Core-shell structure composite cathode material Fe (at) Co / GF, bio-electro-Fenton system, preparation method and application

Abstract

The invention provides a core-shell structure composite cathode material Fe (at) Co / GF, a biological electro-Fenton system, a preparation method and application. When the Fe-coated Co / GF composite cathode is applied to a BEF system, the yield of H2O2 can be better improved, more. OH is generated, extracellular ARGs are directly oxidized, intracellular DNA molecules are oxidized after a cell structure is destroyed, and the Fe-coated Co cathode catalyzes and promotes growth of microorganisms such as L.virens and Nitrospirillum and the like, so that the yield of H2O2 is improved. The abundance of bioanabolism, degradation / utilization / assimilation metabolism, detoxification metabolism, precursor metabolite and energy metabolism of the microorganisms is increased, so that the growth of main host proteobacteria and bacteroides microorganisms of the ARGs is inhibited or killed, the abundance of the ARGs and the MGEs is reduced due to the physical adsorption effect of the inner wall of the reactor and the cathode carbon felt on the free-state ARGs and the MGEs, and the growth of the ARGs and the MGEs is inhibited. The ecological risk of the ARGs can be effectively reduced.

Description

Technical Field

[0001] The present invention relates to the field of water pollution control, and in particular to a core-shell structure composite cathode material Fe@Co / GF, a bioelectric Fenton system, a preparation method and an application thereof. Background Art

[0002] With the growing demand for antibiotics in human medicine, animal husbandry and other industries. The overuse of antibiotics has not only caused environmental pollution, but also led to the high density of antibiotic-resistant bacteria (ARB) and the massive production of antibiotic resistance genes (ARGs). ARGs are considered to be an important emerging pollutant that can spread between pathogens through the horizontal transfer of mobile genetic elements, further transmitting antibiotic resistance, reducing or eliminating the effectiveness of antibiotics in treating diseases, and posing a major threat to public health. The main sources of ARGs in the environment are sewage and excess sludge in sewage treatment plants. Excess sludge is a by-product produced in the biological sewage treatment process. Its composition structure includes microorganisms and extracellular micropolymers. Microorganisms are further subdivided into extracellular polymers (EPS) and bacterial cells ( Figure 1 EPS is a complex polymer mixture existing outside the cells of microbial aggregates. It is composed of a variety of organic macromolecules such as proteins, polysaccharides, humus, nucleic acids, lipids and uronic acid, which are aggregated by dispersion force, electrostatic force, hydrogen bond, hydrophobic effect and other forms. Figure 2 ). Therefore, organic matter in sludge is mainly distributed in EPS, and there are many types, complex components, high molecular weight, and difficult to degrade. Organic pollutants such as antibiotics, dyes, and phenol are pure substances or simple mixtures with fixed and simple molecular structures, and cannot be directly linked to the complex structure of sludge organic matter.

[0003] Sewage treatment plants are the largest source of ARGs. ARGs enter the natural world with effluent and residual sludge. At present, the removal processes for ARGs include biological treatment, disinfection process, and composite process. Among them, the commonly used biological treatment technology is the activated sludge method. The mechanism of removing ARGs by the activated sludge method is that under high-load activated sludge, the activated sludge will adsorb a large amount of ARGs in the sewage. After treatment by the activated sludge method, the abundance of ARGs is reduced by 2-3 orders of magnitude. Since the activated sludge adsorbs the ARGs in the sewage, a large number of ARGs are enriched in the residual sludge. It is urgent to develop economical and efficient treatment methods to effectively remove sludge ARGs. In addition, mobile genetic elements (MGEs) are important genetic materials that carry ARGs and are carriers of ARGs transmission and diffusion. The effective removal of MGEs is of great significance to inhibiting the proliferation of ARGs and reducing the pollution risk of ARGs to the environment. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a method for removing antibiotic resistance genes in sludge by a bio-electro-Fenton method, wherein a Fe@Co catalyst cathode is adopted. The composite catalyst reduces the resistance of electron transfer and improves the efficiency of electron transfer; its special core-shell structure increases the amount of electron transfer; the application of the Fe@Co / GF composite cathode in the BEF system can better improve the yield of H2O2, activate H2O2 to generate more ·OH, have better degradation potential for sludge ARGs, and can effectively reduce the ecological risks of ARGs.

[0005] To achieve the above object, the present invention provides the following technical solutions: a core-shell structure composite cathode material Fe@Co / GF, which is obtained by in-situ growth of a core-shell structure Fe@Co catalyst on a graphite felt GF;

[0006] The Fe@Co catalyst is composed of Fe2O3 nanoparticles constituting the shell structure of the material, and a Fe-CoO mixture constituting the core structure of the material;

[0007] The Fe-CoO mixture has an Fe content of 58.76%-62.38%, a Co content of 20.81%-23.59%, and an O content of 14.62%-16.01%.

[0008] Furthermore, the core-shell structure composite cathode material Fe@Co / GF is prepared by the following method:

[0009] S1: Pretreatment of graphite felt GF: soaking the graphite felt GF in acetone solution, washing with deionized water, soaking in concentrated HNO3 solution, washing with deionized water, and then drying the graphite felt GF to complete the pretreatment of the graphite felt GF;

[0010] S2: Place the graphite felt GF pretreated in step S1 into a 3+ and Co 2+ The mixture was ultrasonically treated, then immersed in potassium borohydride solution, and washed with ethanol and deionized water to obtain a core-shell structured composite cathode material Fe@Co / GF.

[0011] Further, in step S1, the graphite felt GF is soaked in a 1 mol / L acetone solution for 12 hours, taken out and rinsed with deionized water for 2-3 times, then soaked in a concentrated HNO3 solution for 2 hours, taken out and rinsed with deionized water for 2-3 times, and finally dried in an oven at 105°C for use.

[0012] Further, in step S2, the Fe 3+ and Co 2+The mixed solution is formed by mixing FeCl3·6H2O and CoCl2·6H2O, wherein the molar ratio of FeCl3·6H2O to CoCl2·6H2O is 3:1;

[0013] And / or, the concentration of the potassium borohydride solution is 15-20 g / L, and the potassium borohydride solution is slowly added at a speed of 0.5-1.0 mL / min;

[0014] The ultrasonic treatment time is 30-60min;

[0015] The soaking time is 2-4 hours.

[0016] To achieve the above-mentioned purpose, the present invention also provides the following technical solution: a bioelectric Fenton system, comprising the core-shell structure composite cathode material Fe@Co / GF.

[0017] To achieve the above object, the present invention also provides the following technical solution: a method for constructing the bioelectric Fenton system, comprising the following steps:

[0018] It includes an anode chamber and a cathode chamber, which are separated by a proton exchange membrane, with graphite felt as the anode, a core-shell structure composite cathode material Fe@Co / GF as the cathode, titanium wire as the conductor in the external circuit, and an aeration device is arranged outside the cathode chamber; the anode and the cathode are connected through the external circuit, and a 100-1000Ω resistor is connected in series as the external circuit load to form a bioelectric Fenton system.

[0019] Furthermore, the anode is pretreated graphite felt, and the processing method of the graphite felt is:

[0020] The graphite felt is sequentially soaked in acetone solution, washed with deionized water, soaked in concentrated HNO3 solution, washed with deionized water, and then dried to complete the pretreatment of the graphite felt GF.

[0021] Furthermore, the volume ratio of the anode chamber to the cathode chamber is 1:1.

[0022] To achieve the above object, the present invention also provides the following technical solution: The method for removing antibiotic resistance genes in sludge using the bioelectric Fenton system comprises the following steps:

[0023] Anaerobic sludge and sodium acetate solution are mixed as the filler of the anode chamber, so that electroactive microorganisms are attached to and grown on the anode surface. Cathodic liquid is injected into the cathode chamber. The cathode liquid in the cathode chamber is replaced at set intervals until the system voltage is constant. Anaerobic sludge with a pH of 3.0±0.1 is added to the cathode chamber to replace the cathode liquid. The reaction is carried out for a specific time to achieve the removal of antibiotic resistance genes in the sludge.

[0024] Furthermore, 0.1 mol / L H2SO4 solution was added to the cathode chamber to adjust the pH of the sludge to acidic.

[0025] Furthermore, the water content of the anaerobic sludge is above 98%, and the anaerobic sludge contains at least one of sulfonamide resistance genes, tetracycline resistance genes, macrolide resistance genes, β-lactam resistance genes, and aminoglycoside resistance genes.

[0026] Furthermore, the anaerobic sludge is the sludge after the ARGs in the sewage are adsorbed by the sewage treatment plant. The organic matter in the sludge is mainly extracellular polymers (EPS), which are composed of high molecular polymers such as polysaccharides, glycoproteins, nucleic acids, lipids and humic acid. Before breaking the cell wall of the microorganism, the EPS structure needs to be broken first. It can be seen that if the resistance genes in the cells in the sludge are to be destroyed, the EPS structure needs to be broken. In the process of EPS destruction, a large number of resistance genes are degraded, and then the cell wall and cell membrane are further broken, and the genetic material in the cell is reacted to break and degrade the resistance genes.

[0027] The treatment mechanism of removing antibiotic resistance genes in sludge based on the bioelectric Fenton system involved in the present invention is:

[0028] First, the electrogenic bacteria on the anode produce protons and electrons when oxidizing organic matter. The protons and electrons are transferred to the cathode through an external circuit and react with O2 to generate H2O2 in situ. The core-shell Fe@Co catalyst evenly distributed on the composite cathode surface promotes electron transfer between catalyst gaps due to low interfacial resistance, thereby greatly improving the yield of H2O2. High H2O2 concentration can destroy the cell membrane, thereby inhibiting the growth of microorganisms and further inhibiting the horizontal transfer of ARGs. At the same time, Fe 2+ Dissolved from the catalyst, it reacts with H2O2 to generate hydroxyl radical ·OH. 2+ Similar, Co 2+ A Fenton-like reaction can also occur at the cathode, activating the decomposition of H2O2 to generate OH. Based on the standard reduction potential of metals, it is believed that Fe 2+ / Fe 3+ and Co 3+ / Co 2+ The conversion of ·OH can realize the closed valence cycle of bimetallic, thereby further promoting the production of ·OH. The high H2O2 yield will also promote the system to generate more ·OH. ·OH can directly oxidize extracellular ARGs, or destroy the cell structure and then oxidize intracellular DNA molecules, while also inhibiting the horizontal transfer of ARGs.

[0029] Secondly, the catalytic action of the Fe@Co catalytic cathode promoted the growth of Chloroflexi, Nitrospira, Firmicutes and Actinobacteria, further increasing the abundance of biosynthetic metabolism, degradation / utilization / assimilation metabolism, detoxification metabolism, precursor metabolites and energy metabolism of these microorganisms, and reducing the abundance of glycan metabolism, macromolecular modification metabolism and metabolome. The changes in these metabolic processes inhibited or killed the growth of Proteobacteria and Bacteroidetes microorganisms in the sludge, and since these types of microorganisms are the main hosts of ARGs, the total abundance of ARGs decreased.

[0030] In addition, the physical adsorption of the reactor inner wall and cathode carbon felt is also the reason for the reduction in the abundance of ARGs and MGEs.

[0031] In summary, the present invention has the following beneficial effects:

[0032] First, the present invention uses Fe@Co catalyst cathode to activate H2O2 to generate ·OH, thereby improving the pollutant degradation performance of the BEF system. The composite catalyst reduces the resistance of electron transfer and improves the efficiency of electron transfer; its special core-shell structure increases the amount of electron transfer; and there is a synergistic effect between Fe and Co. Based on the advantages of Fe@Co catalyst, the application of Fe@Co / GF composite cathode in the BEF system can better improve the yield of H2O2, activate H2O2 to generate more ·OH, have better degradation potential for sludge ARGs, and can effectively reduce the ecological risks of ARGs;

[0033] Second, the catalytic effect of the Fe@Co catalytic cathode promoted the growth of Chloroflexi, Nitrospira, Firmicutes and Actinobacteria, further increasing the abundance of these microorganisms' biosynthetic metabolism, degradation / utilization / assimilation metabolism, detoxification metabolism, precursor metabolites and energy metabolism, and reducing the abundance of glycan metabolism, macromolecular modification metabolism and metabolome. Changes in these metabolic processes inhibited or killed the growth of Proteobacteria and Bacteroidetes microorganisms in the sludge. Since these types of microorganisms are the main hosts of ARGs, the total abundance of ARGs decreased;

[0034] Third, the absolute abundance of ARGs was effectively reduced after treatment with the Fe@Co / GF-BEF system, and the degradation rate of total ARGs was 70.55%, which reduced the ecological pollution risk of ARGs.

[0035] Fourth, the physical adsorption of free ARGs and MGEs inside the bioelectric Fenton system and on the cathode carbon felt reduces the abundance of ARGs and MGEs;

[0036] Fifth, the Fe@Co / GF-BEF system reduced the abundance of MGEs, inhibited the further spread of ARGs in the environment, and reduced the risk of ARGs pollution transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0038] Figure 1 It is a schematic diagram of sludge structure in the prior art;

[0039] Figure 2 It is a schematic diagram of the structure of bacterial cells and extracellular polymers in the prior art;

[0040] Figure 3 SEM (magnification, a: 100 times; b: 10000 times), TEM and XPS images of GF and Fe@Co / GF composite cathode in the embodiment;

[0041] Figure 4 The distribution of ARGs and MGEs in sludge after treatment with different BEF systems;

[0042] Figure 5 The effects of catalyst and O2 on the removal of ARGs in the BEF system of the embodiment of the present invention (the effects of catalyst and O2 on MGEs and total ARGs a, b; the effects of catalyst and O2 on various types of ARGs c, d);

[0043] Figure 6 is the change of hydroxyl radical concentration in the cathode chamber of the GF-BEF system and the Fe@Co / GF-BEF system of the present invention;

[0044] Figure 7 The heat map of the dominant microbial flora in the raw mud (RS), TQ-BEF, the Fe@Co / GF-BEF system of the present invention, and the GF-BEF system;

[0045] Figure 8 It is the principal component analysis diagram of microbial communities among RS, TQ-BEF, Fe@Co / GF-BEF system of the present invention, and GF-BEF system;

[0046] Fig. 9 is the network relationship diagram of ARGs, MEGs and bacterial genera;

[0047] Fig.10The metabolic pathway changes of sludge microorganisms in RS, TQ-BEF, Fe@Co / GF-BEF system of the present invention, and GF-BEF system;

[0048] Fig.11 This is a diagram showing the mechanism of reducing sludge ARGs by the Fe@Co / GF-BEF system of the present invention. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described below using a small laboratory test as an example. Based on the embodiments of the present invention, the process can be enlarged proportionally when enlarged, and all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] Example of a Bioelectric Fenton System

[0051] The method for constructing a bioelectric Fenton system involved in the present invention comprises the following steps:

[0052] (1) Preparation of core-shell structure composite cathode material Fe@Co / GF:

[0053] S1: Pretreatment of graphite felt GF: soak the graphite felt GF in 1 mol / L acetone solution for 12 hours, take it out and rinse it with deionized water twice, then soak it in concentrated HNO3 (mass fraction 68%) solution for 2 hours, take it out and rinse it with deionized water twice, and finally dry it in an oven at 105°C for use;

[0054] S2: The graphite felt GF pretreated in step S1 was placed in a mixed solution of FeCl3·6H2O (concentration of 7.5mmol / L) and CoCl2·6H2O (concentration of 2.5mmol / L) with a molar ratio of 3:1, and ultrasonically treated for 30min, and then 25mL of KBH4 solution with a concentration of 15g / L was slowly dripped into the mixed solution at a speed of 1.0mL / min. During this process, a black precipitate was generated and deposited on the GF electrode. After GF was further immersed in the mixed solution for 2 hours, it was washed with ethanol and deionized water 3 times to obtain a core-shell structure composite cathode material Fe@Co / GF;

[0055] (2) Production of anode materials:

[0056] The graphite felt GF was soaked in a 1 mol / L acetone solution for 12 hours, washed twice with deionized water after being taken out, and then soaked in a concentrated HNO3 solution for 2 hours, washed twice with deionized water after being taken out, and finally dried in an oven at 105°C for standby use to obtain an anode material;

[0057] (3) Construction of bioelectric Fenton system:

[0058] The method comprises an anode chamber and a cathode chamber, which are separated by a proton exchange membrane. The anode is the graphite felt treated in step (2), and the cathode is the graphite felt pretreated in step (1). A titanium wire is used as a conductor in an external circuit, and an aeration device is arranged outside the cathode chamber. The anode and the cathode are connected through an external circuit, and a 1000Ω resistor is connected in series as an external circuit load to form a bioelectric Fenton system. After the bioelectric Fenton system is successfully domesticated, the cathode is replaced with the Fe@Co / GF composite cathode obtained in step (1), and the external resistor is replaced with 100Ω, which is named as the Fe@Co / GF-BEF system.

[0059] Comparative Example 1

[0060] The only difference from the embodiment is that the replaced cathode is pretreated graphite felt, and the rest of the method is the same as the embodiment. The obtained system is named GF-BEF system.

[0061] Comparative Example 2

[0062] The only difference from the embodiment is that the system is not aerated, and the rest of the method is the same as the embodiment, and is named TQ-BEF system.

[0063] The following experiments were used to verify the beneficial effects of the bioelectric Fenton system of the present invention.

[0064] (I) Morphology and structure analysis of core-shell structure composite cathode material Fe@Co / GF

[0065] The morphology and structure of the graphite felt GF and the Fe@Co / GF composite cathode material of the embodiment were analyzed respectively.

[0066] Analysis method: Scanning electron microscopy (SEM, Zeiss SUPRATM55, Germany) and transmission electron microscopy (TEM, JEOL-2011F, Japan) were used to analyze the surface morphology and elements of the prepared cathode. X-ray photoelectron spectroscopy (XPS, AXIS SUPRATM, Japan) was used to analyze the elemental valence state of the Fe@Co catalyst. The analysis results are shown in Figure 3 and Table 1

[0067] Figure 3The SEM, TEM and XPS images of GF and Fe@Co / GF composite cathode in the embodiment. The existing GF surface is smooth and cross-network (a); Fe@Co catalyst is evenly distributed on the GF surface (b); TEM images of Fe@Co (c, d) and element (merge; Co, green; O, blue; Fe, red) mapping images (e); Fe / GF and Fe@Co / GF cathode adsorption capacity and electron transfer mechanism (f); XPS full spectrum scan of Fe@Co / GF cathode (g); Fe@Co / GF XPS Fe 2p shows six state peaks (h); Fe@Co / GF XPS Co 2p shows five different state peaks (i)

[0068] from Figure 3 As can be seen from the SEM image, ordinary GF is composed of a 3D carbon fiber network with a diameter of 14-22μm and a relatively clean and smooth surface ( Figure 3 a). In contrast, the surface of Fe@Co / GF is covered with a large number of spherical nanoparticles with a diameter of 30-50 nm formed by Fe and Co ( Figure 3 b).

[0069] from Figure 3 From the TEM image, we can see that the nanoparticles covered on the surface of Fe@Co / GF are mainly composed of a core-shell structure consisting of Fe (58.76%), Co (23.59%), and O (16.01%). Figure 3 cd and Table 1). Its core is composed of high-density Fe and Co elements, while its shell is mainly composed of a large amount of O and a small amount of Fe and Co ( Figure 3 e). These well-structured and uniformly distributed Fe@Co / GF can increase the exposure of adsorption active sites and stimulate the transfer of electrons from the anode to the electron acceptor ( Figure 3 f), thereby improving the Fenton catalytic efficiency.

[0070] Table 1 Element content of Fe@Co / GF in Example

[0071] element Line Type K Factor Adsorption correlation Wt% Wt%Sigma C K series 2.50675 1.00 1.65 0.40 O K series 1.86867 1.00 16.01 0.64 Fe K series 1.19079 1.00 58.76 0.76 Co K series 1.26119 1.00 23.59 0.62 sum 100.00

[0072] In addition, based on Figure 3 g, four main element peaks were obtained, namely the Fe, Co and O peaks from the catalyst and the C peak from the GF surface. Detailed Fe 2p XPS spectrum ( Figure 3 h) shows six main peaks. The additional peaks at 717.3 and 733.6 eV are probably satellite peaks of Fe2p, and the positions of the two satellite peaks indicate that Fe in the catalyst is mainly in the Fe(III) oxidation state. The peaks near 712.7 and 725.4 eV correspond to the 2p oxidation state of Fe(III).3 / 2 and 2p 1 / 2 In addition, the peaks near 710.9eV and 719.9eV correspond to the binding energies of Fe(II) and Fe(0), respectively. Detailed Co 2p XPS spectrum ( Figure 3 i) Five main peaks are shown near 803.7, 797.4, 786.8, 782.5 and 781.2 eV, among which the peaks near 797.1, 782.5 and 781.2 eV are similar to the XPS spectrum of CoO, indicating that cobalt is in an oxide state in the composite catalyst. Therefore, the Fe@Co synthesized in the present invention is a spherical core-shell composite catalyst containing a Fe-CoO mixture core and a Fe2O3 shell. This multivalent composite core-shell structure catalyst exhibits excellent catalytic performance for electrochemical reduction reactions, and it is expected that the Fe@Co / GF composite cathode can effectively improve the electron transfer efficiency and H2O2 yield of the BEF system.

[0073] (II) Effect of removing antibiotic resistance genes in sludge

[0074] The method for removing antibiotic resistance genes in sludge by using a bioelectric Fenton system according to the present invention comprises the following steps:

[0075] A mixture of 45 mL of anaerobic sludge and 5 mL of sodium acetate solution (2.0 g / L) was used as the filler of the anode chamber to allow electroactive microorganisms to attach and grow on the anode surface. A mixed solution of 0.1 mol / L potassium dihydrogen phosphate and 0.1 mol / L potassium ferrocyanide was used as the cathode electrolyte with a nearly neutral pH value. The cathode liquid in the cathode chamber was replaced every 2 days. When the output voltage of the reactor reached a stable value (>300 mV), the biofilm was considered to have been successfully domesticated.

[0076] In order to further test the effect of the above-mentioned bio-electro-Fenton system on the removal of antibiotic resistance genes in sludge, the successfully domesticated reactor was selected to replace the cathode, and anaerobic sludge from a sewage treatment plant in Dalian was mixed with sodium acetate solution (2.0 g / L) and inoculated into the anode chamber to enrich the biofilm. In addition, anaerobic sludge with a pH of 3.0±0.1 was added to the cathode chamber and aerated at a flow rate of 150 mL / min to achieve the removal of antibiotic resistance genes in the sludge. Among them, the sludge that was not treated was named RS.

[0077] The total DNA of each sample was extracted using the FastDNA SPIN Kit for soil (MP Biomedicals, USA). TM4Fluorometer (Invitrogen, USA) was used to detect the concentration of extracted DNA. Ultra-high throughput fluorescence quantitative PCR (Wafergen, USA) was used to detect ARGs and MGEs in the samples. The test results are shown in Figure 4 .

[0078] from Figure 4 It can be seen that 23 ARGs and 5 MGEs were detected in the original mud samples, and their absolute abundances were 3.30×10 8 copies / g and 1.43×10 8 The detected ARGs included two sulfonamide resistance genes (sul1 and sul2), six tetracycline resistance genes (tetE, tetM, tetO, tetQ, tetS, and tetX), four macrolide resistance genes (ereA, ermB, ermF, and ermX), and three β-lactam resistance genes (bla PSE ,bla TEM and cphA) and eight aminoglycoside resistance genes (aac(6')-Ib, aac(6')-II, aacA / aphD, aacC2, aadA2-01, aadA5-01, aadE and strB). Among them, sulfonamides (1.95×10 8 copies / g) and macrolide resistance genes (6.30×10 7 copies / g) was the largest, accounting for 78.17% of the total ARGs. In contrast, Int1 (7.23×10 7 copies / g) and IS26 (6.16×10 7 copies / g) accounted for 50.49% and 42.98% of the absolute abundance of the five MGEs, respectively, and were the main genetic elements of the microorganisms in the system.

[0079] After 48 h of treatment, the absolute abundance of total ARGs and MGEs in the system decreased, and the removal rates of β-lactam, streptocin macrolide, sulfonamide resistance genes and MGEs reached 78.73%, 78.00%, 83.82% and 63.88%, respectively. Fe@Co / GF-BEF had the most obvious removal effect on sulfonamide resistance genes sul1 and sul2, with the absolute abundance reduced by 1.00×10 8 and 6.29×10 7copies / g. Among them, there is a significant difference in the removal effect of sul1 and sul2, and the relationship between the two is: sul1>sul2. In addition, the removal rate of aminoglycoside and tetracycline resistance genes by the system of the present invention is relatively low, which are 19.99% and 34.77% respectively. The reduction rate of aminoglycoside resistance genes is much lower than that of sulfonamide resistance genes, indicating that aminoglycoside-resistant bacteria are more tolerant to oxidative stress than sulfonamide-resistant bacteria.

[0080] (III) Effect of Fe@Co / GF-BEF system on the reduction of ARGs

[0081] Ultra-high throughput fluorescence quantitative PCR (Wafergen, USA) was used to compare the abundance of ARGs and MEGs in sludge after treatment with conventional GF and Fe@Co / GF cathode BEF system. The test results are shown in Figure 5 .

[0082] from Figure 5 It can be seen that after 48 hours of treatment with the Fe@Co / GF-BEF system, the absolute abundance of total ARGs in the sludge was significantly reduced, and the total ARGs reduction rate was 70.55%, which was higher than the degradation rate of ARGs by MFC (47%). At the same time, in the Fe@Co / GF-BEF system, the removal rates of total ARGs and total MGEs (63.88%) were significantly higher than those of the GF-BEF system, increasing by 4.13 times and 2.02 times, respectively. Compared with the original sludge, the reduction rates of β-lactam resistance genes, macrolide resistance genes, and sulfonamide resistance genes all reached more than 75%. Among them, bla in the β-lactam resistance gene PSE The reduction effect of GF-BEF system was the best, with a reduction rate of nearly 100%. Secondly, the removal effect of ermB in macrolide resistance gene and sul1 in sulfonamide resistance gene was also very significant, with reduction rates of 92.64% and 94.66%, respectively. The degradation rate of aminoglycoside resistance gene was the lowest, with a reduction rate of less than 20.00%. After treatment with GF-BEF system, the absolute abundance of total ARGs increased from 3.30×10 8 The copies / g increased to 3.43×10 8 copies / g, among which the abundance of aminoglycoside resistance genes increased most significantly, from 5.30×10 7 The copies / g increased to 1.02×10 8 Although the absolute abundance of ARGs showed an overall increasing trend, the aadE (68.54%) in aminoglycoside resistance genes and the bla (68.54%) in β-lactam resistance genes were significantly higher than those in β-lactam resistance genes. PSEThe removal effects of the above genes were better, including ereA (63.07%) and ermB (75.64%) among the macrolide resistance genes and tetQ (70.80%) among the tetracycline resistance genes.

[0083] (IV) Effect of Fe@Co / GF-BEF system on hydroxyl radicals

[0084] Test method: Use methylene blue (MB) as a hydroxyl radical scavenger. The concentration of methylene blue solution consumed in the reaction is the concentration of methylene blue scavenging hydroxyl radicals (MB-OH), which is the concentration of hydroxyl radicals. The principle is to use free radicals to change the color developer, and indirectly measure the free radical content based on the change in absorbance. MB solution is at 20×10 -6 ~140×10 -6 mol·L -1 There is a good linear relationship between the concentration range and the absorbance of the system. - 6 mol·L -1 ,30×10 -6 mol·L -1 , 40×10 -6 mol·L -1 , 50×10 -6 mol·L -1 , 60×10 -6 mol·L -1 70×10 -6 mol·L -1 The solution was measured with a spectrophotometer at a wavelength of 664nm. Distilled water was used for calibration each time, and the relationship between the solution concentration and the absorbance value was established. Methylene blue was used as a capture agent and an ultraviolet spectrophotometer was used for determination. During the test, each sample was tested for absorbance three times, and the average value was taken. The test results were included in the Figure 6 .

[0085] from Figure 6 It can be seen that in this study, the concentration of ·OH in the Fe@Co / GF-BEF system was 65.08 μmol / L, while no ·OH was detected in the GF-BEF system ( Figure 6 ), which also explains why Fe@Co / GF-BEF has a better reduction effect on ARGs than GF-BEF system.

[0086] (V) Effect of aeration on ARGs removal

[0087] Figure 5The reduction of ARGs in the cathode chamber of the Fe@Co / GF-BEF system under aerated and non-aerated conditions is shown. Under non-aerated conditions, the reduction rate of ARGs in the cathode chamber is 40.17%, while the reduction rate of MGEs is only 5.17%. Under this reaction condition, the oxygen content in the cathode chamber is extremely low, and the Fenton reaction cannot occur normally. At this time, the physical adsorption of the carbon felt cathode electrode and the cathode chamber surface and a trace amount of Fenton reaction in the system contribute to the reduction of ARGs.

[0088] Compared with the non-aerated condition, the Fe@Co / GF-BEF system increased the ARGs reduction rate by 30.37% and the MGEs removal rate by 58.71% under aerated conditions. Under this condition, in addition to the physical adsorption on the carbon felt cathode electrode and the reactor surface, the ·OH produced by the Fenton reaction in the cathode chamber is the main cause of ARGs degradation. In other words, aeration not only increases the DO content in the solution, but also improves the mass transfer rate of the reactants. At the same time, the Fe@Co catalyst promotes the electron transfer of the system and generates more H2O2 through two-electron reduction (Equation (1)). H2O2 reacts with Fe on the composite cathode surface. 2+ The Fenton reaction generated more hydroxyl radicals with strong oxidizing properties (Formula (3)), thereby enhancing the degradation ability of ARGs.

[0089] 5. Impact on microbial communities

[0090] The changes in the microbial community structure in the sludge after treatment with the Fe@Co / GF-BEF system were analyzed according to the Alpha diversity index (Table 2). Compared with the original sludge, the Chao1 and Observed_species indices in the three systems were reduced, among which the microbial richness in the sludge samples in GF-BEF was the lowest. Similarly, according to the Simpson and Shannon indices, the microbial diversity in GF-BEF was also the lowest. The results shown by the Faith_pd index were consistent with the above results, and the evolutionary diversity was TQ-BEF>Fe@Co / GF-BEF>GF-BEF. In summary, the richness and diversity of microorganisms in the sludge after treatment with TQ-BEF, GF-BEF and Fe@Co / GF-BEF decreased to varying degrees, and the GF-BEF treatment had a significant effect on the reduction of microorganisms in the sludge. Compared with GF-BEF, the Fe@Co / GF-BEF treatment had less damage to the sludge microbial community structure.

[0091] Table 2 Species richness and diversity analysis

[0092]

[0093] The distribution structure of microbial flora in the reactor was analyzed by metagenomic sequencing ( Figure 7 ). As can be seen from the figure, the dominant bacterial species in the original sludge are Proteobacteria, Bacteroidetes, Chloroflexi, Nitrospirae, Firmicutes, Actinobacteria, Acidobacteria, Gemmatimonadetes, Patescibacteria and Planctomycetes, among which Proteobacteria and Bacteroidetes are the most important, accounting for 35.54% and 30.12% of the total community, respectively, and the abundance of the remaining species is less than 10.00%. After continuous reaction, the microbial community structure in each reactor has changed significantly. The main dominant bacterial species in Fe@Co / GF-BEF are Proteobacteria, Bacteroidetes, Chloroflexi and Firmicutes, accounting for 71.85% of the total community. Among them, the abundance of Bacteroidetes and Firmicutes changed the most, decreasing from 30.12% to 15.21% and increasing from 5.60% to 17.16%, respectively. The results showed that Fe@Co / GF-BEF had an inhibitory effect on Proteobacteria and Bacteroidetes microorganisms, but promoted the growth of Chloroflexus, Nitrospira, Firmicutes and Actinobacteria microorganisms. Compared with Fe@Co / GF-BEF, the community structure of microorganisms in GF-BEF had a similar trend of change, and the change was more significant. The main dominant bacterial species in GF-BEF were Proteobacteria, Chloroflexus, Nitrospira and Actinobacteria, accounting for 78.87% of the total community. Among them, the abundance of Chloroflexus, Nitrospira and Actinobacteria increased significantly, while the abundance of Proteobacteria and Bacteroidetes decreased significantly, decreasing from 35.54% to 21.54% and 30.12% to 1.80%, respectively. GF-BEF showed a strong inhibitory effect on Bacteroidetes microorganisms. Like Fe@Co / GF-BEF and GF-BEF, TQ-BEF also inhibited the proliferation of Bacteroidetes.

[0094] The top 10 genus-level microorganisms detected in the original mud accounted for 35.93% of the total microorganisms, among which the main genus-level microorganisms were Denitratisoma and Methylotenera of Proteobacteria, AKYH767, Bacteroidetes_vadinHA17 and NS9_marine_group of Bacteroidetes, Subgroup_17 of Acidobacteria, and DTU014 of Firmicutes. Compared with the original mud, the genus-level community structure of microorganisms after GF-BEF treatment changed most significantly, and the abundance of Nitrospira increased significantly from 0.54% to 18.47%. At the same time, GF-BEF inhibited the growth of AKYH767, Bacteroidetes_vadinHA17 and Methylotenera, and their abundance decreased to varying degrees. Similar to GF-BEF, TQ-BEF and Fe@Co / GF-BEF treatments promoted the growth of Nitrospira, and its abundance increased from 0.54% to 11.59% and 0.54% to 8.98%, respectively. At the same time, it had different degrees of inhibitory effects on Bacteroidetes_vadinHA17, DTU014, Denitratisoma and Subgroup_17 genus-level microorganisms, but the effects on other genus-level microorganisms were not significant. The results showed that all three treatments promoted the growth and reproduction of Nitrospira microorganisms, among which Fe@Co / GF-BEF had the least promoting effect, and the Fe@Co / GF-BEF treatment also had the least effect on the entire microbial genus-level community structure. This is consistent with the above-mentioned analysis results of changes in the microbial community structure at the phylum level.

[0095] The principal component analysis (PCA) method was used to analyze the differences between microbial communities ( Figure 8 ). In the PCA graph, the distance between the GF-BEF-treated sample and the RS sample is the farthest, indicating that the GF-BEF treatment has the greatest impact on the microbial community structure. The distance between the TQ-BEF-treated sample and the RS sample is the closest, indicating that there is a similar microbial community distribution structure. The distance between Fe@Co / GF-BEF and RS is significantly greater than that between TQ-BEF and RS, indicating that aeration has a greater impact on the microbial community structure. It may be that most of the microorganisms in the sludge sample are anaerobic or facultative anaerobic bacteria, so aeration and oxygenation cause the microbial community to differ significantly from the original sludge.

[0096] The host bacteria of ARGs were studied at the genus level using network analysis. Although the positive correlation between microorganisms and ARGs cannot be used as evidence that the microorganisms carry antibiotic resistance, it can identify potential host bacteria of ARGs. Fig. 9 As shown, the possible host bacteria of cphA are mainly Ellin6067, Smithella, Rhodoferax, Geobacter, SAR324_clade (Marine_group_B), Piscinibacter of Proteobacteria and AKYH767, OLB8 of Bacteroidetes. In the Fe@Co / GF-BEF system, the relative abundance of these possible host bacteria decreased significantly. It can be seen that the Fe@Co / GF-BEF treatment inhibits the growth and reproduction of cphA host bacteria and promotes the reduction of cphA, which is consistent with the above analysis results of cphA removal rate of 83.06% and the decrease in the abundance of Proteobacteria and Bacteroidetes. In terms of tetracycline ARGs, most potential host bacteria are mainly concentrated in Chloroflex. In this study, RBG-13-54-9 of Chloroflex is a common potential host bacteria of tetX and tetM. Different from this, this study found that the possible host bacteria of tetQ were Terrimonas and Bacteroidetes_vadinHA17 of Bacteroidetes and Saccharimonad-ales and WS6_(Dojkabacteria) of Patescibacteria, indicating that Bacteroidetes and Patescibacteria may also be potential hosts of tetracycline ARGs. According to network analysis, DTU014 of Firmicutes and OM190 of Planctomycetes may be the common potential host bacteria of blaPSE and sul1, while the possible host bacteria of sul2 is SBR1031 of Chloroflexi. These potential host bacteria were inhibited in the Fe@Co / GF-BEF system, and the relative abundance decreased. The results showed that Proteobacteria were the main bacteria carrying ARGs. Fe@Co / GF-BEF treatment can inhibit the horizontal transfer of ARGs by killing the host bacteria or slowing down the growth of the host bacteria, thereby achieving the purpose of reducing ARGs in the system.

[0097] 6. Effects on metabolism

[0098] Bacterial community and metabolic analysis methods:

[0099] The 16S_ region was amplified using primers 341F (CCTACGGGNGGCWGCAG) and 806R (GACTACNVGGGTATCTAAT). Sequences with a similarity of 97% were clustered using vsearch_v2.7.1 software to obtain representative sequences of OUT. The RDP classifier was used to identify species between the representative sequences of OUT and the corresponding database to obtain species information annotations of typical OTU sequences. The abundance data of metabolic pathways in each sample were obtained using PICRUSt2 software. The Alpha diversity index of the sample was calculated using QIIME software to analyze species richness (Chao 1 and Observed_species index) and diversity (Simpson and Shannon index). Faith's PD index characterized evolution-based diversity, and Good's coverage index characterized coverage. The test results are shown in Fig.10 .

[0100] from Fig.10 It can be seen that the Fe@Co / GF-BEF system not only has a good degradation performance for ARGs, but also has a great influence on the metabolic pathways in the system. Fig.10 As shown in the figure, the main metabolic pathways in different systems are biosynthesis, production of precursor metabolites and energy, and degradation / utilization / assimilation, with relative abundances of biosynthesis (66.51%-69.12%), production of precursor metabolites and energy (14.22%-15.40%), degradation / utilization / assimilation (12.41%-14.08%), metabolic group (2.59%-2.79%), glycan pathway (0.75%-0.93%), macromolecular modification (0.72%-0.79%), and detoxification (0.02%-0.15%). After the sludge was treated by the system, the functions of detoxification, production of precursor metabolites and energy, and glycan pathway were enhanced, while the functions of macromolecular modification and metabolic group were weakened.

[0101] Compared with RS, the GF-BEF system has enhanced functions of degradation / utilization / assimilation, production of precursor metabolites and energy, glycan pathway, and detoxification; while the functions of biosynthesis, macromolecular modification, and metabolic group are weakened. Specifically, the abundance of biosynthetic metabolism decreased by 3.90%, the abundance of degradation / utilization / assimilation metabolism increased by 7.20%, the abundance of detoxification metabolism increased by 1.70 times, the abundance of precursor metabolites and energy metabolism increased by 2.95%, glycan metabolism increased by 13.11%, macromolecular modification metabolism decreased by 3.79%, and the metabolic group decreased by 4.70%.

[0102] Compared with RS, the TQ-BEF system has enhanced functions of detoxification, production of precursor metabolites and energy, and glycan pathways; while the functions of biosynthesis, degradation / utilization / assimilation, macromolecular modification, and metabolic group are weakened. Specifically, the abundance of biosynthetic metabolism decreased by 9.22%, the abundance of degradation / utilization / assimilation metabolism decreased by 1.68%, the abundance of detoxification metabolism increased by 2.99 times, the abundance of precursor metabolites and energy metabolism increased by 1.43%, the glycan metabolism increased by 16.20%, the macromolecular modification metabolism decreased by 13.87%, and the metabolic group decreased by 2.79%.

[0103] Compared with the abundance of metabolic pathways in the Fe@Co-BEF system and the GF-BEF system, the degradation / utilization / assimilation and detoxification changed significantly, among which: the abundance of biosynthetic metabolism increased by 5.55%, the abundance of degradation / utilization / assimilation metabolism increased by 14.92%, the abundance of detoxification metabolism increased by 92.06%, the abundance of precursor metabolites and energy metabolism increased by 4.09%, the abundance of glycan metabolism decreased by 0.66%, the abundance of macromolecule modification metabolism increased by 4.94%, and the abundance of metabolic groups decreased by 1.32%.

[0104] Compared with the abundance of metabolic pathways in the Fe@Co-BEF and TQ-BEF systems, the abundance of detoxification metabolism changed greatly, among which: the abundance of biosynthesis metabolism decreased by 0.30%, the abundance of degradation / utilization / assimilation metabolism increased by 5.31%, the abundance of detoxification metabolism increased by 1.84 times, the abundance of precursor metabolites and energy metabolism increased by 2.55%, the abundance of glycan metabolism increased by 2.05%, the abundance of macromolecule modification metabolism decreased by 6.06%, and the abundance in the metabolic group increased by 0.66%.

[0105] (VII) The complete mechanism of Fe@Co / GF-BEF system in reducing sludge ARGs

[0106] Based on the above results, we proposed a possible degradation mechanism of sludge ARGs in the BEF system with Fe@Co / GF composite cathode ( Fig.11 ). First, the electrogenic bacteria oxidize organic matter at the anode to produce protons and electrons, which are transferred to the cathode through an external circuit and react with O2 to generate H2O2 in situ (Equation (1)). The core-shell Fe@Co catalyst evenly distributed on the surface of the composite cathode promotes electron transfer between catalyst gaps due to its low interfacial resistance, thereby greatly improving the yield of H2O2. High H2O2 concentration can destroy the cell membrane, thereby inhibiting the growth of microorganisms and further inhibiting the horizontal transfer of ARGs, which may also be one of the reasons for the reduced abundance of Proteobacteria and Chloroflexi in the Fe@Co / GF-BEF system. At the same time, Fe 2+ Dissolved from the catalyst (Formula (4) and (6)), and reacted with H2O2 to generate hydroxyl radical ·OH (Formula (3)).2+ Similar, Co 2 + A Fenton-like reaction can also occur at the cathode, activating the decomposition of H2O2 to generate ·OH (Equation (5)). According to the standard reduction potential of metals (Equations (2), (7-8)), it is believed that Fe 2+ / Fe 3+ and Co 3+ / Co 2+ The conversion of ·OH can realize the closed valence cycle of the bimetallic metal, thereby further promoting the generation of ·OH. At the same time, the high H2O2 yield will also promote the system to generate more ·OH (Equations (3) and (5)). ·OH can directly oxidize extracellular ARGs, or it can destroy the cell structure and then oxidize intracellular DNA molecules, while also inhibiting the horizontal transfer of ARGs. Therefore, the generation of a large amount of ·OH is one of the main reasons for the significant reduction in the absolute abundance of ARGs (reduced by 70.55%) and MGEs (reduced by 63.88%) in the system.

[0107] In addition, the catalytic effect of the Fe@Co catalytic cathode promoted the growth of Chloroflexi, Nitrospira, Firmicutes and Actinobacteria, further increased the abundance of biosynthetic metabolism, degradation / utilization / assimilation metabolism, detoxification metabolism, precursor metabolites and energy metabolism of these microorganisms, and reduced the abundance of glycan metabolism, macromolecular modification metabolism and metabolome. The changes in these metabolic processes inhibited or killed the growth of Proteobacteria and Bacteroidetes microorganisms in the sludge. Since these types of microorganisms are the main hosts of ARGs, the total abundance of ARGs decreased. The physical adsorption of free ARGs and MGEs by the inner wall of the reactor and the cathode carbon felt also reduced the abundance of ARGs and MGEs.

[0108] After treatment with the Fe@Co / GF-BEF system, the absolute abundance of ARGs was effectively reduced, and the degradation rate of total ARGs was 70.55%, reducing the ecological pollution risk of ARGs. In addition, the Fe@Co / GF-BEF system reduced the abundance of mobile genetic elements, inhibited the further spread of ARGs in the environment, and reduced the risk of ARGs pollution transmission.

[0109] In addition, the physical adsorption of the reactor inner wall and cathode carbon felt is also one of the reasons for the reduction in the abundance of ARGs and MGEs.

[0110] Fe 0 +O2+2H + →Fe 2+ +H2O2 (4)

[0111] Co 2+ +H2O2→Co 3+ + OH+OH- (5)

[0112] 2Fe 3+ +Fe→3Fe 2+ (6)

[0113] Co 3+ +e - →Co 2+ E 0 =1.81V (7)

[0114] Fe 2+ +Co 3+ →Fe 3+ +Co 2+ E 0 =1.04V (8)

[0115] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A core-shell structure composite cathode material Fe@Co / GF, characterized in that: The core-shell structured Fe@Co catalyst was grown in situ on graphite felt GF; The Fe@Co catalyst is composed of Fe2O3 nanoparticles constituting the shell structure of the material, and a Fe-CoO mixture constituting the core structure of the material; The Fe-CoO mixture has an Fe content of 58.76%-62.38%, a Co content of 20.81%-23.59%, and an O content of 14.62%-16.01%.

2. The core-shell structure composite cathode material Fe@Co / GF according to claim 1, characterized in that: The core-shell structure composite cathode material Fe@Co / GF is prepared by the following method: S1: Pretreatment of graphite felt GF: soaking the graphite felt GF in acetone solution, washing with deionized water, soaking in concentrated HNO3 solution, washing with deionized water, and then drying the graphite felt GF to complete the pretreatment of the graphite felt GF; S2: Place the graphite felt GF pretreated in step S1 into a 3+ and Co 2+ The mixture was ultrasonically treated, then immersed in potassium borohydride solution, and washed with ethanol and deionized water to obtain a core-shell structured composite cathode material Fe@Co / GF.

3. The core-shell structure composite cathode material Fe@Co / GF according to claim 2, characterized in that: In step S2, the Fe 3+ and Co 2+ The mixed solution is a mixture of FeCl3·6H2O and CoCl2·6H2O.

4. A bioelectric Fenton system, characterized in that: The invention comprises the core-shell structure composite cathode material Fe@Co / GF as described in any one of claims 1 to 3.

5. A method for constructing a bioelectric Fenton system according to claim 4, characterized in that: The steps include: It includes an anode chamber and a cathode chamber, which are separated by a proton exchange membrane, with graphite felt as the anode, a core-shell structure composite cathode material Fe@Co / GF as the cathode, titanium wire as the conductor in the external circuit, and an aeration device is arranged outside the cathode chamber; the anode and the cathode are connected through the external circuit, and a 100-1000Ω resistor is connected in series as the external circuit load to form a bioelectric Fenton system.

6. The method according to claim 5, characterized in that The anode is pretreated graphite felt, and the processing method of the graphite felt is: The graphite felt is sequentially soaked in acetone solution, washed with deionized water, soaked in concentrated HNO3 solution, washed with deionized water, and then dried to complete the pretreatment of the graphite felt GF.

7. The method according to claim 5, characterized in that The volume ratio of the anode chamber to the cathode chamber is 1:

1.

8. A method for removing antibiotic resistance genes in sludge based on the bioelectric Fenton system according to any one of claims 5 to 7, characterized in that: The steps include: Anaerobic sludge and sodium acetate solution are mixed as the filler of the anode chamber, so that electroactive microorganisms are attached to and grown on the anode surface. Cathodic liquid is injected into the cathode chamber. The cathode liquid in the cathode chamber is replaced at set intervals until the system voltage is constant. Anaerobic sludge with a pH of 3.0±0.1 is added to the cathode chamber to replace the cathode liquid. The reaction is carried out for a specific time to achieve the removal of antibiotic resistance genes in the sludge.

9. The method according to claim 8, characterized in that Add 0.1 mol / L H2SO4 solution into the cathode chamber to adjust the pH of the sludge to acidic.

10. The method according to claim 8, characterized in that The water content of the anaerobic sludge is above 98%, and the anaerobic sludge contains at least one of sulfonamide resistance genes, tetracycline resistance genes, macrolide resistance genes, β-lactam resistance genes, and aminoglycoside resistance genes.

Images