Method for hydro-thermal treatment of sludge based on synergism of tea residues and organic acid

Abstract

The invention discloses a method for synergistically hydro-thermally treating sludge based on tea residue and organic acid, which comprises the following steps: mixing sludge with organic acid and tea residue, and performing hydro-thermal treatment and dehydration treatment on the obtained mixed slurry to obtain filtrate and a mud cake. According to the method for carrying out the synergistic hydrothermal treatment on the sludge based on the tea residues and the organic acid, the hydrothermal reaction temperature can be remarkably reduced under the synergistic effect of the tea residues and the organic acid, meanwhile, the sludge is subjected to the synergistic hydrothermal treatment through the organic acid and the tea residues, the dehydration performance of the sludge can be effectively improved, and meanwhile generation of nondegradable organic matter such as melanoidins can be effectively inhibited; therefore, efficient, environment-friendly, recycling and low-cost treatment of the sludge can be realized by fully utilizing the characteristics of the organic acid and the tea residues and cooperating with a hydrothermal treatment technology, and the method has the advantages of low reaction temperature, high treatment efficiency, low energy consumption, good dehydration effect, greenness, environmental protection and the like; wide application prospects and popularization values are realized.

Description

Technical Field

[0001] The invention belongs to the technical field of sludge treatment and disposal, and relates to a sludge treatment method, and specifically to a sludge treatment method based on the synergistic hydrothermal treatment of tea residues and organic acids. Background Art

[0002] In the physical process of urban sewage, how to properly handle and dispose of sludge is an important issue. Since sludge has high water content, is easy to rot, has a strong odor, and contains a large number of pathogens, parasite eggs, heavy metals and some toxic and harmful substances that are difficult to degrade. Therefore, achieving safe, economical and efficient treatment and disposal of sludge has become an urgent need and problem for cities. At the same time, due to the complex floc structure of the sludge itself and the high hydrophilicity of the sludge surface, it is difficult to dehydrate the sludge without pretreatment. Therefore, the sludge pretreatment environment has become a key link affecting the energy consumption and cost of treatment. Through effective pretreatment, the water content of the sludge can be reduced and its dehydration performance can be improved, thereby reducing the difficulty and cost of subsequent treatment and disposal.

[0003] At present, the mainstream sludge treatment processes at home and abroad are mainly "sludge concentration-sludge chemical conditioning-plate and frame filter press dewatering process". Concentration is the initial dehydration of sludge; sludge chemical conditioning is mainly to improve the chemical properties of sludge by adding acid (inorganic acid), alkali (sodium hydroxide, calcium hydroxide and calcium oxide, etc.), coagulant (iron salt and aluminum salt), flocculant (polyacrylamide) and Fenton reagent and other chemical reagents to the sludge, thereby improving the flocculation of sludge and improving the stability of sludge. It has the advantages of high efficiency, flexibility and easy engineering application, but it also has defects such as large amount of chemical agent addition, high equipment requirements, safety issues and secondary pollution. Therefore, it is urgent to find an environmentally friendly and economical sludge treatment technology.

[0004] As an effective sludge treatment technology, subcritical hydrothermal technology involves a non-evaporative thermochemical conversion process. In this process, through a series of chemical reactions such as hydrolysis, dehydration, decarboxylation, polymerization and aromatization, the sludge volume and dry weight are significantly reduced, while the sludge colloidal structure is destroyed, the sludge viscosity is reduced, and most of the bound water in the sludge is converted into free water, thereby improving the sludge dewatering performance and reducing the sludge moisture content and volume. However, some problems will arise in the process, such as high temperature (such as temperature above 180°C) conditions will promote the formation of colored and difficult-to-degrade substances such as melanoidins, which may reduce the biodegradability of the filtrate, thereby affecting the subsequent treatment and disposal process; in addition, there are problems such as excessive energy consumption. Therefore, in order to solve the related problems of filtrate treatment at the back end, it is very important to deeply dehydrate the residual sludge at a relatively low temperature.

[0005] Existing methods for treating and disposing sludge based on hydrothermal / thermal hydrolysis technology have the following defects: (1) By adding inorganic acids, strong oxidants, alkalis, iron salts, etc. as catalysts into the hydrothermal / thermal hydrolysis system, the addition of these reagents not only increases the treatment cost, but also may cause secondary pollution. In particular, the addition of inorganic acids and alkalis corrodes the equipment and increases 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 also may have a negative impact on the final disposal of the sludge; (3) The use of multiple auxiliary agents further increases the complexity of the treatment process; (4) It is difficult to balance the treatment efficiency and reaction temperature. By lowering the hydrothermal temperature, the occurrence of the Maillard reaction is suppressed, but the hydrothermal treatment efficiency may be reduced. In other words, by increasing the hydrothermal temperature, the treatment efficiency is improved, but under high temperature conditions, the formation of colored and difficult-to-degrade substances such as melanoidins will be promoted; (5) By adding reducing substances to suppress the occurrence of the Maillard reaction, it is easy to increase the treatment cost and there may be secondary pollution problems. For example, some researchers have proposed a high-efficiency sludge dehydration treatment process based on low-temperature hydrothermal treatment, which first performs hydrothermal treatment and then adds tannic acid for chemical conditioning. The disadvantage is that the added chemical conditioner is expensive, and the problem of inhibiting the Maillard reaction in the hydrothermal process is not addressed; some researchers have proposed a sewage sludge hydrothermal treatment method, which performs hydrothermal treatment on the sludge at a temperature of 250-400°C. The method has the defect of high hydrothermal treatment temperature and is difficult to inhibit the occurrence of the Maillard reaction; some researchers have proposed a method for deep dehydration of sludge by hydrothermal catalytic oxidation, which adds a variety of chemical reagents and performs hydrothermal treatment on the sludge at a temperature of 180-250°C. The method has the defect of high hydrothermal treatment temperature and is difficult to inhibit the Maillard reaction. In addition, the large-scale use of chemical agents is likely to increase the treatment cost and capacity. It is easy to bring about the risk of secondary pollution; some researchers have proposed a method for treating sludge based on sodium sulfite-assisted thermal hydrolysis. The addition of sulfite reduces the hydrothermal temperature and inhibits the Maillard reaction in the hydrothermal process. However, sulfite, as a carcinogen, may cause problems such as secondary pollution; some researchers have proposed a method for improving sludge dehydration by using thermal treatment and flocculants. Although it is carried out at a relatively low temperature (80~90℃), sulfuric acid and flocculants (PAM) need to be added. PAM is highly toxic and there are risks during the addition process. Moreover, the addition of sulfuric acid places high demands on the equipment and the sludge dehydration rate is poor; some researchers have proposed a method and system for the coordinated dehydration treatment of aged leachate from landfills. Lime needs to be added, which results in high alkalinity and hardness of the subsequent filtrate, increasing the subsequent treatment cost.In addition, in the existing municipal sludge treatment method, biomass and sludge conditioners are added to the subcritical water reaction system to modify the sludge and improve its dehydration performance. However, this method cannot effectively reduce the temperature of the subcritical water reaction. Under subcritical conditions of 180°C to 230°C, the Maillard reaction occurs, which promotes the formation of colored and difficult-to-degrade substances such as melanoidins. At the same time, after being naturally placed for 24 hours after being treated with biomass / sludge conditioners in a synergistic subcritical water reaction, the moisture content of the sludge is still above 50%, and the dehydration effect is poor.

[0006] Therefore, in view of the shortcomings and defects in the above-mentioned prior art, it is necessary to provide a sludge treatment method with low reaction temperature, high treatment efficiency, low energy consumption, good dehydration effect, and green environmental protection, which plays 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 deficiencies of the prior art and provide a method for hydrothermal treatment of sludge based on the synergistic hydrothermal treatment of tea residues and organic acids, which has low reaction temperature, high treatment efficiency, low energy consumption, good dehydration effect and is green and environmentally friendly.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions: A method for treating sludge by hydrothermal treatment based on tea residue and organic acid, comprising the following steps: Step S1, mixing the sludge with the organic acid and the tea residue to obtain a mixed slurry; Step S2, performing hydrothermal treatment on the mixed slurry obtained in step S1; Step S3, dehydrating the product obtained after the hydrothermal treatment in step S2 to obtain a filtrate and a mud cake.

[0009] The above method is further improved, in step S1, the mass ratio of the organic acid to TS in the sludge is 0.02-0.15:1; the organic acid is at least one of citric acid, acetic acid, lactic acid, tartaric acid and oxalic acid.

[0010] The above method is further improved, in step S1, the mass ratio of the tea residue to TS in the sludge is 0.05-0.2:1.

[0011] The above method is further improved, in step S2, the temperature of the hydrothermal treatment is 110° C. to 160° C.; the time of the hydrothermal treatment is 15 min to 60 min.

[0012] The above method is further improved in that in step S2, saturated steam or supersaturated steam is used to perform hydrothermal treatment on the mixed slurry obtained in step S1.

[0013] The above method is further improved, in step S2, the hydrothermal treatment process also includes the following treatment: stirring the mixed slurry at a rotation speed of 100 rpm to 300 rpm.

[0014] The above method is further improved, and step S2 also includes the following treatment: introducing the secondary steam generated during the hydrothermal treatment into the mixed slurry obtained in step S1 for preheating treatment, so that the temperature of the mixed slurry is increased to 60°C to 90°C.

[0015] The above method is further improved, in step S3, a plate and frame machine is used to dehydrate the product obtained after the hydrothermal treatment; during the dehydration process, the mud inlet pressure is controlled to be 8 kg to 12 kg, and the filter press pressure is controlled to be 15 kg to 20 kg.

[0016] The above method is further improved, and step S3 also includes the following treatment: the filtrate is passed into the sludge for tempering 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 water content of the sludge is 75%-85%.

[0017] The above method is further improved, and step S3 also includes the following treatment: exchanging heat 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°C.

[0018] Compared with the prior art, the advantages of the present invention are: (1) In view of the shortcomings of the method for treating sludge based on hydrothermal / thermal hydrolysis technology combined with chemical agents, such as large dosage of agents and multiple types, high raw material cost, complex process, risk of secondary pollution, difficulty in improving treatment efficiency under lower temperature conditions and difficulty in inhibiting the occurrence of Maillard reaction, and poor sludge dehydration effect, the present invention creatively provides a method for treating sludge based on the synergistic hydrothermal treatment of tea residues and organic acids. The sludge is first mixed with organic acid and tea residues to form a mixed slurry, and then the mixed slurry is subjected to hydrothermal treatment. The acidity of tea polyphenols and other antioxidants in the organic acid and tea residues can be adjusted. The effect of adjusting the pH value of sludge can not only effectively decompose sludge flocs and improve the enzyme accessibility of particulate organic matter, but also improve the physical and chemical properties of sludge and destroy the colloidal structure of sludge. In particular, organic acids can also remove multivalent cations used for bridging in sludge, effectively breaking the interaction between sludge flocs and promoting the coagulation and precipitation of particulate matter. At the same time, organic matter and cellulose in tea residues can also increase the porosity and permeability of sludge, which helps to improve the dewatering performance of sludge. Under the joint action of organic acids and tea residues, the hydrolysis of organic matter in sludge is achieved, so it can effectively Lowering the temperature of the hydrothermal treatment can construct a subcritical hydrothermal reaction system with a lower reaction temperature, release more internal bound water, and effectively remove heavy metals and harmful microorganisms in the sludge, thereby improving the dewatering performance of the sludge and reducing the toxicity of the sludge. More importantly, hydrothermal treatment of the sludge using a subcritical hydrothermal reaction system under the synergistic effect of tea residues and organic acids can quickly improve the dewatering performance of the sludge under lower temperature conditions, with lower energy consumption and higher treatment efficiency, and can effectively inhibit the generation of difficult-to-degrade organic matter such as melanoidin during the hydrothermal treatment process. The generation of organic acid and tea dregs is more conducive to the subsequent treatment and disposal of the filtrate. In addition, the acidity adjustment of organic acids and antioxidant substances such as tea polyphenols contained in tea dregs can also inhibit the oxidation step in the Maillard reaction, thereby effectively slowing down the generation of colored and difficult-to-degrade organic matter. Therefore, when organic acids and tea dregs are used in the synergistic hydrothermal treatment of sludge, the generation of difficult-to-degrade organic matter such as melanoidins can be effectively inhibited while effectively improving the dewatering performance of sludge, which is convenient for the reduction treatment and resource utilization of sludge. Finally, the product (sludge) after hydrothermal treatment is dehydrated to achieve the reduction treatment and resource utilization of sludge. Compared with the conventional method of treating sludge based on hydrothermal / thermal hydrolysis technology combined with chemical agents, the method of treating sludge based on tea dregs and organic acids in the present invention has the following advantages: (a) low hydrothermal treatment temperature and low energy consumption. In the present invention, the dewatering performance of sludge can be effectively improved under hydrothermal conditions of 110°C to 160°C, while in the conventional method, it is at least above 180°C. At the same time, the sludge is treated under lower hydrothermal temperature conditions, which is conducive to reducing energy consumption.(b) High treatment efficiency. In the present invention, hydrothermal treatment of sludge at a temperature of 110°C to 160°C can effectively improve the dewatering performance of sludge within 15 min to 60 min, while the conventional method of hydrothermal treatment at 180°C for 60 min cannot effectively improve the dewatering performance of sludge. (c) Low treatment cost. The organic acid used is low in price, and the tea residue comes from the solid organic waste generated during the production and processing of tea leaves and deep processing, sales, and drinking. It has the characteristics of wide sources and low prices. Therefore, using tea residue and organic acid as auxiliary agents can reduce the treatment cost. At the same time, the dewatering performance of sludge can be improved under lower hydrothermal treatment temperature conditions, which can also reduce the treatment cost. (d) The sludge has a good reduction effect. After treatment by the method of the present invention, the water content of the sludge can be reduced to 45%, while the water content of the sludge after treatment by the conventional method is still as high as 50% or even 55%. (e) Good resource utilization effect. On the one hand, by inhibiting the formation of colored and difficult-to-degrade organic pollutants such as melanoidins, the subsequent treatment and resource utilization of the filtrate and mud cake are facilitated. For example, the filtrate can be recycled and utilized in multiple stages. For example, the filtrate is used to condition the sludge, which can further reduce the amount of organic acid used without the 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, thereby rationally utilizing the heat in the hydrothermal treatment system and further reducing energy consumption. At the same time, the organic matter in the tea residue can be transferred to the mud cake, which can also increase the content of nutrients in the mud cake, facilitating the resource utilization of the mud cake. (f) Green and environmentally friendly. On the one hand, by inhibiting the generation 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 adverse effects on operators, the environment, and equipment, but also because the organic acid is easy to degrade, it will not increase the difficulty and cost of subsequent treatment of the filtrate after entering the filtrate. At the same time, using tea residue as a raw material can achieve waste treatment with waste, promote the resource utilization of solid waste resources, and avoid secondary pollution caused by large-scale accumulation of waste, with good economic and environmental benefits. The present invention is based on a method for hydrothermal treatment of sludge using tea residue and organic acid. By making full use of the characteristics of organic acid and tea residue and coordinating hydrothermal treatment technology, efficient, environmentally friendly, resource-based and low-cost treatment of sludge can be achieved. It has the advantages of low reaction temperature, high treatment efficiency, low energy consumption, good dehydration effect, green and environmental protection, etc., and has broad application prospects and promotion value.

[0019] (2) In the present invention, by optimizing the ratio of organic acid to tea residue, the reaction temperature and reaction time of the hydrothermal treatment can be significantly reduced, thereby being more conducive to achieving efficient treatment of sludge.

[0020] (3) Compared with other biomass materials, the tea residue used in the present invention contains abundant active groups, which can effectively inhibit the Maillard reaction in the hydrothermal process. Specifically, the tea residue contains active substances such as tea polyphenols. These polyphenols have antioxidant properties and can inhibit the activity of oxidases. They can also chelate with metal ions that promote enzymatic browning, thereby inhibiting browning. The second is the adsorption effect of tea residue. It 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. The third is the antioxidant property of tea residue, which inhibits the oxidation step in the reaction and slows down the formation of colored and difficult-to-degrade organic matter, thereby inhibiting the Maillard reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0022] Figure 1 This is a schematic diagram of the process flow of hydrothermal treatment of sludge based on the synergistic effect of tea residues and organic acid in Example 1 of the present invention. DETAILED DESCRIPTION

[0023] The present invention is further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

[0024] In the following examples 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.

[0025] Aiming at the shortcomings of the method for treating sludge based on hydrothermal / thermal hydrolysis technology combined with chemical agents, such as large dosage of agents and many types, high raw material cost, complex process, risk of secondary pollution, difficulty in improving treatment efficiency under lower temperature conditions and difficulty in inhibiting the occurrence of Maillard reaction, and poor sludge dehydration effect, the present invention creatively provides a method for treating sludge based on hydrothermal treatment of tea residues and organic acid. The sludge is first mixed with organic acid and tea residues to form a mixed slurry, and then the mixed slurry is subjected to hydrothermal treatment. The acidity regulating effect of tea polyphenols and other antioxidant substances in the organic acid and tea residues can be utilized to regulate the acidity of the sludge. Controlling the pH value of sludge can not only effectively decompose sludge flocs and improve the enzyme accessibility of particulate organic matter, but also improve the physical and chemical properties of sludge and destroy the colloidal structure of sludge. In particular, organic acids can also remove multivalent cations used for bridging in sludge, effectively breaking the interaction between sludge flocs and promoting the coagulation and precipitation of particulate matter. At the same time, organic matter and cellulose in tea residues can also increase the porosity and permeability of sludge, which helps to improve the dewatering performance of sludge. Under the joint action of organic acids and tea residues, the hydrolysis of organic matter in sludge is achieved, so it can effectively reduce The temperature of the hydrothermal treatment can construct a subcritical hydrothermal reaction system with a lower reaction temperature, release more internal bound water, and effectively remove heavy metals and harmful microorganisms in the sludge, thereby improving the dehydration performance of the sludge and reducing the toxicity of the sludge. More importantly, the sludge is hydrothermally treated using a subcritical hydrothermal reaction system under the synergistic effect of tea residues and organic acids, which can quickly improve the dehydration performance of the sludge under lower temperature conditions, have lower energy consumption and higher treatment efficiency, and can effectively inhibit the degradation of difficult-to-degrade organic matter such as melanoidins during the hydrothermal treatment process. The generation of organic acids is more conducive to the subsequent treatment and disposal of the filtrate. In addition, the acidity adjustment of organic acids and the antioxidants such as tea polyphenols contained in tea residues can also inhibit the oxidation step in the Maillard reaction, thereby effectively slowing down the generation of colored and difficult-to-degrade organic matter. Therefore, when organic acids and tea residues are used in synergistic hydrothermal treatment of sludge, the generation of difficult-to-degrade organic matter such as melanoidins can be effectively inhibited while the sludge dewatering performance is effectively improved, which is convenient for the reduction treatment and resource utilization of sludge. Finally, the product (sludge) after hydrothermal treatment is dehydrated to achieve the reduction treatment and resource utilization of sludge.

[0026] In order to better understand the innovation of the technical solution of the present invention, the following embodiments and comparative examples are provided.

[0027] Example 1 A method for treating sludge by hydrothermal treatment based on tea residue and organic acid, specifically using tea residue and citric acid to treat sludge by hydrothermal treatment, the process flow chart is as follows Figure 1 As shown, the following steps are included: Step S1: Mixing sludge, citric acid and tea residue to obtain a mixed slurry.

[0028] In step S1, the mass ratio of citric acid to TS in the sludge is 0.1:1, that is, the amount of citric acid added is 0.1 g / gTS based on the TS in the sludge. The mass ratio of tea residue to TS in the sludge is 0.1:1, that is, the amount of tea residue added is 0.1 g / gTS based on the TS in the sludge. If the filtrate is used to condition the sludge, TS refers to the total solid content data of the sludge after conditioning.

[0029] In step S1, the sludge used is the residual sludge from a sewage treatment plant in Changsha, and its moisture content is 80%, that is, TS is 20%, and pH is neutral.

[0030] In step S1, the tea residues used are further processed before use: the tea residues are crushed. In this step, the tea residues are wastes generated from tea beverage factories, tea polyphenols deep processing and planting processes. Generally speaking, 5% to 15% of tea polyphenols, 0.1% to 0.3% of caffeine, 17% to 9% of crude protein, and 16% to 18% of crude fiber remain in the tea residues.

[0031] Step S2, introducing steam into the mixed slurry obtained in step S1, and introducing the mixed slurry into a hydrothermal device for hydrothermal treatment, wherein the hydrothermal treatment temperature is 150° C. and the time is 30 min.

[0032] In step S2, the steam introduced during the hydrothermal treatment is saturated steam or supersaturated steam.

[0033] In step S2, the hydrothermal treatment process also includes the following treatment: stirring the mixed slurry at a rotation speed of 150 rpm.

[0034] Step S2 also includes the following processing: 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 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.

[0035] Step S3: using a plate-and-frame mill to dehydrate the product obtained after the hydrothermal treatment in step S2 to obtain a filtrate and a mud cake.

[0036] In step S3, the plate-and-frame machine is a diaphragm plate-and-frame machine.

[0037] In step S3, during the dehydration process, the mud inlet pressure is controlled to be 10 kg and the filter press pressure is controlled to be 15 kg.

[0038] Step S3 also includes the following treatment: passing the filtrate into the sludge for conditioning treatment, wherein the mass ratio of the sludge to the filtrate is 1:1.

[0039] Step S3 also includes the following treatment: exchanging heat between the filtrate and the product obtained after the hydrothermal treatment to reduce the temperature of the product obtained after the hydrothermal treatment to 60°C.

[0040] After testing, in step S3, the SCOD in the mud cake increased to 30.951 g / L, and the water content decreased to 45%.

[0041] In this example, the effect of different hydrothermal treatment temperatures on the sludge dehydration effect was also investigated. Except for the different hydrothermal treatment temperatures, other conditions were the same as in Example 1. The results are shown in Table 1.

[0042] Table 1 Dehydration effect of sludge at different hydrothermal treatment temperatures

[0043] It can be seen from Table 1 that with the continuous increase of hydrothermal temperature, the SCOD of the sludge shows an increasing trend, and the increase is not obvious at 150°C; at the same time, with the continuous increase of hydrothermal temperature, the water content of the sludge first decreases and then increases, and the lowest water content can be obtained when the hydrothermal temperature is 150°C.

[0044] Comparative Example 1 A method for treating sludge based on citric acid and hydrothermal treatment is basically the same as Example 1, except that only 0.1 g / gTS of citric acid is added in Comparative Example 1, but no tea residue is added.

[0045] After testing, the SCOD of the treated sludge was 26.041 g / L and the moisture content was 55%.

[0046] Comparative Example 2 A method for treating sludge based on hydrothermal technology is basically the same as Example 1, except that: in Comparative Example 2, citric acid and tea residues are not added, and only hydrothermal treatment is performed.

[0047] After testing, the SOCD of the sludge obtained after treatment was 21.549 g / L and the moisture content was 62%.

[0048] By comparing the results of Example 1 and Comparative Examples 1 and 2, it can be seen that the addition of citric acid and tea residues promoted the hydrothermal treatment of the sludge, and there was a synergistic effect. The SCOD and dehydration performance of the sludge were further improved after the synergistic treatment, which significantly improved the hydrothermal treatment efficiency and dehydration performance of the sludge.

[0049] It can be seen from the above results that compared with the conventional method of treating sludge based on hydrothermal / thermal hydrolysis technology combined with chemical agents, the method of treating sludge based on tea residue and organic acid in the present invention has the following advantages: (a) Low hydrothermal treatment temperature and low energy consumption. The present invention can effectively improve the dewatering performance of sludge under hydrothermal conditions of 110℃ to 160℃, while the conventional method is at least above 180℃, and the sludge is treated under lower hydrothermal temperature conditions, which is conducive to reducing energy consumption. (b) High treatment efficiency. In the present invention, hydrothermal treatment of sludge at a temperature of 110℃ to 160℃ can effectively improve the dewatering performance of sludge within 15min to 60min, while the conventional method hydrothermal treatment at 180℃ for 60min cannot effectively improve the dewatering performance of sludge. (c) Low treatment cost. The organic acid used is low in price. Tea residues come from solid organic waste generated during tea production and processing, deep processing, sales, and drinking. They have the characteristics of wide sources and low prices. Therefore, using tea residues and organic acids as auxiliary agents can reduce treatment costs. At the same time, the dewatering performance of sludge can be improved under lower hydrothermal treatment temperature conditions, which can also reduce treatment costs. (d) The sludge has a good reduction effect. After treatment by the method of the present invention, the water content of the sludge can be reduced to 45%, while the water content of the sludge after treatment by conventional methods is still as high as 50% or even 55%. (e) Good resource utilization effect. On the one hand, by inhibiting the formation of colored and difficult-to-degrade organic pollutants such as melanoidins, the subsequent treatment and resource utilization of the filtrate and mud cake are facilitated. For example, the filtrate can be recycled and utilized in multiple stages. For example, the filtrate is used to condition the sludge, which can further reduce the amount of organic acid used without the 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, thereby rationally utilizing the heat in the hydrothermal treatment system and further reducing energy consumption. At the same time, the organic matter in the tea residue can be transferred to the mud cake, which can also increase the content of nutrients in the mud cake, facilitating 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 have adverse effects on operators, the environment, and equipment. Moreover, since the organic acid is easy to degrade, it will not increase the difficulty and cost of subsequent treatment of the filtrate after entering the filtrate. At the same time, using tea residue as raw material can achieve waste treatment, promote the resource utilization of solid waste resources, and avoid secondary pollution caused by large-scale accumulation of waste, which has good economic and environmental benefits.

[0050] The above embodiments are only preferred implementations of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for treating sludge by hydrothermal treatment of tea residues and organic acid, characterized in that: The following steps are involved: Step S1, mixing the sludge with the organic acid and the tea residue to obtain a mixed slurry; Step S2, performing hydrothermal treatment on the mixed slurry obtained in step S1; Step S3, dehydrating the product obtained after the hydrothermal treatment in step S2 to obtain a filtrate and a mud cake.

2. The method according to claim 1, characterized in that In step S1, the mass ratio of the organic acid to TS in the sludge is 0.02-0.15:1; 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, characterized in that In step S1, the mass ratio of the tea residue to TS in the sludge is 0.05-0.2:

1.

4. The method according to any one of claims 1 to 3, characterized in that In step S2, the temperature of the hydrothermal treatment is 110° C. to 160° C.; the time of the hydrothermal treatment is 15 min to 60 min.

5. The method according to claim 4, characterized in that In step S2, the mixed slurry obtained in step S1 is hydrothermally treated with saturated steam or supersaturated steam.

6. The method according to claim 4, characterized in that In step S2, the hydrothermal treatment process further includes the following treatment: stirring the mixed slurry at a rotation speed of 100 rpm to 300 rpm.

7. The method according to claim 4, characterized in that Step S2 also includes the following treatment: introducing the secondary steam generated during the hydrothermal treatment into the mixed slurry obtained in step S1 for preheating treatment, so that the temperature of the mixed slurry is increased to 60°C to 90°C.

8. The method according to any one of claims 1 to 3, characterized in that: In step S3, a plate-and-frame mill is used to dehydrate the product obtained after the hydrothermal treatment; during the dehydration process, the mud inlet pressure is controlled to be 8 kg to 12 kg, and the filter press pressure is controlled to be 15 kg to 20 kg.

9. The method according to claim 8, characterized in that Step S3 also includes the following treatments: passing the filtrate into sludge for 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 water content of the sludge is 75%-85%.

10. The method according to claim 8, characterized in that Step S3 further includes the following treatment: exchanging heat between the filtrate and the product obtained after the hydrothermal treatment to reduce the temperature of the product obtained after the hydrothermal treatment to below 60°C.

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