An Enhanced Thermal Hydrolysis Method for Excess Sludge Based on Extracellular Polymer Dissociation

Abstract

This invention discloses an enhanced thermal hydrolysis method for excess sludge based on extracellular polymer dissociation, belonging to the field of excess sludge treatment and disposal technology. The method first prepares an extracellular polymer dissociation solution composed of sodium citrate and sodium dodecyl sulfate, mixes it with dewatered excess sludge, and performs dissociation treatment. After solid-liquid separation, a solid sludge free of extracellular polymers is obtained. This sludge is then replenished with water and mixed thoroughly before undergoing low-temperature thermal hydrolysis at 100-150℃. This achieves efficient sludge reduction and yields a high-concentration organic matter pyrolysis solution, while mitigating the deterioration of dewaterability after low-temperature thermal hydrolysis. This invention significantly improves the efficiency of low-temperature thermal hydrolysis by dissociating extracellular polymers to break their protection of microbial cells, reducing energy consumption and operating costs. The dissociation agents used are inexpensive and non-toxic, the process is simple, it is compatible with existing equipment, there is no secondary pollution, and it also enables the resource utilization of extracellular polymers and pyrolysis solution, possessing significant practical application and promotion value.

Description

Technical Field

[0001] This invention relates to an enhanced thermal hydrolysis method for excess sludge based on the dissociation of extracellular polymers, belonging to the field of excess sludge treatment and disposal technology. Background Technology Wastewater sludge is a byproduct of wastewater treatment. Its complex composition and challenging treatment can easily lead to secondary pollution if not handled properly. Therefore, sludge reduction, harmlessness, and resource recovery have become crucial research topics and industry demands in the wastewater treatment field. Hot water hydrolysis technology, as a new and efficient approach to wastewater sludge treatment, leverages its core advantages—using water as a medium in a closed system and employing specific temperature and self-pressure to break down sludge flocs and microbial cell structures, releasing large amounts of organic matter—to become a key technology for achieving sludge reduction, harmlessness, and resource recovery, and has garnered widespread attention in the industry.

[0002] However, the industrial promotion and application of traditional waste sludge hot water hydrolysis technology is limited by the core issues of high energy consumption and high operating costs: the technology requires a relatively high temperature of 180-220℃ to achieve efficient sludge treatment. High temperature conditions not only significantly increase equipment energy consumption and operating costs, but also place stringent requirements on the high temperature and high pressure resistance of the reaction equipment, further increasing the initial investment and subsequent maintenance costs of the project.

[0003] To address the aforementioned issues, existing technologies primarily attempt to reduce operating costs by controlling the hydrolysis temperature, shortening the hydrolysis time, or adding catalysts or oxidants for co-hydrolysis. However, these methods all have significant technical drawbacks: simply adjusting the temperature and time directly leads to a substantial decrease in hydrolysis efficiency, making it difficult to meet industry treatment requirements for sludge reduction and organic matter release, and also causing a deterioration in sludge dewatering properties; while adding catalysts or oxidants can improve the low-temperature hydrolysis effect to some extent, it increases the additional cost of the reagents, and some chemical reagents are prone to secondary pollution, increasing the difficulty and cost of subsequent sludge treatment, and failing to fundamentally solve the pain points of traditional technologies.

[0004] Currently, some existing improved hot water hydrolysis technologies (such as the method of co-hydrolysis of sodium sulfite and residual sludge disclosed in patent CN 115611492 A) are not targeted enough to break down the sludge structure and fail to optimize the hydrolysis process at the level of sludge microstructure. As a result, the final hot water hydrolysis enhancement effect is not obvious and it is difficult to meet the actual industrial demand for efficient and low-cost treatment.

[0005] Furthermore, patent CN 114890636 A only focuses on the extraction and purification of extracellular polymers in activated sludge. Its core is to achieve efficient EPS extraction by complexing divalent cations with sodium citrate. It does not involve the hot hydrolysis treatment of excess sludge or its impact on the dewatering properties of sludge after pyrolysis. It also does not mention the coupling use of sodium dodecyl sulfate and sodium citrate, and there is no relevant research or inspiration on low-temperature hot hydrolysis. Moreover, the technical goal of this patent is to obtain pure EPS, which is different from the goal of this invention to enhance the hot hydrolysis of sludge through EPS dissociation, thereby achieving sludge reduction and organic matter release.

[0006] In summary, the industry urgently needs an improved method for thermal hydrolysis of waste sludge that can achieve efficient thermal hydrolysis of sludge under low-temperature conditions, while also being energy-efficient, cost-effective, pollution-free, and enhancing the resource utilization potential of the pyrolysis liquid. This would break through the development bottlenecks of existing technologies and promote the large-scale and industrial application of thermal hydrolysis technology for waste sludge. Summary of the Invention

[0007] Technical issues Existing methods for treating excess sludge by thermal hydrolysis suffer from problems such as high energy consumption, high cost, and poor low-temperature treatment effect.

[0008] Technical solution Excess sludge flocs are composed of microorganisms, extracellular polymers, and inorganic matter. Extracellular polymers are the core component that maintains sludge structural stability and protects microbial cells. Addressing the pain points of traditional hot hydrolysis technologies, such as high temperature and high energy consumption, poor low-temperature performance, and easy deterioration of sludge dewatering properties, this invention proposes an innovative approach to enhanced low-temperature hot hydrolysis using pre-dissociation of extracellular polymers. First, a specialized dissociation solution is used to efficiently dissociate and separate the extracellular polymers from the sludge, removing their protective barrier to microbial cells. This allows the energy from hot hydrolysis to be concentrated on disrupting the cell structure, achieving efficient sludge breakdown, full release of organic matter, and sludge reduction at a low temperature of 100-150℃. Simultaneously, it significantly improves the dewatering properties of the sludge after pyrolysis. This method, with pre-dissociation of extracellular polymers as its core, constructs a low-energy-consumption, high-efficiency, and green economical enhanced hot hydrolysis technology for excess sludge, providing a new technical path for sludge reduction and resource utilization. It can effectively promote the industrial application of low-temperature hot hydrolysis technology and has broad application prospects.

[0009] This invention preferably uses a combination of sodium citrate (a complexing agent) and sodium dodecyl sulfate (a surfactant) as the core components for dissociation: sodium citrate dissociates extracellular polymers by chelating divalent cations such as calcium and magnesium, while sodium dodecyl sulfate enhances the solubility of extracellular polymers through surface activation. The two work synergistically to achieve more thorough dissociation of extracellular polymers. After dissociation, the energy utilization rate of hot water hydrolysis is significantly improved, enhancing hydrolysis efficiency without deteriorating sludge dewatering properties. Furthermore, both agents are widely available, inexpensive, non-toxic, harmless, and have a mild effect, meeting the needs of engineering applications. Based on this, this invention forms a complete method for enhanced hot water hydrolysis of excess sludge based on extracellular polymer dissociation.

[0010] This invention provides an enhanced thermal hydrolysis method for excess sludge based on extracellular polymer dissociation, comprising the following steps: S1. Treatment of extracellular polymeric substances in residual sludge: The dissociation solution was mixed with the remaining sludge to obtain a mixture, which was then subjected to extracellular polymer dissociation treatment. S2, Separation of extracellular polymers: The mixture after the dissociation of extracellular polymers was subjected to solid-liquid separation, and the solid phase was taken to obtain sludge free of extracellular polymers. S3. Thermal hydrolysis of sludge depolymerized: After the sludge containing extracellular polymeric substances is mixed evenly with water, it is subjected to low-temperature hot hydrolysis to break down and release the organic matter in the remaining sludge, thereby achieving efficient sludge reduction with low energy consumption. At the same time, a sludge pyrolysis liquid with high concentration of organic matter is obtained, and it is ensured that the sludge can continue to be efficiently dehydrated and solidified after pyrolysis.

[0011] Furthermore, the residual sludge in step S1 is specifically residual sludge that has undergone dewatering treatment and has a moisture content of 80%-85%.

[0012] Furthermore, the dissociated substances in the dissociation liquid in step S1 include complexing agents and surfactants.

[0013] Furthermore, the complexing agent is sodium citrate and / or sodium oxalate.

[0014] Furthermore, the surfactant is sodium dodecyl sulfate and / or hexadecyltrimethylammonium bromide.

[0015] Furthermore, the mass ratio of the complexing agent to the surfactant is 0.5~2.5:0.2~1.

[0016] Furthermore, the concentration of the dissociated substance in the dissociation solution is 0.01~0.1 g / mL.

[0017] Preferably, the concentration of the dissociated substance in the dissociation solution is 0.05~0.1 g / mL.

[0018] Furthermore, the dissociation solution in step S1 is preferably a combination of sodium citrate and sodium dodecyl sulfate.

[0019] Furthermore, the mass ratio of sodium citrate to sodium dodecyl sulfate is 2~3:1.

[0020] Furthermore, in step S1, the mass ratio of the remaining sludge to the dissociation liquid is 1:0.5~2.

[0021] Furthermore, the dissociation treatment in step S1 includes one or more of the following: mechanical stirring (500 rpm / min, 3-5 h), mechanical vibration (150 rpm / min, 5-10 h), aeration rinsing (1 L / min, 0.5-2 h), or ultrasonic treatment (40 kHz, 0.5-1 h).

[0022] Furthermore, the solid-liquid separation method in step S2 includes centrifugation, natural sedimentation, and vacuum filtration; the liquid phase is a dissociated extracellular polymer solution, which can be used for resource recovery.

[0023] Specifically, the solid-liquid separation method in step S2 is: centrifugation (8000-12000 rmp / min, 10 min), natural sedimentation (standing for 5-8 h), or vacuum filtration (the mixture is filtered through a 0.45 μm filter membrane).

[0024] Furthermore, in step S3, the amount of water used is 80-150% of the volume of the exopolymer-depleted sludge.

[0025] Furthermore, the method for achieving uniform mixing in step S3 is as follows: mechanical stirring, magnetic stirring (500 rpm / min, 1-0.5 h), mechanical vibration (150 rpm / min, 0.5-1 h), aeration and flushing (1 L / min, 0.5-1 h), or ultrasonic treatment (40 kHz, 0.5-1 h).

[0026] Furthermore, the conditions for low-temperature hot hydrolysis in step S4 are as follows: hydrolysis is carried out at 100-150℃, the reactor is heated to the predetermined temperature and held for 0.1-2 h, and then cooled.

[0027] Beneficial effects 1. Reduced energy consumption and operating costs: This invention reduces the hot water hydrolysis temperature from the traditional 180-220℃ to a low temperature range of 100-150℃ by pre-dissociating extracellular polymers, significantly reducing energy consumption and the requirements for equipment pressure resistance and high temperature resistance; the sodium citrate and sodium dodecyl sulfate used are inexpensive, readily available, non-toxic and mild, the process is simple and does not require special equipment, and can be directly connected to existing hot water hydrolysis equipment, resulting in lower overall costs.

[0028] 2. Significantly enhanced hot water hydrolysis effect: In this invention, the dissociation liquid synergistically breaks down the extracellular polymer protective barrier, allowing the hot water hydrolysis energy to act efficiently on microbial cells. At 120℃, a sludge dry weight reduction rate of over 38% and an organic matter release rate of over 58% can be achieved. The treatment effect is better than traditional 180℃ high-temperature hot water hydrolysis, and the reduction and resource utilization efficiency are greatly improved.

[0029] 3. Improved sludge dewatering performance and green pollution control: This invention effectively alleviates the problem of deterioration of sludge dewatering performance after traditional low-temperature hot water hydrolysis. The CST value of sludge after pyrolysis is significantly reduced, and the dewatering efficiency is higher. The dissociation agent is safe and harmless, the reaction process is mild, no toxic byproducts are produced, there is no risk of secondary pollution, and it is highly environmentally friendly.

[0030] 4. Achieving sludge reduction and resource utilization: While efficiently reducing sludge volume, the dissociated extracellular polymers and the high-concentration organic matter pyrolysis liquid generated by pyrolysis can be utilized as resources. The technology breaks through the shortcomings of traditional improvements from the microstructure perspective, has a wide range of applications, and can strongly promote the large-scale and industrial application of low-temperature hot water hydrolysis technology for excess sludge. Attached Figure Description

[0031] Figure 1 The effect of sodium dodecyl sulfate dosage on sludge dry weight reduction when used alone.

[0032] Figure 2 The effect of sodium dodecyl sulfate dosage on the release rate of organic matter when used alone.

[0033] Figure 3 The effect of sodium citrate dosage alone on sludge dry weight reduction.

[0034] Figure 4 The effect of sodium citrate dosage alone on the release rate of organic matter. Detailed Implementation

[0035] The present invention will be further described below with reference to embodiments, but this does not limit the scope of protection of the present invention.

[0036] The pharmaceuticals and other substances mentioned in the following examples were all purchased from the market.

[0037] Example 1 S1. Preparation of extracellular polymer dissociation solution: 2.5 g sodium citrate and 1.0 g sodium dodecyl sulfate were mixed and dissolved in 50 mL of water and thoroughly mixed to prepare the dissociation solution; S2. Treatment of extracellular polymer dissociation in residual sludge: Weigh 50.00 g of dewatered residual activated sludge (80% moisture content), measure 50 mL of dissociation liquid, mix it thoroughly with the dewatered residual activated sludge, and carry out extracellular polymer dissociation treatment at 25 degrees Celsius by magnetic stirring (500 rpm / min, 5 h). S3. Separation of extracellular polymers: The dissociated sludge mixture is centrifuged (8000-12000 rmp / min, 10 min) to separate solids and liquids, and the solid is taken to obtain the sludge mixture after dissociation of extracellular polymers. S4. Low-temperature hot water hydrolysis of sludge: The sludge mixture is placed in a high-pressure closed reactor and hot water hydrolysis is carried out at 120°C. The reactor is heated to 120°C, held for 0.5 h and then the heating is stopped. The mixture is cooled to room temperature to complete the hot water hydrolysis. The solid and liquid phases after the hot water hydrolysis are collected and analyzed, and the sludge dewatering performance (CST) is tested.

[0038] The results are analyzed as follows: The thermal hydrolysis efficiency of excess sludge was significantly improved through pre-dissociation treatment with extracellular polymers. Without this pre-dissociation treatment, the dry weight loss rate, organic matter release rate, and sludge dewatering performance index (CST) after pyrolysis were 20.99%, 39.31%, and 854 s, respectively. Notably, the sludge dewatering performance deteriorated significantly compared to before pyrolysis (CST = 143 s). After pre-dissociation treatment, the dry weight loss rate, organic matter release rate, and CST were 38.11%, 58.58%, and 324 s, respectively. This demonstrates that the pre-dissociation treatment significantly improved the thermal hydrolysis efficiency of the sludge and significantly mitigated the trend of sludge deterioration. This is because the dissociation solution effectively removes extracellular polymers, breaking down their protective effect on microbial cell structures, thus making the thermal hydrolysis of sludge more direct and efficient in destroying cells, thereby improving the thermal hydrolysis efficiency.

[0039] Comparative Example 1 Comparison of extracellular polymer dissociation efficiency in pretreated and untreated hot water hydrolysis at different temperatures: I. The sludge did not undergo the extracellular polymer dissociation and hydrolysis process: S1. Preparation of sludge mixed liquor: Take 50.00 g of residual sludge and 50.00 mL of water, mix the two together and stir evenly to obtain sludge mixed liquor; S2. Sludge hot hydrolysis: The sludge mixture obtained in step S1 is placed in a high-pressure closed reactor and hot hydrolysis is carried out at 120℃, 150℃, 180℃, 220℃ and 500 rpm / min respectively. After the reactor is heated to the target temperature, heating is stopped and the temperature is reduced to room temperature to complete the hot hydrolysis. The solid and liquid phases after hot hydrolysis are then collected for analysis and the sludge dewatering performance (CST) is tested.

[0040] II. Hot hydrolysis steps for the dissociation of extracellular polymers in sludge: Steps S2 and S3 are the same as in Example 1, except that step S1 requires the use of a dissociation solution for the experiment. S4. Hot water hydrolysis of sludge: After dissociation, the sludge was subjected to hot water hydrolysis at 120℃, 150℃, 180℃, and 220℃ at 500 rpm / min. After the reactor was heated to the target temperature, it was held for 0.5 h and then the heating was stopped. The sludge was cooled to room temperature to complete the hot water hydrolysis. The solid and liquid phases after hot water hydrolysis were then collected for analysis and the sludge dewatering performance (CST) was tested.

[0041] Results analysis: Table 1 Comparison of extracellular polymer dissociation efficiency of sludge in pretreated and untreated sludge at different temperatures.

[0042] Table 1 shows the comparison of the thermal hydrolysis efficiency (sludge dry weight reduction rate and organic matter release rate) of sludge with and without extracellular polymer dissociation pretreatment at different temperatures. Under different temperature conditions, dissociation pretreatment significantly enhanced the thermal hydrolysis efficiency of sludge, and both the sludge dry weight reduction rate and organic matter release rate were significantly improved. To achieve a sludge dry weight reduction rate of over 30% and an organic matter release rate of over 50% in untreated sludge thermal hydrolysis, a pyrolysis temperature of at least 180℃ is required. However, after extracellular polymer dissociation treatment, a 38.11% sludge dry weight reduction and a 58.58% organic matter release can be achieved at a lower temperature (120℃), significantly reducing the required pyrolysis temperature and thus significantly reducing the energy consumption and operating costs of the sludge thermal hydrolysis process. Moreover, the dewatering performance of untreated sludge deteriorates after thermal hydrolysis, with the CST reaching 854s. The pyrolysis temperature needs to be increased to above 180℃ to reduce the CST to below 350s. However, after pretreatment with extracellular polymer dissociation, the CST of the sludge after pyrolysis at 120℃ is 324s, which shows better dewatering performance.

[0043] Comparative Example 2 Comparison of the enhanced pyrolysis effects of sodium citrate, sodium dodecyl sulfate, and composite dissociation solution.

[0044] S1. Preparation of extracellular polymeric dissociation solutions: 0.5, 1.25, and 2.5 g sodium citrate, and 0.2, 0.5, and 1.0 g sodium dodecyl sulfate were dissolved in 50 mL of water to prepare corresponding single dissociation solutions; then, the above dissociation solutions with different contents were mixed in combinations of sodium citrate + sodium dodecyl sulfate: 0.5 + 0.2 g, 1.25 + 0.5 g, and 2.5 + 1.0 g to prepare composite dissociation solutions; Steps S2, S3, and S4 are the same as in Example 1. The liquid and solid phases of the hydrolyzed sludge after pretreatment with different dissociation liquids are obtained, and the organic matter release rate, dry weight reduction rate, and sludge dewatering properties are analyzed.

[0045] Results analysis: Depend on Figure 1 and 2 It is evident that both sodium citrate and sodium dodecyl sulfate can dissociate extracellular polymers, thereby enhancing the efficiency of sludge hydrolysis. Furthermore, the hydrolysis efficiency gradually increases with increasing dosage. Using sodium dodecyl sulfate alone as the dissociation solution, at a concentration of 0.5 g / 50 mL, achieves the best enhanced sludge hydrolysis effect, resulting in a dry weight reduction rate of 28.45% and an organic matter release rate of 47.18%. Further increasing the dosage of sodium dodecyl sulfate does not significantly improve the enhanced sludge hydrolysis effect. Similarly, using sodium citrate alone as the dissociation solution, at a concentration of 2.0 g / 50 mL, achieves the best enhanced sludge hydrolysis effect, resulting in a dry weight reduction rate of 28.22% and an organic matter release rate of 49.23%. Again, further increasing the dosage of sodium citrate does not further improve the hydrolysis effect.

[0046] Table 2 Comparison of the enhanced sludge pyrolysis effect of the composite dissociation solution of sodium citrate and sodium dodecyl sulfate.

[0047] When the two are mixed, under the conditions of sodium dodecyl sulfate + sodium citrate: 0.2 g + 0.5 g / 50 mL, the sludge reduction rate and organic matter release rate of sludge thermal hydrolysis can reach 29.91% and 47.32%, respectively, which are basically equivalent to the optimal values ​​of using sodium dodecyl sulfate alone (0.5 g / mL, sludge reduction rate 28.45%, organic matter release rate 47.28%) or sodium citrate alone (2.0 g / mL, sludge reduction rate 28.22%, organic matter release rate 49.23%). When the conditions of sodium dodecyl sulfate + sodium citrate: 0.5 g + 2.0 g / 50 mL are met, the efficiency of sludge thermal hydrolysis is further increased, with the sludge weight reduction rate and organic matter release rate reaching 39.32% and 58.91%, respectively. At the same time, the dewatering property of sludge after pyrolysis is also improved, and the CST decreases from 388 s to 318 s. This indicates that the combination of the two significantly enhances the effect of extracellular polymeric substance (EPS) dissociation on the thermal hydrolysis of sludge, making it a more efficient pretreatment method. This is because the two dissociation solutions operate on different mechanisms: sodium dodecyl sulfate primarily increases the solubility of EPS through surface activation, while sodium citrate primarily dissociates EPS through chelation of multivalent ions such as calcium and magnesium. The combination of the two results in a synergistic dissociation effect, thereby improving the efficiency of thermal hydrolysis of sludge based on extracellular polymeric substance (EPS) dissociation.

[0048] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for enhanced thermal hydrolysis of excess sludge based on extracellular polymer dissociation, characterized in that, Includes the following steps: S1. Treatment of extracellular polymeric substances in residual sludge: The dissociation solution is mixed with the remaining sludge to obtain a mixed solution, which is then subjected to extracellular polymer dissociation treatment. The dissociation product of the dissociation solution includes a complexing agent and a surfactant. The complexing agent is sodium citrate and / or sodium oxalate. The surfactant is sodium dodecyl sulfate and / or hexadecyltrimethylammonium bromide. The mass ratio of the complexing agent to the surfactant is 0.5~2.5:0.2~1. The concentration of the dissociation product in the dissociation solution is 0.01~0.1 g / mL. S2, Separation of extracellular polymers: The mixture after the dissociation of extracellular polymers was subjected to solid-liquid separation, and the solid phase was taken to obtain sludge free of extracellular polymers. S3. Thermal hydrolysis of sludge depolymerized: After the sludge containing extracellular polymeric substances is mixed evenly with water, it is subjected to low-temperature hot hydrolysis to break down and release the organic matter in the remaining sludge, thereby achieving efficient sludge reduction with low energy consumption. At the same time, a sludge pyrolysis liquid with high concentration of organic matter is obtained, and it is ensured that the sludge can continue to be efficiently dehydrated and solidified after pyrolysis.

2. The enhanced thermal hydrolysis method for excess sludge according to claim 1, characterized in that, The residual sludge in step S1 is specifically residual sludge that has undergone dewatering treatment and has a moisture content of 80%-85%.

3. The enhanced thermal hydrolysis method for excess sludge according to claim 1, characterized in that, The concentration of the dissociated phase in the dissociation solution is 0.05~0.1 g / mL.

4. The enhanced thermal hydrolysis method for excess sludge according to claim 1, characterized in that, In step S1, the dissociation solution is preferably a combination of sodium citrate and sodium dodecyl sulfate; the mass ratio of sodium citrate to sodium dodecyl sulfate is 2~3:

1.

5. The enhanced thermal hydrolysis method for excess sludge according to claim 1, characterized in that, In step S1, the mass ratio of the remaining sludge to the dissociation liquid is 1:0.5~2.

6. The enhanced thermal hydrolysis method for excess sludge according to claim 1, characterized in that, The dissociation process in step S1 includes one or more of the following: mechanical stirring, mechanical vibration, aeration rinsing, or ultrasonic treatment.

7. The enhanced thermal hydrolysis method for excess sludge according to claim 1, characterized in that, The solid-liquid separation method in step S2 includes centrifugation, natural sedimentation, and vacuum filtration; the liquid phase is a dissociated extracellular polymer solution that can be used for resource recovery.

8. The enhanced thermal hydrolysis method for excess sludge according to claim 1, characterized in that, In step S3, the amount of water used is 80-150% of the volume of the exopolymer-free sludge.

9. The enhanced thermal hydrolysis method for excess sludge according to claim 1, characterized in that, The method for achieving uniform mixing in step S3 is: mechanical stirring, magnetic stirring, mechanical vibration, aeration rinsing, or ultrasonic treatment.

10. The enhanced thermal hydrolysis method for excess sludge according to claim 1, characterized in that, The conditions for low-temperature hot hydrolysis in step S4 are as follows: hydrolysis is carried out at 100-150℃, the reactor is heated to the predetermined temperature and held for 0.1-2 h, and then cooled.

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