Application of artificial humus in increasing yield of volatile fatty acid

Abstract

The invention discloses an application of artificial humus in increasing the yield of volatile fatty acid. According to the invention, the artificial humus accelerant is added, so that the electron transfer capability among microorganisms in an anaerobic fermentation system can be enhanced, the methanogenesis metabolism process is inhibited, and the accumulation of volatile fatty acid is promoted. The method treats wastes with wastes, is simple and convenient to operate and low in treatment cost, is expected to realize synergistic reduction, harmless and resourceful treatment of agricultural wastes and residual sludge, and has better environmental benefits and application values.

Description

Technical Field

[0001] The present invention relates to the application of artificial humus in increasing the production of volatile fatty acids, belonging to the field of artificial humus. Background Art

[0002] Excess sludge is the main by-product generated in the sewage treatment process. It mainly consists of microbial cells, floc gel, organic matter fragments, and organic and inorganic substances in particulate form. In the biological sewage treatment process, excess sludge mainly comes from activated sludge, and its production increases with the increase in sewage treatment volume and treatment rate. Moreover, excess sludge may also contain dangerous components such as pathogenic bacteria, heavy metals, and persistent organic pollutants outside the conventional mixture system. If it is discharged without effective treatment, it will surely cause environmental pollution. Its treatment and disposal have always been a major challenge in the environmental field.

[0003] Anaerobic digestion is an effective technology for the resource utilization of excess sludge, which can convert the organic matter in the sludge into volatile fatty acids (VFAs) and methane, and can well achieve the reduction, resource utilization, and harmlessness of sludge. However, although methane can be used as a new energy source, a large amount of carbon dioxide will be generated, and methane itself is also a greenhouse gas, which will exacerbate the greenhouse effect and is harmful to the environment. In contrast, VFAs, as one of the important products in the fermentation process, can be used as a carbon source for biological nitrogen and phosphorus removal, biosynthesis of biodegradable plastics, etc., and have broad application prospects. In recent years, it has also been found that it can be used in the fields of single-cell protein production, spice synthesis, etc. VFAs have greater advantages than methane and are more beneficial to both the environment and economic development.

[0004] However, traditional anaerobic digestion of excess sludge has problems such as low VFAs production rate and long fermentation cycle, which limit its popularization and application. In the traditional anaerobic digestion process, acidogenic bacteria can produce acid through electron transfer, but the acid production effect is not very ideal, the electron transfer efficiency is low, and the high hydrogen partial pressure will also inhibit the acid production process. Therefore, a method that can increase the production of short-chain fatty acids in the anaerobic digestion of sludge plays an important role in realizing the reduction, resource utilization, and harmlessness of sludge. Summary of the Invention

[0005] Object of the Invention: The technical problem to be solved by the present invention is to provide the application of artificial humus in increasing the production of volatile fatty acids, aiming to solve the problems such as low VFAs production rate and long fermentation cycle in the prior art.

[0006] Technical solution: To solve the above technical problems, the present invention provides an application of artificial humus in increasing the production of volatile fatty acids, and the artificial humus is prepared from agricultural solid waste. The present invention promotes the electron transfer of sludge anaerobic digestion by adding artificial humus, and improves the production of volatile fatty acids in the anaerobic digestion process of excess sludge.

[0007] The present invention also provides an application of artificial humus in the preparation of volatile fatty acids, and the artificial humus is prepared from agricultural solid waste.

[0008] The present invention also provides a method for increasing the production of volatile fatty acids by using artificial humus, which includes the following steps:

[0009] (1) Synthesize artificial humus from agricultural solid waste by hydrothermal humification technology;

[0010] (2) Mix the artificial humus obtained in step (1) with sludge and carry out anaerobic fermentation to obtain the volatile fatty acids; the mass-volume ratio of the artificial humus to the sludge is 0.05-0.2 g: 100 mL.

[0011] Preferably, the mass-volume ratio of the artificial humus to the sludge is 0.05-0.15 g: 100 mL.

[0012] Preferably, the mass-volume ratio of the artificial humus to the sludge is 0.05-0.1 g: 100 mL.

[0013] Among them, the agricultural solid waste in step (1) includes one or more of straws, forest tree branches, and fruit husks.

[0014] Among them, the pH value of the sludge in step (2) is 7-9; this pH value is the pH range for sludge anaerobic digestion.

[0015] Among them, the preparation method of the artificial humus in step (1) includes the following steps: Grind and screen the agricultural solid waste to obtain a powdery material, ensuring that the average particle size is <0.15 mm; Add the agricultural waste powder, alkali solution and water into a reaction kettle for hydrothermal humification reaction; Carry out solid-liquid separation on the obtained humification solution, wash the solid product, and dry it.

[0016] Among them, the alkali solution includes one or both of sodium hydroxide and potassium hydroxide.

[0017] Among them, the mass ratio of the agricultural waste powder to the alkali in the alkali solution is 5-20; the mass ratio of the agricultural waste powder to water is 1:10-1:30.

[0018] Among them, the reaction conditions of the hydrothermal humification technology are as follows: 160-200°C, the reaction pressure is 1-3 Mpa, and the reaction time is 2-6 h.

[0019] Among them, in step (2), the temperature of the anaerobic fermentation is 25-55°C, and the fermentation time is 3-20 days.

[0020] Among them, in step (2), a culture solution containing various elements and nutrients can also be added to the sludge. The culture solution contains a carbon source of glucose, potassium dihydrogen phosphate, a nitrogen source of ammonium chloride, minerals and vitamins. Adding the culture solution can accelerate the anaerobic reaction rate.

[0021] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages:

[0022] (1) Artificial humus can be used as an electron shuttle to promote electron transfer in the process of sludge anaerobic digestion. Moreover, it is not easily affected by the activities of microorganisms and consumes less energy during the electron transfer process. It is a relatively good electron shuttle. By adding artificial humus to the anaerobic fermentation system of excess sludge, the present invention can significantly promote the metabolic activity of the microbial population during the fermentation process, optimize the microbial community structure. The artificial humus, as an electron shuttle, accelerates the electron transfer process, improves the electron transfer efficiency, and promotes the catabolism of organic matter. In addition, artificial humus is beneficial to inhibiting the activity of methanogens and reducing their consumption of volatile fatty acids (VFAs), thereby increasing the yield of VFAs and shortening the fermentation cycle. The experimental results show that by using the method of the present invention, the main products of the reaction are short-chain fatty acids such as acetic acid and propionic acid with relatively high economic value.

[0023] (2) The method provided by the present invention is simple to operate, low in cost, easy to realize industrial application, and has good economic and environmental benefits. Moreover, the present invention recycles straw again through a concept of "treating waste with waste" and manufactures it into humus for treating excess sludge. The added humus has the ability to transfer electrons during the sludge anaerobic digestion process and can strengthen anaerobic digestion to produce acid. It can be used as an electron acceptor for volatile fatty acids to increase the yield of volatile fatty acids in the acidification stage. This method of the present invention enhances the acid production of anaerobic digestion and provides a better solution for the low conversion rate of organic matter in sludge anaerobic digestion and the treatment of straw. Description of the Drawings

[0024] Figure 1 It is a graph showing the change of short-chain fatty acid production over time in anaerobic digestion experiments of different examples and comparative examples;

[0025] Figure 2 It is a graph showing the change of cumulative methane production over time in anaerobic digestion experiments of different examples and comparative examples. Detailed Embodiments

[0026] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings.

[0027] Example 1 Preparation of Straw-based Artificial Humus

[0028] Mix straw powder (average particle size < 0.15 mm) with potassium hydroxide solution (the mass ratio of straw powder to potassium hydroxide is 10:1), and carry out hydrothermal humification in a reaction kettle. The reaction conditions are 200 °C, the reaction time is 6 h, the reaction pressure is 2 Mpa, and the mass ratio of straw powder to water is 1:20. After the reaction is completed, precipitate and centrifuge to obtain a solid product, namely straw-based artificial humus.

[0029] Example 2

[0030] Mix straw powder (average particle size < 0.15 mm) with sodium hydroxide solution (the mass ratio of straw powder to sodium hydroxide is 5:1), and carry out hydrothermal humification in a reaction kettle. The reaction conditions are 160 °C, the reaction time is 2 h, the reaction pressure is 1 Mpa, and the mass ratio of straw powder to water is 1:10. After the reaction is completed, precipitate and centrifuge to obtain a solid product, namely straw-based artificial humus.

[0031] Example 3

[0032] Mix straw powder (average particle size < 0.15 mm) with potassium hydroxide solution (the mass ratio of straw powder to potassium hydroxide is 20:1), and carry out hydrothermal humification in a reaction kettle. The reaction conditions are 180 °C, the reaction time is 4 h, the reaction pressure is 3 Mpa, and the mass ratio of straw powder to water is 1:30. After the reaction is completed, precipitate and centrifuge to obtain a solid product, namely straw-based artificial humus.

[0033] Comparative Example 1 Preparation of Leaf-based Artificial Humus

[0034] After grinding dry leaves to an average particle size < 0.15 mm, mix them with potassium hydroxide solution (the mass ratio of leaves to potassium hydroxide is 10:1), and carry out hydrothermal humification in a reaction kettle. The reaction conditions are 200 °C and the reaction time is 6 h. After the reaction is completed, precipitate and centrifuge to obtain a solid product, namely leaf-based artificial humus.

[0035] Functional group quantitative analysis was carried out on the artificial humus products prepared in Examples 1-3 and Comparative Example 1, as shown in Table 1.

[0036] Table 1

[0037] Total acidic groups (mmol / g) Carboxyl groups (mmol / g) Phenolic hydroxyl groups (mmol / g) Example 1 13.23 9.16 4.07 Comparative Example 1 5.58 3.45 2.13 Example 2 9.55 4.58 4.97 Example 3 6.87 4.10 2.77

[0038] Under the same conditions, the contents of phenolic hydroxyl groups and carboxyl groups in the straw-based artificial humus are 2.66 and 1.91 times those of the leaf-based humus, respectively. This indicates that the straw-based artificial humus has stronger amphiphilic molecular properties and ion exchangeability, which helps to promote the electron transfer process during the anaerobic digestion of sludge. In addition, the content of acidic functional groups in the straw-based artificial humus under the preparation conditions described in Example 1 is higher than that in Example 2 and Example 3.

[0039] Example 4

[0040] Add 100 mL of excess sludge (from a wastewater treatment plant) to a 200 mL fermenter. The solid content (TS) of the excess sludge used is 10 g / L. Add 0.05 g of the straw-based artificial humus prepared in Example 1. After uniform mixing of the two, purge the system with nitrogen to remove oxygen, and seal it to maintain an anaerobic environment. Place the fermenter in a constant temperature shaker and carry out anaerobic digestion in the dark. The reaction temperature is 35 °C, the shaker speed is 150 rpm / min, and the reaction time is 10 days.

[0041] Example 5

[0042] Add 100 mL of excess sludge to a 200 mL fermenter. The solid content (TS) of the excess sludge used is 10 g / L. Add 0.1 g of the straw-based artificial humus prepared in Example 1. After uniform mixing of the two, purge the system with nitrogen to remove oxygen, and seal it to maintain an anaerobic environment. Place the fermenter in a constant temperature shaker and carry out anaerobic digestion in the dark. The reaction temperature is 25 °C, the shaker speed is 150 rpm / min, and the reaction time is 20 days.

[0043] Example 6

[0044] Add 100 mL of excess sludge to a 200 mL fermenter. The solid content (TS) of the excess sludge used is 10 g / L. Add 0.15 g of the straw-based artificial humus prepared in Example 1. After uniform mixing of the two, purge the system with nitrogen to remove oxygen, and seal it to maintain an anaerobic environment. Place the fermenter in a constant temperature shaker and carry out anaerobic digestion in the dark. The reaction temperature is 55 °C, the shaker speed is 150 rpm / min, and the reaction time is 3 days.

[0045] Example 7

[0046] Add 100 mL of excess sludge to a 200 mL fermenter. The solid content (TS) of the excess sludge used is 10 g / L. Add 0.2 g of the straw-based artificial humus prepared in Example 1. After uniform mixing of the two, purge the system with nitrogen to remove oxygen, and seal it to maintain an anaerobic environment. Place the fermenter in a constant temperature shaker and carry out anaerobic digestion in the dark. The reaction temperature is 35 °C, the shaker speed is 150 rpm / min, and the reaction time is 15 days.

[0047] Blank Example 1

[0048] The implementation process of this comparative example refers to Example 5. The difference from Example 5 is that no straw-based artificial humus is added in this comparative example.

[0049] Comparative Example 2

[0050] The implementation process of this comparative example refers to Example 5. The difference from Example 5 is that 0.05 g of leaf-based artificial humus is added in this comparative example.

[0051] Results and Analysis:

[0052] The results of the short-chain fatty acid production in Examples 4-7, Blank Example 1 and Comparative Example 2 of the present invention are as Figure 1 shown, and the results of the cumulative methane production are as Figure 2 shown. It can be seen from Figure 1 that there is no obvious difference in the acid production between Comparative Example 2 and Blank Example 1, indicating that the promotion effect of leaf-based artificial humus is not obvious. For the fermenters with straw-based artificial humus added in Examples 4-7, the maximum volatile fatty acid production increases as the addition amount of artificial humus gradually increases from 0 to 0.1 g. Among them, the VFAs production in Example 5 reaches the highest (1441.724 mg / L) on the 6th day of fermentation, which is 2.1 times that of Blank Example 1; however, when the addition amount of straw-based humus is further increased to 0.15 g and 0.2 g, the maximum VFAs production drops to 880.699 mg / L and 744.903 mg / L. This result shows that the addition of artificial humus within a certain range promotes the anaerobic co-fermentation of excess sludge to produce VFAs, but excessive addition of GO may cause electron competition and inhibit the microbial activity, resulting in a decrease in acid production.

Claims

1. An application of artificial humus in increasing the yield of volatile fatty acids, characterized in that: The artificial humus is prepared from agricultural solid waste.

2. An application of artificial humus in the preparation of volatile fatty acids, characterized in that: The artificial humus is prepared from agricultural solid waste.

3. A method for increasing the yield of volatile fatty acids using artificial humus, characterized in that: The following steps are involved: (1) Using agricultural solid waste to synthesize artificial humus through hydrothermal humification technology; (2) The artificial humus and sludge described in step (1) are mixed and then subjected to anaerobic fermentation to obtain the volatile fatty acids; the mass volume ratio of the artificial humus and sludge is 0.05-0.2 g:100 mL.

4. The method according to claim 3, characterized in that: The agricultural solid waste in step (1) includes one or more of straw, tree branches, and fruit shells.

5. The method according to claim 3, characterized in that: The pH value of the sludge in step (2) is 7-9.

6. The method according to claim 3, characterized in that: The preparation method of artificial humus described in step (1) comprises the following steps: grinding and sieving agricultural solid waste to obtain powdered material, ensuring that the average particle size is less than 0.15 mm; adding the agricultural waste powder, alkali solution and water into a reactor for hydrothermal humification reaction; performing solid-liquid separation on the obtained humified solution, washing the solid product and drying it.

7. The method according to claim 6, characterized in that: The alkali solution includes one or both of sodium hydroxide and potassium hydroxide.

8. The method according to claim 6, characterized in that: The mass ratio of the agricultural waste powder to the alkali in the alkali solution is 5-20:1; the mass ratio of the agricultural waste powder to water is 1:10-1:

30.

9. The method according to claim 3, characterized in that: The reaction conditions of the hydrothermal humification technology are: 160-200° C., reaction pressure of 1-3 MPa, and reaction time of 2-6 hours.

10. The method according to claim 3, characterized in that: The temperature of the anaerobic fermentation in step (2) is 25 to 55° C., and the fermentation time is 3 to 20 days.

Images