A method for effectively removing microplastics and denitrifying wastewater using constructed wetlands

Abstract

This invention discloses a method for effectively removing microplastics and denitrifying wastewater in constructed wetlands. Wastewater is fed into a microplastic and denitrification system, which comprises an aeration zone, a microplastic interception zone, a nitrification zone, a denitrification zone, and a sulfur autotrophic denitrification zone connected in sequence. The microplastic interception packing layer is composed of modified volcanic rock. The volcanic rock is immersed in hydrochloric acid solution, ultrasonically or oscillating it, and washed until the effluent is neutral to obtain pretreated volcanic rock. The pretreated volcanic rock is then immersed in sodium dodecyl sulfate solution, ultrasonically or oscillating it, and washed and dried to obtain modified volcanic rock. This invention, through the modification treatment of volcanic rock, can significantly improve the removal rate of microplastics and reduce the impact on nitrogen removal in constructed wetlands. Combined with the nitrification, denitrification, and sulfur autotrophic denitrification zones, it further improves the removal rate of total nitrogen in constructed wetlands.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a method for effectively removing microplastics and denitrifying wastewater using constructed wetlands. Background Technology

[0002] Microplastics (MPs) are tiny plastic particles with a diameter of less than 5 millimeters present in the environment, and are a new type of pollutant widely present in the environment today. The main sources of MPs include the fragmentation of larger plastic products, the shedding of synthetic fibers, damage to agricultural plastic films, wear and tear on vehicle tires, and direct emissions from personal care products and industrial production processes. MPs are not easily degraded, can continuously accumulate in the environment, and can migrate long distances, thus adversely affecting ecological security and human health. Domestic sewage is an important sink for MPs and also a significant potential source of MPs entering the ecological environment. A study by Simon et al. found that wastewater treatment plants in Denmark discharge approximately 3 tons of MPs into the environment annually, and MP removal has become a research hotspot in recent years.

[0003] Wastewater treatment is an effective means of treating microplastics (MPs), with its main removal mechanisms including sedimentation, adsorption, and retention at various stages of wastewater treatment. Most MPs are ultimately transferred to sludge. Although wastewater treatment plants achieve good removal rates for MPs, a large amount is still discharged into the environment daily. Constructed wetland systems, formed by human factors, utilize the synergistic physical, chemical, and biological processes of soil, artificial media, plants, and microorganisms to treat wastewater and sludge. However, studies have found that the accumulation of MPs reduces the removal rate of total nitrogen (TN) in constructed wetlands by approximately 8-16%. MP accumulation alters the structure and function of microorganisms, inhibiting important genes involved in nitrite oxidation, denitrification, and electron generation. It also changes the species contribution of nitrogen transformation genes, interfering with nitrogen transformation metabolism and weakening the denitrification performance of carbon-based wetlands (CWs). Therefore, a method for effectively removing microplastics and denitrifying wastewater using constructed wetlands is needed, one that not only effectively removes microplastics but also does not affect subsequent denitrification treatment and achieves high-efficiency denitrification. Summary of the Invention

[0004] In view of the above-mentioned prior art, the purpose of this invention is to provide a method for effectively removing microplastics and denitrifying wastewater in constructed wetlands. This invention, through modification treatment of volcanic rock, can significantly improve the removal rate of microplastics and reduce the impact on denitrification in constructed wetlands. Combined with nitrification, denitrification, and sulfur autotrophic denitrification zones, it further improves the total nitrogen removal rate of constructed wetlands.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A first aspect of the present invention provides a method for effectively removing microplastics and denitrifying wastewater in constructed wetlands. The method comprises: passing wastewater into a microplastic removal and denitrification system, the microplastic removal and denitrification system including a microplastic interception zone, the microplastic interception zone having a microplastic interception packing layer inside; one end of the microplastic interception zone being connected to an aeration zone and the other end being connected to a nitrification zone; the nitrification zone being connected to a denitrification zone; the denitrification zone being connected to a sulfur autotrophic denitrification zone; an aerator being installed inside the aeration zone; a water distribution device being installed at the top of the nitrification zone and a nitrification packing layer being installed at the bottom; a denitrification packing layer being installed inside the denitrification zone; and a sulfur autotrophic denitrification packing layer being installed inside the sulfur autotrophic denitrification zone. Wastewater enters the aeration zone for oxidation, then enters the microplastic interception zone to remove the microplastics it contains, then passes through the nitrification zone for natural oxygen-enriched nitrification, enters the denitrification zone for denitrification, and finally enters the sulfur autotrophic denitrification zone to reduce nitrates to nitrogen gas and discharge the treated wastewater.

[0006] Preferably, the microplastic is a PVC microplastic.

[0007] Preferably, the aeration zone is provided with an inlet at the top; the autotrophic denitrification zone is provided with an outlet pipe at the bottom; both the aeration zone and the nitrification zone are provided with drain outlets at the bottom; the aeration zone and the microplastic interception zone are connected through a first inlet, the nitrification zone and the denitrification zone are connected through a second inlet, and the denitrification zone and the autotrophic denitrification zone are both connected through a third inlet; the aeration zone is connected to the nitrification zone through a water distribution device.

[0008] Preferably, the first water inlet is located at the bottom of the microplastic interception zone; the second water inlet is located at the bottom of the denitrification zone; and the third water inlet is located at the top of the sulfur autotrophic denitrification zone.

[0009] Preferably, the water distribution device includes a main pipe with one end open, which is connected to several longitudinally connected branch pipes; both the main pipe and the branch pipes are provided with several spray holes.

[0010] Preferably, the water distribution device is located above the nitrification packing layer, and the distance between the water spray hole and the top of the nitrification packing layer is 20~40cm; the nitrification packing layer is composed of gravel.

[0011] Preferably, the denitrification packing layer is composed of gravel with progressively increasing particle size from top to bottom, with the upper part of the denitrification packing layer being a gravel layer with a particle size of 5-6 mm and the lower part of the denitrification packing layer being a gravel layer with a particle size of 8-12 mm.

[0012] Preferably, the microplastic trapping filler layer is composed of modified volcanic rock; the modified volcanic rock is prepared by the following method: (1) Immerse the volcanic rock in hydrochloric acid solution, treat it with ultrasound or vibration, and wash the volcanic rock until the washing liquid is neutral to obtain pretreated volcanic rock; (2) The pretreated volcanic rock was immersed in sodium dodecyl sulfate (SDS) solution, ultrasonically or oscillated, and then washed and dried to obtain modified volcanic rock.

[0013] Preferably, the concentration of the hydrochloric acid solution is 5 wt%; the concentration of the sodium dodecyl sulfate solution is 0.1 mol / L; and the drying temperature is 105°C for 12 hours.

[0014] Preferably, the sulfur autotrophic denitrification packing layer is composed of gravel, sulfur autotrophic denitrification packing, and limestone from top to bottom; the volume ratio of the gravel, sulfur autotrophic denitrification packing, and limestone is 1:6:2.

[0015] A second aspect of the invention provides the application of the above-described method in the simultaneous removal of microplastics and denitrification in constructed wetlands.

[0016] The beneficial effects of this invention are: This invention provides an constructed wetland technology that effectively removes microplastics and efficiently denitrifies. The constructed wetland technology features a scientifically designed, rationally structured, and convenient construction, with readily available materials. Building upon traditional constructed wetland technology, it removes microplastics (MPs) from the upstream filler material and combines this with sulfur autotrophic denitrification technology to treat domestic sewage. This effectively removes MPs, preventing them from affecting the subsequent denitrification performance of the constructed wetland. Furthermore, compared to traditional constructed wetlands, it significantly enhances denitrification performance, avoids secondary pollution, is environmentally friendly, and is suitable for decentralized rural sewage treatment. Attached Figure Description

[0017] Figure 1 Schematic diagram of a microplastic denitrification system; Figure 2 Top view of the microplastic denitrification system; Figure 3 : Front view of the microplastic denitrification system; Wherein: 1-Aeration zone, 2-Microplastic interception zone, 3-Nitrification zone, 4-Denitrification zone, 5-Sulfur autotrophic denitrification zone, 6-Aerator, 7-Microplastic interception packing layer, 8-Water distribution device, 9-Nitrification packing layer, 10-Denitrification packing layer, 11-Sulfur autotrophic denitrification packing layer, 12-Inlet, 13-Outlet pipe, 14-Drain outlet, 15-First outlet, 16-Second outlet, 17-Third outlet, 18-Main pipe, 19-Branch pipe, 20-Spray hole; Figure 4 The removal status of microplastics by the microplastic denitrification system; Figure 5 The effectiveness of the microplastic denitrification system in removing pollutants such as nitrogen (TN) from water. Detailed Implementation

[0018] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0019] As introduced in the background section, the accumulation of MPs reduces the removal rate of total nitrogen (TN) in constructed wetlands by about 8-16%. The accumulation of MPs causes changes in the structure of microorganisms and functional differences. Some important genes in the processes of nitrite oxidation, denitrification and electron generation are inhibited. At the same time, the species contribution of nitrogen transformation genes is changed, which interferes with nitrogen transformation metabolism and weakens the nitrogen removal performance of CWs.

[0020] Based on this, the purpose of this invention is to provide a method for effectively removing microplastics and denitrifying wastewater using constructed wetlands. This invention designs a novel constructed wetland system that can be used for microplastic removal and efficient nitrogen conversion, which has the following characteristics: (1) Extremely high MPs retention rate: Numerous studies have proven that constructed wetlands can very effectively retain MPs in water, with a retention rate of over 98%; (2) Long-term removal of microplastics: The "MPs retention zone" at the front end of the constructed wetland system is designed as an upflow vertical subsurface flow structure, with most MPs retained at the bottom of the packing material, which can be regenerated by backwashing periodically; (3) MPs removal and wastewater purification can operate normally simultaneously: The constructed wetland system is designed with multiple independent wetland units, and the "MPs retention zone" at the front end can efficiently remove microplastics, ensuring the normal removal of pollutants such as COD, ammonia nitrogen, TP, and TN in the wastewater at the back end; (4) Efficient denitrification: The constructed wetland system is equipped with a "nitrification zone" and a "denitrification zone", combined with the "sulfur autotrophic denitrification zone" at the back end, which can efficiently remove nitrate nitrogen without the need for additional carbon sources, reducing TN in the effluent. This invention, through screening modifiers to treat volcanic rocks, discovered that volcanic rocks treated with SDS after acid washing not only have improved microplastic retention capacity but also enhanced subsequent denitrification and other pollutant removal capabilities. The method of this invention not only removes over 98% of microplastics (MPs) generated during equipment operation but also deeply removes nitrogen and phosphorus pollutants from effluent. The design is simple, the raw materials used are widely available and inexpensive, and it is easy to scale up production and apply in practice. The packing material in the microplastic interception unit is removable and flushable, facilitating reuse and improving operational convenience and feasibility, aligning with the concept of sustainable development.

[0021] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to specific embodiments.

[0022] The test materials used in the embodiments of this invention are all conventional test materials in the art and can be purchased through commercial channels.

[0023] Example 1: Preparation of modified volcanic rock (1) Pickling stage Weigh 100g of volcanic rock with a particle size of 5-6mm, accurate to 0.001g, and place it in a clean beaker. Add sufficient 5wt% HCl solution to the beaker to completely submerge the volcanic rock packing. Ensure that the HCl solution is in excess to guarantee a complete reaction. Place the beaker containing the volcanic rock packing and HCl solution in a constant temperature shaker or ultrasonic cleaner, set the ultrasonic frequency to 30-40kHz, and sonicate for 60 minutes at room temperature. After treatment, rinse the volcanic rock packing repeatedly with deionized water until the washing solution is neutral (pH value approximately 7) to remove residual acidic substances. Place the cleaned volcanic rock packing in an oven and dry it at 105℃ for 12 hours, then remove it and cool it to room temperature for later use.

[0024] (2) SDS processing stage Prepare a 0.1 mol / L SDS solution. Place the acid-washed and dried volcanic rock packing material back into a clean beaker, and add the prepared SDS solution at a solid-liquid ratio of 1:10. Place the mixture in an ultrasonic cleaner, set the ultrasonic frequency to 30-40 kHz, and vibrate or sonicate at room temperature for 30 minutes. After treatment, allow the volcanic rock packing material to settle naturally for a period of time. Carefully pour off the supernatant, retaining the solid portion. Rinse the SDS-treated volcanic rock packing material multiple times with deionized water, draining as much water as possible after each rinse until the washing liquid no longer contains SDS. Finally, place the treated volcanic rock packing material back into an oven and dry it at 105°C for 12 hours until completely dry, then it can be used for subsequent research. Example 2: Microplastic Removal and Denitrification System like Figures 1-3As shown, the microplastic denitrification system includes a microplastic interception zone 2, inside which is a microplastic interception packing layer 7; one end of the microplastic interception zone 2 is connected to an aeration zone 1, and the other end is connected to a nitrification zone 3; the nitrification zone 3 is connected to a denitrification zone 4; the denitrification zone 4 is connected to a sulfur autotrophic denitrification zone 5; an aerator 6 is installed inside the aeration zone 1; a water distribution device 8 is installed at the top of the nitrification zone 3, and a nitrification packing layer 9 is installed at the bottom; The denitrification zone 4 is equipped with a denitrification packing layer 10; the autotrophic denitrification zone 5 is equipped with an autotrophic denitrification packing layer 11; the aeration zone 1 has an inlet 12 at its top; the autotrophic denitrification zone 5 has an outlet pipe 13 at its bottom; both the aeration zone 1 and the nitrification zone 3 have outlets 14 at their bottoms; the aeration zone 1 is connected to the microplastic interception zone 2 through a first outlet 15, and the nitrification zone 3 is connected to the denitrification zone 4 through a second outlet 16. The denitrification zone 4 and the autotrophic denitrification zone 5 are both connected through a third inlet 17; the aeration zone 1 is connected to the nitrification zone 3 through a water distribution device 8; the first inlet 15 is located at the bottom of the microplastic interception zone 2; the second inlet 16 is located at the bottom of the denitrification zone 4; the third inlet 17 is located at the top of the autotrophic denitrification zone 5; the water distribution device 8 includes a main pipe 18 with one end open, and the main pipe is connected to several longitudinally connected branch pipes 19; the main pipe 18 and the branch pipes 19... Each of the 9 layers is provided with several water spray holes 20; the water distribution device 8 is located above the nitrification packing layer 9, and the distance between the water spray holes 20 and the top of the nitrification packing layer 9 is 20~40cm; the nitrification packing layer 9 is composed of gravel; the denitrification packing layer 10 is composed of gravel with progressively increasing particle size from top to bottom, the upper part of the denitrification packing layer 10 is padded with gravel with a particle size of 5~6mm, and the lower part of the denitrification packing layer 10 is padded with gravel with a particle size of 8~12mm. The microplastic intercepting packing layer is composed of modified volcanic rock prepared in Example 1. The sulfur autotrophic denitrification packing layer 11 is composed of gravel, sulfur autotrophic denitrification packing, and limestone from top to bottom; the volume ratio of gravel, sulfur autotrophic denitrification packing, and limestone is 1:6:2.

[0025] Example 3: Wastewater Treatment Wastewater treatment using the microplastic removal and denitrification system of Example 2: Wastewater enters the aeration zone at a rate of 40 L / d through the inlet. Oxygen (5.25 L / min) supplied by an aerator (Yuting brand ACO-001 aeration pump) is used for oxidation. Then, it enters the microplastic interception zone where modified volcanic rock removes the microplastics. Next, it passes through the nitrification zone, where a water distribution device sprays the wastewater into the bottom gravel-based nitrification packing layer. During this spraying process, natural oxygen enrichment is created, leading to natural aerobic nitrification. In this layer, microorganisms convert ammonia nitrogen into nitrate. The wastewater then enters the denitrification zone for further denitrification. The upper gravel of the denitrification packing layer has a particle size of 5-6 mm and a height of approximately 25 cm, while the lower gravel gradually increases to 8-12 mm and a height of approximately 10 cm. Under anoxic conditions, denitrifying bacteria reduce nitrate and nitrite to nitrogen gas. Finally, the wastewater enters the autotrophic denitrification zone. Gravel, autotrophic denitrification packing material (purchased from Shandong Longantai Environmental Protection Technology Co., Ltd., particle size 2-6mm), and limestone are arranged in a volume ratio of 1:6:2, forming the autotrophic denitrification packing layer from top to bottom. Under anoxic or anaerobic conditions, microorganisms utilize reduced sulfur as an electron donor to reduce nitrates to nitrogen gas. This achieves the removal of microplastics and denitrification from the wastewater.

[0026] Comparative Example 1: Microplastic Removal and Nitrogen Desorption System The difference from Example 2 is that the modified volcanic rock is replaced with an equal amount of volcanic rock.

[0027] Comparative Example 2: Microplastic Removal and Nitrogen Desorption System (1) Prepare an SDS solution with a concentration of 0.1 mol / L. Weigh 100 g of volcanic rock with a particle size of 5-6 mm and place it in a clean beaker. Add the prepared SDS solution at a solid-liquid ratio of 1:10. Place the mixture in an ultrasonic cleaner and set the ultrasonic frequency to 30-40 kHz. Vibrate or sonicate at room temperature for 30 minutes. After treatment, let it stand for a period of time to allow the volcanic rock packing to settle naturally. Carefully pour off the supernatant and retain the solid part. Rinse the SDS-treated volcanic rock packing multiple times with deionized water. After each rinse, drain the water as much as possible until the washing liquid no longer contains SDS. Finally, put the treated volcanic rock packing back into the oven and dry it at 105℃ for 12 hours to obtain SDS-treated volcanic rock.

[0028] (2) The difference from Example 2 is that the modified volcanic rock is replaced with an equal amount of SDS-treated volcanic rock prepared in step (1).

[0029] Comparative Example 3: Microplastic Removal and Nitrogen Desorption System (1) Pickling stage Weigh 100g of volcanic rock with a particle size of 5-6mm, accurate to 0.001g, and place it in a clean beaker. Add sufficient 5wt% HCl solution to the beaker to completely submerge the volcanic rock packing. Ensure that the HCl solution is in excess to guarantee a complete reaction. Place the beaker containing the volcanic rock packing and HCl solution in a constant temperature shaker or ultrasonic cleaner, set the ultrasonic frequency to 30-40kHz, and sonicate for 60 minutes at room temperature. After treatment, rinse the volcanic rock packing repeatedly with deionized water until the washing solution is neutral (pH value approximately 7) to remove residual acidic substances. Place the cleaned volcanic rock packing in an oven and dry it at 105℃ for 12 hours, then remove it and cool it to room temperature for later use.

[0030] (2) Hexadecyltrimethylammonium chloride treatment stage Prepare a 0.1 mol / L SDS solution. Place the acid-washed and dried volcanic rock packing material back into a clean beaker, and add the prepared hexadecyltrimethylammonium chloride solution at a solid-liquid ratio of 1:10. Place the mixture in an ultrasonic cleaner, set the ultrasonic frequency to 30-40 kHz, and vibrate or sonicate at room temperature for 30 minutes. After treatment, allow the volcanic rock packing material to settle naturally for a period of time, carefully pour off the supernatant, and retain the solid portion. Rinse the hexadecyltrimethylammonium chloride-treated volcanic rock packing material multiple times with deionized water, draining as much water as possible after each rinse until the washing liquid no longer contains SDS. Finally, place the treated volcanic rock packing material back into an oven and dry it at 105°C for 12 hours until completely dry, then it can be used for subsequent research.

[0031] (2) The difference from Example 2 is that the modified volcanic rock is replaced with an equal amount of hexadecyltrimethylammonium chloride modified volcanic rock prepared in step (1).

[0032] Test case Wastewater effluent from the Southwest University of Science and Technology's wastewater treatment plant was collected. The concentrations of PVC microplastic particles, total nitrogen (TN), total phosphorus, chemical oxygen demand (COD), and ammonia nitrogen were measured using LDIR laser infrared spectroscopy, alkaline potassium persulfate digestion ultraviolet spectrophotometry, ammonium molybdate spectrophotometry, rapid digestion spectrophotometry, and Nessler's reagent spectrophotometry. The PVC concentration was 226.8 particles / L, TN was 19.17 mg / L, total phosphorus was 4.03 mg / L, COD was 16.39 mg / L, and ammonia nitrogen was 11.99 mg / L. This wastewater was divided into four equal portions and fed into four microplastic removal and denitrification systems (Examples 2 and 3) at a rate of 40 L / day, and treated according to the method in Example 3. The concentrations of microplastics, total nitrogen (TN), total phosphorus (TP), total oxygen (COD), and ammonia nitrogen (MNO) in treated wastewater were determined using LDIR laser infrared spectroscopy, alkaline potassium persulfate digestion ultraviolet spectrophotometry, ammonium molybdate spectrophotometry, rapid digestion spectrophotometry, and Nessler's reagent spectrophotometry. The results are shown below. Figure 4-5 .

[0033] according to Figure 4 As can be seen, the concentration of PVC microplastics in the influent sample was very high, reaching 226.8 CFU / L. However, after treatment by the microplastic removal and denitrification system in Example 2, the concentration of microplastics in the effluent was significantly reduced to only 3 CFU / L, with a removal rate as high as 98.68%. This result indicates that the system in Example 2 performs excellently in removing microplastics. In contrast, the treatment effect of the microplastic removal and denitrification systems in Comparative Examples 1-3 was slightly inferior. Specifically, the microplastic concentrations in the effluent of Comparative Examples 1, 2, and 3 were 53.4 CFU / L, 36.1 CFU / L, and 24.3 CFU / L, respectively, with corresponding removal rates of 76.46%, 84.08%, and 89.29%. Although the removal performance of these systems gradually improved, it still did not reach the level of Example 2. From the perspective of microplastic emissions, the daily influent volume of these systems was 40L. Calculations show that Example 2 emits approximately 3,600 microplastics into the environment per month, while Comparative Examples 1 to 3 emit approximately 64,080, 43,320, and 29,160 microplastics per month, respectively. This demonstrates that the system of Example 2 has a significant advantage in reducing microplastic emissions, achieving a substantial monthly reduction compared to the comparative examples. In conclusion, the microplastic removal and denitrification system of Example 2 performs exceptionally well in removing microplastics, with a removal rate and emission reduction effect significantly superior to the systems of Comparative Examples 1 to 3. This effectively reduces microplastic pollution to the environment.

[0034] according to Figure 5As can be seen, the concentrations of total nitrogen (TN), ammonia nitrogen, total phosphorus (TP), and chemical oxygen demand (COD) in the influent were 19.17 mg / L, 11.99 mg / L, 4.03 mg / L, and 16.39 mg / L, respectively. All four microplastic removal and denitrification systems in Example 2 and Comparative Examples 1-3 effectively removed these four pollutants. Example 2 showed the most significant removal performance, achieving removal rates of 84.92%, 90.66%, 80.65%, and 61.93% for TN, ammonia nitrogen, TP, and COD, respectively. In contrast, while the systems in Comparative Examples 1-3 could also remove these pollutants, their removal rates were relatively low. Specifically, the TN removal rates of Comparative Examples 1-3 were 75.64%, 80.96%, and 81.17%, respectively; the ammonia nitrogen removal rates were 80.15%, 84.24%, and 85.24%, respectively; the TP removal rates were 74.19%, 76.67%, and 77.92%, respectively; and the COD removal rates ranged from 30% to 42%. This indicates that Example 2 has a significant advantage in pollutant removal. Constructed wetland systems are commonly used for advanced effluent treatment in wastewater treatment plants or equipment. Based on the data above, the system of Example 2 can more effectively remove these pollutants, especially TN and TP, thereby significantly reducing pollutant emissions in the effluent. This is of great significance for reducing the risk of eutrophication. In summary, the microplastic removal and denitrification system of Example 2 performs excellently in removing pollutants such as TN, ammonia nitrogen, TP, and COD, with removal rates far exceeding those of the systems in Comparative Examples 1-3. This highly efficient removal capability not only improves water cleanliness but also effectively reduces the risk of eutrophication, possessing significant environmental significance and application value.

[0035] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for effectively removing microplastics and denitrifying wastewater in constructed wetlands, characterized in that, The method is as follows: wastewater is fed into a microplastic removal and denitrification system, the microplastic removal and denitrification system includes a microplastic interception zone, and the interior of the microplastic interception zone is provided with a microplastic interception packing layer; One end of the microplastic trapping zone is connected to the aeration zone, and the other end is connected to the nitrification zone; the nitrification zone is connected to the denitrification zone; the denitrification zone is connected to the sulfur autotrophic denitrification zone; the aeration zone is equipped with an aerator; the top of the nitrification zone is equipped with a water distribution device, and the bottom is equipped with a nitrification packing layer; the denitrification zone is equipped with a denitrification packing layer; the sulfur autotrophic denitrification zone is equipped with a sulfur autotrophic denitrification packing layer. Wastewater enters the aeration zone for oxidation, then enters the microplastic interception zone to remove the microplastics it contains, then passes through the nitrification zone for natural oxygen-enriched nitrification, enters the denitrification zone for denitrification, and finally enters the sulfur autotrophic denitrification zone to reduce nitrates to nitrogen gas and discharge the treated wastewater. The microplastic trapping filler layer is composed of modified volcanic rock; the modified volcanic rock is prepared by the following method: (1) Immerse the volcanic rock in hydrochloric acid solution, treat it with ultrasound or vibration, and wash the volcanic rock until the washing liquid is neutral to obtain pretreated volcanic rock; the concentration of the hydrochloric acid solution is 5 wt%; (2) The pretreated volcanic rock was immersed in sodium dodecyl sulfate solution, ultrasonically or oscillated, and then washed and dried to obtain modified volcanic rock; The concentration of the sodium dodecyl sulfate solution is 0.1 mol / L; the drying temperature is 105℃ and the time is 12 h.

2. The method according to claim 1, characterized in that, The aeration zone is provided with an inlet at the top; the autotrophic denitrification zone is provided with an outlet pipe at the bottom; both the aeration zone and the nitrification zone are provided with drain outlets at the bottom; the aeration zone and the microplastic interception zone are connected through a first water outlet, the nitrification zone and the denitrification zone are connected through a second water outlet, and the denitrification zone and the autotrophic denitrification zone are both connected through a third water outlet; the aeration zone is connected to the nitrification zone through a water distribution device.

3. The method according to claim 2, characterized in that, The first water inlet is located at the bottom of the microplastic interception zone; the second water inlet is located at the bottom of the denitrification zone; and the third water inlet is located at the top of the sulfur autotrophic denitrification zone.

4. The method according to claim 2, characterized in that, The water distribution device includes a main pipe with one end open, which is connected to several longitudinally connected branch pipes; both the main pipe and the branch pipes are provided with several water spray holes.

5. The method according to claim 4, characterized in that, The water distribution device is located above the nitrification packing layer, and the distance between the water spray hole and the top of the nitrification packing layer is 20~40cm; the nitrification packing layer is composed of gravel.

6. The method according to claim 1, characterized in that, The denitrification packing layer is composed of gravel with increasing particle size from top to bottom. The upper part of the denitrification packing layer is pavement of gravel with a particle size of 5-6 mm, and the lower part of the denitrification packing layer is pavement of gravel with a particle size of 8-12 mm.

7. The method according to claim 1, characterized in that, The sulfur autotrophic denitrification packing layer is composed of gravel, sulfur autotrophic denitrification packing and limestone from top to bottom; the volume ratio of gravel, sulfur autotrophic denitrification packing and limestone is 1:6:

2.

8. The application of the method according to any one of claims 1 to 7 in the simultaneous removal of microplastics and denitrification in constructed wetlands.

Images