1. A method for producing biogas by the joint anaerobic fermentation of pig farm liquid dung and corn straws treated by biochar loaded with nano zero-valent iron is characterized by comprising the following steps:

(1) filtering the pig farm liquid dung to remove impurities;

(2) crushing the corn straws to 1-3cm in length and drying to constant weight;

(3) treating the pig farm liquid dung by using charcoal loaded nano zero-valent iron, and performing oscillation treatment;

(4) uniformly mixing the dried corn straw material with the pig farm liquid dung obtained in the step (3), and storing for 2-3 days under the condition of medium temperature;

(5) adding active strains into the mixture obtained in the step (4) according to the total volume of the fermentation liquid, adding water to adjust the content of the dry matter (TS) of the corn straws to 6-8% according to the total mass of the fermentation liquid, adjusting the pH value of the fermentation liquid to 6-8, and performing medium-temperature combined anaerobic fermentation.

2. The method for producing biogas by the combined anaerobic fermentation of the pig farm wastewater treated by the biochar-loaded nano zero-valent iron and the corn stalks according to claim 1, wherein the mass ratio of the biochar-loaded nano zero-valent iron to the pig farm wastewater in the step (3) is 1:8 to 1:14, the oscillation frequency is 60 to 100rpm, and the oscillation time is 12 to 36 hours.

3. The method for producing the biogas by the joint anaerobic fermentation of the pig farm liquid manure and the corn stalks treated by the biochar-loaded nano zero-valent iron according to claim 1, wherein in the step (4), the mass ratio of the pig farm liquid manure to the corn stalks is 1:1 to 1: 5.

4. The method for producing biogas by the joint anaerobic fermentation of pig farm wastewater and corn stover treated with charcoal-loaded nano zero-valent iron according to claim 1, wherein in step (5), the pH value is adjusted to 7.

5. The method for producing biogas by the combined anaerobic fermentation of the pig farm wastewater and the corn stalks treated by the biochar loaded with the nano zero-valent iron according to claim 1, wherein in the step (5), the fermentation temperature is 25 ℃ to 35 ℃.

6. The method for producing biogas by the combined anaerobic fermentation of the pig farm liquid manure and the corn stalks treated by the biochar loaded with the nano zero-valent iron, according to the claim 1, is characterized in that in the step (5), the addition amount of the active strains is 10-20% based on the total volume of the fermentation liquid.

7. The method for producing biogas by the combined anaerobic fermentation of the pig farm manure water and the corn stalks treated by the biochar loaded with the nano zero-valent iron according to claim 1, wherein in the step (5), the active strains are biogas slurry which is rich in anaerobic microbial flora with higher activity and is obtained after the corn stalks and the pig manure water are mixed at 35 ℃ (the dry matter (TS) content of the corn stalks is 6-8%) in the mixture) and the wet anaerobic fermentation is carried out for 60 days.

8. The method for producing biogas by the combined anaerobic fermentation of the pig farm liquid manure and the corn stalks treated by the biochar-loaded nano zero-valent iron according to any one of claims 1 to 7, wherein the pig farm liquid manure is a liquid part after the dry-wet separation of the large-scale pig farm liquid manure.

9. The method for producing biogas by combined anaerobic fermentation of pig farm wastewater and corn stover treated with nano zero-valent iron loaded with biochar according to claim 8, wherein the method is capable of increasing the biogas yield by at least 70% compared to the combined anaerobic fermentation of pig farm wastewater and corn stover that is not treated with nano zero-valent iron loaded with biochar.

10. The method for producing biogas by combined anaerobic fermentation of pig farm wastewater and corn stover treated with nano zero-valent iron loaded with biochar according to claim 1, wherein the method can shorten the fermentation period by at least 42 days compared to the combined anaerobic fermentation of pig farm wastewater and corn stover which is not treated with nano zero-valent iron loaded with biochar.

Background

As is well known, the technology of producing biogas by anaerobic fermentation is one of the most common technologies for treating the culture wastewater and various agricultural wastes at present. However, the gas production efficiency of the pig farm wastewater by single fermentation is low, the economic value is difficult to realize, and the gas production efficiency can be greatly improved if the pig farm wastewater and the crop straws are used for producing the methane by combined anaerobic fermentation. The existing research shows that the combined anaerobic fermentation technology of two or more than two organic materials can not only realize the problem of normalization treatment of different organic wastes, but also obviously improve the gas production efficiency of a fermentation system, has the advantages of maintaining the operation stability of the system, relieving the inhibition effect of toxic chemical substances, ensuring the nutrition balance of the system and the like, has convenient treatment of residues after fermentation, can be directly used as organic fertilizers, and does not have the problem of secondary pollution.

Studies by Pongpeng et al (2019, safety and environmental bulletin, 19(05): 1767-: the mixed anaerobic fermentation gas production performance of the pig manure and the corn straw is obviously better than that of single pig manure fermentation, the suitable mixture ratio of the pig manure and the corn straw is 8:2, the average methane mass fraction reaches 64.54%, the cumulative gas production and the dry matter (TS) gas production are 9943.1mL and 0.273L/g respectively, and the gas production is 79.33% and 79.61% higher than that of single pig manure fermentation respectively. Research on Liao et al (2019, China methane 37(06):3-10) shows that the cumulative yield of methane in a test group with 1:1 of pig manure and straw under the same inoculation amount is higher than 2: 1; the ratio of pig manure to straw is 1:1, the starting speed of the test group with the inoculation amount of 50% is the fastest, the accumulated methane yield is also the highest, the test group is the best combination of the raw material proportion and the inoculation amount in the research, and the accumulated methane yield and the accumulated VS methane yield are 6801.67mL and 127.07mL g-1VS respectively.

In the anaerobic fermentation technology which uses the microorganism to be converted into the core, the combined anaerobic fermentation technology of two or more substrates has the advantages of improving the gas production of the biological substrates, maintaining the stability of the system, diluting toxic chemical substances, ensuring the nutrient balance of the system and the like, and residues after fermentation are convenient to treat, can be directly used as organic fertilizers, and does not have the problem of secondary pollution. Although a plurality of scholars do some research work aiming at the mixed fermentation of the pig manure and the crop straws, the prior art still has the technical problems of long fermentation and low gas yield.

Therefore, there is a need in the art for new methods for producing biogas by anaerobic fermentation.

Disclosure of Invention

In view of the above, the invention aims to provide a method for producing biogas by performing anaerobic fermentation on pig farm liquid dung and corn straws treated by using charcoal loaded with nano zero-valent iron, so as to solve the technical problems of long fermentation period and low gas production rate in the prior art.

The object of the present invention and the solution of the technical problem can be achieved by the following technical solutions.

The invention provides a method for producing biogas by the joint anaerobic fermentation of pig farm liquid dung and corn straws treated by biochar loaded with nano zero-valent iron, which comprises the following steps:

(1) filtering the pig farm liquid dung to remove impurities;

(2) crushing the corn straws to 1-3cm in length and drying to constant weight;

(3) treating the pig farm liquid dung by using charcoal loaded nano zero-valent iron, and performing oscillation treatment;

(4) uniformly mixing the dried corn straw material with the pig farm liquid dung obtained in the step (3), and storing for 2-3 days at a medium temperature;

(5) adding active strains into the mixture obtained in the step (4) according to the total volume of the fermentation liquid, adding water to adjust the content of dry matters (TS) of the corn straws to 6-8% according to the total mass of the fermentation liquid, adjusting the pH value of the fermentation liquid to 6-8, and performing medium-temperature combined anaerobic fermentation.

In an embodiment of the method, in the step (3), the mass ratio of the biochar-loaded nano zero-valent iron to the pig farm liquid manure is 1:8 to 1:14, the oscillation frequency is 60-100rpm, and the oscillation time is 12-36 h.

In an embodiment of the process of the present invention, in step (4), the mass ratio of the pig farm liquid manure to the corn stover is 1:1 to 1: 5.

In an embodiment of the process of the invention, in step (5), the pH is adjusted to 7.

In an embodiment of the process of the present invention, in step (5), the temperature of the mesophilic fermentation is 25 ℃ to 35 ℃.

In an embodiment of the method of the present invention, in the step (5), the active species is added in an amount of 10 to 20% based on the total volume of the fermentation broth.

In the embodiment of the method, in the step (5), the active strain is biogas slurry which is rich in anaerobic microbial flora with higher activity and is obtained after the corn straw and the pig manure water are mixed under the condition of 35 ℃ (in the mixture, the content of the dry matter (TS) of the corn straw is 6-8%) and the wet anaerobic fermentation is carried out for 60 days.

In an embodiment of the process of the invention, the pig farm liquid manure is the liquid fraction of the large-scale pig farm liquid manure after dry-wet separation.

In an embodiment of the method, compared with the combined anaerobic fermentation of pig farm liquid manure and corn straws which are not treated by biochar loaded with nano zero-valent iron, the method can improve the biogas yield by at least 70%.

In an embodiment of the method, compared with the combined anaerobic fermentation of the pig farm liquid manure and the corn straws which are not treated by the biochar loaded with the nano zero-valent iron, the method can shorten the fermentation period by at least 42 days.

Compared with the prior art, the method has the beneficial technical effects. According to the implementation scheme, the method provided by the invention combines the biochar loaded nano zero-valent iron to treat the pig farm liquid manure and the corn straws to generate the biogas, can realize multi-material normalization treatment, greatly improves the biogas production efficiency, increases the biochar and iron ion content in the biogas residue and biogas slurry, and improves the fertilizer efficiency.

Drawings

FIG. 1 shows a device for producing biogas by combining pig farm liquid dung and corn straws treated by the biochar loaded with nano zero-valent iron and anaerobic fermentation.

FIG. 2 shows a comparison graph of biogas production efficiency of pig farm liquid manure treated by biological carbon loaded with nano zero-valent iron and corn straw through combined anaerobic fermentation.

Detailed Description

The present invention will be further described with reference to specific examples to provide those skilled in the art with a better understanding of the present invention, but the present invention is not limited to the following examples. It should be noted that variations and modifications can be made by persons skilled in the art without departing from the spirit of the invention. All falling within the scope of the present invention.

The inventors of the present invention have surprisingly found that when pig farm liquid manure and corn stalks are treated to produce biogas in combination with biochar-loaded nano zero-valent iron, the fermentation period can be significantly shortened, the gas yield can be increased, and the methane content can be increased. Therefore, the invention provides a method for producing biogas by the joint anaerobic fermentation of pig farm liquid dung and corn straws treated by biochar loaded with nano zero-valent iron, which comprises the following steps:

(1) filtering the pig farm liquid dung to remove impurities;

(2) crushing the corn straws to 1-3cm in length and drying to constant weight;

(3) treating the pig farm liquid dung by using charcoal loaded nano zero-valent iron, and performing oscillation treatment;

(4) uniformly mixing the dried corn straw material with the pig farm liquid dung obtained in the step (3), and storing for 2-3 days at a medium temperature;

(5) adding active strains into the mixture obtained in the step (4) according to the total volume of the fermentation liquid, adding water according to the total mass of the fermentation liquid to adjust the content of dry matters (TS) of the corn straws to 6-8%, adjusting the pH value of the fermentation liquid to 6-8, and performing medium-temperature combined anaerobic fermentation.

In an embodiment of the method of the present invention, the corn stover is post-harvest corn stover in autumn.

The liquid manure of the pig farm refers to the liquid part of the dry-wet separation of the manure of the large-scale pig farm, and the dry matter (TS) content of the liquid manure is less than 1 percent. The pig farm waste water often contains impurities such as sand, stones, plastics and the like, and therefore, in an embodiment of the method of the present invention, the above impurities in the pig farm waste water may be removed by filtering through a screen.

In one embodiment of the invention, to increase the water absorption of the corn stover after mixing with the pig farm manure water, the stover may be comminuted to a length of 1 to 3cm, for example to 1cm, 1.5 cm, 2.0cm, 2.5cm, 3cm, and any number between any two, for example 1.2 cm, 1.3cm, etc. The straw is crushed and dried and then is uniformly mixed with the pig farm liquid dung, so that the pig farm liquid dung can be fully absorbed.

In one embodiment of the invention, the biochar-supported nano zero-valent iron is well known in the art and can be prepared by a liquid phase reduction method.

In one embodiment of the invention, in the step (3), the mass ratio of the biochar-loaded nano zero-valent iron to the pig farm liquid manure is 1:8 to 1:14. The frequency of the oscillation treatment is 60-100rpm, and the oscillation time is 12-36 h.

In a specific embodiment of the present invention, in step (3), the frequency of the oscillation treatment may be 60, 70, 75, 80, 85, 90, 95, 100rpm, and the oscillation time may be 12h, 12.5h, 13h, 13.5h, 13h, 14h, 14.5h, 15h, 15.5h, 16h, 16.5h, 17h, 17.5h, 18h, 18.5h, 19h, 19.5h, 20h, 20.5h, 21h, 21.5h, 226h, 22.5h, 23h, 23.5h, 24h, 24.5h, 25h, 25.5h, 26h, 26.5h, 27h, 27.5h, 28h, 28.5h, 29h, 29.5h, 30h, 30.5h, 31h, 31.5h, 32h, 32.5h, 33h, 33.5h, 34h, 34.5h, 34h, 35h, 36 h.

In a specific embodiment of the present invention, in step (3), the mass ratio of the biochar-loaded nanoscale zero-valent iron to the pig farm liquid manure may be, for example, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, and any ratio therebetween, such as 1:8.2, 1:9.3, 1:10.4, 1:11.2, 1:12.3, 1:13.5, 1:14.5, and the like.

In a specific embodiment of the present invention, in step (4), the mass ratio of the pig farm liquid manure to the dried straw may be, for example, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, and any ratio between two ratios, for example, 1:1.1, 1:1.2, 1:2.3, 1:2.4, 1:4.2, 1:4.3, etc.

In the preferred embodiment of the invention, after the dried corn stalk material and the pig farm liquid manure obtained in the step (3) are uniformly mixed according to the mass ratio of 1:1-5, the mixture of the dried corn stalk material and the pig farm liquid manure can be vibrated for 12-36h at the temperature of 35.0 +/-0.5 ℃ and the frequency of 60-100rpm, so as to ensure that the corn stalk can fully absorb the pig farm liquid manure obtained in the step (3). In a specific embodiment of the present invention, the frequency of the oscillation treatment may be 60, 70, 75, 80, 85, 90, 95, 100rpm, and the oscillation time may be 12h, 12.5h, 13h, 13.5h, 13h, 14h, 14.5h, 15h, 15.5h, 16h, 16.5h, 17h, 17.5h, 18h, 18.5h, 19h, 19.5h, 20h, 20.5h, 21h, 21.5h, 226h, 22.5h, 23h, 23.5h, 24h, 24.5h, 25h, 25.5h, 26h, 26.5h, 27h, 27.5h, 28h, 28.5h, 29h, 29.5h, 30h, 30.5h, 31h, 31.5h, 32h, 32.5h, 33h, 33.5h, 34h, 34.5h, 35.5h, 35h, 36 h.

In the embodiment of the invention, the active strain is biogas slurry which is rich in anaerobic microbial flora with higher activity and is obtained after the mixture of corn straws and pig manure water (the content of dry matter (TS) of the corn straws in the mixture is 6-8%) is subjected to wet anaerobic fermentation for 60 days at the temperature of 35 ℃. The active strain contains a large amount of active methanogenic flora, and can rapidly improve the number and the activity of the effective methanogenic flora after being added into a fermentation system, greatly shorten the starting time and greatly improve the gas production efficiency.

In the embodiment of the invention, in order to remove the large undegradable particle substances such as stones, sands, lignins and the like in the active strain, the active strain can be sieved by a 40-mesh sieve.

In the embodiment of the invention, the fermentation liquid is a mixture at the beginning of anaerobic fermentation, and comprises corn straws, pig farm manure water treated by charcoal-loaded nano zero-valent iron, active strains and water. In the step (5), 10-20% of active anaerobic bacteria is added according to the total volume of the fermentation liquid. In particular embodiments of the invention, the amount of active species added may be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% of the total volume of the fermentation liquor.

In the embodiment of the present invention, in order to sufficiently perform anaerobic fermentation and increase the biogas yield, the fermentation liquid should be uniformly mixed and the pH thereof should be adjusted to 6 to 8 during anaerobic fermentation. In a particular embodiment of the invention, in step (5), the fermentation liquor pH is adjusted to 6, 6.5, 7, 7.5, 8, and values between any two values, e.g. 6.2, 6.4, 7.4, 7.6, 7.7, 7.8, 7.9, preferably to neutral, i.e. pH 7.

In an embodiment of the invention, in step (5), after adding the active anaerobic bacteria, the dry matter (TS) content of the corn stalks is adjusted to 6 to 8 percent by adding water based on the total mass of the fermentation liquor. In a specific embodiment of the present invention, the corn stover dry matter (TS) content may be adjusted to 6%, 6.1%, 6.2%, 6.3%, 6.4%, 6.5%, 6.6%, 6.7%, 6.8%, 6.9%, 7.0%, 7.1%, 7.2%, 7.3%, 7.4%, 7.5%, 8%, preferably the straw dry matter (TS) content is adjusted to 8%.

It is well known to those skilled in the art that mesophilic fermentation refers to fermentation conducted at temperatures not higher than 35 ℃, for example at fermentation temperatures of 25 ℃ to 35 ℃. In a specific embodiment, the fermentation temperature may be 26 ℃, 27 ℃, 28 ℃, 29 ℃, 30 ℃, 31 ℃, 32 ℃, 33 ℃, 34 ℃ and 35 ℃.

In an embodiment of the invention, the method of the invention can increase the biogas yield by at least 70%, such as 71%, 72%, 72.5%, 73%, 74%, 74.5%, 75% under the same conditions as compared to anaerobic fermentation of pig farm manure in combination with corn stover without biochar-loaded nano zero valent iron treatment.

In an embodiment of the present invention, the method of the present invention can shorten the fermentation period by at least 42 days, for example, 42 days, 43 days, 44 days, etc., under the same conditions, compared to fermenting the pig farm manure in combination with corn stover without the treatment of the biochar-supported nano zero valent iron.

Preferred embodiments of the present invention will be described in detail with reference to the following examples. It should be understood that the following examples are given for illustrative purposes only and are not intended to limit the scope of the present invention. Numerous modifications and alterations of this invention may be made by those skilled in the art without departing from the spirit and scope of this invention, all of which fall within the purview of the appended claims.

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.

In the following examples, the active strain is biogas slurry containing abundant anaerobic microorganism flora with higher activity after mixing corn stalks and pig manure water (the content of corn stalk dry matter (TS) in the mixture is 6-8%) and performing anaerobic fermentation for 60 days at 35 ℃).

The piggery wastewater is a liquid part obtained after dry-wet separation of the excrement of a large-scale piggery, and the dry matter (TS) content of the piggery wastewater is less than 1%.

The air-blast drying oven is DHG-9023A produced by Shanghai-Hengyun scientific instruments Co.

The air bath constant temperature oscillator is CHA-S produced by State electric appliances, Inc.

Example 1

Biochar is prepared from corn straws by an oxygen-limited cracking method at 400 ℃ (Douguna, preparation modification of straw biochar and research on adsorption efficiency of nitrogen and phosphorus in water [ D ]. Harbin Industrial university, 2018. academic thesis), and biochar-loaded nano zero-valent iron is prepared by a pyrolysis-liquid phase reduction method (Zhuqing Tao, Wu Yidao, Guo Hui, etc.. preparation of biochar-loaded nano zero-valent iron and research progress on removal of pollutants in water [ J ]. energy chemical industry, 2018,39(04): 73-77).

In this embodiment, the method for producing biogas by the anaerobic fermentation of the pig farm liquid dung treated by the biochar loaded with the nano zero-valent iron and the corn stalks in a combined manner is realized by the following steps:

step one, pig farm liquid dung is filtered to remove sand, plastics and other impurities, and the pig farm liquid dung is filled into a plastic barrel for standby.

And step two, crushing the corn straws to 1-3cm, and drying the crushed corn straws to constant weight by using a blast drying oven.

And step three, subpackaging the pig farm liquid dung into 500mL serum bottles, and filling 376 mL into each serum bottle.

And step four, filling 40mg of the biochar loaded nano zero-valent iron into a 500mL serum bottle, and quickly placing the serum bottle into an air bath constant-temperature oscillator with the temperature of 35.0 +/-0.5 ℃ to oscillate for 12 hours at the frequency of 60rpm so as to uniformly mix.

Weighing 24g of dried corn straws, putting the weighed corn straws into a serum bottle in the fourth step, storing the corn straws for 2 days at the medium temperature, adding 40mL (10 percent of the total volume of fermentation liquid) of active strains which pass through 40 meshes, adding water to adjust the content of dry matters (TS) of the corn straws to 6 percent, adjusting the pH value to 7, and fermenting at the medium temperature of 35 ℃.

In addition, 3 parts of corn straw 5g and 5mL of pig farm manure were weighed and the straw TS and VS (organic dry matter) contents were measured using a high temperature drying oven and a muffle furnace. Weighing 24g (calculated by TS) of corn straw and 376 mL of pig farm liquid dung (TS content is less than 1%) treated by biochar loaded nano zero-valent iron, adding 40mL of active strains which pass through 40 meshes, and adjusting the pH value to be neutral; weighing 24g (calculated by TS) of corn straw and untreated pig farm liquid dung, adding 40mL of active strains which pass through 40 meshes, adding water to adjust the content of dry matter (TS) of the corn straw to 6%, adjusting the pH value to 7, and carrying out medium-temperature (35 ℃) anaerobic fermentation to obtain a Control (CK).

The anaerobic fermentation reactor used in the test mainly comprises a 500mL serum bottle, a 1000mL triangular bottle and a 500mL glass tube with scales (see figure 1), and is respectively used as a digestion bottle, a biogas gas collection bottle and a water collection measuring cylinder of raw materials. A latex tube is connected to form a set of gas communication device, the digestion bottle and the gas collection bottle must be strictly sealed, a gas taking port and a liquid taking port are arranged, glass cement is matched with a rubber plug to seal, and gas tightness inspection is carried out at any time.

21100mL of biogas is co-produced by the method of pre-treating and re-fermenting within 60 days, and the amount of untreated biogas is 12400 mL. Therefore, after the pig farm liquid dung treated by the biochar loaded with the nano zero-valent iron and the corn straw are subjected to combined anaerobic fermentation to produce the biogas, compared with CK, the method in the embodiment 1 improves the biogas yield by 70.16%; the treatment process produces 8700mL more biogas than CK, and the gas production amount still needs 42 days to reach 21100mL according to the average gas production amount of 206mL/d of CK, so that the gas production fermentation period can be shortened by 42 days.

Example 2

In this embodiment, the method for producing biogas by the anaerobic fermentation of the pig farm liquid dung treated by the biochar loaded with the nano zero-valent iron and the corn stalks in a combined manner is realized by the following steps:

step one, filtering the pig farm liquid dung to remove impurities such as sand, plastics and the like, and filling the pig farm liquid dung into a plastic barrel for standby;

step two, crushing the corn straws to 1-3cm, and drying the crushed corn straws to constant weight by using a blast drying oven;

step three, subpackaging the pig farm liquid dung into 500mL serum bottles, and filling 372mL of each serum bottle;

step four, filling 30mg of biochar-loaded nano zero-valent iron into a 500mL serum bottle, and quickly placing the serum bottle into an air bath constant-temperature oscillator at 35.0 +/-0.5 ℃ to oscillate for 24 hours at the frequency of 80 rpm;

weighing 28g of dried corn straws, putting into a serum bottle in the fourth step, storing for 3 days at the medium temperature, adding 40mL of active strains which pass through 40 meshes, adding water to adjust the content of dry substances (TS) of the corn straws to 7%, adjusting the pH value to 7, and fermenting at the medium temperature of 35 ℃.

In addition, 3 parts of corn stover 5g and 5mL of pig farm manure were weighed and the dry matter (TS) and VS (organic dry matter) contents of the corn stover were measured using a high temperature drying oven and a muffle furnace. Weighing 28g (calculated by TS) of corn straw and 372mL of pig farm liquid dung processed by biochar loaded with nano zero-valent iron, adding 40mL of active strains passing through 40 meshes, adding water to adjust the content of dry matter (TS) of the corn straw to 7%, and adjusting the pH value to 7; weighing 24g (in TS) of corn straw and untreated pig farm liquid manure, adding 40mL of active strain passing through 40 meshes, adjusting the pH value to be neutral, and performing medium-temperature (35 ℃) anaerobic fermentation to serve as a Control (CK).

The anaerobic fermentation reactor used in the test mainly comprises a 500mL serum bottle, a 1000mL triangular bottle and a 500mL glass tube with scales (see figure 1), and is respectively used as a digestion bottle, a biogas collecting bottle and a water collecting measuring cylinder of raw materials. A set of gas communication device is formed by connecting latex tubes, a digestion bottle and a gas collecting bottle must be strictly sealed, a gas taking port and a liquid taking port are arranged, glass cement is matched with a rubber plug for sealing, and gas tightness inspection is carried out at any time.

22300mL of biogas is co-produced by the method of pre-treating and re-fermenting within 60 days, and the amount of untreated biogas is 13100 mL. Therefore, after the pig farm liquid dung treated by the biochar loaded with the nano zero-valent iron and the corn straw are subjected to combined anaerobic fermentation to produce the biogas, compared with CK, the method in the embodiment 2 improves the biogas yield by 70.23%; 9200mL of biogas is produced more than CK in the treatment process, and the biogas production amount still needs 42 days to reach 21100mL according to the average gas production amount of 278mL/d of CK, so that the biogas production fermentation period can be shortened by 42 days.

Example 3

In this embodiment, the method for producing biogas by the anaerobic fermentation of the pig farm liquid dung treated by the biochar loaded with the nano zero-valent iron and the corn stalks in a combined manner is realized by the following steps:

step one, filtering pig manure water to remove impurities such as sand, plastics and the like, and filling the pig manure water into a plastic barrel for later use;

step two, crushing the corn straws to 1-3cm, and drying the crushed corn straws to constant weight by using a blast drying oven;

and step three, subpackaging the pig manure into 500mL serum bottles, and filling 368 mL into each serum bottle.

And step four, filling 50mg of the biochar loaded nano zero-valent iron into a 500mL serum bottle, and quickly placing the serum bottle into an air bath constant-temperature oscillator at 35.0 +/-0.5 ℃ to oscillate for 36h at the frequency of 100 rpm.

Weighing 32g of dried corn straws, putting into a serum bottle in the fourth step, storing for 3 days at the medium temperature, adding 40mL of active strains, adding water to adjust the TS 8 percent of the corn straws, adjusting the pH value to 7, and fermenting at the medium temperature of 35 ℃.

In addition, 3 parts of corn straw 5g and about 5mL of pig farm liquid manure were weighed and the straw TS and VS (organic dry matter content) contents were measured using a high temperature drying oven and a muffle furnace. Weighing 32g (calculated by TS) of corn straw and untreated pig farm liquid dung, adding 40mL of active strains which pass through 40 meshes, adding water to adjust the content of the dry matter (TS) of the corn straw to 8 percent, adjusting the pH value to 7, and carrying out medium-temperature 35 ℃ anaerobic fermentation to be used as a Control (CK).

The anaerobic fermentation reactor used in the test mainly consists of a 500mL serum bottle and a 100mL measuring cylinder (see FIG. 1), and is respectively used as a digestion bottle, a biogas collecting bottle and a water collecting measuring cylinder of raw materials. A set of gas communication device is formed by connecting latex tubes, a digestion bottle and a gas collecting bottle must be strictly sealed, a gas taking port and a liquid taking port are arranged, glass cement is matched with a rubber plug for sealing, and gas tightness inspection is carried out at any time.

The method for pre-treating and then fermenting produces 23500mL of biogas in 60 days, and the amount of untreated biogas is 13600 mL. Therefore, after the pig farm liquid dung treated by the biochar loaded with the nano zero-valent iron and the corn straw are subjected to combined anaerobic fermentation to produce the biogas, compared with CK, the method in the embodiment 2 improves the biogas yield by 72.79%; 9900mL of methane is produced more than CK in the treatment process, and the methane production amount still needs 44 days to reach 21100mL according to the average gas production amount of the CK of 227mL/d, so that the gas production fermentation period can be shortened by 44 days.

FIG. 2 shows the gas production efficiency of examples 1 to 3 compared with the respective Control (CK). As is apparent from FIG. 2, the efficiency of biogas production by the combined anaerobic fermentation of pig farm liquid manure and corn stalks treated by the biochar loaded with the nano zero-valent iron is significantly higher than the efficiency of biogas production by the combined anaerobic fermentation of pig farm liquid manure and corn stalks not treated by the biochar loaded with the nano zero-valent iron.