Enhanced method for acid production from sludge based on synergistic degradation of melanoidins by thermal hydrolysis and potassium permanganate
By using a combined hot water hydrolysis and potassium permanganate treatment method, the problems of melanin inhibition and low organic matter release efficiency in sludge were solved, achieving efficient anaerobic fermentation of sludge to produce acid, and reducing treatment costs and environmental risks.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- XIANGTAN UNIV
- Filing Date
- 2025-04-07
- Publication Date
- 2026-06-26
AI Technical Summary
Existing technologies are unable to effectively address the inhibitory effect of melanoidins in sludge and the low efficiency of organic matter release, resulting in low acid production rates and long cycles during anaerobic fermentation of sludge. Furthermore, traditional pretreatment methods pose a risk of secondary pollution.
A combined treatment method of hot water hydrolysis and potassium permanganate was adopted. The physical barrier of sludge was destroyed by hot water hydrolysis under high temperature and pressure. Then, potassium permanganate selectively oxidized melanoidins and used manganese dioxide, an oxidation byproduct, as an electron transfer medium to promote the metabolism of acid-producing bacteria.
It significantly improved the yield and fermentation efficiency of short-chain fatty acids, shortened the fermentation cycle, reduced the inhibitory effect of melanoidins, and realized the resource utilization of manganese dioxide, avoiding secondary pollution.
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Figure CN120518293B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of sludge resource utilization and environmental protection technology, specifically relating to a method for enhancing the acid production performance of sludge anaerobic fermentation through hot water hydrolysis combined with potassium permanganate pretreatment. Background Technology
[0002] With accelerated urbanization and the widespread adoption of wastewater treatment facilities, the amount of residual sludge generated by wastewater treatment plants globally each year exceeds 100 million tons, and continues to grow at an average annual rate of 5%. Sludge is rich in organic matter, pathogens, and heavy metals; improper treatment can easily lead to secondary pollution (such as greenhouse gas emissions, soil acidification, and groundwater pollution), seriously threatening the ecological environment and human health. Traditional sludge disposal technologies (such as landfill, incineration, and composting) are increasingly unable to meet the demands of sustainable development due to high costs, resource waste, and large carbon emissions. Against this backdrop, sludge resource utilization technologies have become a research hotspot, with anaerobic fermentation attracting significant attention due to its ability to convert organic matter in sludge into high-value-added products (such as short-chain fatty acids and biogas).
[0003] Short-chain fatty acids (SCFAs), as one of the main products of anaerobic fermentation, are important precursors for the synthesis of bioplastics and biofuels, and their market demand continues to grow. However, approximately 60%–70% of the organic matter in sludge exists in the form of polymers inside microbial cells or encapsulated in extracellular polymeric substances (EPS). These substances are difficult to directly decompose by hydrolytic enzymes due to the physical barriers of semi-rigid cell walls and EPS, making the hydrolysis rate the rate-limiting step in traditional anaerobic fermentation. In the direct fermentation of untreated sludge, the low yield of SCFAs and the excessively long fermentation cycle present significant technical bottlenecks for its industrial application.
[0004] To overcome the bottleneck of hydrolysis, physical, chemical and biological pretreatment technologies have been widely studied. Among them, hot hydrolysis technology has become the mainstream method because it can efficiently destroy the structure of sludge flocs and cell walls. Through high temperature (120-180℃) and high pressure (0.5-2.0MPa) treatment, the release rate of intracellular organic matter in sludge can be increased by more than 50%, and the yield of SCFAs is significantly increased. However, the high temperature environment will induce amino compounds (such as proteins) in sludge to undergo Maillard reaction with reducing sugars to generate melanoidins. These substances have complex aromatic structures and antioxidant properties, are difficult to be degraded by microorganisms, and will inhibit anaerobic fermentation through the following pathways: (1) Competition for electron donors: The quinone groups in melanoidins can act as electron acceptors, competing with acid-producing bacteria for electrons and inhibiting the accumulation of volatile fatty acids; (2) Toxicity effect: Melanoidins and their degradation intermediates (such as furan compounds) have cytotoxicity to acid-producing bacteria, reducing their metabolic activity; (3) Shielding effect: Melanoidins are adsorbed on the surface of sludge particles, hindering the contact between microorganisms and substrates. In addition, the hot hydrolysis process also releases humic acid and other recalcitrant organic compounds, further exacerbating the fermentation inhibition problem.
[0005] To address the negative impacts of melanoidins, existing technologies primarily rely on adding chemical reagents to block their formation or enhance their degradation. For example, patent CN113461283A proposes adding sulfites before thermal hydrolysis to inhibit the Maillard reaction. However, sulfites themselves have strong reducing properties and may remain in the sludge, forming sulfides that not only toxicize acid-producing bacteria but also lead to the emission of malodorous gases such as H2S, posing a risk of secondary pollution. Another approach (patent CN117985914A) utilizes ferrous ions to activate the oxidative degradation of melanoidins, but it suffers from poor targeting of complex melanoidin molecules, resulting in insufficient degradation efficiency, and ferrous ions are easily oxidized to Fe. 3+ This can lead to the formation of precipitates that clog the reaction system. Other methods, such as ozone oxidation and Fenton's reagent, can degrade melanoidins, but they are costly or produce harmful byproducts, making them difficult to apply on a large scale.
[0006] Meanwhile, potassium permanganate (KMnO4), as a strong oxidant, has shown unique potential in sludge pretreatment. Its oxidizing power originates from MnO4. -Potassium permanganate (KP) possesses highly efficient electron-capturing properties, allowing it to selectively attack organic matter rich in electron-donating groups (such as phenolic hydroxyl groups and double bonds). Since these groups are widely present in melanoidin molecules, theoretically, KP could target and degrade melanoidin while simultaneously disrupting the EPS structure, promoting the dissolution of organic matter. Studies have also shown that the manganese dioxide (MnO2) particles generated by KP oxidation can adsorb onto the surface of acid-producing bacteria, acting as an electron transfer medium to accelerate extracellular electron transfer, thereby improving acid production efficiency. However, KP pretreatment alone has two major drawbacks: first, excessive oxidant dosage: to achieve effective degradation, 0.2–0.3 g / gTS of KP needs to be added, significantly increasing treatment costs; second, limited reaction conditions: oxidation alone is insufficient to completely break down sludge cell walls, resulting in limited organic matter release efficiency.
[0007] Therefore, how to achieve efficient degradation of melanoidins and maximize the release of organic matter through combined technologies while avoiding secondary pollution has become a key issue that urgently needs to be addressed in this field. This invention combines thermal hydrolysis with potassium permanganate oxidation, fully utilizing their synergistic effect: thermal hydrolysis preferentially breaks down the physical barriers of sludge and releases organic matter, while potassium permanganate targets and oxidizes the subsequently generated melanoidins, ultimately overcoming the dual bottlenecks of existing technologies and providing an efficient and environmentally friendly solution for sludge resource utilization. Summary of the Invention
[0008] This invention provides a method for enhancing anaerobic acid production in sludge based on the synergistic degradation of melanoidins using hot water hydrolysis and potassium permanganate. This method addresses the challenges of low organic matter release efficiency and melanoidin inhibition in sludge through a phased pretreatment process. First, high-temperature, high-pressure hot water hydrolysis disrupts the physical barriers of the sludge, releasing intracellular organic matter. Then, potassium permanganate selectively oxidizes the melanoidins generated during hot water hydrolysis, eliminating their toxicity to microorganisms. Simultaneously, manganese dioxide, an oxidation byproduct, is used as an electron transport medium to accelerate the metabolism of acid-producing bacteria, ultimately achieving efficient production of short-chain fatty acids. The core of this invention lies in the synergistic mechanism of hot water hydrolysis and potassium permanganate, which overcomes the limitations of single technologies and reduces treatment costs through resource utilization of byproducts.
[0009] Specific implementation steps of the present invention:
[0010] 1. Sludge thickening and pretreatment
[0011] After the raw sludge is filtered through a 20-25 mesh screen to remove large particulate impurities, it undergoes gravity settling at a low temperature of 3-5℃ for 24-48 hours, increasing the total solids concentration of the concentrated sludge to 15-40 g / L. Low temperature conditions inhibit microbial activity, prevent premature degradation of organic matter, and ensure efficient subsequent treatment.
[0012] 2. Hot water hydrolysis synergistic pretreatment
[0013] The concentrated sludge was transferred to a sealed hot hydrolysis reactor and treated at 120–160°C and 0.5–1.5 MPa for 15–30 minutes. The high temperature and pressure environment caused the sludge cell walls to rupture and the EPS structure to disintegrate, releasing approximately 60% of the intracellular organic matter (such as proteins and polysaccharides). After depressurization, the sludge was rapidly cooled to 45–60°C to prevent the Maillard reaction from continuing.
[0014] 3. Potassium permanganate targeted oxidation
[0015] Powdered potassium permanganate (0.05–0.1 g / g TS) was added to the hydrolyzed sludge, and the mixture was stirred for 20–40 minutes while simultaneously applying ultrasonic treatment (energy density 0.1–0.5 W / mL, time 10–30 minutes). The ultrasonic cavitation effect promoted the contact between potassium permanganate and melanoidins. Its selective oxidation mechanism preferentially attacked electron-donating groups such as phenolic hydroxyl groups and double bonds in melanoidin molecules, achieving a degradation efficiency of over 60%. The resulting manganese dioxide (MnO2) was ultrasonically dispersed into 50–100 nm particles, which uniformly adhered to the surface of acid-producing bacteria.
[0016] 4. Anaerobic fermentation to enhance acid production
[0017] Oxidized sludge and anaerobic activated sludge (taken from wastewater treatment plants or breweries) are mixed at a volatile suspended solids (VSS) ratio of 1:2 to 1:10, with an inoculum concentration of 8–10 kg VSS / m³. 3 After purging with nitrogen to remove oxygen, seal the container. Ferment at 25–40°C with stirring (80–120 rpm) for 6–10 days. Manganese dioxide acts as an electron acceptor, accelerating extracellular electron transfer in acid-producing bacteria and promoting the accumulation of SCFAs such as acetic acid and propionic acid.
[0018] 5. Product separation and by-product recovery
[0019] After fermentation, the supernatant was separated by centrifugation, and short-chain fatty acids (total percentage ≥75%) were extracted. Residual manganese dioxide particles were recovered by acid washing with 0.5–1.0 mol / L dilute sulfuric acid or hydrochloric acid, with a recovery rate ≥90%, avoiding heavy metal residues.
[0020] The innovation and synergistic mechanism of this invention are as follows:
[0021] Firstly, the stages of hot hydrolysis and oxidation are synergistic. Hot hydrolysis preferentially disrupts the physical structure of the sludge, releasing organic matter and inducing the formation of melanoidins; potassium permanganate then targets and degrades the melanoidins, forming a synergistic "cell wall disruption-detoxification" chain, avoiding the problem of excessive oxidant addition in traditional technologies.
[0022] Secondly, selective degradation of melanoidins. Potassium permanganate precisely attacks the active groups in melanoidins through an electron transfer mechanism, and the degradation product is a small molecule carboxylic acid that can be directly utilized by acid-producing bacteria. The UV254 value decreased from 2.79 to 0.87, and the inhibition effect was eliminated by 70%.
[0023] Thirdly, the resource utilization of manganese dioxide. The nano-manganese dioxide generated by oxidation not only serves as an electron transfer medium to increase the acid production rate, but can also be recycled through acid washing, reducing treatment costs (saving approximately 15% in reagent costs per ton of sludge).
[0024] Compared with existing technologies, the present invention has significant advantages: First, it has high acid production efficiency: the SCFAs yield reaches up to 456 mg / g VS, which is 65% higher than that of single hot water hydrolysis treatment (276 mg / g VS); second, it has a short fermentation cycle: shortened to 4-5 days (traditional methods require 7-9 days); third, it has fewer recalcitrant substances: the UV254 value is reduced by 68.7% and the humic acid concentration is reduced by 55%; fourth, it is environmentally friendly: the manganese dioxide recovery rate is ≥90%, with no risk of secondary pollution.
[0025] This invention improves the acid production efficiency of anaerobic fermentation of sludge to an industry-leading level through multi-stage synergistic treatment, while solving the problems of melanin inhibition and by-product pollution, providing an efficient, economical and environmentally friendly technical path for sludge resource utilization. Attached Figure Description
[0026] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation
[0027] The present invention will be further described below with reference to specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.
[0028] In the following embodiments, unless otherwise specified, the materials and processing techniques are commercially available materials or conventional processing techniques in the art.
[0029] Example 1 (Optimal Conditions)
[0030] Sludge from the secondary sedimentation tank of a wastewater treatment plant in Changsha City was collected. The total solids (TS) concentration was 10.5 g / L, and the volatile solids (VS) content was 65%. The sludge was filtered through a 25-mesh sieve (0.71 mm aperture) to remove impurities such as sand and fibers. The sludge was then placed in a low-temperature sedimentation tank at 4°C and allowed to stand for 48 hours, resulting in a concentrated TS concentration of 28.4 g / L. The concentrated sludge was pumped into a stainless steel hot water hydrolysis reactor, filling it to 75% of its volume. The temperature was increased to 160°C at a rate of 5°C / min, and the pressure was increased to 1.2 MPa, maintained for 30 minutes. The pressure was then slowly released to atmospheric pressure and cooled to 50°C using a circulating water cooling system. 0.1 g / g TS powdered potassium permanganate (99% purity) was added to the hydrolyzed sludge, and the stirring speed was 250 rpm for 30 minutes. Simultaneously, ultrasonic treatment (energy density 0.25 W / mL, frequency 28 kHz) was applied for 10 minutes. After ultrasonic treatment, 50-80 nm MnO2 particles were generated in the sludge and uniformly suspended. The treated sludge was pumped into an anaerobic digester, and anaerobic activated sludge (taken from an anaerobic digester in a wastewater treatment plant, VSS = 18 g / L) was inoculated at a volatile suspended solids (VSS) ratio of 1:5. Nitrogen gas was purged for 15 minutes, and the dissolved oxygen concentration was reduced to 0.05 mg / L before sealing. Fermentation was carried out at 37°C with stirring (100 rpm) for 4 days. The fermentation broth was centrifuged at 8000 rpm for 10 minutes to separate the supernatant and residue. The supernatant was decolorized with activated carbon and then distilled. The total yield of short-chain fatty acids was measured to be 456 mg / g VS, of which acetic acid accounted for 52%, propionic acid 28%, and butyric acid 20%. The residue was washed with 1.0 mol / L dilute sulfuric acid for 30 minutes, filtered, and manganese dioxide was recovered. The melanin degradation rate was 68.7% (UV254 value decreased from 2.79 to 0.87), the fermentation cycle was 4 days, and no secondary pollutants were generated; the manganese dioxide recovery rate was 92%.
[0031] Example 2 (Medium Dosage)
[0032] Differences in procedure: The amount of potassium permanganate added was adjusted to 0.075 g / g TS, and the other conditions were the same as in Example 1.
[0033] Results: SCFAs yield was 423 mg / g VS (acetic acid 48%, propionic acid 30%, butyric acid 22%); melanoidin degradation rate was 58.3% (UV254 value 1.02); manganese dioxide recovery rate was 89%.
[0034] Example 3 (Low-temperature fermentation)
[0035] Differences in procedure: The fermentation temperature was adjusted to 25℃, and the other conditions were the same as in Example 1.
[0036] Results: SCFAs yield was 312 mg / g VS (fermentation period extended to 8 days); melanoidin degradation rate was 52.1% (UV254 value 1.35); acid-producing bacteria activity decreased, and the proportion of acetic acid decreased to 45%.
[0037] Comparative Example 1 (Hot water hydrolysis pretreatment only)
[0038] Differences in procedure: After hot hydrolysis, anaerobic fermentation is carried out directly, and the other conditions are the same as in Example 1.
[0039] Results: SCFAs yield was 276 mg / g VS (fermentation cycle 7 days); UV254 value was 2.79 (melanoidins were not degraded); humic acid concentration reached 120 mg / L, inhibiting acid-producing bacteria metabolism.
[0040] Comparative Example 2 (No pretreatment)
[0041] Difference in steps: Anaerobic fermentation of concentrated sludge is carried out directly.
[0042] Results: SCFAs yield was 112 mg / g VS (fermentation cycle 9 days); UV254 value was 0.61 (low melanin content, but insufficient organic matter release rate); intracellular organic matter release rate was only 18%, and acid production efficiency was extremely low.
[0043] Comparative Example 3 (Single Potassium Permanganate Treatment)
[0044] Difference in procedure: 0.1 g / g TS potassium permanganate was added directly to the concentrated sludge, and the other conditions were the same as in Example 1.
[0045] Results: SCFAs yield was 198 mg / g VS (fermentation cycle 6 days); melanoidin degradation rate was 42.5% (UV254 value 1.60); sludge cell walls were not fully destroyed, and organic matter release rate was only 35%.
[0046] The comparative analysis of the effects of each embodiment is shown in Table 1:
[0047] Table 1 Comparison of the effects of each embodiment
[0048]
[0049] The anaerobic fermentation performance of sludge treated with a combination of hot water hydrolysis and potassium permanganate (Example 1) was significantly better than that of single pretreatment or no pretreatment. Under optimal conditions (hot water hydrolysis 160℃, 1.2 MPa, potassium permanganate 0.1 g / g TS, fermentation 37℃), Example 1 achieved a SCFAs yield of 456 mg / g VS, representing increases of 65% and 130% compared to hot water hydrolysis alone (Comparative Example 1) and potassium permanganate alone (Comparative Example 3), respectively. The fermentation cycle was shortened to 4 days, the melanoidin degradation rate reached 68.7%, and the manganese dioxide recovery rate was 92%. In Example 2, even with a reduced potassium permanganate dosage (0.075 g / g TS), the SCFAs yield still reached 423 mg / g VS, and the melanoidin degradation rate was 58.3%, demonstrating the flexibility of reagent dosage. However, low-temperature fermentation (Example 3, 25℃) resulted in a decrease in acid production efficiency to 312 mg / g VS and an extended cycle to 8 days, indicating that temperature is crucial for bacterial activity. In summary, the synergistic effect of hot water hydrolysis and potassium permanganate, through the "cell wall disruption-detoxification-enhancing" mechanism, takes into account efficient acid production, rapid degradation of inhibitors, and resource utilization of by-products, providing a more technically and economically superior solution for sludge resource utilization.
Claims
1. A method for enhancing anaerobic acid production from sludge based on the synergistic degradation of melanoidins by hot water hydrolysis and potassium permanganate, characterized in that, Includes the following steps: (1) Impurity removal and concentration: The raw sludge is filtered through a 20-25 mesh screen to remove impurities, and then subjected to gravity settling at 3-5 ℃ for 24-48 hours to obtain concentrated sludge with a total solids concentration of 15-40 g / L; (2) Hot water hydrolysis: The concentrated sludge is placed in a hot water hydrolysis reactor and treated for 15 to 30 minutes at 120 to 160 ℃ and 0.5 to 1.5 MPa. After depressurization, it is cooled to 45 to 60 ℃. (3) Targeted oxidation: Add powdered potassium permanganate to the sludge after step (2) at a dosage of 0.05~0.1 g / g TS, stir for 20~40 minutes, and simultaneously apply ultrasonic treatment with an ultrasonic energy density of 0.1~0.5 W / mL for 10~30 minutes; (4) Anaerobic fermentation: The oxidized sludge is mixed with anaerobic activated sludge at a volatile suspended solids ratio of 1:2 to 1:10, and the inoculum concentration is 8 to 10 kg VSS / m³. 3 After being sealed with nitrogen, fermentation is carried out at 25-40℃ for 6-10 days; (5) Product separation: Separate the supernatant of the fermentation broth and extract short-chain fatty acids.
2. The method according to claim 1, characterized in that, The manganese dioxide generated by potassium permanganate oxidation in step (3) is dispersed into nanoparticles by ultrasonication, which are attached to the surface of acid-producing microorganisms as an electron transfer medium. After fermentation, the manganese dioxide is recovered by acid washing, with a recovery rate of ≥90%.
3. The method according to claim 1, characterized in that, The total solids concentration of the sludge after gravity settling in step (1) is 15~40 g / L.
4. The method according to claim 1, characterized in that, The temperature of the hot water hydrolysis treatment in step (2) is 120~160 ℃, the pressure is 0.5~1.5 MPa, and the treatment time is 15~30 minutes.
5. The method according to claim 1, characterized in that, The amount of potassium permanganate added in step (3) is 0.05~0.1 g / g TS, and the ultrasonic energy density is 0.1~0.5 W / mL.
6. The method according to claim 1, characterized in that, The anaerobic activated sludge mentioned in step (4) is taken from the anaerobic digester of a sewage treatment plant or the fermentation tank of a brewery, and the stirring rate during the fermentation process is 80~120 rpm.
7. The method according to claim 1, characterized in that, The fermentation temperature in step (4) is 25~40 ℃, and the sludge retention time is 6~10 days.
8. The method according to claim 1, characterized in that, The short-chain fatty acids mentioned in step (5) include acetic acid, propionic acid and butyric acid, with a total proportion of ≥75%.
9. The method according to claim 2, characterized in that, The acid used for pickling and recovery is dilute sulfuric acid or hydrochloric acid with a concentration of 0.5~1.0 mol / L.