Method for increasing yield of volatile fatty acid in straw anaerobic hydrolysis process

Abstract

The invention belongs to the technical field of anaerobic acid production, and discloses a method for increasing the yield of volatile fatty acid in a straw anaerobic hydrolysis process, which comprises the following steps of: filling straws into an anaerobic reactor, adding oxygen micro-nano bubble water and anaerobic inoculum, blowing headspace for 1 minute by using nitrogen to keep an anaerobic state, the mass ratio of the straw to the oxygen micro-nano bubble water is (1: 8)-(1: 15), and the oxygen micro-nano bubble water is obtained by filling 20 L of deionized water into a water tank, introducing oxygen according to the flow rate of 1 L / min and operating for 15 minutes. According to the method, oxygen micro-nano bubble water and anaerobic inoculation are jointly used in the straw, nutrient substance exchange and transfer between microorganisms and the external environment are accelerated, the microbial activity can be improved, release of hydrolase is promoted, the hydrolytic acidification process of the straw is accelerated, the organic matter decomposition rate of the microorganisms is increased, and the yield of the straw is increased. The yield of the volatile fatty acid is improved.

Description

Technical Field

[0001] The invention relates to the technical field of anaerobic acid production, and in particular to a method for increasing the yield of volatile fatty acids in the process of anaerobic hydrolysis of straw. Background Art

[0002] As a major grain producer, my country has abundant crop straw resources. In recent years, with the development of new rural construction and urbanization, the improvement of energy consumption structure and the application of various alternative raw materials, there is still a surplus of straw in the main agricultural production areas. How to reasonably utilize straw resources has become an urgent issue to promote green development in rural areas.

[0003] Anaerobic digestion can transform crop straw into biogas with high calorific value. However, the current crop straw biogas projects generally have long process flow, low biogas added value and poor economic benefits. In recent years, some people have produced high-value-added volatile fatty acid VFA (such as acetic acid, butyric acid, etc.) products by regulating the anaerobic process. These products, as platform compounds, are widely used in the fields of food, medicine, chemical industry, etc., and have become a research hotspot and have shown great market potential. However, straw is mainly composed of cellulose, hemicellulose and lignin, and the dense structure of its polymers seriously limits the efficiency of hydrolysis and acid production during anaerobic digestion. Although some existing strengthening methods (such as alkali treatment, exogenous enzymes, micro-oxygen treatment and biochar, etc.) can improve the bioaccessibility of straw and enhance the activity of anaerobic microorganisms, these methods still have many problems, such as high additive costs, easy generation of secondary pollutants and complex treatment processes.

[0004] At present, there is no report on the combined use of oxygen micro-nano bubble water and anaerobic sludge to treat straw to increase the yield of high value-added volatile fatty acids during the anaerobic hydrolysis of straw. Therefore, exploring the application effect of oxygen micro-nano bubble water in this field may become a new direction for future bioenergy and environmental engineering research. Summary of the invention

[0005] In order to solve the above technical problems, the present invention aims to provide a method for increasing the yield of volatile fatty acids during anaerobic hydrolysis of straw.

[0006] Based on the above purpose, the present invention adopts the following technical solution:

[0007] The invention provides a method for improving the yield of volatile fatty acids in the process of anaerobic hydrolysis of straw. The method comprises the following steps: placing the straw into an anaerobic reactor, adding oxygen micro-nano bubble water and anaerobic inoculum, blowing the headspace with nitrogen for 1 minute to maintain the anaerobic state, and performing sealed constant temperature anaerobic fermentation and hydrolysis to produce acid at 35°C to 55°C, wherein the mass ratio of the straw to the oxygen micro-nano bubble water is (1:8) to (1:15), and the oxygen micro-nano bubble water is obtained by placing 20L of deionized water in a water tank, introducing oxygen at a flow rate of 1L / min, and running the reactor for 15 minutes.

[0008] Preferably, the mass ratio of the straw to the micro-nano bubble water is 1:10.

[0009] According to the above method, preferably, the mass ratio of the straw to the anaerobic inoculant is (1:1) to (6:1).

[0010] According to the above method, preferably, the mass ratio of the straw to the anaerobic inoculant is 4:1.

[0011] Preferably, the fermentation temperature is 35°C to 40°C for medium temperature fermentation or 50°C to 55°C for high temperature fermentation.

[0012] Preferably, the fermentation temperature is 37°C.

[0013] Preferably, the oxygen micro-nano bubble water is prepared by mixing oxygen and deionized water at high speed using hydrodynamic cavitation to form micro-nano bubbles.

[0014] Preferably, the anaerobic inoculum is anaerobic sludge; more preferably, the anaerobic sludge is high-solid content anaerobic sludge obtained by centrifuging biogas tank sludge and discarding the supernatant.

[0015] Preferably, the straw is air-dried and crushed before being loaded into the anaerobic reactor, and then passed through a 5-40 mesh sieve.

[0016] Preferably, the straw is one or more of corn, rice and wheat; more preferably, the straw is rice straw.

[0017] Preferably, the fermentation time is 3 to 7 days.

[0018] Preferably, the fermentation time is 5 days. Compared with the prior art, the beneficial effects of the present invention are:

[0019] The present invention uses oxygen micro-nano bubble water and anaerobic sludge in combination and adds them to a straw reactor. A small amount of exogenous oxygen introduced by the oxygen micro-nano bubble water changes the absolute anaerobic environment in the acid production process, improves the activity of facultative bacteria, and thus promotes the rate at which microorganisms decompose organic matter. At the same time, the oxygen micro-nano bubble water has higher fluidity, which helps to improve the exchange and transfer efficiency of nutrients between the microorganism and the external environment, thereby enhancing the activity of the microorganism and promoting the release of hydrolytic enzymes. In addition, since the content of microorganisms attached to the straw itself is relatively small, exogenous anaerobic sludge is added as an inoculant, which provides abundant hydrolytic microorganisms for the pre-hydrolysis process, accelerates the hydrolysis and acidification process of the straw, and increases the yield of volatile fatty acids, especially increases the content of acetic acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a flow chart of Embodiment 1 of the present invention;

[0021] Figure 2 Graph showing the volatile fatty acid content of each test group in Examples 1 to 4 of the present invention. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below through specific examples, but the scope of the present invention is not limited thereto.

[0023] Example 1

[0024] This embodiment provides a method for increasing the yield of volatile fatty acids during anaerobic hydrolysis of rice straw. The rice straw used was taken from a place in Hubei. The operation process is as follows: Figure 1 As shown, the specific method is as follows:

[0025] (1) Preparation of oxygen micro-nano bubble water: A commercial micro-nano bubble rapid generation device was used to prepare oxygen micro-nano bubble water. The device used the hydrodynamic cavitation method to mix oxygen and deionized water at high speed to form micro-nano bubbles. The air intake flow rate was set to 1 L / min, the volume of deionized water in the water tank was 20 L, and the operation time was 15 min. After the micro-nano bubble water was prepared, it was added and used immediately.

[0026] (2) Treatment of straw and inoculum: The harvested rice straw was air-dried and then crushed to pass through a 20-mesh sieve for later use; anaerobic sludge was taken from a long-running biogas digester in a sewage treatment plant in Beijing. After centrifugation, the supernatant was discarded and stored for later use.

[0027] (3) Anaerobic acid production test: Add 6g of crushed rice straw into a 500mL blue-capped bottle, and add oxygen micro-nano bubble water at a solid-liquid ratio of 1:10 between straw and oxygen micro-nano bubble water. Add anaerobic sludge at a volatile solid (VS) mass ratio of 4:1 between straw and anaerobic sludge. Then use nitrogen to blow the headspace for 1 minute to maintain the anaerobic state, seal with a rubber stopper, and place in a 37°C constant temperature box for 5 days. During this period, shake manually for 1 minute every day to ensure the uniformity of mixing between the material and the liquid. Immediately after the test, take a sample with a syringe and centrifuge it at a speed of 10,000r / min for 15 minutes. After taking the supernatant and diluting it to a certain multiple, use gas chromatography to detect the content of volatile fatty acids. The specific results are shown in Figure 2 .

[0028] Example 2

[0029] The content of this embodiment is basically the same as that of embodiment 1, except that the oxygen micro-nano bubble water in the anaerobic acid production process is replaced with deionized water. The results of the volatile fatty acid content test are shown in Figure 2 .

[0030] Example 3

[0031] The content of this embodiment is basically the same as that of embodiment 1, except that no anaerobic sludge was added during the anaerobic acid production process. Figure 2 .

[0032] Example 4

[0033] The content of this embodiment is basically the same as that of embodiment 1, except that the oxygen micro-nano bubble water in the anaerobic acid production process is replaced with deionized water, and no anaerobic sludge is added. The results of the volatile fatty acid content test are shown in Figure 2 .

[0034] The experimental setting parameters of Example 1 to Example 4 are specifically shown in Table 1.

[0035] Table 1 Test setting parameters

[0036]

[0037] Depend on Figure 2 It can be seen that after 5 days of anaerobic fermentation, the total volatile fatty acid content of group S1: using oxygen micro-nano bubble water and anaerobic sludge was 8901 mg-COD / L, of which the acetic acid content was 3952 mg-COD / L.

[0038] Group S2: using deionized water and anaerobic sludge, the total volatile fatty acid content was 8336 mg-COD / L, of which the acetic acid content was 3709 mg-COD / L.

[0039] Group S3: Using oxygen micro-nano bubble water without adding anaerobic sludge, the total volatile fatty acid content was 4337 mg-COD / L, of which the acetic acid content was 2561 mg-COD / L.

[0040] Group S4: Deionized water was used without adding anaerobic sludge. The total volatile fatty acid content was 2269 mg-COD / L, of which the acetic acid content was 701 mg-COD / L.

[0041] Compared with the S4 group, the total volatile fatty acid content of the S1 group increased significantly by 2.9 times, and the acetic acid content increased by 4.6 times; at the same time, the total volatile fatty acid content of the S3 group increased by 91.1%, and the acetic acid content increased by 265.3%; compared with the S2 group, the total volatile fatty acid and acetic acid content of the S1 group increased by 6.8% and 6.6%. Compared with the S3 group, the total volatile fatty acids in the S1 group increased by 105.2%, and the acetic acid content increased by 54.3%. Therefore, under the condition of no additional microbial inoculation (no exogenous addition of anaerobic sludge), the addition of oxygen micro-nano bubble water can enhance the anaerobic acid production process of straw, increase the yield of volatile fatty acids, and especially increase the content of acetic acid. This is because compared with deionized water, the addition of oxygen micro-nano bubble water has higher fluidity, which helps to improve the exchange and transfer efficiency of nutrients between microorganisms and the external environment, thereby enhancing the activity of microorganisms and promoting the release of hydrolases. This accelerates the hydrolysis and acidification process of straw and increases the yield of volatile fatty acids. In addition, the small amount of exogenous oxygen introduced by oxygen micro-nano bubble water changes the absolute anaerobic environment during the acid production process, increases the activity of facultative bacteria, and thus promotes the rate of microbial decomposition of organic matter. However, in the case of abundant microorganisms (addition of exogenous inoculants), anaerobic sludge plays a leading role in the production of volatile fatty acids. At this time, the introduction of oxygen micro-nano bubble water can further increase the total volatile fatty acid production.

[0042] The above is an explanation of the embodiments of the present invention. By describing the disclosed embodiments, professionals in the field can implement or use the present invention, but it is not used to limit the present invention. It is impossible to fully reflect the various contents involved in the present invention in the above embodiments. Any equivalent changes or modifications made by any professional familiar with this technology without departing from the spirit or scope of the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. A method for increasing the yield of volatile fatty acids during anaerobic hydrolysis of straw, characterized in that: The straw was loaded into an anaerobic reactor, oxygen micro-nano bubble water and anaerobic inoculum were added, and then nitrogen was blown into the headspace for 1 min to maintain the anaerobic state. The sealed constant temperature anaerobic fermentation and hydrolysis to produce acid were carried out at 35°C to 55°C, wherein the mass ratio of straw to oxygen micro-nano bubble water was (1:8) to (1:15).

2. The method according to claim 1, characterized in that The mass ratio of the straw to the anaerobic inoculant is (1:1) to (6:1).

3. The method according to claim 1, characterized in that The fermentation temperature is 35°C to 40°C or 50°C to 55°C.

4. The method according to claim 1, characterized in that: The oxygen micro-nano bubble water uses a hydrodynamic cavitation method to mix oxygen and deionized water at high speed to form micro-nano bubbles.

5. The method according to claim 1, characterized in that The anaerobic inoculum is anaerobic sludge.

6. The method according to claim 5, characterized in that The anaerobic sludge is high-solid content anaerobic sludge obtained by centrifuging biogas tank sludge and discarding the supernatant.

7. The method according to claim 1, characterized in that Before the straw is loaded into the anaerobic reactor, it is firstly air-dried and crushed, and then passed through a 5-40 mesh sieve.

8. The method according to claim 7, characterized in that The straw is one or more of corn, rice and wheat.

9. The method according to claim 8, characterized in that The straw is rice straw.

10. The method according to claim 1, characterized in that The fermentation time is 3 to 7 days.

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