CN110877985A - Method and device for preparing compound phosphate fertilizer by using waste water - Google Patents

Method and device for preparing compound phosphate fertilizer by using waste water Download PDF

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CN110877985A
CN110877985A CN201911162598.3A CN201911162598A CN110877985A CN 110877985 A CN110877985 A CN 110877985A CN 201911162598 A CN201911162598 A CN 201911162598A CN 110877985 A CN110877985 A CN 110877985A
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pipe
adsorbent
crystallization
phosphate fertilizer
reactor
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CN110877985B (en
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赵茜
王洪波
李梅
张克峰
王宁
刘承芳
刘磊
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Shandong Jianzhu University
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    • C—CHEMISTRY; METALLURGY
    • C05—FERTILISERS; MANUFACTURE THEREOF
    • C05F—ORGANIC FERTILISERS NOT COVERED BY SUBCLASSES C05B, C05C, e.g. FERTILISERS FROM WASTE OR REFUSE
    • C05F7/00—Fertilisers from waste water, sewage sludge, sea slime, ooze or similar masses
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
    • B01J20/04—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising compounds of alkali metals, alkaline earth metals or magnesium
    • B01J20/041—Oxides or hydroxides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
    • B01J20/06—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising oxides or hydroxides of metals not provided for in group B01J20/04
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
    • B01J20/06—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising oxides or hydroxides of metals not provided for in group B01J20/04
    • B01J20/08—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising oxides or hydroxides of metals not provided for in group B01J20/04 comprising aluminium oxide or hydroxide; comprising bauxite
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
    • B01J20/10—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising silica or silicate
    • B01J20/103—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising silica or silicate comprising silica
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
    • B01J20/28002—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their physical properties
    • B01J20/28009—Magnetic properties
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/28—Treatment of water, waste water, or sewage by sorption
    • C02F1/281—Treatment of water, waste water, or sewage by sorption using inorganic sorbents
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/48—Treatment of water, waste water, or sewage with magnetic or electric fields
    • C—CHEMISTRY; METALLURGY
    • C05—FERTILISERS; MANUFACTURE THEREOF
    • C05G—MIXTURES OF FERTILISERS COVERED INDIVIDUALLY BY DIFFERENT SUBCLASSES OF CLASS C05; MIXTURES OF ONE OR MORE FERTILISERS WITH MATERIALS NOT HAVING A SPECIFIC FERTILISING ACTIVITY, e.g. PESTICIDES, SOIL-CONDITIONERS, WETTING AGENTS; FERTILISERS CHARACTERISED BY THEIR FORM
    • C05G1/00—Mixtures of fertilisers belonging individually to different subclasses of C05
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2220/00—Aspects relating to sorbent materials
    • B01J2220/40—Aspects relating to the composition of sorbent or filter aid materials
    • B01J2220/42—Materials comprising a mixture of inorganic materials
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2220/00—Aspects relating to sorbent materials
    • B01J2220/40—Aspects relating to the composition of sorbent or filter aid materials
    • B01J2220/48—Sorbents characterised by the starting material used for their preparation
    • B01J2220/4806—Sorbents characterised by the starting material used for their preparation the starting material being of inorganic character
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/10—Inorganic compounds
    • C02F2101/105—Phosphorus compounds
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2303/00—Specific treatment goals
    • C02F2303/16—Regeneration of sorbents, filters
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A40/00—Adaptation technologies in agriculture, forestry, livestock or agroalimentary production
    • Y02A40/10—Adaptation technologies in agriculture, forestry, livestock or agroalimentary production in agriculture
    • Y02A40/20—Fertilizers of biological origin, e.g. guano or fertilizers made from animal corpses

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  • Fertilizers (AREA)

Abstract

The invention provides a device for preparing a compound phosphate fertilizer from wastewater, which comprises a mixed adsorption reaction unit, a magnetic separation and regeneration unit and a compound phosphate fertilizer crystallization unit. The invention also provides a method for preparing phosphate fertilizer by adopting the device, which can be used for preparing phosphate fertilizerCOD treatment is less than or equal to 2000mg/L, BOD5Less than or equal to 500mg/L, ammonia nitrogen less than or equal to 500mg/L, phosphate less than or equal to 80mgP/L and pH value of 6.0-7.0. The device organically combines the adsorption reactor, the magnetic separation coupling regeneration reactor and the crystallization reactor together, and finally can prepare the high-purity phosphate fertilizer, and the adsorption material can be recycled; the crystallization reactor can realize the online production of phosphate fertilizer, and the final yield of the phosphate fertilizer can reach 400-500g/t waste liquid. The wastewater recycling method can realize high-efficiency and high-selectivity adsorption of phosphate; the one-stop phosphate fertilizer production is realized, the adding amount of the adsorbent is small, a complex crystallization and separation process is avoided, the separation effect is good, and the operation cost is saved.

Description

Method and device for preparing compound phosphate fertilizer by using waste water
Technical Field
The invention belongs to the field of wastewater treatment, and relates to a method and a device for preparing a compound phosphate fertilizer by using wastewater.
Background
The phosphorus recovery technology of the urban sewage plant is one of the hot spots of research; for a sewage treatment plant, phosphorus in the sewage is easily accumulated in sludge digestion liquid, especially dewatered sludge waste liquid. The chemical phosphorus removal method comprises a calcium phosphate crystallization method, a struvite precipitation method, an ion exchange adsorption method and the like, but the adsorption amount of the materials or the methods in phosphate is small. The method has the advantages of slightly harsh operating conditions, poor selectivity to phosphate, difficult regeneration, and even generation of phosphorus-containing sludge which is difficult to treat, changes the waste water problem into the waste problem, and more importantly, interferes components in the dewatered sludge to influence the adsorption and phosphate fertilizer generation effects, thereby becoming one of the barriers for recycling the phosphorus-containing pollutants. Therefore, new adsorbing materials and methods for treating wastewater with high phosphorus content are needed.
Disclosure of Invention
Aiming at the problems of low phosphorus removal adsorption amount, difficult regeneration of an adsorbent, harsh conditions and low purity of a phosphate fertilizer in the prior art, the invention further aims to provide the device for preparing the compound phosphate fertilizer from the dewatered sludge waste liquid, wherein the device can complete the steps of phosphorus separation, phosphorus recovery and adsorbent regeneration, and reduce the volume of equipment and the steps of a process flow.
The invention provides a method for preparing a compound phosphate fertilizer by using the device and taking dewatered sludge waste liquid as a raw material.
In order to achieve the purpose, the invention adopts the following technical scheme.
A device for preparing a compound phosphate fertilizer from waste water comprises a mixed adsorption reaction unit (1), a magnetic separation and regeneration unit (2) and a compound phosphate fertilizer crystallization unit (3).
The mixed adsorption reaction unit (1) comprises an adsorption reactor (4), a nano adsorbent dosing box (5), a first stirring device (6) and a water outlet weir (7); a water inlet pipe (8) and an emptying pipe (9) are arranged on the adsorption reactor (4), and an emptying pipe valve (9-1) is arranged on the emptying pipe (9); the nano adsorbent dosing box (5) is connected to a mixing pump (11) through a mixing pump liquid inlet pipe (10), and the mixing pump (11) is connected to the adsorption reactor (4) through a mixing pump liquid outlet pipe (12); the first stirring device (6) comprises a first motor (13) and a first stirring paddle (14) which are arranged in the center of the adsorption reactor (4).
The magnetic separation and regeneration unit (2) comprises a first regulating reservoir (16) and a magnetic separation coupling regeneration reactor (17); the first regulating tank (16) is connected with the water outlet weir (7) through a water outlet pipe (7-1) of the water outlet weir, and the first regulating tank (16) is connected to a regeneration pump (19) through a water inlet pipe (18) of the regeneration pump; the magnetic separation coupling regeneration reactor (17) is a closed organic glass container and is connected to a regeneration pump (19) through a regeneration pump water outlet pipe (20); a movable magnet sucker (21), an adsorbent scraping blade (22), a regenerated liquid spray pipe (23) and a receiving hopper (24) are arranged in the regeneration device; the adsorbent scraping blade (22) is arranged in the middle of the inner wall of the magnetic separation coupling regeneration reactor (17); the regenerated liquid spray pipe (23) enters the magnetic separation coupling regeneration reactor (17) from the upper part and directly reaches the blade of the adsorbent scraping blade (22); the lower part of the receiving hopper (24) is connected with a collecting main pipe (25), the collecting main pipe (25) is connected with a waste liquid discharge pipe (27) and a main discharge pipe (28) through a first three-way pipe (26), a waste liquid discharge pipe valve (29) is arranged on the waste liquid discharge pipe (27), and the main discharge pipe (28) is connected with an adsorbent return pipe (31) and a phosphorus solution outlet pipe (32) through a second three-way pipe (30); a reflux pipe valve (33) is arranged on the adsorbent reflux pipe (31) and is connected to the nano adsorbent dosing tank (5) through a reflux pump (34); and a phosphorus solution outlet pipe valve (35) is arranged on the phosphorus solution outlet pipe (32).
The compound phosphate fertilizer crystallization unit (3) comprises a second adjusting tank (36), a magnesium chloride dissolving tank (37), a crystallization reactor (38) and a phosphate fertilizer collecting hopper (39); the second regulating reservoir (36) is connected with a phosphorus solution outlet pipe (32), the crystallization reactor (38) is connected with a second regulating reservoir liquid outlet pipe (40), a phosphorus solution supply pump (41) is arranged on the second regulating reservoir liquid outlet pipe (40), a water inlet pipe (8) in the mixed adsorption reaction unit (1) is connected with a water inlet branch pipe (8-2) through a third tee joint (8-1), and the other end of the water inlet branch pipe (8-2) is connected to the second regulating reservoir liquid outlet pipe (40) through a branch pipe supply pump (8-3); the magnesium chloride dissolving tank (37) is connected to the crystallization reactor (38) through a magnesium chloride solution pipe (42), and a magnesium chloride solution supply pump (43) is arranged on the magnesium chloride solution pipe (42); a second stirring device (44) is arranged in the center of the crystallization reactor (38), and the second stirring device (44) comprises a second motor (45) and a second stirring paddle (46); the upper end of the phosphate fertilizer collecting hopper (39) is connected with a crystallization waste liquid discharge pipe (47), the lower end of the phosphate fertilizer collecting hopper is connected with a phosphate fertilizer collecting pipe (48), and a crystallization waste liquid discharge pipe valve (47-1) and a phosphate fertilizer collecting pipe valve (48-1) are arranged on the crystallization waste liquid discharge pipe (47).
In the device, the outer edge of the movable magnet sucker (21) is made of neodymium iron boron magnet material, and the magnetic field intensity is about 500-.
In the device, the flow rate of the water inlet branch pipe (8-2) supplied by the branch pipe supply pump (8-3) and the flow rates of the phosphorus solution supply pump (41) and the magnesium chloride solution supply pump (43) are ensured to be in a certain proportion through an automatic control system, and the proportion is determined by the concentration of the phosphorus solution and the concentration of the magnesium chloride solution.
In the device, the first stirring paddle (14) and the second stirring paddle (46) are made of non-metal materials, preferably PEEK (polyetheretherketone) wear-resistant rigid plastics or glass fibers.
A method for preparing phosphate fertilizer from waste water by using the device comprises the following steps:
(1) adsorption treatment: magnetic adsorbent suspension in a nano adsorbent dosing tank (5) enters an adsorption reactor (4) through a mixing pump liquid inlet pipe (10), wastewater enters the adsorption reactor (4) through a water inlet pipe (8), the adsorbent suspension and the wastewater are fully mixed under the stirring of a first stirring device (6) for adsorption reaction, and the adsorbed mixed solution enters a first regulating tank (16) through a water outlet weir (7);
(2) separation and regeneration treatment: the magnetic separation coupling regeneration reactor (17) adopts an intermittent operation mode of water inlet-magnetic separation-water discharge-regeneration-phosphorus solution recovery-adsorbent recovery: in the water inlet stage, a waste liquid discharge pipe valve (29), a return pipe valve (33) and a phosphorus solution outlet pipe valve (35) are closed, and the mixed liquid in the first regulating tank (16) intermittently enters the magnetic separation coupling regeneration reactor (17) through a regeneration pump (19); in the magnetic separation stage, the movable magnet sucker (21) rotates, and the adsorbent is adsorbed on the movable magnet sucker (21); in the drainage stage, a waste liquid discharge pipe valve (29) is opened, and residual waste liquid is collected in a receiving hopper (24) and discharged through a waste liquid discharge pipe (27); in the regeneration stage, the movable magnet sucker (21) moves downwards to the adsorbent scraping blade (22), the regeneration liquid spray pipe (23) sprays NaOH solution in the rotation process of the movable magnet sucker (21), and the mixture of the adsorbent and the phosphorus solution is collected in the receiving hopper (24); in the stage of recovering the phosphorus solution, the movable magnet sucker (21) moves downwards to rotate, the adsorbent is adsorbed on the movable magnet sucker (21), after the movable magnet sucker (21) moves upwards, a phosphorus solution outlet pipe valve (35) is opened, and the phosphorus solution enters a second regulating tank (36) through a water outlet pipe (32); in the adsorbent recovery stage, the movable magnet sucker (21) moves downwards again to the adsorbent scraping blade (22) and rotates, in the rotation process, the regeneration liquid spray pipe (23) sprays clean water, the reflux pipe valve (33) is opened, and the adsorbent suspension is collected in the receiving hopper (24) and flows back to the nano adsorbent dosing box (5) through the reflux pump (34);
(3) and (3) crystallizing the phosphate fertilizer: the crystallization reactor (38) adopts an intermittent operation mode of 'water inlet-crystallization reaction-water discharge-phosphate fertilizer collection': in the water inlet stage, a branch pipe supply pump (8-3), a phosphorus solution supply pump (41) and a magnesium chloride solution supply pump (43) are started, a crystallization waste liquid discharge pipe valve (47-1) and a phosphate fertilizer collection pipe valve (48-1) are closed, phosphorus solution in a second regulating reservoir (36) intermittently enters a crystallization reactor (38) through a phosphorus solution second regulating reservoir liquid outlet pipe (40), dehydrated sludge waste liquid enters the crystallization reactor (38) through a water inlet branch pipe (8-2), and magnesium chloride solution enters the crystallization reactor (38) through a magnesium chloride solution pipe (42); in the crystallization reaction stage, the branch pipe supply pump (8-3), the phosphorus solution supply pump (41) and the magnesium chloride solution supply pump (43) are closed, the second stirring device (44) is started, and the solutions are uniformly mixed and subjected to crystallization reaction under the stirring action; in the drainage stage, the second stirring device (44) is closed, and after the crystallization waste liquid is settled, a valve (47-1) of a crystallization waste liquid discharge pipe is opened to discharge the crystallization waste liquid; in the stage of collecting the phosphate fertilizer, a valve (48-1) of a phosphate fertilizer collecting pipe is opened, and then drying treatment is carried out to obtain the phosphate fertilizer.
The COD of the wastewater is less than or equal to 2000mg/L, BOD5Less than or equal to 500mg/L, ammonia nitrogen less than or equal to 500mg/L, phosphate less than or equal to 80mgP/L and pH value of 6.0-7.0.
Preferably, in the step (1), the magnetic adsorbent is a superparamagnetic response nano phosphorus adsorbent, the shape of the magnetic adsorbent is a granular core-shell structure, and the inner core is Fe3O4The outer shell of the tube is sequentially SiO from inside to outside2And magnesium aluminum double hydroxides (Mg-Al-LDHs) on which transition metal oxides are complexed; the average diameter of the particles is 30-80 nm, and the average thickness of the shell is 10-20 nm; the transition metal is selected from lanthanum, cerium or hafnium.
In the superparamagnetic response nano phosphorus adsorbent, the mass percentage content of the magnesium-aluminum bimetal hydroxide and the transition metal oxide is 20-60%; preferably 30% -60%; the mass percentage of the transition metal oxide counted by metal is 20-60% of the total mass of the magnesium-aluminum bimetal hydroxide and the transition metal oxide.
The saturation magnetization of the superparamagnetic response nano-phosphorus adsorbent is 65-70 emu/g, and the specific surface area is 130-140 m2/g。
The preparation method of the magnetic adsorbent comprises the following steps:
(a) adding aluminum chloride, magnesium chloride and transition metal chloride into a NaOH solution to obtain a transition metal oxide-loaded magnesium-aluminum double hydroxide solution;
(b) mixing SiO2Encapsulated Fe3O4And (2) adding the particles into the solution obtained in the step (1), stirring, pressurizing and carrying out ultrasonic treatment to obtain the superparamagnetic response nano phosphorus adsorbent.
In the step (1), the stirring speed of the first stirring device (6) is 200-300 r/min.
In the step (2), the rotation speed of the central shaft of the movable magnetic sucker (21) is 120-.
In the step (3), the stirring speed of the second stirring device (44) is 120-180 r/min.
The molar ratio of the NaOH to the P content in the wastewater is 10:1-20: 1.
The molar ratio of the magnesium chloride to the phosphorus solution is 1:1.05-1.05: 1.
The invention has the following advantages:
the device organically combines the adsorption reactor, the magnetic separation coupling regeneration reactor and the crystallization reactor together, and finally can prepare the high-purity phosphate fertilizer, and the adsorption material can be recycled; the crystallization reactor can realize the online production of phosphate fertilizer: according to the recovery condition of phosphate in the dehydrated sludge waste liquid, the crystal yield of the compound phosphate fertilizer is controlled by controlling the dosage of magnesium chloride and the dosage of ammonia nitrogen, and the final yield can reach 400-500g/t waste liquid. The wastewater recycling method can realize high-efficiency and high-selectivity adsorption of phosphate, and the capture rate of the phosphate can reach over 90 percent; can realize one-stop formula phosphorus fertilizer output, the adsorbent input volume is economized, does not have loaded down with trivial details crystallization separation process, and the separation is effectual, saves the working costs, is a green sustainable sewage treatment technology.
Drawings
FIG. 1 is a schematic diagram of a mixed adsorption reaction unit;
FIG. 2 is a schematic diagram of a magnetic separation and regeneration unit;
FIG. 3 is a schematic diagram of a compound phosphate crystallization unit;
FIG. 4 is a schematic combination of parts;
wherein, 1 is a mixed adsorption reaction unit, 2 is a magnetic separation and regeneration unit, 3 is a composite phosphate fertilizer crystallization unit, 4 is a composite phosphate fertilizer crystallization unit comprising an adsorption reactor, 5 is a nano adsorbent dosing box, 6 is a first stirring device, 7 is an effluent weir, 7-1 is an effluent weir water outlet pipe, 8 is a water inlet pipe, 9 is an exhaust pipe, 10 is a mixing pump liquid inlet pipe, 11 is a mixing pump, 12 is a mixing pump liquid outlet pipe, 13 is a motor, 14 is a stirring paddle, 15 is an adsorbent, 16 is a first regulating tank, 17 is a magnetic separation coupling regeneration reactor, 18 is a regeneration pump water inlet pipe, 19 is a regeneration pump, 20 is a regeneration pump water outlet pipe, 21 is a movable magnet suction disc, 22 is an adsorbent scraping blade, 23 is a regeneration liquid spray pipe, 24 is a receiving hopper, 25 is a collecting main pipe, 26 is a first three-way pipe, 27 is a waste liquid discharge pipe, 28 is a total discharge pipe, 29 is a waste liquid discharge pipe valve, 30 is a second three-way pipe, 31 is an adsorbent return pipe, 32 is a phosphorus solution outlet pipe, 33 is a return pipe valve, 34 is a return pump, 35 is a phosphorus solution outlet pipe valve, 36 is a second regulating reservoir, 37 is a magnesium chloride dissolving reservoir, 38 is a crystallization reactor, 39 is a phosphate fertilizer collecting hopper, 40 is a second regulating reservoir outlet pipe, 41 is a phosphorus solution supply pump, 42 is a magnesium chloride solution pipe, 43 is a magnesium chloride solution supply pump, 44 is a second stirring device, 45 is a second motor, 46 is a second stirring paddle, 47 is a crystallization waste liquid discharge pipe, 47-1 is a crystallization waste liquid discharge pipe valve, 48 is a phosphate fertilizer collecting pipe, and 48-1 is a phosphate fertilizer collecting pipe valve.
Detailed Description
The present invention will be further described with reference to the following examples and drawings, but the present invention is not limited to the following examples.
Example 1 preparation of lanthanum loaded sorbent
（1）N2Under protection, 0.42mol/L FeCl3Solution with 0.21mol/L FeCl2Mixing and stirring the solution and 25wt% of ammonia monohydrate solution according to the volume ratio of 1:1:2, adding 0.50mol/L nitric acid, and adjusting the pH value to 3 to obtain Fe3O466 mL of nano magnetic core precursor suspension;
(2) under the water bath heating condition of 70 ℃, 5mL of 10wt% trimethylsiloxy silicate ethanol solution is slowly injected into the suspension prepared in the step (1) until the concentration of sodium silicate is 2.5wt%, and the precipitate is magnetically separated, washed and dried to obtain SiO2Encapsulated Fe3O45.2g of particles;
(3) adding 3.65g of magnesium chloride hexahydrate (18 mmol), 0.3176g of aluminum trichloride hexahydrate (3 mmol) and 1.11g of lanthanum chloride heptahydrate (3 mmol) into 400mL of NaOH solution with the concentration of 1.5mol/L to obtain magnesium-aluminum double hydroxide (Mg-Al-LDHs-La) solution loaded with lanthanum oxide, wherein the concentration is 0.85 wt%;
(4) adding the particles obtained in the step (2) into the solution obtained in the step (3) to enable SiO to be generated2Encapsulated Fe3O4The concentration of the particles in the solution was 1.27wt%, the particles were stirred for 1min under 0.40Mpa and then sonicated at 35 kH, power 180W for 2min, and magnetic separation was carried out to obtain about 8.46g of adsorbent.
The diameter of the adsorbent was determined to range from 35 to 50nm, with a shell thickness of about 10 nm. At the normal temperature of 298K, SQUID magnetic test shows that the material is a superparamagnetic response material, and the saturation magnetization is 65.43 emu/g; the specific surface area of the material is 132.5m when measured by BET-N22/g。
Example 2 hafnium loaded sorbent preparation
（1）N2Under protection, 0.42mol/L FeCl3Solution with 0.21mol/L FeCl2Mixing and stirring the solution and 25wt% of ammonia monohydrate solution according to the volume ratio of 1:1:2, adding 0.50mol/L nitric acid, and adjusting the pH value to 3 to obtain Fe3O466 mL of nano magnetic core precursor suspension;
(2) 70 ℃ waterUnder the bath heating condition, slowly injecting 5mL of 10wt% trimethylsiloxy silicate ethanol solution into the suspension prepared in the step (1) until the concentration of sodium silicate is 2.5wt%, magnetically separating the precipitate, cleaning, and drying to obtain SiO2Encapsulated Fe3O45.2g of particles;
(3) adding 3.65g of magnesium chloride hexahydrate (18 mmol), 0.3176g of aluminum trichloride hexahydrate (3 mmol) and 1.7g of hafnium oxychloride octahydrate (3 mmol) into 400mL of NaOH solution with the concentration of 1.5mol/L to obtain magnesium-aluminum double hydroxide (Mg-Al-LDHs-La) solution loaded with hafnium oxide, wherein the concentration is 0.85 wt%;
(4) adding the particles obtained in the step (2) into the solution obtained in the step (3) to enable SiO to be generated2Encapsulated Fe3O4The concentration of the particles in the solution was 1.27wt%, the particles were stirred for 1min under 0.40Mpa and then sonicated at 35 kH, power 180W for 2min, and magnetic separation was carried out to obtain about 8.95g of adsorbent.
The adsorbent was determined to have a diameter in the range of 32-60nm and a shell thickness of about 10 nm. At the normal temperature of 298K, SQUID magnetic test shows that the material is a superparamagnetic response material, and the saturation magnetization is 66.13 emu/g; the specific surface area of the material is 136.2m when measured by BET-N22/g。
Example 3 preparation of cerium Supported adsorbents
（1）N2Under protection, 0.42mol/L FeCl3Solution with 0.21mol/L FeCl2Mixing and stirring the solution and 25wt% of ammonia monohydrate solution according to the volume ratio of 1:1:2, adding 0.50mol/L nitric acid, and adjusting the pH value to 3 to obtain Fe3O466 mL of nano magnetic core precursor suspension;
(2) under the water bath heating condition of 70 ℃, 5mL of 10wt% trimethylsiloxy silicate ethanol solution is slowly injected into the suspension prepared in the step (1) until the concentration of sodium silicate is 2.5wt%, and the precipitate is magnetically separated, washed and dried to obtain SiO2Encapsulated Fe3O45.2g of particles;
(3) adding 3.65g of magnesium chloride hexahydrate (18 mmol), 0.3176g of aluminum trichloride hexahydrate (3 mmol) and 1.8g of cerium chloride hydrate (3 mmol) into 400mL of NaOH solution with the concentration of 1.5mol/L to obtain a magnesium-aluminum double hydroxide (Mg-Al-LDHs-La) solution loaded with cerium oxide, wherein the concentration is 0.85 wt%;
(4) adding the particles obtained in the step (2) into the solution obtained in the step (3) to enable SiO to be generated2Encapsulated Fe3O4The concentration of the particles in the solution was 1.27wt%, the particles were stirred for 1min under 0.40Mpa and then sonicated at 35 kH, power 180W for 2min, and magnetic separation was carried out to obtain about 8.95g of adsorbent.
The diameter of the adsorbent was determined to be in the range of 40-55nm and the shell thickness was about 8 nm. At the normal temperature of 298K, SQUID magnetic test shows that the material is a superparamagnetic response material, and the saturation magnetization is 69.21 emu/g; the specific surface area of the material is 139.10m measured by BET-N22/g。
EXAMPLE 4 apparatus for preparing Compound phosphate from wastewater
The device for preparing the compound phosphate fertilizer from the waste water as shown in the figures 1-4 comprises a mixed adsorption reaction unit 1, a magnetic separation and regeneration unit 2 and a compound phosphate fertilizer crystallization unit 3.
The mixed adsorption reaction unit 1 comprises an adsorption reactor 4, a nano adsorbent dosing box 5, a first stirring device 6 and an effluent weir 7; the adsorption reactor 4 is provided with a water inlet pipe 8, an emptying pipe 9 and an adsorbent 15 dispersed inside; an emptying pipe valve 9-1 is arranged on the emptying pipe 9; the nano adsorbent dosing box 5 is connected to a mixing pump 11 through a mixing pump liquid inlet pipe 10, and the mixing pump 11 is connected to the adsorption reactor 4 through a mixing pump liquid outlet pipe 12; the first stirring device 6 comprises a first motor 13 arranged in the center of the adsorption reactor 4 and a first stirring paddle 14 made of PEEK (polyetheretherketone) wear-resistant hard plastic.
The magnetic separation and regeneration unit 2 comprises a first regulating reservoir 16 and a magnetic separation coupling regeneration reactor 17; the first regulating reservoir 16 is connected with the effluent weir 7 through an effluent weir water outlet pipe 7-1, and the first regulating reservoir 16 is connected to a regeneration pump 19 through a regeneration pump water inlet pipe 18; the magnetic separation coupling regeneration reactor 17 is a closed organic glass container and is connected to a regeneration pump 19 through a regeneration pump water outlet pipe 20; inside is provided with movable magnet sucking disc 21, adsorbent and strikes off blade 22, regeneration liquid shower 23 and receives fill 24, movable magnet sucking disc 21 outward flange is neodymium iron boron magnet material, and magnetic field intensity is 800 Gauss. (ii) a The adsorbent scraping blade 22 is arranged in the middle of the inner wall of the magnetic separation coupling regeneration reactor 17; the regenerated liquid spray pipe 23 enters the magnetic separation coupling regeneration reactor 17 from the upper part and directly reaches the blade of the absorbent scraping blade 22; the lower part of the receiving hopper 24 is connected with a collecting header pipe 25, the collecting header pipe 25 is connected with a waste liquid discharge pipe 27 and a main discharge pipe 28 through a first three-way pipe 26, the waste liquid discharge pipe 27 is provided with a waste liquid discharge pipe valve 29, and the main discharge pipe 28 is connected with an adsorbent return pipe 31 and a phosphorus solution outlet pipe 32 through a second three-way pipe 30; the adsorbent return pipe 31 is provided with a return pipe valve 33 and is connected to the nano adsorbent dosing tank 5 through a return pump 34; and a phosphorus solution outlet pipe valve 35 is arranged on the phosphorus solution outlet pipe 32.
The compound phosphate fertilizer crystallization unit 3 comprises a second adjusting tank 36, a magnesium chloride dissolving tank 37, a crystallization reactor 38 and a phosphate fertilizer collecting hopper 39; the second regulating reservoir 36 is connected with the phosphorus solution outlet pipe 32, the crystallization reactor 38 is connected with a second regulating reservoir liquid outlet pipe 40, a phosphorus solution supply pump 41 is arranged on the second regulating reservoir liquid outlet pipe 40, the water inlet pipe 8 in the mixed adsorption reaction unit 1 is connected with a water inlet branch pipe 8-2 through a third tee joint 8-1, and the other end of the water inlet branch pipe 8-2 is connected to the second regulating reservoir liquid outlet pipe 40 through a branch pipe supply pump 8-3; the magnesium chloride dissolving tank 37 is connected to the crystallization reactor 38 through a magnesium chloride solution pipe 42, and a magnesium chloride solution supply pump 43 is arranged on the magnesium chloride solution pipe 42; a second stirring device 44 is arranged in the center of the crystallization reactor 38, and the second stirring device 44 comprises a second motor 45 and a second stirring paddle 46 made of PEEK (polyetheretherketone) wear-resistant hard plastic; the upper end of the phosphate fertilizer collecting hopper 39 is connected with a crystallization waste liquid discharge pipe 47, the lower end is connected with a phosphate fertilizer collecting pipe 48, and the crystallization waste liquid discharge pipe 47 is provided with a crystallization waste liquid discharge pipe valve 47-1 and a phosphate fertilizer collecting pipe valve 48-1.
The PLC system automatically controls the valve opening and closing and the flow of the adsorption reaction unit 1, the magnetic separation and regeneration unit 2 and the compound phosphate fertilizer crystallization unit 3.
EXAMPLE 5 preparation of waste Water phosphate
(1) Adsorption treatment: 5 batches of dehydrated sludge waste liquid with COD less than or equal to 2000mg/L, BOD5 less than or equal to 500mg/L, ammonia nitrogen less than or equal to 500mg/L, phosphate less than or equal to 80mgP/L and pH value of 6.3-6.5 enter an adsorption reactor 4 through a water inlet pipe 8, adsorbent suspension in a nano adsorbent dosing tank 4 is pumped to the adsorption reactor 5 through a mixing pump liquid inlet pipe 10 by a mixing pump 11, the dehydrated sludge waste liquid and an adsorption material are fully mixed under the stirring action of a stirring paddle 14 for phosphate adsorption treatment, the stirring speed is 180r/min, the adsorption treatment time is 4 hours, and the mixture enters a first regulating tank 16;
the adsorbent is prepared in the embodiment 1, the concentration of the nano adsorbent in the dosing box 4 is about 3g/L, and the concentration of the adsorbent in the adsorption reactor is about 100mg/L by controlling the flow ratio of the waste liquid inlet water to the mixing pump 11.
(2) Separating and regenerating the adsorbent: the mixture of the dewatered sludge waste liquid and the adsorbent enters a magnetic separation coupling regeneration reactor 17, the reactor adopts a working mode of six stages of 'water inlet-magnetic separation-drainage-regeneration-phosphorus solution recovery-adsorbent recovery' and intermittent operation, and the duration of the six stages is 5min-15min-5min-210min-5min in sequence. In the water inlet stage, the mixed liquor in the first regulating reservoir 16 intermittently enters the magnetic separation coupling regeneration reactor 17 through the regeneration pump 19; in the magnetic separation stage, the adsorbent is adsorbed on the movable magnetic chuck 21; in the draining stage, the residual waste liquid is collected in the receiving hopper 24 and discharged through the waste liquid discharge pipe 27; in the regeneration stage, the movable magnetic sucker 21 moves downwards to the adsorbent scraping blade 22, the movable magnetic sucker 21 rotates at a rotation speed of 150 r/min, the regeneration liquid spray pipe 23 sprays 2mol/L NaOH solution, and the washing strength is 8L/(s.m)2) The mixture of the adsorbent and the phosphorus solution is collected in a receiving hopper 24; in the stage of recovering the phosphorus solution, the movable magnet sucker 21 moves downwards and rotates at the rotating speed of 120 r/min, after the adsorbent is adsorbed on the movable magnet sucker 21 and moves upwards, the valve 35 of the phosphorus solution outlet pipe is opened, and the phosphorus solution enters the second regulating tank 36 through the water outlet pipe 32; during the adsorbent recovery stage, the movable magnetic chuck 21 moves down again to the adsorbent scraping blade 22 and rotatesDuring the rotation process, the regeneration liquid spray pipe 23 sprays clean water with the washing intensity of 8L/(s.m)2) And the reflux pipe valve 33 is opened, and the adsorbent suspension is collected in the receiving hopper 24 and is refluxed to the nano adsorbent dosing tank 5 through the reflux pump 34.
(3) And (3) crystallizing to prepare a phosphate fertilizer: the crystallization reactor 38 adopts an intermittent operation mode of 'water inlet-crystallization reaction-water discharge-phosphate fertilizer collection', and the duration of the four stages is 5min-40min-5min-10 min: in the water inlet stage, the phosphorus solution in the second regulating reservoir 36 intermittently enters the crystallization reactor 38 through a phosphorus solution second regulating reservoir liquid outlet pipe 40, the dewatered sludge waste liquid enters the crystallization reactor 38 through a water inlet branch pipe 8-2, and 0.1M magnesium chloride solution enters the crystallization reactor 38 through a magnesium chloride solution pipe 42; in the crystallization reaction stage, under the stirring action of the second stirring device 44, the above solutions are uniformly mixed and crystallization reaction occurs; in the drainage stage, after standing and settling for 10min, opening a valve 47-1 of a crystallization waste liquid discharge pipe, and discharging crystallization waste liquid; in the stage of collecting the phosphate fertilizer, a valve 48-1 of a phosphate fertilizer collecting pipe is opened, and the solution is dried and crystallized to obtain the phosphate fertilizer.
After 5 batches of wastewater treatment, data statistics shows that the recovery rate of phosphorus is 95-99%, the reuse rate of the adsorbent is 95-99%, and the yield of the phosphate fertilizer is 0.33-0.35kg/m3。
EXAMPLE 6 preparation of waste Water phosphate
The procedure is as in example 5, except that:
in the step (1), the adsorbent is prepared in example 2;
in the step (2), the concentration of the adopted NaOH solution is 3mol/L, and the washing strength is 6L/(s.m)2)。
After 5 batches of wastewater treatment, data statistics shows that the recovery rate of phosphorus is 85-90%, the reuse rate of the adsorbent is 95-99%, and the yield of the phosphate fertilizer is 0.26-0.32kg/m3。
EXAMPLE 7 preparation of waste Water phosphate
The procedure is as in example 5, except that:
in the step (1), the adsorbent is the adsorbent prepared in example 3;
in the step (2),the concentration of the NaOH solution used was 1mol/L, and the washing strength was 8L/(s.m)2)。
After 5 batches of wastewater treatment, data statistics shows that the recovery rate of phosphorus is 90-95%, the reuse rate of the adsorbent is 95-99%, and the yield of the phosphate fertilizer is 0.31-0.37kg/m3。
COMPARATIVE EXAMPLE 1 preparation of phosphate Fertilizer
The procedure is as in example 5, except that:
the first stirring paddle 14 and the second stirring paddle 46 in the apparatus of example 4 were replaced with stirring paddles made of steel;
the concentration of the NaOH solution is 3mol/L, and the washing strength is 4L/s.
After 5 batches of wastewater treatment, data statistics shows that the recovery rate of phosphorus is 80-94%, the reuse rate of the adsorbent is 90-95%, and the yield of the phosphate fertilizer is 0.29-0.33kg/m3。

Claims (8)

1. A device for preparing a compound phosphate fertilizer from waste water is characterized by comprising a mixed adsorption reaction unit (1), a magnetic separation and regeneration unit (2) and a compound phosphate fertilizer crystallization unit (3);
the mixed adsorption reaction unit (1) comprises an adsorption reactor (4), a nano adsorbent dosing box (5), a first stirring device (6) and a water outlet weir (7); a water inlet pipe (8) and an emptying pipe (9) are arranged on the adsorption reactor (4), and an emptying pipe valve (9-1) is arranged on the emptying pipe (9); the nano adsorbent dosing box (5) is connected to a mixing pump (11) through a mixing pump liquid inlet pipe (10), and the mixing pump (11) is connected to the adsorption reactor (4) through a mixing pump liquid outlet pipe (12); the first stirring device (6) comprises a first motor (13) and a first stirring paddle (14) which are arranged in the center of the adsorption reactor (4);
the magnetic separation and regeneration unit (2) comprises a first regulating reservoir (16) and a magnetic separation coupling regeneration reactor (17); the first regulating tank (16) is connected with the water outlet weir (7) through a water outlet pipe (7-1) of the water outlet weir, and the first regulating tank (16) is connected to a regeneration pump (19) through a water inlet pipe (18) of the regeneration pump; the magnetic separation coupling regeneration reactor (17) is a closed organic glass container and is connected to a regeneration pump (19) through a regeneration pump water outlet pipe (20); a movable magnet sucker (21), an adsorbent scraping blade (22), a regenerated liquid spray pipe (23) and a receiving hopper (24) are arranged in the regeneration device; the adsorbent scraping blade (22) is arranged in the middle of the inner wall of the magnetic separation coupling regeneration reactor (17); the regenerated liquid spray pipe (23) enters the magnetic separation coupling regeneration reactor (17) from the upper part and directly reaches the blade of the adsorbent scraping blade (22); the lower part of the receiving hopper (24) is connected with a collecting main pipe (25), the collecting main pipe (25) is connected with a waste liquid discharge pipe (27) and a main discharge pipe (28) through a first three-way pipe (26), a waste liquid discharge pipe valve (29) is arranged on the waste liquid discharge pipe (27), and the main discharge pipe (28) is connected with an adsorbent return pipe (31) and a phosphorus solution outlet pipe (32) through a second three-way pipe (30); a reflux pipe valve (33) is arranged on the adsorbent reflux pipe (31) and is connected to the nano adsorbent dosing tank (5) through a reflux pump (34); a phosphorus solution outlet pipe valve (35) is arranged on the phosphorus solution outlet pipe (32);
the compound phosphate fertilizer crystallization unit (3) comprises a second adjusting tank (36), a magnesium chloride dissolving tank (37), a crystallization reactor (38) and a phosphate fertilizer collecting hopper (39); the second regulating reservoir (36) is connected with a phosphorus solution outlet pipe (32), the crystallization reactor (38) is connected with a second regulating reservoir liquid outlet pipe (40), a phosphorus solution supply pump (41) is arranged on the second regulating reservoir liquid outlet pipe (40), a water inlet pipe (8) in the mixed adsorption reaction unit (1) is connected with a water inlet branch pipe (8-2) through a third tee joint (8-1), and the other end of the water inlet branch pipe (8-2) is connected to the second regulating reservoir liquid outlet pipe (40) through a branch pipe supply pump (8-3); the magnesium chloride dissolving tank (37) is connected to the crystallization reactor (38) through a magnesium chloride solution pipe (42), and a magnesium chloride solution supply pump (43) is arranged on the magnesium chloride solution pipe (42); a second stirring device (44) is arranged in the center of the crystallization reactor (38), and the second stirring device (44) comprises a second motor (45) and a second stirring paddle (46); the upper end of the phosphate fertilizer collecting hopper (39) is connected with a crystallization waste liquid discharge pipe (47), the lower end of the phosphate fertilizer collecting hopper is connected with a phosphate fertilizer collecting pipe (48), and a crystallization waste liquid discharge pipe valve (47-1) and a phosphate fertilizer collecting pipe valve (48-1) are arranged on the crystallization waste liquid discharge pipe (47).
2. The device as claimed in claim 1, wherein the outer edge of the movable magnetic chuck (21) is made of neodymium-iron-boron magnet material, and the magnetic field strength is about 500-.
3. A method for preparing a phosphate fertilizer from wastewater using the apparatus of claim 1 or 2, comprising the steps of:
(1) adsorption treatment: magnetic adsorbent suspension in a nano adsorbent dosing tank (5) enters an adsorption reactor (4) through a mixing pump liquid inlet pipe (10), wastewater enters the adsorption reactor (4) through a water inlet pipe (8), the adsorbent suspension and the wastewater are fully mixed under the stirring of a first stirring device (6) for adsorption reaction, and the adsorbed mixed solution enters a first regulating tank (16) through a water outlet weir (7);
(2) separation and regeneration treatment: the magnetic separation coupling regeneration reactor (17) adopts an intermittent operation mode of water inlet-magnetic separation-water discharge-regeneration-phosphorus solution recovery-adsorbent recovery: in the water inlet stage, a waste liquid discharge pipe valve (29), a return pipe valve (33) and a phosphorus solution outlet pipe valve (35) are closed, and the mixed liquid in the first regulating tank (16) intermittently enters the magnetic separation coupling regeneration reactor (17) through a regeneration pump (19); in the magnetic separation stage, the movable magnet sucker (21) rotates, and the adsorbent is adsorbed on the movable magnet sucker (21); in the drainage stage, a waste liquid discharge pipe valve (29) is opened, and residual waste liquid is collected in a receiving hopper (24) and discharged through a waste liquid discharge pipe (27); in the regeneration stage, the movable magnet sucker (21) moves downwards to the adsorbent scraping blade (22), the regeneration liquid spray pipe (23) sprays NaOH solution in the rotation process of the movable magnet sucker (21), and the mixture of the adsorbent and the phosphorus solution is collected in the receiving hopper (24); in the stage of recovering the phosphorus solution, the movable magnet sucker (21) moves downwards to rotate, the adsorbent is adsorbed on the movable magnet sucker (21), after the movable magnet sucker (21) moves upwards, a phosphorus solution outlet pipe valve (35) is opened, and the phosphorus solution enters a second regulating tank (36) through a water outlet pipe (32); in the adsorbent recovery stage, the movable magnet sucker (21) moves downwards again to the adsorbent scraping blade (22) and rotates, in the rotation process, the regeneration liquid spray pipe (23) sprays clean water, the reflux pipe valve (33) is opened, and the adsorbent suspension is collected in the receiving hopper (24) and flows back to the nano adsorbent dosing box (5) through the reflux pump (34);
(3) and (3) crystallizing the phosphate fertilizer: the crystallization reactor (38) adopts an intermittent operation mode of 'water inlet-crystallization reaction-water discharge-phosphate fertilizer collection': in the water inlet stage, a branch pipe supply pump (8-3), a phosphorus solution supply pump (41) and a magnesium chloride solution supply pump (43) are started, a crystallization waste liquid discharge pipe valve (47-1) and a phosphate fertilizer collection pipe valve (48-1) are closed, phosphorus solution in a second regulating reservoir (36) intermittently enters a crystallization reactor (38) through a phosphorus solution second regulating reservoir liquid outlet pipe (40), dehydrated sludge waste liquid enters the crystallization reactor (38) through a water inlet branch pipe (8-2), and magnesium chloride solution enters the crystallization reactor (38) through a magnesium chloride solution pipe (42); in the crystallization reaction stage, the branch pipe supply pump (8-3), the phosphorus solution supply pump (41) and the magnesium chloride solution supply pump (43) are closed, the second stirring device (44) is started, and the solutions are uniformly mixed and subjected to crystallization reaction under the stirring action; in the drainage stage, the second stirring device (44) is closed, and after the crystallization waste liquid is settled, a valve (47-1) of a crystallization waste liquid discharge pipe is opened to discharge the crystallization waste liquid; in the stage of collecting the phosphate fertilizer, a valve (48-1) of a phosphate fertilizer collecting pipe is opened, and then drying treatment is carried out to obtain the phosphate fertilizer.
4. The method of claim 3, wherein the wastewater has a COD of 2000mg/L, BOD or less5Less than or equal to 500mg/L, ammonia nitrogen less than or equal to 500mg/L, phosphate less than or equal to 80mgP/L and pH value of 6.0-7.0.
5. The method of claim 3, wherein the molar ratio of NaOH to P content in wastewater is 20: 1; the molar ratio of the magnesium chloride to the phosphorus solution is 1:1.
6. The method as claimed in claim 3, wherein in the step (1), the stirring speed of the first stirring device (6) is 200-300 r/min; in the step (2), the rotation speed of the central shaft of the movable magnet sucker (21) is 120-; in the step (3), the stirring speed of the second stirring device (44) is 120-180 r/min.
7. The method according to claim 3, wherein in the step (1), the magnetic adsorbent is a superparamagnetic response nano phosphorus adsorbent, and the shape of the magnetic adsorbent is a granular core-shell structure, and the inner core is Fe3O4The outer shell of the tube is sequentially SiO from inside to outside2And magnesium aluminum double hydroxides (Mg-Al-LDHs) on which transition metal oxides are complexed; the average diameter of the particles is 30-80 nm, and the average thickness of the shell is 10-20 nm; the transition metal is selected from lanthanum, cerium or hafnium.
8. The method according to claim 7, wherein in the step (1), the weight percentage content of the magnesium aluminum bimetal hydroxide and the transition metal oxide in the superparamagnetic response nano phosphorus adsorbent is 20% -60%; preferably 30% -60%; the mass percentage of the transition metal oxide counted by metal is 20-60% of the total mass of the magnesium-aluminum bimetal hydroxide and the transition metal oxide.
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