Carbon dioxide biological methanation method

Abstract

The invention belongs to the technical field of biological energy sources, and particularly relates to a carbon dioxide biological methanation method which comprises the following steps: S1, performing anaerobic domestication treatment on sludge to obtain sludge subjected to anaerobic domestication treatment; s2, carrying out anaerobic reaction on the sludge subjected to anaerobic domestication treatment to obtain methane; wherein the sludge subjected to anaerobic domestication treatment contains hydrogen-consuming methanogens. According to the method for producing methane, CO2 is converted into CH4 through a biological method by treating hydrogen-consuming methanogens in sludge through anaerobic domestication, meanwhile, the method has the advantages of being easy to operate, mild in operation condition, good in gas-liquid mass transfer effect, high in methane conversion efficiency, high in methane concentration in produced gas and the like, can be applied to biogas purification, and is wide in application range; and the method is suitable for large-scale industrial methane production.

Description

Technical Field

[0001] The invention belongs to the technical field of bioenergy, and in particular relates to a method for biomethanation of carbon dioxide. Background Art

[0002] The biogas produced by anaerobic digestion of biomass mainly contains 50% to 70% CH4, 25% to 45% CO2, and a small amount of H2S and H2O, and its calorific value is about 21 to 28 MJ / m 3 To improve the calorific value of biogas and further reach the standard calorific value of biogas 33-38MJ / m 3 , it is necessary to focus on removing the impurity CO2 in the biogas.

[0003] At present, the commonly used biogas purification technologies are mainly divided into two categories: one is to directly separate and remove CO2 from biogas. This type of method mainly includes pressure swing adsorption, absorption, low-temperature separation, membrane separation, etc. Although this type of method has a good purification effect, the energy consumption of the operation process is high, the operation cost is relatively expensive, and it may cause the loss of CH4. The second is to convert CO2 in biogas into CH4 through chemical or biological methods to increase gas production. Compared with the former, this type of method has the advantages of small investment and simple process. Among them, although the microbial conversion reaction rate is slower than that of the chemical conversion method, the microbial conversion process has the advantages of not requiring high temperature and high pressure conditions, mild reaction conditions, good enzyme specificity, few by-products, microorganisms are tolerant to sulfides in biogas, and less environmental pollution. It has great potential in biomass energy recovery.

[0004] However, the process of converting CO2 in biogas into CH4 through biological methods is a multiphase reaction process, including gas, liquid and solid phases such as gas substrate, culture medium and microorganisms. Therefore, the gas-liquid mass transfer efficiency becomes a limiting factor in optimizing the biogas purification effect. At present, the completely mixed reactor (CSTR) has the advantages of easy mixing and simple reactor structure, making it one of the most important reactor forms, but it also has negative effects such as high-speed stirring that destroys microbial flocs, thereby limiting the efficiency of biogas purification.

[0005] Therefore, there is an urgent need to develop a biological method that is simple to operate, has mild operating conditions, good gas-liquid mass transfer effect, high methane conversion efficiency, high methane concentration in the produced gas, and is suitable for large-scale industrial production to meet the needs of large-scale industrial production of biogas purification. Summary of the invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art to a certain extent. To this end, the present invention provides a method for bio-methanation of carbon dioxide. The method for producing methane of the present invention has the advantages of simple operation, mild operating conditions, good gas-liquid mass transfer effect, high methane conversion efficiency, high methane concentration in the produced gas, etc. It can be applied to biogas purification, has a wide range of applications, and is suitable for large-scale industrial production of methane.

[0007] The present invention proposes a method for producing methane. According to an embodiment of the present invention, it includes: S1: subjecting sludge to anaerobically acclimated treatment to obtain sludge subjected to anaerobically acclimated treatment; S2: subjecting the sludge subjected to anaerobically acclimated treatment to anaerobic reaction to obtain methane; wherein the sludge subjected to anaerobically acclimated treatment contains hydrogen-consuming methanogens. According to the production method of an embodiment of the present invention, CO2 is converted into CH4 by a biological method through hydrogen-consuming methanogens in the sludge subjected to anaerobically acclimated treatment, and it has the advantages of simple operation, mild operating conditions, good gas-liquid mass transfer effect, high methane conversion efficiency, and high methane concentration in the produced gas. It can be applied to biogas purification, has a wide range of applications, and is suitable for large-scale industrial production of methane.

[0008] According to an embodiment of the present invention, the above method for producing methane may also have the following additional technical features:

[0009] According to an embodiment of the present invention, the sludge comes from sludge treated by anaerobic process; wherein the temperature of the anaerobic process treatment is 30°C to 35°C.

[0010] According to an embodiment of the present invention, the anaerobic acclimation treatment comprises the following steps: (1) mixing a nutrient solution with sludge to obtain a sludge nutrient mixture; and (2) contacting the sludge nutrient mixture with carbon dioxide and hydrogen to obtain the sludge that has been anaerobic acclimated.

[0011] According to an embodiment of the present invention, in step (1), the volume ratio of the nutrient solution to the sludge in the mixing treatment is 1:1 to 3:1.

[0012] According to an embodiment of the present invention, in step (2), the volume ratio of the hydrogen to the sludge nutrient mixture is 1:1 to 1:3.

[0013] According to an embodiment of the present invention, in step (2), the contact treatment time is 13 to 20 days and the temperature is 65 to 80°C.

[0014] According to an embodiment of the present invention, in step (2), the volume ratio of the carbon dioxide to the hydrogen is 1:3 to 1:5.

[0015] According to an embodiment of the present invention, the hydrogen-consuming methanogens include: Methanothermobacter.

[0016] According to an embodiment of the present invention, the sludge subjected to anaerobically acclimated treatment further comprises: Gelria and / or Coprothermobacter and / or Tepidiphilus.

[0017] According to an embodiment of the present invention, the nutrient solution is used to provide nutrients other than the carbon source.

[0018] According to an embodiment of the present invention, the anaerobic reaction comprises the following steps: adding the sludge and nutrient solution that have undergone anaerobically acclimated treatment into an anaerobic drum reactor, introducing carbon dioxide and hydrogen into the anaerobic drum reactor, performing an anaerobic reaction, and collecting the outflowing gas to obtain the methane.

[0019] According to an embodiment of the present invention, in the anaerobic reaction, based on 1L of the sludge nutrient mixture, the total intake amount of carbon dioxide and hydrogen is 10L / d to 50L / d.

[0020] According to an embodiment of the present invention, in the anaerobic reaction, the volume ratio of carbon dioxide to hydrogen is 1:3 to 1:5.

[0021] According to an embodiment of the present invention, the temperature of the anaerobic drum reactor is 60-80°C, the internal circulation flow rate is 60mL / min-90mL / min, the drum speed is 3rpm-6rpm, the hydraulic retention time is 12d-18d, and the gas residence time is 18h-48h.

[0022] According to an embodiment of the present invention, the nutrient solution is used to provide nutrients other than the carbon source. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0024] Figure 1 Schematic diagram of the structure of the continuous flow anaerobic horizontal drum reactor in Example 1 of the present invention, wherein 1 is an air outlet pipe, 2 is a temperature gauge, 3 is a sampling port; 4 is an air inlet pipe connected to a microporous aeration pipe, 5 is a drain valve; 6 is an air bag; 7 is a water bath jacket, 8 is a steel mesh drum and a magnetic stirrer is used to drive the drum to rotate at a uniform speed, 9 is a pressure gauge, and 10 is a hygrometer;

[0025] Figure 2The figure is a result diagram of the change of gas components in the reaction system under different air intake amounts in Example 1 of the present invention, wherein volume is the measured volume of the corresponding gas, and percent is the percentage of the corresponding component in the total volume of the continuous flow anaerobic horizontal drum reactor;

[0026] Figure 3 This is a graph showing the fitting curve results of the Gompertz model for methane production in the reaction system at different air intake amounts in Example 1 of the present invention. DETAILED DESCRIPTION

[0027] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be understood as limiting the present invention.

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

[0029] In this document, the terms “include” or “comprising” are open expressions, that is, including the contents specified in the present invention but not excluding other contents.

[0030] As used herein, the terms "optionally", "optional" or "optionally" generally mean that the subsequently described event or circumstance may but need not occur, and that the description includes instances where the event or circumstance occurs and instances where it does not.

[0031] Terms and Definitions

[0032] In this article, the term "head space" refers to the head space of the serum bottle, that is, the space above the liquid phase in the serum bottle. In the embodiment of the present invention, the air there is replaced by the H2 / CO2 matrix, thereby achieving the purpose of acclimating the microorganisms in the anaerobic granular sludge.

[0033] In this article, the term "ex situ biogas purification" refers to a biogas post-treatment technology in which the biogas purification process is carried out outside the location where the biogas is produced. The generated biogas is collected from the anaerobic digester or other biogas-producing sites, and then transported to a special purification facility. Physical, chemical or biological methods are used to purify the biogas to remove impurity gases such as carbon dioxide (CO2) and hydrogen sulfide (H2S) in the biogas.

[0034] Herein, the term "internal circulation flow rate" refers to the rate at which hydrogen and carbon dioxide circulate inside the anaerobic rotating drum reactor.

[0035] As used herein, the term "hydraulic retention time" refers to the average time that the liquid supernatant remains in the anaerobic rotating drum reactor.

[0036] As used herein, the term "gas residence time" refers to the average time that the introduced CO2 and H2 gases reside in the anaerobic rotating drum reactor.

[0037] method

[0038] The present invention proposes a method for producing methane. According to an embodiment of the present invention, it includes: S1: subjecting sludge to anaerobically acclimated treatment to obtain sludge subjected to anaerobically acclimated treatment; S2: subjecting the sludge subjected to anaerobically acclimated treatment to anaerobic reaction to obtain methane; wherein the sludge subjected to anaerobically acclimated treatment contains hydrogen-consuming methanogens. According to the production method of an embodiment of the present invention, CO2 is converted into CH4 by a biological method through hydrogen-consuming methanogens in the sludge subjected to anaerobically acclimated treatment, and it has the advantages of simple operation, mild operating conditions, good gas-liquid mass transfer effect, and high methane conversion efficiency. It can be applied to biogas purification, has a wide range of applications, and is suitable for large-scale industrial production of methane.

[0039] According to an embodiment of the present invention, the sludge is derived from sludge treated by an anaerobic process; wherein the temperature of the anaerobic process treatment is 30-35°C. Exemplarily, the temperature of the anaerobic process treatment is 30°C, 31°C, 32°C, 33°C, 34°C, 35°C, preferably 34-35°C, and more preferably 35°C. Thus, the activity and quantity of methanogenic microorganisms in the microbial community of the sludge collected by preliminary condition screening are improved compared with ordinary sludge, providing a microbial basis for subsequent anaerobic reactions, and preliminarily obtaining microorganisms with better methanogenic performance.

[0040] According to an embodiment of the present invention, the anaerobic acclimation treatment comprises the following steps: (1) mixing the nutrient solution with the sludge to obtain a sludge nutrient mixture; (2) contacting the sludge nutrient mixture with carbon dioxide and hydrogen to obtain the sludge that has been anaerobic acclimation treated. Thus, through the anaerobic acclimation treatment, sludge rich in hydrogen-consuming methanogens is obtained, the microbial community in the sludge is optimized, and microorganisms with better methanogenic performance are further screened.

[0041] According to an embodiment of the present invention, in step (1), the volume ratio of the nutrient solution to the sludge in the mixing process is 1:1 to 3:1. Exemplarily, in step (1), the volume ratio of the nutrient solution to the sludge in the mixing process is 1:1, 2:1, 3:1, preferably 1:1 to 2:1, and more preferably 2:1, thereby, by mixing the nutrient solution with the sludge, a suitable nutritional environment is provided for the microorganisms, promoting their growth and metabolic activities, and thus screening and obtaining microorganisms with better methanogenic performance.

[0042] According to an embodiment of the present invention, in step (2), the volume ratio of the hydrogen to the sludge nutrient mixture is 1:1 to 1:3. Exemplarily, in step (2), the volume ratio of the hydrogen to the sludge nutrient mixture is 1:1, 1:2, 1:3, preferably 1:1 to 1:2, more preferably 1:2, thereby providing sufficient hydrogen and carbon dioxide for the sludge nutrient mixture, providing suitable environmental conditions for screening microorganisms with better methanogenic performance.

[0043] According to an embodiment of the present invention, in step (2), the contact treatment time is 13 to 20 days, and the temperature is 65 to 80°C. Exemplarily, the contact treatment time in step (2) is 12 days, 14 days, 16 days, 18 days, 20 days, 22 days, 24 days, preferably 12 to 14 days, and more preferably 14 days, thereby, carbon dioxide and hydrogen are fully contacted with the sludge nutrient mixture, and then microorganisms with better methanogenic performance are screened. Exemplarily, the contact treatment temperature in step (2) is 60°C, 65°C, 70°C, 75°C, 80°C, preferably 65 to 70°C, and more preferably 70°C, thereby screening out methanogenic microorganisms that survive and have high activity within this temperature range.

[0044] According to an embodiment of the present invention, in step (2), the volume ratio of carbon dioxide to hydrogen is 1:3 to 1:5. Exemplarily, the volume ratio of carbon dioxide to hydrogen in step (2) is 1:3, 1:3.2, 1:3.4, 1:3.6, 1:3.8, 1:4.0, 1:4.2, 1:4.4, 1:4.6, 1:4.8, 1:5, preferably 1:3.8 to 1:4.2, more preferably 1:4.0. Thus, suitable environmental conditions are provided for screening microorganisms with better methanogenic performance.

[0045] According to an embodiment of the present invention, the hydrogen-consuming methanogens include: Methanothermophilus. Thus, under the action of the hydrogen-consuming methanogens, the required methane is efficiently produced.

[0046] It should be noted that the "hydrogen-consuming methanogens" in the present invention refer to microorganisms that can consume hydrogen (H2) and convert it into methane (CH4) under anaerobic conditions.

[0047] According to an embodiment of the present invention, the sludge subjected to anaerobically acclimated treatment further comprises: Gerlia and / or Thermofaecium and / or Hydrogenophilus. Exemplarily, although Gerlia does not directly produce methane, it forms a symbiotic relationship with hydrogen-consuming methanogens to assist them in efficiently producing the required methane. Thus, under the joint action of hydrogen-consuming methanogens, Gerlia and / or Thermofaecium and / or Hydrogenophilus bacteria, the required methane is efficiently produced.

[0048] According to a specific embodiment of the present invention, the sludge derived from anaerobic process treatment contains hydrogen-consuming methanogens and other microorganisms. The hydrogen-consuming methanogens are functional microorganisms that mainly produce the required methane. For example, the sludge is derived from the medium-temperature anaerobic upflow reactor of pulp effluent from a paper mill, wherein the hydrogen-consuming methanogens include archaea of ​​the genus Methanothermophilus; in addition, the sludge also contains bacteria of the genera Gerlia, Faecalibacterium and Hydrogenophilus, which together exert better methanogenesis performance.

[0049] According to an embodiment of the present invention, the nutrient solution is used to provide nutrients other than carbon sources, thereby providing a suitable nutrient environment for microorganisms through the nutrient solution, promoting their growth and metabolic activities, and further improving the methane conversion efficiency.

[0050] According to an embodiment of the present invention, the anaerobic reaction comprises the following steps: adding the anaerobic acclimation treated sludge and nutrient solution into an anaerobic drum reactor, then passing carbon dioxide and hydrogen into the anaerobic drum reactor, performing anaerobic reaction, collecting the outflowing gas, and obtaining the methane. The inventor selected a stainless steel mesh with good mass transfer effect and easy biofilm formation as the immobilized growth filler for microorganisms, thereby improving the gas-liquid mass transfer efficiency and further improving the methane conversion efficiency; at the same time, by providing carbon dioxide and hydrogen, a metabolic substrate is provided for microorganisms, thereby efficiently producing methane.

[0051] According to an embodiment of the present invention, the anaerobic drum reactor is mainly composed of a reactor tank and a control host. The reactor tank is made of glass, with an inner diameter of 12.3cm, a barrel depth of 20.8cm, and a total volume of 2.5L, of which 2 / 5 is the effective volume of the liquid phase (liquid phase volume 1L, headspace 1.5L), and a 2.5cm thick water bath interlayer is wrapped outside for heat preservation. A stainless steel wire mesh drum with a diameter of 10.0cm is set inside the reactor. The drum is rolled with 100-mesh 304 steel wire mesh, welded at both ends and driven by a magnetic stirrer to rotate at a constant speed. The stainless steel tank cover connected to the drum is flange-connected to the glass outer cylinder, and an O-type silicone gasket with good waterproofness and high temperature resistance is added in the middle to ensure the sealing of the reaction device. The tank cover is provided with an inlet and outlet air pipe, a sludge sampling port and a drain valve, and a temperature and pressure detection device is provided to facilitate real-time monitoring of the stability of the anaerobic system. The reactor is connected to a host control cabinet that regulates the drum speed and gas flow rate. The gas internal circulation and water bath circulation are driven by a peristaltic pump. This improves the gas-liquid mass transfer efficiency, and by providing carbon dioxide and hydrogen, provides metabolic substrates for microorganisms, thereby efficiently and stably producing methane, further improving the methane conversion efficiency.

[0052] According to an embodiment of the present invention, in the anaerobic reaction, based on 1L of the sludge nutrient mixture, the total intake of carbon dioxide and hydrogen is 10L / d to 50L / d. Exemplarily, based on 1ml of the sludge nutrient mixture, the total intake of carbon dioxide and hydrogen is 10L / d, 15L / d, 20L / d, 25L / d, 30L / d, 35L / d, 40L / d, 45L / d, 50L / d, preferably 30 to 40L / d, more preferably 30L / d, thereby contacting the sludge nutrient mixture with an appropriate amount of carbon dioxide and hydrogen, regulating the metabolic activity of microorganisms, while avoiding the decrease in conversion efficiency caused by excessive carbon dioxide and hydrogen, and further improving the methane conversion efficiency.

[0053] According to an embodiment of the present invention, in the anaerobic reaction, the volume ratio of carbon dioxide to hydrogen is 1:3 to 1:5. Exemplarily, in the anaerobic digestion reaction, the volume ratio of carbon dioxide to hydrogen is 1:3, 1:3.2, 1:3.4, 1:3.6, 1:3.8, 1:4.0, 1:4.2, 1:4.4, 1:4.6, 1:4.8, 1:5, preferably 1:3.8 to 1:4.2, more preferably 1:4.0. Thus, by optimizing the volume ratio of carbon dioxide to hydrogen, the introduced carbon dioxide and hydrogen are fully utilized by hydrogen-consuming methanogens, further improving the methane conversion efficiency.

[0054] According to an embodiment of the present invention, the temperature of the anaerobic drum reactor is 60-80° C. Exemplarily, the temperature of the anaerobic drum reactor is 60° C., 65° C., 70° C., 75° C., 80° C., preferably 65-70° C., more preferably 70° C., thereby providing a suitable temperature environment for microorganisms, promoting their growth and metabolic activities, and further improving methane conversion efficiency.

[0055] According to an embodiment of the present invention, the internal circulation flow rate of the anaerobic drum reactor is 60 mL / min to 90 mL / min. Exemplarily, the internal circulation flow rate of the anaerobic drum reactor is 60 mL / min, 65 mL / min, 70 mL / min, 75 mL / min, 80 mL / min, 85 mL / min, 90 mL / min, preferably 75 to 80 mL / min, more preferably 80 mL / min, thereby allowing the sludge rich in hydrogen-consuming methanogens to fully contact with carbon dioxide and hydrogen, further improving the methane conversion efficiency.

[0056] According to an embodiment of the present invention, the drum speed of the anaerobic drum reactor is 3 rpm to 6 rpm. Exemplarily, the drum speed of the anaerobic drum reactor is 3 rpm, 4 rpm, 5 rpm, 6 rpm, preferably 3 to 4 rpm, more preferably 4 rpm, thereby allowing the sludge rich in hydrogen-consuming methanogens to fully contact with carbon dioxide and hydrogen, further improving the methane conversion efficiency.

[0057] According to an embodiment of the present invention, the hydraulic retention time of the anaerobic rotary drum reactor is 12d to 18d. Exemplarily, the hydraulic retention time of the anaerobic rotary drum reactor is 12d, 13d, 14d, 15d, 16d, 17d, 18d, preferably 13 to 14d, and more preferably 14d. Thus, the sludge rich in hydrogen-consuming methanogens is fully contacted with carbon dioxide and hydrogen, thereby further improving the methane conversion efficiency.

[0058] According to an embodiment of the present invention, the gas residence time of the anaerobic drum reactor is 18h to 48h. Exemplarily, the gas residence time of the anaerobic drum reactor is 18h, 24h, 28h, 32h, 36h, 40h, 44h, 48h, preferably 18 to 24h, more preferably 24h, thereby allowing the sludge rich in hydrogen-consuming methanogens to fully contact with carbon dioxide and hydrogen, further improving the methane conversion efficiency.

[0059] According to an embodiment of the present invention, the nutrient solution is used to provide nutrients other than carbon sources, thereby providing a suitable nutrient environment for microorganisms through the nutrient solution, promoting their growth and metabolic activities, and further improving the methane conversion efficiency.

[0060] Unless otherwise specified, the pH in the embodiments of the present invention is measured using a German WTW Multi 3510IDS digital pH meter.

[0061] Unless otherwise specified, the total solids (TS) in the embodiments of the present invention are determined as follows: TS = (drying weight - crucible weight) ÷ sludge volume; wherein, the drying weight is the weight of the crucible containing the sludge after drying it to a constant weight at a certain temperature, in g; the crucible weight is the weight of an empty crucible that was washed and dried to a constant weight before the start of the experiment, in g; and the sludge volume is the volume of the sludge sample, in mL.

[0062] Unless otherwise specified, the determination method of volatile solids (VS) in the embodiments of the present invention is VS = (drying weight - ignition weight) ÷ sludge volume; wherein, the drying weight is the weight obtained by drying the crucible containing the sludge at a certain temperature to a constant weight, and the unit is g; the ignition weight is the weight obtained by further igniting the dried sludge sample at a high temperature of 600°C to a constant weight (this weight is the weight of non-volatile inorganic substances in the sludge), and the unit is g; the sludge volume is the volume of the sludge sample, and the unit is mL.

[0063] Unless otherwise specified, the formula of the nutrient solution in the embodiments of the present invention is shown in Table 1. The specific method for preparing 1L of nutrient solution is to add 10mL of component A, 2mL of component B, 1mL of component C, 1mL of component D and 1mL of component E in sequence, and dilute to 1L with distilled water.

[0064] Table 1 Formula of nutrient solution

[0065]

[0066]

[0067] The scheme of the present invention will be explained below in conjunction with the embodiments. It will be appreciated by those skilled in the art that the following embodiments are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. Where specific techniques or conditions are not indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used are not indicated by the manufacturer and are all conventional products that can be obtained commercially.

[0068] Example 1: Experiment on improving CO2 methanogenesis yield and efficiency in anaerobic drum reactor

[0069] In order to improve the yield and efficiency of CO2 methanation, and further provide new ideas for improving ex situ biogas purification technology and solving problems such as resource shortages in the energy field, the inventors introduced exogenous hydrogen into an anaerobic reactor through a microbial process, used it as a reaction system, increased the intake volume of CO2 and H2 through a gradient, and while increasing the reactor intake load, the drum rotated at a uniform speed to promote mass transfer, so as to improve the yield and efficiency of methane. The specific method is as follows:

[0070] 1. H2 / CO2 domestication of microorganisms

[0071] (1) Source of anaerobic granular sludge: The anaerobic granular sludge used in the present invention comes from a medium-temperature anaerobic upflow reactor in the pulp wastewater of a paper mill in Jiangsu Province, and the temperature of the medium-temperature anaerobic upflow reactor is 35°C.

[0072] The results showed that the anaerobic granular sludge was black in color, with a pH of 8.0±0.1, a TS of 162.7±6.5 g / L, and a VS of 134.1±5.3 g / L.

[0073] (2) Acclimation of microorganisms in anaerobic granular sludge: Take 90 ml of the above anaerobic granular sludge and put it into a 500 ml serum bottle. Add nutrient solution to maintain the liquid working volume in the serum bottle at 300 ml. The headspace is filled with H2 / CO2 matrix (volume ratio of H2 / CO2 matrix = 4:1) that is replaced daily. Place it in a 70°C shaker (oscillation frequency 60 times / min) and culture it continuously for 14 days to obtain acclimated anaerobic sludge.

[0074] The results showed that the pH of the domesticated anaerobic granular sludge was 7.6±0.1, TS was 25.5±0.4g / L, and VS was 19.6±0.3g / L.

[0075] The above results show that compared with anaerobic granular sludge, the total solids in the domesticated anaerobic sludge water are reduced, and the amount of organic matter in the suspended solids, colloids and dissolved substances in the water is reduced, which means that the amount of microorganisms in the sludge is reduced and the microbial community is more homogeneous.

[0076] 2. Preparation of anaerobic reactor under continuous flow conditions

[0077] CO2 and H2 were introduced into the continuous flow anaerobic horizontal rotating drum reactor. The parameters of the continuous flow anaerobic horizontal rotating drum reactor were set as follows: internal circulation flow rate was 80 mL / min, drum speed was 4 rpm, hydraulic retention time was 14 days, and gas residence time was 24 hours.

[0078] 3. Intake volume gradient experiment under continuous flow

[0079] The temperature of the continuous flow anaerobic horizontal drum reactor was maintained at 70°C through water bath circulation, and four working conditions were set according to the gradient. The volume ratio of the inlet components H2 / CO2 in each working condition was H2 / CO2=4:1. The other setting parameters of the working conditions were as follows:

[0080] Working condition S1-0: The air intake volume is 20L / d, and the corresponding reaction time is 112 to 131 days.

[0081] Working condition S1-1: The air intake volume is 40L / d, and the corresponding reaction time is 132 to 148 days.

[0082] Condition S1-2: Restart the continuous flow anaerobic horizontal drum reactor at low load, with an air intake of 20 L / d and a corresponding time of 0 to 20 days.

[0083] Working condition S1-3: daily air intake volume is 30L / d, corresponding to a reaction time of 21 to 63 days.

[0084] 4. Air intake gradient experiment under batch conditions

[0085] When the air intake volume is 20L / d (operating condition S1-0), 30L / d (operating condition S1-3), and 40L / d (operating condition S1-1), 10mL of the air bag gas is taken every 1h, and the gas composition analysis and air bag volume measurement are performed. This can be used to obtain the substrate consumption and methane generation at different times when the reaction starts, until there is no significant change in the cumulative volume of methane. Three parallel experiments are performed for each air intake gradient, and the modified Gompertz model is used to fit the methanogenesis process to the obtained mean, thereby determining the characteristic parameters such as the maximum methane production, the maximum gas production rate, and the hysteresis period. The specific formula is as follows:

[0086]

[0087] Where: P is the theoretical maximum methane production, unit is NL;

[0088] R is the maximum methane production rate, in NLmethane / h;

[0089] λ is the hysteresis period of methanogenesis, in h;

[0090] x is the independent variable, which refers to the reaction time, in h;

[0091] y is the dependent variable, which refers to the methane production at that moment, in NL.

[0092] 5. Methane production and efficiency analysis

[0093] (1) Determination of methane production

[0094] After changing the gas bag every 24 hours, use a 50mL syringe to connect the gas bag replaced from the three-way pipe to take a 50mL sample, put it into a sealed bag, store it in a refrigerator at 4°C and complete the measurement within three days. The gas (H2, N2, CH4, CO2) content determination is all done by gas chromatography. The gas chromatograph model is Agilent 6890N, equipped with a thermal conductivity detector (TCD), equipped with three chromatographic columns, the models are 80 / 100M Hayseq Q 0.5M×1 / 8in pre-column (column 1), 80 / 100M Hayseq Q6ft×1 / 8in (column 2) and 60 / 100M Molsieve 5A6ft×1 / 8in (column 3). The injector, furnace temperature and detector operating temperature are set to 120°C, 35°C and 250°C. The carrier gas is high-purity helium (>99.99%) with a flow rate of 20mL / min. The gas injection volume is 0.2mL.

[0095] After replacing the air bag every 24 hours, the total volume of gas in the replaced air bag was measured with a 500mL syringe. The total volume of methane in the air bag was converted according to the percentage of each component measured by the gas chromatograph. The working conditions S1-0, S1-3, and S1-1 were measured continuously for 20 days, 42 days, and 16 days, respectively. The methane production data of each working condition was averaged to obtain the average daily methane production.

[0096] (2) Determination of methane synthesis efficiency

[0097] The synthesis efficiency refers to the ratio of the actual methane production to the theoretical value calculated based on the hydrogen consumption. The specific calculation formula is as follows:

[0098]

[0099] (3) Determination of methane purity in outlet gas

[0100] The methane purity in the outlet gas is the percentage of methane content measured by the gas chromatograph, which is the outlet gas CH4 concentration.

[0101] Schematic diagram of the structure of a continuous flow anaerobic horizontal rotating drum reactor Figure 1 The results of the changes in gas components in the reaction system under different inlet rates are shown in Figure 2 The fitting curve results of the Gompertz model for methanogenesis in the reaction system under different air intake rates are shown in Figure 3 .

[0102] The results show:

[0103] 1) When the air intake was 20L / d and the system was running stably for 132 days, the air intake was increased to 40L / d to examine the air intake load bearing capacity of the reaction system: At the beginning of the change of air intake load, due to the increase in air intake, H2 and CO2 appeared in the reaction system, indicating that 40L / d exceeded the maximum air intake that the reaction system could bear. As time went by, the CH4 production in the reaction system showed a downward trend, while the residual amount of H2 and CO2 gradually increased ( Figure 2 ).

[0104] The above results show that: under continuous flow conditions, before the air intake was increased to 40L / d, the concentrations of gas substrates H2 and CO2 in the reaction system were low, and gas-liquid mass transfer, as a limiting factor for hydrogen-consuming methanogenesis, caused the microorganisms in the reaction system to be in a state of starvation for a long time. After the air intake was increased to 40L / d, the gas-liquid mass transfer rate improved, and the digestion capacity of the microorganisms in the reaction system was temporarily oversaturated.

[0105] 2) On the 142nd day, the methane production in the reaction system gradually stabilized, and the average daily methane production in the whole stage reached 6.40±0.36NL / d, and the synthesis efficiency was 97.7±3.5%; among them, in the whole S1-2 condition, the average daily methane production was 3.20±0.32NL / d, and the synthesis efficiency was 87.3±4.4%; in the whole condition S1-3, the average daily methane production was 4.86±0.31NL / d, and the synthesis efficiency was 90.4±10.2% ( Figure 2 ).

[0106] The above results indicate that, under continuous flow conditions, when the air intake volume is ≤40 L / d, increasing the air intake load, i.e., the air intake volume, increases the methane production and methane production efficiency in the reaction system.

[0107] 3) In batch mode, the Gompertz model was used to fit the kinetic parameters of methanogenesis under different air intakes, and the anaerobic hydrogen consumption methanogenesis reaction process under different air intakes was compared. When the air intakes were 20L, 30L, and 40L, the maximum methane production was 3.04±0.03NL, 5.19±0.11NL, and 7.57±0.09NL, respectively; among them, when the air intake was 40L, its maximum methane production was 2.5 times that of the air intake of 20L ( Figure 3 ). When the air intake volume is 20L, 30L, and 40L, the maximum gas production rate is 0.29±0.01(NL / h), 0.30±0.01(NL / h), and 0.34±0.01(NL / h) respectively. Figure 3 ).

[0108] The above results show that under batch conditions, when the air intake volume is ≤40L / d, the maximum methane production increases with the increase of the air intake volume.

[0109] The results of continuous flow and batch conditions are as follows: when the internal circulation flow rate is 80 mL / min, the drum speed is 4 rpm, the hydraulic retention time is 14.2 d, and the gas residence time is 24 h, the total intake volume of carbon dioxide and hydrogen is controlled to be 30 L, and the H2:CO2 intake volume ratio is 4:1, which can simultaneously ensure a larger methane yield, a higher methane conversion efficiency, and a higher outlet methane purity.

[0110] (4) The inventors have compiled data on the methane production, methane synthesis efficiency, and outlet methane concentration that can be achieved by the present invention, as shown in Table 2.

[0111] Table 2 Methane production and substrate utilization under various conditions

[0112]

[0113] Among them, the intake load is: intake volume ÷ total volume of the reactor, the intake volume is: the total volume of hydrogen and carbon dioxide introduced into the air bag, the average daily production of CH4 is: the percentage of methane in the air bag measured by the gas chromatograph × the total volume of the remaining gas in the air bag, and the CH4 synthesis efficiency is: The outlet CH4 concentration is: the methane percentage in the air bag measured by the gas chromatograph, the H2 consumption is: the total volume of H2 intake air - the H2 percentage in the air bag measured by the gas chromatograph × the total volume of the remaining gas in the air bag, and the CO2 consumption is: the total volume of CO2 intake air - the CO2 percentage in the air bag measured by the gas chromatograph × the total volume of the remaining gas in the air bag.

[0114] (5) The inventors collected and sorted out data on the methane production, methane concentration, and hydrogen utilization rate that can be achieved by different existing technologies, as shown in Table 3.

[0115] Table 3 Comparison of biogas purification operation efficiency of different types of reactors

[0116]

[0117]

[0118] Among them, HRB is the horizontal drum reactor of this study; CSTR is a continuous stirred reactor; BCR is a bubble column reactor; FB is a fixed bed reactor; MB is a membrane bioreactor; HRB is a horizontal drum reactor; nd means no relevant data; ~ means approximately the data (the data is obtained from the result graph of the relevant literature);

[0119]

[0120] The methane concentration is the percentage of methane in the outlet gas measured by gas chromatograph.

[0121] [1]Bassani I, Kougias PG, Treu L, Angelidaki I. Biogas Upgrading via Hydrogenotrophic Methanogenesis in Two-Stage Continuous Stirred Tank Reactors at Mesophilic and Thermophilic Conditions. Environ Sci Technol 2015;49:12585-12593.

[0122] [2]Luo G,Angelidaki I.Integrated biogas upgrading and hydrogenutilization in an anaerobic reactor containing enriched hydrogenotrophicmethanogenic culture.Biotechnol Bioeng 2012;109:2729-2736.

[0123] [3]Kougias PG,Treu L,Benavente DP,Boe K,Campanaro S,Angelidaki I.Ex-situ biogas upgrading and enhancement in different reactorsystems.Bioresource Technol 2017;225:429-437.

[0124] [4]Lee JC,Kim JH,Chang WS,Pak D.Biological conversion of CO2 to CH4using hydrogenotrophic methanogen in a fixed bed reactor.J Chem Technol Biot2012;87:844-847.

[0125] [5]Ju DH,Shin JH,Lee HK,Kong SH,Kim JI,Sang BI.Effects of pHconditions on the biological conversion of carbon dioxide to methane in ahollow-fiber membrane biofilm reactor(Hf-MBfR).Desalination 2008;234:409-415.

[0126] The results show that compared with the biogas purification operation efficiency of different types of reactors in the prior art, the methanogenesis method of the present invention can obtain a higher methane yield and a higher outlet methane concentration. Compared with the CSTR with a higher methane yield, the maximum methane yield of the methaneogenesis method of the present invention is increased by 1.46 to 4.26 L / (L·d) when the air intake volume is 40 L / d; the methane concentration (%) of the methaneogenesis method of the present invention is as high as 87.5% when the air intake volume is 30 L / d, and the maximum methane yield is as high as 7.2 L / (L·d) at the same time.

[0127] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0128] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for producing methane, characterized in that: include: S1: performing anaerobic acclimation treatment on the sludge to obtain anaerobic acclimation treated sludge; S2: subjecting the anaerobic acclimation treated sludge to anaerobic reaction to obtain methane; Wherein, the sludge subjected to anaerobically acclimated treatment contains hydrogen-consuming methanogens.

2. The method according to claim 1, characterized in that The sludge is derived from sludge treated by anaerobic process; Wherein, the temperature of the anaerobic process treatment is 30°C to 35°C.

3. The method according to claim 1, characterized in that The anaerobic acclimation process comprises the following steps: (1) mixing the nutrient solution with the sludge to obtain a sludge nutrient mixed solution; (2) contacting the carbon dioxide and hydrogen with the sludge nutrient mixture to obtain the sludge that has been anaerobic acclimated; Optionally, in step (1), the volume ratio of the nutrient solution to the sludge in the mixing treatment is 1:1 to 3:1; Optionally, in step (2), the volume ratio of the hydrogen to the sludge nutrient mixture is 1:1 to 1:3; Optionally, in step (2), the contact treatment time is 13 to 20 days and the temperature is 65 to 80° C.; Optionally, in step (2), the volume ratio of the carbon dioxide to the hydrogen is 1:3 to 1:

5.

4. The method according to claim 1, characterized in that: The hydrogen-consuming methanogens include: Methanothermophilus spp.; Optionally, the anaerobic acclimation treated sludge further comprises: Gerlia and / or Thermofaecium and / or Hydrogenophilus.

5. The method according to claim 3, characterized in that: The nutrient solution is used to provide nutrients other than the carbon source.

6. The method according to claim 1, characterized in that The anaerobic reaction comprises the following steps: The sludge subjected to anaerobically acclimated treatment is mixed with a nutrient solution and added into an anaerobic drum reactor, carbon dioxide and hydrogen are introduced into the anaerobic drum reactor to carry out anaerobic reaction, and the outflowing gas is collected to obtain the methane.

7. The method according to claim 6, characterized in that In the anaerobic reaction, based on 1L of the sludge nutrient mixture, the total intake amount of carbon dioxide and hydrogen is 10 to 50L / d; Optionally, the volume ratio of carbon dioxide to hydrogen is 1:3 to 1:

5.

8. The method according to claim 6, characterized in that The temperature of the anaerobic drum reactor is 60-80° C., the internal circulation flow rate is 60 mL / min-90 mL / min, the drum speed is 3 rpm-6 rpm, the hydraulic retention time is 12 d-18 d, and the gas retention time is 18 h-48 h.

9. The method according to claim 6, characterized in that The nutrient solution is used to provide nutrients other than the carbon source.

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