Three-phase process for producing medium-chain fatty acid by using kitchen waste

Abstract

The invention discloses a three-phase process for producing medium-chain fatty acid by using kitchen waste, which comprises the following steps of: (1) collecting the kitchen waste, pretreating the kitchen waste, stirring the kitchen waste by using a stirrer until the kitchen waste is pasty, and storing the pasty kitchen waste for later use; (2) taking a reaction container, adding the kitchen waste slurry and anaerobic sludge, adjusting the pH value, maintaining an anaerobic environment in the reaction container, and carrying out anaerobic fermentation to generate short-chain acid; (3) adding the kitchen waste slurry into another reaction container, adding saccharomycetes, adjusting the pH value, maintaining an anaerobic environment in the reaction container, and carrying out anaerobic fermentation to generate ethanol; and (4) centrifugally filtering the fermentation supernatant in the steps (2) and (3), taking another reaction container, mixing the filtered supernatant in the steps (2) and (3), inoculating the domesticated chain extension sludge, adjusting the pH value, maintaining the anaerobic environment in the reaction container, and carrying out chain extension reaction to generate the medium-chain fatty acid. The process disclosed by the invention realizes multi-dimensional value-added utilization of producing short-chain acid, ethanol and medium-chain fatty acid from the kitchen waste.

Description

Technical Field

[0001] The invention relates to the field of restaurant waste treatment, disposal and resource recovery, and in particular to a three-phase process for producing medium-chain fatty acids using restaurant waste. Background Art

[0002] With the rapid development of social economy, the contradiction between the huge consumption of fossil energy and its availability is becoming increasingly severe. Biochemical resources, as renewable alternative resources, have important application prospects and can effectively alleviate the severe energy crisis and environmental situation.

[0003] Medium-chain fatty acids (MCFA) are carboxylic acids with 6-12 carbon atoms. Compared with traditional anaerobic fermentation products such as short-chain fatty acids (SCFA) and biogas, MCFA have higher energy density and stronger hydrophobicity, which can greatly reduce the cost of subsequent separation and extraction processes. In addition, MCFA is a precursor for further processing into biofuels and industrial products such as antimicrobial agents, food additives and spices, which has significant economic and environmental advantages. MCFA is produced through the chain extension (CE) technology of anaerobic fermentation. Electron donors and acceptors are important media in the production process. The acceptors are often short-chain fatty acids, and the donors are ethanol, lactic acid, CO2, H2, etc.

[0004] Kitchen waste is a type of organic waste with high degradable organic matter content and high water content. It is highly biodegradable and can not only be easily hydrolyzed and acidified to produce SCFA, but also produce ethanol and lactic acid. Its unique properties determine that kitchen waste is a good substrate for the production of MCFA. The annual amount of kitchen waste generated in cities in my country is as high as more than 90 million tons, which is a rich recyclable resource. However, for a long time, the actual treatment rate of kitchen waste has been less than 20%, and its resource utilization and treatment are imminent. In recent years, some studies have been conducted on the production of MCFA using organic waste, but the source of electron donors in most studies is external ethanol, lactic acid, etc. Long-term application will undoubtedly increase production costs and hinder the large-scale application of MCFA. Using kitchen waste to produce MCFA can not only achieve the harmlessness, reduction and resource utilization of kitchen waste, but also realize the self-production and sales of electron donors and acceptors, reduce the cost of raw materials and equipment for MCFA production, and achieve higher economic benefits.

[0005] At present, the process of producing MCFA from food waste is mainly achieved through anaerobic fermentation and chain extension, which specifically includes three steps: hydrolysis, acidification, and chain extension. These steps are often included in a single-phase or two-phase reactor, that is, the process of hydrolysis and acidification followed by chain extension is completed in one reactor, or hydrolysis and acidification are first carried out in one reactor to produce SCFA and ethanol / lactic acid, and then the fermentation liquid in the previous reactor is transferred to another reactor for chain extension process. In the second phase process, an external electron donor or acceptor is often required. The operation of the single-phase or two-phase process is relatively simple. However, through research, it is found that the optimal conditions for hydrolysis to produce short-chain acids, ethanol or lactic acid are not matched, such as pH, temperature, inoculum, substrate concentration, etc., and the concentration of ethanol in the reactor is difficult to control, which will cause toxicity to the system and affect the hydrolysis and acidification and chain extension effects, and affect the further improvement of MCFA production and yield. The addition of acceptors or donors in the two-phase process also increases the overall production cost. In addition, some processes also include the three major steps of hydrolysis and acidification, ethanol production, and chain extension, but before hydrolysis and acidification and ethanol production, external enzyme preparations (such as saccharifying enzymes) are used to perform saccharification reactions, solid-liquid separation and other auxiliary pretreatment or strengthening measures on the kitchen waste, so it is actually a four-phase reaction. Some processes also add ethanol in the process of using saccharification liquid to produce ethanol, but the overall ethanol yield is still relatively low. This will not only increase the instability of the reaction system, making the overall reaction more complicated and time-consuming, but the long-term use of enzyme preparations will bring high costs and reduce the overall economic benefits. Summary of the invention

[0006] In order to solve the problems existing in the prior art, the present invention provides a three-phase process for producing medium-chain fatty acids using food waste, which couples hydrolysis and acidification to produce short-chain acids, anaerobic fermentation to produce ethanol, and chain extension to produce medium-chain fatty acids in three phases, and does not adopt external strengthening processes such as enzyme-assisted and ultrasonic-assisted, and does not need to be treated by solid-liquid separation and other treatments on food waste, but directly utilizes it, fully ensuring the amount of substrate used for fermentation to produce acid or alcohol, making the reaction more sufficient, and no external acid or alcohol is needed, so as to achieve self-sufficiency and self-production and sales of ethanol. The route can make the process flow simpler and more efficient, and each phase process can obtain the corresponding optimal conditions, effectively avoiding the adsorption of MCFA on organic solid particles, and avoiding the toxicity caused by excessive ethanol concentration in a single-phase reactor, reducing time consumption, thereby bringing higher MCFA production and yield, and realizing multi-dimensional resource utilization of food waste.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] The present invention provides a three-phase process for producing medium-chain fatty acids using kitchen waste, the process comprising the following steps:

[0009] (1) collecting food waste, mixing it into a slurry with a blender after pretreatment, and storing it for later use;

[0010] (2) adding food waste slurry and anaerobic sludge into a reaction container, adjusting the pH, maintaining an anaerobic environment in the reaction container, and performing anaerobic fermentation to produce short-chain acids;

[0011] (3) adding food waste slurry to another reaction container, adding yeast, adjusting the pH, maintaining an anaerobic environment in the reaction container, and performing anaerobic fermentation to produce ethanol;

[0012] (4) Centrifugally filter the fermentation supernatant in steps (2) and (3), take another reaction container, mix the filtered supernatants of steps (2) and (3), inoculate the acclimated chain extension sludge, adjust the pH, maintain an anaerobic environment in the reaction container, and carry out chain extension reaction to produce medium-chain fatty acids.

[0013] Preferably, in step (1), the pretreatment step of the food waste is: collecting the food waste, picking, sorting, removing large bones and hard objects, etc., and then filtering with a sieve and washing with clean water to remove floating oil.

[0014] Preferably, the TS of the kitchen waste slurry after treatment in step (1) is 5-10%.

[0015] Preferably, in step (2), the anaerobic sludge is acclimated before inoculation, and the acclimation step is: taking the sludge from the sewage treatment plant, heating it at 100-110°C for 25-35 minutes to kill the methanogens, and then placing it in an anaerobic environment; in some specific embodiments of the present invention, the acclimation step is: taking the sludge from the sewage treatment plant, heating it at 105°C for 30 minutes.

[0016] Preferably, in step (2), the volume ratio of the food waste slurry to the anaerobic sludge is 4-6:1; the pH is adjusted to 6-9; the temperature of the anaerobic fermentation is 30-37° C., and the time of the anaerobic fermentation is 5-15 days.

[0017] Preferably, in step (3), the food waste slurry needs to be diluted before adding yeast, and the concentration of the diluted food waste slurry is 20-40 g COD / L.

[0018] Preferably, in step (3), the amount of yeast added is 5-12% of the dry weight of the substrate.

[0019] Preferably, in step (3), the pH is adjusted to 4.0-5.5; and the time for producing ethanol by anaerobic fermentation is 24-96 hours.

[0020] Preferably, in step (4), the supernatants of steps (2) and (3) after filtration are mixed in a molar ratio of short-chain acid to ethanol of (1-4):1.

[0021] Preferably, in step (4), the pH is adjusted to 5.5-7.5, and the chain extension reaction time is 6-20 days.

[0022] Preferably, in step (4), the method for acclimating the chain extension sludge comprises the following steps: taking sewage treatment plant sludge and inoculating it into a culture medium for acclimation and culture, wherein the culture medium comprises: 3.6 g / L NH4H2PO4, 0.6 g / L MgCl2, 0.2 g / LMgSO4, 0.15 g / LKCl, 0.2 g / L CaCl2, 5.04 g / LNaHCO3, 10 g / L 2-BES, 1 g / L East Extract, 1 mL / L vitamin solution, 1 mL / L trace element solution, 20-30 mM / L acetic acid, and 100-150 mM / L ethanol. The vitamin element solution is composed of 2mg / L biotin, 2mg / L vitamin B, 10mg / L pyridoxine hydrochloride, 5mg / L thiamine hydrochloride, 5mg / L riboflavin, 5mg / L niacin, 5mg / L calcium pantothenate, 0.1mg / L vitamin B12, 5mg / L p-aminobenzoic acid and 5mg / L ZnSO4. The trace element solution is composed of 1.5mg / L FeCl3·4H2O, 0.01mg / L CuCl2·H2O, 0.1mg / L ZnSO4·7H2O, 0.2mg / L CoCl2·6H2O, 0.02mg / L NiCl2·6H2O, 0.03mg / L MnCl2·4H2O, 0.03mg / L NaMoO4·2H2O, 0.3mg / L H3BO3 and 0.01mg / L Na2SeO3.

[0023] The present invention discloses a three-phase process for producing medium-chain fatty acids from kitchen waste, which realizes the multi-dimensional value-added utilization of kitchen waste to produce short-chain acids, ethanol, and medium-chain fatty acids. Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The three-phase process provided is targeted and practical. The present invention proposes to respectively arrange the production of short-chain acids, ethanol, and medium-chain fatty acids in three independent reactors, so that each reactor can be carried out under its own most suitable conditions, which improves the efficiency of its own reaction on the one hand, and reduces the competition between different reaction paths on the other hand. The three-phase process effectively avoids the toxicity caused by excessive ethanol and MCFA concentrations in a single-phase reactor, and improves the yield and production efficiency of medium-chain fatty acids. In addition, the process does not use other strengthening methods such as external enzyme preparations, which further improves the overall economic benefits.

[0025] (2) Using food waste as a substrate can produce both short-chain acids as electron acceptors and ethanol as electron donors. The mixed short-chain acids produced from food waste can be directly used as substrates in the chain extension process, eliminating the separation and purification steps and reducing energy consumption. In addition, there is no need to add ethanol, lactic acid, etc. as electron donors, which reduces the production cost of medium-chain fatty acids and makes the chain extension process more economical and practical.

[0026] (3) It promotes the utilization dimension and utilization value of organic waste of food waste. As a kind of organic matter with complex components, food waste is different from other pure matrix organic matter. The hydrolysis and acidification effect of food waste can be improved by adjusting pH and other methods, and the production of ethanol can be enhanced by inoculating yeast. The production of medium-chain fatty acids can be enhanced by adjusting the molar ratio of hydrolysis acidification liquid and yeast fermentation liquid. This can realize the multi-dimensional resource utilization of food waste, a typical organic solid waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the three-phase separation process for producing medium-chain fatty acids using food waste;

[0028] Figure 2 is the content of short-chain acids in the fermentation broth at different days in Example 1;

[0029] Figure 3 is the ethanol content in the fermentation broth at different times in Example 1;

[0030] Figure 4 The content changes of ethanol, short-chain acids and medium-chain fatty acids in the fermentation broth at different times in Example 1;

[0031] Figure 5 The content changes of ethanol, short-chain acids and medium-chain fatty acids in the fermentation broth at different times in Example 2;

[0032] Figure 6 The content changes of ethanol, short-chain acids and medium-chain fatty acids in the fermentation broth at different times in Comparative Example 1;

[0033] Figure 7 The content changes of ethanol, short-chain acids and medium-chain fatty acids in the fermentation broth at different times in Comparative Example 2. DETAILED DESCRIPTION

[0034] The specific embodiments of the present invention are further described below. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0035] The experimental methods in the following examples are conventional methods unless otherwise specified, and the experimental materials used in the following examples are commercially available unless otherwise specified.

[0036] Example 1

[0037] This embodiment provides a three-phase separation process for producing medium-chain fatty acids using kitchen waste, as shown in the attached Figure 1 As shown, the specific steps include:

[0038] (1) Collect the canteen food waste, sort and pick out large bones and hard objects, filter with a 1 mm mesh, rinse with clean water to remove floating oil, add appropriate amount of water to keep TS between 5-10%, stir with a blender to a slurry, and store in a 4°C refrigerator for later use.

[0039] (2) Pretreated food waste slurry and anaerobic sludge were added to the fermentation container at a volume ratio of 4:1, the pH of the reaction system was adjusted to between 7 and 8 with 5 mol / L NaOH and 5 mol / L HCl solutions, and N2 was blown to maintain the anaerobic environment in the reaction container. The fermentation bottle was placed in a shaker at a temperature of 37°C and a rotation speed of 170 rpm for 7-8 days.

[0040] Anaerobic sludge is obtained by acclimating the sludge from the sewage treatment plant. The acclimation method is as follows: after static sedimentation, heat shock at 105°C for 30 minutes is performed to kill the methanogens and maintain anaerobic conditions.

[0041] (3) Take another fermentation container, add food waste with a diluted concentration of 30 g COD / L, add yeast at a dry weight of 10% of the substrate mass directly into the powder, adjust the pH of the reaction system to 5 with 5 mol / L NaOH and 5 mol / L HCl solution, blow with N2 to maintain the anaerobic environment in the reaction container, and place the fermentation bottle in a shaker at a temperature of 35°C and a rotation speed of 170 rpm for 48 hours.

[0042] (4) The fermentation supernatants in (2) and (3) were collected by centrifugation and vacuum filtration combined with 0.45 μm microfiltration membrane suction filtration, and another reaction container was taken. The short-chain acid and ethanol were mixed in a molar ratio of 2:1 in the reaction container, and the domesticated chain extension sludge was added in a volume ratio of 10:1. The pH of the reaction system was adjusted to 6.5-7, and N2 was blown to maintain the anaerobic environment in the reaction container. The fermentation bottles were placed in a shaker at a temperature of 35°C and a rotation speed of 170 rpm for different reaction days.

[0043] The acclimation method of chain extension sludge is as follows: using acclimation medium: 3.6g / L NH4H2PO4, 0.6g / LMgCl2, 0.2g / LMgSO4, 0.15g / L KCl, 0.2g / L CaCl2, 5.04g / L NaHCO3, 10g / L 2-BES, 1g / L East Extract, 1mL / L vitamin solution, 1mL / L trace element solution, 20mM / L acetic acid, 100mM / L ethanol. The vitamin solution is composed of: 2mg / L biotin, 2mg / L vitamin B, 10mg / L pyridoxine hydrochloride, 5mg / L thiamine hydrochloride, 5mg / L riboflavin, 5mg / L nicotinic acid, 5mg / L calcium pantothenate, 0.1mg / L vitamin B12, 5mg / L p-aminobenzoic acid and 5mg / L ZnSO4. The composition of the trace element solution is: 1.5mg / L FeCl3·4H2O, 0.01mg / L CuCl2·H2O, 0.1mg / LZnSO4·7H2O, 0.2mg / L CoCl2·6H2O, 0.02mg / LNiCl2·6H2O, 0.03mg / L MnCl2·4H2O, 0.03mg / LNaMoO4·2H2O, 0.3mg / LH3BO3, and 0.01mg / LNa2SeO3.

[0044] (5) Centrifugation and filtration to obtain a fermentation broth containing fatty acids such as caproic acid, heptanoic acid, and octanoic acid.

[0045] Determine the concentration of mixed short-chain acids in the final fermentation broth after different reaction days, such as Figure 2 As shown, the concentration of the mixed short-chain acids in the fermentation broth in step (2) can reach 140 mM / L. Figure 3 As shown, the maximum concentration of ethanol in the fermentation broth in step (3) can reach 195 mM / L. Figure 4 As shown, the maximum concentration of medium-chain fatty acids is 43.6 mM / L. For all liquid organic matter in the system, the selectivity of MCFA is 46.32%, of which the selectivity of C6 is 34.87%.

[0046] Example 2

[0047] On the basis of Example 1, the molar ratio in step (4) was changed so that the molar ratio of short-chain acid to ethanol was 3:1. The maximum concentration of medium-chain fatty acids obtained from the experiment was 49.6 mM / L (e.g. Figure 5 ), for all the liquid organic matter in the system, the selectivity of MCFA is 58.25%, of which the selectivity of C6 is 41.54%.

[0048] Comparative Example 1 (single-phase reaction)

[0049] Collect the canteen food waste, sort and pick out large bones and hard objects, filter with a 1mm mesh, rinse with water to remove floating oil, add appropriate amount of water to keep TS between 5-10%, and stir with a mixer until it becomes slurry. Then add food waste slurry and anaerobic sludge at a volume ratio of 4:1 in the same reactor, and inoculate yeast accounting for 10% of the dry weight of food waste at the same time, adjust the pH of the reaction system to 6-6.5 with 5mol / L NaOH and 5mol / L HCl solution, and put the fermentation bottle into a shaker at a temperature of 35℃ and a speed of 170rpm for anaerobic fermentation after blowing N2. The results are as follows: Figure 6 The maximum concentration of medium-chain fatty acids obtained from the experiment was 13.3 mM / L. For all liquid organic matter in the system, the selectivity of MCFA was 32.24%, of which the selectivity of C6 was 30.17%.

[0050] Comparative Example 2 (two-phase reaction)

[0051] Collect the canteen food waste, sort and pick out large bones and hard objects, filter with a 1mm mesh, rinse with water to remove floating oil, add appropriate amount of water to keep TS between 5-10%, and stir with a mixer until it is slurry. Take a fermentation container, add food waste with a diluted concentration of 30g COD / L, add yeast at 10% of the substrate mass dry weight directly, adjust the pH of the reaction system to 5 with 5mol / L NaOH and 5mol / L HCl solution, blow with N2 to maintain the anaerobic environment in the reaction container, and place the fermentation bottle in a shaker at a temperature of 35℃ and a speed of 170rpm for 48h. After centrifugal filtration to obtain ethanol fermentation liquid, pour the ethanol fermentation liquid into another container, inoculate the acclimated chain extension sludge at a volume ratio of 10:1, adjust the pH to 5-7, blow N2, and place the fermentation bottle in a shaker at a temperature of 35℃ and a speed of 170rpm for chain extension reaction. The maximum concentration of medium-chain fatty acids obtained from the experiment was 22.9 mM / L (e.g. Figure 7 ), for all the liquid organic matter in the system, the selectivity of MCFA is 27.23%, of which the selectivity of C6 is 22.8%.

[0052] The embodiments of the present invention are described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions and variations of these embodiments are made without departing from the principles and spirit of the present invention, and still fall within the protection scope of the present invention.

Claims

1. A three-phase process for producing medium-chain fatty acids using kitchen waste, characterized in that: The process includes the following steps: (1) collecting food waste, mixing it into a slurry with a blender after pretreatment, and storing it for later use; (2) adding food waste slurry and anaerobic sludge into a reaction container, adjusting the pH, maintaining an anaerobic environment in the reaction container, and performing anaerobic fermentation to produce short-chain acids; (3) adding food waste slurry to another reaction container, adding yeast, adjusting the pH, maintaining an anaerobic environment in the reaction container, and performing anaerobic fermentation to produce ethanol; (4) Centrifugally filter the fermentation supernatant in steps (2) and (3), take another reaction container, mix the filtered supernatants of steps (2) and (3), inoculate the acclimated chain extension sludge, adjust the pH, maintain an anaerobic environment in the reaction container, and carry out chain extension reaction to produce medium-chain fatty acids.

2. The three-phase process for producing medium-chain fatty acids using kitchen waste according to claim 1, characterized in that: The TS of the kitchen waste slurry after being treated in step (1) is 5-10%.

3. The three-phase process for producing medium-chain fatty acids using kitchen waste according to claim 1, characterized in that: In step (2), the anaerobic sludge is acclimated before inoculation, and the acclimation treatment steps are: taking sludge from a sewage treatment plant, heating it at 100-110° C. for 25-35 minutes to kill methanogens, and then placing it in an anaerobic environment.

4. The three-phase process for producing medium-chain fatty acids using kitchen waste according to claim 1, characterized in that: In step (2), the volume ratio of the kitchen waste slurry to the anaerobic sludge is (4-6):1; the pH is adjusted to 6.0-9.0; the temperature of the anaerobic fermentation is 30-37°C, and the time of the anaerobic fermentation is 5-15 days.

5. The three-phase process for producing medium-chain fatty acids using kitchen waste according to claim 1, characterized in that: In step (3), the amount of yeast added is 5-12% of the dry weight of the substrate.

6. The three-phase process for producing medium-chain fatty acids using kitchen waste according to claim 1, characterized in that: In step (3), the pH is adjusted to 4.0-5.5; and the time for producing ethanol by anaerobic fermentation is 24-96 hours.

7. The three-phase process for producing medium-chain fatty acids using kitchen waste according to claim 1, characterized in that: In step (4), the supernatants of steps (2) and (3) after filtration are mixed in a molar ratio of short-chain acid to ethanol of (1-4):

1.

8. The three-phase process for producing medium-chain fatty acids using kitchen waste according to claim 1, characterized in that: In step (4), the pH is adjusted to 5.5-7.5, and the chain extension reaction time is 6-20 days.

9. The three-phase process for producing medium-chain fatty acids using kitchen waste according to claim 1, characterized in that: In step (4), the method for acclimating the chain extension sludge comprises the following steps: taking sewage treatment plant sludge and inoculating it into a culture medium for acclimation and culture, wherein the culture medium comprises: 3.6 g / L NH4H2PO4, 0.6 g / LMgCl2, 0.2 g / L MgSO4, 0.15 g / L KCl, 0.2 g / L CaCl2, 5.04 g / L NaHCO3, 10 g / L 2-BES, 1 g / L East Extract, 1 mL / L vitamin solution, 1 mL / L trace element solution, 20-30 mM / L acetic acid, and 100-150 mM / L ethanol.

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