Method for treating sludge by hydrothermal process based on tea residue and organic acid

Abstract

The application discloses a method for synergistically hydrothermally treating sludge based on tea dregs and organic acid, which comprises the following steps: mixing sludge, organic acid and tea dregs, hydrothermally treating the obtained mixed slurry, and dehydrating to obtain filtrate and mud cake. The method for synergistically hydrothermally treating sludge based on tea dregs and organic acid can significantly reduce the hydrothermal reaction temperature under the synergistic action of tea dregs and organic acid, and can effectively inhibit the generation of refractory organic matters such as melanoidins while effectively improving the dewatering performance of sludge under the synergistic hydrothermal treatment of organic acid and tea dregs, so as to facilitate the reduction and resource utilization of sludge. Therefore, by fully utilizing the characteristics of organic acid and tea dregs and synergistically hydrothermal treatment technology, efficient, environment-friendly, resourceful and low-cost treatment of sludge can be realized, and the method has the advantages of low reaction temperature, high treatment efficiency, low energy consumption, good dewatering effect, green environmental protection and the like, and has a wide application prospect and popularization value.

Description

Technical Field

[0001] This invention belongs to the field of sludge treatment and disposal technology, and relates to a sludge treatment method, specifically a method for sludge treatment based on the synergistic hydrothermal treatment of tea residue and organic acid. Background Technology

[0002] In the physical processes of urban wastewater treatment, the proper handling and disposal of sludge is a crucial issue. Sludge is characterized by high water content, easy decay, strong odor, and the presence of numerous pathogens, parasite eggs, heavy metals, and persistent toxic and harmful substances. Therefore, achieving safe, economical, and efficient sludge treatment and disposal has become an urgent need and a challenge for cities. Furthermore, due to the complex flocculent structure and high hydrophilicity of sludge surfaces, dewatering sludge without pretreatment is extremely difficult. Thus, the sludge pretreatment environment becomes a key factor influencing energy consumption and cost. Effective pretreatment can reduce the water content of sludge, improve its dewatering performance, and thereby reduce the difficulty and cost of subsequent treatment and disposal.

[0003] Currently, the mainstream sludge treatment process both domestically and internationally is "sludge thickening - sludge chemical conditioning - plate and frame filter press dewatering." Thickening is the initial dewatering of sludge; sludge chemical conditioning mainly involves adding chemical reagents such as acids (inorganic acids), alkalis (sodium hydroxide, calcium hydroxide, and calcium oxide, etc.), coagulants (iron salts and aluminum salts), flocculants (polyacrylamide), and Fenton's reagent to the sludge to improve its chemical properties, thereby improving its flocculation and stability. This process has advantages such as high efficiency, flexibility, and ease of engineering application, but it also has drawbacks such as large chemical dosages, high equipment requirements, safety issues, and secondary pollution. Therefore, there is an urgent need to find an environmentally friendly and economical sludge treatment technology.

[0004] Subcritical hydrothermal technology, as an effective sludge treatment technology, involves a non-evaporative thermochemical transformation process. During this process, through a series of chemical reactions such as hydrolysis, dewatering, decarboxylation, polymerization, and aromatization, it significantly reduces sludge volume and dry weight while disrupting the sludge's colloidal structure, lowering its viscosity, and converting most of the bound water into free water. This improves sludge dewatering performance and reduces sludge moisture content and volume. However, this process can generate several problems. For example, high temperatures (e.g., above 180°C) can promote the formation of colored, recalcitrant substances such as melanoidins, potentially reducing the biodegradability of the filtrate and affecting subsequent treatment processes. Furthermore, excessive energy consumption is also a concern. Therefore, to address the related issues in the downstream treatment of filtrate, deep dewatering of excess sludge at relatively low temperatures is crucial.

[0005] The existing methods for treating and disposing of sludge based on hydrothermal / thermal hydrolysis technology have the following drawbacks: (1) Adding inorganic acids, strong oxidants, alkalis, iron salts, etc. as catalysts to the hydrothermal / thermal hydrolysis system not only increases the treatment cost but may also cause secondary pollution. In particular, the addition of inorganic acids and alkalis can corrode equipment and increase the difficulty of subsequent filtrate treatment; (2) In order to improve the efficiency of hydrothermal treatment, a large amount of chemical reagents are usually added, which not only increases the treatment cost but may also have a negative impact on the final disposal of sludge; (3) Using a variety of auxiliary agents further increases the complexity of the treatment process; (4) It is difficult to balance the treatment efficiency with the reaction temperature. Lowering the hydrothermal temperature can inhibit the Maillard reaction, but it may reduce the hydrothermal treatment efficiency. Alternatively, increasing the hydrothermal temperature can improve the treatment efficiency, but it can promote the formation of colored and difficult-to-degrade substances such as melanoidins under high temperature conditions; (5) Adding reducing substances to inhibit the Maillard reaction can not only easily increase the treatment cost but may also cause secondary pollution problems. For example, some researchers have proposed a high-efficiency sludge dewatering process based on low-temperature hydrothermal treatment, which involves hydrothermal treatment followed by the addition of tannic acid for chemical conditioning. However, the added chemical conditioning agents are expensive, and the issue of inhibiting the Maillard reaction during the hydrothermal process is not addressed. Other researchers have proposed a hydrothermal treatment method for sewage sludge, treating the sludge at temperatures of 250–400°C. This method suffers from the drawback of high hydrothermal temperatures, making it difficult to inhibit the Maillard reaction. Still others have proposed a method for deep dewatering sludge through hydrothermal catalytic oxidation, adding various chemical reagents and treating the sludge at temperatures of 180–250°C. This method also suffers from the drawback of high hydrothermal temperatures, making it difficult to inhibit the Maillard reaction, and the large-scale use of chemical reagents can easily increase treatment costs and volume. There are risks of secondary pollution. Some researchers have proposed a method for treating sludge based on sodium sulfite-assisted hot water hydrolysis, which lowers the hydrothermal temperature and inhibits the Maillard reaction during the hydrothermal process by adding sulfite. However, sulfite is a carcinogen and may pose secondary pollution risks. Other researchers have proposed a method to improve sludge dewatering through heat treatment and flocculants. Although this method is carried out at a relatively low temperature (80~90℃), it requires the addition of sulfuric acid and flocculants (PAM). PAM has high toxicity and poses risks during its application. Moreover, the addition of sulfuric acid requires sophisticated equipment and results in poor sludge dewatering rates. Some researchers have proposed a method and system for treating aging leachate from landfills in conjunction with sludge dewatering. This method requires the addition of lime, which results in high alkalinity and hardness of the subsequent filtrate, increasing subsequent treatment costs.In addition, existing municipal sludge treatment methods involve adding biomass and sludge conditioners to the subcritical water reaction system to modify the sludge and improve its dewatering performance. However, this method cannot effectively reduce the temperature of the subcritical water reaction. Under subcritical conditions of 180℃ to 230℃, the Maillard reaction occurs, which promotes the formation of colored and recalcitrant substances such as melanoidins. At the same time, after being treated by biomass / sludge conditioner in conjunction with the subcritical water reaction and left to stand naturally for 24 hours, the moisture content of the sludge is still above 50%, indicating poor dewatering effect.

[0006] Therefore, in view of the shortcomings and defects in the existing technology, it is necessary to provide a sludge treatment method with low reaction temperature, high treatment efficiency, low energy consumption, good dewatering effect, and green environmental protection, which will play an important role in promoting the treatment, disposal and resource utilization of sludge. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for sludge treatment based on the synergistic hydrothermal treatment of tea residue and organic acid, which has low reaction temperature, high treatment efficiency, low energy consumption, good dehydration effect, and is green and environmentally friendly.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] A method for synergistic hydrothermal treatment of sludge based on tea residue and organic acids includes the following steps:

[0010] Step S1: Mix the sludge with organic acid and tea residue to obtain a mixed slurry;

[0011] Step S2: Perform hydrothermal treatment on the mixed slurry obtained in step S1;

[0012] Step S3: Dehydrate the product obtained after hydrothermal treatment in step S2 to obtain filtrate and mud cake.

[0013] In a further improvement to the above method, in step S1, the mass ratio of the organic acid to the TS in the sludge is 0.02 to 0.15:1; the organic acid is at least one of citric acid, acetic acid, lactic acid, tartaric acid, and oxalic acid.

[0014] In a further improvement to the above method, in step S1, the mass ratio of the tea residue to the TS in the sludge is 0.05 to 0.2:1.

[0015] In a further improvement to the above method, in step S2, the temperature of the hydrothermal treatment is 110℃~160℃; and the time of the hydrothermal treatment is 15 min~60 min.

[0016] In a further improvement to the above method, in step S2, saturated steam or supersaturated steam is used to perform hydrothermal treatment on the mixed slurry obtained in step S1.

[0017] In a further improvement to the above method, step S2 further includes the following process during the hydrothermal treatment: stirring the mixed slurry at a speed of 100 rpm to 300 rpm.

[0018] The above method is further improved by adding the following process to step S2: the secondary steam generated during the hydrothermal treatment is introduced into the mixed slurry obtained in step S1 for preheating treatment, so that the temperature of the mixed slurry is raised to 60°C to 90°C.

[0019] In a further improvement to the above method, in step S3, a plate and frame filter press is used to dehydrate the product obtained after hydrothermal treatment; during the dehydration process, the sludge inlet pressure is controlled at 8 kg to 12 kg, and the filter press pressure is controlled at 15 kg to 20 kg.

[0020] The above method is further improved by adding the following treatment to step S3: passing the filtrate into sludge for conditioning treatment; the mass ratio of the sludge to the filtrate is 1:1 to 2; the sludge is dewatered sludge from a municipal wastewater treatment plant; and the water content of the sludge is 75% to 85%.

[0021] The above method is further improved by adding the following step S3: exchanging heat between the filtrate and the product obtained after hydrothermal treatment, so that the temperature of the product obtained after hydrothermal treatment is reduced to below 60°C.

[0022] Compared with the prior art, the advantages of the present invention are as follows:

[0023] (1) In view of the shortcomings of the method of treating sludge based on hydrothermal / hot water hydrolysis technology combined with chemical agents, such as large amount and variety of agents, high raw material cost, complex process, risk of secondary pollution, difficulty in improving treatment efficiency at lower temperature conditions, difficulty in inhibiting Maillard reaction, and poor sludge dewatering effect, this invention creatively provides a method for sludge treatment based on the synergistic hydrothermal treatment of tea residue and organic acid. First, the sludge is mixed with organic acid and tea residue to form a mixed slurry. Then, the mixed slurry is subjected to hydrothermal treatment. The acidity can be adjusted by utilizing the organic acid and tea polyphenols and other antioxidants in the tea residue. The organic acid adjusts the pH of the sludge, effectively decomposing sludge flocs and improving the enzyme accessibility of particulate organic matter. It also improves the physicochemical properties of the sludge, disrupting its colloidal structure. Specifically, the organic acid removes polyvalent cations used for bridging in the sludge, effectively breaking down the interactions between sludge flocs and promoting particle aggregation and sedimentation. Simultaneously, the organic matter and cellulose in the tea residue increase the porosity and permeability of the sludge, contributing to improved dewatering performance. Through the combined action of the organic acid and tea residue, the hydrolysis of organic matter in the sludge is achieved, thus effectively... Lowering the hydrothermal treatment temperature allows for the construction of a subcritical hydrothermal reaction system with a lower reaction temperature, releasing more internally bound water. This also effectively removes heavy metals and harmful microorganisms from the sludge, improving its dewatering performance and reducing its toxicity. More importantly, the subcritical hydrothermal reaction system, with the synergistic effect of tea residue and organic acids, can rapidly improve sludge dewatering performance at lower temperatures, resulting in lower energy consumption and higher treatment efficiency. Furthermore, it effectively inhibits recalcitrant organic matter such as melanoidins during the hydrothermal treatment process. The generation of organic acids and the presence of tea polyphenols and other antioxidants in tea residues can also inhibit the oxidation step in the Maillard reaction, thereby effectively slowing down the generation of colored and recalcitrant organic matter. Therefore, the synergistic hydrothermal treatment of sludge with organic acids and tea residues can effectively improve the dewatering performance of sludge while effectively inhibiting the generation of recalcitrant organic matter such as melanoidins, facilitating the reduction and resource utilization of sludge. Finally, the product (sludge) after hydrothermal treatment is dewatered to achieve the reduction and resource utilization of sludge. Compared with conventional methods for treating sludge based on hydrothermal / hot water hydrolysis technology combined with chemical agents, the method of sludge treatment based on the synergistic hydrothermal treatment of tea residues and organic acids in this invention has the following advantages: (a) Low hydrothermal treatment temperature and low energy consumption. In this invention, the dewatering performance of sludge can be effectively improved under hydrothermal conditions of 110℃~160℃, while conventional methods require at least 180℃. At the same time, treating sludge under lower hydrothermal temperatures helps to reduce energy consumption.(b) High processing efficiency: In this invention, hydrothermal treatment of sludge at 110℃~160℃ can effectively improve the dewatering performance of sludge within 15 min~60 min, while conventional methods, hydrothermal treatment at 180℃ for 60 min, cannot effectively improve the dewatering performance of sludge. (c) Low processing cost: The organic acid used is inexpensive, and tea residue comes from solid organic waste generated during tea production, processing, sales, and consumption, which has the characteristics of wide availability and low price. Therefore, using tea residue and organic acid as auxiliary agents can reduce processing costs. At the same time, improving the dewatering performance of sludge under lower hydrothermal treatment temperature conditions can also reduce processing costs. (d) Good sludge reduction effect: After treatment by the method of this invention, the moisture content of sludge can be reduced to 45%, while the moisture content of sludge after treatment by conventional methods is still as high as 50% or even 55%. (e) The resource utilization effect is good. On the one hand, by inhibiting the generation of colored and difficult-to-degrade organic pollutants such as melanoidins, it is easy to realize the subsequent treatment and resource utilization of filtrate and mud cake. For example, the filtrate can be recycled and utilized in multiple stages. For example, the filtrate can be used to condition the sludge, which can further reduce the amount of organic acid used, and there is no need to supplement other water sources. On the other hand, the waste heat in the hydrothermal treatment process can also be used to preheat the sludge and filtrate. Thus, the heat in the hydrothermal treatment system can be rationally utilized and energy consumption can be further reduced. At the same time, the organic matter in the tea residue can be transferred to the mud cake, which can also increase the nutrient content in the mud cake, making it easier to realize the resource utilization of the mud cake. (f) Green and environmentally friendly. On the one hand, by inhibiting the formation of colored and recalcitrant organic pollutants such as melanoidins, secondary pollution problems can be avoided. On the other hand, the organic acid used is a biodegradable organic acid, which will not only not have adverse effects on operators, the environment, or equipment, but also, because organic acids are easily degraded, will not increase the difficulty and cost of subsequent treatment of the filtrate after entering it. At the same time, using tea residue as raw material can realize waste-to-waste treatment, promote the resource utilization of solid waste resources, and avoid secondary pollution caused by large-scale waste accumulation, thus having good economic and environmental benefits. This invention is based on a method for synergistic hydrothermal treatment of sludge using tea residue and organic acid. By fully utilizing the characteristics of organic acid and tea residue and synergistically combining hydrothermal treatment technology, it can achieve efficient, environmentally friendly, resource-based, and low-cost treatment of sludge. It has advantages such as low reaction temperature, high treatment efficiency, low energy consumption, good dewatering effect, and green environmental protection, and has broad application prospects and promotion value.

[0024] (2) In this invention, by optimizing the ratio of organic acid and tea residue, the reaction temperature and reaction time of hydrothermal treatment can be significantly reduced, which is more conducive to achieving efficient treatment of sludge.

[0025] (3) Compared with other biomass materials, the tea residue used in this invention contains abundant active groups, which can effectively inhibit the Maillard reaction during hydrothermal processes. Specifically, the active substances such as tea polyphenols in the tea residue are utilized. These polyphenols have antioxidant properties, which can inhibit the activity of oxidases and chelate with metal ions that promote enzymatic browning, thereby inhibiting browning. Secondly, the adsorption effect of tea residue can adsorb heavy metal ions, reduce or inhibit the catalytic effect of heavy metal ions in the Maillard reaction, thereby indirectly inhibiting the Maillard reaction. Thirdly, the antioxidant properties of tea residue can inhibit the oxidation step in the reaction, slow down the generation of colored and difficult-to-degrade organic matter, thereby inhibiting the Maillard reaction. Attached Figure Description

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0027] Figure 1 This is a schematic diagram of the process flow for the sludge treatment based on the synergistic hydrothermal treatment of tea residue and organic acids in Embodiment 1 of the present invention. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0029] In the following embodiments of the present invention, unless otherwise specified, the materials and instruments used are commercially available, the equipment used is conventional equipment, and the data obtained are the average values ​​of more than three repeated experiments.

[0030] To address the shortcomings of traditional sludge treatment methods based on hydrothermal / hot water hydrolysis combined with chemical agents, such as large dosage and variety of agents, high raw material costs, complex processes, risks of secondary pollution, difficulty in improving treatment efficiency at lower temperatures, difficulty in inhibiting Maillard reactions, and poor sludge dewatering, this invention creatively provides a method for sludge treatment based on the synergistic hydrothermal treatment of tea residue and organic acids. First, sludge is mixed with organic acids and tea residue to form a mixed slurry. Then, the mixed slurry is subjected to hydrothermal treatment. The acidity-regulating effect of organic acids and tea polyphenols and other antioxidants in the tea residue can be utilized to adjust the pH. Adjusting the pH value of sludge not only effectively decomposes sludge flocs and improves the enzyme accessibility of particulate organic matter, but also improves the physicochemical properties of sludge, disrupting its colloidal structure. In particular, organic acids can remove polyvalent cations used for bridging in the sludge, effectively breaking down the interactions between sludge flocs and promoting the coagulation and sedimentation of particles. Simultaneously, organic matter and cellulose in tea residue can increase the porosity and permeability of the sludge, contributing to improved dewatering performance. Through the combined action of organic acids and tea residue, the hydrolysis of organic matter in the sludge is achieved, thus effectively reducing... The lower temperature of hydrothermal treatment allows for the construction of a subcritical hydrothermal reaction system with a lower reaction temperature, releasing more internally bound water. It also effectively removes heavy metals and harmful microorganisms from the sludge, thereby improving its dewatering performance and reducing its toxicity. More importantly, the subcritical hydrothermal reaction system, with the synergistic effect of tea residue and organic acids, can rapidly improve the dewatering performance of sludge at lower temperatures, resulting in lower energy consumption and higher treatment efficiency. Furthermore, it effectively inhibits the degradation of recalcitrant organic matter such as melanoidins during hydrothermal treatment. The generation of organic acids and the presence of tea polyphenols and other antioxidants in tea residues can also inhibit the oxidation step in the Maillard reaction, thereby effectively slowing down the generation of colored and recalcitrant organic matter. Therefore, the synergistic hydrothermal treatment of sludge with organic acids and tea residues can effectively improve the sludge dewatering performance while effectively inhibiting the generation of recalcitrant organic matter such as melanoidins, facilitating the reduction and resource utilization of sludge. Finally, the product (sludge) after hydrothermal treatment is dewatered to achieve the reduction and resource utilization of sludge.

[0031] To better understand the innovation of the technical solution of this invention, the following embodiments and comparative examples are provided.

[0032] Example 1

[0033] A method for synergistic hydrothermal treatment of sludge based on tea residue and organic acids, specifically utilizing tea residue and citric acid for synergistic hydrothermal treatment of sludge, is illustrated in the process flow diagram below. Figure 1 As shown, it includes the following steps:

[0034] Step S1: Mix the sludge with citric acid and tea residue to obtain a mixed slurry.

[0035] In step S1, the mass ratio of citric acid to total solids (TS) in the sludge is 0.1:1, meaning the amount of citric acid added is 0.1 g / gTS based on the TS content in the sludge. Similarly, the mass ratio of tea residue to TS in the sludge is 0.1:1, meaning the amount of tea residue added is 0.1 g / gTS based on the TS content in the sludge. If filtrate is used to condition the sludge, then TS refers to the total solids content of the sludge after conditioning.

[0036] In step S1, the sludge used is the residual sludge from a sewage treatment plant in Changsha, with a water content of 80%, i.e., TS of 20% and pH of neutral.

[0037] In step S1, the tea residue used includes the following treatment before use: crushing the tea residue. In this step, the tea residue comes from waste generated during tea beverage factories, deep processing of tea polyphenols, and planting. Generally speaking, tea residue contains 5% to 15% tea polyphenols, 0.1% to 0.3% caffeine, 17% to 9% crude protein, and 16% to 18% crude fiber.

[0038] Step S2: Steam is introduced into the mixed slurry obtained in step S1 and then into a hydrothermal device for hydrothermal treatment, wherein the hydrothermal treatment temperature is 150℃ and the time is 30 min.

[0039] In step S2, the steam introduced during the hydrothermal treatment process is saturated steam or supersaturated steam.

[0040] In step S2, the hydrothermal treatment process also includes the following treatment: stirring the mixed slurry at a speed of 150 rpm.

[0041] Step S2 also includes the following process: after the hydrothermal treatment is completed, the hydrothermal device is depressurized until the product temperature drops to 100°C, the secondary steam generated during the depressurization process is collected, and it is introduced into the mixed slurry obtained in step S1 for preheating treatment, so that the temperature of the mixed slurry is raised to 80°C.

[0042] Step S3: Use a plate and frame mill to dehydrate the product obtained after hydrothermal treatment in step S2 to obtain filtrate and mud cake.

[0043] In step S3, the plate and frame machine used is a diaphragm plate and frame machine.

[0044] In step S3, the sludge inlet pressure is controlled at 10 kg and the filter press pressure is controlled at 15 kg during the dewatering process.

[0045] Step S3 also includes the following treatment: passing the filtrate into the sludge for conditioning treatment, wherein the mass ratio of sludge to filtrate is 1:1.

[0046] Step S3 also includes the following process: exchanging heat between the filtrate and the product obtained after hydrothermal treatment, so that the temperature of the product obtained after hydrothermal treatment is reduced to 60°C.

[0047] Tests showed that in step S3, the SCOD in the mud cake increased to 30.951 g / L, and the moisture content decreased to 45%.

[0048] In this embodiment, the effect of different hydrothermal treatment temperatures on sludge dewatering was also investigated. Except for the different hydrothermal treatment temperatures, the other conditions were the same as in Example 1, and the results are shown in Table 1.

[0049] Table 1. Dewatering effect of sludge at different hydrothermal treatment temperatures

[0050]

[0051] As shown in Table 1, the SCOD of sludge increases with the continuous increase of hydrothermal temperature, but the increase is not significant at 150℃. At the same time, the water content of sludge decreases first and then increases with the continuous increase of hydrothermal temperature, with the lowest water content obtained at a hydrothermal temperature of 150℃.

[0052] Comparative Example 1

[0053] A method for sludge treatment based on citric acid and synergistic hydrothermal treatment is basically the same as that in Example 1, except that only 0.1 g / gTS of citric acid is added in Comparative Example 1, but tea residue is not added.

[0054] Tests showed that the SCOD of the treated sludge was 26.041 g / L and the moisture content was 55%.

[0055] Comparative Example 2

[0056] A method for treating sludge based on hydrothermal technology is basically the same as that in Example 1, except that citric acid and tea residue were not added in Comparative Example 2, and only hydrothermal treatment was performed.

[0057] Tests showed that the SOCD in the treated sludge was 21.549 g / L and the moisture content was 62%.

[0058] Comparing the results of Example 1 and Comparative Examples 1 and 2, it can be seen that the addition of citric acid and tea residue promoted the hydrothermal treatment of sludge and had a synergistic effect. The SCOD and dewatering performance of the sludge were further improved after synergistic treatment, significantly improving the hydrothermal treatment efficiency and dewatering performance of the sludge.

[0059] The results above show that, compared with conventional methods for treating sludge based on hydrothermal / hot water hydrolysis combined with chemical agents, the method of sludge treatment based on the synergistic hydrothermal treatment of tea residue and organic acids has the following advantages: (a) Low hydrothermal treatment temperature and low energy consumption. In this invention, the dewatering performance of sludge can be effectively improved under hydrothermal conditions of 110℃ to 160℃, while conventional methods require at least 180℃. Treating sludge at a lower hydrothermal temperature also helps reduce energy consumption. (b) High treatment efficiency. In this invention, hydrothermal treatment of sludge at 110℃ to 160℃ can effectively improve the dewatering performance of sludge within 15 min to 60 min, while conventional methods, even with hydrothermal treatment at 180℃ for 60 min, cannot effectively improve the dewatering performance of sludge. (c) Low treatment cost: The organic acids used are inexpensive, and tea residue comes from solid organic waste generated during tea production, processing, sales, and consumption. It has the characteristics of wide availability and low price. Therefore, using tea residue and organic acids as auxiliary agents can reduce treatment costs. At the same time, improving the dewatering performance of sludge under lower hydrothermal treatment temperature conditions can also reduce treatment costs. (d) Good sludge reduction effect: The moisture content of sludge treated by the method of this invention can be reduced to 45%, while the moisture content of sludge treated by conventional methods is still as high as 50% or even 55%. (e) The resource utilization effect is good. On the one hand, by inhibiting the generation of colored and difficult-to-degrade organic pollutants such as melanoidins, it is easy to realize the subsequent treatment and resource utilization of filtrate and mud cake. For example, the filtrate can be recycled and utilized in multiple stages. For example, the filtrate can be used to condition the sludge, which can further reduce the amount of organic acid used, and there is no need to supplement other water sources. On the other hand, the waste heat in the hydrothermal treatment process can also be used to preheat the sludge and filtrate. Thus, the heat in the hydrothermal treatment system can be rationally utilized and energy consumption can be further reduced. At the same time, the organic matter in the tea residue can be transferred to the mud cake, which can also increase the nutrient content in the mud cake, making it easier to realize the resource utilization of the mud cake. (f) Green and environmentally friendly. On the one hand, by inhibiting the formation of colored and difficult-to-degrade organic pollutants such as melanoidins, secondary pollution problems can be avoided. On the other hand, the organic acid used is a biodegradable organic acid, which will not only not have an adverse impact on operators, the environment, or equipment, but also, because organic acids are easy to degrade, will not increase the difficulty and cost of subsequent treatment of the filtrate after entering it. At the same time, using tea residue as raw material can realize the treatment of waste with waste, promote the resource utilization of solid waste resources, and avoid secondary pollution caused by the large accumulation of waste, which has good economic and environmental benefits.

[0060] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for synergistically hydrothermal treatment of sludge based on tea residue and organic acid, characterized in that, The method comprises the following steps: Step S1, mixing sludge with organic acid and tea residue to obtain a mixed slurry; the mass ratio of the organic acid to TS in the sludge is 0.02-0.15:1; the mass ratio of the tea residue to TS in the sludge is 0.05-0.2:1; Step S2, performing hydrothermal treatment on the mixed slurry obtained in step S1; the temperature of the hydrothermal treatment is 130-160 DEG C; the time of the hydrothermal treatment is 15-60 min; Step S3, performing dewatering treatment on the product obtained after the hydrothermal treatment in step S2 to obtain filtrate and mud cake.

2. The method of claim 1, wherein, In step S1, the organic acid is at least one of citric acid, acetic acid, lactic acid, tartaric acid and oxalic acid.

3. The method according to claim 1 or 2, characterized in that, In step S2, saturated steam or supersaturated steam is used to perform hydrothermal treatment on the mixed slurry obtained in step S1.

4. The method of claim 3, wherein, In step S2, the process of the hydrothermal treatment further comprises the following treatment: stirring the mixed slurry at a rotation speed of 100-300 rpm.

5. The method of claim 3, wherein, In step S2, the process further comprises the following treatment: passing secondary steam generated in the process of the hydrothermal treatment into the mixed slurry obtained in step S1 to perform preheating treatment, so that the temperature of the mixed slurry is increased to 60-90 DEG C.

6. The method of claim 1 or 2, wherein, In step S3, a plate-and-frame machine is used to perform dewatering treatment on the product obtained after the hydrothermal treatment; the process of the dewatering treatment controls the sludge inlet pressure to be 8-12 kg and the filter pressing pressure to be 15-20 kg.

7. The method of claim 6, wherein, In step S3, the process further comprises the following treatment: passing the filtrate into sludge to perform conditioning treatment; the mass ratio of the sludge to the filtrate is 1:1-2; the sludge is dewatered sludge from a municipal sewage treatment plant; the moisture content of the sludge is 75-85%.

8. The method of claim 7, wherein, In step S3, the process further comprises the following treatment: performing heat exchange between the filtrate and the product obtained after the hydrothermal treatment, so that the temperature of the product obtained after the hydrothermal treatment is reduced to below 60 DEG C.

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