Plant type composite flocculant for removing microplastics and fluorides

Abstract

The invention discloses a plant type composite flocculant for removing microplastics and fluorides, and belongs to the technical field of sewage treatment. The plant type composite flocculant is prepared from an inorganic coagulant, a polymeric flocculant and a jute water-based extracting solution, and acts on a water body through a flocculation-sedimentation process in a synergistic manner, so that efficient removal of micro-plastics and fluorides is realized. The jute water-based extracting solution is obtained by cleaning, drying, crushing and sieving a jute raw material to obtain jute powder, and then performing ultrasonic extraction and centrifugal standing to obtain the jute water-based extracting solution. According to the invention, an inorganic coagulant-polymeric flocculant-plant coagulant aid ternary system is constructed, and the jute water-based extracting solution is introduced as the coagulant aid, so that the dosage of the inorganic coagulant and the polymeric flocculant in a traditional binary system can be greatly reduced, and the synergistic removal rate of micro-plastics and fluorides in a water body can also be remarkably improved; meanwhile, the formed floc is denser, is easy to settle and separate, and has the characteristics of greenness, high efficiency and economy.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a plant-based composite flocculant composed of an inorganic coagulant, a polymeric flocculant, and an aqueous extract of jute, as well as a method and application of using the flocculant to remove microplastics and fluorides from water. Background Technology

[0002] Currently, the problem of complex water pollution is becoming increasingly serious. Microplastics and fluorides, represented by perfluorooctanoic acid (PFOA), are two typical persistent new pollutants that have attracted widespread global attention. Microplastics are widely present in oceans, rivers, soil, and even drinking water sources. Their small particle size and large specific surface area make them prone to adsorbing organic pollutants and heavy metals, and they can accumulate in organisms through the food chain, posing a potential threat to ecosystems and human health. Meanwhile, fluorides such as PFOA, due to their extremely high chemical stability and surface activity, are widely used in many industrial fields, making them extremely difficult to degrade in the environment. They have also been proven to have hepatotoxicity, immunotoxicity, and potential carcinogenicity. Therefore, developing water treatment technologies that can efficiently and economically remove complex pollutants such as microplastics and fluorides from water bodies has become a critical issue that urgently needs to be addressed in the field of environmental engineering.

[0003] However, existing water treatment technologies face significant challenges in addressing these pollutants. Traditional flocculation and sedimentation technologies often rely on binary systems composed of inorganic metal salts (such as polyaluminum chloride) and synthetic organic polymeric flocculants (such as polyacrylamide). While this system can effectively remove suspended particulate matter through mechanisms such as charge neutralization and adsorption bridging, it often exhibits drawbacks when treating complex pollution from microplastics and dissolved fluorides, including high reagent dosages, high treatment costs, and limited removal efficiency for dissolved fluorides. More critically, the use of synthetic flocculants may pose a risk of secondary pollution, and their residual monomers have potential ecotoxicity, which to some extent restricts the green and sustainable development of this technology.

[0004] To overcome the shortcomings of traditional methods, researchers have begun to explore the use of natural polymeric flocculants. For example, chitosan derivatives and moringa cationic protein have been shown to have certain flocculation effects on microplastics. However, these biomass materials generally face bottlenecks such as complex extraction processes, high preparation costs, and difficulties in large-scale production, which restrict their practical application. Existing improved patented technologies, such as improving the dispersibility of chitosan through physical modification (CN120518159A), utilizing mineral-bioviscous composite systems (CN120903665A), or compounding inorganic salts with organic polymers (CN119528300A), although improving flocculation performance to some extent, often still have shortcomings in terms of process complexity, secondary pollution risk, or long-term operational stability, failing to achieve efficient removal of multiple pollutants.

[0005] Regarding the utilization of natural plant materials, some studies have revealed the potential application value of jute. For example, patents from Diruihe Co., Ltd. (CN107427813A, CN107427745A, etc.) disclose the application of jute powder as a filter aid, but its mechanism of action is mainly attributed to physical interception. A patent from the Institute of Bast Fiber Crops, Chinese Academy of Agricultural Sciences (CN110142029A) proposes a composite adsorption flocculant of jute leaf powder and iron salts. However, these technologies either focus on physical filtration or are merely simple physical mixing, and do not provide clear technical insights into how to utilize the chemically active components extracted from jute to construct a synergistic system with inorganic coagulants and polymeric flocculants, thereby enhancing the removal effect on dissolved pollutants and micro / nano-scale particles at the molecular level.

[0006] In summary, simplifying the process, reducing reagent consumption, and improving environmental friendliness while ensuring efficient removal of microplastics and fluorides remain key technological bottlenecks in this field. This invention addresses these challenges by proposing and validating a novel method for constructing a ternary synergistic flocculation system using jute aqueous extract as a natural synergist: an inorganic coagulant, a polymeric flocculant, and a plant-based coagulant aid. This system aims to enhance pollutant removal mechanisms at the molecular level through the synergistic effect of its components, achieving green, economical, and efficient synergistic control of new pollutants in water bodies. Summary of the Invention

[0007] This invention aims to overcome the shortcomings of existing technologies and solve the technical problems of traditional binary systems of "inorganic coagulant-organic flocculant" in treating microplastics and fluorides, such as high dosage, high treatment cost, poor removal effect on dissolved fluorides, and potential secondary pollution. Therefore, this invention provides a plant-based composite flocculant for the removal of microplastics and fluorides and its application. This composite flocculant achieves efficient, economical, and green removal of microplastics and fluorides from water by constructing a ternary synergistic system of "inorganic coagulant-polymer flocculant-plant-based coagulant aid".

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A plant-based composite flocculant for the removal of microplastics and fluorides is composed of inorganic coagulants, polymeric flocculants, and aqueous jute extract. It works synergistically with water through a "flocculation-sedimentation" process to achieve efficient removal of microplastics and fluorides.

[0009] The plant-based composite flocculant is dissolved in the water to be treated during use.

[0010] The inorganic coagulant is one or more of polyaluminum chloride, polyferric chloride, polyaluminum sulfate, polyferric sulfate, aluminum trichloride, ferric trichloride, and alum.

[0011] Furthermore, the concentration range of the inorganic coagulant added during the water treatment process is 1~500 mg / L. Preferably, it is 1~100 mg / L.

[0012] The polymeric flocculant is one or more of the following: polyacrylamide, sodium polyacrylate, sodium polymethacrylate, polyethyleneimine, chitosan, starch, and guar gum.

[0013] Furthermore, the concentration range of the polymeric flocculant added during the water treatment process is 1~100 mg / L. Preferably, it is 1~10 mg / L.

[0014] The preparation method of the jute aqueous extract includes the following steps: First, the jute raw material is washed and dried, then mechanically pulverized by a pulverizer, and then sieved to obtain jute powder; then the jute powder is dispersed in a solution, ultrasonically treated, and then the solid residue is removed by centrifugation; after the obtained solution is allowed to stand, the supernatant is taken to obtain the jute aqueous extract.

[0015] Furthermore, the jute raw material is any one or more combinations of jute leaves, stalks or roots, preferably jute leaves.

[0016] Furthermore, the sieving process uses a mesh size of 40-400, preferably 50-150 mesh.

[0017] Furthermore, the amount of jute powder / water used is 0.3~0.7 g / 50~150 mL, preferably 0.4~0.6 g / 80~120 mL.

[0018] Furthermore, the ultrasonic treatment time is 0.5 to 3 hours, preferably 0.7 to 1.5 hours.

[0019] Furthermore, the solution is allowed to stand for 12 to 36 hours, preferably 20 to 30 hours.

[0020] Furthermore, the dosage of the jute aqueous extract in water treatment is 0.1~2 mL / L, preferably 1~1.5 mL / L.

[0021] The "flocculation-sedimentation" process specifically includes: after adding the plant-based composite flocculant, the water body is rapidly stirred, then slowly stirred, and then allowed to settle.

[0022] Furthermore, the rapid stirring conditions are: 300~500 rpm for 2~5 minutes.

[0023] Furthermore, the slow stirring conditions are: 50-150 rpm and 5-15 minutes.

[0024] Furthermore, the settling conditions are: 20-40 minutes.

[0025] The microplastic is one or more of polyethylene, polypropylene, polyethylene terephthalate, polystyrene, and polyvinyl chloride.

[0026] Furthermore, the microplastic particle size ranges from 50 μm to 500 μm.

[0027] The fluoride is one or more of perfluoroalkyl carboxylic acids and perfluoroalkyl sulfonic acids.

[0028] The beneficial effects of this invention are: (1) This invention breaks through the traditional flocculation process framework and innovatively constructs an "inorganic-organic-biomass" synergistic flocculation system: while retaining inorganic coagulants and organic flocculants, it introduces natural jute aqueous extract as a functional synergist. The synergistic effect of jute aqueous extract is reflected in the uniqueness of its molecular structure: First, jute has a cellulose content as high as 60-70%, containing extremely rich functional groups such as hydroxyl, carboxyl, and carbonyl groups, thus it can form a hydrogen bond network with fluorides and efficiently remove fluorides through specific adsorption; Second, these functional groups enable the jute aqueous solution to construct a uniform negative charge network, which, through charge neutralization effect, synergistically removes microplastics and fluorides with inorganic coagulants and organic flocculants; Third, the long-chain structure of cellulose enhances the removal functions of adsorption bridging and sweeping net trapping.

[0029] (2) Compared with the traditional binary system of "inorganic coagulant-organic flocculant", due to the above-mentioned gain effect of plant-based composite flocculant, the ternary system disclosed in this invention successfully achieves a significant reduction in the amount of inorganic coagulant and organic flocculant, while ensuring a high removal rate of pollutants.

[0030] (3) The process is simple to operate, has mild conditions, and is widely applicable, making it suitable for treating water bodies containing various common types of microplastics and fluorides. At the same time, jute, as a natural plant material, is widely available, inexpensive, and biodegradable, significantly reducing the risk of secondary pollution.

[0031] (4) This invention not only provides a feasible path for water plants to “reduce costs and increase efficiency”, but also effectively reduces dependence on toxic agents and powerfully promotes the sustainable development of water treatment processes. Attached Figure Description

[0032] Figure 1 This is a flowchart illustrating the preparation process of jute aqueous extract.

[0033] Figure 2 The removal efficiency of polyethylene, polystyrene, and polyethylene terephthalate microplastics was compared to that of comparative examples 1-5.

[0034] Figure 3 The removal efficiency of polyethylene, polystyrene, and polyethylene terephthalate microplastics was compared with that of comparative examples 1, 6-9.

[0035] Figure 4 Example 1 shows the removal efficiency of polyethylene, polystyrene, and polyethylene terephthalate microplastics.

[0036] Figure 5 Images of flocs formed in Comparative Example 2 (without inorganic coagulant and organic flocculant), Comparative Example 9 (with inorganic coagulant and organic flocculant), and Example 1 (with inorganic coagulant, organic flocculant, and jute aqueous extract).

[0037] Figure 6 The removal efficiency of perfluorooctanoic acid (PFOA) in Examples 2, 10, and 11 is shown. Detailed Implementation

[0038] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0039] Preparation of Aqueous Extract of Jute In the following examples and comparative examples, the aqueous extract of jute was prepared according to the following process: 0.5 g of jute leaf powder was weighed and dispersed in 100 mL of water. After ultrasonic treatment for 1 hour, the solid residue was separated by centrifugation. The resulting solution was allowed to stand for 24 hours, and the supernatant was taken to obtain the aqueous extract of jute. This process is as follows: Figure 1 As shown.

[0040] Microplastic Removal Efficiency Test Method In the following examples and comparative examples, three microplastics—polyethylene, polystyrene, and polyethylene terephthalate—were selected as the research objects, with a particle size of 75 μm. After the "flocculation-sedimentation" process, the supernatant was collected, and 2 mL of 1M hydrochloric acid was added to remove flocculants and other impurities. The mixture was then filtered using a weighed 0.45 μm glass fiber membrane (weight denoted as M1). Finally, the microplastic-loaded membrane was dried at 60°C until a constant weight was achieved (the weight of the membrane at this point is recorded as M2). The removal rate (R) was calculated using the formula: R = [(0.1 + M1 - M2) / 0.1] × 100%.

[0041] Where 0.1 represents the theoretical mass (g) of the initially added 100 mg / L microplastics in the water sample.

[0042] Perfluorooctanoic acid removal efficiency test method The concentration of perfluorooctanoic acid (PFOA) in the water sample was determined using high-performance liquid chromatography-mass spectrometry (HPLC-MS). After the flocculation-sedimentation process, the supernatant was collected, filtered through a 0.22 μm cellulose acetate membrane, and then analyzed. The removal rate (R) was calculated using the formula: R = (C0 - C) / C0 × 100%, where C0 is the initial concentration and C is the concentration of water after treatment.

[0043] Example 1: Adjust the pH of 500 mL of simulated microplastic wastewater with a concentration of 100 mg / L to 8.0; Mix rapidly at a speed of 400 rpm for 30 seconds; Add the inorganic coagulant polyaluminum chloride (PAC) at a dosage of 50 mg / L, and continue stirring for 1 minute; Add the organic flocculant polyacrylamide (PAM) at a dosage of 3 mg / L, and simultaneously add 0.6 mL of jute aqueous extract, and continue stirring for 1 minute; Switch to slow stirring, stirring at 100 rpm for 10 minutes; Stop stirring and let it stand and settle for 30 minutes; Take the supernatant, determine the concentration of residual microplastics, and calculate the removal rate.

[0044] Example 2: Add 500 mL of perfluorooctanoic acid wastewater with a concentration of 500 μg / L to a beaker; Mix rapidly at a speed of 400 rpm for 30 seconds; Add PAC at a dosage of 300 mg / L and continue stirring for 1 minute; Add PAM at a dosage of 5 mg / L, and simultaneously add 0.5 mL of jute aqueous extract, and continue stirring for 1 minute; Switch to slow stirring, stirring at 100 rpm for 10 minutes; Stop stirring and let it stand and settle for 30 minutes; Take the supernatant, determine the concentration of perfluorooctanoic acid (PFOA), and calculate the removal rate.

[0045] Comparative Example 1: Adjust the pH of 500 mL of simulated wastewater containing 100 mg / L microplastics to 8.0; Mix rapidly at a speed of 400 rpm for 30 seconds; Add PAC at a dosage of 100 mg / L and continue stirring for 2 minutes; Switch to slow stirring, stirring at 100 rpm for 10 minutes; Stop stirring and let it stand and settle for 30 minutes; Take the supernatant, determine the concentration of residual microplastics, and calculate the removal rate.

[0046] Comparative Example 2: The experimental procedure was similar to that of Comparative Example 1, except that the PAC dosage was changed to 0 mg / L.

[0047] Comparative Example 3: The experimental procedure was similar to that of Comparative Example 1, except that the PAC dosage was changed to 200 mg / L.

[0048] Comparative Example 4: The experimental procedure was similar to that of Comparative Example 1, except that the PAC dosage was changed to 300 mg / L.

[0049] Comparative Example 5: The experimental procedure was similar to that of Comparative Example 1, except that the PAC dosage was changed to 400 mg / L.

[0050] Comparative Example 6: Adjust the pH of 500 mL of simulated microplastic wastewater with a concentration of 100 mg / L to 8.0; Mix rapidly at a speed of 400 rpm for 30 seconds; Add PAC at a dosage of 100 mg / L and continue stirring for 1 minute; Add PAM at a dosage of 10 mg / L and continue stirring for 1 minute. Switch to slow stirring, stirring at 100 rpm for 10 minutes; Stop stirring and let it stand and settle for 30 minutes; Take the supernatant, determine the concentration of residual microplastics, and calculate the removal rate.

[0051] Comparative Example 7: The experimental procedure was similar to that of Comparative Example 6, except that the PAM dosage was changed to 20 mg / L.

[0052] Comparative Example 8: The experimental procedure was similar to that of Comparative Example 6, except that the PAM dosage was changed to 30 mg / L.

[0053] Comparative Example 9: The experimental procedure was similar to that of Comparative Example 6, except that the PAM dosage was changed to 40 mg / L.

[0054] Comparative Example 10: Add 500 mL of perfluorooctanoic acid wastewater with a concentration of 500 μg / L to a beaker; Mix rapidly at a speed of 400 rpm for 30 seconds; Add PAC at a dosage of 300 mg / L and continue stirring for 1 minute; Add PAM at a dosage of 5 mg / L and continue stirring for 1 minute; Switch to slow stirring, stirring at 100 rpm for 10 minutes; Stop stirring and let it stand and settle for 30 minutes; Take the supernatant, determine the concentration of perfluorooctanoic acid (PFOA), and calculate the removal rate.

[0055] Comparative Example 11: The experimental procedure was similar to that of Comparative Example 10, except that the amount of PAM added was changed to 0 mg / L.

[0056] Results Analysis: First, under natural settling conditions without the addition of any flocculant (Comparative Example 2), the removal efficiency of the three microplastics varied due to their density differences. Lower density polyethylene (0.93 g / cm³) had the highest removal efficiency. 3 The removal rate was only 5.77%; polystyrene with a density close to that of water (1.05 g / cm³) 3 The removal rate was 26.58%; while the higher density polyethylene terephthalate (1.37 g / cm³) had a lower removal rate. 3 It exhibits good natural settling properties, with a removal rate of 49.61%.

[0057] The effect of using only the inorganic coagulant PAC was investigated (Comparative Examples 1-5). Figure 2 As shown, the removal efficiency of the three microplastics all increased with the increase of PAC dosage from 0 mg / L to 400 mg / L. When the PAC dosage reached 400 mg / L, the removal rate of polyethylene increased to 67.6%, the removal rate of polystyrene increased to 93.84%, and the removal rate of polyethylene terephthalate increased to 85.77%.

[0058] The effect of the organic flocculant PAM on microplastic removal rate was investigated (Comparative Examples 1, 6-9). The PAC dosage was kept constant at 100 mg / L, and only the PAM dosage was varied. Figure 3 As shown, the results indicate that the removal efficiency of the three microplastics gradually increases with the increase of PAM dosage. When the PAM dosage is 40 mg / L, the removal rate of polyethylene increases to 64.8%, the removal rate of polystyrene increases to 93.84%, and the removal rate of polyethylene terephthalate increases to 91.76%.

[0059] The effect of jute aqueous extract on microplastic removal rate was investigated (Example 1). Figure 4 As shown, when the dosages of inorganic coagulant and organic flocculant are 50 mg / L and 3 mg / L respectively, a small amount of jute aqueous extract can achieve better removal results: the removal rates of polyethylene, polystyrene, and polyethylene terephthalate reach 92.88%, 94.02%, and 98.36%, respectively. The results indicate that, compared with the traditional binary system of "inorganic coagulant-organic flocculant" (Comparative Example 9), the ternary system of "inorganic coagulant-organic flocculant-plant-based coagulant aid" disclosed in this invention successfully reduces the dosage of PAC by 50% and the dosage of PAM by 92.5% while ensuring high-efficiency removal, significantly reducing reagent consumption and treatment costs.

[0060] Observations from the "flocculation-sedimentation" process ( Figure 5 In the absence of PAC and PAM (Comparative Example 2), microplastics were uniformly dispersed in the beaker without aggregation. Only some microplastics settled to the bottom of the beaker due to gravity, and the settling amount varied among different types of microplastics, consistent with the lower removal efficiency under these conditions. After the addition of PAC and PAM (Comparative Example 9), several large flocs formed in the water (marked by red circles in the figure), effectively adsorbing and encapsulating the microplastics. This indicates that PAC and PAM have a significant adsorption and aggregation effect on microplastics, promoting their aggregation and accelerating sedimentation. However, after the addition of PAC, PAM, and jute aqueous extract (Example 1), the flocs were more concentrated and denser, with almost all microplastics encapsulated within the large flocs. The amount of residual dispersed microplastics was significantly reduced, consistent with the higher removal rate data.

[0061] The removal efficiency of different systems for perfluorooctanoic acid (PFOA) was investigated. The results are as follows: Figure 6 As shown, when only PAC (300 mg / L) was added, the perfluorooctanoic acid (PFOA) removal rate was approximately 62.2% (Comparative Example 11). When PAC (300 mg / L) and PAM (5 mg / L) were added, the PFOA removal rate increased to approximately 79.19% (Comparative Example 10). However, using the ternary system of this invention (Example 2, PAC / PAM / jute extract = 300 / 5 mg / L + 0.5 mL), the PFOA removal rate reached 93.92%. This indicates that the aqueous jute extract has a significant adsorption and removal capacity for PFOA, and its abundant functional groups form hydrogen bonds with the carboxyl and fluorine atoms of PFOA, thereby achieving efficient removal.

[0062] Analysis of the combined dosage of reagents, flocculation effect, and removal capacity for different pollutants shows that the ternary system of this invention not only achieves better removal effects of microplastics and fluorides while significantly reducing the dosage of PAC and PAM, but also the morphology of the formed flocs is more conducive to the operation of the subsequent solid-liquid separation unit. This fully demonstrates the advantages of this system in the treatment of emerging pollutants such as microplastics and fluorides, which combines high efficiency and economy.

[0063] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A plant-based composite flocculant, characterized in that: It is composed of inorganic coagulant, polymeric flocculant and jute aqueous extract.

2. The plant-based composite flocculant according to claim 1, characterized in that: The inorganic coagulant is at least one of polyaluminum chloride, polyferric chloride, polyaluminum sulfate, polyferric sulfate, aluminum trichloride, ferric trichloride, and alum.

3. The plant-based composite flocculant according to claim 1, characterized in that: The polymeric flocculant is at least one of polyacrylamide, sodium polyacrylate, sodium polymethacrylate, polyethyleneimine, chitosan, starch, and guar gum.

4. The plant-based composite flocculant according to claim 1, characterized in that: The preparation method of the jute aqueous extract includes the following steps: First, the jute raw material is washed, dried, and pulverized, and passed through a 40-400 mesh sieve to obtain jute powder; then, 0.3-0.7 g of jute powder is dispersed in 50-150 mL of water, ultrasonically treated for 0.5-3 hours, centrifuged, and the solution is allowed to stand for 12-36 hours. The supernatant is then taken to obtain the jute aqueous extract.

5. The plant-based composite flocculant according to claim 4, characterized in that: The jute raw material is at least one of jute leaves, stalks, and roots.

6. The application of a plant-based composite flocculant as described in any one of claims 1-5 in the removal of microplastics and fluorides from polluted water bodies.

7. The application according to claim 6, characterized in that: The plant-based composite flocculant is dissolved in the polluted water body, wherein the concentration of the inorganic coagulant is 1~500 mg / L, the concentration of the polymeric flocculant is 1~100 mg / L, and the dosage of the jute aqueous extract is 0.1~2 mL / L.

8. The application according to claim 6, characterized in that: The "flocculation-sedimentation" process for treating polluted water includes the following steps: after adding the plant-based composite flocculant to the polluted water, the mixture is rapidly stirred at a speed of 300-500 rpm for 2-5 minutes, then slowly stirred at a speed of 50-150 rpm for 5-15 minutes, and then allowed to settle for 20-40 minutes.

9. The application according to claim 6, characterized in that: The microplastics are at least one of polyethylene, polypropylene, polyethylene terephthalate, polystyrene, and polyvinyl chloride, with a particle size range of 50-500 μm; the fluorides are at least one of perfluoroalkyl carboxylic acids and perfluoroalkyl sulfonic acids.

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