Iron-carbon composite conductive particles with core-shell structure, preparation method and application thereof in anaerobic treatment of wastewater

Abstract

The application discloses a kind of iron-carbon composite conductive particles of core-shell structure, preparation method and its application in wastewater anaerobic treatment, belong to wastewater treatment technical field.The iron-carbon composite conductive particles of the application is the core-shell structure conductive particle of carbon-coated zero-valent iron.Montmorillonite powder is used as binder, and the synthesized iron-carbon conductive powder with core-shell structure is kneaded into particles to prevent it from being lost with effluent in continuous flow anaerobic reactor, prolong the service life, improve the stability of reactor operation.The particles provided by the application make the close contact of iron and carbon two materials, and the good electric conductivity and the existing potential difference constitute micro-electrolysis reaction, accelerate the interspecies direct electron transfer of microbial metabolism organic pollutants to produce methane, create more suitable growth environment for anaerobic microorganisms.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a core-shell structured iron-carbon composite conductive particle, its preparation method, and its application in enhancing methanogenesis in the biological treatment of antibiotic-containing wastewater. Background Technology

[0002] There are still some shortcomings in the anaerobic biological treatment technology for antibiotic wastewater that need to be addressed, mainly in the following aspects: 1) Anaerobic biological treatment systems have limited resistance to high-concentration harmful wastewater. High-concentration antibiotic wastewater inhibits the activity of methanogens, resulting in acidity and even system collapse; 2) Traditional anaerobic biological treatment uses hydrogen or formic acid as interspecies electron transport carriers, requiring the participation of multiple enzymes. Only when the concentration of acetic acid in the digester is low and the partial pressure of hydrogen does not exceed 100 Pa can hydrogen-producing and acetic acid-producing bacteria decompose organic acids with three or more carbon atoms in the solution into acetic acid and hydrogen, providing metabolic substrates for acetic acid-producing and hydrogen-producing methanogens to produce methane. This results in slow interspecies electron transport rate and low electron utilization, limiting the activity of methanogens.

[0003] Summers et al. first demonstrated in the journal Science that conductive pili and cytochrome c distributed on the surface of microbial cells possess the ability for direct interspecies electron transfer (DIET), significantly improving the rate and utilization of interspecies electron transfer and allowing more energy to be used for methanogenesis. Based on this discovery of a new interspecies electron transfer mechanism, various conductive materials have been added to anaerobic systems to promote direct electron transfer between acid-producing and methanogenic bacteria, directly reducing carbon dioxide and hydrogen ions to methane and improving methane conversion efficiency. Currently, widely used conductive materials are iron-based (magnetite, hematite, iron filings, and zero-valent iron, etc.) and carbon-based (graphite, biochar, activated carbon, and graphene, etc.) materials. As redox mediators, iron-based and carbon-based materials are usually applied to anaerobic biological treatment systems either individually or in combination. For zero-valent iron, oxidation occurs in the digester, releasing electrons and simultaneously generating Fe. 2+ This not only lowers the redox potential of anaerobic systems, providing a suitable growth environment for methanogens, but also releases Fe... 2+As an important component of many enzymes, zero-valent iron (ZVFe) enhances the metabolic activity of microorganisms. However, ZVFe has poor stability in water and is prone to passivation and aggregation, affecting its enhancement effect. Carbon-based materials typically have a large specific surface area and high porosity, and there is a potential difference between them and ZVFe, constituting an iron-carbon micro-electrolysis effect. Therefore, people often mix the two to fully utilize their enhancement effect. Common methods include mixing ZVFe and carbon-based material powders or co-precipitating ZVFe onto the surface of the carbon-based material. However, mixed addition suffers from insufficient contact between the two materials, the powdered enhancement medium is easily lost with the effluent in continuous flow reactors, the content of ZVFe loaded on the surface is limited, and there is a risk of detachment during long-term operation.

[0004] Based on the current application status of iron-based and carbon-based materials in enhancing direct interspecies electron transfer in anaerobic systems, there is a need to develop a tightly bonded iron-carbon composite conductive particle with stable structure and properties to prevent passivation and excessive loss of iron-based materials, extend their action time, and more stably exert their direct interspecies electron transfer capabilities, thereby improving methane yield. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention aims to design and provide a core-shell structured iron-carbon composite conductive particle, its preparation method, and its application in anaerobic wastewater treatment.

[0006] The core-shell structured iron-carbon composite conductive particles of this invention possess stable structural properties, certain mechanical strength, and fluidization characteristics, avoiding the shortcomings of other powder-mixed or surface-loaded iron-carbon conductive materials. Applying these core-shell structured iron-carbon composite conductive particles to an anaerobic biological treatment system for antibiotic pharmaceutical wastewater can promote the rapid removal of recalcitrant organic pollutants and direct interspecies electron transfer among anaerobic microorganisms, accelerating the rate and utilization of electron transfer, increasing methane production, and avoiding the involvement and energy consumption of multiple enzymes that use H2 / formic acid as electron carriers.

[0007] Montmorillonite powder is used as a binder to knead the synthesized iron-carbon conductive powder with a core-shell structure into granules to prevent it from being lost with the effluent in the continuous flow anaerobic reactor, thereby extending its service life and improving the stability of reactor operation.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: On one hand, the present invention provides a core-shell structured iron-carbon composite conductive particle, wherein the iron-carbon composite conductive particle is a core-shell structured conductive particle in which carbon encapsulates zero-valent iron.

[0009] Secondly, the present invention provides a method for preparing a core-shell structured iron-carbon composite conductive particle, comprising the following steps: (1) Weigh urea and ferric chloride hexahydrate, dissolve them in glucose solution and stir evenly. After obtaining the mixture, place it in a reaction vessel and carry out hydrothermal reaction at high temperature to obtain a solid precipitate. After washing with ethanol and deionized water several times by centrifugation, dry it, grind and sieve it to obtain a carbon-encapsulated iron oxide core-shell structure conductive material. (2) Weigh the binder and the carbon-coated iron oxide core-shell structure conductive material, mix them thoroughly, dissolve them in deionized water to make a viscous substance, knead them into granules, dry them, and obtain carbon-coated iron oxide core-shell structure conductive particles. (3) The carbon-coated iron oxide core-shell structure conductive particles are placed in a tube furnace and calcined in the absence of air to obtain carbon-coated zero-valent iron composite conductive particles.

[0010] In the preparation method described above, the mass ratio of urea to ferric chloride hexahydrate in step (1) is 7:3 to 7:8, the concentration of glucose solution is 100 to 200 g / L, and the mass ratio of glucose to ferric chloride hexahydrate in glucose solution is 1:1 to 1:5. The conditions for the hydrothermal reaction are: reaction temperature 150-250℃, reaction time 12-18h; The conditions for centrifugal washing are: 3 to 5 times of centrifugation, centrifugation speed of 4000 to 8000 rpm, and centrifugation time of 5 to 15 minutes; The drying conditions are: drying temperature 60-100℃, drying time 12-24h; The grinding and sieving conditions are as follows: grinding with a mortar and pestle, and sieving with a mesh size of 100 to 200.

[0011] In the preparation method described above, the binder in step (2) includes montmorillonite powder or polytetrafluoroethylene; The mass ratio of the binder to the carbon-encapsulated iron oxide core-shell conductive material is 1:5 to 1:10. The particle size is 2-4 mm, and the particle shape includes spherical, but other shapes are also acceptable, as long as they have a certain size (millimeter level), are not easily lost with the effluent in the reactor, and can be separated from the reactor to observe their morphological changes.

[0012] The drying includes vacuum drying; The drying conditions are: drying temperature 60-100℃, drying time 10-20h.

[0013] The preparation method described herein, in step (3), the calcination conditions are as follows: under a nitrogen or argon atmosphere, iron oxide undergoes a reduction reaction to generate zero-valent iron, the heating rate is 5-10℃ / min, the calcination temperature is 600-900℃, and the calcination time is 1-3h.

[0014] Thirdly, the present invention provides the use of the core-shell structured iron-carbon composite conductive particles in anaerobic biological treatment of wastewater containing recalcitrant organic matter to improve methane yield.

[0015] The aforementioned uses include antibiotics.

[0016] Fourthly, the present invention provides a method for using the aforementioned core-shell structured iron-carbon composite conductive particles, comprising the following steps: Anaerobic granular sludge and core-shell structured iron-carbon composite conductive particles are mixed evenly and placed in an anaerobic reactor. The organic wastewater to be treated is then introduced to carry out biological treatment of organic pollutants through biodegradation and biomass energy generation reaction.

[0017] The aforementioned method of use, wherein the mixing conditions are: mixed culture for 3 to 5 days to eliminate the adsorption of organic matter by the particles; The particle size of the anaerobic granular sludge is 0.50–2.00 mm; The volume ratio of the anaerobic granular sludge to the organic wastewater to be treated is 1:3 to 2:3. The amount of core-shell structured iron-carbon composite conductive particles added to the anaerobic reactor is 2-5 g / L. The anaerobic reactor includes intermittent flow, semi-continuous flow, and continuous flow reactors; The anaerobic reactor is kept at a constant temperature of 30–38°C, and the anaerobic environment is preferably achieved by nitrogen blowing. The biological treatment conditions are as follows: shaking is performed at a rate of 90–180 r / min, and the pH is between 6.80 and 8.5.

[0018] The method of use, specifically the operation of the intermittent flow anaerobic reactor: Before running the intermittent flow anaerobic reactor, nitrogen gas is introduced into the bottle to eliminate air interference and control the internal environment of the reactor to be anaerobic. The nitrogen gas is introduced for 10 to 30 minutes, and the gas flow rate is 50 to 100 mL / min.

[0019] The wastewater containing recalcitrant organic matter mainly refers to antibiotic wastewater discharged by pharmaceutical companies, such as chloramphenicol wastewater, and complex organic wastewater discharged by chemical companies, which contains recalcitrant organic matter.

[0020] The anaerobic sludge was acclimated in a laboratory EGSB reactor, with a TSS of 20.50–25.30 g / L and a VSS of 18.50–22.80 g / L.

[0021] The ratio of the amount of core-shell structured iron-carbon composite conductive particles to the amount of wastewater to be treated is as follows: the amount of core-shell structured iron-carbon composite conductive particles added is determined by the volume and concentration of the wastewater to be treated. When the concentration of chemical oxygen demand in the wastewater is 2000 mg / L to 4000 mg / L, the amount of core-shell structured iron-carbon composite conductive particles added per liter of wastewater is 3 to 5 g.

[0022] Compared with the prior art, the present invention has the following beneficial effects: 1. The iron-carbon composite conductive particles with core-shell structure have abundant mesopores and micropores on their surface, resulting in a large specific surface area, tight iron-carbon bonding, good conductivity, certain mechanical strength and fluidization properties, and the ability to exist stably in water treatment systems for a long time.

[0023] 2. The present invention features carbon-encapsulated zero-valent iron core-shell structure particles with porous surfaces, which on the one hand prevent other substances (such as PO4) in organic wastewater from being affected. 3- Iron ions can co-precipitate with zero-valent iron (ZVFe), or the ferrooxides produced by the oxidation of ZVFe can coat the surface of ZVFe, preventing effective contact between ZVFe and the digestive fluid or microorganisms, thus hindering its further function. On the other hand, the core-shell structured iron-carbon composite conductive particles of this invention allow for close contact between iron and carbon, forming numerous galvanic cells in the digestive fluid. This promotes short-chain or ring-opening reactions of recalcitrant organic pollutants, enhancing their biodegradability. Simultaneously, it provides electrons and hydrogen to anaerobic microorganisms, which are utilized by methanogens to produce more methane.

[0024] 3. The core-shell structure of the iron-carbon composite conductive particles exhibits stable performance and excellent conductivity, making them ideal as direct interspecies electron carriers between acid-producing and methanogenic bacteria. This accelerates electron transfer rates, promotes rapid pollutant degradation, and increases methane production rates. Experiments have verified that the removal rate of organic matter (COD) increased by 10–25%; cumulative methane production increased by 15–20%; and the removal rate of antibiotics was accelerated. Attached Figure Description

[0025] Figure 1 This is a flowchart illustrating the preparation process of the core-shell structured iron-carbon composite conductive spherical particles in Example 1. Figure 2 The nitrogen adsorption-desorption isotherm diagram (a) and pore structure diagram (b) of the core-shell structured iron-carbon composite conductive spherical particles in Example 1 are shown. Figure 3 Scanning electron microscope (a) and transmission electron microscope (b) images of the core-shell structured iron-carbon composite conductive spherical particles in Example 1; Figure 4 This is a schematic diagram of the anaerobic bioreactor in Example 2; Figure 5This is a graph showing the COD concentration of water samples taken at different reaction times during the enhanced anaerobic biological treatment of wastewater using core-shell structured iron-carbon composite conductive spherical particles in Example 2. Figure 6 The graph shows the change in chloramphenicol concentration over time in water samples taken at different reaction times during the anaerobic biological treatment of wastewater enhanced by the core-shell structured iron-carbon composite conductive spherical particles in Example 2. Figure 7 This shows the cumulative gas production during the enhanced anaerobic biological treatment of wastewater using core-shell structured iron-carbon composite conductive spherical particles in Example 2. Among them, 1-granular sludge, 2-ZVI@C-MP granules, 3-agglomerates, 4-gas collection bag, 5-main reaction zone, 6-headspace gas, and 7-sampling needle. Detailed Implementation

[0026] The following embodiments are merely some, not all, of the embodiments of the present invention. Therefore, the detailed descriptions of the embodiments provided below are not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0027] Unless otherwise specified, the reagents, instruments, preparation methods or processes described in the following embodiments are conventional techniques in the art.

[0028] Example 1: The preparation flow chart of core-shell structured iron-carbon composite conductive particles is shown below. Figure 1 .

[0029] The preparation method of core-shell structured iron-carbon composite conductive particles is as follows: 1. Preparation of carbon-encapsulated iron(III) oxide core-shell conductive material: Dissolve 3.5g of urea and 2.5g of ferric chloride hexahydrate in 50mL of glucose solution with a concentration of 150g / L, and stir thoroughly in a glass for 30min to obtain a mixed solution; The above mixed solution was introduced into a 100mL reaction vessel, and the reaction vessel was placed in a forced-air drying oven for hydrothermal reaction; the hydrothermal reaction time was 14h, and the hydrothermal temperature was 200℃. The solid precipitate obtained after hydrothermal treatment was washed three times by alternating centrifugation with ethanol and deionized water, each time at a centrifugation rate of 6000 rpm and a centrifugation time of 10 min. The solid precipitate after centrifugation was vacuum dried in a vacuum drying oven at 80°C for 12 hours. The dried material is ground and passed through a 100-mesh sieve to obtain a carbon-carbon composite conductive material with a core-shell structure of carbon-encapsulated iron oxide.

[0030] 2. Preparation of carbon-encapsulated iron(III) oxide core-shell structured conductive spherical particles: A carbon-coated iron oxide core-shell conductive material and montmorillonite powder binder were mixed at a mass ratio of 5:1. Deionized water was added to the mixed powder to obtain a viscous solid. The viscous solid was then kneaded by hand to prepare spherical particles with a diameter of about 3 mm. The particles were then placed in a vacuum drying oven and dried again at 80°C for 12 hours to obtain carbon-coated iron oxide core-shell conductive spherical particles.

[0031] 3. Preparation of carbon-encapsulated core-shell structured conductive spherical particles: Conductive spherical particles with a core-shell structure of carbon-coated iron(III) oxide were placed in a tube furnace. Nitrogen or argon gas was introduced into the furnace to isolate it from air at a flow rate of 80 mL / min. The furnace was heated at a rate of 5 °C / min, and the particles were calcined at 800 °C for 2 hours to obtain iron-carbon composite conductive spherical particles with a core-shell structure dominated by zero-valent iron, named ZVI@C-MP.

[0032] The density of the core-shell structured iron-carbon composite conductive spherical particles prepared in this embodiment was tested to be 983.675 kg / m³. 3 The specific surface area is 167.985 m². 2 / g, porosity 0.248 cm³ 3 / g, water absorption rate is 177.80%, and particle size is 3.0~3.3mm.

[0033] like Figure 2 The images show the nitrogen adsorption-desorption isotherms (a) and pore structure diagram (b) of the ZVI@C-MP. Figure 3 The images shown are scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the ZVI@C-MP.

[0034] Example 2: 1. Preparation of carbon-encapsulated iron(III) oxide core-shell conductive material: Dissolve 3.5g of urea and 3.5g of ferric chloride hexahydrate in 50mL of glucose solution with a concentration of 150g / L, and stir thoroughly in a glass for 30min to obtain a mixed solution; The above mixed solution was introduced into a 100mL reaction vessel, and the reaction vessel was placed in a forced-air drying oven for hydrothermal reaction; the hydrothermal reaction time was 12h, and the hydrothermal temperature was 150℃. The solid precipitate obtained after hydrothermal treatment was washed four times by alternating centrifugation with ethanol and deionized water, each time at a centrifugation rate of 4000 rpm and a centrifugation time of 5 min. The solid precipitate after centrifugation was vacuum dried in a vacuum drying oven at 60°C for 18 hours. The dried material is ground and passed through a 200-mesh sieve to obtain a carbon-carbon composite conductive material with a core-shell structure of carbon-encapsulated iron oxide.

[0035] 2. Preparation of carbon-encapsulated iron(III) oxide core-shell structured conductive spherical particles: A carbon-carbon conductive material with a core-shell structure of carbon-coated iron oxide (Fe3O4) and a binder of montmorillonite powder were mixed at a mass ratio of 7:1. Deionized water was added to the mixed powder to obtain a viscous solid. The viscous solid was then kneaded by hand to prepare spherical particles with a diameter of about 2 mm. These particles were then placed in a vacuum drying oven and dried again at 60°C for 10 hours to obtain carbon-coated iron oxide core-shell structure conductive spherical particles.

[0036] 3. Preparation of carbon-encapsulated core-shell structured conductive spherical particles: Conductive spherical particles with a core-shell structure of carbon-coated iron(III) oxide were placed in a tube furnace. Nitrogen or argon gas was introduced into the furnace to isolate it from air at a flow rate of 80 mL / min. The furnace was heated at a rate of 8 °C / min, and the particles were calcined at 600 °C for 1 h to obtain iron-carbon composite conductive spherical particles with a core-shell structure dominated by zero-valent iron, named ZVI@C-MP-1.

[0037] Example 3: Dissolve 3.5g of urea and 3.5g of ferric chloride hexahydrate in 50mL of glucose solution with a concentration of 150g / L, and stir thoroughly in a glass for 30min to obtain a mixed solution; The above mixed solution was introduced into a 100mL reaction vessel, and the reaction vessel was placed in a forced-air drying oven for hydrothermal reaction; the hydrothermal reaction time was 18h, and the hydrothermal temperature was 250℃. The solid precipitate obtained after hydrothermal treatment was washed five times by alternating centrifugation with ethanol and deionized water, each time at a centrifugation rate of 8000 rpm and a centrifugation time of 15 min. The centrifuged solid precipitate was vacuum dried in a vacuum drying oven at 100°C for 24 hours. The dried material is ground and passed through a 200-mesh sieve to obtain a carbon-carbon composite conductive material with a core-shell structure of carbon-encapsulated iron oxide.

[0038] 2. Preparation of carbon-encapsulated iron(III) oxide core-shell structured conductive spherical particles: A carbon-coated iron oxide core-shell conductive material and montmorillonite powder binder were mixed at a mass ratio of 10:1. Deionized water was added to the mixed powder to obtain a viscous solid. The viscous solid was then kneaded by hand to prepare spherical particles with a diameter of about 4 mm. These particles were then placed in a vacuum drying oven and dried again at 100°C for 20 h to obtain carbon-coated iron oxide core-shell conductive spherical particles.

[0039] 3. Preparation of carbon-encapsulated core-shell structured conductive spherical particles: Conductive spherical particles with a core-shell structure of carbon-coated iron(III) oxide were placed in a tube furnace. Nitrogen or argon gas was introduced into the furnace to isolate it from air at a flow rate of 80 mL / min. The heating rate of the tube furnace was 10 °C / min. After calcination at 900 °C for 3 h, iron-carbon composite conductive spherical particles with a core-shell structure and predominantly zero-valent iron were obtained, named ZVI@C-MP-2.

[0040] Example 2: Using a 100mL serum bottle as an anaerobic reactor, a simulated anaerobic biological treatment reactor for organic wastewater was constructed. Figure 4 As shown. 0.3g of ZVI@C-MP obtained in Example 1 was added to the serum bottle, followed by 30mL of anaerobic granular sludge (1) and 70mL of simulated antibiotic wastewater, with a volume ratio of approximately 3:7. The sludge adhered to the surface of the granules, forming aggregates (3). The anaerobic granular sludge was taken from granular sludge acclimated in EGSB, with a TSS of 22.13g / L, a VSS of 20.17g / L, and a VSS / TSS ratio of 0.91. The liquid area at the bottom of the serum bottle was the main reaction zone (5), and the upper part was the headspace (6). A gas collection bag (4) was connected to it to collect the biogas generated by the reactor. The serum bottle was sealed tightly with a rubber stopper, and a steel needle with a three-way valve, i.e., a sampling needle (7), was inserted into the rubber stopper for aeration and water sampling. The bottom of the steel needle was submerged above the liquid surface. The liquid in the serum bottle was aerated with nitrogen for 30 minutes to eliminate air interference. After connecting the serum bottles, they were placed in a constant temperature shaker at 35°C and the rotation speed was maintained at 100 r / min. Water samples were taken at reaction times of 0 h, 24 h, 48 h, 72 h, and 96 h to determine the concentrations of COD and chloramphenicol in the solution. The cumulative gas production was also measured at the end of the reaction to evaluate the enhancing effect of the core-shell structured conductive spherical particles on the anaerobic digestion system of antibiotic wastewater.

[0041] like Figure 5As shown, the antibiotic wastewater added in this embodiment is chloramphenicol wastewater. The COD of the influent is provided by sucrose at a concentration of 3500 mg / L. Urea and potassium dihydrogen phosphate are used to provide the nitrogen and phosphorus sources required for microbial growth and metabolism, respectively, with a carbon, nitrogen, and phosphorus mass ratio of 200:5:1. The concentration of chloramphenicol is 20 mg / L. To adjust the pH of the solution and prevent acidification, 0.7 g of sodium bicarbonate is added per liter of influent as a pH buffer. In this embodiment, sucrose, as a co-metabolite substrate, can improve the physiological activity of microorganisms, enhance their resistance to chloramphenicol toxicity, and accelerate the metabolic rate of chloramphenicol. Sucrose and chloramphenicol, as electron donors, enter the microbial cells and are oxidized and decomposed to produce small molecule intermediate metabolites, thereby reducing the content of organic matter in the water. Sucrose is first metabolized by acid-producing bacteria to produce volatile fatty acids such as acetic acid, propionic acid, and butyric acid. Then, fatty acids with three or more carbon atoms, such as propionic acid and butyric acid, are broken down by hydrogen-producing acetic acid bacteria into acetic acid, carbon dioxide, and hydrogen. The generated electrons are donated to methanogens through core-shell conductive spherical particles. Acetic acid and hydrogen are then converted into methane by acetic acid-producing and hydrogen-producing methanogens. Chloramphenicol undergoes dechlorination through microbial oxidation, producing intermediate metabolites that reduce its toxicity and minimize its harmful effects on microorganisms.

[0042] Example 3: Determination of water quality indicators Measurement methods: Water samples were taken at different reaction times to determine the concentrations of COD and chloramphenicol (CAP). A rapid COD assay was used to determine the change in COD over time to investigate the removal rate of organic matter. High-performance liquid chromatography (HPLC) was used to determine the content of chloramphenicol and the concentration of interspecific metabolites in the water samples to investigate ZVI@C. The effect of MP on methanogenesis from anaerobic biological treatment of chloramphenicol wastewater. In this test, the enhanced group was the anaerobic bioreactor with enhanced ZVI@C-MP, named R1, and the control group was the anaerobic bioreactor without ZVI@C-MP, named R0.

[0043] (1) Changes in COD over time in anaerobic digestion systems like Figure 5 The COD concentration of water samples was measured over time at different reaction times. The graph shows that the COD concentration gradually decreased to a stable level, with the degradation rate initially rapid and then slowing down. Furthermore, the COD degradation rate in the enhanced group was higher than that in the control group. At 96 hours of reaction, the COD removal rate in R1 increased by 24.04% compared to R0. Throughout the entire reaction process, the COD removal rate in the enhanced group remained higher than that in the control group. This is mainly due to ZVI@C MP's excellent conductivity makes it an electron transport carrier between microbial communities, promoting the rapid conversion of volatile organic acids in digestive fluids into methane, enhancing the synergistic metabolic effects between hydrolytic acidifying bacteria and methanogenic bacteria, and increasing the degradation rate of organic matter.

[0044] (2) Changes in chloramphenicol over time in anaerobic digestion systems To investigate the removal efficiency of ZVI@C-MP in an anaerobic treatment system for chloramphenicol, the concentration and removal rate of chloramphenicol in the solution were measured at different time points within 96 hours before the reaction. The results are as follows: Figure 6 As shown, the removal rate of chloramphenicol was significantly higher than that of organic matter. When the reaction proceeded to the 48th hour, the removal rate of chloramphenicol in the control group and the enhanced group reached 99.87%, indicating that chloramphenicol was basically completely degraded or transformed into other low-toxicity intermediate metabolites within the first 48 hours, thereby reducing the toxicity of the digestive fluid and mitigating the inhibitory effect on the activity of anaerobic microorganisms. The first 24 hours of reactor operation showed that the removal rate of chloramphenicol in the enhanced group was higher than that in the control group. When the reaction reached the 10th hour, the removal rates of chloramphenicol in the control group and the enhanced group were 72.22% and 89.46%, respectively. The removal rate of chloramphenicol in R1 was 10.24% higher than that in R0, indicating that the addition of the ZVI@C-MP enhanced carrier can accelerate the degradation and transformation of chloramphenicol. This is mainly due to the rich porous structure and large specific surface area of ​​the enhanced carrier, which rapidly adsorbs chloramphenicol in the water onto the surface, thereby rapidly reducing the toxicity of the solution and increasing the contact between chloramphenicol, microorganisms, and the enhanced carrier. This decomposes and metabolizes chloramphenicol in the water into non-toxic or low-toxic substances. Subsequently, the chloramphenicol adsorbed on the ZVI@C-MP surface is gradually desorbed into the solution and finally decomposed and metabolized by anaerobic organic matter, thus achieving the purpose of treating chloramphenicol wastewater.

[0045] Example 4: Determination of Gas Indicators Measurement Method: Biogas production was measured using a graduated syringe up to 96 hours of reaction to investigate the effect of ZVI@C-MP on the activity of methanogenic bacteria in the anaerobic digestion system and evaluate the effect of the enhancement material on gas production in the anaerobic digestion system. In this test, the enhancement group, designated R1, consisted of anaerobic reactors with ZVI@C-MP added, while the control group, designated R0, consisted of anaerobic reactors without ZVI@C-MP added.

[0046] To further confirm the effect of ZVI@C-MP on the cumulative gas production of the anaerobic digestion system, the cumulative gas production throughout the reaction process was collected using gas bags in both the control and enhanced groups. The results are as follows: Figure 7As shown, when the reaction proceeded to 96 hours, the gas production was basically stable. At this time, the cumulative gas production in the enhanced group and the control group was 84.5 mL and 176 mL, respectively, with the enhanced group being 2.08 times that of the control group. This is because ZVI@C-MP, as an electron transfer intermediate, promotes the synergistic metabolic process between acid-producing bacteria and methanogens. Hydrogen-producing acetic acid bacteria use ZVI@C-MP as a carrier for interspecies electron transfer to convert volatile fatty acids such as propionic acid and butyric acid into acetic acid, and then transfer the released electrons to acetic acid-type methanogens, reducing acetic acid to methane energy, thus accelerating the electron transfer rate.

[0047] Through the above embodiments and effect tests, it can be seen that the ZVI@C-MP provided by this invention has a better biological anaerobic treatment effect. Its rich pore structure and large specific surface area not only serve as an excellent carrier for microbial attachment and growth, enhancing the richness and diversity of functional microorganisms in the anaerobic system, but also adsorb antibiotics in the water, rapidly reducing the concentration of antibiotics in the solution and decreasing their inhibitory effect on microbial activity. Organic matter is rapidly degraded and produces more methane under the combined action of hydrolytic acidifying bacteria and methanogenic bacteria. More importantly, ZVI@C-MP exhibits iron-carbon micro-electrolysis in the digestion liquid, where zero-valent iron is oxidized to produce Fe. 2+ Providing microorganisms with essential trace elements enhances their activity. In addition, H... + The gain of electrons first generates highly reducing [H], which causes ring-opening or short-chain reactions in macromolecules that are difficult for microorganisms to metabolize directly, thereby improving the biodegradability of organic wastewater. Therefore, ZVI@C-MP can act as an electron shuttle, capturing electrons to achieve electron transfer, and as a redox medium to enhance extracellular electron transfer in organisms, thus increasing the yield of methane.

[0048] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A core-shell structured iron-carbon composite conductive particle, characterized in that, The iron-carbon composite conductive particles are core-shell structure conductive particles with carbon encapsulating zero-valent iron. The preparation method of the core-shell structured iron-carbon composite conductive particles includes the following steps: (1) Weigh urea and ferric chloride hexahydrate, dissolve them in glucose solution and stir evenly. After obtaining the mixture, place it in a reaction vessel and carry out hydrothermal reaction at high temperature to obtain a solid precipitate. After washing with ethanol and deionized water several times by centrifugation, dry it, grind and sieve it to obtain a carbon-encapsulated iron oxide core-shell structure conductive material. In step (1), the mass ratio of urea to ferric chloride hexahydrate is 7:3 to 7:8, the concentration of glucose solution is 100 to 200 g / L, and the mass ratio of glucose to ferric chloride hexahydrate in glucose solution is 1:1 to 5:1; the conditions for the hydrothermal reaction are: reaction temperature 150 to 250°C, reaction time 12 to 18 h. (2) Weigh the binder and the carbon-coated iron oxide core-shell structure conductive material, mix them thoroughly, dissolve them in deionized water to make a viscous substance, knead them into granules, dry them, and obtain carbon-coated iron oxide core-shell structure conductive particles. The binder mentioned in step (2) includes montmorillonite powder; the mass ratio of the binder to the carbon-encapsulated iron oxide core-shell structure conductive material is 1:5 to 1:10; (3) The carbon-coated iron oxide core-shell structure conductive particles were placed in a tube furnace and calcined in the absence of air to obtain carbon-coated zero-valent iron composite conductive particles. The calcination conditions described in step (3) are: under a nitrogen or argon atmosphere, the heating rate is 5-10℃ / min, the calcination temperature is 600-900℃, and the calcination time is 1-3h.

2. The core-shell structured iron-carbon composite conductive particles as described in claim 1, characterized in that, The conditions for centrifugal washing in step (1) are: 3 to 5 times of centrifugal washing, centrifugal speed of 4000 to 8000 rpm, and centrifugation time of 5 to 15 min; The drying conditions are: drying temperature 60-100℃, drying time 12-24h; The grinding and sieving conditions are as follows: grinding with a mortar and pestle, and sieving with a mesh size of 100 to 200.

3. The core-shell structured iron-carbon composite conductive particles as described in claim 1, characterized in that, The size of the particles in step (2) is 2 to 4 mm, and the shape of the particles includes spherical. The drying includes vacuum drying; The drying conditions are: drying temperature 60-100℃, drying time 10-20h.

4. The use of the core-shell structured iron-carbon composite conductive particles as described in claim 1 in anaerobic biological treatment of wastewater containing recalcitrant organic matter to improve methane yield, wherein the recalcitrant organic matter includes antibiotics.

5. The method of using the core-shell structured iron-carbon composite conductive particles as described in claim 1, characterized in that, Includes the following steps: Anaerobic granular sludge and core-shell structured iron-carbon composite conductive particles are mixed evenly and placed in an anaerobic reactor. The organic wastewater to be treated is introduced to carry out biological treatment of organic pollutants through biodegradation and biomass energy generation reaction. The mixing conditions are: mixed culture for 3-5 days; The particle size of the anaerobic granular sludge is 0.50–2.00 mm; The volume ratio of the anaerobic granular sludge to the organic wastewater to be treated is 1:3 to 2:

3. The amount of core-shell structured iron-carbon composite conductive particles added to the anaerobic reactor is 2-5 g / L. The anaerobic reactor includes intermittent flow, semi-continuous flow, and continuous flow reactors; The anaerobic reactor is kept at a constant temperature of 30–38°C, and the anaerobic environment is achieved by nitrogen blowing. The biological treatment conditions are as follows: shaking is performed at a rate of 90–180 r / min, and the pH is between 6.80 and 8.

5.

6. The method of using the core-shell structured iron-carbon composite conductive particles as described in claim 5, characterized in that, The specific operation of the intermittent flow anaerobic reactor is as follows: Before running the intermittent flow anaerobic reactor, nitrogen gas is introduced into the bottle to eliminate the interference of air and control the internal environment of the reactor to be anaerobic. The nitrogen gas is introduced for 10 to 30 minutes and the gas flow rate is 50 to 100 mL / min.

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