阅读说明：本技术 一种预处理促进剩余污泥厌氧发酵生产中链脂肪酸的方法 (method for producing medium-chain fatty acid by promoting anaerobic fermentation of excess sludge through pretreatment ) 是由 倪丙杰 张雨婷 王云 孙婧 徐秋翔 于 2019-10-30 设计创作，主要内容包括：本发明涉及一种预处理促进剩余污泥厌氧发酵生产中链脂肪酸的方法,取活性污泥,静置后去除上清液,向活性污泥中添加亚硝酸钠溶液并控制pH、温度,进行游离亚硝酸(FNA)预处理,将经预处理后污泥添加到厌氧反应器中,加入电子供体进行厌氧发酵反应生产中链脂肪酸。与现有技术相比,本发明利用游离亚硝酸促进污泥中的有机物质的溶出,提高污泥水解速率,从而提高了厌氧发酵体系中链脂肪酸的产量。游离亚硝酸可以从污水处理厂厌氧消化液亚硝化产物中原位获得,在污泥资源化利用的同时合理利用现有资源进行更有价值的能源制备,该发明具有产物产量高、操作简便、节能降耗等优势。(The invention relates to a method for producing medium-chain fatty acid by using kinds of pretreated and promoted excess sludge anaerobic fermentation, which comprises the steps of taking activated sludge, removing supernatant after standing, adding sodium nitrite solution into the activated sludge, controlling pH and temperature, carrying out pretreatment of Free Nitrous Acid (FNA), adding the pretreated sludge into an anaerobic reactor, and adding an electron donor to carry out anaerobic fermentation reaction to produce the medium-chain fatty acid.)

The method for promoting anaerobic fermentation of excess sludge to produce medium-chain fatty acid by using kinds of pretreatment is characterized in that the sludge is pretreated by using free nitrous acid, and the method comprises the following steps:

taking waste activated sludge, standing, removing supernatant,

adding sodium nitrite solution into the waste activated sludge, controlling the pH and the temperature, performing Free Nitrous Acid (FNA) pretreatment,

adding the pretreated sludge into an anaerobic reactor, and adding an electron donor to perform anaerobic fermentation reaction to produce medium-chain fatty acid.

2. The method for promoting anaerobic fermentation of excess sludge to produce medium-chain fatty acids according to claim 1, wherein the activated sludge is concentrated sludge obtained by gravity settling of excess sludge from a secondary sedimentation tank of a municipal sewage treatment plant.

3. The pretreatment method for promoting the anaerobic fermentation of excess sludge to produce medium-chain fatty acids according to claim 1, wherein the concentration of sodium nitrite added to the sludge is 50-300 mg/L.

4. The method for producing medium-chain fatty acids by anaerobic fermentation of excess sludge through pretreatment of claim 1, wherein the pH value of the pretreatment of free nitrous acid is 5-6 and the temperature is controlled at 20-30 ℃.

5. The method for promoting anaerobic fermentation of excess sludge to produce medium-chain fatty acids according to claim 4, wherein the concentration of Free Nitrous Acid (FNA) is 0.10-7.69mg HNO at 20-30 deg.C and pH 5-6₂-N/L。

6. The method for producing medium-chain fatty acids by anaerobic fermentation of excess sludge through pretreatment methods as claimed in claim 1, wherein the pretreatment time is about 24 ± 1h, and the sufficient contact of the pretreatment reaction system is ensured by stirring.

7. The pretreatment methods for promoting anaerobic fermentation of excess sludge to produce medium chain fatty acids as claimed in claim 1, wherein the electron donor is ethanol, lactic acid, hydrogen or methanol, and the concentration of the electron donor is 40-200mM, preferably 80-180mM ethanol is used.

8. The method for promoting anaerobic fermentation of excess sludge to produce medium-chain fatty acids according to claim 1, wherein the volume ratio of waste activated sludge to growth medium is 1:20-1:5, the mass ratio of inoculated anaerobic sludge to waste activated sludge is 1:2-2:1, and the amount of methane inhibitor added is 15-30 g/L.

9. The method of pretreatment for promoting anaerobic fermentation of excess sludge to produce medium-chain fatty acids, according to claim 8, wherein the growth medium contains macroelements, trace elements and vitamins necessary for the growth of microorganisms, the inoculated anaerobic sludge is a microorganism acclimated in an anaerobic digestion/fermentation reactor capable of producing medium-chain fatty acids, and comprises microorganisms related to chain elongation of the genus Clostridium, Oscilobacter, Denloromonas or Ruminococcaceae, and the methane inhibitor is 2-bromoacetyl sulfonic acid.

10. The method for producing the medium-chain fatty acids by promoting the anaerobic fermentation of the excess sludge through kinds of pretreatment according to claim 1, wherein the reaction for producing the medium-chain fatty acids through the anaerobic fermentation is controlled at pH 5-6, temperature 35-40 ℃, rotation speed 160-180 rpm, and the operation lasts for 25-30 days.

Technical Field

The invention belongs to the technical field of environmental protection, relates to the field of resource utilization of solid organic wastes, and particularly relates to a method for producing medium-chain fatty acids by anaerobic fermentation of excess activated sludge pretreated by kinds of free nitrous acids.

Background

Excess sludge (WAS) is used as a main byproduct in the sewage treatment process, the management cost of the WAS is as high as 60 percent of the operation cost of the whole sewage treatment plant, according to statistics, only a small part of the excess sludge is properly treated, most of the excess sludge is randomly stacked and buried, pathogens, heavy metals, persistent organic pollutants and other toxic and harmful substances in the excess sludge enter soil and water environment times, the environmental safety and public health are threatened, the environmental benefit of the whole sewage treatment system is greatly reduced, and the excess sludge contains a large amount of organic matters and is cheap and valuable resources, so that the recycling of energy and resources in the excess sludge in the principles of safety, environmental protection, recycling, energy conservation, consumption reduction, and appropriate ground conditions and reliability are researched by major scholars at home and abroad.

At present, anaerobic fermentation is considered as the most effective treatment strategy for sludge reduction and stabilization, and organic matters are finally converted into recoverable energy substances such as methane hydrogen and organic acids under the action of microorganisms. Reducing substances are added into an anaerobic fermentation system to serve as electron donors (such as ethanol), methanogenic bacteria activity is inhibited by adding a methanogenic inhibitor or reducing pH, and Volatile Fatty Acid (VFA) which is a product in an acid production stage in the anaerobic fermentation process is converted into medium-chain fatty acid through a carbon chain extension reaction. Medium Chain Fatty Acids (MCFA) refer to carboxylic acids having 6 to 12 carbon atoms, including n-hexanoic, n-heptanoic, n-octanoic and the like, and have longer hydrophobic carbon chains, relatively low solubility in water, potential for extraction and separation from water, and lower oxygen to carbon ratios, higher energy densities, and better suitability as fuels than Volatile Fatty Acids (VFAs).

The anaerobic fermentation of sludge generally comprises hydrolysis, acidification and methanation, the hydrolysis is used as the anaerobic fermentation rate-limiting step of sludge and can influence the subsequent reaction, at present, methods for improving the hydrolysis rate of sludge comprise heat treatment, mechanical treatment (microwave, ultrasonic, high pressure and the like), chemical treatment (acid, alkali and the like), biological treatment (enzyme, inoculated bacteria and the like), however, the pretreatment method is greatly limited in practical application due to various considerations such as economy, environment, energy consumption and the like.

Chinese patent CN105238822A discloses a combined pretreatment method for producing short-chain volatile fatty acids by enhancing anaerobic fermentation of sludge and a preparation method of the short-chain volatile fatty acids, wherein the combined pretreatment method and the preparation method of the short-chain volatile fatty acids comprise the steps of taking sludge in a secondary sedimentation tank of an urban sewage treatment plant as a fermentation substrate, inoculating anaerobic activated sludge into the fermentation substrate, adding sodium nitrite and sodium dodecyl benzene sulfonate into a fermentation system, pretreating for 2 days in an acidic environment (pH is 6.0), fermenting, and adjusting to be neutral to carry out anaerobic fermentation to produce the short-chain volatile fatty acids, but the patent cannot produce the medium-chain fatty acids.

Disclosure of Invention

The invention aims to overcome the defects of high cost and low treatment efficiency of the existing pretreatment technology, and provides a method for promoting anaerobic fermentation of excess sludge to produce medium-chain fatty acid by utilizing Free Nitrous Acid (FNA) pretreatment, so that the hydrolysis rate of anaerobic fermentation of the excess sludge is enhanced, and the yield of the medium-chain fatty acid is improved.

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

1) taking waste activated sludge of a secondary sedimentation tank of an urban sewage treatment plant, performing gravity concentration, and taking the sludge with supernatant removed as a fermentation substrate;

2) adding sodium nitrite solution into the cleaned excess sludge;

3) continuously stirring and reacting the sludge and the sodium nitrite solution under certain reaction conditions;

4) adding the pretreated excess sludge, a growth medium (comprising macroelements, microelements and vitamins), a methane inhibitor and an electron donor into a reactor according to a certain proportion of , inoculating quantitative anaerobic sludge according to a corresponding proportion, and adjusting the pH and the temperature to a state suitable for the growth of microorganisms;

5) purging and exhausting air in the reactor by using high-purity nitrogen, and rapidly sealing the reactor by using a rubber plug and an aluminum cover to provide sealed anaerobic environments for subsequent reactions;

6) and a constant-temperature shaking incubator is used for ensuring uniform contact and optimal reaction conditions of an anaerobic fermentation system, and the medium-chain fatty acid is produced continuously.

The concentration of the sodium nitrite added in the sludge is 50-300 mg/L.

The pH value of the pretreatment of the free nitrous acid is controlled to be 5-6, and the temperature is controlled to be about 20-30 DEG C

The concentration of Free Nitrous Acid (FNA) is 0.10-7.69mgHNO under the conditions of pH 5-6 and temperature 20-30 deg.C₂-N/L。

The pretreatment time is about 24 +/-1 h, and the full contact of a pretreatment reaction system is ensured by stirring.

The electron donor can promote the reaction to the carbon chain extending direction, ethanol, lactic acid, hydrogen or methanol is adopted, the concentration of the electron donor is 40-200mM, preferably 80-180mM ethanol, the electron donor is substrates necessary for producing the medium chain fatty acid, and the electron donor is proved to be effective in promoting the production of the medium chain fatty acid by the microorganism.

And during anaerobic fermentation, a growth medium, a methane inhibitor and anaerobic sludge are also added, the volume ratio of the waste activated sludge to the growth medium is 1:20-1:5, the mass ratio of the inoculated anaerobic sludge to the waste activated sludge is 1:2-2:1, and the addition amount of the methane inhibitor is 15-30 g/L.

The inoculated anaerobic sludge is subjected to long-term anaerobic acclimation, and is rich in microorganisms capable of producing medium-chain fatty acids.

The microorganism culture medium contains macroelements, microelements, vitamins and the like required by the growth of microorganisms, and the inoculated anaerobic sludge is a microorganism which is domesticated in an anaerobic digestion/fermentation reactor and can produce medium-chain fatty acid, wherein the microorganism comprises microorganisms related to chain elongation, such as Clostridium, Oscillibacter, Dechloromonas, Ruminococcus family and the like. The methane inhibitor is 2-bromoacetyl sulfonic acid

The reaction for producing the medium-chain fatty acid by anaerobic fermentation is controlled to be at the pH of 5-6 (methane bacteria compete for substrates with medium-chain fatty acid bacteria, the activity of the methane bacteria is lower under the pH), the temperature is 35-40 ℃ (the optimum temperature range of functional bacteria for producing the medium-chain fatty acid and the like), the rotating speed is 160-180 rpm, and the operation lasts for 25-30 days.

The medium-chain fatty acid produced comprises n-hexanoic acid, n-heptanoic acid or n-octanoic acid.

In the invention, various electron donors are added at the pH of 5-6 (methane bacteria compete with medium-chain fatty acid bacteria for substrates, and the activity of the methane bacteria is low at the pH), and finally the medium-chain fatty acid can be obtained. Medium-chain fatty acids have higher hydrophobicity and are easier to separate from water than short-chain fatty acids, and can be used as precursors of biochemicals or biofuels.

Compared with the prior art, the invention adopts Free Nitrous Acid (FNA) which is a protonation form of nitrite, is anaerobic digestion liquid nitrosation products which can be regenerated in situ and have low cost, has extremely strong destructive effect on extracellular polymers and cell walls, thus releasing intracellular substances, accelerating the hydrolysis rate of anaerobic sludge fermentation and providing more available organic matters for subsequent fermentation.

Detailed Description

The present invention is described in detail below with reference to specific examples, which will assist those skilled in the art to further the present invention but not to limit the invention in any way.

The method for promoting anaerobic fermentation of excess sludge to produce medium-chain fatty acid by utilizing pretreatment of Free Nitrous Acid (FNA) enhances the hydrolysis rate of anaerobic fermentation of excess sludge and improves the yield of medium-chain fatty acid, and comprises the following steps:

1) taking waste activated sludge of a secondary sedimentation tank of an urban sewage treatment plant, performing gravity concentration, and taking the sludge with supernatant removed as a fermentation substrate;

2) adding sodium nitrite solution into the cleaned excess sludge, wherein the concentration of the sodium nitrite added into the sludge is 50-300 mg/L;

3) continuously stirring the sludge and the sodium nitrite solution to react for 24 +/-1 h under the reaction conditions that the pH value is controlled to be 5-6 and the temperature is controlled to be 20-30 ℃, ensuring the full contact of a pretreatment reaction system through stirring, and ensuring the concentration of Free Nitrous Acid (FNA) to be 0.10-7.69mgHNO under the conditions that the pH value is 5-6 and the temperature is 25-30 DEG C₂-N/L；

4) Adding pretreated excess sludge, growth medium (including macroelements, microelements and vitamins), methane inhibitor and electron donor into a reactor, inoculating anaerobic sludge, adjusting pH and temperature to a state suitable for microbial growth, wherein the added electron donor can promote reaction to the direction of carbon chain elongation, the inoculated anaerobic sludge is subjected to long-term anaerobic acclimation to be rich in microorganisms capable of producing medium-chain fatty acids, the added electron donor can adopt ethanol, lactic acid, hydrogen or methanol, ethanol with the concentration of 40-200mM, preferably 80-180mM, the electron donor is substrates necessary for producing medium-chain fatty acids, and the electron donor is proved to be effective in promoting medium-chain fatty acids in microbial production, adding microbial culture medium, methane inhibitor and anaerobic sludge, the microbial culture medium contains macroelements, microelements and vitamins required by microbial growth, and the like, inoculating anaerobic sludge is an acclimated microorganism capable of producing medium-chain fatty acids in an anaerobic digestion/fermentation reactor, wherein the added amount of Clostridia, Decloromyces and Rumoc is 1-2, the added amount of active sludge is 1-2: 2, and the inoculated active sludge is added in an anaerobic digestion/fermentation reactor, and the activated sludge for growing medium is 1-2: 2.

5) Purging and exhausting air in the reactor by using high-purity nitrogen, and rapidly sealing the reactor by using a rubber plug and an aluminum cover to provide sealed anaerobic environments for subsequent reactions;

6) the method comprises the steps of using a constant-temperature shaking incubator to ensure uniform contact of an anaerobic fermentation system, controlling the pH to be 5-6 and the temperature to be 35-40 ℃, controlling the rotation speed of the constant-temperature shaking incubator to be 160-180 rpm, and continuously operating for 25-30 days to produce medium-chain fatty acid which can be used for producing n-hexanoic acid, n-heptanoic acid or n-octanoic acid.

The following is a more detailed embodiment, and the technical solution of the present invention and the technical effects obtained by the technical solution are further illustrated in by the following embodiment.