A composite bacterial community for degrading methane in waste gas, a cultivation method thereof, and an application thereof

Abstract

The present invention discloses a composite bacterial community for degrading methane in waste gas, a cultivation method thereof, and an application thereof. The present invention selects activated sludge from the reflux outlet of the aerobic tank of an oil refinery wastewater treatment station for screening and sedimentation concentration, uses loofah capsules to make a loofah capsule gel carrier, and uses it together with polyurethane sponge and ball ring filler as a carrier for fixing microorganisms. The carrier with fixed microorganisms is filled into a biological filter column, and single n-pentane, a composite pollutant of n-pentane and methane, and single methane are successively introduced for acclimation and cultivation. Finally, the acclimated biological filter column is applied to treat actual methane-containing waste gas. The cultivation method of the composite bacterial community for degrading methane in waste gas disclosed by the present invention has the characteristics of simple operation, economical and easy implementation, energy saving and environmental protection, and at the same time has the advantages of strong methane degradation performance, no secondary pollution, and easy engineering promotion. It can be used to treat organic waste gas with methane as a characteristic pollutant and has broad application prospects in the actual treatment of methane-containing waste gas.

Description

Technical Field

[0001] The invention belongs to the technical fields of microbial cultivation, air pollution control and environmental protection, and relates to a composite bacterial community for degrading methane in waste gas, a cultivation method and an application thereof. Background Art

[0002] In recent years, the growing greenhouse effect has not only led to glacier melting and sea level rise, but has also resulted in frequent natural disasters such as typhoons, hurricanes, droughts, and floods, causing serious damage to people's lives, property, and the social economy. Controlling the greenhouse effect has become a hot topic of public concern and a key area of effort.

[0003] The main greenhouse gases that contribute to the greenhouse effect include carbon dioxide, methane, nitrous oxide, and chlorofluorocarbons. Methane, as a primary component of clean energy natural gas, plays an irreplaceable role in industrial production and daily life, including combustion in industrial boilers, heating, and household cooking. However, due to its exceptionally strong shortwave radiation, methane's greenhouse effect is 28-120 times greater than that of carbon dioxide. On April 2, 2018, researchers at the U.S. Department of Energy's Lawrence Berkeley National Laboratory directly demonstrated that methane is a contributing factor to the increasing greenhouse effect on Earth's surface. Therefore, the greenhouse effect of methane cannot be ignored. Both domestically and internationally, the greenhouse effect is being closely monitored. Countries around the world are implementing global agreements to reduce greenhouse gas emissions. China announced its carbon peak and carbon neutrality targets at the United Nations General Assembly.

[0004] Methane in the atmosphere comes from a wide range of sources, including natural gas and coal gas leaks, decaying plant and animal carcasses, landfill gas generated during landfilling, biogas from biogas digesters in rural areas, gas generated in coal mining areas, and intestinal fermentation in ruminants. However, until now, neither domestic nor international regulations have regulated methane emissions as an environmental pollutant, leading to annual increases in atmospheric methane concentrations and exacerbating the greenhouse effect. As the greenhouse effect caused by methane becomes increasingly severe, the development of a green, efficient, and energy-efficient technology for purifying organic methane waste gas is urgently needed.

[0005] Traditional treatment technologies, such as high-temperature incineration, have the advantage of high removal efficiency, but are often only applicable to organic waste gas with high methane concentration (such as in the middle stage of landfill), and have the characteristics of high energy consumption and large carbon dioxide production. Although the adsorption method is suitable for treating low-concentration organic waste gas, methane is desorbed and returned to the atmosphere during the adsorbent regeneration process, and the subsequent treatment of the waste adsorbent produced by the adsorbent recovery will further increase the operating cost. Biological method is currently the most green and economical method for treating organic waste gas. It is also the method with the most application prospects and the most effective way to alleviate the greenhouse effect caused by methane. However, since methane is a hydrophobic organic matter, there are problems such as large gas-liquid mass transfer resistance, low tolerance of microorganisms to methane, and weak stability of the biological treatment system during the treatment process using biological methods. The existence of these unfavorable factors restricts the widespread application of biological methods in the treatment of methane organic waste gas.

[0006] Microorganisms are the main force in the treatment of wastewater and waste gas pollution. Strengthening their tolerance to the target substance methane and cultivating microbial communities with specific methane degradation capabilities are key to biological purification of methane pollution and mitigation of the greenhouse effect. Therefore, inventing a method for cultivating aerobic methane-oxidizing bacteria that remove methane from waste gas, thereby obtaining a specific microbial community that can use methane as a nutrient and achieving efficient biodegradation of methane organic waste gas, is of great significance for effectively purifying methane organic waste gas and achieving the goals of carbon peak and carbon neutrality. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing biological degradation and removal of hydrophobic methane, and provide a method for cultivating aerobic methane-oxidizing bacteria that is simple to operate, economical and environmentally friendly, safe and energy-saving, and easy to be promoted in engineering, so as to provide a method for treating methane organic waste gas that can efficiently degrade methane and alleviate the greenhouse effect.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0009] A composite bacterial community for degrading methane in waste gas, a cultivation method thereof, and an application thereof, comprising the following steps:

[0010] Step 1) Selection and pretreatment of microbial strains: Activated sludge with a sludge settling ratio (SV) of 20%-25% and a sludge volume index (SVI) of 80-120 mL / g at the reflux outlet of an aerobic tank of an oil refinery wastewater treatment station is selected and screened and concentrated by sedimentation;

[0011] Step 2) Preparation of loofah gel carrier: select old breeding loofah capsule, remove seeds and dry it, first soak it in sodium alginate solution, then soak it in calcium chloride and boric acid composite solution, take out clean water and wash it for standby use;

[0012] Step 3) Cultivation and fixation of microorganisms: preparing a nutrient solution and culturing the microorganisms under aeration conditions, placing the loofah gel, polyurethane sponge and Pall ring filler in a microbial culture system to fix the microorganisms;

[0013] Step 4) gradual domestication and cultivation of microorganisms: placing the loofah gel, polyurethane sponge and Pall ring filler immobilized with microorganisms in a biofilter column, and sequentially introducing single n-pentane, n-pentane and methane composite pollutants, and single methane into the biofilter column in stages to domesticate and cultivate the composite bacterial community that degrades methane in the waste gas;

[0014] Step 5) Using the domesticated microorganisms to treat methane-containing organic waste gas: introducing the methane-containing organic waste gas generated in the actual production process into the domesticated and cultivated biofilter column for treatment.

[0015] Preferably, the activated sludge selected in step 1) is passed through a 100-200 mesh sieve, and the supernatant is discarded during the sedimentation and concentration process, and the obtained activated sludge concentration (MLSS) is 10.0-20.0 g / L.

[0016] Preferably, in step 2), the loofah capsule is immersed in the sodium alginate solution for 5-12 hours, the mass concentration of sodium alginate is 0.05%-0.5%, and in the composite solution of calcium chloride water and boric acid, the mass concentration of calcium chloride solution is 1.0%-2.5%, the mass concentration of boric acid is 4.0%-5.3%, and the immersion time is 5-12 hours.

[0017] Preferably, the nutrient solution formula in step 3) is NaNO3 (500 mg / L), NaHCO3 (25 mg / L), MgSO4 (4.5 mg / L), K2HPO4 (30 mg / L), KH2PO4 (9 mg / L), CaCl2 (2.7 mg / L), CoCl2·6H2O (0.9 mg / L), FeCl3 (0.0926 mg / L), CuCl2·4H2O (0.062 mg / L), MnCl2·4H2O (0.144 mg / L), folic acid (0.89 ug / L), D-pantothenic acid (3.5 ug / L), vitamin B2 (2.3 ug / L), niacin (2.3 ug / L), biotin (2.3 ug / L), 5-10 mL of n-pentane / 30 L of nutrient solution, and 3-5 mL of n-pentane is added every 6-8 h; the aeration condition is continuous aeration, and the aeration rate is 100-200 L / h;

[0018] The polyurethane sponge and ball ring are pre-soaked in water for 10-24 hours before being put into the microbial culture system. The volume ratio of the loofah gel, polyurethane sponge and ball ring is 1:20-30:4-5. The polyurethane sponge has a PPI of 10-20, a porosity of more than 95%, and an apparent density of 15-30 kg / m 3 , Ball ring is made of plastic, diameter The fixed time is 36-48h.

[0019] Preferably, in step 4), the stacking order of the fillers in the biofilter column from top to bottom is polyurethane sponge, loofah gel, and Pall ring, and the height-to-diameter ratio of the biofilter column is 1:0.2-0.25. During the acclimation process, the nutrient solution is atomized and sprayed from the top of the biofilter column, and the waste gas containing n-pentane is introduced from the bottom of the biofilter column, and the n-pentane concentration is 500-800 mg / m 3 , gas-liquid ratio is 0.05-0.10L / m 3 The single n-pentane incubation time is 15-30 days; the n-pentane and methane composite pollutant concentration is n-pentane 500-800 mg / m 3 , methane 500-1000mg / m 3 The culture time is 15-30 days; the single methane concentration is 500-1000 mg / m 3 The cultivation time is 15-30 days.

[0020] The complex bacterial group capable of degrading methane in waste gas includes Proteus, Planctomyces, Chloroflexus, Anabacterium, Actinomycetes, Bacillus, Verrucomicrobia, Myxococcus and Dental Mononas.

[0021] Preferably, the actual methane-containing organic waste gas treated in step 5) mainly comes from early and late landfill gas in landfills, organic waste gas generated in coal mining areas, and methane-containing organic waste gas generated in the production process of the petrochemical industry and in refinery wastewater treatment stations.

[0022] Compared with the prior art, the advantages of the present invention are:

[0023] (1) The present invention provides a method for cultivating aerobic methane-oxidizing bacteria that is simple to operate and easy to perform;

[0024] (2) The composite bacterial community cultivated by the present invention for degrading methane in waste gas can use methane as nutrition and has a high efficiency in degrading and metabolizing methane greenhouse gas;

[0025] (3) The composite bacterial community cultivated by the present invention for degrading methane in waste gas has good resistance to the shock load of the treated methane waste gas;

[0026] (4) The biological degradation method for removing methane organic waste gas provided by the present invention does not require additional energy input, has the advantages of being economical, energy-saving, and free of secondary pollution. It is a green, safe, and economical method for treating organic waste gas with high use value and good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0028] Figure 1 This is a process flow chart of the waste gas treatment process in Example 1 of the present invention.

[0029] Figure 2 This is a diagram showing the treatment performance of the biofilter column for pentane in Example 1 of the present invention.

[0030] Figure 3 This is a diagram showing the methane treatment performance of the biofilter column in Example 1 of the present invention.

[0031] Figure 4 This is a diagram showing the methane treatment performance of the biofilter column in Example 2 of the present invention.

[0032] Figure 5 The present invention is a flow chart for cultivating a composite bacterial community for degrading methane in waste gas. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the scope of protection of the present invention is not limited thereby.

[0034] Example 1

[0035] The exhaust gas from the exhaust gas treatment facility of a certain oil refinery wastewater treatment station was tested and its non-methane hydrocarbon emission concentration met the local standards. The methane content was 0.084%, equivalent to a mass concentration of about 600 mg / m 3 Direct discharge will inevitably increase the methane content in the atmosphere, exacerbating the greenhouse effect. In order to reduce the methane concentration at the exhaust outlet and further purify the organic waste gas generated by the refinery wastewater treatment plant, aerobic activated sludge is obtained from the aeration tank of the refinery wastewater treatment plant to cultivate a complex bacterial community that can degrade methane in the waste gas. A biofilter column with a well-tamed microbial community is also added at the end of the existing waste gas treatment facility to purify the methane. The specific steps are as follows:

[0036] (1) The old, seeded and dried loofah was soaked in a sodium alginate solution with a mass concentration of 0.05% for 12 h, then taken out and soaked in a composite solution with a mass concentration of 1.0% calcium chloride and a mass concentration of 5.3% boric acid for 12 h. The 15PPI polyurethane sponge and Soak the ball ring packing in water for 24 hours.

[0037] (2) The activated sludge in the aeration tank of the refinery wastewater treatment plant was detected and analyzed. The sludge settling ratio (SV) was 25%, the sludge volume index (SVI) was 100 mL / g, and the sludge density was 2.5 g / m 3 , indicating that the activated sludge in the aeration tank of the refinery wastewater treatment plant has good sludge activity. The activated sludge in the aeration tank was selected on site and passed through a 200-mesh sieve, allowed to settle, and when the volume of the supernatant reached more than 80% of the total volume, the supernatant was discarded to obtain concentrated sludge.

[0038] (3) The concentrated sludge obtained is aerated at a rate of 200 L / h, and the soaked filler is placed into the concentrated sludge being aerated for microbial fixation.

[0039] (4) Prepare the nutrient solution for microbial culture, the formula is NaNO3 (500 mg / L), NaHCO3 (25 mg / L), MgSO4 (4.5 mg / L), K2HPO4 (30 mg / L), KH2PO4 (9 mg / L), CaCl2 (2.7 mg / L), CoCl2·6H2O (0.9 mg / L), FeCl3 (0.0926 mg / L), CuCl2 ·4H2O (0.062mg / L), MnCl2·4H2O (0.144mg / L), folic acid (0.89ug / L), D-pantothenic acid (3.5ug / L), vitamin B2 (2.3ug / L), niacin (2.3ug / L), biotin (2.3ug / L), 10mL n-pentane / 30L nutrient solution, add 5mL of n-pentane every 8h, and complete the immobilized culture of microorganisms after 48h.

[0040] (5) The loofah gel, polyurethane sponge, and Pall ring packings for immobilizing microorganisms were transferred to the biofilter column. The order of packing installation from bottom to top was Pall ring, loofah gel, and polyurethane sponge, with a corresponding volume ratio of 5:1:25.

[0041] (6) After the packing is installed, it is fed into the refinery wastewater treatment station for acclimatization and cultivation of organic waste gas with pentane and methane as the main pollutants. The pentane concentration is 600-800 mg / m 3 (Phase a).

[0042] (7) After 15 days of acclimatization and cultivation, the pentane load was reduced and the organic waste gas generated by the refinery wastewater treatment station was divided into two sections and respectively entered the original treatment facility and the newly added biofilter column treatment facility (stage b).

[0043] (8) After 25 days of staged treatment, the organic waste gas passage directly entering the newly added biofilter column is closed. The organic waste gas from the wastewater treatment station is treated by the original treatment facilities and then enters the newly added biofilter column treatment system for methane removal (stage c). The process is as follows: Figure 1 shown.

[0044] (9) The concentrations of pentane and methane at the inlet and outlet of the biofilter column were monitored using a gas chromatograph. The results were as follows: Figure 2 、 Figure 3 As shown, in stage a, the microorganisms in the biofilter column primarily feed on pentane. The pentane concentration at the exhaust outlet shows a decreasing trend, while the methane concentration remains almost constant, indicating that the microorganisms in the biofilter column are gradually adapting to the pentane exhaust environment. In stage b, after the pentane load is reduced, the microorganisms in the biofilter column gradually begin to feed on methane. The methane concentration at the exhaust outlet gradually decreases, indicating that the microorganisms have begun to adapt to the methane exhaust environment. In stage c, when the pentane load in the biofilter column is extremely low, the methane removal rate in the exhaust gas can reach approximately 95%. The microorganisms in the biofilter column can now use methane as a nutrient, thus cultivating aerobic methane-oxidizing bacteria.

[0045] (10) The microorganisms on the biofilter column packing that had been in operation for 70 days were bioidentified. The results showed that the composite bacterial community that could degrade methane in the exhaust gas after acclimation included Proteobacteria, Planctomyces, Chloroflexus, Bacillus, Actinomycetes, Bacillus, and Odontomonas.

[0046] Example 2

[0047] The methane content detected in the exhaust gas of a liquefied natural gas plant was as high as 0.105%-0.14%, which is equivalent to a mass concentration of about 750-1000 mg / m 3 Direct discharge has caused a sharp increase in methane levels in the surrounding environment, exacerbating the greenhouse effect. To reduce methane concentrations at the exhaust outlet, the liquefied natural gas plant purchased a set of biofilters to treat methane-containing waste gas. Before the biofilters were activated, activated sludge was obtained from the aeration tank of a refinery wastewater treatment plant and cultivated using traditional methods. The specific steps are as follows:

[0048] (1) 15PPI polyurethane sponge and Soak the ball ring packing in water for 24 hours.

[0049] (2) The sludge settling ratio (SV) of the activated sludge in the aeration tank of the refinery wastewater treatment plant was 20%, the sludge volume index (SVI) was 95 mL / g, and the sludge density was 2.3 g / m 3 , indicating that the activated sludge in the aeration tank of the refinery wastewater treatment plant has good sludge activity. The activated sludge in the aeration tank was selected on site and passed through a 200-mesh sieve, allowed to settle, and when the volume of the supernatant reached more than 80% of the total volume, the supernatant was discarded to obtain concentrated sludge.

[0050] (3) The concentrated sludge obtained is aerated at a rate of 200 L / h, and the soaked filler is placed into the concentrated sludge being aerated for microbial fixation.

[0051] (4) Prepare the nutrient solution for microbial culture with the formula of NaNO3 (500 mg / L), NaHCO3 (25 mg / L), MgSO4 (4.5 mg / L), K2HPO4 (30 mg / L), KH2PO4 (9 mg / L), CaCl2 (2.7 mg / L), CoCl2·6H2O (0.9 mg / L), FeCl3 (0.0926 mg / L), CuCl2·4H2O (0.062 mg / L), MnCl2·4H2O (0.144 mg / L), folic acid (0.89 ug / L), D-pantothenic acid (3.5 ug / L), vitamin B2 (2.3 ug / L), niacin (2.3 ug / L), biotin (2.3 ug / L), and glucose (4200 mg / L). The immobilized culture of microorganisms was completed after 48 hours.

[0052] (5) The polyurethane sponge and ball ring packings for immobilizing microorganisms were transferred to the biofilter column. The packings were installed in the order of ball ring at the bottom and polyurethane sponge at the top, with a corresponding volume ratio of 5:25 (1:5).

[0053] (6) After the packing is installed, methane-containing waste gas from the liquefied natural gas plant is introduced for acclimatization, cultivation and treatment.

[0054] (7) The methane concentration at the inlet and outlet of the biofilter column was monitored using a gas chromatograph. The results were as follows: Figure 4 As shown in the figure, in the absence of loofah gel carrier and in the case of acclimation and cultivation according to the traditional method, the biofiltration system has a low performance in removing hydrophobic methane. Even after the system stabilized after 70 days of operation, the methane removal rate was only 50%.

[0055] The traditional microbial domestication method generally uses pollutants as nutrition to domesticate specific microorganisms. This method may be a good domestication method for domesticating and cultivating microorganisms that specifically degrade and remove water pollutants or microorganisms that specifically degrade and remove hydrophilic organic matter. However, for hydrophobic organic matter with stable properties such as methane, it is difficult to cultivate a composite bacterial community that can efficiently degrade methane in waste gas due to the large gas-liquid mass transfer resistance and low microbial tolerance. The method for cultivating a composite bacterial community that degrades methane in waste gas provided by the present invention has the advantages of simple operation, green economy, energy saving and environmental protection, and easy engineering promotion. It can be widely used to treat organic waste gas containing methane, and is of great significance for effectively purifying organic waste gas containing methane, reducing the global greenhouse effect, and achieving carbon peak and carbon neutrality goals. In particular, for wastewater treatment plants with aerobic treatment processes such as refinery wastewater treatment plants and municipal domestic sewage treatment plants, local materials can be used for the cultivation and domestication of microorganisms.

[0056] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions that fall within the scope of protection of the present invention are within the scope of protection of the present invention. It should be noted that improvements and modifications that can be made by a person skilled in the art without departing from the principles of the present invention are also considered to be within the scope of protection of the present invention.

Claims

1. A method for cultivating a composite bacterial consortium for degrading methane in waste gas, comprising the following steps: Step 1) Selection and pretreatment of microbial strains: Activated sludge with a sludge settling ratio of 20%-25% and a sludge volume index of 80-120 mL / g at the reflux outlet of an aerobic tank of an oil refinery wastewater treatment station is selected and screened and concentrated by sedimentation; Step 2) Preparation of loofah gel carrier: select old breeding loofah capsule, remove seeds and dry it, first soak it in sodium alginate solution, then soak it in calcium chloride and boric acid composite solution, take out clean water and wash it for standby use; Step 3) Cultivation and fixation of microorganisms: preparing a nutrient solution and culturing the microorganisms under aeration conditions, placing the loofah gel, polyurethane sponge and Pall ring filler in a microbial culture system to fix the microorganisms; Step 4) gradual domestication and cultivation of microorganisms: placing the loofah gel, polyurethane sponge and Pall ring filler immobilized with microorganisms in a biofilter column, and sequentially introducing single n-pentane, n-pentane and methane composite pollutants, and single methane into the biofilter column in stages to domesticate and cultivate the composite bacterial community that degrades methane in the waste gas; Step 5) Using the domesticated microorganisms to treat methane-containing organic waste gas: introducing the methane-containing organic waste gas generated in the actual production process into the domesticated and cultivated biofilter column for treatment.

2. The method for cultivating a composite bacterial community for degrading methane in waste gas according to claim 1, characterized in that: Step 1) The selected activated sludge is passed through a 100-200 mesh sieve, and the supernatant is discarded during sedimentation and concentration to obtain an activated sludge concentration of 10.0-20.0 g / L.

3. The method for cultivating a composite bacterial community for degrading methane in waste gas according to claim 1, characterized in that: Step 2) the loofah capsule is immersed in the sodium alginate solution for 5-12 hours, the mass concentration of sodium alginate is 0.05%-0.5%, the mass concentration of the calcium chloride solution in the composite solution of calcium chloride water and boric acid is 1.0%-2.5%, the mass concentration of boric acid is 4.0%-5.3%, and the immersion time is 5-12 hours.

4. The method for cultivating a composite bacterial community for degrading methane in waste gas according to claim 1, characterized in that: Step 3) The nutrient solution formula is 500 mg / L NaNO3, 25 mg / L NaHCO3, 4.5 mg / L MgSO4, 30 mg / L K2HPO4, 9 mg / L KH2PO4, 2.7 mg / L CaCl2, 0.9 mg / L CoCl2·6H2O, 0.0926 mg / L FeCl3, 0.062 mg / L CuCl2·4H2 O, 0.144 mg / L MnCl2·4H2O, 0.89 ug / L folic acid, 3.5 ug / L D-pantothenic acid, 2.3 ug / L vitamin B2, 2.3 ug / L niacin, 2.3 ug / L biotin, and 5-10 mL n-pentane / 30 L nutrient solution, and 3-5 mL of n-pentane is added every 6-8 hours; the aeration condition is continuous aeration, and the aeration rate is 100-200 L / h; The polyurethane sponge and ball ring are pre-soaked in water for 10-24 hours before being put into the microbial culture system. The volume ratio of the loofah gel, polyurethane sponge and ball ring is 1:20-30:4-5. The polyurethane sponge has a PPI of 10-20, a porosity of more than 95%, and an apparent density of 15-30 kg / m 3 The ball ring is made of plastic, with a diameter of φ25-50mm, and the fixing time is 36-48h.

5. The method for cultivating a composite bacterial community for degrading methane in waste gas according to claim 1, characterized in that: Step 4) The stacking order of the fillers in the biofilter column from top to bottom is polyurethane sponge, loofah gel, and Pall ring. The height-to-diameter ratio of the biofilter column is 1:0.2-0.

25. During the acclimation process, the nutrient solution is atomized and sprayed from the top of the biofilter column, and the waste gas containing n-pentane is introduced from the bottom of the biofilter column. The n-pentane concentration is 500-800 mg / m 3 , gas-liquid ratio is 0.05-0.10L / m 3 The single n-pentane incubation time is 15-30 days; the n-pentane and methane composite pollutant concentration is n-pentane 500-800 mg / m 3 , methane 500-1000mg / m 3 The cultivation time is 15-30 days; the single methane concentration is 500-1000 mg / m 3 The cultivation time is 15-30 days.

6. The method for cultivating a composite bacterial consortium for degrading methane in waste gas according to claim 1, characterized in that: The actual methane-containing organic waste gas treated in step 5) mainly comes from early and late landfill gas in landfills, organic waste gas generated in coal mining areas, and methane-containing organic waste gas generated in the production process of the petrochemical industry and in refinery wastewater treatment stations.

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