Ultraviolet aging modified PBAT microplastics for inhibiting release of endogenous phosphorus in sediments in water bodies and preparation method thereof

Abstract

The present application relates to the technical field of water body ecological restoration, and particularly relates to a kind of ultraviolet aging modified PBAT microplastics for inhibiting endogenous phosphorus release in water body sediments and a preparation method thereof.The conventional method for inhibiting endogenous phosphorus release in water body sediments by using metal-based inorganic passivation material is difficult to overcome the risk of secondary pollution caused by the dissolution or reduction of metal-based passivation agent.In view of the above problems, the present application provides a kind of ultraviolet aging modified PBAT microplastics for inhibiting endogenous phosphorus release in water body sediments, which can regulate the abundance and steady-state metabolism of core iron-reducing functional bacteria groups such as improved bacillaceae in sediments, mediate the directional transformation of endogenous phosphorus forms, convert the easily released active phosphorus into bound phosphorus, thereby reducing the release of endogenous phosphorus and achieving a longer period of phosphorus control effect.Compared with traditional physical and chemical restoration methods, the present application can improve the instability of phosphorus fixation and the problem of phosphorus release rebound.The PBAT material used in the present application is completely biodegradable, and there is no persistent microplastic residue after the regulation period ends.

Description

Technical Field

[0001] This invention relates to the field of water body ecological restoration technology, specifically to a UV-aged modified PBAT microplastic that inhibits the release of endogenous phosphorus from sediments in water bodies and its preparation method. Background Technology

[0002] Eutrophication of lakes and rivers is one of the core long-standing problems in my country's water environment management. Despite continuous efforts to control external pollution discharge, many water bodies still frequently experience recurring algal blooms and water quality that is difficult to fundamentally improve. Extensive research and practice have shown that the continuous release of endogenous phosphorus accumulated in sediments into overlying water when environmental conditions change is a key contributing factor to recurring eutrophication. Even with effective control of external inputs, the release of endogenous phosphorus from sediments can maintain eutrophication in water bodies for decades.

[0003] Phosphorus in sediments does not exist in a single form; it exists in various forms, mainly including weakly adsorbed phosphorus, iron-aluminum bound phosphorus, calcium-bound phosphorus, and occluded phosphorus. Different forms of phosphorus differ significantly in their physicochemical properties and release risks, with weakly adsorbed phosphorus and iron-aluminum bound phosphorus being particularly sensitive to environmental changes. When redox conditions fluctuate, disturbance intensity changes, or microbial activity increases, these readily release phosphorus forms can easily re-enter interstitial water and migrate to overlying water via diffusion or convection, directly increasing the phosphorus concentration in the water. Therefore, effectively reducing the content of readily release phosphorus in sediments or promoting its conversion to stable bound forms is a key technological focus for endogenous pollution control.

[0004] Currently, the main remediation technology for endogenous phosphorus in sediments employs in-situ passivation methods. This involves adding inorganic passivating materials such as iron-based, aluminum-based, lanthanum-based, and calcium-based materials to the water body or sediment surface, relying on adsorption and precipitation to fix phosphates. While these metal-based passivating materials have seen some application in practical engineering, they have also revealed significant technical drawbacks. First, under anoxic conditions, iron-phosphate complexes are prone to reductive dissolution, leading to the release of fixed phosphates back into the water. Second, the application of some passivating agents may be accompanied by changes in the behavior of metal elements such as iron, manganese, cadmium, cobalt, and lead, posing a potential risk of secondary pollution. Studies have shown that commonly used passivating agents reduce the amount of phosphorus available to cyanobacteria in sediments by less than 58%, and although their inhibition rate of phosphorus release potential is higher than 75%, phytoplankton can still utilize some weakly adsorbed phosphorus in the sediment. Therefore, relying solely on chemical fixation strategies using metal-based materials suffers from a single mechanism, insufficient long-term effectiveness, and significant secondary risks.

[0005] To date, no relevant technical solutions have been found for using UV aging to modify PBAT microplastics or for controlling the release of endogenous phosphorus from sediments by controlling a specific carbonyl index range. Summary of the Invention

[0006] A problem with existing technologies is that conventional methods for suppressing the release of endogenous phosphorus from sediments in water using metal-based inorganic passivating materials struggle to overcome the risk of secondary pollution caused by the dissolution or reduction of the metal-based passivating agent. To address this issue, this invention provides a UV-aged modified PBAT microplastic for suppressing the release of endogenous phosphorus from sediments in water, the preparation method of which includes the following steps: (1) PBAT microplastics are washed with water, dried and then passed through a 100-200 mesh sieve to obtain pretreated PBAT; (2) Pretreated PBAT was subjected to ultraviolet irradiation to obtain UV-aged modified PBAT microplastics with a carbonyl index of 0.95 to 1.4.

[0007] The carbonyl index (CI) is used to characterize the degree of oxidation of PBAT microplastics after UV aging. Test method: Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) was used to detect PBAT microplastics before and after UV aging, and baseline correction was performed after spectral acquisition.

[0008] The carbonyl index is defined as: the peak area of ​​the characteristic absorption peak of the carbonyl group (C=O) of PBAT ester near 1720 cm⁻¹, divided by 1456 cm⁻¹. -1 The peak area of ​​the characteristic absorption peak of the stable CH reference is CI = A1720 / A1456.

[0009] Preferably, step (1) specifically includes the following steps: The PBAT microplastics are washed 2-3 times with deionized water, then air-dried in a ventilated place at room temperature. After drying, they are sieved using a 100-200μm standard sieve to obtain the final product.

[0010] Preferably, in step (2), the ultraviolet wavelength is 320–400 nm, the irradiation power is 60–70 W, and the irradiation intensity is 180–200 mW / cm². 2 The irradiation duration is 100–110 hours.

[0011] Preferably, the vertical irradiation distance is 4-6 cm.

[0012] A method for inhibiting the release of endogenous phosphorus from sediments in water bodies involves adding the aforementioned UV-aged modified PBAT microplastics as an inhibitor to the water body. The addition amount of UV-aged modified PBAT microplastics in the water body is 0.3-1.0 kg / m³. 2 .

[0013] Beneficial effects: (1) This invention utilizes UV-aged modified PBAT degradable microplastics to inhibit the release of endogenous phosphorus from aquatic sediments. These microplastics can regulate the abundance and homeostatic metabolism of core iron-reducing bacteria such as modified Bacillus in the sediments, mediating the directional transformation of endogenous phosphorus forms, converting readily releaseable reactive phosphorus into bound phosphorus, thereby reducing endogenous phosphorus release and achieving a longer-lasting phosphorus control effect. Compared to traditional physical and chemical remediation methods, this invention can improve the problems of unstable phosphorus fixation and phosphorus release rebound.

[0014] (2) The PBAT material used in this invention is completely biodegradable and leaves no persistent microplastic residue after the regulation cycle ends. At the same time, no exogenous metal agents are added throughout the process, which can avoid secondary pollution such as metal leaching and heavy metal activation in the sediment, and the water environment has good ecological compatibility.

[0015] (3) The raw materials of the present invention are easy to obtain, the modification and control process is simple, the operation is convenient, no complex equipment or harsh working conditions are required, the cost is low, the repeatability is good, and it is easy to scale up the subsequent process and apply it to the actual water environment remediation.

[0016] (4) The oxygen-containing functional groups generated by UV aging in this invention are accompanying products of interface regulation. They are not aimed at building adsorption sites. Unlike conventional UV modification, which focuses on enhancing adsorption as the main mechanism of phosphorus fixation, they have their own mechanism of action. Attached Figure Description

[0017] Figure 1 : These are SEM images of the UV-aged modified PBAT microplastics obtained in Example 1 (Figure b) and the commercially available PBAT microplastics in Comparative Example 1 (Figure a).

[0018] Figure 2 : These are the Fourier transform infrared spectra of the UV-aged modified PBAT microplastics obtained in Example 1 and the commercially available PBAT microplastics in Comparative Example 1.

[0019] Figure 3 This is a comparison of the relative abundance of modified Bacillus species obtained in Example 1 after UV aging modified PBAT microplastics, commercially available PBAT microplastics in Comparative Example 1, and blank control experimental group after 30 days of culture in a reactor.

[0020] Figure 4 This is a comparison of the endogenous phosphorus release inhibition rates of the UV-aged modified PBAT microplastics obtained in Example 1, the commercially available PBAT microplastics in Comparative Example 1, and the blank control group after 30 days of cultivation in a reactor. Detailed Implementation

[0021] The present invention will be described in detail below with reference to embodiments. However, it should be understood that the following embodiments are merely illustrative examples of implementation of the present invention and are not intended to limit the scope of the present invention.

[0022] The commercially available PBAT microplastic raw material used in the embodiments of this invention has a number average molecular weight Mn of 50,000 to 80,000 Da. Example 1 A UV-aged modified PBAT microplastic for inhibiting the release of endogenous phosphorus from sediments in water is prepared as follows: (1) Raw material pretreatment: Commercially available PBAT microplastics were washed three times with deionized water, air-dried at room temperature, and then screened through a 100μm standard sieve. The sieved particles were collected for later use. (2) Ultraviolet aging modification: A 70W ultraviolet mercury lamp was used as the irradiation source, and the irradiation intensity was set to 200mW / cm. 2 PBAT microplastics were continuously irradiated for 100 hours at a vertical irradiation distance of 5 cm to obtain UV-aged PBAT microplastics. The carbonyl index of the UV-aged PBAT microplastics was 1.2.

[0023] Example 2 is the same as Example 1, except that the pore size of the standard sieve in step (1) of Example 2 is 200 μm.

[0024] Example 3 is the same as Example 1, except that the irradiation time in Example 3 is 110 hours. The carbonyl index of the UV-aged modified PBAT microplastics is 1.35.

[0025] Comparative Example 1 is the same as Example 1, except that Comparative Example 1 is commercially available PBAT microplastics that have been sieved through a 100μm standard sieve without any modification.

[0026] Figure 1 The images show SEM images of the UV-aged modified PBAT microplastics obtained in Example 1 (Figure b) and the commercially available PBAT microplastics in Comparative Example 1 (Figure a).

[0027] Figure 2 The Fourier transform infrared spectra are those of the UV-aged modified PBAT microplastics obtained in Example 1 and the commercially available PBAT microplastics in Comparative Example 1.

[0028] Performance testing Sediment treatment: Several cylindrical plexiglass reactors, each 200mm in diameter and 600mm high, with open tops and sealed bottoms, were constructed. Surface sediments from a river channel were divided into several equal portions. One portion was injected into the bottom of the reactor, creating a 200mm thick layer of sediment. Overlying water, 10cm thick, was slowly added to the reactors using a siphon method to collect the sediment from the riverbed. The water flow was carefully controlled to avoid disturbing the surface sediments. Inhibitors were added according to the reactor surface area, specifically at 0.5kg / m². 2The inhibitors obtained in the examples and comparative examples were added to the corresponding reactors and incubated statically. The blank control refers to a reactor in which no endogenous phosphorus inhibitor was added. The concentration of soluble reactive phosphorus (SRP) in the overlying water was measured on day 0 and day 30. In this invention, surface sediment is defined as sediment extending 0-5 cm downwards from the interface between the sediment and overlying water. This layer is the most active area for endogenous phosphorus migration and transformation, as well as microbial activity, and is the main source of endogenous phosphorus release from rivers and lakes. Sediment samples were collected up to 0-5 cm.

[0029] Phosphorus content detection method: The total phosphorus concentration in the overlying water body was determined by the "Water Quality Ammonium Molybdate Spectrophotometric Method" (HJ 11893-89).

[0030] The formula for calculating the endogenous phosphorus release inhibition rate is as follows: .

[0031] Where η is the endogenous phosphorus release inhibition rate; C CK，0d C represents the concentration of soluble active phosphorus in the overlying water of the reactor on day 0 (as a blank control). CK，30d The concentration of soluble active phosphorus in the overlying water after 30 days of culture (as a control group); C exp，30d The concentration of soluble active phosphorus in the overlying water was measured during the 30-day culture period as an example.

[0032] Figure 3 This is a comparison of the relative abundance of modified Bacillus species obtained in Example 1 after UV aging modified PBAT microplastics, commercially available PBAT microplastics in Comparative Example 1, and blank control experimental group after 30 days of culture in a reactor.

[0033] Relative abundance test of *Modified Bacteria*: Sediment samples were collected after 30 days of culture and high-throughput amplicon sequencing of the 16S rRNA gene V3-V4 region was performed by Ling'en Testing Center. After quality control, noise reduction, and species annotation, the sequences were statistically analyzed at the family level. Relative abundance of *Modified Bacteria* = number of valid *Modified Bacteria* sequences in the sample ÷ total number of valid sequences of all bacteria in the sample × 100%.

[0034] Figure 4 This is a comparison of the endogenous phosphorus release inhibition rates of the UV-aged modified PBAT microplastics obtained in Example 1, the commercially available PBAT microplastics in Comparative Example 1, and the blank control group after 30 days of cultivation in a reactor.

[0035] The test results are shown in Table 1.

[0036] Table 1 In Examples 1-3, the UV-aged PBAT microplastics showed an inhibition rate of 13.8%-16.2% on the release of endogenous phosphorus from sediments, which was significantly better than Comparative Example 1 (addition of unaged microplastics), indicating that UV aging modification can effectively reduce the release of endogenous phosphorus.

[0037] The phosphorus inhibition rate of the unaged PBAT microplastics in Comparative Example 1 was only 1.1% to 2.7%, further demonstrating that the original microplastics without UV modification could not produce a significant phosphorus control effect, thus verifying the necessity of the UV aging modification step in this invention.

[0038] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A UV-aged modified PBAT microplastic for inhibiting the release of endogenous phosphorus from sediments in water, characterized in that, The preparation method includes the following steps: (1) PBAT microplastics are washed with water, dried and then passed through a 100-200 mesh sieve to obtain pretreated PBAT; (2) Pretreated PBAT was subjected to ultraviolet irradiation to obtain UV-aged modified PBAT microplastics with a carbonyl index of 0.95 to 1.

4.

2. The UV-aged modified PBAT microplastic for inhibiting the release of endogenous phosphorus from sediments in water, as described in claim 1, is characterized in that... Step (1) specifically includes the following steps: The PBAT microplastics are washed 2-3 times with deionized water, then air-dried in a ventilated place at room temperature. After drying, they are sieved using a 100-200μm standard sieve to obtain the final product.

3. The UV-aged modified PBAT microplastic for inhibiting the release of endogenous phosphorus from sediments in water, as described in claim 1, is characterized in that... In step (2), the ultraviolet wavelength is 320–400 nm, the irradiation power is 60–70 W, and the irradiation intensity is 180–200 mW / cm². 2 The irradiation duration is 100–110 hours.

4. The UV-aged modified PBAT microplastic for inhibiting the release of endogenous phosphorus from sediments in water, as described in claim 3, is characterized in that... The vertical irradiation distance is 4-6 cm.

5. The UV-aged modified PBAT microplastic for inhibiting the release of endogenous phosphorus from sediments in water, as described in claim 1, is characterized in that... The number-average molecular weight of the PBAT microplastic is Mn = 50,000 to 80,000 Da.

6. A method for inhibiting the release of endogenous phosphorus from sediments in water, characterized in that, The UV-aged modified PBAT microplastics obtained according to any one of claims 1-4 are added to the water as an inhibitor.

7. A method for inhibiting the release of endogenous phosphorus from sediments in water as described in claim 6, characterized in that, The addition amount of UV-aged modified PBAT microplastics in water is 0.3-1.0 kg / m³. 2 .

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