CN114195560A - Method for co-producing fiber, biogas and bio-organic fertilizer by using agricultural straws - Google Patents

Abstract

The invention discloses a method for co-producing fiber, biogas and bio-organic fertilizer by using agricultural straws and livestock and poultry manure as raw materials, firstly processing the agricultural straws by adopting a mechanical pulping method to obtain prepared waste, pulping waste liquid and fiber, then mixing the prepared waste, the pulping waste liquid and the livestock and poultry manure for fermentation to obtain bio-biogas, biogas slurry and biogas residues, and composting the biogas residues to obtain solid bio-organic fertilizer, wherein the biogas slurry is liquid bio-organic fertilizer and is directly used. A large number of experiments prove that the waste liquid generated in the chemical mechanical fiber manufacturing process is added with a proper amount of prepared waste for fermentation, a large amount of biogas can be generated, and simultaneously biogas slurry and biogas residues generated in biogas fermentation can be used for producing bio-organic fertilizers.

Description

Method for co-producing fiber, biogas and bio-organic fertilizer by using agricultural straws

Technical Field

The invention relates to the field of clean treatment and efficient utilization of crop straws, in particular to a method for co-producing fibers, biological methane and a biological organic fertilizer by using agricultural straws.

Background

China is a big agricultural country, the annual grain yield and the annual consumption are the first world, a large amount of crop straws are produced, the annual production amount exceeds 7 hundred million tons, an effective large-scale utilization way is lacked, and the straws are mainly returned to the field, buried and incinerated at present, so that the environment is polluted, and the resource waste is caused. The comprehensive utilization of crop straws has become a difficult problem which needs to be solved urgently in developing green agriculture and building new rural areas in China.

The biomass biogas fermentation refers to a process for producing biogas by taking various organic wastes such as livestock manure, crop straws, food wastes, agricultural and sideline product processing and the like as raw materials. The traditional biogas fermentation is carried out under low concentration (the concentration is generally lower than 10%), and most of the livestock manure is used as a main raw material, and a large amount of water resources are consumed in the fermentation process; meanwhile, sewage discharged in the process of biogas fermentation is difficult to treat, secondary pollution is easy to cause, and particularly for large-scale biogas fermentation plants, the existing biogas production by using crop straws as main raw materials has no mature process and industrial application.

Pulping and papermaking are important components of national economy, and China consumes more than 1 hundred million tons of paper pulp every year. However, the pulping raw materials in China are seriously deficient, the external dependence degree is over 50 percent, and certain threats are caused to national economy and national safety. The traditional pulping and papermaking raw materials mainly comprise wood, such as poplar and eucalyptus, and under the background that the pulping raw materials are in short supply and the crop straws are difficult to treat, the research on the pulping and papermaking process by taking the agricultural straws as the raw materials becomes a hotspot. The existing agricultural straw papermaking production process mainly comprises the steps of material preparation, steaming, chemical preimpregnation, disc grinding and the like, wherein a large amount of solid waste and liquid waste are generated in the steps of material preparation, steaming, chemical preimpregnation and the like and are difficult to treat, and the solid waste is mainly treated in an incineration mode at present to cause serious pollution; the waste liquid is treated by combining anaerobic fermentation with Fenton deep oxidation, so that the cost is high, the treatment of solid waste and liquid waste in the pulping and papermaking process becomes the most important problem which hinders the development of the industry, and a clean treatment way is urgently needed to be found. .

The crop straw belongs to a valuable biomass resource in an agricultural ecological system, and the comprehensive utilization of the crop straw resource has great significance for promoting the income increase of farmers, environmental protection, resource saving and sustainable development of agricultural economy. Therefore, how to use the agricultural straws as raw materials to co-produce products such as fibers, biogas and biological fertilizer and realize the clean treatment, the full quality and the high-efficiency utilization of the agricultural straws is an important problem in front of people.

Disclosure of Invention

Aiming at the technical problems of high treatment cost, high pollution, difficult treatment and the like of agricultural straws, the invention aims to provide a method for co-producing fiber, biological methane and a biological organic fertilizer by the agricultural straws, so as to realize the clean treatment, full quality and high-efficiency utilization of the agricultural straws.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows:

a method for co-producing fiber, biogas and bio-organic fertilizer by using agricultural straw and livestock and poultry manure as raw materials comprises the steps of firstly treating the agricultural straw by adopting a mechanical pulping method to obtain prepared waste, pulping waste liquid and fiber, then mixing the prepared waste, the pulping waste liquid and the livestock and poultry manure for fermentation to obtain bio-biogas, biogas slurry and biogas residue, and carrying out composting treatment on the biogas residue to obtain solid bio-organic fertilizer, wherein the biogas slurry is liquid bio-organic fertilizer and is directly used.

The method for co-producing the fiber, the biological methane and the biological organic fertilizer by the agricultural straw comprises the following steps:

1) pretreating agricultural straws to obtain grass pieces and feed preparation wastes;

2) cleaning, steaming and softening and treating the grass pieces by a double-screw extruder to obtain steaming liquid and steaming materials;

3) pre-impregnating the steamed material, then mechanically grinding the steamed material into thick liquid, and washing and sending the ground material to obtain fiber and high-concentration washing liquid;

4) mixing the prepared waste, the steaming liquid, the high-concentration washing liquid and the excrement, adjusting the C/N ratio and the pH value, performing anaerobic fermentation, and collecting methane; after fermentation, carrying out solid-liquid separation to obtain biogas slurry and biogas residues; the biogas slurry is a liquid organic fertilizer;

5) and carrying out composting treatment on the biogas residues to obtain the solid biological organic fertilizer.

In the method for coproducing the fiber, the biological methane and the biological organic fertilizer by the agricultural straw, the steam temperature of a steaming section is 140 ℃ for 100-.

The method for co-producing the fiber, the biological methane and the biological organic fertilizer by the agricultural straws comprises the pre-impregnation stage process, wherein the using amount of sodium hydroxide is 1-10%, the material concentration is 10-30%, the reaction temperature is 90-120 ℃, and the heat preservation time is 10-60 min.

In the method for co-producing the fiber, the biological methane and the biological organic fertilizer by the agricultural straw, a double-screw extruder is adopted in a steaming section for solid-liquid separation; the chemical prepreg is disc milled and then washed with a small amount of water to obtain fibers and a high consistency scouring slurry.

The method for coproducing the fiber, the biological methane and the biological organic fertilizer by the agricultural straws has the system solid concentration of 5-10 percent, the C/N ratio of 20-30 and the pH value of 7.8-8.4, and the anaerobic fermentation is carried out in a sealed manner.

The method for co-producing the fiber, the biological methane and the biological organic fertilizer by the agricultural straws has the methane fermentation conditions of 35-40 ℃, 7.8-8.4 of pH value and 30-60 days of fermentation time.

The method for co-producing the fiber, the biological methane and the biological organic fertilizer by using the agricultural straws comprises rice straws, wheat straws, corn straws and cotton stalks.

The method for co-producing the fiber, the biological methane and the biological organic fertilizer by the agricultural straw comprises the following steps:

1) cutting and screening the agricultural straws, removing the prepared wastes such as leaves, ears and barks in the agricultural straws and obtaining grass sheets;

2) washing the grass slices with water to remove impurities, dehydrating to obtain a washing material, precipitating washing water to remove impurities such as dust, sandy soil and the like, and repeatedly using the washing water for washing the grass slices;

3) transferring the water-washed material to a steaming bin, introducing 100-140 ℃ high-temperature steam, and preserving heat at 90-120 ℃ for 10-60min for steaming and softening; after steaming, performing solid-liquid separation by adopting a double-screw extruder to obtain steaming liquid and a steaming material;

4) adding sodium hydroxide which is 1-10% of the absolute dry weight into the steamed material, adding a proper amount of water to ensure that the concentration of a system solid is 10-30%, uniformly mixing, and inputting into a pre-impregnation bin; introducing 100-140 ℃ high-temperature steam into the pre-impregnation bin, and pre-impregnating for 10-60min at 90-120 ℃; a prepreg material is obtained.

5) Inputting the preimpregnated material into a disc mill for pulping, wherein the distance between a grinding disc and a grinding disc is 0.1mm in the pulping process, and carrying out disc milling treatment for 4 times to obtain agricultural straw fibers with different freeness; then, carrying out high-concentration pulp washing, diversion, washing, screening and other steps to obtain pulp fibers;

6) mixing the steaming liquid and the high-concentration washing liquid, adding the prepared waste, adjusting the concentration of the system to 5-10%, supplementing excrement and mixing, adjusting the C/N to 20-30, adjusting the pH value to 7.8-8.4, sealing the system, carrying out anaerobic fermentation at 35-40 ℃ for 1-2 months, and collecting biogas;

7) after fermentation is finished, carrying out solid-liquid separation to obtain biogas slurry and biogas residues; transporting the biogas residues to a storage yard, naturally fermenting at 20-30 ℃ for 10-15d, and air-drying to obtain a solid bio-organic fertilizer; the biogas slurry is liquid organic fertilizer.

The fiber, the biological methane and the biological organic fertilizer obtained by the method for co-producing the fiber, the biological methane and the biological organic fertilizer by the agricultural straw.

According to the method for co-producing the fiber, the biological methane and the biological organic fertilizer by the agricultural straw, in the production of the paper pulp fiber, the agricultural straw is firstly prepared to remove the components such as the mixed cells and the like which cannot be used for producing the fiber, and the material and the prepared waste are collected. The material is firstly washed by water to remove impurities such as ash and dust in the material, and then high-temperature steam is introduced for steaming and softening. Performing solid-liquid separation on the steamed material by adopting a double-screw extruder, and obtaining a steamed material and a steaming liquid; adding a proper amount of sodium hydroxide into the steamed material, and then introducing high-temperature steam again to carry out chemical pre-impregnation; the preimpregnated material is beaten by a disc mill, and the pulp fiber is obtained by the steps of high-concentration pulp washing (generating high-concentration pulp washing liquid), dispatching, washing, screening and the like of the material treated by the disc mill. In the anaerobic fermentation process, after the steaming liquid and the high-concentration washing liquid are mixed, a proper amount of straw preparation waste is added, a proper amount of livestock manure is supplemented, and fermentation is carried out in a sealed manner; after fermentation is finished, carrying out solid-liquid separation, and carrying out composting treatment on biogas residues and then air-drying to obtain a solid bio-organic fertilizer; the biogas slurry is a liquid organic fertilizer. A large number of experiments prove that waste liquid (steaming liquid and high-concentration washing slurry) in the chemical mechanical method fiber manufacturing process is mixed, a proper amount of prepared waste (solid waste) is added for fermentation, a large amount of methane can be generated, and simultaneously, biogas slurry and biogas residue obtained by methane fermentation can be used for producing bio-organic fertilizer.

Has the advantages that: compared with the prior art, the method adopts agricultural straws as raw materials, comprehensively utilizes liquid waste (steaming liquid and high-concentration washing liquid) and solid waste (material preparation waste) generated in the production process while producing the paper pulp fibers, fully utilizes the characteristics of fiber production waste liquid (namely, pH is alkalescent, and the waste liquid is rich in carbohydrate), and realizes the efficient and high-quality preparation of the methane. A large number of experiments prove that fibers are obtained by pulping agricultural straws by a chemical mechanical method, waste liquid generated in the pulping process is used as a substrate, feed-prepared waste is added to perform anaerobic fermentation to prepare biogas, the generation amount of the biogas is greatly increased, biogas residues and biogas slurry generated after biogas fermentation are natural biomass organic fertilizers, and the technical indexes of the biogas residues and the biogas slurry exceed the corresponding national standards. Therefore, the method realizes the whole quality and resource utilization of the agricultural straw, is an environment-friendly and high-benefit industrial production process, and has very good industrial application value.

Drawings

FIG. 1 is a process flow diagram of the present application;

FIG. 2 is a graph showing the results of the amount of biogas generated by the process;

fig. 3 is a graph showing the results of methane content in biogas.

Detailed Description

The invention is further illustrated by the following examples. The examples are intended to illustrate, but not to limit, the invention. Those of ordinary skill in the art will understand that these embodiments do not limit the invention in any way, and that appropriate modifications can be made without departing from the spirit and scope of the invention.

According to the method for co-producing the fiber, the biological methane and the biological organic fertilizer by using the agricultural straw, the process flow is shown in figure 1, the agricultural straw and the livestock manure are used as raw materials, the mechanical pulping method is firstly adopted to treat the agricultural straw to obtain material preparation waste, pulping waste liquid and the fiber, then the material preparation waste, the pulping waste liquid and the livestock manure are mixed and fermented to obtain the biological methane, the methane liquid and the methane residue, the methane residue is subjected to composting treatment to obtain the solid biological organic fertilizer, and the methane liquid is the liquid biological organic fertilizer and is directly used.

During specific production, according to the method for co-producing the fiber, the biological methane and the biological organic fertilizer by using the agricultural straw, in the production of the paper pulp fiber, the agricultural straw is firstly prepared to remove the components such as the mixed cells and the like which cannot be used for fiber production, and the materials and prepared waste are collected. The material is firstly washed by water to remove impurities such as ash and dust in the material, and then high-temperature steam is introduced for steaming and softening. Performing solid-liquid separation on the steamed material by adopting a double-screw extruder, and obtaining a steamed material and a steaming liquid; adding a proper amount of sodium hydroxide into the steamed material, and then introducing high-temperature steam again to carry out chemical pre-impregnation; the preimpregnated material is beaten by a disc mill, and the pulp fiber is obtained by the steps of high-concentration pulp washing (generating high-concentration pulp washing liquid), dispatching, washing, screening and the like of the material treated by the disc mill. In the anaerobic fermentation process, after the steaming liquid and the high-concentration washing liquid are mixed, a proper amount of straw preparation waste is added, a proper amount of livestock manure is supplemented, and fermentation is carried out in a sealed manner; after fermentation is finished, carrying out solid-liquid separation, and carrying out composting treatment on biogas residues and then air-drying to obtain a solid bio-organic fertilizer; the biogas slurry is a liquid organic fertilizer. The main core technology is as follows:

1. the agricultural straws comprise rice straws, wheat straws, corn straws, cotton stalks and the like, and when the agricultural straws are pretreated, the agricultural straws are cut and screened, so that material preparation wastes such as leaves, ears, skins and the like in the agricultural straws are removed, and grass sheets are obtained; then washing the grass pieces to remove impurities, dehydrating to obtain a washing material, precipitating the used water to remove impurities such as dust, sandy soil and the like, and repeatedly washing the grass pieces; all raw materials of the process are classified and treated, the used water is reused, no new pollutants are generated, and no waste materials are generated.

2. Mechanical pulping: steaming and softening the grass pieces, and treating the grass pieces by using a double-screw extruder to obtain steaming liquid and steaming materials; pre-impregnating the steamed material, then mechanically grinding the steamed material into thick liquid, and washing and sending the ground material to obtain fiber and high-concentration washing liquid; the steam temperature of the steaming section is 140 ℃ under the temperature of 100-; after steaming, performing solid-liquid separation by adopting a double-screw extruder to obtain steaming liquid and a steaming material; during the pre-impregnation period, the using amount of sodium hydroxide is 1-10%, the material concentration is 10-30%, the reaction temperature is 90-120 ℃, and the temperature is kept for 10-60 min; the chemical prepreg is disc milled and then washed with a small amount of water to obtain fibers and a high consistency scouring slurry. Adding sodium hydroxide which is 1-10% of the absolute dry weight into the steamed material, adding a proper amount of water to ensure that the concentration of a system solid is 10-30%, uniformly mixing, and inputting into a pre-impregnation bin; introducing 100-140 ℃ high-temperature steam into the pre-impregnation bin, and pre-impregnating for 10-60min at 90-120 ℃; obtaining a prepreg material; inputting the preimpregnated material into a disc mill for pulping, wherein the distance between a grinding disc and a grinding disc is 0.1mm in the pulping process, and carrying out disc milling treatment for 4 times to obtain agricultural straw fibers with different freeness; then, carrying out high-concentration pulp washing, diversion, washing, screening and other steps to obtain pulp fibers;

3. and (3) fermenting to produce biogas: mixing the prepared waste, steaming liquid, high-concentration washing liquid and excrement, adjusting the C/N ratio and the pH value, wherein the concentration of a solid matter in the system is 5-10%, the C/N ratio is 20-30, and the pH value is 7.8-8.4, and sealing for anaerobic fermentation; the biogas fermentation conditions are 35-40 deg.C, pH 7.8-8.4, and fermentation time 30-60 d. Collecting biogas; after fermentation, carrying out solid-liquid separation to obtain biogas slurry and biogas residues; the biogas slurry is liquid organic fertilizer.

4. Preparing a biological organic fertilizer: transporting the biogas residues to a storage yard, naturally fermenting at 20-30 ℃ for 10-15d, and air-drying to obtain a solid bio-organic fertilizer; the biogas slurry is liquid organic fertilizer.

The method adopts agricultural straws as raw materials, comprehensively utilizes liquid waste (steaming liquid and high-concentration washing liquid) and solid waste (material preparation waste) generated in the production process while producing paper pulp fibers, fully utilizes the characteristics of fiber production waste liquid (namely, pH alkalescence and carbohydrate-rich waste liquid), and realizes the efficient and high-quality preparation of the methane. A large number of experiments prove that fibers are obtained by pulping agricultural straws by a chemical mechanical method, waste liquid generated in the pulping process is used as a substrate, feed-prepared waste is added to perform anaerobic fermentation to prepare biogas, the generation amount of the biogas is greatly increased, biogas residues and biogas slurry generated after biogas fermentation are natural biomass organic fertilizers, and the technical indexes of the biogas residues and the biogas slurry exceed the corresponding national standards. Therefore, the method realizes the whole quality and resource utilization of the agricultural straw, is an environment-friendly and high-benefit industrial production process, and has very good industrial application value.

Example 1

A method for co-producing fiber, biogas and bio-organic fertilizer by agricultural straws comprises the following specific steps:

1) the straw is cut and screened, and the prepared wastes such as leaves, spikes, barks and the like are removed, and the straw pieces are obtained.

2) Washing the grass slices with water to remove impurities, dewatering to obtain washed materials, precipitating the used water to remove impurities such as dust, sandy soil and the like, and repeatedly using the water for washing the grass slices.

3) Transferring the water-washed material to a steaming bin, introducing high-temperature steam at 110 ℃, preserving the heat at 95 ℃ for 30min, and steaming and softening; after steaming, a double-screw extruder (TSPI) is adopted for solid-liquid separation to obtain steaming liquid and steaming materials, and biochemical indexes of the steaming liquid are detected.

4) Adding sodium hydroxide equivalent to the absolute dry weight of 4% into the steamed material, supplementing a proper amount of tap water, adjusting the solid concentration of the system to be 30%, uniformly mixing, and inputting into a pre-impregnation bin. Introducing high-temperature steam of 110 ℃ into the prepreg bin, and keeping the temperature at 95 ℃ for prepreg for 30 min. After the pre-impregnation, a pre-impregnated material was obtained.

5) The preimpregnated material is input into a disc mill, pulping is carried out under the condition that the distance between a grinding disc and a grinding disc is 0.1mm, and the disc mill is carried out for 4 times (sampling analysis is carried out after each grinding, and the result is shown in table 1), so that straw fibers with different freeness are obtained. Then, carrying out high-concentration pulp washing (obtaining high-concentration pulp washing liquid), dispatching, washing, screening and other steps to obtain paper pulp fibers; and detecting biochemical indexes of the high-concentration washing slurry.

TABLE 1 agricultural straw fiber Properties

Item	Disc-grinding for 1 time	Disc-grinding for 2 times	Disc-grinding for 3 times	Disc-grinding for 4 times
					Canadian freeness (CSF), ml	390	240	160	110
Tightness, g/cm3	0.42	0.44	0.50	0.54
					Bulk, cm3/g	2.39	2.26	2.00	1.84
Burst number, kPa.m2/g	1.30	1.75	1.83	1.90
					Number of tears, mN.m2/g	5.75	5.03	4.87	4.39
Elongation percentage of%	0.9	1.0	1.0	1.1
					Tensile energy absorption, J/m2	9.21	11.78	13.88	13.88
Tensile index, N.m/g	28.58	36.58	41.75	45.65
					Length of fracture km	2.650	3.222	3.879	4.251

The properties of the straw fiber produced by the method are shown in table 1. As can be seen from table 1, at 4% sodium hydroxide dosage, the fiber freeness decreased from 390 to 240, 160 and 110mL with increasing disc count, indicating a higher degree of fiber dissociation; meanwhile, the bulk of the fiber handsheet is gradually reduced, which is mainly caused by that the agricultural straw fibers are dissociated in the pulping process to expose more hydroxyl groups, so that the connection between the fibers is increased; the mechanical properties of the handsheets improved with fiber dissociation, increasing from 28.58 Nm/g with one lap to 45.65 Nm/g with 4 laps, taking tensile strength as an example. The agricultural straw fiber treated by 2-3 times of disc grinding can be found to have mechanical strength meeting the requirements of corrugated paper and boxboard paper, and can be used for preparing the paper products.

TABLE 2 pH of the fiber production waste stream and the respective carbohydrate content

	pH	Glucose (g/L)	Xylose (g/L)	Oligosaccharide (g/L)
					Steaming liquid	5.9	0.15	0.69	1.32
High-concentration washing liquid	6.7	0.68	0.95	5.67

In the agricultural straw fiber production process, the properties of the waste liquid and the content of carbohydrates in the waste liquid at each stage are shown in table 2. As can be seen from Table 2, the wastewater at each stage is weakly acidic, 5.9 and 6.7 respectively, mainly because the acetyl part of hemicellulose is stripped off due to high temperature, and weak acids such as acetic acid are formed. After steaming and sodium hydroxide impregnation, part of carbohydrate is dissolved out, wherein the detectable carbohydrate mainly comprises glucose, xylose and part of oligosaccharide. In the steaming stage, wheat straw is softened at high temperature, but the dissolved carbohydrates are less, namely 0.15g/L of glucose, 0.69g/L of xylose and 1.32g/L of oligosaccharide; the carbohydrate digestion mainly takes place in the sodium hydroxide impregnation stage, where sodium hydroxide attacks hemicellulose and cellulose, causing partial degradation thereof, and the degradation products are mainly present in the form of oligomers, with oligomer content of 5.67g/L in the high-strength wash liquor, and furthermore 0.68g/L and 0.95g/L for glucose and xylose, respectively. In conclusion, during the fiber production process, carbohydrates, especially hemicellulose is greatly degraded, and degradation products mainly exist in the form of oligomers, so that the degradation products are high-quality microbial carbon sources.

6) Mixing the steaming liquid and the high-concentration washing liquid, taking 2.5L of mixed liquid, adding the prepared waste into the mixed liquid to enable the solid concentration of the system to be 8%, supplementing a proper amount of livestock and poultry manure to adjust the C/N ratio of the system to be 25, adjusting the pH of the system to be 8.1 by adopting a sodium hydroxide solution, inputting the system into a fermentation tank, sealing, carrying out anaerobic fermentation at 38 ℃ for 60 days, and detecting the generation amount of methane and the methane content in the methane during the fermentation.

The amount of biogas generated in the anaerobic fermentation process of the fiber production waste liquid is shown in figure 2. As can be seen from FIG. 2, the biogas fermentation by using the waste liquid (steaming liquid and high-concentration washing slurry) is remarkable, and the gas production process has 2 times of peak periods. In the aspect of gas production speed, the previous week is a strain adaptation period, and the gas production rate in the process is low; after the strain adaptation period, the gas production rate gradually rises, and reaches a stable value of 500 mL/day at 25 th day, which is the first gas production peak period, and the process lasts for 10 d; beginning on day 35, gas production rose rapidly, probably due to degradation of the feed stock waste added, and the process continued to day 50d and reached a peak of 863 mL/day, with a slight decrease thereafter. Compared with the traditional process for preparing the methane by fermentation (water replaces the steaming liquid and the high-concentration washing slurry in the method, and other parameters are the same), the daily gas production amount of the process is obviously higher, mainly because the waste liquid is rich in low-molecular-weight carbohydrate, methane bacteria can be directly utilized, and the gas production efficiency is high.

The content of the effective component methane in the biogas during the fermentation process is changed as shown in fig. 3. As can be seen from fig. 3, the methane content of the gas generally has a steady rising trend and 2 stationary phases occur. In a system using the fiber production waste liquid as a fermentation medium, the methane content in the biogas can reach 25% at the beginning of fermentation (the next day), but the methane content is not detected in the initial stage of the traditional process. Then, the methane content is at a relatively stable level, kept at about 30%; after fermenting for 10 days, the methane content in the methane rises again and reaches 56 percent in 14 days; after two weeks, the methane content in the gas slowly rises, and on the 24 th day of fermentation, the methane content in the biogas reaches the maximum value, which is 69%; thereafter, the methane content of the gas gradually decreased and finally decreased to 41% (30 days). The results show that in the anaerobic fermentation process, the microorganisms can rapidly utilize carbohydrates in the waste liquid as carbon sources to produce methane. Compared with the traditional method which uses water as a medium, the methane content is obviously higher, which shows that the methane produced by the method has higher quality.

7) After fermentation is finished, performing solid-liquid separation in a centrifugal mode to obtain biogas slurry and biogas residues.

TABLE 4 heavy metal and organic matter content of biogas slurry

Index (I)	The product content	National standard (NY1110)
			Total arsenic (g/L)	0.005	0.01
Total mercury (g/L)	0.004	0.005
			Total lead(g/L)	0.015	0.05
Total chromium (g/L)	0.035	0.05
			Humus (%)	4.1	3.0

The contents of common heavy metals and humus in the biogas slurry are detected, and the results are shown in table 4. As can be seen from Table 4, the total arsenic, total mercury, total lead and total chromium contents in the biogas slurry are respectively 0.005, 0.004, 0.015 and 0.035g/L, and the contents are lower than the national standard (the limit requirements of the water-soluble fertilizers of mercury, arsenic, cadmium, lead and chromium of NY 1110-2010); in addition, the content of humus in the biogas slurry is 4.1 percent and is higher than the national standard by 3.0 percent. The result shows that the liquid organic fertilizer produced by the process has the safety reaching the national standard and is rich in humus required by plant growth.

8) And (3) putting the biogas residues into a constant-temperature constant-humidity incubator with the temperature of 25 ℃ and the humidity of 50% for composting, turning the biogas residues once every 12h in the composting process to promote oxygen circulation and microbial metabolic growth, and taking out the composted biogas residues after 10d and naturally drying to obtain the solid bio-organic fertilizer.

TABLE 5 index content of solid organic fertilizer

Index (I)	The product content	National standard
			Effective viable count (cfu)	0.53	0.2
Organic matter (%)	68.3	25
			Moisture (%)	11.2	15
pH	7.9	5.5-8.5
			Death rate (%) of roundworm egg	98.5	＞98

The obtained solid organic fertilizer was examined for each index, and the results are shown in table 5. As can be seen from Table 5, the water content of the organic fertilizer is only 11.2%, and the organic matter content is as high as 68.3%, which is far higher than 25% of the national standard (NY 884-; meanwhile, the organic fertilizer is prepared by an anaerobic fermentation method, so that the effective viable count of the organic fertilizer reaches 0.53cfu, which is higher than 0.2cfu of the national standard, and the prepared organic fertilizer can effectively improve the soil fertility and reduce the using amount of chemical fertilizers. In addition, the pH value of the anaerobic fermentation system is 8.1, and the pH value of the obtained organic fertilizer is close to that of the organic fertilizer and is 7.9; meanwhile, the death rate of roundworm eggs reaches 98.5 percent, which indicates that the organic fertilizer has little pollution to soil. In conclusion, all main indexes of the organic fertilizer reach the national standard, and the organic fertilizer has the potential of replacing common organic fertilizers in the market.

Claims (10)

1. A method for co-producing fiber, biogas and bio-organic fertilizer by using agricultural straw and livestock and poultry manure as raw materials is characterized in that the agricultural straw is treated by a mechanical pulping method to obtain material preparation waste, pulping waste liquid and fiber, then the material preparation waste, the pulping waste liquid and the livestock and poultry manure are mixed and fermented to obtain bio-biogas, biogas slurry and biogas residues, and the biogas residues are subjected to composting treatment to obtain solid bio-organic fertilizer, wherein the biogas slurry is liquid bio-organic fertilizer and is directly used.

2. The method for co-producing fiber, biogas and bio-organic fertilizer by using agricultural straws as claimed in claim 1, which is characterized by comprising the following steps:

1) pretreating agricultural straws to obtain grass pieces and feed preparation wastes;

2) cleaning, steaming and softening and treating the grass pieces by a double-screw extruder to obtain steaming liquid and steaming materials;

3) pre-impregnating the steamed material, then mechanically grinding the steamed material into thick liquid, and washing and sending the ground material to obtain fiber and high-concentration washing liquid;

4) mixing the prepared waste, the steaming liquid, the high-concentration washing liquid and the excrement, adjusting the C/N ratio and the pH value, performing anaerobic fermentation, and collecting methane; after fermentation, carrying out solid-liquid separation to obtain biogas slurry and biogas residues; the biogas slurry is a liquid organic fertilizer;

5) and carrying out composting treatment on the biogas residues to obtain the solid biological organic fertilizer.

3. The method for co-producing fiber, biogas and bio-organic fertilizer by using agricultural straws as claimed in claim 1, which is characterized in that: in the fiber production process, the steam temperature of the steaming section is 100-140 ℃, the steaming temperature is 90-120 ℃, and the heat preservation time is 10-60 min.

4. The method for co-producing fiber, biogas and bio-organic fertilizer by using agricultural straws as claimed in claim 1, which is characterized in that: during the pre-impregnation period, the sodium hydroxide is used in 1-10 wt%, the material concentration is 10-30 wt%, the reaction temperature is 90-120 deg.c, and the temperature is maintained for 10-60 min.

5. The method for co-producing fiber, biogas and bio-organic fertilizer by using agricultural straws as claimed in claim 1, which is characterized in that: the steaming section adopts a double-screw extruder to carry out solid-liquid separation; the chemical prepreg is disc milled and then washed with a small amount of water to obtain fibers and a high consistency scouring slurry.

6. The method for co-producing fiber, biogas and bio-organic fertilizer by using agricultural straws as claimed in claim 1, which is characterized in that: the anaerobic fermentation system has solid concentration of 5-10%, C/N ratio of 20-25, pH of 7.8-8.4, and sealed for anaerobic fermentation.

7. The method for co-producing fiber, biogas and bio-organic fertilizer by using agricultural straws as claimed in claim 1, which is characterized in that: the biogas fermentation conditions are 35-40 deg.C, pH 7.8-8.4, and fermentation time 30-60 d.

8. The method for co-producing fiber, biogas and bio-organic fertilizer by using agricultural straws as claimed in claim 1, which is characterized in that: the agricultural stalks include rice straws, wheat straws, corn stalks and cotton stalks.

9. The method for co-producing fiber, biogas and bio-organic fertilizer by using agricultural straws as claimed in claim 1, which is characterized by comprising the following steps:

1) cutting and screening the agricultural straws, removing the prepared wastes such as leaves, ears and barks in the agricultural straws and obtaining grass sheets;

2) washing the grass slices with water to remove impurities, dehydrating to obtain a washing material, precipitating with water to remove impurities such as dust, sandy soil and the like, and repeatedly washing the grass slices with water;

3) transferring the water-washed material to a steaming bin, introducing 100-140 ℃ high-temperature steam, and preserving heat at 90-120 ℃ for 10-60min for steaming and softening; after steaming, performing solid-liquid separation by adopting a double-screw extruder to obtain steaming liquid and a steaming material;

4) adding sodium hydroxide which is 1-10% of the absolute dry weight into the steamed material, adding a proper amount of water to ensure that the concentration of a system solid is 10-30%, uniformly mixing, and inputting into a pre-impregnation bin; introducing 100-140 ℃ high-temperature steam into the pre-impregnation bin, and pre-impregnating for 10-60min at 90-120 ℃; a prepreg material is obtained.

5) Inputting the preimpregnated material into a disc mill for pulping, wherein the distance between a grinding disc and a grinding disc is 0.1mm in the pulping process, and carrying out disc milling treatment for 4 times to obtain agricultural straw fibers with different freeness; then, carrying out high-concentration pulp washing, diversion, washing, screening and other steps to obtain pulp fibers;

6) mixing the steaming liquid and the high-concentration washing liquid, adding the prepared waste, adjusting the concentration of the system to 5-10%, supplementing excrement and mixing, adjusting the C/N to 20-25, adjusting the pH value to 7.8-8.4, sealing the system, carrying out anaerobic fermentation at 35-40 ℃ for 1-2 months, and collecting biogas;

7) after fermentation is finished, carrying out solid-liquid separation to obtain biogas slurry and biogas residues; transporting the biogas residues to a storage yard, naturally fermenting at 20-30 ℃ for 10-15d, and air-drying to obtain a solid bio-organic fertilizer; the biogas slurry is liquid organic fertilizer.

10. Fiber, biogas and bio-organic fertilizer obtained by the method for co-producing fiber, biogas and bio-organic fertilizer from agricultural straw according to any one of claims 1 to 9.

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