Method for reducing nitrogen loss in biogas slurry returning-to-field utilization process

Abstract

The invention relates to a method for reducing nitrogen loss in a biogas slurry returning and utilization process. The method comprises the following steps: providing biochar; mixing the biochar with kitchen biogas slurry, and mixing and stirring under a constant temperature condition to obtain a biochar biogas slurry mixture; the charcoal and biogas slurry mixture is mixed with soil, so that the nitrogen loss can be reduced. According to the method, kitchen biogas slurry generated by anaerobic fermentation of kitchen waste and biochar are mixed and returned to the field, so that the use cost of wood vinegar is reduced, and the influence of biogas slurry coupled straw returning to the field on crops is avoided. The biochar can fix nitrogen nutrients in the biogas slurry through adsorption, slow release and immobilization effects of the biochar; nitrification can be inhibited, conversion of ammonia nitrogen to nitrate nitrogen is delayed, nitrate is promoted to be reduced into ammonia, and nitrate nitrogen is converted into ammonia nitrogen to be reserved; in addition, the biochar provides a habitat for nitrogen circulating microorganisms, nitrogen turnover of the farmland is accelerated, and therefore nitrogen loss caused by returning of the biogas slurry to the field is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment, and in particular to a method for reducing nitrogen loss during the process of returning biogas slurry to fields. Background Art

[0002] Returning biogas slurry to the field can absorb a large amount of biogas slurry at one time. When returning biogas slurry to the field, the nutrients in the biogas slurry can be fully utilized by field crops as fertilizers, which can not only reduce the use of nitrogen fertilizers, but also reduce irrigation water, and has good application prospects. However, there is currently a serious problem of nitrogen loss when biogas slurry is returned to the field, mainly including nitrogen leaching and ammonia volatilization. When biogas slurry is directly returned to the field, high-concentration ammonia nitrogen enters the soil, and a part of it undergoes nitrification reaction and is converted into nitrate nitrogen. Nitrate ions are negatively charged and are easily leached during leaching. Nitrates seep into groundwater, causing groundwater pollution and eutrophication of water bodies; while the other part volatilizes in the form of ammonia gas, reducing the efficiency of nitrogen utilization in farmland, causing air pollution, greenhouse effect and other environmental problems. Therefore, effectively reducing nitrogen loss is an urgent problem to be solved in the return of biogas slurry to the field.

[0003] At present, the methods to reduce nitrogen loss in biogas slurry return to the field include biogas slurry combined with wood vinegar and biogas slurry coupled with straw return to the field. Wood vinegar refers to the liquid byproduct condensed at room temperature in addition to biomass charcoal and fuel gas during the pyrolysis and gasification of biomass such as straw and sawdust. It is often too expensive to be used in industrial production. When biogas slurry is coupled with straw return to the field, there are problems such as affecting crop emergence, aggravating the occurrence of pests and diseases, and accumulating heavy metals in the soil. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a method for reducing nitrogen loss during the process of returning biogas slurry to the field. The present invention uses the biogas slurry produced by anaerobic fermentation of food waste and biochar to mix and return it to the field, thereby reducing the cost of using wood vinegar and avoiding the impact of biogas slurry coupled with straw return to the field on crops. Biochar can not only fix nitrogen nutrients in biogas slurry through its adsorption, slow release and retention effects; but also inhibit nitrification, delay the conversion of ammonia nitrogen to nitric nitrogen, promote the reduction of nitrate to ammonia, and convert nitric nitrogen into ammonia nitrogen for retention; in addition, biochar provides a habitat for nitrogen cycle microorganisms, accelerates the turnover of nitrogen in farmland, and thus reduces nitrogen loss caused by returning biogas slurry to the field.

[0005] The object of the present invention is to provide a method for reducing nitrogen loss in the process of returning biogas slurry to farmland, comprising the following steps: Provide a biochar; The biochar is mixed with kitchen biogas slurry, and the mixture is stirred under a constant temperature condition to obtain a biochar-biogas slurry mixture; Mix the biochar-liquid mixture with the soil.

[0006] In some embodiments of the present invention, the biochar is prepared by the following method: drying and compacting the biomass, and then heating and calcining the biochar under an inert atmosphere to obtain the biochar.

[0007] In some embodiments of the present invention, the biomass includes one or more of coconut shells, straws, wood chips, and bamboo.

[0008] In some embodiments of the present invention, the pH of the kitchen biogas slurry is about 7-8, and the total nitrogen and ammonia nitrogen contents are 4-5 g / L and 3-4 g / L respectively.

[0009] In some embodiments of the present invention, the inert gas of the inert atmosphere is nitrogen and / or argon; The heating calcination temperature is 300~700℃ and the time is 2.5-3h.

[0010] In some embodiments of the present invention, the mass ratio of the biochar to the kitchen digester is 1:(1.4-2.4).

[0011] In some embodiments of the present invention, the temperature under constant temperature conditions is 28-30°C.

[0012] In some embodiments of the present invention, the mixing speed is 120-150 r / min, and the mixing time is 33-72h.

[0013] In some embodiments of the present invention, the mass ratio of the biochar-biogas slurry mixture to soil is 1:(44.5-52.5).

[0014] In some embodiments of the present invention, the soil is a mixed soil with a mass ratio of base soil to vermiculite of (3-4):1.

[0015] In some embodiments of the present invention, the culturing time is 28-30 days.

[0016] The above technical solution of the present invention has the following advantages compared with the prior art: After the biochar of the present invention is mixed with biogas slurry, the biochar absorbs ammonia nitrogen in the kitchen biogas slurry through its own adsorption ability. The desorption process of ammonia nitrogen in farmland after adsorption can provide plants with available nitrogen, and the fixation capacity of biochar can reduce the loss of nitrogen, thereby reducing nitrogen leaching.

[0017] After the leaching experiment described in the invention, it was found that the mixed treatment of biochar and biogas liquid had relatively lower nitrate and total nitrogen content in the leachate. This result shows that the return of biochar and biogas liquid to the field mainly reduces the loss of nitrate in farmland soil. First, the adsorption capacity of biochar itself retains nitrate; secondly, biochar can promote hydroxylamine reduction to inhibit nitrification by increasing the abundance of hcp functional genes, reduce the conversion of ammonia nitrogen to nitric nitrogen, and thus reduce nitrate nitrogen leaching; then, biochar also increases the abundance of genes such as narB, nasA, nasB, nirB, nirD, and nrfA in the soil, promotes the reduction of nitrate to ammonia, and converts nitrate nitrogen into ammonia nitrogen, ultimately reducing nitrate nitrogen leaching; biochar provides a habitat for soil microorganisms, enhances microbial diversity, promotes soil nitrogen turnover, and thus reduces the loss of total nitrogen.

[0018] The present invention utilizes biochar mixed with kitchen biogas slurry to return to the field, thereby reducing the cost of using wood vinegar, solving the problem of heavy metal accumulation in the soil caused by returning straw-coupled biogas slurry to the field, and reducing nitrogen loss in the process of returning biogas slurry to the field. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein: Figure 1 These are the test results of total nitrogen and nitric nitrogen in the leachate in the leaching experiments of the embodiments of the present invention and the comparative examples. DETAILED DESCRIPTION

[0020] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0021] Embodiment 1:

[0022] 1. Dry 50g of coconut shell and put it into a 0.6L stainless steel container. After compacting, pass nitrogen to exhaust the air. Then put the container into a preheated tubular furnace. During the experiment, the nitrogen carrier gas flow rate was 0.1L / min. Biochar was prepared at 300℃. After the container was placed in the tubular furnace for 3 hours, it was taken out and sampled after natural cooling to obtain coconut shell biochar.

[0023] 2. Mix 14.51 g of coconut shell biochar obtained in step 1 with 34.5 mL of kitchen biogas slurry, and shake on a shaker at a constant temperature of 30°C and a speed of 120 r / min for 33 h to obtain a biochar-biogas slurry mixture.

[0024] 3. Mix the biochar-liquid mixture obtained in step 2 with 2.577 kg of experimental soil (75 wt% base soil and 25 wt% vermiculite) and place it in a flower pot. Repeat three times.

[0025] 4. Then place the flower pot in a static light box and place the device in an environment with a temperature of 21~23℃ for 30 days.

[0026] 5. Set up 7 leaching experiments, which were carried out on the 3rd, 7th, 11th, 15th, 19th, 23rd and 27th days, and 189 mL of soil was leached into each pot. After each leaching, the leachate was collected to determine the volume, total nitrogen and nitrate nitrogen. The experimental results are shown in Table 2 and Figure 1 .

[0027] Embodiment 2:

[0028] 1. After drying 100g of coconut shell, put it into a 0.6L stainless steel container, compact it, pass nitrogen to exhaust the air, and then put the container into a preheated tubular furnace. During the experiment, the nitrogen carrier gas flow rate was 0.1L / min. Biochar was prepared at 700℃. After the container was placed in the tubular furnace for 3 hours, it was taken out and sampled after natural cooling to obtain coconut shell biochar.

[0029] 2. Mix 20 g of coconut shell biochar obtained in step 1 with 34.5 mL of kitchen biogas slurry, and shake on a shaker at a constant temperature of 30 °C and a speed of 120 r / min for 33 h to obtain a biochar-biogas slurry mixture.

[0030] 3. Mix the biochar-liquid mixture obtained in step 2 with 2.577 kg of experimental soil (75 wt% base soil and 25 wt% vermiculite) and place it in a flower pot. Repeat three times.

[0031] 4. Then place the flower pot in a static light box and place the device in an environment with a temperature of 21~23℃ for 30 days.

[0032] 5. Set up 7 leaching experiments, which were carried out on the 3rd, 7th, 11th, 15th, 19th, 23rd and 27th days, and 189 mL of soil was leached into each pot. After each leaching, the leachate was collected to determine the volume, total nitrogen and nitrate nitrogen. The experimental results are shown in Table 2 and Figure 1 .

[0033] Embodiment 3:

[0034] 1. After drying 120g of coconut shell, put it into a 0.6L stainless steel container, compact it, and then pass nitrogen to exhaust the air. Then put the container into a preheated tubular furnace. During the experiment, the nitrogen carrier gas flow rate was 0.1L / min. Biochar was prepared at 700℃. After the container was placed in the tubular furnace for 3 hours, it was taken out and sampled after natural cooling to obtain straw biochar.

[0035] 2. Mix 22.94 g of straw biochar obtained in step 1 with 34.5 mL of kitchen biogas slurry, and shake on a shaker at a speed of 120 r / min for 33 h at a constant temperature of 30°C to prepare a biochar-biogas slurry mixture.

[0036] 3. Mix the biochar-liquid mixture obtained in step 2 with 2.577 kg of experimental soil (75 wt% base soil and 25 wt% vermiculite) and place it in a flower pot. Repeat three times.

[0037] 4. Then place the flower pot in a static light box and place the device in an environment with a temperature of 21~23℃ for 30 days.

[0038] 5. Set up 7 leaching experiments, which were carried out on the 3rd, 7th, 11th, 15th, 19th, 23rd and 27th days, and 189 mL of soil was leached into each pot. After each leaching, the leachate was taken to measure the volume, total nitrogen and nitrate nitrogen. The experimental results are shown in Table 2 and Figure 1 .

[0039] Comparative Example 1: 1. Mix 34.5 mL of kitchen biogas slurry with 2.577 kg of experimental soil (75 wt% basic soil and 25 wt% vermiculite) and place it in a flower pot. Repeat three times.

[0040] 2. Then place the flower pot in a static light box and place the device in an environment with a temperature of 21~23℃ for 30 days.

[0041] 3. Set up 7 leaching experiments, which were carried out on the 3rd, 7th, 11th, 15th, 19th, 23rd and 27th days, and 189 mL of soil was leached into each pot. After each leaching, the leachate was taken to measure the volume, total nitrogen and nitrate nitrogen. The experimental results are shown in Table 2 and Figure 1 .

[0042] Comparative Example 2: 1. Mix 0.309g urea with 2.577kg experimental soil (75wt% base soil and 25wt% vermiculite) and place it in a flower pot. Repeat three times.

[0043] 2. Then place the flower pot in a static light box and place the device in an environment with a temperature of 21~23℃ for 30 days.

[0044] 3. Set up 7 leaching experiments, which were carried out on the 3rd, 7th, 11th, 15th, 19th, 23rd and 27th days, and 189 mL of soil was leached into each pot. After each leaching, the leachate was taken to measure the volume, total nitrogen and nitrate nitrogen. The experimental results are shown in Table 2 and Figure 1 .

[0045] Table 1 shows the nitrogen cycle gene abundance and microbial diversity of different experimental groups in the present invention

[0046] As can be seen from Table 1, the abundance of nitrogen cycle functional genes and microbial diversity in different experimental groups of the present invention explain how biochar reduces nitrogen loss when returning biogas slurry to fields from the perspective of microorganisms.

[0047] Table 2

[0048] After the leaching experiment, the volume, total nitrogen and nitric nitrogen content of the leachate treated in each example and comparative example were measured, and the cumulative nitrogen loss of each group of treatments was calculated. The results show that Example 1 (300℃ coconut shell biochar + biogas slurry) reduces 11.1% of total nitrogen loss and 8.26% of nitrate loss of Comparative Example 1 (biogas slurry), and reduces 2.49% of total nitrogen loss and 26.39% of nitrate loss of Comparative Example 2 (urea); Example 2 (700℃ coconut shell biochar + biogas slurry) reduces 14.6% of total nitrogen loss and 5.81% of nitrate loss of Comparative Example 1 (biogas slurry), and reduces 6.38% of total nitrogen loss and 24.43% of nitrate loss of Comparative Example 2 (urea). Example 3 (700℃ straw biochar + biogas slurry) reduces 29.13% of total nitrogen loss and 47.46% of nitrate loss of Comparative Example 1 (biogas slurry), and reduces 22.27% of total nitrogen loss and 57.84% of nitrate loss of Comparative Example 2 (urea). Comparison between Comparative Example 2 and the examples shows that when biochar and biogas slurry are mixed and returned to the field instead of chemical fertilizer application, nitrogen loss can also be reduced.

[0049] Cultivation experiment The biochar-biogas mixture obtained in Example 3 was subjected to a cultivation test, and a control group (basic soil) and an experimental group (Example 3) were set up. The specific steps were as follows: the Chinese cabbage seed variety was No. 49-19 Chinese cabbage. Treatment of Chinese cabbage seeds: Soak in warm water at 30°C for 6 hours, sow evenly after leveling the soil, sow directly into the pot, cover the soil with a thickness of 3 times the diameter of the seed, and then water thoroughly and wait for germination. The soil used in this cultivation experiment was consistent with the experimental soil used in the soil leaching experiment (volume ratio of soil: vermiculite: 3:1), and the experiment was carried out in a flowerpot filled with 9 cm high experimental soil (1.16 kg). After the seeds germinated, the number of germinations was measured, and the emergence rate was calculated. The experimental results are shown in Table 3.

[0050] Table 3 is the results of the experiment on the emergence of Chinese cabbage seedlings using the biochar-biogas mixture obtained in the example

[0051] From the experimental results in Table 3, it can be seen that the biochar-biogas slurry mixture can promote the emergence of crops.

[0052] In summary, through the comparison between the embodiments and the comparative examples, it can be seen that coconut shell / straw biochar and kitchen biogas slurry can synergistically enhance soil nitrogen turnover and reduce the loss of total nitrogen.

[0053] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A method for reducing nitrogen loss during the process of returning biogas slurry to farmland, characterized in that: The following steps are involved: Provide a biochar; The biochar is mixed with kitchen biogas slurry, and the mixture is stirred under a constant temperature condition to obtain a biochar-biogas slurry mixture; Mix the biochar-liquid mixture with the soil.

2. The method according to claim 1, characterized in that The biochar is prepared by the following method: drying and compacting the biomass, and then heating and calcining the biochar under an inert atmosphere to obtain the biochar.

3. The method according to claim 2, characterized in that The biomass includes one or more of coconut shells, straws, wood chips and bamboo.

4. The method according to claim 2, characterized in that: The inert gas of the inert atmosphere is nitrogen and / or argon, with a flow rate of 0.1-0.12 L / min.

5. The method according to claim 2, characterized in that: The heating calcination temperature is 300~700℃ and the time is 2.5-3h.

6. The method according to claim 1, characterized in that The mass ratio of the biochar to the kitchen digester liquid is 1:(1.4-2.4).

7. The method according to claim 1, characterized in that The temperature under constant temperature conditions is 28-30℃.

8. The method according to claim 1, characterized in that The mixing speed is 120-150 r / min and the mixing time is 33-72 h.

9. The method according to claim 1, characterized in that: The mass ratio of the biochar-biogas liquid mixture to soil is 1:(44.5-52.5).

10. The method according to claim 1, characterized in that The soil is a mixed soil in which the mass ratio of base soil to vermiculite is (3-4):1.

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