A method for biomass mixed pressure-switching two-phase anaerobic fermentation

Abstract

The present invention provides a method for mixed pressure-variable two-phase anaerobic fermentation of biomass, comprising the following process steps: straw crushing → alkaline ozone treatment → solid-liquid alternating decomposition → mixing of straw decomposition liquid with livestock and poultry manure → solid-liquid separation → suspended liquid enters a pressure-variable acidification tank for anaerobic acid and hydrogen production fermentation → liquid enters a pressure-variable methane production tank by pressure difference for anaerobic methane production fermentation → biogas enters a biogas tank after dehydration and desulfurization, and biogas liquid is diluted and returned to the field. Under the action of a composite microbial flora, the purpose of increasing the straw decomposition rate and accelerating straw decomposition is achieved by repeatedly alternating solid and liquid states. Pressure difference is used to transfer the liquid from the acidification tank to the methane production tank, saving power; the entire fermentation process does not emit any gas into the atmosphere, does not pollute the environment, and ultimately produces a high content of methane gas.

Description

Technical Field

[0001] The invention belongs to the field of anaerobic fermentation treatment of agricultural waste, and in particular relates to a method for biomass mixed pressure-variable two-phase anaerobic fermentation.

[0002] This invention belongs to 4.5.4 Biogas, under 4.4 Biomass Energy Industry, in the Catalogue of Strategic Emerging Industries. It is a fermentation process, purification technology, and complete equipment with high volumetric gas production rates for different biomass raw materials such as agricultural and forestry residues, livestock and poultry manure, urban domestic waste, and industrial organic wastewater. Background Art

[0003] my country has extensive biomass energy resources. In rural areas, a large amount of waste, such as crop straw and livestock manure, can be used as biomass energy. Annual agricultural production generates 700 million tons of straw and 4.5 billion tons of livestock manure, rich in biomass energy. These "agricultural wastes" have great potential for energy and resource utilization. Effective energy utilization of these wastes can not only solve the problem of waste disposal, but also turn waste into treasure, generating energy for production and daily life.

[0004] Anaerobic fermentation of straw and livestock manure for biogasification is one of the best ways to utilize their resources. The basic principle of anaerobic fermentation is that under anaerobic conditions, a variety of microorganisms work together to decompose organic matter to produce CH4 (methane) and CO2 (carbon dioxide). The fermentation process is generally divided into three processes: hydrolysis, hydrogen and acetic acid production, and methanogenic fermentation. At present, the main processes of anaerobic fermentation include anaerobic contact process, anaerobic biofilm process, and anaerobic activated sludge bed process. The technology is relatively mature and widely used. However, its efficiency is relatively low, and the gas production rate per unit volume is generally 0.8-1m 3 / m3.d, and related technologies have not seen breakthroughs for many years. Conventional straw processing methods suffer from slow decomposition, and the problem of insufficient utilization of large amounts of cellulose, hemicellulose, and lignin persists. Large-scale biogas projects, which are currently widely used, also produce large amounts of biogas slurry and residue, which, without a suitable disposal method, can easily cause secondary pollution. Summary of the Invention

[0005] In order to improve the utilization rate of straw in the anaerobic fermentation process, shorten the fermentation cycle, reduce the water retention time, and improve the efficiency and volumetric gas production rate of anaerobic fermentation of straw and livestock and poultry manure to produce biogas, the present invention provides a biomass mixed pressure-variable two-phase anaerobic fermentation method that can quickly complete the decomposition of straw and accelerate the anaerobic acid and methane production processes of the fermented product.

[0006] The object of the present invention is achieved in the following manner:

[0007] A biomass mixed pressure-swing two-phase anaerobic fermentation method comprises the following process steps: straw crushing → alkaline ozone treatment → solid-liquid alternating decomposition → mixing of straw decomposition liquid with livestock and poultry manure → solid-liquid separation → suspended liquid enters a pressure-swing acidification tank for anaerobic acid and hydrogen production fermentation → liquid enters a pressure-swing methane production tank based on pressure difference for anaerobic methane production fermentation → biogas enters a biogas tank after dehydration and desulfurization, and biogas liquid is diluted and returned to the field.

[0008] The specific solid-liquid alternating decomposition is as follows: the decomposition liquid is prepared according to the weight ratio of straw: composite microbial agent: water = 1:0.05: (10-20), the straw treated with alkali ozone is placed in the hanging basket, the hanging basket is sunk into the decomposition liquid, the bottom of the decomposition liquid is aerated with oxygen, the amount of composite microbial cells increases rapidly, and the amount of composite microbial cells is greater than 10 8 After the amount of complex microbial cells and LiP enzyme activity in the decomposition liquid reaches 10u / mL, the hanging basket is lifted up and separated from the decomposition liquid. The straw is in a solid-state fermentation state. The growth of bacteria attached to the straw consumes carbon and nitrogen sources, leading to a carbon and nitrogen-limited state, thereby stimulating the complex microorganisms to produce enzymes. After the LiP enzyme activity is greater than 10u / mg, the hanging basket is sunk into the decomposition liquid again. According to the amount of complex microbial cells and LiP enzyme activity in the decomposition liquid, the operation of immersing the hanging basket in the liquid and lifting it out of the liquid is repeated. The decomposition is stopped when the straw decomposition reaches more than 50% or the COD of the decomposition liquid is lower than 5000 mg / L.

[0009] The composite microbial agent includes white rot fungi, green Trichoderma and black Aspergillus, and the three fungi are mixed according to the bacterial volume ratio of 1:0.5:0.1.

[0010] The conditions for lifting the hanging basket out of the decomposition liquid again are that the hanging basket is immersed in the decomposition liquid for more than 4 hours and the amount of composite microorganisms is greater than 10 8 / mL, and the condition for sinking the basket into the decomposition solution again is that the enzyme activity is greater than 10u / mg.

[0011] When the COD concentration in the decomposition liquid is greater than 20,000 mg / L, release part of the decomposition liquid and add an equal amount of clean water and nitrogen source.

[0012] The white rot fungi in the composite microbial agent are cultured in a PDA medium at 28°C for 48 hours, and then acclimated in an acclimation medium at 30°C for 72 hours. The acclimation culture medium contains carbon sources such as glucose or brown sugar, nitrogen sources such as urea, ammonium sulfate and soy milk, inorganic salts such as magnesium sulfate and dipotassium hydrogen phosphate, complex vitamins, alkaline ozone treatment liquid, and fly ash leaching liquid, wherein the carbon-nitrogen ratio is 1:1-2:1.

[0013] The mixing ratio of straw decomposition liquid and livestock and poultry manure is such that the carbon-nitrogen ratio of the mixed mixture is 25:1.

[0014] The pressure bearing capacity of the acidification tank and the methane production tank is greater than 0.44MPa. The pressure inside the tank gradually increases to 0.3-0.4MPa as the fermentation gas is produced, and anaerobic fermentation is carried out. The stable operating pressure of the acidification tank and the methane production tank fluctuates between 0.3-0.4MPa.

[0015] When the pressure in the acidification tank reaches 0.4 MPa, the gas in the acidification tank is introduced into the methane production tank to stir the liquid in the methane production tank until the pressure in the acidification tank drops to 0.3 MPa.

[0016] Compared to existing technologies, the present invention utilizes a composite microbial community and a repeated alternating solid-liquid cycle to achieve both increased straw decomposition efficiency and accelerated decomposition. The decomposed liquid from the straw is mixed with livestock and poultry manure, then undergoes solid-liquid separation. The suspended liquid enters a pressure-switching acidification tank for anaerobic acid and hydrogen production. The fermented liquid then enters a pressure-switching methane production tank via a pressure differential for anaerobic methane production. This pressure differential is used to transfer the liquid from the acidification tank to the methane tank, saving energy. The entire fermentation process produces no atmospheric emissions, preventing environmental pollution, while ultimately producing a high level of methane gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0018] like Figure 1 As shown, a method for biomass mixed pressure-swing two-phase anaerobic fermentation includes the following process steps: straw crushing → alkaline ozone treatment → solid-liquid alternating decomposition → mixing of straw decomposition liquid with livestock and poultry manure → solid-liquid separation → suspended liquid enters a pressure-swing acidification tank for anaerobic acid and hydrogen production fermentation → the liquid enters a pressure-swing methane production tank based on pressure difference for anaerobic methane production fermentation → biogas enters a biogas tank after dehydration and desulfurization, and the biogas liquid is diluted and returned to the field.

[0019] To improve decomposition efficiency, straw is pulverized to approximately 5cm in size before aerobic decomposition. The pulverized straw is then treated with alkaline ozone. Specifically, the pulverized straw is mixed with limewater, with straw (based on dry matter) comprising 3%-15% of the total liquid, and limewater comprising 0.3%-1%. Low-flux ozone is then introduced into the mixture for 1-4 hours, followed by a 6-24-hour standstill. This kills any harmful bacteria in the straw, decomposes any pesticide residue, and accelerates subsequent decomposition. For details, refer to Invention Patent 200710139494.1.

[0020] Then, a decomposition solution is prepared according to the weight ratio of straw: composite microbial agent: water = 1:0.05:(10-20), wherein the composite microbial agent includes white rot fungi (No.:ACCC 30942), Trichoderma viride (No.:ACCC 20059) and Aspergillus niger (No. AS3.4309), and the three bacteria are mixed at a bacterial volume ratio of 1:0.5:0.1. The straw treated with alkaline ozone is placed in a hanging basket, which is sunk into the decomposition solution. The bottom of the decomposition solution is aerated with oxygen, and the composite microbial cell volume increases rapidly, and the composite microbial cell volume is greater than 10 8 After the amount of complex microorganisms in the decomposition liquid and the activity of LiP enzyme are greater than 10u / mg, the hanging basket is immersed in the liquid and lifted out of the liquid again. The conditions for lifting the hanging basket out of the decomposition liquid again are that the hanging basket is immersed in the decomposition liquid for more than 4 hours and the amount of complex microorganisms is greater than 10 8 / mL, the condition for sinking the basket into the decomposition liquid again is that the enzyme activity is greater than 10u / mg. When the COD concentration in the decomposition liquid is greater than 20,000mg / L, release part of the decomposition liquid and replenish equal amounts of clean water and nitrogen source. The optimal amount of decomposition liquid released each time is half of the total amount. Stop when the straw decomposition reaches more than 50% or the COD of the decomposition liquid is lower than 5,000 mg / L. The judgment standard for straw decomposition reaching 50% is: the COD concentration of the partial decomposition liquid released from the decomposition liquid for the second time reaches or approaches 20,000mg / L, which is considered to be 50% straw decomposition. Taking into account the efficiency maximization in a relatively short time, the decomposition reaction can be terminated at this time. In actual circumstances, the decomposition time is continued to be extended to maximize the decomposition effect until the COD of the decomposition liquid is lower than 5,000 mg / L and the decomposition reaction is stopped. This situation usually takes a long time. Taking into account the time, cost and effect, it is generally not recommended to use this decomposition termination condition.

[0021] After the microbial growth reaches its stable stage or the temperature inside the straw rises by more than 50°C, the submersible pump is activated to extract the bottom liquid of the decomposition solution and then return it to the liquid surface or onto the straw. Specifically, when the basket sinks into the decomposition solution, the submersible pump is activated to extract the bottom liquid of the decomposition solution and then return it to the liquid surface. When the basket is lifted out of the decomposition solution, the submersible pump is activated to extract the bottom liquid of the decomposition solution and then return it to the straw. This timely return of temperature through temperature monitoring lowers the fermentation temperature, prevents the temperature of the solid portion of the straw from rising beyond the microbial tolerance range, and ensures the environment for continued microbial growth and enzyme production.

[0022] The white-rot fungi in the composite microbial inoculant are cultured in PDA medium at 28°C for 48 hours and then acclimated in an acclimation medium at 30°C for 72 hours. The acclimation medium contains a carbon source of glucose or brown sugar, a nitrogen source of urea, ammonium sulfate, and soy milk, inorganic salts of magnesium sulfate and dipotassium hydrogen phosphate, a complex of vitamins, an alkaline ozone treatment solution, and a fly ash leachate, wherein the carbon-nitrogen ratio is 1:1-2:1. The alkaline ozone treatment solution is referenced in Invention Patent 200710139494.1. The fly ash leachate can be any conventional commercially available product. Trichoderma viride and Aspergillus niger can be cultured in conventional culture medium, which is outside the scope of the present invention and will not be described in detail.

[0023] The carbon-nitrogen ratio of traditional white rot fungi culture is usually 20-30:1. There is also a high-carbon culture (carbon-nitrogen ratio of 80-100:1). The present invention uses a carbon-nitrogen ratio different from conventional culture to expand the culture of white rot fungi. The present invention uses a high-nitrogen and low-carbon culture medium and culture solution. The purpose is to enable the white rot fungi to quickly pass through the adaptation period and enter the logarithmic growth period. The experimental results show that the cell volume of the cultured white rot fungi can reach 3×10 9 The time required is shortened from about 5 days in conventional methods to 1-2 days.

[0024] The acclimated white rot fungi were mixed with viride and niger in a ratio of 1:0.5:0.1 to form a composite microbial agent. The culture was expanded using an expansion medium. The expansion medium consisted of 10 g / L brown sugar, 100 ml / L soy milk, 2 g / L urea, 2 g / L ammonium sulfate, 2 g / L bran, and 900 ml / L alkaline ozone treatment solution. The preparation of the alkaline ozone treatment solution is described in invention patent 200710139494.1.

[0025] Since the most suitable environmental conditions for microbial growth and reproduction are in a liquid state, they can only produce large amounts of enzymes under conditions of nutrient restriction and the presence of inducers. However, the enzyme and substrate (straw cellulose) need to be in full contact to complete the enzymatic decomposition process. In a solid state, the mass transfer contact between the enzyme and the substrate (straw cellulose) is poor. Therefore, the present invention adopts a composite addition of three types of microorganisms and an alternating solid-liquid method to achieve optimal conditions for bacterial growth and enzyme production: after the nutrient restriction and enzyme production in the solid-state fermentation stage, the straw carrying a large amount of enzyme is immersed in a liquid, ensuring mass transfer contact between the enzyme and the substrate, which greatly improves the decomposition efficiency. The COD content in the decomposition liquid is highly correlated with the straw decomposition rate. The higher the straw decomposition rate, the higher the COD content in the decomposition liquid. According to the experimental results, after straw was soaked in clean water for six days, the COD of the decomposition liquid was only 2000-3000 mg / L; after six days of treatment using conventional decomposition methods, the COD of the decomposition liquid reached about 10,000 mg / L; after six days of treatment using solid-liquid alternation, the COD of the decomposition liquid could reach more than 22,000 mg / L, which is 1-2 times higher than the COD of the traditional method.

[0026] The decomposed straw residue is returned to the fields to improve arable soil. The decomposed liquid enters a storage tank and is mixed with livestock and poultry manure in a proportionate and thorough mixing process. The principle for the mixing ratio of the decomposed liquid to livestock and poultry manure is to determine the mixture's carbon-nitrogen ratio to be 25:1. The mixture undergoes solid-liquid separation, and large solid particles are composted. The liquid suspension is pumped through an inlet pipe to the bottom of a pressure swing acidification tank. After solid-liquid separation, the suspension is free of large solid particles and has a COD of approximately 25,000 mg / L. In the acidification tank, the mixed liquid undergoes anaerobic fermentation under the action of microorganisms, primarily acid-producing bacteria, breaking down large molecules in the liquid into small molecules such as acetic acid, while also producing gases such as hydrogen and carbon dioxide.

[0027] Both the acidification tank and the methanogen tank have a pressure tolerance greater than 0.44 MPa. As fermentation gas is produced, the pressure within the tanks gradually increases to 0.3-0.4 MPa for anaerobic fermentation. The stable operating pressure of the acidification tank and methanogen fluctuates between 0.3 and 0.4 MPa. When the pressure in the acidification tank reaches 0.4 MPa, the gas in the acidification tank is passed through a gas pipeline to the methanogen tank, stirring the liquid in the methanogen tank until the pressure in the acidification tank drops to 0.3 MPa. After acidification is complete, the pressure in the acidification tank is higher than that in the methanogen tank. The acidified liquid enters the methanogen tank through a pressure differential inlet pipe. After the acidification liquid is introduced, the pressure differential inlet valve is closed, and the gas valve is opened. Carbon dioxide and hydrogen at the top of the acidification tank enter the methanogen tank through the gas pipeline. The gas valve is then closed. Methanogens thrive in this acidified atmosphere of carbon dioxide, hydrogen, and acidification, completing the methanogenic fermentation process. After fermentation is completed, the pressure in the methane production tank will rise, and the constant pressure exhaust valve will be opened. The biogas produced during the fermentation process will be transported to the biogas tank through the exhaust pipe after dehydration and desulfurization. After the gas transmission is completed, the drain pipe will be opened to discharge the clear liquid in the upper part of the inner cavity of the methane production tank into the biogas temporary storage tank, and returned to the field after dilution. The remaining sludge and other parts will be discharged through the sludge pipe.

[0028] Compared to existing technologies, the present invention utilizes a composite microbial community and a repeated alternating solid-liquid cycle to achieve both increased straw decomposition efficiency and accelerated decomposition. The decomposed liquid from the straw is mixed with livestock and poultry manure, then undergoes solid-liquid separation. The suspended liquid enters a pressure-switching acidification tank for anaerobic acid and hydrogen production. The fermented liquid then enters a pressure-switching methane production tank via a pressure differential for anaerobic methane production. This pressure differential is used to transfer the liquid from the acidification tank to the methane tank, saving energy. The entire fermentation process produces no atmospheric emissions, preventing environmental pollution, while ultimately producing a high level of methane gas.

[0029] The above is only a preferred embodiment of the present invention. It should be pointed out that for those skilled in the art, several changes and improvements can be made without departing from the overall concept of the present invention, and these should also be regarded as the scope of protection of the present invention.

Claims

1. A method for biomass mixed pressure-switch two-phase anaerobic fermentation, characterized by: The process includes the following steps: straw crushing → alkaline ozone treatment → solid-liquid alternating decomposition → mixing of straw decomposition liquid with livestock and poultry manure → solid-liquid separation → suspended liquid enters the pressure swing acidification tank for anaerobic acid and hydrogen production fermentation → liquid enters the pressure swing methane production tank based on pressure difference for anaerobic methane production fermentation → biogas enters the biogas tank after dehydration and desulfurization, and the biogas liquid is diluted and returned to the field; The specific solid-liquid alternating decomposition is as follows: the decomposition liquid is prepared according to the weight ratio of straw: composite microbial agent: water = 1:0.05: (10-20), the straw treated with alkali ozone is placed in the hanging basket, the hanging basket is sunk into the decomposition liquid, the bottom of the decomposition liquid is aerated with oxygen, the amount of composite microbial cells increases rapidly, and the amount of composite microbial cells is greater than 10 8 After the amount of complex microbial cells in the decomposition liquid reaches 10 u / mL, the hanging basket is lifted out of the decomposition liquid. The straw is in a solid-state fermentation state. The growth of bacteria attached to the straw consumes carbon and nitrogen sources, leading to a carbon and nitrogen-limited state, thereby stimulating the complex microorganisms to produce enzymes. After the LiP enzyme activity is greater than 10 u / mg, the hanging basket is submerged in the decomposition liquid again. Based on the amount of complex microbial cells in the decomposition liquid and the LiP enzyme activity, the operation of immersing the hanging basket in the liquid and lifting it out of the liquid is repeated. The decomposition is stopped when the straw decomposition reaches more than 50% or the COD of the decomposition liquid is less than 5000 mg / L. The composite microbial agent includes white rot fungi, green Trichoderma and black Aspergillus, and the three fungi are mixed according to the bacterial volume of 1:0.5:0.1; The white rot fungi in the composite microbial agent are cultured in a PDA medium at 28°C for 48 hours, and then acclimated in an acclimation medium at 30°C for 72 hours. The acclimation culture medium contains carbon sources such as glucose or brown sugar, nitrogen sources such as urea, ammonium sulfate and soy milk, inorganic salts such as magnesium sulfate and dipotassium hydrogen phosphate, complex vitamins, alkaline ozone treatment liquid, and fly ash leaching liquid, wherein the carbon-nitrogen ratio is 1:1-2:

1.

2. The method for biomass mixed pressure-switch two-phase anaerobic fermentation according to claim 1, characterized in that: The conditions for lifting the hanging basket out of the decomposition liquid again are that the hanging basket is immersed in the decomposition liquid for more than 4 hours and the amount of composite microorganisms is greater than 10 8 / mL, and the condition for sinking the basket into the decomposition solution again is that the enzyme activity is greater than 10u / mg.

3. The method for biomass mixed pressure-switch two-phase anaerobic fermentation according to claim 1, characterized in that: When the COD concentration in the decomposition liquid is greater than 20,000 mg / L, release part of the decomposition liquid and add an equal amount of clean water and nitrogen source.

4. The method for biomass mixed pressure-switch two-phase anaerobic fermentation according to claim 1, characterized in that: The mixing ratio of straw decomposition liquid and livestock and poultry manure is such that the carbon-nitrogen ratio of the mixed mixture is 25:

1.

5. The method for biomass mixed pressure-switch two-phase anaerobic fermentation according to claim 1, characterized in that: The pressure bearing capacity of the acidification tank and the methane production tank is greater than 0.44MPa. The pressure inside the tank gradually increases to 0.3-0.4MPa as the fermentation gas is produced, and anaerobic fermentation is carried out. The stable operating pressure of the acidification tank and the methane production tank fluctuates between 0.3-0.4MPa.

6. The method for biomass mixed pressure-switch two-phase anaerobic fermentation according to claim 5, characterized in that: When the pressure in the acidification tank reaches 0.4MPa, the gas in the acidification tank is introduced into the methane production tank to stir the liquid in the methane production tank until the pressure in the acidification tank drops to 0.3MPa.

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