阅读说明：本技术 在厌氧反应体系中添加生物炭促进中链脂肪酸产出的方法 (Method for promoting medium-chain fatty acid production by adding biochar in anaerobic reaction system ) 是由 倪丙杰 吴书林 孙婧 王云 徐秋翔 于 2019-10-30 设计创作，主要内容包括：本发明涉及在厌氧反应体系中添加生物炭促进中链脂肪酸产出的方法,选择厌氧反应器培养后的二沉池浓缩污泥作为底物,将接种物和底物混合,在厌氧环境下,加入乙醇和生物炭,产出高浓度的中链脂肪酸。与现有技术相比,本发明解决了现有污泥在厌氧发酵过程中有机质和电子传输利用率低,高浓度反应底物和产物对微生物造成毒性影响等问题,为污泥厌氧发酵处理工艺提供了新思路。(The invention relates to a method for promoting medium-chain fatty acid to be produced by adding biochar in an anaerobic reaction system. Compared with the prior art, the invention solves the problems that the organic matter and electron transmission utilization rate is low, and high-concentration reaction substrates and products have toxic influence on microorganisms in the anaerobic fermentation process of the existing sludge, and provides a new idea for the anaerobic fermentation treatment process of the sludge.)

1. A method for promoting the production of medium-chain fatty acid by adding biochar in an anaerobic reaction system is characterized in that secondary sedimentation tank concentrated sludge cultured by an anaerobic reactor is selected as a substrate, an inoculum and the substrate are mixed, and ethanol and biochar are added in an anaerobic environment to produce high-concentration medium-chain fatty acid.

2. The method for promoting the production of medium-chain fatty acids by adding biochar in an anaerobic reaction system according to claim 1, which is characterized by adopting the following steps:

carrying out high-temperature pyrolysis reaction on the sludge to generate biochar, and grinding the biochar until the particle size is 0.05-15 mm;

the concentrated sludge of a secondary sedimentation tank cultured by an anaerobic reactor is used as a substrate, and the sludge domesticated by an anaerobic fermentation tank is used as an inoculum and inoculated into a serum bottle;

adding ethanol and the biochar obtained by grinding, introducing nitrogen to remove oxygen, ensuring an anaerobic reaction environment, adjusting the pH value, sealing a serum bottle, performing constant-temperature shake culture, and fermenting to prepare the medium-chain fatty acid.

3. The method for promoting the production of medium-chain fatty acids by adding biochar into an anaerobic reaction system according to claim 2, wherein the biochar is sludge residue obtained by burning sludge at a high temperature of 600 ℃.

4. The method for promoting the production of medium-chain fatty acids by adding the biochar in the anaerobic reaction system according to claim 2, wherein the method for concentrating the sludge in the secondary sedimentation tank cultured by the anaerobic reactor is as follows: before inoculating the sludge in the secondary sedimentation tank, the anaerobic reactor is blown by nitrogen to ensure that the interior of the reactor is in a complete anaerobic environment, and then the sludge in the secondary sedimentation tank of a sewage treatment plant is added for acclimatization and culture for 20 days to obtain the concentrated sludge in the secondary sedimentation tank as a substrate.

5. The method for promoting the production of medium-chain fatty acids by adding biochar into an anaerobic reaction system according to claim 2, wherein a periodic positive rotation stirring mode is adopted in the anaerobic fermentation tank, the stirring frequency is 20.0Hz, the stirring time is 3 minutes and the standing time is 10 minutes in the stirring period.

6. The method for promoting the production of medium-chain fatty acids by adding biochar to an anaerobic reaction system as claimed in claim 2, wherein the anaerobic fermentation tank is operated in a semi-continuous flow mode, and the same amount of sludge is required to be fed in and out every day.

7. The method for promoting the production of medium-chain fatty acids by adding biochar in an anaerobic reaction system according to claim 1 or 2, wherein the mass ratio of the substrate to the inoculum is 1:2-2: 1.

8. The method for promoting the production of medium-chain fatty acids by adding biochar in an anaerobic reaction system according to claim 1 or 2, wherein the concentration of the added ethanol in the system is 20-300mmol/L, and the concentration of the added biochar in the system is 5-40 g/L.

9. The method for promoting the production of medium-chain fatty acids by adding biochar in an anaerobic reaction system according to claim 2, wherein the pH value in a serum bottle is adjusted to be not more than 7.5.

10. The method as claimed in claim 2, wherein the temperature of constant temperature oscillation is set to 37 ± 1 ℃, and the oscillation frequency is 100-170 rpm.

Technical Field

The invention belongs to the technical field of environmental engineering and microbial fermentation, and particularly relates to a method for improving the yield of medium-chain fatty acid in anaerobic fermentation of waste activated sludge by using biochar.

Background

Due to the increasing population and the rapid development of industrial revolution, fossil energy is gradually exhausted and has an adverse effect on environmental problems. On the other hand, the organic waste is increasing in yield and difficult to treat, and needs to be solved urgently. Therefore, how to convert organic waste into renewable energy is a hot spot of current social attention and research. At present, biological resources (methane and fatty acid) produced by anaerobic digestion combine organic wastes with Chemical Oxygen Demand (COD) effective conversion, and attract the attention of a plurality of scientific researchers. The main byproduct, namely waste activated sludge, produced by the sewage treatment plant is counted to 4646 ten thousand tons in 2018, the COD value contained in the sludge is about 25-60 g/L, and the sludge has great application value. Compared with the most researched methane at present, the medium-chain fatty acid has the advantages of high energy density, convenience in transportation, capability of serving as a precursor of energy fuels and the like, and besides, the methane is a greenhouse effect gas, the potential of the greenhouse effect is 30 times that of carbon dioxide, so that the medium-chain fatty acid is a more excellent sludge recycling product.

At present, the following problems are faced in the research process of preparing medium-chain fatty acid by anaerobic sludge fermentation: (1) microorganisms participating in acid production by anaerobic fermentation are fragile and easily affected by toxicity of fermentation substrates and acidic products, and when the concentration of the substrates or the products is too high, the activity is weakened, so that the high-concentration output of medium-chain fatty acid is further affected; (2) the metabolism rate of anaerobic microorganisms is slow, the transmission efficiency of organic matter electrons in a substrate is low, and the yield of medium-chain fatty acid produced by the reaction is very limited; (3) sludge substrate digestion is generally carried out through four processes of dissolution, hydrolysis, acidification and methanation generation, and when medium-chain fatty acid is taken as a target product, an effective methane inhibition method needs to be adopted. In conclusion, factors such as improving the fermentation activity of the microorganisms, promoting the electron transfer of the organic substrate, inhibiting the methanation and the like play a key role in promoting the reaction of producing the medium-chain fatty acid by anaerobic fermentation of the sludge. However, in the reaction process of producing medium-chain fatty acid by anaerobic sludge fermentation, no report is found about research on the yield of medium-chain fatty acid by using biochar to promote anaerobic sludge fermentation. Only chinese patent CN106834365A discloses a method for promoting anaerobic fermentation of sludge to produce short chain fatty acids by using biochar prepared from sludge by a hydrothermal method, which specifically comprises the following steps: the excess sludge of a sewage treatment plant is used as an anaerobic fermentation substrate, a certain amount of biochar prepared by a hydrothermal method is added, and anaerobic fermentation is carried out under the condition of medium-temperature stirring. However, the reaction can only use organic matters in the sludge as reaction substrates to carry out anaerobic fermentation, and the final product is short-chain fatty acid.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provide a simple, feasible and effective method for promoting anaerobic fermentation of sludge to produce medium-chain fatty acid by using biochar so as to solve the problems of poor microbial activity, low organic matter utilization rate, low concentrations of reaction substrates and acidic products and the like of the conventional sludge in the anaerobic fermentation process.

The purpose of the invention can be realized by the following technical scheme:

a method for promoting anaerobic fermentation of sludge to produce medium-chain fatty acid by adopting biochar selects sludge in a secondary sedimentation tank of an urban sewage treatment plant as a substrate, adds a proper amount of biochar in an anaerobic microbial reactor, adds the biochar to improve organic matter and electron transmission, provides a binding site for a reaction substrate and a product, avoids toxic influence on microorganisms, promotes the production of the medium-chain fatty acid, improves the anaerobic fermentation efficiency of the sludge, promotes organic wastes in the urban sludge to be converted into biochemical substances in the form of the medium-chain fatty acid, and realizes the improvement of the recycling treatment efficiency. The method is mainly realized by the following steps:

(1) the sludge is domesticated and cultured by using a reactor, and the reactor is purged by nitrogen before being inoculated with the sludge, so that the interior of the reactor is in a completely anaerobic environment. The reactor is cylindrical in shape, the total volume is 1.5L, a water bath interlayer is arranged outside the reactor, an exhaust port and a sludge inlet are arranged at the upper part of the reactor, and sludge is discharged from a sludge outlet at the lower part after anaerobic digestion. The gas outlet of the reactor is connected with a wet gas flowmeter to detect the gas production rate;

(2) inoculating the sludge domesticated in the anaerobic fermentation tank into a reaction serum bottle as an inoculum, adding the secondary sedimentation tank concentrated sludge cultured in the reactor into the serum bottle as a substrate, adding ethanol and biochar, introducing nitrogen, adjusting pH, sealing the serum bottle, plugging, sealing, culturing in a constant-temperature shaking box, and detecting gas components and liquid products. 3 replicates were set up for each reaction condition.

After the operation is carried out according to the steps and the continuous culture and observation are carried out for 30-120 days, the yield of medium-chain fatty acid in the serum bottle added with a proper amount of biochar can be improved, the organic matter conversion efficiency is higher, and the addition of the biochar is proved to promote the degradation of organic matter and improve the anaerobic fermentation capacity of sludge.

The sludge used is sludge in a secondary sedimentation tank of a municipal sewage treatment plant.

The reactor is used for stirring the sludge in the reactor, the stirring mode is periodic positive rotation, the stirring frequency is 20.0Hz, the stirring time is 3 minutes and the standing time is 10 minutes in the stirring period, and the temperature of a material bin and the temperature of a water bath layer in the reactor are both set to be 35 ℃.

Anaerobic digestion sludge is added into a reactor, the total volume of the sludge is set to be 1.3L, and the anaerobic sludge is firstly subjected to activity recovery culture. Adding secondary sedimentation tank sludge as a substrate into the reactor every day, setting the sludge age as 20 days, and observing the gas production condition in the reactor, wherein the sludge inlet and outlet amount is 65mL, and completing the domestication culture of the inoculated microorganisms after the daily gas production of the anaerobic reactor is stable.

The biochar is obtained by pyrolyzing secondary sedimentation tank sludge obtained from an urban sewage treatment plant. Firstly, drying the sludge in the secondary sedimentation tank for 24 hours at the temperature of 80 ℃, then putting the dried sludge into a ceramic crucible, burning the dried sludge for 2 hours at high temperature in a muffle furnace under an oxygen-deficient environment, cooling the obtained residual residue to the room temperature, and grinding the residual residue into particles of 0.05-15 mm. Repeatedly washing the biochar particles with ultrapure water for several times, and drying to obtain the biochar for later use.

The mass ratio of the substrate to the inoculum is 1:2-2: 1.

The concentration of the added ethanol in the system is 20-300mmol/L, and the concentration of the added biochar in the system is 5-40 g/L.

The pH value in the serum bottle is adjusted to be not more than 7.5.

The temperature of the constant temperature oscillator is set to be 37 +/-1 ℃, and the oscillation frequency is 100-170 rpm.

The biochar prepared by pyrolyzing sludge at high temperature is a stable porous material, and gaps on the surface of the biochar provide shelters for microorganisms, provide binding sites for toxic substances (fermentation substrates and acidic products), and further relieve the adverse effect of substances in a reaction system on the microorganisms.

According to the invention, the biochar is prepared by pyrolyzing the sludge at a higher temperature (600 ℃), and ethanol is added as an electron donor to promote the short-chain fatty acid produced by anaerobic fermentation of the sludge to be further extended to the medium-chain fatty acid, so that the product value is improved.

Compared with the prior art, the invention has the following advantages:

(1) holes and gaps on the surface of the biochar can form a complex with anaerobic microorganisms to promote electron transfer of the microorganisms, so that the mass transfer efficiency is improved, and the anaerobic fermentation metabolic process is promoted;

(2) biochar can provide binding sites for reaction substrates and products, further mitigating adverse effects on microorganisms at too high a concentration.

(3) The process for adding the biochar into the sludge has the advantages of simple operation, low energy consumption value, low price and strong stability. And the biochar is from high-temperature pyrolysis of sludge, so that sludge treatment modes are increased, the product output efficiency is improved, and the sludge recycling efficiency is promoted.

Drawings

FIG. 1 is a schematic diagram of the structure of an inoculum acclimatization reactor used in example 1;

FIG. 2 is a schematic view showing the structure of a sludge anaerobic fermentation reaction vessel used in example 1.

In the figure, 1-water inlet; 2-a sludge inlet; 3-a stirrer; 4-an exhaust port; 5-a sludge outlet; 6-water outlet; 7-a gas flow meter; 8-mixing the solution; adding an aluminum cap on the 9-butyl rubber plug; 10-biochar.

Detailed Description

The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. 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.