Method for removing microplastics in tail water through benthonic animal reinforced constructed wetland

Abstract

The invention provides a method for removing micro-plastics in tail water through a benthonic animal reinforced constructed wetland, and relates to the technical field of micro-plastic removal. The artificial wetland combines physical filtration and chemical adsorption through the multi-layer design of the front and rear composite substrate layers; due to the graded filtering function of the coarse sand layer and the fine sand layer and the adsorption effect of the modified biochar layer on micro-plastic, the system can effectively capture and remove micro-plastic particles with different particle sizes; by introducing the benthonic animals with strong filtering and particle capturing capabilities, the capturing capability of the wetland system is enhanced, and the benthonic animals intake and filter micro-plastic particles, so that the content of micro-plastics is directly reduced, and the biological activity of bottom microorganisms is also promoted; the degradation effect of the microorganisms can further decompose the micro-plastics, and the bioremediation effect is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of microplastic removal, and in particular to a method for removing microplastics in tail water by using benthic animal-enhanced artificial wetlands. Background Art

[0002] Microplastics refer to plastic particles with a particle size of less than 5mm. The appearance of microplastics in aquatic environments has become a growing concern worldwide. Since its birth in the 1870s, plastics have been integrated into our modern life, with advantages such as light weight, low price, flexibility, durability (heat-resistant, electrical-resistant, not easy to degrade) and incredible practical uses. With the continuous development of the times, the production of plastics has been increasing worldwide in recent years, and any plastic in human production and life will become a potential source of microplastics. According to the way of production, microplastics are currently divided into two categories: one is the micron-sized primary microplastics produced by the plastics industry, such as microbeads in the beauty field, and microplastic particles involved in industrial raw materials such as paints; the other is the secondary microplastics formed by the conversion of large-sized plastics from large-sized plastics in the environment after physical and chemical effects such as weathering, friction and light.

[0003] Microplastics, as a new type of pollutant, can be widely present and accumulated in the environment, especially in water bodies, due to their tiny size (less than 5 mm in diameter) and high specific surface area, posing a serious threat to the entire ecosystem. These tiny plastic particles are not only difficult to be naturally degraded, but also easily absorb and carry other pollutants, such as persistent organic pollutants such as polychlorinated biphenyls and bisphenol A, and then enter organisms through the food chain, posing a potential risk to human health.

[0004] As a natural ecological water treatment system, artificial wetlands have been widely used in tailwater treatment, sewage purification and ecological restoration due to their low cost, high efficiency and environmental protection. However, when faced with microplastics, a new type of pollutant, traditional artificial wetland systems often show limited removal effects. This is mainly due to the small size and light weight of microplastics, which make it easy for them to penetrate the filter layer of the wetland without being effectively intercepted. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method for removing microplastics in tailwater by using benthic animals to enhance artificial wetlands, which solves the problem that artificial wetlands are not effective in removing microplastics.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0007] A method for removing microplastics from tailwater by using benthic animal-enhanced artificial wetlands, the method comprising the following steps:

[0008] S1. Establishing a composite matrix layer, the composite matrix layer comprising: a front composite matrix layer and a rear composite matrix layer; the bottom layers of the front composite matrix layer and the rear composite matrix layer are connected, and the middle and upper layers are separated by a baffle;

[0009] The front composite matrix layer includes, from top to bottom, a coarse sand layer, a fine sand and biochar layer, and a humus layer;

[0010] The composite matrix layer in the rear section includes, from bottom to top, a sand cushion layer, a gravel layer and a crushed stone chip layer;

[0011] Aquatic plants are planted on the composite substrate layer, and microplastic-degrading microorganisms are inoculated in the composite substrate layer;

[0012] S2. Select benthic animals with filter feeding and particle capture capabilities and add them to the artificial wetland system;

[0013] S3. Pump the tail water containing microplastics into the artificial wetland system. The water flows from top to bottom through the front composite matrix layer, and then from bottom to top through the rear composite matrix layer.

[0014] Preferably, the layer height of the coarse sand layer, the fine sand and biochar layer and the humus layer is 300-400 mm, the particle size of the coarse sand is 30-50 mm, and the fine sand and biochar in the fine sand and biochar layer are combined in a mass ratio of 2:1;

[0015] The layer heights of the gravel layer and the crushed stone chip layer are both 200-300 mm, the layer height of the sand cushion layer is 100-200 mm, and the particle size of the crushed stone chip is 30-50 mm.

[0016] Preferably, the biochar is modified biochar, and the preparation method of the modified biochar is as follows:

[0017] A1. The biomass material is sequentially washed with water, treated with a 1% to 2% concentration NaOH solution, and neutralized with dilute acid to obtain a pretreated biomass material;

[0018] A2, the pretreated biomass material is subjected to low-temperature rapid pyrolysis at 300°C to 400°C for 0.5 to 1 hour; the temperature is raised to 600°C to 700°C for secondary pyrolysis for 1 to 2 hours to obtain biochar;

[0019] A3. Put the biochar into 0.5 mol / L iron salt solution, stir evenly, slowly add 1 mol / L sodium hydroxide solution while stirring, adjust the pH value to 8-10, then add 1 mol / L NaBH4 solution, react at room temperature for 12-24 hours, wash the precipitate, and dry to obtain modified biochar.

[0020] Preferably, the biomass material is corn cobs and / or sugarcane bagasse.

[0021] Preferably, the iron salt solution comprises: one or more of ferric chloride, ferric sulfate, ferric nitrate, ferric acetate, ferrous chloride, ferrous sulfate, ferrous nitrate and ferrous acetate.

[0022] Preferably, in A3, the solid-liquid ratio of biochar to iron salt solution is 5-15g:100-200ml.

[0023] Preferably, the aquatic plants are one or more of canna, yellow iris, and loosestrife.

[0024] Preferably, the microplastic-degrading microorganism is a bacterium of the genus Bacillus or Bacillus.

[0025] Preferably, the benthic animals are water earthworms and / or river clams.

[0026] Preferably, the doping density of the benthic animals is: 13000-15000 water earthworms / m 2 , river mussels 1000-1100 / m 2 .

[0027] The present invention provides a method for removing microplastics from tailwater by using benthic animals to strengthen artificial wetlands. Compared with the prior art, the method has the following beneficial effects:

[0028] In the present invention, the artificial wetland combines physical filtration with chemical adsorption through the multi-layer design of the front and rear composite matrix layers; the graded filtration function of the coarse sand and fine sand layers, plus the adsorption effect of the modified biochar layer on microplastics, enables the system to effectively capture and remove microplastic particles of different particle sizes; and by introducing benthic animals with strong filter feeding and particle capture capabilities, the capture capacity of the wetland system is enhanced. By ingesting and filtering microplastic particles, benthic animals not only directly reduce the microplastic content, but also promote the biological activity of bottom microorganisms; the degradation effect of microorganisms can further decompose microplastics to achieve a bioremediation effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1 Schematic diagram of the structure of the composite matrix layer in Example 1 of the present invention;

[0031] Figure 2 This is a table of microplastic removal rates for Examples 1 to 10 of the present invention;

[0032] The reference numerals in the figure are set as: coarse sand layer 1, fine sand and biochar layer 2, humus layer 3, crushed stone layer 4, gravel layer 5, sand cushion layer 6, baffle 7. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] The embodiments of the present application solve the problem of poor removal of microplastics by artificial wetlands by providing a method for removing microplastics in tailwater by using benthic animals to enhance artificial wetlands.

[0035] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0036] Embodiment 1:

[0037] The present invention provides a method for removing microplastics in tailwater by using benthic animal-enhanced artificial wetlands, the method comprising the following steps:

[0038] S1. Construction of artificial wetland system

[0039] like Figure 1 As shown, a composite matrix layer is established, and the composite matrix layer includes: a front composite matrix layer and a rear composite matrix layer;

[0040] The bottom layers of the front composite matrix layer and the rear composite matrix layer are connected, and the middle and upper layers are separated by a baffle 7;

[0041] The front composite matrix layer includes, from top to bottom, a coarse sand layer 1, a fine sand and biochar layer 2, and a humus layer 3;

[0042] The rear composite matrix layer includes, from bottom to top, a sand cushion layer 6, a gravel layer 5 and a crushed stone chip layer 4;

[0043] Aquatic plants are planted on the composite substrate layer, and microplastic-degrading microorganisms are inoculated in the composite substrate layer;

[0044] S2. Introduction of benthic animals

[0045] Select benthic animals with filter feeding and particle capture capabilities to be added to the artificial wetland system;

[0046] S3, pump in tail water

[0047] The tail water containing microplastics is pumped into the artificial wetland system, and the water flows from top to bottom through the front composite matrix layer, and then from bottom to top through the rear composite matrix layer.

[0048] The layer heights of the coarse sand layer 1, the fine sand and biochar layer 2 and the humus layer 3 are all 350 mm, the particle size of the coarse sand is 30-50 mm, and the fine sand and biochar in the fine sand and biochar layer 2 are combined in a mass ratio of 2:1.

[0049] The gravel layer 5 and the crushed stone layer 4 have a layer height of 250 mm, the sand cushion layer 6 has a layer height of 150 mm, and the particle size of the crushed stone is 30 to 50 mm;

[0050] The biochar is modified biochar, and the preparation method of the modified biochar is as follows:

[0051] A1, 10 kg of biomass material was washed with water, put into 50 L of 1.5% NaOH solution and diluted acid for neutralization, and 8.5 kg of pretreated biomass material was obtained;

[0052] A2, 8.5 kg of pretreated biomass material was subjected to low-temperature rapid pyrolysis at 350 °C for 0.75 hours; the temperature was raised to 650 °C for secondary pyrolysis for 1.5 hours to obtain 2.2 kg of biochar;

[0053] A3. Put 2.2 kg of biochar into 4.4 L of 0.5 mol / L ferric chloride solution, stir evenly, slowly add 1 mol / L sodium hydroxide solution while stirring, adjust the pH value to 9, and then add 6.6 L of 1 mol / L NaBH 4 The solution was reacted at room temperature for 18 hours, the precipitate was washed and dried to obtain 2.64 kg of modified biochar;

[0054] The aquatic plant is Canna indica, and the microplastic degradation microorganism is Bacillus subtilis;

[0055] The benthic animals are water earthworms.

[0056] Embodiment 2:

[0057] The differences between this embodiment and Embodiment 1 include:

[0058] The preparation method of the modified biochar is as follows:

[0059] A1, 10 kg of biomass material was washed with water, put into 50 L of 1% NaOH solution and diluted acid for neutralization, and 8.5 kg of pretreated biomass material was obtained;

[0060] A2, 8.5 kg of pretreated biomass material was subjected to low-temperature rapid pyrolysis at 300 °C for 1 hour; the temperature was raised to 600 °C for secondary pyrolysis for 2 hours to obtain 2.7 kg of biochar;

[0061] A3. Put 2.7 kg of biochar into 5.4 L of 0.5 mol / L ferric chloride solution, stir evenly, slowly add 1 mol / L sodium hydroxide solution while stirring, adjust the pH value to 8, and then add 8.1 L of 1 mol / L NaBH 4 The solution was reacted at room temperature for 12 hours, the precipitate was washed and dried to obtain 2.86 kg of modified biochar.

[0062] Embodiment 3:

[0063] The differences between this embodiment and Embodiment 1 include:

[0064] The preparation method of the modified biochar is as follows:

[0065] A1, 10 kg of biomass material was washed with water, put into 50 L of 2% NaOH solution and diluted acid for neutralization, and 8.5 kg of pretreated biomass material was obtained;

[0066] A2, 8.5 kg of pretreated biomass material was subjected to low-temperature rapid pyrolysis at 400 °C for 0.5 hours; the temperature was raised to 700 °C for secondary pyrolysis for 1 hour to obtain 1.7 kg of biochar;

[0067] A3. Put 1.7 kg of biochar into 3.4 L of 0.5 mol / L ferric chloride solution, stir evenly, slowly add 1 mol / L sodium hydroxide solution while stirring, adjust the pH value to 10, and then add 5.1 L of 1 mol / L NaBH 4 The solution was reacted at room temperature for 24 hours, the precipitate was washed and dried to obtain 2.86 kg of modified biochar.

[0068] Embodiment 4:

[0069] The differences between this embodiment and Embodiment 1 include:

[0070] The layer heights of the coarse sand layer 1, the fine sand and biochar layer 2 and the humus layer 3 are all 300 mm; the layer heights of the gravel layer 5 and the crushed stone layer 4 are all 200 mm, and the layer height of the sand cushion layer 6 is 100 mm.

[0071] Embodiment 5:

[0072] The differences between this embodiment and Embodiment 1 include:

[0073] The layer heights of the coarse sand layer 1, the fine sand and biochar layer 2 and the humus layer 3 are all 400 mm; the layer heights of the gravel layer 5 and the crushed stone layer 4 are all 300 mm, and the layer height of the sand cushion layer 6 is 200 mm.

[0074] Embodiment 6:

[0075] The differences between this embodiment and Embodiment 1 include:

[0076] The aquatic plant is Iris flavescentis, and the microplastic-degrading microorganism is Bacillus cereus.

[0077] Embodiment 7:

[0078] The differences between this embodiment and Embodiment 1 include:

[0079] The aquatic plant is Lythrum salicina and the microplastic degrading microorganism is Bacillus licheniformis.

[0080] Embodiment 8:

[0081] The differences between this embodiment and Embodiment 1 include:

[0082] The benthic animals are river clams.

[0083] Embodiment 9:

[0084] The differences between this embodiment and Embodiment 1 include:

[0085] The biochar is ordinary biochar.

[0086] Example 10

[0087] Pumping tailwater containing microplastics into common artificial wetlands.

[0088] The tail water containing microplastics was pumped into the artificial wetland system through a peristaltic pump, and the hydraulic retention time was set to 3 days. The microplastic removal rates of Examples 1 to 10 are shown in the table below: Figure 2 shown.

[0089] In summary, compared with the prior art, the present invention has the following beneficial effects:

[0090] 1. In the embodiments of the present invention, the artificial wetland significantly improves the removal efficiency of microplastic particles of different sizes in the tail water through the multi-layer design of the front and rear composite matrix layers, combining physical filtration with chemical adsorption; the graded filtration function of the coarse sand and fine sand layers, coupled with the adsorption effect of the modified biochar layer on microplastics, enables the system to effectively capture and remove microplastic particles of different sizes; and by introducing benthic animals with strong filter feeding and particle capture capabilities, the capture capacity of the wetland system is enhanced; benthic animals ingest and filter microplastic particles, which not only directly reduces the microplastic content, but also promotes the biological activity of bottom microorganisms; the degradation effect of microorganisms can further decompose microplastics to achieve a bioremediation effect.

[0091] 2. In the embodiments of the present invention, the biomass raw materials are treated by a combination of low-temperature and high-temperature pyrolysis, and the organic matter in the material is fully decomposed. This process not only ensures that there is enough space inside the biochar for adsorbing pollutants, but also its large specific surface area provides more contact sites for pollutants; the high-temperature treatment not only further enables the modified biochar to resist the influence of the external environment (such as temperature changes, physical wear, etc.) during use and maintain good structural integrity and durability; it promotes iron ions to form nano-scale iron particles on the surface of the biochar and evenly disperse them in its pore structure; it significantly enhances the adsorption capacity and reaction activity of the biochar, because the iron nanoparticles provide more active sites, so that physical adsorption and chemical catalysis processes can be more effectively combined, thereby greatly improving the removal efficiency of pollutants such as microplastics.

[0092] 3. In the embodiments of the present invention, the unique filtering and particle capturing abilities of benthic organisms are utilized, and through their active ecological behaviors and complex interaction mechanisms such as parasitism and predation with microorganisms, the composition of microbial communities in aquatic ecosystems can be subtly regulated; this process not only promotes the dynamic balance and mutual influence among various environmental elements within the ecosystem, but also realizes the effective degradation and removal of pollutants in the water, thereby optimizing the overall environmental quality.

[0093] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0094] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for removing microplastics from tailwater by using benthic animal-enhanced artificial wetlands, characterized in that: The method comprises the following steps: S1. Establishing a composite matrix layer, the composite matrix layer comprising: a front composite matrix layer and a rear composite matrix layer; the bottom layers of the front composite matrix layer and the rear composite matrix layer are connected, and the middle and upper layers are separated by a baffle (7); The front-stage composite matrix layer includes, from top to bottom, a coarse sand layer (1), a fine sand and biochar layer (2), and a humus layer (3); The rear composite matrix layer includes, from bottom to top, a sand cushion layer (6), a gravel layer (5) and a crushed stone chip layer (4); Aquatic plants are planted on the composite substrate layer, and microplastic-degrading microorganisms are inoculated in the composite substrate layer; S2. Select benthic animals with filter feeding and particle capture capabilities and add them to the artificial wetland system; S3. Pump the tail water containing microplastics into the artificial wetland system. The water flows from top to bottom through the front composite matrix layer, and then from bottom to top through the rear composite matrix layer.

2. The method for removing microplastics from tailwater by using benthic animal-enhanced artificial wetlands as claimed in claim 1, characterized in that: The coarse sand layer (1), the fine sand and biochar layer (2) and the humus layer (3) have a layer height of 300 to 400 mm, the particle size of the coarse sand is 30 to 50 mm, and the fine sand and biochar in the fine sand and biochar layer (2) are combined in a mass ratio of 2:1; The layer heights of the gravel layer (5) and the crushed stone layer (4) are both 200-300 mm, the layer height of the sand cushion layer (6) is 100-200 mm, and the particle size of the crushed stone is 30-50 mm.

3. The method for removing microplastics from tailwater by benthic animal-enhanced artificial wetlands according to claim 1, characterized in that: The biochar is modified biochar, and the preparation method of the modified biochar is as follows: A1. The biomass material is sequentially washed with water, treated with a 1% to 2% concentration NaOH solution, and neutralized with dilute acid to obtain a pretreated biomass material; A2, the pretreated biomass material is subjected to low-temperature rapid pyrolysis at 300°C to 400°C for 0.5 to 1 hour; the temperature is raised to 600°C to 700°C for secondary pyrolysis for 1 to 2 hours to obtain biochar; A3. Put the biochar into 0.5 mol / L iron salt solution, stir evenly, slowly add 1 mol / L sodium hydroxide solution while stirring, adjust the pH value to 8-10, then add 1 mol / L NaBH4 solution, react at room temperature for 12-24 hours, wash the precipitate, and dry to obtain modified biochar.

4. The method for removing microplastics from tailwater by using benthic animal-enhanced artificial wetlands as claimed in claim 3, characterized in that: The biomass material is corn cobs and / or sugarcane bagasse.

5. The method for removing microplastics from tailwater by benthic animal-enhanced artificial wetlands as claimed in claim 3, characterized in that: The iron salt solution includes one or more of ferric chloride, ferric sulfate, ferric nitrate, ferric acetate, ferrous chloride, ferrous sulfate, ferrous nitrate and ferrous acetate.

6. The method for removing microplastics from tailwater by benthic animal-enhanced artificial wetlands as claimed in claim 3, characterized in that: In A3, the solid-liquid ratio of biochar to iron salt solution is 5-15g:100-200ml.

7. The method for removing microplastics from tailwater by using benthic animal-enhanced artificial wetlands as claimed in claim 1, characterized in that: The aquatic plants are one or more of canna, yellow iris and loosestrife.

8. The method for removing microplastics from tailwater by using benthic animal-enhanced artificial wetlands as claimed in claim 1, characterized in that: The microplastic-degrading microorganisms are bacteria of the genus Bacillus or Bacillus.

9. The method for removing microplastics from tailwater by using benthic animal-enhanced artificial wetlands as claimed in claim 1, characterized in that: The benthic animals include water earthworms and / or river clams.

10. The method for removing microplastics from tailwater by using benthic animal-enhanced artificial wetlands as claimed in claim 9, characterized in that: The doping density of benthic animals is: 13000-15000 water earthworms / m 2 , river mussels 1000-1100 / m 2 .

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