Method for promoting short-chain fatty acid production in anaerobic digestion of residual sludge by microwave coupling with ionic liquid

Abstract

This invention discloses a method for promoting the anaerobic digestion of waste sludge to produce short-chain fatty acids using microwave-coupled ionic liquids. The method includes the following steps: adding an ionic liquid to the waste sludge and heating it in a microwave to obtain treated waste sludge; inputting the treated waste sludge into an anaerobic digester and adding untreated waste sludge for anaerobic fermentation; recovering high-quality short-chain fatty acids by recycling the fermentation broth during the acid production stage of anaerobic fermentation. This method, through the synergistic effect of microwaves and ionic liquids, significantly improves the solubility of organic matter in the sludge and promotes the efficient and targeted acid production of short-chain fatty acids during sludge fermentation. Compared with traditional sludge pretreatment methods, this invention has higher treatment efficiency and lower energy consumption.

Description

Technical Field

[0001] This invention relates to the field of solid waste treatment, disposal, and resource utilization technology, and in particular to a method for promoting the anaerobic digestion of residual sludge to produce short-chain fatty acids using microwave-coupled ionic liquids. Background Technology

[0002] With the continuous advancement of urbanization and the increase in industrial wastewater discharge, the treatment and resource utilization of excess sludge has become a major challenge in current environmental governance. Statistics show that millions of tons of sludge are produced globally each year, and this sludge mostly contains large amounts of organic matter, heavy metals, and pathogenic microorganisms. Without effective treatment, it can cause serious environmental pollution. Traditional sludge treatment methods, including anaerobic fermentation, aerobic digestion, composting, and incineration, while able to reduce sludge volume and render it harmless to some extent, generally face problems such as low acid production efficiency, long treatment cycles, high energy consumption, and secondary pollution. The treatment effect is often unsatisfactory, especially when treating high-concentration or highly viscous sludge.

[0003] In recent years, microwave pretreatment technology, as an emerging physical method, has received widespread attention for its application in sludge treatment. Microwave heating directly acts on the material through electromagnetic waves, rapidly generating a thermal effect. This not only accelerates the evaporation of water in the sludge but also promotes the decomposition of organic matter and cell rupture, thereby improving the efficiency of anaerobic fermentation. However, using microwave technology alone often suffers from problems such as high energy consumption, uneven heating, and limited effectiveness in treating recalcitrant organic matter in sludge.

[0004] Ionic liquids have become a research hotspot in the field of sludge pretreatment in recent years due to their high solubility, low volatility, and environmental friendliness. Compared with traditional solvents, ionic liquids have a stronger ability to dissolve organic matter and can effectively degrade recalcitrant organic matter and extracellular polymers in sludge. Furthermore, the low volatility of ionic liquids makes them a green and environmentally friendly option, reducing pollution. However, using ionic liquids alone to treat sludge often requires long processing times and high energy consumption. Therefore, improving the efficiency of ionic liquid use and the treatment effect on sludge remains a key challenge for this technology.

[0005] Therefore, it is of great significance to develop a waste sludge treatment technology with short processing time, low energy consumption, and high processing efficiency. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention proposes an innovative method for treating waste sludge using microwave-coupled ionic liquids. Through the synergistic effect of microwaves and ionic liquids, the dissolution efficiency of the ionic liquid can be effectively improved, promoting the dissolution of organic matter and cell rupture in the waste sludge. Simultaneously, it can regulate microbial metabolism, thereby significantly improving the efficiency of anaerobic fermentation of the sludge. Furthermore, under microwave action, ions in the ionic liquid achieve rapid energy transfer through both ionic conduction and dipole polarization mechanisms, promoting efficient energy utilization and reducing energy loss. In addition, the ionic liquid can enhance the uniformity of microwave heating, improving the treatment effect of waste sludge and providing a more efficient and low-energy-consumption technical path for sludge resource utilization, harmlessness, and volume reduction.

[0007] Specifically, the method of the present invention for promoting the anaerobic digestion of excess sludge to produce short-chain fatty acids using microwave-coupled ionic liquids includes the following steps: Step S1: Add ionic liquid to the remaining sludge; Step S2: Place the sludge obtained in step S1 in a microwave oven and heat it to obtain the treated residual sludge; Step S3: Input the treated residual sludge into the anaerobic digester and add untreated residual sludge for anaerobic fermentation; Step S4: In the anaerobic fermentation acid production stage, high-quality short-chain fatty acids are recovered by recycling the fermentation broth.

[0008] This invention utilizes the rapid heating and "hot spot" effect of microwaves, combined with the unique dissolving and destructive capabilities of ionic liquids for biomass components, to synergistically break down the complex structure of residual sludge. Microwave radiation instantly heats the polar molecules and water in the sludge, generating a strong thermal effect and mechanical shear force, effectively destroying sludge flocs and microbial cell walls. Ionic liquids, as green solvents, allow their anions and cations to interact with extracellular polymers (EPS) and lipids and proteins on cell membranes in the sludge, further promoting the release and solubilization of organic matter. The coupling of these two processes produces a synergistic effect of "1+1>2," providing richer and more easily degradable substrates for acid-producing microorganisms in the subsequent anaerobic fermentation stage. Furthermore, the residual sludge in step S1 is the residual sludge or returned sludge generated from the secondary sedimentation tank of the sewage treatment plant.

[0009] Furthermore, in step S1, the ionic liquid is selected from one of [Emim]OTF, [Bmim]PF6, [Emim]PF6, and [Emim]Br.

[0010] Furthermore, in step S1, the dosage of ionic liquid is 0.01~0.5 g / g VSS (calculated per gram of volatile suspended solids sludge).

[0011] Furthermore, in step S1, after adding the ionic liquid to the remaining sludge, the mixture is stirred at 50-400 rpm for 0.5-3 hours.

[0012] Furthermore, in step S2, the microwave power is 200-700W, and the heating time is 1-15 minutes.

[0013] Furthermore, the temperature for anaerobic fermentation in step S2 is 36-38℃.

[0014] Furthermore, in step S3, the volume ratio of treated residual sludge to untreated residual sludge is 4:1 to 8:1.

[0015] Furthermore, the anaerobic fermentation time in step S3 is 3-21 days.

[0016] Untreated residual sludge refers to the residual sludge or returned sludge produced in the secondary sedimentation tank of a wastewater treatment plant. After fermentation, the fermentation broth is separated by centrifugation or filtration. Short-chain fatty acids in the fermentation broth can be recovered and purified using methods such as distillation, extraction, or membrane separation.

[0017] Compared with the prior art, the present invention has the following advantages: 1. The method of promoting the anaerobic digestion of waste sludge to produce short-chain fatty acids using microwave-coupled ionic liquids of the present invention significantly improves the solubility of organic matter in sludge through the synergistic effect of microwaves and ionic liquids, thereby promoting the efficient and targeted production of short-chain fatty acids (SCFAs) during sludge fermentation. Compared with traditional sludge pretreatment methods, the present invention has higher treatment efficiency and lower energy consumption.

[0018] 2. The method of microwave-coupled ionic liquid to promote the anaerobic digestion of waste sludge to produce short-chain fatty acids of the present invention can more effectively destroy the EPS structure and microbial cells of sludge through the synergistic effect of microwave and ionic liquid, and significantly improve the dissolution rate and bioavailability of organic matter.

[0019] 3. This invention, through the pretreatment of adding ionic liquid to residual sludge and then heating it in microwave, alters the microenvironment and substrate composition of the fermentation system, selectively promoting the activity of functional microbial communities such as homoacetic acid-producing bacteria, thereby increasing the proportion of acetic acid in the product and enhancing the resource value of the product.

[0020] 4. Compared with single physical or chemical pretreatment, the microwave-coupled ionic liquid method in this invention is more flexible in control, and the pretreatment effect can be optimized by adjusting microwave parameters and ionic liquid type / dosage.

[0021] 5. The method of this invention for promoting anaerobic digestion of waste sludge to produce short-chain fatty acids using microwave-coupled ionic liquids converts waste sludge into high-value-added short-chain fatty acids (which can be used as a carbon source for biological nitrogen and phosphorus removal or as a chemical raw material), meeting the treatment goals of sludge reduction, stabilization, and resource utilization. Attached Figure Description

[0022] Figure 1 This refers to the dissolved chemical oxygen demand (COD) of the residual sludge lysing and pyrolysis in Examples 1 and Comparative Examples 1-4. Figure 2 This refers to the situation of acid production after sludge treatment in Examples 2, 1, and 5-7. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] It should be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0025] Unless otherwise specified, the raw materials or processing techniques used in the following embodiments and comparative examples are conventional commercially available raw materials or conventional processing techniques in the art.

[0026] The residual sludge used in the following examples and comparative examples was taken from the secondary sedimentation tank of a municipal wastewater treatment plant in Shanghai.

[0027] The models of instruments and equipment used in the following embodiments and comparative examples are as follows: Microwave Oven P70D20TL-D4, manufactured by Guangdong Galanz Microwave Home Appliances Manufacturing Co., Ltd. Magnetic stirrer 84-1A, Shanghai Sile.

[0028] Example 1 This embodiment provides a method for promoting the anaerobic digestion of excess sludge to produce short-chain fatty acids using microwave-coupled ionic liquids, comprising the following steps: Step S1: The residual sludge from the secondary sedimentation tank of the wastewater treatment plant is used as the treatment object. The total solids concentration of the residual sludge is 12 ± 0.5 g / L, and the amount of residual sludge to be treated is 400 mL. [Emim]OTF ionic liquid is added to the residual sludge at a dosage of 0.05 g / gVSS. After adding the ionic liquid, the mixture is stirred at 200 rpm for 2 hours. Step S2: Place the sludge obtained in step S1 in a microwave oven and heat it for 15 minutes at a microwave power of 460W to obtain the treated residual sludge. Step S3: Input the treated residual sludge into an anaerobic digester for anaerobic fermentation, and anaerobic fermentation for 5 days in a constant temperature environment of 37 ℃. Step S4: In the anaerobic fermentation acid production stage, high-quality short-chain fatty acids are recovered by recycling the fermentation broth.

[0029] Comparative Example 1 This comparative example provides a method for producing short-chain fatty acids from anaerobic digestion of waste sludge. The specific steps are as follows: Waste sludge from the secondary sedimentation tank of a wastewater treatment plant is used as the treatment object. The total solids concentration of the waste sludge is 12 ± 0.5 g / L, and the waste sludge treatment volume is 400 mL. The waste sludge is fed into an anaerobic digester for anaerobic fermentation. Anaerobic fermentation is carried out in a constant temperature environment of 37 ℃ for 5 days. During the acid production stage of anaerobic fermentation, high-quality short-chain fatty acids are recovered by recycling the fermentation liquid.

[0030] Comparative Example 2 This comparative example also provides a method for producing short-chain fatty acids from the anaerobic digestion of excess sludge, the specific steps of which are as follows: Step S1: The residual sludge from the secondary sedimentation tank of the wastewater treatment plant is used as the treatment object. The total solids concentration of the residual sludge is 12 ± 0.5 g / L, and the amount of residual sludge to be treated is 400 mL. [Emim]OTF ionic liquid is added to the residual sludge at a dosage of 0.05 g / gVSS. After adding the ionic liquid, the mixture is stirred at 200 rpm for 2 hours. Step S2: The remaining sludge after adding ionic liquid is fed into an anaerobic digester for anaerobic fermentation, and anaerobic fermentation is carried out for 5 days in a constant temperature environment of 37 ℃. Step S3: In the anaerobic fermentation acid production stage, high-quality short-chain fatty acids are recovered by recycling the fermentation broth.

[0031] Comparative Example 3 This comparative example also provides a method for producing short-chain fatty acids from the anaerobic digestion of excess sludge, the specific steps of which are as follows: Step S1: The residual sludge from the secondary sedimentation tank of the wastewater treatment plant is used as the treatment target. The total solids concentration of the residual sludge is 12 ± 0.5 g / L, and the amount of residual sludge to be treated is 400 mL. Step S2: Place the sludge in a microwave oven and heat it for 15 minutes at a microwave power of 460W to obtain the treated residual sludge. Step S3: Input the treated residual sludge into an anaerobic digester for anaerobic fermentation, and anaerobic fermentation for 5 days in a constant temperature environment of 37 ℃. Step S4: In the anaerobic fermentation acid production stage, high-quality short-chain fatty acids are recovered by recycling the fermentation broth.

[0032] Comparative Example 4 This comparative example provides a method for promoting the anaerobic digestion of excess sludge to produce short-chain fatty acids using microwave-coupled ionic liquids, comprising the following steps: Step S1: The residual sludge from the secondary sedimentation tank of the sewage treatment plant is used as the treatment object. The total solids concentration of the residual sludge is 12 ± 0.5 g / L, the amount of residual sludge to be treated is 400 mL, and the sludge is heated in a microwave with a power of 460w for 15 minutes. Step S2: Add [Emim]OTF ionic liquid to the remaining sludge after step S1. The dosage of the ionic liquid is 0.05 g / gVSS. After adding the ionic liquid, stir at 200 rpm for 2 hours to obtain the treated remaining sludge. Step S3: Input the treated residual sludge into an anaerobic digester for anaerobic fermentation, and anaerobic fermentation for 5 days in a constant temperature environment of 37 ℃. Step S4: In the anaerobic fermentation acid production stage, high-quality short-chain fatty acids are recovered by recycling the fermentation broth.

[0033] Measuring dissolved chemical oxygen demand (SCOD) can confirm that the combined use of microwaves and ionic liquids promotes the lysis of residual sludge cells. This is because once sludge cells experience membrane damage, leakage of intracellular substances, or depolymerization / dissolution of extracellular polymeric substances (EPS), organic matter that was originally in a solid or bound state will be transferred to the liquid phase, directly resulting in an increase in SCOD. From a microscopic perspective, the polarization oscillation and rapid internal and external heating of microwaves weaken the structural stability of cell membranes and EPS, generating thermal stress and local rupture. Ionic liquids, on the other hand, can further promote increased cell membrane permeability and the dissolution of macromolecules such as proteins and polysaccharides by weakening hydrogen bonds, disrupting hydrophobic interactions, reducing interfacial stability, and enhancing permeability. Therefore, when SCOD increases significantly, it means that more poorly soluble organic matter is released into the aqueous phase, indirectly proving that lysis is enhanced.

[0034] SCOD was determined using the national standard potassium dichromate method: The sludge sample was first centrifuged, and the supernatant was collected and filtered through a membrane to obtain the dissolved phase sample. Then, digestion was performed according to the "Determination of Chemical Oxygen Demand in Water - Dichromate Method" (GB 11914-89). This involved using potassium dichromate as the oxidant under strong acid conditions, adding a sulfuric acid-silver sulfate digestion solution, and masking chloride ion interference with mercuric sulfate. Digestion was carried out at 200℃ for approximately 2 hours. After cooling, the remaining potassium dichromate was back-titrated with ferrous ammonium sulfate standard solution, and the endpoint was determined using ferriin indicator. The instruments used typically included a COD digester (SH-101), manufactured by Shanghai Jinghong Experimental Equipment Co., Ltd.

[0035] This application demonstrates, by measuring the concentration of dissolved chemical oxygen demand (COD), that the combined use of microwave and ionic liquid can promote the lysis and decomposition of excess sludge. Results are as follows: Figure 1As shown, the dissolved chemical oxygen demand (COD) concentrations of the residual sludge, from lowest to highest, are as follows: Comparative Example 1 ( Figure 1 (Blank bar chart in the middle), Comparative Example 2 ( Figure 1 (Bar chart of ionic liquids), Comparative Example 3 () Figure 1 The bar chart of medium microwave), Comparative Example 4 ( Figure 1 (Bar chart of microwave + ionic liquid), Example 1 () Figure 1 The bar chart shows the effects of microwave / ionic liquid treatment (where microwave / ionic liquid indicates the addition of ionic liquid followed by microwave treatment). The chart shows that the dissolved chemical oxygen demand (COD) concentration of the untreated sludge was lowest in Comparative Example 1 (no treatment required), indicating minimal release of soluble organic matter. Both ionic liquid and microwave treatments promoted cell lysis and intracellular organic matter release in the untreated sludge to varying degrees. The COD concentrations in Comparative Examples 2 and 3 were higher than in Comparative Example 1. This is because ionic liquids can weaken the sludge's structural stability and enhance organic matter dissolution by disrupting hydrogen bonds, hydrophobic interactions, and electrostatic interactions in cell membranes and extracellular polymers. Microwave treatments, on the other hand, generate thermal stress through rapid oscillation of polarized molecules and uneven internal and external heating, causing the sludge to lyse and release organic matter. Cell membrane rupture promotes an increase in SCOD, indicating that both ionic liquids and microwaves can enhance sludge lysis. Comparative Example 4 involved microwave heating of the remaining sludge before adding ionic liquid. The concentration of dissolved chemical oxygen demand in the remaining sludge in this method was lower than that in Example 1. Example 1 involved adding ionic liquid to the remaining sludge before microwave heating. The reason is that after the ionic liquid acts on the sludge first, it can destroy the cell membrane and EPS structure and improve the system's absorption and conversion efficiency of microwaves. This makes it easier for microwave heating to form high temperature, high pressure and local stress inside the cells, thereby more fully promoting the release of organic matter. This shows that the treatment sequence of "ionic liquid first, then microwave" has a stronger synergistic lysis effect and can more effectively increase the release of SCOD in the remaining sludge.

[0036] In Example 1, after adding ionic liquid to the waste sludge and then heating it with microwave, the dissolved chemical oxygen demand (COD) concentration of the waste sludge was 2303.6 mg / L, which was 22.36 times that of the untreated waste sludge (Comparative Example 1). This indicates that the combination of ionic liquid pretreatment and microwave heating can significantly enhance the cytolysis and release of intracellular organic matter from the waste sludge, and the two have a significant synergistic effect.

[0037] Example 2 This embodiment provides a method for promoting the anaerobic digestion of excess sludge to produce short-chain fatty acids using microwave-coupled ionic liquids, comprising the following steps: Step S1: The residual sludge from the secondary sedimentation tank of the wastewater treatment plant is used as the treatment object. The total solids concentration of the residual sludge is 12 ± 0.5 g / L, and the amount of residual sludge to be treated is 400 mL. [Emim]OTF ionic liquid is added to the residual sludge at a dosage of 0.05 g / gVSS. After adding the ionic liquid, the mixture is stirred at 200 rpm for 2 hours. Step S2: Place the sludge obtained in step S1 in a microwave oven and heat it for 15 minutes at a microwave power of 460W to obtain the treated residual sludge. Step S3: Input the treated residual sludge into the anaerobic digester and add untreated residual sludge for anaerobic fermentation. Anaerobic fermentation is carried out in a constant temperature environment of 37 ℃ for 5 days. The volume ratio of treated residual sludge to untreated residual sludge is 4:1. Step S4: In the anaerobic fermentation acid production stage, high-quality short-chain fatty acids are recovered by recycling the fermentation broth.

[0038] Comparative Example 5 This comparative example also provides a method for producing short-chain fatty acids from the anaerobic digestion of excess sludge, the specific steps of which are as follows: Step S1: The residual sludge from the secondary sedimentation tank of the wastewater treatment plant is used as the treatment object. The total solids concentration of the residual sludge is 12 ± 0.5 g / L, and the amount of residual sludge to be treated is 400 mL. [Emim]OTF ionic liquid is added to the residual sludge at a dosage of 0.05 g / gVSS. After adding the ionic liquid, the mixture is stirred at 200 rpm for 2 hours. Step S2: Input the remaining sludge after adding ionic liquid into the anaerobic digester, and add untreated remaining sludge for anaerobic fermentation. Anaerobic fermentation is carried out in a constant temperature environment of 37 ℃ for 5 days. The volume ratio of treated remaining sludge to untreated remaining sludge is 4:1. Step S3: In the anaerobic fermentation acid production stage, high-quality short-chain fatty acids are recovered by recycling the fermentation broth.

[0039] Comparative Example 6 This comparative example also provides a method for producing short-chain fatty acids from the anaerobic digestion of excess sludge, the specific steps of which are as follows: Step S1: The residual sludge from the secondary sedimentation tank of the wastewater treatment plant is used as the treatment target. The total solids concentration of the residual sludge is 12 ± 0.5 g / L, and the amount of residual sludge to be treated is 400 mL. Step S2: Place the sludge in a microwave oven and heat it for 15 minutes at a microwave power of 460w to obtain the remaining sludge after treatment. Step S3: Input the treated residual sludge into the anaerobic digester and add untreated residual sludge for anaerobic fermentation. Anaerobic fermentation is carried out in a constant temperature environment of 37 ℃ for 5 days. The volume ratio of treated residual sludge to untreated residual sludge is 4:1. Step S4: In the anaerobic fermentation acid production stage, high-quality short-chain fatty acids are recovered by recycling the fermentation broth.

[0040] Comparative Example 7 This comparative example provides a method for promoting the anaerobic digestion of excess sludge to produce short-chain fatty acids using microwave-coupled ionic liquids, comprising the following steps: Step S1: The residual sludge from the secondary sedimentation tank of the sewage treatment plant is used as the treatment object. The total solids concentration of the residual sludge is 12 ± 0.5 g / L, the amount of residual sludge to be treated is 400 mL, and the sludge is heated in a microwave with a power of 460w for 15 minutes. Step S2: Add [Emim]OTF ionic liquid to the remaining sludge after step S1. The dosage of the ionic liquid is 0.05 g / gVSS. After adding the ionic liquid, stir at 200 rpm for 2 hours to obtain the treated remaining sludge. Step S3: Input the treated residual sludge into the anaerobic digester and add untreated residual sludge for anaerobic fermentation. Anaerobic fermentation is carried out in a constant temperature environment of 37 ℃ for 5 days. The volume ratio of treated residual sludge to untreated residual sludge is 4:1. Step S4: In the anaerobic fermentation acid production stage, high-quality short-chain fatty acids are recovered by recycling the fermentation broth.

[0041] To ensure an anaerobic environment throughout the anaerobic fermentation process, N2 was introduced into the anaerobic digester after each sampling in the above embodiments. The amount of short-chain fatty acids produced during fermentation was determined (after sludge sampling, centrifugation at 8000 rpm for 15 min was performed, and an appropriate amount of supernatant was filtered through a 0.45 mm aqueous polyethersulfone membrane; since the detection limit is 200 mg / L, a 3% formic acid solution was used for dilution, and 2 mL of the sample was placed in a brown vial. Gas chromatography (GC-2018, supplier: Shimadzu Corporation, Japan) was used for analysis). This confirmed that the combination of microwave and ionic liquid can promote the anaerobic digestion of excess sludge to produce high-quality short-chain fatty acid resources.

[0042] like Figure 2 As shown, in the fermentation acid production stage of Examples 2, Comparative Example 1, and Comparative Examples 5-7, under the same reaction time conditions, the concentrations of recovered volatile fatty acids from low to high are as follows: Comparative Example 1 ( Figure 2 (blank lines in the text), Comparative Example 5 ( Figure 2 (Lines of medium ionic liquid), Comparative Example 6 () Figure 2 Microwave lines), Comparative Example 7 ( Figure 1 Microwave + Ionic Liquid Lines), Example 2 ( Figure 2 The graph shows the concentration of volatile fatty acids recovered under the same fermentation time when the sludge was not treated (Comparative Example 1). This indicates that the hydrolysis and acidification of organic matter in the untreated sludge were limited, resulting in insufficient substrate release and difficulty in providing a sufficient usable substrate for acid-producing bacteria. The concentration of volatile fatty acids recovered in Comparative Examples 5 and 6 was higher than that in Comparative Example 1. This is because ionic liquids can disrupt sludge flocs, cell membranes, and extracellular polymer structures, while microwaves can promote cell rupture and organic matter dissolution through rapid heating and thermal stress, thereby improving the accessibility of fermentable substrates. This suggests that either ionic liquids or microwaves alone can promote the fermentation of sludge-water... To deacidify and increase the yield of volatile fatty acids, Comparative Example 7 involved microwaving the remaining sludge before adding an ionic liquid. The concentration of volatile fatty acids recovered in this method was lower than that in Example 2. Example 2 involved adding an ionic liquid to the remaining sludge before microwaving. The reason for this is that ionic liquid pretreatment can weaken the structural stability of the sludge and improve the system's absorption efficiency of microwaves, making it easier for subsequent microwaves to act on the cells and further promote the release of organic matter. However, when microwaves are added first and then ionic liquids are added, the synergistic effect of cell disruption and substrate release is weaker. This indicates that the treatment sequence of "ionic liquid first, then microwave" is more conducive to strengthening the fermentation and acid production process of the remaining sludge and increasing the recovery of volatile fatty acids.

[0043] In Example 2, after adding ionic liquid to the waste sludge and then heating it with microwave, the maximum amount of short-chain fatty acids produced on the third day was 978.4 mg / L, which was 4.52 times that of the amount of short-chain fatty acids produced by anaerobic fermentation of untreated waste sludge (Comparative Example 1). This indicates that the combination of ionic liquid pretreatment and microwave heating can significantly promote the hydrolysis, acidification and short-chain fatty acid generation of organic matter in waste sludge, and has a significant synergistic effect on enhancing acid production during anaerobic fermentation.

[0044] Although the present invention has been illustrated and described with reference to preferred embodiments, those skilled in the art should understand that various changes and modifications can be made to the present invention without departing from the scope defined by the claims.

Claims

1. A method for promoting the anaerobic digestion of waste sludge to produce short-chain fatty acids using microwave-coupled ionic liquids, characterized in that, Includes the following steps: Step S1: Add ionic liquid to the remaining sludge; Step S2: Place the sludge obtained in step S1 in a microwave oven and heat it to obtain the treated residual sludge; Step S3: Input the treated residual sludge into the anaerobic digester and add untreated residual sludge for anaerobic fermentation; Step S4: In the anaerobic fermentation acid production stage, high-quality short-chain fatty acids are recovered by recycling the fermentation broth.

2. The method according to claim 1, characterized in that, The residual sludge in step S1 is the residual sludge or return sludge generated from the secondary sedimentation tank of the sewage treatment plant.

3. The method according to claim 1, characterized in that, In step S1, the ionic liquid is selected from one of [Emim]OTF, [Bmim]PF6, [Emim]PF6 and [Emim]Br.

4. The method according to claim 1, characterized in that, In step S1, the dosage of ionic liquid is 0.01~0.5 g / g VSS.

5. The method according to claim 1, characterized in that, In step S1, after adding the ionic liquid to the remaining sludge, stir at 50-400 rpm for 0.5-3 hours.

6. The method according to claim 1, characterized in that, In step S2, the microwave power is 200-700W and the heating time is 1-15 minutes.

7. The method according to claim 1, characterized in that, The temperature for anaerobic fermentation in step S2 is 36-38℃.

8. The method according to claim 1, characterized in that, In step S3, the volume ratio of treated residual sludge to untreated residual sludge is 4:1 to 8:

1.

9. The method according to claim 1, characterized in that, The anaerobic fermentation time in step S3 is 3-21 days.

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