Pre-fermentation method for improving biogas production of straw and biogas production fermentation system

Abstract

The invention relates to a pre-fermentation method for improving biogas production of straws and a biogas production fermentation system. The pre-fermentation method comprises the following steps: S1, preparing a mixed microbial agent to be fermented; the mixed microbial agent is prepared by inoculating the following zymophyte in parts by weight into a fermentation culture medium according to the total inoculation amount of 3-10% (v / v): 5-50 parts of bacillus subtilis, 10-20 parts of white-rot fungi, 5-10 parts of aspergillus oryzae, 5-10 parts of trametes versicolor and 5-10 parts of trichoderma viride; s2, uniformly mixing the mixed microbial agent with the micro-nano bubble water, and fermenting to form an enhanced hydrolysis bacterium solution containing a microbial agent fermentation solution and an enzyme solution; s3, spraying enhanced hydrolysis bacteria liquid onto the straws for enhanced hydrolysis so as to complete pretreatment before fermentation and biogas production; wherein the volume of the reinforced hydrolytic bacteria liquid required by each kg of straw is 3-5L. Compared with the prior art, the mixed microbial agent and the micro-nano bubble water are used for carrying out cooperative treatment on the straw, so that the gas production efficiency and the methane production amount of the straw can be effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of anaerobic fermentation technology, and in particular relates to a pre-fermentation method for improving biogas production from straw and a biogas production fermentation system. Background Art

[0002] In recent years, anaerobic biological treatment technology has been widely used in the field of agricultural waste treatment and disposal. Through anaerobic biological technology treatment, agricultural waste is degraded and usable biogas is produced. At the same time, the slurry and residue after anaerobic fermentation can be used as crop fertilizer, realizing the energy utilization of agricultural waste and solving the environmental pollution problem of agricultural waste. In the current crop straw energy utilization biogas project, due to the physical barrier formed by the complex structure of lignocellulose in crop straw, the hydrolysis rate of anaerobic fermentation biogas production is slow and the substrate conversion rate is low. In the practice of straw anaerobic fermentation biogas production engineering, there are still problems such as the fermentation concentration of materials should not be too high, long-term operation will cause the material to float and crust, and it is difficult to operate stably and continuously. In addition, incomplete straw degradation leads to a large amount of solid residue, a long fermentation cycle, unsatisfactory gas production rate, and poor economic efficiency of engineering operation.

[0003] The main component of straw is lignocellulose. Pretreatment, as an important step, plays a vital role in improving the anaerobic efficiency of straw materials. Appropriate technical means are used to destroy the complex anti-biodegradation barrier of lignocellulose, so that degradable components such as cellulose and hemicellulose can be effectively utilized by microorganisms, and the degradation degree and conversion efficiency of each component are improved, thereby improving the organic load and volumetric gas production rate of the fermentation system. Therefore, more and more processes are trying to improve the gas production efficiency and methane production of lignocellulosic materials by strengthening hydrolysis. Economical and effective pretreatment processes will significantly improve the gas production efficiency and operating benefits of straw biogas projects.

[0004] Bio-augmentation, also known as biological pretreatment, refers to the addition of microorganisms with specific functions to the reaction system to promote the material conversion effect, so that the entire reaction proceeds in the direction of the target product generation, shortens the lag period, and increases the yield. However, the long fermentation time of biological pretreatment and the large loss of cellulose and polysaccharides during the pretreatment process are also a difficult problem that restricts the improvement of gas production rate. CN 109370915A discloses a method for producing a biological agent for pretreatment of straw biogas fermentation and its application, including the cultivation of seed liquid, fermentation cultivation, solid-liquid separation, solid drying, liquid atomization drying, mixing and the like. However, when the biological agent prepared by the method is applied to straw treatment, the process flow is long, and many reactors and auxiliary equipment are set up. Due to the complex process, the operation and maintenance are difficult, and the whole system consumes high energy and has low reaction efficiency.

[0005] Therefore, in view of the problems of complex process and low straw hydrolysis efficiency in the above-mentioned existing treatment methods, a new straw pre-fermentation method is still to be developed to further improve the gas production efficiency and methane production of straw. Summary of the invention

[0006] The purpose of the present invention is to overcome the defects of the prior art such as complex process and low straw hydrolysis efficiency and to provide a pre-fermentation method and a biogas fermentation system for improving biogas production from straw, so as to further improve the gas production efficiency and methane production of straw.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A pre-fermentation method for improving biogas production from straw comprises the following steps:

[0009] S1: preparing a mixed microbial agent to be fermented; the mixed microbial agent is inoculated into a fermentation medium with the following fermentation bacteria in a total inoculation amount of 3-10% (v / v): 5-50 parts of Bacillus subtilis, 10-20 parts of white rot fungi, 5-10 parts of Aspergillus oryzae, 5-10 parts of Trametes versicolor, and 5-10 parts of Trichoderma viride;

[0010] S2: Evenly mix the mixed microbial agent and micro-nano bubble water and ferment them to form an enhanced hydrolysis solution containing microbial agent fermentation solution and enzyme solution;

[0011] The number of micro-nano bubbles in the micro-nano bubble water is 0.1-1.0×10 8 / mL, the volume ratio of mixed microbial agents to micro-nano bubble water is (0.4-0.8):1;

[0012] S3: Spraying enhanced hydrolysis bacterial solution onto the straw for enhanced hydrolysis to complete the pretreatment before fermentation and biogas production; wherein, the volume of enhanced hydrolysis bacterial solution required for each kg of straw is 3-5L.

[0013] Furthermore, in step S1, the mixed microbial agent includes the following mixed fermentation bacteria in parts by weight: 25-45 parts of Bacillus subtilis, 10-20 parts of white rot fungi, 5-10 parts of Aspergillus oryzae, 5-10 parts of Trametes versicolor, and 5-10 parts of Trichoderma viride.

[0014] Furthermore, in step S1, the fermentation medium comprises the following components in percentage by weight: 1.5-2.5 wt % molasses, 0.8-1.2 wt % sodium carboxymethyl cellulose, 0.4-0.6 wt % beef extract, and the remaining components are water.

[0015] Furthermore, in step S2, the gas matrix for preparing the micro-nano bubbles is air or pure oxygen.

[0016] Furthermore, in step S2, the pH of the fermentation is 3-5, preferably 3.5-3.9; and the fermentation time is 3-7 days, preferably 5 days.

[0017] Furthermore, in step S2, the stirring speed during the fermentation is 100-150 rpm, preferably 120 rpm.

[0018] Furthermore, in step S2, the enzyme solution in the enhanced hydrolysis bacterial solution contains cellulose hydrolase and lignin hydrolase, and has the ability to enhance the hydrolysis and fermentation of straw substrates.

[0019] Furthermore, in step S3, the straw is crushed into particles with a particle size of 2-3 cm for later use.

[0020] Furthermore, in step S3, the volume ratio of the straw stack is 0.08-0.12 t / m 3 , preferably 0.1t / m 3 .

[0021] Furthermore, in step S3, the spraying rate of the enhanced hydrolysis bacterial liquid is 2-4 L / (t·min).

[0022] Furthermore, the enhanced hydrolysis lasts for 3-5 days, the spraying frequency is 2-7 times a day, and the single spraying time is 2-30 minutes.

[0023] The present invention also provides a biogas production and fermentation system in conjunction with the above-mentioned pre-fermentation method, wherein the biogas production and fermentation system comprises a micro-nano bubble generating device, a bacterial agent fermentation tank and a straw fermentation reactor connected in sequence;

[0024] A spraying device is arranged between the bacterial agent fermentation tank and the straw fermentation reactor, and is used for spraying the enhanced hydrolyzate in the bacterial agent fermentation tank onto the straw in the straw fermentation reactor.

[0025] Furthermore, a stirring device is provided in the bacterial agent fermentation tank.

[0026] Furthermore, the bacterial agent fermentation tank is connected to the spraying device through a pipeline, and a spray pump is provided on the pipeline.

[0027] Furthermore, the straw fermentation reactor is connected to a biogas collection system.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) The present invention mixes the mixed microbial agent with micro-nano bubble water and then performs mixed fermentation and microbial propagation in a bacterial agent fermentation tank, and then sprays the mixture onto the straw for enhanced hydrolysis treatment. This can improve the biodegradability of the straw during the anaerobic fermentation and hydrolysis stage of the straw, shorten the anaerobic start-up time during the straw methane production stage, solve the problem of low anaerobic methane production and efficiency of the straw, and increase the biogas production.

[0030] (2) The present invention is based on microbial enhanced regulation technology, optimizes the hydrolysis microbial agent for mixed fermentation and expansion (optimization of the ratio of Bacillus subtilis, white rot fungi, Aspergillus oryzae, Trametes versicolor, and Trichoderma viride), and forms an absolutely dominant environment for enhanced hydrolysis bacteria in the straw fermentation reactor, which can effectively break the entanglement of straw lignin and hemicellulose, reduce the crystallinity and polymerization degree of cellulose, and improve the biodegradability of straw-like materials, so that the straw-like biomass is fully hydrolyzed and acidified before entering the anaerobic methanogenesis, which is beneficial to the conversion of the material into methane in the subsequent anaerobic reaction, and solves the problem of incomplete hydrolysis of lignocellulose in the prior art.

[0031] (3) The micro-nano bubble water used in the present invention has the characteristics of long residence time in water, large specific surface area, high mass transfer efficiency, etc. It can also increase the dissolved oxygen content in water, continuously provide dissolved oxygen for microorganisms, which is beneficial to the growth and reproduction of microorganisms and the degradation and removal of organic pollutants, and can improve the hydrolysis and methanogenesis steps of anaerobic fermentation, thereby improving process stability.

[0032] (4) The present invention uses micro-nano bubble water to expand and cultivate the mixed hydrolysis bacteria, which helps to create a micro-oxygen environment required for microbial fermentation in the bacteria fermentation tank, is beneficial to the growth balance of fungi and bacteria, and improves the activity of lignocellulose hydrolyzing enzymes. The mixed microbial bacteria fermentation liquid from the bacteria fermentation tank is rich in lignocellulose hydrolyzing enzymes and is used for pre-fermentation of straw raw materials. The cellulose crystallinity is reduced by 14-20%, the hydrolysis and acidification efficiency is effectively promoted, the polysaccharide concentration in the hydrolyzate is significantly improved, and the cumulative methane production of the digestive system is ultimately increased by 18-50%, and the stagnation period before the straw material produces gas is reduced by 25-50%, which can effectively shorten the straw fermentation cycle.

[0033] (5) The pre-fermentation method of the present invention for increasing biogas production from straw aims to reduce costs and increase efficiency of biogas projects. The upstream and downstream supporting technologies are developed to increase gas production per ton of straw, open up the resource utilization of agricultural waste, and create the possibility of increasing the profit margin of agricultural waste biogas projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the overall structure of the biogas fermentation system of the present invention.

[0035] Figure 2 Schematic diagram of TS and VS degradation rate results during the straw pretreatment stage.

[0036] Figure 3 Schematic diagram of the cumulative methane production during the anaerobic digestion stage.

[0037] Description of the markings in the figure:

[0038] 1-micro-nano bubble generating device, 2-bacterial agent fermentation tank, 3-straw fermentation reactor, 4-spraying device, 5-stirring device, 6-spraying pump, 7-biogas collecting system. DETAILED DESCRIPTION

[0039] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0040] Unless otherwise specified, the reagents, methods, instruments and equipment used in the present invention are conventional reagents, methods, instruments and equipment in the art. Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0041] The biogas fermentation system used in the following examples and comparative examples is as follows: Figure 1 As shown, it specifically includes a micro-nano bubble generator 1, a bacterial fermentation tank 2 and a straw fermentation reactor 3 connected in sequence. The bacterial fermentation tank 2 uses an enamel splicing tank and is equipped with a top stirring device 5. The water inlet pipe is provided with a micro-nano bubble generator 1. The straw fermentation reactor 3 is in the form of a garage-type anaerobic dry fermentation warehouse with a volume of 1000m 3 A spray device 4 is provided on the top of the straw fermentation reactor 3. The bacterial fermentation tank 2 is connected to the spray device 4 through a pipeline. A spray pump 6 is provided on the pipeline. The enhanced hydrolyzate in the bacterial fermentation tank 2 is sprayed onto the straw in the straw fermentation reactor 3 through the spray pump 6 and the spray device 4. The straw fermentation reactor 3 is also connected to a biogas collection system 7.

[0042] Embodiment 1:

[0043] This embodiment provides a pre-fermentation method for improving biogas production from straw, and the specific implementation steps are as follows:

[0044] (1) Rice straw is used as raw material and is crushed to a particle size of 2 to 3 cm and a moisture content of 35%.

[0045] (2) After mixing 26 parts of Bacillus subtilis, 15 parts of white rot fungi, 7 parts of Aspergillus oryzae, 6 parts of Trametes versicolor, and 8 parts of Trichoderma viride by weight, the mixed bacterial agent is inoculated into a fermentation medium at an inoculation rate of 5% (v / v) (the fermentation medium contains 2wt% molasses, 1wt% sodium carboxymethyl cellulose, and 0.5wt% beef extract). The inoculated mixed fermentation microbial agent is input into a micro-nano bubble generating device to disperse the agent in the micro-nano bubbles. The micro-nano bubbles use air as the gas matrix. The oxygen micro-nano bubble water not only activates the activity of the bacterial agent, but also promotes the secretion of a variety of lignocellulose hydrolyzing enzymes. The number of micro-nano bubbles in the micro-nano bubble water is 0.1-1.0×10 8 / mL, and the volume ratio of mixed microbial agents to micro-nano bubble water was 0.6:1.

[0046] (3) The micro-nano bubble water and the mixed microbial agent are input into a fermentation tank for mixed fermentation and microbial propagation. The pH is controlled at 3.5-3.9, the rotation speed is 120 rpm, and the fermentation is performed for 5 days to form an enhanced hydrolyzed bacterial solution.

[0047] (4) Volume ratio 0.1t / m 3 After the straw stacking is completed, the dry fermentation bin door is closed, and the airtight door strip is inflated and sealed, the hydrolysis solution in the bacterial fermentation tank is pumped to the dry fermentation bin spray system through the hydrolysis solution spray pump, sprayed into the material, forming an absolutely dominant growth environment for hydrolysis bacteria, and the enhanced hydrolysis stage begins. The volume of enhanced hydrolysis solution required for each kg of straw is 4L. The enhanced hydrolysis stage runs for about 5 days, with the solution sprayed 3 times a day, each spraying time 8min, and the flow rate of the hydrolysis solution during spraying is 3L / (t·min), ensuring that the moisture content of the material in the bin after spraying is not higher than 55%.

[0048] (5) After the enhanced hydrolysis stage, the garage-type dry fermentation chamber enters the high-efficiency anaerobic methane production stage, and the biogas produced by dry fermentation is sent to the biogas collection system for storage.

[0049] Embodiment 2:

[0050] The present embodiment provides a pre-fermentation method for improving biogas production from straw, which is different from the embodiment 1 in that the fermentation microorganisms of the present embodiment are 38 parts of Bacillus subtilis, 11 parts of white rot fungi, 8 parts of Aspergillus oryzae, 6 parts of Trametes versicolor, and 7 parts of Trichoderma viride.

[0051] Embodiment 3:

[0052] The present embodiment provides a pre-fermentation method for improving biogas production from straw. The difference from the embodiment 1 is that the fermentation microorganisms of the present embodiment are 45 parts of Bacillus subtilis, 18 parts of white rot fungi, 5 parts of Aspergillus oryzae, 5 parts of Trametes versicolor, and 6 parts of Trichoderma viride.

[0053] Comparative Example 1:

[0054] The difference from Example 1 is that this comparative example does not add mixed microbial inoculants and does not provide air micro-nano bubble water.

[0055] Comparative Example 2:

[0056] The difference from Example 1 is that this comparative example does not add mixed microbial agents, and only provides air micro-nano bubble water.

[0057] Comparative Example 3:

[0058] The difference from Example 1 is that this comparative example does not add air micro-nano bubble water, and only provides a mixed microbial agent.

[0059] The present invention carries out the following tests on the above-mentioned embodiments and comparative examples:

[0060] (1) Test of straw degradation rate in the pretreatment stage: TS (Total Solids) degradation rate and VS (Volatile Solids) degradation rate are two important indicators to measure the conversion efficiency of biomass during anaerobic digestion. They represent the percentage of total solids and volatile solids decomposed by microorganisms during anaerobic digestion. Total solids (TS) and volatile solids (VS) are determined by the loss on ignition method (HJ 761-2017).

[0061] (2) Methane production test in anaerobic digestion stage:

[0062] The pretreated straw was placed in a sealed reactor of the methane potential test device, and the fermentation material and inoculum (methane-producing sludge) were configured in a 2:1 (v / v) ratio. The fermentation temperature was set at 35°C, and the daily gas production and methane content were recorded to calculate the cumulative methane production. The experiment was stopped when the cumulative production tended to be stable. The experimental period was generally 30 days.

[0063] Figure 2 The TS and VS degradation rate results of each embodiment and comparative example in the pretreatment of straw are shown in the figure. Compared with the comparative example, adding the composite mixed microbial agent in Examples 1-3 and adding nano bubble water to strengthen the hydrolysis of straw can significantly improve the TS and VS degradation rates in the pretreatment of straw, and the degradation efficiency is significantly higher than that of pure straw (Comparative Example 1), nano bubble water alone (Comparative Example 2) or microbial agent alone (Comparative Example 3). Among them, the TS and VS degradation rates of the Example 2 group are the best, which are 33.5% and 22.5%, respectively, indicating that the suitable microbial agent compound ratio has a significant degradation effect on cellulose, hemicellulose and lignin in the straw, and the synergistic cooperation of the composite microbial agent and nano bubble water is indispensable.

[0064] Figure 3 It is a schematic diagram of the cumulative methane production in the anaerobic digestion stage. It can be seen from the figure that the methane production after pre-treatment of straw in Example 2 group can reach 185mL, which is significantly higher than other comparative groups and example groups, and the cumulative methane production per unit VS is 47.51mL / g VS. The cumulative methane production of Example 3 group is only lower than that of Example 2 group, which corresponds to the TS and VS degradation rates of straw in the pretreatment stage. The above results show that micro-nano bubble water can increase the dissolved oxygen in water, which is beneficial to provide oxygen for aerobic bacteria, thereby improving the degradation rate of straw. Air micro-nano bubble water has a certain promoting effect on the anaerobic digestion of straw pretreated with bacterial agents.

[0065] In addition, the present invention uses Example 2 with the best straw degradation rate as an example to verify the effect on a large scale. Three dry fermentation bins are operated simultaneously, with a total reaction volume of 3900m 3 , 675t straw can be processed in one batch, and the total volume of the mixture is about 2100m 3 The reaction cycle of one batch is about 30 days. After entering the efficient methane production stage, the daily biogas production is about 10500m 3 The average methane content is 53.1%, and the biogas production per unit material is 355mL / (g﹒Ts).

[0066] In summary, the present invention aims at the bottleneck problem of low reaction efficiency in straw biogas projects, and proposes a pre-fermentation process method and system for improving the efficiency of anaerobic biogas production from straw, which also involves the preparation of mixed microbial agents for treating straw materials and a pre-fermentation optimization method, which can quickly break the lignin and hemicellulose wrapping in the anaerobic fermentation and hydrolysis stage of straw, reduce the crystallinity and polymerization degree of cellulose, and improve the biodegradability of straw. The anaerobic start-up time is shortened in the straw methane production stage, the fermentation methane production cycle is reduced, the problem of low anaerobic methane production and efficiency of straw is solved, and the biogas production is increased.

[0067] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A pre-fermentation method for improving biogas production from straw, characterized in that: The following steps are involved: S1: preparing a mixed microbial agent to be fermented; the mixed microbial agent is inoculated into a fermentation medium with the following fermentation bacteria in a total inoculation amount of 3-10% (v / v): 5-50 parts of Bacillus subtilis, 10-20 parts of white rot fungi, 5-10 parts of Aspergillus oryzae, 5-10 parts of Trametes versicolor, and 5-10 parts of Trichoderma viride; S2: Evenly mix the mixed microbial agent and micro-nano bubble water and ferment them to form an enhanced hydrolysis solution containing microbial agent fermentation solution and enzyme solution; The number of micro-nano bubbles in the micro-nano bubble water is 0.1-1.0×10 8 / mL, the volume ratio of mixed microbial agents to micro-nano bubble water is (0.4-0.8):1; S3: Spraying enhanced hydrolysis bacterial solution onto the straw for enhanced hydrolysis to complete the pretreatment before fermentation and biogas production; wherein, the volume of enhanced hydrolysis bacterial solution required for each kg of straw is 3-5L.

2. A pre-fermentation method for improving biogas production from straw according to claim 1, characterized in that: In step S1, the fermentation medium comprises the following components in percentage by weight: 1.5-2.5 wt % of molasses, 0.8-1.2 wt % of sodium carboxymethyl cellulose, 0.4-0.6 wt % of beef extract, and the remaining component is water.

3. A pre-fermentation method for improving biogas production from straw according to claim 1, characterized in that: In step S2, the gas matrix for preparing the micro-nano bubbles is air or pure oxygen.

4. A pre-fermentation method for improving biogas production from straw according to claim 1, characterized in that: In step S2, the pH of the fermentation is 3-5, and the fermentation time is 3-7 days.

5. A pre-fermentation method for improving biogas production from straw according to claim 1, characterized in that: In step S2, the stirring speed during the fermentation is 100-150 rpm.

6. A pre-fermentation method for improving biogas production from straw according to claim 1, characterized in that: In step S2, the enzyme solution in the enhanced hydrolysis bacterial solution contains cellulose hydrolyzing enzyme and lignin hydrolyzing enzyme.

7. A pre-fermentation method for improving biogas production from straw according to claim 1, characterized in that: In step S3, the straw is crushed into particles with a particle size of 2-3 cm for later use; The volume ratio of the straw stack is 0.08-0.12t / m 3 .

8. A pre-fermentation method for improving biogas production from straw according to claim 1, characterized in that: In step S3, the spraying rate of the enhanced hydrolysis bacterial solution is 2-4 L / (t·min); The enhanced hydrolysis lasts for 3-5 days, the spraying frequency is 2-7 times per day, and the single spraying time is 2-30 minutes.

9. A biogas fermentation system in accordance with the pre-fermentation method according to any one of claims 1 to 8, characterized in that: It comprises a micro-nano bubble generating device (1), a bacterial agent fermentation tank (2) and a straw fermentation reactor (3) which are connected in sequence; A spraying device (4) is provided between the bacterial agent fermentation tank (2) and the straw fermentation reactor (3) for spraying the enhanced hydrolyzate in the bacterial agent fermentation tank (2) onto the straw in the straw fermentation reactor (3).

10. A biogas fermentation system according to claim 9, characterized in that: The bacterial agent fermentation tank (2) is provided with a stirring device (5); The bacterial fermentation tank (2) and the spraying device (4) are connected via a pipeline, and a spraying pump (6) is provided on the pipeline; The straw fermentation reactor (3) is connected to a biogas collection system (7).

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