Method for removing nano-plastic in water based on in-situ oxidation coagulation process

Abstract

This disclosure proposes a method for removing nanoplastics from water based on in-situ oxidative coagulation, comprising: preparing a ferrous coagulant: adding an alkaline solution to a ferrous solution to obtain a ferrous coagulant; preparing and activating an oxidant solution; and in-situ oxidative coagulation: under stirring conditions, simultaneously adding the activated oxidant solution and the ferrous coagulant to the water containing nanoplastics, wherein the feeding ratio of the ferrous coagulant to the oxidant solution is controlled so that the mass concentration ratio of Fe to oxidant is within the range of 1:0.05 to 1:0.3, thereby partially converting the ferrous ions in the ferrous coagulant into iron ions, which then recrystallize and form flexible network flocs with sheet-like or flower-like flexible nanosheet structures, trapping nanoplastic monomer particles and thus efficiently removing them.

Description

Technical Field

[0001] This disclosure belongs to the field of water treatment technology, and in particular relates to a method for removing nanoplastics from water based on in-situ oxidation coagulation process. Background Technology

[0002] Plastic materials are widely used due to their lightweight, durability, and low cost. However, the nanoplastics (NPs) produced by their degradation have become emerging environmental pollutants due to their small particle size (typically <100nm), high chemical stability, negatively charged surface, and ability to easily penetrate biological barriers. NPs are widely present in drinking water systems, natural water bodies, and groundwater. They can enter the human body through drinking water, inducing oxidative stress, inflammatory responses, and damage to the neuroendocrine system, posing a serious threat to ecosystems and public health.

[0003] Coagulation is the most widely used pollutant removal technology in water treatment. It mainly relies on the hydrolysis of aluminum salts (such as aluminum sulfate) or iron salts (such as ferric chloride) to form charged flocs, which then settle pollutants through adsorption-trapping. However, traditional coagulation processes face many key bottlenecks when treating polysaccharides (NPs). For example, NPs have extremely small particle sizes, strong dispersibility, and densities close to water (1.02-1.2 g / cm³). 3 NPs are difficult to be effectively captured by conventional flocculants; at the same time, common flocculants have low treatment efficiency and are prone to toxic side effects; and in related technologies, the micromorphology of flocculants is not controlled, and spherical flocculants have insufficient adsorption sites for NPs, making it difficult to overcome the colloidal stability of NPs.

[0004] In summary, traditional coagulation processes are inefficient at removing nanoplastics from water due to structural defects in the flocs, chemical risks, and lack of morphology control. Therefore, developing efficient, safe, and practical nanoplastic removal technologies has become an urgent issue in the water treatment field. Summary of the Invention

[0005] In view of this, and to solve at least one technical problem in related technologies and other aspects, this disclosure proposes a method for removing nanoplastics from water based on in-situ oxidation coagulation process, comprising:

[0006] Preparation of ferrous coagulant: Add alkali solution to ferrous solution to obtain ferrous coagulant;

[0007] Prepare an oxidizing agent solution and activate the oxidizing agent solution;

[0008] In-situ oxidative coagulation: Under stirring conditions, the activated oxidant solution and ferrous coagulant are simultaneously added to the water body to be treated containing nanoplastics. The feeding ratio of ferrous coagulant to oxidant solution is controlled so that the mass concentration ratio of Fe:oxidant is in the range of 1:0.05 to 1:0.3. This converts the ferrous ions in the ferrous coagulant into iron ions, which are then adsorbed on the surface of the nanoplastic particles and rearranged and crystallized to form flocs with a flexible nanosheet structure in the form of sheets or flowers.

[0009] According to embodiments of this disclosure, in the ferrous solution, the dissolved oxygen concentration is less than 1 mg / L, and the ferrous ion concentration is 1~5 mol / L.

[0010] According to embodiments of this disclosure, the dissolved oxygen concentration of the alkaline solution is less than 1 mg / L.

[0011] According to embodiments of this disclosure, in ferrous coagulants, [OH - The ratio of Fe ion concentration to Fe ion concentration is (0.5:1) to (2:1).

[0012] According to embodiments of this disclosure, the addition of alkaline solution to the ferrous solution is carried out under a nitrogen atmosphere and with stirring at a speed of 400-600 rpm.

[0013] According to embodiments of this disclosure, the oxidant includes any one of sodium percarbonate, persulfate, or hydrogen peroxide;

[0014] The concentration of the oxidant solution is 1-5 g / L.

[0015] According to embodiments of this disclosure, the activating oxidant solution comprises:

[0016] Add acid to the oxidant solution to make the pH of the oxidant solution less than 4.

[0017] According to embodiments of this disclosure, the concentration range of the ferrous coagulant dosage is 0.05-0.4 mmol / L.

[0018] According to embodiments of this disclosure, stirring includes: first stirring at a speed of 100-300 rpm for 30 seconds to 1 minute, and then stirring at a speed of 20-70 rpm for 30 minutes.

[0019] According to embodiments of this disclosure, the activated oxidant solution and the ferrous coagulant are added at the same rate, which is 0.1~0.3 mL / min.

[0020] According to embodiments of this disclosure, based on a charge transfer mechanism, flexible flocs with sheet-like or flower-like structures are generated in situ on the surface of nanoplastics through synergistic regulation of oxidation and coagulation. The disclosure also attempts to improve coagulation performance, particularly the removal of pollutants, primarily nanoplastics, by controlling the type and oxidation state of the ferric salt coagulant. Specifically, the directional activation of the oxidant and its simultaneous addition with the ferrous coagulant, on the one hand, inhibits the destruction of floc morphology by strong oxidants, maintaining the growth of sheet-like crystals, and on the other hand, promotes the growth of Fe... 2+ To Fe 3+ The in-situ transformation allows ferrous and ferric ions to hydrolyze and rearrange directly on the surface of nanoplastics, forming tightly coated flocculant-pollutant complexes, thus enhancing the separation effect. Among them, the flexible flocculant structure with sheet-like or flower-like structure has a high specific surface area and flexible coating characteristics, which significantly enhances the adsorption sites and encapsulation capacity of nanoplastics, overcoming the problem of low capture efficiency caused by the compact structure of traditional spherical flocculants. Attached Figure Description

[0021] Figure 1 This is a flowchart of a method for removing nanoplastics from water based on in-situ oxidation coagulation in this embodiment of the present disclosure;

[0022] Figure 2 These are electron microscope images from Test Example 1 of this disclosure, where a is an electron microscope image of the flocs after treatment with Fe(III) solution in Comparative Example 1, b is an electron microscope image of the flocs after treatment with Fe(II) solution in Comparative Example 2, c is an electron microscope image of the flocs after treatment with a flocculant containing Fe(III) solution and Fe(II):SPC=1:0.05 in Example 1, and d is an electron microscope image of the flocs after treatment with a flocculant containing Fe(II):SPC=1:0.5 in Example 1.

[0023] Figure 3 This is the floc growth curve showing the change in the macroscopic size of the sheet-like flocs over time in Test Example 1 of this publication;

[0024] Figure 4 This is a comparison chart of the overall turbidity of the supernatant in the water body, the turbidity contributed by the nanoplastics, and the zeta potential of the flocculants in Test Example 1 of this publication;

[0025] Figure 5 This is a floc growth curve diagram showing the change in the macroscopic size of the reaction flocs over time under different dosage conditions in Example 2 of this disclosure;

[0026] Figure 6 This is a floc growth curve of the macroscopic size of the reaction flocs changing over time under different dosage conditions in Comparative Example 3 of this disclosure;

[0027] Figure 7This is a comparison diagram of the overall turbidity of the supernatant in the water body after treatment in Embodiment 2 of this disclosure, the turbidity contributed by the nanoplastics, and the zeta potential of the flocculants;

[0028] Figure 8 This is a comparison chart of the overall turbidity of the supernatant in the water body after treating water bodies with different pH values, the turbidity contributed by nanoplastics, and the zeta potential of flocculants in Test Example 3 of this disclosure;

[0029] Figure 9 This is a comparison chart of the overall turbidity of the supernatant, the turbidity contributed by nanoplastics, and the zeta potential of flocculants in the water body treated with fulvic acid in Test Example 4 of this publication.

[0030] Figure 10 This is a comparison chart of the overall turbidity of the supernatant, the turbidity contributed by nanoplastics, and the zeta potential of flocculants in the water body treated with humic acid in Test Example 4 of this publication.

[0031] Figure 11 This is a comparison chart of the overall turbidity of the supernatant, the turbidity contributed by nanoplastics, and the zeta potential of flocculants in the water body treated in Test Example 4 of this publication when treating polluted water containing dissolved organic matter. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0033] The endpoints and any values ​​of the ranges disclosed in this disclosure are not limited to the precise ranges or values, and such ranges or values ​​should be understood to include values ​​close to such ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this disclosure.

[0034] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0035] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0036] It should be noted that, unless otherwise defined, the technical or scientific terms used in this disclosure should have the ordinary meaning understood by a person with ordinary skill in the art to which this disclosure pertains. Where the terms "first," "second," etc., are used throughout, they are used only to distinguish similar objects and should not be construed as indicating or implying their relative importance, order of precedence, or implicitly specifying the number of technical features indicated. It should be understood that the data described by "first," "second," etc., can be interchanged where appropriate.

[0037] Similarly, to simplify this disclosure and aid in understanding one or more of the various aspects of the disclosure, in the above description of exemplary embodiments of the present disclosure, various features of the present disclosure are sometimes grouped together in a single embodiment, figure, or description thereof. The use of terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refers to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present disclosure. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0038] Furthermore, the technical solutions of the various embodiments can be combined with each other, but only if they are based on the ability of a person skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed in this disclosure.

[0039] Among existing flocculants, the spherical nanoparticles formed by typical ferric salts have a compact structure and limited specific surface area, resulting in insufficient coating capacity for nanoparticles (NPs). Under low concentration conditions, the removal rate is typically below 50%. For example, when treating wastewater with 0.2 mmol / L ferric salts, the removal rate of nanoplastics is only about 37.5%. Residual aluminum ions (Al) from aluminum salts... 3+ Traditional coagulation strategies face significant limitations in the treatment of nano-pollutants, posing a serious risk of neurotoxicity, while organic polymeric coagulants (such as polyacrylamide and chitosan) can easily induce microbial proliferation and the generation of disinfection byproducts. Innovation in mechanisms and material structures is urgently needed.

[0040] During the implementation of this public disclosure, it was discovered that: Fe 2+ Different behaviors are observed during hydrolysis and precipitation, resulting in hydroxide particles of various shapes, including plate-like, needle-like, and spherical. This phenomenon is attributed to a geochemical mechanism known as charge transfer: Fe 2+ Ions can transfer electrons to Fe that has already been oxidized. 3+In the primary particles, induced atomic rearrangement transforms amorphous particles into a more ordered crystalline structure. As the particle morphology changes significantly, from tiny spherical shapes to plate-like or needle-like structures, the aggregation behavior of Fe salts also changes significantly. The presence of organic matter and redox potential also influence the morphology of Fe particles through this process. Oxidizing agents such as potassium permanganate and sodium hypochlorite, due to their strong oxidizing properties, accelerate the oxidation of Fe. 2+ Hydrolysis and precipitation can disrupt the subsequent growth of nanosheets; conversely, weakly oxidizing agents can accelerate the in-situ formation of flocs while maintaining their sheet-like properties. Therefore, the rational selection of weakly oxidizing agents is of great significance for controlling crystal growth.

[0041] Figure 1 This is a flowchart of a method for removing nanoplastics from water based on in-situ oxidation coagulation in this embodiment of the present disclosure.

[0042] This disclosure proposes a method for removing nanoplastics from water based on in-situ oxidative coagulation, such as... Figure 1 As shown, the process includes the following steps S101-S103:

[0043] Step S101: Preparation of ferrous coagulant: Add alkali solution to ferrous solution to obtain ferrous coagulant;

[0044] Step S102: Prepare the oxidant solution and activate the oxidant solution;

[0045] Step S103: In-situ oxidative coagulation: Under stirring conditions, the activated oxidant solution and ferrous coagulant are simultaneously added to the water body to be treated containing nanoplastics. The feeding ratio of ferrous coagulant to oxidant solution is controlled so that the mass concentration ratio of Fe: oxidant is in the range of 1:0.05 to 1:0.3, thereby converting ferrous ions in the ferrous coagulant into ferric ions, and allowing the ferric ions to be adsorbed on the surface of nanoplastic particles and rearranged and crystallized to form flocs with a flexible nanosheet structure in the form of sheets or flowers.

[0046] According to embodiments of this disclosure, based on a charge transfer mechanism, flexible flocs with sheet-like or flower-like structures are generated in situ on the surface of nanoplastics through synergistic regulation of oxidation and coagulation. The disclosure also attempts to improve coagulation performance, particularly the removal of pollutants, primarily nanoplastics, by controlling the type and oxidation state of the ferric salt coagulant. Specifically, the directional activation of the oxidant and its simultaneous addition with the ferrous coagulant, on the one hand, inhibits the destruction of floc morphology by strong oxidants, maintaining the growth of sheet-like crystals, and on the other hand, promotes the growth of Fe... 2+ To Fe 3+The in-situ transformation allows iron ions to be directly adsorbed onto the surface of nanoplastics and hydrolyzed and rearranged to form tightly coated flocculant-pollutant complexes, enhancing the separation effect. Among them, the flexible flocculant structure with sheet-like or flower-like structure has a high specific surface area and flexible coating characteristics, which significantly enhances the adsorption sites and encapsulation capacity of nanoplastics, overcoming the problem of low capture efficiency caused by the compact structure of traditional spherical flocculants.

[0047] According to embodiments of this disclosure, the method proposed here abandons the traditional approach of adding additional organic or inorganic coagulants to achieve the desired NP removal rate. Instead, it chooses to overcome the limitations of traditional coagulation methods in NP removal by controlling the crystal structure of the precipitated particles in the flocculant. Compared with traditional Fe(III) coagulants, this method exhibits superior nanoplastic removal performance in actual water bodies (such as surface water and drinking water sources).

[0048] According to embodiments of this disclosure, in the ferrous solution, the dissolved oxygen concentration is less than 1 mg / L, and the ferrous ion concentration is 1~5 mol / L.

[0049] According to embodiments of this disclosure, dissolved oxygen (DO) is a natural oxidant; if DO ≥ 1 mg / L, it will trigger the formation of ferrous ions (Fe). 2+ Uncontrolled oxidation occurs before addition, consuming available ferrous iron and generating ineffective precipitate. Strict control of DO < 1 mg / L ensures Fe... 2 + The activity is retained until the actual application stage, ensuring the initial reactant concentration for in-situ oxidation coagulation. Furthermore, a high DO environment will compete with the oxidant solution for Fe. 2+ This leads to a decrease in oxidant utilization; while a low DO environment allows the oxidant to concentrate its action on the target reaction (Fe). 2+ →Fe 3+ (Conversion), improving oxidation efficiency. A high-concentration ferrous solution of 1~5 mol / L can provide sufficient iron source to ensure that a sufficient amount of flake-like FeOOH flocs are generated in situ on the surface of nanoplastics, overcoming the defect of incomplete floc coating at low concentrations.

[0050] According to embodiments of this disclosure, the dissolved oxygen concentration of the alkaline solution is less than 1 mg / L.

[0051] According to embodiments of this disclosure, if the alkaline solution contains oxygen, the generated Fe(OH)3 colloids will become heterogeneous nucleation sites, promoting subsequent Fe... 2+ Oxidation products rapidly deposit on its surface, forming aggregates with uneven particle size. Low-DO alkaline solution ensures that the coagulant is a homogeneous ferrous solution, blocking the ferrous pre-oxidation failure chain and allowing subsequent oxidation-hydrolysis to start simultaneously on the nanoplastic surface, thus blocking the ferrous pre-oxidation failure chain.

[0052] According to embodiments of this disclosure, in ferrous coagulants, [OH- The ratio of Fe ion concentration to Fe ion concentration is (0.5:1) to (2:1).

[0053] According to embodiments of this disclosure, when [OH - When Fe < 0.5, due to OH - Insufficient ferrous ions lead to incomplete hydrolysis, resulting in the formation of unstable Fe(OH)₂. + The intermediate readily forms amorphous Fe(OH)3 colloids during subsequent oxidation, exhibiting weak adsorption capacity; when [OH - When Fe > 2, OH - Excessive amounts will induce forced precipitation, directly forming large-sized Fe(OH)₂ precipitates (e.g., particle size > 1 μm), thus losing reactivity. Therefore, controlling the ratio of ferrous iron to Fe(OH)₂ to 0.5–2 can maintain ferrous iron in a soluble hydrolyzed complex state (e.g., Fe(OH)₂). + Fe2(OH)2 4+ This provides an ideal precursor for subsequent oxidation-rearrangement.

[0054] According to embodiments of this disclosure, the addition of alkaline solution to the ferrous solution is carried out under a nitrogen atmosphere and with stirring at a speed of 400-600 rpm.

[0055] According to embodiments of this disclosure, nitrogen covering forms an inert gas curtain, causing the oxygen partial pressure at the gas-liquid interface to approach zero, thus stabilizing and suppressing the dissolved oxygen (DO) concentration and eliminating Fe. 2+ Uncontrolled oxidation preserves the ferrous oxide form. When the stirring speed is <400 rpm, insufficient mixing leads to a local pH spike, triggering explosive nucleation of Fe(OH)2. When the stirring speed is >600 rpm, high shear forces destabilize the ferrous complex, inducing colloidal aggregation. A stirring speed of 400~600 rpm precisely balances mixing and shear, ensuring the stability of the complex size.

[0056] According to embodiments of this disclosure, the oxidant includes any one of percarbonate, persulfate, or hydrogen peroxide; the concentration of the oxidant solution is 1-5 g / L.

[0057] According to embodiments of this disclosure, the standard oxidation potentials of the selected oxidants are all within a mild range of 0.38 to 1.44 V: the standard oxidation potential of hydrogen peroxide is 0.38 V (acidic), the standard oxidation potential of persulfate (which generates sulfate after activation) is 1.44 V, and the standard oxidation potential of percarbonate (which slowly releases hydrogen peroxide) is 0.38 V. This potential range can drive Fe 2+ →Fe 3+ Transformation, while avoiding excessive oxidation leading to Fe 3+The octahedral structure collapses (strong oxidizing agents such as potassium permanganate, with a standard oxidation potential of 1.51V, will disrupt lattice rearrangement). When the oxidizing agent concentration is <1 g / L, Fe... 2+ Low oxidation rate, residual Fe 2+ The inhibition of charge transfer mechanisms leads to insufficient crystallinity of the flocs; when the concentration is >5 g / L, excess free radicals initiate secondary oxidation (Fe). 3+ →Fe2O3), which disrupts the lamellar structure. A precise mass ratio of 1-5 g / L Fe:oxidant = 1:0.05~1:0.3 (based on Fe...) 3+ (Based on complete generation), ensuring oxidation rate.

[0058] According to embodiments of this disclosure, activating the oxidant solution includes adding an acid solution to the oxidant solution to make the pH of the oxidant solution less than 4.

[0059] According to embodiments of this disclosure, acidification activation enhances the reactivity of the oxidant, enabling free radicals to precisely act on the surface modification of nanoplastics and drive the in-situ directional growth of sheet-like flocs.

[0060] According to embodiments of this disclosure, the concentration range of the ferrous coagulant dosage is 0.05-0.4 mmol / L.

[0061] According to embodiments of this disclosure, stirring includes: first stirring at a speed of 100-300 rpm for 30 seconds to 1 minute, and then stirring at a speed of 20-70 rpm for 30 minutes.

[0062] According to embodiments of this disclosure, the high-speed shearing during the high-speed phase (100-300 rpm) rapidly homogenizes the oxidant and ferrous ions, eliminating Fe... 3+ A concentration gradient is used to prevent homogeneous nucleation and the formation of free flocs. The low-shear field in the low-speed stage (20-70 rpm) promotes the formation of flower-like multi-level structures through edge-face orientation of FeOOH nanosheets, increasing specific surface area and preventing the random accumulation of spherical aggregates. In other words, the high-speed stirring stage enables in-situ nucleation of pollutants on the surface, while the low-speed stirring stage allows for the construction of an open flower-like network through oriented epiphytic growth. Compared to the dense aggregates formed by traditional single-speed stirring, this improves the pollutant retention capacity.

[0063] According to embodiments of this disclosure, the activated oxidant solution and the ferrous coagulant are added at the same rate, which is 0.1~0.3 mL / min.

[0064] According to the embodiments of this disclosure, the synchronous addition of 0.1~0.3 mL / min dynamically locks the stoichiometric ratio of the reactants, thereby matching the diffusion rate of iron salts with the crystal growth rate, realizing the near-field reaction on the surface of nanoplastic pollutants, and enabling the sheet-like flocs to have atomic-level coating precision and single-crystal-level structural uniformity.

[0065] According to embodiments of this disclosure, by synergistically utilizing the controlled hydrolysis of Fe(II) and the oxidation-induced reaction of sodium percarbonate, this disclosure achieves for the first time the structural coating and stable removal of nanoplastics in the coagulation stage, providing a novel, green, and stable solution for the efficient removal of micropollutants, and has significant environmental application prospects.

[0066] It should be noted that the described embodiments are merely some, not all, of the embodiments disclosed herein. Other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without inventive effort are all within the scope of protection of this disclosure.

[0067] Example 1

[0068] Step 1: Prepare ferrous coagulant

[0069] Provide two 500mL bottles of deionized water and pass nitrogen gas through them for deoxygenation treatment for 30 minutes until the dissolved oxygen concentration drops below 1mg / L.

[0070] Add hydrated ferrous sulfate powder to one of the bottles of deionized water that has undergone the above deoxygenation treatment, and stir with a magnetic stirrer at 500 rpm to fully dissolve it, preparing a 2 mol / L ferrous sulfate solution. Nitrogen gas is continuously introduced during stirring to prevent Fe(II) from being oxidized.

[0071] Sodium hydroxide granules were added to another bottle of deionized water after deoxygenation treatment. The mixture was stirred at 500 rpm using a magnetic stirrer to prepare a 2 mol / L sodium hydroxide solution, with nitrogen gas continuously purging to maintain anaerobic conditions. The prepared sodium hydroxide solution was then transferred to a syringe pump and slowly added dropwise to the ferrous sulfate solution at a rate of 10 mL / min, while maintaining a stirring rate of 500 rpm to prevent excessive hydrolysis and precipitation. Nitrogen gas was continuously purged into the ferrous sulfate solution throughout the entire addition process.

[0072] After the addition was completed, a ferrous coagulant (Fe(II) coagulant) with an iron ion concentration of 1 mol / L and an alkalinity [OH-]:[Fe] of 1 was obtained.

[0073] Step 2: Prepare the oxidant solution and activate it.

[0074] A measured amount of sodium percarbonate powder was added to 500 mL of deionized water, stirred and dissolved, and then sonicated for 10 minutes to prepare a sodium percarbonate solution (SPC) with a concentration of 2.5 g / L.

[0075] The pH of the sodium percarbonate solution was adjusted to 4 using dilute sulfuric acid to obtain the activated oxidant solution, which was then transferred to a brown glass bottle for storage in the dark for later use.

[0076] Step 3: In-situ oxidative coagulation

[0077] Use a coagulation mixer to rapidly mix 1L of polluted water to be treated, with the speed set to 200rpm.

[0078] Simultaneously, the Fe(II) solution prepared in steps 1 and 2 and the activated sodium percarbonate solution were added to the water from the left and right sides of the stirrer at a rate of 0.2 mL / min, respectively, so that the final iron ion concentration added to the system was 0.2 mmol / L.

[0079] Furthermore, in this Example 1, the injection volume of the sodium percarbonate syringe was adjusted to obtain a series of Fe:sodium percarbonate concentration ratio gradients (Fe(II):SPC) of 1:0; 1:0.05; 1:0.1; 1:0.133; 1:0.2; 1:0.3.

[0080] After stirring at 200 rpm for 30 seconds, reduce the speed to 50 rpm and continue stirring for 30 minutes. After coagulation, allow the mixture to settle for 15 minutes to form flocs.

[0081] Comparative Example 1

[0082] Use a coagulation mixer to rapidly mix 1L of polluted water to be treated, with the speed set to 200rpm.

[0083] Iron coagulant (Fe(III) solution) was added directly to the polluted water body to be treated at a rate of 0.2 mL / min, so that the final iron ion concentration added to the system was 0.2 mmol / L.

[0084] After stirring at 200 rpm for 30 seconds, reduce the speed to 50 rpm and continue stirring for 30 minutes. After coagulation, allow the mixture to settle for 15 minutes to form flocs.

[0085] Comparative Example 2

[0086] Use a coagulation mixer to rapidly mix 1L of polluted water to be treated, with the speed set to 200rpm.

[0087] The ferrous coagulant (Fe(II) solution or Fe(II):SPC=1:0) prepared in Example 1 was directly added to the polluted water body to be treated at a rate of 0.2 mL / min, so that the final iron ion concentration added to the system was 0.2 mmol / L.

[0088] After stirring at 200 rpm for 30 seconds, reduce the speed to 50 rpm and continue stirring for 30 minutes. After coagulation, allow the mixture to settle for 15 minutes to form flocs.

[0089] Test Example 1

[0090] The microstructure of the flocs obtained by removing nanoplastics from water in Example 1 (Fe(II):SPC=1:0.05, Fe(II):SPC=1:0.5), Comparative Examples 1 and 2 was observed by transmission electron microscopy.

[0091] Figure 2 These are electron microscope (EM) images of the flocs in Test Example 1 of this disclosure, where a is an EEM image of the flocs after treatment with Fe(III) solution in Comparative Example 1, b is an EEM image of the flocs after treatment with Fe(II) solution in Comparative Example 2, c is an EEM image of the flocs after treatment with a flocculant containing Fe(III) solution and Fe(II):SPC=1:0.05 in Example 1, and d is an EEM image of the flocs after treatment with a flocculant containing Fe(II):SPC=1:0.5 in Example 1.

[0092] like Figure 2 As shown in figures c and d, under a transmission electron microscope, it can be clearly observed that the in-situ oxidative coagulation process, by changing the feed ratio of oxidant and coagulant, controls the morphology of the formed nanosheets. The resulting flower-like nanosheet structure can completely encapsulate nanoplastic monomers with a particle size of approximately 200 nm. In comparison, such as Figure 2 As shown in a and b, the flocs in Comparative Example 1, which used a traditional ferric coagulant, and the control group in Comparative Example 2, which used only a single ferrous coagulant, only formed a small number of spherical particles attached to the surface of the nanoplastics, and could not achieve effective encapsulation and stable binding.

[0093] Furthermore, the changes in the macroscopic size of the flocs in Example 1, Comparative Examples 1 and 2 over time were analyzed.

[0094] Figure 3 This is a floc growth curve showing the change in the macroscopic size of the flocculents over time in Test Example 1 of this publication.

[0095] like Figure 3 As shown, the flocs formed in Example 1 (Fe(II):SPC=1:0.05) are significantly superior in macroscopic size to those formed by traditional trivalent iron coagulants. The larger floc size facilitates sedimentation and efficient adsorption of nanoplastics in water. After being broken by external disturbance, the flocs generated by in-situ oxidation in Example 1 exhibit stronger elastic recovery capabilities, quickly re-aggregating and growing to a larger size, demonstrating good structural stability and suitability for fluid disturbance conditions that may occur in actual water treatment processes.

[0096] The water bodies after water treatment in Example 1, Comparative Examples 1 and 2 were tested.

[0097] Figure 4 This is a comparison graph of the overall turbidity of the supernatant in the treated water body, the turbidity contributed by the nanoplastics, and the zeta potential of the flocculants in Test Example 1 of this disclosure.

[0098] like Figure 4 As shown, the performance of Examples 1, Comparative Examples 1, and 2 in removing water turbidity and nanoplastics under different dosages of oxidant solution (sodium percarbonate) is compared. The initial turbidity of the simulated wastewater used in the experiment was 11.8 NTU. Under the same iron salt dosage, the traditional trivalent iron coagulant in Comparative Example 1 could only reduce the water turbidity to 7.08 NTU, while Example 1 could reduce the turbidity to a maximum of 1.64 NTU. More importantly, after being broken by external force, traditional flocculants would release some of the removed nanoplastics, causing the turbidity to rise again, while the flocculants formed in Example 1 could still maintain a stable coating of nanoplastics after being broken, achieving efficient and long-lasting removal of nanoplastics.

[0099] Example 2

[0100] In Example 2, the preparation and activation of the Fe(II) coagulant solution and sodium percarbonate oxidant, as well as the in-situ oxidative coagulation process, were the same as in Example 1. The difference from Example 1 was that the amount of Fe(II) coagulant was changed so that the final iron ion concentrations added to the system were 0.05, 0.1, 0.2, 0.3, and 0.4 mmol / L, respectively. Simultaneously, the injection volume of the sodium percarbonate syringe was adjusted to maintain the Fe:sodium percarbonate concentration ratio in the coagulation system at a constant 1:0.2.

[0101] Comparative Example 3

[0102] In Comparative Example 3, the Fe(III) coagulant solution and coagulation process were the same as in Comparative Example 1. The difference from Comparative Example 1 was that the amount of Fe(II) coagulant was changed so that the final iron ion concentrations added to the system were 0.05, 0.1, 0.2, 0.3, and 0.4 mmol / L, respectively.

[0103] Test Example 2

[0104] The water bodies after water treatment in Example 2 and Comparative Example 3 were tested.

[0105] Figure 5 , Figure 6 These are floc growth curves showing the change in macroscopic size of the flocs over time under different dosage conditions in Examples 2 and 3 of this disclosure.

[0106] like Figure 5, Figure 6 As shown, the flocs formed in Example 2 are significantly superior in macroscopic size to those formed by traditional ferric coagulants. The larger floc particle size is beneficial for sedimentation and efficient adsorption of nanoplastics in water. Furthermore, Example 2 verified that increasing the amount of coagulant can significantly increase the overall size of the flocs.

[0107] Figure 7 This is a comparison diagram of the overall turbidity of the supernatant in the water body after treatment in Embodiment 2 of this disclosure, the turbidity contributed by the nanoplastics, and the zeta potential of the flocculants.

[0108] like Figure 7 As shown, under different coagulant dosage conditions, Example 2 demonstrates significantly better performance in removing water turbidity and nanoplastics than traditional ferric coagulants. The initial turbidity of the simulated wastewater used in the experiment was 11.8 NTU. Example 2 achieves highly efficient nanoplastic removal with lower coagulant dosage, effectively alleviating the pressure on subsequent flocculated sludge treatment.

[0109] Example 3

[0110] In Example 2, the preparation and activation of the Fe(II) coagulant solution and sodium percarbonate oxidant, as well as the in-situ oxidation coagulation process, were the same as in Example 1. The difference from Example 1 was that the pH values ​​of the polluted water to be treated were 5, 6, 7, 8, and 9, respectively.

[0111] Comparative Example 4

[0112] In Comparative Example 4, the Fe(III) coagulant solution and coagulation process were the same as in Comparative Example 1. The difference from Comparative Example 1 was that the pH values ​​of the polluted water to be treated were 5, 6, 7, 8, and 9, respectively.

[0113] Test Example 3

[0114] The water bodies after water treatment in Example 3 and Comparative Example 4 were tested.

[0115] Figure 8 This is a comparison chart of the overall turbidity of the supernatant in the water body after treating water bodies with different pH values, the turbidity contributed by nanoplastics, and the zeta potential of flocculants in Test Example 3 of this disclosure.

[0116] like Figure 8 As shown, under different pH conditions, Example 3 can achieve highly efficient removal of turbidity and nanoplastics from water, overcoming the shortcomings of traditional ferric coagulants, such as poor coagulation effect under acidic conditions and excessive particle size under alkaline conditions. Its performance is far superior to traditional ferric coagulants. The initial turbidity of the simulated wastewater used in the experiment was 11.8 NTU. Example 3 can achieve highly efficient removal of nanoplastics over a wide pH range.

[0117] Example 4

[0118] In Example 2, the preparation and activation of the Fe(II) coagulant solution and sodium percarbonate oxidant, as well as the in-situ oxidation coagulation process, were the same as in Example 1. The difference from Example 1 was that a coagulation mixer was used to rapidly stir 1L of polluted water containing different types of organic matter (fulvic acid, humic acid, and dissolved organic matter) at a speed of 200 rpm.

[0119] Comparative Example 5

[0120] In Comparative Example 4, the Fe(III) coagulant solution and coagulation process were the same as in Comparative Example 1. The difference from Comparative Example 1 was that a coagulation mixer was used to rapidly stir 1 L of polluted water containing different types of organic matter (fulvic acid, humic acid, and dissolved organic matter) at a speed of 200 rpm.

[0121] Test Example 4

[0122] The water bodies after water treatment in Example 4 and Comparative Example 5 were tested.

[0123] Figure 9 , Figure 10 , Figure 11 These are comparison charts showing the overall turbidity of the supernatant, the turbidity contributed by nanoplastics, and the zeta potential of flocculants in Test Example 4 of this disclosure when treating polluted water containing fulvic acid, humic acid, and dissolved organic matter.

[0124] like Figure 9 , Figure 10 , Figure 11 As shown, in actual water bodies containing different types of organic matter, Example 4 effectively overcomes the obstruction caused by organic matter to coagulation, achieving highly efficient removal of turbidity and nanoplastics. It exhibits superior treatment performance compared to traditional ferric coagulants in various types of organic water bodies. This demonstrates that Example 4 can achieve highly efficient removal of nanoplastics in various actual water bodies.

[0125] In summary, the method for removing nanoplastics from water based on in-situ oxidative coagulation proposed in this disclosure introduces an activated oxidant (e.g., percarbonate) during coagulation to induce an in-situ oxidation reaction of Fe(II), promoting the in-situ formation of flower-like nanosheet structures, thereby achieving complete encapsulation of nanoplastic particles. Compared to the single spherical particles formed by traditional ferric flocculants, the multi-layered flocs generated by the method proposed in this disclosure have stronger interfacial adsorption and physical encapsulation capabilities. This in-situ oxidative coagulation method can significantly reduce water turbidity, decreasing it from 11.8 NTU to 1.64 NTU with the same amount of iron, far superior to traditional methods. Furthermore, the flocs formed by this method do not release nanoplastics again after floc breakage, solving the problem of pollutant re-release caused by floc breakage in traditional coagulation methods, achieving efficient, long-lasting, and irreversible removal of nanoplastics. Moreover, the nanosheet structure generated by this method results in larger macroscopic sizes of flocs with superior hydrodynamic properties, including elastic resilience and settling properties. After being disturbed by external forces, the flocs can maintain their structural integrity or quickly recover their original state, exhibiting excellent elastic resilience, which is significantly better than the brittle flocs generated by traditional trivalent iron coagulants. At the same time, this method has a wider range of applications than traditional methods and is less affected by the pH of the external water body and other dissolved organic matter. This ensures the stable removal of nanoplastics in practical applications. The method proposed in this disclosure operates under normal temperature and pressure conditions, the preparation of coagulants and oxidants is simple, the equipment is highly versatile, and it is easy to integrate into existing water treatment systems, demonstrating good engineering promotion value.

[0126] The specific embodiments described above further illustrate the purpose, technical solutions, and beneficial effects of this disclosure. It should be understood that the above descriptions are merely specific embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A method for removing nanoplastics from water based on in-situ oxidation coagulation, comprising: Preparation of ferrous coagulant: Add alkali solution to ferrous solution to obtain ferrous coagulant, wherein the dissolved oxygen concentration in the ferrous solution is less than 1 mg / L and the concentration of ferrous ions is 1~5 mol / L; An oxidizing agent solution is prepared by adding an acid solution to the oxidizing agent solution to make the pH of the oxidizing agent solution less than 4, wherein the oxidizing agent is sodium percarbonate; In-situ oxidative coagulation: Under stirring conditions, the activated oxidant solution and the ferrous coagulant are simultaneously added to the water body to be treated containing nanoplastics. The feeding ratio of ferrous coagulant to oxidant solution is controlled so that the mass concentration ratio of Fe:oxidant is in the range of 1:0.05 to 1:0.3, thereby converting the ferrous ions in the ferrous coagulant into iron ions, and causing the iron ions to be adsorbed on the surface of nanoplastic particles and rearranged and crystallized to form flocs with a flexible nanosheet structure in the form of sheets or flowers.

2. The method according to claim 1, wherein, The dissolved oxygen concentration of the alkaline solution is less than 1 mg / L.

3. The method according to claim 1, wherein, In the ferrous coagulant, [OH - The ratio of Fe ion concentration to Fe ion concentration is (0.5:1) to (2:1).

4. The method according to claim 1, wherein, The addition of alkaline solution to the ferrous solution is carried out under a nitrogen atmosphere and with stirring at a speed of 400-600 rpm.

5. The method according to claim 1, wherein, The concentration of the oxidant solution is 1~5 g / L.

6. The method according to claim 5, wherein, The concentration range of the ferrous coagulant is 0.05-0.4 mmol / L.

7. The method according to claim 1, wherein, The stirring process includes: first stirring at a speed of 100-300 rpm for 30 seconds to 1 minute, and then stirring at a speed of 20-70 rpm for 30 minutes.

8. The method according to claim 1, wherein, The activated oxidant solution and the ferrous coagulant are added at the same rate, which is 0.1~0.3 mL / min.

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