A sorting-immobilized microbial degradation reaction system and a method for removing microplastics from seawater

Abstract

This invention provides a sorting-immobilized microbial degradation reaction system and a method for removing microplastics from seawater, belonging to the field of marine aquaculture wastewater treatment technology. The sorting-immobilized microbial degradation reaction system provided by this invention includes a sequentially connected inlet unit, a sorting and filtration unit 3, and a permeation reaction wall 9. The sorting and filtration unit 3 is equipped with a filter screen 13, the pore size of which is designed to be 2-2.5 mm. Following the direction from inlet to outlet, the permeation reaction wall 9 is sequentially arranged with a modified zeolite packing layer, an immobilized microbial packing combination layer, and an adsorption packing layer laid longitudinally. The sorting-immobilized microbial degradation reaction system provided by this invention can achieve highly efficient removal of microplastics from seawater.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of mariculture wastewater treatment, and particularly relates to a sorting-immobilized microorganism degradation reaction system and a method for removing microplastics in seawater. BACKGROUND

[0002] Microplastics (MP) belong to new pollutants, and are broadly defined as plastic particles, fragments or fibers with a diameter of less than 5 mm. Microplastics have strong migration and are difficult to degrade, and have almost invaded every corner of the earth, even including the Arctic region. Microplastics migrate through surface runoff and gradually spread in most rivers, lakes and sea water bodies.

[0003] Microplastic pollutants can interfere with the endocrine system of organisms in the aquaculture environment, cause various physiological diseases, and thus pose potential risks to human health. Moreover, because microplastics cannot be metabolized and absorbed by animal and human bodies, the part that cannot be excreted accumulates in the body, causing cell damage and local inflammation, and ultimately damaging the immune system. Compared with plastics visible to the naked eye, microplastics have a larger specific surface area and can act as carriers for heavy metals, persistent organic pollutants and other pollutants, causing stronger synergistic toxicity to the water environment. Therefore, the microplastic management problem is increasingly prominent.

[0004] At present, the management technology for microplastic pollution in the water environment mainly includes physical and chemical methods (such as flocculation and sedimentation and multiple filtration), biological adsorbent adsorption and artificial wetland cooperative removal method, etc. The most safe and effective way is to complete the degradation of microplastics through specific microorganisms, and the process will not cause secondary pollution to the water environment, but the efficiency of single use of microbial degradation is not high. Moreover, the current related technology is mainly aimed at the removal of microplastics in aquaculture ponds or groundwater. The salt content in mariculture wastewater is high, and how to achieve efficient removal of microplastics in mariculture wastewater is a technical problem that needs to be solved at present. SUMMARY

[0005] The present application relates to the technical field of mariculture wastewater treatment, and particularly relates to a sorting-immobilized microorganism degradation reaction system and a method for removing microplastics in seawater.

[0006] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0007] The present application provides a sorting-immobilized microorganism degradation reaction system, which comprises a water inlet unit, a sorting and filtering unit 3 and a permeation reaction wall 9 connected in sequence;

[0008] The sorting and filtering unit 3 comprises a water inlet 10, a shell 12, and a water outlet 11, the inside of the shell 12 is provided with a filter screen 13, the aperture size of the filter screen 13 is designed to be 2-2.5 mm, the inside of the cavity formed by the filter screen 13 is provided with an ultrasonic vibrator 14; the channel between the inner wall of the shell 12 and the filter screen 13 is communicated with the water inlet 10, the water inlet 10 is communicated with a water inlet unit; the channel between the filter screen 13 and the ultrasonic vibrator 14 is communicated with the water outlet 11, the water outlet 11 is communicated with the permeation reaction wall 9 through a liquid outlet pipe 5; the bottom of the shell 12 is provided with a valve 15, the outlet of the valve 15 is provided with a receiving box 4;

[0009] In the permeation reaction wall 9, from the direction of water inlet to water outlet, a modified zeolite filler layer, a fixed microorganism filler combination layer, and an adsorption filler layer are sequentially arranged in the longitudinal direction;

[0010] The modified zeolite filler layer is filled with modified zeolite, the modified zeolite is obtained by soaking natural zeolite in a KMnO4 solution for modification treatment, and the concentration of the KMnO4 solution is 0.1-0.2 mol / L;

[0011] The fixed microorganism filler combination layer comprises multiple groups of fixed microorganism filler layers arranged at intervals and a group of carbon release material layers inserted between adjacent two groups of fixed microorganism filler layers; the fixed microorganism filler layer is filled with fixed microorganism filler, the fixed microorganism filler is prepared by an adsorption-embedding-crosslinking method using first biochar, microbial slurry, and polyvinyl alcohol-sodium alginate composite melt, the mass ratio of the first biochar, the microbial slurry, and the polyvinyl alcohol-sodium alginate composite melt is 20-30:25-35:45-55, the microbial slurry is a mixture of bacillus licheniformis slurry, bacillus pumilus slurry, marinobacterium slurry, and alcanivorax dieselnoxidans slurry; the carbon release material layer is filled with carbon release material, the carbon release material comprises a polyvinyl alcohol carrier and starch and α-amylase loaded on the polyvinyl alcohol carrier;

[0012] The adsorption filler layer is filled with modified kaolin-biochar filler, the modified kaolin-biochar filler is obtained by calcining a mixture of kaolin and second biochar;

[0013] The first biochar and the second biochar are obtained by carbonizing coastal wetland plants.

[0014] Preferably, the water inlet unit comprises a water pump 1 and a flow meter 2, the flow meter 2 is arranged on the pipeline between the water pump 1 and the sorting and filtering unit 3.

[0015] Preferably, the sorting filter unit 3 further comprises a backwashing device arranged between the liquid outlet pipe 5 and the permeation reaction wall 9, the backwashing device comprising a one-way valve 6, a booster pump 7 and a backwashing liquid bottle 8 connected in sequence, and the one-way valve 6 is communicated with the pipeline between the liquid outlet pipe 5 and the permeation reaction wall 9.

[0016] Preferably, the thickness of the modified zeolite filler layer is 0.2-0.3 m, and the particle size of the modified zeolite is 1-2 mm; the modification treatment comprises: after water bath heating at 30-40 DEG C for 2-3 h, discarding the supernatant, and washing the obtained solid material with deionized water to neutral.

[0017] Preferably, the number of immobilized microbial filler layers in the immobilized microbial filler combined layer is 3-4 groups, and the thickness of each immobilized microbial filler layer is 0.3-0.5 m, and the particle size of the immobilized microbial filler is 2-3 mm.

[0018] The mass ratio of bacillus licheniformis paste, bacillus pumilus paste, marinobacter paste and diesel alkanes paste in the microbial paste is 20-30:30-40:20-30:10-20, and the total number of colonies of each paste is greater than or equal to 10 8 CFU / mL.

[0019] Preferably, the thickness of each carbon release material layer in the immobilized microbial filler combined layer is 0.2-0.3 m, and the particle size of the carbon release material is 3-4 mm.

[0020] Preferably, the thickness of the adsorption filler layer is 0.6-0.8 m, and the particle size of the modified kaolin-biochar filler is 3-5 mm; when preparing the modified kaolin-biochar filler, the mass ratio of the kaolin to the second biochar is 1:0.8-1.2, the calcination treatment temperature is 250-350 DEG C, the holding time is 60-150 min, and the calcination treatment is carried out in a nitrogen or argon protective atmosphere.

[0021] Preferably, the coastal wetland plants include yellow flag and / or reed; the carbonization treatment temperature is 150-200 DEG C, the holding time is 60-90 min, and the carbonization treatment is carried out in a nitrogen or argon protective atmosphere.

[0022] The application provides a method for removing microplastics in seawater by using the sorting-immobilized microbial degradation reaction system.

[0023] S1, the seawater to be treated is transported into the sorting filter unit 3 through the water inlet unit for sorting treatment, and small particle microplastics and large particle microplastics are obtained, and the large particle microplastics are collected into the storage box 4;

[0024] S2, the seawater containing small particle microplastics is transported into the penetration reaction wall 9 to sequentially reduce the salinity and alkalinity of the seawater, carry out a degradation reaction, and adsorb degradation products, so as to obtain purified water which is discharged from the sorting-immobilized microbial degradation reaction system.

[0025] Preferably, the seawater to be treated is seawater aquaculture wastewater; the sorting-immobilized microbial degradation reaction system is operated in a continuous water feeding mode or an intermittent water feeding mode; when the operation mode is the intermittent water feeding mode, each operation cycle includes three days, in which two days are full water stages of the sorting-immobilized microbial degradation reaction system, and the other day is an emptying stage of the sorting-immobilized microbial degradation reaction system, and the full water stage and the emptying stage are periodically alternated.

[0026] Beneficial effects: the sorting-immobilized microbial degradation reaction system provided by the present application can effectively improve the microplastic removal efficiency. The modified zeolite filler layer in the penetration reaction wall 9 has two effects: the modified zeolite has strong ion exchange capacity, which can effectively reduce the salinity and alkalinity of seawater to a suitable level, which is conducive to maintaining the activity of microbial sludge; and the modified zeolite releases primary oxygen with extremely strong oxidation when it comes into contact with water, which can continuously supplement the dissolved oxygen required for microbial growth, so that the active microbial sludge remains in an aerobic state, which is conducive to efficient and long-term degradation reaction; the immobilized microbial filler layer has good sedimentation performance, so that the microbial flora in the immobilized microbial filler layer can remain fixed even under high water load operating conditions, thereby improving the efficiency of microplastic degradation; the carbon release material layer can supply carbon source for microbial growth, which helps the continuous reproduction and growth of microorganisms, so that the degradation reaction can continue; the adsorption filler layer can fully adsorb the degradation products and aged biological membranes produced after the degradation of microplastics by microbial sludge, thereby promoting the forward progress of the degradation reaction and improving the degradation efficiency. Therefore, the sorting-immobilized microbial degradation reaction system provided by the present application can achieve efficient removal of microplastics in seawater. The structure of the sorting-immobilized microbial degradation reaction system provided by the present application is constructed quickly, economically and reasonably, is easy to maintain and manage, has low energy consumption, and is conducive to practical popularization and application. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 Figure 1 is a structural schematic diagram of the sorting-immobilized microbial degradation reaction system in the embodiments of the present application;

[0028] Figure 2 Figure 2 is a cross-sectional structural schematic diagram of the sorting filtration unit;

[0029] Wherein 1 is a water pump, 2 is a flow meter, 3 is a sorting filter unit, 4 is a storage box, 5 is a liquid outlet pipe, 6 is a one-way valve, 7 is a booster pump, 8 is a backwashing liquid bottle, 9 is a penetration reaction wall, 10 is a water inlet, 11 is a water outlet, 12 is a shell, 13 is a filter screen, 14 is an ultrasonic vibrator, and 15 is a valve;

[0030] Figure 3 It is a cross-sectional structure diagram of the penetration reaction wall.

[0031] Figure 4 It is a comparison diagram of the removal rate of small particle microplastics with a particle size of less than 2mm in each embodiment and the comparative example. DETAILED DESCRIPTION

[0032] The application provides a sorting-immobilized microorganism degradation reaction system, which comprises a water inlet unit, a sorting filter unit 3 and a penetration reaction wall 9 connected in sequence.

[0033] The sorting filter unit 3 comprises a water inlet 10, a shell 12 and a water outlet 11, the inside of the shell 12 is provided with a filter screen 13, the pore size of the filter screen 13 is designed to be 2-2.5mm, and the inside of the cavity formed by the filter screen 13 is provided with an ultrasonic vibrator 14; the channel between the inner wall of the shell 12 and the filter screen 13 is communicated with the water inlet 10, and the water inlet 10 is communicated with the water inlet unit; the channel between the filter screen 13 and the ultrasonic vibrator 14 is communicated with the water outlet 11, and the water outlet 11 is communicated with the penetration reaction wall 9 through a liquid outlet pipe 5; the bottom of the shell 12 is provided with a valve 15, and the outlet of the valve 15 is provided with a storage box 4.

[0034] In the penetration reaction wall 9, a modified zeolite filler layer, an immobilized microorganism filler combination layer and an adsorption filler layer are sequentially arranged along the longitudinal direction from the water inlet to the water outlet.

[0035] The modified zeolite filler layer is filled with modified zeolite, the modified zeolite is obtained by soaking natural zeolite in a KMnO4 solution for modification treatment, and the concentration of the KMnO4 solution is 0.1-0.2mol / L.

[0036] The immobilized microbial filler combined layer comprises multiple groups of immobilized microbial filler layers arranged at intervals and a group of carbon release material layers inserted between adjacent two groups of immobilized microbial filler layers; the immobilized microbial filler layer is filled with immobilized microbial filler prepared by adsorption-embedding-crosslinking method from first biochar, microbial slurry and polyvinyl alcohol-sodium alginate complex molten liquid, and the mass ratio of the first biochar, microbial slurry and polyvinyl alcohol-sodium alginate complex molten liquid is 20-30:25-35:45-55, the microbial slurry is a mixture of bacillus licheniformis slurry, bacillus pumilus slurry, marinobacterium slurry and alkanibacter diesel slurry; the carbon release material layer is filled with carbon release material, and the carbon release material comprises a polyvinyl alcohol carrier and starch and alpha-amylase loaded on the polyvinyl alcohol carrier.

[0037] The adsorption filler layer is filled with modified kaolin-biochar filler prepared by calcining treatment after mixing kaolin and second biochar.

[0038] The first biochar and the second biochar are obtained by carbonization treatment of coastal wetland plants.

[0039] The sorting-immobilized microbial degradation reaction system comprises a water inlet unit. As an embodiment of the present application, the water inlet unit comprises a water pump 1 and a flow meter 2, and the flow meter 2 is arranged on the pipeline between the water pump 1 and a sorting filter unit 3, so as to facilitate the adjustment of the water inlet speed at any time.

[0040] The sorting-immobilized microbial degradation reaction system comprises a sorting filter unit 3 and a permeation reaction wall 9 which are sequentially communicated with the water inlet unit, which will be described in detail below.

[0041] In the present application, the sorting filter unit 3 comprises a water inlet 10, a shell 12 and a water outlet 11, the inside of the shell 12 is provided with a filter screen 13, the pore size of the filter screen 13 is designed to be 2-2.5 mm, and the inside of the cavity formed by the filter screen 13 is provided with an ultrasonic vibrator 14; the channel between the inner wall of the shell 12 and the filter screen 13 is communicated with the water inlet 10, and the water inlet 10 is communicated with the water inlet unit; the channel between the filter screen 13 and the ultrasonic vibrator 14 is communicated with the water outlet 11, and the water outlet 11 is communicated with the permeation reaction wall 9 through a liquid outlet pipe 5; the bottom of the shell 12 is provided with a valve 15, and the outlet of the valve 15 is provided with a storage box 4.

[0042] The pore size of the filter screen 13 is designed to be 2-2.5 mm, so that the microplastics can be sorted into large-particle microplastics and small-particle microplastics. For example, when the pore size of the filter screen 13 is set to 2 mm, the large-particle microplastics with a particle size of 2-5 mm and the small-particle microplastics with a particle size of less than 2 mm are separated when the seawater to be treated flows through the filter screen 13. The ultrasonic vibrator 14 is used to assist the detachment of the particles attached to the filter screen 13. The valve 15 is opened and closed to control the communication state with the storage box 14. The storage box 4 is used to collect the large-particle microplastics sorted out.

[0043] As an embodiment of the present application, the sorting and filtering unit 3 can further comprise a backwashing device arranged between the liquid outlet pipe 5 and the permeation reaction wall 9. The backwashing device comprises a one-way valve 6, a booster pump 7 and a backwashing liquid bottle 8 connected in sequence. The one-way valve 6 is in communication with the pipeline between the liquid outlet pipe 5 and the permeation reaction wall 9. The backwashing device of the present application is used to automatically backwash the filter screen 13, which not only effectively prevents the filter screen 13 from being blocked, but also improves the filtering efficiency, simplifies the operation process, and significantly reduces the frequency of manual cleaning of the filter screen 13. The one-way valve 6 is closed during normal operation of the sorting and immobilized microorganism degradation reaction system, and is opened to backwash the filter screen 13 when the filtering efficiency is reduced.

[0044] As an embodiment of the present application, the filter screen 13 is a detachable accessory arranged between the shell 12 and the ultrasonic vibrator 14, which is convenient for maintenance and replacement.

[0045] As an embodiment of the present application, the material of the filter screen 13 can be corrosion-resistant stainless steel. The materials of the shell 12 and the backwashing liquid bottle 8 can be transparent quartz glass. The materials of the valve 15 and the booster pump 7 can be corrosion-resistant stainless steel. The use of stainless steel or quartz glass components in the present application can avoid interference of the chemical composition of the material itself with the determination of the sorting and removal rate of microplastics.

[0046] In the present application, according to the direction from the inlet to the outlet, the permeation reaction wall 9 is sequentially provided with a modified zeolite filler layer, an immobilized microorganism filler combination layer and an adsorption filler layer arranged in the longitudinal direction, which correspond to three functional regions respectively. The following will be described in detail.

[0047] The modified zeolite filler layer is filled with modified zeolite. As an embodiment of the present application, the thickness of the modified zeolite filler layer can be 0.2-0.3 m; the particle size of the modified zeolite can be 1-2 mm, and the porosity can be 50-55%, specifically 52.2%. The modified zeolite of the present application is obtained by soaking natural zeolite in a KMnO4 solution for modification treatment, and the concentration of the KMnO4 solution is 0.1-0.2 mol / L. As an embodiment of the present application, the modification treatment can include discarding the supernatant after water bath heating at 30-40℃ for 2-3 h, and washing the obtained solid material with deionized water until neutral. As an embodiment of the present application, the heating can include first stage heating and second stage heating; the temperature of the first stage heating can be 38-40℃, and the time can be 1.5-2 h, and the first stage heating can be carried out under stirring; the temperature of the second stage heating can be 30-32℃, and the time can be 0.5-1 h, and the second stage heating can be carried out under oscillation. As an embodiment of the present application, the deionized water washing until neutral can further include drying treatment. The present application uses KMnO4 solution to modify the zeolite, so that the obtained modified zeolite has strong ion exchange capacity, and can effectively reduce the salinity and alkalinity of seawater to a suitable level, which is conducive to maintaining the activity of microbial sludge; and the modified zeolite releases strong oxidizing primary ecological oxygen when it comes into contact with water, which can continuously supplement the dissolved oxygen required for microbial growth, so that the active microbial sludge remains in an aerobic state, which is conducive to efficient and long-term degradation reaction.

[0048] The immobilized microbial filler combined layer of the present application includes multiple groups of immobilized microbial filler layers arranged at intervals and a group of carbon release material layers inserted between adjacent two groups of immobilized microbial filler layers. The present application combines immobilized microbial filler layers with carbon release material layers, and the carbon release material layers can continuously supply carbon sources for microbial growth. The two functional layers are described in detail below.

[0049] As an embodiment of the present application, the number of immobilized microbial filler layers in the immobilized microbial filler combined layer is 3-4 groups, and the thickness of each group of immobilized microbial filler layers can be 0.3-0.5 m, specifically 0.4 m. The immobilized microbial filler layer of the present application is filled with immobilized microbial filler, and the particle size of the immobilized microbial filler can be 2-3 mm.

[0050] The immobilized microbial filler of the present application is prepared by adsorption-embedding-crosslinking method using first biochar, microbial sludge and polyvinyl alcohol-sodium alginate complex melt. The mass ratio of the first biochar, microbial sludge and polyvinyl alcohol-sodium alginate complex melt is 20-30:25-35:45-55, specifically 25:30:50.

[0051] As an embodiment of the present application, the first biochar is obtained by carbonizing treatment of coastal wetland plants, which can include Acorus calamus and / or Phragmites australis, and specifically can be Acorus calamus or Phragmites australis. The present application uses coastal wetland plants, which not only realizes the localization of raw materials, but also significantly reduces the cost of raw material procurement and transportation. As an embodiment of the present application, the coastal wetland plants are sequentially subjected to water washing, air drying, crushing and drying before carbonization treatment. As an embodiment of the present application, the carbonization treatment temperature can be 150-200℃, further can be 170-190℃, and specifically can be 180℃; the temperature rising rate for rising to the temperature required for carbonization treatment can be 4-6℃ / min, and specifically can be 5℃ / min; the holding time for carbonization treatment can be 60-90min, and specifically can be 60-70min; the carbonization treatment can be carried out in a nitrogen or argon protective atmosphere. As an embodiment of the present application, the carbonization treatment can further include sequentially cooling, grinding and sieving, and the mesh size of the sieve used for sieving can be 100 mesh, and the undersize is collected as the first biochar. The first biochar in the present application is prepared by slow pyrolysis, which has simple preparation process, wide raw material sources, low cost and is more green and environmentally friendly.

[0052] In the present application, the microbial slurry is a mixture of Bacillus licheniformis slurry, Bacillus pumilus slurry, Marinobacter salinexigens slurry and Alcanivorax dieselolei slurry; the mass ratio of Bacillus licheniformis slurry, Bacillus pumilus slurry, Marinobacter salinexigens slurry and Alcanivorax dieselolei slurry in the microbial slurry can be 20-30:30-40:20-30:10-20, and specifically can be 25:35:25:15; the total number of colonies of each slurry is ≥10 8CFU / mL. As an embodiment of the present application, the obtaining method of the B. licheniformis slurry, B. pumilus slurry, H. oceanosedimentum slurry and A. dieselkumae slurry can include: continuously acclimatizing indigenous microorganisms (specifically, B. licheniformis, B. pumilus, H. oceanosedimentum or A. dieselkumae) in situ for 4-5 weeks, then continuously subculturing and enriching for more than three times, and then obtaining a strain culture solution through two rounds of screening; and the strain culture solution is centrifuged to discard the supernatant to obtain the corresponding type of slurry. In the embodiment of the present application, specifically, a plastic film (for example, a polyethylene film) is placed in the natural habitat corresponding to each of the four types of microbial strains, and the indigenous microorganisms are continuously acclimatized in situ for 4-5 weeks, and the plastic film and the coated root slurry sample are taken as the inoculum; under sterile operation conditions, 10% of the inoculum is added to the culture medium to complete continuous subculture and enrichment for more than three times, and then two rounds of screening are performed to obtain a strain culture solution; the strain culture solution is centrifuged to discard the supernatant, and the microbial slurry of each type is reserved for use. The microorganisms in the microbial slurry obtained by the above method of the present application can adhere to the surface of microplastics, produce extracellular enzymes such as esterase, lipase, lignin peroxidase and cutinase, etc., and can convert polymers into oligomers, dimers or monomers, thereby achieving effective degradation of microplastics.

[0053] As an embodiment of the present application, the mass ratio of polyvinyl alcohol to sodium alginate in the polyvinyl alcohol-sodium alginate composite melt solution can be 8-10:1, and specifically can be 9:1. As an embodiment of the present application, the preparation method of the polyvinyl alcohol-sodium alginate composite melt solution can include the following steps: mixing polyvinyl alcohol and sodium alginate, heating and melting, and then cooling to obtain the polyvinyl alcohol-sodium alginate composite melt solution.

[0054] As an embodiment of the present application, the preparation method of the immobilized microbial filler can comprise the following steps: mixing an emulsifier, a first cross-linking agent and water to obtain a mixed solution; mixing a first biochar, microbial slurry and the polyvinyl alcohol-sodium alginate composite melt solution, adding the obtained mixed raw materials into the mixed solution by using a shaper, and then adjusting the pH value of the obtained system to 7 to obtain the immobilized microbial filler. As an embodiment of the present application, the emulsifier can be an OP emulsifier, the first cross-linking agent can be CaCl2 and H3BO3, the concentration of the OP emulsifier in the mixed solution can be 45-55 mol / L, and specifically can be 50 mol / L; the concentration of CaCl2 can be 0.8-1.2 wt%, and specifically can be 1 wt%; and the H3BO3 can be a saturated concentration. In the embodiment of the present application, the OP emulsifier and CaCl2 are added into the saturated H3BO3 solution to obtain the mixed solution. As an embodiment of the present application, the reagent used for adjusting the pH value can be a Na2CO3 solution, and the concentration of the Na2CO3 solution can be 8-12 wt%, and specifically can be 10 wt%. As an embodiment of the present application, after the pH value of the obtained system is adjusted to 7, gel particles appear in the system, and then filtration is preferably performed, the gel particles are collected and washed with water to obtain the immobilized microbial filler. The immobilized microbial filler is prepared by using the adsorption-embedding-cross-linking method, wherein the first biochar serves as a skeleton carrier of the immobilized microbial filler and plays a role of adsorption and support; the microbial slurry serves as a key active substance and can produce extracellular enzymes for degrading microplastics; and the polyvinyl alcohol-sodium alginate composite melt solution serves as a cross-linking forming liquid and promotes embedding to form the immobilized microbial filler with high impact strength.

[0055] As an embodiment of the present application, the thickness of each group of the carbon-releasing material layer in the combined layer of the immobilized microbial filler can be 0.2-0.3 m. In the present application, the carbon-releasing material layer is filled with carbon-releasing material, and the particle size of the carbon-releasing material can be 3-4 mm. In the present application, the carbon-releasing material comprises a polyvinyl alcohol carrier and starch and α-amylase loaded on the polyvinyl alcohol carrier; and the starch can be corn starch.

[0056] As an embodiment of the present application, the preparation method of the carbon release material can comprise the following steps: mixing starch, polyvinyl alcohol, sodium alginate, alpha-amylase and water to obtain a mixed raw material solution; mixing a second crosslinking agent and water to obtain a crosslinking agent solution; adding the mixed raw material solution dropwise into the crosslinking agent solution to perform crosslinking treatment to obtain the carbon release material. As an embodiment of the present application, the mass ratio of the starch, polyvinyl alcohol and sodium alginate can be 18-22:16-20:8-12, and specifically can be 20:18:10. As an embodiment of the present application, the use amount ratio of starch and water in the mixed raw material solution can be 18-22g:350-450mL, and specifically can be 20g:400mL; in the present application, starch, polyvinyl alcohol, sodium alginate and water can be mixed, heated to 40-50℃ (specifically 45℃) under stirring, and then cooled to room temperature, and alpha-amylase is added to the obtained mixture to obtain the mixed raw material solution. As an embodiment of the present application, the second crosslinking agent can be CaCl2; the use amount ratio of the second crosslinking agent and water in the crosslinking agent solution can be 14-18g:450-550mL, and specifically can be 16g:500mL. As an embodiment of the present application, the dropping rate can be 1 drop / s; the crosslinking treatment temperature can be 4-6℃, and specifically can be 5℃; the time can be 25-30h, and specifically can be 28h. As an embodiment of the present application, the crosslinking treatment is preferably followed by filtration, and the collected solid material is washed with water to obtain the carbon release material. The carbon release material of the present application uses starch as raw material, polyvinyl alcohol as skeleton carrier, and obtains solid-state slow-release carbon source through low-temperature gel technology; the present application inserts a group of carbon release material layers between two adjacent groups of immobilized microbial filler layers, which can supply carbon source for microbial growth, helps the continuous reproduction and growth of microorganisms, and enables the degradation reaction to continue.

[0057] The adsorption filler layer is filled with modified kaolin-biochar filler. As an embodiment of the present application, the thickness of the adsorption filler layer can be 0.6-0.8 m; the particle size of the modified kaolin-biochar filler can be 3-5 mm. The modified kaolin-biochar filler of the present application is obtained by calcining the mixture of kaolin and second biochar. As an embodiment of the present application, the preparation method of the second biochar can be consistent with that of the first biochar, which will not be repeated here. As an embodiment of the present application, the mass ratio of the kaolin to the second biochar in preparing the modified kaolin-biochar filler can be 1:0.8-1.2, and specifically can be 1:1. As an embodiment of the present application, the calcining temperature can be 250-350℃, further can be 280-320℃, and specifically can be 300℃; the holding time can be 60-150 min, further can be 80-120 min, and specifically can be 90-100 min; the calcining process can be carried out in a nitrogen or argon protective atmosphere. As an embodiment of the present application, the kaolin is preferably crushed and sieved before calcining, and the undersize is collected and mixed with the second biochar for calcining. The mesh size of the sieve used for sieving can be 100 mesh. The modified kaolin-biochar filler of the present application can fully adsorb the degradation products and aged biofilm produced by the degradation reaction of microplastics with microbial sludge, thereby promoting the forward progress of the degradation reaction and improving the degradation efficiency.

[0058] The present application provides a method for removing microplastics from seawater using the sorting-immobilized microorganism degradation reaction system described in the above technical solution, which comprises the following steps:

[0059] S1, the seawater to be treated is transported to the sorting filtration unit 3 through the water inlet unit for sorting treatment, and seawater containing small particle microplastics and large particle microplastics are obtained, respectively, and the large particle microplastics are collected into the storage box 4;

[0060] S2, the seawater containing small particle microplastics is transported to the permeation reaction wall 9 for sequentially reducing the salinity and alkalinity of seawater, degradation reaction, and adsorption of degradation products, to obtain purified water, which is discharged from the sorting-immobilized microorganism degradation reaction system.

[0061] In the present application, specifically, first start the water inlet unit to deliver the seawater to be treated into the sorting and filtering unit 3, when the seawater flows through the filter screen 13, the large particle microplastics and the small particle microplastics are sorted out, obtaining the large particle microplastics and the seawater containing small particle microplastics; open the valve 15 at the bottom of the sorting and filtering unit 3, the large particle microplastics are collected into the storage box 4, and are transferred and dried regularly, and are recycled or reasonably landfilled; the seawater containing small particle microplastics flows into the permeation reaction wall 9, sequentially flows through the modified zeolite filler layer, the immobilized microorganism filler combination layer and the adsorption filler layer three functional areas, realizes the reduction of seawater salinity and alkalinity, fully occurs the degradation reaction and the adsorption of degradation products, and obtains the purified water which is discharged by the water outlet pipe.

[0062] As an embodiment of the present application, the seawater to be treated can be seawater aquaculture wastewater. As an embodiment of the present application, the operation mode of the sorting-immobilized microorganism degradation reaction system can adopt continuous water inlet method or intermittent water inlet method; when the operation mode is intermittent water inlet method, each operation cycle contains three days, in which two days the sorting-immobilized microorganism degradation reaction system is in full water stage (or humid stage), and the other day the sorting-immobilized microorganism degradation reaction system is in emptying stage (or oxygen-rich stage), and the full water stage and the emptying stage are alternately operated periodically. In the embodiment of the present application, the intermittent water inlet method is adopted, in which the oxygen-rich stage can provide sufficient oxygen for the microorganisms, thereby improving the degradation efficiency of microplastics.

[0063] As an embodiment of the present application, during the sorting process, the valve 15 is preferably in the closed state, which can ensure that the seawater to be treated entering the shell 12 is discharged from the water outlet 11 after being screened through the filter screen 13, so that the large particle microplastics are enriched in the shell 12, and then the valve 15 is opened to collect the large particle microplastics into the storage box 4. As an embodiment of the present application, when it is observed that the water flow speed in the shell 12 is obviously slowed down, the one-way valve 6 connected beside the water outlet 11 and the booster pump 7 can be opened, the booster pump 7 can promote the backwash liquid to be injected into the shell 12 through the water outlet 11, to backwash the particles deposited on the filter screen 13, at the same time, the ultrasonic vibrator 14 inside the shell 12 can also assist the deposited particles to be efficiently detached from the filter screen 13, thereby improving the degradation efficiency.

[0064] Figure 1 The structure diagram of the sorting-immobilized microorganism degradation reaction system in the embodiment of the present application is shown in FIG. 1, Figure 2 The cross-sectional structure diagram of the sorting and filtering unit is shown in FIG. 2, Figure 3Fig. 1 is a schematic view of a cross-sectional structure of a permeable reaction wall. The technical solutions in the present application will be clearly and completely described below in combination with the embodiments in the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative effort shall fall within the protection scope of the present application.

[0065] The specific conditions not mentioned in the following experiments of the present application are carried out according to the conventional conditions or the conditions recommended by the manufacturer, and the reagents or instruments not mentioned by the manufacturer are all conventional products that can be purchased on the market.

[0066] The Bacillus licheniformis BL-2 used in the following experiments of the present application is purchased from the China Center for Type Culture Collection of Wuhan University, and the preservation number is CCTCC No. M2012458; the Bacillus pumilus DS-3 is purchased from the China Center for Type Culture Collection of Wuhan University, and the preservation number is CCTCC No. M20221849; the Marinobacter salinexigens is purchased from the China General Microbiological Culture Collection Center, and the preservation number is CGMCC No. 25242; and the Alcanivorax dieselolei is purchased from the China General Microbiological Culture Collection Center, and the preservation number is CGMCC No. 26017.

[0067] Preparation Example 1

[0068] The modified zeolite is prepared by the following steps:

[0069] The natural zeolite is weighed and soaked in a KMnO4 solution with a concentration of 0.2 mol / L, heated in a water bath at 40℃ for 2h under stirring, then oscillated in a constant temperature oscillator at 30℃ at a shaking rate of 200r / min for 30min, after the oscillation, the obtained solid material is washed to neutral with deionized water, and then dried to obtain the modified zeolite (with a particle size of 1-2mm), which is sealed and stored for use.

[0070] Preparation Example 2

[0071] The immobilized microbial filler is prepared by the following steps:

[0072] (1) The polyvinyl alcohol (PVA) and sodium alginate (SA) are uniformly mixed according to a mass ratio of 9:1, heated and melted into a viscous liquid, and then cooled to room temperature to obtain a polyvinyl alcohol-sodium alginate composite melt;

[0073] (2) sequentially washing, air-drying, crushing and drying the reed, heating the obtained dried reed to 180℃ at a heating rate of 5℃ / min in a nitrogen atmosphere, keeping the temperature for 60 min for carbonization treatment, then cooling to room temperature, grinding and sieving with a 100 mesh sieve, collecting the undersize to obtain biochar particles;

[0074] (3) placing polyethylene (PE) plastic film in the natural habitat of Bacillus licheniformis, Bacillus pumilus, Marinobacter and Alcanivorax dieselolei respectively, continuously acclimatizing indigenous microorganisms in situ for 4 weeks, taking the plastic film and the coated root mud sample as inoculum; under aseptic operation conditions, adding the inoculum to the enrichment medium at an inoculation amount of 10% for continuous subculture enrichment for 4 times, then sequentially performing primary screening and rescreening to obtain a strain culture solution; centrifuging the strain culture solution and discarding the supernatant to obtain Bacillus licheniformis sludge, Bacillus pumilus sludge, Marinobacter sludge and Alcanivorax dieselolei sludge respectively; uniformly mixing the Bacillus licheniformis sludge, Bacillus pumilus sludge, Marinobacter sludge and Alcanivorax dieselolei sludge at a mass ratio of 25:35:25:15 to obtain mixed sludge;

[0075] (4) uniformly mixing CaCl2, OP emulsifier and H3BO3 saturated solution to obtain a mixed solution, the concentration of CaCl2 in the mixed solution is 1wt%, and the concentration of OP emulsifier is 50mol / L; uniformly mixing the biochar particles, mixed sludge and polyvinyl alcohol-sodium alginate complex melt at a mass ratio of 25:30:50, at room temperature, using a former to add the obtained mixed raw materials to the mixed solution, using a 10wt% Na2CO3 solution to adjust the pH value of the system to 7, gel particles appear in the system, then filtering, collecting the gel particles and washing with deionized water to obtain the immobilized microbial filler (particle size is 2-3mm).

[0076] Preparation Example 3

[0077] Preparation of carbon release material, comprising the following steps:

[0078] (1) uniformly mixing 18g of polyvinyl alcohol, 10g of sodium alginate, 20g of corn starch and 400mL of deionized water to obtain a viscous mixed liquid, heating to 45℃ in a water bath under stirring at a speed of 280r / min, then cooling to room temperature, adding α-amylase to the obtained mixed liquid to obtain a mixed raw material solution;

[0079] (2) adding 16 g of CaCl2 in 500 mL of deionized water to obtain a crosslinking agent solution; dropping the mixed raw material solution into the crosslinking agent solution at a rate of 1 drop / s, and performing crosslinking treatment at 5°C for 28 h; during the crosslinking treatment, spherical particles appeared in the system; after the crosslinking treatment was completed, the spherical particles were collected by filtration, washed with deionized water, and the carbon release material (particle size of 3-4 mm) was obtained.

[0080] Preparation Example 4

[0081] The modified kaolin-biochar filler was prepared by the following steps:

[0082] The kaolin was crushed and sieved with a 100-mesh sieve to collect the undersize to obtain kaolin particles; the kaolin particles and biochar particles (prepared according to the method of Preparation Example 2) were uniformly mixed at a mass ratio of 1:1 to obtain a mixed raw material; the mixed raw material was calcined at 300°C for 90 min in a nitrogen atmosphere, and then cooled to room temperature to obtain the modified kaolin-biochar filler (particle size of 3-5 mm).

[0083] Example 1

[0084] The sorting-immobilized microorganism degradation reaction system shown in Figure 1 was used to treat the water body, and according to the direction from the inlet to the outlet, the sorting-immobilized microorganism degradation reaction system was sequentially provided with a modified zeolite filler layer, an immobilized microorganism filler combination layer, and an adsorption filler layer laid along the longitudinal direction, and the fillers used in each layer were prepared according to the methods of Preparation Examples 1-4, as follows:

[0085] The modified zeolite filler layer was filled with modified zeolite, and the thickness of the modified zeolite filler layer was 0.3 m;

[0086] The immobilized microorganism filler combination layer included three groups of immobilized microorganism filler layers laid along the longitudinal direction and two groups of carbon release material layers laid between adjacent two groups of immobilized microorganism filler layers; wherein the immobilized microorganism filler layer was filled with immobilized microorganism filler, and the thickness of each group of immobilized microorganism filler layer was 0.4 m; the carbon release material layer was filled with carbon release material, and the thickness of each group of carbon release material layer was 0.2 m;

[0087] The adsorption filler layer was filled with modified kaolin-biochar filler, and the thickness of the adsorption filler layer was 0.6 m.

[0088] The method for removing microplastics in seawater by using the sorting-immobilized microorganism degradation reaction system in this example included the following steps:

[0089] The test water source is a local large-scale seawater aquaculture wastewater. The sorting-immobilized microorganism degradation reaction system is opened. The water is transported to the sorting filter unit 3 through the water inlet unit (pump 1 and flow meter 2). The valve 15 at the bottom of the sorting filter unit 3 is opened. The large particle microplastics with a particle size of 2-5 mm and the small particle microplastics with a particle size of <2 mm in the water are sorted out. The large particle microplastics with a particle size of 2-5 mm are collected into the storage box 4 and are periodically transferred and dried for recycling or reasonable landfill disposal. The water containing the small particle microplastics with a particle size of <2 mm is transported to the permeation reaction wall 9 through the liquid outlet pipe 5 to complete the reduction of seawater salinity and alkalinity, the degradation reaction, and the adsorption process of the degradation products. The effluent is discharged through the effluent pipe of the permeation reaction wall 9. The system adopts a continuous water inlet method. The water inlet load is adjusted to 0.15 m 3 / m 2 / day-0.4 m 3 / m 2 / day through the flow meter 2. The stable operation time is 30 days.

[0090] Example 2

[0091] Referring to the method steps of Example 1, the difference lies in that the system adopts an intermittent water inlet method. Each operation cycle contains three days (two days in full water state and one day in empty state), and the operation is repeated for 10 cycles.

[0092] Comparative Example 1

[0093] Referring to the method steps of Example 2, the difference lies in that the modified zeolite filler in the permeation reaction wall 9 is replaced by untreated natural zeolite filler. Specifically, the natural zeolite is crushed and sieved in sequence. The natural zeolite with a particle size of 1-2 mm is obtained by sieving and used as the filler.

[0094] Comparative Example 2

[0095] Referring to the method steps of Example 2, the difference lies in that the adsorption filler layer in the permeation reaction wall 9 is omitted, that is, only the modified zeolite filler layer and the immobilized microorganism filler combination layer are provided.

[0096] Comparative Example 3

[0097] Referring to the method steps of Example 2, the difference lies in that the immobilized microorganism filler layer is replaced by a microbial slurry filler layer. The preparation method of the microbial slurry filler includes the following steps: uniformly mixing Bacillus licheniformis slurry, Bacillus pumilus slurry, Marinobacterium slurry, and diesel fuel alkanes slurry according to a mass ratio of 25:35:25:15 to obtain mixed slurry; and uniformly mixing biochar particles and the mixed slurry according to a mass ratio of 25:30 to obtain the microbial slurry filler.

[0098] Comparative Example 4

[0099] Referring to the method steps of Example 2, the difference lies in that only bacillus licheniformis slurry is used to prepare the immobilized microbial filler (i.e., only one kind of slurry is used, and the other three kinds of slurry are omitted).

[0100] Comparative Example 5

[0101] Referring to the method steps of Example 2, the difference lies in that only bacillus licheniformis slurry is used to prepare the immobilized microbial filler (i.e., only one kind of slurry is used, and the other three kinds of slurry are omitted).

[0102] Test Example 1

[0103] On the initial day of system start-up and the 30th day of stable operation, effluent samples of the examples and comparative examples were collected, and Fourier transform micro-infrared spectroscopy was used to identify the chemical composition of microplastics and to count the abundance of microplastics. Each group of tests of the examples or comparative examples included two parallel groups to ensure that the system operation results were not accidental and to make the removal rate data calculation more accurate.

[0104] Figure 4 The removal rate comparison chart of small particle microplastics with a particle size of <2 mm in each example and comparative example is shown in FIG. 2. Figure 4 As can be seen from FIG. 2, after 30 days of operation, the removal rate of small particle microplastics with a particle size of <2 mm in the influent is 91.2% using the continuous influent method in Example 1; and the removal rate of small particle microplastics with a particle size of <2 mm in the influent is improved to 95.6% using the intermittent influent method in Example 2.

[0105] At the same time, as can be seen from FIG. 2, Figure 4 As can be seen from FIG. 2, in Comparative Example 1, the natural zeolite filler layer has a low removal rate (76.3%) of small particle microplastics because the natural zeolite cannot release oxygen when it comes into contact with water; in Comparative Example 2, the degradation products in seawater are difficult to be completely adsorbed because of the lack of an adsorption filler layer, so the removal rate of small particle microplastics is low (74.6%); in Comparative Example 3, the microbial slurry filler in the permeable reactive barrier is not embedded and fixed by a polyvinyl alcohol-sodium alginate composite melt, which leads to unstable morphology of the microbial slurry filler and easy loss of the microbial slurry filler due to water flow scouring, so the removal rate of small particle microplastics is low (71.5%); in Comparative Examples 4 and 5, the removal rate of small particle microplastics is low because only one kind of slurry is used in the immobilized microbial filler layer, and the removal rates are 84.6% and 79.2%, respectively.

[0106] In summary, the present application has at least the following beneficial effects:

[0107] (1) The design idea of sorting and removing the large and small particle microplastics, on the one hand, can greatly improve the processing efficiency of the permeation reaction wall 9, and on the other hand, can avoid the blockage of the filler in each layer when the water continues to flow.

[0108] (2) The filter screen 13 in the sorting and filtering unit 3 in the application is provided as a detachable accessory, which is convenient for cleaning and maintenance to maintain the filtering efficiency, and when the efficiency of the reaction system decreases, only the filter screen accessory needs to be updated, without replacing the entire sorting and filtering unit, thereby reducing the long-term operation cost of the system.

[0109] (3) The one-way valve 6, the booster pump 7 and the backwashing liquid bottle 8 are matched in the application, and the automatic backwashing function of the filter screen 13 can be realized through the liquid outlet pipe 5, which not only can effectively prevent the filter screen 13 from being blocked, but also can significantly reduce the replacement frequency of the filter screen 13.

[0110] (4) Compared with the natural fillers such as untreated gravel and zeolite commonly used in the prior art, the modified zeolite treated by KMnO4 releases strong oxidizing nascent oxygen when it meets water, promotes the continuous supply of dissolved oxygen, and thus provides a high-quality physicochemical environment for the growth and reproduction of microbial flora, in addition, the modified zeolite in the application also has the function of adsorbing nitrogen and phosphorus to improve the substrate.

[0111] (5) The application realizes the effective fixation of microbial sludge by adsorption-embedding-crosslinking method, and the structure has good sedimentation performance, so that the microbial sludge form is still stable even under high hydraulic load operating conditions, avoiding the problem that the flocculent microorganisms exposed in the prior art are washed out of the system as inoculums; experiments have proved that the immobilized microbial filler layer after secondary and tertiary circulation still shows stable degradation performance, thereby saving a lot of cost.

[0112] (6) The application combines the microbial sludge of bacillus licheniformis, bacillus pumilus, marinobacter and diesel alkane bacteria, which produces a synergistic effect, and the degradation efficiency is higher than that of the microbial sludge using a single strain.

[0113] (7) The application inserts a group of carbon release material layer between each adjacent two groups of immobilized microbial filler layers, which can supply slow-release carbon source for microbial growth, is beneficial to the self-reproduction and metabolism of microorganisms, and thus improves the degradation efficiency.

[0114] (8) The raw materials for preparing the biochar in the application are widely available and easy to obtain, and the preparation process is simple, which can realize the recycling of waste, such as solving the nearby disposal problem of a large amount of harvested wetland plants such as reed and yellow flag iris in autumn and winter, and the biochar does not have the risk of secondary pollution to aquaculture water.

[0115] (9) The modified kaolin-biochar filler prepared by the special process in the application can be combined with the degradation reaction products through cation bridge bond, so that the adsorption efficiency is greatly improved, and the preparation method can realize the repeated use of the biochar raw material.

[0116] (10) When the water inlet unit regulation system runs in the intermittent water inlet method, the periodic water inlet mode of the alternation of the "filling / wetting" stage and the "draining / drying" stage can improve the reoxidation efficiency, and in turn effectively improve the microplastic removal rate.

[0117] (11) Compared with coagulation sedimentation, membrane separation and advanced oxidation, the structure of the sorting-immobilized microorganism degradation reaction system is constructed quickly, economically and reasonably, is easy to maintain and manage, and has very low energy consumption, which is conducive to practical promotion.

[0118] The above only describes the preferred embodiments of the application, and it should be pointed out that for ordinary skilled persons in the art, several improvements and refinements can be made without departing from the principles of the application, and these improvements and refinements should also be considered as the protection scope of the application.

Claims

1. A method for removing microplastics in seawater by using a sorting-immobilized microbial degradation reaction system, The sorting-immobilized microbial degradation reaction system comprises a water inlet unit, a sorting filter unit (3) and a permeation reaction wall (9) connected in sequence; The sorting filter unit (3) comprises a water inlet (10), a shell (12) and a water outlet (11), the inside of the shell (12) is provided with a filter screen (13), the aperture size of the filter screen (13) is designed to be 2-2.5 mm, the inside of the cavity formed by the filter screen (13) is provided with an ultrasonic vibrator (14); the channel between the inner wall of the shell (12) and the filter screen (13) is communicated with the water inlet (10), the water inlet (10) is communicated with the water inlet unit; the channel between the filter screen (13) and the ultrasonic vibrator (14) is communicated with the water outlet (11), the water outlet (11) is communicated with the permeation reaction wall (9) through a liquid outlet pipe (5); the bottom of the shell (12) is provided with a valve (15), the outlet of the valve (15) is provided with a storage box (4); In the permeation reaction wall (9), from the inlet to the outlet, a modified zeolite filler layer, an immobilized microbial filler combination layer and an adsorption filler layer are arranged in sequence along the longitudinal direction; The modified zeolite filler layer is filled with modified zeolite, the modified zeolite is obtained by soaking natural zeolite in a KMnO4 solution for modification treatment, and the concentration of the KMnO4 solution is 0.1-0.2 mol / L; The immobilized microbial filler combined layer comprises multiple groups of immobilized microbial filler layers arranged at intervals and a group of carbon release material layers inserted between adjacent two groups of immobilized microbial filler layers; the immobilized microbial filler layer is filled with immobilized microbial filler prepared by adsorption-embedding-crosslinking method from first biochar, microbial slurry and polyvinyl alcohol-sodium alginate composite melt, and the mass ratio of the first biochar, microbial slurry and polyvinyl alcohol-sodium alginate composite melt is 20-30:25-35:45-55, the microbial slurry is a mixture of bacillus licheniformis slurry, bacillus pumilus slurry, marinobacter slurry and alkanibacter dieseloleophilus slurry, and the mass ratio of the bacillus licheniformis slurry, bacillus pumilus slurry, marinobacter slurry and alkanibacter dieseloleophilus slurry in the microbial slurry is 20-30:30-40:20-30:10-20, and the total number of colonies of each slurry is ≥10 8 CFU / mL; the carbon release material layer is filled with carbon release material comprising polyvinyl alcohol carrier and starch and alpha-amylase loaded on the polyvinyl alcohol carrier; The adsorption filler layer is filled with modified kaolin-biochar filler, the modified kaolin-biochar filler is obtained by mixing kaolin and a second biochar and then calcining; The first biochar and the second biochar are obtained by carbonizing coastal wetland plants; The method comprises the following steps: S1, delivering seawater to be treated to the sorting filter unit (3) through the water inlet unit for sorting treatment, to obtain seawater containing small particle microplastics and large particle microplastics, and the large particle microplastics are collected into the storage box (4); S2, delivering the seawater containing small particle microplastics to the permeation reaction wall (9) to sequentially reduce the salinity and alkalinity of the seawater, perform a degradation reaction and adsorb degradation products, to obtain purified water, which is discharged from the sorting-immobilized microbial degradation reaction system; The operation mode of the sorting-immobilized microbial degradation reaction system adopts an intermittent water inlet method, each operation cycle comprises three days, two days are full water stages of the sorting-immobilized microbial degradation reaction system, and the other day is an emptying stage of the sorting-immobilized microbial degradation reaction system, and the full water stage and the emptying stage are periodically alternately operated.

2. The method of claim 1, wherein, The water inlet unit comprises a water pump (1) and a flow meter (2), and the flow meter (2) is arranged on the pipeline between the water pump (1) and the sorting filter unit (3).

3. The method according to claim 1 or 2, characterized in that, The sorting and filtering unit (3) further comprises a backwashing device arranged between the liquid outlet pipe (5) and the permeation reaction wall (9), the backwashing device comprising a one-way valve (6), a booster pump (7) and a backwashing liquid bottle (8) connected in sequence, the one-way valve (6) being communicated with the pipeline between the liquid outlet pipe (5) and the permeation reaction wall (9).

4. The method of claim 1, wherein, The thickness of the modified zeolite filler layer is 0.2-0.3 m, and the particle size of the modified zeolite is 1-2 mm. The modification treatment comprises: discarding the supernatant after water bath heating at 30-40 ℃ for 2-3 h, and washing the obtained solid material with deionized water until neutral.

5. The method of claim 1, wherein, The number of the immobilized microbial filler layers in the immobilized microbial filler combined layer is 3-4 groups, the thickness of each immobilized microbial filler layer is 0.3-0.5 m, and the particle size of the immobilized microbial filler is 2-3 mm.

6. The method according to claim 1 or 5, characterized in that, The thickness of each carbon-releasing material layer in the immobilized microbial filler combined layer is 0.2-0.3 m, and the particle size of the carbon-releasing material is 3-4 mm.

7. The method of claim 1, wherein, The thickness of the adsorption filler layer is 0.6-0.8 m, and the particle size of the modified kaolin-biochar filler is 3-5 mm; during the preparation of the modified kaolin-biochar filler, the mass ratio of the kaolin to the second biochar is 1:0.8-1.2, the calcination treatment is performed at a temperature of 250-350 ℃ for 60-150 min, and the calcination treatment is performed in a nitrogen or argon protective atmosphere.

8. The method of claim 1, wherein, The coastal wetland plants comprise Acorus gramineus Soland and / or Phragmites communis Trin; the carbonization treatment is performed at a temperature of 150-200 ℃ for 60-90 min, and the carbonization treatment is performed in a nitrogen or argon protective atmosphere.

9. The method of claim 1, wherein, The seawater to be treated is mariculture wastewater.

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