Method for treating sludge by combining hydrodynamic cavitation and subcritical wet oxidation technology

Abstract

The application discloses a method for treating sludge by combining hydraulic cavitation and subcritical wet oxidation technology, which is implemented in an integrated continuous reaction system and comprises the following steps: adding a metal catalyst to the sludge and heating and stirring; performing hydraulic cavitation treatment on the treated sludge through a Venturi tube; passing the treated sludge into a cavitation-oxidation coupling area for reaction; performing subcritical wet oxidation treatment on the treated sludge; using an expander and a heat exchanger system after a subcritical wet oxidation reaction kettle, the waste heat of the treated sludge is used for preheating the feed sludge, so that partial waste heat recovery is realized; and the sludge after waste heat recovery is sent into a three-phase separator, balanced gas pressure is achieved, and solid-liquid separation is completed. The method solves the problems of high energy consumption and large amount of reagent demand in the existing sludge treatment, has the advantages of strong universality, small reagent addition amount, high oxygen utilization rate and no secondary pollution, and the economic efficiency is improved by waste heat recovery; and the solid-liquid separation products can be resourceized.

Description

Technical Field

[0001] This invention relates to environmental protection technology, and in particular to a method for treating sludge using a combination of hydraulic cavitation and subcritical wet oxidation technology. Background Technology

[0002] A large amount of sludge is generated during the wastewater treatment process, making it urgent to achieve the reduction, harmlessness, stabilization, resource utilization, and treatment of sludge.

[0003] Subcritical wet oxidation for sludge treatment has become a research hotspot in recent years. This method not only significantly reduces the amount and volume of sludge but also yields organic matter and struvite, offering low cost and minimal pollution, thus achieving sludge reduction and resource recovery. This method typically involves placing sludge in a closed reactor and treating pollutants using high temperature and pressure, while introducing air or oxygen as an oxidant. The reaction conditions usually range from subcritical to supercritical. Subcritical wet oxidation operates at moderate temperature and pressure, offering higher energy efficiency compared to supercritical methods, while still achieving significant organic matter degradation, converting high-molecular-weight organic matter into smaller organic and inorganic molecules through processes such as hydrolysis, pyrolysis, and oxidation. However, this technology still has some drawbacks. Its energy consumption during the reaction process is high, resulting in poor economic efficiency. Furthermore, it is prone to reactor blockage, corrosion, and slow start-up due to the deposition of inorganic matter (such as sand particles) in the sludge and high organic matter content. Sludge settling also reduces treatment efficiency. Hydraulic cavitation technology can break down the cell walls of sludge and release interstitial water. This invention found that when traditional hydraulic cavitation technology is applied to sludge treatment, its low free radical yield leads to insufficient cell wall breaking efficiency, a sludge reduction rate of only about 30%, and incomplete degradation of macromolecular organic matter in sludge, which can easily inhibit subsequent biochemical treatment.

[0004] It should be noted that the information disclosed in the background section above is only for understanding the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] The main objective of this invention is to overcome the deficiencies in the aforementioned background technology and provide a method for treating sludge by combining hydraulic cavitation and subcritical wet oxidation technologies, thereby achieving a comprehensive sludge treatment solution that can simultaneously achieve efficient degradation, low energy consumption, anti-clogging, and resource-recoverable products.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for treating sludge using a combination of hydraulic cavitation and subcritical wet oxidation technologies, wherein the method is carried out in an integrated continuous reaction system, and includes the following steps:

[0008] S1) Add a metal catalyst to the sludge and heat and stir;

[0009] S2) The sludge treated in step S1) is subjected to hydraulic cavitation treatment through a venturi tube;

[0010] S3) The sludge treated in step S2) is passed into the cavitation-oxidation coupling zone for reaction;

[0011] S4) The sludge treated in step S3) is subjected to subcritical wet oxidation treatment.

[0012] S5) The sludge treated in step S4) is preheated using the expander and heat exchanger system after the subcritical wet oxidation reactor to recover part of the waste heat.

[0013] S6) The sludge after recovering waste heat in step S5) is fed into a three-phase separator to balance the gas pressure and perform solid-liquid separation of the product.

[0014] Furthermore, in step S1), the sludge has a moisture content of 80 wt% to 95 wt% and an organic matter content of ≥30% (VSS / DS).

[0015] Furthermore, the content of the transition metal catalyst added in step S1) is from 0.05 wt% to 1.0 wt%.

[0016] Furthermore, in step S1), the rotation speed for heating and stirring the sludge is 80 rpm to 120 rpm.

[0017] Furthermore, in step S1), 0.01 to 0.05 wt% of hydrogen peroxide is added as an auxiliary initiator.

[0018] Furthermore, in step S1), the sludge is heated to a temperature of 80 to 100 degrees Celsius, preferably 90 degrees Celsius.

[0019] Furthermore, in step S2), the inlet pressure of the hydraulic cavitation reactor is 0.2 MPa to 1.2 MPa.

[0020] Furthermore, a rotating shear chamber connected in series with a venturi tube is provided in the hydraulic cavitation reactor.

[0021] Furthermore, in step S3), a stagnation-mixing coupling cavity is set between the outlet of the cavitation reactor and the inlet of the subcritical wet oxidation reactor.

[0022] Furthermore, in step S3), the residence time is 0.5 to 5 minutes, and the turbulent kinetic energy is greater than or equal to 0.5 m. 2 / s 3 .

[0023] Further, in step S4), the subcritical wet oxidation treatment is carried out at a temperature of 230°C to 280°C, a pressure of 4 MPa to 22 MPa, an oxygen partial pressure of 0.3 MPa to 3 MPa, and a subcritical reaction time of 15 min to 60 min.

[0024] The present invention has the following beneficial effects:

[0025] This invention provides a method for treating sludge using a combination of hydraulic cavitation and subcritical wet oxidation technologies. The core of this method is the synergistic coupling of these two technologies, combined with pretreatment control, pre-reaction enhancement, waste heat recovery, and resource separation mechanisms, resulting in a highly efficient and economical sludge treatment solution. In the pretreatment stage, a metal catalyst (or supplemented with hydrogen peroxide) is added to the sludge and heated and stirred to form a homogeneous slurry, providing a uniform active environment for subsequent reactions. Hydraulic cavitation utilizes the hydrodynamic effects of a venturi tube (or a superimposed rotating shear chamber) to generate localized high temperature and pressure, which can break down extracellular polymers and microbial cells in the sludge to release interstitial water and improve reaction contact efficiency, while also separating sand particles to prevent clogging and wear in the subcritical system. The retention-mixed flow coupling chamber controls the residence time and turbulent kinetic energy, allowing free radicals generated by cavitation to pre-react with oxygen, reducing COD and lessening the burden on subcritical oxidation. Subcritical wet oxidation deeply degrades macromolecular organic matter under specific temperature and pressure, while simultaneously achieving efficient inactivation of pathogens (fecal coliform inactivation rate ≥99.9999%, reaching US EPA Class). The system employs a standard (A) and heavy metal stabilization (over 90% transfer to the liquid phase); subsequently, an expander and heat exchanger are used to recover waste heat, maintaining a system energy self-sufficiency rate of 50%, significantly reducing energy consumption. Finally, a three-phase separator achieves solid-liquid separation. The solid residue (VSS ≤ 10%, oil content ≤ 1.2 wt%) can be used as building materials or compost, while the liquid phase can recover magnesium ammonium phosphate. This overall technology not only features low energy consumption, low reagent dosage, and high oxygen utilization, but also significant treatment effects (VSS removal rate ≥ 87%, crude oil component degradation rate ≥ 93%), no secondary pollution, and strong versatility, effectively solving the pain points of existing sludge treatment methods such as high energy consumption, easy clogging, and incomplete degradation.

[0026] Other beneficial effects of the embodiments of the present invention will be further described below. Attached Figure Description

[0027] Figure 1 This is a flowchart of the method for treating sludge using a combination of hydraulic cavitation and subcritical wet oxidation technologies according to the present invention. Detailed Implementation

[0028] The embodiments of the present invention will be described in detail below. It should be emphasized that the following description is merely exemplary and not intended to limit the scope and application of the present invention.

[0029] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as "connected to" another component, it can be directly connected to or indirectly connected to that other component. Furthermore, a connection can be used for fixing, coupling, or communication.

[0030] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0031] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of the present invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0032] See Figure 1 This invention provides a method for treating sludge using a combination of hydraulic cavitation and subcritical wet oxidation technologies. The method is carried out in an integrated continuous reaction system and includes the following steps:

[0033] S1) Add a metal catalyst to the sludge and heat and stir.

[0034] In some embodiments, the sludge in step S1) includes municipal sludge or chemical plant sludge.

[0035] In some embodiments, the sludge in step S1) has a moisture content of 80 wt% to 95 wt% and an organic matter content of ≥30% (VSS / DS).

[0036] In some embodiments, the transition metal catalyst (such as Fe) added in step S1) 2+ / Cu 2+ The content of the composite catalyst is 0.05 wt% to 1.0 wt%.

[0037] In some embodiments, the rotation speed for heating and stirring the sludge in step S1) is 80 rpm to 120 rpm.

[0038] In some embodiments, 0.01 to 0.05 wt% of hydrogen peroxide is added as an auxiliary initiator in step S1).

[0039] In some embodiments, step S1) further heats the sludge to a temperature of 80 to 100 degrees Celsius, preferably 90 degrees Celsius.

[0040] S2) The sludge treated in step S1) is subjected to hydraulic cavitation treatment through a venturi tube.

[0041] In some embodiments, the inlet pressure of the hydraulic cavitation reactor in step S2) is 0.2 MPa to 1.2 MPa.

[0042] In some embodiments, for sludge with high viscosity or high oil content, the hydraulic cavitation treatment, after passing through a venturi tube, is further processed by a rotating shear chamber to enhance local shear force, further break up extracellular polymers and oil droplets, and avoid clogging.

[0043] S3) The sludge treated in step S2) is passed into the cavitation-oxidation coupling zone for reaction.

[0044] In some embodiments, in step S3), a stagnation-mixing coupling cavity is provided between the outlet of the cavitation reactor and the inlet of the subcritical wet oxidation reactor.

[0045] In some embodiments, the residence time in step S3) is 0.5 minutes to 5 minutes, and the turbulent kinetic energy is greater than or equal to 0.5 m. 2 / s 3 .

[0046] S4) The sludge treated in step S3) is subjected to subcritical wet oxidation treatment.

[0047] In some embodiments, the subcritical wet oxidation treatment in step S4) is carried out at a temperature of 230°C to 280°C, a pressure of 4 MPa to 22 MPa, an oxygen partial pressure of 0.3 MPa to 3 MPa, and a subcritical reaction time of 15 min to 60 min.

[0048] S5) The sludge treated in step S4) is preheated using an expander and heat exchanger system after the subcritical wet oxidation reactor to recover some of the waste heat.

[0049] In some embodiments, step S5) includes an expansion work unit and / or an indirect heat exchange unit.

[0050] S6) The sludge after recovering waste heat in step S5) is fed into a three-phase separator to balance the gas pressure and perform solid-liquid separation of the product.

[0051] In some embodiments, step S6) includes a solid-liquid separation unit to separate the treated waste liquid.

[0052] This invention reveals that sludge contains up to 50% or more inorganic matter and sand particles. Furthermore, during subcritical wet oxidation of sludge, even with high moisture content, blockage, reactor corrosion, and slow start-up are still common, with these issues becoming more pronounced at high organic matter content. Additionally, sludge settling can reduce efficiency during subcritical wet oxidation. In this invention, hydraulic cavitation technology, as a pretreatment step in subcritical wet oxidation, can both break down reactor walls and remove sand afterward, reducing wear and blockage in the subcritical wet oxidation system.

[0053] This invention achieves efficient sludge treatment through the synergistic coupling of hydraulic cavitation and subcritical wet oxidation technologies, combined with an integrated process of pretreatment, coupled reaction, waste heat recovery, and product separation. In the initial stage of treatment, the sludge undergoes pretreatment: a transition metal catalyst is added to the sludge and heated and stirred to form a homogeneous slurry. The uniform dispersion of the catalyst provides the active conditions for subsequent oxidation reactions. If it is necessary to enhance the reaction initiation effect, a small amount of hydrogen peroxide can be added as an auxiliary initiator. This step lays the reaction foundation for the entire treatment process and avoids fluctuations in subsequent reaction efficiency due to uneven sludge distribution.

[0054] The pretreated sludge enters the hydraulic cavitation treatment stage. Through a venturi tube (and in some scenarios, a rotary shear chamber), the sludge slurry reaches a set flow rate under specific pressure control, utilizing fluid dynamics to generate a localized high-temperature and high-pressure environment. This environment effectively breaks down extracellular polymers and microbial cells in the sludge, releasing interstitial water and sand particles from within the sludge. This achieves sludge cell disruption, improving the contact efficiency of subsequent reactions with organic matter; and reduces structural wear and clogging risks in the subsequent subcritical wet oxidation system by removing sand, thus solving problems such as clogging, reactor corrosion, and slow start-up that easily occur in traditional subcritical treatment when there is high water content and high organic matter content.

[0055] After cavitation treatment, the sludge enters the retention-mixed flow coupling chamber. Under controlled residence time and turbulent kinetic energy, the free radicals generated during cavitation fully contact oxygen and undergo pre-reaction, degrading part of the chemical oxygen demand in advance and providing easily degradable substrates for subsequent subcritical wet oxidation. This transitional stage further enhances the synergy between hydraulic cavitation and subcritical oxidation, avoiding the direct entry of large organic molecules into the main reaction zone, which would lead to incomplete oxidation.

[0056] Subsequently, the pre-reacted sludge enters a subcritical wet oxidation reactor, where it reacts for a certain period of time under specific temperature, pressure, and oxygen partial pressure conditions. Since the sludge cell wall has already been broken down by hydraulic cavitation in the initial stage, the subcritical system does not require additional energy for cell disruption. It can focus on the deep degradation of macromolecular organic matter, while efficiently inactivating pathogens in the sludge and transferring heavy metals to the liquid phase for stabilization. This ensures that the sludge treatment meets the harmless standard, solving the problems of incomplete degradation and inhibitory effects on subsequent biological treatment caused by traditional hydraulic cavitation.

[0057] The high-temperature fluid after the reaction first passes through an expander to drive the front-end feeding equipment, and then preheats the sludge slurry to be treated through a heat exchanger. Waste heat recovery significantly reduces the overall energy consumption of the system, achieving a certain degree of energy self-sufficiency and effectively improving the high energy consumption of single subcritical technology. Finally, the heat-exchanged mixture enters a three-phase separator, where solid-liquid separation is completed while balancing the gas pressure. The separated solid residue, due to its low oil content and low volatile suspended solids content, can be recycled for use as building materials or compost; the liquid phase can be used for subsequent recovery of resources such as magnesium ammonium phosphate, truly realizing the resource utilization of sludge treatment, with no secondary pollution generated throughout the process.

[0058] Overall, this invention not only enables deep treatment of different types of sludge, ensuring the thoroughness and stability of the treatment effect, but also balances economy and environmental protection through energy recovery, precise dosing of reagents and product resource utilization. It solves the problems of high energy consumption, large reagent demand, easy secondary pollution and resource waste in existing sludge treatment technologies.

[0059] The following further describes specific embodiments of the present invention and their experimental verification.

[0060] A method for treating sludge using a combination of hydraulic cavitation and subcritical wet oxidation technologies mainly includes the following processes (see...). Figure 1 The process involves the following steps: S1) Adding a metal catalyst to the sludge and heating and stirring; S2) Performing hydraulic cavitation treatment on the sludge from S1) through a venturi tube; S3) Passing the sludge from S2) into a cavitation-oxidation coupling zone for reaction; S4) Performing subcritical wet oxidation treatment on the sludge treated in S3); S5) Preheating the feed sludge after S4) using an expander + heat exchanger system after the subcritical wet oxidation reactor to recover some waste heat; S6) Allowing the sludge after waste heat recovery in S5) to enter a three-phase separator to balance the gas pressure and simultaneously separate the solid and liquid products. Through this method, sludge treated by hydraulic cavitation and subcritical wet oxidation forms a sludge treatment method that is universally applicable, has low energy consumption, requires less reagent dosage, has high oxygen utilization, and produces no secondary pollution, solving the problems of high energy consumption and large reagent requirements in existing sludge treatment technologies.

[0061] Example 1:

[0062] Raw material properties: Moisture content: 78 wt%; Oil content (as DS, i.e., the percentage of oil mass to dry solids mass): 28 wt%; Inorganic solids content: 72 wt% DS; Heavy metals Cd: 45 mg / kg-DS; Pb: 380 mg / kg-DS; Viscosity (25℃): Recommended 12,000 mPa·s

[0063] S1), a metal catalyst is added to the sludge and heated and stirred.

[0064] Seawater was injected into the oily sludge to dilute it to a water content of 88 wt%, and 0.30 wt% (based on DS) of Fe was added. 2+ / Cu 2 + The composite catalyst (molar ratio 2:1) was subjected to high-speed shearing for 5 min to obtain a homogeneous slurry, and the sludge was heated and stirred for 15 min.

[0065] S2), the pretreated sludge is subjected to hydraulic cavitation treatment through a Venturi tube. The homogenized slurry is pressurized to 0.70 MPa by a screw pump and fed into the Venturi reactor: Venturi throat flow velocity: 42 m / s.

[0066] S3), the cavitation-treated sludge from S2) is introduced into the retention-mixed flow coupling chamber, with an average residence time of 2.0 min; the turbulent kinetic energy is controlled at 1.1 m. 2 / s 3 This allows free radicals to pre-react with molecular oxygen, resulting in an average decrease of 18% in COD of sludge sampled from this area.

[0067] S4) The slurry from S3) is continuously injected into the subcritical reactor by a high-pressure plunger pump:

[0068] Oxidation was carried out continuously for 45 min under conditions of oxygen-containing gas, maintained at a temperature of 280 ℃, a pressure of 4 MPa, and an oxygen partial pressure of 1 MPa. During the reaction, the VSS removal rate was ≥90%, and the crude oil component (C...) was... 10 –C 40 The degradation rate is ≥93%, and more than 90% of heavy metals are transferred to the liquid phase and stabilized. The COD content of the sludge solid phase after subcritical wet oxidation is almost 0, and the average COD content of the liquid phase is 509.3 mg / L.

[0069] S5) The high-temperature fluid (280 ℃, 4 MPa) after the reaction first passes through a positive displacement expander to drive a cavitation feed pump. After the work is done, the fluid temperature drops to 165 ℃. The cold slurry is then preheated by a shell-and-tube heat exchanger and finally discharged at a temperature ≤85 ℃. The system energy self-sufficiency rate is maintained at 50%.

[0070] S6) After heat exchange, the mixture enters a horizontal three-phase separator, where the solid and liquid phases are separated while balancing the gas pressure. The oil content of the solid phase residue is ≤1.2 wt%, which can be recycled for use as building materials or compost; the liquid phase can be used for subsequent recovery of magnesium ammonium phosphate.

[0071] Example 2:

[0072] Raw material properties: Moisture content: 82 wt%; VSS / DS: 68 wt%; Total nitrogen (as DS, i.e., the percentage of dry solids in the sludge to the total sludge mass): 6.2 wt%; Total phosphorus (as DS): 1.4 wt%; Pathogens (fecal coliforms): 1.2 × 10⁻⁶ 7 MPN / g-DS.

[0073] S1), a metal catalyst is added to the sludge and heated and stirred.

[0074] In this embodiment, the step of performing hydraulic cavitation pretreatment on the sludge further includes injecting fresh water into the sludge to dilute it to a water content of 91 wt%, and adding 0.25 wt% (based on DS) of Fe. 2+ / Cu 2+ The composite catalyst was added, and 0.05 wt% hydrogen peroxide was added as an auxiliary initiator. The mixture was homogenized and stirred for 3 minutes, and the sludge was heated and stirred for 10 minutes.

[0075] S2), the pretreated sludge undergoes hydraulic cavitation treatment via a Venturi tube and rotating shear chamber. The homogenized slurry is pressurized to 0.55 MPa by a screw pump and fed into the Venturi reactor: Venturi throat flow velocity: 38 m / s. As the slurry temperature rises, the soluble COD (SCOD) increases from 1200 mg / L to 4600 mg / L, indicating the breakdown of extracellular polymers.

[0076] In this embodiment, the sludge undergoes hydraulic cavitation treatment, during which the sticky organic matter and microbial community in the sludge will decompose under local high temperature and pressure. The microbial cells in the sludge will separate or break down, releasing sand particles between and within the microbial cells, which prepares for subsequent subcritical wet oxidation.

[0077] S3), the cavitation-treated sludge from S2) is introduced into the retention-mixed flow coupling chamber, where it is retained for an average of 1.5 minutes; the turbulent kinetic energy is controlled at 1.0 m³ / s. 2 / s 3 This allows free radicals to pre-react with molecular oxygen, resulting in an apparent 12% decrease in SCOD in this segment, NH4 + -N increased by 15%, providing readily degradable substrates for subsequent subcritical oxidation.

[0078] S4) The slurry from S3) is continuously injected into the subcritical reactor by a high-pressure plunger pump:

[0079] In this embodiment, oxidation was carried out for 45 minutes under the conditions of oxygen-containing gas, temperature of 280°C, pressure of 4 MPa, and oxygen partial pressure of 1 MPa. During the reaction, the VSS removal rate was 87%, the total nitrogen removal rate was 52% (converted to N2), more than 90% of the total phosphorus entered the liquid phase, the fecal coliform inactivation rate was ≥99.9999%, meeting the USEPA Class A standard, and more than 90% of the heavy metals were transferred to the liquid phase and stabilized.

[0080] After the reaction (S5), the high-temperature fluid (28℃, 4MPa) first passes through a positive displacement expander to drive a cavitation feed pump. After the work is done, the fluid temperature drops to 165℃. The cold slurry is then preheated by a shell-and-tube heat exchanger and finally discharged at a temperature ≤85℃. The system energy self-sufficiency rate is maintained at 50%.

[0081] S6) After heat exchange, the mixture enters a horizontal three-phase separator, where the solid and liquid phases are separated while balancing the gas pressure. The solid phase residue VSS ≤ 10wt% and contains 48%wt% water, which can be recycled for use as building materials or compost. The liquid phase can be used for subsequent recovery of magnesium ammonium phosphate mother liquor.

[0082] In summary, this invention focuses on the synergistic coupling of hydraulic cavitation and subcritical wet oxidation technologies. It achieves efficient sludge treatment through an integrated process of pretreatment, cavitation cell disruption, pre-reaction, deep oxidation, waste heat recovery, and resource-based separation. In the pretreatment stage, a metal catalyst (or supplemented with hydrogen peroxide) is added to the sludge and heated and stirred to form a homogeneous slurry, creating a uniform and active environment for subsequent reactions. Hydraulic cavitation utilizes the hydrodynamic effects of a venturi tube (or a superimposed rotating shear chamber) to generate localized high temperature and pressure, which can break down extracellular polymers and microbial cells in the sludge to release interstitial water, and separate sand particles to prevent clogging and wear in the subcritical system. The retention-mixing coupling chamber controls the residence time and turbulent kinetic energy, allowing free radicals generated by cavitation to pre-react with oxygen, reducing COD and providing easily degradable substrates for subcritical oxidation. Subcritical wet oxidation deeply degrades macromolecular organic matter under specific temperature and pressure, while simultaneously inactivating pathogens and stabilizing heavy metals. Finally, an expander and heat exchanger recover waste heat (maintaining a system energy self-sufficiency rate of 50%), and a three-phase separator achieves solid-liquid separation. The experimental results of the examples verify that the method has significant treatment effects, with a VSS removal rate of ≥87%, a crude oil component (C10–C40) degradation rate of ≥93%, a fecal coliform inactivation rate of ≥99.9999% (meeting US EPA Class A standards), more than 90% of heavy metals are transferred to the liquid phase for stabilization, and the oil content of the solid residue is ≤1.2wt%, which can be used as building materials or compost. Magnesium ammonium phosphate can be recovered in the liquid phase. This method successfully solves the problems of high energy consumption, large reagent requirements, easy clogging, and incomplete degradation in existing sludge treatments, and has the advantages of universality, environmental protection, and economy.

[0083] The above description provides a further detailed explanation of the present invention in conjunction with specific / preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various substitutions or modifications can be made to these described embodiments without departing from the concept of the present invention, and all such substitutions or modifications should be considered within the scope of protection of the present invention. In the description of this specification, the reference to terms such as "an embodiment," "some embodiments," "preferred embodiment," "example," "specific example," or "some examples," etc., indicates that the specific features, structures, materials, or characteristics described in connection with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. Without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and modifications can be made herein without departing from the scope of protection of the patent application.

Claims

1. A method for treating sludge using a combination of hydraulic cavitation and subcritical wet oxidation technologies, characterized in that, The method is carried out in an integrated continuous reaction system and includes the following steps: S1) Add a metal catalyst to the sludge and heat and stir; S2) The sludge treated in step S1) is subjected to hydraulic cavitation treatment through a Venturi tube; the inlet pressure of the hydraulic cavitation reactor is 0.2MPa to 1.2MPa; a rotary shearing chamber connected in series with the Venturi tube is provided in the hydraulic cavitation reactor. S3) The sludge treated in step S2) is introduced into the cavitation-oxidation coupling zone for reaction; a retention-mixing coupling chamber is set between the outlet of the hydraulic cavitation reactor and the inlet of the subcritical wet oxidation reactor; the residence time is 0.5 minutes to 5 minutes, and the turbulent kinetic energy is greater than or equal to 0.5 m. 2 / s 3 ; S4) The sludge treated in step S3) is subjected to subcritical wet oxidation treatment; the treatment temperature is 230℃ to 280℃, the pressure is 4MPa to 22MPa, the oxygen partial pressure is 0.3MPa to 3MPa, and the subcritical reaction time is 15min to 60min. S5) The sludge treated in step S4) is preheated using the expander and heat exchanger system after the subcritical wet oxidation reactor to recover part of the waste heat. S6) The sludge after recovering waste heat in step S5) is fed into a three-phase separator to balance the gas pressure and perform solid-liquid separation of the product.

2. The method according to claim 1, characterized in that, In step S1), the sludge has a moisture content of 80 wt% to 95 wt% and an organic matter content of ≥30% (VSS / DS).

3. The method according to claim 1, characterized in that, The content of the transition metal catalyst added in step S1) is 0.05 wt% to 1.0 wt%.

4. The method according to claim 1, characterized in that, In step S1), the sludge is heated and stirred at a speed of 80 rpm to 120 rpm.

5. The method according to claim 1, characterized in that, In step S1), 0.01 to 0.05 wt% of hydrogen peroxide is also added as an auxiliary initiator.

6. The method according to claim 1, characterized in that, In step S1), the sludge is also heated to a temperature of 80 to 100 degrees Celsius.

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