A method for comprehensive utilization of biogas slurry

Abstract

The present invention belongs to the field of fertilizers, and specifically relates to a method for comprehensive utilization of biogas slurry, which adopts aeration, fine filtration, re-aeration, bioflocculant flocculation, filter press, ultrafiltration, nanofiltration, and reverse osmosis technology, has high concentration efficiency, is environmentally friendly, and biogas slurry is fully utilized. Aeration, fine filtration, and re-aeration are performed before biogas slurry flocculation to reduce the content of particulate matter in biogas slurry, providing a feasible space for flocculation of bioflocculants. According to the characteristics of biogas slurry, a combination of NOC-1 and RL-2 is screened out from common bioflocculant combinations, which can significantly improve the bioflocculation effect of biogas slurry. The filter residue prepared after flocculation and filter press of the present invention is easy to disperse and has good air permeability after drying, and is aerobic fermented with humic acid powder and biogas residue, and bentonite and Bacillus subtilis are added, and low-temperature drying is performed to prepare a soil conditioner with high organic matter content, rich in biologically active substances such as humic acid and amino acids, and can effectively improve soil permeability and alleviate soil compaction.

Description

Technical Field

[0001] The invention belongs to the field of fertilizers, and in particular relates to a method for comprehensive utilization of biogas slurry. Background Art

[0002] With the advancement of science and technology, agriculture has also undergone earth-shaking changes. With the large-scale input of chemical fertilizers and pesticides, crop yields are getting higher and higher, but the soil quality is also declining year by year. The soil is severely compacted, organic matter is lost, the soil organic matter content is extremely low, the microorganisms are out of balance, and the soil's ability to retain water and fertilizer is getting worse and worse. Only by relying on the input of large amounts of chemical fertilizers and pesticides can the yield be maintained. Some lands are even uncultivable. Therefore, soil improvement is of great significance.

[0003] As one of the products of anaerobic fermentation of livestock and poultry manure, biogas slurry is rich in nitrogen, phosphorus, potassium nutrients, organic matter, humic acid, plant growth hormones, calcium, iron, zinc, boron, molybdenum and other trace elements, and is a good soil conditioner and fertilizer. However, due to its large, concentrated and continuous output, it is difficult to quickly consume it in a local area. Therefore, the consumption of biogas slurry is still a bottleneck in the development of the biogas industry. At present, the main directions of biogas slurry utilization are direct return to the field and concentration as fertilizer. Direct return to the field requires a large amount of land and supporting water conservancy facilities. It is more suitable for areas with developed planting industry and has obvious seasonality. Therefore, in large-scale biogas projects, its biogas slurry cannot be consumed in time by directly returning to the field. Concentration technology is to make the concentrated liquid into fertilizer through concentration, and the clear liquid is discharged in compliance with the standards. At present, concentration technologies are mainly divided into two types: one is sedimentation, filtration, ultrafiltration, nanofiltration, and reverse osmosis, and the other is flocculation, ultrafiltration, nanofiltration, and reverse osmosis. The first type has good treatment effect and retains the nutrients of the concentrated liquid to the greatest extent, but the treatment cost is extremely high, and the membrane requirements are high, and the membrane replacement frequency is high. The second type has lower costs, but the commonly used flocculants are mostly aluminum or polyacrylamide, which are highly corrosive and the monomers are toxic. The flocculated solids have high viscoelasticity and poor uniformity, making them difficult to use and generating new garbage, which does not meet the needs of environmentally friendly social development.

[0004] After searching, regarding the concentration of biogas slurry: CN2014102846560 discloses the physical concentration of biogas slurry: the biogas slurry is first subjected to sedimentation and filtration to remove macromolecular substances, and then enters the aeration tank for aeration, acidification and hydrolysis to decompose the remaining macromolecules, and then passes through a 30-mesh security filter and enters the ultrafiltration membrane for ultrafiltration. The ultrafiltration clear liquid is subjected to nanofiltration, and the nanofiltration clear liquid is subjected to reverse osmosis. The reverse osmosis clear liquid can meet the discharge standards, and different concentrated liquid fertilizers are obtained by mixing the ultrafiltration concentrate, nanofiltration concentrate and reverse osmosis concentrate in different proportions; CN201610520919 discloses the chemical concentration of biogas slurry: after the biogas slurry is precipitated and filtered, it enters the flocculation tank, and flocculation is carried out by adding polyacrylamide flocculants. The liquid is subjected to ultrafiltration, nanofiltration and reverse osmosis to meet the discharge standards, and the remaining concentrate is used as liquid fertilizer.

[0005] Regarding biogas flocculation, CN103396950A discloses the use of algae to flocculate biogas; CN102795725 A discloses the use of microbial flocculants or polyferric salts or polyaluminium salts for flocculation; the document “Study on the coagulation effect of different flocculants on pig biogas wastewater” discloses the study on the flocculation effect of polyaluminium chloride (PAC), polyaluminium sulfate (PFS) and polyacrylamide (PAM) on biogas; the document “Study on the treatment of biogas using biological flocculants” discloses the flocculation treatment of biogas slurry by biological flocculants prepared from sludge. The document “Development of RL-2 biological flocculant and study on flocculation mechanism” discloses the preparation of RL-2 flocculant and its use for flocculation of wastewater; the document “Study on the characteristics of four kinds of microbial flocculants” discloses the study on the flocculation effect of wastewater.

[0006] For the preparation of fertilizer from biogas slurry: Existing soil remediation agents are mostly chemical products or mixtures of biogas slurry with solid waste and functional ingredients. Chemical products are mostly polyacrylamide, slaked lime, phosphogypsum, attapulgite, struvite, etc. The dosage should be strictly controlled when using them. Improper use may affect crop growth and cause new soil pollution problems. Mixtures of biogas slurry with solid waste and functional ingredients are mostly waste resource utilization and functional superposition. Most of their products are for the improvement of saline-alkali land, and their use is limited. CN113501732A discloses the preparation of fertilizer by mixing biogas slurry with raw materials such as humic acid and Bacillus subtilis; CN 106929034 A discloses the use of microbial flocculants or polyferric salts or polyaluminum salts for flocculation.

[0007] It can be seen that although the prior art discloses the concentration technology of biogas slurry, it has the defects of frequent replacement of concentration membrane, high concentration cost, strong corrosiveness of flocculants, toxic monomers, and unfriendly environment. Although there is a trend towards biological flocculation in recent years, there is no aeration, fine filtration, and re-aeration before biological flocculation for the characteristics of biogas slurry and biological flocculation, which reduces the content of particulate matter in biogas slurry, and provides a feasible space for the flocculation of biological flocculants, and there is no research on the effects of different biological flocculants and their combinations on biogas slurry flocculation. The present invention adopts aeration, fine filtration, re-aeration, bioflocculant flocculation, filter press, ultrafiltration, nanofiltration, and reverse osmosis technology for the characteristics of biogas slurry and biological flocculation, with high concentration efficiency and environmental friendliness. Aeration, fine filtration, and re-aeration are performed before flocculation to reduce the content of particulate matter in biogas slurry, which provides a feasible space for the flocculation of biological flocculants. After the biological flocculation filter press, the macromolecules in the biogas slurry are significantly reduced, and the membrane is less damaged when the semi-liquid fertilizer is concentrated in the subsequent preparation, and the frequency of membrane replacement is significantly reduced. According to the characteristics of biogas slurry, the combination of NOC-1 and RL-2 was selected from the common bioflocculant combinations, which can significantly improve the bioflocculation effect of biogas slurry. The present invention also makes full use of biogas slurry, and makes soil conditioner and semi-liquid fertilizer according to the different nutrients extracted, thus finding a sustainable development path for biogas slurry utilization. Summary of the invention

[0008] The present invention provides a method for comprehensive utilization of biogas slurry, which adopts aeration, fine filtration, re-aeration, bioflocculant flocculation, filter pressing, ultrafiltration, nanofiltration, and reverse osmosis technology, has high concentration efficiency, is environmentally friendly, and fully utilizes biogas slurry. Aeration, fine filtration, and re-aeration are performed before biogas slurry flocculation to reduce the content of particulate matter in the biogas slurry, providing a feasible space for flocculation of bioflocculants. According to the characteristics of biogas slurry, a combination of NOC-1 and RL-2 is screened out from common bioflocculant combinations, which can significantly improve the bioflocculation effect of biogas slurry. The filter residue prepared after flocculation and filter pressing of the present invention is easy to disperse and has good air permeability after drying. It is aerobically fermented with humic acid powder and biogas residue, and bentonite and Bacillus subtilis are added. It is dried at low temperature to prepare a soil conditioner with high organic matter content and rich in biologically active substances such as humic acid and amino acids, which can effectively improve soil permeability and alleviate soil compaction.

[0009] The present invention provides a method for comprehensive utilization of biogas slurry, comprising the following steps:

[0010] (1) Biogas slurry pretreatment: The biogas slurry after solid-liquid separation is firstly sent to the primary and secondary biogas slurry tanks for two-stage secondary fermentation, and then sent to the aeration tank for aeration for 24-48 hours to kill the residual anaerobic microorganisms and promote the continued decomposition of macromolecular substances, so that the particle size of all substances in the biogas slurry is controlled to less than 100 μm, thereby increasing the filtration speed of the subsequent fine filter and increasing the contact area with the flocculant to accelerate flocculation;

[0011] (2) Fine filtration and re-aeration: The biogas slurry pretreated in step (1) is filtered through a 200-mesh fine filter to extract macromolecular biogas residue 1 larger than 75 μm in the biogas slurry, thereby reducing the solid content in the biogas slurry to below 25 g / L and meeting the requirements for later flocculation; the biogas slurry after fine filtration is aerated for 48-72 hours to reduce the particle size of the solids in the biogas slurry to less than 10 μm;

[0012] (3) Flocculation: Select a combination of bioflocculants NOC-1 and RL-2 in a mass ratio of 1-2:1-3, add water at a temperature of 25-30°C, add the combined bioflocculants while stirring, and stir at a speed of 200-400 rpm. Dissolve for 2-4 hours to prepare a bioflocculant solution with a concentration of 1.5-3‰. Add the bioflocculant solution to the finely filtered and aerated biogas slurry obtained in step (2) for flocculation. The volume ratio of biogas slurry to flocculating agent is 10:1-10:3, the flow rate ratio of biogas slurry to flocculating agent is 10:1-10:3, the biogas slurry flow rate is 5 t / h, and the mixing time is 5-10 min.

[0013] (4) screw filter press; subjecting the flocculated biogas slurry in step (3) to screw filter press to obtain filter residue and screw filter press filtrate;

[0014] (5) Preparing a soil conditioner: the filter residue obtained in step (4) is mixed with humic acid powder and biogas residue 1 obtained in step (2) in a mass ratio of 3-4:1-3:4-5, and then aerobically fermented for 10-20 days to obtain a decomposed material. When the temperature rises to 65°C, the decomposed material is turned over and tossed. The temperature is raised and the turning over and tossed is repeated three times. When the moisture content is reduced to 50%-55%, bentonite and Bacillus subtilis are added and mixed evenly. The mixture is dried at low temperature to prepare a soil conditioner, wherein the mass ratio of the decomposed material with a moisture content of 50%-55% to bentonite to Bacillus subtilis is 8-9:0.5-1:0.5-1.

[0015] (6) Preparing semi-liquid fertilizer: filtering the screw press filtrate obtained in step (4) with a multi-media filter to obtain a concentrate 1 with a particle size of more than 5 μm and a filtrate 1, wherein the water-insoluble matter in the filtrate 1 is less than 100 mg / L and the turbidity of the filtrate 1 is less than 50 NTU; ultrafiltration of the filtrate 1 with a tubular ultrafiltration membrane to obtain a concentrate 2 and a filtrate 2; nanofiltration of the filtrate 2 with a nanofiltration system to obtain a concentrate 3 and a filtrate 3, wherein the water-insoluble matter meets the requirements of ≤1 mg / L and the turbidity meets the requirements of ≤5 NTU; reverse osmosis of the filtrate 3 with a reverse osmosis system, wherein the reverse osmosis system adopts a DTRO membrane to obtain a reverse osmosis concentrate 4 and a permeate, wherein the permeate meets the discharge standard for agricultural irrigation water; and mixing the concentrate 1, the concentrate 2, the concentrate 3 and the reverse osmosis concentrate 4 to prepare a semi-liquid fertilizer.

[0016] Preferably, the aeration time in step (1) is 48 hours.

[0017] Preferably, step (2) is aerated for a further 72 hours.

[0018] Preferably, in step (3), a combination of bioflocculants NOC-1 and RL-2 in a mass ratio of 1:1 is selected, water at a temperature of 28°C is added, and the combined bioflocculant is added while stirring, the stirring speed is 300 rpm, and the mixture is dissolved for 2 hours to prepare a bioflocculant solution with a concentration of 3‰.

[0019] Preferably, in step (3), a combination of bioflocculants NOC-1 and RL-2 in a mass ratio of 2:1 is selected, water at a temperature of 25°C is added, and the combined bioflocculant is added while stirring, the stirring speed is 200 rpm, and the mixture is dissolved for 4 hours to prepare a bioflocculant solution with a concentration of 1.5‰.

[0020] Preferably, in step (3), the volume ratio of the biogas slurry to the flocculating agent is 10:3, the flow rate ratio of the biogas slurry to the flocculating agent is 10:3, the biogas slurry flow rate is 5 t / h, and the mixing time is 5 min.

[0021] Preferably, in step (3), the volume ratio of the biogas slurry to the flocculating agent is 10:2, the flow rate ratio of the biogas slurry to the flocculating agent is 10:3, the biogas slurry flow rate is 5 t / h, and the mixing time is 7 min.

[0022] Preferably, in step (5), the filter residue obtained in step (4) is mixed with humic acid powder and biogas residue 1 obtained in step (2) in a mass ratio of 4:3:5 and then aerobic fermentation is carried out for 20 days.

[0023] Preferably, in step (5), the filter residue obtained in step (4) is mixed with humic acid powder and biogas residue 1 obtained in step (2) in a mass ratio of 3:1:4 and then aerobic fermentation is carried out for 10 days.

[0024] Preferably, the mass ratio of the decomposed material with a moisture content of 50%-55%: bentonite: Bacillus subtilis is 9:1:1.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The present invention adopts the technology of extracting macromolecular organic matter from biogas slurry to extract the nutrients in biogas slurry, prepare solid soil remediation agent, concentrate the concentrate to make semi-liquid fertilizer, and discharge the clear liquid in compliance with the standards. The biogas slurry is fully utilized, thus opening up a sustainable development path for the utilization of biogas slurry.

[0027] (2) The present invention aims at the deficiencies of existing biogas slurry concentration technologies (existing concentration technologies include: sedimentation, filtration, ultrafiltration, nanofiltration, reverse osmosis, or chemical flocculant flocculation, ultrafiltration, nanofiltration, reverse osmosis; existing concentration technologies have the disadvantages of frequent replacement of concentration membranes, high concentration costs, strong corrosiveness of flocculants, toxic monomers, and environmental unfriendliness). The present invention adopts aeration, fine filtration, re-aeration, bioflocculant flocculation, filter press, ultrafiltration, nanofiltration, and reverse osmosis technologies, which have high concentration efficiency and are environmentally friendly.

[0028] (3) The present invention performs aeration, fine filtration and re-aeration before flocculation to reduce the content of particulate matter in the biogas slurry, providing a feasible space for the flocculation of the biological flocculant. After the biological flocculation and filtration, the macromolecules in the biogas slurry are significantly reduced, and the membrane is less damaged during the subsequent concentration in the preparation of semi-liquid fertilizer, and the frequency of membrane replacement is significantly reduced.

[0029] (4) In view of the characteristics of biogas slurry, the present invention screened out a combination of NOC-1 and RL-2 from common bioflocculant combinations, which can significantly improve the bioflocculation effect of biogas slurry.

[0030] (5) The filter residue prepared after flocculation and filtration in the present invention is easy to disperse and has good air permeability after drying. It is aerobically fermented with humic acid powder and biogas residue, and bentonite and Bacillus subtilis are added and dried at low temperature to prepare a soil conditioner with high organic matter content and rich in biologically active substances such as humic acid and amino acids. It can effectively improve soil permeability and alleviate soil compaction. Compared with the chemical fertilizer control group, the soil bulk density can be increased from 1.37 g / cm 3 Down to 1.26g / cm 3 , the bulk density decreased by 1.1 units, and the total number of soil bacteria increased from 1.32×10 7 / g soil increased to 1.41×10 8 / g, an increase of 10.68 times, the percentage of soil aggregates increased from 75.3% to 89.6%, the soil solid phase ratio in the three phases of 0-20cm soil decreased from 59.2% to 44.7%, a decrease of 24.49%, the soil liquid phase ratio increased from 18.5% to 25.9%, the soil gas phase ratio increased from 22.3% to 29.4%, the soil liquid phase ratio and soil gas phase ratio increased by 40% and 31.8% respectively, and the soil water holding capacity increased from 288.4g / kg to 381.2g / kg. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a picture of the filter residue in step (4) of Example 1 after further drying. DETAILED DESCRIPTION

[0032] The specific embodiments of the present invention are described below with reference to the accompanying drawings. The experimental methods used in the examples are conventional methods unless otherwise specified; the materials and reagents used are all commercially available unless otherwise specified.

[0033] Example 1 Flocculation effect of different combinations of bioflocculants on biogas slurry

[0034] (1) Biogas slurry pretreatment: The biogas slurry after solid-liquid separation is firstly sent to the primary and secondary biogas slurry tanks for two-stage secondary fermentation, and then sent to the aeration tank for aeration for 48 hours to kill the residual anaerobic microorganisms and promote the continued decomposition of macromolecular substances, so that the particle size of all substances in the biogas slurry is controlled to less than 100 μm, thereby increasing the filtration speed of the subsequent fine filter and increasing the contact area with the flocculant to accelerate flocculation;

[0035] (2) Fine filtration and re-aeration: The biogas slurry pretreated in step (1) is filtered through a 200-mesh fine filter to extract macromolecular biogas residue 1 larger than 75 μm in the biogas slurry, thereby reducing the solid content in the biogas slurry to below 25 g / L and meeting the requirements for later flocculation; the biogas slurry after fine filtration is aerated for 72 hours to reduce the particle size of the solids in the biogas slurry to less than 10 μm;

[0036] (3) Flocculation: Common biological flocculants NOC-1, DP-152, RL-2, and MBF8 were selected and combined. Water at a temperature of 28°C was added while stirring. The stirring speed was 250 rpm and the mixture was dissolved for 2 hours to prepare a biological flocculant to improve the flocculation effect. The combination was as follows: Group 1 was a combination of NOC-1 and DP-152, Group 2 was a combination of NOC-1 and RL-2, Group 3 was a combination of NOC-1 and MBF8, Group 4 was a combination of DP-152 and RL-2, Group 5 was a combination of DP-152 and MBF8, and Group 6 was a combination of RL-2 and MBF8. The mass ratio of the two biological flocculants in each group was 1:1.

[0037] 6 equal portions of the finely filtered and aerated biogas slurry obtained in step (2) were taken, and the bioflocculation agents of groups 1 to 6 were added respectively for flocculation, the volume ratio of biogas slurry to flocculation agent was 10:3, the concentration of flocculation agent was 3‰, the flow rate ratio of biogas slurry to flocculation agent was 10:3, the biogas slurry flow rate was 5 t / h, and the mixing time was 5 min;

[0038] (4) screw filter press; subjecting the flocculated biogas slurry in step (3) to screw filter press to obtain filter residue and screw filter press filtrate.

[0039] The filter residue of step (4) or the filter residue after further drying can be used as a raw material for preparing a soil conditioner, wherein the attached Figure 1 This is a picture of the filter residue in step (4) after further drying. It is easy to disperse and has good air permeability, which can effectively improve soil permeability and alleviate soil compaction.

[0040] The contents of COD (mg / L), TP (mg / L), TN (mg / L), and NH4+-N (mg / L) in the screw filter press filtrate were measured in steps (4) of groups 1 to 6, respectively, as shown in Table 1 below:

[0041]

[0042] As can be seen from Table 1, under the condition of the same addition amount, different combinations of common bioflocculants NOC-1, DP-152, RL-2, and MBF8 have a greater impact on the flocculation effect of biogas slurry. Among them, combination 2, i.e., the combination of NOC-1 and RL-2, has the best flocculation effect on biogas slurry, and the COD (mg / L), TP (mg / L), TN (mg / L), and NH4+-N (mg / L) contents in the obtained filtrate are lower, followed by group 1, i.e., the combination of NOC-1 and DP-152. According to the results in Table 1, the combination of NOC-1 and RL-2 is selected to flocculate biogas slurry.

[0043] Comparative Example 1: The difference from the scheme of Group 2 of Example 1 is that step (1) is omitted, and the rest is the same as the scheme of Group 2 of Example 1.

[0044] Comparative Example 2: The difference from the scheme of Group 2 of Example 1 is that step (2) is omitted, and the rest is the same as the scheme of Group 2 of Example 1.

[0045] The results show that: since the biogas slurry contains a lot of large particles, when step (1) is omitted in comparative example 1, the filter holes of the fine filter with a mesh of 200 are blocked soon after filtration, and the filtration speed is extremely slow afterwards, and the fine filtrate cannot be further filtered.

[0046] After the pretreatment of the biogas slurry, the particle size of all substances in the biogas slurry was controlled to be less than 100 μm. The particles were still relatively large, and step (2) was omitted. The surface area of ​​the biogas slurry in contact with the flocculant became smaller, and the flocculation efficiency was significantly reduced. The COD (mg / L), TP (mg / L), TN (mg / L), and NH4+-N (mg / L) in the biogas slurry after flocculation were 4915.26, 141.59, 944.78, and 813.01, respectively.

[0047] Example 2

[0048] A biogas slurry comprehensive utilization method comprises the following steps:

[0049] (1) Biogas slurry pretreatment: The biogas slurry after solid-liquid separation is firstly sent to the primary and secondary biogas slurry tanks for two-stage secondary fermentation, and then sent to the aeration tank for aeration for 48 hours to kill the residual anaerobic microorganisms and promote the continued decomposition of macromolecular substances. The particle size of all substances in the biogas slurry is controlled to be less than 100um, which increases the filtration speed of the subsequent fine filter and increases the contact area with the flocculant to accelerate flocculation.

[0050] (2) Fine filtration and re-aeration: The biogas slurry pretreated in step (1) is filtered through a 200-mesh fine filter to extract macromolecular biogas residue 1 larger than 75 μm in the biogas slurry, thereby reducing the solid content in the biogas slurry to below 25 g / L and meeting the requirements for later flocculation; the biogas slurry after fine filtration is aerated for 72 hours to reduce the particle size of the solids in the biogas slurry to less than 10 μm;

[0051] (3) Flocculation: Select a combination of bioflocculants NOC-1 and RL-2 in a mass ratio of 1:1, add water at a temperature of 28°C, add the combined bioflocculants while stirring, stir at a speed of 250 rpm, dissolve for 2 hours, and prepare a bioflocculant solution with a concentration of 3‰. Add the bioflocculant solution to the finely filtered and aerated biogas slurry obtained in step (2) for flocculation. The volume ratio of biogas slurry to flocculating agent is 10:3, the flow rate ratio of biogas slurry to flocculating agent is 10:3, the biogas slurry flow rate is 5 t / h, and the mixing time is 5 min.

[0052] (4) screw filter press; subjecting the flocculated biogas slurry in step (3) to screw filter press to obtain filter residue and screw filter press filtrate;

[0053] (5) Preparing a soil conditioner: the filter residue obtained in step (4) is mixed with humic acid powder and biogas residue 1 obtained in step (2) in a mass ratio of 4:3:5, and then aerobically fermented for 20 days to obtain a decomposed material. When the temperature rises to 65° C., the decomposed material is turned over and tossed. The temperature is raised and the turning over and tossed is repeated three times. When the moisture content is reduced to 55%, bentonite and Bacillus subtilis are added and mixed evenly. The mixture is dried at low temperature to prepare a soil conditioner, wherein the mass ratio of the decomposed material with a moisture content of 55%: bentonite: Bacillus subtilis is 9:1:1;

[0054] (6) Preparing semi-liquid fertilizer: filtering the screw press filtrate obtained in step (4) with a multi-media filter to obtain a concentrate 1 with a particle size of more than 5 μm and a filtrate 1, wherein the water-insoluble matter in the filtrate 1 is less than 100 mg / L and the turbidity of the filtrate 1 is less than 50 NTU; ultrafiltration of the filtrate 1 with a tubular ultrafiltration membrane to obtain a concentrate 2 and a filtrate 2; nanofiltration of the filtrate 2 with a nanofiltration system to obtain a concentrate 3 and a filtrate 3, wherein the water-insoluble matter meets the requirements of ≤1 mg / L and the turbidity meets the requirements of ≤5 NTU; reverse osmosis of the filtrate 3 with a reverse osmosis system, wherein the reverse osmosis system adopts a DTRO membrane to obtain a reverse osmosis concentrate 4 and a permeate, wherein the permeate meets the discharge standard for agricultural irrigation water; and mixing the concentrate 1, the concentrate 2, the concentrate 3 and the reverse osmosis concentrate 4 to prepare a semi-liquid fertilizer.

[0055] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that the bioflocculant in step (3) is replaced by the combination of Group 1 of Example 1 (i.e., the combination of NOC-1 and RL-2), and the rest is the same as Example 2.

[0056] The soil conditioner and fertilizer prepared in step (5) of Example 2 and step (5) of Comparative Example 3 were applied to three soils with the same physical and chemical properties, respectively, and marked as Example 2, Comparative Example 3 and Control Group, 300-500 kg were applied per mu, twice a year. After one year, the soil bulk density, total soil bacteria count, percentage of water-stable soil aggregates, soil solid phase, soil liquid phase, soil gas phase, and soil water holding capacity of the soils of Example 2, Comparative Example 3 and Control Group were measured, as shown in Table 2 below:

[0057]

[0058] As can be seen from Table 2, the Example 2 and Comparative Example 3 groups using the bioflocculant can effectively improve soil permeability and alleviate soil compaction compared with the chemical fertilizer control group. The Example 2 group has the best improvement effect. Compared with the chemical fertilizer group, the soil bulk density of the Example 2 group can be increased from 1.37 g / cm 3 Down to 1.26g / cm3 , the bulk density decreased by 1.1 units, and the total number of soil bacteria increased from 1.32×10 7 / g soil increased to 1.41×10 8 , an increase of 10.68 times. Soil conditioners can increase the water-stable aggregate structure of soil. The percentage of soil aggregates increased from 75.3% to 89.6%. Soil conditioners can enhance the water and fertilizer retention capacity of soil. Among the three phases of 0-20cm soil, the soil solid phase ratio decreased from 59.2% to 44.7%, a decrease of 24.49%. The soil liquid phase ratio increased from 18.5% to 25.9%, and the soil gas phase ratio increased from 22.3% to 29.4%. The soil liquid phase ratio and soil gas phase ratio increased by 40% and 31.8% respectively, and the soil water holding capacity increased from 288.4g / kg to 381.2g / kg.

[0059] Example 3

[0060] A biogas slurry comprehensive utilization method comprises the following steps:

[0061] (1) Biogas slurry pretreatment: The biogas slurry after solid-liquid separation is firstly sent to the primary and secondary biogas slurry tanks for two-stage secondary fermentation, and then sent to the aeration tank for aeration for 24 hours to kill the residual anaerobic microorganisms and promote the continued decomposition of macromolecular substances. The particle size of all substances in the biogas slurry is controlled to be less than 100 μm, which increases the filtration speed of the subsequent fine filter and increases the contact area with the flocculant to accelerate flocculation.

[0062] (2) Fine filtration and re-aeration: The biogas slurry pretreated in step (1) is filtered through a 200-mesh fine filter to extract macromolecular biogas residue 1 larger than 75 μm in the biogas slurry, thereby reducing the solid content in the biogas slurry to below 25 g / L and meeting the requirements for later flocculation; the biogas slurry after fine filtration is aerated for 48 hours to reduce the particle size of the solids in the biogas slurry to less than 10 μm;

[0063] (3) Flocculation: Select a combination of bioflocculants NOC-1 and RL-2 in a mass ratio of 1:3, add water at a temperature of 25°C, add the combined bioflocculants while stirring, stir at a speed of 200 rpm, dissolve for 3 hours, and prepare a bioflocculant solution with a concentration of 1.5‰. Add the bioflocculant solution to the finely filtered and re-aerated biogas slurry obtained in step (2) for flocculation. The volume ratio of biogas slurry to flocculating agent is 10:1, the flow rate ratio of biogas slurry to flocculating agent is 10:1, the biogas slurry flow rate is 5 t / h, and the mixing time is 10 min.

[0064] (4) screw filter press; subjecting the flocculated biogas slurry in step (3) to screw filter press to obtain filter residue and screw filter press filtrate;

[0065] (5) Preparing a soil conditioner: the filter residue obtained in step (4) is mixed with humic acid powder and biogas residue 1 obtained in step (2) in a mass ratio of 3:1:4, and then aerobically fermented for 10 days to obtain a decomposed material. When the temperature rises to 65° C., the decomposed material is turned over and tossed. The temperature is raised and the turning over and tossed is repeated three times. When the moisture content is reduced to 50%, bentonite and Bacillus subtilis are added and mixed evenly. The mixture is dried at low temperature to prepare a soil conditioner, wherein the mass ratio of the decomposed material with a moisture content of 50% to bentonite to Bacillus subtilis is 8:0.5:0.5.

[0066] (6) Preparing semi-liquid fertilizer: filtering the screw press filtrate obtained in step (4) with a multi-media filter to obtain a concentrate 1 with a particle size of more than 5 μm and a filtrate 1, wherein the water-insoluble matter in the filtrate 1 is less than 100 mg / L and the turbidity of the filtrate 1 is less than 50 NTU; ultrafiltration of the filtrate 1 with a tubular ultrafiltration membrane to obtain a concentrate 2 and a filtrate 2; nanofiltration of the filtrate 2 with a nanofiltration system to obtain a concentrate 3 and a filtrate 3, wherein the water-insoluble matter meets the requirements of ≤1 mg / L and the turbidity meets the requirements of ≤5 NTU; reverse osmosis of the filtrate 3 with a reverse osmosis system, wherein the reverse osmosis system adopts a DTRO membrane to obtain a reverse osmosis concentrate 4 and a permeate, wherein the permeate meets the discharge standard for agricultural irrigation water; and mixing the concentrate 1, the concentrate 2, the concentrate 3 and the reverse osmosis concentrate 4 to prepare a semi-liquid fertilizer.

[0067] Example 4

[0068] A biogas slurry comprehensive utilization method comprises the following steps:

[0069] (1) Biogas slurry pretreatment: The biogas slurry after solid-liquid separation is firstly sent to the primary and secondary biogas slurry tanks for two-stage secondary fermentation, and then sent to the aeration tank for aeration for 36 hours to kill the residual anaerobic microorganisms and promote the continued decomposition of macromolecular substances. The particle size of all substances in the biogas slurry is controlled to be less than 100 μm, which increases the filtration speed of the subsequent fine filter and increases the contact area with the flocculant to accelerate flocculation.

[0070] (2) Fine filtration and re-aeration: The biogas slurry pretreated in step (1) is filtered through a 200-mesh fine filter to extract macromolecular biogas residue 1 larger than 75 μm in the biogas slurry, thereby reducing the solid content in the biogas slurry to below 25 g / L and meeting the requirements for later flocculation; the biogas slurry after fine filtration is aerated for 60 hours to reduce the particle size of the solids in the biogas slurry to less than 10 μm;

[0071] (3) Flocculation: Select a combination of bioflocculants NOC-1 and RL-2 in a mass ratio of 2:1, add water at a temperature of 30°C, add the combined bioflocculants while stirring, stir at a speed of 350 rpm, dissolve for 2.5 hours, and prepare a bioflocculant solution with a concentration of 2.5‰. Add the bioflocculant solution to the finely filtered and re-aerated biogas slurry obtained in step (2) for flocculation. The volume ratio of biogas slurry to flocculating agent is 10:2, the flow rate ratio of biogas slurry to flocculating agent is 10:3, the biogas slurry flow rate is 5 t / h, and the mixing time is 7 min.

[0072] (4) screw filter press; subjecting the flocculated biogas slurry in step (3) to screw filter press to obtain filter residue and screw filter press filtrate;

[0073] (5) Preparing a soil conditioner: the filter residue obtained in step (4) is mixed with humic acid powder and biogas residue 1 obtained in step (2) in a mass ratio of 4:2:4, and then aerobically fermented for 15 days to obtain a decomposed material. When the temperature rises to 65° C., the decomposed material is turned over and tossed. The temperature is raised and the turning over and tossed is repeated three times. When the moisture content is reduced to 53%, bentonite and Bacillus subtilis are added and mixed evenly. The mixture is dried at low temperature to prepare a soil conditioner, wherein the mass ratio of the decomposed material with a moisture content of 53%: bentonite: Bacillus subtilis is 9:0.5:1;

[0074] (6) Preparing semi-liquid fertilizer: filtering the screw press filtrate obtained in step (4) with a multi-media filter to obtain a concentrate 1 with a particle size of more than 5 μm and a filtrate 1, wherein the water-insoluble matter in the filtrate 1 is less than 100 mg / L and the turbidity of the filtrate 1 is less than 50 NTU; ultrafiltration of the filtrate 1 with a tubular ultrafiltration membrane to obtain a concentrate 2 and a filtrate 2; nanofiltration of the filtrate 2 with a nanofiltration system to obtain a concentrate 3 and a filtrate 3, wherein the water-insoluble matter meets the requirements of ≤1 mg / L and the turbidity meets the requirements of ≤5 NTU; reverse osmosis of the filtrate 3 with a reverse osmosis system, wherein the reverse osmosis system adopts a DTRO membrane to obtain a reverse osmosis concentrate 4 and a permeate, wherein the permeate meets the discharge standard for agricultural irrigation water; and mixing the concentrate 1, the concentrate 2, the concentrate 3 and the reverse osmosis concentrate 4 to prepare a semi-liquid fertilizer.

[0075] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A method for comprehensive utilization of biogas slurry, characterized in that The steps include: (1) Biogas slurry pretreatment: The biogas slurry after solid-liquid separation is firstly sent to the primary and secondary biogas slurry tanks for two-stage secondary fermentation, and then sent to the aeration tank for aeration for 24-48 hours to kill the residual anaerobic microorganisms and promote the continued decomposition of macromolecular substances, so that the particle size of all substances in the biogas slurry is controlled to less than 100 μm, thereby increasing the filtration speed of the subsequent fine filter and increasing the contact area with the flocculant to accelerate flocculation; (2) Fine filtration and re-aeration: The biogas slurry pretreated in step (1) is filtered through a 200-mesh fine filter to extract macromolecular biogas residue 1 larger than 75 μm in the biogas slurry, thereby reducing the solid content in the biogas slurry to below 25 g / L and meeting the requirements for later flocculation; the biogas slurry after fine filtration is aerated for 48-72 hours to reduce the particle size of the solids in the biogas slurry to less than 10 μm; (3) Flocculation: Select a combination of bioflocculants NOC-1 and RL-2 in a mass ratio of 1:1, add water at a temperature of 28°C, add the combined bioflocculants while stirring, stir at a speed of 250 rpm, dissolve for 2 hours, and prepare a bioflocculant solution with a concentration of 3‰. Add the bioflocculant solution to the finely filtered and aerated biogas slurry obtained in step (2) for flocculation. The volume ratio of biogas slurry to flocculating agent is 10:3, the flow rate ratio of biogas slurry to flocculating agent is 10:3, the biogas slurry flow rate is 5 t / h, and the mixing time is 5 min. Or select a combination of bioflocculants NOC-1 and RL-2 in a mass ratio of 1:3, add water at a temperature of 25°C, add the combined bioflocculants while stirring, stir at a speed of 200 rpm, dissolve for 3 hours, and prepare a bioflocculant solution with a concentration of 1.5‰, add the bioflocculant solution to the finely filtered and re-aerated biogas slurry obtained in step (2) for flocculation, the volume ratio of biogas slurry to flocculating agent is 10:1, the flow rate ratio of biogas slurry to flocculating agent is 10:1, the biogas slurry flow rate is 5 t / h, and the mixing time is 10 min; Or select a combination of bioflocculants NOC-1 and RL-2 in a mass ratio of 2:1, add water at a temperature of 30°C, add the combined bioflocculants while stirring, stir at a speed of 350 rpm, dissolve for 2.5 hours, and prepare a bioflocculant solution with a concentration of 2.5‰, add the bioflocculant solution to the finely filtered and re-aerated biogas slurry obtained in step (2) for flocculation, the volume ratio of biogas slurry to flocculating agent is 10:2, the flow rate ratio of biogas slurry to flocculating agent is 10:3, the biogas slurry flow rate is 5 t / h, and the mixing time is 7 min; (4) screw filter press; subjecting the flocculated biogas slurry in step (3) to screw filter press to obtain filter residue and screw filter press filtrate; (5) Preparing a soil conditioner: the filter residue obtained in step (4) is mixed with humic acid powder and biogas residue 1 obtained in step (2) in a mass ratio of 3-4:1-3:4-5, and then aerobically fermented for 10-20 days to obtain a decomposed material. When the temperature rises to 65°C, the decomposed material is turned over and tossed. The temperature is raised and the turning over and tossed is repeated three times. When the moisture content is reduced to 50%-55%, bentonite and Bacillus subtilis are added and mixed evenly. The mixture is dried at low temperature to prepare a soil conditioner, wherein the mass ratio of the decomposed material with a moisture content of 50%-55% to bentonite to Bacillus subtilis is 8-9:0.5-1:0.5-1. (6) Preparing semi-liquid fertilizer: filtering the screw press filtrate obtained in step (4) with a multi-media filter to obtain a concentrate 1 with a particle size of more than 5 μm and a filtrate 1, wherein the water-insoluble matter in the filtrate 1 is less than 100 mg / L and the turbidity of the filtrate 1 is less than 50 NTU; ultrafiltration of the filtrate 1 with a tubular ultrafiltration membrane to obtain a concentrate 2 and a filtrate 2; nanofiltration of the filtrate 2 with a nanofiltration system to obtain a concentrate 3 and a filtrate 3, wherein the water-insoluble matter meets the requirements of ≤1 mg / L and the turbidity meets the requirements of ≤5 NTU; reverse osmosis of the filtrate 3 with a reverse osmosis system, wherein the reverse osmosis system adopts a DTRO membrane to obtain a reverse osmosis concentrate 4 and a permeate, wherein the permeate meets the discharge standard for agricultural irrigation water; and mixing the concentrate 1, the concentrate 2, the concentrate 3 and the reverse osmosis concentrate 4 to prepare a semi-liquid fertilizer.

2. A biogas slurry comprehensive utilization method according to claim 1, characterized in that Step (1) aeration time: 48 hours.

3. A biogas slurry comprehensive utilization method according to claim 1, characterized in that Step (2) was aerated for a further 72 hours.

4. The method for comprehensive utilization of biogas slurry according to claim 1, characterized in that In step (5), the filter residue obtained in step (4) is mixed with humic acid powder and biogas residue 1 obtained in step (2) in a mass ratio of 4:3:5 and then aerobic fermentation is carried out for 20 days.

5. The method for comprehensive utilization of biogas slurry according to claim 1, characterized in that In step (5), the filter residue obtained in step (4) is mixed with humic acid powder and biogas residue 1 obtained in step (2) in a mass ratio of 3:1:4 and then aerobic fermentation is carried out for 10 days.

6. The method for comprehensive utilization of biogas slurry according to claim 1, characterized in that The mass ratio of decomposed material with a moisture content of 50%-55%: bentonite: Bacillus subtilis is 9:1:1.

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