Device and method for improving anaerobic digestion effect

Abstract

The invention discloses a device and a method for improving anaerobic digestion effect, the device comprises a fermentation tank and an adjustable static magnetic field device, and the magnetic flux density of the bottom of the fermentation tank is less than or equal to 18.7 mT. According to the device, by constructing the static magnetic field with the magnetic flux density smaller than or equal to 18.7 mT, the iron bio-availability of the system can be remarkably improved, the activity of microorganisms and enzymes can be improved, the anaerobic digestion effect of the system is better, and the device has the advantages of being high in anaerobic digestion efficiency, short in fermentation period, high in gas production rate, good in applicability, low in operation and maintenance cost, high in use value and good in application prospect. The method comprises the following steps: mixing camellia oleifera shells and sludge to prepare a fermentation raw material, and carrying out anaerobic digestion under the condition that the magnetic flux density is less than or equal to 18.7 mT, so that methane gas with higher yield can be obtained under the condition of shorter time, and the method has the advantages of simple process, convenience in operation, low cost, high treatment efficiency, high gas yield and the like; the method has an important promotion effect on the resource utilization of the camellia oleifera shells and the sludge.

Description

Technical Field

[0001] The present invention belongs to the technical fields of renewable energy and resource environment, and relates to a device and method for improving anaerobic digestion effect. Background Art

[0002] With the continuous depletion of fossil energy and the increasing environmental problems, the development and utilization of clean and renewable energy have become an important issue of global concern. Biomass has the characteristics of universality, abundance, and renewability, and has been recognized as a natural renewable resource that can be used to replace traditional fossil energy. Among various technical routes for biomass energy utilization, anaerobic digestion, as an efficient and environmentally friendly biological conversion technology, can convert organic substances such as cellulose and hemicellulose in lignocellulosic biomass into methane through the metabolic action of microorganisms, thereby realizing energy recovery and resource recycling.

[0003] Anaerobic digestion is the degradation and stabilization of organic substances by anaerobic bacteria under anaerobic conditions, while producing biogas. Since lignin and hemicellulose in lignocellulosic biomass materials are combined by covalent bonds and wrap cellulose molecules therein, the three are intertwined to form a dense spatial network structure with low porosity, constituting a strong natural barrier. Therefore, it is difficult for anaerobic microorganisms to quickly convert cellulose and hemicellulose in biomass into methane. On the other hand, the macromolecular structure and hydrophobic properties of lignin can physically hinder the contact and reaction between cellulase and cellulose molecules, and the compounds in lignin can also react with the active sites or key groups in cellulase, resulting in conformational changes or functional inhibition of the enzyme, reducing the degradation ability of cellulase to cellulose, and further affecting the degradation and conversion of cellulose, leading to a series of problems such as low biodegradation rate, poor gas production capacity, and long fermentation cycle in the anaerobic digestion process. Therefore, it is very necessary to obtain an anaerobic digestion technology that can effectively improve gas production capacity and shorten the fermentation cycle.

[0004] Applying a static magnetic field in an anaerobic digestion system is a new technology for enhancing anaerobic digestion performance. As a physical intervention method, it has the advantages of low energy consumption, small environmental impact, and low maintenance cost. In existing fermentation devices based on static magnetic fields, a magnetic field generating device (such as an energized coil, permanent magnet, or magnetic material) is usually set at the bottom, inside, or beside the fermentation tank. By using the magnetic field generating device to form a static magnetic field inside and around the fermentation tank, the electron transfer efficiency in the fermentation system is enhanced by the static magnetic field, while promoting the reproduction of microorganisms and increasing the activity of microbial product enzymes, thus accelerating the anaerobic digestion rate of organic waste and improving the gas production efficiency. However, the above devices still have the following defects: (1) In the anaerobic digestion system, it is difficult to improve the biological availability of iron in the fermentation system, which not only makes it difficult to synthesize various key enzymes closely related to the biogas fermentation process, but also difficult to increase the activity of these key enzymes, and thus makes it difficult for the microorganisms in the adopted anaerobic digestion system to utilize lignocellulosic biomass materials. (2) The constructed static magnetic field is unevenly distributed, making it difficult to achieve a comprehensive and uniform stimulation of microorganisms (such as methanogens) in the fermentation system, difficult to promote the rapid reproduction of microorganisms, and the adaptability of microorganisms is poor, resulting in a still low anaerobic digestion rate and gas production, especially, the degradation rate of lignocellulosic biomass materials is lower and the degradation effect is worse, making it difficult to achieve efficient utilization of lignocellulosic biomass materials; (3) Setting the magnetic field generating device inside the fermentation tank not only is not conducive to the daily maintenance and management of the magnetic field generating device, but also easily causes damage to the magnetic field generating device. Especially, when the magnetic field generating device is a magnetic material, there is also the defect that it is difficult to completely separate the magnetic material from the fermentation system, which is likely to cause secondary pollution. Therefore, it is also very necessary to obtain a fermentation device that can effectively improve the biological availability of iron and promote the effective degradation of lignocellulosic biomass materials.

[0005] In addition, most of the iron in the anaerobic digestion system exists in the form of residual state and is not easily utilized by microorganisms, with low biological availability. At the same time, the regulation of iron biological availability in the anaerobic digestion system is mainly achieved through methods such as the addition of exogenous iron salts and chelating agents, the adjustment of system pH, and the anaerobic co-digestion of materials. However, the above methods may bring problems such as increased operating costs, microbial community imbalance, increased operation complexity, and secondary pollution.

[0006] In addition, the shell of Camellia oleifera fruit contains a large amount of lignocellulose, which can be used as raw material for anaerobic digestion to produce gas, showing good prospects. However, due to the complex structure and difficult degradation of the shell of Camellia oleifera fruit, and the components such as high content of lignin and hemicellulose in the shell of Camellia oleifera fruit are prone to directly inhibit the activity of microbial enzymes and easily cause obvious acid inhibition, which makes the existing anaerobic digestion methods based on the shell of Camellia oleifera fruit still have defects such as long fermentation cycle, low degradation efficiency, and low gas production, and it is difficult to realize the resource utilization of the shell of Camellia oleifera fruit.

[0007] Therefore, how to improve the biological availability of iron in the anaerobic digestion system and promote the efficient utilization of the shell of Camellia oleifera fruit plays an important promoting role in promoting the anaerobic digestion effect of the anaerobic digestion system on the shell of Camellia oleifera fruit and improving the economic benefits of the shell of Camellia oleifera fruit. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a device and method for improving anaerobic digestion effect with high anaerobic digestion efficiency, short fermentation cycle, high gas production, good applicability, and low operation and maintenance costs.

[0009] To solve the above technical problems, the present invention adopts the following technical solutions: A device for improving anaerobic digestion effect includes a fermentation tank for anaerobic digestion and an adjustable static magnetic field device for adjusting the magnetic flux density in the fermentation tank, and the magnetic flux density at the bottom of the fermentation tank ≤ 18.7 mT; the adjustable static magnetic field device is located below the fermentation tank; the adjustable static magnetic field device includes at least one permanent magnet, the permanent magnet is detachably installed on a tray, and a movable adjusting mechanism is connected to the tray for adjusting the distance between the permanent magnet and the bottom of the fermentation tank; the distance between the permanent magnet and the fermentation tank is 10 mm - 40 mm; the material of the permanent magnet is neodymium iron boron material; the magnetic permeability of the permanent magnet is 1.05, and the residual magnetic flux density is 1.45 T; when the number of the permanent magnets is one, the permanent magnet is horizontally distributed, and the center point is located on the central axis of the bottom of the fermentation tank; when the number of the permanent magnets is two or more, the permanent magnets are symmetrically distributed about the center, and the center point is located on the central axis of the bottom of the fermentation tank; the coverage area of the permanent magnet is 30% - 35% of the bottom area of the fermentation tank.

[0010] For the above device, further improved, the magnetic flux density at the bottom of the fermentation tank is 4.99 mT - 18.7 mT.

[0011] For the above device, further improved, the permanent magnet is a cylinder, and the height of the permanent magnet is 2% - 15% of its diameter.

[0012] For the above-mentioned device, in a further improvement, the material of the fermentation tank is a non-magnetic material; the non-magnetic material is at least one of glass and fiberglass.

[0013] For the above-mentioned device, in a further improvement, the fermentation tank is a cylindrical barrel, and the height-diameter ratio of the fermentation tank is 2; the filling volume of the material in the fermentation tank is 60% - 80% of the volume of the fermentation tank.

[0014] For the above-mentioned device, in a further improvement, a heat preservation mechanism is further provided outside the fermentation tank. The heat preservation mechanism includes a heat preservation layer, and the heat preservation layer is wrapped outside the fermentation tank; a heater is provided in the heat preservation layer.

[0015] For the above-mentioned device, in a further improvement, a stirring mechanism is further provided in the fermentation tank. The stirring mechanism includes a stirrer, and the stirring blades of the stirrer are located in the material in the fermentation tank; a motor is further connected to the rotating shaft of the stirrer; the motor is located at the top of the fermentation tank.

[0016] For the above-mentioned device, in a further improvement, a gas collection mechanism is further provided at the top of the fermentation tank. The gas collection mechanism includes a gas storage tank, and the gas storage tank is communicated with the fermentation tank through an exhaust pipe; a barometer and a first valve are further provided on the exhaust pipe between the gas storage tank and the fermentation tank, and the first valve is located between the barometer and the fermentation tank.

[0017] For the above-mentioned device, in a further improvement, a storage tank is connected to the top of the fermentation tank through a feed pipe, and a feed pump is provided on the feed pipe.

[0018] For the above-mentioned device, in a further improvement, a sampling pipe is connected to the top of the fermentation tank, and a second valve is provided on the sampling pipe.

[0019] For the above-mentioned device, in a further improvement, a discharge port is provided at the bottom of the fermentation tank.

[0020] As a general technical concept, the present invention also provides a method for improving the anaerobic digestion effect, including the following steps: S1. Mix camellia oleifera shell and sludge to make a fermentation raw material, and load it into a fermentation tank; S2. Install an adjustable static magnetic field device below the fermenter, adjust the distance between the adjustable static magnetic field device and the bottom of the fermenter so that the magnetic flux density at the bottom of the fermenter ≤ 18.7 mT, and perform anaerobic digestion treatment on the fermentation raw materials in the fermenter; the adjustable static magnetic field device includes at least one permanent magnet, the permanent magnet is detachably installed on a tray, and a movable adjusting mechanism is connected to the tray for adjusting the distance between the permanent magnet and the bottom of the fermenter; the distance between the permanent magnet and the fermenter is 10 mm - 40 mm; the material of the permanent magnet is neodymium iron boron material; the magnetic permeability of the permanent magnet is 1.05, and the remanent magnetic flux density is 1.45 T; when the number of the permanent magnets is one, the permanent magnet is horizontally distributed, and the center point is located on the central axis of the bottom of the fermenter; when the number of the permanent magnets is more than two, the permanent magnets are symmetrically distributed about the center, and the center point is located on the central axis of the bottom of the fermenter; the coverage area of the permanent magnet is 30% - 35% of the bottom area of the fermenter.

[0021] In the above method, further improved, in step S2, make the magnetic flux density at the bottom of the fermenter be 4.99 mT - 18.7 mT.

[0022] In the above method, further improved, the permanent magnet is a cylinder, and the height of the permanent magnet is 2% - 15% of its diameter.

[0023] In the above method, further improved, the material of the fermenter is a non-magnetic material; the non-magnetic material is at least one of glass and fiberglass.

[0024] In the above method, further improved, the fermenter is a cylindrical barrel, and the height-diameter ratio of the fermenter is 2; the filling volume of the materials in the fermenter is 60% - 80% of the volume of the fermenter.

[0025] In the above method, further improved, in step S1, the mass percentage content of oil-tea fruit shell in the fermentation raw materials is 88% - 94%; the particle size of the oil-tea fruit shell is 0.7 mm - 1.0 mm; the mass percentage content of sludge in the fermentation raw materials is 3% - 4%; the sludge is the surplus sludge from a sewage treatment plant; the iron element content in the sludge is 0.2 wt% - 10.9 wt%; the sludge also includes the following treatment before use: continuously introduce nitrogen into the sludge for 10 min - 15 min to form an anaerobic environment, and then culture it for more than 30 days at 35 °C in the anaerobic environment.

[0026] For the above method, in a further improvement, before the anaerobic digestion treatment in step S2, it further includes: continuously introducing nitrogen into the fermentation raw material for 10 min to 15 min to form an anaerobic environment; the temperature of the anaerobic digestion treatment is 30 °C to 40 °C; the anaerobic digestion treatment is carried out under the condition of a rotation speed of 150 rpm; the time of the anaerobic digestion treatment is 20 days to 50 days.

[0027] Compared with the prior art, the advantages of the present invention are as follows: (1) In view of the deficiencies existing in the existing anaerobic digestion devices, such as low biological availability of iron in the system, low degradation rate and poor degradation effect of lignocellulosic biomass materials, difficult maintenance and management, and the resulting low gas production, long fermentation cycle, high cost, and difficulty in applying to treat lignocellulosic biomass materials such as oil-tea fruit shells, etc., the present invention provides a device for improving anaerobic digestion effect, including a fermentation tank for anaerobic digestion and an adjustable static magnetic field device for adjusting the magnetic flux density in the fermentation tank. By using the adjustable static magnetic field device to adjust the magnetic flux density at the bottom of the fermentation tank ≤ 18.7 mT and form a static magnetic field, under the magnetic interference effect of the static magnetic field, the corrosion of iron can be promoted and the production of extracellular polymers can be increased, thereby promoting the transformation of iron elements in the sludge from carbonate-bound F3 and exchangeable F2 to water-soluble F1, and from residual F5 to organic / sulfide-bound F4. Furthermore, the biological availability of iron in the anaerobic digestion system can be significantly improved, and it can ensure that the biological availability of iron in the anaerobic digestion system always remains at a relatively high level, where the biological availability of iron in this anaerobic digestion system is increased by 9.8% - 20.9%; further, with the significant improvement of the biological availability of iron in the anaerobic digestion system, microorganisms can directly absorb and utilize the iron elements in the system to achieve rapid growth and reproduction, thereby accelerating the degradation rate of microorganisms on organic waste. At the same time, the iron elements in the system can also activate and further promote the improvement of the activities of various key enzymes closely related to the biogas fermentation process. For example, with the significant improvement of the biological availability of iron, not only can it promote the synthesis of neutral xylanase for degrading hemicellulose and β-glucosidase for degrading cellulose, but also can improve the activities of neutral xylanase and β-glucosidase. The activity of neutral xylanase is increased by 15.8%, and the activity of β-glucosidase is increased by 39.7%. Thus, these highly active hydrolases can be used to achieve the efficient utilization and degradation of lignocellulosic biomass such as oil-tea fruit shells in the anaerobic digestion system, showing a higher degradation rate, stronger gas production capacity, and at the same time, it can also significantly shorten the fermentation cycle, where the biogas production is increased by more than 33.4%, the methane purity is increased by more than 8.4%, and the fermentation cycle is shortened by more than 35%. Compared with the conventional anaerobic digestion device constructed based on static magnetic field, the device of the present invention has higher anaerobic digestion efficiency, shorter fermentation cycle, higher gas production capacity. In particular, it can directly utilize the abundant iron elements contained in the inoculum (such as sludge), and can significantly improve the biological availability of iron in the anaerobic digestion system without the need to supplement iron source. Furthermore, it can significantly improve the anaerobic digestion effect under the conditions of lower cost and more environmental protection, and can be widely used for the harmless and resource treatment of lignocellulosic biomass materials such as oil-tea fruit shells, bringing considerable economic and environmental benefits, having the advantages of high anaerobic digestion efficiency, short fermentation cycle, high gas production, good applicability, low operation and maintenance cost, etc., with high use value and good application prospect.

[0028] (2) Aiming at the deficiencies in the existing anaerobic digestion methods, such as low biological availability of iron in the system, low degradation rate and poor degradation effect of lignocellulosic biomass materials, difficult maintenance and management, etc., and the resulting defects such as low gas production, long fermentation period, high cost, and difficulty in applying to treat lignocellulosic biomass materials such as oil-tea camellia fruit shells, the present invention provides a method for improving anaerobic digestion effect. Using oil-tea camellia fruit shells as the lignocellulosic biomass raw material and sludge as the inoculum, after mixing, they are made into fermentation raw materials and filled into a fermentation tank. On this basis, the magnetic flux density at the bottom of the fermentation space of the fermentation tank is adjusted to ≤18.7 mT, and the fermentation raw materials in the fermentation tank are subjected to anaerobic digestion treatment. On the one hand, under the action of a static magnetic field with a magnetic flux density ≤18.7 mT, the biological availability of iron in the anaerobic digestion system can be significantly improved. On the other hand, with the significant improvement of the biological availability of iron in the anaerobic digestion system, the metabolic activity of microorganisms is further enhanced, the activity of hydrolase is increased, and thus the efficient utilization of oil-tea camellia fruit shells can be realized, and finally a higher methane yield can be obtained in a shorter time. The method for improving anaerobic digestion effect of the present invention has the advantages of simple process, convenient operation, low cost, high treatment efficiency, high gas production, etc., and can obtain a higher yield of methane gas under shorter time conditions, which has an important promoting effect on realizing the resource utilization of oil-tea camellia fruit shells and sludge.

[0029] (3) In the method of the present invention, by optimizing the mass percentage content of oil-tea camellia fruit shells in the fermentation raw materials to be 88% - 94%, on the premise of effectively reducing the inhibitory effect brought by oil-tea camellia fruit shells, it can also ensure that the total gas production in the anaerobic digestion system is significantly increased within a shorter fermentation period, which is more conducive to improving the utilization rate of oil-tea camellia fruit shells, and bringing better economic and environmental benefits. This is because: when the dosage of oil-tea camellia fruit shells is too high, it will prolong the acid inhibition period and fermentation period, while when the dosage is too low, it is difficult to increase the total gas production and the economic benefit is poor. At the same time, by optimizing the mass percentage content of sludge in the fermentation raw materials to be 3% - 4%, on the one hand, the rapid start-up of the anaerobic digestion system can be realized, which is convenient for shortening the fermentation period. On the other hand, it can also promote the increase of methane production. This is because when the dosage of sludge is too high, the competition relationship between microorganisms is strong, which easily leads to poor activity of methanogens and difficult to increase methane production, while when the dosage of sludge is too low, it may cause excessive acidification of the anaerobic digestion system and reduce methane production. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0031] Figure 1 It is a schematic structural diagram of the device for improving anaerobic digestion effect in Embodiment 1 of the present invention.

[0032] Figure 2 It is a sectional view of the magnetic flux density distribution at 0 cm at the bottom of the fermentation space when the single - magnet layout mode is adopted in the device of Embodiment 1 of the present invention.

[0033] Figure 3 It is a sectional view of the magnetic flux density distribution at 4.5 cm above the bottom of the fermentation space when the single - magnet layout mode is adopted in the device of Embodiment 1 of the present invention.

[0034] Figure 4 It is a sectional view of the magnetic flux density distribution at 9 cm above the bottom of the fermentation space when the single - magnet layout mode is adopted in the device of Embodiment 1 of the present invention.

[0035] Figure 5 It is a graph showing the variation of the maximum magnetic flux density in the upper fermentation space with height under different maximum magnetic flux density levels at the bottom in the device of Embodiment 1 of the present invention.

[0036] Figure 6 It is a data distribution graph of the magnetic flux density in the upper fermentation space under different maximum magnetic flux density levels at the bottom in the device of Embodiment 1 of the present invention.

[0037] Figure 7 It is a sectional view of the magnetic flux density distribution in the upper fermentation space in the magnet - decentralized and single - magnet layout modes when the maximum magnetic flux density at the bottom is 18.7 mT in the device of Embodiment 1 of the present invention.

[0038] Figure 8 It is a data distribution graph of the magnetic flux density in the upper fermentation space in the magnet - decentralized and single - magnet layout modes when the maximum magnetic flux density at the bottom is 18.7 mT in the device of Embodiment 1 of the present invention.

[0039] Figure 9 It is a graph showing the variation of the daily gas production of oil - tea fruit shells after anaerobic digestion under different magnetic flux densities in Embodiment 1 of the present invention.

[0040] Figure 10 It is a graph showing the variation of the cumulative gas production of oil - tea fruit shells after anaerobic digestion under different magnetic flux densities in Embodiment 1 of the present invention.

[0041] Figure 11 It is a graph showing the variation of the methane content of oil - tea fruit shells after anaerobic digestion under different magnetic flux densities in Embodiment 1 of the present invention.

[0042] Figure 12 It is a graph showing the variation of the cumulative methane production of oil - tea fruit shells after anaerobic digestion under different magnetic flux densities in Embodiment 1 of the present invention.

[0043] Figure 13In Example 1 of the present invention, the changes in neutral xylanase, β-glucosidase, acetate kinase, and coenzyme in the anaerobic digestion device with different magnetic flux densities for oil-tea camellia shell F420 are shown in the figure.

[0044] Figure 14 In Example 1 of the present invention, the change diagram of the iron bioavailability of oil-tea camellia shell in the anaerobic digestion device with different magnetic flux densities is shown.

[0045] Legend: 1. Gas storage tank; 2. Feed pipe; 3. Feed pump; 4. Storage tank; 5. Barometer; 6. First valve; 7. Exhaust pipe; 8. Motor; 9. Sampling pipe; 10. Second valve; 11. Thermal insulation layer; 12. Fermentation tank; 13. Agitator; 14. Adjustable static magnetic field device; 15. Permanent magnet; 16. Tray; 17. Adjusting mechanism; 18. Discharge port. Specific implementation mode

[0046] Next, the technical solution of the present invention will be clearly and completely described in conjunction with the drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work shall fall within the protection scope of the present invention.

[0047] Example 1 As Figure 1 shown, the device for improving the anaerobic digestion effect in this embodiment includes a fermentation tank 12 for anaerobic digestion and an adjustable static magnetic field device 14 for adjusting the magnetic flux density in the fermentation tank 12, and the magnetic flux density at the bottom of the fermentation tank 12 is 18.7 mT.

[0048] In this embodiment, the adjustable static magnetic field device 14 is installed below the fermentation tank 12, but is not limited thereto. Other installation methods that can achieve a magnetic flux density of 18.7 mT at the bottom of the fermentation tank 12 can be used in the present invention.

[0049] In this embodiment, the adjustable static magnetic field device 14 includes at least one permanent magnet 15. The permanent magnet 15 can be removably installed on the tray 16, and a movable adjusting mechanism 17 is connected to the tray 16 for adjusting the distance between the permanent magnet 15 and the bottom of the fermentation tank 12. In the present invention, generally, the type, quantity, and mixed layout method of the permanent magnet 15 are first selected. At this time, the magnetic permeability and residual magnetic flux density of the permanent magnet 15 are fixed. Then, the movable adjusting mechanism 17 is used to adjust the distance between the permanent magnet 15 and the bottom of the fermentation tank 12 so that the magnetic flux density at the bottom of the fermentation tank 12 (the bottom of the fermentation space) is within a suitable range.

[0050] In this embodiment, the distance between the permanent magnet 15 and the fermentation tank 12 is 17.9 mm, but it is not limited thereto.

[0051] In this embodiment, the material of the permanent magnet 15 is neodymium iron boron material; the magnetic permeability of the permanent magnet 15 is 1.05, and the residual magnetic flux density is 1.45 T.

[0052] In this embodiment, when the number of the permanent magnets 15 is one, that is, in a single layout mode, the permanent magnets 15 are horizontally distributed, and the center point is located on the central axis of the bottom of the fermentation tank 12.

[0053] In other embodiments, when the number of the permanent magnets 15 is more than two, that is, in a decentralized layout mode, the permanent magnets 15 are centrally symmetrically distributed, and the center point is located on the central axis of the bottom of the fermentation tank 12. Specifically, the number of the permanent magnets 15 can be two, three, four, or five. When the number of the permanent magnets 15 is five, the five permanent magnets 15 are centrally symmetrically distributed, and the center point is located on the central axis of the bottom of the fermentation tank 12. The center point of one of the permanent magnets 15 is located on the central axis of the bottom of the fermentation tank 12, and the other four permanent magnets are arranged around it, and the distance between them and the central permanent magnet 15 is specifically 27.34 mm.

[0054] In the present invention, when the permanent magnet 15 adopts a single layout, the advantages are: the layout is direct and simple. When the permanent magnet 15 adopts a decentralized layout, the advantages are: the difference in magnetic flux density of the same cross-section in the upper fermentation space is smaller, and the attenuation amplitude is smaller with the increase of the cross-section height. Under the condition of reaching the same magnetic flux density level, the magnet volume is reduced by 78%, greatly saving the material cost, and providing the possibility of further reducing the volume of the adjustable static magnetic field mechanism. In particular, considering the uniformity of the distribution, in the present invention, when a central symmetric distribution layout is adopted and five permanent magnets are selected, better effects can be achieved.

[0055] In this embodiment, the permanent magnet 15 is a cylinder, but it is not limited thereto, and magnetic materials of other shapes can also be used in the present invention.

[0056] In this embodiment, the coverage area of the permanent magnet 15 is 30% of the bottom area of the fermentation tank 12. In other embodiments, the coverage area of the permanent magnet 15 can be 32%, 33%, or 35% of the bottom area of the fermentation tank 12.

[0057] In the present invention, the coverage area of the permanent magnet 15 is the projected area of the permanent magnet, that is, the ratio of the projected area of the permanent magnet and the bottom of the fermentation tank. Further, when the coverage area of the permanent magnet 15 is 30% - 35% of the bottom area of the fermentation tank 12, the magnetic field interference effect of the permanent magnet on the fermentation system in the fermentation tank can be effectively improved. In addition, when the coverage area is larger, the magnetic flux density difference at the same cross-section in the upper space of the fermentation is smaller, and the longitudinal attenuation is also smaller. Moreover, the amount of the permanent magnet used is increased, and the material cost is increased. When the coverage area is smaller, it is difficult to improve the magnetic field interference effect on the fermentation system in the fermentation tank.

[0058] In this embodiment, the height of the permanent magnet 15 is 10% of its diameter. In other embodiments, the height of the permanent magnet 15 can be 2%, 5%, 6%, 8%, 12%, 15% of its diameter. For example, when the number of the permanent magnets 15 is five, the height of the permanent magnet 15 is 5% of its diameter. It can be seen that under the condition of a certain coverage area, by optimizing the height of the permanent magnet, it is beneficial to reduce the amount of raw materials used and the installation space, and the installation is more convenient.

[0059] In this embodiment, the material of the fermentation tank 12 is a non-magnetic material, and the non-magnetic material is glass. In other embodiments, the non-magnetic material can be fiberglass reinforced plastic.

[0060] In this embodiment, the fermentation tank 12 is a cylindrical barrel, but it is not limited to this. Fermentation tanks of other shapes can also be used in the present invention.

[0061] In this embodiment, the height-to-diameter ratio of the fermentation tank 12 is 2.

[0062] In this embodiment, the filling volume of the material in the fermentation tank 12 is 80% of the volume of the fermentation tank 12. In other embodiments, the filling volume of the material in the fermentation tank 12 is 60%, 65%, 70%, 75% of the volume of the fermentation tank 12.

[0063] In this embodiment, a heat preservation mechanism is further provided outside the fermentation tank 12 for stabilizing the temperature in the fermentation tank 12 to ensure the stable operation of the anaerobic digestion treatment. In this embodiment, the heat preservation mechanism includes a heat preservation layer 11, and the heat preservation layer 11 is wrapped outside the fermentation tank 12; a heater (not shown in the figure), such as an electric heating rod, is provided in the heat preservation layer 11.

[0064] In this embodiment, a stirring mechanism is further provided in the fermentation tank 12 for stirring the material in the fermentation tank 12, which can promote the comprehensive and uniform stimulation of the static magnetic field on the microorganisms in the material. The stirring mechanism includes a stirrer 13, and the stirring blades of the stirrer 13 are located in the material in the fermentation tank 12; a motor 8 is further connected to the rotating shaft of the stirrer 13; the motor 8 is located at the top of the fermentation tank 12.

[0065] In this embodiment, a gas collection mechanism is further provided at the top of the fermentation tank 12. The gas collection mechanism includes a gas storage tank 1, and the gas storage tank 1 is communicated with the fermentation tank 12 through an exhaust pipe 7. A barometer 5 and a first valve 6 are further provided on the exhaust pipe 7 between the gas storage tank 1 and the fermentation tank 12, and the first valve 6 is located between the barometer 5 and the fermentation tank 12.

[0066] In this embodiment, a storage tank 4 is connected to the top of the fermentation tank 12 through a feed pipe 2, and a feed pump 3 is provided on the feed pipe 2.

[0067] In this embodiment, a sampling pipe 9 is connected to the top of the fermentation tank 12, and a second valve 10 is provided on the sampling pipe 9.

[0068] In this embodiment, a discharge port 18 is provided at the bottom of the fermentation tank 12.

[0069] In this embodiment, an aeration mechanism (not shown in the drawings) is further provided in the fermentation tank 12. The aeration mechanism includes an aeration pipe, the aeration pipe is located at the bottom of the fermentation tank 12, and a plurality of aeration holes are provided on the aeration pipe.

[0070] Perform magnetic flux density simulation and gas production efficiency correlation analysis on the device in this embodiment as follows: Through the COMSOL simulation software, use the remanent magnetic flux density magnetization model in the "Magnetic Field, No Current" module to simulate the magnetic flux density and distribution inside the device. The simulation parameter settings are as follows: (1) Fermentation space: Refer to the size data of the device, set a cylinder with a height of 173 mm and a diameter of 85 mm, the height of the biogas slurry inside is 90 mm, and the boundary material is glass.

[0071] (2) Single magnet layout: Set 1 neodymium iron boron magnet with a diameter of 50 mm and a height of 5 mm, the magnetic permeability is 1.05, and the remanent magnetic flux density is 1.45 T. The magnet is located at the bottom of the fermentation space, and their central axes coincide. By setting the distances between the magnet and the bottom of the fermentation space to be 10.9 mm, 15.1 mm, 17.9 mm, 22 mm, and 25.5 mm respectively, the maximum magnetic flux densities at the bottom of the fermentation space are simulated and calculated to be 43.4 mT, 27.2 mT, 18.7 mT, 12.7 mT, and 9.3 mT respectively, basically achieving synchronization with the measured data of the device.

[0072] (3) Magnet decentralized layout: While maintaining the same contact area, five neodymium iron boron magnets with smaller volumes are set. One magnet is located at the bottom of the fermentation space, and their central axes coincide. The remaining four magnets are symmetrically distributed around the central magnet at a distance of 27.34 mm. By setting the distances between the magnets and the bottom of the fermentation space to be 10.9 mm, 15.1 mm, 17.9 mm, 22 mm, and 25.5 mm respectively, the maximum magnetic flux densities at the bottom of the fermentation space are maintained at 43.4 mT, 27.2 mT, 18.7 mT, 12.7 mT, and 9.3 mT respectively, basically achieving synchronization with the measured data of the device and the single magnet layout. Under the condition that the magnetic permeability and residual magnetic flux density of the magnets still remain at 1.05 and 1.45 T, the diameters of the five magnets are simulated and calculated to be 22.36 mm and the height is 1.1 mm.

[0073] The results are as follows: (1) The cross-sectional magnetic flux density distributions at 0 cm at the bottom, 4.5 cm in the middle, and 9.0 cm at the top of the fermentation space in the single magnet layout mode of the magnet are simulated respectively. The magnetic flux density at the center of the same cross-section in the fermentation space is higher than that at the edge. The results are as Figures 2 - 4 shown.

[0074] Figure 2 It is the cross-sectional magnetic flux density distribution diagram at 0 cm at the bottom of the fermentation space when the single magnet layout mode of the magnet is adopted in the device of Embodiment 1 of the present invention. Figure 2 Among them, a is the three-dimensional view, and the corresponding magnetic flux densities of b-f are 43.4 mT, 27.2 mT, 18.7 mT, 12.7 mT, and 9.3 mT.

[0075] Figure 3 It is the cross-sectional magnetic flux density distribution diagram at 4.5 cm above the bottom of the fermentation space when the single magnet layout mode of the magnet is adopted in the device of Embodiment 1 of the present invention. Figure 3 Among them, a is the three-dimensional view, and the corresponding magnetic flux densities of b-f are 43.4 mT, 27.2 mT, 18.7 mT, 12.7 mT, and 9.3 mT.

[0076] Figure 4 It is the cross-sectional magnetic flux density distribution diagram at 9 cm above the bottom of the fermentation space when the single magnet layout mode of the magnet is adopted in the device of Embodiment 1 of the present invention. Figure 4 Among them, a is the three-dimensional view, and the corresponding magnetic flux densities of b-f are 43.4 mT, 27.2 mT, 18.7 mT, 12.7 mT, and 9.3 mT.

[0077] From Figures 2 - 4 it can be seen that the magnetic flux density at the center of the same height cross-section is higher than that at the edge, and the magnetic flux density rapidly decays as the cross-sectional height increases.

[0078] Figure 5 It is a diagram showing the variation of the maximum magnetic flux density in the upper fermentation space with height under different maximum magnetic flux density levels at the bottom in the device of Embodiment 1 of the present invention.

[0079] From Figure 5 it can be seen that the magnetic flux density decays exponentially with the increase of the cross-sectional height.

[0080] Figure 6 It is a distribution diagram of the magnetic flux density data in the upper fermentation space in the device of Embodiment 1 of the present invention under different maximum magnetic flux density levels at the bottom. Figure 6 In [reference], the magnetic flux densities corresponding to a are 43.4 mT, 27.2 mT, 18.7 mT, 12.7 mT, 9.3 mT; the magnetic flux densities corresponding to b are 18.7 mT, 12.7 mT, 9.3 mT. From Figure 5 it can be seen that 18.7 mT is set as the critical value of the maximum magnetic flux density ( Figure 6 a), that is, when the magnetic flux density > 18.7 mT, it has an inhibitory effect on the anaerobic digestion process. Through simulation calculation, there are sites with a magnetic flux density > 18.7 mT at heights of 2.8 mm and 7 mm at the bottom of the anaerobic digestion devices with magnetic flux densities of 27.2 mT and 43.4 mT respectively, which may be the main reasons for the decrease in the gas production efficiency of anaerobic digestion. Further comparing the distribution of the magnetic flux density data in the upper fermentation space under the horizontal conditions of the maximum magnetic flux density at the bottom of 9.3 mT, 12.7 mT, and 18.7 mT ( Figure 6 b), under the adverse condition that the magnetic flux density decays exponentially with the cross-sectional height, 18.7 mT has the widest magnetic flux density distribution range and has the advantage of the balance of the magnetic flux density level and spatial distribution uniformity. Therefore, there is a relationship of low promotion and high inhibition between the gas production efficiency of anaerobic digestion and different magnetic flux density levels. Therefore, under a certain magnetic flux density level condition, it is necessary to further optimize the uniformity of the magnetic flux density distribution in the upper fermentation space.

[0081] Figure 7 It is a diagram showing the cross-sectional magnetic flux density distribution in the upper fermentation space in the device of Embodiment 1 of the present invention when the maximum magnetic flux density at the bottom is 18.7 mT in the magnet decentralized and single layout modes. Figure 7Among them, a is the three-dimensional view corresponding to the bottom 0 cm of the fermentation space in the magnet decentralized layout mode, b is the magnetic flux density distribution map corresponding to the bottom 0 cm of the fermentation space in the magnet decentralized layout mode, c is the magnetic flux density distribution map corresponding to the bottom 0 cm of the fermentation space in the magnet single layout mode, d is the three-dimensional view corresponding to 4.5 cm above the bottom of the fermentation space in the magnet decentralized layout mode, e is the magnetic flux density distribution map corresponding to 4.5 cm above the bottom of the fermentation space in the magnet decentralized layout mode, f is the magnetic flux density distribution map corresponding to 4.5 cm above the bottom of the fermentation space in the magnet single layout mode, g is the three-dimensional view corresponding to 9 cm above the bottom of the fermentation space in the magnet decentralized layout mode, h is the magnetic flux density distribution map corresponding to 9 cm above the bottom of the fermentation space in the magnet decentralized layout mode, and i is the magnetic flux density distribution map corresponding to 9 cm above the bottom of the fermentation space in the magnet single layout mode.

[0082] It can be seen from Figure 7 that, compared with the magnet single layout, the magnetic flux density difference of the same cross-section in the upper fermentation space of the magnet decentralized layout is smaller, and the attenuation amplitude is smaller with the increase of the cross-section height.

[0083] Figure 8 This is the magnetic flux density data distribution map of the upper fermentation space in the magnet decentralized and single layout modes when the maximum magnetic flux density at the bottom in the device of Embodiment 1 of the present invention is 18.7 mT.

[0084] Figure 8 Among them, the magnetic flux density data distribution in the upper fermentation space under the two layout modes is compared. The results show that the decentralized layout improves the magnetic flux density distribution range, which will inevitably further improve the anaerobic fermentation efficiency. On the other hand, under the condition of reaching the same magnetic flux density level, the magnet volume is reduced by 78%, greatly saving the material cost and providing the possibility of further reducing the volume of the adjustable static magnetic field mechanism.

[0085] A device in the above-mentioned embodiment is used for anaerobic digestion treatment of oil-tea fruit shells. Specifically, the oil-tea fruit shells are used as lignocellulosic biomass materials and biogas is produced through anaerobic digestion, including the following steps: S1. Clean, dry, crush, grind the oil-tea fruit shells, and pass through a 0.875 mm sieve to obtain oil-tea fruit shell particles with a particle size of 0.875 mm.

[0086] S2. Take the excess sludge from the sludge storage tank at the end of the MBR process of a sewage treatment plant in Changsha (the content of iron element in this sludge is 66425 mg / kg). Remove the sediment through a sieve, let it stand for 24 h, then discard the supernatant. Continuously introduce nitrogen into the excess sludge for 30 min to remove the oxygen in the sludge, and then put it into a constant temperature incubator and cultivate it at 35 °C for 30 days to obtain the inoculated sludge.

[0087] S3. According to the mass percentage content (TS) of camellia shell particles in the fermentation raw material being 2.6%, add 7.316 g of camellia shell particles with a particle size of 0.875 mm prepared in step S1 to the storage tank 4, and then add 120 mL of the inoculated sludge prepared in step S2 and 272.68 mL of deionized water to ensure the same reaction volume, thus obtaining the fermentation raw material. According to the feeding volume of the fermentation raw material being 80% of the volume of the fermentation tank 12, use the feeding pump 3 to pump the fermentation raw material into the fermentation tank 12, introduce nitrogen for 15 min to remove the oxygen in the fermentation tank 12, forming an anaerobic environment. Install an adjustable static magnetic field device 14 at the bottom of the fermentation tank 12, and control the height of the tray 16 through the adjusting mechanism 17, so that the distances between the permanent magnet 15 and the bottom of the fermentation tank 12 are 10.9 mm, 15.1 mm, 17.9 mm, 22 mm, and 25.5 mm respectively, and keep the maximum magnetic flux density at the bottom of the fermentation space being 43.4 mT, 27.2 mT, 18.7 mT, 12.7 mT, and 9.3 mT respectively. Apply a static magnetic field to the fermentation tank 12. At the same time, under the heat preservation of the heat preservation layer 11, raise the temperature of the fermentation material in the fermentation tank 12 to 35 °C, and carry out anaerobic digestion treatment for 40 days under this condition. During this period, use the stirrer 13 to stir the fermentation raw material, use the barometer 5 to detect the gas flow of biogas, collect and store the biogas in the gas storage tank, open the second valve 10 and use the sampling tube 9 to take samples, and at the same time, discharge the material through the discharge port 18 after the anaerobic digestion ends.

[0088] Control group: Do not place the adjustable static magnetic field device 14 at the bottom of the fermentation tank 12, and keep other conditions the same.

[0089] In this embodiment, the influence of static magnetic fields with different magnetic flux densities on the anaerobic digestion effect is investigated. During the anaerobic cultivation process in step S2, use a GMH 3151 barometer to monitor the daily gas production. Among them, the daily gas production and cumulative gas production of camellia shells under different magnetic flux densities are as follows Figures 9 to 10 shown.

[0090] Figure 9 This is the change diagram of the daily gas production of camellia shells after anaerobic digestion treatment under different magnetic flux densities in Example 1 of the present invention. As Figure 9As shown, during the entire fermentation process, the overall changing trend of the daily gas production of different magnetic flux density groups is similar. The gas production first rises to the peak, then decreases to a gentle level and rises again to show the second and third gas production peaks, and finally gradually decreases until the end of fermentation. The first gas production peak is due to the rapid hydrolysis of easily degradable organic matter. After that, the acid accumulation inhibits the reaction to proceed gently. The second gas production peak is due to the hydrolysis of easily degradable substrates such as hemicellulose and monosaccharides. The third gas production peak is due to the hydrolysis fermentation flora hydrolyzing the relatively difficult-to-hydrolyze complex organic matter (cellulose, protein, lipid) in the substrate and converting it into small-molecule organic matter, corresponding to a fast rising rate of the cumulative gas production.

[0091] Figure 10 This is the change diagram of the cumulative gas production of camellia fruit shells after anaerobic digestion under different magnetic flux densities in Example 1 of the present invention. From Figure 4 the results of the cumulative gas production, it can be seen that the cumulative gas production of the static magnetic field groups with different magnetic flux densities applied is increased compared with the group without applying the static magnetic field. When the magnetic flux density is less than 18.7 mT, the cumulative gas production increases with the increase of the magnetic flux density. However, when the magnetic flux density is greater than 18.7 mT, the cumulative gas production decreases with the increase of the magnetic flux density. Applying a static magnetic field with a magnetic flux density of 18.7 mT increases the cumulative gas production from 716 mL to 955 mL, an increase of 239 mL (33.4 %), and the time corresponding to reaching a gas production of 716 mL is shortened from 34 days to 22 days. Thus, it can be seen that when the magnetic flux density is 18.7 mT, it is beneficial to increase the gas production and shorten the fermentation cycle.

[0092] In this example, the influence of static magnetic fields with different magnetic flux densities on the anaerobic digestion effect was investigated. During the anaerobic culture process in step S2, a GMH 3151 barometer was used to monitor the daily gas production. When the cumulative gas production was close to the total volume of the serum bottle, a 10 mL syringe was used to collect the gas into an aluminum foil gas collection bag, and the methane content was measured by GC-MC. The results are as Figure 11 and Figure 12 shown.

[0093] Figure 11 This is the change diagram of the methane content of camellia fruit shells after anaerobic digestion under different magnetic flux densities in Example 1 of the present invention. As shown in Figure 5 it, after applying static magnetic fields with different magnetic flux densities, the methane content in the biogas is increased compared with the group without applying the static magnetic field. This indicates that applying a static magnetic field improves the purity of methane in the gas production from the anaerobic digestion of camellia fruit shells. Applying a static magnetic field with a magnetic flux density of 18.7 mT increases the methane purity from 53.2 % to 57.7 %, an increase of 8.4 %.

[0094] Figure 12This is a graph showing the change in the cumulative methane production of oil-tea camellia shell after anaerobic digestion under different magnetic flux densities in Example 1 of the present invention. From Figure 12 the results of the cumulative methane production in

[0095] It can be seen that applying a static magnetic field with different magnetic flux densities increases the methane production of the anaerobic digestion of oil-tea camellia shell. When applying a static magnetic field with a magnetic flux density of 18.7 mT, the methane production increases from 187.3 mL to 293.1 mL, an increase of 56.7%. (1) Under the conditions of 8000 rpm and 4 °C, centrifuge the biogas slurry for 15 min using a centrifuge to remove the supernatant and obtain the solid phase. (2) Transfer the solid phase to a vacuum freeze dryer and freeze-dry it for 48 h. (3) Weigh 1 g of the solid phase with a TS content using an electronic scale, add 50 mL of deionized water, centrifuge at 8000 rpm and 4 °C for 15 min, collect the supernatant and filter it; add 10 mL of ammonium acetate with a concentration of 1 mol / L and a pH of 7 to the solid phase, react at 25 °C for 1 h, centrifuge at 8000 rpm and 4 °C for 15 min, collect the supernatant and filter it; add 10 mL of acetic acid with a concentration of 1 mol / L and a pH of 5.5 to the solid phase, react at 25 °C for 1 h, centrifuge at 8000 rpm and 4 °C for 15 min, collect the supernatant and filter it; add 10 mL of hydrogen peroxide with a concentration of 30% w / w and a pH adjusted to 2 with nitric acid to the solid phase, react at 35 °C for 3 h, centrifuge at 8000 rpm and 4 °C for 15 min, collect the supernatant and filter it; dry the remaining solid phase at 105 °C for 24 h.

[0096] (4) Take 5 mL of the filtered supernatant into a beaker respectively, add 5 mL of deionized water and 0.5 mL of nitric acid, place it on an electric heating furnace for heating and digestion, slowly heat it until it is almost dry, repeat this process until the color of the sample solution becomes lighter or remains stable, after cooling, make up the volume to 10 mL with deionized water, shake it, and filter it.

[0097] (5) Weigh 0.1 g of the dried solid phase using an electronic scale, add 5 mL of nitric acid, place it on a digestion plate, digest it at 130 °C for 1 h, add 3 mL of perchloric acid, digest it at 180 °C for 7 h, make up the volume to 50 mL with deionized water, shake it, and filter it.

[0098] Use a kit to measure the enzyme activities of neutral xylanase, β-glucosidase, acetate kinase, and coenzyme F420 The results are as follows: Figure 13In Example 1 of the present invention, the neutral xylanase, β-glucosidase, acetate kinase, and coenzyme in the anaerobic digestion device with different magnetic flux densities for the oil-tea camellia shell F420 Change diagram. Figure 13 In Figure 13 , a-d are the activities of neutral xylanase, β-glucosidase, acetate kinase, and coenzyme F420 in turn.

[0099] The test results show that in the early stage of the reaction, the activity of neutral xylanase in each reactor group gradually increases and reaches the peak at 18 days. As shown in Figure 13 , at 18 days of anaerobic digestion treatment, the activity of neutral xylanase in the device with a magnetic flux density of 18.7 mT applied is 15.8% higher than that in the device without applying a static magnetic field, while the activity of neutral xylanase in the device with a magnetic flux density of 43.4 mT applied is 3.9% higher than that in the reactor group without applying a static magnetic field. After that, the activity of neutral xylanase in each device gradually decreases until the end of fermentation. This result indicates that compared with the static magnetic field with a magnetic flux density of 43.4 mT, the static magnetic field with a magnetic flux density of 18.7 mT can significantly increase the activity of neutral xylanase in the anaerobic digestion system, promote the degradation of hemicellulose, thereby improving the hydrolysis efficiency in the anaerobic digestion process and providing more substrates for methane production.

[0100] The test results show that in the initial stage of anaerobic digestion, there is no significant difference in the activity of β-glucosidase in each reactor group. As the anaerobic digestion process progresses, the activity of β-glucosidase in the groups with different magnetic flux density static magnetic fields applied is higher than that in the group without applying a static magnetic field, and the difference gradually increases and reaches the peak at 18 days. As shown in Figure 13 , at 18 days of anaerobic digestion treatment, the activity of β-glucosidase in the device with a magnetic flux density of 18.7 mT applied is 39.7% higher than that in the reactor group without applying a static magnetic field, while the activity of β-glucosidase in the device with a magnetic flux density of 43.4 mT applied is 13.2% higher than that in the reactor group without applying a static magnetic field. This result indicates that compared with the static magnetic field with a magnetic flux density of 43.4 mT, the static magnetic field with a magnetic flux density of 18.7 mT in the present invention can significantly increase the activity of β-glucosidase in the anaerobic digestion system, promote the degradation of cellulose in the oil-tea camellia shell, thereby improving the hydrolysis efficiency in the anaerobic digestion process and providing more substrates for methane production.

[0101] In addition, as shown in Figure 13 , in the device with a magnetic flux density of 18.7 mT in the present invention, the activities of acetate kinase and coenzyme F420 also increase significantly.

[0102] It can be seen that in the present invention, by constructing a static magnetic field with a magnetic flux density of 18.7 mT, the activities of neutral xylanase, β-glucosidase, acetate kinase, and coenzyme F420 can be significantly improved, and the acid production and methane production capabilities of the system can be significantly enhanced.

[0103] Figure 14 This is a graph showing the change in the iron bioavailability of camellia fruit shells in the anaerobic digestion device with different magnetic flux densities in Example 1 of the present invention. Iron is usually divided into five forms, including water-soluble state (F1), exchangeable state (F2), metal carbonate-bound state (F3), organic / sulfide-bound state (F4), and residual state (F5). Among them, F1 and F2 have higher bioavailability; the bioavailability of F3 and F4 is lower, and F5 has no bioavailability. Figure 14 In it, a - e correspond to water-soluble state (F1), exchangeable state (F2), metal carbonate-bound state (F3), organic / sulfide-bound state (F4), and residual state (F5) in sequence, and f is the iron bioavailability.

[0104] The test results show that most of the iron forms in the anaerobic digestion process are F5 that is not bioavailable. In the early stage of the reaction, the contents of F1 and F4 in each reactor increased, while the contents of F2, F3, and F5 decreased. This is mainly because the pH decreased, and the iron in F5 was released into F4, while the iron in F3 and F2 was released into F1. At this stage, the iron bioavailability increased. In the middle stage of the reaction, the contents of F1 - F4 in each reactor decreased, while the content of F5 increased. This is mainly because the pH began to increase at this stage, reducing the solubility of iron, and thus resulting in a decrease in iron bioavailability. In the late stage of the reaction, the contents of F1, F2, and F4 in each reactor continued to decrease, while the content of F3 began to increase and the content of F5 continued to increase. The iron bioavailability continued to decrease at this stage. Applying a static magnetic field promoted the transformation of F3 and F2 to F1 and F5 to F4, improving the iron bioavailability, and thus increasing the iron bioeffectiveness. During the 8th - 40th day of the anaerobic digestion process, the iron bioavailability ranges of the reactors with magnetic flux densities of 18.7 mT and 43.4 mT were 1.8% - 8.6% and 1.6% - 8% respectively, while the iron bioavailability range of the reactor without applying a static magnetic field was 1.5% - 7.8%, and the increases were 9.8% - 20.9% and 2.7% - 8.7% respectively.

[0105] In addition, from Figure 14 it can be seen that most of the iron forms in the anaerobic digestion process are F5 that is not bioavailable. Compared with the static magnetic field with a magnetic flux density of 43.4 mT, the static magnetic field with a magnetic flux density of 18.7 mT constructed in the present invention can significantly improve the iron bioavailability in the anaerobic digestion system, which is consistent with the conclusion in Figure 13 .

[0106] As can be seen from the above results, in the device of this embodiment, there is a fermentation tank for anaerobic digestion and an adjustable static magnetic field device for adjusting the magnetic flux density in the fermentation tank. By using the adjustable static magnetic field device to adjust the magnetic flux density at the bottom of the fermentation tank to ≤18.7 mT and form a static magnetic field, under the magnetic interference effect of the static magnetic field, the corrosion of iron can be promoted and the production of extracellular polymers can be increased. Thus, the conversion of iron elements in the sludge from carbonate-bound F3 and exchangeable F2 to water-soluble F1, and from residual F5 to organic / sulfide-bound F4 can be promoted. Furthermore, the biological availability of iron in the anaerobic digestion system can be significantly increased, and it can be ensured that the biological availability of iron in the anaerobic digestion system always remains at a relatively high level. Among them, the biological availability of iron in this anaerobic digestion system has increased by 9.8% - 20.9%. Further, with the significant increase in the biological availability of iron in the anaerobic digestion system, microorganisms can directly absorb and utilize the iron elements in the system to achieve rapid growth and reproduction, thereby accelerating the degradation rate of organic waste by microorganisms. At the same time, the iron elements in the system can also activate and further promote the activity of a variety of key enzymes closely related to the biogas fermentation process. For example, with the significant increase in the biological availability of iron, not only the synthesis of neutral xylanase for degrading hemicellulose and β-glucosidase for degrading cellulose can be promoted, but also the activity of neutral xylanase and β-glucosidase can be increased. Among them, the activity of neutral xylanase has increased by 15.8%, and the activity of β-glucosidase has increased by 39.7%. Thus, these highly active hydrolases can be used to achieve the efficient utilization and degradation of lignocellulosic biomass such as oil-tea fruit shells in the anaerobic digestion system, showing a higher degradation rate, stronger gas production capacity, and at the same time, the fermentation period can be significantly shortened. Among them, the biogas production has increased by more than 33.4%, the methane purity has increased by more than 8.4%, and the fermentation period has been shortened by more than 35%. Compared with the conventional anaerobic digestion device constructed based on static magnetic fields, the device of the present invention has higher anaerobic digestion efficiency, a shorter fermentation period, and stronger gas production capacity. In particular, it can directly utilize the abundant iron elements contained in the inoculum (such as sludge) and can significantly increase the biological availability of iron in the anaerobic digestion system without the need to supplement iron sources. Furthermore, it can significantly improve the anaerobic digestion effect under lower-cost and more environmentally friendly conditions, and can be widely used for the harmless and resource treatment of lignocellulosic biomass materials such as oil-tea fruit shells, bringing considerable economic and environmental benefits. It has the advantages of high anaerobic digestion efficiency, short fermentation period, high gas production, good applicability, and low operation and maintenance costs, with high use value and good application prospects.

[0107] The above embodiments are only the preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the concept of the present invention belong to the protection scope of the present invention. It should be noted that for those of ordinary skill in the art, improvements and refinements made without departing from the principle of the present invention should also be regarded as within the protection scope of the present invention.

Claims

1. An apparatus for improving anaerobic digestion effect, comprising a fermentation tank (12) for anaerobic digestion and an adjustable static magnetic field device (14) for adjusting the magnetic flux density in the fermentation tank (12), characterized in that, The magnetic flux density at the bottom of the fermentation tank (12) is ≤18.7 mT; the adjustable static magnetic field device (14) is located below the fermentation tank (12); the adjustable static magnetic field device (14) comprises at least one permanent magnet (15), the permanent magnet (15) is removably mounted on a tray (16), and a movable adjustment mechanism (17) is connected to the tray (16) for adjusting the distance between the permanent magnet (15) and the bottom of the fermentation tank (12); the distance between the permanent magnet (15) and the fermentation tank (12) is 10 mm to 40 mm; the material of the permanent magnet (15) is neodymium iron boron material; the magnetic permeability of the permanent magnet (15) is 1.05, and the residual magnetic flux density is 1.45 T; when the number of the permanent magnets (15) is one, the permanent magnets (15) are horizontally distributed, and the center point is located on the central axis of the bottom of the fermentation tank (12); when the number of the permanent magnets (15) is two or more, the permanent magnets (15) are centrally symmetrically distributed, and the center point is located on the central axis of the bottom of the fermentation tank (12); the coverage area of ​​the permanent magnets (15) is 30% to 35% of the bottom area of ​​the fermentation tank (12).

2. The device according to claim 1, characterized in that The magnetic flux density at the bottom of the fermentation tank (12) is 4.99 mT to 18.7 mT.

3. The device according to claim 1 or 2, characterized in that, The permanent magnet (15) is a cylinder, and the height of the permanent magnet (15) is 2% to 15% of its diameter; The fermentation tank (12) is made of a non-magnetic material; the non-magnetic material is at least one of glass and fiberglass reinforced plastic; The fermentation tank (12) is a cylindrical body, and the height-to-diameter ratio of the fermentation tank (12) is 2; the filling volume of the material in the fermentation tank (12) is 60% to 80% of the volume of the fermentation tank (12).

4. The device according to claim 3, characterized in that, The fermentation tank (12) is also provided with a heat preservation mechanism on the outside, the heat preservation mechanism comprising a heat preservation layer (11), the heat preservation layer (11) wrapping the outside of the fermentation tank (12); a heater is provided in the heat preservation layer (11); The fermentation tank (12) is also provided with a stirring mechanism, the stirring mechanism comprising a stirrer (13), the stirring blades of the stirrer (13) being located in the material in the fermentation tank (12); the rotating shaft of the stirrer (13) is also connected to a motor (8); the motor (8) is located at the top of the fermentation tank (12); A gas collecting mechanism is also provided on the top of the fermentation tank (12), the gas collecting mechanism comprising a gas storage tank (1), the gas storage tank (1) being connected to the fermentation tank (12) via an exhaust pipe (7); a barometer (5) and a first valve (6) are also provided on the exhaust pipe (7) between the gas storage tank (1) and the fermentation tank (12), the first valve (6) being located between the barometer (5) and the fermentation tank (12); The top of the fermentation tank (12) is connected to a storage tank (4) via a feed pipe (2), and a feed pump (3) is provided on the feed pipe (2); The top of the fermentation tank (12) is connected to a sampling tube (9), and a second valve (10) is provided on the sampling tube (9); The bottom of the fermenter (12) is provided with a discharge port (18).

5. A method for improving anaerobic digestion effect, characterized in that, It includes the following steps: S1. Mix camellia oleifera husks and sludge to make a fermentation raw material, and load it into the fermenter; S2. Install an adjustable static magnetic field device below the fermenter, adjust the distance between the adjustable static magnetic field device and the bottom of the fermenter so that the magnetic flux density at the bottom of the fermenter ≤ 18.7 mT, and carry out anaerobic digestion treatment on the fermentation raw material in the fermenter; the adjustable static magnetic field device includes at least one permanent magnet, the permanent magnet can be disassembled and installed on the tray, and a movable adjustment mechanism is connected to the tray for adjusting the distance between the permanent magnet and the bottom of the fermenter; the distance between the permanent magnet and the fermenter is 10 mm - 40 mm; the material of the permanent magnet is neodymium iron boron material; the magnetic permeability of the permanent magnet is 1.05, and the residual magnetic flux density is 1.45 T; when the number of the permanent magnets is one, the permanent magnet is horizontally distributed, and the center point is located on the central axis of the bottom of the fermenter; when the number of the permanent magnets is more than two, the permanent magnets are centrally symmetrically distributed, and the center point is located on the central axis of the bottom of the fermenter; the coverage area of the permanent magnet is 30% - 35% of the bottom area of the fermenter.

6. The method according to claim 5, wherein In step S2, make the magnetic flux density at the bottom of the fermenter be 4.99 mT - 18.7 mT.

7. The method according to claim 6, characterized in that, The permanent magnet is a cylinder, and the height of the permanent magnet is 2% - 15% of its diameter.

8. The method according to claim 7, wherein The material of the fermenter is a non-magnetic material; the non-magnetic material is at least one of glass and fiberglass; The fermenter is a cylindrical barrel, and the height-diameter ratio of the fermenter is 2; the filling volume of the material in the fermenter is 60% - 80% of the volume of the fermenter.

9. The method according to any one of claims 5 to 8, characterized in that, In step S1, the mass percentage content of camellia oleifera husks in the fermentation raw material is 88% - 94%; the particle size of the camellia oleifera husks is 0.7 mm - 1.0 mm; the mass percentage content of sludge in the fermentation raw material is 3% - 4%; the sludge is the excess sludge from a sewage treatment plant; the iron element content in the sludge is 0.2 wt% - 10.9 wt%; the following treatment is also included before using the sludge: continuously introduce nitrogen into the sludge for 10 min - 15 min to form an anaerobic environment, and then culture it at 35 °C in an anaerobic environment for more than 30 days.

10. The method according to any one of claims 5 to 8, characterized in that, In step S2, before the anaerobic digestion treatment, it also includes: continuously introduce nitrogen into the fermentation raw material for 10 min - 15 min to form an anaerobic environment; the temperature of the anaerobic digestion treatment is 30 °C - 40 °C; the anaerobic digestion treatment is carried out under the condition of a rotation speed of 150 rpm; the time of the anaerobic digestion treatment is 20 days - 50 days.

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