Method for preparing methane by anaerobic fermentation of straws
By pretreating straw with hydrogen-producing biogas slurry produced by dark fermentation, and combining it with anaerobic fermentation to produce methane, the problems of slow system start-up and high pretreatment costs in the process of producing methane from straw biomass through anaerobic fermentation have been solved, achieving efficient methane production and resource utilization.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ZHENYI GREEN CARBON (BEIJING) ENERGY TECHNOLOGY CO LTD
- Filing Date
- 2026-01-19
- Publication Date
- 2026-05-12
AI Technical Summary
In the existing process of producing methane from straw biomass through anaerobic fermentation, the system starts up slowly, fermentation time is long, and existing pretreatment technologies and equipment are costly, economically expensive, or have pollution problems, resulting in limited effectiveness of biogas slurry pretreatment.
The straw was pretreated by soaking it in a biogas slurry produced by dark fermentation. Combined with the method of producing methane through anaerobic fermentation, the straw was soaked in the resulting biogas slurry, which was then mixed with animal manure for anaerobic fermentation to produce methane.
It significantly increased the methane production of straw, enabled multi-level utilization of organic waste, improved resource utilization, simplified the pretreatment process, reduced costs, and avoided pollution.
Smart Images
Figure CN122012631A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of biogas production methods, and more particularly to a method for producing methane using anaerobic fermentation of straw. Background Technology
[0002] The main chemical component of straw-based biomass is lignocellulose, whose dense crystalline structure severely hinders the digestion and degradation of substrates for anaerobic fermentation, leading to slow system start-up and long fermentation times. Therefore, straw-based raw materials often require more complex pretreatment steps to improve the biodegradability of the substrate before anaerobic fermentation.
[0003] Existing pretreatment technologies include physical, chemical, and biological methods. Physical pretreatment alters the structure of straw through grinding, crushing, and extrusion, reducing its degree of polymerization and making it easier to decompose. This method typically involves high equipment costs and energy consumption. Chemical pretreatment uses various chemical reagents to break the covalent bonds of lignocellulose, dissolving some hemicellulose and lignin, thereby increasing the contact area between cellulose and anaerobic microorganisms and improving digestibility. However, this method usually requires expensive chemical reagents, resulting in high economic costs and a risk of secondary pollution. Furthermore, to avoid residual chemical reagents inhibiting the activity of anaerobic fermentation microorganisms, the straw must be washed to neutrality after pretreatment. Biological pretreatment utilizes specific microorganisms that secrete enzymes that degrade lignocellulose, making the straw easier to digest. This method offers good degradation efficiency, is pollution-free, and low-cost, and has great development potential.
[0004] As a biological treatment method, biogas slurry pretreatment is rich in various microorganisms capable of degrading lignocellulose, enabling the recycling of biogas slurry and effectively improving the hydrolysis and acidification of straw. However, currently, most pretreatment methods utilize anaerobic fermentation biogas slurry for soaking, resulting in a relatively simple microbial community. After multiple rounds of methanogenesis, the concentration of some nutrients is low, limiting the effect on promoting the growth of methanogenic bacteria. Summary of the Invention
[0005] To address the issue of low methane production from straw through anaerobic fermentation of pretreated biogas slurry in existing technologies, the present invention aims to provide a method for pretreating straw with biogas slurry produced by dark fermentation followed by anaerobic fermentation to produce methane, thereby significantly increasing the methane production from straw.
[0006] This invention provides a method for producing methane using anaerobic fermentation of straw, the preparation method comprising the following steps: S1. Mix kitchen waste with anaerobic granular sludge, adjust the pH to 5.5~6.2, and then carry out dark fermentation to produce hydrogen, to obtain dark fermentation biogas slurry; S2. Use the dark fermentation biogas slurry described in step S1 to pre-treat the straw by soaking, and then anaerobic ferment the pre-treated straw to produce methane.
[0007] In this invention, the term "TS" represents total solids content by mass, and the term "VS" represents volatile solids content by mass.
[0008] Preferably, in step S1, the organic load of the kitchen waste is 38~42 TS / L.
[0009] More preferably, in step S1, the organic load of the kitchen waste is 40 gTS / L.
[0010] In step S1 of this scheme, the organic load of kitchen waste is controlled at 40g TS / L. During the dark fermentation hydrogen production process, this ensures that there is enough organic load to produce enough volatile fatty acids (VFAs), while avoiding excessive organic load that could lead to system rancidity and inhibit microbial activity.
[0011] Preferably, in step S1, the particle size of the kitchen waste is <5mm.
[0012] Preferably, in step S1, before mixing the kitchen waste with the anaerobic granular sludge, the anaerobic granular sludge is subjected to thermal pretreatment at a temperature of 85~100 ℃, preferably 90~95 ℃.
[0013] In step S1 of this scheme, before mixing kitchen waste with anaerobic granular sludge, the anaerobic granular sludge is subjected to thermal pretreatment at a temperature of 85~100 ℃, which can remove hydrogen-consuming microorganisms in the anaerobic granular sludge.
[0014] Preferably, in step S1, the organic loading ratio of the kitchen waste to the anaerobic granular sludge is 1:(1~2).
[0015] More preferably, in step S1, the organic load ratio of the kitchen waste to the anaerobic granular sludge is 1:1.
[0016] Preferably, in step S1, the temperature for dark fermentation hydrogen production is 34–36 °C.
[0017] Preferably, in step S1, the time for dark fermentation to produce hydrogen is 22 to 28 hours.
[0018] In step S1, the time for dark fermentation hydrogen production is controlled to be 22-28 h. This ensures sufficient time for dark fermentation hydrogen production to fully convert the substrate into volatile fatty acids (VFAs), while also preventing the accumulation of inhibitory products such as ammonia nitrogen due to excessively long dark fermentation hydrogen production time, which would significantly reduce the biological pretreatment capacity of the dark fermentation slurry.
[0019] Preferably, in step S2, the mass ratio of the straw to the dark fermentation biogas slurry is 1:(6~10).
[0020] Preferably, in step S2, the specific conditions for the soaking pretreatment are: soaking the straw in the dark fermentation biogas slurry at 34-36 ℃ for 24-72 h.
[0021] Preferably, in step S2, the specific conditions for anaerobic fermentation to produce methane include: mixing pretreated straw with animal manure for anaerobic fermentation to produce methane, wherein the organic load ratio of the pretreated straw to the animal manure is 1:(1~2).
[0022] Preferably, the organic load ratio of the pretreated straw to the animal manure is 1:2.
[0023] Preferably, the animal excrement is domesticated cow dung, and the method for preparing the domesticated cow dung includes the following steps: S1. Fresh cow dung is sealed and placed in a 35℃ constant temperature water tank to start the acclimatization process; S2. Shake well daily and record the gas production, and determine the gas composition; S3. When the gas production is stable for 5 consecutive days, the daily gas production fluctuation is ≤10%, and the methane volume fraction is stable at ≥50 vol%, the acclimatization is complete.
[0024] Preferably, in step S2, the specific conditions for anaerobic fermentation to produce methane further include: adjusting the pH of the anaerobic fermentation system to 7.5~8.2, and carrying out anaerobic fermentation to produce methane at a fermentation temperature of 34~36 ℃.
[0025] In this invention, the term "anaerobic granular sludge" is a well-known term in the art, specifically including anaerobic granular sludge from a continuously operating anaerobic fermentation treatment plant for kitchen waste.
[0026] Compared with the prior art, the beneficial technical effects of the present invention are as follows: This invention provides a method for producing methane through anaerobic fermentation of straw. The method involves pretreating straw with a dark fermentation slurry obtained through a specific process, followed by anaerobic fermentation of the pretreated straw to produce methane, resulting in excellent gas production. This method of pretreating straw with dark fermentation slurry for anaerobic fermentation also achieves multi-stage utilization of organic waste. Compared to using anaerobic fermentation slurry alone, pretreating straw with dark fermentation slurry improves the resource utilization rate of organic waste and provides a theoretical foundation for subsequent hydrogen and methane co-production. Attached Figure Description
[0027] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0028] Figure 1 The images show scanning electron microscope (SEM) images of the pretreated corn stalks and cross sections of Examples 1 and 5.
[0029] Figure 2 The images show X-ray diffraction (XRD) patterns of corn stalks after pretreatment in Example 1 and Comparative Examples 1-5.
[0030] Figure 3 The Fourier transform infrared (FTIR) spectra of corn stalks after pretreatment in Example 1 and Comparative Examples 1-5 are shown.
[0031] Figure 4 The graph shows the daily gas production changes during the anaerobic fermentation process of corn stalks after pretreatment in Example 1 and Comparative Examples 1-5.
[0032] Figure 5 The graph shows the cumulative gas production changes during the anaerobic fermentation process of corn stalks after pretreatment in Example 1 and Comparative Examples 1-5.
[0033] Figure 6 The graph shows the change in methane content in the daily gas production during the anaerobic fermentation process of corn stalks after pretreatment in Example 1 and Comparative Examples 1-5.
[0034] Figure 7 The graph shows the changes in the cumulative methane production per unit during the anaerobic fermentation process of corn stalks after pretreatment in Example 1 and Comparative Examples 1-5. Detailed Implementation
[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.
[0036] Each of the following embodiments and comparative examples is set to 3 parallels.
[0037] Example 1 (DF treatment group) This embodiment provides a method for producing methane using anaerobic fermentation of straw, including the following steps: S1. Preparation of dark fermentation biogas slurry: S11. Take 600 g of anaerobic granular sludge (anaerobic granular sludge taken from a continuously operating anaerobic fermentation treatment plant for kitchen waste in Shandong Province, with TS of 6.14% and VS of 4.72%) and place it in a 1 L beaker. Cover the mouth of the beaker with plastic wrap and heat it in a 90℃ water bath for 1 hour to remove hydrogen-consuming microorganisms. After completion, let it stand to room temperature to obtain the heat-pretreated anaerobic granular sludge for later use.
[0038] S12. Food waste (directly taken from the school cafeteria kitchen, with bones, plastic bag impurities, and potential inhibitors like chili peppers removed) is pulverized to a particle size <5mm (TS: 21.98%, VS: 20.51%, organic load: 40gTS / L) and temporarily stored in a 4℃ refrigerator. Before use, thaw the waste and weigh 145.59g of the pulverized food waste into an anaerobic reactor (1L blue-capped screw-top bottle (effective volume 800mL)). Then, add 521.17g of pre-treated anaerobic granular sludge and adjust the pH to 6.2 with 3mol / L hydrochloric acid. Ferment in a constant temperature batch tank at 35±1℃ for 1 day.
[0039] After fermentation, the solid and liquid phases were separated by centrifugation (5000 rpm, 10 min). The supernatant was collected as dark fermentation broth (butyric acid concentration of 7000 mg / L) and stored at 4°C for later use.
[0040] S2. Straw pretreatment and anaerobic fermentation for methane production: S21. After air-drying the corn stalks (TS 91.81%, VS 88.16%), crush them and pass them through a 20-mesh sieve. Weigh 6.54g of the crushed corn stalks and add 39.21g of dark fermentation biogas slurry, just enough to submerge the crushed corn stalks. Mix well and place them in a sealed bag. Pre-treat them in a 35℃ water tank with micro-oxygen for 72 hours (the sealed bag is not completely sealed, and air can enter). Then, the treated corn stalks do not need to be washed or dried and can be left to stand for later use.
[0041] S22. The method for anaerobic fermentation of corn stalks pretreated in step S21 is as follows: Take the pretreated corn stalks into a fermentation bottle (rinse the sealed bag with a small amount of water), add 37.66g of acclimatized cow dung (fresh cow dung, after removing stones, plastic and other impurities, is placed in a 2L anaerobic fermentation bottle (with an external gas collection bottle), sealed, and placed in a 35℃ constant temperature water bath to start acclimatization. Shake manually every day, record the gas production and measure the gas composition. Acclimatization is complete when the daily gas production fluctuation is ≤10% and the methane volume fraction is ≥50 vol% for 5 consecutive days. The fresh cow dung is from Beijing Jinyindao Farm, with TS of 15.93% and VS of 11.80%). Mix evenly, adjust the effective volume to 200mL with deionized water, control the TS at 10%, and adjust the pH of the fermentation liquid to 8 with 3mol / L hydrochloric acid or sodium hydroxide solution. The reactor was then sealed and placed in a constant-temperature batch tank at 35±1℃ for anaerobic digestion. The liquid level in the tank was kept higher than the height of the mixture in the reactor. The mixture was manually shaken twice a day to ensure a more complete reaction. The gas produced during fermentation was collected and its composition was determined by the water displacement method. This allowed for the measurement of daily and cumulative gas production changes.
[0042] Methane content was measured by gas chromatography using a gas chromatograph (Shimadzu GC-2014, Japan) to determine the gas components (H2, N2, CH4 and CO2). The GC was equipped with a TDX-01 column and a thermal conductivity detector (TCD). The daily methane production and cumulative methane production were calculated from the gas production and gas components under standard conditions.
[0043] Comparative Example 1 (Con Treatment Group) The method for producing methane from straw using anaerobic fermentation provided in this comparative example differs from that in Example 1 in that: in step S21, corn straw is pretreated with an equal mass of water instead of dark fermentation biogas slurry.
[0044] Comparative Example 2 (Alk Treatment Group) The method for producing methane from straw using anaerobic fermentation provided in this comparative example differs from that in Example 1 in that: in step S21, 65.4g of 5% sodium hydroxide solution is used instead of 39.21g of dark fermentation biogas slurry to pretreat corn straw for 24 hours, and the treated straw is then washed with water until neutral.
[0045] Comparative Example 3 (Aci Treatment Group) The method for producing methane from straw using anaerobic fermentation provided in this comparative example differs from that in Example 1 in that: in step S21, corn straw is pretreated for 24 hours with a 1% mass fraction butyric acid solution instead of dark fermentation biogas slurry, and then washed with water until neutral.
[0046] Comparative Example 4 (AF Treatment Group) Preparation of anaerobic fermentation biogas slurry: 1. Corn stalk pretreatment Dry the corn stalks, crush them to a particle size of 2-5mm using a pulverizer, and pass them through a 20-mesh sieve to remove coarse fiber impurities. Mix the dry matter (TS) of the stalks with water at a ratio of 1:10, and soak them in hot water at 35℃ for 24 hours to soften the cellulose.
[0047] 2. Anaerobic fermentation The pretreated corn stalks were transferred to an anaerobic reactor, and inoculum (anaerobic digested sludge) was added at a ratio of 2:1 (inoculum to dry matter of stalks). Distilled water was added to adjust the total TS (total dissolved solids) in the reactor to 10%, and the reactor was sealed. Fermentation was carried out at a mesophilic temperature of 35±1℃ for 30 days. The reactor was stirred twice daily for 5 minutes each time to prevent the stalks from floating on the surface and to ensure contact between the substrate and the microorganisms.
[0048] 3. Solid-liquid separation After fermentation, filter the mixture through two to three layers of gauze to separate the biogas slurry and biogas residue, and obtain anaerobic fermented biogas slurry.
[0049] The method for producing methane from straw using anaerobic fermentation provided in this comparative example differs from that in Example 1 in that: in step S21, anaerobic fermentation biogas slurry is used instead of dark fermentation biogas slurry to pretreat corn straw.
[0050] Comparative Example 5 (AFA Treatment Group) Preparation of anaerobic fermentation biogas slurry: The preparation method of the anaerobic fermentation biogas slurry in this comparative example is the same as that in comparative example 4.
[0051] Preparation of anaerobic fermentation biogas slurry with added n-butyric acid: Adding butyric acid to the anaerobic fermentation broth prepared in this comparative example yielded an anaerobic fermentation broth with a butyric acid concentration of 7000 mg / L.
[0052] The method for producing methane from straw using anaerobic fermentation provided in this comparative example differs from that in Example 1 in that: in step S21, anaerobic fermentation biogas slurry with a butyric acid concentration of 7000 mg / L is used instead of dark fermentation biogas slurry to pretreat corn straw.
[0053] Performance testing Figure 1 Scanning electron microscope (SEM) images of corn stalks and their cross-sections after different pretreatments. Figure 1 f-(1) shows that the corn stalks pretreated with water in the Con treatment group were relatively smooth, with dense and orderly cellulose arrangement. Although some wrinkles were produced, the surface structure of the corn stalks was not damaged. Furthermore, from... Figure 1 f-(2) Looking at the cross-section of corn stalks, the complete plant cell wall structure is still preserved, and the cells are interdependent to form a honeycomb structure. Figure 1As can be seen from the image, the surface of the pretreated corn stalks was significantly damaged, becoming loose and rough, with fractures and voids appearing. The cell walls also showed varying degrees of cracking and collapse. This structural change indicates that the binding force between cell walls was disrupted, thus increasing the exposure of lignin. This was especially true in the dark fermentation biogas slurry treatment group ( Figure 1 a) The original structure of corn stalks was significantly damaged after pretreatment, with a porous, fragmented surface. These pores and cracks can be attributed to the separation of hemicellulose and lignin, and the disintegration of the cellulose network structure. Furthermore, the AF treatment group of the anaerobic fermentation slurry also showed significant differences. Due to changes in the charge of cell wall components under a weakly alkaline environment, the hydrophilicity of fibers increased, leading to fibrous aggregation of the stalks and affecting the efficiency of anaerobic fermentation.
[0054] Figure 2 X-ray diffraction (XRD) patterns of corn stalks after different pretreatments are shown. XRD was used to characterize the crystal structure and crystallinity of crystalline compounds in the corn stalks after different pretreatments. Two clear diffraction peaks were found at 16° and 22°, corresponding to the (101) and (002) crystal planes, respectively, representing the typical crystal structures of cellulose Iα (triclinic) and cellulose Iβ (monoclinic). Compared with the Con-treated group, the diffraction peak intensities of the (002) crystal plane and the (am) amorphous region were both improved, and as shown in Table 1, the overall crystallinity index (CrI) of the pretreated samples was higher than that of the Con-treated group. This phenomenon is due to the elimination of amorphous components (such as lignin and some hemicellulose) during the pretreatment process. Figure 2 The diffraction peaks in the 27.5°–28.5° range gradually transform into broad, diffuse peaks, confirming this. Simultaneously, the spectrum shows a leftward shift of the crystallization peaks, indicating a decrease in the structural integrity of the corn stalks and an increase in pore size, allowing more cellulose to be exposed. This increases the contact area for cellulase, thereby improving enzymatic hydrolysis efficiency.
[0055] Table 1. Effects of different pretreatments on the crystallinity of corn straw
[0056] In Table 1, a I 002 The diffraction intensity of peak 002 at a diffraction angle of 2θ = 22.0°. b I am The diffraction intensity is the diffraction angle at 2θ = 16.0.
[0057] Figure 3 Fourier transform infrared (FTIR) spectra of corn stalks after different pretreatments were obtained. The changes in chemical functional groups in the corn stalks were further determined by FTIR, 3300–3420 cm⁻¹. -1The absorption peak at 2902-2923 cm⁻¹ is the vibrational peak of the hydroxyl group (–OH). -1 The absorption peaks at these locations originate from the vibration of (C–H) bonds. Compared to the Con-treated group, the intensities of these two characteristic peaks in the pretreated corn stalk samples were weakened to varying degrees. The former indicates the dehydration reaction of hemicellulose, cellulose, and lignin during pretreatment, with the hydroxyl groups gradually breaking and being eliminated; the latter can be attributed to the demethylation and methylene reactions between hemicellulose and cellulose, generating various hydrocarbon gases such as CH4, C2H6, and C2H4. (1728–1778 cm⁻¹) -1 The peak at 1690–1450 cm⁻¹ represents the stretching vibration of the carbonyl group (C=O) in hemicellulose and cellulose. Compared with the comparative example, this absorption peak is weakened, especially in the Alk-treated group, where the peak is significantly weakened. The decarbonylation and decarboxylation reactions in corn stalks lead to the breakage and removal of the C=O group, which in turn generates small molecule gases such as CO and CO₂. This indicates that strong alkali pretreatment for delignination is accompanied by the formation of potential inhibitors. -1 The characteristic absorption peak at this location originates from the aromatic skeleton vibration of lignin. After straw pretreatment, the characteristic absorption peak at this location weakens or even disappears completely in the cellulose-rich matrix, indicating that delignification occurred during the pretreatment process. (1475–1000 cm⁻¹) -1 The peaks at 896–900 cm⁻¹ are mainly stretching vibrations of carbon-oxygen (C–O) and carbon-hydrogen (C–H) bonds in ethers and phenols, with the absorption peak intensity gradually decreasing, reflecting the degradation of hemicellulose. -1 The absorption peak at this point is attributed to the β-(1,4)-glycosidic bond (C–O–C), a characteristic absorption peak of cellulose. The decrease in absorption peaks in each pretreatment group indicates that some bonds between monosaccharide units have been broken, which is consistent with the XRD results, indicating that the amorphous cellulose structure was partially disrupted after pretreatment.
[0058] Figure 4 and Figure 5 The graphs show the daily and cumulative gas production changes during the anaerobic fermentation of corn straw after different pretreatments; from Figure 4 It can be seen that gas production begins on days 2-3 of anaerobic fermentation, with the daily gas production gradually increasing. The fermentation broth after inoculation rapidly undergoes the first stage of anaerobic fermentation, the acid production reaction, and the accumulation of volatile fatty acids accelerates CO3 production. 2-Ions escaped as CO2. Initial analysis showed that the gas composition was primarily carbon dioxide, with negligible methane content. Acidification of varying degrees occurred between 5 and 7 days of fermentation, followed by spontaneous recovery of gas production. Except for the Alk treatment group, all other groups reached peak gas production between 10 and 14 days, exhibiting similar patterns. However, after 15 days of fermentation, the daily gas production in the Alk treatment group fluctuated and increased, reaching a maximum of 180 mL. A significant trough occurred before and after the peak, suggesting the presence of inhibitors such as phenols and Na+ interfering with microbial metabolism. Figure 5 It can be seen that the cumulative gas production of the DF treatment group was the highest at 2000 mL, the cumulative gas production of the Con treatment group was the lowest at 1655 mL, and the cumulative gas production of the other groups ranged from 1791 to 1900 mL, with little difference.
[0059] Figure 6 and Figure 7 This chart shows the changes in methane content in daily gas production and the changes in cumulative methane production per unit during the anaerobic fermentation of corn straw after different pretreatments. The methane content in each group ranged from approximately 50% to 85%, with differences observed among the different pretreatment groups. The DF treatment group showed a significantly higher methane content in the early stages of fermentation than the other groups, with a maximum methane content of 81.2%, 9.6% higher than the Con treatment group. In the later stages of anaerobic fermentation, the methane content increased in the Alk and Aci groups. This was mainly due to acidification of the system in the early stages of anaerobic digestion, leading to a large accumulation of total volatile fatty acids (TVFA) and a decrease in system pH, thus inhibiting the activity of methanogenic bacteria. The bacterial community self-regulated, and gas production resumed in the later stages, with methane content rapidly increasing, reaching maximums of 85.6% and 83.6%, respectively. Figure 7 It can be seen that the cumulative methanogenesis per unit of TS increases with time, and all treatment groups are higher than the Con treatment group, with the Con treatment group having a cumulative methanogenesis per unit of 144.66 mL / gTS. Furthermore, the cumulative methanogenesis per unit of DF treatment group is significantly higher than all other groups, reaching 212.86 mL / gTS, even surpassing the traditional alkali pretreatment group (Alk group), indicating that biological pretreatment (especially utilizing the biogas slurry from the dark fermentation of kitchen waste) has great potential in improving the biodegradability of corn straw. The Alk group showed a significant lag in methanogenesis, which is related to the residual Na+ after alkali pretreatment. +The release of phenolic substances may inhibit methanogenic bacteria activity, requiring a longer buffering time. The Aci group showed only moderate gas production, indicating that 1% butyric acid pretreatment alone is insufficient to effectively disrupt the lignocellulose structure and may lead to decreased microbial activity due to pH inhibition. Although the AFA group underwent a combined pretreatment, it did not surpass the DF or Alk groups, suggesting that the synergistic effect of chemical and biological treatments was not maximized in this system, possibly limited by the butyric acid concentration. Therefore, we can see that the DF treatment group was the most effective in the entire experiment. This is related to the fact that the VFA and enzyme system in the dark fermentation slurry mainly act on lignin and the lignin-carbohydrate complex (LCC), maximizing the retention of fermentable carbon sources.
[0060] The anaerobic fermentation cycle was 30 days, and the final cumulative methane content per unit was 33.16% higher in Example 1 compared to the Con treatment group.
[0061] The chemical composition of corn stalks consists of cellulose, hemicellulose, and lignin. Microscopically, the polysaccharide network formed by cellulose and hemicellulose is tightly bound by lignin through a three-dimensional cross-linked structure. Simultaneously, hemicellulose is covalently bonded to cellulose fibers, forming a complex anti-degradation barrier. This unique structural and chemical composition significantly hinders the biomass conversion process of corn stalks, directly limiting anaerobic digestion efficiency and becoming a key bottleneck restricting the large-scale anaerobic fermentation utilization of corn stalks.
[0062] To overcome this limitation, pretreatment technology is widely used in the pretreatment process of anaerobic digestion of corn straw. Through physical, chemical, or biological intervention, the structural integrity of the straw can be effectively disrupted, the contact efficiency between fermenting microorganisms and degradable substrates can be improved, and favorable conditions can be provided for the subsequent metabolic activities of anaerobic microorganisms (including hydrolysis, acid production, and methanogenesis), thereby increasing the amount and rate of gas production.
[0063] This invention utilizes the dark fermentation of waste biomass to produce hydrogen, specifically through the dark fermentation of kitchen waste. The resulting biogas slurry is weakly acidic and contains a large amount of volatile fatty acids (VFAs), such as acetic acid, propionic acid, and butyric acid. The total VFA concentration typically reaches 9000~25000 mg / L, far exceeding the 2000~7000 mg / L of traditional anaerobic fermentation biogas slurry. On one hand, these VFAs can be directly or through simple conversion used as a high-quality carbon source by methanogenic bacteria. On the other hand, this acidic substance avoids the excessive degradation of cellulose and hemicellulose in straw by acid-base pretreatment and the straw fiber aggregation that may occur in traditional anaerobic fermentation biogas slurry treatment, maintaining the porous structure of the straw and facilitating subsequent microbial attachment and metabolism.
[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for producing methane using anaerobic fermentation of straw, characterized in that, The preparation method includes the following steps: S1. Mix kitchen waste with anaerobic granular sludge, adjust the pH to 5.5~6.2, and then carry out dark fermentation to produce hydrogen, to obtain dark fermentation biogas slurry; S2. Use the dark fermentation biogas slurry described in step S1 to pre-treat the straw by soaking, and then anaerobic ferment the pre-treated straw to produce methane.
2. The method for producing methane from straw using anaerobic fermentation according to claim 1, characterized in that, In step S1, the organic load of the kitchen waste is 38~42 TS / L.
3. The method for producing methane by anaerobic fermentation of straw according to claim 1 or 2, characterized in that, In step S1, before mixing the kitchen waste with the anaerobic granular sludge, the anaerobic granular sludge is subjected to thermal pretreatment. The temperature of the thermal pretreatment is 85~100 ℃, preferably 90~95 ℃.
4. The method for producing methane by anaerobic fermentation of straw according to claim 1 or 3, characterized in that, In step S1, the organic loading ratio of the kitchen waste to the anaerobic granular sludge is 1:(1~2).
5. The method for producing methane by anaerobic fermentation of straw according to claim 1 or 4, characterized in that, In step S1, the temperature for the dark fermentation hydrogen production is 34–36 °C.
6. The method for producing methane from straw using anaerobic fermentation according to claim 1 or 5, characterized in that, In step S1, the time for dark fermentation to produce hydrogen is 22 to 28 hours.
7. The method for producing methane by anaerobic fermentation of straw according to claim 1 or 6, characterized in that, In step S2, the mass ratio of the straw to the dark fermentation biogas slurry is 1:(6~10).
8. The method for producing methane from straw using anaerobic fermentation according to claim 1 or 7, characterized in that, In step S2, the specific conditions for the soaking pretreatment are as follows: the straw is soaked in the dark fermentation biogas slurry at 34-36 ℃ for 24-72 h.
9. The method for producing methane by anaerobic fermentation of straw according to claim 1 or 8, characterized in that, In step S2, the specific conditions for anaerobic fermentation to produce methane include: mixing pretreated straw with animal manure for anaerobic fermentation to produce methane, wherein the organic load ratio of the pretreated straw to the animal manure is 1:(1~2).
10. The method for producing methane by anaerobic fermentation of straw according to claim 1 or 9, characterized in that, In step S2, the specific conditions for anaerobic fermentation to produce methane also include: adjusting the pH of the anaerobic fermentation system to 7.5~8.2, and carrying out anaerobic fermentation to produce methane at a fermentation temperature of 34~36 ℃.