Method for preparing high-purity L-lactic acid by regulating and controlling fermentation of kitchen waste through eggshell waste

Abstract

The invention discloses a method for preparing high-purity L-lactic acid by regulating and controlling fermentation of kitchen waste through eggshell waste. The method mainly comprises the following steps: preparing a fermentation excitant from eggshells, carrying out staged heating fermentation, carrying out impurity removal treatment, carrying out acidification heating treatment, carrying out resin adsorption decoloration and deodorization, carrying out evaporation concentration, carrying out multi-gradient cooling crystallization purification, washing and acidifying. Compared with a traditional engineering bacterium screening fermentation method, the method disclosed by the invention can adapt to more diversified production environments and application requirements; meanwhile, aiming at a kitchen waste lactic acid fermentation liquid system with high grease and high protein characteristics, a lactic acid extraction process is optimized, by-products are volatilized by utilizing various modes of high-efficiency impurity removal and acidification heating treatment, and by virtue of modes of adjusting the total concentration of a surfactant, multi-gradient temperature control crystallization purification and the like, the content of the lactic acid in the kitchen waste is greatly improved. The high-purity lactic acid is separated from a kitchen fermentation system. The invention provides a low-cost, rapid, high-yield and directional L-lactic acid production method for regulating and controlling fermentation of kitchen waste by using eggshell waste.

Description

Technical Field

[0001] The invention relates to a method for preparing high-purity L-lactic acid by regulating the fermentation of restaurant and kitchen waste using eggshell waste, and belongs to the technical field of solid waste resource utilization and environmental protection. Background Art

[0002] The existence of restaurant kitchen waste is large in quantity, widespread, and increasing year by year. It has the dual attributes of pollution and resources, and has received extensive attention in the field of resource utilization. Anaerobic fermentation is the main way to utilize restaurant kitchen waste as a resource. The fermentation products include methane, short-chain fatty acids, L-lactic acid (LA), etc. Among them, methane has problems such as strict storage and transportation conditions, great risks and low product returns; short-chain fatty acids are easily soluble and volatile, and the extraction and storage costs are high, which limits its industrial application. L-lactic acid has stable properties, convenient storage and transportation, and wide market demand. It can be used as a raw material for products such as tobacco moisturizers, degradable plastics and paints.

[0003] At present, the challenges of preparing L-lactic acid from food waste mainly include fermentation process regulation and lactic acid extraction. In terms of fermentation process regulation, lactic acid fermentation takes a long time and has low fermentation efficiency; chemical reagents need to be added to adjust the pH environment to alleviate acid inhibition, resulting in high fermentation costs; the material composition of food waste is mixed, resulting in complex microbial metabolic pathways, many fermentation by-products, and low lactic acid production. In addition, lactic acid fermentation products usually exist as a mixture of D / L isomers, making it difficult to obtain L-lactic acid alone. In terms of lactic acid extraction, due to the complex composition of food waste and the high fat and protein characteristics of the fermentation liquid, the purification effect of the existing calcium salt method is severely reduced.

[0004] In summary, the field of food waste resource utilization urgently needs to develop a low-cost, rapid, high-yield and directional regulation method for L-lactic acid production. At the same time, a new process is needed to overcome the influence of impurities in the system and efficiently separate and purify the product from the fermentation broth. Summary of the invention

[0005] The technical problem to be solved by the present invention is that the existing technology for preparing L-lactic acid from food waste has high cost, low efficiency, low lactic acid yield and difficulty in directional fermentation of L-lactic acid. At the same time, the fermentation liquid of the food waste system contains many impurities, and the existing calcium salt extraction process is difficult to obtain high-purity lactic acid.

[0006] In order to solve the above technical problems, the present invention provides a method for preparing high-purity L-lactic acid by regulating the fermentation of kitchen waste using eggshell waste, comprising the following steps:

[0007] Step 1): filtering the kitchen waste to remove hard objects, adding water and crushing the kitchen waste to obtain kitchen waste slurry for later use;

[0008] Step 2): adding the prepared food waste slurry into a fermentation tank and adding a bacterial source;

[0009] Step 3): After washing the eggshells, crushing, drying, calcining and sieving to prepare a fermentation stimulant, the fermentation stimulant is added to the fermentation tank;

[0010] Step 4): nitrogen is introduced to drive oxygen, so that the dissolved oxygen concentration in the fermenter meets the concentration required for microaerobic fermentation, the fermentation tank is sealed, and the fermentation liquid is fermented in a stage-by-stage heating manner under mechanical stirring conditions to finally obtain a fermentation liquid;

[0011] Step 5): removing impurities from the obtained fermentation broth to obtain an aqueous fermentation broth containing surfactant components and a solid phase, and the obtained solid phase is partially reused for the next fermentation;

[0012] Step 6): placing the aqueous fermentation liquid in a ventilated place, adding acid to perform acidification and heating treatment under stirring conditions to remove volatile by-products;

[0013] Step 7): passing the fermented liquid treated in step 6) into a macroporous resin layer for adsorption, decolorization and deodorization;

[0014] Step 8): The fermented liquid after decolorization is evaporated and concentrated, and the obtained concentrated liquid is subjected to multi-gradient cooling crystallization. After the crystallization is completed, solid-liquid separation is performed to obtain crystals and crystallization mother liquor;

[0015] Step 9): washing the crystals and drying them to obtain calcium lactate;

[0016] Step 10): adding ultrapure water as a pure diluent to calcium lactate, heating and dissolving, and then adding sulfuric acid to react to obtain calcium sulfate precipitate and lactic acid solution; collecting the lactic acid solution after solid-liquid separation, evaporating and concentrating to obtain a high-purity lactic acid product. The high-purity lactic acid refers to lactic acid purity ≥ 90%.

[0017] Furthermore, the concentration of the kitchen waste slurry in step 1) is 30-50 g VSS / L.

[0018] Furthermore, the bacterial source in step 2) is at least one of granular sludge, residual sludge and distiller's yeast; the addition ratio of the bacterial source and the kitchen waste slurry is calculated based on volatile solids VS, which is 3 to 5:1.

[0019] Furthermore, the bacterial source is a combination of excess sludge and distiller's yeast; the ratio of excess sludge to distiller's yeast in the bacterial source is preferably VS 剩余污泥 :VS 酒曲 =1:1.

[0020] Furthermore, the step 2) also includes adding a supplementary bacterial source, and the supplementary bacterial source comes from the solid phase separated in the previous fermentation process (ie, the solid phase separated in step 5)).

[0021] Furthermore, the eggshell waste in the step 3) is at least one of duck eggshells, goose eggshells, and quail eggshells; the drying temperature is 100-110°C, and the time is 60-120 min; the calcination temperature is 500-600°C, and the time is 0.5-8 h; the particle size of the fermentation stimulant is 75-150 μm, and the addition concentration is 10-40 g / L.

[0022] Furthermore, the fermentation in step 4) is divided into three stages, specifically including:

[0023] The first stage is low-temperature fermentation, with a fermentation temperature of 15-25°C and a fermentation time of 5-15 hours;

[0024] The second stage is medium temperature fermentation, the fermentation temperature is 30-40℃, and the time is 5-15h;

[0025] The third stage is high temperature fermentation, with a fermentation temperature of 45-60°C and a fermentation time of 10-20 hours.

[0026] Preferably, in step 4), the fermentation dissolved oxygen concentration is 0.1 to 0.5 mg / L, the redox potential is -250 to +100 mV, and the pH is 5 to 9.

[0027] Furthermore, the impurity removal in step 5) specifically includes: removing impurities from the fermentation broth by ultrasonic vibration, mechanical oil removal and solid-liquid separation, and the calcium lactate salt content in the aqueous fermentation broth obtained after impurity removal is 1% to 50%, the solid content does not exceed 1%, the oil content does not exceed 3%, and the soluble protein content does not exceed 5%.

[0028] Furthermore, the surfactant in step 5) is a biosurfactant produced during the fermentation of food waste, and its main components include glycolipids, fatty acids and phospholipids, among which glycolipids account for 1 to 90wt%, fatty acids account for 2 to 80wt%, phospholipids account for 0.5% to 20%, and the total concentration of surfactants is 10 to 100 mg / L.

[0029] Furthermore, the purpose of solid phase recycling in step 5) is to supplement the abundance of lactic acid bacteria in the early stage of fermentation and to recycle the remaining fermentation stimulant after the fermentation is completed. The recycling ratio is 30% to 80% of the total mass of the solid phase.

[0030] Further, the acid in step 6) is concentrated nitric acid and / or concentrated hydrochloric acid, the heating temperature is 60-100°C, the stirring speed is 20-100rpm, and the VFA concentration in the fermentation broth obtained after the acidification and heating treatment does not exceed 0.1g COD / L. In this step, the purpose of acidification and heating is to remove volatile by-products, and the volatile by-products mainly include acetic acid, propionic acid, n-butyric acid and isobutyric acid, and the removal rates are 98.4%-99.6%, 97.9%-99.3%, 98.1%-99.4%, and 97.6%-99.3%, respectively.

[0031] Furthermore, in the step 7), the adsorption flow rate is 3-6 BV / h, the adsorption temperature is 20°C-40°C, and the total protein content in the fermentation broth obtained after adsorption does not exceed 4.6 mg / mL, the total polysaccharide content does not exceed 1.5 mg / mL, the soluble protein content does not exceed 3.7 mg / mL, and the soluble polysaccharide content does not exceed 1.3 mg / mL.

[0032] Furthermore, the concentration of calcium lactate in the concentrated solution in step 8) is 30-220 g / L, and the concentrated solution is cooled from 100°C to 4-25°C in 2-10 stages, and each stage lasts for 30 min-10 h; the solid-liquid separation is carried out by suction filtration, and the process conditions of the suction filtration are: vacuum degree 0.01-0.1 MPa, time 0.5-2 h, filter paper pore size 30-50 μm. The crystal component obtained in this step is mainly Ca(LA)2, and the mass ratio of Ca(LA)2 to impurities is 100:1-5:1, and further purification will be carried out later.

[0033] Furthermore, the cleaning agent used for washing in step 9) is an alcohol solvent.

[0034] Furthermore, the cleaning agent is a mixed solvent of methanol and ethanol, wherein the volume ratio of methanol to ethanol is preferably 1:2-10.

[0035] Furthermore, in step 9), the drying temperature is 40 to 130° C., and the drying time is 30 min to 10 h.

[0036] Furthermore, the pure diluent in step 10) is ultrapure water, the heating and dissolving temperature is controlled at 50-80° C., and the dissolving time is 10-30 min.

[0037] Furthermore, the amount of sulfuric acid added in step 10) is Ca 2+ (mol):H2SO4(mol)=1:1~1:5.

[0038] Furthermore, the solid-liquid separation in step 10) is performed by filter pressing, the pressure is 1-3 MPa, the time is 5-20 min, and the pore size of the filter paper is 30-50 μm.

[0039] The present invention aims to solve the problems of low yield, chiral lactic acid mixing and high consumption of chemical agents in the existing technology of producing lactic acid by fermentation of kitchen waste. By adding eggshell waste and stage-by-stage temperature fermentation, a method for regulating the fermentation of kitchen waste with low cost, rapidity, high yield and directional production of L-lactic acid is provided. Compared with the traditional engineering bacteria screening and fermentation method, the method of the present invention can adapt to more diverse production environments and application requirements. At the same time, for the high-fat and high-protein kitchen waste lactic acid fermentation liquid system, the present invention optimizes the existing calcium salt method lactic acid extraction process, and uses a variety of methods for efficient impurity removal, acidification and heating treatment to volatilize by-products, and by adjusting the total concentration of surfactants and multi-gradient temperature control crystallization purification, so as to achieve separation of high-purity lactic acid from the kitchen fermentation system.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) The present invention adds a fermentation stimulant prepared from eggshell waste during the lactic acid fermentation process. Compared with adding chemical agents to overcome acidification inhibition, no external calcium source is required in the subsequent product extraction process, thereby reducing the fermentation cost and increasing the lactic acid yield; at the same time, the fermentation stimulant provides L-lactic acid regulatory factors, significantly enriches L-lactic acid bacteria, and increases the optical activity of L-lactic acid;

[0042] (2) The present invention improves the fermentation efficiency by introducing staged temperature increase fermentation. Compared with the screening of efficient engineered bacteria, the application scope of this technology is wider, enabling it to adapt to more diverse production environments and application requirements;

[0043] (3) Compared with the existing calcium salt extraction process, the purification process designed by the present invention is more suitable for the fermentation broth of a food waste system with complex components and high fat and protein characteristics, thereby improving the purity of lactic acid separation, thereby achieving the goal of recycling food waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 Process flow chart for preparing high-purity L-lactic acid by fermentation of food waste.

[0045] Figure 2 This is a diagram of lactic acid production from food waste fermentation in Example 2.

[0046] Figure 3 This is a physical comparison chart of the purity of calcium lactate crystals in Example 3 and Comparative Example 1. DETAILED DESCRIPTION

[0047] In order to make the present invention more clearly understood, preferred embodiments are described in detail below with reference to the accompanying drawings.

[0048] In the following embodiments and comparative examples, the kitchen waste was collected from a cafeteria of a university in Shanghai, and the residual sludge was collected from a sewage treatment plant in Songjiang District, Shanghai; the distiller's yeast was a commercially available product; and the remaining materials, reagents, etc. used, unless otherwise specified, can be obtained through commercial channels.

[0049] Example 1

[0050] A method for preparing high-purity L-lactic acid by regulating the fermentation of kitchen waste using eggshell waste, the process flow is as follows Figure 1 As shown, this example investigates the effect of lactic acid production under stage heating and constant temperature fermentation process conditions, and is specifically carried out according to the following steps:

[0051] 1. Use a filter to separate the bamboo sticks, bones and other impurities in the kitchen waste, add distilled water, heat it, and use a blender to crush it to remove the surface grease to obtain a kitchen waste slurry sample (40g VSS / L), which is placed in a 4℃ refrigerator for later use.

[0052] 2. Put the food waste slurry into the fermentation tank, add distiller's yeast and residual sludge (VS = 1:1) as bacterial sources at a volatile solid (VS) ratio of food waste: bacterial source = 4:1, and add the solid phase recovered in the impurity removal stage.

[0053] 3. After cleaning the impurities attached to the surface of the duck egg shells with distilled water, crush them into powder using a blender, place them in an oven at 105°C for 60-120 minutes, place the dried egg shells in a crucible, ashed at 500-600°C for 0.5-8 hours, and crush them into powder using a blender after cooling. The fermentation stimulant is sieved to obtain a particle size of 100 μm. Add the fermentation stimulant into the fermentation tank at a dosage of 40 g / L.

[0054] 4. Nitrogen was introduced to control the dissolved oxygen concentration in the fermenter to 0.4 mg / L, the redox potential to -250~+100 mV, the pH to 7, and the fermentation tank was sealed. The fermentation liquid was mechanically stirred with the rotation speed controlled at 110 rpm. The total fermentation time was 36 h. Constant temperature fermentation and stage-by-stage temperature fermentation were adopted. The constant temperature fermentation was 35~38°C, and the stage-by-stage temperature fermentation was divided into three stages. The early fermentation period (0~10 h) was low-temperature fermentation at 25°C, the middle fermentation period (11~20 h) was medium-temperature fermentation at 37°C, and the late fermentation period (21~36 h) was high-temperature fermentation at 50°C.

[0055] 5. The fermentation liquid is decontaminated by ultrasonic vibration, mechanical oil removal and solid-liquid separation. Part of the oil and surfactant can be removed by decontamination to obtain an aqueous fermentation liquid and a solid phase. The oil content in the aqueous fermentation liquid is 1.3wt%, and the total concentration of the surfactant is 50mg / L. The solid phase is recovered, and 50% (by weight) is reused for the next fermentation. The solid phase component contains a large number of active microorganisms that produce lactic acid bacteria, which is beneficial to the fermentation to produce lactic acid.

[0056] 6. Move the aqueous fermentation liquid to a ventilated place, add concentrated nitric acid at 5% of the volume of the fermentation liquid, heat it while stirring continuously, keep the fermentation liquid temperature at about 60°C, stir at a speed of 20-100 rpm, and last for 10 minutes.

[0057] 7. The acidified and heated food fermentation liquid was passed through a macroporous adsorption resin (D101 type) layer, and the flow rate during the adsorption process was 4BV / h and the adsorption temperature was 36°C for decolorization and deodorization. The total protein content of the food fermentation liquid after decolorization and deodorization was 4.5 mg / mL, the total polysaccharide content was 1.4 mg / mL, the soluble protein content was 3.6 mg / mL, and the soluble polysaccharide content was 1.2 mg / mL.

[0058] 8. The fermentation liquid was evaporated and concentrated, and then the calcium lactate crystals were precipitated by cooling. The cooling was divided into 4 stages, first from 100°C to 75°C, then from 75°C to 50°C, then from 50°C to 25°C, and finally to 4°C. The cooling time of each stage of the 4 stages was 45 minutes. After the crystallization was completed, the vacuum degree was 0.05MPa, the time was 0.5h, and the pore size of the filter paper was 50μm.

[0059] 9. The obtained crystals were washed with a cleaning agent having a volume ratio of methanol to ethanol of 1:4 for 5 minutes and then dried at a drying temperature of 80°C for 30 minutes. Figure 3 (Left) shown.

[0060] 10. Add ultrapure water as a pure diluent to the calcium lactate crystals, heat and dissolve at 60°C for 20 minutes, then add sulfuric acid to fully react to obtain calcium sulfate precipitate and lactic acid solution.

[0061] 11. The lactic acid solution was extracted by filter pressing, the pressure was 1 MPa, the time was 15 min, and the pore size of the filter paper was 50 μm. The filtrate was evaporated and concentrated to obtain a high-purity lactic acid product, and the purity reached 90% after HPLC (high performance liquid chromatography) detection and analysis.

[0062] In this embodiment, the maximum L-lactic acid concentration and fermentation rate ratio obtained at different fermentation temperatures are as follows:

[0063] Fermentation temperature constant temperature Stage heating Maximum L-lactic acid concentration (g COD / L) 8.2 28.4 L-lactic acid fermentation rate (g COD / L·h) 0.3 1.2

[0064] It can be seen from the above table that different temperature control methods have a great influence on the L-lactic acid fermentation rate and the maximum L-lactic acid concentration in the fermentation system. Compared with constant temperature fermentation, the L-lactic acid fermentation rate and the maximum L-lactic acid concentration are greatly improved by adopting the staged temperature increase fermentation method.

[0065] Example 2

[0066] A method for preparing high-purity L-lactic acid by regulating the fermentation of food waste using eggshell waste, this embodiment investigates the effect of different dosages (0, 10, 20, 30, 40 g / L) of fermentation stimulants on lactic acid production, specifically according to the following steps:

[0067] 1. Use a filter to separate the bamboo sticks, bones and other impurities in the kitchen waste, add distilled water, heat it, and use a blender to crush it to remove the surface grease to obtain a kitchen waste slurry sample (40g VSS / L), which is placed in a 4℃ refrigerator for later use.

[0068] 2. Put the food waste slurry into the fermentation tank, add distiller's yeast and residual sludge (VS = 1:1) as bacterial sources at a VS ratio of food waste: bacterial source = 4:1, and add the solid phase recovered in the impurity removal stage.

[0069] 3. After cleaning the impurities attached to the surface of the duck egg shells with distilled water, crush them into powder using a blender, place them in an oven at 105°C for 60-120 minutes, place the dried egg shells in a crucible, ashed at 500-600°C for 0.5-8 hours, and crush them into powder using a blender after cooling. Sieve to obtain a fermentation stimulant with a particle size of 100 μm. Add the fermentation stimulant into the fermentation tank at dosages of 0, 10, 20, 30, and 40 g / L, respectively.

[0070] 4. Nitrogen was introduced to control the dissolved oxygen concentration in the fermenter to 0.4 mg / L, the redox potential to -250 to +100 mV, the pH to 7, and the fermentation tank was sealed. The fermentation liquid was mechanically stirred with the rotation speed controlled at 110 rpm. The total fermentation time was 36 h, and the temperature was increased in stages. The fermentation was divided into three stages. The early fermentation period (0 to 12 h) was low-temperature fermentation at 25 °C, the middle fermentation period (13 to 24 h) was medium-temperature fermentation at 37 °C, and the late fermentation period (25 to 36 h) was high-temperature fermentation at 50 °C.

[0071] Fifth, the fermentation liquid is cleaned by ultrasonic vibration, mechanical oil removal and solid-liquid separation to obtain an aqueous fermentation liquid and a solid phase. The oil content in the aqueous fermentation liquid is 1.3wt%, and the total concentration of surfactants is 50mg / L. The solid phase is recovered and 50% (by weight) is reused for the next fermentation.

[0072] 6. Move the aqueous fermentation liquid to a ventilated place, add concentrated nitric acid at 5% of the volume of the fermentation liquid, heat it while stirring continuously, keep the fermentation liquid temperature at about 60°C, stir at a speed of 20-100 rpm, and last for 10 minutes.

[0073] 7. The acidified and heated food fermentation liquid was passed through a macroporous adsorption resin (D101 type) layer, and the flow rate during the adsorption process was 4BV / h and the adsorption temperature was 36°C for decolorization and deodorization. The total protein content of the food fermentation liquid after decolorization and deodorization was 4.5 mg / mL, the total polysaccharide content was 1.4 mg / mL, the soluble protein content was 3.6 mg / mL, and the soluble polysaccharide content was 1.2 mg / mL.

[0074] 8. The fermentation liquid was evaporated and concentrated, and then the calcium lactate crystals were precipitated by cooling. The cooling was divided into 4 stages, first from 100°C to 75°C, then from 75°C to 50°C, then from 50°C to 25°C, and finally to 4°C. The cooling time of the 4 stages was 45 minutes. After the crystallization was completed, the vacuum degree was 0.05MPa, the time was 0.5h, and the pore size of the filter paper was 50μm.

[0075] 9. The obtained calcium lactate crystals were washed with a cleaning agent having a methanol:ethanol volume ratio of 1:4 for 5 minutes and then dried at a drying temperature of 80°C and a drying time of 30 minutes.

[0076] 10. Add ultrapure water as a pure diluent to the calcium lactate crystals, heat and dissolve at 60°C for 20 minutes, then add sulfuric acid to fully react to obtain calcium sulfate precipitate and lactic acid solution.

[0077] 11. The lactic acid solution was extracted by filter pressing, the pressure was 1 MPa, the time was 15 min, and the pore size of the filter paper was 50 μm. The filtrate was evaporated and concentrated to obtain a high-purity lactic acid product, and the purity reached 90% after HPLC (high performance liquid chromatography) detection and analysis.

[0078] In this embodiment, the maximum lactic acid concentration and the proportion of L-lactic acid obtained by adding different fermentation stimulants are as follows: Figure 2 As shown:

[0079] Fermentation stimulant dosage (g / L) 0 10 20 30 40 Maximum lactic acid concentration (g COD / L) 2.8 35.9 51.5 42.4 36.1 L-lactic acid ratio (%) 51.3 92.1 86.4 81.3 78.7

[0080] It can be seen from the above table that when the dosage of the fermentation stimulant prepared from eggshell waste is 20g / L, the maximum lactic acid concentration of the fermentation system is the highest, up to 51.5g COD / L, and the proportion of L-lactic acid is also high; when the dosage of the fermentation stimulant is 10g / L, the proportion of L-lactic acid (%) in the fermentation system is the highest, up to 92.1%, but the maximum lactic acid concentration is only 35.9g COD / L.

[0081] Example 3

[0082] A method for preparing high-purity L-lactic acid by regulating the fermentation of food waste using eggshell waste. This embodiment investigates the effect of different crystallization process conditions - using different cooling methods to separate and purify L-lactic acid, and is specifically carried out in the following steps:

[0083] 1. Use a filter to separate the bamboo sticks, bones and other impurities in the kitchen waste, add distilled water, heat it, and use a blender to crush it to remove the surface grease to obtain a kitchen waste slurry sample (40g VSS / L), which is placed in a 4℃ refrigerator for later use.

[0084] 2. Put the food waste slurry into the fermentation tank, add distiller's yeast and residual sludge (VS = 1:1) as bacterial sources at a VS ratio of food waste: bacterial source = 4:1, and add the solid phase recovered in the impurity removal stage.

[0085] 3. After cleaning the impurities attached to the surface of the duck egg shells with distilled water, crush them into powder using a mixer, place them in an oven at 105°C for 60-120 minutes, place the dried egg shells in a crucible, ashed at 500-600°C for 0.5-8 hours, and crush them into powder using a mixer after cooling. Sieve to obtain a fermentation stimulant with a particle size of 100 μm. Add the fermentation stimulant into the fermentation tank at a dosage of 20 g / L.

[0086] 4. Nitrogen was introduced to control the dissolved oxygen concentration in the fermenter to 0.4 mg / L, the redox potential to -250 to +100 mV, the pH to 7, and the fermentation tank was sealed. The fermentation liquid was mechanically stirred with the rotation speed controlled at 110 rpm. The total fermentation time was 36 h, and the temperature was increased in stages. The fermentation was divided into three stages. The early fermentation stage (0 to 12 h) was fermented at 25 °C, the middle fermentation stage (13 to 24 h) was fermented at 37 °C, and the late fermentation stage (25 to 36 h) was fermented at 50 °C.

[0087] 5. The fermentation liquid is cleaned by ultrasonic vibration, mechanical oil removal and solid-liquid separation to obtain aqueous fermentation liquid and solid phase. The oil content in the aqueous fermentation liquid is 1.3%, and the total concentration of surfactant is 50 mg / L. The solid phase is recovered and 50% (by weight) is reused for the next fermentation.

[0088] 6. Move the aqueous fermentation liquid to a ventilated place, add concentrated nitric acid at 5% of the volume of the fermentation liquid, heat it while stirring continuously, keep the fermentation liquid temperature at about 60°C, stir at a speed of 20-100 rpm, and last for 10 minutes.

[0089] 7. The acidified and heated food fermentation liquid was passed through a macroporous adsorption resin (D101 type) layer, and the flow rate during the adsorption process was 4BV / h and the adsorption temperature was 36°C for decolorization and deodorization. The total protein content of the food fermentation liquid after decolorization and deodorization was 4.5 mg / mL, the total polysaccharide content was 1.4 mg / mL, the soluble protein content was 3.6 mg / mL, and the soluble polysaccharide content was 1.2 mg / mL.

[0090] 8. The fermentation liquid was evaporated and concentrated, and then the calcium lactate crystals were precipitated by cooling. One group of cooling was divided into 4 stages, first from 100°C to 75°C, then from 75°C to 50°C, then from 50°C to 25°C, and finally to 4°C. The cooling time of each stage was the same, and the cooling time of the 4 stages was set to 45, 90, 180, and 360 minutes respectively. One group was directly cooled to 4°C, and the cooling time was 360 minutes. After the crystallization was completed, the vacuum degree was 0.05MPa, the time was 0.5h, and the filter paper pore size was 50μm.

[0091] 9. The obtained calcium lactate crystals were washed with a cleaning agent having a methanol:ethanol volume ratio of 1:4 for 5 minutes and then dried at a drying temperature of 80°C and a drying time of 30 minutes.

[0092] 10. Add ultrapure water as a pure diluent to the calcium lactate crystals, heat and dissolve at 60°C for 20 minutes, then add sulfuric acid to fully react to obtain calcium sulfate precipitate and lactic acid solution.

[0093] 11. The lactic acid solution was extracted by filter pressing, the pressure was 1 MPa, the time was 15 min, and the pore size of the filter paper was 50 μm. The filtrate was evaporated and concentrated to obtain a high-purity lactic acid product, and the purity reached 90% after HPLC (high performance liquid chromatography) detection and analysis.

[0094] The lactic acid yield and lactic acid purity obtained at different single-stage cooling times are shown in the following table:

[0095] Single stage cooling time (min) 45 90 180 360 Direct cooling Lactic acid yield (%) 74.9 75.4 78.3 78.9 63.9 Lactic acid purity (%) 99.3 99.2 99.1 99.3 96.2

[0096] It can be seen from the above table that the lactic acid yield and purity obtained by stage cooling are higher than those obtained by direct cooling, and the single-stage cooling time has little effect on the lactic acid yield and purity.

[0097] Example 4

[0098] A method for preparing high-purity L-lactic acid by regulating the fermentation of food waste using eggshell waste. This example investigates the effect of controlling different concentrations of biosurfactants (0, 10, 50, 100 mg / L) on the separation of L-lactic acid by impurity removal, and is specifically carried out in the following steps:

[0099] 1. Use a filter to separate the bamboo sticks, bones and other impurities in the kitchen waste, add distilled water, heat it, and use a blender to crush it to remove the surface grease to obtain a kitchen waste slurry sample (40g VSS / L), which is placed in a 4℃ refrigerator for later use.

[0100] 2. Put the food waste slurry into the fermentation tank, add distiller's yeast and residual sludge (VS = 1:1) as bacterial sources at a VS ratio of food waste: bacterial source = 4:1, and add the solid phase recovered in the impurity removal stage.

[0101] 3. After cleaning the impurities attached to the surface of the duck egg shells with distilled water, crush them into powder using a mixer, place them in an oven at 105°C for 60-120 minutes, place the dried egg shells in a crucible, ashed at 500-600°C for 0.5-8 hours, and crush them into powder using a mixer after cooling. Sieve to obtain a fermentation stimulant with a particle size of 100 μm. Add the fermentation stimulant into the fermentation tank at a dosage of 20 g / L.

[0102] 4. Nitrogen was introduced to control the dissolved oxygen concentration in the fermenter to 0.4 mg / L, the redox potential to -250 to +100 mV, the pH to 7, and the fermentation tank was sealed. The fermentation liquid was mechanically stirred with the rotation speed controlled at 110 rpm. The total fermentation time was 36 h, and the temperature was increased in stages. The fermentation was divided into three stages. The early fermentation stage (0 to 12 h) was fermented at 25 °C, the middle fermentation stage (13 to 24 h) was fermented at 37 °C, and the late fermentation stage (25 to 36 h) was fermented at 50 °C.

[0103] Fifth, the fermentation liquid is cleaned by ultrasonic oscillation, mechanical oil removal and solid-liquid separation to obtain aqueous fermentation liquid and solid phase. The total concentration of surfactant in the aqueous fermentation liquid is 0, 10, 50 and 100 mg / L respectively, and the oil content is 0.5-1.3%. The total concentration of surfactant can be adjusted by adjusting the time and frequency of ultrasonic oscillation. By increasing the ultrasonic time and the ultrasonic frequency, more surfactant can be retained in the aqueous phase. The solid phase is recovered, and 50% (by weight) is reused for the next fermentation.

[0104] 6. Move the aqueous fermentation liquid to a ventilated place, add concentrated nitric acid at 5% of the volume of the fermentation liquid, heat it while stirring continuously, keep the fermentation liquid temperature at about 60°C, stir at a speed of 20-100 rpm, and last for 10 minutes.

[0105] 7. The acidified and heated food fermentation liquid is passed through a macroporous adsorption resin (D101 type) layer, and the flow rate during the adsorption process is 4BV / h and the adsorption temperature is 36°C for decolorization and deodorization. The total protein content in the food fermentation liquid after decolorization and deodorization does not exceed 4.6 mg / mL, the total polysaccharide content does not exceed 1.5 mg / mL, the soluble protein content does not exceed 3.7 mg / mL, and the soluble polysaccharide content does not exceed 1.3 mg / mL.

[0106] 8. The fermentation liquid was evaporated and concentrated, and then the calcium lactate crystals were precipitated by cooling. The cooling was divided into 4 stages, first from 100°C to 75°C, then from 75°C to 50°C, then from 50°C to 25°C, and finally to 4°C. The cooling time of each of the 4 stages was 90 minutes. After the crystallization was completed, the vacuum degree was 0.05MPa, the time was 0.5h, and the pore size of the filter paper was 50μm.

[0107] 9. The obtained calcium lactate crystals were washed with a cleaning agent having a methanol:ethanol volume ratio of 1:4 for 5 minutes and then dried at a drying temperature of 80°C and a drying time of 30 minutes.

[0108] 10. Add ultrapure water as a pure diluent to the calcium lactate crystals, heat and dissolve at 60°C for 20 minutes, then add sulfuric acid to fully react to obtain calcium sulfate precipitate and lactic acid solution.

[0109] 11. The lactic acid solution was extracted by filter pressing, the pressure was 1 MPa, the time was 15 min, and the pore size of the filter paper was 50 μm. The filtrate was evaporated and concentrated to obtain a high-purity lactic acid product, and the purity reached 90% after HPLC (high performance liquid chromatography) detection and analysis.

[0110] The lactic acid yield and lactic acid purity obtained with different concentrations of biosurfactants are shown in the following table:

[0111] Total surfactant concentration (mg / L) 0 10 50 100 Lactic acid yield (%) 64.5 72.6 75.4 73.2 Lactic acid purity (%) 97.3 98.8 99.2 99.0

[0112] As can be seen from the table above, when the total surfactant concentration is 50 mg / L, the yield and purity of lactic acid are the highest, and the total surfactant concentration has a certain influence on the yield and purity of lactic acid. Controlling the total surfactant concentration within a certain range is beneficial to subsequent crystallization separation, for example.

[0113] Comparative Example 1

[0114] In this comparative example, no eggshell waste was added, and the pH was intermittently adjusted using HCl and NaOH solutions. The bacterial source inoculation was consistent with Example 2, and the traditional calcium salt method was used to extract lactic acid, which was used for comparison with Examples 2 and 3:

[0115] 1. Use a filter to separate the bamboo sticks, bones and other impurities in the kitchen waste, add distilled water, heat it, and use a blender to crush it to remove the surface grease to obtain a kitchen waste slurry sample (40g VSS / L), which is placed in a 4℃ refrigerator for later use.

[0116] 2. Put the food waste slurry into the fermentation tank, add sludge according to the VS ratio of food waste: bacterial source = 4:1, and add the solid phase recovered in the impurity removal stage.

[0117] 3. Nitrogen flushing, control the dissolved oxygen concentration in the fermenter to 0.4 mg / L, the redox potential to -250~+100 mV, the pH to 7, seal, mechanically stir the fermentation liquid, control the speed at 110 rpm, the total fermentation time is 36 hours, stage heating, fermentation is divided into three stages, the early fermentation (0~12 hours) adopts 25°C low-temperature fermentation, the middle fermentation (13~24 hours) adopts 37°C medium-temperature fermentation, and the late fermentation (25~36 hours) adopts 50°C high-temperature fermentation.

[0118] 4. Use 5M HCl or 5M NaOH to intermittently adjust the pH of the fermentation system. The adjustment frequency is once a day, twice a day, and three times a day respectively.

[0119] 5. Carry out solid-liquid separation on the kitchen fermentation liquid to remove solid impurities, obtain water phase and solid phase, and reflux 50% of the solid phase to the fermentation tank.

[0120] 6. Add an appropriate amount of calcium carbonate to the obtained aqueous phase.

[0121] 7. Add 5% concentrated hydrochloric acid to the aqueous phase to reduce the pH value and form calcium lactate precipitate. Separate the precipitate by suction filtration at a vacuum degree of 0.05 MPa for 0.5 h and a filter paper pore size of 50 μm.

[0122] 8. Wash the calcium lactate precipitate with an appropriate amount of water or alcohol solvent to remove residual impurities. The obtained calcium lactate product is as follows Figure 3 (right) shown.

[0123] 9. Add pure diluent to calcium lactate, heat to dissolve, then add sulfuric acid to react fully, filter to obtain calcium sulfate precipitate and lactic acid solution, the vacuum degree is 0.05MPa, the time is 0.5h, and the pore size of the filter paper is 50μm.

[0124] 10. Add activated carbon to the lactic acid solution for decolorization and deodorization. The adsorption temperature is 36°C. After adsorption, the activated carbon is recovered by filtration. The vacuum degree is 0.05MPa, the time is 0.5h, and the filter paper pore size is 50μm. The total protein content of the decolorized and deodorized food fermentation liquid is 6.5mg / mL, the total polysaccharide content is 4.1mg / mL, the soluble protein content is 5.3mg / mL, and the soluble polysaccharide content is 3.3mg / mL.

[0125] 11. The fermentation liquid is evaporated and concentrated to obtain L-lactic acid product, and the purity thereof is 50-60% after testing and analysis.

[0126] In this comparative example, the maximum lactic acid concentration and the proportion of L-lactic acid obtained at different adjustment frequencies are shown in the following table. The yield and purity of lactic acid obtained from the kitchen fermentation broth whose pH is intermittently adjusted by HCl and NaOH solutions using the traditional calcium salt method are 41.9% and 75.5%, respectively, while 1.43 g / g LA of calcium carbonate is consumed.

[0127] Adjust frequency Once a day Twice a day Three times a day Maximum lactic acid concentration (g COD / L) 18.1 22.5 23.3 L-lactic acid ratio (%) 55.3 54.1 56.8

[0128] It can be clearly seen from the experimental results of the above embodiments and comparative examples that the regulation of lactic acid production by staged temperature-raising fermentation and addition of fermentation stimulants has a positive effect on lactic acid production. The addition of impurity removal treatment, acidification heating and multi-gradient cooling crystallization processes in the process of lactic acid purification of food fermentation broth also significantly improves the lactic acid recovery effect of food fermentation broth. Compared with constant temperature fermentation, staged temperature-raising fermentation effectively increases the yield and rate of L-lactic acid; by comparing the comparative example of intermittently adjusting the pH with HCl and NaOH solutions, it can be found that the fermentation stimulant prepared from eggshell waste successfully replaces chemical reagents to control the pH while promoting lactic acid production. Multi-gradient cooling crystallization obtains a better lactic acid yield than direct cooling crystallization, and impurity removal treatment provides a suitable crystallization environment; by comparing the comparative example of extracting lactic acid using the traditional calcium salt method, it can be found that the lactic acid purification process in the method of the present invention has a higher lactic acid yield and purity.

[0129] The above embodiments are only preferred embodiments of the present invention and are not any formal or substantial limitations of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the present invention, and these improvements and supplements should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing high-purity L-lactic acid by regulating the fermentation of kitchen waste using eggshell waste, characterized in that: The following steps are involved: Step 1): filtering the kitchen waste to remove hard objects, adding water and crushing the kitchen waste to obtain kitchen waste slurry for later use; Step 2): adding the prepared food waste slurry into a fermentation tank and adding a bacterial source; Step 3): After washing the eggshells, crushing, drying, calcining and sieving to prepare a fermentation stimulant, the fermentation stimulant is added to the fermentation tank; Step 4): nitrogen is introduced to drive oxygen, so that the dissolved oxygen concentration in the fermenter meets the concentration required for microaerobic fermentation, the fermentation tank is sealed, and the fermentation liquid is fermented in a stage-by-stage heating manner under mechanical stirring conditions to finally obtain a fermentation liquid; Step 5): removing impurities from the obtained fermentation broth to obtain an aqueous fermentation broth containing surfactant components and a solid phase, and the obtained solid phase is partially reused for the next fermentation; Step 6): placing the aqueous fermentation liquid in a ventilated place, adding acid to perform acidification and heating treatment under stirring conditions to remove volatile by-products; Step 7): passing the fermented liquid treated in step 6) into a macroporous resin layer for adsorption, decolorization and deodorization; Step 8): The fermented liquid after decolorization is evaporated and concentrated, and the obtained concentrated liquid is subjected to multi-gradient cooling crystallization. After the crystallization is completed, solid-liquid separation is performed to obtain crystals and crystallization mother liquor; Step 9): washing the crystals and drying them to obtain calcium lactate; Step 10): adding ultrapure water as a pure diluent to calcium lactate, heating to dissolve, and then adding sulfuric acid to react to obtain calcium sulfate precipitate and lactic acid solution; After solid-liquid separation, the lactic acid solution is collected and evaporated and concentrated to obtain a high-purity lactic acid product with a purity of ≥90%.

2. The method according to claim 1, characterized in that The concentration of the kitchen waste slurry in step 1) is 30-50 g VSS / L; And / or, the addition ratio of the bacteria source and the kitchen waste slurry in the step 2) is calculated based on the volatile solids VS and is 3-5:

1.

3. The method according to claim 1, characterized in that The bacterial source in step 2) is at least one of granular sludge, excess sludge and distiller's yeast; And / or, the step 2) further comprises adding a supplementary bacterial source, wherein the supplementary bacterial source is derived from the solid phase obtained in step 5) during the previous fermentation process.

4. The method according to claim 1, characterized in that: The eggshell waste in step 3) is at least one of duck eggshells, goose eggshells, and quail eggshells; the drying temperature is 100-110°C, and the time is 60-120 min; the calcination temperature is 500-600°C, and the time is 0.5-8 h; the particle size of the fermentation stimulant is 75-150 μm, and the addition concentration is 10-40 g / L.

5. The method according to claim 1, characterized in that The fermentation in step 4) is divided into three stages, specifically including: The first stage is low-temperature fermentation, with a fermentation temperature of 15-25°C and a fermentation time of 5-15 hours; The second stage is medium temperature fermentation, the fermentation temperature is 30-40℃, and the time is 5-15h; The third stage is high temperature fermentation, with a fermentation temperature of 45-60°C and a fermentation time of 10-20 hours.

6. The method according to claim 1, characterized in that The impurity removal in step 5) specifically includes: removing impurities from the fermentation broth by ultrasonic vibration, mechanical oil removal and solid-liquid separation, and the calcium lactate salt content in the aqueous fermentation broth obtained after impurity removal is 1% to 50%, the solid content does not exceed 1%, the oil content does not exceed 3%, and the soluble protein content does not exceed 5%.

7. The method according to claim 1, characterized in that The surfactant in step 5) is a biosurfactant produced during the fermentation of food waste, and its main components include glycolipids, fatty acids and phospholipids, among which glycolipids account for 1-90wt%, fatty acids account for 2-80wt%, phospholipids account for 0.5%-20%, and the total concentration of surfactants is 10-100mg / L.

8. The method according to claim 1, characterized in that The acid in step 6) is concentrated nitric acid and / or concentrated hydrochloric acid, the heating temperature is 60-100° C., the stirring speed is 20-100 rpm, and the VFA concentration in the fermentation liquid obtained after the acidification and heating treatment does not exceed 0.1 g COD / L.

9. The method according to claim 1, characterized in that In the step 7), the adsorption flow rate is 3-6 BV / h, the adsorption temperature is 20°C-40°C, and the total protein content in the fermentation broth obtained after adsorption does not exceed 4.6 mg / mL, the total polysaccharide content does not exceed 1.5 mg / mL, the soluble protein content does not exceed 3.7 mg / mL, and the soluble polysaccharide content does not exceed 1.3 mg / mL.

10. The method according to claim 1, characterized in that The concentration of calcium lactate in the concentrated solution in step 8) is 30-220 g / L, and the concentrated solution is cooled from 100° C. to 4-25° C. in 2-10 stages, and each stage lasts for 30 min-10 h. The solid-liquid separation is performed by suction filtration, and the process conditions of the suction filtration are: vacuum degree 0.01-0.1 MPa, time 0.5-2 h, and filter paper pore size 30-50 μm.

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