Method for improving in-situ fermentation of kitchen waste to produce caproic acid by using ferroferric oxide

Abstract

The invention discloses a method for improving caproic acid production through in-situ fermentation of kitchen waste by using ferroferric oxide, and relates to the field of organic solid waste treatment and recycling, in particular to a method for promoting the efficiency of caproic acid production through anaerobic fermentation by adding a conductive accelerant ferroferric oxide. According to the method, a proper amount of ferroferric oxide is added into a fermentation system, so that hydrolysis and acidification of a substrate are accelerated, electron transfer of microorganisms is promoted, anaerobic microorganisms are enriched, the carbon chain extension process of an anaerobic system can be promoted, and production of hexanoic acid is further promoted. Fe3O4 enhances the oxidation-reduction performance by inducing Fe < 2 + > and Fe < 3 + > to circulate, so that electron transfer is facilitated, and the anaerobic fermentation acid production efficiency of the kitchen waste is better regulated and controlled. Kitchen waste is fermented under an anaerobic condition to form lactic acid which is used as an electron donor, so that external electron donor source supplementation is not needed, and the method is a more sustainable hexanoic acid biosynthesis method; and the ferroferric oxide can be recycled after magnetic separation, so that the method has remarkable development potential and application prospect.

Description

Technical Field

[0001] The invention relates to the field of organic solid waste treatment and resource utilization, and in particular to a method for promoting the efficiency of producing caproic acid by anaerobic fermentation by adding a conductive promoter, ferrosoferric oxide. Background Art

[0002] Food waste is a component of urban organic solid waste, accounting for more than 14.5% of the total urban solid waste production by weight. According to the Food and Agriculture Organization of the United Nations (FAO), about 1.3 billion tons of food are lost in the food supply chain each year, accounting for one-third of the production for human consumption. The rapid increase in the production of this type of waste is highly perishable. If it is not handled properly, it may cause environmental pollution, leading to public food safety issues and environmental safety crises. Therefore, seeking and developing effective food waste resource treatment technology is of great significance to achieve harmless, resource-based and reduced treatment of food waste.

[0003] At present, the technology of using microorganisms to convert organic waste into high-value-added hexanoic acid is becoming more and more mature. The carbon chain extension technology using alcohols as electron donors has shown the potential for industrialization. For example, the Dutch Chain-Craft company has carried out carbon chain extension synthesis of medium-chain fatty acids (MCFAs) using ethanol as an electron donor, and has achieved industrial production and promotion. However, since the alcohol-induced carbon chain extension process mostly relies on the addition of ethanol as an electron donor, it significantly increases the cost.

[0004] The patent with publication number CN110734933A proposes a method of using waste activated sludge from urban sewage treatment plants as a fermentation substrate and optimizing fermentation conditions by introducing electron donors. Zero-valent iron powder is added to the anaerobic reactor for anaerobic fermentation to produce medium-chain fatty acids. The core of this technical solution is to innovatively add zero-valent iron powder to the anaerobic reactor to promote the anaerobic fermentation process. Although this method has achieved a significant increase in the production of medium-chain fatty acids, the high cost of iron powder and its unstable chemical properties limit its feasibility of industrial promotion.

[0005] In addition, the patent with publication number CN110819662A proposed a method for adding biochar to an anaerobic reaction system to promote the production of medium-chain fatty acids. The concentrated sludge in the secondary sedimentation tank after anaerobic reactor cultivation was selected as the substrate, the inoculum and the substrate were mixed, and ethanol and biochar were added under an anaerobic environment. Although this method has achieved the production of medium-chain fatty acids to a certain extent, the current output concentration needs to be further improved.

[0006] In recent years, in terms of food waste resource utilization, anaerobic treatment technology that uses lactic acid as an electron donor to bioconvert short-chain fatty acids into caproic acid through carbon chain extension has attracted more and more attention. However, the practical application of this technology is restricted by its dependence on electron donors, low carbon conversion efficiency, and low yield.

[0007] In view of the above background, the present invention proposes a technical improvement scheme for producing caproic acid by anaerobic fermentation of kitchen waste, which solves the problems of low caproic acid yield and low conversion rate in the prior art. Summary of the invention

[0008] In view of the current low efficiency of producing caproic acid by original fermentation of kitchen waste, the present invention proposes a method for promoting anaerobic fermentation to produce caproic acid by adding a conductive promoter ferric oxide to overcome the defects of the above-mentioned prior art. At the same time, no exogenous electron donor is required to be supplemented, thereby demonstrating a more environmentally friendly and sustainable caproic acid biosynthesis pathway, which is suitable for industrial-scale application and promotion.

[0009] To achieve the above objectives, the present invention adopts the following core technical solutions.

[0010] The first aspect of the present invention provides a method for producing caproic acid by in-situ fermentation of kitchen waste, comprising the following steps:

[0011] S1. Domestication of functional bacteria producing caproic acid: anaerobic sludge is inoculated into a microbial culture medium with lactic acid and acetic acid as the main matrix for cultivation and enrichment;

[0012] S2. The caproic acid-producing functional bacteria domesticated in step S1 are inoculated into the food waste, and Fe3O4 is added to the fermentation liquid for anaerobic fermentation.

[0013] The raw material of the present invention is food waste, which has a high carbohydrate content. Under anaerobic conditions, food waste is easily fermented to form lactic acid, which is an ideal electron donor for carbon chain extension, and thus does not need to be supplemented externally.

[0014] Furthermore, in step S1, the pH of the acclimation step system is 5-6.

[0015] In a preferred embodiment, in step S1, the pH of the acclimation step system is 5.5.

[0016] Further, in step S2, the amount of ferrosoferric oxide added is 2-10 g / L;

[0017] Furthermore, during the fermentation process in step S2, the pH of the system is controlled to be 5-6. The pH is preferably 5.5.

[0018] Furthermore, in step S2, the inoculation ratio of the kitchen waste and the caproic acid-producing functional bacteria is 1:2-6:1, calculated in terms of VS value.

[0019] Furthermore, the total COD concentration of the system is 60-90 g COD / L.

[0020] Furthermore, the caproic acid-producing functional bacteria include lactic acid-producing bacteria, butyric acid-producing bacteria, and carbon chain-extending bacteria;

[0021] Furthermore, the lactic acid producing bacteria include Lactococcus, Latilactobacillus and Lactobacillus;

[0022] Furthermore, the butyrate-producing bacteria include Latilactobacillus and Stenotrophomonas;

[0023] Furthermore, the carbon chain-extending bacteria include caproiciproducens and clostridium-sensu-strict-11.

[0024] In some embodiments, the VS value of the food waste is between 8% and 18%.

[0025] Furthermore, step S2 also includes the step of introducing N2 into the reaction solution to remove oxygen before anaerobic fermentation.

[0026] Furthermore, the fermentation reactor is kept in an anaerobic state during the fermentation process, and the anaerobic fermentation temperature is maintained at 32-38°C; preferably 37±2°C.

[0027] The second aspect of the present invention is to provide a method for increasing the abundance of carbon chain extension functional bacteria based on the method described above.

[0028] In some embodiments, the addition of Fe3O4 to the system promotes the enrichment of microorganisms related to caproic acid production, especially the carbon chain extension functional bacteria Caproiciproducens, which reached 91%, 90% and 92% in the groups with added Fe3O4 (2g / L, 5g / L, 10g / L), respectively, which is also significantly improved compared with the control group (84%).

[0029] The beneficial effects of the technical solution of the present invention are at least:

[0030] (1) This method provides an efficient way to promote the dissolution of organic solid particles and accelerate the degradation of substrates by adding ferric oxide to the anaerobic system. Acidogenic microorganisms can use iron oxides as the terminal electron acceptor / donor for microbial extracellular respiration, thereby promoting the metabolism of the microorganisms themselves. 2+ and Fe 3+The cycle can enhance the redox performance, thereby facilitating electron transfer and better regulating the acid production efficiency of anaerobic fermentation of food waste.

[0031] (2) Another advantage of this method is that the process is simple and easy to operate. Since food waste has a high carbohydrate content and can be easily fermented to form lactic acid under anaerobic conditions, and lactic acid is an ideal electron donor for carbon chain extension, it does not require external electron donor source supplementation. It is a more sustainable method for hexanoic acid biosynthesis and has significant development potential and application prospects.

[0032] (3) The addition of a small amount of Fe3O4 can effectively increase the lactic acid production in the system. When the addition amount is 2 g / L, the lactic acid production increases by 17.4%. The increased lactic acid further acts as an electron donor, effectively promoting the conversion of caproic acid.

[0033] (4) The process of adding ferroferric oxide to the anaerobic fermentation system is simple to operate, has low energy consumption, is cheap, and has strong stability. In addition, the ferroferric oxide can be recycled after magnetic separation, further reducing the operating cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings are used to provide a further understanding of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the present application and do not constitute a limitation of the present application. In the accompanying drawings:

[0035] Figure 1 Example 2-5: Changes in the production of key organic acids under different concentrations of Fe3O4 during fermentation; Changes in the contents of (a) lactic acid, (b) acetic acid, (c) butyric acid, and (d) caproic acid during fermentation;

[0036] Figure 2 is the relative activity of the microbial electron transport system (ETS) and Fe 2+ and Fe 3+ Content graph; (a) relative ETS activity and (b) Fe at the end of hexanoic acid fermentation 2+ and Fe 3+ content;

[0037] Figure 3 Distribution diagram of microorganisms at the genus level in different Fe3O4 dosage groups of Example 2-5;

[0038] Figure 4 Example 10: Changes in lactic acid production at different Fe3O4 concentrations. DETAILED DESCRIPTION

[0039] The technical scheme of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The experimental methods in the following embodiments, unless otherwise specified, are conventional methods in the art. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the art without making creative work are within the scope of protection of the present invention.

[0040] The following core technical solutions are adopted in the embodiments.

[0041] 1. Source and treatment of substrate and sludge:

[0042] The anaerobic inoculum sludge used in the examples was taken from the long-term operating anaerobic digestion facility of restaurant kitchen waste of Wuxi Huilian Resource Recycling Technology Co., Ltd.

[0043] In order to ensure the consistency of the properties of the food waste substrate during the experiment, the food waste used in the experiment was formulated according to the actual food waste composition. Then it was crushed and homogenized with a grinder. The formulated food waste was stored in a -20℃ refrigerator, thawed at 4℃ before use, and stored at 4℃ for no more than 15 days.

[0044] The main components of the kitchen waste used in the embodiment include 41.8% staple food (21.8% of which are rice and 20% are noodles), 34.6% vegetables (including 12% cabbage, 5.6% carrots, 5% onions and 12% potatoes), 9.2% protein (4.6% eggs and 4.6% tofu), 3% mushrooms, 8.2% pork and 3.2% condiments. After these raw materials are mixed in proportion, they are steamed for 0.5 hours and then crushed and homogenized using a pulverizer. The processed kitchen waste is stored in a refrigerator at -20°C, thawed at 4°C before use, and stored at 4°C for no more than 15 days. In order to better simulate the actual situation, the VS value is controlled between 8% and 18%.

[0045] 2. Anaerobic inoculation mud acclimation:

[0046] In order to effectively enrich carbon chain extension functional bacteria, the seed mud was acclimated for one month before inoculation. A carbon chain extension microbial culture medium with lactic acid and acetic acid as the main matrix was used, and the pH was adjusted to 5.5 with 1M sodium hydroxide and hydrochloric acid.

[0047] 3. Fermentation experiment technical plan

[0048] (1) Effect of Fe3O4 concentration gradient on lactic acid fermentation

[0049] First, four groups of Fe3O4 with different concentration gradients (0, 2, 5, 10 g / L) were set up in serum bottles with a working volume of 300 mL, with three replicates in each group. The oxygen was expelled by nitrogen blow-off for 10 minutes, and then the serum bottles were placed in a shaker for incubation at a speed of 120 rpm and the temperature was maintained at 37 ± 2 ° C. The pH was adjusted to 5.0 with sodium hydroxide (6 M) and hydrochloric acid (6 M) every 1 day. Samples were taken every two days for observation.

[0050] (2) Effect of Fe3O4 concentration gradient on hexanoic acid production by fermentation (inoculation ratio S / I = 1:2)

[0051] First, four groups of Fe3O4 with different concentration gradients (0, 2, 5, 10 g / L) were set up to explore the effect on the production of caproic acid by food waste fermentation. The TCOD concentration in the serum bottle was controlled to 70.0 g / L, the inoculation ratio S / I was 1:2, and the reaction was carried out in a serum bottle with a working volume of 300 mL, with 3 replicates per group. The oxygen was expelled by nitrogen stripping for 10 minutes, and then the serum bottle was placed in a shaker for incubation at a speed of 120 rpm and the temperature was maintained at 37 ± 2 ° C. The pH was adjusted to 5.5 with sodium hydroxide (6 M) and hydrochloric acid (6 M) every 1 day, and samples were taken every two days.

[0052] (3) Effect of Fe3O4 concentration gradient on hexanoic acid production by fermentation (inoculation ratio S / I is 6:1)

[0053] The S / I (VS ratio) of food waste to inoculum was changed to 6:1, and the operating conditions were the same as (2).

[0054] Example 1 Acquisition of Caproic Acid Functional Bacteria Source

[0055] The anaerobic inoculated sludge in this example was taken from the long-term anaerobic digestion facility of food waste of Wuxi Huilian Resource Recycling Technology Co., Ltd. In order to enrich the bacterial flora with carbon chain extension function, the seed sludge (VS = 8.6 ± 0.2 g / L) was acclimated for one month before inoculation. The carbon chain extension microbial culture medium with lactic acid and acetic acid as the main matrix, and the pH of the water was adjusted to 5.5 with 1M sodium hydroxide and hydrochloric acid. The composition of 1L culture medium is shown in the table below.

[0056]

[0057] The specific components of the vitamin solution in the table include: 2.00 mg / L biotin, 2.00 mg / L folic acid, 10.00 mg / L vitamin B6, 5.00 mg / L vitamin B1, 5.00 mg / L vitamin B2, 5.00 mg / L niacin, 5.00 mg / LD calcium pantothenate, 0.10 mg / L vitamin B12, 5.00 mg / L p-aminobenzoic acid, 5.00 mg / L lipoic acid;

[0058] The specific components of the trace element solution in the table include: 1.50g / L nitrotriacetic acid, 3.00g / L MgSO4·7H2O, 0.50g / L MnSO4·H2O, 1.00g / L NaCl, 0.10g / L FeSO4·7H2O, 0.18g / L CoSO4·7H2O, 0.10g / L CaCl2·2H2O, 0.18g / L ZnSO4·7H2O, 0.01g / L CuSO4·5H2O, 0.02g / L KAI(SO4)2·12H2O, 0.01g / L H3BO3, 0.01g / L Na2MoO4·2H2O, 0.03g / L NiCl2·6H2O, 0.30mg / L Na2SeO3·5H20, 0.40mg / LNa2WO4·2H2O. Adjust pH to 7.0.

[0059] After about 30 days of cultivation, when it is observed that the caproic acid production in the acclimation solution tends to be stable, and the proportion of caproic acid production in the total volatile fatty acids (VFAs) production exceeds 30%, the caproic acid production reaches 3.3±0.3gCOD / L, marking the completion of the acclimation process. Subsequently, the obtained caproic acid functional bacterial solution is centrifuged, 30g of centrifugal sediment, 100ml of kitchen waste, 500ml of carbon chain extension microbial culture medium (without lactic acid and acetic acid) and 2400ml of deionized water are added to a semi-continuous reactor with a working volume of 3L for further enrichment, and after 20 days (one cycle) of stable operation, the effluent is taken for batch experiments.

[0060] Example 2 In-situ production of caproic acid from kitchen waste

[0061] Kitchen waste was added, and caproic acid functional bacteria were used to perform fermentation conversion of lactic acid to caproic acid, with an inoculation ratio (F / M=gVS / gVS) of 1:2, and the effluent obtained in Example 1 was inoculated.

[0062] During the experiment, the total COD concentration of the reaction was controlled to be 70 g COD / L, and the reaction volume was 300 ml. Subsequently, N2 was introduced for 8 min to exclude air, and the sealed reactor was placed in a constant temperature shaker at 37°C and 120 rpm for cultivation.

[0063] Example 3

[0064] The operation steps of this embodiment are the same as those of embodiment 2, except that the dosage of ferrosoferric oxide is 2 g / L.

[0065] Example 4

[0066] The operation steps of this embodiment are the same as those of embodiment 2, except that the dosage of ferrosoferric oxide is 5 g / L.

[0067] Example 5

[0068] The operation steps of this embodiment are the same as those of embodiment 2, except that the dosage of ferrosoferric oxide is 10 g / L.

[0069] Example 6

[0070] Add food waste to produce lactic acid in situ, and then use caproic acid functional bacteria to ferment lactic acid to caproic acid. The inoculation ratio (F / M) is 6:1, the total COD concentration of the reaction is controlled at 70gCOD / L, and the reaction volume is 300mL. Subsequently, N2 is introduced for 8min to remove air, and the sealed tube is placed in a constant temperature shaker at 37℃ and 120rmp for cultivation.

[0071] Example 7

[0072] The operation steps of this embodiment are the same as those of embodiment 6, except that the dosage of ferrosoferric oxide is 2 g / L.

[0073] Example 8

[0074] The operation steps of this embodiment are the same as those of embodiment 6, except that the dosage of ferrosoferric oxide is 5 g / L.

[0075] Example 9

[0076] The operation steps of this embodiment are the same as those of embodiment 6, except that the dosage of ferrosoferric oxide is 10 g / L.

[0077] Example 10 Effect of Fe3O4 concentration gradient on lactic acid fermentation

[0078] The kitchen waste produces lactic acid in situ without external bacterial source; the total COD is controlled at 70g / L, the temperature is 37±2℃, and the pH is 5.5.

[0079] The dosage of ferroferric oxide was 0, 2, 5, and 10 g / L respectively; it was carried out in serum bottles with a working volume of 300 mL, and each group was paralleled for 3 times. Nitrogen was blown off for 10 minutes to expel oxygen, and then the serum bottles were placed in a shaker for incubation at a speed of 120 rpm and the temperature was maintained at 37 ± 2 ° C. The pH was adjusted to 5.0 with sodium hydroxide (6 M) and hydrochloric acid (6 M) every 1 day. Samples were taken every two days for observation.

[0080] The experimental results are shown in Figure 3 As shown in the table below: It can be seen that by adding a small amount of Fe3O4 (2g / L), the lactic acid production and yield are greatly improved, and the lactic acid production increase rate is 17.4%.

[0081] <![CDATA[Fe3O4(g / L)]]> Lactic acid production (gCOD / L) Lactic acid yield (g / gCOD) 0 25.17 0.523 2 29.54 0.613 5 31.49 0.654 10 31.52 0.655

[0082] Comparative Example

[0083] The data disclosed in the prior art documents are used in the comparative examples. The prior art 1-6 in Table 2 corresponds to the prior art documents [1]-[6] respectively; the prior art documents are as follows:

[0084] Table 1 Experimental conditions and caproic acid production of each case in this patent

[0085]

[0086] Table 2 Experimental conditions and caproic acid production of some related cases reported in the literature

[0087]

[0088] Caproic acid production increase rate = (caproic acid production of the embodiment - caproic acid production of the comparative example) / caproic acid production of the comparative example × 100%;

[0089] The increase rate of caproic acid production was used as an evaluation index to assess the effect of increasing caproic acid production under different conditions. The experimental results showed that under the condition of an inoculation ratio of 1:2, that is, under low load, increasing the Fe3O4 concentration helped to promote the production of caproic acid. When 10g / LFe3O4 was added, the maximum caproic acid yield reached 0.125g / g COD. From the perspective of intermediate product conversion metabolism analysis, Fe3O4 promoted the conversion of lactic acid, thereby promoting the extension of the carbon chain and the production of caproic acid.

[0090] like Figure 2 and Figure 3 As shown, from the perspective of electron transfer, the increase of Fe3O4 makes more Fe 3+ and Fe 2+ It participated in the electron transfer in the system, and its electron transfer capacity index ETS increased by 7.1%, 209.6%, and 258.3% respectively compared with the embodiment without adding Fe3O4, which can be explained that the electron transfer capacity of the system increases with the increase of Fe3O4. From the perspective of microorganisms, Fe3O4 promoted the enrichment of microorganisms related to caproic acid production, especially the carbon chain extension functional bacteria Caproiciproducens, which reached 91%, 90%, and 92% in the groups with added Fe3O4 (2g / L, 5g / L, 10g / L), respectively, which was also significantly improved compared with the control group (84%).

[0091] Under the condition of an inoculation ratio of 6:1, that is, under high load, the effect of Fe3O4 on the production of caproic acid in food waste is different. High concentrations of Fe3O4 promote the conversion of lactic acid to butyric acid, but this also leads to insufficient subsequent electron donors being available, which is not conducive to the production of caproic acid. However, from the perspective of yield, under high load conditions, the caproic acid yield is significantly improved. When 2g / LFe3O4 is added, the maximum caproic acid yield is 0.330g / g COD. Obviously, at relatively high loads, that is, high F / M ratios, adding 2g / LFe3O4 under these conditions can effectively increase the yield of in-situ caproic acid.

[0092] like Figure 3 As shown in the figure, after analyzing the distribution of microorganisms at the genus level in different Fe3O4 groups, we found that the four groups had similar microbial community composition. These microbial communities included genera related to lactic acid production (Lactococcus, Latilactobacillus and Lactobacillus) and butyrate production (Latilactobacillus and Stenotrophomonas) as well as carbon chain extension bacteria (caproiciproducens and clostridium-sensu-strict-11). The addition of Fe3O4 significantly increased the abundance of some functional microorganisms; in particular, the carbon chain extension functional bacteria Caproiciproducens reached 91%, 90% and 92% in the groups with Fe3O4 (2g / L, 5g / L, 10g / L), respectively, which was significantly improved compared with the control group (84%). This result is consistent with the difference in hexanoic acid concentration at the end of fermentation. In addition, we also observed more abundant Latilactobacillus and Leuconostoc in the group with Fe3O4 added. These results indicate that when Fe3O4 was introduced into the fermentation system, the abundance of both acidogenic and hexanoic acid-producing microorganisms increased, thereby promoting the in situ production of hexanoic acid.

[0093] In summary, the present invention proposes a method for improving the in-situ fermentation production of caproic acid from food waste by using ferroferric oxide. First, a carbon chain extension microbial culture medium with lactic acid and acetic acid as main matrices is used to effectively enrich carbon chain extension functional bacteria; based on the domesticated and enriched carbon chain extension functional bacteria, the food waste is anaerobically fermented; further, by adding an appropriate amount of ferroferric oxide to the fermentation system, not only the hydrolysis and acidification of the substrate are accelerated, but also the electron transfer of the microorganisms is promoted, and the anaerobic microorganisms are enriched, the carbon chain extension process of the anaerobic system is promoted, and the production of caproic acid is further promoted.

[0094] Prior art literature:

[0095] [1]TONANZI B,GALLIPOLI A,FRUGIS A,et al.Bio-based production ofmedium-chain carboxylic acids from food waste and sludge without chemicaladdition:The pivotal role of mix ratio and pretreatment[J].JOURNAL OF CLEANERPRODUCTION,2024,436.

[0096] [2]YANYAN Z,JIAZHE B,JIANE Z.Performance and mechanisms of medium-chain fatty acid production by anaerobic fermentation of food waste withoutexternal electron donors[J].Bioresource Technology,2023,374:128735-.

[0097] [3]CHEN R,JI X,CHEN Z,et al.Regulation of hydraulic retention time oncaproic acid production via two-phase anaerobic fermentation of Chinesecabbage waste with autopoietic electron donors[J].JOURNAL OF BIOTECHNOLOGY,2024,381:1-10.

[0098] [4]ARHIN S G,CESARO A,DI CAPUA F,et al.Acidogenic fermentation offood waste to generate electron acceptors and donors towards medium-chaincarboxylic acids production[J].JOURNAL OF ENVIRONMENTAL MANAGEMENT,2023,348.

[0099] [5]JI

[0100] [6] CONTRERAS-DAVILA CA, CARRION VJ, VONK VR, et al. Consecutivelactate formation and chain elongation to reduce exogenous chemicals input inrepeated-batch food waste fermentation[J]. WATER RESEARCH, 2020,169.

[0101] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. Those familiar with the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for producing caproic acid by in-situ fermentation of kitchen waste, characterized in that: The following steps are involved: S1. Domestication of functional bacteria producing caproic acid: anaerobic sludge is inoculated into a microbial culture medium with lactic acid and acetic acid as the main matrix for cultivation and enrichment; S2. The caproic acid-producing functional bacteria domesticated in step S1 are inoculated into the food waste, and Fe3O4 is added to the fermentation liquid for anaerobic fermentation.

2. The method for producing caproic acid by in-situ fermentation of kitchen waste according to claim 1, characterized in that: In step S1, the pH of the acclimatization system is 5-6.

3. The method for producing caproic acid by in-situ fermentation of kitchen waste according to claim 1, characterized in that: In step S2, the amount of ferrosoferric oxide added is 2-10 g / L.

4. The method for producing caproic acid by in-situ fermentation of kitchen waste according to claim 1, characterized in that: During the fermentation process in step S2, the pH of the system is 5-6.

5. The method for producing caproic acid by in-situ fermentation of kitchen waste according to claim 1, characterized in that: In step S2, the inoculation ratio of food waste to caproic acid-producing functional bacteria is 1:2-6:

1.

6. The method for producing caproic acid by in-situ fermentation of kitchen waste according to claim 1, characterized in that: In step S2, the total COD concentration of the system is 60-90 g COD / L.

7. The method for producing caproic acid by in-situ fermentation of kitchen waste according to claim 1, characterized in that: The caproic acid-producing functional bacteria include lactic acid-producing bacteria, butyric acid-producing bacteria and carbon chain-extending bacteria; The lactic acid producing bacteria include Lactococcus, Latilactobacillus and Lactobacillus; The butyrate-producing bacteria include Latilactobacillus and Stenotrophomonas; The carbon chain-extending bacteria include caproiciproducens and clostridium-sensu-strict-11.

8. The method for producing caproic acid by in-situ fermentation of kitchen waste according to claim 1, characterized in that: Step S2 also includes the step of introducing N2 into the reaction solution to remove air before anaerobic fermentation.

9. The method for producing caproic acid by in-situ fermentation of kitchen waste according to claim 1, characterized in that: During the fermentation process, the fermentation reactor was kept in an anaerobic state and the anaerobic fermentation temperature was kept at 32-38°C.

10. A method for increasing the abundance of carbon chain extension functional bacteria based on the method described in any one of claims 1 to 9.

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