Lactic acid separating and refining method for agricultural waste micro-aerobic fermentation liquor

Abstract

The invention relates to the technical field of agricultural waste recycling, in particular to a lactic acid separating and refining method for agricultural waste micro-aerobic fermentation liquor. The method provided by the invention comprises the following steps: by taking fermentation liquor obtained by producing lactic acid through micro-aerobic fermentation of agricultural wastes as a raw material, carrying out solid-liquid separation pretreatment on the fermentation liquor to obtain clear filtrate, and adjusting the pH value of the clear filtrate to obtain pretreatment liquid; loading the pretreatment solution to a weakly alkaline anion exchange resin adsorption column, carrying out lactic acid adsorption in a segmented dynamic adsorption mode, eluting the resin in a gradient alkaline elution mode after the adsorption is finished, and collecting an eluent containing lactic acid. The method provided by the invention has the advantages of wide raw material source, low cost, mild process conditions, simplicity and convenience in operation, higher selectivity and adsorption rate on lactic acid, high elution rate, high yield of lactic acid products and the like, and is suitable for large-scale popularization and application.

Description

Technical Field

[0001] This invention relates to the field of agricultural waste resource utilization technology, and in particular to a method for separating and refining lactic acid from micro-aerobic fermentation broth of agricultural waste. Background Technology

[0002] Lactic acid is an important organic acid widely used in food, medicine, chemicals, and biodegradable plastics (such as polylactic acid). With the development of green industries, the demand for lactic acid is increasing year by year, and its efficient and economical production and separation purification technologies have attracted widespread attention.

[0003] Currently, lactic acid is mainly obtained through microbial fermentation of starchy or sugary raw materials, but this method suffers from high raw material costs and competition for resources with grains. In recent years, the anaerobic fermentation method using agricultural waste as a low-cost carbon source to produce lactic acid has become a new direction for promoting the resource utilization of agricultural waste and the development of a circular economy. However, the fermentation broth system of agricultural waste is complex, usually containing a large amount of impurities such as proteins, polysaccharides, pigments, and inorganic salts, making the efficient separation and purification of lactic acid a key factor restricting its industrial application.

[0004] Traditional methods for lactic acid separation include solvent extraction, membrane separation, crystallization, and chemical precipitation. While these methods can extract lactic acid, they generally suffer from drawbacks such as high energy consumption, large reagent consumption, complex operation, high equipment investment, or heavy environmental burden. For example, extraction methods easily produce solvent residues, precipitation methods generate a large amount of salt byproducts, and membrane separation is prone to membrane fouling and flux reduction. Therefore, developing a lactic acid separation and purification technology with mild process conditions, high efficiency, low cost, and suitability for complex agricultural waste fermentation broth systems has become an urgent technical challenge.

[0005] Ion exchange resins have gradually become a research hotspot in the field of lactic acid separation due to their strong selective adsorption capacity for organic acids, ease of operation, and recyclability. However, existing applications of ion exchange resins are mostly concentrated in fermentation broths containing monosaccharides or single substrates. For fermentation broths of agricultural waste containing multiple components and complex impurities, their adsorption rate and lactic acid recovery rate are still significantly insufficient, limiting their widespread application in the actual resource utilization process of agricultural waste. Summary of the Invention

[0006] This invention provides a method for separating and refining lactic acid from micro-aerobic fermentation broth of agricultural waste.

[0007] Specifically, the present invention provides the following technical solutions.

[0008] In a first aspect, the present invention provides a method for separating and refining lactic acid from microaerobic fermentation broth of agricultural waste. The method includes: using fermentation broth from agricultural waste to produce lactic acid through microaerobic fermentation as raw material, performing solid-liquid separation pretreatment on the fermentation broth to obtain a clarified filtrate, and adjusting the pH of the clarified filtrate to 2.0-3.0 to obtain a pretreated liquid. The pretreated solution was injected into a weakly basic anion exchange resin adsorption column, and lactic acid was adsorbed using a segmented dynamic adsorption method. After adsorption, the resin was eluted using a gradient alkaline elution method, and the eluent containing lactic acid was collected. The segmented dynamic adsorption includes three stages of dynamic adsorption: the first stage of dynamic adsorption is fed into the liquid at a flow rate of 1.8-2.2 BV / h, the second stage of dynamic adsorption is fed into the liquid at a flow rate of 0.8-1.2 BV / h, and the third stage of dynamic adsorption is fed into the liquid at a flow rate of 0.3-0.7 BV / h. The gradient alkaline elution includes two stages: the first stage elution is carried out with 0.1-0.3 mol / L sodium hydroxide solution, and the second stage elution is carried out with 0.8-1.5 mol / L sodium hydroxide solution.

[0009] To address the technical bottlenecks in lactic acid production broth from agricultural waste under microaerobic conditions, such as high solid content, complex impurities, low resin adsorption rate, and insufficient elution concentration, this invention develops a method for separating and purifying lactic acid from this broth. Through extensive analysis of the composition and physicochemical properties of the fermentation broth, this invention determines that ion exchange resins are used for lactic acid separation. Specifically, through pH optimization before column loading, dynamic adsorption optimization, and elution optimization, a separation and purification method combining pre-column pH adjustment, segmented dynamic adsorption (using a specific gradient to gradually reduce the flow rate) for lactic acid adsorption, and gradient elution with different concentrations of eluent is obtained. Compared with conventional ion exchange resin methods, this method significantly improves the adsorption and elution rates of lactic acid, more effectively removes impurities from the fermentation broth, and significantly increases the recovery rate of lactic acid. In this method, the pH of the pretreatment solution, the feed flow rate settings for dynamic adsorption at each stage, and the concentration gradient settings of the eluent used in gradient elution play a key role in the removal of impurities, the adsorption rate of lactic acid, the elution rate, and the recovery rate of lactic acid.

[0010] Preferably, the pH of the clarified filtrate is adjusted to 2.0-2.2 to obtain a pretreated solution.

[0011] Preferably, the first stage of dynamic adsorption is fed into the liquid at a flow rate of 2.0-2.2 BV / h, the second stage of dynamic adsorption is fed into the liquid at a flow rate of 1.0-1.2 BV / h, and the third stage of dynamic adsorption is fed into the liquid at a flow rate of 0.5-0.6 BV / h.

[0012] Preferably, the gradient alkaline elution includes two-stage elution: the first stage elution is carried out with 0.1-0.2 mol / L sodium hydroxide solution, and the second stage elution is carried out with 0.8-1.0 mol / L sodium hydroxide solution.

[0013] Preferably, the dynamic adsorption feed volume is 1.5-2.5 BV in the first stage, 2.5-3.5 BV in the second stage, and 1.5-2.5 BV in the third stage.

[0014] In the dynamic adsorption described above, the first stage of dynamic adsorption mainly aims to rapidly occupy weak binding sites in the resin; the second stage mainly aims to enhance the binding between lactic acid and the active groups of the resin; and the third stage mainly aims to ensure sufficient mass transfer of lactic acid in the bed and improve adsorption saturation. The combined effect of these three stages can significantly improve mass transfer efficiency, resin utilization, and the adsorption rate of lactic acid.

[0015] Preferably, both the first-stage elution and the second-stage elution elute 1.5-3 BV.

[0016] In the gradient alkaline elution described above, the first stage of elution primarily serves to elute weakly bound components, while the second stage primarily serves to elute lactic acid. Gradient elution can significantly improve the elution rate of lactic acid, thereby increasing the recovery rate.

[0017] In the above method, the weakly basic anion exchange resin is a resin with an acrylic acid-divinylbenzene copolymer backbone and secondary amine groups on its surface.

[0018] Preferably, the average particle size of the weakly basic anion exchange resin is 500~750μm.

[0019] Preferably, the water content of the weakly basic anion exchange resin is 56-64 wt%.

[0020] In some embodiments of the present invention, the weakly basic anion exchange resin is Amberlite IRA 67.

[0021] Optionally, the top of the adsorption column is provided with a protective layer composed of quartz sand, ceramic particles or other inert particles to reduce the clogging of the resin bed by impurities.

[0022] In the above method, the pH adjustment is achieved by adding an acidic regulator, preferably an inorganic acid (e.g., hydrochloric acid) or an organic acid. Adjusting the pH to 2.0-3.0 allows lactic acid to exist primarily in its undissociated form, thereby improving adsorption selectivity.

[0023] In the above method, the solid-liquid separation pretreatment of the fermentation broth adopts a staged solid-liquid separation pretreatment method.

[0024] The staged solid-liquid separation pretreatment includes a combination of at least two methods selected from coarse filtration, gravity sedimentation, centrifugation, and microfiltration. For example, large particulate impurities are first removed by coarse filtration and sedimentation, and then a clear filtrate is obtained by centrifugation and / or microfiltration.

[0025] Preferably, the fractional solid-liquid separation pretreatment includes: centrifugation followed by microfiltration. The centrifugation speed is preferably 3000-5000 rpm, and the centrifugation time is preferably 5-15 min. The microfiltration uses a ceramic membrane with a pore size of 1.0-1.4 μm and an operating pressure of 4-6 bar.

[0026] In the above method, the agricultural waste includes one or more selected from livestock and poultry manure, straw waste, and fruit and vegetable waste.

[0027] Preferably, the agricultural waste includes livestock and poultry manure, straw waste, and / or fruit and vegetable waste. More preferably, it includes livestock and poultry manure and fruit and vegetable waste.

[0028] Preferably, the livestock and poultry manure includes pig manure, and the fruit and vegetable waste includes apple waste.

[0029] Preferably, the fermentation broth is obtained by co-fermenting livestock and poultry manure and fruit and vegetable waste. The fermentation process is an open operation, requiring no aseptic technique.

[0030] Preferably, the fermentation broth is obtained by inoculating livestock and poultry manure and fruit and vegetable waste with lactic acid bacteria and fermenting under microaerobic conditions. The preferred mass ratio of livestock and poultry manure to fruit and vegetable waste is 1:(1-2). The lactic acid bacteria preferably include *Lactobacillus casei* (…). Lactobacillus casei ), Lactobacillus acidophilus ( Lactobacillus acidophilus Lactobacillus delbrueckii subsp. bulgaricus ( Lactobacillus delbrueckii subsp. Bulgarian ), Streptococcus thermophilus ( Streptococcus thermophilic ) and Lactobacillus plantarum ( Lactobacillus plantarum Preferably, among the lactic acid bacteria, *Lactobacillus casei* (…). Lactobacillus casei ), Lactobacillus acidophilus ( Lactobacillus acidophilus Lactobacillus delbrueckii subsp. bulgaricus ( Lactobacillus delbrueckii subsp. Bulgarian ), Streptococcus thermophilus ( Streptococcus thermophilus ) and Lactobacillus plantarum ( Lactobacillus plantarum The ratio of viable bacteria to live bacteria is (1-3): (1-3): (1-3): (1-3): (1-3): (1-3).

[0031] The initial pH of the fermentation is preferably 6.5 ± 0.2; the fermentation temperature is preferably 35 ± 2℃; and the fermentation time is preferably 8-12 days. The microaerobic conditions are achieved by introducing air at a rate of 800-1200 mL / L / day.

[0032] In the above method, the lactic acid content in the fermentation broth is 10~50g / L.

[0033] In this invention, the process of separating lactic acid using an adsorption column of a weakly basic anion exchange resin is carried out at room temperature and can be operated intermittently or continuously.

[0034] In the above method, the lactic acid eluent obtained by gradient alkaline elution can be further concentrated, evaporated or purified to obtain lactic acid products.

[0035] The beneficial effects of this invention include at least the following: the method provided by this invention uses agricultural waste fermentation broth as raw material, which has a wide range of sources and low cost, in line with the direction of resource utilization of agricultural by-products; separation is carried out through ion exchange resin, the process conditions are mild, eliminating complex steps such as decolorization and distillation in traditional processes, reducing the generation of waste residue and waste liquid, and the operation is simple, which is conducive to automation and large-scale promotion; it has high selectivity and adsorption rate for lactic acid, high elution rate, and high lactic acid product yield; the process has a high degree of continuity, high separation efficiency, low equipment investment and operating costs, and has the advantages of industrial scale-up and clean production, making it suitable for large-scale promotion and application, and providing an efficient and economical method for resource utilization of agricultural waste and lactic acid production. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0037] The fermentation broth used in the following examples and comparative examples for producing lactic acid from agricultural waste contained 30 g / L of lactic acid, and its preparation method is as follows: (1) Mix pig manure and apple waste at a mass ratio of 40:60 (volatile solids content of 7% VS), and inoculate with mixed lactic acid bacteria (mainly containing Lactobacillus casei with a live bacteria ratio of 1:1:1:1:1). Lactobacillus casei ), Lactobacillus acidophilus ( Lactobacillus acidophilus Lactobacillus delbrueckii subsp. bulgaricus ( Lactobacillus delbrueckii subsp. Bulgarian ), Streptococcus thermophilus ( Streptococcus thermophilus) and Lactobacillus plantarum ( Lactobacillus plantarum The initial pH of the substrate in the reactor was adjusted to 6.5 ± 0.1 using 3M NaOH and HCl. Each reactor was cultured in a constant temperature incubator at 35 ± 1℃. During the fermentation process, 1000 mL / L / d of air was introduced daily to ensure a micro-aerobic environment. Lactic acid fermentation broth was obtained after 10 days of operation.

[0038] The weakly basic anion exchange resin used in the following examples and comparative examples is an acrylic acid-divinylbenzene copolymer backbone resin with secondary amine groups on the surface, having an average particle size of 600 μm and a water content of 60 wt%. This weakly basic anion exchange resin was purchased from Rohm and Haas Electronic Materials (Shanghai) Co., Ltd., under the trade name Amberlite IRA 67. The preparation method of the adsorption column packed with the weakly basic anion exchange resin is as follows: The weakly basic anion exchange resin is packed into a glass adsorption column with a resin bed volume of 500 mL (1 BV), a column height to diameter ratio of 5:1, and a quartz sand protective layer of approximately 2 cm thickness is laid on top of the adsorption column.

[0039] In the following examples and comparative examples, high-performance liquid chromatography (HPLC) was used to analyze the adsorption and desorption efficiency of lactic acid and the content of lactic acid in the final collected eluent. The HPLC conditions were as follows: Detector: Agilent 1100 high-performance liquid chromatograph - ultraviolet detector; Chromatographic column: Waters X select HSS T3 (4.6×250mm, 5μm); Mobile phase: 100 mm of (NH4)2HPO4; Flow rate: 1.0 mL / min; Column temperature: 30℃; Injection volume: 10 μL.

[0040] In the following examples and comparative examples, the adsorption rate of lactic acid (E) 吸 The calculation method for E is as follows: 吸 =(C 初始乳酸浓度 -C 吸附后乳酸浓度 ) / C 初始乳酸浓度 ×100%. Lactic acid recovery rate (E 回 The calculation method for E is as follows: 回 =(C 解吸液乳酸浓度 ×V 解吸液体积 ) / [(C 初始乳酸浓度 -C 吸附后乳酸浓度 )×V 发酵液体积 Lactic acid purity = lactic acid peak area / total organic acid peak area × 100%.

[0041] Example 1 This embodiment provides a method for separating and refining lactic acid from microaerobic fermentation broth of agricultural waste, the steps of which are as follows: 1. The fermentation broth for producing lactic acid from agricultural waste via microaerobic fermentation was centrifuged at 4000 rpm for 10 min to remove large suspended particles. The resulting supernatant was further subjected to microfiltration to remove fine particles and colloidal substances. The microfiltration process used a ceramic membrane with a pore size of 1.2 μm and an operating pressure of 5 bar to obtain a clear filtrate. The pH of the clear filtrate was adjusted to 2.0 using hydrochloric acid solution with a concentration of 1.0-2.0 mol / L, added slowly and stirred until homogeneous, and set aside for later use.

[0042] 2. Under normal temperature conditions, lactic acid is separated using an adsorption column packed with a weakly basic anion exchange resin: (1) A segmented dynamic adsorption method was adopted, in which the clarified filtrate after pH adjustment in step 1 was introduced into the adsorption column in three segments for dynamic adsorption: First stage: Inject 2 BV of liquid at a flow rate of 2.0 BV / h; Second stage: Reduce the flow rate to 1.0 BV / h and continue to inject 3 BV of liquid; Third stage: Further reduce the flow rate to 0.5 BV / h, and inject 2 BV of liquid.

[0043] After adsorption was completed under the above conditions, the lactic acid concentration was detected by high performance liquid chromatography, and the lactic acid adsorption rate was calculated to be 73.2%, thus improving the resin utilization rate.

[0044] (2) Gradient alkaline elution Desorption of the adsorption column was performed using a gradient alkaline elution method: First, 2BV was eluted with 0.2mol / L sodium hydroxide solution, mainly to remove weakly adsorbed impurities and some coexisting organic acids; The 2 BV was then eluted with 1.0 mol / L sodium hydroxide solution, and the lactic acid eluent was collected. The lactic acid concentration in the lactic acid eluent was determined by high performance liquid chromatography. The calculated lactic acid recovery rate was 91.2% and the purity was 84.6%.

[0045] Example 2 This embodiment provides a method for separating and refining lactic acid from microaerobic fermentation broth of agricultural waste. The method differs from that of Example 1 only in that the pH of the clarified filtrate from step 1 is adjusted to 3.0. The dynamic adsorption in step 2 is modified as follows: First stage: 2 BV of liquid is injected at a flow rate of 2.2 BV / h; Second stage: 3 BV of liquid is injected at a flow rate of 1.2 BV / h; Third stage: 2 BV of liquid is injected at a flow rate of 0.6 BV / h. After adsorption, the lactic acid concentration is detected by high-performance liquid chromatography, and the calculated lactic acid adsorption rate is 68.5%. After adsorption, the adsorption column is desorbed using a gradient alkaline elution method: First stage: 2 BV is eluted with 0.1 mol / L sodium hydroxide solution; Second stage: 2 BV is eluted with 0.8 mol / L sodium hydroxide solution, and the lactic acid eluent is collected.

[0046] The lactic acid concentration in the eluent was determined by high performance liquid chromatography, and the lactic acid recovery rate was calculated to be 86.4%, with a purity of 80.3%.

[0047] Comparative Example 1 This comparative example provides a method for separating and refining lactic acid from microaerobic fermentation broth of agricultural waste. The difference between this method and the method in Example 1 lies only in that: the dynamic adsorption in step 2(1) is changed to static adsorption, and the gradient alkaline elution in step (2) is changed to non-gradient alkaline elution. Specifically, step 2 is as follows: (1) The clarified filtrate after pH adjustment in step 1 is directly placed into a beaker containing a weakly basic anion exchange resin and adsorbed for 120 min. Under these conditions, the lactic acid adsorption rate was detected to be 51.9%. (2) The lactic acid adsorbed on the resin is eluted with a 1.0 mol / L sodium hydroxide solution. The lactic acid concentration in the eluent is detected by high performance liquid chromatography. The calculated recovery rate of lactic acid is 76.8%, and the purity is 71.5%.

[0048] Comparative Example 2 This comparative example provides a method for separating and refining lactic acid from microaerobic fermentation broth of agricultural waste. The only difference between this method and the method in Example 1 is that the pH of the clarified filtrate was not adjusted in step 1. The pH of the clarified filtrate was measured to be 3.8, and it was directly used in step 2.

[0049] Under these conditions, the adsorption rate of lactic acid was 46.5%, the recovery rate was 79.8%, and the purity was 70.5%.

[0050] Comparative Example 3 This comparative example provides a method for separating and refining lactic acid from microaerobic fermentation broth of agricultural waste. The difference between this method and the method in Example 1 is only that in step 2, the clarified filtrate after pH adjustment is continuously fed at a constant flow rate of 1.0 BV / h, with a cumulative treatment volume of 7 BV, without segmented flow rate control. After adsorption, elution is performed only once using a 1.0 mol / L sodium hydroxide solution at a volume of 4 BV, without gradient elution.

[0051] Under these conditions, the adsorption rate of lactic acid was measured to be 60.8%, which was significantly lower than that in Example 1. The recovery rate of lactic acid was 80.2%, and the purity was 75.6%.

[0052] Comparative Example 4 This comparative example provides a method for separating and refining lactic acid from microaerobic fermentation broth of agricultural waste. The only difference between this method and the method in Example 1 is that in step 2, the flow rate of the three-stage dynamic adsorption is changed to: first stage: 2BV of liquid is fed in at a flow rate of 2.0BV / h; second stage: 3BV of liquid is fed in at a flow rate of 1.5BV / h; third stage: 2BV of liquid is fed in at a flow rate of 1.0BV / h.

[0053] Under these conditions, high performance liquid chromatography (HPLC) analysis showed that the adsorption rate of lactic acid was 67.4%, the recovery rate was 84.1%, and the purity was 76.0%.

[0054] Comparative Example 5 This comparative example provides a method for separating and refining lactic acid from microaerobic fermentation broth of agricultural waste. The difference between this method and the method in Example 1 lies only in the change of sodium hydroxide concentration in each stage of the gradient alkaline elution in step 2. The elution conditions are adjusted as follows: First stage elution: elution of 2 BV using 0.1 mol / L sodium hydroxide solution; Second stage elution: elution of 2 BV using 0.6 mol / L sodium hydroxide solution.

[0055] High performance liquid chromatography (HPLC) analysis showed that the adsorption rate of lactic acid was comparable to that of Example 1, but the recovery rate of lactic acid was 79.6%, which was significantly lower than the 91.2% of Example 1, and its purity was 73.9%.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for separating and refining lactic acid from microaerobic fermentation broth of agricultural waste, characterized in that, The method includes: using fermentation broth from agricultural waste to produce lactic acid through microaerobic fermentation as raw material, performing solid-liquid separation pretreatment on the fermentation broth to obtain a clarified filtrate, and adjusting the pH of the clarified filtrate to 2.0-3.0 to obtain a pretreated solution; The pretreated solution was injected into a weakly basic anion exchange resin adsorption column, and lactic acid was adsorbed using a segmented dynamic adsorption method. After adsorption, the resin was eluted using a gradient alkaline elution method, and the eluent containing lactic acid was collected. The segmented dynamic adsorption includes three stages of dynamic adsorption: the first stage of dynamic adsorption is fed into the liquid at a flow rate of 1.8-2.2 BV / h, the second stage of dynamic adsorption is fed into the liquid at a flow rate of 0.8-1.2 BV / h, and the third stage of dynamic adsorption is fed into the liquid at a flow rate of 0.3-0.7 BV / h. The gradient alkaline elution includes two stages: the first stage elution is carried out with 0.1-0.3 mol / L sodium hydroxide solution, and the second stage elution is carried out with 0.8-1.5 mol / L sodium hydroxide solution.

2. The method for separating and refining lactic acid from microaerobic fermentation broth of agricultural waste according to claim 1, characterized in that, The first stage of dynamic adsorption involves an influent volume of 1.5-2.5 BV, the second stage involves an influent volume of 2.5-3.5 BV, and the third stage involves an influent volume of 1.5-2.5 BV.

3. The method for separating and refining lactic acid from microaerobic fermentation broth of agricultural waste according to claim 1, characterized in that, Both the first and second stage elutions resulted in 1.5-3 BV of elution.

4. The method for separating and refining lactic acid from microaerobic fermentation broth of agricultural waste according to any one of claims 1 to 3, characterized in that, The weakly basic anion exchange resin is a resin with an acrylic acid-divinylbenzene copolymer backbone and secondary amine groups on its surface.

5. The method for separating and refining lactic acid from microaerobic fermentation broth of agricultural waste according to claim 4, characterized in that, The average particle size of the weakly basic anion exchange resin is 500~750μm.

6. The method for separating and refining lactic acid from microaerobic fermentation broth of agricultural waste according to claim 4, characterized in that, The water content of the weakly basic anion exchange resin is 56~64wt%.

7. The method for separating and refining lactic acid from microaerobic fermentation broth of agricultural waste according to any one of claims 1 to 3, 5, and 6, characterized in that, The solid-liquid separation pretreatment of the fermentation broth adopts a staged solid-liquid separation pretreatment method, which includes: first centrifugation, and then microfiltration.

8. The method for separating and refining lactic acid from microaerobic fermentation broth of agricultural waste according to any one of claims 1 to 3, 5, and 6, characterized in that, The agricultural waste includes livestock and poultry manure, as well as straw waste and / or fruit and vegetable waste.

9. The method for separating and refining lactic acid from microaerobic fermentation broth of agricultural waste according to claim 8, characterized in that, The livestock and poultry manure includes pig manure, and the fruit and vegetable waste includes apple waste.

10. The method for separating and refining lactic acid from microaerobic fermentation broth of agricultural waste according to any one of claims 1 to 3, 5, 6, and 9, characterized in that, The lactic acid content in the fermentation broth is 10~50g / L.