Method for promoting anaerobic fermentation of excess sludge to produce acetic acid by using choline chloride-urea eutectic solvent
Pretreatment of residual sludge with a choline chloride-urea eutectic solvent promotes anaerobic fermentation and acid production, solving the problem of extracellular polymer barriers in sludge, achieving efficient and economical short-chain fatty acid production, and promoting the resource utilization of sludge.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-08
- Publication Date
- 2026-04-07
AI Technical Summary
In existing technologies, the extracellular polymers widely present in sludge form a dense barrier, hindering the hydrolysis and release of organic matter, resulting in low efficiency of anaerobic fermentation for acid production. Furthermore, existing pretreatment methods are costly and have unstable effects, making it difficult to achieve efficient resource utilization.
Choline chloride-urea eutectic solvent was used as a pretreatment agent. After being mixed with sludge, it was fermented under anaerobic conditions to promote the rupture of sludge cell walls and the hydrolysis of organic matter, thereby increasing the yield of short-chain fatty acids, especially acetic acid.
It significantly increased the yield of short-chain fatty acids and the proportion of acetic acid, shortened the fermentation cycle, achieved efficient resource utilization of sludge, reduced costs, and avoided secondary pollution.
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Figure CN121801976A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of solid waste resource utilization, and particularly relates to a method for promoting production of acetic acid by anaerobic fermentation of residual sludge by using choline chloride-urea deep eutectic solvent (DES). BACKGROUND
[0002] The residual sludge produced by the biological treatment unit of a municipal sewage treatment plant has a large output, contains a high concentration of pathogenic bacteria and heavy metals, and has a high treatment cost, which has become an environmental problem that needs to be solved urgently. However, the residual sludge is rich in organic matter, especially recyclable components such as proteins, and has good potential as a resource material. Under the promotion of the "carbon peak and carbon neutral" goal, the resource utilization of residual sludge has become one of the research hotspots. Among various resource recovery technologies, anaerobic fermentation, as an environmentally friendly and widely applicable biological conversion technology, has attracted much attention. Through a series of complex biochemical reactions such as hydrolysis, acidification, acetic acid production, and methane production, the technology gradually converts the organic matter in the sludge into biogas.
[0003] Compared with methane, short-chain fatty acids (SCFAs) have higher market value and are more convenient and safe in storage and transportation. SCFAs are widely used, not only as an alternative carbon source for denitrification and phosphorus removal in the wastewater treatment process, but also as an important precursor for the synthesis of bioplastics, biodiesel, and other high-value chemicals. Recycling SCFAs to realize carbon source reuse helps to reduce greenhouse gas emissions and promote the "zero-carbon" operation of sewage treatment plants. However, the widespread presence of extracellular polymeric substances in sludge forms a dense barrier, which seriously hinders the hydrolysis and release of organic matter, and is a fundamental bottleneck that restricts the improvement of anaerobic fermentation acid production efficiency. In recent years, mechanical, thermal, chemical, biological, and combined pretreatment methods have been widely used to promote sludge lysis and hydrolysis, and have been proven to be effective strategies for improving the efficiency of SCFAs production by anaerobic fermentation of residual sludge. However, these methods still face problems such as high operating cost, unstable treatment effect, and potential secondary pollution. In addition, the release efficiency of organic matter in sludge and its conversion rate to SCFAs in the anaerobic fermentation process still need to be further improved. To overcome the existing bottlenecks and promote the large-scale application of residual sludge anaerobic fermentation acid production technology in sewage treatment plants, and thus achieve efficient resource recovery, developing more economical, efficient, and environmentally friendly sludge pretreatment strategies is still a direction that needs to be explored.
[0004] The patent document CN2019103181957 discloses a method for pretreating straw with a new type of deep eutectic solvent and fermenting butanol. A new type of donor deep eutectic solvent is synthesized by using lactic acid as a hydrogen bond donor and ethylamine hydrochloride as a hydrogen bond acceptor, and then the straw is pretreated. Then cellulase is added for enzymatic hydrolysis, and the enzymatic hydrolysate is used as a carbon source for fermentation of butanol. The pretreatment of rice straw has a high hemicellulose removal rate and lignin removal rate. The whole process has the advantages of low cost, less waste, etc. And the straw hydrolysate after pretreatment can be used for fermentation to produce butanol. The patent document uses deep eutectic solvent to pretreat straw for butanol fermentation, and does not use choline chloride-urea deep eutectic solvent to promote anaerobic fermentation of residual sludge to produce acetic acid.
[0005] The patent document CN2023110226658 discloses a low-dose deep eutectic solvent-based efficient replacement of inorganic coagulant for sludge dewatering conditioning method, which comprises the following steps: mixing the hydrogen bond acceptor and the hydrogen bond donor sufficiently, and forming a transparent deep eutectic solvent under certain temperature conditions; adding the deep eutectic solvent in a certain proportion; stirring and mixing the deep eutectic solvent with plant or biochar, and forming a solid-liquid mixture after reacting for a certain time under certain temperature conditions; adding the solid-liquid mixture in a certain proportion; and adding an inorganic flocculant to continue conditioning the sludge. The green and environmentally friendly biodegradable deep eutectic solvent partially replaces the inorganic flocculant, and the conditioning process is simple and flexible, and has a good application prospect. The patent document discloses a deep eutectic solvent-based efficient replacement of inorganic coagulant for sludge dewatering conditioning, and does not use choline chloride-urea deep eutectic solvent to promote anaerobic fermentation of residual sludge to produce acetic acid. SUMMARY
[0006] To solve the above technical problems, the present application provides a method for promoting anaerobic fermentation of residual sludge to produce acetic acid by using choline chloride-urea deep eutectic solvent. The method uses a deep eutectic solvent synthesized from choline chloride and urea as a pretreatment agent to strengthen the anaerobic fermentation process of residual sludge, so as to achieve efficient production of short-chain fatty acids, especially acetic acid. The method is simple, low-cost and efficient, and the product can be directly used as a high-quality electron donor for the denitrification process in wastewater treatment plants, achieving the dual goals of sludge disposal and resource utilization.
[0007] To solve the above technical problems, the present application provides a method for promoting anaerobic fermentation of residual sludge to produce acetic acid by using choline chloride-urea deep eutectic solvent. The method uses a deep eutectic solvent synthesized from choline chloride and urea as a pretreatment agent to strengthen the anaerobic fermentation process of residual sludge, so as to achieve efficient production of short-chain fatty acids, especially acetic acid. The method is simple, low-cost and efficient, and the product can be directly used as a high-quality electron donor for the denitrification process in wastewater treatment plants, achieving the dual goals of sludge disposal and resource utilization.
[0008] The method for promoting the production of acetic acid by anaerobic fermentation of residual sludge by using choline chloride-urea deep eutectic solvent comprises the following specific steps: Step S1, treatment of residual sludge: the settling time of the residual sludge is 24 h, and the concentrated sludge is obtained after skimming the supernatant, and the suspended solid concentration of the concentrated sludge is controlled to be between 18-20 g / L; Step S2, preparation of choline chloride-urea deep eutectic solvent: choline chloride and urea with a molar ratio of 1:2 are placed in a reaction container, and the mixture is continuously stirred and heated at 80 DEG C until a uniform, clear and colorless liquid is formed, which is the choline chloride-urea deep eutectic solvent; Step S3, fermentation: the choline chloride-urea deep eutectic solvent is added to the concentrated sludge and mixed uniformly, and anaerobic fermentation is carried out under anaerobic conditions, and a short-chain fatty acid solution is obtained by centrifugation, the yield of short-chain fatty acid is as high as 8973.84 mg COD / L, and the proportion of acetic acid is as high as 77%, the anaerobic fermentation conditions are: fermentation temperature 33-35 DEG C, rotation speed 150-180 r / min, fermentation time 14 d, fermentation environment nitrogen environment, and the dosage of the deep eutectic solvent is 0.2-1.0 g of choline chloride-urea deep eutectic solvent per gram of suspended solid.
[0009] Compared with the prior art, the present application has the following advantages and beneficial effects: The present application provides a method for producing acetic acid by anaerobic fermentation of residual sludge using a deep eutectic solvent composed of choline chloride and urea, which can effectively promote the rupture of sludge cell wall and the hydrolysis of organic matter through pretreatment of residual sludge by the DES system, thereby significantly increasing the yield of SCFAs and specifically enhancing the proportion of acetic acid in the products. At the same time, this method can greatly improve the conversion efficiency of organic matter and effectively shorten the anaerobic fermentation period. After using this method, the yield of SCFAs can reach 8973.84 mg COD / L, and the proportion of acetic acid is as high as 77%, which is much higher than the level of 3000-5000 mg COD / L usually obtained by existing pretreatment methods.
[0010] The DES system used in the present application is composed of choline chloride and urea, which has the advantages of easy availability, low cost and good environmental compatibility. Among them, choline chloride, as a mild hydrogen bond acceptor, has a lower cost than most conventional chemical pretreatment reagents and good environmental compatibility; urea, as a hydrogen bond donor, is widely available and economical. Both of them have good biodegradability and can be utilized by microorganisms in the subsequent fermentation process, thereby avoiding secondary pollution from the source and ensuring the greenness and economy of the entire pretreatment and fermentation process.
[0011] This invention achieves efficient dissolution and targeted conversion of organic components (such as proteins and polysaccharides) in sludge through DES pretreatment. This process not only significantly increases the total yield of SCFAs and the selectivity of acetic acid within them, but also drastically shortens the fermentation cycle required to achieve optimal acid production, thereby powerfully promoting the reduction and resource utilization of excess sludge. Based on the comprehensive advantages of this DES system in terms of raw material cost, treatment efficiency, and environmental compatibility, this technical solution demonstrates outstanding feasibility and significant economic and environmental benefits in large-scale industrial applications. Attached Figure Description
[0012] Figure 1 A schematic diagram illustrating the effect of DES addition on the yield and composition of short-chain fatty acids. Detailed Implementation
[0013] The following examples further illustrate the above-described content of the present invention, but it should not be construed as limiting the scope of the subject matter of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention.
[0014] The method for preparing residual sludge used in the following experiment is as follows: after settling the residual sludge from the wastewater treatment plant, the supernatant is skimmed off to obtain concentrated sludge. The total suspended solids (SS) concentration of the concentrated sludge is controlled between 18 and 20 g / L.
[0015] The synthesis method of DES used in the following experiment is as follows: choline chloride and urea are mixed in a molar ratio of 1:2 and heated and stirred in an 80°C water bath until a homogeneous and stable transparent liquid is formed.
[0016] The anaerobic fermentation conditions are as follows: The reactor used for anaerobic fermentation to produce acid is a serum bottle with an effective volume of 250 mL (sealed with a rubber cap), containing 200 mL of concentrated sludge with a sludge concentration of 18.37 g / L. The mixing method is water bath shaking, with the temperature controlled at 35℃ and the rotation speed at 150 r / min. Example 1
[0017] (1) Add 0.2 g / g SS of DES to the anaerobic reactor, purge with nitrogen for 5 minutes to remove oxygen and create an anaerobic environment, then seal and place in a water bath shaker for anaerobic fermentation for 14 days. During the fermentation process, collect the sludge fermentation liquid on days 1, 2, 3, 4, 5, 6, 8, 10, 12 and 14 respectively.
[0018] (2) The sludge fermentation liquid was separated into solid and liquid by centrifugation (speed of 8000 rpm, centrifugation temperature of 4℃) to obtain a supernatant containing short-chain fatty acids.
[0019] (3) The total amount of SCFAs in the fermentation broth was determined by gas chromatography. The total amount of SCFAs gradually decreased with the extension of fermentation time. The maximum SCFAs yield obtained on the third day of fermentation was 4661.51 mg COD / L, of which acetic acid was 2712.72 mg COD / L, accounting for 58.19% of the total amount of SCFAs. Example 2
[0020] (1) Add 0.4 g / g SS of DES to the anaerobic reactor, purge with nitrogen for 5 minutes to remove oxygen and create an anaerobic environment, then seal and place in a water bath shaker for anaerobic fermentation for 14 days. During the fermentation process, collect sludge fermentation liquid on days 1, 2, 3, 4, 5, 6, 8, 10, 12 and 14 respectively.
[0021] (2) The sludge fermentation liquid was separated into solid and liquid by centrifugation (speed of 8000 rpm, centrifugation temperature of 4℃) to obtain a supernatant containing short-chain fatty acids.
[0022] (3) The total amount of SCFAs in the fermentation broth was determined by gas chromatography. The total amount of SCFAs tended to stabilize as the fermentation time increased. The maximum SCFAs yield obtained on the 8th day of fermentation was 6785.61 mg COD / L, of which acetic acid was 4501.16 mg COD / L, accounting for 66.33% of the total amount of SCFAs. Example 3
[0023] (1) Add 0.6 g / g SS of DES to the anaerobic reactor, purge with nitrogen for 5 minutes to remove oxygen and create an anaerobic environment, then seal and place in a water bath shaker for anaerobic fermentation for 14 days. During the fermentation process, collect sludge fermentation liquid on days 1, 2, 3, 4, 5, 6, 8, 10, 12 and 14 respectively.
[0024] (2) The sludge fermentation liquid was separated into solid and liquid by centrifugation (speed of 8000 rpm, centrifugation temperature of 4℃) to obtain a supernatant containing short-chain fatty acids.
[0025] (3) The total amount of SCFAs in the fermentation broth was determined by gas chromatography. The total amount of SCFAs tended to stabilize as the fermentation time increased. The maximum SCFAs yield obtained on the 8th day of fermentation was 8973.84 mg COD / L, of which acetic acid was 6922.20 mg COD / L, accounting for 77.14% of the total amount of SCFAs. Example 4
[0026] (1) Add 0.8 g / g SS of DES to the anaerobic reactor, purge with nitrogen for 5 minutes to remove oxygen and create an anaerobic environment, then seal and place in a water bath shaker for anaerobic fermentation for 14 days. During the fermentation process, collect sludge fermentation liquid on days 1, 2, 3, 4, 5, 6, 8, 10, 12 and 14 respectively.
[0027] (2) The sludge fermentation liquid was separated into solid and liquid by centrifugation (speed of 8000 rpm, centrifugation temperature of 4℃) to obtain a supernatant containing short-chain fatty acids.
[0028] (3) The total amount of SCFAs in the fermentation broth was determined by gas chromatography. The total amount of SCFAs tended to stabilize as the fermentation time increased. The maximum SCFAs yield obtained on the 8th day of fermentation was 7098.42 mg COD / L, of which acetic acid was 5245.12 mg COD / L, accounting for 73.89% of the total amount of SCFAs. Example 5
[0029] (1) Add 1.0 g / g SS of DES to the anaerobic reactor, purge with nitrogen for 5 minutes to remove oxygen and create an anaerobic environment, then seal and place in a water bath shaker for anaerobic fermentation for 14 days. During the fermentation process, collect sludge fermentation liquid on days 1, 2, 3, 4, 5, 6, 8, 10, 12 and 14 respectively.
[0030] (2) The sludge fermentation liquid was separated into solid and liquid by centrifugation (speed of 8000 rpm, centrifugation temperature of 4℃) to obtain a supernatant containing short-chain fatty acids.
[0031] (3) The total amount of SCFAs in the fermentation broth was determined by gas chromatography. The total amount of SCFAs tended to stabilize as the fermentation time increased. The maximum SCFAs yield obtained on the 8th day of fermentation was 4503.04 mg COD / L, of which acetic acid was 3251.76 mg COD / L, accounting for 72.21% of the total amount of SCFAs.
[0032] Comparative Example 1 (1) Nitrogen gas was introduced into the anaerobic reactor for 5 minutes to remove oxygen and create an anaerobic environment. Then the reactor was sealed and placed in a water bath shaker for anaerobic fermentation for 14 days. During the fermentation process, the sludge fermentation liquid was collected on days 1, 2, 3, 4, 5, 6, 8, 10, 12 and 14.
[0033] (2) The sludge fermentation liquid was separated into solid and liquid by centrifugation (speed of 8000 rpm, centrifugation temperature of 4℃) to obtain a supernatant containing short-chain fatty acids.
[0034] (3) The total amount of SCFAs in the fermentation broth was determined by gas chromatography. The total amount of SCFAs gradually decreased with the extension of fermentation time. The maximum SCFAs yield obtained on the 10th day of fermentation was only 439.65 mg COD / L, of which acetic acid was 248.99 mg COD / L, accounting for 56.63% of the total SCFAs. The total yield of SCFAs and the proportion of acetic acid were both lower than those in the 5 examples, and the fermentation time to reach the maximum SCFAs yield was longer than that in the 5 examples.
[0035] The results of Examples 1-5 and Comparative Example 1 demonstrate that the method proposed in this invention, which uses a choline chloride-urea eutectic solvent to enhance the production of SCFAs from anaerobic fermentation of waste sludge, can significantly increase the yield of SCFAs in the fermentation broth by 10.24-20.41 times under the same operating conditions, while simultaneously increasing the proportion of acetic acid in the product by 2.76%-36.21%. This method effectively enhances the SCFAs generation capacity during anaerobic fermentation of sludge, providing an efficient and feasible enhancement technology for the resource utilization of sludge.
[0036] The above embodiments describe the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are only illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from the scope of the principles of the present invention, and all such changes and modifications fall within the protection scope of the present invention.
Claims
1. A method for promoting anaerobic fermentation of waste sludge to produce acetic acid using a choline chloride-urea eutectic solvent, characterized in that... The specific process is as follows: the residual sludge from the sewage treatment plant is settled, the supernatant is skimmed off to obtain concentrated sludge, choline chloride-urea eutectic solvent is added to the concentrated sludge and mixed evenly, and anaerobic fermentation is carried out under anaerobic conditions. Centrifugation is then used to obtain a solution containing short-chain fatty acids.
2. The method for promoting anaerobic fermentation of residual sludge to produce acetic acid using a choline chloride-urea eutectic solvent according to claim 1, characterized in that... The specific steps are as follows: Step S1, Treatment of excess sludge: The settling time of excess sludge is 24 hours. After skimming off the supernatant, concentrated sludge is obtained. The suspended solids concentration of the concentrated sludge is controlled between 18 and 20 g / L. Step S2, Preparation of choline chloride-urea eutectic solvent: Choline chloride and urea in a molar ratio of 1:2 are placed in a reaction vessel and continuously stirred and heated at 80°C until a homogeneous, clear, colorless liquid is formed, which is the choline chloride-urea eutectic solvent. Step S3, Fermentation: Add choline chloride-urea eutectic solvent to the concentrated sludge and mix well. Perform anaerobic fermentation under anaerobic conditions. Centrifuge to obtain a solution containing short-chain fatty acids. The yield of short-chain fatty acids is as high as 8973.84 mg COD / L, of which acetic acid accounts for as high as 77%. The anaerobic fermentation conditions are: fermentation temperature 33~35℃, rotation speed 150~180 r / min, fermentation time 14d, fermentation environment is nitrogen environment, and the dosage of eutectic solvent is 0.2~1.0g of choline chloride-urea eutectic solvent per gram of suspended solids.
3. The method for promoting anaerobic fermentation of residual sludge to produce acetic acid using a choline chloride-urea eutectic solvent according to claim 1, characterized in that... The specific steps are as follows: Step S1, Treatment of excess sludge: The settling time of excess sludge is 24 hours. After skimming off the supernatant, concentrated sludge is obtained. The suspended solids concentration of the concentrated sludge is controlled between 18 and 20 g / L. Step S2, Preparation of choline chloride-urea eutectic solvent: Choline chloride and urea in a molar ratio of 1:2 are placed in a reaction vessel and continuously stirred and heated at 80°C until a homogeneous, clear, colorless liquid is formed, which is the choline chloride-urea eutectic solvent. Step S3, Fermentation: Add choline chloride-urea eutectic solvent to the concentrated sludge and mix thoroughly. The dosage of the eutectic solvent is 0.6g of choline chloride-urea eutectic solvent per gram of suspended solids. Anaerobic fermentation is carried out under anaerobic conditions. Centrifugation yields a solution containing short-chain fatty acids. The yield of short-chain fatty acids is as high as 8973.84mg COD / L, of which acetic acid is 6922.20mg COD / L, accounting for 77.14% of the total short-chain fatty acids. The anaerobic fermentation conditions are: fermentation temperature 35℃, rotation speed 150r / min, fermentation time 14d, and fermentation environment is a nitrogen environment.