Methane production method based on electrochemistry and biological reinforcement of sludge anaerobic digestion

Abstract

The application discloses a sludge anaerobic digestion methanogenesis method based on electrochemistry and biological reinforcement, which effectively realizes better sludge conversion effect and comprises the following steps: S1, electrochemical pretreatment: sludge containing microplastics is introduced into an electrochemical reactor, an electric field is applied for pretreatment, so that sludge zoogloea is broken, microplastics are degraded, and biological toxicity of the microplastics is reduced; S2, biological reinforcement anaerobic digestion: the pretreated sludge is sent into an anaerobic digestion reactor, and functional bacterial agents containing microplastic-degrading bacteria are added into the anaerobic digestion reactor for biological reinforcement; after mixing, digestion reaction is carried out under anaerobic conditions; and generated methane gas is collected; the application has the advantages of ingenious concept, simple and convenient operation, effective optimization of the efficiency of electrochemical pretreatment and control of energy consumption, provision of reaction substrates for methanogenic bacteria, improvement of the yield and stability of hydroxyl radicals, degradation of plastics, improvement of the methane generation efficiency, and the purpose of energy saving is achieved.

Description

Technical Field

[0001] This invention belongs to the field of anaerobic sludge treatment technology, and relates to a method for anaerobic digestion of sludge to produce methanogens based on electrochemical and biological enhancement. Background Technology

[0002] Mixed microplastics (MPs) present in anaerobic sludge treatment have been shown to hinder fermentation performance by suppressing microbial activity. Bioelectrochemical systems (BES), as a treatment technology combining microbial metabolism and electrochemical reactions, are increasingly being used to treat recalcitrant pollutants due to their superior redox reaction characteristics. However, their ability to mitigate microplastic pollution in wastewater is limited, and improving the inhibition of MPs in anaerobic sludge digestion by modifying the electrodes remains a research gap.

[0003] Therefore, a methanogenic method based on electrochemical and bioenhanced anaerobic digestion of sludge is needed to reduce the impact of mixed microplastics. BES-coupled anaerobic digestion is not a simple additive effect, but rather produces a powerful synergistic effect. It can not only transform the anaerobic digestion system from a "microplastic suppressor" to a "value-added agent," significantly improving energy recovery efficiency, but also reduce microplastic pollution at its source, making it a highly promising green and sustainable new technology for sludge treatment. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes a method for methanogenesis through anaerobic digestion of sludge based on electrochemical and bioenhanced processes, which effectively solves the problems in the prior art.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for methanogenesis from sludge anaerobic digestion based on electrochemical and bioenhanced processes includes the following steps: S1. Electrochemical pretreatment: Sludge containing microplastics is passed into an electrochemical reactor and pretreated by applying an electric field to break down sludge flocs, degrade microplastics and reduce their biotoxicity. S2. Bioenhanced Anaerobic Digestion: Pretreated sludge is fed into an anaerobic digestion reactor, and a functional bacterial agent containing microplastic-degrading bacteria is added for bioenhancing. After mixing, the digestion reaction is carried out under anaerobic conditions, and the generated methane gas is collected.

[0006] Preferably, in step S1, the electrochemical reactor uses composite modified carbon felt as the anode and composite modified nickel foam as the cathode.

[0007] Preferably, the preparation method of the composite modified carbon felt anode includes: cleaning the carbon felt substrate by acid washing, loading iron oxide particles by hydrothermal method, depositing tin dioxide-antimony coating by electrodeposition method, and finally obtaining the anode by high-temperature calcination treatment.

[0008] Preferably, the method for preparing the composite modified nickel foam cathode includes: cleaning the nickel foam substrate by acid washing, loading a molybdenum disulfide structure by hydrothermal method, depositing a nickel-iron alloy coating by electrodeposition method, and finally annealing the substrate.

[0009] Preferably, in step S1, the current density of the electrochemical pretreatment is 10 mA / cm². 2 Up to 50mA / cm 2 The pretreatment time is 0.5 to 2 hours.

[0010] Preferably, in step S2, the functional microbial agent further includes hydrogen-producing and acid-producing bacteria and methanogenic bacteria; the microplastic-degrading bacteria are strains capable of degrading at least one of PET, PE, PS, and PP.

[0011] Preferably, in step S2, the conditions for the anaerobic digestion reaction are: temperature controlled at 35±1℃, pH value maintained at 6.5 to 7.5, and hydraulic retention time of 15 to 35 days.

[0012] Preferably, in step S1, the electrical energy required for the electrochemical pretreatment comes from solar energy or biogas generated by the anaerobic digestion reaction.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention has an electrochemical pretreatment process, which pretreatment is performed by applying an electric field, which can break down sludge flocs, degrade microplastics and reduce their biotoxicity.

[0014] 2. This invention features a bio-enhanced anaerobic digestion process that, through the addition of relevant functional microbial agents, achieves targeted and efficient degradation of microplastics and completely converts them into methane. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the overall process of the present invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] The following is in conjunction with the appendix Figure 1 The specific embodiments of the present invention will be described in further detail below.

[0018] Depend on Figure 1As shown, in order to achieve better sludge conversion results, the present invention includes the following steps: S1. Electrochemical pretreatment: Sludge containing microplastics is passed into an electrochemical reactor and pretreated by applying an electric field to break down sludge flocs, degrade microplastics and reduce their biotoxicity. S2. Bio-enhanced anaerobic digestion: The pretreated sludge is fed into the anaerobic digestion reactor, and a functional bacterial agent containing microplastic degrading bacteria is added to it for bio-enhanced digestion. After mixing, the digestion reaction is carried out under anaerobic conditions, and the generated methane gas is collected. It should be noted that sludge containing microplastics can be taken from the residual sludge in the secondary sedimentation tank of urban wastewater treatment plants that have received wastewater from industries such as textiles, plastics processing, or cosmetics. The role of electrochemical pretreatment is to simultaneously achieve the dual objectives of breaking down sludge flocs, releasing intracellular organic matter, and breaking down long-chain polymers of microplastics (MPs) to make them hydrophilic, and to provide readily available substrates for subsequent bioaugmentation steps. Biofortification involves adding relevant functional microbial agents to achieve targeted and efficient degradation of microplastics and completely convert them into methane. By setting up electrochemical pretreatment and bio-enhanced treatment, the two can promote each other, thereby achieving better sludge conversion effect.

[0019] Furthermore, in order to provide reaction substrates for methanogens, in step S1, the electrochemical reactor uses composite modified carbon felt as the anode and composite modified nickel foam as the cathode. It should be noted that the composite modified carbon felt anode and the composite modified foamed nickel cathode are high-performance electrodes with higher catalytic activity than ordinary electrodes. In one embodiment, the anode size is 65cm*3cm*1cm, and the cathode size matches the anode size. The two are arranged in a parallel plate manner in the reactor with a spacing controlled at 2cm. Magnetic stirring is used to ensure full contact between the sludge and the electrodes. Through this electrode combination design, sufficient strong oxidizing free radicals (such as ·OH) can be generated to optimize the reaction interface environment.

[0020] Furthermore, in order to improve the yield and stability of hydroxyl radicals, the preparation method of the composite modified carbon felt anode includes: cleaning the carbon felt substrate by acid washing, loading iron oxide nanoparticles by hydrothermal method, depositing tin dioxide-antimony coating by electrodeposition method, and finally obtaining the anode by high-temperature calcination. In this embodiment, the preparation method of the composite modified carbon felt anode is as follows: 1. Substrate pretreatment: The carbon felt was ultrasonically cleaned in acetone and anhydrous ethanol for 30 minutes each, then immersed in 2 mol / L dilute nitric acid and heated and stirred in a water bath at 70°C for 3 hours. After that, it was washed with deionized water until neutral and dried at 80°C. 2. Fe3O4 loading: Dissolve 5 mmol FeCl3·6H2O and 2.5 mmol FeSO4·7H2O in 40 mL of deionized water (Fe 3+ :Fe 2+ =2:1), oxygen was removed by passing N2, and 0.8g urea and 0.1g PEG-1000 were added. The pretreated carbon felt was immersed in this solution and placed in a high-pressure reactor, reacting at 140℃ for 8 hours. After cooling, it was removed, washed with water and ethanol, and dried at 60℃ to obtain Fe3O4 / CF; 3. Electrodeposition of SnO2-Sb coating: Using Fe3O4 / CF as the working electrode, in an electrolyte containing Sn and Sb precursors, at a current density of 3 mA / cm². 2 Electrodeposition for 40 minutes; 4. High-temperature calcination: The deposited electrode is calcined in a muffle furnace at 500°C for 1 hour to finally obtain a high-performance composite anode.

[0021] The above preparation method can effectively improve the ·OH yield and stability of the composite modified carbon felt anode.

[0022] Furthermore, the preparation method of the composite modified nickel foam cathode includes: cleaning the nickel foam substrate by acid washing, loading molybdenum disulfide nanostructures by hydrothermal method, depositing a nickel-iron alloy coating by electrodeposition method, and finally annealing the substrate. In this embodiment, the preparation method of the composite modified nickel foam cathode is as follows: 1. Substrate pretreatment: The nickel foam was ultrasonically treated with 3 mol / L hydrochloric acid for 10 minutes, then ultrasonically cleaned with acetone and ethanol in sequence, and dried at 60°C. 2. Hydrothermal loading of MoS2: 0.5 g Na2MoO4·2H2O and 1.2 g thiourea were dissolved in 40 mL of deionized water, stirred until clear, and nickel foam was placed in a polytetrafluoroethylene liner. The solution was poured in, sealed in a reactor, and reacted at 200 °C for 20 hours. After cooling, the mixture was removed, washed with water and ethanol, and dried under vacuum at 60 °C to obtain MoS2 / NF. 3. Electrodeposition of Ni-Fe alloy: Using MoS2 / NF as the working electrode, in an electrolyte containing 0.1M NiCl2 and 0.1M FeCl2, at a current density of 8 mA / cm². 2 Electrodeposition for 100 seconds; 4. Annealing treatment: The composite cathode was finally prepared by annealing at 350℃ under an argon atmosphere for 1.5 hours. This cathode can efficiently catalyze the hydrogen evolution reaction (HER) and provide substrates for hydrogen-nutritive methanogens.

[0023] Furthermore, to optimize the efficiency of the electrochemical pretreatment and control energy consumption, in step S1, the current density of the electrochemical pretreatment is 10 mA / cm². 2Up to 50mA / cm 2 The pretreatment time is 0.5 to 2 hours; It should be noted that, as verified by experiments, the current density is 10 mA / cm². 2 Up to 50mA / cm 2 Within this range, it can achieve good "cell wall breaking" and "chain breaking" effects, and the energy consumption is relatively economical. In an optimal embodiment, the controlled current density is 30 mA / cm². 2 The pretreatment time is 1 hour. Under these conditions, the degradation efficiency of mixed microplastics can reach over 50%, and the sludge breakdown effect is significant. If the current density is too low or the time is too short, the effect will be poor; if it is too high or too long, it may lead to excessive oxidation of organic matter into CO2, wasting energy.

[0024] Furthermore, in order to degrade plastics, in step S2, the functional microbial agent also includes hydrogen-producing and acid-producing bacteria and methanogenic bacteria; the microplastic-degrading bacteria are strains capable of degrading at least one of PET, PE, PS, and PP. It should be understood that functional microbial agents constitute a complete microbial community system, added in lyophilized powder form. Among them: Microplastic-degrading bacteria: These bacteria specifically degrade microplastic fragments after electrical pretreatment. Strains such as Ideonella sakaiensis (which degrades PET) can be selected. Hydrogen-producing and acid-producing bacteria: responsible for further converting intermediate products generated during degradation into small molecule organic acids, hydrogen, etc. Methanogens: including acetic acidophilic and hydrogenotrophic types, are responsible for converting acetic acid, H2 / CO2 into methane.

[0025] The above three components form an efficient metabolic chain in the anaerobic digester, with the preferred dosage being 2%-3% (v / v) of the volatile solids (VS) content of the sludge.

[0026] Furthermore, in order to improve the methane production efficiency, the anaerobic digestion reaction conditions in step S2 are as follows: the temperature is controlled at 35±1℃, the pH value is maintained at 6.5 to 7.5, and the hydraulic retention time is 15 to 35 days. It should be noted that under these conditions, microbial activity is highest and the system is most stable. In particular, the hydraulic retention time (HRT) is significantly reduced; traditional anaerobic digestion typically requires 20-30 days, while this method, due to pretreatment, can significantly shorten the reaction time. In one embodiment, controlling the HRT to 20 days achieves a higher methane yield than the traditional 30-day digestion method, demonstrating its high efficiency. Furthermore, to prevent acidification, the pH can be automatically or manually controlled by adding buffers such as NaHCO3, maintaining the pH between 6.5 and 7.5.

[0027] Furthermore, in order to achieve the goal of saving energy, in step S1, the electrical energy required for the electrochemical pretreatment includes electricity generated from solar energy or biogas produced by the anaerobic digestion reaction. In this embodiment, solar photovoltaic panels can be configured to supply DC power, or the collected biogas can be desulfurized and dehydrated before being used to drive a biogas generator set, with the generated electricity then supplied to the electrochemical reactor. This design enables partial energy self-sufficiency for the entire system, significantly reducing operating costs and the carbon footprint of the technology.

[0028] The following experimental examples and comparative examples illustrate this scheme: Experimental materials and basic conditions: Sludge samples: Both the experimental and comparative examples used residual sludge from the secondary sedimentation tank of a municipal wastewater treatment plant from the same batch. The sludge was tested and found to have an initial solids content of approximately 5%, a volatile solids (VS) content of approximately 70%, and a high concentration of polyethylene (PE) and polyethylene terephthalate (PET) microplastics (concentration approximately 50 ± 5 mg / kg TS).

[0029] Basic parameters: The anaerobic digestion stages of the experimental examples and comparative examples were carried out under mesophilic conditions (35±0.5℃), with the initial pH adjusted to 7.0 and the mixture kept completely mixed.

[0030] The comparative example (traditional anaerobic digestion process) is as follows: The raw sludge (without any pretreatment) was directly fed into an anaerobic digester with an effective volume of 4L.

[0031] In this process, there is no electrochemical pretreatment; no exogenous bioenhancement, and digestion is carried out solely by the original microbial community inherent in the sludge; the hydraulic retention time (HRT) is set to 30 days.

[0032] The monitoring method was set as follows: throughout the entire 30-day digestion cycle, the cumulative methane production, pH value, and volatile fatty acid (VFA) concentration were monitored regularly, and the residual amount of microplastics in the sludge was measured after the experiment.

[0033] The experimental procedure is as follows: 1. Electrochemical pretreatment An equal amount of raw sludge as the comparative sample was introduced into an electrochemical reactor. The reactor was equipped with a composite modified carbon felt anode and a composite modified nickel foam cathode. An application of 30 mA / cm² was applied inside the reactor. 2 The current density was maintained at a constant level for 60 minutes. During the treatment, magnetic stirring was used to ensure full contact between the sludge and the electrode, thereby achieving the breakdown of sludge cell walls and the degradation or modification of microplastics.

[0034] 2. Bio-enhanced anaerobic digestion All pretreated sludge was transferred to the same anaerobic digester as the control group. A compound functional microbial agent (containing PET / PE degrading bacteria, hydrogen-producing and acid-producing bacteria, and methanogens) was then added at a ratio of 3% (v / v) of volatile solids (VS) content in the sludge. During this period, the hydraulic retention time (HRT) was shortened to 20 days compared to the control group, while other conditions (temperature, pH) remained the same.

[0035] The monitoring method is exactly the same as the comparison method, so as to make direct comparisons.

[0036] The monitoring results of the experimental examples and comparative examples are shown in the table below:

[0037] The above comparison clearly shows that the present invention achieves higher methane yield and microplastic removal efficiency than traditional processes in a shorter processing time through the synergistic effect of electrochemical and bio-enhanced processes, while ensuring stable system operation.

[0038] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for methanogenesis from anaerobic sludge digestion based on electrochemical and bioenhanced processes, characterized in that: Includes the following steps: S1. Electrochemical pretreatment: Sludge containing microplastics is passed into an electrochemical reactor and pretreated by applying an electric field to break down sludge flocs, degrade microplastics, and reduce their biotoxicity; the current density of the electrochemical pretreatment is 10 mA / cm² to 50 mA / cm², and the pretreatment time is 0.5 hours to 2 hours. The electrochemical reactor uses composite modified carbon felt as the anode and composite modified nickel foam as the cathode. The preparation method of the composite modified carbon felt anode includes: cleaning the carbon felt substrate by acid washing, loading iron oxide particles by hydrothermal method, depositing tin dioxide-antimony coating by electrodeposition method, and finally calcining at high temperature to obtain the anode. The method for preparing the composite modified nickel foam cathode includes: cleaning the nickel foam substrate by acid washing, loading a molybdenum disulfide structure by hydrothermal method, depositing a nickel-iron alloy coating by electrodeposition method, and finally annealing the substrate. S2. Bio-enhanced anaerobic digestion: The pretreated sludge is fed into the anaerobic digestion reactor, and a functional bacterial agent containing microplastic degrading bacteria is added to it for bio-enhanced digestion. After mixing, the digestion reaction is carried out under anaerobic conditions, and the generated methane gas is collected. The functional microbial agent also includes hydrogen-producing and acid-producing bacteria and methanogenic bacteria; the microplastic-degrading bacteria are strains capable of degrading at least one of PET, PE, PS, and PP; The conditions for the anaerobic digestion reaction are: temperature controlled at 35±1℃, pH value maintained at 6.5 to 7.5, and hydraulic retention time of 15 to 35 days; In step S1, the electrical energy required for the electrochemical pretreatment comes from solar energy or the electrical energy obtained from biogas power generation produced by the anaerobic digestion reaction.

2. The method for anaerobic digestion of sludge to produce methanogens based on electrochemical and bioenhanced methods according to claim 1, characterized in that: In step S1, the current density is controlled at 30 mA / cm², and the pretreatment time is 1 hour.

3. The method for anaerobic digestion of sludge to produce methanogens based on electrochemical and bioenhanced methods according to claim 1, characterized in that: In step S2, the functional microbial agent is added in the form of lyophilized powder.

4. The method for anaerobic digestion of sludge to produce methanates based on electrochemical and bioenhanced methods according to claim 1, characterized in that: The microplastic-degrading bacteria include Ideonella sakaiensis.

5. The method for anaerobic digestion of sludge to produce methanogens based on electrochemical and bioenhanced methods according to claim 1, characterized in that: In step S1, the anode and cathode are arranged in a parallel plate configuration with a spacing of 2 cm, and are stirred magnetically.

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