Method and device for improving phosphorus recovery of CaP crystals in sewage by using microbubbles

Abstract

The invention discloses a method and device for improving phosphorus recovery of CaP crystals in sewage by using microbubbles, and the method comprises the following steps: adjusting the pH value of phosphorus-containing sewage to be alkaline, mixing the phosphorus-containing sewage with calcium salt, entering a nucleation reaction zone to obtain sewage containing calcium phosphate microcrystals, and enabling the sewage to flow into an air flotation zone after passing through a flow guide zone; high-pressure dissolved air water in the pressure dissolved air tank is pumped into a perforated pipe at the bottom of the air flotation area, and the perforated pipe releases the high-pressure dissolved air water to generate microbubbles; calcium phosphate microcrystals and microbubbles in the sewage in the air floatation area are flocculated into clusters and float upwards into the scum area; the calcium phosphate microcrystals in the scum area are agglomerated and cured under the shearing action caused by stirring and breaking of the microbubbles to obtain calcium phosphate crystals with the target particle size, and the calcium phosphate crystals are scraped into a scum tank by a scum scraper to realize phosphorus recovery; residual sewage after phosphorus recovery is discharged through a water outlet in the bottom of the air flotation area. The recovery method is simple to operate, and the recovered calcium phosphate crystals are controllable in particle size and high in recovery rate.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of phosphorus recovery and treatment in wastewater, and particularly relates to a method and device for improving phosphorus recovery by CaP crystallization in wastewater using micro-bubbles. BACKGROUND

[0002] Phosphorus is a key factor leading to water eutrophication, and is also a non-renewable and scarce resource. Traditional methods for phosphorus recovery in wastewater, such as chemical precipitation, biological phosphorus removal, and adsorption, essentially only separate phosphorus from the liquid phase, and do not achieve true phosphorus recovery. Chemical crystallization, represented by calcium phosphate crystallization, separates phosphorus from the liquid phase in the form of a poorly soluble phosphate salt, which is true phosphorus recovery.

[0003] The phosphorus concentration in wastewater is relatively high, and when a homogeneous crystallization phosphorus recovery scheme is used, the calcium phosphate crystallization nucleation process is quickly completed once the crystallization agent Ca 2+ The calcium phosphate microcrystals are small in size and have poor sedimentation separation performance, and it is difficult to achieve solid-liquid separation within a limited sedimentation time, which results in a limited calcium phosphate phosphorus recovery rate despite a very high calcium phosphate crystallization rate in wastewater.

[0004] To improve the phosphorus recovery rate of chemical crystallization, a technical solution that can be used is to change the homogeneous crystallization mode to an induced crystallization mode, and to add seed crystals to the phosphorus-containing wastewater to control the particle size of the seed crystals by induced crystallization, improve the particle size of the crystallization product, and achieve the effect of improving the sedimentation performance of the crystallization product. Chinese Invention Patent (CN104973723A) discloses an induced crystallization reactor and a connected solid-liquid separation device, which uses calcite as seed crystals to induce the recovery of phosphorus in wastewater in the form of calcium phosphate crystals, thereby improving the phosphorus recovery rate. Chinese Invention Patent (CN110395822B) discloses a phosphorus recovery method using seed crystals to force calcium phosphate agglomeration crystallization, which improves the phosphorus recovery effect. However, induced crystallization requires the use of a fluidized bed as a reactor, and the seed crystals fed into the fluidized bed are prone to loss during operation, which leads to a continuous decline in the crystallization effect. Currently, there is no treatment for the loss of seed crystals.

[0005] Blowing aeration can strengthen the mass transfer process of a poorly soluble salt crystallization system, promote the agglomeration of crystal nuclei, and thus improve the crystallization rate. Chinese Invention Patent (CN103723874A) discloses a method for efficiently recovering phosphorus from wastewater, which uses blowing aeration to improve the phosphorus recovery rate. However, blowing aeration still cannot effectively solve the problem of poor sedimentation performance of the product in the homogeneous crystallization mode of a poorly soluble salt, and even accelerates the loss of seed crystals in the induced crystallization mode.

[0006] Therefore, there is an urgent need to develop a new method for recovering phosphorus in wastewater. SUMMARY

[0007] The present application aims to at least solve one of the technical problems in the related art. To this end, the present application embodiment proposes a method and device for improving CaP crystallization phosphorus recovery from sewage by using microbubbles, which has simple operation, controllable particle size of the crystalline product, and high phosphorus recovery rate.

[0008] In order to achieve the above-mentioned application purposes, the present application adopts the following technical solutions: In a first aspect, the present application embodiment proposes a method for improving CaP crystallization phosphorus recovery from sewage by using microbubbles, comprising the following steps: (1) After adjusting the pH of the phosphorus-containing sewage to alkaline, mixing with calcium salt, entering the nucleation reaction zone, and performing nucleation reaction, obtaining sewage containing calcium phosphate microcrystals, and flowing into the gas floating zone after the guide zone; (2) Pumping high-pressure dissolved gas water in the pressure dissolved gas tank into the perforated pipe at the bottom of the gas floating zone, the perforated pipe releases high-pressure dissolved gas water to generate microbubbles; then, the calcium phosphate microcrystals in the sewage in the gas floating zone flocculate into groups with the microbubbles, and float to the dregs area with the microbubbles; (3) The calcium phosphate microcrystals in the dregs area are subjected to agglomeration and maturation under the stirring and shearing effect caused by the rupture of the microbubbles, obtaining calcium phosphate crystals with a target particle size, and scraping to the dregs tank by a dregs scraper to realize phosphorus recovery; the remaining sewage after phosphorus recovery is discharged through the water outlet at the bottom of the gas floating zone.

[0009] In some embodiments, in the step (1), the pH of the phosphorus-containing sewage is adjusted to 9.0-11.0; And / or, the calcium salt is one or a mixture of two of CaCl2 or Ca(OH)2; And / or, the reaction temperature of the nucleation reaction is room temperature, and the reaction time is 30-60 s.

[0010] In some embodiments, in the step (2), the dissolved gas pressure of the pressure dissolved gas tank is 0.3-0.5 MPa; And / or, the gas-water volume ratio in the gas floating zone is 10-15%:1.

[0011] In some embodiments, in the step (2), the hydraulic retention time of the gas floating zone is 1-20 min.

[0012] In some embodiments, in the step (3), the time of agglomeration and maturation is ≥6 h.

[0013] In a second aspect, the embodiments of the present application also provide a device for improving CaP crystallization and phosphorus recovery from sewage by using microbubbles, which is used for implementing the method of the first aspect and comprises an alkali storage tank, a calcium salt storage tank, a crystallization air flotation tank, a pressure dissolved gas tank, a slag scraper and a slag tank; a nucleation reaction zone, a flow guide zone and an air flotation zone are sequentially arranged in the length direction inside the tank body of the crystallization air flotation tank, and a slag floating zone is arranged on the top of the air flotation zone; a plurality of parallel arranged perforated pipes are arranged on the bottom of the air flotation zone, and the inlets of the perforated pipes are communicated with the outlet of the pressure dissolved gas tank; the outlet of the alkali storage tank is communicated with the bottom inlet of the nucleation reaction zone, and the outlet of the calcium salt storage tank is communicated with the bottom inlet of the nucleation reaction zone.

[0014] In some embodiments, the slag scraper is connected with the top of the slag floating zone, and is used for scraping the slag in the slag floating zone to the slag tank for collection.

[0015] In some embodiments, the height ratio of the air flotation zone to the slag floating zone is 3:1, and the length-height ratio of the air flotation zone is not less than 4.

[0016] In some embodiments, the nucleation reaction zone and the flow guide zone are separated by a baffle, the flow guide zone and the air flotation zone are separated by a perforated plate, and a plurality of water holes are arranged in the middle and lower part of the perforated plate.

[0017] In some embodiments, a stirring mechanism is arranged in the nucleation reaction zone, and the stirring rotation speed of the nucleation reaction zone is 300-500 rpm.

[0018] The embodiments of the present application have the following advantages and beneficial effects: (1) The embodiments of the present application can effectively inhibit the agglomeration between the microcrystals by controlling the mechanical stirring intensity and nucleation reaction time of the nucleation reaction zone, while ensuring the yield of the calcium phosphate microcrystals in the sewage, and create conditions for the subsequent efficient air flotation of the microcrystals.

[0019] (2) The embodiments of the present application utilize the strong agglomeration effect between the microbubbles released by the high-pressure dissolved gas water and the calcium phosphate microcrystals in the crystallization air flotation tank, and realize the efficient solid-liquid separation of the calcium phosphate crystallization product and water in the form of air flotation.

[0020] (3) The embodiments of the present application provide power for the agglomeration and ripening of the calcium phosphate microcrystals by means of the stirring effect and shearing effect of the microbubbles when they break, and promote the growth of the calcium phosphate crystallization product.

[0021] (4) The embodiments of the present application make the calcium phosphate microcrystals stay in the slag floating zone for a long time by means of the jacking effect of the microbubbles, provide a stable environment for the agglomeration and ripening of the calcium phosphate microcrystals, and obtain calcium phosphate crystals with controllable particle size by controlling the slag scraping time of the slag floating zone. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 Figure 1 is a structural schematic diagram of a device for improving phosphorus recovery by CaP crystallization in wastewater using microbubbles according to an embodiment of the present application.

[0023] Figure 1 is a structural schematic diagram of a device for improving phosphorus recovery by CaP crystallization in wastewater using microbubbles according to an embodiment of the present application. Figure 1 is a structural schematic diagram of a device for improving phosphorus recovery by CaP crystallization in wastewater using microbubbles according to an embodiment of the present application. DETAILED DESCRIPTION

[0024] The embodiments of the present application are described in detail below, which are exemplary and intended to explain the present application, and cannot be understood as a limitation of the present application.

[0025] In the present application, in the case of describing a value as a range, it should be understood that such disclosure includes the disclosure of all possible sub-ranges within the range, and the specific numerical values falling within the range, regardless of whether the specific numerical values or specific sub-ranges are explicitly indicated.

[0026] In the present application, the words "comprise" and "include" and their various variants mean that other elements or whole bodies that can be allowed but are not specifically described can be included.

[0027] In the present application, the term "and / or" is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone.

[0028] In the present application, "CaP crystallization" refers to calcium phosphate crystallization, which is abbreviated as CaP crystallization.

[0029] The present application is based on the discovery and understanding of the inventors on the following facts and problems: The inventors found that when calcium phosphate is used to recover phosphorus in wastewater, although the crystallization rate of phosphorus is high, the recovery rate is often limited. The main reasons are as follows: when a homogeneous crystallization mode is used, the nucleation process of calcium phosphate crystallization cannot be effectively controlled, and a large amount of calcium phosphate microcrystals that are difficult to settle and difficult to separate from the liquid are generated, which weakens the phosphorus recovery effect; when a seed-induced crystallization mode is used, although the control of the nucleation process can be achieved, and the particle size of the crystallization product can be controlled, the seed is easy to be lost from the fluidized bed, which leads to a rapid decrease in the phosphorus recovery rate. Therefore, the key to improving the phosphorus recovery effect of calcium phosphate crystallization in wastewater is to promote the agglomeration and growth of microcrystals, so as to obtain a calcium phosphate crystallization product with controllable particle size and easy solid-liquid separation.

[0030] Based on this, the present application uses the air floatation, stirring and shearing effects of the micro-bubbles released by the high-pressure dissolved gas water to obtain a calcium phosphate crystalline product with controllable particle size and easy solid-liquid separation. First, by controlling the stirring intensity and nucleation reaction time of the calcium phosphate nucleation reaction zone, the effects of improving the yield of calcium phosphate microcrystals and inhibiting the agglomeration of calcium phosphate microcrystals are achieved simultaneously, thereby creating good conditions for the air floatation separation of calcium phosphate microcrystals by micro-bubbles. Second, the micro-bubbles released by the high-pressure dissolved gas water flocculate with the calcium phosphate microcrystals, and the calcium phosphate microcrystals rapidly rise to the floating dregs area at the top of the crystallization air floatation tank under the air floatation effect of the micro-bubbles, thereby realizing efficient and rapid solid-liquid separation. Finally, the calcium phosphate microcrystals gathered in the floating dregs area are agglomerated and matured in the floating dregs area due to the stirring effect of the micro-bubbles and the shearing effect caused by the breaking of the micro-bubbles, thereby obtaining a calcium phosphate crystalline product with a particle size of more than 500 μm. In addition, the particle size of the calcium phosphate crystalline product can be adjusted by controlling the scraping period (i.e. the agglomeration and maturation time) of the floating dregs area surface dregs scraper. The longer the dregs scraper period, the larger the particle size of the calcium phosphate crystalline product.

[0031] In a first aspect, the present application provides a method for improving the recovery of phosphorus by CaP crystallization in wastewater by using micro-bubbles, which comprises the following steps: (1) After adjusting the pH of the phosphorus-containing wastewater to alkaline, the wastewater is mixed with a calcium salt and enters a nucleation reaction zone to perform a nucleation reaction, thereby obtaining wastewater containing calcium phosphate microcrystals, and the wastewater flows into an air floatation zone through a guide area; (2) High-pressure dissolved gas water in a pressure dissolved gas tank is pumped into a perforated pipe at the bottom of the air floatation zone, the perforated pipe releases the high-pressure dissolved gas water to generate micro-bubbles, and then the calcium phosphate microcrystals in the wastewater in the air floatation zone flocculate into groups with the micro-bubbles and float to a floating dregs area with the micro-bubbles; (3) The calcium phosphate microcrystals in the floating dregs area are agglomerated and matured under the stirring and shearing effects caused by the breaking of the micro-bubbles, thereby obtaining calcium phosphate crystals with a target particle size, and the calcium phosphate crystals are scraped to a floating dregs tank by a dregs scraper to realize the recovery of phosphorus; the remaining wastewater after the recovery of phosphorus is discharged through a drainage port at the bottom of the air floatation zone.

[0032] In some embodiments, in the step (1), the pH of the phosphorus-containing wastewater is adjusted to 9.0-11.0. The inventors have found through research that when the pH of the phosphorus-containing wastewater is controlled in the range of 9.0-11.0, not only is the generation rate of calcium carbonate microcrystals relatively fast, but also the generated calcium carbonate microcrystals are suitable for air floatation separation; if the pH of the phosphorus-containing wastewater is lower than 9.0, PO4 3- and Ca 2+ will be sent to the air floatation zone before crystallization; and when the pH of the phosphorus-containing wastewater is higher than 11.0, part of the calcium phosphate microcrystals will settle before being sent to the air floatation zone; And / or, the calcium salt is one or a mixture of both of CaCl2 or Ca(OH)2, wherein Ca(OH)2 is advantageous in that it can not only provide Ca 2+ , but also adjust the pH of the reaction system, and it is low in price, but because the solubility of Ca(OH)2 is limited, when the phosphorus concentration in the wastewater is high, a higher concentration of Ca 2+ is required, that is, CaCl2 is preferred; And / or, the reaction temperature of the nucleation reaction is room temperature, and the reaction time is 30-60 s; and the inventors have found that if the reaction time of the nucleation reaction is less than 30 s, PO4 3- and Ca 2+ crystallization is not sufficient; but if the reaction time of the nucleation reaction is more than 60 s, part of the calcium phosphate microcrystals begin to agglomerate, which weakens the subsequent air floatation efficiency, therefore, the inventors control the reaction time of the nucleation reaction in the range of 30-60 s.

[0033] In some embodiments, in step (2), the dissolved gas pressure of the pressure dissolved gas tank is 0.3-0.5 MPa, so that the diameter of the micro-bubbles generated is about 30 μm; And / or, the gas-water volume ratio in the air floatation zone is 10-15%:1, which can ensure that the calcium phosphate microcrystals in the wastewater obtain a good air floatation effect.

[0034] In some embodiments, in step (2), the hydraulic retention time of the air floatation zone is 1-20 min.

[0035] In some embodiments, in step (3), the agglomeration and maturation time is ≥6 h, so that the average particle size of the recovered calcium phosphate crystals can be stabilized at more than 500 μm, the solid-liquid separation effect is better, and thus the recovery effect of phosphorus in the wastewater is improved.

[0036] Further, the specific process of step (3) is as follows: the calcium phosphate microcrystals obtained in step (2) are gathered in the dross area under the action of air floatation, and then under the stirring action of the micro-bubbles and the shearing action caused by the breakage of the micro-bubbles, part of the microcrystals agglomerate into larger crystal nuclei, that is, the agglomeration process; another part of the microcrystals dissolve, and the generated crystal-forming ions (PO4 3- and Ca 2+ ) occur surface crystallization on the surface of the aforementioned crystal nuclei, that is, the maturation process. Then, by adjusting the agglomeration and maturation time of the microcrystals in the dross area, the particle size of the crystallization product is controlled. When the average particle size of the crystallization product reaches a preset value, a surface dross scraper is started to scrape the crystallization product to a dross discharge tank, and thus the recovery and utilization of phosphorus is realized.

[0037] In the second aspect, as Figure 1As shown, the embodiment of the present application also proposes a device for improving CaP crystallization and phosphorus recovery of sewage by using microbubbles, which is used to implement the method of the first aspect and comprises a lye storage tank 1, a calcium salt storage tank 2, a crystallization air flotation tank 3, a pressure dissolved air tank 4, a slag scraper 5 and a slag tank 6; the crystallization air flotation tank 3 is internally provided with a nucleation reaction zone 301, a flow guide zone 302 and an air flotation zone 303 in sequence along the length direction, and the top of the air flotation zone 303 is provided with a slag zone 304; the bottom of the air flotation zone 303 is provided with a plurality of parallel arranged perforated pipes 3031, the inlet of the perforated pipe 3031 is communicated with the outlet of the pressure dissolved air tank 4; the outlet of the lye storage tank 1 is communicated with the bottom inlet of the nucleation reaction zone 301, and the outlet of the calcium salt storage tank 2 is communicated with the bottom inlet of the nucleation reaction zone 301.

[0038] It should be noted that the alkali solution in the lye storage tank 1 is not particularly limited, and those skilled in the art can store lye according to actual needs, for example, the alkali solution in the lye storage tank 1 can use NaOH solution, etc.

[0039] In some embodiments, the slag scraper 5 is connected with the top of the slag zone 304, and is used to scrape the slag in the slag zone 304 to the slag tank 6 for collection.

[0040] In some embodiments, the height ratio of the air flotation zone 303 to the slag zone 304 is 3:1; and the length-height ratio of the air flotation zone 303 is not less than 4. By controlling the length-height ratio of the air flotation zone and the height ratio of the air flotation zone to the slag zone, sufficient air flotation time can be ensured, and the stability of the water flow can be ensured.

[0041] In some embodiments, the nucleation reaction zone 301 and the flow guide zone 302 are separated by a baffle 305, the flow guide zone 302 and the air flotation zone 303 are separated by a perforated plate 306, and the middle and lower parts of the perforated plate 306 are provided with a plurality of water holes. By providing the flow guide zone, the downward flow can be adjusted to a stable horizontal flow; and the provision of the flow guide zone can also avoid the short flow phenomenon between the nucleation reaction zone and the air flotation zone.

[0042] In some embodiments, the nucleation reaction zone 301 is provided with a stirring mechanism 3011, and the stirring speed of the nucleation reaction zone 301 is 300-500 rpm. The mechanical stirring promotes the mixing of phosphate ions and calcium salt in the sewage, and then promotes the nucleation reaction to generate calcium phosphate microcrystals.

[0043] In some embodiments, a water pump 7 is arranged on the connecting pipeline between the outlet of the pressure dissolved air tank 4 and the inlet of the perforated pipe 3031, and is used to pump the high-pressure dissolved air water in the pressure dissolved air tank 4 into the perforated pipe 3031.

[0044] The technical solutions of the present application will be further described in detail below in combination with specific examples. The experimental methods not specified in the examples are conventional methods and conventional conditions well known in the art.

[0045] Example 1 The phosphorus-containing sewage in this example is supernatant of a concentrated pool of a municipal sewage plant, and the phosphorus concentration is 8-12 mg / L, wherein the PO4 3- content accounts for more than 90%, and the average water inflow is 2 m 3 The method for recovering phosphorus from the sewage comprises the following steps: (1) mixing the phosphorus-containing sewage with Ca(OH)2 delivered from a calcium salt storage tank to adjust the pH value of the phosphorus-containing sewage to 10.0, and delivering the mixture to a nucleation reaction zone for nucleation reaction, wherein the stirring speed of the nucleation reaction zone is controlled to be 500 rpm, and the hydraulic retention time is controlled to be 50 s, to obtain sewage containing calcium phosphate microcrystals, which is immediately turned over a baffle plate to enter a flow guide zone, and flows into a flotation zone (the length-height ratio of the flotation zone is 5:1) through a perforated plate; (2) pumping high-pressure dissolved gas water (dissolved gas pressure is 0.4 MPa) in a pressure dissolved gas tank into a perforated pipe at the bottom of the flotation zone, and a large amount of micro-bubbles (diameter is about 30 μm) are generated by the high-pressure dissolved gas water released from the perforated pipe, which is mixed with the sewage containing calcium phosphate microcrystals in the flotation zone, the gas-water ratio of the flotation zone is controlled to be 15%, and the hydraulic retention time of the flotation zone is controlled to be 5 min, so that the calcium phosphate microcrystals are intensively flocculated and quickly floated to a scum zone (the height ratio of the flotation zone to the scum zone is 3:1) by the micro-bubbles; (3) the calcium phosphate microcrystals gathered in the scum zone are stably suspended in the scum zone under the support of the micro-bubbles, and occur agglomeration and maturation for 6 h under the shearing action caused by the stirring and rupture of the micro-bubbles, to obtain calcium phosphate crystals with an average particle size of 800 μm, then a scum scraper located on the surface of the scum zone is started to scrape the surface scum (calcium phosphate crystal particles) to a scum tank, and the calcium phosphate crystals collected in the scum tank are naturally dried to realize the recovery of phosphorus; then the remaining sewage after phosphorus recovery is discharged through a drainage port at the bottom of the flotation zone.

[0046] In this example, the phosphorus concentration of the effluent is stably controlled to be below 0.5 mg / L, and the phosphorus recovery rate is stably controlled to be more than 90%. The average particle size of the recovered product calcium phosphate crystal particles is 800 μm, and the water content is less than 40%.

[0047] Example 2 The phosphorus-containing sewage in this example is digestion liquid of an anaerobic digestion tank of a municipal sewage plant, and the phosphorus concentration is 120-180 mg / L, wherein the PO4 3- content accounts for more than 90%, and the average water inflow is 2 m 3 The method for recovering phosphorus from the sewage comprises the following steps: (1) the NaOH solution in the alkali storage tank is used to adjust the pH value of the phosphorus-containing wastewater to 10.0, and is mixed with CaCl2 delivered from the calcium salt storage tank (controlling the Ca / P molar ratio to be 2:1) to be delivered to the nucleation reaction zone for nucleation reaction, the stirring speed of the nucleation reaction zone is controlled to be 400 rpm, and the hydraulic retention time is controlled to be 40 s, to obtain wastewater containing calcium phosphate microcrystals, the wastewater is immediately turned over the baffle to enter the flow guide zone, and flows into the air flotation zone through the perforated plate (the length-height ratio of the air flotation zone is 5:1); (2) the high-pressure dissolved gas water (dissolved gas pressure is 0.4 MPa) in the pressure dissolved gas tank is pumped into the perforated pipe at the bottom of the air flotation zone by a water pump, a large amount of micro-bubbles (diameter is about 30 μm) are generated by the high-pressure dissolved gas water released by the perforated pipe, and are mixed with the wastewater containing calcium phosphate microcrystals in the air flotation zone, the gas-water ratio of the air flotation zone is controlled to be 15%, and the hydraulic retention time of the air flotation zone is controlled to be 8 min, the calcium phosphate microcrystals are intensively flocculated and are quickly floated to the scum zone (the height ratio of the air flotation zone to the scum zone is 3:1) by air flotation; (3) the calcium phosphate microcrystals gathered in the scum zone are stably suspended in the scum zone under the support of the micro-bubbles, and are subjected to agglomeration and maturation for 8 h under the stirring and shearing effect caused by the breakage of the micro-bubbles, to obtain calcium phosphate crystals with an average particle size of 1000 μm, then a scum scraper located on the surface of the scum zone is started to scrape the surface scum (calcium phosphate crystal particles) to the scum tank, the calcium phosphate crystals collected in the scum tank are naturally dried to realize the recovery of phosphorus; then the remaining wastewater after the recovery of phosphorus is discharged through the water outlet at the bottom of the air flotation zone.

[0048] In this embodiment, the effluent phosphorus concentration is stably controlled to be below 0.5 mg / L, and the phosphorus recovery rate is stably controlled to be above 99%. The average particle size of the recovered product calcium phosphate crystal particles is 1000 μm, and the water content is below 40%.

[0049] Example 3 The phosphorus-containing wastewater in this embodiment is high-phosphorus-concentration wastewater from a phosphate fertilizer plant, the phosphorus concentration is 650-800 mg / L, the PO4 3- content is above 95%, and the average water inflow is 2 m 3 / h. The phosphorus recovery method of the wastewater comprises the following steps: (1) the NaOH solution in the alkali storage tank is used to adjust the pH value of the phosphorus-containing wastewater to 10.0, and is mixed with CaCl2 delivered from the calcium salt storage tank (controlling the Ca / P molar ratio to be 2:1) to be delivered to the nucleation reaction zone for nucleation reaction, the stirring speed of the nucleation reaction zone is controlled to be 500 rpm, and the hydraulic retention time is controlled to be 30 s, to obtain wastewater containing calcium phosphate microcrystals, the wastewater is immediately turned over the baffle to enter the flow guide zone, and flows into the air flotation zone through the perforated plate (the length-height ratio of the air flotation zone is 5:1); (2) The high-pressure dissolved gas water (dissolved gas pressure is 0.4 MPa) in the pressure dissolved gas tank is pumped into the perforated pipe at the bottom of the air flotation zone by a water pump, a large amount of micro-bubbles (diameter is about 30 μm) are generated by the high-pressure dissolved gas water released by the perforated pipe, and the micro-bubbles are mixed with the sewage containing calcium phosphate microcrystals in the air flotation zone, the gas-water ratio of the air flotation zone is controlled to be 15%, and the hydraulic retention time of the air flotation zone is controlled to be 15 min, so that the calcium phosphate microcrystals and the micro-bubbles are intensively flocculated and rapidly floated to the scum zone (the height ratio of the air flotation zone to the scum zone is 3:1) by air flotation; (3) The calcium phosphate microcrystals gathered in the scum zone are stably suspended in the scum zone under the support of the micro-bubbles, and under the shearing action caused by the stirring and rupture of the micro-bubbles, agglomeration and maturation are performed for 10 h, so that the calcium phosphate crystals with an average particle size of 1500 μm are obtained, then a scum scraper located on the surface of the scum zone is started to scrape the surface scum (calcium phosphate crystal particles) to the scum tank, and the calcium phosphate crystals collected in the scum tank are naturally dried to realize the recovery of phosphorus; then the remaining sewage after the recovery of phosphorus is discharged through the water outlet at the bottom of the air flotation zone.

[0050] In the present embodiment, the outflow phosphorus concentration is stably controlled to be below 0.5 mg / L, and the phosphorus recovery rate is stably controlled to be above 99.9%. The average particle size of the recovered product calcium phosphate crystal particles is 1500 μm, and the water content is below 40%.

[0051] In the description of the present application, it should be understood that the orientations or positional relationships indicated by the terms “center”, “longitudinal”, “transverse”, “length”, “width”, “thickness”, “upper”, “lower”, “front”, “rear”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inner”, “outer”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential” are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements indicated must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0052] In addition, the terms “first” and “second” are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with “first” and “second” can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of “a plurality of” is at least two, such as two, three, etc., unless otherwise specifically limited.

[0053] In the present application, unless specifically defined otherwise, the terms "mounting", "connected", "connecting", "fixed", "fixedly connected", "connection", "fixedly connected", "connected", "fixed", and the like should be construed broadly, for example, can be fixed connection, can be detachable connection, or integral; can be mechanical connection, can be electrical connection or communication with each other; can be directly connected, or indirectly connected through an intermediate medium, can be the internal communication of two elements or the interaction relationship between two elements, unless otherwise specifically defined. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0054] In the present application, unless specifically defined otherwise, the first feature is "on" or "under" the second feature. The first and second features can be in direct contact, or the first and second features can be in indirect contact through an intermediate medium. Moreover, the first feature "above", "over" and "on" the second feature can be that the first feature is directly above or obliquely above the second feature, or only indicates that the first feature is higher than the second feature in horizontal height. The first feature "below", "under" and "under" the second feature can be that the first feature is directly below or obliquely below the second feature, or only indicates that the first feature is lower than the second feature in horizontal height.

[0055] In the present application, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples described in the specification and the features of different embodiments or examples without contradiction.

[0056] Although the embodiments of the present application have been shown and described above, it is understood that the above embodiments are exemplary and cannot be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

Claims

1. A method for improving CaP crystalline phosphorus recovery from wastewater using microbubbles, characterized in that, Includes the following steps: (1) After adjusting the pH of the phosphorus-containing wastewater to alkaline, it is mixed with calcium salt and enters the nucleation reaction zone to carry out the nucleation reaction, resulting in wastewater containing calcium phosphate microcrystals, which then flows into the flotation zone after passing through the guide zone. (2) The high-pressure dissolved air water in the pressure dissolved air tank is pumped into the perforated pipe at the bottom of the air flotation zone. The perforated pipe releases the high-pressure dissolved air water and generates microbubbles. Then, the calcium phosphate microcrystals in the wastewater in the air flotation zone flocculate with the microbubbles and float to the scum zone with the microbubbles. (3) The calcium phosphate microcrystals in the scum zone agglomerate and mature under the shearing action caused by the stirring and rupture of the microbubbles, and obtain calcium phosphate crystals of the target particle size. They are then scraped into the scum tank by the scum scraper to realize phosphorus recovery. The remaining wastewater after phosphorus recovery is discharged through the bottom drain of the flotation zone.

2. The method for improving CaP crystalline phosphorus recovery from wastewater using microbubbles according to claim 1, characterized in that, In step (1), the pH of the phosphorus-containing wastewater is adjusted to 9.0~11.0; And / or, the calcium salt is one or a mixture of two of CaCl2 or Ca(OH)2; And / or, the nucleation reaction is carried out at room temperature for 30 to 60 seconds.

3. The method for improving CaP crystalline phosphorus recovery from wastewater using microbubbles according to claim 1, characterized in that, In step (2), the dissolved gas pressure of the pressure dissolved gas tank is 0.3~0.5 MPa; And / or, the air-to-water volume ratio in the air flotation zone is 10~15%:

1.

4. The method for improving CaP crystalline phosphorus recovery from wastewater using microbubbles according to claim 1, characterized in that, In step (2), the hydraulic residence time of the air flotation zone is 1~20 min.

5. The method for improving CaP crystalline phosphorus recovery from wastewater using microbubbles according to claim 1, characterized in that, In step (3), the maturation time is ≥6 h.

6. A device for improving CaP crystalline phosphorus recovery from wastewater using microbubbles, characterized in that, The apparatus is used to implement the method according to any one of claims 1-5, comprising an alkali storage tank, a calcium salt storage tank, a crystallization flotation tank, a pressure dissolved air tank, a scum scraper, and a scum trough; the crystallization flotation tank has a nucleation reaction zone, a flow guiding zone, and a flotation zone arranged sequentially along its length inside the tank body, and a scum zone is provided at the top of the flotation zone; a plurality of parallel perforated pipes are provided at the bottom of the flotation zone, and the inlet of the perforated pipes is connected to the outlet of the pressure dissolved air tank; the outlet of the alkali storage tank is connected to the bottom inlet of the nucleation reaction zone, and the outlet of the calcium salt storage tank is connected to the bottom inlet of the nucleation reaction zone.

7. The apparatus for improving CaP crystalline phosphorus recovery from wastewater using microbubbles according to claim 6, characterized in that, The slag scraper is connected to the top of the slag area and is used to scrape the slag in the slag area into the slag trough for collection.

8. The apparatus for improving CaP crystalline phosphorus recovery from wastewater using microbubbles according to claim 6, characterized in that, The height ratio of the air flotation zone to the scum zone is 3:1; the length-to-height ratio of the air flotation zone is not less than 4.

9. The apparatus for improving CaP crystalline phosphorus recovery from wastewater using microbubbles according to claim 6, characterized in that, The nucleation reaction zone is separated from the flow guiding zone by a baffle, and the flow guiding zone is separated from the air flotation zone by a perforated plate. The lower middle part of the perforated plate is provided with a number of water holes.

10. The apparatus for improving CaP crystalline phosphorus recovery from wastewater using microbubbles according to claim 6, characterized in that, The nucleation reaction zone is equipped with a stirring mechanism, and the stirring speed of the nucleation reaction zone is 300~500 rpm.

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