System and method for dredged sediment treatment and resource utilization based on ultrasonic extraction and flotation synergy

Abstract

The application discloses a kind of based on ultrasonic extraction floatation cooperation's dredged sediment treatment resource system, comprising: pretreatment unit, first stage ultrasonic extraction reaction unit, second stage solid-phase adsorption reaction unit, third stage floatation separation unit, dehydration treatment unit, residual water treatment unit and nitrogen and phosphorus recovery unit.It also discloses a kind of based on ultrasonic extraction floatation cooperation's dredged sediment treatment resource method.The application solves the problems of low pollutant removal rate, high risk of secondary pollution of dredged soil and limited resource utilization in traditional dredged sediment treatment.Through the cooperation of "ultrasonic-liquid extraction-solid-phase adsorption-micro-nano bubble floatation" multi-unit, efficient release of nitrogen and phosphorus, simultaneous removal of microplastics, rapid separation of clean silt and pollution, and recycling of nitrogen and phosphorus for fertilizer production, the application realizes the resource utilization of clean silt.The whole process is green and low in consumption, suitable for compact arrangement on water or near shore, and can simultaneously meet the needs of sediment reduction, harmless and resource utilization.

Description

Technical Field

[0001] This invention belongs to the field of water ecological restoration and sediment dredging technology, specifically a resource utilization system and method for dredged sediment treatment based on ultrasonic extraction and flotation synergy. Background Technology

[0002] Existing remediation technologies for contaminated soil, such as soil washing and high-temperature incineration, can separate pollutants from the soil matrix to achieve soil remediation. However, these technologies cannot be directly applied to the pollution reduction process of dredged sediment. This is due to fundamental differences in the treatment targets, process objectives, and system characteristics: dredged sediment is a complex mud system with high water and solids content; secondly, the high content of fine particles and organic matter in the sediment affects the processing yield of remediation technologies, limiting the efficiency of many technologies developed for soil when applied to sediment; more importantly, existing remediation technologies are mostly intermittent or in-situ treatments aimed at fixing or degrading pollutants, while dredged sediment pollution reduction is a continuous, large-scale process whose core objective is to separate pollutants from the mud phase to reduce the land required for subsequent treatment.

[0003] Ultrasonic technology, as an enhancement method, has demonstrated great potential in water and soil remediation. Its core mechanism lies in sonochemical effects, including cavitation, acoustic flow, and thermal effects. The high-speed microjets and high-pressure shock waves generated when ultrasonic cavitation bubbles collapse can effectively disrupt the aggregated structure of soil particles, promoting the desorption of pollutants from the particle surface. Studies have shown that ultrasonic-assisted soil washing significantly improves pollutant removal efficiency and shortens treatment time compared to mechanical agitation. However, the primary function of ultrasonic technology is to "release" pollutants into the liquid phase, rather than to "separate" them; therefore, it needs to be combined with other separation technologies to achieve thorough sludge separation.

[0004] Micro- and nanobubble (MNB) technology has gained widespread attention in the field of environmental remediation due to its unique physicochemical properties. MNBs refer to tiny bubbles with diameters in the micrometer (1-100 μm) and nanometer (1-1000 nm) ranges, possessing characteristics such as a large specific surface area, high zeta potential, extremely long residence time in water, and high mass transfer efficiency. These properties make them far superior to traditional macrobubbles in flotation separation and pollutant oxidative degradation. In flotation applications, MNBs can more efficiently collide with and adhere to fine pollutant particles, achieving solid-liquid separation through buoyancy. Their removal efficiency for recalcitrant particles such as microplastics is significantly higher than that of traditional air flotation technology. Despite the significant advantages of MNB technology, its application in high-solids-content dredging slurry systems still faces considerable challenges.

[0005] Chemical extraction, which uses specific reagents to transfer target extractants from one phase to another, has been widely applied in the food, chemical, and biopharmaceutical industries. In the environmental remediation industry, the concept of extraction is broader. Current research has explored the use of various extractants, such as water, organic acids, and surfactants, to remove pollutants from soil by transferring them from the solid phase. However, there are no reports of its application to complex dredging mud systems. Furthermore, many highly efficient extractants target functional organic components, potentially causing secondary pollution or toxicity. Additionally, extractants used alone have limited efficiency and are difficult to process pollutants tightly encapsulated within particles.

[0006] In summary, most of these technologies are currently being studied in single fields or for water or soil media. There is no integrated technology for treating dredged mud that can efficiently couple physical destruction, chemical extraction and physical separation processes to achieve the reduction, harmlessness and resource utilization of dredged mud and promote the green and low-carbon development of river and lake sediment treatment technology.

[0007] Therefore, a resource recovery system and method for dredged sediment treatment based on ultrasonic extraction and flotation synergy is provided. Summary of the Invention

[0008] To address the aforementioned problems in existing technologies, this invention provides a resource recovery system and method for dredged sediment treatment based on ultrasonic extraction and flotation synergy. This system solves the problems of low pollutant removal rate, high risk of secondary pollution of dredged soil, and limited resource recovery in traditional dredged sediment treatment. Through the synergistic effect of multiple units including "ultrasonic extraction, liquid phase extraction, solid phase adsorption, and micro / nano bubble flotation," it achieves efficient release of nitrogen and phosphorus, simultaneous removal of microplastics, and rapid separation of clean sediment from polluted phases. It also recovers nitrogen and phosphorus for fertilizer production and recovers clean sediment for resource recovery. The entire process is green and low-consumption, suitable for compact layout on water or near shore, and meets the integrated needs of sediment reduction, harmlessness, and resource recovery.

[0009] The technical solution to achieve the above objectives is:

[0010] One of the present inventions discloses a resource recovery system for dredged sediment treatment based on ultrasonic extraction and flotation synergy, comprising:

[0011] The pretreatment unit is used to pretreat the dredged mud by passing it through a screen or vibrating screen to remove impurities, and to perform initial separation by sedimentation concentration or centrifugation to form an upper suspension and a lower viscous slurry. The upper turbid liquid is filtered and pumped into the waste water treatment unit, while the lower viscous slurry is passed into the first-stage ultrasonic extraction reaction unit.

[0012] The first-stage ultrasonic extraction reaction unit is used to add a green liquid-phase extractant to a thick slurry for extraction, promoting the release of pollutants. The thick slurry containing the extractant is broken down by ultrasound, and the thick slurry after ultrasonic extraction is separated into solid and liquid phases, forming an upper layer of extraction waste liquid containing high concentrations of nitrogen and phosphorus pollutants and a lower layer of concentrated mud. The upper layer of extraction waste liquid containing high concentrations of nitrogen and phosphorus pollutants is pumped to the nitrogen and phosphorus recovery unit, and the lower layer of concentrated mud is fed into the second-stage solid-phase adsorption reaction unit.

[0013] The second-stage solid-phase adsorption reaction unit is used to add solid-phase adsorbent to the concentrated mud to further capture residual pollutants and stir to form a mixed mud; the mixed mud is then passed into the third-stage flotation separation unit.

[0014] The third-stage flotation separation unit is used to carry pollutants to the surface through micro-nano bubbles, thereby separating the mixed mud into a clean mud phase, residual water after skimming, and solid adsorbent. The clean mud phase is fed into the dewatering treatment unit, the residual water after skimming is fed into the residual water treatment unit, and the solid adsorbent is collected and recovered to the nitrogen and phosphorus recovery unit.

[0015] The dewatering unit is used to mechanically dewater the clean mud phase to obtain clean mud cakes with total nitrogen and total phosphorus content that meet the resource utilization standards. The cakes are then transported off-site for use in the production of building materials, soil conditioners, landscaping soil, or for direct in-situ backfilling. The excess water generated during dewatering is collected into the waste water treatment unit.

[0016] The wastewater treatment unit is used to coagulate and settle the incoming wastewater. The sediment obtained after sedimentation is transported off-site for disposal. The remaining wastewater is treated biochemically and then used as water supply in the first-stage ultrasonic extraction reaction unit, high-pressure flushing water from a cutter suction dredger, or directly discharged as ecological water replenishment for rivers and lakes.

[0017] The nitrogen and phosphorus recovery unit is used to recover nitrogen and phosphorus from the extraction waste liquid of nitrogen and phosphorus pollutants through the struvite precipitation method to make fertilizer. The collected solid phase adsorbent is desorbed by acid and alkali addition, and the regenerated adsorbent is returned to the second-stage solid phase adsorption reaction unit. The resulting supernatant is fed into the waste water treatment unit.

[0018] Preferably, the pretreatment unit includes: a mud buffer tank and a primary separation device.

[0019] The mud buffer is used to store dredged mud that has been pretreated by bar screen or vibrating screen to remove impurities.

[0020] The primary separation equipment is used to perform preliminary solid-liquid separation on pretreated dredged mud through sedimentation concentration or centrifugation, forming an upper suspension and a thick slurry.

[0021] Preferably, the first-stage ultrasonic extraction reaction unit includes: a mud reaction tank, a washing and homogenization module, an extractant dosing module, an ultrasonic module, and a solid-liquid separation module;

[0022] A mud reaction vessel is used as the main reaction container for ultrasonic extraction of thick slurries.

[0023] The flushing and homogenization module is used to inject river or lake water or treated waste water into the mud reaction tank. It uses tangential water spray to form a rotating water film on the tank wall and generates tangential flow through stirring. It also uses a dual-frequency ultrasonic array to homogenize and break up the mud.

[0024] The extractant dosing module is used to add green liquid phase extractant to the mud reaction tank, and change the mud-water interface properties by adjusting pH and ionic strength, thereby achieving the extraction of thick slurry.

[0025] The ultrasonic module is used to homogenize and break down thick slurries containing extractants by employing a dual-frequency combination of ultrasound with frequencies of 20-30 kHz and 500 kHz-1 MHz.

[0026] The solid-liquid separation module is used to separate the solid and liquid components of the slurry after ultrasonic extraction, forming an upper layer of extraction waste liquid containing high concentrations of nitrogen and phosphorus pollutants and concentrated slurry.

[0027] Preferably, the rinsing and homogenization module includes: a tangential water spray device, a central water replenishment device, a liquid level interlock control system, and a stirring device;

[0028] A tangential water spray device is used to create a rotating water film on the tank wall of the mud reaction tank;

[0029] The central water supply device is used to inject river or lake water or treated waste water into the mud reaction tank;

[0030] The liquid level interlock control system is used to control the liquid level in the mud reaction tank to be constant within ±5 cm, and to cut off the water supply when the liquid level is exceeded;

[0031] The stirring device includes a variable frequency side-mounted shear pump for generating tangential flow;

[0032] The ultrasonic module includes: a dual-frequency ultrasonic generator and an ultrasonic probe movement control module;

[0033] A dual-frequency ultrasonic generator is used to generate a dual-frequency ultrasonic array through low and high frequency ultrasonic probes, thereby homogenizing and breaking down a thick slurry containing an extractant.

[0034] The ultrasonic probe movement control module is used to control the ultrasonic probe to rise and fall and move circumferentially along the inner wall of the mud reaction tank;

[0035] The solid-liquid separation module includes: a hydrocyclone and a centrifuge;

[0036] Hydrocyclones are used to achieve rapid classification of solid-liquid mixtures by utilizing centrifugal force and tangential fluid motion.

[0037] Centrifuges are used to separate tiny particles or colloidal substances by using the strong centrifugal force generated by high-speed rotation, forming an upper layer of extraction waste liquid and concentrated slurry containing high concentrations of nitrogen and phosphorus pollutants.

[0038] Preferably, the second-stage solid-phase adsorption reaction unit includes: a contact reaction vessel, an adsorbent silo, and an adsorbent dosing module;

[0039] Contact reaction vessel, used as the main reaction vessel for solid phase adsorption of concentrated mud.

[0040] The adsorbent silo is used for pre-loading compounded solid-phase adsorbents, which are magnetically modified solid-phase adsorbents.

[0041] The adsorbent dosing module is used to add the compound solid-phase adsorbent from the adsorbent silo to the contact reaction tank.

[0042] Preferably, the third-stage flotation separation unit includes: a flotation reaction module, a bubble generation module, a foam collection module, and a bottom sludge discharge module;

[0043] The flotation reaction module is used to separate the mixed mud by flotation and to collect the residual water after skimming into the residual water treatment unit;

[0044] The bubble generation module is used to shear air into 50 nm-50 μm micro-nano bubbles under the action of hydraulic cavitation or membrane diffusion, and then deliver them to the flotation reaction module.

[0045] The foam collection module is used to collect the floating pollutant floc layer after flotation, so as to separate the clean sludge phase from the pollutants.

[0046] The bottom sludge discharge module is used to output clean sludge phase to the dewatering treatment unit.

[0047] Preferably, the flotation reaction module includes: a flotation reaction tank, an activator dosing device, and a flow meter;

[0048] The flotation reaction tank is used as a reaction vessel for flotation separation of mixed mud. It is equipped with an annular overflow weir at the top. After the air intake is stopped, it is allowed to stand for 5 minutes. After skimming, the residual water flows along the weir into the annular water collection weir and then into the residual water treatment unit through the overflow pipe. The bottom is equipped with a bottom sludge discharge module.

[0049] An activator dosing device is used to add an activator to the mixed mud.

[0050] Flow meter, used to monitor and control the amount of activator added in real time;

[0051] The bubble generating module includes: an air compressor, an air tank, a pressure reducing valve, an annular air distribution pipe, a gas-liquid mixing chamber, and a pressure stabilizing valve;

[0052] An air compressor is used to deliver compressed air into an air storage tank.

[0053] An air storage tank is used to store compressed air and stabilize its pressure.

[0054] Pressure reducing valve, used to connect the gas storage tank to the gas-liquid mixing chamber;

[0055] The gas-liquid mixing chamber is used to shear the stabilized compressed air into micro-nano bubbles of 50nm-50μm under the action of hydraulic cavitation or film diffusion.

[0056] Pressure stabilizing valve, used to output micro / nano bubbles to an annular gas distribution pipe;

[0057] The annular gas distribution pipe is used to stably and uniformly release micro-nano bubbles into the bottom of the flotation reaction tank;

[0058] The foam collection module includes: a mechanical skimming plate, a vacuum collection port, a collection tank, and a magnetic spiral chute;

[0059] Mechanical skimming plate is used to collect the pollutant floc layer that is generated after micro-nano bubbles collide and adhere with pollutant aggregates in mud and float to the surface.

[0060] A vacuum collection port is located at the end of the active area of ​​the mechanical skimming plate for auxiliary foam recovery.

[0061] Collection tank, used to store the collected pollutant floc layer;

[0062] The magnetic spiral chute is used to store the foam liquid that flows in by gravity from the collection tank. The last turn of the magnetic spiral chute has two outlets tangentially. The cutting point is controlled by an adjustable distributor. The inner side recovers the magnetic solid phase adsorbent, and the outer side outputs the microplastic enrichment. The collected magnetic solid phase adsorbent is then added to the nitrogen and phosphorus recovery unit.

[0063] Preferably, the wastewater treatment unit includes: a water collection tank, an automatic dosing device, a coagulation sedimentation module, and a deep purification module;

[0064] The water collection tank is used to store the suspension in the pretreatment unit, as well as the residual water in the third-stage flotation separation unit and the dewatering treatment unit.

[0065] Automatic dosing equipment is used to add PAC flocculant according to flow rate and water quality signals;

[0066] The coagulation and sedimentation module is used to rapidly flocculate and react the suspension and residual water with the flocculant PAC in the pipeline mixer to form flocs and settle the sludge.

[0067] The deep purification module is used to nitrify and denitrify the remaining water after flocculation, and then use it as water supply in the first-stage ultrasonic extraction reaction unit, high-pressure flushing by a cutter suction dredger, or direct discharge as ecological water replenishment for rivers and lakes.

[0068] The nitrogen and phosphorus recovery unit includes: an acid and alkali dosing device, a desorption chamber, a magnesium salt dosing device, and a nutrient salt recovery chamber;

[0069] An acid-base dosing device is used to add acid or base into the desorption chamber;

[0070] The desorption chamber is used to store the collected magnetic solid phase adsorbent. Nitrogen and phosphorus in the magnetic solid phase adsorbent are desorbed by adding acid and alkali, and the resulting supernatant is introduced into the nutrient salt recovery chamber.

[0071] Magnesium salt dosing device, used to add magnesium salts into the nutrient salt recovery chamber;

[0072] The nutrient recovery chamber is used to store the collected extraction waste liquid containing high concentrations of nitrogen and phosphorus pollutants. Nutrients are extracted from the extraction waste liquid by magnesium salt extraction and recovered by struvite method. The resulting supernatant is fed into the waste water treatment unit.

[0073] A second aspect of the present invention provides a method for resource recovery of dredged sediment based on synergistic ultrasonic extraction and flotation, comprising:

[0074] Step S1: The dredged sediment is pretreated by removing impurities through a screen and collected in a mud buffer tank, and then pumped to a mud reaction tank.

[0075] Step S2: Add green liquid extractant to the mud reaction tank, stir for 10 minutes, form a rotating water film on the tank wall through a tangential water spraying device, and inject river or lake water or treated residual water into the mud reaction tank from bottom to top through the central water replenishment device.

[0076] Step S3: The liquid level in the tank is kept constant by the liquid level interlock control system, and tangential flow is generated by the stirring device. The dual-frequency ultrasonic generator is started and the dual-frequency ultrasonic array is used to homogenize and break the mud. The mud is treated with alternating ultrasonic treatment at 20-30 kHz and 500 kHz for 30 minutes to form an upper layer of extraction waste liquid and concentrated mud containing high concentration of nitrogen and phosphorus pollutants.

[0077] Step S4: After ultrasonic treatment, the solid-liquid mixture is separated by centrifugation and allowed to stand for 10-20 minutes. The upper layer of extraction waste liquid containing high concentrations of nitrogen and phosphorus pollutants is pumped out to the nutrient salt recovery chamber, and the concentrated sludge is fed into the contact reaction tank through a pipeline equipped with a rinsing and homogenizing device.

[0078] Step S5: The pre-filled compound magnetic solid adsorbent in the adsorbent silo is added to the contact reaction tank through the adsorbent dosing module and stirred at 100 r / min for 30 minutes to form a mixed slurry which is then fed into the flotation reaction tank.

[0079] In step S6, the air compressor first sends compressed air into the storage tank for pressure stabilization, and then introduces it into the gas-liquid mixing chamber through the pressure reducing valve. Under the action of hydraulic cavitation or film diffusion, it is sheared to generate micro-nano bubbles of 50 nm-50 μm, and then output through the pressure stabilizing valve and released into the bottom of the flotation reaction tank stably and evenly through the annular air distribution pipe.

[0080] Step S7: After micro-nano bubbles collide and adhere to the pollutant aggregates in the mixed mud, they float to the surface. The flotation time is 20-60 minutes. After stopping the air intake, let it stand for 5 minutes. After skimming off the scum, the remaining water flows by gravity into the annular water collection weir, and then flows into the residual water collection bin through the overflow pipe. The clean mud phase is output from the bottom of the bottom mud discharge module to the dewatering treatment unit. If the flotation effect is not good, a small amount of activator is added to the mixed mud using a flotation activator addition device. After stirring for 5-15 minutes, flotation is performed again.

[0081] Step S8: After flotation, a mechanical skimmer is used to collect the floating pollutant floc layer in a collection tank. The vacuum collection port at the end of the moving section of the mechanical skimmer assists in the recovery of foam, thereby separating the clean sludge phase from the pollutants. The foam liquid in the collection tank flows into the composite magnetic spiral chute by gravity, recovering the magnetic solid phase adsorbent on the inner side and outputting the microplastic enrichment on the outer side, thus effectively separating the magnetic solid phase adsorbent and the microplastics.

[0082] Step S9: The collected magnetic solid phase adsorbent is added to the desorption chamber after collection. Pollutants are desorbed by adding acid and alkali. The regenerated magnetic adsorbent is returned to the adsorbent silo. Nitrogen and phosphorus are released in the liquid phase. The supernatant is introduced into the nutrient salt recovery chamber. Subsequently, magnesium salt is added to the nutrient salt recovery chamber. Nitrogen and phosphorus are recovered by struvite precipitation to make fertilizer.

[0083] In step S10, the mud phase separated by flotation is fed into the dewatering unit. After being squeezed and dewatered by mechanical dewatering equipment, clean mud cake is obtained. It is then transported to be used for the production of building materials, soil conditioners, and landscaping soil, or directly backfilled into rivers and lakes. The excess water generated during dewatering is collected in the water collection tank.

[0084] In step S11, the tailwater generated from flotation and sludge dewatering is collected in the collection tank for homogenization and equalization. The flocculant PAC is added by the automatic dosing equipment according to the flow rate and water quality signal. After rapid flocculation in the pipeline mixer, it enters the coagulation and sedimentation module, and then enters the deep purification module for simultaneous nitrification and denitrification. After treatment, it is used as feed water in the first-stage ultrasonic extraction reaction unit, high-pressure flushing water from the cutter suction dredger, or directly discharged as ecological water replenishment for rivers and lakes.

[0085] Preferably, in step S2, the green liquid phase extractant is one or more of the following compound systems: bio-based small molecule organic acids, natural polymer compounds, and green surfactants. Stirring for 10-20 minutes allows the extractant to fully contact the mud.

[0086] If bio-based small molecule organic acids are selected, the addition amount is 0.3-2.0 kg / m³. 3 If natural polymers are chosen, the addition amount is 0.2-2.0 kg / m³. 3 If a green surfactant is selected, the amount of green surfactant added is 2.0. - 5.0g / m 3 When using a compound system, the mass ratio of each component is organic acid: surfactant = 5:5-8:2, or natural polymer: surfactant = 7:3-9:1;

[0087] In step S3, ultrasonic treatment employs a dual-frequency combination of 20-30 kHz and 500 kHz-1 MHz frequencies to treat the dredged mud containing the extractant. The low-frequency and high-frequency ultrasound are used synchronously or alternately. When alternating, the duration of a single treatment of each frequency is 5-15 min, and the ultrasonic treatment time is controlled between 30-120 min. The contact depth between the ultrasonic probe and the mud concentrate is 10-30 cm, and the ultrasonic probe moves at a uniform speed of 5-20 cm / s during the treatment process.

[0088] Low-frequency ultrasound, through the high-speed microjets and high-pressure shock waves generated by the cavitation effect, destroys the flocculation structure and particle agglomerates of the bottom sediment, while high-frequency ultrasound generates a large number of micro- and nano-bubbles, increasing the reaction surface area and enhancing the penetration of liquid-phase extractants into the particles.

[0089] In step S5, the solid-phase adsorbent is a lightweight, fine-particle or powdered porous adsorbent, and the adsorbent dosage is 0.5-2.0 kg / m³. 3 Control the stirring rate to 50-150 r / min and the reaction time to 30-120 min, so that the solid phase extractant can fully capture nitrogen and phosphorus pollutants in the liquid phase through physical adsorption and chemical complexation.

[0090] During the synthesis of solid-phase adsorbents, magnetic Fe3O4 nanoparticles can be added to prepare magnetic adsorbent composite materials.

[0091] Solid-phase adsorbents are produced using the following materials or combinations thereof:

[0092] Lightweight porous biochar: Biochar materials with rich pore structure and low density are prepared by precisely controlling the pyrolysis temperature and atmosphere;

[0093] Modified natural minerals: Zeolite and ceramsite natural minerals are selected, and their pore structure and surface properties are controlled through hot processing granulation and foaming processes;

[0094] Natural polymer materials: By using chitosan and cellulose-based materials, phosphate, amine and carboxyl functional groups are introduced through grafting modification to enhance their adsorption capacity and selectivity for nitrogen and phosphorus pollutants.

[0095] The compounding ratio should be 40%-60% lightweight porous biochar, 35%-50% modified natural minerals, and 0%-5% natural polymer materials.

[0096] In step S6, micro- and nano-bubbles are generated using hydrocavitation or membrane diffusion. The bubble size distribution is 50 nm-50 μm, with nano-sized bubbles accounting for ≥20% and micro-sized bubbles accounting for ≤80%. The bubble generation rate is 0.5-2 L / min·m. 3 .

[0097] Compared with the prior art, the beneficial effects of the present invention are:

[0098] 1) This invention utilizes a three-stage treatment process (liquid phase extraction + solid phase adsorption + flotation separation) and the synergistic effect of multiple technologies (ultrasound, micro-nano bubbles) to form a cascade effect of "physical destruction - chemical extraction - three-phase separation," which efficiently separates pollutants from the sediment matrix, reducing the endogenous pollution load by more than 70%. This lays the foundation for the separate treatment and disposal of sludge and wastewater and its resource utilization, and solves the fundamental defect of the traditional technology of "mixed treatment of sludge and wastewater."

[0099] 2) This invention uses bio-based, biodegradable green extractants throughout the process, avoiding the use of toxic reagents in traditional chemical methods. The recycling and reuse of extractants and adsorbents further reduces environmental risks and meets the requirements of green and low-carbon development. The coupling of dual-frequency moving ultrasound and green extraction technology promotes the release of pollutants in sediment, with nitrogen and phosphorus elution rates both exceeding 70%, which is more than 20% higher than that of single-frequency fixed probes. Lightweight magnetic porous adsorbents capture nitrogen and phosphorus in the liquid phase through adsorption. Flotation and magnetic separation provide double protection for recovery, with an adsorbent recovery rate of over 95%. The adsorbent can be recycled and reused.

[0100] 3) This invention is aimed at large-scale high-solids-content dredging mud systems, overcoming the limitations of in-situ remediation technology. Its modular and continuous design can be directly embedded into the post-processing process of existing environmentally friendly dredging vessels, realizing the integration of dredging and remediation, and solving the pain points of difficult land acquisition and high off-site transportation costs in traditional landfill disposal.

[0101] 4) The clean sludge phase and enriched nitrogen and phosphorus resources produced by this invention have high-value-added resource utilization pathways, transforming the pollution control process into a resource recycling process, which has good economic and environmental benefits.

[0102] In summary, the various technical units of this invention are interconnected and synergistic, resulting in an overall processing efficiency far exceeding that of simply adding up any single technology. Attached Figure Description

[0103] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0104] Figure 1 This is a block diagram of a dredged sediment treatment and resource recovery system based on ultrasonic extraction and flotation synergy, according to the present invention.

[0105] Figure 2 This is a detailed block diagram of the pretreatment unit and the first-stage ultrasonic extraction reaction unit in this invention;

[0106] Figure 3 This is a detailed module diagram of the rinsing and homogenization module in the first-stage ultrasonic extraction reaction unit of this invention;

[0107] Figure 4 This is a detailed block diagram of the ultrasonic module in the first-stage ultrasonic extraction reaction unit of this invention;

[0108] Figure 5 This is a detailed module diagram of the solid-liquid separation module in the first-stage ultrasonic extraction reaction unit of this invention;

[0109] Figure 6 This is a detailed block diagram of the second-stage solid-phase adsorption reaction unit in this invention;

[0110] Figure 7 This is a detailed block diagram of the third-stage flotation separation unit in this invention;

[0111] Figure 8 This is a detailed block diagram of the flotation reaction module, bubble generation module, and foam collection module in the third-stage flotation separation unit of this invention;

[0112] Figure 9 This is a detailed block diagram of the waste water treatment unit in this invention;

[0113] Figure 10 This is a detailed block diagram of the nitrogen and phosphorus recovery unit in this invention;

[0114] Figure 11 This is a partial flowchart of a method for resource recovery of dredged sediment based on the synergistic effect of ultrasonic extraction and flotation according to the present invention.

[0115] Figure 12 This is another part of the flowchart of the resource utilization method for dredged sediment treatment based on ultrasonic extraction and flotation synergy of the present invention. Detailed Implementation

[0116] 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 some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0117] like Figure 1 As shown, a resource recovery system for dredged sediment treatment based on ultrasonic extraction and flotation synergy includes: a pretreatment unit 1, a first-stage ultrasonic extraction reaction unit 2, a second-stage solid-phase adsorption reaction unit 3, a third-stage flotation separation unit 4, a dewatering treatment unit 5, a residual water treatment unit 6, and a nitrogen and phosphorus recovery unit 7.

[0118] Pretreatment unit 1 is used to pretreat dredged mud by passing it through a screen or vibrating screen to remove impurities, and to perform initial separation by sedimentation concentration or centrifugation to form an upper suspension and a lower viscous slurry. The upper suspension is filtered and pumped into the waste water treatment unit 6, while the lower viscous slurry is fed into the first-stage ultrasonic extraction reaction unit 2.

[0119] like Figure 2 As shown, the pretreatment unit 1 includes: a mud buffer tank 11 and a primary separation device 12.

[0120] The mud buffer 11 is used to store dredged mud that has been pretreated by bar screen or vibrating screen for impurity removal.

[0121] The primary separation device 12 is used to perform preliminary solid-liquid separation on the pretreated dredged mud by sedimentation concentration or centrifugation to form an upper suspension and a thick slurry.

[0122] The first-stage ultrasonic extraction reaction unit 2 is used to add a green liquid phase extractant to a thick slurry for extraction, promoting the release of pollutants. The thick slurry containing the extractant is broken down by ultrasound, and the thick slurry after ultrasonic extraction is separated into solid and liquid phases to form an upper layer of extraction waste liquid containing high concentrations of nitrogen and phosphorus pollutants and a lower layer of concentrated mud. The upper layer of extraction waste liquid containing high concentrations of nitrogen and phosphorus pollutants is pumped to the nitrogen and phosphorus recovery unit 7, and the lower layer of concentrated mud is fed into the second-stage solid phase adsorption reaction unit 3.

[0123] like Figure 2 As shown, the first-stage ultrasonic extraction reaction unit 2 includes: a mud reaction tank 21, a rinsing and homogenization module 22, an extractant addition module 23, an ultrasonic module 24, and a solid-liquid separation module 25.

[0124] The mud reaction vessel 21 is used as the main reaction vessel for ultrasonic extraction of thick slurry.

[0125] The flushing and homogenization module 22 is used to inject river or lake water or treated residual water into the mud reaction tank 21. It uses tangential water spray to form a rotating water film on the tank wall and generates tangential flow through stirring. It uses a dual-frequency ultrasonic array to homogenize and break up the mud.

[0126] like Figure 3 As shown, the rinsing and homogenization module 22 includes: a tangential water spray device 221, a central water replenishment device 222, a liquid level interlock control system 223, and a stirring device 224;

[0127] Tangential water spray device 221 is used to form a rotating water film on the tank wall of mud reaction tank 21;

[0128] The central water supply device 222 is used to inject river or lake water or treated residual water into the mud reaction tank 21.

[0129] The liquid level interlock control system 223 is used to control the liquid level in the mud reaction tank 21 to be constant at ±5 cm. When the liquid level is exceeded, the water inlet is cut off to prevent dry running or overflow.

[0130] The mixing device 224 includes a variable frequency side-mounted shear pump and other mixing devices to generate tangential flow and uses a dual-frequency ultrasonic array to homogenize and break up the mud.

[0131] The extractant dosing module 23 is used to add green liquid phase extractant to the mud reaction tank 21, thereby changing the mud-water interface properties by adjusting pH and ionic strength, and thus achieving the extraction of thick slurry.

[0132] The ultrasonic module 24 is used to homogenize and break down a thick slurry containing an extractant by employing a dual-frequency combination of ultrasound at frequencies of 20-30 kHz and 500 kHz-1 MHz.

[0133] like Figure 4 As shown, the ultrasonic module 24 includes: a dual-frequency ultrasonic generator 241 and an ultrasonic probe movement control module 242;

[0134] The dual-frequency ultrasonic generator 241 is used to generate a dual-frequency ultrasonic array through low and high frequency ultrasonic probes, thereby homogenizing and breaking down a thick slurry containing an extractant.

[0135] The ultrasonic probe movement control module 242 is used to control the ultrasonic probe to rise and fall and move circumferentially along the inner wall of the mud reaction tank 21.

[0136] The solid-liquid separation module 25 is used to separate the solid and liquid in the slurry after ultrasonic extraction to form an upper layer of extraction waste liquid containing high concentrations of nitrogen and phosphorus pollutants and concentrated slurry.

[0137] like Figure 5 As shown, the solid-liquid separation module 25 includes: a hydrocyclone 251 and a centrifuge 252;

[0138] Hydrocyclone 251 is used to achieve rapid classification of solid-liquid mixtures by utilizing centrifugal force field and fluid tangential motion;

[0139] Centrifuge 252 is used to separate fine particles or colloidal substances by using the strong centrifugal force generated by high-speed rotation, forming an upper layer of extraction waste liquid and concentrated slurry containing high concentrations of nitrogen and phosphorus pollutants.

[0140] The second-stage solid-phase adsorption reaction unit 3 is used to add solid-phase extractant to the concentrated mud to further capture residual pollutants and stir to form a mixed mud; wherein, the mixed mud is passed into the third-stage flotation separation unit 4.

[0141] like Figure 6 As shown, the second-stage solid-phase adsorption reaction unit 3 includes: a contact reaction tank 31, an adsorbent silo 32, and an adsorbent dosing module 33;

[0142] Contact reaction vessel 31 is used as the main reaction vessel for solid-phase adsorption of concentrated mud.

[0143] The adsorbent silo 32 is used for pre-loading compound solid-phase adsorbents, which are magnetically modified solid-phase adsorbents.

[0144] The adsorbent dosing module 33 is used to add the compound solid-phase adsorbent in the adsorbent silo 32 to the contact reaction tank 31.

[0145] The third-stage flotation separation unit 4 is used to carry pollutants to the surface through micro-nano bubbles, thereby separating the mixed mud by flotation to form a clean mud phase, residual water after skimming, and solid adsorbent. The clean mud phase is fed into the dewatering treatment unit 5, the residual water after skimming is fed into the residual water treatment unit 6, and the solid adsorbent is collected and recovered to the nitrogen and phosphorus recovery unit 7.

[0146] like Figure 7 As shown, the third-stage flotation separation unit 4 includes: a flotation reaction module 41, a bubble generation module 42, a foam collection module 43, and a bottom sludge discharge module 44;

[0147] The flotation reaction module 41 is used to separate the mixed mud by flotation and to collect the residual water after skimming into the residual water treatment unit 6.

[0148] like Figure 8 As shown, the flotation reaction module 41 includes: a flotation reaction tank 411, an activator dosing device 412, and a flow meter 413;

[0149] The flotation reaction tank 411 is used as a reaction vessel for flotation separation of mixed mud. An annular overflow weir is set at the top. After the air intake is stopped, the tank is left to stand for 5 minutes. After skimming off the slag, the residual water flows along the weir into the annular water collection weir and flows into the residual water treatment unit 6 through the overflow pipe. A bottom sludge discharge module 44 is set at the bottom.

[0150] Activator dosing device 412 is used to add activator to the mixed mud;

[0151] Flow meter 413 is used to monitor and control the amount of activator added in real time.

[0152] The bubble generating module 42 is used to shear air into micro-nano bubbles of 50 nm-50 μm under the action of hydraulic cavitation or membrane diffusion, and then transport them to the flotation reaction module 41.

[0153] like Figure 8 As shown, the bubble generating module 42 includes: an air compressor 421, an air tank 422, a pressure reducing valve 423, an annular air distribution pipe 424, a gas-liquid mixing chamber 425, and a pressure stabilizing valve 426.

[0154] Air compressor 421 is used to deliver compressed air into air tank 422;

[0155] Air tank 422 is used to store compressed air and stabilize its pressure;

[0156] Pressure reducing valve 423 is used to connect gas storage tank 422 and gas-liquid mixing chamber 425;

[0157] The gas-liquid mixing chamber 425 is used to shear the stabilized compressed air into micro-nano bubbles of 50 nm-50 μm under the action of hydraulic cavitation or film diffusion.

[0158] Pressure stabilizing valve 426 is used to output micro-nano bubbles to annular gas distribution pipe 424;

[0159] The annular gas distribution pipe 424 is used to stably and uniformly release micro-nano bubbles into the bottom of the flotation reaction vessel 411.

[0160] The foam collection module 43 is used to collect the floating pollutant floc layer after flotation, so as to separate the clean sludge phase from the pollutants.

[0161] like Figure 8 As shown, the foam collection module 43 includes: a mechanical skimming plate 431, a vacuum collection port 432, a collection tank 433, and a magnetic spiral chute 434;

[0162] Mechanical skimming plate 431 is used to collect the pollutant floc layer generated after micro-nano bubbles collide and adhere with pollutant aggregates in the mud and float to the surface. The mechanical skimming plate 431 has an inclination angle of 30°-45° and a contact width with the liquid surface of the third-stage flotation separation unit 4 of ≥0.8m. The skimming speed can be adjusted according to the thickness of the foam layer.

[0163] The vacuum collection port 432 is located at the end of the active area of ​​the mechanical skimming plate 431 and is used to assist in the recovery of foam. The vacuum collection port 432 is equipped with a floating weir suction head to prevent the solid adsorbent from being lost due to bubble rupture.

[0164] Collection tank 433 is used to store the collected pollutant floc layer;

[0165] The magnetic spiral chute 434 is used to store the foam liquid that flows in by gravity in the collection tank 433. The last turn of the magnetic spiral chute 434 has two outlets tangentially. The cutting point is controlled by an adjustable diverter. The inner side recovers the magnetic solid phase adsorbent, and the outer side outputs the microplastic enrichment. The collected magnetic solid phase adsorbent is added to the nitrogen and phosphorus recovery unit 7 after collection.

[0166] Bottom sludge discharge module 44 is used to output clean sludge phase to dewatering treatment unit 5.

[0167] The dewatering treatment unit 5 is used to mechanically dewater the clean mud phase to obtain clean mud cake, whose total nitrogen and total phosphorus content meets the resource utilization standards. It is then transported off-site for the production of building materials, soil conditioners, landscaping soil, or directly backfilled in situ. The excess water generated during dewatering is collected in the excess water treatment unit 6.

[0168] Wastewater treatment unit 6 is used to coagulate and settle the incoming wastewater. The sediment obtained after sedimentation is transported off-site for disposal. The remaining wastewater is treated biochemically and then used as water supply in the first-stage ultrasonic extraction reaction unit 2, high-pressure flushing by a cutter suction dredger, or directly discharged as ecological water replenishment for rivers and lakes.

[0169] like Figure 9 As shown, the waste water treatment unit 6 includes: a water collection tank 61, an automatic dosing device 62, a coagulation sedimentation module 63, and a deep purification module 64;

[0170] Water collection tank 61 is used to store the suspension in pretreatment unit 1, as well as the residual water in third-stage flotation separation unit 4 and dewatering treatment unit 5;

[0171] Automatic dosing equipment 62 is used to add flocculant PAC according to flow rate and water quality signals;

[0172] The coagulation and sedimentation module 63 is used to rapidly flocculate and react the suspension and residual water with the flocculant PAC in the pipeline mixer to form flocs and settle the sludge.

[0173] The deep purification module 64 is used to nitrify and denitrify the remaining water after flocculation, and then use it as water supply in the first-stage ultrasonic extraction reaction unit 2, high-pressure flushing by a cutter suction dredger, or direct discharge as ecological water replenishment for rivers and lakes.

[0174] Nitrogen and phosphorus recovery unit 7 is used to recover nitrogen and phosphorus from the extraction waste liquid of nitrogen and phosphorus pollutants through struvite precipitation to make fertilizer. The collected solid phase adsorbent is desorbed by acid and alkali addition, and the regenerated magnetic adsorbent is returned to the second-stage solid phase adsorption reaction unit 3. The resulting supernatant is fed into the waste water treatment unit 6.

[0175] like Figure 10 As shown, the nitrogen and phosphorus recovery unit 7 includes: an acid and alkali dosing device 71, a desorption chamber 72, a magnesium salt dosing device 73, and a nutrient salt recovery chamber 74;

[0176] The acid-base dosing device 71 is used to add acid or base into the desorption chamber 72;

[0177] The desorption chamber 72 is used to store the collected magnetic solid phase adsorbent. Nitrogen and phosphorus in the magnetic solid phase adsorbent are desorbed by adding acid and alkali, and the resulting supernatant is introduced into the nutrient salt recovery chamber 74.

[0178] Magnesium salt dosing device 73 is used to add magnesium salt into nutrient salt recovery chamber 74;

[0179] Nutrient recovery chamber 74 is used to store the collected extraction waste liquid containing high concentrations of nitrogen and phosphorus pollutants. Nutrients in the extraction waste liquid are extracted by magnesium salts and recovered by struvite method. The resulting supernatant is fed into waste water treatment unit 6.

[0180] like Figure 1-12 As shown, a method for resource recovery from dredged sediment based on the synergistic effect of ultrasonic extraction and flotation includes:

[0181] Step S1: The dredged sediment is pretreated by passing it through a screen to remove impurities and then collected in the mud buffer tank 11, and pumped to the mud reaction tank 21.

[0182] Step S2: Add green liquid extractant to mud reaction tank 21, stir for 10 minutes, form a rotating water film on the tank wall through tangential water spray device 221, and inject river or lake water or treated residual water into mud reaction tank 21 from bottom to top through central water replenishment device 222.

[0183] In this embodiment, the green liquid phase extractant is one or more of the following compound systems: bio-based small molecule organic acids (such as citric acid and oxalic acid), natural polymers (such as humic acid), and green surfactants (such as Tween 80, rhamnolipids, and trehaloses). The extractant is stirred for 10-20 minutes to ensure full contact between the extractant and the mud. These extractants can adjust the pH and ionic strength to change the properties of the mud-water interface and promote the release of encapsulated pollutants.

[0184] If bio-based small molecule organic acids are selected, the addition amount is 0.3-2.0 kg / m³. 3If natural polymers are chosen, the addition amount is 0.2-2.0 kg / m³. 3 If a green surfactant is selected, the amount of green surfactant added is 2.0. - 5.0g / m 3 When using a compound system, the mass ratio of each component is organic acid:surfactant = 5:5-8:2, or natural polymer:surfactant = 7:3-9:1.

[0185] Step S3: The liquid level in the tank is kept constant by the liquid level interlock control system 223, and tangential flow is generated by the stirring device 224. The dual-frequency ultrasonic generator 241 is started, and the slurry is homogenized and broken by the dual-frequency ultrasonic array. The slurry is treated alternately with ultrasonic treatment at 20-30 kHz and 500 kHz for 30 minutes to form an upper layer of extraction waste liquid and concentrated slurry containing high concentrations of nitrogen and phosphorus pollutants.

[0186] In this embodiment, ultrasonic treatment employs a dual-frequency combination of 20-30 kHz and 500 kHz-1 MHz frequencies to treat dredged mud containing extractant. The low-frequency and high-frequency ultrasounds are used synchronously or alternately. When alternating, the duration of a single treatment of each frequency is 5-15 minutes, and the ultrasonic treatment time is controlled between 30-120 minutes. The contact depth between the ultrasonic probe and the mud concentrate is 10-30 cm, and the ultrasonic probe moves at a uniform speed of 5-20 cm / s during the treatment process.

[0187] Low-frequency (20-30kHz) ultrasound, through the high-speed microjets and high-pressure shock waves generated by the cavitation effect, destroys the flocculation structure and particle agglomerates of the sediment. High-frequency (500kHz-1MHz) ultrasound generates a large number of micro- and nano-bubbles, increasing the reaction surface area and enhancing the penetration of liquid extractants into the particles.

[0188] Step S4: After ultrasonic treatment, the solid-liquid mixture is separated by centrifuge 252 and allowed to stand for 10-20 minutes. The upper layer of extraction waste liquid containing high concentrations of nitrogen and phosphorus pollutants is pumped out to nutrient salt recovery chamber 74. The concentrated sludge is fed into contact reaction tank 31 through a pipeline equipped with a rinsing and homogenizing device.

[0189] In step S5, the pre-filled compound magnetic solid adsorbent in the adsorbent silo 32 is added to the contact reaction tank 31 through the adsorbent dosing module 33, and stirred at 100 r / min for 30 minutes to form a mixed slurry which is then fed into the flotation reaction tank 411.

[0190] In the embodiments, the solid-phase adsorbent is a lightweight, fine-particle or powdered porous adsorbent. Preferably, a magnetic component (such as Fe3O4 nanoparticles) can be added during the material synthesis process to prepare a magnetic adsorbent composite material, so as to achieve rapid and efficient separation and recovery through a magnetic field. The adsorbent dosage is 0.5 kg-2.0 kg / m³. 3 Control the stirring rate to 50-150 r / min and the reaction time to 30-120 min, so that the solid phase extractant can fully capture nitrogen and phosphorus pollutants in the liquid phase through physical adsorption and chemical complexation.

[0191] During the synthesis of solid-phase adsorbents, magnetic Fe3O4 nanoparticles are added to create magnetic solid-phase adsorbent composite materials, which can then be rapidly and efficiently separated and recovered using a magnetic field.

[0192] Solid-phase adsorbents are produced using the following materials or combinations thereof:

[0193] Lightweight porous biochar: Biochar materials with rich pore structure and low density are prepared by precisely controlling the pyrolysis temperature and atmosphere;

[0194] Modified natural minerals: Zeolite and ceramsite natural minerals are selected, and their pore structure and surface properties are controlled through hot processing granulation and foaming processes;

[0195] Natural polymer materials: By using chitosan and cellulose-based materials, phosphate, amine and carboxyl functional groups are introduced through grafting modification to enhance their adsorption capacity and selectivity for nitrogen and phosphorus pollutants.

[0196] The compounding ratio should be 40%-60% lightweight porous biochar, 35%-50% modified natural minerals, and 0%-5% natural polymer materials.

[0197] In step S6, the air compressor 421 first sends compressed air into the air storage tank 422 for pressure stabilization, and then introduces it into the gas-liquid mixing chamber 425 through the pressure reducing valve 423. Under the action of hydraulic cavitation or film diffusion, the compressed air is sheared to generate micro-nano bubbles of 50 nm-50 μm, and then output through the pressure stabilizing valve 426. The bubbles are then stably and uniformly released into the bottom of the flotation reaction tank 411 through the annular air distribution pipe 424, with a bubble concentration of ≈5×108 bubbles / mL.

[0198] In the embodiments, micro- and nano-bubbles are generated using hydrocavitation or membrane diffusion methods. The bubble size distribution is 50 nm-50 μm, with nano-sized bubbles accounting for ≥20% and micro-sized bubbles accounting for ≤80%. The bubble generation rate is 0.5-2 L / min·m. 3Micro- and nano-bubbles, with their large specific surface area, long residence time, and surface charge, enable solid-phase adsorbents carrying nitrogen and phosphorus pollutants to adhere efficiently to microplastics, forming low-density aggregates. Under buoyancy, these aggregates float to the liquid surface, forming a foam layer, while the clean sludge phase settles to the bottom. Mechanical skimming and underflow discharge achieve "sludge-fouling separation," further enhancing the system's dissolved oxygen (DO) and oxidation-reduction potential (ORP), promoting stable phosphorus fixation.

[0199] In step S7, micro-nano bubbles collide and adhere to pollutant aggregates in the mixed mud, then float to the surface. The flotation time is 20-60 minutes. After stopping the air intake, the mixture is allowed to stand for 5 minutes. After skimming off the scum, the remaining water flows by gravity into the annular water collection weir and then flows into the residual water collection tank 61 through the overflow pipe. The bottom mud discharge module 44 outputs the clean mud phase to the dewatering treatment unit 5. If the flotation effect is not good, a small amount of activator is added to the mixed mud using the flotation activator addition device 412. After stirring for 5-15 minutes, the mixture is floated again.

[0200] In step S8, after flotation, the floating pollutant floc layer is collected in the collection tank 433 using a mechanical skimmer 431. The vacuum collection port 432 at the end of the active section of the mechanical skimmer 431 assists in the recovery of foam, thereby separating the clean sludge phase from the pollutants. The foam liquid in the collection tank 433 flows into the composite magnetic spiral chute 434 by gravity, where the magnetic solid phase adsorbent is recovered on the inner side and the microplastics are output on the outer side, thus effectively separating the magnetic solid phase adsorbent and the microplastics.

[0201] In this embodiment, a flexible neodymium iron boron magnetic tape is continuously pasted on the outer surface of the bottom of the magnetic spiral chute 434. Magnetic particles are enriched towards the inner side of the chute under the triple action of centrifugal force, gravity, and continuous magnetic field, and spiral downward with the flow film, while non-magnetic particles such as microplastics are pushed to the middle and outer edges, forming two clear material strips. Two outlets are opened tangentially in the last turn of the spiral chute, and the cutting point is controlled by an adjustable distributor. The magnetic solid phase adsorbent is recovered on the inner side, and the microplastic enrichment is output on the outer side. The collected magnetic solid phase adsorbent is added to the desorption chamber 72 of the nitrogen and phosphorus recovery unit 7 for regeneration and reuse. The microplastic enrichment can be subsequently subjected to vibration draining and drying for low-temperature pyrolysis / cement kiln co-processing.

[0202] In step S9, the collected magnetic solid phase adsorbent is added to the desorption chamber 72 after collection. Pollutants are desorbed by adding acid and alkali. The regenerated magnetic adsorbent is returned to the adsorbent silo 32. Nitrogen and phosphorus are released in the liquid phase. The supernatant is introduced into the nutrient salt recovery chamber 74. Subsequently, magnesium salt is added to the nutrient salt recovery chamber 74. Nitrogen and phosphorus are recovered by the struvite precipitation method to make fertilizer.

[0203] In step S10, the mud phase separated by flotation is fed into the dewatering treatment unit 5. After being squeezed and dewatered by the mechanical dewatering equipment 51, clean mud cake is obtained. It is transported to the outside for the production of building materials, soil conditioners, landscaping soil or directly backfilled into rivers and lakes. The excess water generated during dewatering is fed into the water collection tank 61.

[0204] In step S11, the tailwater generated from flotation and sludge dewatering is collected in the collection tank 61 for homogenization and equalization. The flocculant PAC is added by the automatic dosing equipment 62 according to the flow rate and water quality signal. After rapid flocculation in the pipeline mixer, it enters the coagulation and sedimentation module 63, and then enters the deep purification module 64 for simultaneous nitrification and denitrification. After treatment, it is used as water supply in the first-stage ultrasonic extraction reaction unit 2, high-pressure flushing by a cutter suction dredger, or directly discharged as ecological water replenishment for rivers and lakes.

[0205] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A resource recovery system for dredged sediment treatment based on ultrasonic extraction and flotation synergy, characterized in that, include: The pretreatment unit (1) is used to pretreat the dredged mud by passing it through a screen or vibrating screen to remove impurities, and to perform initial separation by sedimentation concentration or centrifugation to form an upper suspension and a lower viscous slurry; wherein, the upper suspension is filtered and pumped into the waste water treatment unit (6), and the lower viscous slurry is passed into the first-stage ultrasonic extraction reaction unit (2). The first-stage ultrasonic extraction reaction unit (2) is used to add green liquid phase extractant to the thick slurry for extraction, promote the release of pollutants, break down the thick slurry containing the extractant by ultrasonic waves, and perform solid-liquid separation on the thick slurry after ultrasonic extraction to form an upper layer of extraction waste liquid containing high concentration of nitrogen and phosphorus pollutants and a lower layer of concentrated mud; wherein, the upper layer of extraction waste liquid containing high concentration of nitrogen and phosphorus pollutants is pumped out to the nitrogen and phosphorus recovery unit (7), and the lower layer of concentrated mud is fed into the second-stage solid phase adsorption reaction unit (3). The second-stage solid-phase adsorption reaction unit (3) is used to add solid-phase adsorbent to the concentrated mud to further capture residual pollutants and stir to form a mixed mud; wherein, the mixed mud is passed into the third-stage flotation separation unit (4). The third-stage flotation separation unit (4) is used to carry pollutants to the surface through micro-nano bubbles, thereby separating the mixed mud by flotation to form a clean mud phase, residual water after skimming, and solid adsorbent; wherein, the clean mud phase is fed into the dewatering treatment unit (5), the residual water after skimming is fed into the residual water treatment unit (6), and the solid adsorbent is collected and recovered to the nitrogen and phosphorus recovery unit (7). The dewatering treatment unit (5) is used to mechanically dewater the clean mud phase to obtain clean mud cake, whose total nitrogen and total phosphorus content meets the resource utilization standards and is transported to be used for the production of building materials, soil conditioners, landscaping soil or directly backfilled in situ; among them, the residual water generated by dewatering is collected into the residual water treatment unit (6). The wastewater treatment unit (6) is used to coagulate and settle the incoming wastewater. The sediment obtained after sedimentation is transported off-site for disposal. The remaining wastewater is treated by biochemical processes and then used as water supply in the first-stage ultrasonic extraction reaction unit (2), high-pressure flushing by a cutter suction dredger, or directly discharged as ecological water replenishment for rivers and lakes. The nitrogen and phosphorus recovery unit (7) is used to recover nitrogen and phosphorus from the extraction waste liquid of nitrogen and phosphorus pollutants by the struvite precipitation method to make fertilizer, and to desorb pollutants by adding acid and alkali to the collected solid phase adsorbent, and regenerate the adsorbent and return it to the second-stage solid phase adsorption reaction unit (3), and the resulting supernatant is fed into the waste water treatment unit (6).

2. The resource recovery system for dredged sediment treatment based on ultrasonic extraction and flotation synergy as described in claim 1, characterized in that, The pretreatment unit (1) includes a mud buffer (11) and a primary separation device (12). The mud buffer (11) is used to store dredged mud that has been pretreated by bar screen or vibrating screen for impurity removal; The primary separation equipment (12) is used to perform preliminary solid-liquid separation on the pretreated dredging slurry by sedimentation concentration or centrifugation to form an upper suspension and a thick slurry.

3. The resource recovery system for dredged sediment treatment based on ultrasonic extraction and flotation synergy as described in claim 1, characterized in that, The first-stage ultrasonic extraction reaction unit (2) includes: a mud reaction tank (21), a rinsing and homogenization module (22), an extractant addition module (23), an ultrasonic module (24), and a solid-liquid separation module (25). The mud reaction vessel (21) is used as the main reaction vessel for ultrasonic extraction of thick slurry. The flushing and homogenization module (22) is used to inject river or lake water or treated residual water into the mud reaction tank (21), form a rotating water film on the tank wall by tangential water spraying, and generate tangential flow by stirring. The mud is homogenized and broken by dual-frequency ultrasonic array. The extractant addition module (23) is used to add green liquid phase extractant to the mud reaction tank (21), and change the mud-water interface properties by adjusting pH and ionic strength, thereby realizing the extraction of thick slurry. The ultrasonic module (24) is used to homogenize and break up a thick slurry containing an extractant by using a dual-frequency combination of ultrasound with frequencies of 20-30 kHz and 500 kHz-1 MHz. The solid-liquid separation module (25) is used to separate the solid and liquid of the slurry after ultrasonic extraction to form an upper layer of extraction waste liquid containing high concentrations of nitrogen and phosphorus pollutants and concentrated slurry.

4. The resource recovery system for dredged sediment treatment based on ultrasonic extraction and flotation synergy as described in claim 3, characterized in that, The rinsing and homogenization module (22) includes: a tangential water spray device (221), a central water replenishment device (222), a liquid level interlock control system (223), and a stirring device (224). A tangential water spray device (221) is used to form a rotating water film on the wall of the mud reaction tank (21); The central water supply device (222) is used to inject river or lake water or treated waste water into the mud reaction tank (21); The liquid level interlock control system (223) is used to control the liquid level in the mud reaction tank (21) to be constant at ±5 cm, and to cut off the water supply when the liquid level exceeds the limit. The stirring device (224) includes a variable frequency side-mounted shear pump for generating tangential flow; The ultrasonic module (24) includes: a dual-frequency ultrasonic generator (241) and an ultrasonic probe movement control module (242). A dual-frequency ultrasonic generator (241) is used to generate a dual-frequency ultrasonic array through low and high frequency ultrasonic probes, thereby homogenizing and breaking up a thick slurry containing an extractant. The ultrasonic probe movement control module (242) is used to control the ultrasonic probe to rise and fall and move circumferentially along the inner wall of the mud reaction tank (21); The solid-liquid separation module (25) includes: a hydrocyclone (251) and a centrifuge (252); Hydrocyclone (251) is used to achieve rapid classification of solid-liquid mixtures by utilizing centrifugal force field and fluid tangential motion; Centrifuge (252) is used to separate fine particles or colloidal substances by means of strong centrifugal force generated by high-speed rotation, forming an upper layer of extraction waste liquid and concentrated mud containing high concentrations of nitrogen and phosphorus pollutants.

5. The resource recovery system for dredged sediment treatment based on ultrasonic extraction and flotation synergy as described in claim 1, characterized in that, The second-stage solid-phase adsorption reaction unit (3) includes: a contact reaction tank (31), an adsorbent silo (32), and an adsorbent dosing module (33). Contact reaction vessel (31) is used as the main reaction vessel for solid phase adsorption of concentrated mud. The adsorbent silo (32) is used to pre-load compound solid adsorbents, and the solid adsorbents are magnetically modified solid adsorbents. The adsorbent dosing module (33) is used to add the compound solid adsorbent in the adsorbent silo (32) into the contact reaction tank (31).

6. The resource utilization system for dredged sediment treatment based on ultrasonic extraction and flotation synergy as described in claim 1, characterized in that, The third-stage flotation separation unit (4) includes: a flotation reaction module (41), a bubble generation module (42), a foam collection module (43), and a bottom sludge discharge module (44). The flotation reaction module (41) is used to separate the mixed mud by flotation and to collect the residual water after skimming into the residual water treatment unit (6). The bubble generating module (42) is used to generate 50 nm-50 μm micro-nano bubbles by shearing air under the action of hydraulic cavitation or membrane diffusion, and then transport them to the flotation reaction module (41). The foam collection module (43) is used to collect the floating pollutant floc layer after flotation, so as to separate the clean mud phase from the pollutants; Bottom sludge discharge module (44) is used to output clean sludge phase to dewatering treatment unit (5).

7. The resource recovery system for dredged sediment treatment based on ultrasonic extraction and flotation synergy as described in claim 6, characterized in that, The flotation reaction module (41) includes: a flotation reaction tank (411), an activator dosing device (412), and a flow meter (413). The flotation reaction tank (411) is used as a reaction vessel for flotation separation of mixed mud. An annular overflow weir is set at the top. After the air intake is stopped, it is left to stand for 5 minutes. After skimming, the residual water flows along the weir into the annular water collection weir and flows into the residual water treatment unit (6) through the overflow pipe. A bottom sludge discharge module (44) is set at the bottom. An activator dosing device (412) is used to add an activator to the mixed mud; Flow meter (413) is used to monitor and control the amount of activator added in real time; The bubble generating module (42) includes: an air compressor (421), an air tank (422), a pressure reducing valve (423), an annular air distribution pipe (424), a gas-liquid mixing chamber (425), and a pressure stabilizing valve (426). An air compressor (421) is used to deliver compressed air into an air tank (422). Air storage tank (422) is used to store compressed air and stabilize its pressure; Pressure reducing valve (423) is used to connect gas storage tank (422) and gas-liquid mixing chamber (425); The gas-liquid mixing chamber (425) is used to shear the stabilized compressed air into micro-nano bubbles of 50 nm-50 μm under the action of hydraulic cavitation or film diffusion. Pressure stabilizing valve (426) is used to output micro / nano bubbles to an annular gas distribution pipe (424). An annular gas distribution pipe (424) is used to stably and uniformly release micro-nano bubbles into the bottom of the flotation reaction vessel (411); The foam collection module (43) includes: a mechanical skimming plate (431), a vacuum collection port (432), a collection tank (433), and a magnetic spiral chute (434). Mechanical skimming plate (431) is used to collect the pollutant floc layer generated after micro-nano bubbles collide and adhere with pollutant aggregates in mud and float to the surface. A vacuum collection port (432) is located at the end of the active area of ​​the mechanical skimming plate (431) for auxiliary recovery of foam; Collection tank (433) is used to store the collected pollutant floc layer; The magnetic spiral chute (434) is used to store the foam liquid that flows in by gravity in the collection tank (433). The last turn of the magnetic spiral chute (434) has two outlets tangentially. The cutting point is controlled by an adjustable diverter. The inner side recovers the magnetic solid phase adsorbent, and the outer side outputs the microplastic enrichment. The collected magnetic solid phase adsorbent is added to the nitrogen and phosphorus recovery unit (7) after collection.

8. The resource recovery system for dredged sediment treatment based on ultrasonic extraction and flotation synergy as described in claim 1, characterized in that, The wastewater treatment unit (6) includes: a water collection tank (61), an automatic dosing device (62), a coagulation sedimentation module (63), and a deep purification module (64); The water collection tank (61) is used to store the suspension in the pretreatment unit (1), as well as the residual water in the third-stage flotation separation unit (4) and the dewatering treatment unit (5); Automatic dosing equipment (62) is used to add flocculant PAC according to flow rate-water quality signal; The coagulation and sedimentation module (63) is used to rapidly flocculate and react the suspension and residual water with the flocculant PAC in the pipeline mixer to form flocs and settle the sludge. The deep purification module (64) is used to nitrify and denitrify the remaining water after flocculation, and then use it as water supply in the first-stage ultrasonic extraction reaction unit (2), high-pressure flushing by the cutter suction boat, or direct discharge as ecological water replenishment for rivers and lakes. The nitrogen and phosphorus recovery unit (7) includes: an acid and alkali dosing device (71), a desorption chamber (72), a magnesium salt dosing device (73), and a nutrient salt recovery chamber (74); An acid-base dosing device (71) is used to add acid or base into the desorption chamber (72); The desorption chamber (72) is used to store the collected magnetic solid phase adsorbent. The nitrogen and phosphorus in the magnetic solid phase adsorbent are desorbed by adding acid and alkali, and the resulting supernatant is introduced into the nutrient salt recovery chamber (74). Magnesium salt dosing device (73) is used to add magnesium salt into nutrient salt recovery chamber (74); The nutrient recovery chamber (74) is used to store the collected extraction waste liquid containing high concentrations of nitrogen and phosphorus pollutants. The nutrients in the extraction waste liquid are extracted by magnesium salts and the nutrients are recovered by the struvite method. The resulting supernatant is fed into the waste water treatment unit (6).

9. A method for the treatment and resource recovery of dredged sediment based on the ultrasonic extraction-flotation synergistic system according to any one of claims 1-8, characterized in that, include: Step S1: The dredged sediment is pretreated by removing impurities through a screen and collected in a mud buffer tank (11), and then pumped to a mud reaction tank (21). Step S2: In the mud reaction tank (21), add green liquid extractant and stir for 10 minutes. A rotating water film is formed on the tank wall by the tangential water spray device (221). The central water replenishment device (222) injects river or lake water or treated residual water into the mud reaction tank (21) from bottom to top. Step S3: The liquid level in the tank is kept constant by the liquid level interlock control system (223), and tangential flow is generated by the stirring device (224). The dual-frequency ultrasonic generator (241) is started, and the slurry is homogenized and broken by the dual-frequency ultrasonic array. The slurry is treated with alternating ultrasonic treatment at 20-30 kHz and 500 kHz for 30 min to form an upper layer of extraction waste liquid and concentrated slurry containing high concentrations of nitrogen and phosphorus pollutants. Step S4: After ultrasonic treatment, the solid-liquid separation is performed by centrifuge (252) and the mixture is left to stand for 10-20 minutes. The upper layer of extraction waste liquid containing high concentrations of nitrogen and phosphorus pollutants is pumped out to the nutrient salt recovery chamber (74). The concentrated mud is fed into the contact reaction tank (31) through the pipeline equipped with the flushing and homogenization equipment. Step S5: The pre-filled compound magnetic solid adsorbent in the adsorbent silo (32) is added to the contact reaction tank (31) through the adsorbent addition module (33), and stirred at 100r / min for 30 minutes to form a mixed slurry which is then fed into the flotation reaction tank (411). In step S6, the air compressor (421) first sends compressed air into the air storage tank (422) for pressure stabilization, and then introduces it into the gas-liquid mixing chamber (425) through the pressure reducing valve (423). Under the action of hydraulic cavitation or film diffusion, it is sheared to generate micro-nano bubbles of 50 nm-50 μm, and then output through the pressure stabilizing valve (426), and is stably and uniformly released into the bottom of the flotation reaction tank (411) through the annular air distribution pipe (424). Step S7: After micro-nano bubbles collide and adhere to the pollutant aggregates in the mixed mud, they float to the surface. The flotation time is 20-60 minutes. After stopping the air intake, let it stand for 5 minutes. After skimming off the slag, the remaining water flows into the annular water collection weir by gravity along the weir and flows into the residual water collection tank (61) through the overflow pipe. The bottom mud discharge module (44) outputs the clean mud phase to the dewatering treatment unit (5) at the bottom. If the flotation effect is not good, a small amount of activator is added to the mixed mud using the flotation activator addition device (412). After stirring for 5-15 minutes, flotation is carried out again. Step S8: After flotation, the floating pollutant floc layer is collected in the collection tank (433) using a mechanical skimmer (431). The vacuum collection port (432) at the end of the active section of the mechanical skimmer (431) assists in the recovery of foam, thereby separating the clean sludge phase from the pollutants. The foam liquid in the collection tank (433) flows into the composite magnetic spiral chute (434) by gravity, recovering the magnetic solid phase adsorbent on the inner side and outputting the microplastic enrichment on the outer side, thus effectively separating the magnetic solid phase adsorbent and the microplastics. Step S9: The collected magnetic solid phase adsorbent is added to the desorption chamber (72) after collection. Pollutants are desorbed by adding acid and alkali. The regenerated magnetic adsorbent is returned to the adsorbent silo (32). Nitrogen and phosphorus are released in the liquid phase. The supernatant is introduced into the nutrient salt recovery chamber (74). Subsequently, magnesium salt is added to the nutrient salt recovery chamber (74). Nitrogen and phosphorus are recovered by the struvite precipitation method to make fertilizer. In step S10, the mud phase separated by flotation is fed into the dewatering treatment unit (5), and after being squeezed and dewatered by the mechanical dewatering equipment (51), clean mud cake is obtained. It is transported to the outside for the production of building materials, soil conditioners, landscaping soil or directly backfilled in rivers and lakes. The excess water generated by dewatering is fed into the water collection tank (61). In step S11, the tailwater generated from flotation and sludge dewatering is collected in the collection tank (61) for homogenization and equalization. The flocculant PAC is added by the automatic dosing equipment (62) according to the flow rate-water quality signal. After rapid flocculation in the pipeline mixer, it enters the coagulation sedimentation module (63) and then enters the deep purification module (64) for simultaneous nitrification-denitrification. After treatment, it is used as water supply in the first-stage ultrasonic extraction reaction unit (2), high-pressure flushing by the cutter suction boat, or directly discharged as ecological water replenishment for rivers and lakes.

10. The resource recovery method according to claim 9, characterized in that, In step S2, the green liquid phase extractant is one or more of the following compound systems: bio-based small molecule organic acids, natural polymer compounds, and green surfactants. Stir for 10-20 minutes to ensure that the extractant is in full contact with the mud. If bio-based small molecule organic acids are selected, the addition amount is 0.3-2.0 kg / m³. 3 If natural polymers are chosen, the addition amount is 0.2-2.0 kg / m³; if green surfactants are chosen, the addition amount is 2.0-5.0 g / m³. 3 When using a compound system, the mass ratio of each component is organic acid: surfactant = 5:5-8:2, or natural polymer: surfactant = 7:3-9:1; In step S3, ultrasonic treatment employs a dual-frequency combination of 20-30 kHz and 500 kHz-1 MHz frequencies to treat the dredged mud containing the extractant. The low-frequency and high-frequency ultrasound are used synchronously or alternately. When alternating, the duration of a single treatment of each frequency is 5-15 min, and the ultrasonic treatment time is controlled between 30-120 min. The contact depth between the ultrasonic probe and the mud concentrate is 10-30 cm, and the ultrasonic probe moves at a uniform speed of 5-20 cm / s during the treatment process. Low-frequency ultrasound, through the high-speed microjets and high-pressure shock waves generated by the cavitation effect, destroys the flocculation structure and particle agglomerates of the bottom sediment, while high-frequency ultrasound generates a large number of micro- and nano-bubbles, increasing the reaction surface area and enhancing the penetration of liquid-phase extractants into the particles. In step S5, the solid-phase adsorbent is a lightweight, fine-particle or powdered porous adsorbent, and the adsorbent dosage is 0.5-2.0 kg / m³. 3 Control the stirring rate to 50-150 r / min and the reaction time to 30-120 min, so that the solid phase extractant can fully capture nitrogen and phosphorus pollutants in the liquid phase through physical adsorption and chemical complexation. During the synthesis of solid-phase adsorbents, magnetic component Fe3O4 nanoparticles are added to prepare magnetic solid-phase adsorbent composite materials. Solid-phase adsorbents are produced using the following materials or combinations thereof: Lightweight porous biochar: Biochar materials with rich pore structure and low density are prepared by precisely controlling the pyrolysis temperature and atmosphere; Modified natural minerals: Zeolite and ceramsite natural minerals are selected, and their pore structure and surface properties are controlled through hot processing granulation and foaming processes; Natural polymer materials: By using chitosan and cellulose-based materials, phosphate, amine and carboxyl functional groups are introduced through grafting modification to enhance their adsorption capacity and selectivity for nitrogen and phosphorus pollutants. The compounding ratio should be 40%-60% lightweight porous biochar, 35%-50% modified natural minerals, and 0%-5% natural polymer materials. In step S6, micro- and nano-bubbles are generated using hydrocavitation or membrane diffusion. The bubble size distribution is 50 nm-50 μm, with nano-sized bubbles accounting for ≥20% and micro-sized bubbles accounting for ≤80%. The bubble generation rate is 0.5-2 L / min·m. 3 .

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