Surface functionalized coir fibers, methods of making and using the same

Abstract

The application discloses surface functionalized coconut shell fibers and a preparation method and application thereof, the surface of the coconut shell fiber is rich in negative charges after oxidation treatment, and at least three layers of films formed by microorganisms are attached to the surface. Compared with the prior art, the application has the following advantages: (1) efficient adsorption and degradation: through surface functionalization treatment and construction of multiple biological films, the specific surface area and adsorption capacity of the coconut shell fiber are greatly improved, so that the coconut shell fiber has a significant advantage in capturing and removing microplastics, and the removal efficiency reaches 85-95%; meanwhile, the microorganisms in the biological film also have the ability to degrade microplastics, further reducing the accumulation of microplastics in the environment; (2) wide application scenarios: the coconut shell fiber is suitable for various types and particle sizes of microplastics; (3) strong economic feasibility: the coconut shell fiber is a cheap and easily available natural material, and has high application value after the technical treatment of the application, can effectively reduce the water treatment cost, and has a wide industrial application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of ecological environment pollution treatment, and relates to a method for treating microplastics in wastewater by combining natural materials with microorganisms, in particular to surface-functionalized coconut shell fibers and a preparation method and application thereof. BACKGROUND

[0002] Microplastics refer to plastic particles with a diameter of less than 5 mm, which widely exist in water bodies and are one of the sources of water pollution. Microplastics mainly come from daily life, industrial production and agricultural activities, and are divided into primary microplastics (such as microbeads in cleaning agents and cosmetics) and secondary microplastics (such as particles generated after degradation of larger plastic objects in the environment). They are not only difficult to degrade, but also easy to adsorb toxic and harmful substances in the environment, and pose a serious threat to aquatic organisms and human health after entering the food chain.

[0003] Wastewater treatment plants are considered as an important hub for the transfer of microplastics between human and natural environments, and an important link for controlling the entry of microplastics into the earth's material cycle. At present, the removal technologies for microplastics in wastewater mainly include physical, chemical and biological treatment methods. Common physical methods include filtration, sedimentation and air flotation, etc. These methods are effective for larger size microplastics, but have poor removal effect on micron or even nanoscale microplastics. Chemical treatment methods, such as flocculation and coagulation, can improve the sedimentation efficiency of microplastics, but may cause secondary pollution in the process of using chemical reagents. Biological treatment methods are the focus and hotspot of current research, such as Chinese patent application 200810228636.6 discloses a method for decolorizing printing and dyeing wastewater by using immobilized fungal thalli, which specifically is to mix one or several fungal spores or mycelium segments into a certain concentration of inoculation suspension, inoculate the inoculation suspension into a liquid medium containing immobilized substrate material, then culture at 20-30℃ for 3-7 days until the mycelium covers the substrate material and is fixed, and finally high-temperature inactivate it and put it into the printing and dyeing wastewater for decolorization treatment. The prior art utilizes the high porosity and high elasticity structure formed by culturing fungal spores or mycelium for a period of time to achieve the adsorption of excess dyes in printing and dyeing wastewater. However, in the above application process, the fungal spores need to be inactivated, so the activity of the thalli itself is not used. Chinese patent application 202280022561.4 discloses a method, device and system for removing microplastics in water, which specifically discloses that this process can be achieved by carefully selecting the root structure and developing a solid shell for the wetland mat, so that it can effectively operate in a strong current. The prior art uses coconut shell fibers as its growth substrate layer to capture microplastics in the water flow by utilizing its physical adsorption. However, the existing biological technology has not been widely studied for microplastics, and the degradation efficiency of microorganisms on plastic particles is low, which cannot fundamentally solve the pollution problem of microplastics.

[0004] In the current technical background, natural materials are gradually attracting attention due to their environmental friendliness and renewable characteristics. Coconut shell fiber, as a renewable natural material, has a large specific surface area and good mechanical properties, and is suitable for water treatment. However, untreated coconut shell fiber has limited adsorption capacity for removing microplastics, especially for positively charged microplastics, and its capture effect is not good. At the same time, single physical adsorption technology cannot achieve the biodegradation of microplastics. SUMMARY

[0005] The technical problem solved is to overcome the deficiencies of the prior art and improve the adsorption and degradation efficiency of microplastics in wastewater. In view of this, the present application utilizes microorganisms to construct a multilayer biofilm on the surface of coconut shell fiber, and modifies the coconut shell fiber to introduce negatively charged functional groups, i.e., a surface functionalized coconut shell fiber and its preparation method and application.

[0006] Technical solution: The surface functionalized coconut shell fiber has a surface rich in negative charges after oxidation treatment, and at least three layers of films formed by microorganisms are attached to the surface.

[0007] Preferably, the negatively charged functional groups on the surface of the coconut shell fiber are carboxyl and / or hydroxyl groups.

[0008] Preferably, the films formed by microorganisms attached to the surface of the coconut shell fiber, from inside to outside, are: a first layer of film having adsorption capacity for microplastics, a second layer of film increasing the overall thickness and stability of the film, and a third layer of film degrading microplastics.

[0009] Preferably, the films formed by microorganisms attached to the surface of the coconut shell fiber, from inside to outside, are: a film formed by Pseudomonas, a film formed by Candida, and a film formed by Micrococcus.

[0010] Preferably, the Pseudomonas is Pseudomonas veronii, the Candida is Candida tropicalis, and the Micrococcus is Micrococcus luteus.

[0011] The preparation method of any of the above surface functionalized coconut shell fibers comprises the following steps:

[0012] S1, oxidizing the coconut shell fiber at a pH of 6.5-7.0 and a temperature of 50℃ to introduce carboxyl and / or hydroxyl groups on the surface of the coconut shell fiber;

[0013] S2, placing the coconut shell fiber treated in S1 in a Pseudomonas culture medium and culturing at 37℃ for 20-28h to form a first layer of film on the surface;

[0014] S3, placing the coconut shell fiber treated in S2 in a Candida culture medium and culturing at 37 DEG C for 44-52h to form a second layer of film on the surface;

[0015] S4, placing the coconut shell fiber treated in S3 in a Micrococcus culture medium and culturing at 37 DEG C for 68-76h to form a third layer of film on the surface.

[0016] Preferably, in S1, the coconut shell fiber is treated by oxidation with hydrogen peroxide with a volume fraction of 1%.

[0017] The surface functionalized coconut shell fiber as described above is used for removing microplastics in wastewater.

[0018] Preferably, the surface functionalized coconut shell fiber is put into the wastewater to be treated at room temperature to 37 DEG C, the amount of the coconut shell fiber is 3-7g / L, and the stirring time is 2-6h, so that the microplastics in the wastewater are removed.

[0019] Preferably, the microplastics include polyethylene, polypropylene and polyethylene terephthalate with a particle size of 10-100um.

[0020] The design idea or principle of the surface functionalized coconut shell fiber is as follows: firstly, the coconut shell fiber is surface modified by a physical-chemical method to introduce functional groups with negative charges, so as to enhance the adsorption capacity of the coconut shell fiber to the microplastics with positive charges, thereby overcoming the defects of insufficient adsorption performance of the traditional coconut shell fiber. Secondly, a multi-layer biofilm is constructed on the surface of the coconut shell fiber, wherein the first layer from the inside to the outside is a Pseudomonas film layer with strong adsorption capacity to the microplastics, the second layer is a Candida film layer capable of increasing the thickness and stability of the film as a whole, and the third layer is a Micrococcus film layer capable of biodegrading the microplastics; in combination of the oxidized natural fiber and the three kinds of bacteria, the adsorption capacity to the microplastics is improved, the biodegradation of the microplastics is realized, and the composite effect of capturing, adsorbing and degrading the microplastics in the wastewater is achieved.

[0021] Beneficial effects:

[0022] (1) High-efficiency adsorption and degradation: the surface functionalization treatment and the construction of the multi-layer biofilm greatly improve the specific surface area and the adsorption capacity of the coconut shell fiber, so that the coconut shell fiber has a significant advantage in capturing and removing the microplastics, and the removal efficiency reaches 85-95%. Meanwhile, the microorganisms in the biofilm also have the ability to degrade the microplastics, further reducing the accumulation of the microplastics in the environment.

[0023] (2) Adapt to multiple microplastic types and particle sizes, wide application scenarios: The multi-layer biofilm and surface modification technology in the application enables coconut coir to adapt to different types (such as polyethylene, polypropylene, and polyethylene terephthalate) and different particle sizes (such as 10 μm to 100 μm) of microplastics, realizing a wide range of application scenarios.

[0024] (3) Strong economic feasibility: Coconut coir, as a cheap and readily available natural material, has high application value after being processed by the technology of the application, can effectively reduce water treatment costs, and has a wide industrial application prospect.

[0025] In summary, the application solves the problem of microplastic pollution while considering adsorption, degradation, and material environmental protection, etc., and has significant technical advantages and market application prospects. DETAILED DESCRIPTION

[0026] The following examples further illustrate the content of the application, but should not be construed as limiting the application. Modifications and replacements of the methods, steps or conditions of the application without departing from the spirit and essence of the application shall fall within the scope of the application. If not specifically indicated, the technical means used in the examples are conventional means known to those skilled in the art.

[0027] The strains involved in the application are commercially available from Wuhan Gray Algae Biotechnology Co., Ltd.

[0028] Example 1

[0029] (1) Take coconut coir, wash it, and then use 1% hydrogen peroxide solution for oxidation reaction, with pH value kept at 7.0 and temperature at 50℃, for 2 hours.

[0030] (2) Place the functionalized coconut coir in a Pseudomonas culture medium and incubate at 37℃ for 20 hours to form a first layer of biofilm;

[0031] (3) Place the coconut coir with the first layer of biofilm in a Candida culture medium and incubate at 37℃ for 52 hours to form a second layer of biofilm;

[0032] (4) Place the coconut coir with the second layer of biofilm in a Micrococcus culture medium and incubate at 37℃ for 68 hours to form a third layer of biofilm.

[0033] (5) Add the coconut coir composite material based on multi-layer biofilm and surface functionalization treatment to wastewater containing 100 mg / L of polyethylene terephthalate microplastics with particle sizes of 10 μm to 100 μm at an input amount of 3 g / L;

[0034] (6) After stirring at a temperature of 25-37 °C for 4 hours, the number of microplastics in the wastewater was determined, and the removal rate of polyethylene terephthalate microplastics in the wastewater was calculated to be 89.4%.

[0035] Example 2

[0036] (1) Coconut fibers were taken, washed, and then subjected to an oxidation reaction using a 1% hydrogen peroxide solution, with a pH value of 6.5 and a temperature of 50 °C for 2 hours.

[0037] (2) The functionalized coconut fibers were placed in a Pseudomonas culture medium and incubated at 37 °C for 24 hours to form a first layer of biofilm.

[0038] (3) The coconut fibers with the first layer of biofilm were placed in a Candida culture medium and incubated at 37 °C for 48 hours to form a second layer of biofilm.

[0039] (4) The coconut fibers with the second layer of biofilm were placed in a Micrococcus culture medium and incubated at 37 °C for 72 hours to form a third layer of biofilm.

[0040] (5) The coconut fiber composite material based on the multi-layer biofilm and surface functionalization treatment was added to wastewater containing 100 mg / L of polyethylene microplastics with a particle size of 10-100 μm at an input amount of 5 g / L.

[0041] (6) After stirring at a temperature of 25-37 °C for 6 hours, the number of microplastics in the wastewater was determined, and the removal rate of polyethylene microplastics in the wastewater was calculated to be 95.2%.

[0042] Example 3

[0043] (1) Coconut fibers were taken, washed, and then subjected to an oxidation reaction using a 1% hydrogen peroxide solution, with a pH value of 7.0 and a temperature of 50 °C for 2 hours.

[0044] (2) The functionalized coconut fibers were placed in a Pseudomonas culture medium and incubated at 37 °C for 28 hours to form a first layer of biofilm.

[0045] (3) The coconut fibers with the first layer of biofilm were placed in a Candida culture medium and incubated at 37 °C for 44 hours to form a second layer of biofilm.

[0046] (4) The coconut fibers with the second layer of biofilm were placed in a Micrococcus culture medium and incubated at 37 °C for 76 hours to form a third layer of biofilm.

[0047] (5) The coconut shell fiber composite based on multi-layer biofilm and surface functionalization treatment was added to the wastewater containing 100 mg / L of polypropylene microplastics with a particle size of 10-100 pm at a dosage of 7 g / L;

[0048] (6) After stirring at a temperature of 25-37 °C for 2 hours, the number of microplastics in the wastewater was determined, and the removal rate of polypropylene microplastics in the wastewater was calculated to be 85.8%.

[0049] Example 4

[0050] (1) Coconut shell fibers were washed and then subjected to oxidation reaction using 1% hydrogen peroxide solution, with pH value maintained at 6.5 and temperature at 50 °C for 2 hours.

[0051] (2) The functionalized coconut shell fibers were placed in Pseudomonas culture medium and cultured at 37 °C for 24 hours to form a first layer of biofilm;

[0052] (3) The coconut shell fibers with the first layer of biofilm were placed in Candida culture medium and cultured at 37 °C for 48 hours to form a second layer of biofilm;

[0053] (4) The coconut shell fibers with the second layer of biofilm were placed in Micrococcus culture medium and cultured at 37 °C for 72 hours to form a third layer of biofilm.

[0054] (5) The coconut shell fiber composite based on multi-layer biofilm and surface functionalization treatment was added to the wastewater containing 100 mg / L of polypropylene microplastics with a particle size of 10-100 pm at a dosage of 5 g / L;

[0055] (6) After stirring at a temperature of 25-37 °C for 4 hours, the number of microplastics in the wastewater was determined, and the removal rate of polypropylene microplastics in the wastewater was calculated to be 89.3%.

[0056] Comparative Example 1: Removal of polypropylene microplastics by natural coconut shell fibers without functionalization treatment

[0057] (1) The untreated coconut shell fibers were mixed with wastewater containing 100 mg / L of polypropylene microplastics with a particle size of 10-100 pm;

[0058] (2) After stirring at a temperature of 25-37 °C for 4 hours, the number of microplastics in the wastewater was determined, and the removal rate of polypropylene microplastics in the wastewater was calculated to be 43.8%, indicating that the untreated coconut shell fibers had poor adsorption effect on microplastics.

[0059] Comparative Example 2: Removal of polyethylene microplastics by biofilm-free functionalized coconut shell fibers

[0060] (1) Take coconut shell fiber, after cleaning, use 1% hydrogen peroxide solution for oxidation reaction, pH value is kept at 6.5, temperature is 50℃, reaction time is 2 hours.

[0061] (2) The surface functionalized coconut shell fiber composite material is mixed with wastewater containing 100 mg / L of polypropylene microplastics with a particle size of 10 μm to 100 μm;

[0062] (3) After stirring for 6 hours at a temperature of 25℃ to 37℃, the number of microplastics in the wastewater is determined, and it is calculated that the removal rate of polyethylene microplastics in the wastewater reaches 55.2%. Although the functionalization treatment improves the adsorption capacity, the removal efficiency is limited without the biological membrane.

Claims

1. Surface functionalized coir fibers, characterized in that, The surface of the coconut shell fiber is rich in negative charges after oxidation treatment, and the membrane formed by microorganisms attached to the surface of the coconut shell fiber has, from inside to outside, a first layer of membrane having adsorption capacity for microplastics, a second layer of membrane increasing the overall thickness and stability of the membrane, and a third layer of membrane degrading microplastics.

2. The surface functionalized coir fiber according to claim 1, wherein, The negative charge functional groups on the surface of the coconut shell fiber are carboxyl and / or hydroxyl.

3. The surface functionalized coir fiber according to claim 1, wherein, The Pseudomonas is Pseudomonas veronii ( Pseudomonas veronii ); the Candida is Candida tropicalis ( Candida tropicalis ); and the Micrococcus is Micrococcus luteus ( Micrococcus luteus ).

4. The method for preparing surface functionalized coir fiber according to any one of claims 1 to 3, characterized in that, The method comprises the following steps: S1, oxidizing the coconut shell fiber at a pH of 6.5-7.0 and a temperature of 50℃ to introduce carboxyl and / or hydroxyl groups on the surface of the coconut shell fiber; S2, placing the coconut shell fiber treated in S1 in a Pseudomonas culture medium and culturing at 37℃ for 20-28 h to form a first layer of membrane on the surface; S3, placing the coconut shell fiber treated in S2 in a Candida culture medium and culturing at 37℃ for 44-52 h to form a second layer of membrane on the surface; S4, placing the coconut shell fiber treated in S3 in a Micrococcus culture medium and culturing at 37℃ for 68-76 h to form a third layer of membrane on the surface.

5. The method of preparing surface functionalized coir fiber according to claim 4, wherein, In S1, the coconut shell fiber is oxidized by 1% hydrogen peroxide.

6. Use of the surface-functionalized coconut shell fiber according to any one of claims 1-3 for removing microplastics in wastewater.

7. Use according to claim 6, characterized in that, The surface-functionalized coconut shell fiber is added to the wastewater to be treated at room temperature to 37℃, the amount of addition is 3-7 g / L, and stirring is carried out for 2-6 hours to complete the removal of microplastics in the wastewater.

8. Use according to claim 6, characterized in that, The microplastics include one of polyethylene, polypropylene and polyethylene terephthalate with a particle size of 10-100 μm.