplastics, polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), and polylactic acid (PLA), is significant and can be effectively removed in a wide pH range (pH range of 5-10), and the flocculant reaction time can be greatly shortened.

[0027] (3) The present application has good stability in wastewater, low dosage, high removal rate, and can be recycled and removed by an external magnetic field, so that the residual amount of flocculant in the treated wastewater is small and there is no secondary pollution.

[0028] (4) The present application is suitable for a wide range of wastewater temperatures, and can effectively remove microplastics in wastewater with a temperature of 10-40℃, and is suitable for wastewater treatment plants and natural water treatment, and has good application prospects.

[0029] (5) The hydrolysate produced by the hydrolysis of alum in the composite flocculant can sweep away pollutants, so that the flocculation can be quickly separated from the water and settled under the action of gravity, and the settling performance is good. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The infrared analysis diagram of the magnetized hydrophobic chitosan-alum composite flocculant prepared in Example 1 of the present application, wherein the abscissa is the wave number and the ordinate is the light transmittance.

[0031] Figure 2 The contact angle of the magnetized hydrophobic chitosan-alum composite flocculant prepared by chitosan and lauric acid with different molar ratios in the present application; wherein the abscissa is the molar ratio of chitosan to lauric acid and the ordinate is the removal rate.

[0032] Figure 3 The removal effect diagram of PE of the magnetized hydrophobic chitosan-alum composite flocculant prepared by using Al2(SO4)3·18H2O and K2SO4 with different mass ratios in the present application, wherein the abscissa is the mass ratio of Al2(SO4)3·18H2O to K2SO4 and the ordinate is the removal rate.

[0033] Figure 4The figure of the removal effect of different dosages of the magnetized hydrophobic chitosan-alum composite flocculant prepared in the embodiment of the present application on PE, PET, PP and PLA, wherein the abscissa represents dosage, and the ordinate represents removal rate.

[0034] Figure 5 The figure of the removal effect of the magnetized hydrophobic chitosan-alum composite flocculant prepared in the embodiment of the present application on PE, PET, PP and PLA at different temperatures; the abscissa represents temperature, and the ordinate represents removal rate.

[0035] Figure 6 The figure of the removal effect of the magnetized hydrophobic chitosan-alum composite flocculant prepared in the embodiment of the present application on PE, PET, PP and PLA at different pH values; the abscissa represents pH, and the ordinate represents removal rate.

[0036] Figure 7 The figure of the removal effect of the flocculants prepared by adding different amounts of the embodiment 1, comparative example 1, comparative example 2, comparative example 3 and comparative example 4 on PE; the abscissa represents dosage, and the ordinate represents removal rate.

[0037] Figure 8 The figure of the removal effect of different dosages of different composite flocculants on PE; the abscissa represents dosage, and the ordinate represents removal rate. DETAILED DESCRIPTION

[0038] In order to make the personnel in the technical field better understand the scheme of the present application, the technical scheme in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by the person of ordinary skill in the art without making creative labor belong to the scope of protection of the present application.

[0039] Embodiment 1

[0040] A preparation method of a magnetized hydrophobic chitosan-alum composite flocculant, comprising the following steps:

[0041] (1) 1.2 g of chitosan (degree of deacetylation≧95%, molecular weight: 30000) is dissolved in 100 mL of 1% acetic acid, and then the chitosan solution is stored at 4℃ for 24 h.

[0042] (2) 100 mL of methanol is added to the chitosan solution of step (1) and stirred for 10 min, and then the solution pH is adjusted to 4 by 1% (v / v) acetic acid, and ultrasonic treatment is performed for 10 min to obtain an acidified chitosan solution.

[0043] (3) Respectively configure lauric acid, N-hydroxysuccinimide (NHS), 1-ethyl- (3- dimethylaminopropyl) carbodiimide hydrochloride (EDC) concentration of 0.1 g / mL of mother liquor, 20 μmol (4.01 mg) of lauric acid, 40 μmol (4.60 mg) of NHS, 40 μmol (7.67 mg) of EDC was added to 10 mL of ethanol and stirred for 2 h, then the acidified chitosan solution of step (2) was added under stirring and reacted for 24 h.

[0044] (4) The reaction solution of step (3) was ultrasonicated for 10 min, then the pH of the reaction solution was adjusted to 9 using 2 mol / L NaOH solution, and finally the solution was stored at 4°C for 24 h.

[0045] (5) The solution of step (4) was centrifuged at 5000 r / min, and the precipitate was washed with deionized water for 3 times to remove residual NaOH and unreacted lauric acid, EDC and NHS, dried and ground to obtain hydrophobic chitosan powder.

[0046] (6) 1.2 g of hydrophobic chitosan powder obtained in step (5) was prepared into a 30 mL 4.0 wt% hydrophobic chitosan solution with deionized water, and mixed with 1.2 g of Fe3O4 magnetic particles for 12 h to obtain a mixed solution.

[0047] (7) The mixed solution obtained in step (6) was stirred with 150 mL of cyclohexane and 1 mL of emulsifier span-80 in a three-necked flask for 3 h at a stirring speed of 250 r / min, then 0.75 mL of glutaraldehyde was added under the condition of a temperature of 50°C and a stirring speed of 250 r / min, and crosslinking reaction was carried out for 3 h to obtain a magnetized hydrophobic chitosan solution.

[0048] (8) The magnetized hydrophobic chitosan solution obtained in step (7) was collected by an external magnetic field, washed several times with anhydrous ethanol to remove excess chemical reagents, and dried for 24 h to obtain magnetized hydrophobic chitosan powder.

[0049] (9) 1.0 g of magnetized hydrophobic chitosan powder prepared in step (8) was dissolved in 100 mL of 1% acetic acid solution to obtain a magnetized hydrophobic chitosan solution;

[0050] (10) Under the condition of a temperature of 70°C and a stirring speed of 250 r / min, 0.7 g of Al2(SO4)3·18H2O and 2.1 g of K2SO4 were added to the magnetized hydrophobic chitosan solution obtained in step (9), and reacted for 3 h at a stirring speed of 650 r / min, and then stood for 24 h to obtain a magnetized hydrophobic chitosan-alum composite flocculant.

[0051] As Figure 1The infrared analysis chart of the magnetized hydrophobic chitosan-alum composite flocculant prepared in Example 1 is shown.

[0052] Example 2

[0053] The preparation method of this example is the same as that of Example 1, except that the mass of lauric acid in step (2) is different. In this example, the mass of lauric acid is adjusted to 1.60 mg (8 μmol), and the rest remains unchanged.

[0054] Example 3

[0055] The preparation method of this example is the same as that of Example 1, except that the mass of lauric acid in step (2) is different. In this example, the mass of lauric acid is adjusted to 8.01 mg (40 μmol), and the rest remains unchanged.

[0056] Example 4

[0057] The preparation method of this example is the same as that of Example 1, except that the mass of lauric acid in step (2) is different. In this example, the mass of lauric acid is adjusted to 16.03 mg (80 μmol), and the rest remains unchanged.

[0058] Example 5

[0059] The preparation method of this example is the same as that of Example 1, except that the mass of K2SO4 added in step (10) is different. In this example, the mass of K2SO4 is adjusted to 0.7 g, and the rest remains unchanged.

[0060] Example 6

[0061] The preparation method of this example is the same as that of Example 1, except that the mass of K2SO4 added in step (10) is different. In this example, the mass of K2SO4 is adjusted to 1.4 g, and the rest remains unchanged.

[0062] Example 7

[0063] The preparation method of this example is the same as that of Example 1, except that the mass of K2SO4 added in step (10) is different. In this example, the mass of K2SO4 is adjusted to 2.8 g, and the rest remains unchanged.

[0064] Comparative Example 1

[0065] A preparation method of a hydrophobic chitosan flocculant, which is the same as steps (1)-(5) in Example 1, and after obtaining the hydrophobic chitosan powder from step (5), the hydrophobic chitosan powder is made into a solution and then aged for 24 hours to obtain the hydrophobic chitosan flocculant.

[0066] Comparative Example 2

[0067] A method for preparing a magnetized hydrophobic chitosan flocculant is basically the same as that in Example 1, except that step (10) is omitted and the magnetized hydrophobic chitosan solution obtained in step (9) is allowed to stand and mature for 24 hours.

[0068] Comparative Example 3

[0069] A method for preparing a hydrophobic chitosan-alum composite flocculant, which is basically the same as that in Example 1, except that steps (6) to (8) are omitted.

[0070] Comparative Example 4

[0071] A method for preparing a magnetized chitosan-alum composite flocculant, which is basically the same as that in Example 1, except that steps (1) to (5) are omitted and the hydrophobic chitosan in step (6) is replaced with chitosan.

[0072] Effect verification

[0073] First, simulated wastewater was prepared to produce experimental wastewater and then the corresponding effect was verified. The steps for treating microplastics in the wastewater were as follows: (1) Add the flocculants prepared in Examples 1-7 and Comparative Examples 1-4 to the wastewater containing microplastics; (2) Stir and coagulate; (3) Flocculate; (4) Sediment; (5) Adsorb flocs using a magnet.

[0074] I. Hydrophobicity of Magnetized Hydrophobic Chitosan-Alum Composite Flocculants Prepared with Different Molar Mass Ratios of Chitosan and Lauric Acid

[0075] To investigate the effect of different molar ratios of chitosan and lauric acid on the hydrophobicity of the prepared composite flocculants, the composite flocculants prepared in Examples 1-4 were tested, and the results are as follows: Figure 2 As shown, from Figure 2 As can be seen, adding lauric acid to chitosan can improve the hydrophobicity of chitosan compared to chitosan. Moreover, with the molar mass of chitosan remaining constant, the contact angle first increases and then decreases with the increase of the molar mass of lauric acid. The contact angle reaches its maximum value of 126.17° when the molar mass ratio of chitosan to lauric acid is 1:1. This indicates that the magnetized hydrophobic chitosan-alum composite flocculant prepared by this invention has good hydrophobicity.

[0076] II. The effect of magnetized hydrophobic chitosan-alum composite flocculants prepared with different mass ratios of Al2(SO4)3·18H2O and K2SO4 on PE removal.

[0077] The effect of adding magnetized hydrophobic chitosan-alum composite flocculants with different mass ratios of Al2(SO4)3·18H2O and K2SO4 on PE removal efficiency was investigated. First, simulated wastewater was artificially prepared, and then the magnetized hydrophobic chitosan-alum composite flocculants prepared in Examples 1, 5, 6, and 7 were added to the wastewater for testing. The specific steps are as follows:

[0078] First, simulated wastewater containing 100 mg / L polyethylene (PE) was artificially prepared (the other components and content indicators of the simulated wastewater were consistent with those in the actual wastewater, which is a conventional technique and will not be listed here). The pH of the simulated wastewater was adjusted to 7.5 ± 0.1. The simulated wastewater was placed in a 25°C constant temperature shaker for 3 hours (to ensure uniform addition of substances), and then placed in a stirrer (JJ-1A digital display power-increasing electric stirrer) for coagulation experiments. First, the stirrer was run at 300 rpm for 1 minute to ensure uniform mixing. Then, the magnetized hydrophobic chitosan-alum composite flocculant prepared in Examples 1, 5, 6, and 7 was added, and the mixture was rapidly stirred at 400 rpm for 1 minute. After the rapid stirring, the mixture was slowly stirred at 50 rpm for 15 minutes, followed by 60 minutes of sedimentation. At this point, the water sample became clear, and the polyethylene was removed from the water along with the sedimentation of the flocs. After sedimentation, the flocs were collected using an external magnetic field and weighed.

[0079] The results are as follows Figure 3 As shown, from Figure 3 It can be seen that when the mass of Al2(SO4)3·18H2O remains constant, the removal effect on PE increases with the increase of the mass of K2SO4. Among them, the removal effect on PE is best when the mass ratio of Al2(SO4)3·18H2O to K2SO4 is 1:3, with a removal rate of 99.5%.

[0080] III. Effects of different dosages of magnetized hydrophobic chitosan-alum composite flocculant on the removal of PE, PET, PP, and PLA.

[0081] Different amounts of the magnetized hydrophobic chitosan-alum composite flocculant prepared in Example 1 were added to simulated wastewater to investigate the removal effect of different dosages on different microplastics in the wastewater. The simulated wastewater used contained 100 mg / L polyethylene terephthalate (PET), 100 mg / L polyethylene (PE), 100 mg / L polylactic acid (PLA), and 100 mg / L polypropylene (PP), respectively, and the steps were the same as those in Part II of the above effect verification.

[0082] The results are as follows Figure 4 As shown, from Figure 4As can be seen, the removal rates of PET, PE, PP, and PLA increase with increasing dosage (25, 50, 75, 100, 125, 150 ppm). Specifically, when the dosage is 75 ppm (75 mg / L), the removal rates of PET, PE, PP, and PLA reach 99.82%, 99.56%, 99.88%, and 99.85%, respectively. This indicates that the magnetized hydrophobic chitosan-alum composite flocculant prepared in this invention has good removal effects on different types of microplastics, and a removal rate of 99% can be achieved at a dosage of 75 mg / L, demonstrating that good removal effects can be achieved with relatively low dosage.

[0083] IV. Removal Effect of Magnetized Hydrophobic Chitosan-Alum Composite Flocculant on PE, PET, PP, and PLA at Different Temperatures

[0084] To investigate the effect of temperature on the removal efficiency, temperature was set as a variable (10℃, 25℃, 40℃). The magnetized hydrophobic chitosan-alum composite flocculant prepared in Example 1 was added to the wastewater at a dosage of 75 mg / L. The temperature of the simulated wastewater was then varied. The simulated wastewater was the same as that in Part III of the above-mentioned effect verification, and the steps were the same as those in Part II of the above-mentioned effect verification. The removal rates of various types of microplastics in the wastewater at different temperatures were measured, and the results are as follows: Figure 5 As shown.

[0085] from Figure 5 As can be seen, the overall effect of temperature increase on the removal rate is not significant, with fluctuations of less than 0.1%, indicating that temperature has little impact on the removal effect of flocculants. In wastewater at different temperatures, flocculants have a good removal effect on microplastics.

[0086] V. Removal Effect of Magnetized Hydrophobic Chitosan-Alum Composite Flocculant on PE, PET, PP, and PLA at Different pH Levels

[0087] To investigate the effect of pH on the removal efficiency, pH was set as a variable (5, 6, 7, 8, 9, 10). The magnetized hydrophobic chitosan-alum composite flocculant prepared in Example 1 was added to the wastewater at a dosage of 75 mg / L. The pH of the simulated wastewater was then varied. The simulated wastewater was the same as that in Part III of the above-mentioned effect verification, and the steps were the same as those in Part II of the above-mentioned effect verification. The removal rates of various types of microplastics in the wastewater at different pH values ​​were measured. The results are as follows: Figure 6 As shown.

[0088] from Figure 6As can be seen, it has a good removal effect in wastewater with pH 5-10. Among them, as pH increases, the removal first shows an upward trend and then declines. The removal rate reaches 99% when pH is about 7.2. Among them, the removal rate of all microplastics (PE, PET, PP, PLA) reaches more than 95% when pH is 7-9.

[0089] VI. Effect of different dosages of flocculants prepared in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 on PE removal

[0090] To examine the removal efficiency of microplastics (PE) in wastewater under the same dosage of Examples 1, 1, 2, 3, and 4, different amounts of the flocculants prepared in Examples 1, 1, 2, 3, and 4 were added to simulated wastewater (the simulated wastewater was artificially prepared as described in Part II of the above-mentioned effect verification). The results are as follows: Figure 7 As shown. In Figure 7 In the above examples, HCs-alum is a hydrophobic chitosan-alum composite flocculant (Comparative Example 3), MCs-alum is a magnetized chitosan-alum composite flocculant (Comparative Example 4), MHCs-alum is a magnetized hydrophobic chitosan-alum composite flocculant (Example 1), HCs is a hydrophobic chitosan flocculant (Comparative Example 1), and MHCs is a magnetized hydrophobic chitosan flocculant (Comparative Example 2).

[0091] from Figure 7 As can be seen, chitosan flocculants HCs after hydrophobic treatment have a certain removal effect, but the overall removal rate is below 55%. Compared with HCs, MHCs, HCs-alum, and MCs-alum, the removal rate of MHCs-alum prepared by this invention is higher at different dosages. Specifically, at a dosage of 75 mg / L, the removal rate of MHCs-alum reaches 99%, while the removal rates of the other flocculants are below 90%. Compared with MHCs without alum, at a dosage of 75 mg / L, its removal rate is 65%, which is 34% lower than that of MHCs-alum. This indicates that MHCs-alum with alum has a better removal effect and can significantly improve the removal rate of MHCs after being combined with alum.

[0092] When the dosage was 75 mg / L, the removal rates of HCs-alum and MCs-alum were quite similar, around 85%. This indicates that when chitosan was modified by hydrophobicity or magnetization alone before being combined with alum, the removal rate was higher than that of MHCs and HCs without alum, but lower than that of MHCs-alum. This suggests that modifying chitosan by one method (hydrophobicity or magnetization) before combining it with alum was not as effective as modifying chitosan by two methods (hydrophobicity and magnetization) before combining it with alum. The maximum difference in removal rate was about 14% (for both dosages of 75 mg / L).

[0093] VII. Effects of Different Dosages of Composite Flocculants on PE Removal

[0094] To investigate the removal efficiency of complexes obtained by combining magnetized hydrophobic chitosan with different flocculants (inorganic and organic flocculants) on microplastics (PE) in wastewater at the same dosage, different amounts of different types of complexes were added to simulated wastewater (the simulated wastewater was artificially prepared as described in Part II of the above effect verification). The removal efficiency of these complexes on PE in the wastewater is as follows: Figure 8 As shown. In Figure 8 In this context, MHCs-alum is a magnetized hydrophobic chitosan-alum composite flocculant (prepared in Example 1), MHCs-FeCl3 is a magnetized hydrophobic chitosan-ferric chloride composite flocculant, MHCs-AlCl3 is a magnetized hydrophobic chitosan-aluminum chloride composite flocculant, and MHCs-starch is a magnetized hydrophobic chitosan-starch composite flocculant.

[0095] from Figure 8 The results show that the composite flocculant obtained by combining magnetized hydrophobic chitosan (MHCs) with inorganic flocculants (alum, FeCl3, AlCl3) has a better effect on removing microplastics (PE) than the composite flocculant obtained by combining it with organic flocculants (starch). When combined with inorganic flocculants, the removal rate after combining with alum is higher than that after combining with iron salt (FeCl3) and aluminum salt (AlCl3) inorganic flocculants. Specifically, when the dosage is 75 mg / L, the removal rate of MHCs-alum after combining with alum reaches 99%, while the removal rate of MHCs-FeCl3 is about 76%, which is about 23% lower than that of MHCs-alum. The removal rate of MHCs-AlCl3 is about 79%, which is about 20% lower than that of MHCs-alum. This indicates that the effect of combining with alum is the best.

[0096] Although the present application has been described with reference to the preferred embodiments thereof, it is to be understood that the application is not limited to the details described herein and that various modifications and changes can be made without departing from the spirit and scope of the present application.

Claims

1. A process for the preparation of magnetized hydrophobic chitosan-alum composite flocculants characterized by, The preparation method comprises the following steps: (1) dissolving chitosan in acetic acid to obtain a chitosan solution, adding methanol to the chitosan solution, stirring, and adjusting the pH of the solution to obtain an acidified chitosan solution; (2) preparing lauric acid, N-hydroxysuccinimide (NHS) and 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) mother liquor respectively, adding lauric acid, N-hydroxysuccinimide (NHS) and 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) solutions into ethanol respectively and stirring, adding the acidified chitosan solution during stirring to react, adjusting the pH of the reaction solution after reaction, and obtaining hydrophobic chitosan powder through centrifugation, washing, drying and grinding; (3) adding the hydrophobic chitosan powder into water and stirring, then adding Fe3O4 magnetic particles to mix to obtain a mixed solution, adding cyclohexane, an emulsifier and a surfactant into the mixed solution and stirring, then adding glutaraldehyde to cross-link to obtain a magnetized hydrophobic chitosan solution, collecting the magnetized hydrophobic chitosan solution through an external magnetic field, and obtaining magnetized hydrophobic chitosan powder through washing, drying and grinding; (4) dissolving the obtained magnetized hydrophobic chitosan powder into acetic acid solution or hydrochloric acid solution to obtain a magnetized hydrophobic chitosan solution, adding Al2(SO4)3·18H2O and K2SO4 into the magnetized hydrophobic chitosan solution to react, and obtaining a magnetized hydrophobic chitosan-alum composite flocculant through standing and curing.

2. The method of claim 1, wherein the magnetized hydrophobic chitosan-alum composite flocculant is prepared by the steps of: In the step (2), the molar ratio of chitosan to lauric acid is 1:(0.2-2).

3. The preparation method of the magnetized hydrophobic chitosan-alum composite flocculant according to claim 1, characterized in that, In the step (2), the molar ratio of lauric acid, N-hydroxysuccinimide (NHS) and 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) is 1:2:

2.

4. The method of claim 1, wherein the magnetized hydrophobic chitosan-alum composite flocculant is prepared by the steps of: In the step (3), the mass ratio of the hydrophobic chitosan powder to the Fe3O4 magnetic particles is 1:(0.5-3).

5. The method of claim 1, wherein the magnetized hydrophobic chitosan-alum composite flocculant is prepared by the steps of: In the step (3), the volume ratio of cyclohexane, the emulsifier and the surfactant is 150:1:

30.

6. The method of claim 1, wherein the magnetized hydrophobic chitosan-alum composite flocculant is prepared by the steps of: In the step (4), the mass ratio of Al2(SO4)3·18H2O to K2SO4 is 1:(1-4).

7. The method of claim 1, wherein the magnetized hydrophobic chitosan-alum composite flocculant is prepared by the steps of: In the step (1), before adding methanol into the chitosan solution, the chitosan solution is first placed in a storage box at 2-6℃ for 24-28h, the pH of the chitosan solution is adjusted by 1% acetic acid, and the pH of the acidified chitosan solution is 4. In the step (2), the stirring time of lauric acid, N-hydroxysuccinimide (NHS) and 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) in ethanol is 2-4h, the reaction time of the acidified chitosan solution is 24-28h, the reaction solution is first ultrasonically treated for 10-15min, then the pH of the reaction solution is adjusted to 9, and then the reaction solution is placed in a storage box at 2-6℃ for 24-28h, and finally the hydrophobic chitosan powder is obtained through centrifugation, washing, drying and grinding.

8. The method of claim 1, wherein the magnetized hydrophobic chitosan-alum composite flocculant is prepared by the steps of: The time for mixing the hydrophobic chitosan and Fe3O4 magnetic particles in step (3) is 12-15 h, the time for stirring and mixing cyclohexane, emulsifier and surfactant into the mixed solution is 3-5 h, the cross-linking reaction is carried out by adding glutaraldehyde under stirring at 50℃ for 3-5 h, and the drying time is 24-26 h; In step (4), Al2(SO4)3·18H2O and K2SO4 are added into the magnetized hydrophobic chitosan solution at a temperature of 50-80℃, and the reaction is carried out at a rotation speed of 600-750 r / min for 3-5 h, and the standing and curing time is 24-28 h.

9. A magnetized hydrophobic chitosan-alum composite flocculant, characterized by, The magnetized hydrophobic chitosan-alum composite flocculant is prepared by the preparation method of any one of claims 1-8.

10. The application of the magnetized hydrophobic chitosan-alum composite flocculant in wastewater treatment containing microplastics according to claim 9.

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