Method for separating fine sludge from silt

Abstract

This invention discloses a method for separating fine sediment from sludge, belonging to the field of sludge treatment technology. The method includes the following steps: sludge pre-dewatering, neutral low-temperature hydrothermal treatment of sludge, acidic medium-temperature hydrothermal treatment of sludge, high-temperature hydrothermal carbonization treatment of sludge, cooling of the suspension to room temperature and ultrasonic treatment, hydrocyclone separation of the suspension to obtain a fine sediment layer and a biochar layer, and deep dewatering of both the fine sediment layer and the biochar layer. By pre-dewatering the sludge and then performing staged heating hydrothermal treatment, organic matter is converted into biochar, retaining carbon resources, increasing phosphorus release from the sludge, and enhancing passivation of heavy metals in the sludge. The sludge biochar and fine sediment are separated by ultrasonic treatment and hydrocyclone separation. Finally, the organic matter layer and the fine sediment layer are deeply dewatered separately for convenient classification and utilization. This invention can improve the separation efficiency of hydrocyclone separation, reduce the subsequent sludge treatment volume and cost, and maximize the recovery of energy and resources from the sludge.

Description

Technical Field

[0001] This invention belongs to the field of sludge treatment technology, and in particular relates to a method for separating fine sediment from sludge. Background Technology

[0002] Multi-source sludge is a broad category of urban sludge, encompassing solid waste generated during urban construction and development. It is a crucial component of the Yangtze River protection and management efforts, including sewage sludge, drainage sludge, and river and lake sediment. Its characteristics include complex composition, massive production volume, and high water content. Sewage sludge is a byproduct of wastewater treatment, with an annual production exceeding 70 million tons; drainage sludge refers to sediment removed during the maintenance of drainage pipe networks; and river and lake sediment is long-term accumulated sediment at the bottom of rivers, lakes, and reservoirs.

[0003] Sludge from multiple sources exhibits different generation characteristics. In terms of source, sewage sludge has a fixed origin, while ditch sludge and river / lake sediment have dispersed origins. Regarding generation frequency and quantity, sewage sludge is continuously and stably generated, ditch sludge is generated intermittently and in small quantities, and river / lake sediment generation is intermittent but in large quantities. Among various types of sludge, sewage sludge has a relatively stable generation volume and source; therefore, the co-treatment of multi-source sludge should focus on sewage sludge.

[0004] Multi-source sludge is mainly composed of organic matter and inorganic particulate matter. How to efficiently separate the organic and inorganic components in sludge and utilize them separately is the key to improving the efficiency of sludge treatment and comprehensive utilization, and to finding more sludge treatment and disposal pathways.

[0005] Currently, hydrocyclone sand removal technology is a traditional solid-liquid separation method with advantages such as simple structure, high separation efficiency, and low operation and maintenance costs. It has been used in wastewater treatment systems for sand removal for over 60 years. In recent years, due to the low sand removal efficiency of urban wastewater treatment systems, the problem of fine sand in these systems has become increasingly prominent. The presence of numerous microorganisms and extracellular polymers in sludge causes organic and inorganic matter to flocculate, encapsulate, and mix together, reducing the separation efficiency of hydrocyclone sand removal technology, especially for separating fine silt with particle sizes ≤100μm. Summary of the Invention

[0006] The purpose of this invention is to provide a method for separating fine sediment from sludge, which aims to solve the technical problem in the prior art where the separation effect of fine sediment from sludge is poor due to the mixing of organic and inorganic matter.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] A method for separating fine sediment from sludge includes the following steps:

[0009] 1) Sludge pre-dewatering;

[0010] 2) Neutral low-temperature hydrothermal treatment of sludge;

[0011] 3) Acidic medium-temperature hydrothermal treatment of sludge;

[0012] 4) High-temperature hydrothermal carbonization treatment of sludge;

[0013] 5) Cool the suspension to room temperature and sonicate it;

[0014] 6) The suspension was separated by hydrocyclone to obtain a fine silt layer and a biochar layer;

[0015] 7) The fine sediment layer and biochar layer are deeply dehydrated respectively;

[0016] The pre-dewatered sludge undergoes hydrothermal carbonization treatment with progressively increasing temperature. The suspension is then treated with ultrasound and cyclone separation to separate the biochar and fine silt. Finally, after deep dewatering, biochar filter cake and silt filter cake are obtained, and the filtrate is further processed in the wastewater treatment system.

[0017] Preferably, the specific steps of sludge pre-dewatering in step 1) are as follows:

[0018] 11) Add cationic polyacrylamide to the sludge for conditioning, the amount of which is 0.5-1‰ of the oven-dry sludge;

[0019] 12) Mechanically concentrate to a moisture content of 80-90%.

[0020] Preferably, step 2) involves neutral low-temperature hydrothermal treatment under high-pressure closed environment at a temperature of 100-140℃ for a reaction time of 30-60 min.

[0021] Preferably, in step 3), an acidic catalyst is added under a high-pressure closed environment to perform acidic medium-temperature hydrothermal treatment at a temperature of 140-180℃ for a reaction time of 60-90 min.

[0022] Preferably, the acidic catalyst is one or a mixture of two or more of sulfuric acid and hydrochloric acid, and the amount of acidic catalyst added is 1-3% of the oven-dried sludge.

[0023] Preferably, step 4) involves high-temperature hydrothermal carbonization under a high-pressure closed environment, with a temperature of 180-220℃ and a reaction time of 30-60 minutes.

[0024] Preferably, in step 5), the ultrasonic frequency is 10-50kHz, the ultrasonic energy density is 0.1-1W / mL, and the ultrasonic treatment time is 5-60min.

[0025] Preferably, in step 6), a hydrocyclone is used to perform hydrocyclone separation of the suspension. The feed pressure is 0.05-0.5 MPa. The hydrocyclone has a feed inlet at the top, a mud and sand outlet at the bottom, and a biochar outlet at the top.

[0026] Preferably, in step 7), the deep dewatering is carried out by plate and frame filter press or high-pressure belt dewatering, and the resulting organic filter cake has a moisture content of 30%-50% and an organic matter content of 60%-100%, while the fine mud and sand cake has a moisture content of 10%-30% and an organic matter content of 0%-20%.

[0027] Preferably, the sludge is sludge from municipal / industrial wastewater treatment plants, dredged sediment from rivers and lakes, and / or sludge from municipal pipeline drainage ditches.

[0028] The beneficial effects of adopting the above technical solution are as follows: Compared with the prior art, the present invention first pre-dewaters the sludge, then converts organic matter into biochar through staged heating hydrothermal treatment and changing reaction conditions, retaining carbon resources in the sludge, increasing phosphorus release from the sludge, and enhancing passivation of heavy metals in the sludge; then, ultrasonic treatment improves the separability of sludge biochar from fine particles, followed by hydrocyclone separation of sludge biochar and fine silt; finally, the organic matter layer and the fine silt layer are deeply dewatered and disposed of separately. The present invention can improve the separation efficiency of hydrocyclone separation, separating fine silt with a particle size ≤100μm, reducing the amount and cost of subsequent sludge treatment, and achieving sludge reduction, stabilization, harmlessness, and resource utilization, maximizing the recovery of energy and resources from the sludge. Attached Figure Description

[0029] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0030] Figure 1 This is a schematic flowchart of a method for separating fine sediment from sludge provided by the present invention;

[0031] Figure 2 This is a schematic diagram of the sludge fine sediment separation system in an embodiment of the present invention;

[0032] In the diagram: 1-Sludge thickening tank; 2-Sludge pre-dewatering device; 3-Low-temperature hydrothermal reactor; 4-Medium-temperature hydrothermal reactor; 5-High-temperature hydrothermal reactor; 6-Acid storage tank; 7-Ultrasonic vibrator; 8-Cyclone separator; 9-Deep dewatering device; 10-Agitator; 11-Ultrasonic generator. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] Given that multi-source sludge, consisting of sewage sludge, ditch sludge, and river and lake sediment, has different generation characteristics: In terms of source, sewage sludge has a fixed origin, while ditch sludge and river and lake sediment have dispersed origins; in terms of generation frequency and quantity, sewage sludge is continuously and stably generated, ditch sludge is generated intermittently and in small quantities, and river and lake sediment generation is intermittent but in large quantities. Among the various types of sludge, sewage sludge has a relatively stable generation volume and source; therefore, the co-treatment of multi-source sludge should focus on sewage sludge.

[0035] Based on the general principle of "differentiated treatment and utilization," the sludge is classified and treated according to its organic matter content. The three types of sludge, from highest to lowest organic matter content, are: sewage sludge, ditch sludge, and river and lake sediment. The treatment processes for these three types of sludge differ. Sewage sludge can be co-treated with other urban organic solid waste through anaerobic digestion. Depending on the characteristics and needs of different cities, multiple utilization pathways for the products can be explored, such as mine ecological restoration, landfill remediation, urban landscaping, and building material applications. Ditch sludge can be treated using processes such as pretreatment, multi-stage screening, mud-water separation, and solidification. The separated organic matter is co-treated with sewage sludge. Inorganic sand and gravel can be used as roadbed materials, for making flood control sandbags, or as raw materials for other building materials. The mud cake can be processed into engineering backfill soil, permeable bricks, and ceramsite. The treatment process for river and lake sediment is similar to that for ditch sludge. Existing ditch sludge treatment sites can be fully utilized. After dewatering and solidification, the sediment can be used as engineering soil or other construction materials. At the same time, emergency response facilities will be planned to make full use of existing coal-fired power plants, waste incineration plants and landfills to provide emergency treatment for sludge from multiple sources.

[0036] In general, multi-source sludge, composed of sewage sludge, ditch sludge, and river and lake bottom sediment, is mainly composed of organic matter and inorganic particulate matter. The sludge fine sediment separation method developed in this invention can achieve the separation and recycling of organic and inorganic substances in sludge, improve sludge treatment and comprehensive utilization rate, and is especially suitable for sludge treatment in sewage treatment plants, bottom sediment removal in water environment management, and sludge treatment in drainage ditches in pipe networks.

[0037] This invention provides a method for separating fine sludge and sediment from sludge. For details of the process and equipment, please refer to [link / reference needed]. Figure 1 and Figure 2 This includes the following steps:

[0038] 1) Sludge pre-dewatering, the specific steps are as follows:

[0039] 11) Add cationic polyacrylamide to the sludge for conditioning, at a dosage of 0.5-1‰ of the oven-dry sludge. Cationic polyacrylamide has good flocculation and filtration performance in conditioning sludge, thus improving the filtration performance of the sludge.

[0040] 12) Mechanically thicken to a moisture content of 80-90%. The sludge in the sludge thickening tank 1 enters the sludge pre-dewatering device 2 for pre-dewatering. The sludge pre-dewatering device 2 can be a screw press.

[0041] 2) Neutral low-temperature hydrothermal treatment of sludge: Neutral low-temperature hydrothermal treatment is carried out in a low-temperature hydrothermal reactor 3 under high pressure and closed environment at a temperature of 100-140℃ for a reaction time of 30-60min. The pre-dewatered sludge enters the low-temperature hydrothermal reactor 3 for preliminary hydrothermal carbonization treatment.

[0042] 3) Acidic medium-temperature hydrothermal treatment of sludge: Under high pressure and a closed environment, an acidic catalyst is added to the sludge after preliminary hydrothermal carbonization and subjected to acidic medium-temperature hydrothermal treatment in a medium-temperature hydrothermal reactor 4 at a temperature of 140-180℃ for a reaction time of 60-90 minutes. The acidic catalyst is one or a mixture of two or more of sulfuric acid and hydrochloric acid, and the amount of acidic catalyst added is 1-3% of the oven-dry sludge. The acidic catalyst in the acid storage tank 6 is added to the material pipeline between the low-temperature hydrothermal reactor 3 and the medium-temperature hydrothermal reactor 4 according to process requirements.

[0043] 4) High-temperature hydrothermal carbonization treatment of sludge: The material after reaction in step 3) enters the high-temperature hydrothermal reactor 5 and is subjected to high-temperature hydrothermal carbonization treatment in a high-pressure closed environment. The temperature is 180-220℃ and the reaction time is 30-60min.

[0044] 5) Cool the suspension to room temperature and sonicate: The material after reaction in step 4) is put into ultrasonic oscillator 7 for ultrasonic treatment for 5-60 minutes. The ultrasonic frequency of the ultrasonic generator 11 installed on the side wall of ultrasonic oscillator 7 is 10-50kHz and the ultrasonic energy density is 0.1-1W / mL.

[0045] 6) The suspension is separated by hydrocyclone to obtain a fine silt layer and a biochar layer: The suspension is separated by hydrocyclone 8. The feed pressure is 0.05-0.5 MPa. The hydrocyclone 8 has a feed inlet at the top, a silt outlet at the bottom, and a sludge biochar outlet at the top.

[0046] 7) Deep dewatering of the fine silt and biochar layers: The two outlets of the hydrocyclone 8 are connected to the deep dewatering device 9 for deep dewatering of the sludge biochar and silt. Plate and frame filter press or high-pressure belt filter is used for deep dewatering. The resulting biochar organic filter cake has a moisture content of 30%-50% and an organic matter content of 60%-100%, while the resulting fine silt cake has a moisture content of 10%-30% and an organic matter content of 0%-20%.

[0047] The sludge fine sediment separation system used in this invention includes a sludge thickening tank 1, a sludge pre-dewatering device 2, a low-temperature hydrothermal reactor 3, a medium-temperature hydrothermal reactor 4, and a high-temperature hydrothermal reactor 5, connected in sequence, an ultrasonic oscillator 7, a hydrocyclone 8, and two deep dewatering devices 9. After pre-dewatering by the sludge pre-dewatering device 2, the sludge in the sludge thickening tank 1 undergoes hydrothermal carbonization treatment by being heated stepwise through the low-temperature hydrothermal reactor 3, the medium-temperature hydrothermal reactor 4, and the high-temperature hydrothermal reactor 5. The resulting suspension is then subjected to ultrasonic oscillator 7 to facilitate the separation of sludge biochar and fine sediment. The sludge biochar and fine sediment separated by the hydrocyclone 8 are then fed into the deep dewatering devices 9 for deep dewatering, resulting in biochar filter cake and sediment filter cake. The filtrate is then fed into the wastewater treatment system for further treatment and utilization. The low-temperature hydrothermal reactor 3, the medium-temperature hydrothermal reactor 4, the high-temperature hydrothermal reactor 5, and the ultrasonic oscillator 7 are all equipped with a stirrer 10. By fully stirring the materials with the stirrer 10, the reaction speed of the materials can be accelerated and the reaction efficiency can be improved.

[0048] The sludge treated by the above methods includes sludge from municipal / industrial wastewater treatment plants, dredged sediment from rivers and lakes cleared during water environment remediation, and sludge from drainage ditches in municipal pipe networks.

[0049] This invention can be summarized into two processes: sludge hydrothermal carbonization pretreatment and fine sludge separation. Steps 1-4 constitute the sludge hydrothermal carbonization pretreatment process, and steps 5-7 constitute the fine sludge separation process. The specific working principle is as follows:

[0050] The sludge hydrothermal carbonization pretreatment process involves several steps: First, the sludge is conditioned and concentrated to a moisture content of 80%-90%, achieving initial volume reduction and decreasing subsequent treatment energy consumption and costs. Then, it enters a low-temperature hydrothermal reactor at 100-140℃ to convert easily treatable organic matter into biochar, avoiding the high-temperature dissolution and release of organic matter and thus preventing carbon resource loss. Next, an acidic catalyst is added, and the sludge is sterilized in a medium-temperature hydrothermal reactor at 140-180℃. During this process, phosphorus in the sludge is converted into inorganic phosphorus, and more difficult-to-treat organic matter is converted into biochar. Some heavy metals in the sludge are passivated by the inorganic minerals and biochar. The resulting suspension is then processed in a high-temperature hydrothermal reactor at 180-220℃, where phosphorus in the sludge is further converted into inorganic phosphorus, and more difficult-to-treat organic matter is converted into biochar. Heavy metals in the sludge are further passivated by the inorganic minerals and biochar.

[0051] Fine sediment separation process: After the reaction, the suspension is cooled to room temperature and enters an ultrasonic vibrator to improve the separability of sludge biochar and fine particles, causing the sediment to separate from the biochar. It then enters a hydraulic separator, where the fine sediment separates from the biochar due to their density difference. The heavier fine sediment is discharged from the bottom outlet, forming a fine sediment layer, while the lighter biochar is discharged from the overflow outlet, forming a biochar layer. Finally, both the fine sediment layer and the biochar layer are deeply dewatered. The deeply dewatered fine sediment can be used as building materials, etc.; the biochar filter cake can be incinerated, further dried and pulverized for use as a microbial carrier in wastewater treatment plants, or used as a soil amendment material; the deeply dewatered filtrate is combined and used as liquid fertilizer or, after nitrogen and phosphorus removal treatment, returned to the wastewater treatment system as a carbon source for reverse digestion.

[0052] The following are several specific embodiments of the application of this invention. The raw materials are as follows:

[0053] Sludge: Sludge from the secondary sedimentation tank of a wastewater treatment plant in Chuzhou;

[0054] Cationic polyacrylamide: Shandong Nuoer 102NR, ionicity 50, molecular weight 10 million-11 million, concentration used 1‰.

[0055] Sulfuric acid: National Pharmaceutical Reagent

[0056] Example 1

[0057] The sludge was taken from the secondary sedimentation tank of a municipal sewage treatment plant in Chuzhou.

[0058] Step 1) Sludge pre-dewatering: Add cationic polyacrylamide solution to the sludge with a moisture content of 99% in the secondary sedimentation tank. The amount added is 1‰ of the dry sludge. Then, use a screw press to mechanically concentrate the sludge to a moisture content of 80%.

[0059] Step 2) After concentration, the sludge is put into a neutral low-temperature hydrothermal reactor and reacted in a sealed environment at 120°C for 40 minutes; concentrated sulfuric acid is added, the amount of which is 1% of the dry sludge, and the sludge is put into a medium-temperature hydrothermal reactor and reacted in a sealed environment at 160°C for 80 minutes; the sludge is then put into a high-temperature hydrothermal reactor and reacted in a sealed environment at 200°C for 60 minutes.

[0060] Step 3) Ultrasonic treatment, with an ultrasonic frequency of 20kHz, an acoustic energy density of 0.2W / mL, and a treatment time of 20min;

[0061] Step 4) Hydrocyclone separation: The feed pressure of the hydrocyclone is 0.2 MPa. The sludge enters through the sludge inlet, the organic layer of sludge biochar is discharged from the upper overflow outlet, and the fine sludge is discharged from the bottom sand outlet.

[0062] Step 5) Deep dewatering: The sludge biochar organic layer and the fine silt layer are respectively fed into a plate and frame filter press for deep dewatering.

[0063] Step 6) The filtrates are combined and then reused.

[0064] The moisture content and organic matter content of the sludge cakes from the sludge biochar layer and the fine silt layer were tested separately according to the "Test Method for Sludge from Urban Wastewater Treatment Plants (CJ / T221-2017)". After the sludge cakes were dried and crushed, the "Determination of Specific Surface Area of ​​Solid Matter by Gas Adsorption BET Method (GB / T 19587-2017)" was used to calculate the percentage of oven-dry weight in the sludge biochar and fine silt. The results are shown in Table 1.

[0065]

[0066]

[0067] Example 2

[0068] This embodiment is a variation of Embodiment 1, the difference being that: step 3) is ultrasonic treatment, the ultrasonic frequency is 20kHz, the sound energy density is 0.5W / mL, and the treatment time is 20min;

[0069] All other steps and parameters are the same as in Example 1.

[0070] The mud cake test was the same as in Example 1, and the results are shown in Table 1.

[0071] Example 3

[0072] This embodiment is a variation of Embodiment 1, the difference being:

[0073] Step 2) After concentration, the sludge is put into a neutral low-temperature hydrothermal reactor and reacted in a sealed environment at 100°C for 60 minutes; concentrated sulfuric acid is added, the amount of which is 1% of the dry sludge, and the sludge is put into a medium-temperature hydrothermal reactor and reacted in a sealed environment at 140°C for 90 minutes; the sludge is then put into a high-temperature hydrothermal reactor and reacted in a sealed environment at 180°C for 60 minutes.

[0074] All other steps and parameters are the same as in Example 1.

[0075] The mud cake test was the same as in Example 1, and the results are shown in Table 1.

[0076] Example 4

[0077] This embodiment is a variation of Embodiment 1, the difference being:

[0078] Step 2) After concentration, the sludge is put into a neutral low-temperature hydrothermal reactor and reacted in a sealed environment at 140°C for 30 minutes; concentrated sulfuric acid is added, the amount of which is 1% of the dry sludge, and the sludge is put into a medium-temperature hydrothermal reactor and reacted in a sealed environment at 180°C for 60 minutes; then it is put into a high-temperature hydrothermal reactor and reacted in a sealed environment at 220°C for 30 minutes.

[0079] All other steps and parameters are the same as in Example 1.

[0080] The mud cake test was the same as in Example 1, and the results are shown in Table 1.

[0081] Comparative Example 1 (low-temperature treatment only)

[0082] Step 1) Sludge pre-dewatering: Add cationic polyacrylamide solution to the sludge with a moisture content of 99% in the secondary sedimentation tank. The amount added is 1‰ of the dry sludge. Then, use a screw press to mechanically concentrate the sludge to a moisture content of 80%.

[0083] Step 2) After concentration, the sludge is fed into a neutral low-temperature hydrothermal reactor and reacted in a sealed environment at 120°C for 40 minutes.

[0084] Step 3) Ultrasonic treatment, with an ultrasonic frequency of 20kHz, an acoustic energy density of 0.2W / mL, and a treatment time of 20min;

[0085] Step 4) Cyclone separation, with a feed pressure of 0.2 MPa. The sludge biochar organic layer is discharged from the upper overflow port, and the fine sludge and sand are discharged from the bottom sand discharge port.

[0086] Step 5) Deep dewatering: The sludge biochar organic layer and the fine silt layer are respectively fed into a plate and frame filter press for deep dewatering.

[0087] Step 6) The filtrates are combined and processed for use.

[0088] The mud cake test was the same as in Example 1, and the results are shown in Table 1.

[0089] Comparative Example 2 (medium temperature treatment only)

[0090] Step 1) Sludge pre-dewatering: Add cationic polyacrylamide solution to the sludge with a moisture content of 99% in the secondary sedimentation tank. The amount added is 1‰ of the dry sludge. Then, use a screw press to mechanically concentrate the sludge to a moisture content of 80%.

[0091] Step 2) After the above treatment, concentrated sulfuric acid is added to the sludge, the amount of which is 1% of the oven-dry sludge, and the mixture is put into a medium-temperature hydrothermal reactor and reacted in a sealed environment at 160°C for 80 minutes.

[0092] Step 3) Ultrasonic treatment, with an ultrasonic frequency of 20kHz, an acoustic energy density of 0.2W / mL, and a treatment time of 20min;

[0093] Step 4) Cyclone separation, with a feed pressure of 0.2 MPa. The sludge biochar organic layer is discharged from the upper overflow port, and the fine sludge and sand are discharged from the bottom sand discharge port.

[0094] Step 5) Deep dewatering: The sludge biochar organic layer and the fine silt layer are respectively fed into a plate and frame filter press for deep dewatering.

[0095] Step 6) The filtrates are combined and processed for use.

[0096] The mud cake test was the same as in Example 1, and the results are shown in Table 1.

[0097] Comparative Example 3 (High-Temperature Treatment Only)

[0098] Step 1) Sludge pre-dewatering: Add cationic polyacrylamide solution to the sludge with a moisture content of 99% in the secondary sedimentation tank. The amount added is 1‰ of the dry sludge. Then, use a screw press to mechanically concentrate the sludge to a moisture content of 80%.

[0099] Step 2) The treated sludge is fed into a high-temperature hydrothermal reactor and reacted in a sealed environment at 200°C for 60 minutes.

[0100] Step 3) Ultrasonic treatment, with an ultrasonic frequency of 20kHz, an acoustic energy density of 0.2W / mL, and a treatment time of 20min;

[0101] Step 4) Cyclone separation, with a feed pressure of 0.2 MPa. The sludge biochar organic layer is discharged from the upper overflow port, and the fine sludge and sand are discharged from the bottom sand discharge port.

[0102] Step 5) Deep dewatering: The sludge biochar organic layer and the fine silt layer are respectively fed into a plate and frame filter press for deep dewatering.

[0103] Step 6) The filtrates are combined and processed for use.

[0104] The mud cake test was the same as in Example 1, and the results are shown in Table 1.

[0105] Comparative Example 4 (only low temperature and medium temperature treatments)

[0106] Step 1) Sludge pre-dewatering: Add cationic polyacrylamide solution to the sludge with a moisture content of 99% in the secondary sedimentation tank. The amount added is 1‰ of the dry sludge. Then, use a screw press to mechanically concentrate the sludge to a moisture content of 80%.

[0107] Step 2) After concentration, the sludge is put into a neutral low-temperature hydrothermal reactor and reacted in a sealed environment at 120°C for 40 minutes; concentrated sulfuric acid is added, the amount of which is 1% of the dry sludge, and the sludge is put into a medium-temperature hydrothermal reactor and reacted in a sealed environment at 160°C for 80 minutes.

[0108] Step 3) Ultrasonic treatment, with an ultrasonic frequency of 20kHz, an acoustic energy density of 0.2W / mL, and a treatment time of 20min;

[0109] Step 4) Cyclone separation, with a feed pressure of 0.2 MPa. The sludge biochar organic layer is discharged from the upper overflow port, and the fine sludge and sand are discharged from the bottom sand discharge port.

[0110] Step 5) Deep dewatering: The sludge biochar organic layer and the fine silt layer are respectively fed into a plate and frame filter press for deep dewatering.

[0111] Step 6) The filtrates are combined and processed for use.

[0112] The mud cake test was the same as in Example 1, and the results are shown in Table 1.

[0113] Comparative Example 5 (only medium and high temperature treatments)

[0114] Step 1) Sludge pre-dewatering: Add cationic polyacrylamide solution to the sludge with a moisture content of 99% in the secondary sedimentation tank. The amount added is 1‰ of the dry sludge. Then, use a screw press to mechanically concentrate the sludge to a moisture content of 80%.

[0115] Step 2) After the above treatment, concentrated sulfuric acid is added to the sludge, the amount of which is 1% of the oven-dry sludge, and the mixture is put into a medium-temperature hydrothermal reactor and reacted in a sealed environment at 160°C for 80 minutes; then it is put into a high-temperature hydrothermal reactor and reacted in a sealed environment at 200°C for 60 minutes.

[0116] Step 3) Ultrasonic treatment, with an ultrasonic frequency of 20kHz, an acoustic energy density of 0.2W / mL, and a treatment time of 20min;

[0117] Step 4) Cyclone separation, with a feed pressure of 0.2 MPa. The sludge biochar organic layer is discharged from the upper overflow port, and the fine sludge and sand are discharged from the bottom sand discharge port.

[0118] Step 5) Deep dewatering: The sludge biochar organic layer and the fine silt layer are respectively fed into a plate and frame filter press for deep dewatering.

[0119] Step 6) The filtrates are combined and processed for use.

[0120] The mud cake test was the same as in Example 1, and the results are shown in Table 1.

[0121] Comparative Example 6 (only low temperature and high temperature treatments)

[0122] Step 1) Sludge pre-dewatering: Add cationic polyacrylamide solution to the sludge with a moisture content of 99% in the secondary sedimentation tank. The amount added is 1‰ of the dry sludge. Then, use a screw press to mechanically concentrate the sludge to a moisture content of 80%.

[0123] Step 2) After concentration, the sludge is fed into a neutral low-temperature hydrothermal reactor and reacted in a sealed environment at 120°C for 40 minutes; then it is fed into a high-temperature hydrothermal reactor and reacted in a sealed environment at 200°C for 60 minutes.

[0124] Step 3) Ultrasonic treatment, with an ultrasonic frequency of 20kHz, an acoustic energy density of 0.2W / mL, and a treatment time of 20min;

[0125] Step 4) Cyclone separation, with a feed pressure of 0.2 MPa. The sludge biochar organic layer is discharged from the upper overflow port, and the fine sludge and sand are discharged from the bottom sand discharge port.

[0126] Step 5) Deep dewatering: The sludge biochar organic layer and the fine silt layer are respectively fed into a plate and frame filter press for deep dewatering.

[0127] Step 6) The filtrates are combined and processed for use.

[0128] The mud cake test was the same as in Example 1, and the results are shown in Table 1.

[0129] Comparative Example 7 (without ultrasonic treatment)

[0130] Step 1) Sludge pre-dewatering: Add cationic polyacrylamide solution to the sludge with a moisture content of 99% in the secondary sedimentation tank. The amount added is 1‰ of the dry sludge. Then, use a screw press to mechanically concentrate the sludge to a moisture content of 80%.

[0131] Step 2) After concentration, the sludge is put into a neutral low-temperature hydrothermal reactor and reacted in a sealed environment at 120°C for 40 minutes; concentrated sulfuric acid is added, the amount of which is 1% of the dry sludge, and the sludge is put into a medium-temperature hydrothermal reactor and reacted in a sealed environment at 160°C for 80 minutes; the sludge is then put into a high-temperature hydrothermal reactor and reacted in a sealed environment at 200°C for 60 minutes.

[0132] Step 3) Cyclone separation, with a feed pressure of 0.2 MPa. The sludge biochar organic layer is discharged from the upper overflow port, and the fine sludge and sand are discharged from the bottom sand discharge port.

[0133] Step 4) Deep dewatering: The sludge biochar organic layer and the fine silt layer are respectively fed into a plate and frame filter press for deep dewatering;

[0134] Step 5) The filtrates are combined and processed for use.

[0135] The mud cake test was the same as in Example 1, and the results are shown in Table 1.

[0136] Table 1

[0137]

[0138] As demonstrated in Examples 1-4 above, the present invention can achieve the separation of inorganic and organic components in sludge. First, a multi-stage hydrothermal carbonization system is used for treatment, followed by ultrasonic vibration treatment, to achieve thorough separation of organic and inorganic matter in the sludge, especially for fine sediment. Results show that the oven-dry weight of the separated sludge biochar and fine sediment is relatively balanced. The moisture content of the sludge biochar is below 40%, and the organic matter content is above 70%, while the moisture content of the fine sediment is below 20%, and the organic matter content is below 20%. In contrast, processes other than those described in the present invention are less effective at separating inorganic and organic components: in Comparative Examples 1-6, the hydrothermal treatment temperature and time are too short, resulting in insufficient modification of the sludge biochar and incomplete separation of fine sediment from organic matter, leading to poor separation of fine sediment; in Comparative Example 7, the absence of ultrasonic treatment resulted in insufficient separation of sludge biochar and fine sediment after hydrothermal treatment, leading to a poorer separation effect of fine sediment compared to the process described in the present invention.

[0139] In summary, the beneficial effects of the present invention are as follows:

[0140] 1. In the pretreatment of sludge, this invention uses a step-by-step heating hydrothermal carbonization process and changes the reaction conditions to convert organic matter into biochar, retaining carbon resources in the sludge; it also increases the release of phosphorus from the sludge and recovers phosphorus resources; and it enhances the passivation of heavy metals in the sludge and reduces the biotoxicity of heavy metals.

[0141] 2. This invention achieves efficient separation of organic matter and fine silt through high-efficiency hydrothermal modification, resulting in sludge biochar with high organic matter content and high calorific value, and fine silt with low organic matter content and high silt content. The filtrate has high carbon, nitrogen, and phosphorus content, and can be used as liquid fertilizer or, after denitrification and phosphorus removal treatment, as a carbon source for reverse digestion and resource utilization in wastewater treatment systems.

[0142] 3. The present invention first reduces the amount of sludge by pre-dewatering, thereby reducing the amount of sludge to be treated and the treatment cost.

[0143] 4. This invention improves the separation of organic matter and fine silt in sludge by front-end hydrothermal treatment and ultrasonic treatment, and then separates and dewaters the sludge for disposal and utilization, thereby expanding the sludge disposal and utilization pathways and reducing disposal and utilization costs.

[0144] 5. This invention uses only a small amount of sludge conditioner and concentrated sulfuric acid, resulting in low reagent consumption.

[0145] Many specific details have been set forth in the foregoing description in order to provide a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed above.

Claims

1. A method for separating fine sediment from sludge, characterized in that, Includes the following steps: 1) Sludge pre-dewatering; 2) Neutral low-temperature hydrothermal treatment of sludge; Step 2) is carried out in a high-pressure closed environment with a neutral low-temperature hydrothermal treatment at a temperature of 100-140℃ and a reaction time of 30-60min. 3) Acidic medium-temperature hydrothermal treatment of sludge; In step 3), acidic catalyst is added to carry out acidic medium-temperature hydrothermal treatment under high pressure and closed environment, the temperature is 140-180℃, and the reaction time is 60-90min. 4) High-temperature hydrothermal carbonization treatment of sludge; Step 4) is carried out in a high-pressure closed environment with a temperature of 180-220℃ and a reaction time of 30-60min. 5) Cool the suspension to room temperature and sonicate it; in step 5), the ultrasonic frequency is 10-50 kHz, the ultrasonic energy density is 0.1-1 W / mL, and the ultrasonic treatment time is 5-60 min. 6) The suspension is separated by hydrocyclone to obtain a fine silt layer and a biochar layer; in step 6), a hydrocyclone is used to perform hydrocyclone separation of the suspension, with the feed pressure being 0.05-0.5 MPa. The hydrocyclone has a feed inlet at the top, a silt outlet at the bottom, and a biochar outlet at the top. 7) The fine sediment layer and biochar layer are deeply dehydrated respectively; The pre-dewatered sludge undergoes hydrothermal carbonization treatment with progressively increasing temperature. The suspension is then treated with ultrasound and cyclone separation to separate the biochar and fine silt. Finally, after deep dewatering, biochar filter cake and silt filter cake are obtained, and the filtrate is further processed in the wastewater treatment system.

2. The method for separating fine sludge and sediment according to claim 1, characterized in that: The specific steps for sludge pre-dewatering in step 1) are as follows: 11) Add cationic polyacrylamide to the sludge for conditioning, the amount of which is 0.5-1‰ of the oven-dry sludge; 12) Mechanically concentrate to a moisture content of 80-90%.

3. The method for separating fine sludge and sediment according to claim 1, characterized in that: The acidic catalyst is one or both of sulfuric acid and hydrochloric acid, and the amount of acidic catalyst added is 1-3% of the oven-dried sludge.

4. The method for separating fine sludge and sediment according to claim 1, characterized in that: In step 7), deep dewatering is performed using plate and frame filter press or high-pressure belt dewatering. The resulting organic filter cake has a moisture content of 30%-50% and an organic matter content of 60%-100%, while the fine mud and sand cake has a moisture content of 10%-30% and an organic matter content of 0%-20%.

5. The method for separating fine sludge and sediment according to any one of claims 1-4, characterized in that: The sludge refers to sludge from municipal / industrial wastewater treatment plants, dredged sediment from rivers and lakes, and / or sludge from municipal pipeline drainage ditches.

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