A method for promoting anaerobic acidogenic fermentation of kitchen waste to direct production of acetic acid

Abstract

The application belongs to the technical field of anaerobic digestion, and specifically discloses a method for promoting directional acetic acid production in anaerobic acidogenic fermentation of kitchen waste, which comprises the following steps: (1) sorting, crushing, pulping and high-temperature oil removal are performed on the kitchen waste, and then the kitchen waste is stored at 4 DEG C; when used, water is added to adjust the volatile solids in the kitchen waste to 60.0+ / -0.5 g / L; (2) inoculum and volatile solids are added to an anaerobic reactor in a mass ratio of 3:1 for fermentation; after the anaerobic reactor is stably operated, a circulating gas path is opened for gas self-circulation, hydrogen partial pressure in the headspace is reduced, hydrogen dissolution in the liquid phase is promoted, CO2 is converted into acetic acid through the biochemical action of homoacetogenic bacteria, and the Wood-Ljungdahl pathway is finally used to convert CO2 into acetic acid. The application realizes self-circulation of acidogenic phase gas through the circulating gas path, reduces hydrogen partial pressure in the headspace, promotes hydrogen dissolution in the liquid phase, enriches homoacetogenic bacteria, enriches the metabolic pathway (4H2+CO2→CH3COOH+2H2O) of acetic acid production, and promotes directional acetic acid production in anaerobic acidogenic fermentation of kitchen waste.

Description

Technical Field

[0001] This invention relates to the field of anaerobic digestion technology, and specifically discloses a method for promoting the anaerobic acid-producing fermentation of kitchen waste to produce acetic acid. Background Technology

[0002] With the rapid urbanization and improved living standards in my country, food waste has become a significant component of urban household waste. my country generates approximately 130 million tons of food waste annually, containing large amounts of oil, salt, and harmful substances. Improper treatment can severely pollute soil, water, and air, threatening ecological security and public health. How to rationally utilize food waste resources has become a crucial issue for urban green development. Anaerobic digestion is a mainstream and effective strategy for treating solid waste, mitigating its negative environmental impact, and achieving resource recycling. Furthermore, due to the high organic matter content, high moisture content, and susceptibility to acidification of food waste, obtaining more economically valuable carbon source products (volatile fatty acids, VFAs) through acid fermentation can alleviate the widespread carbon source shortage faced by urban wastewater treatment plants in my country. Acetic acid is the most efficient effective carbon source for denitrification in wastewater treatment; therefore, how to enhance the acetic acid content in volatile fatty acids has become a hot research topic for scholars in recent years.

[0003] Currently, anaerobic digestion of food waste mainly produces biogas. However, existing technologies suffer from long process flows, poor stability, and low economic efficiency, severely limiting the development of biogas projects. By improving the process type and controlling anaerobic digestion at the acetic acid production stage, not only can higher value-added carbon source products be obtained, but the process flow can also be reduced, greatly improving production efficiency and offering significant market advantages. Current methods for targeted acetic acid enhancement mainly include environmental condition control, additives, and microbial community screening. However, environmental condition control requires different substrates from different sources and suffers from poor stability; additives require large-scale application, are uneconomical, and are still immature; microbial screening and cultivation are lengthy, difficult, demanding on personnel, and have poor adaptability.

[0004] Hydrogen is the primary energy gas in the hydrolysis and acidification stage of food waste acidification fermentation systems. Higher headspace hydrogen pressure inhibits the growth rate of acetic acid-producing bacteria. Reducing the headspace hydrogen pressure to lower the hydrogen partial pressure in the acidification reactor can improve acetic acid production. Furthermore, H2 is a crucial factor influencing the metabolic pathway of acetic acid production, as it serves not only as a substrate for homoacetic acid-producing bacteria metabolism but also plays a vital role in interspecies electron transfer and cell growth. However, no methods have yet been reported for promoting targeted acetic acid production from food waste based on the self-circulation of the acidification phase gas. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method for promoting the anaerobic acid-producing fermentation of kitchen waste to produce acetic acid in a targeted manner.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0007] This invention provides a method for promoting anaerobic acid production and targeted acetic acid production from kitchen waste, comprising the following steps:

[0008] (1) After sorting, crushing, pulping and high-temperature degreasing of kitchen waste, store it at 4°C. When using it, add water to adjust the volatile solids in the kitchen waste to 60.0±0.5g / L;

[0009] (2) Add the inoculum and volatile solids of kitchen waste to the anaerobic reactor at a mass ratio of 3:1 for fermentation. After the anaerobic reactor is running stably, open the circulation gas path to perform gas self-circulation, reduce the headspace hydrogen partial pressure and promote the dissolution of hydrogen in the liquid phase.

[0010] Preferably, the inoculum in step (2) is derived from the fermentation liquid in the anaerobic reactor for acid fermentation of kitchen waste that is stably operating in the team's laboratory.

[0011] Preferably, in step (2), the temperature of the anaerobic reactor is 37±1℃, the pH is controlled above 5.5, the residence time is 5 days, and the stirring rate is 80~120r / min.

[0012] More preferably, the pH value is adjusted by adding sodium hydroxide at a concentration of 5 mol / L.

[0013] Preferably, the gas flow rate of the gas circulation path in step (2) is set to 0.3 to 0.5 L / min.

[0014] Preferably, in step (2), before fermentation, oxygen is removed by introducing nitrogen into the reactor.

[0015] Preferably, in step (2) during the gas self-circulation process, the gas entering the anaerobic reactor penetrates deep into the liquid and is solubilized by air bubbles.

[0016] Preferably, in step (2) during the gas self-circulation process, the discharged gas is the gas located at the top of the anaerobic reactor.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] This invention introduces the exhaust gas generated during the anaerobic acid-producing fermentation of food waste into an anaerobic reactor via a circulating gas path, and uses air stones to increase gas solubility. The circulating gas increases water flow, improves gas-liquid mass transfer efficiency, promotes the degradation of organic matter, and increases the dissolution of ammonia nitrogen, resulting in a relatively stable pH level, which is beneficial for the targeted increase of acetic acid content in VFAs. Furthermore, the gas introduction consumes the enriched CO2 gas in the system, reducing headspace hydrogen pressure and increasing the relative abundance of homoacetic bacteria. Through the biochemical action of homoacetic bacteria, CO2 is ultimately converted into acetic acid via the Wood-Ljungdahl pathway, enriching the metabolic pathway for acetic acid production (4H2 + CO2 → CH3COOH + 2H2O), promoting the targeted production of acetic acid from volatile fatty acids, and increasing acetic acid yield by nearly 25%. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of the circulating anaerobic reactor of the present invention;

[0020] Figure 2 This is a flowchart of the anaerobic acid production reaction operation of the present invention;

[0021] Figure 3 The graph shows the pH value and ammonia nitrogen content at different stages in the experimental examples of this invention;

[0022] Figure 4 This is a graph showing the content of volatile fatty acids at different stages in the experimental examples of this invention;

[0023] In the diagram, 1 is the anaerobic reactor; 2 is the insulation jacket; 3 is the circulating water bath; 4 is the feed pipe; 5 is the discharge hopper; 6 is the stirring device; 7 is the gas outlet pipe; 8 is the gas collector; 9 is the gas bag; 10 is the air inlet pipe; 11 is the circulating air pump; and 12 is the air stone. Detailed Implementation

[0024] To enable those skilled in the art to more clearly understand the technical solutions of the present invention, the present invention will now be further described in detail through specific embodiments, but these embodiments should not be regarded as limiting the scope of the present invention.

[0025] Example 1

[0026] A circulating anaerobic reactor, see Figure 1The reactor includes an anaerobic reactor 1, which has an insulation jacket 2 on its outer wall and is connected to a circulating water bath 3. A feed pipe 4 is installed at the top of the anaerobic reactor 1, and the feed pipe is equipped with a feed water seal valve. A discharge hopper 5 is installed at the bottom of the anaerobic reactor 1, and the discharge hopper 5 is equipped with a discharge water seal valve. A stirring device 6 is installed inside the anaerobic reactor 1, extending from the feed end to the discharge end. A circulating gas path is connected to the anaerobic reactor 1, which includes a gas outlet pipe 7. The outlet of the gas outlet pipe 7 is connected to a gas collector 8, and the bottom inlet of the gas outlet pipe 7 is higher than the liquid level in the anaerobic reactor 1. The gas collector 8 is connected to a gas bag 9, and the gas bag 9 is connected to the area below the liquid level inside the anaerobic reactor 1 via an air inlet pipe 10. The air inlet pipe 10 is equipped with a circulating air pump 11, and the bottom of the air inlet pipe 10 is connected to an air bubble stone 12.

[0027] A method for producing acetic acid from food waste using the above-mentioned circulating anaerobic reactor, the operation process is as follows: Figure 2 As shown, it includes the following steps:

[0028] (1) Pretreatment of kitchen waste: Kitchen waste collected from enterprise canteens and schools is sorted, crushed, pulped and degreased at high temperature and then stored in a cold storage at 4°C. Due to the different sources of kitchen waste, in order to ensure the stability of raw material properties, the volatile solids (VS) of kitchen waste are adjusted to 60.0±0.5g / L by adding water before use.

[0029] (2) Anaerobic acid production experiment: The inoculum was taken from the fermentation broth of the anaerobic acid production fermentation reactor for kitchen waste, which has been operating continuously and stably for a long time. It was added to the 10L fully mixed anaerobic reactor 1 named CSTR at a volatile solids (VS) ratio of kitchen waste to inoculum of 3:1. Nitrogen gas was introduced to maintain the anaerobic environment. The operating temperature of the anaerobic reactor 1 was kept stable at 37±1℃ by circulating water bath 2. The anaerobic reactor 1 was equipped with a stirring device 6 that runs for 24 hours to ensure the uniformity of mixing between the material and the liquid. The stirring speed was set to 120r / min. The pH value in the reactor was maintained above 5.5 daily by adding 5mol / L sodium hydroxide solution. When the pH value in the anaerobic reactor 1 was detected to be below 5.5 at the time of daily discharge, the pH was adjusted to 6.0 by adding 5mol / L sodium hydroxide. A 50-day acid-producing fermentation experiment was conducted, with 2L of material fed and discharged daily, resulting in a 5-day residence time. After five residence times (25 days), the circulating gas pump 11 was turned on, allowing gas from anaerobic reactor 1 to circulate into it at a rate of 0.5L / min. For the first 25 days, the circulating gas pump 11 was shut off, and the gas collected in gas bag 9 was discharged daily. A portion of the daily output was stored in 50mL sample bottles and kept in a 4°C cold storage for gas chromatography to measure the volatile fatty acid content.

[0030] The anaerobic acid production during the first 25 days of the acid-producing fermentation experiment was designated as group S1 (control group), and the 25 days after the circulating gas pump was turned on were designated as group S2 (experimental group). The pH and ammonia nitrogen concentrations in the acidified liquid at different stages in groups S1 and S2 are shown in the figure. Figure 3 The content of volatile fatty acids at different stages is shown in the figure. Figure 4 .

[0031] Depend on Figure 3 and Figure 4 It can be seen that the S1 group, without the circulating air pump turned on, adjusted the pH three times within 25 days, on days 9, 13, and 21. During the stable phase (days 11-25), the average total volatile fatty acid content was 15.84±6.90 g / L, of which the average acetic acid content was 6.90±0.12 g / L, accounting for 43.56%, and the ammonia nitrogen content was 1356.79±20.23 mg / L. The S2 group, with the circulating air pump turned on, only adjusted the pH twice in the following 25 days (5 residence times), on days 29 and 35. During the stable phase (days 36-50), the average total volatile fatty acid content was 17.18±0.49 g / L, of which the average acetic acid content was 8.60±0.25 g / L, accounting for 50.06%, and the ammonia nitrogen content was 1441.40±13.40 mg / L.

[0032] Compared to group S1, group S2, with its self-circulating acid-producing phase gas, showed an 8.46% increase in total volatile fatty acids and a 24.64% increase in acetic acid content, demonstrating a significantly improved acid production effect, particularly in the targeted increase of acetic acid content among volatile fatty acids. Furthermore, the self-circulation of the acid-producing phase gas promoted the dissolution of ammonia nitrogen, resulting in relative pH stability in the reaction vessel. After 35 days of operation, the pH remained above 5.5 without the need for additional alkalinity. This is because the combination of gas circulation and air stones enhanced gas-liquid mass transfer efficiency, allowing hydrogen and CO2 introduced into the liquid phase to be converted into acetic acid by homoacetic bacteria. This reduced the headspace hydrogen partial pressure while consuming the CO2 enriched in the system. Simultaneously, the dissolution of hydrogen in the acid-producing waste gas in the liquid phase and the suitable pH environment increased the relative abundance of homoacetic bacteria, enriching the metabolic pathway for acetic acid production and thus promoting the targeted generation of acetic acid during acid-producing fermentation.

Claims

1. A method for directional acetic acid production through anaerobic fermentation of kitchen waste, characterized in that, Includes the following steps: (1) After sorting, crushing, pulping and high-temperature degreasing of kitchen waste, it was stored at 4°C. In order to reduce the influence of material fluctuations on the experimental results, water was added to adjust the volatile solids in the kitchen waste to 60.0±0.5 g / L when using it. (2) Add the inoculum and volatile solids to the anaerobic reactor at a mass ratio of 3:1 for fermentation. The temperature of the anaerobic reactor is 37±1℃ and the pH is controlled between 5.5 and 6. After the anaerobic reactor is running stably, open the circulation gas path to carry out gas self-circulation. During the gas self-circulation process, the gas discharged is the gas located at the top of the anaerobic reactor. The gas entering the anaerobic reactor penetrates into the liquid and is solubilized by the bubble stone; reducing the headspace hydrogen partial pressure and promoting the dissolution of hydrogen in the liquid phase.

2. The method according to claim 1, characterized in that, The inoculum in step (2) is the fermentation liquid in the acid-producing fermentation reactor of kitchen waste.

3. The method according to claim 2, characterized in that, Step (2) The residence time in the anaerobic reactor is 5 days, and the stirring rate is 120 r / min.

4. The method according to claim 3, characterized in that, The pH value was adjusted by adding sodium hydroxide at a concentration of 5 mol / L.

5. The method according to claim 4, characterized in that, Step (2) The gas flow rate of the gas circulation path is 0.3 to 0.5 L / min.

6. The method according to claim 5, characterized in that, Before fermentation in step (2), oxygen is removed by introducing nitrogen into the reactor.

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