Method for removing microplastics in effluent water by benthic animal reinforced constructed wetland

Abstract

The application provides a method for removing microplastics in tail water by benthic animal enhanced artificial wetland, and relates to the technical field of microplastic removal. The artificial wetland is designed with multiple layers of composite substrate layers in front and back sections, and combines physical filtration and chemical adsorption. The hierarchical filtration function of coarse sand and fine sand layers, combined with the adsorption of microplastics by the modified biochar layer, enables the system to effectively capture and remove microplastic particles of different particle sizes. By introducing benthic animals with strong filter-feeding and particle-capturing ability, the capture capacity of the wetland system is enhanced. The benthic animals ingest and filter microplastic particles, not only directly reducing the content of microplastics, but also promoting the biological activity of microorganisms at the bottom. The degradation effect of microorganisms can further decompose microplastics, achieving a biological remediation effect.

Description

Technical Field

[0001] This invention relates to the field of microplastic removal technology, specifically to a method for removing microplastics from wastewater using benthic animal-enhanced constructed wetlands. Background Technology

[0002] Microplastics refer to plastic particles with a diameter of less than 5 mm. The presence of microplastics in the aquatic environment has become a growing global concern. Since its inception in the 1870s, plastic has become an integral part of our modern lives, possessing advantages such as light weight, low cost, flexibility, durability (heat-resistant, electrical-resistant, and non-degradable), and incredible practical applications. With continuous development, the global production of plastics has been increasing in recent years, and any plastic produced or used in human life can become a potential source of microplastics. Based on their formation process, microplastics are currently mainly divided into two categories: one is primary microplastics at the micron scale produced by the plastics industry, such as microbeads in the cosmetics industry and microplastic particles involved in industrial raw materials such as paints; the other is secondary microplastics, which are formed from large-diameter plastic particles in the environment through physical and chemical processes such as weathering, friction, and light exposure.

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

[0004] Constructed wetlands, as a natural ecological water treatment system, have been widely used in effluent treatment, wastewater purification, and ecological restoration due to their low cost, high efficiency, and environmental friendliness. However, when faced with microplastics, a novel pollutant, traditional constructed wetland systems often exhibit limited removal efficiency. This is mainly because the small size and light weight of microplastics make them easily penetrate the wetland's filtration layer without being effectively retained. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for removing microplastics from wastewater using benthic animals-enhanced constructed wetlands, thus solving the problem of poor microplastic removal efficiency of constructed wetlands.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for removing microplastics from wastewater using benthic animals in an enhanced constructed wetland, the method comprising the following steps:

[0008] S1. Establish a composite matrix layer, which includes 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 baffles.

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

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

[0011] Aquatic plants are grown 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 to add to the constructed wetland system;

[0013] S3. Pump the tailwater containing microplastics into the constructed wetland system. The water flows from top to bottom through the front composite substrate layer and then from bottom to top through the rear composite substrate layer.

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

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

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

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

[0018] A2. The pretreated biomass material is subjected to low-temperature rapid pyrolysis at 300℃~400℃ for 0.5~1 hour; then heated to 600℃~700℃ for secondary pyrolysis for 1~2 hours to obtain biochar.

[0019] A3. Place the biochar in a 0.5 mol / L iron salt solution and stir until homogeneous. While stirring, slowly add a 1 mol / L sodium hydroxide solution to adjust the pH to 8-10. Then add a 1 mol / L NaBH4 solution and react at room temperature for 12-24 hours. Wash the precipitate and dry it 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 the following: 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 plant is one or more of the following: canna lily, yellow iris, and loosestrife.

[0024] Preferably, the microplastic-degrading microorganisms are bacteria of the genus Bacillus or Bacillus.

[0025] Preferably, the benthic animal is an earthworm and / or a freshwater mussel.

[0026] Preferably, the doping density of the benthic animals is: 13,000-15,000 tubifex worms / m³. 2 1000-1100 freshwater mussels / m 2 .

[0027] This invention provides a method for removing microplastics from wastewater using benthic animals-enhanced constructed wetlands. Compared with existing technologies, it has the following advantages:

[0028] In this invention, the constructed wetland utilizes a multi-layered design of composite matrix layers at both the front and rear sections, combining physical filtration with chemical adsorption. The graded filtration function of the coarse and fine sand layers, along with the adsorption of microplastics by the modified biochar layer, enables the system to effectively capture and remove microplastic particles of different sizes. Furthermore, the introduction of benthic animals with strong filter-feeding and particle-capturing abilities enhances the wetland system's capture capacity. By ingesting and filtering microplastic particles, these benthic animals not only directly reduce the microplastic content but also promote the bioactivity of bottom microorganisms. The degradation effect of these microorganisms further decomposes the microplastics, achieving a bioremediation effect. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the composite matrix layer in Embodiment 1 of the present invention;

[0031] Figure 2 Table of microplastic removal rates for Examples 1-10 of the present invention;

[0032] The reference numerals in the figure are set as follows: 1. Coarse sand layer; 2. Fine sand and biochar layer; 3. Humus layer; 4. Crushed stone layer; 5. Gravel layer; 6. Sand cushion layer; 7. Baffle. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] This application provides a method for removing microplastics from wastewater using benthic animal-enhanced constructed wetlands, which solves the problem of poor microplastic removal efficiency of constructed wetlands.

[0035] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0036] Example 1:

[0037] This invention provides a method for removing microplastics from wastewater using benthic animals-enhanced constructed wetlands, the method comprising the following steps:

[0038] S1. Construction of Constructed Wetland Systems

[0039] like Figure 1 As shown, a composite matrix layer is established, which 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, while the middle and upper layers are separated by baffle 7.

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

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

[0043] Aquatic plants are grown 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 trapping capabilities to be added to the constructed wetland system;

[0046] S3, Pumping in tailwater

[0047] The wastewater containing microplastics is pumped into the constructed wetland system. The water flows from top to bottom through the front composite substrate layer and then from bottom to top through the rear composite substrate layer.

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

[0049] The gravel layer 5 and the crushed stone layer 4 are both 250 mm high, the sand cushion layer 6 is 150 mm high, and the crushed stone has a particle size of 30-50 mm.

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

[0051] A1. 10 kg of biomass material was washed with water and then neutralized in 50 L of 1.5% NaOH solution and dilute acid to obtain 8.5 kg of pretreated biomass material.

[0052] A2. 8.5 kg of pretreated biomass material was subjected to low-temperature rapid pyrolysis at 350℃ for 0.75 hours; then heated to 650℃ for secondary pyrolysis for 1.5 hours to obtain 2.2 kg of biochar.

[0053] A3. Place 2.2 kg of biochar into 4.4 L of 0.5 mol / L ferric chloride solution and stir until homogeneous. While stirring, slowly add 1 mol / L sodium hydroxide solution to adjust the pH to 9. Then add 6.6 L of 1 mol / L NaBH4 solution and react at room temperature for 18 hours. Wash the precipitate and dry it to obtain 2.64 kg of modified biochar.

[0054] The aquatic plant used is canna lily, and the microplastic-degrading microorganism used is Bacillus subtilis;

[0055] The benthic animal used is the water worm.

[0056] Example 2:

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

[0058] The modified biochar is prepared as follows:

[0059] A1. 10 kg of biomass material was washed with water and then neutralized in 50 L of 1% NaOH solution and dilute acid to obtain 8.5 kg of pretreated biomass material.

[0060] A2. 8.5 kg of pretreated biomass material was subjected to low-temperature rapid pyrolysis at 300℃ for 1 hour; then heated to 600℃ for secondary pyrolysis for 2 hours to obtain 2.7 kg of biochar.

[0061] A3. 2.7 kg of biochar was placed in 5.4 L of 0.5 mol / L ferric chloride solution and stirred until homogeneous. While stirring, 1 mol / L sodium hydroxide solution was slowly added dropwise to adjust the pH to 8. Then, 8.1 L of 1 mol / L NaBH4 solution was added. The mixture was reacted at room temperature for 12 hours. The precipitate was washed and dried to obtain 2.86 kg of modified biochar.

[0062] Example 3:

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

[0064] The modified biochar is prepared as follows:

[0065] A1. 10 kg of biomass material was washed with water and then neutralized in 50 L of 2% NaOH solution and dilute acid to obtain 8.5 kg of pretreated biomass material.

[0066] A2. 8.5 kg of pretreated biomass material was subjected to low-temperature rapid pyrolysis at 400℃ for 0.5 hours; then heated to 700℃ for secondary pyrolysis for 1 hour to obtain 1.7 kg of biochar.

[0067] A3. 1.7 kg of biochar was placed in 3.4 L of 0.5 mol / L ferric chloride solution and stirred until homogeneous. While stirring, 1 mol / L sodium hydroxide solution was slowly added dropwise to adjust the pH to 10. Then, 5.1 L of 1 mol / L NaBH4 solution was added and reacted at room temperature for 24 hours. The precipitate was washed and dried to obtain 2.86 kg of modified biochar.

[0068] Example 4:

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

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

[0071] Example 5:

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

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

[0074] Example 6:

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

[0076] The aquatic plant used is yellow iris, and the microplastic-degrading microorganism used is Bacillus cereus.

[0077] Example 7:

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

[0079] The aquatic plant used is Lythrum salicaria, and the microplastic-degrading microorganism used is Bacillus licheniformis.

[0080] Example 8:

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

[0082] The benthic animal used is the freshwater mussel.

[0083] Example 9:

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

[0085] The biochar used is ordinary biochar.

[0086] Example 10

[0087] The wastewater containing microplastics is pumped into ordinary artificial wetlands.

[0088] Wastewater containing microplastics is pumped into an constructed wetland system using a peristaltic pump. The hydraulic retention time is set to 3 days. The microplastic removal rates of Examples 1-10 are shown in the table below. Figure 2 As shown.

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

[0090] 1. In this embodiment of the invention, the constructed wetland, through its multi-layer design of front and rear composite matrix layers, combines physical filtration with chemical adsorption, significantly improving the removal efficiency of microplastic particles of different sizes in the effluent. The graded filtration function of the coarse and fine sand layers, coupled with the adsorption of microplastics by the modified biochar layer, enables the system to effectively capture and remove microplastic particles of different sizes. Furthermore, the introduction of benthic animals with strong filter-feeding and particle-capturing abilities enhances the wetland system's capture capacity. By ingesting and filtering microplastic particles, the 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, achieving a bioremediation effect.

[0091] 2. In this embodiment of the invention, the biomass raw materials are subjected to a combination of low-temperature and high-temperature pyrolysis treatment, which fully decomposes the organic matter in the material. This process not only ensures that the biochar has sufficient space inside for adsorbing pollutants, but also provides more contact sites for pollutants due to its large specific surface area. The high-temperature treatment further enables the modified biochar to resist the influence of the external environment (such as temperature changes, physical wear, etc.) during use, maintaining good structural integrity and durability. It also promotes the formation of nano-sized iron particles on the surface of the biochar and their uniform dispersion within its pore structure. This significantly enhances the adsorption capacity and reactivity of the biochar because the iron nanoparticles provide more active sites, allowing the physical adsorption and chemical catalysis processes to be combined more effectively, thereby greatly improving the removal efficiency of pollutants such as microplastics.

[0092] 3. In this embodiment of the invention, the unique filter-feeding and particle-capturing capabilities of benthic organisms are utilized. Through their active ecological behavior and complex interactions with microorganisms, such as parasitism and predation, the composition of the microbial community in the aquatic ecosystem can be cleverly regulated. This process not only promotes the dynamic balance and mutual influence among various environmental elements within the ecosystem, but also achieves the effective degradation and removal of pollutants in the water, thereby optimizing the overall environmental quality.

[0093] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0094] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for removing microplastics from wastewater using benthic animal-enhanced constructed wetlands, characterized in that, The method includes the following steps: S1. Establish a composite matrix layer, which includes 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 composite matrix layer, from top to bottom, includes: a coarse sand layer (1), a fine sand and biochar layer (2), and a humus layer (3); the rear composite matrix layer, from bottom to top, includes: a sand cushion layer (6), a gravel layer (5), and a crushed stone layer (4). Aquatic plants are grown 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 to add to the constructed wetland system; S3. Pump the tailwater containing microplastics into the constructed wetland system. The water flows from top to bottom through the front composite substrate layer and then from bottom to top through the rear composite substrate layer. The fine sand and biochar layer (2) is combined with biochar in a mass ratio of 2:1; The biochar used is modified biochar, and the preparation method of modified biochar is as follows: A1. The biomass material is washed with water, treated with 1%~2% NaOH solution, and neutralized with dilute acid to obtain pretreated biomass material. A2. The pretreated biomass material is subjected to low-temperature rapid pyrolysis at 300℃~400℃ for 0.5~1 hours; then heated to 600℃~700℃ for secondary pyrolysis for 1~2 hours to obtain biochar. A3. Place the biochar in a 0.5 mol / L iron salt solution and stir until homogeneous. While stirring, slowly add a 1 mol / L sodium hydroxide solution to adjust the pH to 8-10. Then add a 1 mol / L NaBH4 solution and react at room temperature for 12-24 hours. Wash the precipitate and dry it to obtain modified biochar. The coarse sand layer (1), the fine sand and biochar layer (2), and the humus layer (3) have a height of 300-400 mm, and the coarse sand has a particle size of 30-50 mm. The gravel layer (5) and the crushed stone layer (4) are both 200-300 mm high, the sand cushion layer (6) is 100-200 mm high, and the crushed stone has a particle size of 30-50 mm. The iron salt solution includes one or more of the following: ferric chloride, ferric sulfate, ferric nitrate, ferric acetate, ferrous chloride, ferrous sulfate, ferrous nitrate, and ferrous acetate.

2. The method for removing microplastics from tailwater using benthic animal-enhanced constructed wetlands as described in claim 1, characterized in that, The biomass material used is corn cobs and / or sugarcane bagasse.

3. The method for removing microplastics from tailwater using benthic animal-enhanced constructed wetlands as described in claim 1, characterized in that... In A3, the solid-liquid ratio of biochar to iron salt solution is 5~15g:100~200ml.

4. The method for removing microplastics from tailwater using benthic animal-enhanced constructed wetlands as described in claim 1, characterized in that, The aquatic plants are one or more of the following: canna lily, yellow iris, and loosestrife.

5. The method for removing microplastics from tailwater using benthic animal-enhanced constructed wetlands as described in claim 1, characterized in that, The microplastic-degrading microorganisms are bacteria of the genus Bacillus or Bacillus.

6. The method for removing microplastics from tailwater using benthic animal-enhanced constructed wetlands as described in claim 1, characterized in that, The benthic animals are tubifex worms and / or freshwater mussels.

7. The method for removing microplastics from tailwater using benthic animal-enhanced constructed wetlands as described in claim 6, characterized in that, The density of benthic animals was: 13,000-15,000 tubifex worms / m³ 2 1000-1100 freshwater mussels / m 2 .

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