Method for removing micro-plastics in water body through ozone pretreatment-coagulation

Abstract

The invention discloses a method for removing micro-plastics in a water body through ozone pretreatment-coagulation. The method comprises the following steps: (1) introducing ozone into a to-be-treated water sample containing the micro-plastics for pretreatment; the introduction amount of the ozone in each liter of the water sample to be treated is 10-60 mg / min; and (2) adding a coagulant into the water sample subjected to ozone pretreatment, adjusting the pH value of the water sample to 3-9, stirring and flocculating, standing, and filtering out flocculate. According to the method for removing the micro-plastics in the water body through ozone pretreatment and coagulation, the micro-plastics in the water body can be effectively removed, the turbidity is reduced, and meanwhile, the development toxicity in the water is not increased.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and in particular to a method for removing microplastics from water bodies by ozone pretreatment-coagulation. Background Art

[0002] Plastic products are widely used in cosmetics and personal care products, textiles and clothing, packaging materials, agriculture, construction and building materials due to their lightweight and durable properties. The widespread use of plastic products has led to the presence of a large amount of microplastics in water sources.

[0003] Microplastics (MPs), defined as plastic particles with a diameter of less than 5 mm, are a new category of pollutants. Microplastics have the characteristics of small particle size, large specific surface area and strong hydrophobicity. They are widely distributed in the aquatic environment and difficult to degrade. Current research shows that microplastics are commonly found in the ocean, atmosphere, fresh water and soil.

[0004] The presence of a large amount of microplastics in today's environment makes it inevitable for organisms to ingest microplastics from the aquatic environment. Although some microplastics are excreted after ingestion, most of them may remain and accumulate in organisms, leading to adverse effects such as endocrine disorders, cell damage and inflammatory responses, causing immeasurable harm to the ecological environment and human health. Microplastics are also potential carriers of harmful pollutants, and the situation may be even more serious.

[0005] Microplastic pollution is serious, and how to effectively remove microplastics from water bodies has become a new environmental hotspot. At present, the removal of microplastics mainly relies on conventional technologies in water plants and sewage plants. Physical, chemical and biological treatment technologies are often used to remove or degrade MPs in the water environment.

[0006] Filtration and separation are simple and efficient methods widely used to remove microplastics from water environments. Membrane technology is an efficient physical treatment method, but the shape, size and mass of microplastic particles have a great impact on the removal of membrane filtration, and MPs will aggravate membrane pollution.

[0007] The intracellular and extracellular enzymes produced by the microbial community on the surface of microplastics act on the polymer side chains or chemical groups, promoting the cleavage of the microplastic carbon chains and decomposing the microplastics into low polymers, dimers and monomers. The decomposed products are absorbed and utilized by microorganisms as carbon sources and eventually converted into CO through mineralization. 2 , H 2 O、CH 4 Microbial degradation can achieve a higher removal performance, but this method takes a long time, has harsh process conditions and high treatment costs.

[0008] Coagulation is a commonly used water treatment method. By adding coagulants, colloidal suspended matter in water is destabilized and aggregated into flocs that are easy to settle. It is used to treat fine suspended matter and colloidal particles in wastewater, including microplastics. In the water environment, negatively charged microplastic particles remain in a stable dispersed state due to electrostatic repulsion. After adding coagulants, the surface charge of microplastics is neutralized. When the electrostatic repulsion is reduced to a minimum, the microplastic particles aggregate to form large-sized flocs and settle to the bottom, thereby achieving the removal of microplastics. Coagulants play a decisive role in the coagulation and sedimentation of microplastics through electrical neutralization and adsorption. Common flocculants include ferric chloride (FeCl 3 )、Polyaluminium chloride (PAC), Aluminium sulfate (Al 2 (SO 4 ) 3 ), etc. Most studies have shown that the amount of coagulant is large and the efficiency of removing microplastics is very low. Summary of the invention

[0009] The present invention provides a method for removing microplastics from water bodies by ozone pretreatment-coagulation, which can effectively remove microplastics from water bodies and reduce turbidity without increasing the developmental toxicity in water.

[0010] The technical solution of the present invention is as follows:

[0011] A method for removing microplastics from water by ozone pretreatment-coagulation, comprising:

[0012] (1) introducing ozone into a water sample containing microplastics for pretreatment; the amount of ozone introduced into each liter of the water sample is 10-60 mg / min;

[0013] (2) Add a coagulant to the water sample after ozone pretreatment, adjust the pH value of the water sample to 3-9, stir and flocculate, and filter out the flocculants after standing.

[0014] As a strong oxidant, ozone can pre-treat microplastics, change their surface properties, and increase their surface roughness. Ozone can oxidize the surface of microplastics and increase the oxygen-containing functional groups (such as hydroxyl, carboxyl, etc.) on their surface, thereby increasing the hydrophilicity of microplastics. This surface modification helps the subsequent flocculation process, making it easier for microplastics to aggregate with other particles.

[0015] Preferably, the microplastic includes at least one of polyvinyl chloride (PVC) and polyethylene terephthalate (PET).

[0016] Preferably, the particle size of the microplastic is 1 μm-5 mm; further preferably, the particle size of the microplastic is about 10 μm-100 μm.

[0017] Preferably, the content of microplastics in the water sample to be treated is 0.01-100 mg / L.

[0018] Preferably, in step (1), the amount of ozone introduced into each liter of the water sample to be treated is 20-40 mg / min.

[0019] Preferably, the coagulant is aluminum sulfate (Al 2 (SO 4 ) 3 , polyacrylamide (PAM).

[0020] Preferably, in step (2), the dosage of coagulant is 20-200 mg per liter of water sample.

[0021] Further preferably, in step (2), the dosage of aluminum sulfate is 20-200 mg and the dosage of polyacrylamide is 0.0025-0.025 mg per liter of water sample.

[0022] Furthermore, in step (2), the dosage of aluminum sulfate is 40-100 mg per liter of water sample, and the dosage of polyacrylamide is 0.005-0.015 mg per liter of water sample.

[0023] Preferably, in step (2), mineral powder is added to the water sample to be treated.

[0024] The addition of mineral powder increases the number of particles in the water sample, improves the collision between particles, makes microplastics in the water easier to be coagulated and settled, and can relatively improve the coagulation efficiency.

[0025] Preferably, the amount of mineral powder added is 1-5 mg per liter of water sample to be treated; further preferably, the amount of mineral powder added is 1-3 mg per liter of water sample to be treated.

[0026] Preferably, the water sample to be treated is water from a secondary sedimentation tank for printing and dyeing.

[0027] The method of the present invention is based on an improved coagulation process for improving coagulation efficiency and improving water quality. Ozone pretreatment can destroy the surface structure of microplastics and increase the hydroxyl or carboxyl groups on the surface of microplastics, which is beneficial for coagulation to fully exert its electrical neutralization effect and bridging net capture effect and enhance sedimentation performance.

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

[0029] (1) The present invention uses ozone pretreatment to enhance coagulation treatment of microplastics in water, which can effectively remove most of the microplastics without increasing the developmental toxicity in the water.

[0030] (2) The method of removing microplastics from water by ozone pretreatment-coagulation of the present invention has simple process operation, significant effect, and can remove other pollutants at the same time.

[0031] (3) The present invention uses ozone pretreatment to remove microplastics by coagulation, and also has a high removal rate in the suspension. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the removal effect of microplastics by different treatment processes;

[0033] Figure 2 O 3 -Al 2 (SO 4 ) 3 / Schematic diagram of the effect of ozone pretreatment time on microplastic removal in the PAM process;

[0034] Figure 3 Schematic diagram of SEM characterization effect of PET before (a) and after (b) ozone pretreatment;

[0035] Figure 4 Schematic diagram of FTIR characterization effect of PET before (a) and after (b) ozone pretreatment;

[0036] Figure 5 is O in the mineral powder suspension 3 -Al 2 (SO 4 ) 3 / Schematic diagram of the effect of PAM process on removing microplastics. DETAILED DESCRIPTION

[0037] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be pointed out that the embodiments described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on the present invention.

[0038] Unless otherwise specified, all experimental reagents and raw materials of the present invention are commercially available.

[0039] The present invention provides a method for removing microplastics by coagulation after ozone pretreatment. The method is based on ozone pretreatment of microplastics to destroy the surface structure of microplastics, increase their surface roughness and surface hydroxyl groups, and then flocculation treatment of microplastics to make them settle and reduce turbidity.

[0040] Example 1

[0041] (1) 500 ml of simulated water samples were prepared with 40 μm microplastics PVC and PET, respectively. The concentration of microplastics in the water samples was 5 mg / L, and the water samples were pretreated with 20 mg / min ozone for 10 min.

[0042] (2) adding 20% ​​aluminum sulfate solution and 5‰ PAM solution to the simulated water samples of PVC and PET after ozone pretreatment, so that the concentration of aluminum sulfate in the reaction solution is 100 mg / L and the concentration of PAM is 0.015 mg / L;

[0043] (3) adjusting the pH of the reaction solution to neutral with sodium hydroxide;

[0044] (4) The reaction solution was stirred rapidly for 1 min, then slowly stirred for 5 min, and then allowed to stand for 30 min.

[0045] After standing for 30 minutes, the concentration of microplastics in the clear solution was detected and the microplastic removal rate was calculated. The results are as follows Figure 1 shown.

[0046] Comparative Example 1

[0047] (1) Prepare 500 ml of simulated water samples with 40 μm microplastics PVC and PET, respectively, and the concentration of microplastics in the water samples is 5 mg / L;

[0048] (2) Add 20% aluminum sulfate solution and 5‰ PAM solution to the simulated water samples of PVC and PET, so that the aluminum sulfate concentration in the reaction solution is 500 mg / L and the PAM concentration is 5 mg / L;

[0049] (3) adjusting the pH of the reaction solution to neutral with sodium hydroxide;

[0050] (4) The reaction solution was stirred rapidly for 1 min, then slowly stirred for 5 min, and then allowed to stand for 30 min.

[0051] After standing for 30 minutes, the concentration of microplastics in the clear solution was detected and the microplastic removal rate was calculated. The results are as follows Figure 1 shown.

[0052] Comparative Example 2

[0053] (1) Prepare 500 ml of simulated water samples with 40 μm microplastics PVC and PET, respectively, and the concentration of microplastics in the water samples is 5 mg / L;

[0054] (2) adding 20% ​​aluminum sulfate solution to the simulated water samples of PVC and PET to make the aluminum sulfate concentration in the reaction solution 100 mg / L;

[0055] (3) adjusting the pH of the reaction solution to neutral with sodium hydroxide;

[0056] (4) The reaction solution was stirred rapidly for 1 min, then slowly stirred for 5 min, and then allowed to stand for 30 min.

[0057] After standing for 30 minutes, the concentration of microplastics in the clear solution was detected and the microplastic removal rate was calculated. The results are as follows Figure 1 As shown. Figure 1 It can be seen that the removal rates of PVC and PET microplastics using 100 ppm aluminum sulfate solution alone are 40.8% and 38.0%, respectively. 2(SO 4 ) 3 The removal rates of PVC and PET microplastics in combination with PAM were 73.8% and 68.0%, respectively. Ozone pretreatment alone for 10 minutes had almost no removal effect, with the removal rates of PVC and PET being 5.77% and 3.66%, respectively. 2 (SO 4 ) 3 The removal rates of PVC and PET in the PAM / PVC coagulation were as high as 96.23% and 93.2%. 2 (SO 4 ) 3 Compared with the maximum removal rate achieved by PAM, O 3 -Al 2 (SO 4 ) 3 / PAM significantly increased the removal rates of PVC and PET. It can be seen that ozonation has a significant strengthening effect on the removal of microplastics in coagulation.

[0058] Embodiment 2-6

[0059] Compared with Example 1, the time for ozone pretreatment in Examples 2-6 is 2, 3, 5, 20, and 30 minutes, respectively.

[0060] Effects of different ozone pretreatment durations on microplastic removal Figure 2 As shown. Figure 2 It can be seen that when the ozonation pretreatment time is 30 minutes, the removal rate of PVC is as high as 99.84%, and the removal rate of PET is as high as 94.25%. The removal rate does not increase further with the extension of ozonation time. The efficiency of removing PVC is slightly higher than that of PET, which may be due to the different properties of PVC and PET.

[0061] Taking PET as an example, the changes in the surface structure of microplastics before and after ozone pretreatment were observed. Figure 3 As shown in Figure 2, the surface structure of PET was destroyed and the surface roughness increased after ozone treatment. Figure 4 As shown in the figure, carbonyl groups appeared on the PET surface after ozone pretreatment, and the surface hydroxyl peak increased significantly. It can be seen that the increase in microplastic removal rate may be caused by the increase in microplastic surface roughness and surface hydroxyl groups.

[0062] Embodiment 7-9

[0063] (1) 500 ml of simulated water samples were prepared with 40 μm microplastics PVC and PET, respectively, and the concentration of microplastics in the water samples was 5 mg / L. Examples 7-9 were pretreated with 5, 10, and 30 mg / min of ozone for 10 min, respectively;

[0064] (2) adding 20% ​​aluminum sulfate solution and 5‰ PAM solution to the simulated water samples of PVC and PET after ozone pretreatment, so that the concentration of aluminum sulfate in the reaction solution is 100 mg / L and the concentration of PAM is 0.015 mg / L;

[0065] (3) adjusting the pH of the reaction solution to neutral with sodium hydroxide;

[0066] (4) The reaction solution was stirred rapidly for 1 min, then slowly stirred for 5 min, and then allowed to stand for 30 min.

[0067] Table 1 shows the microplastic removal rate under different ozone dosages. It can be seen from Table 1 that the microplastic removal rate is already relatively high when the ozone dosage is 20 mg / min.

[0068] Table 1

[0069] Ozone dosage (mg / min) 5 10 20 30 PET removal rate 75.9％ 89.01％ 93.2％ 89.75％ PVC removal rate 80.1％ 91.35％ 96.23％ 95.4％

[0070] Examples 10-13

[0071] In Examples 10-13, the concentration of aluminum sulfate in the reaction solution was 20, 40, 60, and 200 mg / L, respectively, and the other conditions remained the same as in Example 1.

[0072] Examples 14-17

[0073] In Examples 14-17, the PAM concentrations in the reaction solutions were respectively 0.0025, 0.005, 0.01, and 0.025 mg / L, and other conditions remained consistent with those in Example 1.

[0074] Tables 2 and 3 show the removal rates of microplastics at different dosages of aluminum sulfate and PAM. The results show that Al 2 (SO 4 ) 3 The results of the dosage effect were similar to those of flocculation alone, and the removal rate of microplastics also increased with the increase of Al 2 (SO 4 ) 3 As shown in Table 3, at a constant dose of Al 2 (SO 4 ) 3 When the dosage of PAM solution was 0.015 ppm, the removal rate of microplastics increased with the increase of PAM dosage. 3 -Al 2 (SO 4 ) 3 The removal rates of PVC and PET in the / PAM system were 96.23% and 93.2% respectively. As shown in Table 2 and Table 3, the more the dosage of the agent is, the better.

[0075] Table 2

[0076] Aluminum sulfate dosage (mg / L) 20 40 60 100 200 PET removal rate 89.9％ 91％ 92.1％ 93.2％ 84％ PVC removal rate 88％ 90.2％ 91.32％ 96.23％ 89％

[0077] Table 3

[0078] PAM dosage (mg / L) 0.0025 0.005 0.01 0.015 0.025 PET removal rate 87.7％ 91.0％ 91.2％ 93.2％ 92.62％ PVC removal rate 87.4％ 89.8％ 91.8％ 96.23％ 95.13％

[0079] Embodiment 18

[0080] (1) Prepare 500 mL of a 3 mg / L suspension with mineral powder, and adjust the pH of the reaction solution to 3, 7, and 9 with sodium hydroxide, respectively;

[0081] (2) The concentration of microplastics (40 μm PVC, PET) in the simulated suspension water sample was 5 mg / L and pretreated with 20 mg / min ozone for 10 min;

[0082] (3) adding 20% ​​aluminum sulfate solution and 5‰ PAM solution to the simulated water samples of PVC and PET after ozone pretreatment, so that the concentration of aluminum sulfate in the reaction solution is 100 mg / L and the concentration of PAM is 0.015 mg / L;

[0083] (4) The reaction solution was stirred rapidly for 1 min, then slowly stirred for 5 min, and then allowed to stand for 30 min. After standing for 30 min, the mineral powder in the upper solution was removed with sodium hydroxide to detect the concentration of microplastics in the clear solution and calculate the microplastic removal rate in the suspension;

[0084] from Figure 5 It can be seen that under neutral conditions, in the mineral powder suspension (concentration 3 mg / L), the removal rates of PVC and PET can reach 98.7% and 99.6%. Table 4 shows the removal rate of microplastics under different concentrations of suspension, and the microplastic removal rate is significantly higher than that without mineral powder. The addition of mineral powder increases the number of particles in the water, increases the collision between particles, and makes the microplastics in the water easy to be coagulated and settled.

[0085] Table 4

[0086] Mineral powder dosage (mg / L) 1 2 3 4 PET removal rate 95.33％ 97.01％ 99.6％ 98.3％ PVC removal rate 96.4％ 98.6％ 98.7％ 98.2％

[0087] In the above embodiments, microplastics are almost completely removed.

[0088] Embodiment 19

[0089] Prepare water samples with real wastewater to study the 3 -Al 2 (SO 4 ) 3 / Effect of PAM process on microplastic removal. The pH was adjusted to 7.0 with sodium hydroxide, the dosage of aluminum sulfate and PAM was the same as in Example 1, the ozone flux was 20 mg / L, the pretreatment time was 10 min, and Table 5 shows the removal rate of microplastics in actual wastewater.

[0090] Table 5

[0091] PVC PET <![CDATA[Al 2 (SO 4 ) 3 ]]> 40.24％ 39.6％ <![CDATA[Al 2 (SO 4 ) 3 / PAM]]> 70.6％ 68.3％ <![CDATA[O 3 -Al 2 (SO 4 ) 3 / PAM]]> 90.5％ 89.1％

[0092] Compared with Example 1, in the actual wastewater, O 3 -Al 2 (SO 4 ) 3 / The performance of the PAM process in removing microplastics is reduced. In actual wastewater, organic matter will consume part of the ozone, so that microplastics cannot fully react with ozone.

[0093] In Example 1, in order to determine whether the organic matter produced by ozone pretreatment of microplastics would increase environmental pollution, the possible dissolution of microplastics after ozone treatment was analyzed by liquid chromatography-mass spectrometry. The product m / z 373 in the pretreated PVC was C 12 H 4 Cl 6 O, which may contain C=O. Potential dissolved organic products of PET ozone pretreatment process include m / z 504 product, which may have the molecular formula of C 24 H 7 O 12 It can be seen that after the ozone reaction, microplastics will produce small molecular organic matter. The TEST software was used to conduct toxicity analysis on the organic pollutants that may be produced. It was found that the developmental toxicity of the dissolved substances produced by microplastics after ozonation was lower than that of the microplastics themselves.

[0094] In summary, the method of the present invention can effectively remove microplastics in water. At the same time, its removal efficiency does not decrease significantly in the presence of other organic matter, and still remains between 80% and 90%. In addition, the method has simple steps and high treatment efficiency.

[0095] The embodiments described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for removing microplastics from water by ozone pretreatment-coagulation, characterized in that: include: (1) introducing ozone into a water sample containing microplastics for pretreatment; The amount of ozone introduced into each liter of water sample to be treated is 10-60 mg / min; (2) Add a coagulant to the water sample after ozone pretreatment, adjust the pH value of the water sample to 3-9, stir and flocculate, and filter out the flocculants after standing.

2. The method for removing microplastics from water by ozone pretreatment-coagulation according to claim 1, characterized in that: The microplastics include at least one of polyvinyl chloride and polyethylene terephthalate.

3. The method for removing microplastics from water by ozone pretreatment-coagulation according to claim 1, characterized in that: The particle size of microplastics is 1μm-5mm.

4. The method for removing microplastics from water by ozone pretreatment-coagulation according to claim 1, characterized in that: The content of microplastics in the water samples to be treated is 0.01-100 mg / L.

5. The method for removing microplastics from water by ozone pretreatment-coagulation according to claim 1, characterized in that: In step (1), the amount of ozone introduced into each liter of the water sample to be treated is 20-40 mg / min.

6. The method for removing microplastics from water by ozone pretreatment-coagulation according to claim 1, characterized in that: The coagulant is at least one of aluminum sulfate and polyacrylamide; in step (2), the dosage of the coagulant is 20-200 mg per liter of water sample.

7. The method for removing microplastics from water by ozone pretreatment-coagulation according to claim 6, characterized in that: In step (2), the dosage of aluminum sulfate is 20-200 mg per liter of water sample, and the dosage of polyacrylamide is 0.0025-0.025 mg per liter of water sample.

8. The method for removing microplastics from water by ozone pretreatment-coagulation according to claim 1, characterized in that: In step (2), mineral powder is added to the water sample to be treated.

9. The method for removing microplastics from water by ozone pretreatment-coagulation according to claim 8, characterized in that: The dosage of mineral powder is 1-5 mg per liter of water sample to be treated.

10. The method for removing microplastics from water by ozone pretreatment-coagulation according to claim 1, characterized in that: The water sample to be treated is water from the secondary sedimentation tank of printing and dyeing.

Images