Aquaculture wastewater phosphorus resource recovery method based on struvite process mediation

Abstract

The invention provides an aquaculture wastewater phosphorus resource recovery method based on struvite process mediation, relates to the technical field of livestock and poultry breeding waste recycling and sewage treatment, is applied to an aquaculture wastewater phosphorus resource recovery system, and comprises the following steps: roughly filtering biogas slurry, and then feeding the biogas slurry into a microwave ultrasonic coupling reactor for pretreatment; a magnesium source is added into the pretreated biogas slurry, the pH is adjusted to be alkaline, and the adjusted mixed solution sequentially passes through a primary seed crystal generator, a pulse microwave regulation and control device and a secondary crystal growth reactor to generate struvite crystals; carrying out spiral extrusion dehydration, cutting granulation and spraying coating on the slurry containing struvite crystals to obtain coated slow-release fertilizer particles and separated supernate; wherein the supernate is sent to an adsorption column, and secondary recovery of phosphorus resources is carried out through regeneration of an adsorbent. Therefore, efficient recovery of phosphorus resources, deep purification of wastewater and high value of products are realized.

Description

Technical Field

[0001] This application relates to the field of livestock and poultry breeding waste resource utilization and wastewater treatment technology, specifically to a method for recovering phosphorus resources from livestock wastewater based on struvite process. Background Technology

[0002] The biogas slurry produced from anaerobic fermentation of pig farm wastewater is rich in nutrients such as nitrogen and phosphorus. Direct application to farmland faces risks including seasonal limitations, high transportation costs, and non-point source pollution from excessive application. Furthermore, direct discharge of this slurry results in nitrogen and phosphorus being key factors contributing to eutrophication of water bodies. Phosphorus is an essential element for life and a non-renewable strategic resource. Recovering phosphorus from phosphorus-rich pig farm biogas slurry is a crucial pathway to resource recycling and addressing the phosphorus crisis. Therefore, the efficient recovery of phosphorus resources from biogas slurry is of great significance for pollution control and nutrient cycling.

[0003] Struvite (magnesium ammonium phosphate, MgNH4PO2·6H2O) crystallization is one of the most promising phosphorus recovery technologies. This method involves adding a magnesium source to wastewater containing phosphorus and ammonia nitrogen and adjusting the pH to alkaline, causing the three to co-precipitate in the form of struvite. Struvite precipitate is an excellent slow-release fertilizer that can realize the resource utilization of phosphorus. However, when the traditional struvite process is directly applied to pig farm wastewater biogas slurry, the following prominent bottlenecks are faced, which limit its large-scale engineering application. (1) Complex phosphorus forms and release problems: Phosphorus in biogas slurry exists in various forms. In addition to soluble orthophosphate, it also contains a large amount of phosphorus bound to suspended solids, colloids and organic matter (such as phospholipids, nucleic acids, etc.). These bound phosphorus cannot directly participate in the struvite crystallization reaction, resulting in low and unstable total phosphorus recovery rate. (2) Severe water quality interference: High concentrations of organic matter, suspended solids, and impurities such as calcium ions in biogas slurry will competitively bind magnesium ions, encapsulate crystal nuclei, or interfere with crystal growth, resulting in low crystal purity, poor crystal form, and poor settling performance of struvite. (3) Lengthy process and low product value: Existing technologies usually treat "pretreatment-reaction-solid-liquid separation-drying-granulation" as dispersed unit operations, resulting in a long process, large footprint, and high energy consumption. The struvite obtained is mostly in the form of sludge or powder, which is easy to lose as fertilizer, inconvenient to apply, and has low added value, making it difficult to offset operating costs.

[0004] To overcome the above problems, some improvements have been made to existing technologies. For example, some technologies use acid hydrolysis or bio-enzymatic hydrolysis to release organophosphorus compounds, but these have problems such as slow reaction, high cost, or harsh conditions; some have tried to set up packing materials in the crystallization reactor or use fluidized beds to improve the crystallization effect, but these have poor adaptability to water quality fluctuations; some have carried out subsequent drying, extrusion granulation, and extrusion of the separated struvite wet sludge, but this has increased additional energy consumption and processes. Summary of the Invention

[0005] In view of this, the purpose of this application is to provide a method for recovering phosphorus resources from aquaculture wastewater based on struvite process, which can achieve efficient recovery of phosphorus resources, deep purification of wastewater and high-value utilization of products.

[0006] In a first aspect, embodiments of this application provide a method for recovering phosphorus resources from aquaculture wastewater based on a struvite process, applied to an aquaculture wastewater phosphorus resource recovery system. This system includes a pretreatment unit, a crystallization unit, an online forming unit, and a deep purification unit. The pretreatment unit includes a microwave-ultrasonic coupling reactor. The crystallization unit includes a primary seed crystal generator, a secondary crystal growth reactor, and a pulsed microwave control device disposed between the two. The online forming unit is a spiral extrusion dehydration granulation and coating integrated machine. The deep purification unit is an adsorption column. The method includes the following steps: After coarse filtration, the biogas slurry produced by anaerobic fermentation of aquaculture wastewater is sent to a microwave-ultrasonic coupled reactor for pretreatment to release bound phosphorus in the biogas slurry. Magnesium source was added to the pretreated biogas slurry and the pH was adjusted to alkaline. The adjusted mixture was then passed through a primary seed crystal generator, a pulse microwave control device, and a secondary crystal growth reactor to generate struvite crystals. The slurry containing struvite crystals is fed into a spiral extrusion dewatering granulation and coating integrated machine for spiral extrusion dewatering, cutting granulation, and spray coating to obtain coated slow-release fertilizer granules and the separated supernatant. The supernatant is sent to an adsorption column for secondary recovery of phosphorus resources through adsorbent regeneration.

[0007] In some embodiments, the microwave-ultrasonic coupling reactor releases bound phosphorus from the biogas slurry through the synergistic effect of the microwave thermal effect of the microwave generator and the ultrasonic cavitation effect of the ultrasonic transducer. The ultrasonic transducer is set to a frequency of 20-40kHz and a power density of 40-60W / L, operating in pulse mode; the microwave generator is set to a frequency of 2450MHz, which raises the temperature of the biogas slurry to 70-85℃ within 2 minutes and maintains it for 10-25 minutes; and the action time of the ultrasonic transducer and the microwave generator on the biogas slurry overlaps by at least 5 minutes.

[0008] In some embodiments, the step of adding a magnesium source to the pretreated biogas slurry and adjusting the pH to alkaline, and then sequentially passing the adjusted mixture through a primary seed crystal generator, a pulsed microwave control device, and a secondary crystal growth reactor to generate struvite crystals, includes the following steps: The pretreated biogas slurry is sent to the buffer tank of the crystallization unit, and magnesium sulfate or magnesium chloride is added to the buffer tank as a magnesium source. The concentrations of magnesium (Mg), ammonia nitrogen (N), and phosphorus (P) in the mixed liquid in the buffer tank are monitored in real time, and the amount of magnesium source added is controlled according to the set concentration ratio. Add NaOH solution to the buffer tank to adjust the pH to the set range, and send the pH-adjusted mixture into the primary seed generator to generate seed crystals, thus obtaining a seed crystal suspension; The seed crystal suspension is sent to a pulsed microwave control device, and after the surface energy of the seed crystal is optimized by microwave irradiation, it is sent to a secondary crystal growth reactor to complete the crystallization of struvite.

[0009] In some embodiments, the molar ratio of magnesium (Mg), ammonia nitrogen (N), and phosphorus (P) is set to (1.1-1.3):1.1:1.0; the pH is adjusted to 9.0-9.5; the microwave irradiation time is 1-3 minutes; and the secondary crystal growth reactor is operated in fluidized mode or stirring mode at 50-80 rpm for 40-60 minutes.

[0010] In some embodiments, the integrated spiral extrusion dewatering granulation and coating machine comprises, in sequence along the material feeding direction, a spiral extrusion dewatering section, a pelletizing disc, and a roller coating section. An atomizing nozzle connected to a coating liquid storage tank is disposed above the roller coating section. The process involves feeding a slurry containing struvite crystals into the integrated spiral extrusion dewatering granulation and coating machine for spiral extrusion dewatering, cutting and granulation, and spray coating to obtain coated slow-release fertilizer granules, including the following steps: The slurry containing struvite crystals is fed into the screw extrusion dewatering section for extrusion dewatering to obtain the separated supernatant and wet strips; The wet material strip is fed into the pelletizing disc and cut into particles of a preset size; The cut granules are fed into the coating section of the drum for tumbling, and the coating liquid in the coating liquid storage tank is sprayed onto the surface of the granules through the atomizing nozzle to generate coated slow-release fertilizer granules; wherein, the coating liquid is an organic solution or water-dispersible emulsion of biodegradable polymer material, with a concentration range of 1%-5% (w / v).

[0011] In some embodiments, the following steps are included before performing step S2: The step of sending the supernatant to an adsorption column for secondary phosphorus resource recovery through adsorbent regeneration includes the following steps: The supernatant is fed into an adsorption column; the adsorbent filled in the adsorption column is hydrated iron oxide FeOOH or modified biochar loaded with nano-zero valent iron nZVI. The total phosphorus (TP) concentration at the outlet of the adsorption column is monitored in real time. If the TP concentration is less than or greater than the set threshold, the water is discharged; if the TP concentration is greater than the set threshold, the adsorbent is determined to be saturated. The saturated adsorbent is desorbed using NaOH solution, and the resulting phosphorus-containing desorption solution is collected and sent to the crystallization unit for secondary recovery via a reflux pipeline.

[0012] In some embodiments, the aquaculture wastewater phosphorus resource recovery system further includes an intelligent control unit, and the method further includes the following steps: The system collects and adjusts the operating parameters of other units in real time.

[0013] Secondly, embodiments of this application provide a phosphorus resource recovery system for aquaculture wastewater, including a pretreatment unit, a crystallization unit, an online forming unit, and a deep purification unit, for collaboratively implementing the steps of the method for recovering phosphorus resources from aquaculture wastewater based on struvite process as described in any one of the first aspects.

[0014] Thirdly, this application also provides an electronic device, including: a processor, a memory, and a bus, wherein the memory stores machine-readable instructions executable by the processor, and when the electronic device is running, the processor communicates with the memory via the bus, and when the machine-readable instructions are executed by the processor, the steps of the method for recovering phosphorus resources from aquaculture wastewater based on struvite process as described in any of the second aspects above are executed.

[0015] Fourthly, this application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, performs the steps of the method for phosphorus resource recovery from aquaculture wastewater based on struvite process as described in any one of the first aspects.

[0016] This application describes a method for phosphorus resource recovery from aquaculture wastewater based on struvite technology. Applied to an aquaculture wastewater phosphorus resource recovery system, the method involves coarsely filtering the biogas slurry produced by anaerobic fermentation of aquaculture wastewater and then pre-treating it in a microwave-ultrasonic coupled reactor to release bound phosphorus. A magnesium source is added to the pre-treated biogas slurry to adjust the pH to alkaline. The adjusted mixture is then sequentially passed through a primary crystal seed generator, a pulsed microwave control device, and a secondary crystal growth reactor to generate struvite crystals. The slurry containing the struvite crystals is then fed into a spiral extrusion dewatering, granulation, and coating integrated machine for spiral extrusion dewatering, cutting, granulation, and coating to obtain coated slow-release fertilizer granules and a separated supernatant. The supernatant is then sent to an adsorption column for secondary phosphorus resource recovery through adsorbent regeneration. This method synergistically combines microwave-ultrasonic coupled pretreatment and two-stage crystallization to improve phosphorus recovery efficiency; directly generates high-purity coated slow-release fertilizer, increasing product added value; and achieves secondary phosphorus resource recovery through adsorbent regeneration. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A flowchart of the method for phosphorus resource recovery from aquaculture wastewater based on struvite process described in the embodiments of this application is shown; Figure 2 A schematic diagram of the structure of the aquaculture wastewater phosphorus resource recovery system described in an embodiment of this application is shown; Figure 3 A flowchart illustrating the generation of struvite crystals according to an embodiment of this application is shown; Figure 4 The flowchart illustrating the process of obtaining coated slow-release fertilizer granules according to an embodiment of this application is shown; Figure 5 This document illustrates a flowchart of a phosphorus resource secondary recovery process via adsorbent regeneration, as described in an embodiment of this application. Figure 6 A schematic diagram of the structure of the electronic device described in an embodiment of this application is shown.

[0019] Explanation of key component symbols: 1. Pretreatment unit; 2. Crystallization unit; 21. Primary seed crystal generator; 22. Secondary crystal growth reactor; 3. Online forming unit; 31. Screw extrusion dehydration section; 32. Roller coating section; 4. Deep purification unit; 5. Intelligent control unit. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the accompanying drawings in this application are for illustrative and descriptive purposes only and are not intended to limit the scope of protection of this application. Furthermore, it should be understood that the schematic drawings are not drawn to scale. The flowcharts used in this application illustrate operations implemented according to some embodiments of this application. It should be understood that the operations in the flowcharts may not be implemented in sequence, and steps without logical contextual relationships may be reversed or implemented simultaneously. In addition, those skilled in the art, guided by the content of this application, may add one or more other operations to the flowcharts, or remove one or more operations from the flowcharts.

[0021] Furthermore, the described embodiments are merely some, not all, of the embodiments of this application. The components of the embodiments of this application described and illustrated herein can typically be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0022] It should be noted that the term "comprising" will be used in the embodiments of this application to indicate the presence of the features declared thereafter, but does not exclude the addition of other features.

[0023] In view of the technical problems mentioned in the background, this application provides a method for phosphorus resource recovery from aquaculture wastewater based on struvite process, which can achieve efficient recovery of phosphorus resources, deep purification of wastewater and high-value utilization of products.

[0024] See the instruction manual appendix Figure 1 Included with instruction manual Figure 2 This application provides a method for phosphorus resource recovery from aquaculture wastewater based on struvite technology, applied to an aquaculture wastewater phosphorus resource recovery system. The system includes a pretreatment unit 1, a crystallization unit 2, an online forming unit 3, and a deep purification unit 4. The pretreatment unit 1 includes a microwave-ultrasonic coupled reactor. The crystallization unit 2 includes a primary seed crystal generator 21, a secondary crystal growth reactor 22, and a pulsed microwave control device disposed between the two. The online forming unit is a spiral extrusion dewatering, granulation, and coating integrated machine, which sequentially includes a spiral extrusion dewatering section 31 for cutting and granulation, a granulator disc, and a roller coating section 32 along the material's forward direction. The deep purification unit 4 is an adsorption column. The method includes the following steps: S1. After coarse filtration, the biogas slurry produced by anaerobic fermentation of aquaculture wastewater is sent to a microwave-ultrasonic coupled reactor for pretreatment to release bound phosphorus in the biogas slurry. S2. Add magnesium source to the pretreated biogas slurry and adjust the pH to alkaline. Then, pass the adjusted mixture through a primary seed crystal generator, a pulse microwave control device and a secondary crystal growth reactor to generate struvite crystals. S3. The slurry containing struvite crystals is fed into a spiral extrusion dewatering granulation and coating integrated machine for spiral extrusion dewatering, cutting granulation, and spray coating to obtain coated slow-release fertilizer granules and the separated supernatant. S4. The supernatant is sent to the adsorption column for secondary recovery of phosphorus resources through adsorbent regeneration.

[0025] Step S1 mainly involves pretreatment using a microwave-ultrasonic coupled reactor to deeply release bound phosphorus from the biogas slurry, degrade organic matter that interferes with crystallization, and provide a clean, high-phosphorus-concentration reaction matrix for subsequent crystallization steps.

[0026] Specifically, the pretreatment unit includes a biogas slurry storage tank, a bar screen filter, and a microwave-ultrasonic coupling reactor. In the microwave-ultrasonic coupling reactor, ultrasonic transducers are arranged in an array submerged within the reaction chamber, and a microwave generator radiates energy into the chamber via a waveguide. Both can operate in synchronous, alternating, or power-coupled modes to synergistically treat the biogas slurry, releasing phosphorus and degrading interfering substances. First, the biogas slurry produced from the anaerobic fermentation of aquaculture wastewater is passed through a bar screen filter for coarse filtration to remove large suspended impurities and prevent clogging of subsequent equipment. The coarsely filtered biogas slurry is then temporarily stored in a biogas slurry storage tank to maintain a stable liquid level and provide uniform feed conditions for subsequent continuous treatment. Then, the biogas slurry in the storage tank is pumped into the microwave-ultrasonic coupling reactor using a metering pump, controlling the feed flow rate to match the reactor volume and ensure the treatment time meets requirements. The ultrasonic treatment conditions are set as follows: frequency 20-40kHz, power density 40-60W / L, pulsed operating mode, utilizing the microjets and shear forces generated by cavitation to powerfully break down microbial cells, colloids, and organic particles, releasing intracellular and bound phosphorus. The microwave treatment conditions were set as follows: a frequency of 2450 MHz, raising the material temperature to 70-85°C within 2 minutes and maintaining it for 10-25 minutes; the ultrasonic and microwave treatment times overlapped by at least 5 minutes. The combined thermal and non-thermal effects (molecular polarization and ion conduction) of the microwave altered the hydration structure, promoting the hydrolysis of organophosphorus molecules into orthophosphates, while simultaneously denaturing and coagulating some colloidal proteins. Ultimately, the synergistic effect of the microwave generator and ultrasonic transducer achieved a total phosphorus release rate greater than 95%, and partially degraded large organic molecules, reducing subsequent interference.

[0027] Step S2 mainly involves generating large-particle-size, high-purity struvite crystals through crystallization units, thereby improving the efficiency of subsequent solid-liquid separation and the basic quality of the product.

[0028] See the instruction manual appendix Figure 3 The step of adding a magnesium source to the pretreated biogas slurry and adjusting the pH to alkaline, and then sequentially passing the adjusted mixture through a primary seed crystal generator, a pulsed microwave control device, and a secondary crystal growth reactor to generate struvite crystals, includes the following steps: S201. The pretreated biogas slurry is sent to the buffer tank of the crystallization unit, and magnesium sulfate or magnesium chloride is added to the buffer tank as a magnesium source; wherein, the concentrations of magnesium (Mg), ammonia nitrogen (N), and phosphorus (P) in the mixed liquid in the buffer tank are monitored in real time, and the amount of magnesium source added is controlled according to the set concentration ratio. S202. Add NaOH solution to the buffer tank to adjust the pH to the set range, and send the pH-adjusted mixture into the primary seed generator to generate seed crystals, thus obtaining a seed crystal suspension. S203. The seed crystal suspension is sent to a pulsed microwave control device. After the surface energy of the seed crystal is optimized by microwave irradiation, it is sent to a secondary crystal growth reactor to complete the crystallization of struvite.

[0029] In steps S201 and S202, the pretreated biogas slurry is first sent to the buffer tank of the crystallization unit for a short period to stabilize the water quality and quantity. Then, the automatic dosing system is activated, adding magnesium sulfate or magnesium chloride as a magnesium source to the buffer tank. Simultaneously, the concentrations of ammonia nitrogen (N) and phosphorus (P) in the liquid are monitored in real time using an online monitoring instrument, and the magnesium source dosage is dynamically adjusted to ensure that the Mg:N:P molar ratio is stable at (1.1-1.3):1.1:1.0. Furthermore, NaOH solution is added to precisely control the pH at 9.0-9.5. During the adjustment process, a pH sensor provides real-time feedback to control the dosing rate and avoid drastic pH fluctuations. Next, the adjusted mixture is sent to the primary seed crystal generator, and the stirring device is activated at a speed of 200-300 rpm for 10-15 minutes to rapidly form uniformly dispersed struvite microcrystals (seed crystals).

[0030] In step S203, the obtained seed crystal suspension is first pumped into a pulsed microwave control device, and the microwave irradiation time is set to 1-3 minutes. The surface energy of the crystal is optimized by short-term low-power microwave action, and the formation of impurity crystals is suppressed. Then, the microwave-controlled slurry is fed into a secondary crystal growth reactor. If a stirring mode is used, the rotation speed is set to 50-80 rpm. If a fluidization mode is used, the water flow rate is controlled by a bottom water distributor to form a weak fluidization state, providing a stable environment for crystal growth. The secondary crystal growth reactor is maintained for 40-60 minutes to allow the struvite microcrystals to grow continuously, and finally high-purity struvite crystals with an average particle size greater than 100 μm are formed.

[0031] Step S3 mainly involves directly converting the crystallized slurry obtained in step S2 into high-value coated slow-release fertilizer through an online molding unit, eliminating the dispersion steps of sedimentation tank, dryer, and independent granulator in traditional processes, and realizing one-step conversion from wastewater to product.

[0032] See the instruction manual appendix Figure 4 The process of feeding a slurry containing struvite crystals into a spiral extrusion dewatering granulation and coating integrated machine for spiral extrusion dewatering, cutting and granulation, and spray coating to obtain coated slow-release fertilizer granules includes the following steps: S301. The slurry containing struvite crystals is fed into the screw extrusion dewatering section for extrusion dewatering to obtain the separated supernatant and wet strips. S302. The wet material strip is fed into the pelletizing disc and cut into particles of a preset particle size; S303. The cut granules are fed into the drum coating section for tumbling, and the coating liquid in the coating liquid storage tank is sprayed onto the surface of the granules through the atomizing nozzle to generate coated slow-release fertilizer granules.

[0033] In steps S301 and S302, firstly, the slurry containing struvite crystals after crystallization is pumped to the feed inlet of the integrated screw extrusion dewatering granulation and coating machine. The feed pressure is controlled to be stable to avoid fluctuations in slurry flow rate affecting the processing effect. Then, the screw extrusion dewatering section is started. The free water in the crystal slurry is removed by the mechanical extrusion action of the screw shaft, so that the moisture content of the solid material is reduced to below 30%, and the separated supernatant and wet strips are obtained. The wet strips enter the pelletizing disc through the discharge port. The speed of the pelletizing disc is adjusted according to the preset particle size to cut the wet strips into uniformly sized particles.

[0034] In step S303, the cut granules enter the low-speed rotating drum coating section. The drum drive device is started, and the drum speed is controlled to ensure that the granules tumble fully inside the drum without being broken. A biodegradable polymer coating liquid with a mass concentration of 1%-5% (e.g., a dilute solution of polylactic acid PLA, cellulose acetate CA, or a natural resin emulsion) is delivered to the atomizing nozzle above the drum coating section and atomized and evenly sprayed onto the surface of the tumbling granules. The residual heat generated during the drum operation and the rolling friction heat between the granules are used to quickly solidify the coating liquid on the surface of the granules, forming a dense microporous membrane, and finally producing coated slow-release fertilizer granules with a particle size of 2-5 mm.

[0035] Step S4 mainly removes residual phosphorus from the supernatant separated in the forming stage of step S3 through a deep purification unit, ensuring that the effluent meets the standards for farmland irrigation or discharge. At the same time, phosphorus resources are recycled secondary through adsorbent regeneration to avoid waste.

[0036] See the instruction manual appendix Figure 5 The step of sending the supernatant to an adsorption column for secondary phosphorus resource recovery through adsorbent regeneration includes the following steps: S401. The supernatant is fed into an adsorption column; the adsorbent filled in the adsorption column is hydrated iron oxide FeOOH or modified biochar loaded with nano-zero valent iron nZVI. S402. Real-time monitoring of total phosphorus (TP) concentration at the outlet of the adsorption column. If the TP concentration is less than or greater than the set threshold, discharge is carried out; if the TP concentration is greater than the set threshold, the adsorbent is determined to be saturated. S403. Use NaOH solution to desorb the saturated adsorbent and collect the phosphorus-containing desorption solution generated during desorption. Send the solution to the crystallization unit for secondary recovery through the reflux pipeline.

[0037] In steps S401 and S402, the supernatant separated during the online molding process is first transported to the raw water tank of the deep purification unit through an overflow pipe or centrifugal pump for temporary storage and treatment. Then, the supernatant in the raw water tank is pumped into the iron-modified biochar (FeOOH / nZVI) adsorption column through a constant flow pump, and the empty bed residence time is controlled to ensure that the residual phosphorus is fully adsorbed. The effluent water quality is monitored in real time by an online total phosphorus (TP) monitor at the adsorption column outlet. When the effluent TP ≤ 0.5 mg / L, it is directly discharged or reused. When the effluent TP > 0.5 mg / L is monitored, it is determined that the adsorbent has reached saturation, and the flow path is switched to put the adsorption column into regeneration mode.

[0038] In step S403, a NaOH solution with a concentration of 0.1-0.5 mol / L is introduced into the saturated adsorption column, and the flow rate of the regenerated liquid is controlled to be consistent with that during adsorption for desorption treatment. The phosphorus-containing desorption liquid generated during desorption is collected and transported to the buffer tank of the crystallization unit through the reflux pipeline. After being mixed with the pretreated liquid, it re-participates in struvite crystallization to realize the recycling of phosphorus resources.

[0039] Furthermore, the aquaculture wastewater phosphorus resource recovery system also includes an intelligent control unit, and the method further includes the following steps: real-time acquisition and regulation of the operating parameters of other units.

[0040] Specifically, the intelligent control unit collects real-time parameters such as ultrasonic power, microwave power, material temperature, and processing time from the pretreatment unit; chemical flow rate, pH value, and stirring speed from the crystallization unit; feed flow rate, screw shaft speed, and coating liquid flow rate from the molding unit; and TP concentration in the influent and effluent and adsorption column pressure from the deep purification unit. It then compares and analyzes the collected real-time parameters with preset thresholds. When a parameter deviates from the preset range, it automatically issues adjustment commands. For example, if the phosphorus release rate in the pretreatment unit is insufficient, the ultrasonic power is increased or the processing time is extended; if the pH in the crystallization unit deviates from 9.0-9.5, the NaOH chemical flow rate is adjusted; if the moisture content of the particles in the molding unit exceeds the standard, the screw extrusion speed is increased, thereby achieving optimized operation of the entire system process.

[0041] This application presents a novel method for phosphorus resource recovery from aquaculture wastewater based on struvite technology. It innovatively couples microwave and ultrasonic physical fields for phosphorus release from biogas slurry, resulting in a significant synergistic effect. Compared to single acid hydrolysis or biological methods, the reaction time is shortened by more than 70%, and the total phosphorus release rate is increased from the typical 60-80% to over 95%, with controllable energy consumption. The crystallization process employs a two-stage model of "primary nucleation, microwave regulation, and secondary growth," enabling active control over crystallization kinetics and crystal morphology. The resulting struvite crystals have larger particle size, more regular morphology, and higher purity, significantly improving sedimentation and dewatering performance. The phosphorus recovery rate remains stable above 98%, and the simultaneous ammonia nitrogen recovery rate is >90%. Furthermore, the directly produced coated slow-release fertilizer granules have advantages such as controlled release, anti-caking, and convenient application, with a commercial value far exceeding that of struvite sludge or coarse-grained powder. The coating layer can be further loaded with trace elements or pesticides to develop functional fertilizers.

[0042] Furthermore, by integrating traditional multi-unit operations, particularly the integrated design of "dewatering, granulation, and coating," continuous and automated production from wastewater to finished product is achieved. This eliminates the need for multiple sets of equipment such as sedimentation tanks, dryers, and independent granulators, reducing the floor space by approximately 35% and overall energy consumption by approximately 25%, significantly shortening the process flow. In particular, the intelligent control unit enables online monitoring and feedback adjustment of key parameters throughout the entire process, ensuring efficient and stable operation even when treating biogas slurry with fluctuating water quality, providing a reliable guarantee for large-scale engineering applications.

[0043] The following describes a method for recovering phosphorus resources from aquaculture wastewater based on a struvite process, using specific embodiments and comparative examples. The main technical indicators of the embodiments are shown in Table 1.

[0044]

[0045] Table 1 Example 1: The biogas slurry produced by a biogas project of a 10,000-head pig farm was treated. The raw water had a COD of 4500 mg / L, an SS of 800 mg / L, and a total phosphorus (TP) of 180 mg / L (of which soluble orthophosphate accounted for 55%).

[0046] Pretreatment: After removing coarse slag through a screen, the biogas slurry enters a coupled reactor. It is treated for 20 minutes using a combination of ultrasonic (50W / L, 2s on, 1s off) and microwave (2450MHz, target temperature 80℃). After treatment, the proportion of soluble orthophosphate in TP increases to 94%, and COD decreases by approximately 15%.

[0047] Struvite crystallization: MgCl2·6H2O was added at a ratio of Mg:N:P = 1.2:1.1:1.0, and the pH was adjusted to 9.2 with 10% NaOH solution. Seed crystals were generated by stirring (250 rpm) in a primary reactor for 12 minutes. After treatment with pulsed microwave (1.5 minutes), the crystals flowed into a secondary fluidized bed reactor for growth for 50 minutes. At the end of the reaction, the average crystal size was 125 μm.

[0048] Online molding: The slurry enters the integrated machine, and after extrusion and dehydration, the solid moisture content is 28%. A 2% PLA-acetone solution is used as the coating liquid for spray coating to obtain black, smooth particles with a particle size of approximately 3 mm.

[0049] Purification treatment: After the supernatant is treated by an adsorption column, the TP of the effluent is 0.3 mg / L.

[0050] Final results: The system achieved a total phosphorus recovery rate of 98.5%, an ammonia nitrogen removal rate of 92%, and a purity of up to 97%. The resulting coated fertilizer granules showed a dissolution rate of <10% in static water after 7 days, demonstrating excellent slow-release performance.

[0051] Example 2: Another pig farm's biogas slurry was treated. The raw water had a TP of 260 mg / L (high organic phosphorus content) and a COD as high as 8000 mg / L. The pretreatment time was adjusted to 25 minutes, and the microwave target temperature was set to 85°C. The Mg:N:P ratio during the crystallization stage was adjusted to 1.3:1.1:1.0. The remaining steps were the same as in Example 1. Ultimately, the system achieved a total phosphorus recovery rate of 97.8% even under more complex water conditions, and the produced fertilizer had stable quality, demonstrating the strong adaptability of this application.

[0052] Raw material: Biogas slurry from anaerobic digestion in pig farms, with an initial total phosphorus concentration of 260 mg / L, of which organic phosphorus accounts for about 30%.

[0053] Pretreatment: The biogas slurry was subjected to pulsed ultrasonic treatment (frequency 28 kHz, pulse interval 1 s, duration 5 minutes). The biogas slurry was then pumped into a microwave-induced oxidation reactor, and sodium persulfate (concentration 1.5 mmol / L) was added. The reactor was then subjected to pulsed microwave treatment (power 800 W, on 10 s, off 5 s) for 30 minutes. Tests showed that the organic phosphorus conversion rate exceeded 99%.

[0054] Struvite crystallization: The pretreated supernatant is introduced into a circulating fluidized bed crystallizer. Reaction conditions are controlled as follows: pH = 10.0, Mg:P molar ratio = 1.7, reaction time 20 minutes. Pulsed microwaves (300W power, pulse mode) are applied simultaneously during crystallization. Saturation is monitored in real time using a laser transmission device.

[0055] Deep recovery: After crystallization, the mixture is separated by sedimentation to obtain struvite sludge. The effluent is then treated by a water-carrying iron oxide biochar adsorption column.

[0056] Results: The system achieved a total phosphorus recovery rate of 99.5%, an ammonia nitrogen removal rate of 93%, and a stable total phosphorus concentration in the effluent below 0.5 mg / L. X-ray diffraction analysis of the obtained struvite product showed a purity of up to 96%, and scanning electron microscopy revealed it to be regular prismatic crystals.

[0057] Comparative Example 1: Similar to Example 1, the difference is that the traditional struvite sedimentation method (directly adjusting pH and adding magnesium) was used to treat the same batch of biogas slurry. The total phosphorus recovery rate of the system reached 73%, the ammonia nitrogen removal rate was 82%, the purity was 89%, and the dissolution rate of the resulting coated fertilizer granules in static water after 7 days was 18%, indicating poor slow-release performance.

[0058] Comparative Example 2: Similar to Example 1, the difference is that the traditional struvite sedimentation method (direct pH adjustment and magnesium addition) is used, and only microwave pretreatment is used to treat the same batch of biogas slurry. The total phosphorus recovery rate of the system reaches 78%, the ammonia nitrogen removal rate is 87%, the purity is 91%, and the dissolution rate of the resulting coated fertilizer granules in static water after 7 days is 15%, indicating poor slow-release performance.

[0059] Comparative Example 3: Similar to Example 1, the difference is that the traditional struvite precipitation method (direct pH adjustment and magnesium addition) is used, and only microwave-ultrasonic coupling pretreatment is used without crystallization enhancement. When treating the same batch of biogas slurry, the total phosphorus recovery rate of the system reaches 83%, the ammonia nitrogen removal rate is 86%, the purity is 94%, and the dissolution rate of the resulting coated fertilizer granules in static water after 7 days is 17%, indicating poor slow-release performance.

[0060] Comparative Example 4: Similar to Example 1, the difference is that the traditional struvite precipitation method (directly adjusting pH and adding magnesium agent) is used, and only crystallization enhancement is performed. When treating the same batch of biogas slurry, the total phosphorus recovery rate of the system reaches 88%, the ammonia nitrogen removal rate is 87%, the purity is 90%, and the dissolution rate of the resulting coated fertilizer granules in static water after 7 days is 11%, indicating poor slow-release performance.

[0061] The above-described embodiments and comparative examples were compared under the same conditions of treating biogas slurry, and the results are shown in Table 2.

[0062]

[0063] Table 2 As shown in Table 2, compared with traditional processes, this application innovatively couples microwave and ultrasonic physical fields for phosphorus release from biogas slurry, resulting in a significant synergistic effect. Through a two-stage model of "primary nucleation, microwave control, and secondary growth," active control over crystallization kinetics and crystal morphology is achieved. The resulting struvite crystals have larger particle size, more regular morphology, and higher purity, greatly improving sedimentation and dewatering performance. Phosphorus recovery rate remains stable above 98%, ammonia nitrogen simultaneous recovery rate is >90%, purity is increased to 97%, and slow-release performance is significant.

[0064] Based on the same inventive concept, this application also provides a phosphorus resource recovery system for aquaculture wastewater, including a pretreatment unit, a crystallization unit, an online forming unit, and a deep purification unit. The pretreatment unit includes a microwave-ultrasonic coupling reactor; the crystallization unit includes a primary seed crystal generator, a secondary crystal growth reactor, and a pulsed microwave control device disposed between the two; the online forming unit is a spiral extrusion dehydration granulation and coating integrated machine; and the deep purification unit is an adsorption column. Each unit works collaboratively to implement the steps of the above-described method for phosphorus resource recovery from aquaculture wastewater based on a struvite process. Since the principle of the system in this application embodiment is similar to the above-described method for phosphorus resource recovery from aquaculture wastewater based on a struvite process, the implementation of the system can refer to the implementation of the method, and repeated details will not be elaborated further.

[0065] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

[0066] Based on the same concept of the present invention, as shown in the appendix to the specification. Figure 6 As shown in the figure, an embodiment of this application provides the structure of an electronic device 600, which includes: at least one processor 601, at least one network interface 604 or other user interface 603, memory 605, and at least one communication bus 602. The communication bus 602 is used to realize the connection and communication between these components. The electronic device 600 may optionally include a user interface 603, including a display (e.g., touch screen, LCD, CRT, holographic imaging, or projector, etc.), a keyboard, or a clicking device (e.g., mouse, trackball, touchpad, or touch screen, etc.).

[0067] Memory 605 may include read-only memory and random access memory, and provides instructions and data to processor 601. A portion of memory 605 may also include non-volatile random access memory (NVRAM).

[0068] In some implementations, memory 605 stores executable modules or data structures, or subsets thereof, or extended sets thereof: The 6051 operating system contains various system programs used to implement various basic business functions and handle hardware-based tasks. Application module 6052 contains various applications, such as desktop (launcher), media player (MediaPlayer), browser (Browser), etc., to implement various application services.

[0069] In this embodiment of the application, the processor 601 executes steps such as those of a method for recovering phosphorus resources from aquaculture wastewater based on a struvite process by calling a program or instruction stored in the memory 605.

[0070] This application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, performs steps such as those in a method for recovering phosphorus resources from aquaculture wastewater based on a struvite process.

[0071] Specifically, the storage medium can be a general-purpose storage medium, such as a portable disk or hard disk. When the computer program on the storage medium is run, it can achieve efficient recovery of phosphorus resources, deep purification of wastewater, and high-value utilization of products.

[0072] In the embodiments provided in this application, it should be understood that the disclosed apparatus and methods can be implemented in other ways. The apparatus embodiments described above are merely illustrative. For example, the division of units is only a logical functional division, and there may be other division methods in actual implementation. Furthermore, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Additionally, the mutual coupling or direct coupling or communication connection shown or discussed may be through some communication interface, and the indirect coupling or communication connection of the apparatus or units may be electrical, mechanical, or other forms.

[0073] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment, depending on actual needs.

[0074] In addition, the functional units in the embodiments provided in this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0075] If a function is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0076] Finally, it should be noted that the above embodiments are merely specific implementations of this application, used to illustrate the technical solutions of this application, and not to limit them. The protection scope of this application is not limited thereto. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features, within the scope of the technology disclosed in this application; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application. All should be covered within the protection scope of this application. Therefore, the protection scope of this application should be determined by the protection scope of the claims.

Claims

1. A method for phosphorus resource recovery from aquaculture wastewater based on struvite processing, characterized in that, This invention relates to a phosphorus resource recovery system for aquaculture wastewater. The system includes a pretreatment unit, a crystallization unit, an online forming unit, and a deep purification unit. The pretreatment unit includes a microwave-ultrasonic coupled reactor. The crystallization unit includes a primary seed crystal generator, a secondary crystal growth reactor, and a pulsed microwave control device positioned between them. The online forming unit is a spiral extrusion dehydration granulation and coating integrated machine. The deep purification unit is an adsorption column. The method includes the following steps: After coarse filtration, the biogas slurry produced by anaerobic fermentation of aquaculture wastewater is sent to a microwave-ultrasonic coupled reactor for pretreatment to release bound phosphorus in the biogas slurry. Magnesium source was added to the pretreated biogas slurry and the pH was adjusted to alkaline. The adjusted mixture was then passed through a primary seed crystal generator, a pulse microwave control device, and a secondary crystal growth reactor to generate struvite crystals. The slurry containing struvite crystals is fed into a spiral extrusion dewatering granulation and coating integrated machine for spiral extrusion dewatering, cutting granulation, and spray coating to obtain coated slow-release fertilizer granules and the separated supernatant. The supernatant is sent to an adsorption column for secondary recovery of phosphorus resources through adsorbent regeneration.

2. The method for phosphorus resource recovery from aquaculture wastewater based on struvite process as described in claim 1, characterized in that, The microwave-ultrasonic coupling reactor releases bound phosphorus from the biogas slurry through the synergistic effect of the microwave thermal effect of the microwave generator and the ultrasonic cavitation effect of the ultrasonic transducer. The ultrasonic transducer is set to a frequency of 20-40kHz and a power density of 40-60W / L, operating in pulse mode; the microwave generator is set to a frequency of 2450MHz, which raises the temperature of the biogas slurry to 70-85℃ within 2 minutes and maintains it for 10-25 minutes; and the action time of the ultrasonic transducer and the microwave generator on the biogas slurry overlaps by at least 5 minutes.

3. The method for phosphorus resource recovery from aquaculture wastewater based on struvite process as described in claim 1, characterized in that, The process of adding a magnesium source to the pretreated biogas slurry and adjusting the pH to alkaline, followed by sequentially passing the adjusted mixture through a primary seed crystal generator, a pulsed microwave control device, and a secondary crystal growth reactor to generate struvite crystals, includes the following steps: The pretreated biogas slurry is sent to the buffer tank of the crystallization unit, and magnesium sulfate or magnesium chloride is added to the buffer tank as a magnesium source. The concentrations of magnesium (Mg), ammonia nitrogen (N), and phosphorus (P) in the mixed liquid in the buffer tank are monitored in real time, and the amount of magnesium source added is controlled according to the set concentration ratio. NaOH solution is added to the buffer tank to adjust the pH to the set range, and the pH-adjusted mixture is sent to the primary seed generator to generate seed crystals, thus obtaining a seed crystal suspension. The seed crystal suspension is sent to a pulsed microwave control device, and after the surface energy of the seed crystal is optimized by microwave irradiation, it is sent to a secondary crystal growth reactor to complete the crystallization of struvite.

4. The method for phosphorus resource recovery from aquaculture wastewater based on struvite process as described in claim 3, characterized in that, in, Set the molar ratio of magnesium (Mg), ammonia nitrogen (N), and phosphorus (P) to (1.1-1.3):1.1:1.0; adjust the pH to 9.0-9.5; microwave irradiation time to 1-3 minutes; the secondary crystal growth reactor is operated in fluidized mode or stirring mode at 50-80 rpm for 40-60 minutes.

5. The method for phosphorus resource recovery from aquaculture wastewater based on struvite process as described in claim 1, characterized in that, The integrated spiral extrusion dewatering granulation and coating machine consists of a spiral extrusion dewatering section, a pelletizing disc, and a roller coating section along the material's forward direction. An atomizing nozzle connected to a coating liquid storage tank is installed above the roller coating section. The process involves feeding a slurry containing struvite crystals into the integrated spiral extrusion dewatering granulation and coating machine for spiral extrusion dewatering, cutting and granulation, and spray coating to obtain coated slow-release fertilizer granules, including the following steps: The slurry containing struvite crystals is fed into the screw extrusion dewatering section for extrusion dewatering to obtain the separated supernatant and wet strips; The wet material strip is fed into the pelletizing disc and cut into particles of a preset size; The cut granules are fed into the coating section of the drum for tumbling, and the coating liquid in the coating liquid storage tank is sprayed onto the surface of the granules through the atomizing nozzle to generate coated slow-release fertilizer granules; wherein, the coating liquid is an organic solution or water-dispersible emulsion of biodegradable polymer material, with a concentration range of 1%-5% (w / v).

6. The method for phosphorus resource recovery from aquaculture wastewater based on struvite process as described in claim 5, characterized in that, The step of sending the supernatant to an adsorption column for secondary phosphorus resource recovery through adsorbent regeneration includes the following steps: The supernatant is fed into an adsorption column; the adsorbent filled in the adsorption column is hydrated iron oxide FeOOH or modified biochar loaded with nano-zero valent iron nZVI. The total phosphorus (TP) concentration at the outlet of the adsorption column is monitored in real time. If the TP concentration is less than or greater than the set threshold, the water is discharged; if the TP concentration is greater than the set threshold, the adsorbent is determined to be saturated. The saturated adsorbent is desorbed using NaOH solution, and the resulting phosphorus-containing desorption solution is collected and sent to the crystallization unit for secondary recovery via a reflux pipeline.

7. The method for phosphorus resource recovery from aquaculture wastewater based on struvite process as described in claim 1, characterized in that, The aquaculture wastewater phosphorus resource recovery system also includes an intelligent control unit, and the method further includes the following steps: The system collects and adjusts the operating parameters of other units in real time.

8. A phosphorus resource recovery system for aquaculture wastewater, characterized in that, It includes a pretreatment unit, a crystallization unit, an online forming unit, and a deep purification unit, which are used to collaboratively implement the steps of a method for recovering phosphorus resources from aquaculture wastewater based on struvite process as described in any one of claims 1 to 7.

9. An electronic device, characterized in that, include: The device includes a processor, a memory, and a bus. The memory stores machine-readable instructions executable by the processor. When the electronic device is running, the processor communicates with the memory via the bus. When the machine-readable instructions are executed by the processor, they perform the steps of a method for recovering phosphorus resources from aquaculture wastewater based on struvite technology as described in any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, performs the steps of a method for recovering phosphorus resources from aquaculture wastewater based on a struvite process, as described in any one of claims 1 to 7.

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