A method for enhancing high solid content anaerobic fermentation by micro-aerobic aeration

Abstract

The present invention belongs to the technical field of agricultural waste resource utilization, and specifically relates to a method for strengthening high-solid content anaerobic fermentation by micro-aerobic aeration. The present invention provides a method for strengthening high-solid content anaerobic fermentation. The technical scheme of the present invention improves the utilization efficiency of all components of agricultural waste and improves the gas production rate by performing micro-aerobic aeration on the 1st to 3rd day and / or the 12th to 14th day of anaerobic fermentation. Magnetic porous microspheres (MPMs) are added to enrich efficient methanogens by utilizing the porous characteristics of MPMs, and the electron transfer capacity of the solid-liquid interface is improved by layered inoculation of inoculum and external application of weak magnetic field and weak electric field, thereby improving the degradation of lignocellulose and the efficiency of methanogenesis. Adding biological lipopeptide surfactants in the leachate reflux process can promote the generation of organic acids, increase the activity of coenzyme F420, a key enzyme for methanogenesis, promote the conversion of intermediate products, and improve the biodegradability and gas production rate of agricultural waste.

Description

Technical Field

[0001] The invention belongs to the technical field of agricultural waste resource utilization, and specifically relates to a method for enhancing high-solid content anaerobic fermentation by micro-oxygen aeration. Background Art

[0002] Anaerobic fermentation has become a mature technology for treating agricultural waste. It achieves energy recovery by producing biogas and achieves the effect of carbon fixation and emission reduction. ‌‌Solid content (TS) refers to the percentage of solid components in a mixture. The solid content of conventional anaerobic fermentation materials is only 5%~8%. The equipment is bulky, the fixed asset investment is high, the raw material processing capacity is low, and the gas production efficiency is not high. High-solid anaerobic fermentation technology is an anaerobic digestion technology with a feed solid content of usually more than 10%~15%. It has the advantage of high raw material processing capacity and can solve the above-mentioned defects of conventional anaerobic fermentation to a certain extent. It has become the mainstream development trend of anaerobic fermentation.

[0003] In anaerobic fermentation with lignocellulosic raw materials such as straw as substrates, the conversion and utilization of cellulose and hemicellulose in the hydrolysis and acidification process is particularly important for improving gas production efficiency. The hydrolysis and acidification process converts complex substrates such as cellulose into simple soluble substances, such as volatile fatty acids (VFAs) that can be directly utilized by methanogens. However, in high-solid content anaerobic fermentation, due to the high raw material load and low mass and heat transfer capacity, gas production inhibition caused by VFAs accumulation is prone to occur, and stable gas production in the system is difficult to maintain. The volumetric gas production rate of high-solid content in my country is only 0.5~1 m 3 / m 3 Therefore, how to promote the utilization of lignocellulose raw materials and the generation and efficient conversion of organic acids and other substances under high solid content anaerobic fermentation conditions needs to be solved urgently. Summary of the invention

[0004] In view of this, the present invention provides a method for strengthening high-solid content anaerobic fermentation, which improves the utilization rate of lignocellulose and the production of organic acids, and improves the gas production rate of high-solid content anaerobic fermentation.

[0005] In order to solve the above problems, the present invention provides the following technical solutions:

[0006] The present invention provides a method for enhancing high-solid content anaerobic fermentation by micro-aerobic aeration, comprising the following steps:

[0007] The mixture is inoculated with agricultural waste in layers to perform high-solid content anaerobic fermentation; microaerobic aeration is performed on the 1st to 3rd day and / or the 12th to 14th day of the high-solid content anaerobic fermentation; the mixture includes inoculum and magnetic porous microspheres; the high solid content is 15% to 20%;

[0008] During the high-solid content anaerobic fermentation, the leachate is refluxed, and a biolipopeptide surfactant is added during the leachate reflux;

[0009] During the anaerobic fermentation, a weak magnetic field and a weak electric field are applied; the voltage of the weak electric field is 0.4-0.8V, and the intensity of the weak magnetic field is 10-20mT.

[0010] Preferably, the headspace oxygen concentration of the anaerobic fermentation device during the microaerobic aeration process is greater than 12% and less than 16%.

[0011] Preferably, the added amount of the magnetic porous microspheres is 5wt.%~10wt.% of the dry matter of agricultural waste.

[0012] Preferably, the dry matter ratio of the inoculant to the agricultural waste is 1:(1-2).

[0013] Preferably, the inoculum includes sludge; and before the inoculum is added, acclimatization is also performed.

[0014] Preferably, based on the complete reflux of the stored leachate volume, the first leachate reflux is performed 6 to 8 hours after the mixture and agricultural waste are filled in, and the biolipopeptide surfactant is added to the leachate.

[0015] Preferably, the biolipopeptide surfactant comprises surfactin.

[0016] Preferably, based on the dry matter of agricultural waste, 30-50 mg of surfactin is added per 1 kg of dry matter.

[0017] Preferably, the temperature of the anaerobic fermentation is 36°C to 38°C and the time is 20 to 30 days.

[0018] Preferably, the agricultural waste includes straw and livestock and poultry manure.

[0019] Beneficial effects of the present invention: The present invention provides a method for strengthening high-solid content anaerobic fermentation. The technical solution of the present invention can promote the utilization and transformation of soluble substances in agricultural waste by performing microaerobic aeration on the 1st to 3rd day of anaerobic fermentation, and can improve the utilization efficiency of lignocellulose components in agricultural waste by performing microaerobic aeration on the 12th to 14th day, shorten the sequencing batch anaerobic fermentation cycle, and improve the gas production rate. The addition of magnetic porous microspheres (MPMs) utilizes the porous characteristics of MPMs to enrich efficient methanogens, and further improves the electron transfer capacity of the solid-liquid interface by layered inoculation of inoculum and external weak magnetic field and weak electric field, further regulates the metabolic balance of methanogenic microorganisms, improves the mass transfer capacity of the system, and improves the efficiency of lignocellulose degradation and methanogenesis. The addition of biological lipopeptide surfactants in the leachate reflux process can promote the generation of organic acids, promote the transformation of intermediates, and improve the biodegradability and gas production rate of agricultural waste.

[0020] It can be seen that the technical solution provided by the present invention can improve the utilization of agricultural waste lignocellulose and the production of organic acids, and improve the gas production rate of high-solid content anaerobic fermentation. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Process flow chart for intensified anaerobic fermentation with high solid content. DETAILED DESCRIPTION

[0022] The present invention provides a method for enhancing high-solid content anaerobic fermentation by micro-aerobic aeration, comprising the following steps:

[0023] The mixture is inoculated with agricultural waste in layers to perform high-solid content anaerobic fermentation; microaerobic aeration is performed on the 1st to 3rd day and / or the 12th to 14th day of the high-solid content anaerobic fermentation; the mixture includes inoculum and magnetic porous microspheres; the high solid content is 15% to 20%;

[0024] During the high-solid content anaerobic fermentation, the leachate is refluxed, and a biolipopeptide surfactant is added during the leachate reflux;

[0025] During the anaerobic fermentation, a weak magnetic field and a weak electric field are applied; the weak electric field is 0.4-0.8V, and the weak magnetic field is 10-20mT.

[0026] As an practicable manner, a weak magnetic field and a weak electric field are applied during the anaerobic fermentation process of the present invention; the voltage of the weak electric field is 0.4~0.8v, and in a specific embodiment of the present invention, the voltage of the weak electric field can be 0.4v, 0.5v, 0.6v, 0.7v or 0.8v; the intensity of the weak magnetic field is 10~20mT, and in a specific embodiment of the present invention, the intensity of the weak magnetic field can be 10, 15, 18 or 20mT.

[0027] In a specific embodiment of the present invention, a weak magnetic field is provided by adding a permanent magnet to the fermentation device, and a weak electric field is provided by an external current. By applying a weak magnetic field and a weak electric field to the fermentation device, the electron transfer capacity of the solid-liquid interface is improved, the metabolic balance of methanogenic microorganisms is further adjusted, the mass transfer capacity of the system is improved, and the efficiency of lignocellulose degradation and methanogenesis is improved.

[0028] As an practicable manner, the agricultural waste of the present invention may include straw and livestock and poultry manure; the straw may be dry yellow straw; the dry yellow straw may be dry yellow corn straw and / or dry yellow wheat straw; the present invention has no special restrictions on the source and composition of the straw, and conventional straw may be used. The livestock and poultry manure of the present invention may include one or more of cow manure, pig manure and chicken manure; the present invention has no special restrictions on the source of the livestock and poultry manure, and conventional livestock and poultry manure may be used. As an practicable manner, when the agricultural waste may include straw and livestock and poultry manure, the dry matter ratio of the straw and livestock and poultry manure may be (6-7): (4-3); the dry matter ratio of the straw and livestock and poultry manure of the present invention may be 7:3, 7:4, 6:3 or 6:4. In a specific embodiment of the present invention, the dry matter ratio of the straw and livestock and poultry manure may be 6:4. As an practicable manner, the initial carbon-nitrogen ratio of the agricultural waste after mixing can be 20-25:1, and the setting of the carbon-nitrogen ratio is conducive to the anaerobic fermentation with high solid content.

[0029] As an practicable manner, the present invention inoculates the mixture and agricultural waste in layers to perform high solid content anaerobic fermentation; the mixture of the present invention includes an inoculant and magnetic porous microspheres; the high solid content is 15% to 20%, or 16 to 19%. The high solid content anaerobic fermentation of the present invention can be a sequencing batch high solid content anaerobic fermentation. As an practicable manner, the present invention mixes the inoculant and the magnetic porous microspheres to obtain a mixture. As an practicable manner, the layered inoculation of the present invention can be a layer of mixture and agricultural waste layered into a fermentation device, that is, a layer of mixture and a layer of agricultural waste, then another layer of mixture and a layer of agricultural waste, and then a layer of inoculant and a layer of agricultural waste; the relative position of a layer of agricultural waste and a layer of mixture in the present invention is that the mixture is in the upper layer, and the agricultural waste is in the lower layer; the mixture is superimposed on each layer of agricultural waste in the present invention. The number of layers of the layered inoculation of the present invention is determined according to the volume of the fermentation device, usually 2 to 3 layers. The layered inoculation of the present invention can improve the electron transfer capacity of the solid-liquid interface, adjust the metabolic balance of methanogenic microorganisms, improve the mass transfer capacity of the system, and improve the efficiency of lignocellulose degradation and methanogenesis.

[0030] As an practicable manner, before the inoculum of the present invention is added, acclimation may also be performed; the acclimation method may be placing the inoculum under mesophilic conditions; the mesophilic temperature may be 35-40°C, or 37-38°C; the acclimation time may be 18-21 days, or 20 days, and the mesophilic conditions of acclimation are cultured to increase the abundance and activity of dominant methanogens under mesophilic conditions. The inoculum of the present invention may include activated granular sludge, which is taken from a fermentation device for anaerobic fermentation of UASB. The microbial species in the activated granular sludge of the present invention may include the genus Methanogenum ( Methanosaeta ), Methanobacterium ( Methanobacterium )、Deep Archaea( Bathyarchaeia )、Methanosarcina ( Methanosarcina ) and Methanobacterium ( Methanolinea ). The ratio of the dry matter of the agricultural waste to the dry matter of the inoculum according to the present invention can be (1~2):1. The setting of the dry matter ratio can provide sufficient raw materials and methanogens for the fermentation system. The present invention has requirements for the dry matter ratio of the inoculum and the agricultural waste in the entire layered inoculation, and has no special requirements for the dry matter ratio of the inoculum and the agricultural waste in each layer. The addition amount of the magnetic porous microspheres according to the present invention can be 5wt.%~10wt.% of the dry matter of the agricultural waste, or it can be 6wt.%~8wt.%. In a specific embodiment of the present invention, the addition amount of the magnetic porous microspheres can be 5wt.%, 6wt.%, 7wt.%, 8wt.%, 9wt.% or 10wt.% of the dry matter of the agricultural waste.

[0031] As an implementable method, the present invention has no special limitation on the preparation method of the magnetic porous microspheres, and conventional methods can be used. In the present invention, the magnetic porous microspheres are spherical, composed of a GMA-DVB (glycidyl methacrylate-divinylbenzene) polymer shell and an oleic acid-coated Fe3O4 magnetic core, with a diameter of about 100 μm, an average pore size of 830-840 nm, and a porosity of 60%-65%.

[0032] In a specific embodiment of the present invention, the preparation method of the magnetic porous microspheres may include: mixing FeCl3·6H2O, FeCl2·4H2O and deionized water to obtain a first solution; performing a second mixing of the first solution with NH3·H2O and oleic acid to obtain a gel; performing a first drying of the gel to obtain a Fe3O4 modified gel; sequentially mixing the Fe3O4 modified gel and benzoyl peroxide (BPO) with an organic phase and an aqueous phase, polymerizing, and performing a second drying to obtain magnetic porous microspheres. The present invention utilizes the porous characteristics of MPMs to enrich efficient methanogens.

[0033] As an implementable method, the leachate is refluxed during the high-solid content anaerobic fermentation process described in the present invention. Biolipopeptide surfactants are added during the reflux of the leachate of the high-solid content anaerobic fermentation described in the present invention. Adding biolipopeptide surfactants as promoters promotes the generation of organic acids, improves the activity of the key methane-producing enzyme coenzyme F420, promotes the conversion of intermediates, and improves the degradation rate of agricultural waste; the present invention detects the content of biolipopeptide surfactants in the leachate at different fermentation times by high-performance liquid chromatography. It can be seen that the degradation rate of biolipopeptide surfactants is 33.5% after 12 days of fermentation, and the degradation rate of biolipopeptide surfactants is about 50% after 20 days of fermentation. It can be seen that biolipopeptide surfactants have no adverse effects on the environment and have good biodegradability. After placing the fermentation system in the anaerobic fermentation tank, the liquid in the fermentation system naturally flows out through the screen at the bottom of the fermentation tank by gravity, which is the leachate, and the leachate flows to the matching leachate storage tank. According to the reflux frequency, the leachate of the present invention begins to reflux to the anaerobic fermentation tank after being stored for a certain period of time; the reflux of the leachate can effectively adjust the moisture content of the fermentation system of the high solid content anaerobic fermentation, and improve the mass transfer and heat transfer efficiency. In the first reflux of the leachate, the present invention adds a biological lipopeptide surfactant to the refluxed leachate; the biological lipopeptide surfactant can include surfactin; in the specific embodiment of the present invention, the trade name of the surfactin is Surfactin. After the fermentation material is filled into the anaerobic fermentation device of the present invention for 6 to 8 hours, the leachate flows out to the storage tank, and the first reflux of the leachate begins. When the leachate in the storage tank is completely refluxed, the first reflux of the leachate ends; the outflowing leachate is stored in the storage tank again, and the second reflux is performed after storage for a period of time. The present invention adds a biological lipopeptide surfactant to the leachate. The biological lipopeptide surfactant is only added to the leachate when the first reflux of the leachate is refluxed. In terms of the dry matter of agricultural waste, the present invention adds 30 to 50 mg of surfactin per 1 kg of dry matter. In a specific embodiment of the present invention, based on the dry matter of agricultural waste, 30, 40, 45 or 50 mg of surfactin is added per 1 kg of dry matter.

[0034] The reflux frequency of the leachate of the present invention can be 2 to 4 times / d; on the 1st to 3rd day of high solid content anaerobic fermentation, the reflux frequency of the leachate of the present invention can be 3 to 4 times / d; the interval between the reflux of the leachate every 2 times can be 6 to 7 hours. Since the 1st to 3rd day of fermentation is the initial stage of fermentation, the initial stage of fermentation is the peak of material hydrolysis and acidification, and macromolecular organic matter is quickly converted into small molecules such as organic acids. In order to prevent local acid accumulation caused by high solid content of materials, a higher reflux frequency of leachate is adopted to maintain the uniform and stable distribution of organic acids in the system. From the 4th day of high solid content anaerobic fermentation to the end of high solid content anaerobic fermentation, the reflux frequency of the leachate of the present invention can be 2 to 3 times / d, and the interval between the reflux of the leachate every 2 times can be 8 to 12 hours. After the 4th day of fermentation, the fermentation system gradually turns into a stable gas production stage, so the reflux frequency of the leachate is appropriately reduced to ensure the full utilization of the intermediate product. The volume of the leachate flowing out of the fermentation device every day and the leachate refluxed every day are the same.

[0035] As an practicable manner, microaerobic aeration is performed on the 1st to 3rd day and / or the 12th to 14th day of the anaerobic fermentation described in the present invention. During the microaerobic aeration process of the present invention, the headspace oxygen concentration of the anaerobic fermentation device can be greater than 12% and less than 16%; in a specific embodiment of the present invention, the operation method of maintaining the headspace oxygen concentration at 12% to 16% can be to perform aeration when the headspace oxygen concentration is ≤12%, and to stop aeration when the headspace oxygen concentration is ≥16%. The microaerobic aeration described in the present invention can be achieved by adding stream air to the fermentation device; the air can be added by pumping. The air flow rate of the microaerobic aeration described in the present invention is 0.1~0.4 m 3 / h.

[0036] The anaerobic fermentation process is mainly divided into four stages: hydrolysis, acidogenesis, acetogenesis, and methanogenesis. Each stage provides the necessary raw materials for the next stage in turn and affects each other. The hydrolysis process converts complex substrates into simple soluble substances. This process is particularly important for the efficient utilization of cellulose and hemicellulose in lignocellulosic substrates and is the main rate-limiting stage for anaerobic fermentation of methanogens such as straw. The acidogenesis and acetogenesis processes provide methanogens with VFAs substrates such as acetic acid and butyric acid that can be directly utilized. However, excessive accumulation of volatile fatty acids (VFAs) has an inhibitory effect on high raw material load systems, inhibits the activity of methanogens, and may cause the system to become sour. Injecting a small amount of air or oxygen into the anaerobic fermentation device for microaerobic aeration helps to establish a highly active and diverse hydrolytic and fermentative bacterial community and increase the abundance of facultative microorganisms. The mismatch between the system hydrolysis and acidification caused by high raw material pressure and the methanogenesis rate is the main reason for the low gas production efficiency. The micro-aerobic aeration of the present invention promotes the increase of methane production under high substrate load. The increase of methane production is reflected in two aspects: first, it effectively promotes the hydrolysis of fermentation raw materials and provides more available substrates for methanogens; second, it maintains the stability of the VFAs concentration in the fermentation system and maintains a suitable environment for methanogens. At present, the substrate hydrolysis is usually promoted by micro-aeration of the fermentation material in the pretreatment stage (i.e., the stage without adding inoculum). However, for the high solid content system, the mass transfer and heat transfer conditions are limited, and the degradation of cellulose and hemicellulose is hindered. The micro-aeration in the pretreatment stage mainly promotes the conversion of soluble substances into available VFAs, and the promoting effect on the degradation and conversion of cellulose and hemicellulose is not significant. Therefore, the present invention is aimed at the high solid content anaerobic fermentation system, and performs two-stage micro-aeration on the 1st to 3rd day of fermentation and the 12th to 14th day of fermentation to promote the utilization and conversion of soluble substances and lignocellulose in agricultural waste, respectively, effectively promote the hydrolysis of fermentation raw materials, and provide more available substrates for methanogens; it can also maintain the stability of the VFAs concentration in the fermentation system and maintain a suitable environment for methanogens. By inoculating efficient granular sludge in layers, adding magnetic porous microspheres (MPMs) and applying weak magnetic and electric fields, the porous characteristics of MPMs are used to enrich efficient methanogens, improve the electron transfer capacity of the solid-liquid interface, further adjust the metabolic balance of methanogenic microorganisms, improve the mass transfer capacity of the system, improve the efficiency of lignocellulose degradation and methanogenesis in sequencing batch anaerobic fermentation, and shorten the sequencing batch anaerobic fermentation cycle. The results of the embodiment show that the effective volume methane yield can reach up to 2.5~3 m 3 / (m 3 ·d).

[0037] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0038] ReferenceFigure 1 Embodiment 1 is carried out according to the process flow chart of Example 1.

[0039] Example 1

[0040] 1. Add permanent magnets to the sequencing batch reactor with high solid content and connect external current to achieve a weak electric field of 0.6V and a weak magnetic field of 16-18mT. The weak electric field is provided by a regulating power supply, and the weak magnetic field is provided by a rubber magnet.

[0041] 2. The corn stalks were crushed and mixed with cow dung at a dry matter ratio of 6:4 as fermentation raw materials. Granular sludge was cultured and acclimated at 37±1℃ for 20 days as inoculum, and the inoculum was added to the fermentation raw materials to obtain a fermentation system. The dry matter ratio of the inoculum to the dry matter of the fermentation raw materials was 1:2, and then water was added to adjust the total solid content of the fermentation system to 15%. Magnetic porous microspheres (MPMs) were added at a ratio of 5wt.% of the dry matter of the fermentation raw materials. The inoculum and MPMs were mixed evenly to obtain a mixture; the fermentation raw materials and the mixture were layered and filled into a sequencing batch high solid content anaerobic fermentation reactor in order from top to bottom; the layered structure obtained by placing a layer of mixture and a layer of fermentation raw materials from top to bottom was regarded as a group, and a total of 3 groups of layered structures were set in the reactor, namely, a layer of mixture and a layer of fermentation raw materials, then another layer of mixture and a layer of fermentation raw materials, and then a layer of mixture and a layer of fermentation raw materials. The relative position of a layer of fermentation raw materials and a layer of mixture was that the fermentation raw materials were in the lower layer and the mixture was in the upper layer. The fermentation system was placed in an anaerobic fermentation reactor for sequencing batch high solid content anaerobic fermentation at a fermentation temperature of 37±1°C.

[0042] The preparation method of MPMs is as follows:

[0043] (1) Synthesis of Fe3O4 modified gel: Under N2 protection, 24.3 g FeCl3·6H2O and 13.0 g FeCl2·4H2O were stirred and dissolved in 200 mL deionized water. After heating to 85°C, 60 mL NH3·H2O was quickly added and reacted for 30 min. Then, 15 mL oleic acid was added within 15 min and stirred at 600 rpm until the solution became clear and a gel was formed. After cooling to room temperature, the gel was separated using a magnet, washed with distilled water, and vacuum dried for 24 h to obtain Fe3O4 modified gel.

[0044] (2) The composition of the organic phase is: 15 g of glycidyl methacrylate (GMA), 3.75 g (25% of GMA) of divinylbenzene (DVB) and 12 g (80% of GMA) of a mixture; the mixture is a mixture of a hexane solution and a toluene solution in a volume ratio of 1:1.

[0045] The water phase composition is: a mixture of 115 g of water, 1.15 g of polyethylene glycol (PEG-1000) and 8.05 g of sodium chloride; the mass of polyethylene glycol accounts for 1% of the mass of water, and the mass of sodium chloride accounts for 7% of the mass of water.

[0046] 3.25 g of Fe3O4 modified gel and 0.15 g of benzoyl peroxide (BPO) were added to the organic phase, ultrasonically mixed for 5 min, and then the aqueous phase was added, with the volume ratio of the aqueous phase to the organic phase being 0.3:1. Under N2 protection, polymerization was carried out at 65 °C for 3 h. MPMs were separated by a magnet, washed with distilled water and ethanol, and dried in a vacuum oven at 60 °C to obtain MPMs.

[0047] 3. On the 1st to 3rd day of fermentation, air is introduced from the bottom of the material through an aeration plate, with an air flow rate of 0.2~0.3m 3 / h, monitor the oxygen content in the headspace of the anaerobic fermentation reactor through a sensor, and control the headspace oxygen concentration to 12%~16% (i.e. greater than 12% and less than 16%); aeration is performed when the oxygen concentration is ≤12%, and aeration is stopped when it is ≥16%.

[0048] After the fermentation system is placed in the anaerobic fermentation reactor, due to gravity, the liquid in the fermentation system flows out of the anaerobic fermentation reactor to leachate, and the leachate flows to the matching leachate storage tank. The first leachate reflux is carried out 6-8 hours after the mixture and agricultural waste are filled in, based on the complete reflux of the stored leachate volume. Before the first leachate reflux, surfactant is added to the leachate storage tank at one time. Based on the dry matter of agricultural waste corn stalks and cow dung, 40 mg of surfactant is added to each 1 kg of dry matter. The frequency of leachate reflux is 3-4 times / d; every day, the amount of leachate flowing out is the same as the amount of leachate refluxed. Surfactant is only added during the first leachate reflux.

[0049] 4. Aeration is stopped from the 4th to 11th day of fermentation, and the fermentation starts from the anaerobic fermentation stage. The frequency of leachate reflux is 2 to 3 times per day. Every day, the amount of leachate flowing out is the same as the amount of leachate refluxed.

[0050] 5. On the 12th to 14th day of fermentation, air is introduced from the bottom of the material using an aeration plate. The aeration control method is the same as in step 3. The frequency of leachate reflux is the same as in step 4. The fermentation process ends after 20 to 22 days of fermentation. MPMs can be recycled using magnetic recovery. The effective volumetric methane yield reaches 2.5 to 3 m 3 / (m 3 ·d).

[0051] Example 2

[0052] 1. Add permanent magnets to the sequencing batch reactor with high solid content and connect external current to achieve a weak electric field of 0.6V and a weak magnetic field of 16-18mT. The weak electric field is provided by a regulating power supply, and the weak magnetic field is provided by a rubber magnet.

[0053] 2. The corn stalks were crushed and mixed with cow dung in a dry matter ratio of 6:4 as fermentation raw materials. Granular sludge was cultured and acclimated at 37±1℃ for 20 days as inoculum, and inoculum was added in a ratio of 1:2 to the dry matter of the inoculum and the fermentation raw material to obtain a fermentation system, and then water was added to adjust the total solid content of the fermentation raw material and the inoculum to 15%. Magnetic porous microspheres (MPMs) were added in a ratio of 5wt.% of the dry matter of the fermentation raw material. The inoculum and MPMs were mixed evenly to obtain a mixture; the fermentation raw material and the mixture were layered and filled into a sequencing batch high solid content anaerobic fermentation reactor in order from top to bottom, and the layered structure obtained by placing a layer of fermentation raw material and a layer of mixture from top to bottom was regarded as a group, and a total of 3 groups of layered structures were set in the reactor. The fermentation temperature was 37±1℃.

[0054] The preparation method of MPMs is the same as that in Example 1.

[0055] 3. On the 1st to 3rd day of fermentation, air is introduced from the bottom of the material through an aeration plate, and the air flow rate is 0.2~0.3m 3 / h, monitor the oxygen content in the headspace through a sensor and control the headspace oxygen concentration within the range of 14~16% (i.e. greater than 14% and less than 16%). Aeration is performed when it is ≤14%, and aeration is stopped when it is ≥16%.

[0056] After the fermentation system is placed in the anaerobic fermentation reactor, due to the action of gravity, leachate flows out of the anaerobic fermentation reactor and flows to the matching leachate storage tank. The first leachate reflux is carried out 6 to 8 hours after the mixture and agricultural waste are filled in, based on the complete reflux of the stored leachate volume. During the first leachate reflux, surfactant is added to the leachate storage tank at one time. Based on the dry matter of agricultural waste corn stalks and cow dung, 40 mg of surfactant is added to each 1 kg of dry matter. The frequency of leachate reflux is 3 to 4 times / d.

[0057] 4. Aeration is stopped from the 4th to 11th day of fermentation, and the fermentation starts from the anaerobic fermentation stage. The frequency of leachate reflux is 2 to 3 times per day. Every day, the amount of leachate flowing out is the same as the amount of leachate refluxed.

[0058] 5. The fermentation process ends after 25-30 days, and MPMs can be recycled by magnetic recovery. The effective volumetric methane yield reaches 2-2.5 m 3 / (m 3 ·d).

[0059] Example 3

[0060] 1. Add permanent magnets to the sequencing batch reactor with high solid content and connect external current to achieve a weak electric field of 0.6V and a weak magnetic field of 16-18mT. The weak electric field is provided by a regulating power supply, and the weak magnetic field is provided by a rubber magnet.

[0061] 2. Corn stalks were crushed and mixed with cow dung at a dry matter ratio of 6:4 as fermentation raw materials. Granular sludge was cultured and acclimated at 37±1℃ for 20 days as inoculum, and inoculum was added at a ratio of 1:2 between the dry matter of inoculum and the dry matter of fermentation raw materials to obtain a fermentation system; water was then added to adjust the total solid content of the fermentation system to 15%. Magnetic porous microspheres (MPMs) were added at a ratio of 5wt.% of the dry matter of the fermentation raw materials. The inoculum and MPMs were mixed evenly to obtain a mixture; the fermentation raw materials and the mixture were layered and filled into a sequencing batch high-solid content anaerobic fermentation reactor in order from top to bottom; the layered structure obtained by placing a layer of fermentation raw materials and a layer of mixture from top to bottom was regarded as a group, and a total of 3 groups of layered structures were set in the reactor. The fermentation temperature was 37±1℃.

[0062] The preparation method of MPMs is the same as that in Example 1.

[0063] 3. No micro-aeration was performed on the 1st to 11th day of fermentation. The first leachate reflux was performed 6 to 8 hours after the mixture and agricultural waste were filled in, based on the complete reflux of the stored leachate volume. Before the first leachate reflux, surfactant was added to the leachate storage tank at one time. Based on the dry matter of agricultural waste corn stalks and cow dung, 40 mg of surfactant was added to each 1 kg of dry matter. The frequency of leachate reflux was 2 to 3 times / d; every day, the amount of leachate flowing out was the same as the amount of leachate refluxed.

[0064] 4. On the 12th to 14th day of fermentation, air is introduced from the bottom of the material through an aeration plate, and the air flow rate is 0.2~0.3 m 3 / h, the oxygen content in the headspace is monitored by a sensor, and the headspace oxygen concentration is controlled within the range of 12~16% (i.e. greater than 12% and less than 16%). Aeration is performed when the oxygen concentration is ≤12%, and aeration is stopped when it is ≥16%. The frequency of leachate reflux is 3~4 times / d; every day, the amount of leachate flowing out is the same as the amount of leachate refluxed.

[0065] 5. The fermentation process ends after 25-30 days of fermentation, and MPMs can be recycled by magnetic recovery. The effective volumetric methane yield reaches 1.5-2.2 m 3 / (m 3 ·d).

[0066] Comparative Example 1

[0067] 1. Add permanent magnets to the sequencing batch reactor with high solid content and connect external current to achieve a weak electric field of 0.6V and a weak magnetic field of 16-18mT. The weak electric field is provided by a regulating power supply, and the weak magnetic field is provided by a rubber magnet.

[0068] 2. The corn stalks were crushed and mixed with cow dung at a dry matter ratio of 6:4 as fermentation raw materials. Granular sludge was cultured and acclimated at 37±1℃ for 20 days and used as inoculum. The inoculum was added to the fermentation raw materials to obtain a fermentation system, and the dry matter ratio of the inoculum to the dry matter of the fermentation raw materials was 1:2, and then water was added to adjust the total solid content of the fermentation system to 15%. Magnetic porous microspheres (MPMs) were added at a ratio of 5wt.% of the dry matter of the fermentation raw materials. The inoculum and MPMs were mixed evenly to obtain a mixture; the fermentation raw materials and the mixture were layered and filled into a sequencing batch high solid content anaerobic fermentation reactor in order from top to bottom; the layered structure obtained by placing a layer of fermentation raw materials and a layer of mixture from top to bottom was regarded as a group, and a total of 3 groups of layered structures were set in the reactor. The fermentation temperature was 37±1℃.

[0069] The preparation method of MPMs is the same as that in Example 1.

[0070] Based on the complete reflux of the stored leachate volume, the first leachate reflux is carried out 6 to 8 hours after the mixture and agricultural waste are filled in. Before the first leachate reflux, surfactant is added to the leachate storage tank at one time. Based on the dry matter of agricultural waste corn straw and cow dung, 40 mg of surfactant is added for every 1 kg of dry matter. The leachate reflux frequency is 2 to 3 times / d, and the amount of leachate flowing out is the same as the amount of leachate refluxed.

[0071] The fermentation process ends after 30-35 days of fermentation, and MPMs can be recycled by magnetic recovery. The effective volumetric methane yield reaches 1-1.2m 3 / (m 3 ·d).

[0072] sCOD was determined by spectrophotometer, VFAs by gas chromatography, lignocellulose by Paradigm washing, methane content by gas chromatography, gas production by drainage method, and effective volumetric yield by average daily gas production / effective volume × methane content.

[0073] The sCOD, VFAs content, lignocellulose degradation rate, effective volumetric methane production rate and maximum methane content during the fermentation process of Examples 1 to 3 and Comparative Example 1 were analyzed.

[0074] The method for determining sCOD is based on “Yuan et al. Enhancing anaerobic digestion of cotton stalk by pretreatment with a microbial consortium (MC1), https: / / doi.org / 10.1016 / j.biortech.2016.02.037.

[0075] For the determination method of VFAs content, please refer to "Li et al. Effect of inoculum and substrate / inoculum ratio on the performance and methanogenic archaeal communitystructure in solid state anaerobic co-digestion of tomato residues with dairymanure and corn stover, https: / / doi.org / 10.1016 / j.wasman.2018.09.042".

[0076] The method for determining the degradation rate of lignocellulose is based on “Yu et al. Accelerated acidification by inoculation with a microbial consortia in a complex open environment, https: / / doi.org / 10.1016 / j.biortech.2016.05.093.”

[0077] The determination methods of effective volumetric methane production rate and maximum methane content refer to "Yu et al. Deeper insights into the synergy of material transformation, microbial network, and energy balance during pilot thermophilic and mesophilic dry anaerobicdigestion systems, https: / / doi.org / 10.1016 / j.scitotenv.2023.164410."

[0078] The results are shown in Table 1.

[0079] Table 1 Determination results of sCOD, VFAs content, lignocellulose degradation rate, effective volumetric methane production rate and maximum methane content of Examples 1 to 3 and Comparative Example 1

[0080]

[0081] Note: VFAs content is the sum of the contents of short-chain volatile fatty acids from C2 to C5, namely acetic acid, propionic acid, n-butyric acid, isobutyric acid, n-valeric acid and isovaleric acid.

[0082] According to Table 1, the embodiments of the present invention can effectively promote the degradation of raw material lignocellulose, and the degradation rate is increased by 20.31-65.99% compared with the control example; the VFAs generation in the early stage of fermentation is improved, and on the 5th day of fermentation, the VFAs are increased to 2.28-2.88 times that of the control example; the conversion of soluble substances is promoted, and the conversion rate of soluble substances is increased by up to 89.16%; the methane production is increased to 2.52L / L / d.

[0083] In summary, the technical solution provided by the present invention can improve the utilization of agricultural waste lignocellulose and the production of organic acids, and increase the gas production rate of high-solid content anaerobic fermentation.

[0084] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for enhancing high solid content anaerobic fermentation by microaerobic aeration, characterized in that: Here are the steps: The mixture is inoculated with agricultural waste in layers to perform high-solid content anaerobic fermentation; microaerobic aeration is performed on the 1st to 3rd day and / or the 12th to 14th day of the high-solid content anaerobic fermentation; the mixture comprises an inoculum and magnetic porous microspheres; the high solid content is 15% to 20%; the agricultural waste is straw and livestock and poultry manure; the headspace oxygen concentration of the anaerobic fermentation device during microaerobic aeration is greater than 12% and less than 16%; the magnetic porous microspheres are composed of a glycidyl methacrylate-divinylbenzene polymer shell and an oleic acid-coated Fe3O4 magnetic core; During the high-solid content anaerobic fermentation, the leachate is refluxed, and a biolipopeptide surfactant is added during the leachate reflux; During the anaerobic fermentation, a weak magnetic field and a weak electric field are applied; the voltage of the weak electric field is 0.4-0.8V, and the intensity of the weak magnetic field is 10-20mT.

2. The method according to claim 1, characterized in that The added amount of the magnetic porous microspheres is 5wt.% to 10wt.% of the dry matter of the agricultural waste.

3. The method according to claim 1, characterized in that The ratio of the dry matter of the inoculum to the dry matter of the agricultural waste is 1:(1-2).

4. The method according to claim 1 or 3, characterized in that: The inoculum includes sludge; before the inoculum is added, acclimatization is also performed.

5. The method according to claim 1, characterized in that Based on the complete reflux of the stored leachate volume, the first leachate reflux is carried out 6 to 8 hours after the mixture and agricultural waste are filled in, and a biolipopeptide surfactant is added to the leachate.

6. The method according to claim 1 or 5, characterized in that: The biological lipopeptide surfactant includes surfactin.

7. The method according to claim 5, characterized in that Based on the dry matter of agricultural waste, 30-50 mg of surfactant is added to every 1 kg of dry matter.

8. The method according to claim 1, characterized in that The temperature of the anaerobic fermentation is 36°C to 38°C, and the time is 20 to 30 days.

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