A system and treatment method for treating high-phosphorus wastewater and resourcefully utilizing phosphorus elements

Abstract

The present invention relates to a system and a treatment method for treating high-phosphorus wastewater and resourcefully utilizing phosphorus elements. The system includes a bipolar membrane electrodialysis device, a phosphorus precipitator, and a membrane treatment device. Inside the bipolar membrane electrodialysis device, there are successively arranged a cathode, a first bipolar membrane, a main cation exchange membrane, a main anion exchange membrane, a second bipolar membrane, and an anode. Between the first bipolar membrane and the main cation exchange membrane is an alkali chamber, between the main cation exchange membrane and the main anion exchange membrane is a wastewater chamber, between the main anion exchange membrane and the second bipolar membrane is an acid chamber, the outside of the first bipolar membrane is a cathode chamber, and the outside of the second bipolar membrane is an anode chamber; the high-phosphorus wastewater is input into the wastewater chamber, the acid chamber is provided with a phosphoric acid recovery pipe, and the alkali chamber and the wastewater chamber are respectively connected to the phosphorus precipitator through an alkali liquid pipe and a first water production pipe; the phosphorus precipitator is provided with a precipitant inlet for inputting a calcium precipitant or a magnesium precipitant, the concentrated water outlet of the membrane treatment device is connected to the wastewater chamber, and the produced water of the membrane treatment device is reused as reclaimed water.

Description

Technical Field

[0001] The present invention belongs to the technical field of wastewater treatment and resource utilization, and particularly relates to a system and a treatment method for treating high-phosphorus wastewater and resource-utilizing phosphorus elements. Background Art

[0002] The mainstream production process of wood-based activated carbon is the phosphoric acid activation method, which mainly includes several processes such as phosphoric acid impregnation, rinsing, carbonization, and activation. Acidic high-phosphorus wastewater will be generated during the production process. If not strictly controlled, it will cause serious pollution to the surrounding environment. At present, the conventional treatment method for wood-based activated carbon production wastewater is the lime neutralization method. Lime serves as both a precipitant and a neutralizing agent, making it difficult to ensure that the total phosphorus and pH value of the treated water meet the standards simultaneously, and it will generate alkaline waste residues with a relatively high water content. As new pollutants, the waste residues are difficult to dispose of.

[0003] In view of the resource attribute of phosphorus, researchers have tried to develop wastewater treatment technologies that combine phosphorus removal and recovery functions. In Chinese invention patent CN110078040B, a method and a system for recovering struvite from wood-based activated carbon production wastewater are disclosed, which can simultaneously achieve stable compliance of the phosphorus concentration in the effluent and the recovery of high-quality struvite slow-release fertilizer. However, the composition of wood-based activated carbon production wastewater is not very stable. When there is less nitrogen element in the wastewater, additional nitrogen sources need to be added to produce struvite. And currently, struvite is mainly used as a fertilizer or industrial raw material, with a low price. Sometimes, adding nitrogen sources will result in too high treatment costs. Therefore, how to efficiently and low-costly treat acid high-phosphorus wastewater and achieve resource utilization is a problem faced by those skilled in the art. Summary of the Invention

[0004] In view of the above problems, the present invention provides a system and a treatment method for treating high-phosphorus wastewater and resource-utilizing phosphorus elements. The wood-based activated carbon production wastewater is treated by a bipolar membrane electrodialysis device, hydroxides and ammonia water are formed in the alkali chamber, and phosphoric acid is formed in the acid chamber, thereby reducing the content of pollutants in the wastewater. The phosphoric acid in the acid chamber is recovered and utilized as a product. According to the nitrogen content of the treated wastewater, hydroxyapatite or struvite is produced under the action of a calcium / magnesium precipitant.

[0005] In the first aspect, the system for treating high-phosphorus wastewater and resource-utilizing phosphorus elements includes a bipolar membrane electrodialysis device, a phosphorus precipitator, and a membrane treatment device. In the bipolar membrane electrodialysis device, a cathode, a first bipolar membrane, a main cation exchange membrane, a main anion exchange membrane, a second bipolar membrane, and an anode are sequentially arranged. The alkali chamber is located between the first bipolar membrane and the main cation exchange membrane, the wastewater chamber is located between the main cation exchange membrane and the main anion exchange membrane, the acid chamber is located between the main anion exchange membrane and the second bipolar membrane, the cathode chamber is outside the first bipolar membrane, and the anode chamber is outside the second bipolar membrane;

[0006] The high-phosphorus wastewater is input into the wastewater chamber. The acid chamber is provided with a phosphoric acid recovery pipe. The alkali chamber and the wastewater chamber are respectively connected to the phosphorus precipitator through an alkali liquid pipe and a first water production pipe, and the obtained alkali liquid and the treated wastewater are input into the phosphorus precipitator for further treatment;

[0007] The phosphorus precipitator is provided with a precipitant inlet for inputting a calcium precipitant or a magnesium precipitant. The phosphorus precipitator is connected to the membrane treatment device through a second water production pipe. The concentrated water outlet of the membrane treatment device is connected to the wastewater chamber, and the produced water of the membrane treatment device is reused as reclaimed water.

[0008] Optionally, the system for treating high-phosphorus wastewater and resource-utilizing phosphorus elements further includes a wastewater tank. The outlet of the wastewater tank is connected to the first inlet of the wastewater chamber to input the high-phosphorus wastewater into the wastewater chamber. The inlet of the wastewater tank is connected to the first outlet of the wastewater chamber, so as to form a cycle between the wastewater chamber and the wastewater tank.

[0009] Optionally, the system for treating high-phosphorus wastewater and resource-utilizing phosphorus elements further includes a water tank, an alkali water tank and an acid water tank. The water tank is connected to the cathode chamber and the anode chamber through pipelines. The alkali water tank is connected to the alkali chamber through a pipeline; the acid water tank is connected to the acid chamber through a pipeline.

[0010] Optionally, the membrane treatment device is selected from one or a combination of a nanofiltration membrane module and a reverse osmosis membrane module, and the membrane treatment device is reasonably selected according to the wastewater quality and the produced water quality of the phosphorus precipitator;

[0011] The concentrated water outlet of the membrane treatment device is connected to the second inlet of the wastewater chamber.

[0012] Optionally, the first inlet of the wastewater chamber is arranged at the bottom of the wastewater chamber, and the first outlet is arranged at the top of the wastewater chamber. The wastewater input from the wastewater tank passes through the wastewater chamber from bottom to top; a plurality of layers of baffle members are arranged in the wastewater chamber from bottom to top. The baffle members are baffle plates or baffle membranes. The baffle plates and the baffle membranes are arranged up and down in sequence, so that there is a baffle plate between two baffle membranes;

[0013] The starting end of each baffle membrane is fixed on the first long side surface, and the end extends towards the second long side surface and leaves a first opening between the end and the second long side surface to allow water flow to pass through; the starting end of each baffle plate is fixed on the second long side surface, and the end extends towards the first long side surface and leaves a second opening between the end and the first long side surface to allow water flow to pass through, that is, the first opening is close to the second long side surface, and the second opening is close to the first long side surface, so that the water flow in the wastewater chamber flows back and forth along the baffle members in the width direction of the bipolar membrane electrodialysis device.

[0014] Further optionally, the baffle plate is a solid plate; the baffle membrane includes a sub-cation exchange membrane close to the main cation exchange membrane and a sub-anion exchange membrane close to the main anion exchange membrane. The sub-cation exchange membrane and the sub-anion exchange membrane are in the same plane and are seamlessly connected in the middle of the wastewater chamber.

[0015] Optionally, the alkali chamber includes a first stirrer near the first bipolar membrane and a second stirrer near the main cation exchange membrane, which are used to agitate the water near the first bipolar membrane and the main cation exchange membrane to prevent hydroxide precipitation from adhering to the membrane material;

[0016] A sedimentation hopper is provided in the lower middle part of the alkali chamber, and the cross-sectional area of the sedimentation hopper is smaller than that of the alkali chamber; a inclined plate area is provided in the upper part of the alkali chamber, and the inclined plate area includes a number of parallel inclined plates, and the cross-sectional area of the inclined plate area is equal to that of the alkali chamber.

[0017] Optionally, the ratio of the cross-sectional area of the sedimentation hopper to that of the alkali chamber is (0.2 - 0.6):1, so as to prevent the hydroxide precipitation in the lower part of the alkali chamber from returning to the upper part of the alkali chamber;

[0018] A pipeline is connected to the bottom of the sedimentation hopper to discharge the sediment slurry out of the alkali chamber. The sedimentation hopper can be mobile, that is, it can move in the alkali chamber to receive more sediments slipping from the inclined plate area.

[0019] In a second aspect, the present invention also provides a treatment method for treating high-phosphorus wastewater and resourcefully utilizing phosphorus elements, including the following steps:

[0020] (1) Input the high-phosphorus wastewater in the wastewater tank into the wastewater chamber, and form a circulation loop between the wastewater tank and the wastewater chamber;

[0021] (2) After the bipolar membrane electrodialysis device is filled with wastewater, power is supplied to the cathode and the anode. The PO4 in the wastewater in the wastewater chamber 3- passes through the main anion exchange membrane and enters the acid chamber. The H generated after electrolyzing water in the anode chamber + also enters the acid chamber through the second bipolar membrane. PO4 3- and H + generate phosphoric acid;

[0022] At the same time, NH4 in the wastewater in the wastewater chamber + and metal ions pass through the main cation exchange membrane and enter the alkali chamber. The OH generated after electrolyzing water in the cathode chamber - also enters the alkali chamber through the first bipolar membrane. NH4 + , metal ions and OH - generate ammonia water and hydroxides;

[0023] (3) After the wastewater treatment in the bipolar membrane electrodialysis device is completed, the phosphoric acid in the acid chamber is discharged from the acid chamber through the phosphoric acid recovery pipe for recycling; the alkali solution in the alkali chamber and the wastewater in the wastewater chamber are both discharged into the phosphorus precipitator, and a calcium precipitant or a magnesium precipitant is added to the phosphorus precipitator. The wastewater reacts with ammonia water and hydroxides to generate hydroxyapatite or struvite for recycling;

[0024] (4) The produced water obtained from the phosphorus precipitator is input into the membrane treatment device. After membrane treatment, the produced water is obtained as reclaimed water for reuse, and the concentrated water obtained is returned to the wastewater chamber for further treatment.

[0025] Optionally, in step (1), the water tank fills the cathode chamber and the anode chamber with water, the alkaline water tank fills the alkaline chamber with water, and the acidic water tank fills the acidic chamber with water.

[0026] Optionally, in step (2), the current density of the bipolar membrane electrodialysis device is 2 - 8 mA / cm 2 .

[0027] Optionally, in step (3), when the N / P molar ratio of NH4 + in the alkaline chamber to PO4 3- in the wastewater chamber is not greater than 1, or when the PO4 3- in the wastewater chamber is lower than 2 mmol / L, it represents that the electrodialysis treatment is completed, and the power supply to the bipolar membrane electrodialysis device is stopped.

[0028] Optionally, in step (3), the dosage of the calcium precipitant or magnesium precipitant is to maintain the Ca / P or Mg / P inside the phosphorus precipitator at 1.2 - 1.5, and the hydraulic retention time of the phosphorus precipitator is 0.5 - 2 h;

[0029] The phosphorus precipitator is selected from a stirred tank or a fluidized bed. When using a stirred tank, the rotation speed of the stirred tank is 120 - 180 rpm; when using a fluidized bed, the upward flow velocity of the fluidized bed is 10 - 30 mm / s, and the reflux ratio is 1 - 4.

[0030] Optionally, in step (3), according to the different N / P molar ratios of NH4 + in the alkaline chamber to PO4 3- in the wastewater chamber, different precipitants are used to obtain different products. Specifically, when the N / P molar ratio of the wastewater is less than 0.3, the nitrogen element in the wastewater is insufficient, and the precipitants are calcium oxide and calcium chloride, and the product of the phosphorus precipitator is hydroxyapatite; when the N / P molar ratio of the wastewater is not less than 0.3 and not greater than 1.0, the precipitants are magnesium oxide and magnesium chloride, and the product of the phosphorus precipitator is struvite.

[0031] The membrane treatment conditions in step (4) are adjusted according to the water quality of the produced water obtained from the phosphorus precipitator. Brief Description of the Drawings

[0032] Figure 1 It is a schematic structural diagram of the system for treating high - phosphorus wastewater and resource - utilizing phosphorus elements in Example 1;

[0033] Figure 2 It is a schematic structural diagram of the length direction of the wastewater chamber in Example 2;

[0034] Figure 3 For Figure 2Cross-sectional view of A-A';

[0035] Figure 4 It is a schematic structural diagram of the alkali chamber in Example 3.

[0036] In the attached drawings, 1 - bipolar membrane electrodialysis device, 2 - phosphorus precipitator, 3 - membrane treatment device, 4 - cathode, 5 - first bipolar membrane, 6 - main cation exchange membrane, 7 - main anion exchange membrane, 8 - second bipolar membrane, 9 - alkali chamber, 10 - wastewater chamber, 11 - acid chamber, 12 - cathode chamber, 13 - anode chamber, 14 - wastewater tank, 15 - first inlet, 16 - first outlet, 17 - baffle plate, 18 - baffle membrane, 19 - first opening, 20 - second opening, 21 - auxiliary cation exchange membrane, 22 - auxiliary anion exchange membrane, 23 - first stirrer, 24 - second stirrer, 25 - anode, 26 - precipitation hopper, 27 - inclined plate area, 28 - rotating disk, 29 - rotator, 30 - rotating shaft, 31 - connecting seat. Detailed implementation manners

[0037] Example 1

[0038] A system for treating high-phosphorus wastewater and resourcefully utilizing phosphorus elements provided in this example, as Figure 1 shown, includes a bipolar membrane electrodialysis device 1, a phosphorus precipitator 2 and a membrane treatment device 3. Inside the bipolar membrane electrodialysis device 1, there are successively arranged a cathode 4, a first bipolar membrane 5, a main cation exchange membrane 6, a main anion exchange membrane 7, a second bipolar membrane 8 and an anode 25. Between the first bipolar membrane 5 and the main cation exchange membrane 6 is an alkali chamber 9, between the main cation exchange membrane 6 and the main anion exchange membrane 7 is a wastewater chamber 10, between the main anion exchange membrane 7 and the second bipolar membrane 8 is an acid chamber 11. Outside the first bipolar membrane 5 is a cathode chamber 12, and outside the second bipolar membrane 8 is an anode chamber 13;

[0039] The high-phosphorus wastewater is input into the wastewater chamber 10. The acid chamber 11 is provided with a phosphoric acid recovery pipe. The alkali chamber 9 and the wastewater chamber 10 are respectively connected to the phosphorus precipitator 2 through an alkali solution pipe and a first water production pipe, and the obtained alkali solution and treated wastewater are input into the phosphorus precipitator 2 for further treatment;

[0040] The phosphorus precipitator 2 is provided with a precipitant port for inputting a calcium precipitant or a magnesium precipitant. The phosphorus precipitator 2 is connected to the membrane treatment device 3 through a second water production pipe. The concentrated water outlet of the membrane treatment device 3 is connected to the wastewater chamber 10, and the produced water of the membrane treatment device 3 is reused as reclaimed water.

[0041] The bipolar membrane electrodialysis device 1 is a cube. The two opposite side faces in the width direction of the bipolar membrane electrodialysis device 1 are long side faces, and the two opposite side faces in the length direction are wide side faces. The cathode 4 and the anode 25 are respectively close to the two wide side faces. Along the length direction of the bipolar membrane electrodialysis device 1, there are successively arranged a cathode chamber, an alkali chamber 9, a wastewater chamber 10, an acid chamber 11 and an anode chamber 13.

[0042] The system for treating high-phosphorus wastewater and resourcefully utilizing phosphorus also includes a wastewater tank 14. The outlet of the wastewater tank 14 is connected to the first inlet 15 of the wastewater chamber 10 to input high-phosphorus wastewater into the wastewater chamber 10. The inlet of the wastewater tank 14 is connected to the first outlet 16 of the wastewater chamber 10, so as to form a cycle between the wastewater chamber 10 and the wastewater tank 14.

[0043] The system for treating high-phosphorus wastewater and resourcefully utilizing phosphorus also includes a water tank, an alkaline water tank and an acidic water tank. The water tank is connected to the cathode chamber 12 and the anode chamber 13 through pipelines, so as to form a circulating water flow between the cathode chamber 12 and the water tank and a circulating water flow between the anode chamber 13 and the water tank; the alkaline water tank is connected to the alkaline chamber 9 through a pipeline, so as to form a circulating water flow between the alkaline chamber 9 and the alkaline water tank; the acidic water tank is connected to the acidic chamber 11 through a pipeline, so as to form a circulating water flow between the acidic chamber 11 and the acidic water tank.

[0044] Ordinary water is filled in the water tank, the alkaline water tank and the acidic water tank, or ammonia water is filled in the alkaline water tank, phosphoric acid solution is filled in the acidic water tank, and sodium sulfate solution is filled in the water tank.

[0045] The positive film surface of the first bipolar membrane 5 faces the cathode chamber 12, and the negative film surface faces the alkaline chamber 9; the positive film surface of the second bipolar membrane 8 faces the acidic chamber 11, and the negative film surface faces the anode chamber 13.

[0046] High-phosphorus wastewater is input into the wastewater chamber 10 of the electrolytic cell of the bipolar membrane electrodialysis device 1. The cathode 4 is connected to the negative pole of an external power supply, and the anode 25 is connected to the positive pole of the external power supply for electrodialysis. The high-phosphorus wastewater contains PO4 3- , NH4 + and Na + and other metal ions. Under the action of an electric current, metal ions such as NH4 + and Na + permeate through the main cation exchange membrane 6 into the alkaline chamber 9, and PO4 3- permeates through the main anion exchange membrane 7 into the acidic chamber 11, greatly reducing the pollutants in the wastewater. The cathode 4 is located in the cathode chamber 12. The water in the cathode chamber 12 is ionized under the action of an electric current to generate H + and OH - . H + cannot permeate through the first bipolar membrane 5 and remains in the cathode chamber 12. OH - permeates through the first bipolar membrane 5 into the alkaline chamber 9 and forms ammonia water and hydroxides with metal ions such as NH4 + and Na + . The anode 25 is located in the anode chamber 13. The water in the anode chamber 13 is also ionized under the action of an electric current to generate H + and OH - . OH -It cannot stay in the anode chamber 13 through the second bipolar membrane 8, and H + enters the acid chamber 11 through the second bipolar membrane 8 and combines with PO4 3- to form phosphoric acid. The phosphoric acid is discharged through the phosphoric acid recovery pipe and can be reused in the production of wood-based activated carbon.

[0047] One end of the first water production pipe is connected to the second outlet of the wastewater chamber 10, and the other end is connected to the phosphorus precipitator 2.

[0048] The wastewater treated in the wastewater chamber 10 and the alkali produced in the alkali chamber 9 are input into the phosphorus precipitator 2, and then a calcium precipitant or a magnesium precipitant is input, and hydroxyapatite or struvite is produced by reaction for recycling.

[0049] The membrane treatment device 3 is a nanofiltration membrane module, and the concentrated water outlet of the membrane treatment device 3 is connected to the second inlet of the wastewater chamber 10.

[0050] The membrane treatment device 3 is used to deeply remove cations and anions in the produced water of the phosphorus precipitator 2 to produce recycled water that can meet production or cleaning requirements, and the concentrated water of the membrane treatment device 3 returns to the wastewater chamber 10 for re-treatment and acid-base production.

[0051] The first inlet 15 of the wastewater chamber 10 is provided at the bottom of the wastewater chamber 10, and the first outlet 16 is provided at the top of the wastewater chamber 10. The wastewater input from the wastewater tank 14 passes through the wastewater chamber 10 from bottom to top; the second outlet and the second inlet are provided at the bottom of the wastewater chamber 10 to facilitate draining water to the phosphorus precipitator 2 and facilitating water inlet to the wastewater chamber 10.

[0052] The water outlet of the alkali chamber 9 is provided at the top of the alkali chamber 9, and the water inlet is provided at the bottom of the alkali chamber 9, so that an upward water flow is formed inside the alkali chamber 9.

[0053] Example 2

[0054] A system for treating high-phosphorus wastewater and resource-utilizing phosphorus elements provided in this example is the same as that in Example 1, except that, as Figures 2 - 3 shown, several layers of baffle members are arranged from bottom to top in the wastewater chamber 10, and both sides of the baffle members are in contact with the main cation exchange membrane and the main anion exchange membrane to prevent wastewater from flowing out from both sides of the baffle members;

[0055] The baffle members are baffle plates 17 or baffle membranes 18, and the baffle plates 17 and the baffle membranes 18 are arranged vertically in sequence, so that there is a baffle plate 17 between two baffle membranes 18;

[0056] The starting end of each baffle membrane 18 is fixed on the first long side surface, and the ending end extends towards the second long side surface with a first opening 19 left between it and the second long side surface to allow water flow through; the starting end of each baffle plate 17 is fixed on the second long side surface, and the ending end extends towards the first long side surface with a second opening 20 left between it and the first long side surface to allow water flow through. That is, the first opening 19 is close to the second long side surface, and the second opening 20 is close to the first long side surface, so that the water flow in the wastewater chamber 10 flows back and forth along the baffle member in the width direction of the bipolar membrane electrodialysis device 1, increasing mass transfer and improving the treatment efficiency.

[0057] The baffle structure can be horizontal or inclined, that is, inclined towards the acid chamber or the alkali chamber.

[0058] The baffle plate 17 is a solid plate; the baffle membrane 18 includes a sub-cation exchange membrane 21 close to the main cation exchange membrane 6 and a sub-anion exchange membrane 22 close to the main anion exchange membrane 7. The sub-cation exchange membrane 21 and the sub-anion exchange membrane 22 are in the same plane and are seamlessly connected in the middle of the wastewater chamber 10.

[0059] Traditional electrodialysis uses an electric current to make cations and anions in water move in different directions, with relatively low treatment efficiency for wastewater, long treatment time, and high power consumption. In the present invention, a number of baffle members are arranged in the wastewater chamber 10, so that the wastewater entering the bottom of the wastewater chamber 10 rises back and forth along the baffle member in the width direction of the wastewater chamber 10, extending the hydraulic retention time, and finally returning to the wastewater tank 14 through the first outlet 16 to form a circulating flow. When the wastewater flows along the baffle membrane 18 in the present invention, it can perform cation and anion exchange through the baffle membrane 18, that is, PO4 3- passes through the sub-anion exchange membrane 22, NH4 + and metal ions such as Na + pass through the sub-cation exchange membrane 21, and cooperate with the main anion exchange membrane 7 and the main cation exchange membrane 6 to jointly play a role and improve the efficiency. The baffle plates 17 and the baffle membranes 18 are arranged in sequence, which not only ensures the baffle effect but also saves membrane materials and reduces costs.

[0060] Example 3

[0061] A system for treating high-phosphorus wastewater and resource-utilizing phosphorus elements provided in this example is the same as that in Example 1, except that, as Figure 4 shown, the alkali chamber 9 includes a first stirrer 23 close to the first bipolar membrane 5 and a second stirrer 24 close to the main cation exchange membrane 6, which are used to agitate the water bodies close to the first bipolar membrane 5 and the main cation exchange membrane 6 to avoid hydroxide precipitation adhering to the membrane materials;

[0062] A sedimentation hopper 26 is provided in the middle and lower part of the alkali chamber 9, and an inclined plate area 27 is provided in the upper part of the alkali chamber 9. The inclined plate area 27 includes a number of parallel inclined plates. The cross-sectional areas of both the sedimentation hopper 26 and the inclined plate area 27 are smaller than the cross-sectional area of the alkali chamber 9.

[0063] The ratio of the cross-sectional area of the sedimentation hopper 26 to the cross-sectional area of the alkali chamber 9 is 0.2:1, so as to prevent the hydroxide precipitate in the lower part of the alkali chamber 9 from returning to the upper part of the alkali chamber 9.

[0064] A pipeline is connected to the bottom of the sedimentation hopper 26 to discharge the precipitate slurry out of the alkali chamber 9. The sedimentation hopper 26 is movable, that is, it can move within the alkali chamber 9 to receive more precipitates sliding down from the inclined plate area 27.

[0065] Since the wastewater may contain a small amount of calcium and magnesium ions, calcium hydroxide and magnesium hydroxide precipitates are formed in the alkali chamber 9. The fine precipitates adhere to the first bipolar membrane 5 and the main cation exchange membrane 6, contaminating the membrane material and affecting the efficiency of electrodialysis. In the present invention, the first stirrer 23 and the second stirrer 24 agitate the water near the first bipolar membrane 5 and the main cation exchange membrane 6 to avoid fouling on the membrane surface; since the overall flow direction of the wastewater in the wastewater chamber 10 is also from bottom to top, a large amount of calcium and magnesium ions penetrate into the alkali chamber 9 in the lower part of the alkali chamber 9 to form fine particulate precipitates. Under the action of the water flow in the alkali chamber 9, the small particulate precipitates move upward and gradually grow larger during the upward movement. When passing through the inclined plate area 27, the larger particulate precipitates sink into the lower mud hopper.

[0066] The first stirrer 23 and the second stirrer 24 have the same structure, including a rotating disk 28 and a number of rotators 29 evenly distributed on the side surface of the rotating disk 28. One side of the rotator 29 is a stirring part composed of a number of blades, and the other side is a connecting seat 31. The rotator 29 is fixed on the rotating disk 28 through the connecting seat 31. A small motor is provided in the connecting seat 31 to control the rotation of the stirring part.

[0067] The side of the first stirrer 23 with the rotator 29 faces the first bipolar membrane 5, and the side of the second stirrer 24 with the rotator 29 faces the main cation exchange membrane 6. Both ends of a rotating shaft 30 are respectively connected to the centers of the rotating disks 28 of the two stirrers, and can drive the two rotating disks 28 to rotate simultaneously at the same speed. The driving of the rotating shaft 30 can adopt conventional technical means.

[0068] The inclined plates in the inclined plate area can avoid the two rotating disks.

[0069] Example 4

[0070] This example provides a treatment method for treating high-phosphorus wastewater and resourcefully utilizing phosphorus elements. It is implemented using the device of Example 1. The wastewater quality is the wastewater from woody activated carbon production, and the PO4 in the wastewater 3-The concentration of P is 5500 mg / L (177.4 mmol / L), and the concentration of NH4 + (in terms of N) is 240 mg / L (17.1 mmol / L).

[0071] The treatment method includes the following steps:

[0072] (1) Input the high-phosphorus wastewater in the wastewater tank into the wastewater chamber, and form a circulation loop between the wastewater tank and the wastewater chamber; the water tank fills the cathode chamber and the anode chamber with water, the alkali water tank fills the alkali chamber with water, and the acid water tank fills the acid chamber with water;

[0073] (2) After the bipolar membrane electrodialysis device is filled with wastewater, power is supplied to the cathode and the anode. The PO4 3- in the wastewater in the wastewater chamber permeates through the main anion exchange membrane and enters the acid chamber. The H + generated after electrolyzing water in the anode chamber also enters the acid chamber through the second bipolar membrane. PO4 3- and H + react to form phosphoric acid;

[0074] Meanwhile, NH4 + and metal ions in the wastewater in the wastewater chamber permeate through the main cation exchange membrane and enter the alkali chamber. The OH - generated after electrolyzing water in the cathode chamber also enters the alkali chamber through the first bipolar membrane. NH4 + , metal ions and OH - react to form ammonia water and hydroxides; the current density of the bipolar membrane electrodialysis device is 8 mA / cm 2 , and the treatment time is 14 h;

[0075] (3) When the N / P mole ratio of NH4 + in the alkali chamber and PO4 3- in the wastewater chamber is 0.97, it represents that the electrodialysis treatment is completed. Stop supplying power to the bipolar membrane electrodialysis device, and the wastewater treatment in the bipolar membrane electrodialysis device is completed; at this time, the concentration of PO4 3- (in terms of P) in the wastewater chamber drops to 511.5 mg / L (16.5 mmol / L), and the concentration of NH4 + (in terms of N) in the alkali chamber rises to 225.0 mg / L (16.1 mmol / L);

[0076] The phosphoric acid (7.8 wt%) in the acid chamber is discharged from the acid chamber through the phosphoric acid recovery pipe for recycling; the alkali solution in the alkali chamber and the wastewater in the wastewater chamber are both discharged into the phosphorus precipitator. A magnesium precipitant is added to the phosphorus precipitator, and the wastewater reacts with ammonia water and hydroxides to form struvite for recycling;

[0077] Maintain the Mg / P inside the phosphorus precipitator at 1.2, and the hydraulic retention time of the phosphorus precipitator is 2 h; the phosphorus precipitator is a conventional fluidized bed with an upward flow velocity of 30 mm / s and a reflux ratio of 1.0, and struvite products with a purity of 92.3% can be recovered;

[0078] (4) The produced water obtained from the phosphorus precipitator is input into the membrane treatment device. After membrane treatment, the produced water is used as reclaimed water for reuse, and the concentrated water obtained is returned to the wastewater chamber for further treatment.

[0079] Example 5

[0080] This example provides a treatment method for treating high-phosphorus wastewater and resource-utilizing phosphorus elements. It is implemented using the device of Example 1, and the method is the same as that of Example 4, except that the wastewater quality is the wastewater from woody activated carbon production, and the concentration of PO4 3- (calculated as P) is 900 mg / L (29 mmol / L), and the concentration of NH4 + (calculated as N) is 46 mg / L (3.3 mmol / L).

[0081] In step (2), the current density of the bipolar membrane electrodialysis device is 2 mA / cm 2 , and the treatment time is 6 h;

[0082] In step (3), when the molar ratio of NH4 + in the alkali chamber to PO4 3- in the wastewater chamber is 0.11, it represents the completion of electrodialysis treatment, and the power supply to the bipolar membrane electrodialysis device is stopped, and the wastewater treatment in the bipolar membrane electrodialysis device is completed; at this time, the concentration of PO4 3- (calculated as P) in the wastewater chamber drops to 840 mg / L (27.1 mmol / L), and the concentration of NH4 + (calculated as N) in the alkali chamber rises to 40.2 mg / L (2.9 mmol / L);

[0083] Maintain the Ca / P inside the phosphorus precipitator at 1.5:1, and the hydraulic retention time of the phosphorus precipitator is 2 h;

[0084] The phosphorus precipitator is a stirred kettle with a rotation speed of 120 rpm, and hydroxyapatite products with a purity of 89.8% can be recovered.

[0085] Example 6

[0086] This example provides a treatment method for treating high-phosphorus wastewater and resource-utilizing phosphorus elements. It is implemented using the device of Example ②, and the method is the same as that of Example 4, and the electrodialysis treatment time in step (2) is shortened to 10.5 h.

Claims

1. A system for treating high-phosphorus wastewater and recycling phosphorus, characterized in that: The invention comprises a bipolar membrane electrodialysis device, a phosphorus precipitator and a membrane treatment device. The bipolar membrane electrodialysis device is provided with a cathode, a first bipolar membrane, a main cation exchange membrane, a main anion exchange membrane, a second bipolar membrane and an anode in sequence. The base chamber is between the first bipolar membrane and the main cation exchange membrane, the wastewater chamber is between the main cation exchange membrane and the main anion exchange membrane, the acid chamber is between the main anion exchange membrane and the second bipolar membrane, the cathode chamber is outside the first bipolar membrane, and the anode chamber is outside the second bipolar membrane. High-phosphorus wastewater is fed into the wastewater chamber. The acid chamber is equipped with a phosphoric acid recovery pipe. The alkali chamber and the wastewater chamber are connected to the phosphorus precipitator through the alkali liquid pipe and the first water production pipe respectively. The obtained alkali liquid and treated wastewater are fed into the phosphorus precipitator for further treatment. The phosphorus precipitator is provided with a precipitant port for inputting a calcium precipitant or a magnesium precipitant. The phosphorus precipitator is connected to the membrane treatment device through a second water production pipe. The concentrated water outlet of the membrane treatment device is connected to the wastewater chamber. The water produced by the membrane treatment device is reused as reclaimed water. Several layers of baffle components are arranged from bottom to top in the wastewater chamber. The baffle components are baffle plates or baffle membranes. The baffle plates and baffle membranes are arranged in sequence up and down so that there is a baffle plate between two baffle membranes. The baffle is a solid plate; the baffle membrane includes a secondary cation exchange membrane close to the main cation exchange membrane and a secondary anion exchange membrane close to the main anion exchange membrane. The secondary cation exchange membrane and the secondary anion exchange membrane are in the same plane and seamlessly connected in the middle of the wastewater chamber.

2. The system for treating high-phosphorus wastewater and recycling phosphorus according to claim 1, characterized in that: It also includes a wastewater tank, the outlet of the wastewater tank is connected to the first inlet of the wastewater chamber, the high-phosphorus wastewater is input into the wastewater chamber, and the inlet of the wastewater tank is connected to the first outlet of the wastewater chamber, so that a circulation is formed between the wastewater chamber and the wastewater tank; It also includes a water tank, an alkaline water tank and an acid water tank. The water tank is connected to the cathode chamber and the anode chamber through a pipeline, the alkaline water tank is connected to the alkali chamber through a pipeline, and the acid water tank is connected to the acid chamber through a pipeline.

3. The system for treating high-phosphorus wastewater and recycling phosphorus according to claim 1, characterized in that: The membrane treatment device is selected from a nanofiltration membrane assembly, a reverse osmosis membrane assembly, or a combination of the two; The concentrated water outlet of the membrane treatment device is connected to the second inlet of the wastewater chamber.

4. The system for treating high-phosphorus wastewater and recycling phosphorus according to claim 1, characterized in that: The first inlet of the wastewater chamber is arranged at the bottom of the wastewater chamber, and the first outlet is arranged at the top of the wastewater chamber; The starting end of each baffle membrane is fixed on the first long side, and the end extends to the second long side with a first opening between the baffle and the second long side; the starting end of each baffle plate is fixed on the second long side, and the end extends to the first long side with a second opening between the baffle and the first long side, so that the water flow in the wastewater chamber is baffled and flows back and forth along the baffle component in the width direction of the bipolar membrane electrodialysis device.

5. The system for treating high-phosphorus wastewater and recycling phosphorus according to claim 1, characterized in that: The alkaline chamber includes a first agitator near the first bipolar membrane and a second agitator near the main cation exchange membrane, which are used to stir the water near the first bipolar membrane and the main cation exchange membrane to prevent hydroxide precipitation from adhering to the membrane material; A sedimentation hopper is provided in the lower middle part of the alkali chamber, and the cross-sectional area of the sedimentation hopper is smaller than the cross-sectional area of the alkali chamber; an inclined plate area is provided in the upper part of the alkali chamber, and the inclined plate area includes several inclined plates arranged side by side, and the cross-sectional area of the inclined plate area is equal to the cross-sectional area of the alkali chamber.

6. A method for treating high-phosphorus wastewater and recycling phosphorus, characterized in that: The method is implemented using the system for treating high-phosphorus wastewater and recycling phosphorus according to claim 2, and includes the following steps: (1) The high-phosphorus wastewater in the wastewater tank is input into the wastewater chamber, and a circulation loop is formed between the wastewater tank and the wastewater chamber; (2) After the bipolar membrane electrodialysis device is filled with wastewater, the cathode and anode are energized, and the PO4 3- Through the main anion exchange membrane, it enters the acid chamber, and the H generated by electrolysis of water in the anode chamber + PO4 also enters the acid chamber through the second bipolar membrane 3- With H + Produces phosphoric acid; At the same time, the NH4 + and metal ions pass through the main cation exchange membrane and enter the alkali chamber. The OH generated by electrolysis of water in the cathode chamber - NH4 also enters the base chamber through the first bipolar membrane + , metal ions and OH - Produces ammonia and hydroxide; (3) After the wastewater treatment in the bipolar membrane electrodialysis device is completed, the phosphoric acid in the acid chamber is discharged from the acid chamber through the phosphoric acid recovery pipe for recycling; the alkali liquor in the alkali chamber and the wastewater in the wastewater chamber are discharged into the phosphorus precipitator, and a calcium precipitant or a magnesium precipitant is added to the phosphorus precipitator. The wastewater reacts with ammonia water and hydroxide to form hydroxyapatite or struvite, which is recycled; (4) The produced water from the phosphorus precipitator is input into the membrane treatment device, and after membrane treatment, the produced water is reused as reclaimed water, and the concentrated water is returned to the wastewater chamber for further treatment.

7. The processing method according to claim 6, characterized in that In step (3), when the NH4 + PO4 in the wastewater chamber 3- The N / P molar ratio is not greater than 1, or the wastewater chamber PO4 3- When the concentration is lower than 2 mmol / L, the electrodialysis treatment is completed and the power supply to the bipolar membrane electrodialysis device is stopped; the amount of calcium precipitant or magnesium precipitant is to maintain the Ca / P or Mg / P inside the phosphorus precipitator at 1.2-1.

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8. The processing method according to claim 7, characterized in that: When the N / P molar ratio of the wastewater is less than 0.3, the nitrogen element in the wastewater is insufficient, the precipitants are calcium oxide and calcium chloride, and the product of the phosphorus precipitator is hydroxyapatite.

9. The processing method according to claim 7, characterized in that: When the N / P molar ratio of the wastewater is not less than 0.3 and not greater than 1.0, the precipitants are magnesium oxide and magnesium chloride, and the product of the phosphorus precipitator is struvite.

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