In-situ biogas purification method for sludge anaerobic digestion based on exogenous hydrogen supply

Abstract

An in-situ biogas purification method for anaerobic digestion of sludge based on exogenous hydrogen supply relates to the field of solid waste resource utilization and renewable energy technology. The purpose of the present invention is to solve the problems of low hydrogen solubility and insufficient carbon dioxide bioconversion in the biogas purification process, as well as the inhibitory effect of excessive hydrogen dosage on biogas production by anaerobic digestion of sludge. The present invention utilizes the anaerobic digestion process of sludge in an anaerobic environment to produce biogas, and adds hydrogen to the process by direct hydrogen input or zero-valent iron corrosion, so that hydrogen penetrates into the liquid phase. The hydrogenotrophic methanogens in the system use hydrogen as an electron donor and carbon dioxide in the biogas produced by anaerobic digestion of sludge as an electron acceptor to convert hydrogen and carbon dioxide into methane to achieve in-situ biogas purification. The present invention can obtain an in-situ biogas purification method for anaerobic digestion of sludge based on exogenous hydrogen supply.

Description

Technical Field

[0001] The invention relates to the technical field of solid waste resource utilization and renewable energy, and in particular to an in-situ biogas purification method for anaerobic digestion of sludge based on exogenous hydrogen supply. Background Art

[0002] The burning of fossil fuels and the random disposal of production and living wastes cause about 15 billion tons of carbon dioxide to be discharged into the atmosphere every year, accelerating the process of global warming. In addition, the over-exploitation and use of fossil fuels will also lead to serious energy and environmental crises. Therefore, using clean renewable energy to replace fossil energy and reduce greenhouse gas emissions is an important measure to achieve sustainable development.

[0003] my country has a huge amount of solid waste. By 2020, the annual output of dry sludge can reach 13 million tons, and with the acceleration of urbanization, there is a trend of continuous increase. Since sludge is a by-product of sewage treatment, some pollutants in sewage will remain in the sludge, resulting in a large amount of organic matter, microorganisms, harmful substances, heavy metals and inorganic particles in the sludge. If it is not properly treated scientifically, it will inevitably have an adverse impact on the ecological environment. Anaerobic digestion is an effective method for sludge resource utilization. It is divided into three stages (hydrolysis, acidification, and methanogenesis). In the first stage, hydrolytic microorganisms decompose complex organic matter into simple organic matter; in the second stage, acidification microorganisms further convert the macromolecular hydrolysis products of the first stage into acetic acid, hydrogen (H2), and carbon dioxide (CO2); then methanogens use formic acid, acetic acid, methanol, H2 and CO2 as substrates to convert them into biogas, among which the main substrates are acetic acid, H2 and CO2. However, since the biogas produced by anaerobic digestion contains a large amount of carbon dioxide, it reduces the calorific value of biogas combustion and reduces its economic value and application scope. If the methane content in biogas can reach more than 95% (also called biomethane), it can be used more widely, such as for household and industrial power supply and heat generation, injection into natural gas pipelines as a substitute for natural gas, and as vehicle fuel, etc. Therefore, purifying biogas after anaerobic digestion can effectively make up for the shortage of energy in my country and further achieve carbon emission reduction.

[0004] Although traditional physical and chemical biogas purification methods can effectively purify biogas, they have disadvantages such as large energy demand and expensive catalysts. In addition, physical and chemical methods mainly focus on the removal of carbon dioxide, while ignoring the conversion and utilization of carbon dioxide. The in-situ biogas purification method of biohydrogenation uses cheaper hydrogen as an electron donor to convert carbon dioxide into methane through hydrogenotrophic methanogens, which can achieve carbon dioxide emission reduction and high-value utilization of biogas. However, the low solubility and poor gas-liquid mass transfer efficiency of hydrogen are the key limiting factors of hydrogen-driven biogas purification. Therefore, in order to increase the added value of biogas and reduce carbon dioxide emissions while achieving the rational utilization of waste resources, it is imperative to develop an in-situ biogas purification technology for anaerobic digestion of sludge based on exogenous hydrogen supply. Summary of the invention

[0005] The purpose of the present invention is to solve the problems of low hydrogen solubility and insufficient carbon dioxide bioconversion in the biogas purification process, as well as the inhibitory effect of excessive hydrogen addition on biogas production by anaerobic digestion of sludge, and to provide an in-situ biogas purification method for anaerobic digestion of sludge based on exogenous hydrogen supply in order to achieve high-value utilization of solid waste.

[0006] The in-situ biogas purification method for anaerobic digestion of sludge based on exogenous hydrogen supply of the present invention is carried out according to the following steps:

[0007] First, cultured sludge is added into the reactor body, and then hydrogen is injected into the hollow fiber membrane bundle in the reactor body or zero-valent iron is added into the reactor body, wherein the cultured sludge is cultured with anaerobic digestion sludge as inoculum and anaerobic sewage sludge as culture medium; then, the agitator is started and operated for 32 to 41 days under the conditions of a temperature of 34 to 36°C, a rotation speed of 120 to 150 rpm and a sludge retention time of 10 to 13 days, and the methane gas finally produced is collected by a gas collecting device.

[0008] Another in-situ biogas purification method for anaerobic digestion of sludge based on exogenous hydrogen supply of the present invention is carried out according to the following steps:

[0009] First, cultured sludge is added into the reaction device, and then hydrogen and zero-valent iron are injected therein, wherein the cultured sludge is cultured with anaerobic digestion sludge as inoculum and anaerobic sewage sludge as culture medium; then the agitator is started and operated for 23 to 25 days under the conditions of a temperature of 34 to 36° C., a rotation speed of 120 to 150 rpm and a sludge retention time of 10 to 13 days, and the methane gas finally generated is collected by a gas collecting device.

[0010] Technical principle of the present invention:

[0011] Sludge undergoes anaerobic digestion in an anaerobic environment to produce biogas. Hydrogen is added to the process by direct hydrogen input or zero-valent iron corrosion, allowing hydrogen to penetrate into the liquid phase. The hydrogenotrophic methanogens in the system use hydrogen as an electron donor and carbon dioxide in the biogas produced by anaerobic digestion of sludge as an electron acceptor to convert hydrogen and carbon dioxide into methane, thereby achieving in-situ biogas purification (4H2+CO2→CH4+2H2O, △G 0 =-130.7KJ / mol); Zero-valent iron can produce hydrogen when corroded in an anaerobic environment, thereby indirectly providing hydrogen to achieve the purpose of in-situ biogas purification by enhanced anaerobic digestion of sludge (Fe+2H2O→Fe(OH)2+H2; 3Fe(OH)2→Fe3O4+H2+2H2O).

[0012] Note: The inoculum sludge contains hydrogenotrophic methanogens. The principle of biogas upgrading is to use this bacteria to convert hydrogen and carbon dioxide into methane. There are other types of methanogens in the inoculum sludge, such as acetic methanogens, which can use acetic acid to produce methane and by-product carbon dioxide.

[0013] Beneficial effects of the present invention:

[0014] (1) Compared with the prior art, the present invention uses direct or indirect exogenous hydrogen supply to purify the biogas produced by anaerobic digestion of sludge in situ, and uses hydrogenotrophic methanogens in the sludge to react the carbon dioxide in the original biogas with the exogenously introduced hydrogen to produce methane, so that the carbon dioxide content in the original biogas is reduced and the methane content is increased, thereby achieving biogas purification, expanding the application scope of biogas, and effectively achieving high-value utilization of biogas; the indirect exogenous hydrogen supply method is to directly add zero-valent iron, which can not only provide hydrogen through its corrosion in an anaerobic environment, but also promote interspecies electron transfer of microorganisms, improve the activity of key enzymes, and promote the high metabolic activity of functional microorganisms, thereby increasing methane production and biogas purification. In addition, the present invention can also enhance biogas production while achieving biogas purification. Exogenous hydrogen supply (direct or indirect) can increase the activity of anaerobic digestion microorganisms, promote the enrichment of methanogens, improve the methanogenic efficiency, and enhance anaerobic digestion biogas generation. In addition, since the reaction conditions for in-situ biogas purification by biohydrogenation are mild and the source of exogenous hydrogen is wide and low-priced, it overcomes the shortcomings of traditional physicochemical biogas purification technology, such as high energy demand and high cost.

[0015] (2) The present invention utilizes direct exogenous hydrogen supply to purify the biogas produced by anaerobic digestion of sludge in situ, and utilizes a non-porous hollow fiber membrane assembly to supply hydrogen, thereby improving the gas-liquid mass transfer rate of hydrogen and achieving efficient bioconversion of hydrogen and carbon dioxide; in addition, by determining the optimal hydrogen addition range, the efficiency reduction and resource waste caused by excessive hydrogen addition are avoided.

[0016] The invention can obtain an in-situ biogas purification method for anaerobic digestion of sludge based on exogenous hydrogen supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The process flow chart of the in-situ biogas purification method of anaerobic digestion of sludge based on exogenous hydrogen supply of the present invention;

[0018] Figure 2 The schematic diagram of the structure of the in-situ biogas purification system for anaerobic digestion of sludge in which exogenous hydrogen is directly introduced in the present invention, 1 represents a reactor body, 2 represents a hollow fiber membrane bundle, 3 represents a membrane assembly fixing part, 4 represents a pH composite electrode, 5 represents a pH meter, 6 represents a gas collecting bag, 7 represents a liquid level, 8 represents a gas sampling port, 9 represents a liquid sampling port, 10 represents a mud replacement port, 11 represents a heating belt, 12 represents a magnetic stirrer, 13 represents a rotor, 14 represents a high-pressure hydrogen storage tank, 15 represents a hydrogen pressure reducing valve, 16 represents a pressure gauge, and 17 represents an air inlet pipe;

[0019] Figure 3 It is a structural schematic diagram of the in-situ biogas purification system for anaerobic digestion of sludge into which zero-valent iron is injected in the present invention, wherein 1 represents a reactor body, 4 represents a pH composite electrode, 5 represents a pH meter, 6 represents a gas collecting bag, 7 represents a liquid level, 8 represents a gas sampling port, 9 represents a liquid sampling port, 10 represents a mud replacement port, 11 represents a heating belt, and 18 represents iron powder. DETAILED DESCRIPTION

[0020] Specific implementation method 1: This implementation method is based on the in-situ biogas purification method of sludge anaerobic digestion based on exogenous hydrogen supply, and is carried out according to the following steps:

[0021] First, cultured sludge is added into the reactor body, and then hydrogen is injected into the hollow fiber membrane bundle in the reactor body or zero-valent iron is added into the reactor body, wherein the cultured sludge is cultured with anaerobic digestion sludge as inoculum and anaerobic sewage sludge as culture medium; then, the agitator is started and operated for 32 to 41 days under the conditions of a temperature of 34 to 36°C, a rotation speed of 120 to 150 rpm and a sludge retention time of 10 to 13 days, and the methane gas finally produced is collected by a gas collecting device.

[0022] Specific implementation method 2: The difference between this implementation method and specific implementation method 1 is that the injection rate of hydrogen is 26.7-158.4 mL / L / d.

[0023] The other steps are the same as those in the first specific implementation.

[0024] Specific implementation method three: This implementation method is different from specific implementation methods one or two in that the amount of zero-valent iron added is 5 to 20 g / L.

[0025] The other steps are the same as those in the first or second embodiment.

[0026] Specific embodiment 4: The difference between this embodiment and specific embodiments 1 to 3 is that the inoculum anaerobic digestion sludge is prepared according to the following steps: the sludge is anaerobically digested under anaerobic conditions and then degassed for 2 to 3 days; the culture medium anaerobic sewage sludge is prepared according to the following steps: the sludge is heat treated at a temperature of 80 to 90°C for 1 to 2 hours.

[0027] The other steps are the same as those in Specific Embodiments 1 to 3.

[0028] Specific embodiment 5: The difference between this embodiment and specific embodiments 1 to 4 is that when hydrogen is injected into the hollow fiber membrane bundle in the reactor body, the yield of methane gas is 28.7 to 52.0 mL / g-VS / d, and the purity is 80.3 to 88.1%.

[0029] The other steps are the same as those in Specific Embodiments 1 to 4.

[0030] Specific embodiment 6: The difference between this embodiment and specific embodiments 1 to 5 is that when zero-valent iron is added into the reactor body, the yield of methane gas is 22.3-32.2 mL / g-VS / d, and the purity is 85.3-92.0%.

[0031] The other steps are the same as those in Specific Embodiments 1 to 5.

[0032] Specific implementation method seven: This implementation method The in-situ biogas purification method of anaerobic digestion of sludge based on exogenous hydrogen supply is carried out according to the following steps:

[0033] First, cultured sludge is added into the reaction device, and then hydrogen and zero-valent iron are injected therein, wherein the cultured sludge is cultured with anaerobic digestion sludge as inoculum and anaerobic sewage sludge as culture medium; then the agitator is started and operated for 23 to 25 days under the conditions of a temperature of 34 to 36° C., a rotation speed of 120 to 150 rpm and a sludge retention time of 10 to 13 days, and the methane gas finally generated is collected by a gas collecting device.

[0034] Specific embodiment eight: This embodiment differs from specific embodiment seven in that the injection rate of hydrogen is 26.7 to 158.4 mL / L / d, and the addition amount of zero-valent iron is 5 to 20 g / L.

[0035] The other steps are the same as those in the seventh embodiment.

[0036] Specific embodiment nine: The difference between this embodiment and specific embodiment seven or eight is that the inoculum anaerobic digestion sludge is prepared according to the following steps: the sludge is anaerobically digested under anaerobic conditions and then degassed for 2 to 3 days; the culture medium anaerobic sewage sludge is prepared according to the following steps: the sludge is heat treated at a temperature of 80 to 90°C for 1 to 2 hours.

[0037] The other steps are the same as those in Specific Embodiment 7 or 8.

[0038] Specific embodiment 10: This embodiment differs from specific embodiments 7 to 9 in that the yield of methane gas is 8.0 to 9.7 mL / g-VS / d, and the purity is 75.3 to 77.9%.

[0039] The other steps are the same as those in Specific Embodiments 7 to 9.

[0040] The reactors in implementation modes one and seven are provided with a hydrogen pressure reducing valve, a pH meter and a liquid sampling port. The hydrogen pressure reducing valve controls the hydrogen partial pressure to 0.025 atm, and the pressure gauge monitors the pressure within the range of 0 to 0.025 atm; the pH meter is used to detect pH fluctuations in order to determine the stability of the reaction system and to facilitate adjustment of the system pH to 7.0-7.5; the liquid sampling port is used to obtain liquid samples for the purpose of determining the content of volatile fatty acids, soluble chemical oxygen demand, proteins and polysaccharides.

[0041] The following examples are used to verify the beneficial effects of the present invention:

[0042] Example 1: A method for in-situ biogas purification by anaerobic digestion of sludge based on exogenous hydrogen supply (direct introduction of hydrogen), which is carried out according to the following steps:

[0043] First, cultured sludge is added into the reactor body, and then hydrogen (with a purity of 100%) is injected into the hollow fiber membrane bundle in the reactor body. The cultured sludge is obtained by anaerobic digestion sludge as inoculum and anaerobic sewage sludge as culture medium, and the injection rate of hydrogen is 80 mL / L / d. Then, the agitator is started and operated for 33 days under the conditions of a temperature of 35° C., a rotation speed of 150 rpm, and a sludge retention time of 10 days (the sludge is replaced once during the operation time). The methane gas finally produced is collected by a gas collection device, and the maximum methane gas yield is 52.0 mL / g-VS / d (equivalent to 1.14 L / L / d); the maximum methane purity is 88.1%.

[0044] The total amount of gas produced each day was measured, the methane content in the gas was determined using a gas chromatograph, the methane production produced by the reaction system was calculated, and finally the hydrogen dosage of 80 mL / L / d when the cumulative methane production was the highest and the methane percentage content was the highest was determined as the optimal exogenous hydrogen dosage.

[0045] Example 2: A method for in-situ biogas purification by anaerobic digestion of sludge based on exogenous hydrogen supply (addition of zero-valent iron) is carried out according to the following steps:

[0046] First, cultured sludge is added into the reactor body, and then zero-valent iron is added into the reactor body, wherein the cultured sludge is obtained by culture with anaerobic digestion sludge as inoculum and anaerobic sewage sludge as culture medium, and the amount of zero-valent iron added is 10 g / L; then the agitator is started, and the agitator is operated for 33 days under the conditions of a temperature of 35° C., a rotation speed of 150 rpm, and a sludge retention time of 10 days (the sludge is replaced once during the operation time), and the methane gas finally produced is collected by a gas collecting device, and the maximum methane gas yield is 32.2 mL / g-VS / d (equivalent to 0.71 L / L / d); and the maximum methane purity is 92.0%.

[0047] The total amount of gas produced was measured, and the percentage of methane was determined using a gas chromatograph. The methane production was calculated from this. The optimal indirect exogenous hydrogen supply condition was determined to be 10 g / L zero-valent iron through the maximum cumulative methane production and the maximum methane percentage.

[0048] Example 3: A method for in-situ biogas purification from anaerobic digestion of sludge based on exogenous hydrogen supply is carried out according to the following steps:

[0049] First, cultured sludge is added into the reaction device, and then hydrogen (with a purity of 100%) and zero-valent iron are added thereto at the same time, wherein the cultured sludge is obtained by culture with anaerobic digestion sludge as inoculum and anaerobic sewage sludge as culture medium; then the agitator is started and operated for 23 days under the conditions of a temperature of 35° C., a rotation speed of 150 rpm, and a sludge retention time of 10 days (the sludge is replaced once during the operation time), and the methane gas finally produced is collected by a gas collecting device, and the yield of methane gas is 9.7 mL / g-VS / d, and the purity is 77.9%.

[0050] In the above Example 3, an anaerobic bottle with a working volume of 100 mL was used as the reaction device, and the inoculum anaerobic digestion sludge was prepared according to the following steps: the sludge (taken from the anaerobic reflux section of the Wenchang Treatment Plant in Harbin) was anaerobically digested under anaerobic conditions, and then degassed (to exhaust the residual biodegradable organic matter therein) for 2 days; the culture medium anaerobic sewage sludge was prepared according to the following steps: the sludge was heat treated at a temperature of 90°C for 1 hour.

[0051] The hollow fiber membrane bundle in the above-mentioned Example 1 adopts Teijin (Teijin Limited Japan) membrane fibers made of polypropylene, and the inner and outer diameters of the membrane fibers are 90 μm and 200 μm respectively.

[0052] Comparative Example 1:

[0053] In the current study, Hafuka et al. [1] Using an anaerobic membrane bioreactor, waste activated sludge was used as a substrate for anaerobic digestion and in-situ biogas purification. The process was accompanied by gas recirculation, and the maximum methane content was 92.0%, and the maximum methane yield was 14.8 mL / g-VS / d, which was less than the methane yield in the present invention. Alfaro et al. [2] By introducing hydrogen into the sewage sludge anaerobic digestion system using an immersed membrane, the methane yield reached 0.54 L / L / d and the maximum methane percentage reached 73.1%, which is less effective than the present invention.

[0054] In the current study, Zhu et al. [3] Using pig manure as substrate and mesophilic anaerobic digestion sludge as inoculum for anaerobic digestion in situ biogas purification, after adding 7.2 mL / min of hydrogen to the system, 295.7 mL / gsubstrate of methane with a content of 70.0% was produced. The methane production and percentage content were both lower than those of the present invention. Although the present invention uses sewage sludge, which has a low organic matter content, it is similar to Thapa et al. [4] Compared with the studies (0.85L / L / d and 81.0%), there is still a significant effect.

[0055] Charalambous et al. [5] In the cheese whey anaerobic digestion system, 25g / L of zero-valent iron powder was added, which produced 2.1L / L / d of methane and 95.9% methane percentage, which was 28.7% higher than that without adding zero-valent iron. The methane percentage after adding zero-valent iron in the present invention was 46.3% higher than that without adding zero-valent iron, indicating that the present invention has a better purification effect. It is worth noting that the amount of zero-valent iron used in this study is higher than that of the present invention, so its economic cost is also higher than that of the present invention. In addition, because the sewage sludge used in the present invention has a lower organic matter content and is not easily biodegradable than cheese whey, the present invention will have more advantages under the same conditions. Cerrillo et al. [6] When 84 mg / g-VS of zero-valent iron was added to the pig manure anaerobic digestion system, 0.3 L / L / d of methane with a content of 88.0% was produced, which was less effective than the present invention.

[0056] The present invention combines the research results of in-situ biogas purification of anaerobic digestion of sludge with direct and indirect exogenous hydrogen supply, and uses the characteristic that hydrogen consumption can be fine-tuned by hydrogen evolution through corrosion of zero-valent iron, and further investigates the effect of mixed addition of hydrogen and zero-valent iron on in-situ biogas purification of anaerobic digestion of sludge. At present, there is no research in the field on the mixed addition of hydrogen and zero-valent iron for biogas purification. In this study, 10g / L crude iron powder + 26.7mL / L / d hydrogen, 10g / L crude iron powder + 53.3mL / L / d hydrogen and 10g / L crude iron powder + 80mL / L / d hydrogen were simultaneously injected into the in-situ biogas purification system of anaerobic digestion of sludge, and the total gas production was measured, and the percentage of methane was determined by gas chromatography to determine the methane production effect of anaerobic digestion and the biogas purification effect. The hydrogen + zero-valent iron combination with the highest cumulative methane production (242.8 mL / g-VS, 120.7% higher than that without the addition of hydrogen and zero-valent iron) is 10 g / L crude iron powder + 80.0 mL / L / d hydrogen; the combination with the highest methane percentage (77.9%, 23.8% higher than that without the addition of hydrogen and zero-valent iron) is 10 g / L crude iron powder + 53.5 mL / L / d hydrogen.

[0057] References:

[0058] [1]Hafuka,A.,Fujino,S.,Kimura,K.,et al.In-situ biogas upgrading withH2 addition in an anaerobic membrane bioreactor(AnMBR)digesting wasteactivated sludge[J].Science of the Total Environment,2022,828,154573.

[0059] [2]Na A, Fpa B, Fpa B, et al. H2 addition through a submerged membrane for in-situ biogas upgrading in the anaerobic digestion of sewage sludge[J]. Bioresource Technology, 2019, 280: 1-8.

[0060] [3]Zhu,X.,Chen,L.,Chen,Y.,Cao,Q.,Liu,X.,Li,D.,2019b.Differences ofmethanogenesis between mesophilic and thermophilic in situ biogas-upgradingsystems by hydrogen addition.J.Ind.Microbiol.Biotechnol.46,1569–1581.

[0061] [4]Thapa,A.,Park,J.-G.,Yang,H.-M.,Jun,H.-B.,2021.In-situ biogasupgrading in an anaerobictrickling filter bed reactor treating a thermalpost-treated digestate.J.Environ.Chem.Eng.9,106780.

[0062] [5]Charalambous P,Vyrides I.In situ biogas upgrading and enhancementof anaerobic digestion of cheese whey by addition of scrap or powder zero-valent iron(ZVI)[J].J Environ Manage,2021,280:111651.

[0063] [6]Cerrillo M,Burgos L,Ruiz B,et al.In-situ methane enrichment incontinuous anaerobic digestion of pig slurry by zero-valent ironnanoparticles addition under mesophilic and thermophilic conditions[J].RenewEnerg,2021,180:372-82。

Claims

1. A method for in-situ biogas purification by anaerobic digestion of sludge based on exogenous hydrogen supply, characterized in that The purification method is carried out according to the following steps: First, adding cultured sludge into the reactor body, and then injecting hydrogen into the hollow fiber membrane bundle in the reactor body or adding zero-valent iron into the reactor body, wherein the cultured sludge is cultured with anaerobic digestion sludge as inoculum and anaerobic sewage sludge as culture medium; Then the agitator was started and operated for 32-41 days at a temperature of 34-36 °C, a rotation speed of 120-150 rpm, and a sludge retention time of 10-13 days. The methane gas finally produced was collected by a gas collector. The hydrogen injection rate was 26.7-158.4 mL / L / d. The amount of zero-valent iron added is 5~20 g / L; The inoculum anaerobic digestion sludge is prepared according to the following steps: the sludge is anaerobically digested under anaerobic conditions and then degassed for 2 to 3 days; the culture medium anaerobic sewage sludge is prepared according to the following steps: the sludge is heat treated at a temperature of 80 to 90° C. for 1 to 2 hours.

2. The method for in-situ biogas purification by anaerobic digestion of sludge based on exogenous hydrogen supply according to claim 1, characterized in that When hydrogen was injected into the hollow fiber membrane bundle in the reactor body, the yield of methane gas was 28.7~52.0 mL / g-VS / d with a purity of 80.3~88.1%.

3. The in-situ biogas purification method of sludge anaerobic digestion based on exogenous hydrogen supply according to claim 1, characterized in that When zero-valent iron was added to the reactor body, the yield of methane gas was 22.3~32.2 mL / g-VS / d, and the purity was 85.3~92.0%.

4. A method for in-situ biogas purification by anaerobic digestion of sludge based on exogenous hydrogen supply, characterized in that The purification method is carried out according to the following steps: First, cultured sludge is added into a reaction device, and then hydrogen and zero-valent iron are injected therein, wherein the cultured sludge is obtained by using anaerobic digestion sludge as inoculum and anaerobic sewage sludge as culture medium; then, the agitator is started and operated for 23 to 25 days under the conditions of a temperature of 34 to 36 °C, a rotation speed of 120 to 150 rpm, and a sludge retention time of 10 to 13 days, and the methane gas finally generated is collected by a gas collecting device; the injection rate of hydrogen is 26.7 to 158.4 mL / L / d, and the addition amount of zero-valent iron is 5 to 20 g / L; The inoculum anaerobic digestion sludge is prepared according to the following steps: the sludge is anaerobically digested under anaerobic conditions and then degassed for 2 to 3 days; the culture medium anaerobic sewage sludge is prepared according to the following steps: the sludge is heat treated at a temperature of 80 to 90° C. for 1 to 2 hours.

5. The method for in-situ biogas purification by anaerobic digestion of sludge based on exogenous hydrogen supply according to claim 4, characterized in that The yield of methane gas is 8.0~9.7 mL / g-VS / d, and the purity is 75.3~77.9%.

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