Method for synergistically strengthening anaerobic digestion of organic solid waste by micro-aerobic pretreatment and iron ions

Abstract

The invention provides a method for producing biogas by synergistically strengthening anaerobic digestion of organic solid waste through micro-aerobic pretreatment and iron ions, and belongs to the technical field of environmental engineering. According to the method, microaerobic pretreatment is carried out on the organic solid waste according to the type of the organic solid waste so as to improve the concentration of dissolved organic matters in the organic solid waste, then in the anaerobic digestion process, the concentration of re-added iron ions is determined according to the total COD in the organic solid waste and the concentration of original iron ions in a system, and the concentration of the dissolved organic matters in the organic solid waste is improved by adding the iron ions. 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 yield 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 gases such as hydrogen sulfide in the anaerobic digestion process is greatly reduced, the biogas purification cost is reduced, the economic benefits of anaerobic digestion engineering are 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 a coordinated manner using microaerobic pretreatment and iron ions. Background Art

[0003] 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 ferroferric oxide 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. 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.

[0004] 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

[0005] The present invention provides a method for enhancing the biogas production by anaerobic digestion of organic solid waste through micro-aerobic pretreatment and iron ion synergistically. The method effectively improves the organic matter degradation rate and biogas production rate (referring to the volumetric gas production rate of organic solid waste, that is, the biogas production per unit volume of organic solid waste) of the 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 the anaerobic digestion process, reduces the biogas purification cost, and significantly improves the economic benefits of the anaerobic digestion project.

[0006] In order to achieve the above-mentioned object, the present invention provides a method for strengthening the anaerobic digestion of organic solid waste to produce biogas by micro-aerobic pretreatment in coordination with iron ions. 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 concentration of iron ions to be added is determined according to the total COD in the organic solid waste and the original iron ion concentration in the system. The addition of iron ions can synergistically increase the biogas yield.

[0007] It is understandable that in this method, the organic solid waste is first pretreated using 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 microorganisms in the subsequent methanogenic 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 methane yield. During the anaerobic digestion process, the appropriate iron ion addition concentration is determined based on the total COD in the organic solid waste and the iron ion concentration in the original system. The addition of iron ions can further improve the hydrolysis efficiency of difficult-to-degrade organic matter, increase the activity of key methane-producing microorganisms and enzymes in the anaerobic digestion process, improve the utilization efficiency of organic matter and the methane production efficiency, thereby increasing biogas production and improving the organic matter removal rate. At the same time, iron ions reduce the production of malodorous gases such as hydrogen sulfide by reacting with sulfur ions.

[0008] Preferably, the iron ions are derived from any one of ferric chloride and ferric sulfate;

[0009] When the concentration of iron ions added is determined according to the total COD in the organic solid waste, when the added iron ions are derived from ferric chloride, the ferric chloride is prepared into an aqueous solution, and the concentration c0 of the ferric chloride solution is 30000-70000 mg / L, preferably 50000 mg / L;

[0010] When the added iron ions are derived from ferric sulfate, the ferric sulfate is prepared into an aqueous solution, and the concentration c0 of the ferric sulfate solution is 30000-70000 mg / L.

[0011] As a preferred method, the volume of ferric chloride solution added during anaerobic digestion is V a =(V0×w-V0×c i ) / [c0×(56 / 162.5)-w];

[0012] Volume of ferric sulfate solution added V a =(V0×w-V0×c i ) / [c0×(112 / 400)-w];

[0013] Preferably, the iron ion concentration in the anaerobic digestion system is w=0.002×b;

[0014] Wherein, b is the total COD of organic solid waste, in mg / L; V0 is the volume of organic solid waste in the anaerobic digestion process, in L; w is the preferred iron ion concentration in the anaerobic digestion system, in mg / L; c i is the original iron ion concentration in the anaerobic digestion process, in mg / L; c o It is the concentration of iron ions added in the anaerobic digestion process, in mg / L.

[0015] It is understood that the added volume V of the ferric chloride solution is a It is calculated in the following way:

[0016] The total COD of organic solid waste is detected as b (unit: mg / L), and the iron ion concentration w during anaerobic digestion should be controlled at 0.0005×b~0.005×b, preferably 0.002×b (unit: mg / L); then the volume of organic solid waste during anaerobic digestion is set as V0, and the volume of iron ion solution added is set as V a , we can get w=[V0×c i +V a ×c0×(56 / 162.5)] / (V0+V a ), then the volume of ferric chloride solution added V can be calculated a The calculation method of V is as described above. a =(V0×0.002×b-V0×c i ) / [50000×(56 / 162.5)-0.002×b], unit: L.

[0017] Preferably, the volume of the iron ion solution added should meet the following conditions:

[0018] When c i ≥(0.002×b), then there is no need to add iron ion solution;

[0019] When c i <(0.002×b), then the volume of the iron ion solution added is V a =(V0×0.002×b-V0×c i ) / [50000×(56 / 162.5)-0.002×b].

[0020] 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.

[0021] Preferably, the organic solid waste is subjected to micro-aerobic pretreatment according to its type, specifically:

[0022] 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;

[0023] 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;

[0024] 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.

[0025] Preferably, the organic solid waste is subjected to micro-aerobic pretreatment according to its type, specifically:

[0026] 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%;

[0027] 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.

[0028] As a preferred method, 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;

[0029] 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.

[0030] 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 nitrogen ventilation ratio is 0.5vvm, and the ventilation time is 3min.

[0031] Preferably, compared with only microaerobic pretreatment and only adding iron ions, the biogas yield is increased by 20-40% and 30-50%, respectively.

[0032] Compared with the prior art, the advantages and positive effects of the present invention are:

[0033] The present invention provides a method for strengthening anaerobic digestion of organic solid waste by combining micro-aerobic pretreatment with iron ions, which effectively improves the organic matter degradation rate and biogas yield of anaerobic digestion of organic solid waste. Compared with only micro-aerobic pretreatment and only adding iron ions, the biogas yield is increased by 20-40% and 30-50%, 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. The method is suitable for popularization and application. DETAILED DESCRIPTION

[0034] 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.

[0035] Example 1

[0036] A municipal sewage treatment plant in a northern coastal city has a treatment capacity of 200,000 cubic meters per day. 2O+MBR process (anaerobic-anoxic-aerobic+membrane bioreactor process), the total COD of the residual sludge is 37850mg / L, and the pH is 6.74. Take 2L of residual sludge respectively, the inoculated sludge is the sludge from the anaerobic digester of the sewage treatment plant, the volume ratio of inoculated sludge to residual sludge is 1:3, and batch test is adopted; set up blank control group, microaerobic pretreatment control group only, iron ion addition control group only and experimental group, and set up 3 parallel samples in each group.

[0037] Blank control group: no pretreatment, no addition of iron ions, the temperature of the sludge anaerobic digestion system was controlled at 35℃, and anaerobic digestion was carried out for 20 days.

[0038] Only microaerobic pretreatment control group: microaerobic pretreatment (ventilation ratio of 8×10 -6 ×b1=8×10 -6 ×37850=0.3vvm, pretreatment time of 15h, stirring rate of 60r / min), no iron ion solution was added, the temperature of the sludge anaerobic digestion system was controlled at 35°C, and anaerobic digestion was carried out for 20d.

[0039] Only iron ion was added to the control group: no microaerobic pretreatment was performed, the iron ion concentration in the sludge was detected to be 3.25 mg / L, a ferric chloride solution with an iron ion concentration of 50000 mg / L was prepared, the iron ion concentration w of the sludge anaerobic digestion system was controlled to be 75.7 mg / L, and the volume of the prepared ferric chloride solution Va was added to the anaerobic digestion system = ((2×0.002×37850-2×3.25) / [50000×(56 / 162.5)-0.002×37850] = = 0.00845 L = 8.45 mL, the temperature of the sludge anaerobic digestion system was controlled at 35°C, and anaerobic digestion was carried out for 20 days.

[0040] Experimental group: First, the sludge was subjected to microaerobic pretreatment with an aeration ratio of 8×10 -6 ×b1=8×10 -6 ×37850=0.3vvm, pretreatment time is 15h, stirring rate is 60r / min. Then nitrogen is aerated to remove oxygen from the sludge, nitrogen aeration ratio is 0.5vvm; aeration time is 3min. The iron ion concentration in the sludge is detected to be 3.25mg / L, and a ferric chloride solution with an iron ion concentration of 50000mg / L is prepared to control the iron ion concentration w of the sludge anaerobic digestion system to be 0.002×37850=75.7mg / L. The volume of the prepared ferric chloride solution Va added to the anaerobic digestion system is Va=(2×0.002×37850-2×3.25) / [50000×(56 / 162.5)-0.002×37850]==0.00845L=8.45mL. The temperature of the sludge anaerobic digestion system is controlled at 35℃, and anaerobic digestion is carried out for 20d.

[0041] The average cumulative biogas production and average hydrogen sulfide concentration in biogas of the above groups are summarized in Table 1. Batch test was adopted, and the test results are the average values ​​of one batch experiment.

[0042] Table 1

[0043]

[0044]

[0045] As shown in Table 1, the average cumulative biogas production of the microaerobic pretreatment and iron ion addition synergistically enhanced sludge anaerobic digestion test group increased by about 33.6% and the hydrogen sulfide concentration decreased by 255 mg / m 3 Compared with the control group with only iron ions, the average cumulative biogas production increased by about 39.3% and the hydrogen sulfide concentration decreased by 5 mg / m 3 Compared with the blank control group, the average cumulative biogas production increased by about 58.7% and the hydrogen sulfide concentration decreased by about 268 mg / m 3 Compared with conventional anaerobic digestion processes, microaerobic pretreatment and the addition of iron ions can synergistically enhance sludge anaerobic digestion, which can greatly increase biogas production, effectively reduce biogas hydrogen sulfide concentration, achieve sludge reduction and resource utilization, and significantly improve the economic benefits of anaerobic digestion projects.

[0046] Example 2

[0047] A municipal sewage treatment plant in a northern coastal city has a treatment capacity of 200,000 cubic meters per day. 2 O+MBR process (anaerobic-anoxic-aerobic+membrane bioreactor process), the total COD of the residual sludge is 37850mg / L, and the pH is 6.74; the food waste comes from the slurry after screening and crushing from a food waste treatment plant in a coastal city in the north, with a moisture content of 88.5% and a total COD of 183250mg / 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 74200mg / L; the inoculum was the sludge from the anaerobic digester of the sewage treatment plant, and the volume ratio of inoculated sludge and mixed organic solid waste was 1:3, and batch tests were adopted; a blank control group, a microaerobic pretreatment control group, an iron ion addition control group and an experimental group were set up, and 3 parallel samples were set up in each group.

[0048] Blank control group: no pretreatment, no addition of iron ions, the temperature of the mixed organic solid waste anaerobic digestion system was controlled at 35°C, and anaerobic digestion was carried out for 20 days.

[0049] Only microaerobic pretreatment control group: microaerobic pretreatment (ventilation ratio of 5×10-6 ×37850×75%+3×10 -6 ×183250×25%=0.28vvm, pretreatment time is 10h, stirring rate is 50r / min), no iron ion solution is added, the temperature of the mixed organic solid waste anaerobic digestion system is controlled at 35°C, and anaerobic digestion is carried out for 20d.

[0050] Only iron ion was added to the control group: no microaerobic pretreatment was performed, the iron ion concentration in the mixed organic solid waste was detected to be 2.73 mg / L, a ferric chloride solution with an iron ion concentration of 50000 mg / L was prepared, and the iron ion concentration w of the mixed organic solid waste anaerobic digestion system was controlled to be 0.0005×74200=37.1 mg / L, and the volume of the prepared ferric chloride solution Va=(2×0.0005×74200-2×2.73) / [50000×(56 / 162.5)-0.0005×74200]==0.004L=4mL was added to the anaerobic digestion system, the temperature of the mixed organic solid waste anaerobic digestion system was controlled at 35°C, and anaerobic digestion was carried out for 20 days.

[0051] Experimental group: First, the mixed organic solid waste was subjected to microaerobic pretreatment (ventilation ratio of 5×10 -6 ×37850×75%+3×10 -6 ×183250×25%=0.28vvm, pretreatment time is 10h, stirring rate is 50r / min). Then nitrogen is passed through the mixed organic solid waste to remove oxygen, the nitrogen ventilation ratio is 0.5vvm, and the ventilation time is 3min. The iron ion concentration in the mixed organic solid waste was detected to be 2.73 mg / L, and a ferric chloride solution with an iron ion concentration of 50000 mg / L was prepared. The iron ion concentration w of the mixed organic solid waste anaerobic digestion system was controlled to be 0.0005×74200=37.1 mg / L. The volume of the prepared ferric chloride solution Va=(2×0.0005×74200-2×2.73) / [50000×(56 / 162.5)-0.0005×74200]==0.004L=4mL was added to the anaerobic digestion system. The temperature of the mixed organic solid waste anaerobic digestion system was controlled at 35°C, and anaerobic digestion was carried out for 20 days.

[0052] The average cumulative biogas production and average hydrogen sulfide concentration in biogas of the above groups are summarized in Table 1. Batch test was adopted, and the test results are the average values ​​of one batch experiment.

[0053] Table 2

[0054]

[0055]

[0056] As shown in Table 2, the average cumulative biogas production of the anaerobic digestion group of sludge and kitchen waste mixed organic solid waste synergistically enhanced by microaerobic pretreatment and iron ion addition was increased by about 29.0% and the hydrogen sulfide concentration was reduced by 502 mg / m 3 Compared with the control group with only iron ions, the average cumulative biogas production increased by about 39.3% and the hydrogen sulfide concentration decreased by 7 mg / m 3 Compared with the blank control group, the average cumulative biogas production increased by about 57.5%, and the hydrogen sulfide concentration decreased by about 534 mg / m 3 Compared with conventional anaerobic digestion process, micro-aerobic pretreatment and iron ion addition can synergistically enhance the anaerobic digestion of organic solid waste, which can greatly increase the biogas yield, effectively reduce the concentration of hydrogen sulfide in biogas, achieve the reduction and resource utilization of organic solid waste, 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 microaerobic pretreatment in coordination with iron ions, 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 concentration of iron ions to be added is determined according to the total COD in the organic solid waste and the original iron ion concentration in the system. The addition of iron ions can synergistically improve the biogas yield.

2. The method according to claim 1, characterized in that The iron ions are derived from either ferric chloride or ferric sulfate; When the concentration of iron ions added is determined according to the total COD in the organic solid waste, when the added iron ions are derived from ferric chloride, the ferric chloride is prepared into an aqueous solution, and the concentration c0 of the ferric chloride solution is 30,000 to 70,000 mg / L; When the added iron ions are derived from ferric sulfate, the ferric sulfate is prepared into an aqueous solution, and the concentration c0 of the ferric sulfate solution is 30,000 to 70,000 mg / L.

3. The method according to claim 2, characterized in that The volume of ferric chloride solution added during anaerobic digestion V a =(V0×w-V0×c i ) / [c0×(56 / 162.5)-w]; Volume of ferric sulfate solution added V a =(V0×w-V0×c i ) / [c0×(112 / 400)-w]; Preferably, the iron ion concentration in the anaerobic digestion system is w=0.002×b; Wherein, b is the total COD of organic solid waste, in mg / L; V0 is the volume of organic solid waste in the anaerobic digestion process, in L; w is the preferred iron ion concentration in the anaerobic digestion system, in mg / L; c i is the original iron ion concentration in the anaerobic digestion process, in mg / L; c o It is the concentration of iron ions added in the anaerobic digestion process, in mg / L.

4. The method according to claim 3, characterized in that The volume of the iron ion solution added should meet the following conditions: When c i ≥(0.002×b), then there is no need to add iron ion solution; When c i <(0.002×b), then the volume of the iron ion solution added is V a =(V0×0.002×b-V0×c i ) / [50000×(56 / 162.5)-0.002×b], 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 ​​within 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 iron ions, the biogas yield is increased by 20-40% and 30-50% respectively.

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