Surface-functionalized coconut fiber as well as preparation method and application thereof

Abstract

The invention discloses a surface-functionalized coconut fiber and a preparation method and application thereof, the surface of the coconut fiber is subjected to oxidation treatment and is rich in negative charges, and at least three layers of films formed by microorganisms are attached to the surface of the coconut fiber. Compared with the prior art, the invention has the following advantages: (1) efficient adsorption and degradation: through surface functionalization treatment and construction of a multi-layer biological membrane, the specific surface area and adsorption capacity of the coconut shell fiber are greatly improved, so that the coconut shell fiber has significant advantages in capture and removal of micro-plastics, and the removal efficiency reaches 85-95%; meanwhile, microorganisms in the biological membrane further have the capacity of degrading micro-plastics, and accumulation of the microorganisms in the environment is further reduced; (2) the method is suitable for various micro-plastic types and particle sizes, and the application scene is wide; and (3) the economic feasibility is strong: the coconut fiber as a cheap and strong-availability natural material has high application value after being treated by the technology disclosed by the invention, the water treatment cost can be effectively reduced, and the method has wide industrial application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of ecological environmental pollution control, and relates to a method for treating microplastics in wastewater by combining natural materials with microorganisms, specifically surface functionalized coconut shell fiber, and a preparation method and application thereof. Background Art

[0002] Microplastics refer to plastic particles with a diameter of less than 5 mm. They are widely present in water bodies and are one of the sources of water pollution. Microplastics mainly come from daily life, industrial production and agricultural activities. They are divided into primary microplastics (such as microbeads in detergents and cosmetics) and secondary microplastics (such as particles produced after larger plastic items are degraded in the environment). Not only are they difficult to degrade, they are also easy to absorb toxic and harmful substances in the environment, and after entering the food chain, they pose a serious threat to aquatic life and human health.

[0003] Wastewater treatment plants are considered to be an important hub for the transfer of microplastics between the human environment and the natural environment, and an important link in 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, precipitation and flotation, which are effective for larger microplastics, but have poor removal effects on microplastics at the micron or even nanoscale. Chemical treatment methods, such as flocculation and coagulation, can improve the sedimentation efficiency of microplastics, but may cause secondary pollution during the use of chemical reagents. Biological treatment methods are currently the focus and hotspot of research. For example, Chinese patent application 200810228636.6 discloses a method for decolorizing printing and dyeing wastewater using immobilized fungal cells, specifically, one or several fungal spores or hyphae segments are prepared into an inoculation suspension of a certain concentration, the inoculation suspension is inoculated into a liquid culture medium containing an immobilized matrix material, and then cultured at 20-30°C for 3-7 days until the mycelium covers the matrix material and is fixed, and then inactivated at high temperature, and finally placed in the printing and dyeing wastewater for decolorization treatment. This prior art utilizes the high porosity and high elasticity structure formed after fungal spores or hyphae are cultured for a period of time, so as to achieve the adsorption of excess dyes in printing and dyeing wastewater. In the above application process, the fungi need to be inactivated, so the activity of the bacteria themselves is not used. Chinese patent application 202280022561.4 discloses a method, device and system for removing microplastics in water, and specifically discloses that this process can be achieved by carefully selecting the root structure and developing a sturdy shell for the wetland mat, so that it can operate effectively in rapid flow conditions. This prior art uses coconut shell fiber as its growth matrix layer to capture microplastics in the water flow by its physical adsorption effect. However, existing biotechnology has not yet conducted extensive research on 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 technological context, natural materials have gradually attracted attention due to their environmentally friendly and renewable characteristics. Coconut shell fiber, as a renewable natural material, has a large specific surface area and good mechanical properties, making it suitable for water treatment. However, untreated coconut shell fiber has limited adsorption capacity in removing microplastics, especially for positively charged microplastics, and its capture effect is poor. At the same time, a single physical adsorption technology cannot achieve the biodegradation of microplastics. Summary of the invention

[0005] Technical problem to be solved: In order to overcome the shortcomings of the prior art and improve the adsorption and degradation efficiency of microplastics in wastewater; in view of this, the present invention utilizes microorganisms to construct a multilayer biofilm on the surface of coconut shell fiber, and at the same time modifies the coconut shell fiber to introduce negatively charged functional groups, that is, to provide surface functionalized coconut shell fiber and its preparation method and application.

[0006] Technical solution: Surface functionalized coconut shell fiber, the surface of the coconut shell fiber is rich in negative charge after oxidation treatment, and at least three layers of membranes 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 groups and / or hydroxyl groups.

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

[0009] Preferably, the films formed by microorganisms attached to the surface of the coconut shell fiber are, from inside to outside, respectively: 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 method for preparing any of the above surface functionalized coconut shell fibers comprises the following steps:

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

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

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

[0015] S4. Place the coconut shell fiber treated with S3 in a micrococcal culture medium and culture at 37°C for 68-76 hours to form a third layer of membrane on the surface.

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

[0017] Application of any of the above surface functionalized coconut shell fibers in removing microplastics from wastewater.

[0018] Preferably, the surface functionalized coconut shell fiber is added to the wastewater to be treated at room temperature to 37°C, with an addition amount of 3-7 g / L and stirred for 2-6 hours to complete the removal of microplastics in the wastewater.

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

[0020] The idea or principle of the design of the surface functionalized coconut shell fiber described in the present invention is: first, the present invention adopts a physical-chemical method to modify the surface of coconut shell fiber, introduces negatively charged functional groups, so as to enhance the adsorption capacity of coconut shell fiber to positively charged microplastics, thereby overcoming the defect of insufficient adsorption performance of traditional coconut shell fiber. Secondly, a multi-layer biofilm is constructed on the surface of coconut shell fiber. From the inside to the outside, the first layer is a Pseudomonas membrane layer with strong adsorption capacity for microplastics, the second layer is a Candida membrane layer that can increase the overall thickness and stability of the membrane, and the third layer is a Micrococcus membrane layer that can biodegrade microplastics; combined with the effects of oxidized natural fibers and the three bacteria, it not only improves the adsorption capacity for microplastics, but also can achieve biodegradation of microplastics, and achieves a composite effect of capturing, adsorbing and degrading microplastics in wastewater.

[0021] Beneficial effects:

[0022] (1) Efficient adsorption and degradation: The present invention significantly improves the specific surface area and adsorption capacity of coconut shell fiber through surface functionalization treatment and the construction of multi-layer biofilm, making it have significant advantages in capturing and removing microplastics, with a removal efficiency of 85-95%. At the same time, the microorganisms in the biofilm also have the ability to degrade microplastics, further reducing their accumulation in the environment.

[0023] (2) Adaptable to various types and particle sizes of microplastics and wide application scenarios: The multilayer biofilm and surface modification technology in the present invention enable coconut shell fiber to adapt to microplastics of different types (such as polyethylene, polypropylene, polyethylene terephthalate) and different particle sizes (such as 10μm to 100μm), realizing a wide range of application scenarios.

[0024] (3) Strong economic feasibility: Coconut shell fiber is a cheap and readily available natural material. After being processed by the technology of the present invention, it has high application value, can effectively reduce water treatment costs, and has broad industrial application prospects.

[0025] In short, the present invention not only solves microplastic pollution, but also takes into account adsorption, degradation and material environmental protection, and has significant technical advantages and market application prospects. DETAILED DESCRIPTION

[0026] The following examples further illustrate the content of the present invention, but should not be construed as limiting the present invention. Without departing from the spirit and essence of the present invention, modifications and substitutions made to the method, steps or conditions of the present invention all belong to the scope of the present invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art.

[0027] The strains involved in the present invention are all commercially available strains purchased from Wuhan Huizao Biotechnology Co., Ltd.

[0028] Example 1

[0029] (1) Coconut shell fiber was washed and then oxidized using 1% hydrogen peroxide solution, with the pH value maintained at 7.0, the temperature at 50° C., and the reaction time being 2 hours.

[0030] (2) placing the functionalized coconut shell fiber in a Pseudomonas culture medium and culturing it at 37°C for 20 hours to form the first layer of biofilm;

[0031] (3) placing the coconut shell fiber with the first biofilm in a Candida culture medium and culturing at 37°C for 52 hours to form a second biofilm;

[0032] (4) The coconut shell fiber with the second biofilm was placed in a micrococcal culture medium and cultured at 37°C for 68 hours to form a third biofilm.

[0033] (5) The coconut shell fiber composite material based on multilayer biofilm and surface functionalization treatment was added at an input amount of 3 g / L into wastewater containing 100 mg / L of polyethylene terephthalate microplastics with a particle size of 10 μm to 100 μm;

[0034] (6) After stirring for 4 hours at a temperature of 25°C to 37°C, the amount of microplastics in the wastewater was measured. It was calculated that the removal rate of polyethylene terephthalate microplastics in the wastewater reached 89.4%.

[0035] Example 2

[0036] (1) Coconut shell fiber was washed and then oxidized using 1% hydrogen peroxide solution, with the pH value maintained at 6.5, the temperature at 50° C., and the reaction time being 2 hours.

[0037] (2) placing the functionalized coconut shell fiber in a Pseudomonas culture medium and culturing it at 37°C for 24 hours to form the first layer of biofilm;

[0038] (3) placing the coconut shell fiber with the first biofilm in a Candida culture medium and culturing at 37°C for 48 hours to form a second biofilm;

[0039] (4) The coconut shell fiber with the second biofilm was placed in a micrococcal culture medium and cultured at 37°C for 72 hours to form a third biofilm.

[0040] (5) Adding 5 g / L of the coconut shell fiber composite material based on multilayer biofilm and surface functionalization treatment into wastewater containing 100 mg / L of polyethylene microplastics with a particle size of 10 μm to 100 μm;

[0041] (6) After stirring for 6 hours at a temperature of 25°C to 37°C, the amount of microplastics in the wastewater was measured. It was calculated that the removal rate of polyethylene microplastics in the wastewater reached 95.2%.

[0042] Example 3

[0043] (1) Coconut shell fiber was washed and then oxidized using 1% hydrogen peroxide solution, with the pH value maintained at 7.0, the temperature at 50° C., and the reaction time being 2 hours.

[0044] (2) placing the functionalized coconut shell fiber in a Pseudomonas culture medium and culturing it at 37°C for 28 hours to form the first layer of biofilm;

[0045] (3) placing the coconut shell fiber with the first biofilm in a Candida culture medium and culturing at 37°C for 44 hours to form a second biofilm;

[0046] (4) The coconut shell fiber with the second biofilm was placed in a micrococcal culture medium and cultured at 37°C for 76 hours to form a third biofilm.

[0047] (5) The coconut shell fiber composite material based on multilayer biofilm and surface functionalization treatment was added at an input amount of 7 g / L into wastewater containing 100 mg / L of polypropylene microplastics with a particle size of 10 μm to 100 μm;

[0048] (6) After stirring for 2 hours at a temperature of 25°C to 37°C, the amount of microplastics in the wastewater was measured. It was calculated that the removal rate of polypropylene microplastics in the wastewater reached 85.8%.

[0049] Example 4

[0050] (1) Coconut shell fiber was washed and then oxidized using 1% hydrogen peroxide solution, with the pH value maintained at 6.5, the temperature at 50° C., and the reaction time being 2 hours.

[0051] (2) placing the functionalized coconut shell fiber in a Pseudomonas culture medium and culturing it at 37°C for 24 hours to form the first layer of biofilm;

[0052] (3) placing the coconut shell fiber with the first biofilm in a Candida culture medium and culturing at 37°C for 48 hours to form a second biofilm;

[0053] (4) The coconut shell fiber with the second biofilm was placed in a micrococcal culture medium and cultured at 37°C for 72 hours to form a third biofilm.

[0054] (5) adding 5 g / L of the coconut shell fiber composite material based on multilayer biofilm and surface functionalization treatment into wastewater containing 100 mg / L of polypropylene microplastics with a particle size of 10 μm to 100 μm;

[0055] (6) After stirring for 4 hours at a temperature of 25°C to 37°C, the amount of microplastics in the wastewater was measured. It was calculated that the removal rate of polypropylene microplastics in the wastewater reached 89.3%.

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

[0057] (1) Untreated coconut shell fiber was mixed with wastewater containing 100 mg / L of polypropylene microplastics with a particle size of 10 μm to 100 μm;

[0058] (2) After stirring for 4 hours at a temperature of 25°C to 37°C, the amount of microplastics in the wastewater was measured. It was calculated that the removal rate of polypropylene microplastics in the wastewater reached 43.8%, indicating that the untreated coconut shell fiber had a poor adsorption effect on microplastics.

[0059] Comparative Example 2: Removal of polyethylene microplastics by functionalized coconut shell fiber without biofilm

[0060] (1) Coconut shell fiber was washed and then oxidized using 1% hydrogen peroxide solution, with the pH value maintained at 6.5, the temperature at 50° C., and the reaction time being 2 hours.

[0061] (2) mixing the surface functionalized coconut shell fiber composite material 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°C to 37°C, the amount of microplastics in the wastewater was measured, and the removal rate of polyethylene microplastics in the wastewater was calculated to be 55.2%. Although functionalization treatment improves the adsorption capacity, the removal efficiency is limited in the absence of biofilm.

Claims

1. Surface functionalized coconut shell fiber, characterized in that: 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.

2. The surface functionalized coconut shell fiber according to claim 1, characterized in that The negatively charged functional groups on the surface of the coconut shell fiber are carboxyl and / or hydroxyl groups.

3. The surface functionalized coconut shell fiber according to claim 1, characterized in that The films formed by microorganisms attached to the surface of the coconut shell fiber are, from inside to outside, respectively: a first layer of film with adsorption capacity for microplastics, a second layer of film that increases the overall thickness and stability of the film, and a third layer of film that degrades microplastics.

4. The surface functionalized coconut shell fiber according to claim 1, characterized in that The films formed by microorganisms attached to the surface of the coconut shell fiber are respectively formed by Pseudomonas, Candida and Micrococcus from the inside to the outside.

5. The surface functionalized coconut shell fiber according to claim 4, characterized in that: The Pseudomonas is Pseudomonas veronii; the Candida is Candida tropicalis; and the Micrococcus is Micrococcus luteus.

6. The method for preparing the surface functionalized coconut shell fiber according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: S1, oxidizing the coconut shell fiber at a pH value of 6.5-7.0 and a temperature of 50° C. to introduce carboxyl groups and / or hydroxyl groups on the surface of the coconut shell fiber; S2, placing the coconut shell fiber treated by S1 in a Pseudomonas culture medium and culturing at 37°C for 20-28h to form the first layer of film on the surface; S3, placing the coconut shell fiber treated with S2 in a Candida culture medium and culturing at 37°C for 44-52 hours to form a second film on the surface; S4. Place the coconut shell fiber treated with S3 in a micrococcal culture medium and culture at 37°C for 68-76 hours to form a third layer of membrane on the surface.

7. The method for preparing surface functionalized coconut shell fiber according to claim 6, characterized in that: In S1, the coconut shell fiber is oxidized by using hydrogen peroxide with a volume fraction of 1%.

8. Use of the surface functionalized coconut shell fiber according to any one of claims 1 to 5 in removing microplastics from wastewater.

9. The use according to claim 8, characterized in that: At room temperature to 37°C, the surface functionalized coconut shell fiber is added into the wastewater to be treated at an amount of 3-7 g / L and stirred for 2-6 hours to complete the removal of microplastics in the wastewater.

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