Method and system for intensifying methane generation through photo-assisted low-temperature anaerobic fermentation

Abstract

The invention provides a method and system for intensifying methane generation through photo-assisted low-temperature anaerobic fermentation, and relates to the technical field of organic waste treatment.The method for intensifying methane generation through photo-assisted low-temperature anaerobic fermentation comprises the steps that optimal intermediate-temperature anaerobic fermentation technological parameters are obtained; carrying out medium-temperature anaerobic fermentation under the optimal medium-temperature anaerobic fermentation process parameters; carrying out gradient cooling anaerobic fermentation under the optimal intermediate-temperature anaerobic fermentation process parameters except the temperature by taking the fermentation liquor of the intermediate-temperature anaerobic fermentation as an inoculum, and carrying out domestication and enrichment to obtain a low-temperature compound bacterial system; carrying out low-temperature anaerobic fermentation under the optimal intermediate-temperature anaerobic fermentation process parameters except the temperature by taking the low-temperature compound bacterium system as an inoculum, and carrying out light treatment on a reaction system of the low-temperature anaerobic fermentation; wherein the temperature of the low-temperature anaerobic fermentation is 15-20 DEG C. The anaerobic fermentation gas production efficiency under the low-temperature condition can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of organic waste treatment, and in particular to a method and system for enhancing methane generation by light-assisted low-temperature anaerobic fermentation. Background Art

[0002] Anaerobic fermentation technology can degrade organic waste, produce methane and organic fertilizer, and is an important technology for the country to reduce agricultural waste pollution and develop clean energy. As a bioconversion process carried out at conditions below 25°C, low-temperature anaerobic fermentation technology has a significant advantage over traditional medium and high temperature fermentation modes in that it greatly reduces the energy consumption required for heating the bioreactor, thereby achieving effective cost reductions at the engineering construction and daily operation and maintenance levels, while demonstrating excellent eco-friendliness and economic benefits. However, under low temperature conditions, the growth and metabolic activities of microorganisms will be inhibited, and the reduction in enzyme catalytic efficiency will lead to reduced fermentation efficiency, which can easily lead to the accumulation of intermediate metabolites in the reactor and a decrease in methane production, becoming a technical bottleneck restricting its widespread application.

[0003] There is a large temperature difference between different regions in my country. The geographical and climatic conditions of high latitudes and high altitudes are unique. Due to the limitation of low temperature, the development of biogas industry in high latitudes and high altitudes lags behind significantly, which is mainly manifested in low gas production efficiency, high insulation cost and difficulty in stable operation all year round. Although the use of reactor heating strategy or design optimization can ensure the operation of biogas projects to a certain extent, the energy consumption required for medium and high temperature fermentation in cold climates is relatively large, which makes the overall energy yield of biogas low or negative, making it a practical problem to maintain biogas projects in winter. Summary of the invention

[0004] The problem solved by the invention is to improve the gas production efficiency of anaerobic fermentation under low temperature conditions.

[0005] In order to solve the above problems, the present invention provides a method and system for enhancing methane production by light-assisted low-temperature anaerobic fermentation.

[0006] In a first aspect, the present invention provides a method for enhancing methane production by light-assisted low-temperature anaerobic fermentation, comprising: obtaining optimal mesophilic anaerobic fermentation process parameters, and performing mesophilic anaerobic fermentation under the optimal mesophilic anaerobic fermentation process parameters;

[0007] Using the fermentation liquid of the mesophilic anaerobic fermentation as inoculum, performing gradient cooling anaerobic fermentation under the optimal mesophilic anaerobic fermentation process parameters except temperature, and acclimating and enriching to obtain a low-temperature composite bacterial system;

[0008] The low-temperature composite bacteria system is used as an inoculum, and low-temperature anaerobic fermentation is carried out under the optimal medium-temperature anaerobic fermentation process parameters except temperature, and the reaction system of the low-temperature anaerobic fermentation is subjected to light treatment; wherein the temperature of the low-temperature anaerobic fermentation is 15°C to 20°C.

[0009] Optionally, the fermentation liquid of the mesophilic anaerobic fermentation is used as an inoculum, and the gradient cooling anaerobic fermentation is performed under the optimal mesophilic anaerobic fermentation process parameters except the temperature, and the low-temperature composite bacterial system is domesticated and enriched, comprising:

[0010] The fermentation liquid at the time of the highest daily gas production of the mesophilic anaerobic fermentation is used as inoculum, and the gradient cooling anaerobic fermentation is carried out under the optimal mesophilic anaerobic fermentation process parameters except the temperature.

[0011] Optionally, the fermentation liquid of the mesophilic anaerobic fermentation is used as an inoculum, and the gradient cooling anaerobic fermentation is performed under the optimal mesophilic anaerobic fermentation process parameters except the temperature, and the low-temperature composite bacterial system is domesticated and enriched, comprising:

[0012] The fermentation broth of the mesophilic anaerobic fermentation is used as an inoculum, and after being cooled from the initial temperature gradient to the target temperature under the optimal mesophilic anaerobic fermentation process parameters except temperature, it is continuously operated at the target temperature for 10 to 12 hydraulic retention time cycles, and the fermentation broth with the highest cumulative gas production in the hydraulic retention time cycle is selected as the low-temperature composite bacterial system.

[0013] Optionally, the initial temperature of the gradient cooling anaerobic fermentation is 35°C to 40°C, the target temperature is 15°C to 20°C, and the cooling gradient of the gradient cooling anaerobic fermentation is 4°C to 6°C.

[0014] Optionally, the retention time of each cooling stage of the gradient cooling anaerobic fermentation is 3 to 5 hydraulic retention time cycles.

[0015] Optionally, the illumination intensity of the illumination treatment is 5000Lx, and the illumination duration is 12h.

[0016] Optionally, the dominant bacterial phyla of the low-temperature composite bacterial system include Firmicutes, Bacteroidetes and Proteobacteria, and the dominant archaeal phyla include Euryarchaeota.

[0017] Optionally, the dominant bacterial genera of the low-temperature composite bacterial system include Trichococcus and Acinetobacter, and the dominant archaeal genera of the low-temperature composite bacterial system include Methanothrix, Methanosarcina and Methanobacterium.

[0018] Optionally, the optimal mesophilic anaerobic fermentation process parameters are obtained by orthogonal experimental method, and the optimal mesophilic anaerobic fermentation process parameters include: temperature of 35° C., carbon-nitrogen ratio of 25:1, inoculation ratio of 50%, and total solid content of feed of 10%.

[0019] In a second aspect, the present application provides a system for enhancing methane production by light-assisted low-temperature anaerobic fermentation, the system being used to implement the method for enhancing methane production by light-assisted low-temperature anaerobic fermentation involved in the first aspect, the system comprising a medium-temperature anaerobic fermentation reactor, a gradient cooling anaerobic fermentation reactor and a low-temperature anaerobic fermentation reactor connected in sequence;

[0020] The mesophilic anaerobic fermentation reactor is used to carry out mesophilic anaerobic fermentation under the optimal mesophilic anaerobic fermentation process parameters; the gradient cooling anaerobic fermentation reactor is used to carry out gradient cooling anaerobic fermentation under the optimal mesophilic anaerobic fermentation process parameters except temperature, so as to acclimate and enrich the low-temperature composite bacterial system; the low-temperature anaerobic fermentation reactor is used to carry out low-temperature anaerobic fermentation under the optimal mesophilic anaerobic fermentation process parameters except temperature, using the low-temperature composite bacterial system as an inoculum.

[0021] The beneficial effects of the method and system for enhancing methane production by light-assisted low-temperature anaerobic fermentation of the present invention are:

[0022] After determining the optimal anaerobic fermentation process parameters, the embodiment of the present invention obtains the dominant methanogenic bacteria through the optimal medium-temperature anaerobic fermentation, and then uses the fermentation liquid of the medium-temperature anaerobic fermentation as the inoculum, and enriches and constructs the low-temperature composite bacteria system adapted to the low-temperature environment through the gradient cooling strategy, thereby constructing an anaerobic fermentation microbial community that works efficiently in a low-temperature environment. At the same time, combined with the light-assisted process, the gas production efficiency of the low-temperature anaerobic fermentation system is significantly improved, which provides a scientific basis and technical support for the deep integration and efficient utilization of solar energy and anaerobic fermentation technology, and promotes the stable operation of biogas projects in winter in high-cold areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the system for enhancing methane production by light-assisted low-temperature anaerobic fermentation according to the present invention;

[0024] Figure 2 CH is the medium temperature anaerobic fermentation system of Example 1 of the present invention. 4 Daily production and CH 4 Content change trend over time;

[0025] Figure 3 The average accumulated CH in each hydraulic retention time period at 20°C for the gradient cooling anaerobic fermentation of Example 1 of the present invention is 4 Production trend chart;

[0026] Figure 4The CH 4 Daily production over time trend chart;

[0027] Figure 5 is the accumulated CH4 in the low-temperature anaerobic fermentation under different light intensities of Example 1 of the present invention. 4 Production trend over time;

[0028] Figure 6 The CH400 of low-temperature anaerobic fermentation under different illumination times in Example 1 of the present invention is shown in FIG. 4 Daily production over time trend chart;

[0029] Figure 7 is the cumulative CH in the low-temperature anaerobic fermentation of Example 1 of the present invention under different light exposure times 4 Production trend over time;

[0030] Description of reference numerals:

[0031] 1. Medium-temperature anaerobic fermentation reactor; 2. Gradient cooling anaerobic fermentation reactor; 3. Low-temperature anaerobic fermentation reactor. DETAILED DESCRIPTION

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. Although certain embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be interpreted as being limited to the embodiments described herein. On the contrary, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the drawings and embodiments of the present invention are only for exemplary purposes and are not intended to limit the scope of protection of the present invention.

[0033] Unless otherwise defined, all technical and scientific terms used in this application have the same meanings as those commonly understood by those skilled in the art to which this application belongs; the terms used in the specification of this application are only for the purpose of describing specific implementation methods and are not intended to limit this application;

[0034] The term "including" and its variations used in this article are open inclusions, that is, "including but not limited to"; the term "based on" is "based at least in part on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one other embodiment"; the term "some embodiments" means "at least some embodiments"; the term "optionally" means "optional embodiments". The relevant definitions of other terms will be given in the following description. It should be noted that the concepts of "first" and "second" mentioned in the present invention are used to distinguish different objects, rather than to describe a specific order or a primary and secondary relationship. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, the meaning of "multiple" is two or more.

[0035] In related technologies, microbial enhancement is usually used to overcome the effect of low temperature on the methane production efficiency of low-temperature anaerobic fermentation. That is, samples are collected from natural environments such as polar regions, alpine lakes and deep-sea sediments, and then strains with low-temperature adaptability are screened out using enrichment culture, dilution coating and other methods, and long-term domestication is carried out under laboratory conditions to improve their growth rate and metabolic activity in low-temperature environments. However, this method has the disadvantages of difficult sample collection and long domestication cycle, and is not easy to apply on a large scale.

[0036] In addition, although the limitation of low temperature has a great adverse effect on the biogas industry in alpine areas, alpine areas have the characteristics of a stable snow accumulation period of up to six months and a high proportion of direct sunlight due to their unique geographical location and climatic conditions. Therefore, the high reflectivity of snow in this area to sunlight far exceeds that of other surface types, providing unique natural conditions for the collection and efficient use of solar energy. In the current technologies related to anaerobic fermentation and methanogenesis, there are few studies on the effect of light utilization on the efficiency of anaerobic fermentation and methanogenesis, especially for low-temperature anaerobic fermentation, which is common in alpine areas. If we can make full use of solar energy resources in alpine areas to promote the process of low-temperature anaerobic fermentation and methanogenesis, it will be of great significance to the development of the biogas industry in alpine areas.

[0037] Based on the above-mentioned related technologies, an embodiment of the present invention provides a method and system for enhancing methane production by light-assisted low-temperature anaerobic fermentation.

[0038] As a first aspect, an embodiment of the present invention provides a method for enhancing methane production by light-assisted low-temperature anaerobic fermentation, comprising: obtaining optimal mesophilic anaerobic fermentation process parameters, and performing mesophilic anaerobic fermentation under the optimal mesophilic anaerobic fermentation process parameters; using the fermentation liquid of the mesophilic anaerobic fermentation as an inoculum, performing gradient cooling anaerobic fermentation under the optimal mesophilic anaerobic fermentation process parameters except temperature, and acclimating and enriching to obtain a low-temperature composite bacterial system; using the low-temperature composite bacterial system as an inoculum, performing low-temperature anaerobic fermentation under the optimal mesophilic anaerobic fermentation process parameters except temperature, and subjecting the reaction system of the low-temperature anaerobic fermentation to light treatment; wherein the temperature of the low-temperature anaerobic fermentation is 15°C to 20°C.

[0039] After determining the optimal anaerobic fermentation process parameters, the embodiment of the present invention obtains the dominant methanogenic bacteria through the optimal medium-temperature anaerobic fermentation, and then uses the fermentation liquid of the medium-temperature anaerobic fermentation as the inoculum, and enriches and constructs the low-temperature composite bacteria system adapted to the low-temperature environment through the gradient cooling strategy, thereby constructing an anaerobic fermentation microbial community that works efficiently in a low-temperature environment. At the same time, combined with the light-assisted process, the gas production efficiency of the low-temperature anaerobic fermentation system is significantly improved, which provides a scientific basis and technical support for the deep integration and efficient utilization of solar energy and anaerobic fermentation technology, and promotes the stable operation of biogas projects in winter in high-cold areas.

[0040] In some optional embodiments, the fermentation broth of mesophilic anaerobic fermentation is used as inoculum, and gradient cooling anaerobic fermentation is carried out under the optimal mesophilic anaerobic fermentation process parameters except temperature, and the low-temperature composite bacterial system is obtained by acclimation and enrichment, which includes: using the fermentation broth of the mesophilic anaerobic fermentation during the period of maximum daily gas production as inoculum, and gradient cooling anaerobic fermentation is carried out under the optimal mesophilic anaerobic fermentation process parameters except temperature.

[0041] The present invention selects the fermentation liquid at the highest daily gas production period of mesophilic anaerobic fermentation as the inoculum. The inoculum at this period is rich in fermentation functional bacteria with strong microbial activity and high methane production capacity, which is conducive to the smooth progress of the subsequent gradient cooling acclimation process. In some specific embodiments, the period of highest gas production is from the 7th to the 9th day of mesophilic anaerobic fermentation, more specifically the 8th day.

[0042] In some optional embodiments, the fermentation broth of mesophilic anaerobic fermentation is used as an inoculum, and gradient cooling anaerobic fermentation is carried out under optimal mesophilic anaerobic fermentation process parameters except temperature to domesticate and enrich a low-temperature composite bacterial system, including: using the fermentation broth of mesophilic anaerobic fermentation as an inoculum, gradient cooling from the initial temperature to the target temperature under optimal mesophilic anaerobic fermentation process parameters except temperature, and continuing to operate at the target temperature for 10 to 12 hydraulic retention time cycles, and selecting the fermentation broth with the highest cumulative gas production in the hydraulic retention time cycle as the low-temperature composite bacterial system.

[0043] Specifically, in the gradient cooling anaerobic fermentation process, the inoculum is selected from the fermentation broth of the 7th to 9th day of medium-temperature anaerobic fermentation, and then the reaction substrate and the inoculum are added to the anaerobic reactor, and the semi-continuous feeding and discharging operation mode is adopted, and the hydraulic retention time can be set to 25 days (i.e., one hydraulic retention time cycle). The microorganisms are then tamed by gradient cooling, and the operating temperature of the reaction system is finally stabilized at the target temperature. Subsequently, 10 to 12 hydraulic retention time cycles are continued to operate at the target temperature, and the changes in the average cumulative methane production in each cycle are monitored and recorded, and the fermentation broth with the highest cumulative gas production in the hydraulic retention time cycle is selected as the low-temperature composite bacterial system. In some specific embodiments, the hydraulic retention time cycle with the highest cumulative gas production is the 8th hydraulic retention time cycle operated at the target temperature.

[0044] The gradient cooling anaerobic fermentation process of the embodiment of the present invention includes two stages: gradient cooling and low-temperature continuous fermentation. Finally, the fermentation liquid in the hydraulic retention time period with the highest gas production in the low-temperature continuous fermentation stage is selected as the low-temperature composite bacterial system. The fermentation liquid in this period has a fermentation functional bacterial community with the ability to efficiently produce methane at low temperatures, and has a relatively stable adaptability to low temperatures.

[0045] In some optional embodiments, the initial temperature of the gradient cooling anaerobic fermentation is 35°C to 40°C, the target temperature is 15°C to 20°C, and the cooling gradient of the gradient cooling anaerobic fermentation is 4°C to 6°C. Preferably, the initial temperature can be 35°C, the target temperature can be 20°C, and the cooling gradient can be 5°C. Thus, the temperature of the anaerobic fermentation is gradually reduced from the optimal reaction temperature to a low temperature to promote the low temperature adaptability of the bacterial system.

[0046] Optionally, the residence time of each cooling stage of the gradient cooling anaerobic fermentation is 3 to 5 hydraulic retention time cycles. In some specific embodiments, the various temperature points of the gradient cooling anaerobic fermentation can be 35°C, 30°C, 25°C and 20°C, wherein the first cooling stage is 35°C to 30°C, the second cooling stage is 30°C to 25°C, the third cooling stage is 25°C to 20°C, and each cooling stage stays for 4 hydraulic retention time cycles.

[0047] The present invention realizes the gradient cooling of the anaerobic fermentation system by setting different cooling stages. At the same time, each cooling stage is kept for a certain time, so that the microorganisms can gradually adapt to the low temperature environment, thereby improving their survival ability and metabolic activity at low temperatures. At the same time, it can improve the genetic stability of microorganisms, so that they can maintain good performance in the long-term biological treatment process; and promote the interaction and cooperation between microorganisms, thereby optimizing the community structure and improving the overall ecological function.

[0048] In some optional embodiments, the illumination intensity of the illumination treatment is 5000Lx, and the illumination duration is 12h.

[0049] Experimental results show that, for low-temperature anaerobic fermentation, different light intensities and illumination times have positive effects on the gas production performance of low-temperature anaerobic fermentation systems compared to dark conditions. The daily methane production shows a trend of first increasing rapidly and then gradually decreasing, and both reach their respective peaks on the 7th to 9th day of the initial fermentation. In addition, the cumulative methane production shows a trend of first increasing and then decreasing with the increase of light intensity and duration. Under the conditions of light intensity of 5000Lx and light duration of 12h, the cumulative methane production reaches the maximum value.

[0050] In some optional embodiments, the dominant bacterial phyla of the low-temperature composite bacterial system include Firmicutes, Bacteroidetes and Proteobacteria, and the dominant archaeal phyla include Euryarchaeota. More specifically, the dominant bacterial genera of the low-temperature composite bacterial system include Trichococcus and Acinetobacter, and the dominant archaeal genera of the low-temperature composite bacterial system include Methanothrix, Methanosarcina and Methanobacterium.

[0051] It should be noted that the dominant bacterial groups, such as fermentative bacteria, hydrogen-producing and acetogenic bacteria, etc., first decompose complex organic matter into soluble organic matter under anaerobic conditions, and further convert them into intermediates such as volatile fatty acids. These intermediates are then used by methanogens, the dominant bacterial group in the archaea. Methanogens are a type of obligate anaerobes that can convert these intermediates into methane and carbon dioxide. The synergistic effect of bacteria and archaea not only improves the efficiency of methane production, but also makes the anaerobic fermentation process more stable and efficient.

[0052] Specifically, Firmicutes and Bacteroidetes are mainly involved in the hydrolysis stage of anaerobic fermentation, responsible for the degradation of substrates such as carbohydrates, proteins, fats and cellulose, and are indispensable microbial groups in the fermentation process. The Proteobacteria not only have the ability to degrade lignocellulose and protein, but also can reduce organic acids to nitrogen gas through the denitrification mechanism, thus playing an important role in the fermentation process. Among them, the genus Trichococcus has the ability to degrade complex organic compounds and extracellular polysaccharides, which makes it have potential application value in anaerobic fermentation. The genus Acinetobacter is one of the main functional bacterial groups that decompose and metabolize organic compounds during the acid production period, and helps the production of cellulose hydrolases (mainly xylanases).

[0053] Methanobacterium is a hydrogenotrophic methanogenic archaeon, Methanothrix is ​​an obligate acetogenic methanogenic archaeon, and Methanosarcina is a mixed-trophic methanogenic archaeon that mainly uses acetic acid for methanogenic metabolism. Therefore, the inoculum mainly produces methane through acetogenic and hydrogenotrophic metabolic pathways, while also having a methylotrophic metabolic pathway. In addition, Methanosarcina has a strong tolerance to temperature fluctuations, which allows it to gradually gain the upper hand in the competition with other archaea, becoming the key archaea that dominates gas production and showing more outstanding methanogenic performance.

[0054] From the above analysis results, it can be seen that the gradient cooling acclimation strategy promotes the reproduction of complex organic matter degrading bacteria, and the composite bacteria mainly produce methane through acetic acid trophic and hydrogen trophic metabolic pathways, while also having a methyl trophic metabolic pathway. This improves the efficiency of methane generation and makes the anaerobic fermentation process more stable and efficient.

[0055] In some optional embodiments, the optimal medium-temperature anaerobic fermentation process parameters include: temperature of 35°C, carbon-nitrogen ratio of 25:1, inoculation ratio of 50%, and total solid content of feed of 10%. Specifically, the orthogonal experiment method can be used to obtain the optimal medium-temperature anaerobic fermentation process parameters. In some other embodiments, process parameters such as pH and pretreatment of fermentation substrates can also be added, and finally the optimal medium-temperature anaerobic fermentation process parameters are comprehensively determined through orthogonal experiments.

[0056] The present invention determines the optimal medium-temperature anaerobic fermentation conditions and light-assisted process parameters through systematic experiments and data analysis, which is beneficial to obtaining dominant methanogenic bacteria before gradient cooling, ensuring the efficiency and stability of the entire process.

[0057] As a second aspect, the present invention also relates to a system for enhancing methane production by light-assisted low-temperature anaerobic fermentation, referring to Figure 1 As shown, the system includes a mesophilic anaerobic fermentation reactor 1, a gradient cooling anaerobic fermentation reactor 2 and a low-temperature anaerobic fermentation reactor 3 which are connected in sequence. Among them, the mesophilic anaerobic fermentation reactor 1 is used to perform mesophilic anaerobic fermentation under the optimal mesophilic anaerobic fermentation process parameters; the gradient cooling anaerobic fermentation reactor 2 is used to perform gradient cooling anaerobic fermentation under the optimal mesophilic anaerobic fermentation process parameters except temperature, so as to acclimate and enrich the low-temperature composite bacterial system; the low-temperature anaerobic fermentation reactor 3 is used to perform low-temperature anaerobic fermentation under the optimal mesophilic anaerobic fermentation process parameters except temperature using the low-temperature composite bacterial system as an inoculum. Specifically, a control valve can be set between each two adjacent fermentation reactors, and the mesophilic anaerobic fermentation reactor 1, the gradient cooling anaerobic fermentation reactor 2, and the low-temperature anaerobic fermentation reactor 3 are all provided with basic components such as a substrate feed port, an inoculum feed port and a temperature controller to achieve comprehensive control of their respective reaction processes and temperatures.

[0058] In some optional embodiments, the system for enhancing methane production by light-assisted low-temperature anaerobic fermentation may further include a fermentation substrate pretreatment device, which is connected to the feed ports of the medium-temperature anaerobic fermentation reactor 1, the gradient cooling anaerobic fermentation reactor 2, and the low-temperature anaerobic fermentation reactor 3, respectively, and the feed is controlled by control valves. The fermentation substrate pretreatment device can be supporting facilities such as a crusher and a mixer.

[0059] The present invention is further described below in conjunction with specific embodiments.

[0060] Example 1

[0061] (1) Obtaining the optimal medium-temperature anaerobic fermentation process parameters

[0062] On the premise that the optimal carbon-nitrogen ratio is pre-established as 25:1, this embodiment further sets up an orthogonal experiment including three process parameters, in which the fermentation substrate is a mixture of corn straw and cow dung, and the inoculum comes from the Lindian Sihe Township Biogas Engineering Center of Harbin Boneng Environmental Protection Technology Co., Ltd. The effects of three factors on the performance of the anaerobic fermentation process are studied. Specifically including: temperature (20°C, 25°C, 30°C and 35°C), total solid content of feed (7%, 10%, 13% and 16%) and inoculation ratio (20%, 30%, 40% and 50%), monitoring the daily methane production and total production of different experimental groups. The specific data of the orthogonal experiment are shown in Table 1:

[0063] Table 1 Orthogonal experimental data table of optimal medium temperature anaerobic fermentation process parameters

[0064]

[0065] As shown in Table 1, the optimal process conditions obtained through orthogonal experiments are: temperature of 35°C, inoculation ratio of 50%, and total solid content of feed of 10%.

[0066] (2) Verification of optimal medium-temperature anaerobic fermentation process parameters

[0067] Based on the optimal medium-temperature anaerobic fermentation process parameters obtained by the above orthogonal experiment, a verification experiment was carried out, that is, a medium-temperature anaerobic fermentation experiment was carried out under the process of carbon-nitrogen ratio of 25:1, temperature of 35°C, inoculation ratio of 50%, and total solid content of feed of 10%. 4 Daily production and CH 4 Content, experimental results such as Figure 2 shown.

[0068] Depend on Figure 2 It can be seen that on the 8th day, the CH 4 The daily production reached a peak of 412.70±37.49 mL. At this time, the microbial community in the system was in the most active state.4 The content also climbed to the highest level, which was 58.36±6.58%. At the end of fermentation, the accumulated CH 4 The yield was as high as 5136.47±580.07mL.

[0069] (3) Gradient cooling anaerobic fermentation

[0070] A 2.5L wide-mouth bottle was selected as the anaerobic reactor, corn stalks and cow dung were used as substrates, a semi-continuous feeding and discharging operation mode was adopted, and the hydraulic retention time was set to 25 days (1 hydraulic retention time cycle). Based on the verification test in (2), the fermentation liquid on the 8th day of medium-temperature anaerobic fermentation was selected as the inoculum for gradient cooling anaerobic fermentation.

[0071] First, enter the gradient cooling stage: the initial temperature of the anaerobic reactor is set to 35°C, the cooling gradient is 5°C, the first cooling stage is 35°C to 30°C, the second cooling stage is 30°C to 25°C, and the third cooling stage is 25°C to 20°C. Each cooling stage stays for 4 hydraulic retention time cycles.

[0072] Then it entered the low-temperature continuous fermentation stage: it continued to run for 10 hydraulic retention time cycles at 20°C, and monitored and recorded the average accumulated CH in each cycle of this stage. 4 Changes in production, relevant data such as Figure 3 As shown. Figure 3 It can be seen that with the increase of hydraulic retention time period, the average cumulative CH 4 The yield showed a trend of first increasing and then decreasing, reaching a maximum value of 3181.23±466.35mL in the 8th cycle.

[0073] The fermentation liquid of the 8th cycle was taken as the low-temperature composite bacterial system. The microbial sequencing analysis results of the low-temperature composite bacterial system are shown in Tables 2 to 5:

[0074] Table 2 Analysis results of relative abundance ratio at the bacterial community phylum level

[0075]

[0076]

[0077] Table 3 Analysis results of relative abundance ratio at genus level of bacterial community

[0078]

[0079]

[0080] Table 4 Analysis results of relative abundance ratio at the phylum level of archaeal community

[0081]

[0082] Table 5 Analysis results of relative abundance ratio at genus level of archaeal community

[0083]

[0084]

[0085] As shown in Tables 4 and 5, in the low-temperature composite bacterial system of the embodiment of the present invention, the dominant bacterial phyla include Firmicutes, Bacteroidota and Proteobacteria, with relative abundances of 54.6%, 19.41% and 18.55%, respectively. The dominant archaeal phyla include Euryarchaea, with a relative abundance of up to 92.45%; among them, the dominant bacterial genera include Trichococcus and Acinetobacter, with relative abundances of 32.52% and 28.43%, respectively, and the dominant archaeal genera include Methanothrix, Methanosarcina and Methanobacterium, with relative abundances of 32.67%, 31.78% and 10.80%, respectively.

[0086] (4) Low temperature anaerobic fermentation

[0087] A 500 mL conical flask was used as a reactor, a mixture of cow dung and corn stalks was used as a fermentation substrate, the low-temperature composite bacterial system obtained in (3) was used as the bacterial system inoculum, the carbon-nitrogen ratio of cow dung to corn stalks was controlled to be 25:1, the total solid content of the feed was set to 10%, the inoculation ratio of the low-temperature composite bacterial system was 50%, and the fermentation temperature was 20°C. Single factor gradient experiments on light intensity and light time were conducted. Among them, the light was irradiated for the same time at a light intensity of 1000Lx, 2000Lx, 3000Lx, 4000Lx, 5000Lx and 6000Lx; and the light was irradiated for 6 hours, 8 hours, 12 hours and 24 hours at the same light intensity, and the reactor in the dark environment was set as the control group (CK).

[0088] In this example, low-temperature anaerobic fermentation of CH 4 Daily output, cumulative CH 4 The trend of production over time is as follows Figure 4 , Figure 5 As shown in the figure, low temperature anaerobic fermentation of CH 4 Daily output, cumulative CH 4 The yield changes with fermentation time. Figure 6 , Figure 7 As shown. Figure 4-Figure 7 It can be seen that the CH 4 The daily production showed a trend of rapid increase first and then gradual decrease, and reached their respective peaks on the 7th to 9th day of the initial fermentation. 4 The yield of the two groups was higher than that of the control group, and it showed a trend of increasing first and then decreasing with the increase of light intensity and duration. Under the conditions of light intensity of 5000Lx and light duration of 12h, the cumulative CH 4 The yield reached a maximum value of 783.09±56.21 mL, an increase of approximately 49.14% compared with the CK group.

[0089] Comparative Example 1

[0090] The difference between this comparative example and Example 1 is that in step (3), the fermentation liquid on the 8th day of mesophilic anaerobic fermentation is used as inoculum, the carbon-nitrogen ratio of cow dung to corn straw is controlled to be 25:1, the total solid content of the feed is set to 10%, the inoculation ratio is 50%, and the acclimatization culture is directly carried out at 20°C. The average cumulative CH 4 The yield was changed, and then the fermentation liquid of the hydraulic retention time period when the cumulative methane production was the maximum was taken as the low-temperature composite bacterial system. Then, the low-temperature composite bacterial system was used as an inoculum to carry out a low-temperature anaerobic fermentation experiment under the same conditions. Under the conditions of a light intensity of 5000Lx and a light duration of 12h, the cumulative methane production was 321.42±31.03mL, which was reduced by more than 50% compared with Example 1.

[0091] Comparative Example 2

[0092] This comparative example uses a mixture of cow dung and corn straw as the fermentation substrate, controls the carbon-nitrogen ratio of cow dung to corn straw to be 25:1, sets the total solid content of the feed to be 10%, and uses the strain from the Lindian Sihe Township Biogas Engineering Center of Harbin Boneng Environmental Protection Technology Co., Ltd. The inoculation ratio is 50%, and performs mesophilic anaerobic fermentation at 35°C, and then conducts single-factor gradient experiments on light intensity and light duration. The optimal light intensity is 3000lx, and the light duration is 20h / day. Under this condition, the cumulative CH 4 The yield was 14618.5 mL.

[0093] Comparative Example 3

[0094] The fermentation substrate of this comparative example is a synthetic medium: acetate (2.5 g / L), glucose (2.5 g / L), KH 2 PO 4(16mg / L), yeast extract (200mg / L) and trace mineral solution (200mL / L), initial pH 7.0±0.1, ammonia nitrogen concentration 5000mg / L, strains from Harbin Boneng Environmental Protection Technology Co., Ltd. Lindian Sihe Township Biogas Engineering Center, inoculation ratio 50%, fermentation temperature 55℃, semi-continuous reactor for fermentation, and then single factor gradient experiments on light intensity and light time were carried out. The optimal light intensity was 153675lx, light duration was 63min / day, and the cumulative CH under this condition was 153675lx. 4 The yield was 14618.5 mL.

[0095] It can be seen from Comparative Examples 2 and 3 that at different fermentation temperatures (20°C, 35°C, 55°C), the requirements for light intensity and illumination duration are different. In the present invention, at 20°C, the required optimal light intensity and illumination duration are both between 35°C and 55°C.

[0096] Although the present invention is disclosed as above, the protection scope of the present invention is not limited thereto. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A method for enhancing methane production by light-assisted low-temperature anaerobic fermentation, characterized in that: include: Obtaining optimal mesophilic anaerobic fermentation process parameters, and performing mesophilic anaerobic fermentation under the optimal mesophilic anaerobic fermentation process parameters; Using the fermentation liquid of the mesophilic anaerobic fermentation as inoculum, performing gradient cooling anaerobic fermentation under the optimal mesophilic anaerobic fermentation process parameters except temperature, and acclimating and enriching to obtain a low-temperature composite bacterial system; The low-temperature composite bacteria system is used as an inoculum, and low-temperature anaerobic fermentation is carried out under the optimal medium-temperature anaerobic fermentation process parameters except temperature, and the reaction system of the low-temperature anaerobic fermentation is subjected to light treatment; wherein the temperature of the low-temperature anaerobic fermentation is 15°C to 20°C.

2. The method for enhancing methane production by light-assisted low-temperature anaerobic fermentation according to claim 1, characterized in that: The method uses the fermentation liquid of the mesophilic anaerobic fermentation as an inoculum, performs gradient cooling anaerobic fermentation under the optimal mesophilic anaerobic fermentation process parameters except temperature, and acclimates and enriches to obtain a low-temperature composite bacterial system, including: The fermentation liquid at the time of the highest daily gas production of the mesophilic anaerobic fermentation is used as inoculum, and the gradient cooling anaerobic fermentation is carried out under the optimal mesophilic anaerobic fermentation process parameters except the temperature.

3. The method for enhancing methane production by light-assisted low-temperature anaerobic fermentation according to claim 1, characterized in that: The method uses the fermentation liquid of the mesophilic anaerobic fermentation as an inoculum, performs gradient cooling anaerobic fermentation under the optimal mesophilic anaerobic fermentation process parameters except temperature, and acclimates and enriches to obtain a low-temperature composite bacterial system, including: The fermentation broth of the mesophilic anaerobic fermentation is used as an inoculum, and after being cooled from the initial temperature gradient to the target temperature under the optimal mesophilic anaerobic fermentation process parameters except temperature, it is continuously operated at the target temperature for 10 to 12 hydraulic retention time cycles, and the fermentation broth with the highest cumulative gas production in the hydraulic retention time cycle is selected as the low-temperature composite bacterial system.

4. The method for enhancing methane production by light-assisted low-temperature anaerobic fermentation according to any one of claims 1 to 3, characterized in that: The initial temperature of the gradient cooling anaerobic fermentation is 35°C to 40°C, the target temperature is 15°C to 20°C, and the cooling gradient of the gradient cooling anaerobic fermentation is 4°C to 6°C.

5. The method for enhancing methane production by light-assisted low-temperature anaerobic fermentation according to claim 4, characterized in that: The retention time of each cooling stage of the gradient cooling anaerobic fermentation is 3 to 5 hydraulic retention time cycles.

6. The method for enhancing methane production by light-assisted low-temperature anaerobic fermentation according to claim 1, characterized in that: The illumination intensity of the illumination treatment is 5000Lx, and the illumination duration is 12h.

7. The method for enhancing methane production by light-assisted low-temperature anaerobic fermentation according to claim 1, characterized in that: The dominant bacterial phyla of the low-temperature composite bacterial system include Firmicutes, Bacteroidetes and Proteobacteria, and the dominant archaeal phyla include Euryarchaeota.

8. The method for enhancing methane production by light-assisted low-temperature anaerobic fermentation according to claim 7, characterized in that: The dominant bacterial genera of the low-temperature composite bacterial system include Trichococcus and Acinetobacter, and the dominant archaeal genera of the low-temperature composite bacterial system include Methanothrix, Methanosarcina and Methanobacterium.

9. The method for enhancing methane production by light-assisted low-temperature anaerobic fermentation according to claim 1, characterized in that: The optimal mesophilic anaerobic fermentation process parameters were obtained by orthogonal experimental method, and the optimal mesophilic anaerobic fermentation process parameters included: temperature of 35° C., carbon-nitrogen ratio of 25:1, inoculation ratio of 50%, and total solid content of feed of 10%.

10. A system for enhancing methane production by light-assisted low-temperature anaerobic fermentation, characterized in that: The system is used to implement the method for enhancing methane production by light-assisted low-temperature anaerobic fermentation according to any one of claims 1 to 9, and the system comprises a medium-temperature anaerobic fermentation reactor (1), a gradient cooling anaerobic fermentation reactor (2) and a low-temperature anaerobic fermentation reactor (3) which are connected in sequence; The mesophilic anaerobic fermentation reactor (1) is used to carry out mesophilic anaerobic fermentation under optimal mesophilic anaerobic fermentation process parameters; the gradient cooling anaerobic fermentation reactor (2) is used to carry out gradient cooling anaerobic fermentation under the optimal mesophilic anaerobic fermentation process parameters except temperature, so as to acclimate and enrich the low-temperature composite bacterial system; the low-temperature anaerobic fermentation reactor (3) is used to carry out low-temperature anaerobic fermentation under the optimal mesophilic anaerobic fermentation process parameters except temperature, using the low-temperature composite bacterial system as an inoculum.

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