Pretreatment method for increasing anaerobic fermentation methane yield of lignocellulose material

Abstract

The invention discloses a pretreatment method for increasing the yield of anaerobic fermentation methane of a lignocellulose material, and belongs to the technical field of high-efficiency anaerobic fermentation methane production of organic solid waste. The method comprises the following steps: (1) crushing straws; (2) mixing the straw powder and deionized water according to a mass ratio of 1: (19-21), stirring at a rotating speed of 120-180r / min, treating for 22-26h, fully and uniformly mixing, adjusting the pH value of the system to 3.4-3.7, adding 0.08-0.12 wt% of cellulase according to the mass of the straw, and carrying out enzymolysis at 49-51 DEG C for 2-4d to obtain an enzymatic hydrolysate; (3) yeast pre-fermentation: inoculating 4-6% v / v activated angel high-activity dry yeast into the enzymatic hydrolysate in the step (2) for anaerobic pre-fermentation, wherein the pre-fermentation time is 16-20 hours; and (4) anaerobic fermentation for methane production: adding 20-30% v / v of introduction sludge into the fermentation system in the step (3), and carrying out anaerobic fermentation for methane production, wherein the fermentation temperature is 36-38 DEG C. Compared with the prior art, the method has the advantages of being high in adaptability, short in treatment period, good in economic benefit, free of environmental pollution and the like, and has certain guidance and inspiration effects on engineering of producing methane from straw.

Description

Technical Field

[0001] This invention belongs to the field of efficient anaerobic fermentation for methane production from organic solid waste, and particularly relates to a pretreatment method for increasing methane production from lignocellulosic materials during anaerobic fermentation. Background Technology

[0002] Straw-based lignocellulose can produce biogas through anaerobic fermentation, serving as a renewable energy source. However, the stable structure of lignocellulose makes it difficult to biodegrade, and its slow hydrolysis and acidification restricts the operation of anaerobic biogas projects. Secondly, the decomposition of lignocellulose produces a large amount of volatile organic acids, which can easily lead to acid accumulation in the cold seasons of northern regions, resulting in unstable reactor operation.

[0003] Physicochemical pretreatment of lignocellulosic materials can alter their structure, reduce their degree of polymerization, disrupt the bonds between cellulose, hemicellulose, and lignin, decrease the crystallinity of cellulose, and remove the lignin barrier. However, traditional pretreatment methods suffer from low efficiency, high cost, and environmental pollution.

[0004] Cellulose can be hydrolyzed by cellulase to obtain reducing sugars, which can then be utilized by other anaerobic microorganisms. However, traditional anaerobic methanogenesis is inefficient. If the reducing sugars are converted into ethanol before being converted into volatile organic acids, it may be possible to establish methanogenesis based on direct interspecies electron transfer (DIET). This methanogenesis method is more efficient and does not depend on the acidification process. This is because the oxidation of ethanol releases a higher amount of heat, which is more conducive to driving the latter half of the DIET reaction—the reduction of carbon dioxide to methane.

[0005] Straw is rich in cellulose and can be used as a substrate for ethanol production. Using straw as a substrate for directional ethanol production has the following advantages: 1) Ethanol can stimulate the DIET process and enhance the anaerobic methanogenesis effect; 2) The ethanol production process can effectively reduce the accumulation of organic acids and maintain the stability of the reaction system.

[0006] Previous reports have directly added yeast to the anaerobic fermentation system of lignocellulose raw materials, but yeast can only decompose reducing sugars and cannot directly decompose lignocellulose. Therefore, in this invention, cellulase and yeast are to be added simultaneously to the anaerobic fermentation system, so that lignocellulose is rapidly decomposed to produce reducing sugars, thereby directing the yeast to produce ethanol and enhancing the anaerobic methanogenesis effect.

[0007] In summary, the pretreatment method for targeted ethanol production from lignocellulosic materials can continuously generate ethanol within the anaerobic digestion system, thereby promoting the DIET process and enabling efficient methane production. Simultaneously, the yeast within the system utilizes glucose produced from the enzymatic hydrolysis of straw, effectively mitigating the acidification process and further enhancing gas production. This represents a novel approach to effectively utilize straw and achieve the resource utilization of agricultural solid waste straw, while also being an effective measure to promote methane production in anaerobic digestion systems. Summary of the Invention

[0008] This invention provides a pretreatment method for increasing methane yield during anaerobic fermentation of lignocellulosic materials, comprising the following steps: (1) Crush the straw; (2) Mix straw powder and deionized water at a mass ratio of 1:19-21, stir at a speed of 120-180 r / min, and treat for 22-26 h. After thorough mixing, adjust the pH of the system to 3.4-3.7, and then add 0.08-0.12 wt% of cellulase based on the weight of straw for enzymatic hydrolysis at a temperature of 49-51℃. After 2-4 days of enzymatic hydrolysis, the hydrolysate is obtained. (3) Yeast pre-fermentation: Inoculate 4-6% v / v activated Angel high-activity dry yeast into the enzymatic hydrolysate of step (2) for anaerobic pre-fermentation for 16-20 hours; (4) Anaerobic fermentation to produce methane: 20-30% v / v of seed sludge is added to the fermentation system in step (3) for anaerobic fermentation to produce methane at a fermentation temperature of 36-38℃.

[0009] Preferably, the straw in step (1) is at least one of wheat straw, rice straw, corn straw, sorghum straw, and millet straw.

[0010] More preferably, the particle size of the crushed straw in step (1) is 40 mesh and the moisture content does not exceed 10%.

[0011] More preferably, in step (2), the straw powder and deionized water are mixed at a mass ratio of 1:20.

[0012] More preferably, the amount of cellulase added in step (2) is 0.1 wt%.

[0013] More preferably, the amount of activated Angel high-activity dry yeast added in step (3) is 5% v / v.

[0014] More preferably, in step (3), Angel high-activity dry yeast is activated using a 2wt% glucose solution.

[0015] More preferably, the introduced sludge in step (3) needs to be filtered and mixed to ensure consistency.

[0016] The present invention also provides the application of the above-mentioned pretreatment method in the preparation of methane.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This application primarily focuses on pretreating straw to improve the bioavailability of lignocellulosic materials, disrupting their tertiary structure to enable more efficient methane production. This application mainly addresses the environmental pollution issues associated with chemical pretreatment methods and the low efficiency of traditional biological pretreatment methods. Furthermore, it resolves the economic problems arising from continuous ethanol addition, and the ethanol generation within the system effectively inhibits the acidification process. The pretreated straw exhibits a significant increase in methane production, which is directly related to DIET in the anaerobic digestion system. Methanosarcina It has a high content of electroactive bacteria.

[0018] Compared with existing technologies, this application has advantages such as strong adaptability, short processing cycle, good economic benefits, and no environmental pollution, and has certain indicative and inspiring significance for straw-to-methane projects. Attached Figure Description

[0019] Figure 1 The results show the structural comparison between the straw treated with cellulase and the straw not treated with cellulase in Example 1.

[0020] Figure 2 The results of the structural comparison between the straw treated with cellulase and the straw not treated with cellulase in Example 1 were analyzed by infrared spectroscopy to further analyze the structural changes.

[0021] Figure 3 The results show the changes in the content of the three elements in straw after enzymatic hydrolysis of cellulose in Example 1.

[0022] Figure 4 The figure shows the change in ethanol production after the straw underwent ethanol fermentation pretreatment in Example 1.

[0023] Figure 5 The results show the effect of pretreatment on the methanogenesis of straw in Example 1.

[0024] Figure 6 The effect of straw ethanol production fermentation pretreatment on the electron transfer capacity of straw in anaerobic digestion in Example 1 is shown in the capacitance test results.

[0025] Figure 7 The effect of straw ethanol production fermentation pretreatment on the electron transfer capacity of straw in anaerobic digestion in Example 1 is shown in the impedance detection results.

[0026] Figure 8 The results show the detection of humus in the residual sludge after anaerobic digestion of straw in Example 1.

[0027] Figure 9 The results show the detection of the microbial community in the residual sludge after anaerobic digestion of straw in Example 1. Detailed Implementation

[0028] Example 1 This embodiment provides a pretreatment method for efficient methanogenesis of lignocellulose-containing materials, the specific steps of which are as follows: Y1. Collect corn stalks, crush them through a 40-mesh sieve, and then dry them so that the moisture content does not exceed 10%.

[0029] Y2. Mix corn stalk powder and deionized water at a mass ratio of 1:20 in a 200ml blue-necked bottle and place on a shaker at 150 rpm for 24 hours. After thorough mixing, adjust the pH of the system to 3.4-3.7, then add 0.1% (by mass fraction of the stalk powder) of cellulase to the bottle for enzymatic hydrolysis. Finally, place the system in a constant temperature water bath at 50℃ and allow it to hydrolyze for three days to obtain the enzymatic hydrolysate.

[0030] Y3. Yeast pre-fermentation: Inoculate the enzymatic hydrolysate prepared in step Y2 with 5% v / v activated Angel high-activity dry yeast (activation method: 5g dry yeast + 100ml deionized water + 2g glucose, activated at 37℃ for 12h), and aerate with nitrogen for 10min to make the system an anaerobic environment. Then place the system in a constant temperature room at 37℃ for pre-fermentation for 18 hours. After the pre-fermentation is completed, the fermentation broth is obtained.

[0031] Y4. Anaerobic fermentation for methanogenesis: After adding the seed sludge directly to the effluent from step Y3, the amount of seed sludge added is 20% (v / v). The seed sludge should be filtered through a 10-mesh sieve and mixed before being added. Aeration is carried out with nitrogen, and then the mixture is placed in a constant temperature room at 37℃ for anaerobic fermentation to produce methanogens.

[0032] The above steps Y1-Y3 are used as the experimental group.

[0033] Control group: Compared with the experimental group, step Y2 was omitted, that is, there was no enzymatic hydrolysate. Step Y3 was to add 5% v / v activated Angel high-activity dry yeast to the mixture of corn straw powder and deionized water. The rest of the operation was the same.

[0034] 1) Effects of pretreatment on straw structure and the content of the three nutrients 1635cm -1The bending vibration of cellulose absorbing water was observed at a certain point. The results showed that the vibration effect was weakened after cellulase treatment, indicating that the cellulose content in the straw decreased after cellulase treatment. Furthermore, after 3 days of enzymatic hydrolysis with cellulase, the cellulose content at 1728 cm⁻¹ was significantly reduced. -1 The xylan bending vibration was generated at this point, indicating that cellulase further disrupted the three-element structure of the straw (see [link]). Figure 1 , 2 ).

[0035] To further investigate the changes in straw structure, the cellulose, hemicellulose, and lignin contents of corn straw pretreated with cellulase were determined. The results showed that the lignin and hemicellulose contents did not decrease significantly, indicating that cellulase had no effect on the removal of lignin and hemicellulose. Meanwhile, the cellulose content decreased from 41.3% to 31.5%, with a cellulose removal rate of 23.7%, indicating that the cellulase used in this experiment could remove some of the cellulose from the straw (see [link to experiment]). Figure 3 ).

[0036] To investigate the pretreatment process of straw ethanol fermentation, we measured the ethanol content in the solution. The results showed that the group pretreated with ethanol fermentation (enzyme + yeast group) achieved an ethanol concentration of 909.04 mg / L after 18 hours of pre-fermentation, with an ethanol content nearly five times higher and an ethanol yield of 1.52% (0.0152 mg / g straw). See [link to relevant documentation]. Figure 4 Therefore, higher concentrations of ethanol are more beneficial for subsequent straw methanogenesis, because higher concentrations of ethanol will enable straw to utilize the DIET pathway to produce methanogens to a greater extent, thereby improving the methanogenesis effect.

[0037] 2) Effect of pretreatment on straw methanogenesis To investigate whether pretreated straw increased methane production during anaerobic digestion, we set up two groups: a yeast-only group (corresponding to steps Y1 and Y3) and an enzyme + yeast group (corresponding to steps Y1+Y2+Y3) that underwent cellulase hydrolysis followed by yeast fermentation for ethanol production. The pretreated straw from both groups was then directly added to introduced sludge for anaerobic digestion and methane production. The results showed that the cumulative methane production over 36 days was 425.4 ml in the yeast group, 736.9 ml in the enzyme + yeast group, and 736.9 ml in the enzyme + yeast group. The enzyme + yeast group showed a 73.2% increase in cumulative methane production over 36 days compared to the yeast group, indicating that the DIET pathway for methane production from straw is significantly more effective than the traditional acetic acid-based pathway (see [link to DIET pathway]). Figure 5 ).

[0038] 3) Effects of straw ethanol production fermentation pretreatment on electron transport capacity during straw anaerobic digestion To investigate whether the electron transport capacity of straw pretreated with ethanol fermentation is enhanced during anaerobic digestion, the CV curve method was used to determine the electron transport efficiency. Figure 6 As shown, the capacitance of the yeast treatment group was 7.287e-5F, and the capacitance of the enzyme + yeast treatment group was 8.459e-5F. The capacitance of the enzyme + yeast treatment group was 16.1% higher than that of the yeast treatment group, indicating that the sludge in the anaerobic digestion stage of the enzyme + yeast pretreatment group had stronger conductivity, which is more conducive to the formation of the DIET pathway.

[0039] Impedance data from the enzyme-treated group, yeast group, and enzyme + yeast group were analyzed using ZsimDemo software according to... Figure 7 Fitting the simulated circuit shown, the impedances of the yeast group and the enzyme + yeast group were 72.22 ohms and 26.23 ohms, respectively. The results indicate that the impedance of the sludge in the enzyme + yeast group is much lower than that in the yeast group, suggesting that the enzyme + yeast treatment group has higher electroactivity and is more conducive to methanogenesis via the DIET pathway. (The experimental group was the enzyme + yeast group, and the control group was the yeast group).

[0040] 4) Changes in humus in anaerobic digestion sludge from straw Depend on Figure 8 It is known that in the humus region, the color gradation of the enzyme + yeast group is significantly higher than that of the yeast group, which indicates that enzyme + yeast treatment helps to accelerate the formation of humus in the anaerobic digestion of straw.

[0041] 5) Changes in the microbial community of straw anaerobic digestion sludge Depend on Figure 9 To investigate the effects of ethanol fermentation pretreatment on the environment of the straw anaerobic digestion system, the archaeal community composition at the genus level was analyzed. This analysis focused on factors directly related to DIET. Methanosarcina The percentage of strains in the enzyme + yeast treatment group (67.9%) was higher than that in the yeast treatment group (51.9%). This indicates that the electroactive bacteria in the anaerobic digestion system were enriched after ethanol fermentation pretreatment, which is more conducive to the construction of the DIET process.

[0042] After adding yeast for ethanol-producing fermentation during the pretreatment stage, the ethanol in the system can continuously stimulate straw DIET methanogenesis, and may continue to produce ethanol and stimulate straw DIET methanogenesis even during the anaerobic digestion stage. The possible mechanism is that cellulase breaks down cellulose in the straw into glucose, which is then utilized by yeast under anaerobic conditions to convert into ethanol, thereby stimulating the DIET process. In the enzyme-treated group without yeast, glucose is first converted into acetic acid, and then utilized by methanogens via the acetic acid-based methanogenesis pathway. The traditional acetic acid-based methanogenesis pathway has a slow methanogenesis rate, while the enzyme + yeast pretreatment allows the available portion of the straw to continuously produce ethanol, stimulating the DIET process and thus accelerating the system's methanogenesis rate.

[0043] In the circular economy, the utilization of straw cellulose achieves closed-loop resource flow and efficient utilization, reducing waste emissions and resource waste. The utilization of straw cellulose makes a significant contribution to saving resources such as timber and water, and promoting the development of a circular economy. Enzyme + yeast pretreatment of straw to enhance anaerobic digestion and methanogenesis has multiple significant effects: First, it opens up a completely new utilization pathway for straw, greatly improving its utilization efficiency; second, it avoids the labor and resource costs associated with continuous ethanol addition; third, it significantly accelerates the rate of anaerobic digestion and methanogenesis using cellulose as a substrate, and increases methane production; fourth, after enzymatic hydrolysis of straw, the yeast ethanol production process effectively inhibits the acidification process of anaerobic digestion; and fifth, it effectively stabilizes the anaerobic digestion system. Furthermore, this technology also has unique advantages: low investment cost, convenient and easy operation, and considerable production efficiency.

[0044] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A pretreatment method for increasing methane yield from anaerobic fermentation of lignocellulosic materials, characterized in that, Includes the following steps: (1) Crush the straw; (2) Mix straw powder and deionized water at a mass ratio of 1:19-21, stir at a speed of 120-180 r / min, and treat for 22-26 h. After thorough mixing, adjust the pH of the system to 3.4-3.7, and then add 0.08-0.12 wt% cellulase based on the mass of straw for enzymatic hydrolysis at a temperature of 49-51℃. After 2-4 days of enzymatic hydrolysis, the hydrolysate is obtained. (3) Yeast pre-fermentation: Inoculate 4-6% v / v activated Angel high-activity dry yeast into the enzymatic hydrolysate of step (2) for anaerobic pre-fermentation for 16-20 hours; (4) Anaerobic fermentation to produce methane: 20-30% v / v of seed sludge is added to the fermentation system in step (3) for anaerobic fermentation to produce methane at a fermentation temperature of 36-38℃.

2. The pretreatment method according to claim 1, characterized in that, In step (1), the straw is at least one of wheat straw, rice straw, corn straw, sorghum straw, and millet straw.

3. The pretreatment method according to claim 2, characterized in that, In step (1), the particle size of the crushed straw is 40 mesh and the moisture content does not exceed 10%.

4. The pretreatment method according to claim 3, characterized in that, In step (2), straw powder and deionized water are mixed at a mass ratio of 1:

20.

5. The pretreatment method according to claim 4, characterized in that, The amount of cellulase added in step (2) is 0.1 wt%.

6. The pretreatment method according to claim 5, characterized in that, In step (3), the amount of activated Angel high-activity dry yeast added is 5% v / v.

7. The pretreatment method according to claim 5, characterized in that, In step (3), Angel high-activity dry yeast is activated using a 2wt% glucose solution.

8. The pretreatment method according to claim 6, characterized in that, In step (3), the introduced sludge is filtered and mixed.

9. The application of the pretreatment method according to any one of claims 1-8 in the preparation of methane.

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