Method for removing micro-plastics in seawater by using flocculating agent prepared from enteromorpha polysaccharide

Abstract

The invention relates to the technical field of microplastic removal, and particularly discloses a method for removing microplastics in seawater by using a flocculant prepared from enteromorpha polysaccharide, and the preparation of the enteromorpha polysaccharide flocculant comprises the following steps: firstly, crushing dried enteromorpha by using a crusher; adding absolute ethyl alcohol, stirring and extracting fat-soluble pigment and part of impurities, centrifuging and collecting precipitate; adding pure water into the precipitate, extracting in a water bath, centrifuging, collecting a supernatant extracting solution A, and re-extracting precipitate residues once according to the same steps to obtain a supernatant extracting solution B; combining the supernatant extracting solution A and the supernatant extracting solution B, carrying out vacuum rotary evaporation concentration to 1 / 10 of the original volume, adding tetraploid volume of absolute ethyl alcohol, and carrying out overnight alcohol precipitation; centrifuging, collecting a precipitated solid, and drying to obtain a crude polysaccharide extract; grinding the crude polysaccharide extract, and mixing the crude polysaccharide extract with polyaluminum chloride according to a ratio of 1: 1.5 to obtain the flocculant. According to the method, the removal cost of the micro-plastics is greatly reduced, and the removal efficiency of the micro-plastics is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of microplastic removal, and specifically to a method for removing microplastics in seawater by preparing a flocculant using Enteromorpha polysaccharide. Background Art

[0002] According to the patent publication number: CN202411036746.8, a method for removing microplastics in rivers based on magnetic biochar includes the following steps: S1 pre-treating mango kernels and mango peels to obtain mango mixture powder; S2 magnetizing the mango mixture powder; S3 pyrolyzing and cooling the magnetized mango mixture powder; S4 filtering, adjusting the pH value, drying to constant weight, and ball milling the rinsed prepared samples in sequence to obtain magnetic biochar; S5 placing the prepared magnetic biochar in a float, and placing a plurality of floats in a float placement assembly on the top of a microplastic removal shell of a microplastic removal device; the magnetic biochar prepared by the present invention has a good effect in removing microplastics, and a plurality of floats loaded with magnetic biochar are placed in each containing filter screen, and the containing filter screen is fixed relative to the filter frame by a baffle, and a plurality of floats are evenly separated by the containing filter screen, and the floats will not gather together, thereby improving the uniformity of microplastic removal in the area where the microplastic removal shell is located.

[0003] However, this technology has the following defects: this method is aimed at removing microplastics from rivers, and it is difficult to apply to the removal of microplastics in seawater due to the influence of pH, and there are certain limitations.

[0004] According to the patent publication number: CN202110527180.9, a method for purifying microplastics in pond aquaculture seawater is provided, which belongs to the field of environmental pollution research technology, including rapid stirring of aquaculture water at 200-300r / min for 5-6min, adding aluminum salt coagulant and 4-hydroxy-3-methoxybenzyl alcohol to the water, slowly stirring at 100-120r / min for 3-5min, adding microbial flocculant to the water, continuing to slowly stir for 6-8min, standing for 20-30min, solid-liquid separation, and the aluminum salt coagulant used is PAC (polyaluminum chloride). The method for purifying microplastics in pond aquaculture seawater provided by the present invention can increase the collision probability of PAC and colloidal particles, improve the effect of electrical neutralization, promote the stretching of microbial flocculant molecular chains, accelerate floc growth, increase floc particle size, make the floc structure more compact, enhance floc strength, thereby improving the purification effect of microplastics.

[0005] However, this technology has the following defects: the types of microplastics removed by this method are limited, the removal rate of a single PAC is not high, the generated flocs are unstable and easy to decompose, and are not suitable for the removal of microplastics in seawater.

[0006] According to the preparation method and application of a CPAM modified SiO2 / CaSiO3 material with patent publication number: CN202010804889.4. The steps of the preparation method include: first preparing calcium silicate powder with calcium nitrate tetrahydrate and sodium metasilicate nonahydrate as raw materials, then using calcium silicate and tetraethyl orthosilicate to react with hexadecyltrimethylammonium bromide and ammonia water under different conditions, aging, and finally calcining to obtain SiO2 / CaSiO3 powder; then immersing the SiO2 / CaSiO3 powder in a cationic polyacrylamide aqueous solution to obtain CPAM modified SiO2 / CaSiO3. The material prepared by the present invention can be used for the removal of microplastics, and can completely remove microplastics in water.

[0007] However, this technology has the following defects: this patent only removes microplastics from relevant domestic water, and some of the steps cannot be applied to seawater, and there are limitations on the removal of microplastics in seawater.

[0008] Therefore, it can be seen from the above that the existing technology only removes microplastics in relevant living water bodies, has poor effect on the removal of microplastics in other media, and is not suitable for the removal of microplastics in seawater. At present, no patent for the removal of microplastics in seawater has been found; for this purpose, a method for using Enteromorpha polysaccharide to prepare flocculants to remove microplastics in seawater is provided. Summary of the invention

[0009] The purpose of the present invention is to address the defects of the prior art and provide a method for removing microplastics from seawater by preparing flocculants using Enteromorpha polysaccharide, so as to solve the problems raised by the above-mentioned background technology.

[0010] To achieve the above object, the present invention provides the following technical solution: a method for removing microplastics from seawater by preparing a flocculant using Enteromorpha polysaccharide, the specific steps of which are as follows:

[0011] Step 1: Selecting raw materials of polyaluminium chloride and Enteromorpha;

[0012] Step 2: Preparation of Enteromorpha polysaccharide flocculant: First, the dried Enteromorpha is crushed with a crusher and passed through a 45-65 mesh sieve;

[0013] Step 2.1: Add anhydrous ethanol, stir and extract fat-soluble pigments and some impurities at 45-60°C, centrifuge at 6000g for 10 minutes, and collect the precipitate;

[0014] Step 2.3: Add pure water to the precipitate, extract in a 60°C water bath for 4-6 hours, centrifuge at 6000 g for 10 minutes, collect the supernatant extract A, and extract the precipitate residue again according to the same steps to obtain the supernatant extract B;

[0015] Step 2.4: Combine the supernatant extract A and the supernatant extract B, concentrate them by vacuum rotary evaporation to 1 / 10 of the original volume, and add four times the volume of anhydrous ethanol for overnight precipitation;

[0016] Step 2.5: centrifuge at 8000 g for 10 min, collect the precipitated solid and dry it, i.e., the crude polysaccharide extract;

[0017] Step 2.6: After grinding the crude polysaccharide extract, the extract and polyaluminium chloride are mixed in a ratio of 1:1.5 to obtain a flocculant;

[0018] Step 3: Pour the seawater containing a set amount of microplastics into a flocculation test machine containing a flocculant, stir and mix the flocculant and the seawater containing microplastics, and finally let it stand for 2-3 hours. After standing, extract the supernatant by siphoning;

[0019] Step 4: Filter the supernatant in step 3 and detect microplastics.

[0020] As a preferred technical solution of the present invention, 0.1-0.3 g of flocculant is added to every liter of seawater in step 3; and every liter of seawater contains 50-100 mg of microplastics.

[0021] As a preferred technical solution of the present invention, the stirring program of the beaker flocculation tester in step 3 is set to 300 rpm / min for 5 min, 120 rpm / min for 10 min, and 50 rpm / min for 20 min.

[0022] As a preferred technical solution of the present invention, the method for measuring microplastics in step 4 is:

[0023] Step 4.1: Number the microporous membranes required for the experiment and measure their mass as M1. After flocculation, collect the microplastics floating in the upper water for filtration;

[0024] Step 4.2: After filtration, place the filter membrane containing microplastics in an oven at 35°C to dry until the mass remains unchanged. The mass at this time is recorded as M2;

[0025] Step 4.3: Then calculate the microplastic removal rate α according to the formula; α = 0.1-(M2-M1) / 0.1×100%.

[0026] As a preferred technical solution of the present invention, the liquid ratio of Enteromorpha enteromorpha to anhydrous ethanol in step 2.1 is 1:10.

[0027] As a preferred technical solution of the present invention, pure water is added to the precipitate in step 2.3, wherein the solid-liquid ratio of the precipitate obtained in step 2.1 to water is 1:20.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. This invention greatly reduces the cost of removing microplastics and improves the efficiency of removing microplastics. This method helps reduce marine pollution and restore natural biodiversity;

[0030] 2. Provides a dedicated method for removing microplastics from seawater;

[0031] 3. It provides a solid theoretical basis for the subsequent removal of microplastics in seawater, and contributes to the effective implementation of subsequent pollution prevention and control work. DETAILED DESCRIPTION

[0032] The preferred embodiments of the present invention are described in detail below so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0033] The present invention provides a technical solution: a method for removing microplastics in seawater by preparing a flocculant using Enteromorpha polysaccharide, the method being as follows:

[0034] Polyaluminium chloride (PAC) was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.; electric blast drying oven DHG-9240A was purchased from Shanghai Yiheng Scientific Instrument Co., Ltd.; flocculation experiments were carried out with a beaker on a flocculation test machine (NANBEI-78-1).

[0035] Preparation of Enteromorpha polysaccharide flocculant: First, the dried Enteromorpha sample is crushed with a pulverizer and passed through a 60-mesh sieve; anhydrous ethanol (solid-liquid ratio 1:10) is added, and the fat-soluble pigments and some impurities are extracted by stirring at room temperature, centrifuged at 6000g for 10 minutes, and the precipitate is collected; pure water (solid-liquid ratio 1:20) is added to the precipitate, extracted in a 60°C water bath for 4 hours, centrifuged at 6000g for 10 minutes, and the supernatant extract is collected; the precipitate residue is extracted again according to the same steps; the two extracts are combined, vacuum rotary evaporation is concentrated to 1 / 10 of the original volume, and four times the volume of anhydrous ethanol is added for alcohol precipitation overnight; centrifuged at 8000g for 10 minutes, the precipitated solid is collected and dried, that is, the crude polysaccharide extract; after grinding the crude polysaccharide extract, the extract and PAC are mixed in a certain proportion to obtain a flocculant;

[0036] The microplastics used in each experiment weighed 100 mg or 500 aged microplastics were selected; the stirring program of the beaker flocculation tester was set to 300 rpm / min for 5 min, 120 rpm / min for 10 min, 50 rpm / min for 20 min, and finally let stand for 30 min. The dosages of PAC and EP were based on the common dosages of flocculants in tap water; after flocculation, the microplastics floating on the upper layer of the water were collected for subsequent filtration, drying and weighing;

[0037] Method for measuring microplastics: First, the microporous membranes required for the experiment are numbered and their mass is measured as M1. After flocculation, the microplastics floating in the upper water are collected for filtration. After filtration, the filter membrane containing microplastics is placed in an oven at 35°C to dry until the mass remains unchanged. The mass at this time is recorded as M2, and then the microplastic removal rate α is calculated according to the formula, α=0.1-(M2-M1) / 0.1×100%; the removal efficiency of microplastics of different types and particle sizes in the PAC-EP system.

[0038] The experimental results show that the removal rate of small particle size is the lowest, but it is still close to 40%, while the removal rate of medium particle size PVC is the highest, reaching 88%, and the overall removal effect is more stable than other flocculation systems.

[0039] In the PAC-EP system, when the PAC dosage is fixed, the removal rate of PVC microplastics increases first and then decreases with the increase of EP dosage. When the EP dosage reaches 55-65 mg / L, the removal rate reaches the maximum value. When the EP dosage is fixed, when the PAC dosage reaches 60 mg / L, the removal rate reaches the maximum value. It is found that the maximum removal rate can only be achieved when the dosage of PAC and EP reaches 60 mg / L at the same time.

[0040] In practical applications, adding its flocculant into seawater can achieve a good removal effect, and the dosage can be expanded according to the experimental proportion. First, when no flocculant is added, PVC itself is relatively stable, and only a very small part of PVC microplastics precipitates. During the stirring process, PAC and EP fully play their roles to form a large number of floccules. After the stirring stops, these floccules with microplastic particles settle down. Secondly, weathered polyvinyl chloride (microplastics) introduce discrete negative charges on the surface under the irradiation of sunlight ultraviolet rays. After adding PAC-EP, PAC hydrolyzes to generate Al 3+ That is, the positive charge can neutralize the negative charge carried by PVC particles in seawater; this leads to the compression of the electrical double layer of PVC microplastics, weakening the charge repulsion between PVC particles and reducing stability; then the introduction of EP leads to the hydrolysis of new substances, the compression effect of the double layer is enhanced, and the instability of PVC microplastics is further aggravated; this provides good conditions for the sedimentation caused by the collision and aggregation of PVC particles; as the particles aggregate, the flocs become larger and larger, thus achieving the effect of sedimentation; the hydroxide flocs formed by the hydrolysis of PAC-EP can bind to and sweep away the colloidal particles in the water.

[0041] EP can usually form large flocs with a three-dimensional network structure during the flocculation process; due to its large surface area and strong adsorption capacity, it can effectively capture and remove water pollutants and settle them; the introduction of EP makes the PVC removal effect of the PAC-EP composite system more obvious, which also means that this mechanism has been improved; therefore, the introduction of EP does enhance the charge neutralization effect in the PAC flocculation system, which aggravates the instability and sedimentation of PVC microplastics and contributes to the improvement of PVC removal rate.

[0042] Example 1: A method for removing microplastics from seawater by preparing a flocculant using Enteromorpha polysaccharide; the specific steps are as follows:

[0043] Polyaluminium chloride (PAC) was purchased from Shanghai McLean Biochemical Technology Co., Ltd.; electric blast drying oven DHG-9240A was purchased from Shanghai Yiheng Scientific Instrument Co., Ltd.; flocculation experiments were carried out with a beaker on a flocculation test machine (NANBEI-78-1); seawater was taken from the coastal waters of Haizhou Bay, and the aged microplastics used in each experiment weighed 100 mg; after flocculation, the supernatant was collected for subsequent filtration, drying and weighing; simulated water samples were prepared with 150um aged polyvinyl chloride (PVC) microplastics, and the sampled seawater was first filtered through a 0.45um filter membrane after shaking. 1L of filtered seawater was selected to prepare the water sample, and its pH value was measured to be 8, the water sample concentration was 100 mg / L, and PAC was added.

[0044] Table 1: Removal efficiency of microplastics by adding PAC alone

[0045]

[0046] The blank control group was set up as shown in Table 1. After the water sample was configured, no substance was added to compare whether the microplastics had natural sedimentation. By filtering the supernatant, it was found that PVC had natural sedimentation, reaching 13.06%.

[0047] When the PAC dosage was 20 mg / L, the magnetic stirrer was set to stir at 300 rpm / min for 30 seconds, 120 rpm / min for 10 minutes, 50 rpm / min for 10 minutes, and finally allowed to stand for 30 minutes. The supernatant was extracted by siphoning, and then filtered through a 0.45 um filter membrane to obtain the mass of microplastics after flocculation. The calculated microplastic removal rate was 19.08%. Similarly, when the PAC dosage was 50 mg / L, the microplastic removal rate was 21.3%.

[0048] When the PAC dosage was 100 mg / L, the microplastic removal rate was 23.8%. When the PAC dosage was 200 mg / L, the microplastic removal rate was 35.8%. After adding PAC, PAC hydrolyzed to generate Al 3+, which can neutralize the negative charge carried by PVC particles. This leads to the compression of the electrical double layer of PVC microplastics, weakening the charge repulsion between PVC particles and reducing stability. This provides good conditions for sedimentation caused by collision and aggregation of PVC particles.

[0049] Example 2: A method for removing microplastics from seawater by preparing a flocculant using Enteromorpha polysaccharide; the specific steps are as follows:

[0050] Enteromorpha polysaccharide (EP) was purchased from Jiangsu Sanshu Biotechnology Co., Ltd.; electric blast drying oven DHG-9240A was purchased from Shanghai Yiheng Scientific Instrument Co., Ltd.; flocculation experiments were carried out with a beaker on a flocculation tester (NANBEI-78-1); seawater was taken from the nearshore waters of Haizhou Bay, and the aged microplastics used in each experiment weighed 100 mg.

[0051] Table 2: Removal efficiency of microplastics by PAC-EP complex

[0052]

[0053]

[0054] The stirring program of the magnetic stirrer was set to 300 rpm / min for 30 s, 120 rpm / min for 10 min, 50 rpm / min for 10 min, and finally standing for 30 min. The supernatant was extracted by siphon method, and then filtered through a 0.45 um filter membrane to obtain the mass of microplastics after flocculation, and its removal rate was calculated; as shown in Table 2; the hydroxide flocs formed by PAC hydrolysis can bind and sweep away colloidal particles in the water, however, EP can usually form large flocs with a three-dimensional network structure during the flocculation process. Due to its large surface area and strong adsorption capacity, it can effectively capture and remove water pollutants and settle them. The introduction of EP makes the removal effect of PVC by the PAC-EP composite system more obvious.

[0055] Example 3: A method for removing microplastics from seawater by preparing a flocculant using Enteromorpha polysaccharide; the specific steps are as follows:

[0056] Enteromorpha polysaccharide (EP) was purchased from Jiangsu Sanshu Biotechnology Co., Ltd.; electric blast drying oven DHG-9240A was purchased from Shanghai Yiheng Scientific Instrument Co., Ltd.; flocculation experiments were carried out with a beaker on a flocculation tester (NANBEI-78-1); seawater was taken from the nearshore waters of Haizhou Bay, and the aged microplastics used in each experiment weighed 100 mg.

[0057] Table 3: Removal efficiency of microplastics by increasing the dosage of EP in PAC-EP mixture

[0058]

[0059] On the basis of Example 2, the removal rate was calculated when the dosage of EP was changed to 10 mg / L, 20 mg / L, and 50 mg / L respectively. It was found that when the dosage of PAC was 60 mg / L and the dosage of EP was 60 mg / L, the maximum removal rate of PVC reached 92.3%. As shown in Table 3, when the dosage of flocculant was too high, the removal effect of microplastics in the PAC-EP system would be weakened due to the floating of flocs and the formation of mucous film on the surface of the water body. The flocculation mechanism analysis showed that EP strengthened the compression of the PVC electrical double-layer structure. The ions in the water may improve the treatment effect of the system by promoting the hydrolysis of Al to form Al(OH)3 or act as a chemical bridge to enhance the adsorption of substances. Organic matter and various suspended solids will increase the net capture in the flocculation process, making it easier for the system to form flocs during the flocculation process. This can improve the quality of the floccules and at the same time increase the sedimentation rate of microplastic particles. In addition, since the PAC-EP system will form larger floccules during the flocculation process, the system can capture more PVC microplastics.

[0060] In summary, this method can effectively remove microplastics in seawater. The polysaccharide extracted from Enteromorpha is sulfated polysaccharide, which is a new type of natural coagulant, containing a large number of functional groups such as carboxyl (-COOH), hydroxyl (-OH) and sulfonic acid (-SO3H). In the process of water treatment, the -COOH and -OH on the Enteromorpha polysaccharide molecules can react with the Al in the aluminum coagulant. 3+ It can chelate with its polymer to form a network structure, improve the effect of net capture, and promote the formation of large and dense flocs of pollutants, so that the removal efficiency of polluted particles in water bodies can be effectively improved. It plays a good synergistic role in the process of traditional aluminum salt flocculation to remove microplastics, and achieves efficient removal of microplastics.

[0061] The above embodiments only express the implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention.

Claims

1. A method for removing microplastics from seawater by preparing a flocculant using Enteromorpha polysaccharide, characterized in that: The specific steps are as follows: Step 1: Selecting raw materials of polyaluminium chloride and Enteromorpha; Step 2: Preparation of Enteromorpha polysaccharide flocculant: First, the dried Enteromorpha is crushed with a crusher and passed through a 45-65 mesh sieve; Step 2.1: Add anhydrous ethanol, stir and extract fat-soluble pigments and some impurities at 45-60°C, centrifuge at 6000g for 10 minutes, and collect the precipitate; Step 2.3: Add pure water to the precipitate, extract in a 60°C water bath for 4-6 hours, centrifuge at 6000 g for 10 minutes, collect the supernatant extract A, and extract the precipitate residue again according to the same steps to obtain the supernatant extract B; Step 2.4: Combine the supernatant extract A and the supernatant extract B, concentrate them by vacuum rotary evaporation to 1 / 10 of the original volume, and add four times the volume of anhydrous ethanol for overnight precipitation; Step 2.5: centrifuge at 8000 g for 10 min, collect the precipitated solid and dry it, i.e., the crude polysaccharide extract; Step 2.6: After grinding the crude polysaccharide extract, the extract and polyaluminium chloride are mixed in a ratio of 1:1.5 to obtain a flocculant; Step 3: Pour the seawater containing a set amount of microplastics into a flocculation test machine containing a flocculant, stir and mix the flocculant and the seawater containing microplastics, and finally let it stand for 2-3 hours. After standing, extract the supernatant by siphoning; Step 4: Filter the supernatant in step 3 and detect microplastics.

2. The method for removing microplastics from seawater by preparing a flocculant using Enteromorpha polysaccharide according to claim 1, characterized in that: In step 3, 0.1-0.3 g of flocculant is added to every liter of seawater; every liter of seawater contains 50-100 mg of microplastics.

3. The method for removing microplastics from seawater by preparing flocculants using Enteromorpha polysaccharide according to claim 1, characterized in that: In step 3, the stirring program of the beaker flocculation tester is set to 300 rpm / min for 5 min, 120 rpm / min for 10 min, and 50 rpm / min for 20 min.

4. The method for removing microplastics from seawater by preparing flocculants using Enteromorpha polysaccharide according to claim 1, characterized in that: Methods for measuring microplastics in step 4: Step 4.1: Number the microporous membranes required for the experiment and measure their mass as M1. After flocculation, collect the microplastics floating in the upper water for filtration; Step 4.2: After filtration, place the filter membrane containing microplastics in an oven at 35°C to dry until the mass remains unchanged. The mass at this time is recorded as M2; Step 4.3: Then calculate the microplastic removal rate α according to the formula; α = 0.1-(M2-M1) / 0.1×100%.

5. The method for removing microplastics from seawater by preparing flocculants using Enteromorpha polysaccharide according to claim 1, characterized in that: The solid-liquid ratio of Enteromorpha to anhydrous ethanol in step 2.1 is 1:

10.

6. The method for removing microplastics from seawater by preparing flocculants using Enteromorpha polysaccharide according to claim 1, characterized in that: In step 2.3, pure water is added to the precipitate, wherein the solid-liquid ratio of the precipitate obtained in step 2.1 to water is 1:20.

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