Method and application of producing lactic acid by synergistic fermentation of organic solid waste

Abstract

The present invention provides a method and application for producing lactic acid through the coordinated fermentation of organic solid waste, specifically relating to the field of waste disposal technology. In the method for producing lactic acid through the coordinated fermentation of organic solid waste, the organic solid waste includes raw food waste, sewage treatment plant sludge, and polylactic acid waste; the method comprises the following steps: A. converting the raw food waste into a liquid food waste slurry, adding the sewage treatment plant sludge and mixing evenly to obtain a pre-fermentation slurry; B. adding the polylactic acid waste to the pre-fermentation slurry, and fermenting the mixture under anaerobic conditions to obtain a fermentation liquid; and finally, separating and purifying the fermentation liquid to obtain the lactic acid. By utilizing inexpensive and abundant organic solid waste as raw material, this method not only reduces raw material costs but also reduces waste disposal costs, making lactic acid production more economical, feasible, stable, and efficient, further reducing the production cost of lactic acid and promoting the development of downstream industries.

Description

Technical Field

[0001] The present invention relates to the technical field of garbage disposal, and in particular to a method and application of producing lactic acid by cooperative fermentation of organic solid waste. Background Art

[0002] Lactic acid is an organic compound widely used in the food, pharmaceutical, and cosmetics industries. Industrially, it is often used as a food additive, pharmaceutical intermediate, and raw material for degradable plastics. Traditional lactic acid synthesis pathways include fermentation of sugars or chemical synthesis. Sugar fermentation typically utilizes starch-based biomass such as corn and potatoes, or cellulose straw as feedstock. With the growing awareness of resource recycling and environmental protection, the focus of researchers has gradually shifted to organic-rich solid waste.

[0003] With the acceleration of urbanization, food waste, a significant component of municipal solid waste, has been generating increasing amounts annually. In 2024, China's total food waste generation exceeded 100 million tons and is projected to reach approximately 160 million tons by 2030. Food waste, characterized by high moisture content, high organic matter content, and high perishability, poses a significant threat to human health if not properly handled. Currently, anaerobic digestion is the mainstream method for resource-based food waste treatment. It can decompose food waste into energy sources such as methane (CH4), hydrogen (H2), and volatile fatty acids (VFAs), alleviating some of the pressure on municipal solid waste treatment. However, in practical applications, this technology still faces several limitations, such as the need to improve degradation efficiency, long hydraulic retention time, and low organic loading, which hinder its large-scale deployment and application.

[0004] Municipal sewage sludge, another type of organic waste, is characterized by its large volume, widespread distribution, and high pollution. Although sludge fermentation to produce acid has been widely reported, its low selectivity and yield make it difficult to efficiently convert into high-value-added products such as lactic acid.

[0005] Although polylactic acid (PLA), a biodegradable polymer, exhibits excellent degradation properties under specific conditions, its degradation rate in the natural environment remains unsatisfactory. Even under relatively ideal conditions such as room-temperature composting or mesophilic fermentation, complete degradation of PLA still requires hundreds of days. Furthermore, PLA degrades even more slowly in natural water bodies (such as rivers and oceans), and even its complete degradation remains controversial. This slow degradation behavior means that PLA may have long-term environmental impacts in practical applications, particularly in aquatic environments, where residual PLA material may pose a potential threat to ecosystems.

[0006] In summary, the current treatment of organic solid waste still faces many challenges in terms of resource utilization efficiency, degradation rate, and subsequent utilization of products. Furthermore, the high cost of lactic acid production has become a major factor restricting its widespread application.

[0007] In view of this, the present invention is proposed. Summary of the Invention

[0008] One of the objectives of the present invention is to provide a method for producing lactic acid by synergistic fermentation of organic solid waste, aiming to solve at least one of the above-mentioned technical problems in the prior art.

[0009] A second object of the present invention is to provide application of the above method in municipal solid waste treatment.

[0010] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0011] A first aspect of the present invention provides a method for producing lactic acid by co-fermentation of organic solid waste, wherein the organic solid waste includes raw food waste, sewage plant sludge and polylactic acid waste;

[0012] The method comprises the following steps:

[0013] A. preparing a liquid food waste slurry from the raw food waste, adding the sewage treatment plant sludge and mixing evenly to obtain a pre-fermented slurry;

[0014] B1, adding the polylactic acid waste to the pre-fermentation slurry, and fermenting under anaerobic conditions to obtain a fermentation liquid; and finally separating and purifying the fermentation liquid to obtain the lactic acid;

[0015] or,

[0016] B2, sealing and fermenting the pre-fermented slurry under anaerobic conditions, adding the polylactic acid waste during the fermentation process, and continuing the fermentation to obtain a fermentation liquid; finally, separating and purifying the fermentation liquid to obtain the lactic acid. Further, the raw food waste is converted into a liquid food waste slurry, comprising:

[0017] The raw food waste is placed at 20-40° C. for aging treatment for 12-24 hours, and then a screw press is used to separate the liquid phase component to obtain the liquid food waste slurry.

[0018] Furthermore, the sewage treatment plant sludge has a moisture content of 80% to 98%, a volatile solid content of 2% to 5%, a C / N ratio of 4 to 10, a temperature of 20 to 40° C., and a pH value of 6.5 to 8.0.

[0019] Furthermore, the polylactic acid waste includes disposable tableware, food packaging, agricultural mulch or textile fibers.

[0020] The particle size of the polylactic acid waste is ≤0.5 mm.

[0021] Furthermore, in step A, the mass ratio of the liquid food slurry to the sewage treatment plant sludge is 1:0.5-2 in terms of volatile matter.

[0022] Furthermore, in step B1 or B2, the mass ratio of the pre-fermentation slurry to the polylactic acid waste is 1:0.5-2 in terms of volatile matter.

[0023] Furthermore, nitrogen is used to replace the air in the fermentation container to create the anaerobic condition.

[0024] Furthermore, the temperature of the sealed fermentation is 35-42° C., the pH value is 4.0-6.8, and the dissolved organic carbon concentration is 6000-10000 mg / L.

[0025] Furthermore, in step B1 or B2, the hydraulic retention time of the fermentation is 3 to 6 days, and the commissioning period from fresh substrate to achieving stable acid production in the fermentation liquid is 7 to 14 days.

[0026] And / or, after the commissioning period of the reaction system is completed, the fermentation liquid is periodically fed and discharged to maintain the dynamic balance of the fermentation process.

[0027] And / or, the feed rate is consistent with the discharge rate and meets the hydraulic retention time requirement.

[0028] The second aspect of the present invention provides application of the method described in the first aspect in the treatment of urban solid waste.

[0029] Compared with the prior art, the present invention has at least the following beneficial effects:

[0030] The method for producing lactic acid by synergistic fermentation of organic solid waste provided by the present invention realizes efficient resource utilization of waste by synergistically fermenting restaurant kitchen waste, sewage plant sludge and polylactic acid waste. This method does not require an additional inoculation process and utilizes the rich microbial communities in restaurant kitchen waste and sewage plant sludge to naturally initiate fermentation, which significantly simplifies the operation process, reduces production costs and operational difficulty, and avoids the pollution risks that may be caused by the introduction of bacterial strains. Synergistic fermentation gives full play to the characteristics of each waste and significantly improves the yield and purity of lactic acid. In addition, this method shortens the fermentation cycle, improves production efficiency, reduces environmental pollution caused by waste landfill and incineration, avoids the risk of long-term residue of polylactic acid waste in the natural environment and the release of microplastics, and has significant environmental benefits. By utilizing cheap and abundant organic solid waste as raw materials, not only the raw material cost is reduced, but also the waste treatment cost is reduced, making lactic acid production more economically feasible, stable and efficient, further reducing the production cost of lactic acid and promoting the development of downstream industries.

[0031] The application of the method provided by this invention in municipal solid waste treatment offers significant advantages and advancements for municipal solid waste treatment, downstream industries, environmental protection, and the economy. By converting organic solid waste into high-value-added lactic acid products, this method achieves efficient resource utilization while reducing the environmental pollution associated with traditional treatment methods such as landfill and incineration. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0033] Hereinafter, the terms "including", "having" and their cognates, which may be used in various embodiments of the present invention, are intended only to indicate specific features, numbers, steps, operations, elements, components or combinations of the foregoing items, and should not be understood as first excluding the existence of one or more other features, numbers, steps, operations, elements, components or combinations of the foregoing items or the possibility of adding one or more features, numbers, steps, operations, elements, components or combinations of the foregoing items.

[0034] A first aspect of the present invention provides a method for producing lactic acid by co-fermentation of organic solid waste, wherein the organic solid waste includes raw food waste, sewage plant sludge and polylactic acid waste;

[0035] The method comprises the following steps:

[0036] A. preparing a liquid food waste slurry from the raw food waste, adding the sewage treatment plant sludge and mixing evenly to obtain a pre-fermented slurry;

[0037] B1, adding the polylactic acid waste to the pre-fermentation slurry, and fermenting under anaerobic conditions to obtain a fermentation liquid; and finally separating and purifying the fermentation liquid to obtain the lactic acid;

[0038] or,

[0039] B2. Fermenting the pre-fermented slurry in a sealed manner under anaerobic conditions, adding the polylactic acid waste during the fermentation process, and continuing the fermentation to obtain a fermentation liquid; and finally separating and purifying the fermentation liquid to obtain the lactic acid.

[0040] The method for producing lactic acid by synergistic fermentation of organic solid waste provided by the present invention realizes efficient resource utilization of waste by synergistically fermenting restaurant kitchen waste, sewage plant sludge and polylactic acid waste. This method does not require an additional inoculation process and utilizes the rich microbial communities in restaurant kitchen waste and sewage plant sludge to naturally initiate fermentation, which significantly simplifies the operation process, reduces production costs and operational difficulty, and avoids the pollution risks that may be caused by the introduction of bacterial strains. Synergistic fermentation gives full play to the characteristics of each waste and significantly improves the yield and purity of lactic acid. In addition, this method shortens the fermentation cycle, improves production efficiency, reduces environmental pollution caused by waste landfill and incineration, avoids the risk of long-term residue of polylactic acid waste in the natural environment and the release of microplastics, and has significant environmental benefits. By utilizing cheap and abundant organic solid waste as raw materials, not only the raw material cost is reduced, but also the waste treatment cost is reduced, making lactic acid production more economically feasible, stable and efficient, further reducing the production cost of lactic acid and promoting the development of downstream industries.

[0041] Kitchen waste is rich in organic matter, such as starch, fat, protein and trace elements. These ingredients not only provide sufficient nutrition for lactic acid bacteria, but also create a suitable environment for the growth and metabolism of microorganisms. In addition, kitchen waste itself contains a rich indigenous microbial community in the natural environment, including a variety of lactic acid bacteria, such as Lactobacillus amylovora ( Lactobacillus amylophilus )、Lactobacillus plantarum( Lactobacillus plantarum ) and other species of the genus Lactobacillus. These indigenous lactic acid bacteria can naturally adapt to the complex environment of food waste and play an important role in the fermentation process, promoting the production of lactic acid.

[0042] Compared to inoculated lactic acid bacteria, indigenous lactic acid bacteria have significant advantages in the fermentation of food waste. First, they are more adaptable to the fermentation environment, can respond quickly to changes in conditions, and show good tolerance. Second, indigenous lactic acid bacteria can dominate in complex microbial communities, inhibit the growth of other microorganisms, reduce the production of by-products, thereby increasing lactic acid production and purity, and reducing fermentation costs. During the fermentation process, lactic acid bacteria in food waste can hydrolyze large-molecule organic matter into small-molecule compounds through metabolic activities, and further convert them into lactic acid. During the recycling process of food waste, lactic acid bacteria can multiply rapidly and dominate in its open fermentation system, inhibiting the growth of other microorganisms, thereby increasing lactic acid production.

[0043] Sewage plant sludge contains polylactic acid (PLA)-degrading bacteria. These PLA-degrading microorganisms are diverse, including bacteria, actinomycetes, and fungi. These microorganisms are highly adaptable to complex organic environments and secrete a variety of degradative enzymes to degrade macromolecular organic matter, including PLA. The microbial communities in sludge possess strong adaptability and metabolic capacity, enabling them to hydrolyze PLA's ester bonds by secreting specific degradative enzymes (such as esterases and proteases). During PLA degradation, these microorganisms initially break down long-chain polymers into more readily bioavailable substrates, such as lactic acid and oligomers. Lactic acid bacteria then utilize these substrates and, through their own metabolic pathways, reconvert some of them into lactic acid. Therefore, the lactic acid produced in the reactor is derived partly from direct enzymatic degradation of PLA and partly from fermentative synthesis of degradation products by the lactic acid bacteria. This synergistic effect transforms the PLA microbial degradation process from a simple waste treatment to a highly efficient bioconversion process for lactic acid production.

[0044] Environmental conditions in sludge (such as humidity, temperature, and pH) provide optimal conditions for the growth and metabolism of PLA-degrading bacteria. These environmental factors significantly influence the activity of microorganisms in PLA degradation. Microorganisms in sludge are able to accumulate and perform their degradation functions in this complex environment. Therefore, the abundance of PLA-degrading bacteria in sewage plant sludge not only originates from the microbial diversity of the sludge itself but is also closely related to the sludge's environmental conditions and the metabolic capacity of the microorganisms.

[0045] It should be noted that raw food waste refers to organic waste generated directly from food service establishments (such as restaurants, cafeterias, and home kitchens) without any treatment or processing. It primarily includes food scraps, leftovers, vegetable and fruit peels, meat bones, grease, sauces, etc. Raw food waste does not include disposable tableware, plastic bags, napkins, toilet paper, and other non-organic materials used during dining, such as glass bottles, metal cans, and plastic bottles.

[0046] It should be noted that B1 and B2 are two parallel implementation processes with equal status and function in specific implementation, and either one can be used. In actual operation, depending on the actual situation and needs, A and B1 can be combined for implementation, or A and B2 can be combined for implementation. Both options are feasible solutions. Further, the raw food waste is made into a liquid food waste slurry, including:

[0047] The raw food waste is aged at 20-40°C for 12-24 hours to ensure that indigenous lactic acid bacteria can rapidly multiply and dominate during the fermentation process, inhibiting the growth of other microorganisms, thereby increasing lactic acid production and purity. Lactic acid bacteria can also further decompose complex organic matter by secreting extracellular enzymes, promoting fermentation efficiency. A screw press is then used to separate the liquid phase components to obtain the liquid food waste slurry. This liquid food waste slurry can improve fermentation efficiency, optimize resource utilization, and adapt to subsequent process requirements.

[0048] Typically but not limitatively, the aging treatment temperature of the raw food waste can be, for example, 20°C, 25°C, 30°C, 35°C or 40°C, or any value within the range of 20°C to 40°C; the aging treatment time can be, for example, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours or 24 hours, or any value within the range of 12 hours to 24 hours.

[0049] Furthermore, the sewage treatment plant sludge has a moisture content of 80-98%, a volatile solid content of 2-5%, a C / N ratio of 4-10, a temperature of 20-40° C., and a pH value of 6.5-8.0.

[0050] Typically but not limitatively, the moisture content of the sewage treatment plant sludge can be, for example, 80%, 82%, 85%, 88%, 90%, 92%, 95% or 98%, or any value within the range of 80% to 98%; the volatile solids content can be, for example, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, or any value within the range of 2% to 5%; the C / N ratio can be, for example, 4, 5, 6, 7, 8, 9 or 10, or any value within the range of 4 to 10; the temperature can be, for example, 20°C, 22°C, 25°C, 28°C, 30°C, 32°C, 35°C, 38°C or 40°C, or any value within the range of 20°C to 40°C; the pH value can be, for example, 6.5, 6.7, 6.9, 7.0, 7.2, 7.5, 7.8 or 8.0, or any value within the range of 6.5 to 8.0.

[0051] Furthermore, the polylactic acid waste includes disposable tableware, food packaging, agricultural mulch or textile fibers.

[0052] The particle size of the polylactic acid waste is ≤0.5 mm.

[0053] Furthermore, in step A, the mass ratio of the liquid food slurry to the sewage treatment plant sludge is 1:0.5-2 in terms of volatile matter.

[0054] Typically but not limitatively, in step A, the mass ratio of the liquid food slurry to the sewage treatment plant sludge (calculated as volatile matter) can be, for example, 1:0.5, 1:0.75, 1:1, 1:1.25, 1:1.5, 1:1.75 or 1:2, or any value within the range of 1:0.5 to 2.

[0055] Furthermore, in step B1 or B2, the mass ratio of the pre-fermentation slurry to the polylactic acid waste is 1:0.5-2 in terms of volatile matter.

[0056] Typically but not limitatively, in step B1 or B2, the mass ratio of the pre-fermented slurry to the polylactic acid waste (calculated as volatile matter) can be, for example, 1:0.5, 1:0.75, 1:1, 1:1.25, 1:1.5, 1:1.75 or 1:2, or any value within the range of 1:0.5 to 2.

[0057] Furthermore, nitrogen is used to replace the air in the fermentation container to create the anaerobic condition.

[0058] Furthermore, the temperature of the sealed fermentation is 35-42° C., the pH value is 4.0-6.8, and the dissolved organic carbon concentration is 6000-10000 mg / L.

[0059] Typically but not limitatively, the temperature of the sealed fermentation can be, for example, 35°C, 36°C, 37°C, 38°C, 39°C, 40°C, 41°C or 42°C, or any value within the range of 35°C to 42°C.

[0060] Furthermore, in step B1 or B2, the hydraulic retention time of the fermentation is 3 to 6 days, and the commissioning period from fresh substrate to achieving stable acid production in the fermentation liquid is 7 to 14 days.

[0061] Typically but not restrictively, in step B1 or B2, the debugging period may be, for example, 7 days, 8 days, 9 days, 10 days, 11 days, 12 days, 13 days or 14 days, or any value within the range of 7 to 14 days.

[0062] And / or, after the commissioning period of the reaction system is completed, the fermentation liquid is periodically fed and discharged to maintain the dynamic balance of the fermentation process.

[0063] And / or, the feed rate is consistent with the discharge rate and meets the hydraulic retention time requirement.

[0064] After the first fermentation cycle is complete, the fermentation broth reaches a certain level of maturity, and periodic feeding and discharging operations begin. Feeding replenishes the fermentation feedstock to maintain the microbial nutrient supply; discharging removes some of the fermented liquid for subsequent processing or utilization. This periodic operation maintains the dynamic equilibrium of the fermentation process, ensuring stable fermentation conditions, sustained microbial activity, and uniform product quality. This dynamic equilibrium fermentation method is suitable for large-scale industrial production, improving equipment utilization and fermentation efficiency, and achieving a continuous and stable fermentation process.

[0065] After fermentation is complete, the fermentation broth is drained from the fermenter and separated by centrifugation or filtration to separate the solid residue and liquid product. The liquid product contains a high concentration of organic acids, particularly lactic acid. The separated liquid product is further processed using ion exchange resins, membrane separation technology, or evaporative crystallization to extract and purify the lactic acid, resulting in a high-purity lactic acid product. The solid residue after fermentation is rich in organic matter and nutrients and can be used as an organic fertilizer or soil conditioner for agricultural planting or ecological restoration.

[0066] The present invention does not specifically limit the lactic acid separation process and the treatment of the solid residue. Any method that can separate lactic acid from the fermentation broth is applicable to the post-treatment process of the present invention.

[0067] The second aspect of the present invention provides application of the method described in the first aspect in the treatment of urban solid waste.

[0068] The application of the method provided by this invention in municipal solid waste treatment offers significant advantages and advancements for municipal solid waste treatment, downstream industries, environmental protection, and the economy. By converting organic solid waste into high-value-added lactic acid products, this method achieves efficient resource utilization while reducing the environmental pollution associated with traditional treatment methods such as landfill and incineration.

[0069] The following examples describe some embodiments of the present invention in detail. The following examples and features may be combined unless otherwise specified. The raw materials used in Example 5 and the comparative examples of the present invention, unless otherwise specified, were prepared under conventional conditions or manufacturer-recommended conditions. Reagents and instruments used without manufacturer identification are commercially available conventional products.

[0070] Example 1

[0071] This embodiment provides a method for producing lactic acid through collaborative fermentation, which specifically includes the following steps:

[0072] 1. The raw food waste was placed in an environment of 37°C for 18 hours, and then processed with a screw press to separate the liquid phase components to prepare liquid food waste slurry.

[0073] 2. Take 600g (in terms of volatile matter) of liquid food slurry and 600g (in terms of volatile matter) of sewage sludge, mix them, and load them into a fermenter with an effective volume of 1800mL. The sewage sludge has a moisture content of 95.6%, a volatile solids content of 2.66%, a C / N ratio of 6, a temperature of 25°C, and a pH of 7.10. Nitrogen is introduced into the fermenter at a flow rate of 0.3 L / min for 15 minutes to drive out the air in the tank and establish an anaerobic environment. After the aeration is completed, the fermenter is sealed and an electromagnetic stirrer is set to stir at a constant speed of 60 rpm to ensure that the materials are thoroughly mixed. The fermenter retains two silicone tubes for subsequent feeding and discharging operations, and an air bag is used to collect gases generated during the fermentation process. The assembled fermenter is placed in a 38°C water bath and prepared for anaerobic digestion.

[0074] 3. Use a freezer crusher to crush the PLA waste, then sieve through a 30-mesh sieve to obtain PLA material with a particle size of less than 0.5 mm. During the fermentation process, 450 mL of fermentation broth was discharged daily and added to the fermenter as new feed, using a mass ratio of 0.5:0.5:1 between liquid food pulp, sewage sludge, and volatile matter from PLA. Fermentation broth was collected on days 7, 10, 14, 17, and 23.

[0075] Example 2

[0076] This embodiment provides a method for producing lactic acid through collaborative fermentation, which specifically includes the following steps:

[0077] 1. Take 10 kg of raw food waste and age it at 30°C for 16 hours. Then, use a screw press to separate the liquid phase components to obtain liquid food waste slurry.

[0078] 2. 600 g (in terms of volatile matter) of liquid food slurry was mixed evenly with 600 g (in terms of volatile matter) of sewage sludge to obtain a pre-fermentation slurry. The sewage sludge had a moisture content of 80%, a C / N ratio of 8, and a pH of 7.0.

[0079] 3. Add PLA waste (particle size ≤ 0.5 mm) to the pre-fermentation slurry at a mass ratio of 1:1 (based on volatile matter) for pre-fermentation slurry: PLA waste. This mixture was placed in a fermenter with an effective volume of 1800 mL. Nitrogen was used to displace the air in the tank, aerating it at a flow rate of 0.3 L / min for 15 minutes to ensure anaerobic conditions. The fermenter was sealed and placed in a 38°C water bath for anaerobic fermentation. During the fermenter operation, 450 mL of fermentation liquid was drained daily and added to the fermenter at a mass ratio of 0.5:0.5:1 for liquid food slurry, sewage sludge, and volatile matter from PLA. After mixing thoroughly, the 450 mL of feed was added to the fermenter as new feed for fermentation.

[0080] The fermentation broth was collected on the 7th, 10th, 14th, 17th and 23rd day respectively.

[0081] Example 3

[0082] This embodiment provides a method for producing lactic acid by collaborative fermentation. The difference from Example 2 is that in step 3, the temperature of anaerobic fermentation is 42° C. and the time is 14 days. The remaining steps are the same as those in Example 2 and will not be repeated here.

[0083] Example 4

[0084] This embodiment provides a method for producing lactic acid by synergistic fermentation. The difference from Example 2 is that in step 2, 600 g (in terms of volatile matter) of liquid food slurry and 300 g (in terms of volatile matter) of sewage plant sludge are evenly mixed, and the feed amount is supplemented according to this ratio. The remaining steps are the same as in Example 2 and are not repeated here.

[0085] Example 5

[0086] This embodiment provides a method for producing lactic acid by synergistic fermentation. The difference from Example 2 is that in step 2, 600 g (in terms of volatile matter) of liquid food slurry and 1200 g (in terms of volatile matter) of sewage plant sludge are evenly mixed, and the feed amount is supplemented according to this ratio. The remaining steps are the same as in Example 2 and are not repeated here.

[0087] Example 6

[0088] This embodiment provides a method for producing lactic acid by synergistic fermentation. The difference from Example 2 is that in step 2, 600 g (in terms of volatile matter) of liquid food slurry and 100 g (in terms of volatile matter) of sewage plant sludge are evenly mixed, and the feed amount is supplemented according to this ratio. The remaining steps are the same as in Example 2 and are not repeated here.

[0089] Example 7

[0090] This embodiment provides a method for producing lactic acid by synergistic fermentation. The difference from Example 2 is that in step 2, 600 g (in terms of volatile matter) of liquid food slurry and 2 kg (in terms of volatile matter) of sewage plant sludge are evenly mixed, and the feed amount is supplemented according to this ratio. The remaining steps are the same as in Example 2 and are not repeated here.

[0091] Example 8

[0092] This embodiment provides a method for producing lactic acid by collaborative fermentation. The difference from Example 2 is that in step 3, the ratio of pre-fermentation slurry to polylactic acid waste is 1:0.5 (calculated as volatile matter), and the feed amount is supplemented according to this ratio. The remaining steps are the same as in Example 2 and are not repeated here.

[0093] Example 9

[0094] This embodiment provides a method for producing lactic acid by collaborative fermentation. The difference from Example 2 is that in step 3, the ratio of pre-fermentation slurry to polylactic acid waste is 1:2 (calculated as volatile matter), and the feed amount is supplemented according to this ratio. The remaining steps are the same as in Example 2 and will not be repeated here.

[0095] Example 10

[0096] This embodiment provides a method for producing lactic acid by collaborative fermentation. The difference from Example 2 is that in step 3, the ratio of pre-fermentation slurry to polylactic acid waste is 1:0.2 (calculated as volatile matter), and the feed amount is supplemented according to this ratio. The remaining steps are the same as in Example 2 and are not repeated here.

[0097] Example 11

[0098] This embodiment provides a method for producing lactic acid by collaborative fermentation. The difference from Example 2 is that in step 3, the ratio of pre-fermentation slurry to polylactic acid waste is 1:3 (calculated as volatile matter), and the feed amount is supplemented according to this ratio. The remaining steps are the same as in Example 2 and will not be repeated here.

[0099] Comparative Example 1

[0100] This comparative example provides a method for producing lactic acid, and the specific process is as follows:

[0101] 600 g (based on volatile matter) of sewage sludge (80% moisture content, C / N ratio of 8, and pH 7.0) was directly charged into a fermenter. The air in the tank was displaced with nitrogen and aerated at a flow rate of 0.3 L / min for 15 minutes to ensure anaerobic conditions. The fermenter was sealed and placed in a 38°C water bath for anaerobic fermentation. Discharge and feed were performed daily, with the discharge rate matching the feed rate. The hydraulic retention time (HRT) was maintained at 4 days. Fermentation broth was collected on days 7, 10, 14, 17, and 23.

[0102] Comparative Example 2

[0103] This comparative example provides a method for producing lactic acid, and the specific process is as follows:

[0104] 1. Take 10 kg of raw food waste and age it at 30°C for 16 hours. Then, use a screw press to separate the liquid phase components to obtain liquid food waste slurry.

[0105] 2. Take 600 g (based on volatile matter) of liquid food slurry and place it in a fermenter. Displace the air in the tank with nitrogen and aerate at a flow rate of 0.3 L / min for 15 minutes to ensure anaerobic conditions. Seal the fermenter and place it in a 38°C waterbath for anaerobic fermentation. Discharge and replenish the feed daily, keeping the discharge and replenishment rates consistent. Maintain a hydraulic retention time of 4 days. Collect the fermentation broth on days 7, 10, 14, 17, and 23.

[0106] Comparative Example 3

[0107] This comparative example provides a method for producing lactic acid by collaborative fermentation. The difference from Example 2 is that polylactic acid waste is not added in step 3. The remaining steps are the same as those in Example 2 and will not be repeated here.

[0108] Comparative Example 4

[0109] This comparative example provides a method for producing lactic acid through collaborative fermentation, which specifically comprises the following steps:

[0110] 1. Mix 600 g (based on volatile matter) of sewage sludge with PLA waste (particle size ≤ 0.5 mm) at a mass ratio of 1:1 (based on volatile matter). The sewage sludge has a moisture content of 80%, a C / N ratio of 8, and a pH of 7.0.

[0111] 2. Place the above mixture into a fermenter and replace the air in the tank with nitrogen. Aerate the tank at a flow rate of 0.3 L / min for 15 minutes to ensure anaerobic conditions. Seal the fermenter and place it in a 38°C water bath for anaerobic fermentation. Starting on the 7th day, discharge and feed the fermenter daily, with the discharge and feed rates matching the feed rates. Collect the fermentation broth on the 7th, 10th, 14th, 17th, and 23rd days.

[0112] Comparative Example 5

[0113] This comparative example provides a method for producing lactic acid through collaborative fermentation, which specifically comprises the following steps:

[0114] 1. Take 10 kg of raw food waste and age it at 30°C for 16 hours. Then, use a screw press to separate the liquid phase components to obtain liquid food waste slurry.

[0115] 2. Mix 600 g (based on volatile matter) of liquid food pulp with 600 g (based on volatile matter) of polylactic acid waste (particle size ≤ 0.5 mm). Place the mixture into a fermenter and displace the air in the tank with nitrogen at a flow rate of 0.3 L / min for 15 minutes to ensure anaerobic conditions. Seal the fermenter and place it in a 38°C waterbath for anaerobic fermentation. Starting on the 7th day, discharge and feed the fermenter daily, with the discharge and feed rates matching the feed rates. Collect the fermentation broth on the 7th, 10th, 14th, 17th, and 23rd days.

[0116] Comparative Example 6

[0117] This comparative example provides a method for producing lactic acid by synergistic fermentation. Unlike Example 2, the original food waste is not aged but directly mixed with sewage sludge. The remaining raw materials and preparation methods are the same as those in Example 2 and will not be repeated here.

[0118] Test Case

[0119] The collected fermentation broth was tested, specifically the total concentration of organic acids in the fermentation broth and the concentration of lactic acid therein were tested, and the proportion of lactic acid in the organic acids was calculated. The obtained data are shown in Tables 1 and 2.

[0120] Table 1

[0121]

[0122] Table 2

[0123]

[0124] As shown in Tables 1 and 2, the fermentation strategy of the present invention can achieve stable and efficient lactic acid production. In contrast, fermentation of sewage sludge alone has a low acidification potential. While food slurry produces a high total acidity, the resulting organic acids are diverse and cannot be specifically converted to lactic acid. Comparative examples of other material combinations demonstrate that the absence of sewage sludge results in insufficient microbial communities, hindering efficient acid production. The absence of food slurry limits total organic acid production due to a lack of readily degradable substrates. Stable lactic acid conversion can only be achieved when the conditions of the present invention are fully met.

[0125] Finally, it should be noted that the above-described embodiments are only specific implementations of the present invention, which are used to illustrate the technical solutions of the present invention, rather than to limit them. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the above-described embodiments, those skilled in the art should understand that any person skilled in the art can modify or easily conceive of changes to the technical solutions described in the above-described embodiments within the technical scope disclosed by the present invention, or replace some of the technical features therein with equivalents. Such modifications, changes, or replacements do not deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for producing lactic acid by co-fermentation of organic solid waste, characterized in that: The organic solid waste includes raw food waste, sewage plant sludge and polylactic acid waste; The method comprises the following steps: A. preparing a liquid food waste slurry from the raw food waste, adding the sewage treatment plant sludge and mixing evenly to obtain a pre-fermented slurry; B1, adding the polylactic acid waste to the pre-fermentation slurry, and fermenting under anaerobic conditions to obtain a fermentation liquid; and finally separating and purifying the fermentation liquid to obtain the lactic acid; or, B2, sealing and fermenting the pre-fermented slurry under anaerobic conditions, adding the polylactic acid waste during the fermentation process, and continuing the fermentation to obtain a fermentation liquid; and finally separating and purifying the fermentation liquid to obtain the lactic acid; The sealed fermentation temperature is 35-42°C, the pH value is 4.0-6.8, and the dissolved organic carbon concentration is 6000-10000 mg / L. In step A, the mass ratio of the liquid food slurry to the sewage treatment plant sludge is 1:0.5-2 in terms of volatile matter; in step B1 or B2, the mass ratio of the pre-fermented slurry to the polylactic acid waste is 1:0.5-2 in terms of volatile matter; The raw food waste is prepared into a liquid food waste slurry, comprising: The raw food waste is placed at 20-40° C. for aging treatment for 12-24 hours, and then a screw press is used to separate the liquid phase component to obtain the liquid food waste slurry.

2. The method according to claim 1, characterized in that The sewage plant sludge has a moisture content of 80% to 98%, a volatile solid content of 2% to 5%, a C / N ratio of 4 to 10, a temperature of 20 to 40° C., and a pH value of 6.5 to 8.

0.

3. The method according to claim 1, characterized in that The polylactic acid waste includes disposable tableware, food packaging, agricultural mulch or textile fibers; The particle size of the polylactic acid waste is ≤0.5 mm.

4. The method according to any one of claims 1 to 3, characterized in that The anaerobic conditions were created by replacing the air in the fermentation vessel with nitrogen.

5. The method according to any one of claims 1 to 3, characterized in that In step B1 or B2, the hydraulic retention time of the fermentation is 3 to 6 days, and the commissioning period from fresh substrate to achieving stable acid production in the fermentation liquid is 7 to 14 days; And / or, after the commissioning period of the reaction system is completed, the fermentation liquid is periodically fed and discharged to maintain the dynamic balance of the fermentation process; And / or, the feed rate is consistent with the discharge rate and meets the hydraulic retention time requirement.

6. Use of the method according to any one of claims 1 to 5 in the treatment of municipal solid waste.

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