CN111485005B

CN111485005B - Method for producing biogas and fertilizer by mixing and fermenting rapeseed cakes and sheep manure

Info

Publication number: CN111485005B
Application number: CN202010424418.0A
Authority: CN
Inventors: 韩睿; 李屹; 熊荣波; 朱德锐; 陈来生
Original assignee: Qinghai Academy of Agricultural and Forestry Sciences
Current assignee: Qinghai Academy of Agricultural and Forestry Sciences
Priority date: 2020-05-19
Filing date: 2020-05-19
Publication date: 2023-03-28
Anticipated expiration: 2040-05-19
Also published as: CN111485005A

Abstract

The invention discloses a method for producing biogas and fertilizer by mixing and fermenting rapeseed cakes and sheep manure. The method comprises the following steps: 1) Preparing raw materials: using sheep manure and rapeseed cakes as raw materials, and crushing the rapeseed cakes; 2) Mixing the rapeseed cake and the sheep manure, adding inoculum and biogas slurry, mixing, and covering a plastic film for composting; 3) Performing biogas fermentation on the raw materials piled and retted in the step 2) to obtain biogas and fermented biogas residues as fertilizers. According to the invention, the optimal mass ratio of the sheep manure to the rapeseed cake dry matter is screened, so that the biogas yield is maximized, the biogas production lasts for a long time in the later stage of fermentation, the fertilizer efficiency of the obtained biogas residues as a fertilizer meets the organic fertilizer standard, the harmlessness and the recycling of agricultural wastes are realized, and the benign cycle of ecology is realized.

Description

Method for producing biogas and fertilizer by mixing and fermenting rapeseed cakes and sheep manure

Technical Field

The invention relates to a method for producing biogas and fertilizer by mixing and fermenting rapeseed cakes and sheep manure, belonging to the field of biogas and compost preparation.

Background

With the rapid development of the world, the consumption of non-renewable energy sources such as coal, petroleum and the like brings an increasingly serious environmental crisis, and the development and utilization of renewable energy sources become more important. The biogas fermentation technology has important significance at present due to the fact that the biogas fermentation technology can process rural organic wastes and simultaneously generate biogas which is renewable clean energy. However, most of the reasons why the development of biogas engineering is restricted today are that there is not a sufficient source of raw materials. The biogas engineering needs to continue to play a role, and the traditional raw materials such as livestock and poultry manure are not enough to be used alone, so that new potential raw materials need to be developed. In recent years, many researchers at home and abroad do a lot of work to search for new fermentation raw materials and search for a better methane fermentation process.

The rapeseed cake is a byproduct after oil pressing of the rapeseed, and can be generated in a large amount inevitably in the processing process of the rapeseed, so that if the rapeseed is not fully utilized, not only is the resource waste caused, but also the environment is polluted, and therefore, the resource utilization of the rapeseed cake has important value. At present, researches on rapeseed cakes are mostly concentrated on the application of preparing feeds and the like, and researches on methane fermentation by taking the rapeseed cakes as raw materials are only reported.

Disclosure of Invention

The invention aims to provide a method for producing biogas and fertilizer by mixing and fermenting rapeseed cakes and sheep manure.

The invention provides a method for producing biogas and fertilizer by mixing and fermenting rapeseed cakes and sheep manure, which comprises the following steps: 1) Preparing raw materials: using sheep manure and rapeseed cakes as raw materials, and crushing the rapeseed cakes;

2) Mixing the rapeseed cake and the sheep manure, adding inoculum and biogas slurry, mixing, and covering a plastic film for composting;

3) Performing biogas fermentation on the raw materials retted in the step 2) to obtain biogas and fermented biogas residues as fertilizers.

In the above method, the rapeseed cake has a pulverized particle size of 0 to 30mm, excluding 0.

In the method, the mass ratio of the dry matters of the rapeseed cakes to the sheep manure is 1-2: 1.

in the method, the mass ratio of the dry matters of the rapeseed cake to the sheep manure can be 2:1.

in the above method, the inoculum is selected from a well-functioning agricultural biogas digester;

the biogas slurry is selected from a well-operated agricultural biogas digester; in particular to an agricultural methane tank which takes sheep manure as raw material for fermentation and has good running.

In the invention, the agricultural methane tank with good operation is common knowledge in the field, and refers to an agricultural methane tank with good airtightness and capable of stably producing methane.

In the method, the addition mass of the inoculum is 10-30% of the total mass of the rapeseed cake and the sheep manure mixture, and specifically can be 10%, 10-15%, 10-20%, or 10-25%;

the ratio of the addition volume of the biogas slurry to the total volume of the rapeseed cake and the sheep manure mixture is 0.75-1.5, and specifically can be 1.

In the above method, the stack retting process is performed with stirring every day;

the retting time is 3-7 d, i.e. the retting process is followed by filling (i.e. retting the raw material) after 3-7 d for fermentation.

In the above method, the preferable time for the retting is 3-5 days in summer and 5-7 days in spring and autumn; specifically, the temperature in the south is high, generally 3 days in summer, in northwest areas such as the Qinghai, the temperature in summer is not high, the day-night temperature difference is large, a lot of time is still needed in summer, about 5 days and about 7 days in autumn, and the temperature of stack retting is guaranteed to reach more than 50 ℃ and not more than 60 ℃.

In the above method, the 2 nd day of the filling in the stack retting process is the 1 st day of the fermentation;

the time for producing the biogas by fermentation can be 22-50 days, specifically 40 days, 30-40 days or 40-50 days, and the time for obtaining the biogas residue by fermentation can be at least 3 months, specifically 3-6 months. Specifically, a fermentation period can be completed in about 30 days from beginning 8 months to middle 9 months, and a fermentation period is suitable from 22 days to 30 days; after the sheep manure and the rapeseed cake are mixed, the gas can be continuously produced for 15 to 20 days; but when the fertilizer is used for the fertilizer, the fermentation time is ensured to be more than 3 months even if the gas is not produced any more; in the embodiment of the invention, the biogas characteristic index is measured, the fermentation is carried out for 40 days, after 40 days, the biogas characteristic index is not measured any more because the fermentation period is finished, but the fermentation of the batch is continued, and the fertilizer efficiency is measured after 3 months.

The invention provides the fertilizer prepared by the method.

The invention has the following advantages:

the invention carries out mixed anaerobic fermentation on the rapeseed cakes and the sheep manure, explores the gas production potential of the rapeseed cakes as the raw material for biogas fermentation and screens the raw material proportion which is most suitable for biogas fermentation so as to improve the comprehensive utilization rate of agricultural waste resources such as the rapeseed cakes. According to the invention, through the characteristics of the biogas produced by mixed fermentation and the determination of the basic fertilizer efficiency, the rapeseed cakes are discovered to have the potential of being used as biogas fermentation raw materials, and the problem of insufficient raw materials in biogas engineering is solved. Meanwhile, the optimum proportion of screened rapeseed cakes to sheep manure dry matter concentration is 2:1. the proportion can combine the advantages of single fermentation of rapeseed cakes and sheep manure, the biogas yield is maximum, and the gas production duration is long in the later fermentation period. In the aspect of fertilizer efficiency, the concentration ratio of the dry matters of the rapeseed cake and the sheep manure is 2:1, the organic matter content is the highest, and the total nutrient content also meets the organic fertilizer standard. The biogas generated by the research can be directly used as fuel gas after being purified, the fermented biogas residues meet the standard of organic fertilizers, the harmlessness and the reclamation of agricultural wastes are realized, and the virtuous cycle of ecology is realized.

Drawings

FIG. 1 is a graph of the daily gas production for each treatment group in an example of the present invention.

FIG. 2 is a graph of cumulative gas production for each treatment group in an embodiment of the present invention.

FIG. 3 shows the ammonia nitrogen concentration change of each treatment group in the example of the present invention.

FIG. 4 shows the change in the concentration of volatile fatty acids in each treatment group in the example of the present invention.

Fig. 5 is a graph of alkalinity concentration changes for each treatment group in an example of the invention.

FIG. 6 is a graph showing the change in the ratio of volatile fatty acid to alkalinity of each treatment group in examples of the present invention.

FIG. 7 shows the change in pH of each treatment group in the examples of the present invention.

Detailed Description

The experimental procedures used in the following examples are all conventional procedures unless otherwise specified.

Materials, reagents and the like used in the following examples are commercially available unless otherwise specified.

Examples

1. Test materials:

the fermentation raw materials are rapeseed cakes (crushed to the granularity of less than 30mm for later use), sheep manure and inocula (from an agricultural methane tank which takes the sheep manure as the raw material and runs well locally, the tightness is good, and the agricultural methane tank can stably generate gas). The fermentation device is an agricultural methane tank of the river Yin town of Guide county of Qinghai province, and the capacity of the methane tank is 8m ³ 。

2. Method for producing a composite material

1. The test development time is from the beginning of 8 months to the middle of 9 months.

2. Design of experiments

Total 7 treatments (all dry mass ratios): handle CK1 and ferment for pure rapeseed cake, handle CK2 and ferment for pure sheep excrement, handle A and be that rapeseed cake and sheep excrement 1:1 mix, handle B and be that rapeseed cake and sheep excrement 1: 2 mix, handle C and be that rapeseed cake and sheep excrement 1: 3 mix, handle D and mix for rapeseed cake and sheep excrement 1:1 and mixing. Each of the above mixture ratios is the ratio of the dry matter concentrations of the sheep manure and the rapeseed cake, and 10% of the inoculum (from a well-functioning agricultural biogas digester) was added for each treatment. Each methane tank is externally connected with a methane flow meter, and the daily methane production condition can be recorded.

3. And (5) composting. And (3) adding a proper amount of biogas slurry (from an agricultural biogas digester which runs well locally) into the 7 pieces of treatment, uniformly stirring, covering the mixture with a plastic film, performing composting, stirring every day in the composting process, and filling after 5-7 days. And filling after 5 days according to the test time of 8 months, and putting the retted raw materials into an agricultural methane tank for methane fermentation.

4. Biogas fermentation: and putting the piled and retted processing raw materials into an agricultural methane tank for methane fermentation. Fermenting for 40 days. Gas production was recorded at the same time each day, starting on filling day 2 (fermentation day 1). In addition, stirring once every 3 days, and simultaneously taking each treated biogas slurry sample to measure indexes such as ammonia nitrogen, volatile fatty acid, alkalinity, pH value and the like.

5. And (4) measuring the fertilizer efficiency. After fermenting for 3 months, respectively taking biogas residues fermented by each biogas digester, and measuring fertilizer efficiency indexes such as total nitrogen, total phosphorus, total potassium, organic matters, alkaline hydrolysis nitrogen, quick-acting potassium, quick-acting phosphorus and the like.

3. Results and analysis

1. Daily and cumulative gas production for each treatment

As can be seen from FIG. 1, the daily gas production of each treatment group rapidly increased at the initial stage of fermentation, and the peak of gas production was observed almost at day 7. CK2 is treated in the first 15 days of fermentation, the daily gas yield of sheep manure is lowest, and the highest peak appears in the 7 th day, namely 1.996m ³ The gas production rate is rapidly reduced after the gas production peak of 20 days, and is stabilized at 0.3m after 23 days ³ Fluctuating left and right. When CK1 is treated, rapeseed cakes have 3 peak gas production peaks, and the daily gas production of 7 days of fermentationIs 3.001m ³ Then slowly decreased to reach a maximum yield of 5.056m on day 17 ³ After the decrease, the peak reached 4.314m at day 3 on day 20 ³ Then the gas production rate rapidly decreases, the daily gas production rate is basically 0 after 31 days, and the gas production stage is finished. And E, treating rapeseed cakes and sheep manure 2:1 the daily gas production is maximum after mixed fermentation, the peak gas production period lasts 14 days, and the maximum yield is 6.797m on day 7 ³ 。

As can be seen from FIG. 2, after 40 days of fermentation, the cumulative gas production of each treatment group was as follows: CK1 processing is 61.22m ³ (ii) a The CK2 is processed to be 31.28m ³ (ii) a Treatment A was 65.608m ³ (ii) a Treatment B was 54.921m ³ (ii) a Treatment C was 45.041m ³ (ii) a Treatment D was 42.008m ³ (ii) a Treatment E was 79.132m ³ . And E, treating the rapeseed cakes and the sheep manure in a ratio of 2: the cumulative gas production at 1 was the greatest and higher than the other treatment groups. When CK1 is treated and the rapeseed cake is fermented singly, the accumulated gas production is large and is 61.22m ³ And the fermentation period is short, which indicates that the rapeseed cakes have the potential to be used as a biogas fermentation raw material. But no gas is produced after fermentation for 33 days, which indicates that the gas production duration is shorter; when the CK2 is treated and the pure sheep manure is fermented, the accumulated gas production is low, the fermentation period is long, but the gas production duration is long, and the gas can be produced more stably in the later period. Therefore, the two advantages are combined in the mixed fermentation process to make up for the deficiency. As can be seen from figure 2, the accumulated gas production after mixed fermentation is higher than that of pure sheep manure single fermentation, wherein in the step E of treatment, the ratio of rapeseed cakes to sheep manure is 2: the accumulated gas production at 1 hour is the maximum and is higher than other mixing ratios; and the fermentation period is short, the duration is long, and the advantages of the two fermentation raw materials are well integrated.

2. Variation of ammonia nitrogen concentration in each treatment

In the process of methane fermentation, the ammonia nitrogen concentration needs to be stably maintained within a certain range to ensure the smooth production of methane. When the concentration of ammonia nitrogen is too high (more than 800 mg/L), the inhibition effect on a fermentation system can be caused. As can be seen from FIG. 3, the ratio of the treated CK1 rapeseed cake to the treated E rapeseed cake to the sheep manure is 2: the ammoniacal nitrogen concentration at 1 can be in the normal range, indicating that these 2 treatments do not form ammonia inhibition during anaerobic digestion. In other treatments, the ammonia nitrogen concentration is higher than 800mg/L in several days before fermentation, and then gradually decreases to be slowly lower than 800mg/L, which indicates that other treatments have ammonia inhibition of different degrees.

3. Variation of volatile fatty acid concentration for each treatment

Volatile fatty acids are important intermediate products generated by organic matter degradation in the anaerobic digestion process and are also one of main factors influencing anaerobic digestion. The concentration of volatile fatty acids accumulated during fermentation should be less than 3500mg/L, since high concentrations of volatile fatty acids inhibit the action of methanogens.

As can be seen from FIG. 4, the change of the concentration of volatile fatty acids in rapeseed cake fermentation is most obvious when CK1 is treated, and the concentration of volatile fatty acids in rapeseed cake fermentation increases from 7819mg/L to 9890mg/L from day 1 to day 4; from day 4 to day 7, the concentration of the biogas is reduced from 9890mg/L to 1967mg/L, and a biogas production peak appears on day 7; the change is stable in 10 th to 22 th days, the average value is 3081mg/L, the range belongs to the normal range, and most of the gas production rate of the rapeseed cake fermentation is finished in the period; and then the concentration of the volatile fatty acid is increased sharply and reaches 20178mg/L after the test is finished, and in the period, the concentration of the volatile fatty acid is too high, so that the methane production stage is inhibited, and the gas production rate is reduced rapidly until the gas production rate is not increased. Compared with CK1 treatment, the concentration change of volatile fatty acid in the whole anaerobic fermentation process of other treatments is stable and basically within a normal range, and the gas production condition is relatively stable.

4. Variation of alkalinity concentration for each treatment

Alkalinity is often used to reflect the buffering capacity of anaerobic fermentation systems and may indicate the stability of the fermentation system. When the alkalinity is 3000-8500 mg/L, and the ratio of the volatile fatty acid to the alkalinity is 2: when the fermentation temperature is more than 1, the biogas fermentation is stable; when the ratio is higher than 0.8, the anaerobic digestion process is inhibited. Fig. 5 and 6 reflect the variation of the alkalinity concentration and the volatile fatty acid/alkalinity of each treatment. As can be seen from FIGS. 5 and 6, the alkalinity concentration of the rapeseed cake gradually decreased during CK1 treatment, from day 7 to day 22, the alkalinity concentration decreased from 5082.7mg/L to 4264.2mg/L, the ratio of volatile fatty acid/alkalinity was less than 0.8, and the biogas fermentation was stable. After day 22 the ratio of volatile fatty acids/alkalinity was greater than 0.8 and methanogenesis was inhibited. For each of the other treatments, the alkalinity concentration varied entirely within the range, and the ratio of volatile fatty acid/alkalinity was less than 0.8.

5. Comparison of pH values of fermentation systems of the respective treatments

The pH is also one of the major factors affecting the progress of anaerobic digestion. The methanogen can grow at the pH value of 6.0-8.0, and the optimal pH value of the methanogen for gas production is 6.5-7.5. As can be seen from FIG. 7, the overall pH value of the single fermentation of rapeseed cakes is small, between 5.03 and 6.04 when CK1 is treated; treating CK2, wherein the pH value of sheep manure is 7.20-8.19, and the sheep manure is neutral and alkaline; and in other treatment, the sheep manure and the rapeseed cakes are mixed and fermented, and the pH is neutral and relatively reasonable.

6. Comparison of the results of the respective treatments

And (4) carrying out basic fertilizer efficiency determination on 7 fermented biogas residues. As can be seen from Table 1, the treated products were high in the content of nutrients and were usable as fertilizers. Wherein the organic matter content is sequentially treated from E, C, CK2, D, B, A and CK1 from a plurality of times. Treatment E was highest at 327.32g/Kg. The total nutrient is the sum of total nitrogen, total phosphorus and total potassium, and the total nutrient content is more than 5 percent by calculation, meets the standard of organic fertilizer, can be directly returned to the field, and can meet the requirements of people on life and agricultural production.

TABLE 1 determination of various indexes of fertilizer efficiency

In conclusion, the optimal mass ratio of the screened rapeseed cakes to the dry matters of the sheep manure is 2:1, the mixture ratio can combine the advantages of single fermentation of rapeseed cakes and sheep manure, the methane yield is maximum, and the duration of the methane production is long in the later stage of fermentation. In the aspect of fertilizer efficiency, the concentration ratio of the dry matters of the rapeseed cake and the sheep manure is 2:1, the organic matter content is the highest, and the total nutrient content also meets the organic fertilizer standard.

Claims

1. A method for producing biogas and fertilizer by mixing and fermenting rapeseed cakes and sheep manure comprises the following steps: 1) Preparing raw materials: using sheep manure and rapeseed cakes as raw materials, and crushing the rapeseed cakes;

2) Mixing the rapeseed cake and the sheep manure, adding inoculum and biogas slurry, mixing, covering with a plastic film, and composting;

the mass ratio of the dry matters of the rapeseed cake to the sheep manure is 1-2: 1;

2. The method of claim 1, wherein: the crushed grain diameter of the rapeseed cake is 0-30 mm, and 0 is not included.

3. The method of claim 1, wherein: the mass ratio of the dry matters of the rapeseed cake to the sheep manure is 2:1.

4. the method of claim 1, wherein: the inoculum is selected from a well-functioning agricultural biogas digester;

the biogas slurry is selected from a well-operated agricultural biogas digester.

5. The method according to claim 1 or 4, characterized in that: the adding mass of the inoculum is 10-30% of the total mass of the rapeseed cake and the sheep manure mixture;

the ratio of the addition volume of the biogas slurry to the total volume of the rapeseed cake and the sheep manure mixture is 0.75-1.5.

6. The method of claim 1, wherein: stirring every day in the process of composting;

the time for composting is 3-7 days.

7. The method according to claim 1 or 6, characterized in that: the time of the stack retting was as follows: the summer is 3-5 days, and the spring and autumn is 5-7 days.

8. The method of claim 1, wherein: the time for producing the biogas by fermentation is 40-50 days, and the time for obtaining biogas residues by fermentation is at least 3 months.

9. The fertilizer produced by the method of any one of claims 1-8.