Method for promoting kitchen waste anaerobic acidogenic fermentation to directionally produce acetic acid

Abstract

The invention belongs to the technical field of anaerobic digestion, and particularly discloses a method for promoting kitchen waste anaerobic acidogenic fermentation to directionally produce acetic acid, which comprises the following steps: (1) sorting kitchen waste, crushing, pulping, removing oil at high temperature, storing at 4 DEG C, and adding water to adjust volatile solids in the kitchen waste to 60.0 + / -0.5 g / L during use; (2) adding the inoculum and the volatile solid into an anaerobic reactor according to a mass ratio of 3: 1 for fermentation, opening a circulation gas path for gas self-circulation after the anaerobic reactor operates stably, reducing headspace hydrogen partial pressure and promoting dissolution of hydrogen in a liquid phase, cO2 is finally converted into acetic acid through a Wood-honor path under the biochemical action of the homoacetogenic bacteria. According to the invention, the acidogenic phase gas is self-circulated through the circulating gas circuit, the dissolution of hydrogen in a liquid phase is promoted and homoacetogenic bacteria are enriched while the headspace hydrogen partial pressure is reduced, the metabolic pathway (4H2 + CO2-> CH3COOH + 2H2O) for generating acetic acid is enriched, and the directional generation of acetic acid in anaerobic acidogenic fermentation of kitchen waste is promoted.

Description

Technical Field

[0001] The invention relates to the technical field of anaerobic digestion, and specifically discloses a method for promoting directional acetic acid production by anaerobic acidogenic fermentation of kitchen waste. Background Art

[0002] With the acceleration of my country's urbanization process and the improvement of people's living standards, food waste has become an important part of urban domestic waste. How to rationally utilize food waste resources has become an urgent issue for urban green development. Anaerobic digestion is a mainstream and effective strategy for treating solid waste, reducing its negative impact on the environment and achieving resource recovery. In addition, due to the high organic matter content, high water content and easy acidification of food waste, obtaining more economically valuable carbon source products (volatile fatty acids, VFAs) through acid fermentation of food waste can alleviate the problem of insufficient carbon source commonly faced by urban sewage treatment plants in my country. Acetic acid is the most efficient carbon source for denitrification in the process of sewage denitrification. How to enhance the acetic acid content in volatile fatty acids has become a hot topic for many scholars in recent years.

[0003] At present, anaerobic digestion of food waste is mainly used to produce biogas resources. However, the existing technology has problems such as long process flow, poor stability and low economic benefits, which seriously restricts the development of biogas projects. By improving the process type and controlling anaerobic digestion to the acetic acid production stage, not only can higher value-added carbon source products be obtained, but also the process flow can be reduced, greatly improving its production efficiency, and having great market advantages. The current methods for directional enhancement of acetic acid mainly include environmental condition control, additives and microbial community screening. However, environmental condition control has different requirements for substrates from different sources and poor stability; additives need to be added in large quantities, with poor economy and immaturity; microbial screening and cultivation cycles are long and difficult, with high requirements for personnel operation and poor adaptability.

[0004] Hydrogen is the main energy gas in the hydrolysis and acidification stage of the acidogenic fermentation system of food waste. A higher headspace hydrogen pressure will inhibit the growth rate of acetogenic bacteria. Reducing the headspace hydrogen pressure to reduce the hydrogen partial pressure in the acidogenic reactor can improve acetic acid production. In addition, H2 is an important factor affecting the metabolic pathway of acetic acid production, because H2 not only serves as a substrate for the metabolic process of homotypic acetogenic bacteria, but also plays an important role in interspecies electron transfer and cell growth. However, there is no report on a method to promote the directional acetic acid production from food waste based on the self-circulation of acidogenic phase gas. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a method for promoting directional acetic acid production by anaerobic acidogenic fermentation of kitchen waste.

[0006] In order to achieve the above-mentioned invention object, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for promoting directional acetic acid production by anaerobic acidogenic fermentation of kitchen waste, comprising the following steps:

[0008] (1) After sorting, crushing, pulping and high-temperature degreasing of food waste, the food waste was stored at 4°C. When used, water was added to adjust the volatile solids in the food waste to 60.0±0.5 g / L;

[0009] (2) The inoculum and volatile solids from food waste were added to the anaerobic reactor in a mass ratio of 3:1 for fermentation. After the anaerobic reactor was running stably, the circulating gas line was opened for gas self-circulation to 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 acidogenic fermentation of food waste that is stably operated in the team's laboratory.

[0011] Preferably, the temperature of the anaerobic reactor in step (2) is 37±1° C., the pH is controlled above 5.5, the residence time is 5 days, and the stirring rate is 80-120 r / 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 gas circuit in step (2) is set to 0.3-0.5 L / min.

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

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

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

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention introduces the tail gas generated during the anaerobic acid production fermentation of kitchen waste into an anaerobic reactor through a circulating gas path, and increases the gas solubility through air bubble stones. The circulating introduction of gas increases the fluidity of water, improves the gas-liquid mass transfer efficiency, promotes the degradation of organic matter, and increases the dissolution of ammonia nitrogen, so that the pH of the system is relatively stable, which is conducive to directional increase of the content of acetic acid in VFAs. In addition, the introduction of gas consumes the CO2 gas enriched in the system, reduces the headspace hydrogen pressure, and increases the relative abundance of homoacetogenic bacteria. Through the biochemical action of homoacetogenic bacteria, CO2 is finally converted into acetic acid through the Wood-Ljungdahl pathway, enriching the metabolic pathway of acetic acid generation (4H2+CO2→CH3COOH+2H2O), promoting the directional generation of acetic acid in volatile fatty acids, and the acetic acid yield is increased by nearly 25%. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of the circulating anaerobic reaction device of the present invention;

[0020] Figure 2 The anaerobic acid production reaction operation flow chart of the present invention;

[0021] Figure 3 Graphs showing pH values ​​and ammonia nitrogen content at different stages in the experimental examples of the present invention;

[0022] Figure 4 is a graph of volatile fatty acid content at different stages in the experimental example of the present invention;

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

[0024] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the present invention is now 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 reaction device, see Figure 1, including an anaerobic reactor 1, an outer wall of the anaerobic reactor 1 is provided with an insulation jacket 2, connected to a circulating water bath 3, a feed pipe 4 is provided on the top of the anaerobic reactor 1, the feed pipe is provided with a feed water seal valve, a discharge hopper 5 is provided at the bottom of the anaerobic reactor 1, the discharge hopper 5 is provided with a discharge water seal valve, a stirring device 6 is installed in the anaerobic reactor 1, the stirring device 6 extends from the feed end to the discharge end, the anaerobic reactor 1 is connected with a circulating gas circuit, the circulating gas circuit includes an outlet pipe 7, the outlet of the outlet pipe 7 is connected to a gas collector 8, the inlet at the bottom of the outlet pipe 7 is higher than the liquid level of the anaerobic reactor 1, the gas collector 8 is connected to an air bag 9, the air bag 9 is connected to below the liquid level in the anaerobic reactor 1 through an air inlet pipe 10, the air inlet pipe 10 is provided 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 kitchen waste using the above-mentioned circulating anaerobic reaction device, the operation process is as follows Figure 2 As shown, the following steps are included:

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

[0029] (2) Anaerobic acid production test: The inoculum was taken from the fermentation liquid in the anaerobic acid production reactor of food waste that has been in continuous and stable operation for a long time. It was added to the fully mixed anaerobic reactor 1 with an effective volume of 10L, named CSTR, according to the mass ratio of volatile solids (VS) of food waste to inoculum of 3:1. Nitrogen was filled to maintain the anaerobic environment. The operating temperature of the anaerobic reactor 1 was kept stable at 37±1℃ by the circulating water bath 2. The anaerobic reactor 1 was equipped with a stirring device 6 that operated for 24 hours to ensure the uniformity of mixing of materials and liquids. The stirring speed was set to 120r / min. The pH value in the reactor was maintained above 5.5 by 5mol / L sodium hydroxide solution every day. When the pH value in the anaerobic reactor 1 was detected to be lower than 5.5 during daily discharge, 5mol / L sodium hydroxide was added to adjust the pH to 6.0. A 50-day acid production fermentation test was carried out, with 2L of material fed and discharged every day, and the residence time was 5 days. After running for 5 residence times (25 days), the circulating air pump 11 was turned on to circulate the gas in the anaerobic reactor 1 into the anaerobic reactor 1 at a rate of 0.5L / min. The circulating air pump 11 was in the off stage for the first 25 days, and the gas collected in the air bag 9 was discharged every day. A portion of the daily discharge was stored in a 50mL sample bottle and stored in a 4°C cold storage to measure the volatile fatty acid content by gas chromatography.

[0030] The anaerobic acid production in the first 25 days of the acid production fermentation experiment was set as the S1 group (control group), and the 25 days after the circulation air pump was turned on was set as the S2 group (experimental group). The pH value and ammonia nitrogen concentration of the acidified liquid in the S1 group and the S2 group at different stages are shown in Figure 2. Figure 3 The volatile fatty acid content at different stages is shown in Figure 4 .

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

[0032] Compared with the S1 group, the total volatile fatty acids in the S2 group with self-circulation of the acidogenic phase gas increased by 8.46%, and the acetic acid content increased by 24.64%. The acidogenic effect was significantly improved, especially the acetic acid content in the volatile fatty acids was increased in a directional manner. In addition, the self-circulation of the acidogenic phase gas promoted the dissolution of ammonia nitrogen, making the pH value in the reaction tank relatively stable. After the 35th day of operation, the pH value could be kept above 5.5 without the addition of alkalinity. The reason is that the combination of gas circulation and air stone promotes the gas-liquid mass transfer efficiency, so that the hydrogen and CO2 introduced into the liquid phase are converted into acetic acid under the biochemical action of the same type of acetogenic bacteria, reducing the headspace hydrogen partial pressure while consuming the enriched CO2 gas in the system. At the same time, the dissolution of hydrogen in the acidogenic waste gas in the liquid phase and the suitable pH environment increase the relative abundance of the same type of acetogenic bacteria, enrich the metabolic pathway of acetic acid production, and thus promote the directional production of acetic acid in acidogenic fermentation.

Claims

1. A method for producing acetic acid by anaerobic acidogenic fermentation of kitchen waste, characterized in that: The following steps are involved: (1) The food waste was sorted, crushed, pulped, and degreased at high temperature before being stored at 4°C. To reduce the impact of material fluctuations on the experimental results, water was added during use to adjust the volatile solids in the food waste to 60.0±0.5 g / L; (2) The inoculum and volatile solids were added to the anaerobic reactor in a mass ratio of 3:1 for fermentation. After the anaerobic reactor was running stably, the circulating gas line was opened for gas self-circulation to reduce the headspace hydrogen partial pressure and promote 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 reaction tank of kitchen waste.

3. The method according to claim 2, characterized in that The temperature of the anaerobic reactor in step (2) is 37±1° C., the pH is controlled above 5.5, the residence time 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 The gas flow rate of the gas circulation gas circuit in step (2) 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.

7. The method according to claim 6, characterized in that During the gas self-circulation process in step (2), the gas entering the anaerobic reactor penetrates into the liquid and is solubilized by the bubble stone.

8. The method according to claim 7, characterized in that During the gas self-circulation process in step (2), the discharged gas is the gas located at the top of the anaerobic reactor.

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