Method for preparing acetic acid by synergistically strengthening starch hydrolysis through amylase and saccharomycetes

Abstract

The invention discloses a method for preparing acetic acid by synergistically strengthening starch hydrolysis through amylase and saccharomycetes, which comprises the following steps: carrying out hydrolysis strengthening pretreatment on kitchen garbage by adopting amylase, and then inoculating saccharomycetes for fermentation to obtain ethanol; acetic acid is obtained from the ethanol under the action of acid-producing bacteria. The yield of the acetic acid prepared by anaerobic fermentation of the high-solid-content kitchen garbage is improved in a manner of combining yeast addition and amylase pretreatment, the use cost of the microbial inoculum is reduced, and relatively good practical effectiveness and economic benefits are realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy conversion and resource utilization of organic solid waste, and relates to a method for synergistically enhancing starch hydrolysis with amylase and yeast to prepare acetic acid. Background Art

[0002] Food waste is the main component of domestic waste, including kitchen waste, household food waste and other food waste. The "three highs" characteristics of food waste make it extremely easy to rot and deteriorate, emit a foul smell, attract mosquitoes and flies easily during collection, transportation and storage, breed a variety of pathogenic microorganisms, and easily cause a series of infectious diseases, endangering human health; and the relatively high salt content and oil content will inhibit the growth of microorganisms, affecting the treatment effect and the quality of the final product in the resource recovery treatment of food waste.

[0003] A large amount of organic matter is contained in food waste, which can produce biogas through fermentation, or obtain organic fertilizers through microbial treatment for further agricultural production. In addition, a large amount of acetate substances are also contained in food waste, and acetic acid can be prepared by chemical methods. Acetic acid is an important industrial product, widely used in the fields of food, medicine, chemical industry, etc. Preparing acetic acid from food waste can not only reduce resource waste, but also realize resource reuse.

[0004] However, the current problem is that the technologies for the resource recovery and utilization of food waste still need to be further improved, including aspects such as the sorting, fermentation and chemical treatment of food waste, which require improving the treatment efficiency and reducing the cost, and at the same time, it is also necessary to solve the possible pollution problems in the process of garbage recycling and utilization. Summary of the Invention

[0005] Aiming at the problems of low efficiency in the resource utilization of carbon sources such as starch in food waste during high-solid anaerobic fermentation and slow hydrolysis rate of single fermentation in the prior art, the purpose of the present invention is to provide a method for synergistically enhancing starch hydrolysis with amylase and yeast to prepare acetic acid. This method realizes a significant increase in the acetic acid production rate of anaerobic fermentation of high-solid food waste by combining the addition of yeast and amylase pretreatment, and reduces the use cost of the microbial agent.

[0006] In order to achieve the above technical purpose, the present invention provides a method for synergistically enhancing starch hydrolysis with amylase and yeast to prepare acetic acid. This method uses amylase to perform hydrolysis and strengthening pretreatment on food waste, then inoculates yeast for fermentation to obtain ethanol; the ethanol is obtained acetic acid under the action of acid-producing bacteria.

[0007] A large amount of starch is contained in food waste, but the degradation rate of starch is relatively poor. However, in the technical solution of the present invention, adding amylase can improve the hydrolysis of starch to produce more reducing sugars, and yeast can ferment reducing sugars to produce ethanol, and ethanol can be further converted to acetic acid under the action of acid-producing bacteria. Therefore, the combined application of amylase to improve starch degradation and yeast fermentation can effectively improve the starch utilization rate and acetic acid conversion rate during the anaerobic fermentation of food waste.

[0008] As a preferred scheme, the enzyme activity of the amylase is 100-180 U·g -1 . The enzyme activity of amylase has a direct impact on the content of reducing sugars produced by the hydrolysis of starch, and thus affects the yield of acetic acid produced. As the enzyme activity of amylase increases, the content of reducing sugars produced by starch increases, and it is further preferably 140-180 U·g -1 .

[0009] As a preferred scheme, the mass ratio of the amylase to the food waste is (0.7-1.35):600. By controlling the mass ratio of the amylase to the food waste, the enzyme activity of the amylase in the system can be controlled.

[0010] As a preferred scheme, the total solid content (total solid, abbreviated as TS) of the food waste is 13-17 wt%, and the volatile solid content (volatiles solid, abbreviated as VS) is 10-12 wt%.

[0011] As a preferred scheme, the inoculation amount of the yeast is 3-9% of the sum of the masses of the amylase and the total solid content of the food waste. When the inoculation amount of the yeast increases, the acetic acid content shows a trend of first increasing and then decreasing. This is because when the inoculation amount is too high, due to the premature generation of a high concentration of ethanol in the system, the activity of the acid-producing bacteria is inhibited. It is further preferably 3-6%.

[0012] As a preferred scheme, the conditions for the pretreatment are: the temperature is 40-80 °C, and the time is 4-48 h. As the hydrolysis time increases, the content of reducing sugars shows a trend of first rising and then stabilizing. Among them, the content of reducing sugars grows fastest within 0-4 h, and the content of reducing sugars shows a slow upward trend after 4 h, and the content of reducing sugars is the highest after 24 h. The time is further preferably 20-24 h.

[0013] As a preferred scheme, the conditions for the fermentation are: 27.5-28.5 °C, the time is 4-24 h, and the pH is 4.6-5.8. As the fermentation time increases, the acetic acid content shows a trend of first increasing and then decreasing. The acetic acid concentration is the highest at the 20th h of fermentation, and the acetic acid concentration starts to decrease after 20 h. This is because acetic acid begins to be converted into methane. The time is further preferably 16-20 h.

[0014] As a preferred embodiment, the acid-producing bacterium is Clostridium kluyveri, and its dosage is 13 to 15 times the mass of the yeast.

[0015] As a preferred embodiment, the addition of amylase and yeast is achieved through a bacterial agent dosing system; the bacterial agent dosing system consists of a storage tank, a dosage control tank, and a dosing tank.

[0016] As a preferred embodiment, the storage tank is responsible for storing the amylase and yeast bacterial agents and is connected to the dosage control tank; the dosages of amylase and yeast for single dosing are weighed in the dosage control tank, and a dosing tank is connected to the rear end of the dosage control tank; the bacterial agent dosing tank is responsible for dosing the amylase and yeast; the bacterial agent dosing system is controlled remotely by a computer.

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

[0018] 1) The present invention provides a new idea for efficiently preparing acetic acid. By utilizing the characteristic that kitchen waste contains abundant starch, amylase is added first to increase the conversion of starch into reducing sugars, then yeast is used to ferment the reducing sugars into ethanol, and finally acetic acid is obtained under the action of acid-producing bacteria. The combined application of amylase to improve starch degradation and yeast fermentation in the present invention can effectively improve the starch utilization rate and acetic acid conversion rate in the anaerobic fermentation process of kitchen waste, and reduce the use cost of bacterial agents.

[0019] 2) The present invention shortens the fermentation time and obtains a simple, efficient, and economical pretreatment process. Description of the Drawings

[0020] Figure 1 It is the influence of amylase on pH.

[0021] Figure 2 It is the influence of amylase on the content of reducing sugars.

[0022] Figure 3 It is the influence of amylase on the starch content.

[0023] Figure 4 It is the influence of amylase on the starch conversion rate.

[0024] Figure 5 It is the influence of different amylase activities on pH.

[0025] Figure 6 It is the influence of different amylase activities on the content of reducing sugars.

[0026] Figure 7 It is the influence of different amylase activities on the starch conversion rate.

[0027] Figure 8is the change of acetic acid content in each experimental group under sterilization pretreatment conditions.

[0028] Figure 9 is the change of acetic acid content in each experimental group under direct inoculation conditions.

[0029] Figure 10 It is a schematic diagram of the bacterial agent dosing system used in the present invention. DETAILED DESCRIPTION

[0030] The present invention is further illustrated below through the description of examples to help those skilled in the art to have a more complete, accurate and in-depth understanding of the inventive concept and technical solution of the present invention.

[0031] In the present embodiment, the amylase is from Hers Bi Biotechnology Co., Ltd.; the yeast is a highly active dry yeast from Angel Yeast Co., Ltd.; the kitchen waste is taken from a canteen of a unit in Beijing, and after preliminary sorting, it is pulverized with a small grinder and stored in a refrigerator at 4°C for use. The basic physical and chemical properties of the kitchen waste material are shown in Table 1.

[0032] Table 1 Basic physical and chemical properties of kitchen waste

[0033]

[0034] Note: The contents are all in mass percentage.

[0035] The experiment was carried out in multiple serum bottles, and two gas collection bags were connected above each serum bottle to collect the gas produced by the reaction. Nitrogen was introduced before the start to ensure an anaerobic environment.

[0036] Example 1

[0037] 1) Amylase enhanced hydrolysis research experiment The kitchen waste materials were sealed with newspapers and tied with rubber bands before use. The experiment was carried out using a 1L serum bottle. According to the measured TS of the original material, water was added to adjust the TS to 15±2%. While adjusting the TS, a 3mol·L -1 NaOH solution and 3 mol·L -1 The pH of the food waste substrate was adjusted to 5.8±0.05 with HCl solution. After adjusting the pH and TS, 12 portions of the adjusted material with a mass of 600 g were weighed and placed in 12 serum bottles. The total mass of the food waste substrate was 7.2 kg. With the amount of amylase added as a variable, the experiment designed 6 experimental groups with a gradient of amylase addition. The added amylases were 0, 100, 120, 140, 160, and 180 U·g -1 (The corresponding amounts of amylase added were 0g, 0.7g, 0.9g, 1.05g, 1.2g, and 1.35g, respectively), and each group of experiments was set up with 2 parallels.

[0038] The kitchen waste substrate in 12 serum bottles was stirred evenly with amylase and then capped. Hydrolysis was carried out at a constant temperature of 60 °C with shaking for 48 h. During the hydrolysis process, material samples were taken at 8 time stages, namely 0, 4, 8, 12, 16, 20, 24, and 48 h. The mass of each sample taken was approximately 40 g. At the same time, the influence of hydrolysis time on the product quantity and physical and chemical properties was explored.

[0039] The pH values of the samples taken at different hydrolysis times of the samples with an amylase addition amount of 0 g and an addition amount of 1.05 g were measured, and the average value was taken between parallel groups, as Figure 1 shown. As the hydrolysis reaction proceeded, the pH of the experimental group with added amylase decreased significantly. After 24 h, the pH decreased to 5.0. Moreover, the pH of the experimental group with added amylase decreased rapidly within 0 - 4 h. This may be because this period corresponds to the logarithmic growth phase of amylase, and amylase is relatively active, so the reaction is faster.

[0040] The reducing sugar contents of the samples taken at different hydrolysis times of the samples with an amylase addition amount of 0 g and an addition amount of 1.05 g were measured, and the average value was taken between parallel groups, as Figure 2 shown. The reducing sugar content of the experimental group without added amylase increased slightly but did not change significantly within 0 - 24 h, and always remained at 83.30 - 96.91 mg·g -1 , while the reducing sugar content of the experimental group with added amylase showed a trend of first increasing and then stabilizing. Among them, the reducing sugar content increased fastest within 0 - 4 h. After 4 h, the reducing sugar content increased from 83.30 mg·g -1 to 150.71 mg·g -1 , an increase of 80.92%, which is 1.88 times the reducing sugar content of the experimental group without added amylase. After 4 h, the reducing sugar content showed a slow upward trend. After 24 h, the reducing sugar content was the highest, at 202.47 mg·g -1 , which is 2.09 times that of the group without added amylase and 2.43 times the reducing sugar content in the initial material. After that, the reducing sugar concentration decreased somewhat. After 48 h, the reducing sugar concentration was 199.67 mg·g -1 . Amylase can significantly promote the production of reducing sugar in kitchen waste with a high solid content rate, and the reducing sugar concentration is the highest after 24 h of hydrolysis, reaching up to 2.43 times the initial reducing sugar, which is 202.47 mg·g -1 .

[0041] The starch contents of the samples taken at different hydrolysis times of the samples with an amylase addition amount of 0 g and an addition amount of 1.05 g were measured, and the average value was taken between parallel groups, as Figure 3 shown. At the same time, the relationship between the conversion rate of starch content and amylase was calculated, as Figure 4As shown in the figure. The starch content in the experimental group without adding amylase slightly decreased within 0 - 48 h, but the change was not obvious. The lowest starch content was 389.42 mg·g -1 , and at this time, the starch degradation rate was 10.38% ( Figure 4 ). In the experimental group with added amylase, the starch content showed a trend of first decreasing and then stabilizing, and the starch conversion rate showed a trend of first increasing and then stabilizing. Among them, the starch content decreased the most significantly from 0 to 4 h, from 434.53 mg·g -1 to 276.13 mg·g -1 . At this time, the starch degradation rate was 36.45%, which was 3.75 times that of the group without added amylase. From 4 to 8 h, the starch content showed a fluctuating downward trend. After 24 h, the starch content decreased to 243.01 mg·g -1 . At this time, the starch content was only 55.93% of the initial starch content, and the degradation rate was 44.07%, which was 6.03 times that of the group without added amylase. After 24 h, the starch no longer degraded. This indicates that adding amylase can significantly reduce the starch content. After 24 h, the starch content dropped to the lowest, and the lowest content was 55.93% of the initial starch content, which was 243.01 mg·g -1 .

[0042] The tested enzyme activities were: 0, 100, 120, 140, 160, 180 U·g -1 For the pH values of the samples taken at different hydrolysis times in the experimental group with amylase, the average value was taken between parallel groups, as Figure 5 shown. After adding amylase, the change rule of pH at different times changed with the level of amylase activity, but the change was not obvious. The pH of each experimental group decreased relatively fast from 12 to 24 h. During this stage, the pH values of the experimental groups with amylase activities of 120 U·g -1 and 160 U·g -1 were higher than those of other experimental groups. At 24 h, the pH values of all experimental groups with amylase dropped to about 5.0. After that, the pH decrease trend of each experimental group slowed down. After 24 h, the pH values of the experimental groups with 100 U·g -1 and 140 U·g -1 were the highest, both being 4.85. This may be because the reaction systems of these two experimental groups were contaminated by miscellaneous bacteria, and the foreign microorganisms consumed the produced reducing sugars, inhibiting the accumulation process of reducing sugars. Therefore, it can be found that the pH decreased more slowly compared with other groups during this period. And after 24 h, compared with other groups, the pH of these two groups decreased faster. At 48 h, the pH values of the experimental groups with 100 U·g -1 and 140 U·g -1 dropped to 4.73 and 4.62 respectively.

[0043] The tested enzyme activities were: 0, 100, 120, 140, 160, 180 U·g-1 The reducing sugar contents of the samples taken at different hydrolysis times in the amylase experimental group were averaged among parallel groups. As Figure 6 shown. The amylase activities were 100, 140, 180 U·g -1 The reducing sugar content in the experimental group showed a trend of first increasing and then stabilizing. The reducing sugar contents in all three groups reached their maximum values after 24 h of fermentation, which were 189.50, 202.47, and 204.25 mg·g -1 , respectively. There was no obvious change in the reducing sugar content of these three groups during 24 - 48 h thereafter. It can be seen that the reducing sugar content had stabilized after 24 h, and the experimental group with an amylase activity of 180 U·g -1 had the highest reducing sugar content, which was 204.25 mg·g -1 . In the present invention, the amylase activity with the best effect on producing reducing sugar by hydrolyzing kitchen waste with a high solid content was 180 U·g -1 , and the reducing sugar content was 204.25 mg·g -1 .

[0044] The tested enzyme activities were: 0, 100, 120, 140, 160, 180 U·g -1 The starch contents of the samples taken at different hydrolysis times in the amylase experimental group were averaged among parallel groups, and the relationship between the starch conversion rate and the amylase activity was calculated. As Figure 7 shown. The experimental groups with added amylase activities of 100 - 180 U·g -1 as a whole showed a trend of first decreasing and then stabilizing. Among them, the starch content decreased significantly within 0 - 4 h; after 4 h, the starch content decreased with the increase of amylase activity, and the decreasing trend was slower during 4 - 24 h; at the 24th h of the reaction, the starch conversion rate was the highest. At this time, the experimental group with 180 U·g -1 had the highest starch degradation rate, which was 49.68%, 6.79 times that without adding amylase.

[0045] 2) Exploration experiment on yeast - enhanced acetic acid production

[0046] The kitchen waste was evenly divided into two groups. One group was subjected to sterilization pretreatment (the sterilization pretreatment group should first be sealed with newspaper, tied with a rubber band, and placed in a high - temperature sterilization pretreatment pot for 30 min of sterilization pretreatment), and the other group was not subjected to sterilization pretreatment.

[0047] Using the self - made anaerobic fermentation device in the laboratory, a small amount of crushed kitchen waste was taken in a crucible to measure the original material TS and VS. According to the measured original material TS, water was added to adjust TS to 15 ± 2%. While adjusting TS, 3 mol·L -1 NaOH solution and 3 mol·L -1The substrate pH was adjusted to 4.8 ± 0.05 with HCl solution. After adjusting the pH and TS, 250 g of the adjusted material was weighed and loaded into fermentation devices with a specification of 500 mL respectively. According to the set yeast inoculation amounts, corresponding masses of yeast were added. When the inoculation amounts were 0%, 3%, 6%, and 9%, 0 g, 1.125 g, 2.25 g, and 3.375 g of yeast were added to each experimental group respectively, and Clostridium kluyveri was added with a dosage of 15 times the mass of yeast to explore the effect of yeast with different inoculation amounts on the acetic acid content.

[0048] After mixing the substrate and yeast evenly, nitrogen was introduced for 30 s to remove air. The device was connected to a gas collection bag using a rubber hose, and then placed in a constant temperature incubator at 28 ± 0.1 °C to start fermentation. The fermentation times were 4 h, 8 h, 12 h, 16 h, 20 h, and 24 h respectively. Fermentation was immediately terminated after reaching the specified time, and sufficient materials were taken to detect various indicators. At the same time, the effect of fermentation time on the acetic acid content was explored.

[0049] The acetic acid contents at different fermentation times were tested for the yeast inoculation amounts of 0%, 3%, 6%, and 9% in the sterilization pretreatment group, as Figure 8 shown. Under the sterilization pretreatment conditions, the acetic acid concentration in the group without yeast inoculation remained basically unchanged, with the lowest being 513.03 mg·L -1 and the highest being 775.35 mg·L -1 . The acetic acid concentrations in the experimental groups with yeast inoculation amounts of 3%, 6%, and 9% showed a trend of first increasing and then decreasing with time. The acetic acid concentration was the highest at the 16th h of fermentation, being 1680.57, 1750.20, and 1597.30 mg·L -1 respectively. After 16 h, the acetic acid concentrations in each experimental group with yeast inoculation began to decrease, which might be because acetic acid began to be converted into methane. After 24 h, the acetic acid concentrations in each group were 821.44, 789.70, and 789.70 mg·L -1 respectively.

[0050] The acetic acid contents at different fermentation times were tested for the yeast inoculation amounts of 0%, 3%, 6%, and 9% in the non-sterilization pretreatment group (i.e., direct inoculation condition), as Figure 9 shown. Under the direct inoculation condition, the acetic acid concentration in the group without inoculation showed a trend of first increasing and then decreasing, and the acetic acid concentration was the highest at the 12th h, being 4668.96 mg·L -1 . After 12 h, the acetic acid concentration in the experimental group without yeast inoculation began to decrease, and the acetic acid concentration at the 24th h of fermentation was 1770.67 mg·L -1 . The acetic acid concentrations in the experimental groups with yeast inoculation showed a trend of gradually increasing and then decreasing with time. The acetic acid concentration was the highest at the 20th h. The acetic acid concentrations of the experimental groups with yeast inoculation amounts of 3% and 6% at the 20th h were 4317.65 and 4570.26 g·L -1。After 20 h, the acetic acid concentration in each experimental group inoculated with yeast began to decline. After 24 h, the acetic acid concentrations in the experimental groups with yeast inoculation amounts of 3% and 6% were 3624.99 and 3464.73 mg·L -1 。The acetic acid concentration in the experimental group with an inoculation amount of 9% reached the highest value at 12 h, which was 3353.37 mg·L -1 , and then the acetic acid increased slightly. After 24 h, the acetic acid concentration was 2890.69 mg·L -1 , which was much lower than that of other experimental groups. Compared with the non-sterilized pretreatment, the acetic acid concentration in the sterilized pretreatment was much lower because the high temperature during the sterilized pretreatment would kill all microorganisms and destroy the microbial production environment, which was not conducive to the preparation of acetic acid.

[0051] 3) Experimental exploration on the preparation of acetic acid by amylase hydrolysis

[0052] Before using the kitchen waste materials, seal them with newspapers and tie them with rubber bands. Use a 1 L serum bottle for the experiment. According to the measured original material TS, add water to adjust the TS to 15±2%. While adjusting the TS, use the pre-prepared 3 mol·L -1 NaOH solution and 3 mol·L -1 HCl solution to adjust the pH of the kitchen waste substrate to 5.8±0.05. After adjusting the pH and TS, weigh 600 g of the adjusted material and put it into the serum bottle respectively. Taking the amylase addition amount as the variable, design 5 experimental groups with different gradients of amylase addition contents. The added amylase has enzyme activities of: 100, 120, 140, 160, 180 U·g -1 (corresponding amylase addition amounts are 0.75 g, 0.9 g, 1.05 g, 1.2 g, 1.35 g), and set 2 parallels for each group of experiments. After stirring the kitchen waste substrate and amylase in the 12 serum bottles, seal the lids, and carry out hydrolysis at 60℃ under constant shaking for 48 h, and add the same amount of Clostridium kluyveri as in the 2) yeast-enhanced acetic acid production exploration experiment for fermentation.

[0053] After stirring the substrate and Clostridium kluyveri, introduce nitrogen for 30 s to remove air. Connect the device to the gas collection bag with a rubber hose, and then put it into a constant temperature incubator at 28±0.1℃ to start fermentation. The fermentation times are 0 h, 4 h, 8 h, 12 h, 16 h, 20 h, 24 h. Immediately end the fermentation after reaching the specified time, and take sufficient materials to detect various indicators. At the same time, explore the effect of fermentation time on the acetic acid content.

[0054] The effects of different amylase enzyme activities and fermentation times on the acetic acid concentration are shown in Table 2. As the amylase enzyme activity increases, the acetic acid concentration increases; as the fermentation time increases, the acetic acid concentration shows a trend of increasing first and then decreasing, and reaches the peak at 16 h.

[0055] Table 2

[0056]

[0057] 4) Synergistic strengthening of starch hydrolysis by starch and yeast for acetic acid preparation

[0058] Before using the kitchen waste materials, seal them with newspaper and tie them with a rubber band. Use a 1L serum bottle for the experiment. According to the measured total solids (TS) of the original materials, add water to adjust the TS to 15 ± 2%. While adjusting the TS, use the pre-prepared 3mol·L -1 NaOH solution and 3mol·L -1 HCl solution to adjust the pH of the kitchen waste substrate to 5.8 ± 0.05. Weigh 600g of kitchen waste materials and put them into the serum bottle, and add 1.05g of amylase with an enzyme activity of 140U·g -1 . After stirring the kitchen waste substrate and amylase in the serum bottle, seal the bottle and hydrolyze it at a constant temperature of 60°C with shaking for 24h to obtain a hydrolyzed material sample.

[0059] Seal the hydrolyzed material sample with newspaper and tie it with a rubber band. Use a self-made anaerobic fermentation device in the laboratory. Take a small amount of crushed kitchen waste in a crucible to measure the original materials' TS and volatile solids (VS). According to the measured total solids (TS) of the original materials, add water to adjust the TS to 15 ± 2%. While adjusting the TS, use the pre-prepared 3mol·L -1 NaOH solution and 3mol·L -1 HCl solution to adjust the pH of the substrate to 4.8 ± 0.05. After adjusting the pH and TS, weigh 250g of each adjusted hydrolyzed material sample, and add the corresponding mass of yeast according to the set yeast inoculation amount. When the inoculation amounts are 3%, 6%, and 9% (1.125g, 2.25g, and 3.375g respectively), add yeast to each experimental group, and add Clostridium kluyveri, with the dosage being 15 times the mass of the yeast, to explore the effect of different inoculation amounts of yeast on the acetic acid concentration.

[0060] After stirring the substrate and yeast evenly, introduce nitrogen for 30s to remove air. Connect the device to a gas collection bag with a rubber hose, and then place it in a constant temperature incubator at 28 ± 0.1°C to start fermentation. The fermentation times are 0, 4h, 8h, 12h, 16h, 20h, and 24h respectively. Immediately end the fermentation after reaching the specified time, and take sufficient materials to detect various indicators. At the same time, explore the effect of fermentation time on the acetic acid concentration.

[0061] The acetic acid concentrations corresponding to different yeast inoculation amounts and fermentation times are shown in Table 3. As the yeast inoculation amount increases, the acetic acid concentration first increases and then decreases. This is mainly because when the inoculation amount is 9%, a high concentration of ethanol is produced prematurely in the system, inhibiting the activity of acid-producing bacteria in the system. As the fermentation time increases, the acetic acid concentration also shows a trend of first increasing and then decreasing, reaching a peak at 20 h.

[0062] Table 3 Acetic acid production by the synergy of amylase and yeast in kitchen waste

[0063]

Claims

1. A method for synergistically enhancing starch hydrolysis by amylase and yeast to prepare acetic acid, characterized in that: The kitchen waste is subjected to hydrolysis-enhanced pretreatment with amylase, and then inoculated with yeast for fermentation to obtain ethanol; the ethanol is converted into acetic acid under the action of acid-producing bacteria.

2. The method for synergistically enhancing starch hydrolysis to prepare acetic acid by amylase and yeast according to claim 1, wherein: The enzyme activity of the amylase is 100-180 U·g -1 ; The mass ratio of the amylase to the kitchen waste is (0.7 - 1.35):600; The total solid content of the kitchen waste is 13 - 17 wt%, and the volatile solid content is 10 - 12 wt%.

3. A method for synergistically enhancing starch hydrolysis to prepare acetic acid by an amylase and yeast according to claim 1, characterized in that: The inoculation amount of the yeast is 3 - 9% of the sum of the masses of the amylase and the total solid content of the kitchen waste.

4. A method for synergistically enhancing starch hydrolysis to prepare acetic acid by amylase and yeast according to claim 3, characterized in that: The conditions for the pretreatment are: temperature is 40 - 80 °C, and time is 4 - 48 h.

5. A method for synergistically enhancing starch hydrolysis to prepare acetic acid by amylase and yeast according to claim 4, characterized in that: The conditions for the fermentation are: 27.5 - 28.5 °C, time is 4 - 24 h, and pH is 4.6 - 5.

8.

6. The method for preparing acetic acid by synergistically enhancing starch hydrolysis with amylase and yeast according to claim 5, wherein: The acid-producing bacteria is Clostridium kluyveri, and its dosage is 13 - 15 times the mass of the yeast.

7. A method for synergistically enhancing starch hydrolysis by amylase and yeast to prepare acetic acid according to any one of claims 1 to 6, characterized in that: The addition of the amylase and the yeast is realized through a bacterial agent addition system; the bacterial agent addition system consists of a storage tank, a dosage control tank, and a dosing tank.

8. A method for synergistically enhancing starch hydrolysis by amylase and yeast to prepare acetic acid according to claim 7, characterized in that: The storage tank is responsible for storing the amylase and the yeast bacterial agent, and is connected to the dosage control tank; the dosages of the amylase and the yeast for single addition are weighed in the dosage control tank, and a dosing tank is connected to the rear end of the dosage control tank; the bacterial agent dosing tank is responsible for adding the amylase and the yeast; the bacterial agent addition system is remotely controlled by a computer.

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