Method for producing biogas through micro-aerobic pretreatment and nano zero-valent iron reinforced anaerobic digestion of organic solid waste

Abstract

The invention provides a method for producing biogas through micro-aerobic pretreatment and nano zero-valent iron reinforced anaerobic digestion of organic solid waste, and belongs to the technical field of environmental engineering. According to the method, the organic solid waste is subjected to micro-aerobic pretreatment according to the type of the organic solid waste so as to improve the concentration of soluble organic matters in the organic solid waste, then in the anaerobic digestion process, the appropriate nanoscale zero-valent iron adding concentration is determined according to the total COD in the organic solid waste, and the content of the organic solid waste is increased by adding the nanoscale zero-valent iron. And the biogas yield (namely the volume biogas yield of the organic solid waste, namely the biogas yield of the organic solid waste per unit volume) is synergistically improved. According to the method, the organic matter degradation rate and the biogas production rate of anaerobic digestion of the organic solid waste are effectively increased, reduction and recycling treatment of the organic solid waste are achieved, generation of foul gas such as hydrogen sulfide in the anaerobic digestion process is greatly reduced, the biogas purification cost is reduced, the economic benefit of anaerobic digestion engineering is remarkably increased, and the method is suitable for popularization.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental engineering, and relates to a method for producing biogas by anaerobic digestion of organic solid waste in cooperation with nano-zero-valent iron through micro-aerobic pretreatment. Background Art

[0002] The disposal of organic solid waste has become an important development direction in the field of ecological and environmental protection. Anaerobic digestion uses fermentation bacteria and methanogens to degrade organic matter to produce methane, carbon dioxide and water under medium temperature (35°C) or high temperature (55°C), thereby achieving the reduction, stabilization, harmlessness and resource utilization of organic solid waste.

[0003] Anaerobic digestion can not only degrade organic matter, achieve reduction and stabilization, but also produce biogas as a clean energy source. It has become the best technical route for the disposal of organic solid waste such as sludge, food waste, and crop straw.

[0004] Anaerobic digestion usually includes four stages: hydrolysis, acidification, acetic acid production, and methanogenesis. In actual operation, due to the presence of difficult-to-degrade organic matter in organic solid waste (for example, extracellular polymers in residual sludge, cellulose in crop straw, etc.), low activity of methanogens, and accumulation of intermediate products (volatile fatty acids VFA), anaerobic digestion projects have low gas production rates, poor benefits, and are difficult to operate efficiently and stably. At present, in order to solve the above-mentioned problems in anaerobic digestion of organic solid waste, the main method is to enhance pretreatment and add functional materials to improve the methane production efficiency and system operation stability. The pretreatment process of organic solid waste mainly includes heat treatment, ultrasonic treatment, microwave treatment, mechanical treatment, ozone treatment, alkali treatment, etc. Due to the problems of high energy consumption and high cost, it is difficult to apply and promote in actual projects. Functional materials that can be added to anaerobic digestion of organic solid waste include trace metal elements, conductive materials, etc. Among them, trace elements such as iron ions, cobalt ions, and nickel ions can increase the relative abundance of key microbial flora in anaerobic digestion (such as increasing the relative abundance of Methanosarcina in Archaea) and the activity of key biological enzymes (such as iron redox protease and pyruvate formate lyase), thereby improving the efficiency of anaerobic digestion; conductive nanomaterials such as ferric oxide, nano zero-valent iron, and biochar can improve the efficiency of methanogenesis by promoting direct interspecies electron transfer (DIET) of anaerobic digestion microorganisms. However, since the cost of functional materials is usually high, the components of organic solid waste are complex, and the properties of each component are time-varying during continuous production and operation, it is difficult to determine the appropriate concentration of functional materials in actual anaerobic digestion projects. If the concentration is too low, the gas production efficiency will not be significantly improved, and if the concentration is too high, the microbial activity will be inhibited, resulting in a decrease in the degradation rate of organic matter and the gas production rate.

[0005] Organic solid waste is the end product of human production and life, and is also a usable resource. Anaerobic digestion and biogas utilization can achieve organic solid waste reduction, stabilization, harmlessness and resource utilization. Under the severe situation of global water pollution and energy crisis, improving the efficiency and economic benefits of anaerobic digestion of organic solid waste is of great significance for building a resource-saving, environmentally friendly society and achieving sustainable development. Summary of the invention

[0006] The present invention provides a method for enhancing the biogas production by anaerobic digestion of organic solid waste by means of micro-aerobic pretreatment in coordination with nano-zero-valent iron. The method effectively improves the organic matter degradation rate and biogas production rate (referring to the volumetric gas production rate of organic solid waste, i.e., the biogas production per unit volume of organic solid waste) of anaerobic digestion of organic solid waste, realizes the reduction and resource disposal of organic solid waste, and greatly reduces the generation of malodorous gases such as hydrogen sulfide during anaerobic digestion, reduces the biogas purification cost, and significantly improves the economic benefits of anaerobic digestion projects.

[0007] In order to achieve the above-mentioned purpose, the present invention provides a method for enhancing the anaerobic digestion of organic solid waste to produce biogas by synergistically using micro-aerobic pretreatment and nano-zero-valent iron. Micro-aerobic pretreatment is performed on the organic solid waste according to its type to increase the concentration of soluble organic matter in the organic solid waste. Then, during the anaerobic digestion process, the addition concentration of nano-zero-valent iron is determined according to the total COD in the organic solid waste. The addition of nano-zero-valent iron synergistically improves the biogas production rate.

[0008] It is understandable that in this method, the organic solid waste is first pretreated with a microaerobic process, and the microaerobic pretreatment process parameters are determined according to the type of organic solid waste. By providing a microaerobic environment, the types of hydrolysis and acidification functional microorganisms in the anaerobic digestion system are enriched, the abundance and activity of key microbial populations are increased, and the macromolecular organic matter that is difficult to degrade in the organic solid waste is quickly hydrolyzed to produce small molecular organic matter that is easily utilized by anaerobic microorganisms, thereby increasing the concentration of soluble organic matter and providing sufficient substrate for the subsequent methanogenesis stage. It is understandable that the organic matter (total COD) in the organic solid waste is divided into soluble organic matter and macromolecular insoluble organic matter. In order to further improve the gas production rate of anaerobic digestion, the macromolecular insoluble organic matter is degraded into small molecular soluble organic matter by strengthening pretreatment and adding functional materials, so as to improve the organic matter removal rate and biogas production rate. During the anaerobic digestion process, the appropriate concentration of nano-zero-valent iron is determined based on the total COD in the organic solid waste. The activity of key methanogenic microorganisms and enzymes in the anaerobic digestion process is increased by adding nano-zero-valent iron. At the same time, nano-zero-valent iron, as an electron conductor, can promote direct interspecies electron transfer to improve methanogenesis efficiency, thereby increasing biogas production, increasing organic matter removal rate, and reducing the production of odorous gases such as hydrogen sulfide.

[0009] Preferably, the particle size of nano zero-valent iron is in the range of 20nm-10μm, preferably 200-300nm. It is understandable that 200-300nm nano zero-valent iron can be dispersed more evenly in the anaerobic digestion system, release iron ions more quickly, accelerate the decomposition efficiency of refractory organic matter, and increase the relative abundance of key microbial flora in anaerobic digestion (such as increasing the relative abundance of Methanosarcina in Archaea) and key biological enzyme activities (such as iron redox protease, pyruvate formate lyase); at the same time, as a conductive nanomaterial, it improves the efficiency of methanogenesis by promoting direct interspecies electron transfer (DIET) of anaerobic digestion microorganisms.

[0010] Preferably, when determining the appropriate nano-zero-valent iron addition concentration according to the total COD in the organic solid waste, the nano-zero-valent iron is added in the form of a nano-zero-valent iron suspension, wherein the nano-zero-valent iron suspension is obtained by the following method:

[0011] The nano-zero-valent iron was dispersed with a 1 mmol / L sodium dodecyl sulfate solution to form a 30000 mg / L nano-zero-valent iron suspension.

[0012] As a preferred method, during the anaerobic digestion process, the volume V of the nano zero-valent iron suspension added is a =(0.001×b×V 0 ) / (30000-0.001×b)~(0.006×b×V 0 ) / (30000-0.006×b), where b is the total COD of organic solid waste, in mg / L; V 0 V is the volume of organic solid waste in the anaerobic digestion system, in L; a , unit: L.

[0013] It can be understood that the added volume V of the nano zero-valent iron suspension is a It is calculated in the following way:

[0014] The total COD of organic solid waste is detected as b (unit: mg / L), and the concentration of nano zero-valent iron added during anaerobic digestion should be controlled at 0.001×b~0.006×b, preferably 0.0025×b (unit: mg / L); and the volume of organic solid waste during anaerobic digestion is set as V 0 , the volume of nano zero-valent iron suspension added is V a , we can get w=(V a ×30000) / (V a +V 0 ), then the added volume V of nano zero-valent iron suspension can be calculated a The calculation method of V is as described above.a =(0.0025×b×V 0 ) / (30000-0.0025×b), unit: L.

[0015] Preferably, the types of organic solid waste include at least one of residual sludge from municipal sewage treatment plants, crop straw and garden waste, and restaurant kitchen waste.

[0016] Preferably, the organic solid waste is subjected to micro-aerobic pretreatment according to its type, specifically:

[0017] For the excess sludge from municipal wastewater treatment plants, the microaerobic process aeration ratio was set to 5 × 10 -6 ×b~1×10 -5 ×b vvm, pretreatment time is 12-24h, mechanical stirring rate is 50-80r / min; the preferred ventilation ratio is 8×10 -6 ×bvvm, pretreatment time was 15h, and mechanical stirring rate was 60r / min.

[0018] For crop straw and garden waste, the microaerobic process aeration ratio was set to 1 × 10 -5 ×b~2×10 -5 ×bvvm, pretreatment time is 16-28h, mechanical stirring rate is 50-90r / min; the preferred ventilation ratio is 1.5×10 -5 ×bvvm, pretreatment time was 22 h, mechanical stirring rate was 70 r / min;

[0019] For food waste, the microaerobic process aeration ratio was set to 3 × 10 -6 ×b~7×10 -6 ×b vvm, pretreatment time is 8-15h, mechanical stirring rate is 50-80r / min; the preferred ventilation ratio is 5×10 -6 ×b vvm, the pretreatment time was 10 h, and the mechanical stirring rate was 60 r / min.

[0020] Preferably, the organic solid waste is subjected to micro-aerobic pretreatment according to its type, specifically:

[0021] The volume proportions of residual sludge from municipal sewage treatment plants, crop straw and garden waste, and restaurant kitchen waste in organic solid waste are n. 1 、n 2 、n 3 , n 1 +n 2 +n 3 =100%, COD is b 1 、b 2 、b 3(Unit: g / L), then the ventilation ratio is (5×10 -6 ×b 1 ×n 1 +1×10 -5 ×b 2 ×n 2 +3×10 -6 ×b 3 ×n 3 )~(1×10 -5 ×b 1 ×n 1 +2×10 -5 ×b 2 ×n 2 +7×10 -6 ×b 3 ×n 3 )vvm, pretreatment time is 10-24h, mechanical stirring rate is 50-90r / min; n 1 、n 2 、n 3 Any value in the range of 0% to 100%;

[0022] Wherein, b is COD, unit is mg / L; ventilation ratio, unit is vvm, which is the ratio of ventilation volume per minute to the volume of pretreated organic solid waste.

[0023] As a preferred method, the ventilation ratio is (8×10 -6 ×b 1 ×n 1 +1.5×10 -5 ×b 2 ×n 2 +5×10 -6 ×b 3 ×n 3 ), the preprocessing time is (15×n 1 +22×n 2 +10×n 3 )h, the mechanical stirring rate is (60×n 1 +70×n 2 +60×n 3 )r / min;

[0024] Wherein, b is COD, unit is g / L; ventilation ratio, unit is vvm, is the ratio of ventilation volume per minute to the volume of pretreated organic solid waste.

[0025] Preferably, after the pretreatment, nitrogen is passed through the organic solid waste to remove oxygen, the nitrogen ventilation ratio is 0.2-0.8vvm, and the ventilation time is 2-5min; preferably, the ventilation ratio is 0.5vvm, and the ventilation time is 3min.

[0026] As a preferred method, compared with only microaerobic pretreatment and only adding nano zero-valent iron, the biogas production rate is increased by 30-50% and 20-30% respectively.

[0027] Compared with the prior art, the advantages and positive effects of the present invention are:

[0028] The present invention provides a method for synergistically strengthening anaerobic digestion of organic solid waste by micro-aerobic pretreatment and addition of nano-zero-valent iron, which effectively improves the organic matter degradation rate and biogas production rate of anaerobic digestion of organic solid waste. Compared with only micro-aerobic pretreatment and only addition of nano-zero-valent iron, the biogas production rate is increased by 30-50% and 20-30%, respectively, thereby achieving the reduction and resource disposal of organic solid waste, and greatly reducing the generation of malodorous gases such as hydrogen sulfide during anaerobic digestion, reducing the cost of biogas purification, and significantly improving the economic benefits of anaerobic digestion projects, which is suitable for popularization and application. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Example 1

[0031] A municipal sewage treatment plant in a northern coastal city has a treatment capacity of 300,000 cubic meters per day. 2 O+MBBR (anaerobic-anoxic-aerobic+moving bed biofilm reactor) and A 2 O+MBR (anaerobic-anoxic-aerobic-membrane bioreactor) process, the total COD of the residual sludge was 35230 mg / L, and the pH was 6.82. 2L of residual sludge was taken respectively, and the inoculated sludge was the sludge from the anaerobic digester of the sewage treatment plant, and the ratio of inoculated sludge to residual sludge was 1:3; a blank control group, a microaerobic pretreatment control group, a nano-zero-valent iron control group and an experimental group were set up, and 3 parallel samples were set up in each group.

[0032] Blank control group: no microaerobic pretreatment, no addition of nano zero-valent iron, the temperature of the sludge anaerobic digestion system was controlled at 35°C, and anaerobic digestion was carried out for 20 days.

[0033] Only microaerobic pretreatment control group: microaerobic pretreatment (ventilation ratio of 8×10 -6 ×35230=0.3vvm, pretreatment time of 15h, stirring rate of 60r / min), no addition of nano zero-valent iron, ventilation ratio of 0.3vvm, pretreatment time of 15h, stirring rate of 60r / min, control the temperature of sludge anaerobic digestion system at 35℃, and carry out anaerobic digestion for 20d.

[0034] Only nano-zero-valent iron control group was added: no microaerobic pretreatment was performed, nano-zero-valent iron with a particle size of 200 nm was selected, and a nano-zero-valent iron suspension with a concentration of 30000 mg / L was prepared with 1 mmol / L sodium dodecyl sulfate solution; the nano-zero-valent iron suspension was preferably added in a volume V a =(0.0025×b×V 0 ) / (30000-0.0025×b)=(0.0025×35230×2) / (30000-0.0025×35230)=0.00589L=5.89mL, the temperature of the sludge anaerobic digestion system was controlled at 35°C, and anaerobic digestion was carried out for 20 days.

[0035] Experimental group: First, the sludge was subjected to microaerobic pretreatment (ventilation ratio was 8×10 -6 ×35230=0.3vvm, pretreatment time is 15h, stirring rate is 60r / min). Then nitrogen is aerated through the sludge to remove oxygen, the nitrogen aeration ratio is 0.5vvm; the aeration time is 3min. Nano-zero-valent iron with a particle size of 200nm is selected, and a nano-zero-valent iron suspension with a concentration of 30000mg / L is prepared with 1mmol / L sodium dodecyl sulfate solution; the preferred nano-zero-valent iron suspension addition volume (0.0025×b×V 0 ) / (30000-0.0025×b)=(0.0025×35230×2) / (30000-0.0025×35230)=0.00589L=5.89mL. The temperature of the sludge anaerobic digestion system was controlled at 35°C and anaerobic digestion was carried out for 20 days.

[0036] The average cumulative biogas production and average hydrogen sulfide concentration in biogas for the above groups are summarized in Table 1.

[0037] Table 1

[0038]

[0039]

[0040] As shown in Table 1, the average cumulative biogas production of the microaerobic pretreatment and nano-zero-valent iron synergistic enhanced sludge anaerobic digestion test group increased by about 45.8% and the hydrogen sulfide concentration decreased by 241 mg / m 3 Compared with the control group with only nano-zero-valent iron, the average cumulative biogas production increased by about 29.8% and the hydrogen sulfide concentration decreased by 3 mg / m 3 Compared with the blank control group, the average cumulative biogas production increased by about 71% and the hydrogen sulfide concentration decreased by about 256 mg / m 3Compared with conventional anaerobic digestion processes, microaerobic pretreatment and the addition of zero-valent nano-iron can synergistically enhance sludge anaerobic digestion, which can greatly increase the biogas production rate, significantly reduce the production of malodorous gases such as hydrogen sulfide during anaerobic digestion, reduce biogas purification costs, and significantly improve the economic benefits of anaerobic digestion projects.

[0041] Example 2

[0042] A municipal sewage treatment plant in a northern coastal city has a treatment capacity of 300,000 cubic meters per day. 2 O+MBBR (anaerobic-anoxic-aerobic+moving bed biofilm reactor) and A 2 O+MBR (anaerobic-anoxic-aerobic-membrane bioreactor) process, the total COD of the residual sludge is 35230 mg / L, and the pH is 6.82; the food waste comes from the slurry after screening and crushing of a food waste treatment plant in a coastal city in the north, with a moisture content of 88.5% and a total COD of 183250 mg / L. 1.5L of residual sludge and 0.5L of food waste slurry were taken as mixed organic solid waste (the volume of residual sludge accounted for 75% and the volume of food waste accounted for 25%), and the total COD of the mixed organic solid waste was 72235 mg / L. The inoculated sludge was the sludge from the anaerobic digester of the sewage treatment plant, and the volume ratio of the inoculated sludge and the mixed organic solid waste was 1:3; a blank control group, a microaerobic pretreatment control group, a nano-zero-valent iron control group and an experimental group were set up, and 3 parallel samples were set up in each group.

[0043] Blank control group: no microaerobic pretreatment, no addition of nano zero-valent iron, the temperature of the sludge anaerobic digestion system was controlled at 35°C, and anaerobic digestion was carried out for 20 days.

[0044] Only microaerobic pretreatment control group: microaerobic pretreatment (ventilation ratio of 5×10 -6 ×35230×75%+3×10 -6 ×183250×25%=0.27vvm, pretreatment time is 10h, stirring rate is 50r / min), no nano zero-valent iron is added, the ventilation ratio is 0.3vvm, the pretreatment time is 15h, the stirring rate is 60r / min, the temperature of the sludge anaerobic digestion system is controlled at 35°C, and anaerobic digestion is carried out for 20 days.

[0045] Only nano-zero-valent iron control group was added: no microaerobic pretreatment was performed, nano-zero-valent iron with a particle size of 200 nm was selected, and a nano-zero-valent iron suspension with a concentration of 30000 mg / L was prepared with 1 mmol / L sodium dodecyl sulfate solution; the nano-zero-valent iron suspension was preferably added in a volume V a =(0.0025×b×V 0) / (30000-0.0025×b)=(0.0025×72235×2) / (30000-0.0025×72235)=0.0121L=12.1mL, the temperature of the sludge anaerobic digestion system was controlled at 35°C, and anaerobic digestion was carried out for 20 days.

[0046] Experimental group: First, the sludge was subjected to microaerobic pretreatment (ventilation ratio was 5×10 -6 ×35230×75%+3×10 -6 ×183250×25%=0.27vvm, pretreatment time is 10h, stirring rate is 50r / min). Then nitrogen is aerated through the sludge to remove oxygen, the nitrogen aeration ratio is 0.5vvm; the aeration time is 3min. Select nano zero-valent iron with a particle size of 200nm, use 1mmol / L sodium dodecyl sulfate solution to prepare a nano zero-valent iron suspension with a concentration of 30000mg / L; the preferred nano zero-valent iron suspension is added with a volume V a =(0.0025×b×V 0 ) / (30000-0.0025×b)=(0.0025×72235×2) / (30000-0.0025×72235)=0.0121L=12.1mL, the temperature of the sludge anaerobic digestion system was controlled at 35°C, and anaerobic digestion was carried out for 20 days.

[0047] The average cumulative biogas production and average hydrogen sulfide concentration in biogas for the above groups are summarized in Table 2.

[0048] Table 2

[0049]

[0050]

[0051] As shown in Table 2, the average cumulative biogas production of the microaerobic pretreatment and nano-zero-valent iron synergistic enhanced sludge anaerobic digestion test group increased by about 30.3% and the hydrogen sulfide concentration decreased by 496 mg / m 3 Compared with the control group with only nano-zero-valent iron, the average cumulative biogas production increased by about 26.7% and the hydrogen sulfide concentration decreased by 8 mg / m 3 Compared with the blank control group, the average cumulative biogas production increased by about 63.7% and the hydrogen sulfide concentration decreased by about 499 mg / m 3 Compared with conventional anaerobic digestion processes, microaerobic pretreatment and the addition of zero-valent nano-iron can synergistically enhance sludge anaerobic digestion, which can greatly increase the biogas production rate, significantly reduce the production of malodorous gases such as hydrogen sulfide during anaerobic digestion, reduce biogas purification costs, and significantly improve the economic benefits of anaerobic digestion projects.

Claims

1. A method for producing biogas by anaerobic digestion of organic solid waste by micro-aerobic pretreatment and nano-zero-valent iron, characterized in that: According to the type of organic solid waste, micro-aerobic pretreatment is carried out on it to increase the concentration of dissolved organic matter in the organic solid waste. Then, during the anaerobic digestion process, the addition concentration of nano zero-valent iron is determined according to the total COD in the organic solid waste. The addition of nano zero-valent iron can synergistically improve the biogas production rate.

2. The method according to claim 1, characterized in that The particle size of nano zero-valent iron ranges from 20 nm to 10 μm, preferably 200 to 300 nm.

3. The method according to claim 1 or 2, characterized in that: When the addition concentration of nano zero-valent iron is determined according to the total COD in the organic solid waste, the nano zero-valent iron is added in the form of nano zero-valent iron suspension, wherein the nano zero-valent iron suspension is obtained by the following method: The nano-zero-valent iron was dispersed with a 1 mmol / L sodium dodecyl sulfate solution to form a 30000 mg / L nano-zero-valent iron suspension.

4. The method according to claim 3, characterized in that During anaerobic digestion, the volume of nano zero-valent iron suspension added V a =(0.001×b×V0) / (30000-0.001×b)~(0.006×b×V0) / (30000-0.006×b), where b is the total COD of organic solid waste, in mg / L; V0 is the volume of organic solid waste in the anaerobic digestion system, in L; V a , unit: L.

5. The method according to claim 1, characterized in that The types of organic solid waste include at least one of residual sludge from municipal sewage treatment plants, crop straw and garden waste, and food waste.

6. The method according to claim 5, characterized in that According to the type of organic solid waste, micro-aerobic pretreatment is carried out, specifically: For the excess sludge from municipal wastewater treatment plants, the microaerobic process aeration ratio was set to 5 × 10 -6 ×b~1×10 -5 ×bvvm, pretreatment time is 12-24h, mechanical stirring rate is 50-80r / min; For crop straw and garden waste, the microaerobic process aeration ratio was set to 1 × 10 -5 ×b~2×10 -5 ×b vvm, pretreatment time is 16-28h, mechanical stirring rate is 50-90r / min; For food waste, the microaerobic process aeration ratio was set to 3 × 10 -6 ×b~7×10 -6 ×b vvm, pretreatment time is 8 to 15 h, and mechanical stirring rate is 50 to 80 r / min.

7. The method according to claim 6, characterized in that According to the type of organic solid waste, micro-aerobic pretreatment is carried out, specifically: The volume proportions of residual sludge, crop straw, garden waste and kitchen waste in organic solid waste are n1, n2 and n3 respectively, n1+n2+n3=100%, COD is b1, b2 and b3 respectively, then the ventilation ratio is (5×10 -6 ×b1×n1+1×10 -5 ×b2×n2+3×10 -6 ×b3×n3)~(1×10 -5 ×b1×n1+2×10 -5 ×b2×n2+7×10 -6 ×b3×n3)vvm, the pretreatment time is 10 to 24 hours, the mechanical stirring rate is 50 to 90 r / min; n1, n2, and n3 are any values ​​in the range of 0% to 100%; Wherein, b is COD, unit is mg / L; ventilation ratio, unit is vvm, which is the ratio of ventilation volume per minute to the volume of pretreated organic solid waste.

8. The method according to claim 7, characterized in that The ventilation ratio is (8×10 -6 ×b1×n1+1.5×10 -5 ×b2×n2+5×10 -6 ×b3×n3), the pretreatment time is (15×n1+22×n2+10×n3)h, and the mechanical stirring rate is (60×n1+70×n2+60×n3)r / min; Wherein, b is COD, unit is mg / L; ventilation ratio, unit is vvm, which is the ratio of ventilation volume per minute to the volume of pretreated organic solid waste.

9. The method according to claim 1, characterized in that: After the pretreatment, nitrogen is passed through the organic solid waste to remove oxygen. The nitrogen ventilation ratio is 0.2-0.8vvm and the ventilation time is 2-5min.

10. The method according to any one of claims 1 to 9, characterized in that: Compared with only microaerobic pretreatment and only adding nano zero-valent iron, the biogas production rate is increased by 30-50% and 20-30% respectively.

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