An anaerobic sludge-g-C3N4 composite material, its preparation method and application

Abstract

The application relates to the field of environmental function new materials and solid waste treatment technology, and discloses an anaerobic sludge-g-C3N4 composite material and a preparation method and application thereof. The method comprises the following steps: (1) dispersing anaerobic granular sludge in a phosphate buffer solution I to form a sludge culture solution; (2) contacting the sludge culture solution with a glutaraldehyde aqueous solution to perform a cross-linking reaction, and after the reaction, performing washing and drying to obtain cross-linking modified sludge; and (3) mixing the cross-linking modified sludge with g-C3N4 in the presence of a phosphate buffer solution II to perform a composite reaction, and then performing washing and drying to obtain the anaerobic sludge-g-C3N4 composite material. The anaerobic sludge-g-C3N4 composite material prepared by the method can efficiently degrade biodegradable plastics and simultaneously convert the biodegradable plastics into a methane energy source, so that the "waste treatment by waste" and energy recovery are realized.

Description

Technical Field

[0001] This invention relates to the fields of new environmental functional materials and solid waste treatment technology, specifically to an anaerobic sludge-g-C3N4 composite material, its preparation method, and its application. Background Technology

[0002] With the increasing prominence of environmental problems associated with traditional petroleum-based plastics, the production of biodegradable plastics, such as polylactic acid (PLA), polybutylene terephthalate (PBAT), and starch-based plastics, has grown rapidly. However, the degradation rate of these plastics in natural or conventional treatment environments remains slow, and their accumulation in waste treatment systems can easily lead to equipment blockage and aging, posing a serious challenge to their resource recycling.

[0003] Currently, there are two main technological pathways for the degradation of organic pollutants: photocatalysis and anaerobic biodegradation. Photocatalysis (using materials such as g-C3N4, TiO2, and CdS) can utilize light energy to deeply mineralize pollutants, making the process environmentally friendly. However, it typically suffers from limited catalytic efficiency, difficulties in catalyst recovery, and poor economic viability for direct mineralization of large-molecule plastics. Anaerobic biodegradation, on the other hand, can convert biodegradable organic matter into clean energy sources such as methane under anaerobic conditions, making it environmentally friendly. However, it requires high bioavailability of the substrate (such as plastics), has a long degradation cycle, and relatively low efficiency. Neither catalysis nor biodegradation alone can achieve an ideal balance between efficiency, cost, and resource recovery.

[0004] Combining catalytic materials with biomass carriers is a common strategy for improving catalytic performance. In existing technologies, the preparation of composite materials using sewage sludge as a raw material has been reported. For example, CN119951550A discloses a method for using sewage sludge as a carbon source, converting it into biochar through high-temperature pyrolysis with molten salt, and then combining it with g-C3N4. The g-C3N4 / biochar composite material obtained by this method exhibits enhanced photocatalytic activity and can be used for dye degradation or photocatalytic water splitting to produce hydrogen. However, this process involves high-temperature pyrolysis, which essentially involves the complete inorganic treatment of the sludge, aiming to utilize the carbon elements and inorganic mineral components in the sludge, while completely destroying any microbial activity that may exist in the sludge.

[0005] In attempts to construct microbial-material composite systems, traditional microbial immobilization methods, such as adsorption and encapsulation, are widely used due to their ease of operation. Adsorption relies on physical action to attach microorganisms to the carrier surface, while encapsulation traps cells within a gel network. However, these methods have significant limitations: adsorption methods exhibit weak binding forces, making microorganisms susceptible to detachment under fluid shear; encapsulation methods suffer from high mass transfer resistance, affecting substrate and product diffusion, and the carrier's mechanical strength and stability are insufficient. Furthermore, some chemical immobilization methods that provide stronger binding forces are often complex processes, and the chemical reagents used may significantly impact microbial activity, even causing cell damage, limiting their application in sensitive or high-activity strains.

[0006] Therefore, it is difficult to provide a composite material system that can stably support highly active microorganisms, synergistically achieve efficient photocatalytic function, and has a microorganism-friendly preparation process in order to address the dual challenges of degradation and resource utilization of biodegradable plastics. Summary of the Invention

[0007] The present invention aims to provide a composite material that can simultaneously and efficiently degrade biodegradable plastics and convert them into energy (such as methane), and overcome the problem of the difficulty in stable and efficient composite of photocatalytic materials and living microorganisms in the prior art.

[0008] To achieve the above objectives, the first aspect of the present invention provides a method for preparing anaerobic sludge-g-C3N4 composite material, comprising the following steps:

[0009] (1) Disperse the anaerobic granular sludge in phosphate buffer I to form a sludge culture medium;

[0010] (2) The sludge culture medium is contacted with glutaraldehyde aqueous solution to carry out a cross-linking reaction. After the reaction, it is washed and dried to obtain cross-linked modified sludge.

[0011] (3) In the presence of phosphate buffer II, the cross-linked modified sludge is mixed with g-C3N4 for composite reaction, and then washed and dried to obtain the anaerobic sludge-g-C3N4 composite material.

[0012] The second aspect of the present invention provides an anaerobic sludge-g-C3N4 composite material prepared by the preparation method described in the first aspect.

[0013] The third aspect of this invention provides the application of the anaerobic sludge-g-C3N4 composite material described in the second aspect in the degradation of biodegradable plastics and / or the recovery of methane.

[0014] Compared with the prior art, the present invention has at least the following beneficial effects:

[0015] 1. This invention constructs a synergistic system of "photocatalyst-live microorganisms". g-C3N4 generates active species under light irradiation, causing the plastic macromolecular chains to break down and generate smaller, more hydrophilic intermediates, which greatly improves the bioavailability and utilization rate of the substrate by subsequent anaerobic microorganisms, thereby significantly improving the overall degradation rate of plastics and methane conversion efficiency.

[0016] 2. This invention employs a glutaraldehyde crosslinking method to pre-modify sludge, forming a stable covalent network between microbial cells. This method exhibits stronger binding force than traditional adsorption methods, reducing the likelihood of microbial detachment; it also offers lower mass transfer resistance than encapsulation methods, facilitating substrate and product diffusion; furthermore, by controlling the glutaraldehyde concentration and reaction conditions, it can provide sufficient mechanical strength while maximizing microbial activity.

[0017] 3. This invention uses widely available anaerobic granular sludge and inexpensive g-C3N4 as the main raw materials, resulting in low cost. The entire preparation process is carried out in a room temperature or low temperature water bath, requiring no high temperature, high pressure, or complex equipment. It has low energy consumption, simple operation, mild conditions, and is easy to scale up for production.

[0018] 4. The composite material provided by this invention uses activated sludge as a carrier to achieve "waste-to-waste treatment". The main degradation products are CO2 and CH4, of which CH4 can be recovered as clean energy, making the entire process environmentally friendly. This material can not only be used to treat biodegradable plastics, but also provides a new approach for the energy recovery of other recalcitrant organic solid wastes. Attached Figure Description

[0019] Figure 1 This is a scanning electron microscope comparison image of the anaerobic sludge-g-C3N4 composite material, g-C3N4, and anaerobic granular sludge in a preferred embodiment of the present invention.

[0020] Figure 2 These are the flow cytometry test results of the anaerobic sludge-g-C3N4 composite material in the preferred embodiment of the present invention.

[0021] Figure 3 This is a biological transmission electron microscope comparison image of the anaerobic sludge-g-C3N4 composite material and anaerobic granular sludge in a preferred embodiment of the present invention.

[0022] Figure 4 This refers to the microbial activity of the anaerobic sludge-g-C3N4 composite material after it degrades plastic in a preferred embodiment of the present invention.

[0023] Figure 5 The degradation rate of different biodegradable plastics by the anaerobic sludge-g-C3N4 composite material in the preferred embodiment of the present invention;

[0024] Figure 6 This is the degradation effect of the anaerobic sludge-g-C3N4 composite material on plastics of different particle sizes in a preferred embodiment of the present invention;

[0025] Figure 7 This is a thermogravimetric analysis diagram of the degradation of 10mm particle size plastics by the anaerobic sludge-g-C3N4 composite material in a preferred embodiment of the present invention.

[0026] Figure 8 These are atomic force microscopy images of the anaerobic sludge-g-C3N4 composite material before and after the degradation reaction of 2mm particle size plastic in a preferred embodiment of the present invention.

[0027] Figure 9 This is a diagram illustrating the effect of anaerobic sludge-g-C3N4 composite material on the degradation and methanogenesis of PLA plastic in a preferred embodiment of the present invention. Detailed Implementation

[0028] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0029] As mentioned above, the first aspect of this invention provides a method for preparing anaerobic sludge-g-C3N4 composite material, comprising the following steps:

[0030] (1) Disperse the anaerobic granular sludge in phosphate buffer I to form a sludge culture medium;

[0031] (2) The sludge culture medium is contacted with glutaraldehyde aqueous solution to carry out a cross-linking reaction. After the reaction, it is washed and dried to obtain cross-linked modified sludge.

[0032] (3) In the presence of phosphate buffer II, the cross-linked modified sludge is mixed with g-C3N4 for composite reaction, and then washed and dried to obtain the anaerobic sludge-g-C3N4 composite material.

[0033] Preferably, in step (1), the amounts of the anaerobic granular sludge and the phosphate buffer solution I are controlled so that the sludge concentration (based on volatile solids) in the formed sludge culture medium is 10-50 g VS / L. Within this concentration range, it is possible to ensure that the sludge particles are fully dispersed to facilitate subsequent uniform cross-linking, while maintaining sufficient buffering capacity and nutrient concentration in the culture medium to ensure the activity of microorganisms during the pretreatment process.

[0034] Preferably, the method of the present invention further includes, in step (1), culturing the sludge culture medium at 35°C for 12-24 h, and then applying it to the crosslinking reaction in step (2).

[0035] In a preferred embodiment, in step (2), the concentration of the glutaraldehyde aqueous solution is 1-10 wt%, and the volume ratio of the glutaraldehyde aqueous solution to the mass ratio of the volatile solids in the anaerobic granular sludge is 25-50:1.

[0036] It should be noted that in the ratio of the volume of the glutaraldehyde aqueous solution to the mass of volatile solids in the anaerobic granular sludge, the volume of the glutaraldehyde aqueous solution is in mL, and the mass of volatile solids in the anaerobic granular sludge is in g.

[0037] More preferably, in step (2), the concentration of the glutaraldehyde aqueous solution is 2-5 wt%.

[0038] Preferably, in step (2), the washing and drying include: rinsing the product of the crosslinking reaction with phosphate buffer III until neutral, and then drying it in a vacuum oven at 35°C with a vacuum degree of 0.08-0.1 MPa (absolute pressure) for 8-24 hours.

[0039] Preferably, in this invention, the phosphate buffer I, the phosphate buffer II, and the phosphate buffer III are all phosphate buffers; and their concentrations are each independently 0.1-0.2M, and their pH is 7.0-8.0.

[0040] In a preferred embodiment, in step (2), the crosslinking reaction is carried out under stirring conditions, and at least the following conditions are met: temperature is 25-35℃, rotation speed is 150-250rpm, and reaction time is 4-15h.

[0041] According to a preferred embodiment, in step (3), the mass of g-C3N4 used is 0.1-10 times the mass of volatile solids in the crosslinked modified sludge.

[0042] In a preferred embodiment, in step (3), the composite reaction is carried out under stirring conditions and at least meets the following requirements: temperature of 30-37°C, rotation speed of 100-150 rpm, and reaction time of 8-24 h.

[0043] Preferably, in step (3), the washing and drying include: rinsing the product of the crosslinking reaction with phosphate buffer III until neutral, and then drying it in a vacuum oven at 35°C with a vacuum degree of 0.08-0.1 MPa (absolute pressure) for 8-24 hours.

[0044] According to a preferred embodiment, the anaerobic granular sludge is granular sludge produced by anaerobic digestion reactors in urban wastewater treatment plants and / or industrial wastewater treatment systems.

[0045] Preferably, the anaerobic granular sludge is taken from an anaerobic reactor used for treating high-concentration organic wastewater. It is anaerobic activated sludge from an anaerobic biological treatment tank.

[0046] More preferably, the anaerobic granular sludge is taken from the anaerobic reactor of a beer wastewater treatment plant.

[0047] Preferably, the total solids content of the anaerobic granular sludge is 10-20 wt% of the wet matter weight, the volatile solids content (VS / TS) is 40-80 wt% of the total solids, and the methanogenic activity is 200-280 L / kg VS.

[0048] As previously stated, the second aspect of the present invention provides an anaerobic sludge-g-C3N4 composite material prepared by the preparation method described in the first aspect.

[0049] In a preferred embodiment, g-C3N4 is loaded onto the surface and between the microbial communities of the anaerobic granular sludge in the composite material through a combination of physical adhesion and chemical cross-linking.

[0050] As previously stated, the third aspect of the present invention provides the application of the anaerobic sludge-g-C3N4 composite material described in the second aspect in the degradation of biodegradable plastics and / or the recovery of methane.

[0051] In a preferred embodiment, the biodegradable plastic includes at least one of polylactic acid, polybutylene terephthalate, and starch-based plastics.

[0052] Preferably, the application is carried out in an anaerobic environment, supplemented by suitable light conditions, to achieve photocatalytic-anaerobic biocoupled degradation.

[0053] The present invention will be described in detail below through examples. Unless otherwise specified, the raw materials used are all commercially available products.

[0054] Anaerobic granular sludge: from an anaerobic reactor in a brewery wastewater treatment plant, with a total solids content of 10 wt% of wet matter, a volatile solids content (VS / TS) of 50 wt% of total solids, and a methanogenic activity of 250 L / kg VS (measured by the specific methanogenic rate test (SMA) using sodium acetate as a carbon source).

[0055] Glutaraldehyde aqueous solution: concentration 5 wt%;

[0056] Phosphate buffer:

[0057] Phosphate buffer I: 0.2 M, pH 7.0;

[0058] Phosphate buffer II: 0.2M, pH 7.2;

[0059] Phosphate buffer III: 0.2M, pH 7.5;

[0060] g-C3N4: Powder with a purity of 99.998%, its XRD diffraction peak is 27.7, and its ultraviolet absorption peak is A=320. It was purchased from Hefei Keliao New Material Technology Co., Ltd., with the brand name Zhongke Material and the product number 100548.

[0061] Starch-based plastic: Fully biodegradable kitchen waste bags (mainly composed of starch, PLA and PBAT) purchased from Tianren Biotechnology flagship store, item number QT1905009L.

[0062] Example 1

[0063] This embodiment illustrates that the method for preparing anaerobic sludge-g-C3N4 composite material provided by the present invention is carried out according to the following steps:

[0064] (1) 15g of anaerobic granular sludge was dispersed in phosphate buffer I to obtain a sludge culture medium with a sludge concentration (based on volatile solids) of 35g VS / L;

[0065] (2) The sludge culture medium was cultured at 35°C for 24 hours and then contacted with 20 mL of glutaraldehyde aqueous solution for 10 hours (at 35°C) under stirring at 200 rpm. After the reaction, the sludge was washed and dried. The product of the crosslinking reaction was washed with phosphate buffer III until neutral and then dried in a vacuum oven at 35°C under an absolute pressure of 0.1 MPa for 12 hours to obtain crosslinked modified sludge. The volatile solids in the anaerobic granular sludge were 15 g × 10 wt% × 50% = 0.75 g, and the volume ratio of glutaraldehyde aqueous solution to the volatile solids in the anaerobic granular sludge was 20 mL: 0.75 g ≈ 26.7: 1.

[0066] (3) Under stirring conditions of 35°C and 120 rpm, the cross-linked modified sludge was mixed with 0.15 g of g-C3N4 and phosphate buffer II was added for a composite reaction for 12 h.

[0067] After washing and drying: the product of the crosslinking reaction was washed with phosphate buffer III until neutral, and then dried in a vacuum oven at 35°C under an absolute pressure of 0.1 MPa for 12 h; the anaerobic sludge-g-C3N4 composite material was obtained and named P1.

[0068] Figure 1 The image shows SEM images characterizing the morphology of g-C3N4, anaerobic granular sludge, and composite material P1 using scanning electron microscopy (SEM). Figure 1 As can be seen, the surface morphology of anaerobic granular sludge and g-C3N4 are completely different, and the SEM of composite material P1 confirms the successful loading of sludge microorganisms from the morphological perspective.

[0069] To further verify the loading conditions, flow cytometry was performed on P1 and anaerobic granular sludge. Figure 2 The flow cytometry results for P1 are shown. As can be seen in the figure, the activity of microorganisms in composite material P1 is roughly the same compared with anaerobic granular sludge, thus proving that the microorganisms were successfully loaded.

[0070] Figure 3 The images show a comparison of biological transmission electron microscopy (TEM) images of anaerobic granular sludge and P1, showing that the outlines and sizes of the anaerobic microorganisms remain essentially unchanged.

[0071] Example 2

[0072] This embodiment uses a method similar to that of Embodiment 1, except that in step (3), the mass of g-C3N4 used is 0.2g;

[0073] Finally, the anaerobic sludge-g-C3N4 composite material was obtained and named P2.

[0074] Example 3

[0075] This embodiment uses a method similar to that of Embodiment 1, except that in step (3), the mass of g-C3N4 used is 0.3g;

[0076] Finally, the anaerobic sludge-g-C3N4 composite material was obtained and named P3.

[0077] Example 4

[0078] This embodiment uses a method similar to that of Example 1, except that in step (2), the amount of glutaraldehyde aqueous solution used is 25 mL;

[0079] Finally, the anaerobic sludge-g-C3N4 composite material was obtained and named P4.

[0080] Example 5

[0081] This embodiment uses a method similar to that of Embodiment 1, except that in step (1), the mass of anaerobic granular sludge used is 20g.

[0082] Furthermore, in step (2), the amount of the glutaraldehyde aqueous solution used is 25 mL;

[0083] Finally, the anaerobic sludge-g-C3N4 composite material was obtained and named P5.

[0084] Application Example 1

[0085] Application of photocatalytically coupled biodegradable plastics in the anaerobic sludge-g-C3N4 composite material P1 prepared in the above examples:

[0086] Starch-based plastic simulated wastewater was used as the target for the degradation reaction. The parameters and conditions for the degradation reaction are as follows:

[0087] Add 80 mL of starch-based plastic simulated wastewater to each 180 mL serum bottle, then purge the reactor with N2 at a pressure of 0.4 MPa for 5 min to remove internal O2. Then, compact and seal the bottle opening with a rubber stopper and iron sheet to carry out the degradation reaction under anaerobic conditions.

[0088] The pH of the simulated wastewater from starch-based plastics was 9 (pH adjusted using 0.1M NaOH).

[0089] The particle size of starch-based plastics is 10 mm.

[0090] The dosage of anaerobic sludge-g-C3N4 composite material is 5g;

[0091] The ultraviolet light used for photocatalysis has a wavelength of 395 nm and an irradiance of 100 mW / cm². 2 The photocatalytic reaction time is 6 hours of light irradiation followed by 6 hours of dark reaction, and the cycle is repeated.

[0092] The degradation reaction temperature was 35℃, the reaction time was 21 days, and the rotation speed of the constant temperature shaking water bath was 120 rpm.

[0093] After the degradation reaction, the samples were removed and their activity was assessed using flow cytometry. Figure 4 The activity of microorganisms in P1 after the degradation reaction is shown in the figure. As can be seen from the figure, the microbial mortality rate is no more than 50%, and the decrease before and after degradation is no more than 30%, which confirms the operational feasibility of the composite material preparation scheme.

[0094] Application Example 2

[0095] A comparison of the application of the anaerobic sludge-g-C3N4 composite materials P1, P2, and P3 prepared in the above examples with g-C3N4 and anaerobic granular sludge in photocatalytic coupling with biodegradable plastics:

[0096] Simulated wastewater containing PLA, PBAT, and starch-based plastics were used as the subjects of the degradation reaction. The TOC concentration in the simulated wastewater before and after the degradation reaction was measured using a total organic carbon (TOC) analyzer. The parameters and conditions for the degradation reaction included:

[0097] Add 80 mL of PLA simulated wastewater, PBAT simulated wastewater and starch-based plastic simulated wastewater to 180 mL serum bottles respectively. Then purge the reactor with N2 at a pressure of 0.4 MPa for 5 min to remove the internal O2. Then compact and seal the bottle mouth with rubber stopper and iron sheet to carry out the degradation reaction in an anaerobic environment.

[0098] The pH of the three simulated wastewaters was set to 9 (pH adjusted using 0.1M NaOH), and the dosages of PLA, PBAT, and starch-based plastics in each of the three simulated wastewaters were controlled to ensure that their initial TOC concentrations were 30 mg·L⁻¹. -1 20 mg·L -1 and 40 mg·L -1 The total organic carbon (TOC) concentration in the simulated wastewater before and after the degradation reaction was measured using a total organic carbon (TOC) analyzer. The corresponding formula for calculating the degradation rate of the plastic is as follows:

[0099] Degradation rate (%) = (Initial TOC concentration - Final TOC concentration) / Initial TOC concentration × 100%;

[0100] PLA, PBAT, and starch-based plastics all have a particle size of 100 μm;

[0101] The dosage of anaerobic sludge-g-C3N4 composite material is 5g;

[0102] The ultraviolet light used for photocatalysis has a wavelength of 395 nm and an irradiance of 100 mW / cm². 2 The photocatalytic reaction time is 6 hours of light irradiation followed by 6 hours of dark reaction, and the cycle is repeated.

[0103] The degradation reaction temperature was 35℃, the reaction time was 21 days, and the rotation speed of the constant temperature shaking water bath was 120 rpm.

[0104] Figure 5 The degradation rates of different biodegradable plastics by the composite materials are shown. As can be seen from the figure, P1, P2, and P3 exhibit significantly higher degradation efficiencies for PLA, PBAT, and starch-based plastics than g-C3N4 or anaerobic granular sludge alone.

[0105] Application Example 3

[0106] This application example uses a method similar to that of Application Example 2 to perform a conventional commercial biodegradable plastic (starch-based plastic) degradation reaction on the anaerobic sludge-g-C3N4 composite materials P4 and P5 prepared in the above examples. The difference is that:

[0107] The dosage of anaerobic sludge-g-C3N4 composite material is 10g;

[0108] The particle sizes of the starch-based plastics to be degraded are 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm and 10mm.

[0109] The pH of the simulated wastewater containing starch-based plastics was 8.5 (adjusted using 0.1M NaOH), and the initial mass of the starch-based plastics was 0.2g.

[0110] Figure 6 The degradation effect of composite material P4 on starch-based plastics with different particle sizes is shown. The figure reveals significant structural changes in the plastics during degradation: as the plastic particle size decreases, the characteristic peaks of key functional groups detected by Fourier transform infrared spectroscopy (FT-IR) (representing ester bonds in the plastic backbone (OC=O, approximately 1180 cm⁻¹) increase. -1 ), PLA component characteristic methyl group (PLA-CH3, approximately 1450 cm⁻¹) -1 ) and aromatic CH bonds in PBAT (approximately 800-700 cm -1 The intensity gradually decreased, indicating that the degradation was deepening. Meanwhile, at approximately 1700-1720 cm... -1 The absorption peak intensity representing the ketone group (C=O) is significantly enhanced, indicating that the degradation process is accompanied by an oxidation reaction, forming a new carbonyl functional group as an intermediate product after polymer chain breakage. In summary, the degradation of plastics involves chain breaking, primarily ester bond cleavage, and oxidation reactions, leading to the gradual decomposition of large polymer molecules into smaller molecular fragments.

[0111] After the degradation reaction was complete, the composite material was separated by centrifugation and sieving. It was then washed three times with deionized water and vacuum dried for 24 hours at 35°C and 0.8 MPa. The mass was weighed on a balance and compared with the mass of the plastic before degradation. The mass loss rate (%) of the plastic was calculated, and the optimal degradation group was screened for thermogravimetric analysis to characterize its degradation effect.

[0112] To simulate the situation of biodegradable plastics mixed in during actual wet waste treatment, Figure 7 Thermogravimetric analysis (TGA) curves of composite material P5 for degradation of starch-based plastics with a particle size of 10 mm are shown. Figure 7 (a) shows the thermogravimetric (TG) diagrams of the plastic before degradation and the plastic after photocatalytic anaerobic degradation. Figure 7(b) is a differential scanning calorimeter (DSC) of the plastic before degradation and the plastic after photocatalytic anaerobic degradation. Figure 7 As can be seen, the thermal stability and crystallinity of the plastic change after degradation. The TG curve shows that the proportion of residues increases at high temperatures after degradation, which may indicate changes in molecular weight distribution or relative enrichment of non-volatile components. More importantly, DSC analysis shows that the melting temperature and enthalpy of the plastic increase after degradation, which clearly indicates a significant increase in the crystallinity of the material. This is usually due to the preferential removal of amorphous regions during degradation, making it easier for the remaining plastic segments to form a more complete crystal structure.

[0113] Figure 8 Atomic force microscopy (AFM) image showing the degradation effect of composite material P5 on starch-based plastic with a particle size of 2 mm. Figure 8 In the diagram, (a1), (a2), and (a3) ​​are morphological change diagrams of three cross-sections of the plastic before degradation. (a1) is a top view of the overall morphology of the plastic before degradation, (a2) is a 3D scan of the material, and (a3) ​​is a diagram showing the change in height (nm) as a function of distance (μm) for the three longitudinal sections taken in (a1). Similarly, (b1), (b2), and (b3) are morphological change diagrams of three cross-sections of the plastic after degradation. (b1) is a top view of the overall morphology of the plastic after degradation, (b2) is a 3D scan of the material, and (b3) is a diagram showing the change in height (nm) as a function of distance (μm) for the three longitudinal sections taken in (b1). Figure 8 This indicates that significant surface erosion and morphological changes occurred during the degradation of the plastic. Larger surface features were broken down or worn away, resulting in a finer, more uniform surface structure, which is consistent with the breaking of polymer chains and the dissolution / removal process of the material.

[0114] Application Example 4

[0115] This application example illustrates the use of the anaerobic sludge-g-C3N4 composite material prepared according to the present invention in methane recovery:

[0116] First, using a method similar to that in Application Example 2, the anaerobic sludge-g-C3N4 composite material P4 prepared in the above example was subjected to a degradation reaction on simulated PLA wastewater. The difference is that:

[0117] The initial mass of PLA in the simulated wastewater was 0.08 g;

[0118] PLA has a particle size of 50 μm;

[0119] The dosage of anaerobic sludge-g-C3N4 composite material is 10g.

[0120] After the degradation reaction, the gas produced by the anaerobic system was collected periodically using a syringe and a gas bag, and the volume was measured. The methane content was then determined by gas chromatography-TCD.

[0121] Comparative experiments were conducted on g-C3N4, anaerobic granular sludge, and a composite material composed of the two under dark reaction conditions and under ultraviolet light irradiation. Figure 9 The diagram shows the effect of composite material P4 on the degradation of plastic PLA and the production of methane. The carbon source available to the methanogenic microorganisms comes entirely from the degradation of PLA. Therefore, methane is used to characterize the degradation effect of PLA.

[0122] Figure 9 The results show that g-C3N4 alone produces almost no methane under both dark reaction and UV irradiation conditions. Under dark reaction conditions, the methane production of the g-C3N4-anaerobic sludge composite material is only 7.9% higher than that of anaerobic granular sludge, indicating that the synergistic effect of the composite material is limited under light-free conditions. Notably, UV irradiation promotes the production of anaerobic granular sludge itself, increasing its methane production by 28.4%. Under UV irradiation, the anaerobic sludge-g-C3N4 composite material exhibits a strong photocatalytic-biological synergistic effect, with a cumulative methane production of 174.36 L / kg VS, representing a 74.0% increase compared to the dark reaction conditions and a 46.2% increase compared to the anaerobic granular sludge alone under light conditions. This indicates that the photogenerated electrons produced by g-C3N4 as a photocatalyst under UV excitation can effectively promote electron transfer and metabolic activity of methanogenic bacteria, forming a significant photocatalytic-microbial synergistic methanogenesis system with anaerobic granular sludge, thus greatly improving the system's methanogenesis efficiency. This also confirms the reinforcing effect of composite materials on degradation.

[0123] The above experimental results show that the anaerobic sludge-g-C3N4 composite material provided by the present invention can not only achieve efficient degradation and energy conversion (methane production) of biodegradable plastics through the coupling effect of photocatalysis and biodegradation, but also its preparation method is mild and the raw materials are cheap and readily available, showing good prospects for practical application.

[0124] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing an anaerobic sludge-g-C3N4 composite material, characterized in that, Includes the following steps: (1) Disperse the anaerobic granular sludge in phosphate buffer I to form a sludge culture medium; (2) The sludge culture medium is contacted with glutaraldehyde aqueous solution to carry out a cross-linking reaction. After the reaction, it is washed and dried to obtain cross-linked modified sludge. (3) In the presence of phosphate buffer II, the cross-linked modified sludge is mixed with g-C3N4 for composite reaction, and then washed and dried to obtain the anaerobic sludge-g-C3N4 composite material. In step (2), the concentration of the glutaraldehyde aqueous solution is 1-5 wt%, and the volume ratio of the glutaraldehyde aqueous solution to the mass ratio of the volatile solids in the anaerobic granular sludge is 25-50:

1. The volume of the glutaraldehyde aqueous solution is in mL, and the mass ratio of the volatile solids in the anaerobic granular sludge is in g. In step (3), the mass of g-C3N4 used is 0.1-10 times the mass of volatile solids in the crosslinked modified sludge.

2. The preparation method according to claim 1, characterized in that, In step (2), the crosslinking reaction is carried out under stirring conditions and at least meets the following requirements: temperature of 25-35℃, rotation speed of 150-250rpm, and reaction time of 4-15h.

3. The preparation method according to claim 1 or 2, characterized in that, In step (3), the composite reaction is carried out under stirring conditions and at least meets the following requirements: temperature of 30-37℃, rotation speed of 100-150rpm, and reaction time of 8-24h.

4. The preparation method according to claim 1 or 2, characterized in that, The anaerobic granular sludge is granular sludge produced by anaerobic digestion reactors in urban wastewater treatment plants and / or industrial wastewater treatment systems.

5. An anaerobic sludge-g-C3N4 composite material prepared by the preparation method according to any one of claims 1-4.

6. The application of the anaerobic sludge-g-C3N4 composite material according to claim 5 in the degradation of biodegradable plastics and / or the recovery of methane.

7. The application according to claim 6, characterized in that, The biodegradable plastics include at least one of polylactic acid, polybutylene terephthalate (PET), and starch-based plastics.

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