Device and method for removing microplastics in water by combined process of flocculation and electroflotation

Abstract

The present invention discloses a device and method for removing microplastics in water by combining flocculation and electroflotation. The device includes an electroflotation tank, a plurality of cyclone tanks, and an annular flocculation tank. The electroflotation tank is located in the middle of the flocculation tank, and the cyclone tanks are located between the electroflotation tank and the flocculation tank and are arranged at equal intervals. The method includes the following steps: S1, electroflotation treatment; S2, cyclone treatment: S2-1, multi-stage cyclone treatment; S2-2, classification cyclone treatment; S3, flocculation treatment. By integrating and optimizing the electroflotation tank, cyclone tanks and flocculation tank, the present invention realizes the fast and efficient treatment of microplastics in sewage. First, the electroflotation destroys the negative charge stability of microplastic colloidal particles, resulting in a reduction in the surface charge of microplastics and the formation of micro-flocs, which is more conducive to the subsequent use of PAC to achieve colloid destabilization and flocculation sedimentation to remove microplastics, and can effectively remove microplastic particle pollutants of different sizes.

Description

Technical Field

[0001] The present invention relates to the technical field of water microplastic treatment, and in particular to a device and method for removing microplastics in water by combining flocculation and electrical flotation. Background Art

[0002] Microplastics refer to plastic particles with a size of less than 5mm, which usually come from the crushing and degradation process of plastics. They have the characteristics of strong adsorption capacity, difficulty in degradation and sustainable accumulation. At present, microplastics are widely present in water bodies, atmosphere and soil. If these microplastics continue to exist, they will cause serious ecological risks and endanger human health and the natural environment.

[0003] However, current research mainly focuses on the pollution status and characteristics, distribution characteristics, and biological hazards of microplastics. In addition, the removal processes for microplastics in sewage generally have limitations such as high energy consumption, narrow application range, and unstable treatment effects.

[0004] At present, the treatment technologies for microplastics mainly include physical separation, chemical degradation and biodegradation. Physical separation mainly separates microplastics from other substances by screening, filtration and other methods, and is often used for the treatment of microplastics in water bodies such as sewage and seawater. Physical separation technology can quickly separate microplastics from water bodies, and is simple to operate and easy to implement. However, this method has low removal efficiency and is difficult to remove nano-level microplastics. Chemical degradation uses chemical reagents to further decompose microplastics into small molecules under specific conditions, and is often used for the treatment of microplastics in solid waste and wastewater. This method can completely decompose microplastics into small molecules and is suitable for the treatment of various types of microplastics. However, the cost of using chemical agents is high, and improper use may cause secondary pollution to the environment. Biodegradation is an environmentally friendly and green treatment method that uses microorganisms to degrade microplastics into gas, water and substances that are harmless to organisms. This method is mostly used for the treatment of microplastics in soil and water bodies. The biodegradation method has little impact on the environment during the decomposition of microplastics, but the degradation rate is relatively slow, and the degradation process is greatly affected by environmental factors and is difficult to accurately control.

[0005] However, a single treatment method or process is usually difficult to achieve a good treatment effect. Therefore, it is urgent to develop a process for treating microplastic wastewater that is low-cost, has a wide range of applications, and can effectively and stably remove microplastics in a long term. Summary of the invention

[0006] In response to the above-mentioned problems, the present invention provides a device and method for removing microplastics in water by combining flocculation and electrical flotation processes.

[0007] The technical solution of the present invention is:

[0008] An apparatus for removing microplastics in water by a combined process of flocculation and electroflotation, comprising an electroflotation tank, a plurality of cyclone tanks, and an annular flocculation tank. The electroflotation tank is located in the middle of the flocculation tank, and the cyclone tanks are located between the electroflotation tank and the flocculation tank and are arranged at equal intervals.

[0009] One side of the top of the electroflotation tank is provided with a water inlet pipe, the top of the electroflotation tank is provided with a voltage stabilizer, a plurality of anode electrode plates and cathode electrode plates are alternately arranged at equal intervals inside the electroflotation tank, one side of the top of the electroflotation tank is provided with a slag discharge tank, and a first water outlet pipe is provided at the bottom of the electroflotation tank corresponding to each side where the cyclone tanks are located. A diversion pump is provided on the first water outlet pipe, and each first water outlet pipe is connected to the upper side of one corresponding cyclone tank one by one.

[0010] A second water outlet pipe is provided at the top of each cyclone tank, a four-way solenoid valve is provided at the top of the second water outlet pipe, and a conduit is connected between the upper side wall of the cyclone tank corresponding to the previous four-way solenoid valve and the cyclone tank corresponding to the next four-way solenoid valve. The outside of each four-way solenoid valve is connected to the upper part of the flocculation tank through a third water outlet pipe.

[0011] A flocculant storage tank and a coagulant aid storage tank are provided above the flocculation tank, and a drain pipe is provided on the outer wall of the upper part of one side of the flocculation tank.

[0012] Furthermore, the flocculant storage tank and the coagulant aid storage tank are respectively arranged on both sides above the flocculation tank.

[0013] Note: The flocculant and the coagulant aid are added into the flocculation tank through the flocculant storage tank and the coagulant aid storage tank, and the distance between the two is reasonably adjusted to improve the flocculation effect and the stirring and mixing effect.

[0014] Furthermore, there are three cyclone tanks, and the three cyclone tanks and the slag discharge tank respectively correspond to the four faces of the electroflotation tank.

[0015] Note: By optimizing the number of cyclone tanks, the layout can be more reasonable, and the balance between the treatment effect and the treatment time can be maximized, avoiding the state of idle or overloaded redundant cyclone tanks.

[0016] Even further, a filter screen is provided inside the electroflotation tank corresponding to the water inlet pipe. The bottom of the flocculation tank is buried underground and is provided with a first sludge discharge pipe and a second sludge discharge pipe. The first sludge discharge pipe is communicated with both sides of the bottom of the flocculation tank and is communicated with the bottoms of two symmetrically arranged cyclone tanks. The second sludge discharge pipe is communicated with the bottom of another cyclone tank and is communicated with one side of the bottom of the flocculation tank.

[0017] Note: The sediment deposited inside the flocculation tank and the cyclone tanks can be discharged through the two sludge discharge pipes.

[0018] Furthermore, an annular stirring assembly is provided on the outer periphery of the bottom of the flocculation tank. A rotating ring provided on the stirring assembly rotates along the outer wall of the flocculation tank. An upper slider and a lower slider that are slidably connected to the outer wall of the flocculation tank are provided inside the rotating ring. A number of stirring rods are equidistantly provided on the inner side wall of the flocculation tank. A number of blades for stirring the sewage inside the flocculation tank are provided at the front end of each stirring rod. The rear end of each stirring rod passes through the flocculation tank and extends to the rotating ring. Each stirring rod is rotationally and sealingly connected to the outer wall of the flocculation tank. And a first gear provided at the rear end of each stirring rod is rotationally meshed with a first tooth groove provided at the bottom of the upper slider.

[0019] Note: The setting of the stirring assembly can realize the stirring of the sewage inside the flocculation tank and improve the flocculation effect.

[0020] Furthermore, a number of driving motors are provided on the ground outside the flocculation tank. A second gear is provided on the output shaft at the top of each driving motor. Each second gear is rotationally meshed with a circle of second tooth grooves provided on the outer wall of the rotating ring. The upper slider and the lower slider slide respectively in an upper chute and a lower chute provided on the outer wall of the flocculation tank. A number of auxiliary rollers are equidistantly provided at the bottom of the lower slider. The auxiliary rollers slide in a limiting groove provided at the bottom of the lower chute.

[0021] Note: The driving of the stirring assembly is realized by driving the second gear with the driving motor.

[0022] Preferably, the number of the stirring rods is 6 - 8, the number of the blades on each stirring rod is 3 - 4, and the number of the driving motors is 2 - 4.

[0023] Note: By optimizing the number of the stirring rods, the stable operation of the whole stirring assembly is ensured, and setting too many is avoided to prevent excessive load from affecting the stirring effect.

[0024] Furthermore, a magnetic stirrer is provided at the bottom inside the electro - flotation tank. The number of the anode electrode plates and the cathode electrode plates is the same, both being 4 - 16. The distance between the anode electrode plates and the cathode electrode plates is 2 - 20 cm. A slag scraper is provided on one side of the slag discharge tank corresponding to the upper part inside the electro - flotation tank.

[0025] Note: Through the electrode plates, electrolysis occurs using direct current to generate tiny bubbles such as H2 and O2 to wrap the micro - plastic particles, so that small - sized micro - plastic particles in the sewage are carried away during the rising process of the bubbles.

[0026] A method for removing micro - plastics in water by a combined process of flocculation and electro - flotation, based on the above - mentioned device for removing micro - plastics in water by a combined process of flocculation and electro - flotation, includes the following steps:

[0027] S1. Electroflotation treatment: Inject the microplastic - polluted sewage into the electroflotation tank through the inlet pipe. Rectify the 220V alternating current into a direct current of 0.1 - 10A through a voltage - stabilizing power supply. The electrolysis time is 30 - 40 minutes. Bubbles are generated to carry the microplastics in the sewage to the surface and discharge them through the slag discharge tank. Then, the treated sewage is diverted to the cyclone tank through a diversion pump and the first outlet pipe;

[0028] S2. Cyclone treatment: During cyclone treatment, it is divided into three different treatment situations according to the content of microplastics in the sewage. When the content of microplastics with a particle size greater than 20μm in the sewage accounts for more than 60% of the total microplastics, S2 - 1 multi - stage cyclone treatment is carried out. When the content of microplastics with a particle size greater than 20μm in the sewage accounts for less than 60% of the total microplastics, S2 - 2 classified cyclone treatment is carried out;

[0029] S2 - 1. Multi - stage cyclone treatment: The sewage enters the first cyclone tank. Under the action of cyclone centrifugal force and gravity, the sewage rotates downward along the inner wall of the cyclone tank and then discharges upward from the middle. Thus, the microplastics with a larger density sink to the bottom of the cyclone tank, and the microplastics with a smaller density are discharged with the water flow through the second outlet pipe. By adjusting each four - way solenoid valve, the sewage first passes through the first cyclone tank and then is discharged from the top of the cyclone tank, diverted through the four - way solenoid valve and the conduit to the next cyclone tank for cyclone treatment again. After passing through each cyclone tank in turn, it is discharged into the flocculation tank through the four - way solenoid valve and the third outlet pipe;

[0030] S2 - 2. Classified cyclone treatment: The sewage enters each first cyclone tank respectively. Under the action of cyclone centrifugal force and gravity, the sewage rotates downward along the inner wall of the cyclone tank and then discharges upward from the middle. Thus, the microplastics with a larger density sink to the bottom of the cyclone tank, and the microplastics with a smaller density are discharged with the water flow through the second outlet pipe. By adjusting each four - way solenoid valve, the sewage in each cyclone tank is discharged into the flocculation tank through the four - way solenoid valve and the third outlet pipe after one - time cyclone treatment;

[0031] S3. Flocculation treatment: In the flocculation tank, add a flocculant and a coagulant aid through the flocculant storage tank and the coagulant - aid storage tank. The addition amount of the flocculant is 30 - 40mg / L, and the addition amount of the coagulant aid is 0.5 - 1mg / L. The flocculant is alum, aluminum chloride or ferric chloride, and the coagulant aid is chitosan or anionic polyacrylamide. Stir and flocculate for 15 - 20 minutes and precipitate for 20 - 30 minutes. Then, discharge the sewage after flocculation treatment through the drain pipe.

[0032] The beneficial effects of the present invention are:

[0033] (2) The device for removing microplastics in water by the combined process of flocculation and electroflotation of the present invention integrates and optimizes the electroflotation tank, cyclone tank and flocculation tank, realizing the fast and efficient treatment of microplastics in sewage. First, the electroflotation destroys the negative charge stability of microplastic colloidal particles, resulting in a reduction in the surface charge of microplastics and the formation of microflocs, which is more conducive to the subsequent destabilization and flocculation sedimentation of colloids by PAC to remove microplastics. Compared with the existing microplastic sewage treatment technologies, it can save more flocculant usage and has obvious advantages in cost control. It can effectively remove microplastic particle pollutants of different sizes, can be long-term applied to the microplastic sewage generated in various scenarios, and the recovered microplastics have certain reuse value.

[0034] (3) The device for removing microplastics in water by the combined process of flocculation and electroflotation of the present invention stirs the sewage in the flocculation tank through a dedicated stirring component, which can ensure the stirring effect and achieve the best stirring effect with as little power source as possible, saving costs.

[0035] (3) The method for removing microplastics in water by the combined process of flocculation and electroflotation of the present invention differentiates the proportion results of microplastics with different particle sizes in the sewage after electroflotation treatment and conducts different cyclone treatment processes, which can improve the treatment efficiency on the premise of ensuring the treatment effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is the overall structural schematic diagram of the device for removing microplastics in water by the combined process of flocculation and electroflotation of the present invention;

[0037] Figure 2 is the top view of the device for removing microplastics in water by the combined process of flocculation and electroflotation of the present invention;

[0038] Figure 3 is the internal structural schematic diagram of the device for removing microplastics in water by the combined process of flocculation and electroflotation of the present invention after omitting the flocculation tank;

[0039] Figure 4 is the front view of the device for removing microplastics in water by the combined process of flocculation and electroflotation of the present invention after omitting the flocculation tank;

[0040] Figure 5 is the internal structural schematic diagram of the electroflotation tank and cyclone tank of the device for removing microplastics in water by the combined process of flocculation and electroflotation of the present invention;

[0041] Figure 6 is the internal structural schematic diagram of the stirring component of the device for removing microplastics in water by the combined process of flocculation and electroflotation of the present invention.

[0042] Among them, 1 - electroflotation cell, 11 - water inlet pipe, 12 - voltage stabilizer, 13 - anode electrode plate, 14 - cathode electrode plate, 15 - slag discharge tank, 151 - slag scraper, 16 - first water outlet pipe, 17 - diversion pump, 18 - filter screen, 19 - magnetic stirrer, 2 - cyclone tank, 21 - second water outlet pipe, 22 - four-way solenoid valve, 23 - conduit, 24 - third water outlet pipe, 3 - flocculation tank, 31 - flocculant storage tank, 32 - coagulant aid storage tank, 33 - drain pipe, 34 - first sludge discharge pipe, 35 - second sludge discharge pipe, 36 - upper chute, 37 - lower chute, 38 - limit groove, 4 - stirring assembly, 41 - rotating ring, 42 - upper slider, 43 - lower slider, 44 - stirring rod, 45 - blade, 46 - first gear, 47 - first tooth groove, 48 - second tooth groove, 49 - auxiliary roller, 5 - drive motor, 51 - second gear. Detailed implementation mode

[0043] Example 1

[0044] As Figure 1 shown, a device for removing microplastics in water by combining flocculation and electroflotation processes includes an electroflotation cell 1, three cyclone tanks 2 and an annular flocculation tank 3. The electroflotation cell 1 is located in the middle of the flocculation tank 3, and the cyclone tanks 2 are located between the electroflotation cell 1 and the flocculation tank 3 and are arranged at equal intervals.

[0045] As Figure 2 and Figure 5 shown, a water inlet pipe 11 is provided on one side of the top of the electroflotation cell 1. A filter screen 18 is provided inside the electroflotation cell 1 corresponding to the water inlet pipe 11. A voltage stabilizer 12 is provided on the top of the electroflotation cell 1. Four anode electrode plates 13 and cathode electrode plates 14 are alternately arranged at equal intervals inside the electroflotation cell 1. The anode electrode plates 13 and the cathode electrode plates 14 are connected to the voltage stabilizer 12 to obtain direct current for the electroflotation process. A slag discharge tank 15 is provided on one side of the top of the electroflotation cell 1. A first water outlet pipe 16 is provided at the bottom of the electroflotation cell 1 corresponding to each side where the cyclone tanks 2 are located. A diversion pump 17 is provided on the first water outlet pipe 16. Each first water outlet pipe 16 is connected to the upper side of one side of the cyclone tank 2 in a one-to-one correspondence. A magnetic stirrer 19 is provided at the bottom inside the electroflotation cell 1. The number of the anode electrode plates 13 and the cathode electrode plates 14 is the same, and the distance between the anode electrode plates 13 and the cathode electrode plates 14 is 10 cm. A slag scraper 151 is provided on one side of the slag discharge tank 15 corresponding to the upper part inside the electroflotation cell 1.

[0046] As Figure 2 and Figure 3As shown, the three cyclone pools 2 and the slag discharge tank 15 correspond to the four surfaces of the electric floating pool 1 respectively, and the top of each cyclone pool 2 is provided with a second outlet pipe 21, and the top of the second outlet pipe 21 is provided with a four-way solenoid valve 22. The upper side wall of the cyclone pool 2 corresponding to the previous four-way solenoid valve 22 and the next four-way solenoid valve 22 is connected through a conduit 23, and the outer side of each four-way solenoid valve 22 is connected to the top of the flocculation pool 3 through a third outlet pipe 24;

[0047] like Figure 3 and Figure 4 As shown, a flocculant storage tank 31 and a coagulant storage tank 32 are provided above the flocculation tank 3, and the flocculant storage tank 31 and the coagulant storage tank 32 are respectively arranged on both sides above the flocculation tank 3, and both the flocculant storage tank 31 and the coagulant storage tank 32 are equipped with commercially available automatic dosing devices, and the flocculant storage tank 31 and the coagulant storage tank 32 are arranged on the indoor top wall, or fixed on an external fixing frame, and a drainage pipe 33 is provided on the upper outer wall of one side of the flocculation tank 3, and a first mud discharge pipe 34 and a second mud discharge pipe 35 are buried under the ground at the bottom of the flocculation tank 3, and the first mud discharge pipe 34 is connected to both sides of the bottom of the flocculation tank 3 and is connected to the bottoms of two symmetrically arranged cyclone tanks 2, and the second mud discharge pipe 35 is connected to the bottom of another cyclone tank 2 and is connected to one side of the bottom of the flocculation tank 3;

[0048] like Figures 4 to 6 As shown, an annular stirring assembly 4 is provided on the outer periphery of the bottom of the flocculation tank 3, a rotating ring 41 is provided on the stirring assembly 4 and rotates along the outer wall of the flocculation tank 3, an upper slider 42 and a lower slider 43 are provided on the inner side of the rotating ring 41 and are slidably connected to the outer wall of the flocculation tank 3, 6 stirring rods 44 are evenly spaced on the inner side wall of the flocculation tank 3, and each stirring rod 44 has 4 blades 45 at the front end for stirring the sewage inside the flocculation tank 3, and the rear end of each stirring rod 44 penetrates the flocculation tank 3 and extends to the rotating ring 41, and each stirring rod 44 is rotatably sealed and connected to the outer wall of the flocculation tank 3. The first gear 46 provided at the rear end of each stirring rod 44 is rotatably engaged with the first tooth groove 47 provided at the bottom of the upper slider 42. Three driving motors 5 are arranged on the ground outside the flocculation tank 3. The driving motor 5 is a commercially available gear reduction motor. A second gear 51 is provided on the top output shaft of each driving motor 5. Each second gear 51 is rotatably engaged with a circle of second tooth grooves 48 provided on the outer wall of the rotating ring 41. The upper slider 42 and the lower slider 43 slide in the upper slide groove 36 and the lower slide groove 37 provided on the outer wall of the flocculation tank 3 respectively. A plurality of auxiliary rollers 49 are equidistantly provided at the bottom of the lower slider 43. The auxiliary rollers 49 slide in the limit groove 38 provided at the bottom of the lower slide groove 37.

[0049] Example 2

[0050] The difference between this embodiment and embodiment 1 is that:

[0051] Inside the electroflotation cell 1, 8 anode electrode plates 13 and cathode electrode plates 14 are alternately arranged at equal intervals, and the distance between the anode electrode plate 13 and the cathode electrode plate 14 is 2 cm.

[0052] Example 3

[0053] The difference between this example and Example 1 is as follows:

[0054] Inside the electroflotation cell 1, 16 anode electrode plates 13 and cathode electrode plates 14 are alternately arranged at equal intervals, and the distance between the anode electrode plate 13 and the cathode electrode plate 14 is 20 cm.

[0055] Example 4

[0056] The difference between this example and Example 1 is as follows:

[0057] On the inner side wall of the flocculation tank 3, 7 stirring rods 44 are arranged at equal intervals, and at the front end of each stirring rod 44, 3 blades 45 for stirring the sewage inside the flocculation tank 3 are provided. On the ground outside the flocculation tank 3, 2 driving motors 5 are arranged.

[0058] Example 5

[0059] The difference between this example and Example 1 is as follows:

[0060] On the inner side wall of the flocculation tank 3, 8 stirring rods 44 are arranged at equal intervals, and at the front end of each stirring rod 44, 4 blades 45 for stirring the sewage inside the flocculation tank 3 are provided. On the ground outside the flocculation tank 3, 4 driving motors 5 are arranged.

[0061] Note: When the total volume of the flocculation tank 3 is larger, more stirring rods 44, blades 45 and driving motors 5 are selected to ensure that the sewage inside the flocculation tank 3 can be stirred sufficiently.

[0062] Example 6

[0063] A method for removing microplastics in water by a combined process of flocculation and electroflotation. Based on this example, it is a device for removing microplastics in water by a combined process of flocculation and electroflotation in Example 1, and includes the following steps:

[0064] S1. Electroflotation treatment: Inject the microplastic-polluted sewage into the electroflotation cell 1 through the water inlet pipe 11. Rectify the 220V alternating current into 0.5A direct current by the regulated power supply 12. The electrolysis time is 35 minutes to generate bubbles. The anode electrode plate 13 generates O2 microbubbles, and the cathode electrode plate 14 generates H2 microbubbles. These microbubbles can be used as flotation agents to wrap the microplastic particles in the sewage and float them to the liquid surface, thereby removing the microplastic particle pollutants in the sewage, carrying the microplastics in the sewage to the surface and discharging them through the slag discharge tank 15. The slag scraper 151 is used to separate the microplastic particle pollutants accumulated on the liquid surface. The treated sewage is guided to the cyclone cell 2 through the diversion pump 17 and the first water outlet pipe 16;

[0065] S2. Cyclone treatment: During the cyclone treatment, it is divided into three different treatment cases according to the content of microplastics in the sewage. When the content of microplastics with a particle size greater than 20μm in the sewage accounts for more than 60% of the total microplastic content, S2-1 multi-stage cyclone treatment is carried out. When the content of microplastics with a particle size greater than 20μm in the sewage accounts for less than 60% of the total microplastic content, S2-2 classification cyclone treatment is carried out;

[0066] S2-1. Multi-stage cyclone treatment: The sewage enters the first cyclone cell 2. Under the action of cyclone centrifugal force and gravity, the sewage rotates downward along the inner wall of the cyclone cell 2 and then discharges upward from the middle, so that the microplastics with a larger density sink to the bottom of the cyclone cell 2, and the microplastics with a smaller density are discharged through the second water outlet pipe 21 with the water flow. By adjusting each four-way solenoid valve 22, after the sewage is first treated by the first cyclone cell 2, it is discharged from the top of the cyclone cell 2 and is guided to the next cyclone cell 2 through the four-way solenoid valve 22 and the conduit 23 for cyclone treatment again. After passing through each cyclone cell 2 in turn, it is discharged into the flocculation tank 3 through the four-way solenoid valve 22 and the third water outlet pipe 24;

[0067] S2-2. Classification cyclone treatment: The sewage enters each first cyclone cell 2 respectively. Under the action of cyclone centrifugal force and gravity, the sewage rotates downward along the inner wall of the cyclone cell 2 and then discharges upward from the middle, so that the microplastics with a larger density sink to the bottom of the cyclone cell 2, and the microplastics with a smaller density are discharged through the second water outlet pipe 21 with the water flow. By adjusting each four-way solenoid valve 22, the sewage in each cyclone cell 2 is discharged into the flocculation tank 3 through the four-way solenoid valve 22 and the third water outlet pipe 24 after one cyclone treatment;

[0068] In the cyclone tank 2, microplastic flocculated particulate matters with larger and smaller densities are separated. The microplastic flocculated particulate matters with larger density gradually descend to the bottom of the tank under the action of cyclone and are finally discharged from the sand discharge port at the bottom of the cyclone tank 2 into the first sludge discharge pipe 34 and the second sludge discharge pipe 35. The microplastic flocculated particulate matters with smaller density will gradually float up and overflow through the second water outlet pipe 21. Under the action of the cyclone tank, the separation of microplastic flocculated particulate matters with larger and smaller densities is realized;

[0069] S3. Flocculation treatment: In the flocculation tank 3, a flocculant and a coagulant aid are added through the flocculant storage tank 31 and the coagulant aid storage tank 32. The addition amount of the flocculant is 35 mg / L, and the addition amount of the coagulant aid is 0.6 mg / L. The flocculant is alum, aluminum chloride or ferric chloride, and the coagulant aid is chitosan or anionic polyacrylamide. Stir and flocculate for 18 min and precipitate for 25 min. Most of the microplastic particles are wrapped by the macromolecular complex formed by the flocculant and precipitate to the lower part and are discharged through the first sludge discharge pipe 34 and the second sludge discharge pipe 35. The microplastic flocculation precipitate is discharged in time through an external sludge pump to ensure the normal operation of the device, and the supernatant is separated and the sewage after flocculation treatment is discharged through the drain pipe 33.

[0070] Example 7

[0071] The difference between this example and Example 6 is as follows:

[0072] S1. Electroflotation treatment: Inject the microplastic-polluted sewage into the electroflotation tank 1 through the water inlet pipe 11. Rectify the 220V alternating current into 0.1A direct current through the voltage stabilizer 12, and the electrolysis time is 30 min;

[0073] S3. Flocculation treatment: In the flocculation tank 3, a flocculant and a coagulant aid are added through the flocculant storage tank 31 and the coagulant aid storage tank 32. The addition amount of the flocculant is 30 mg / L, and the addition amount of the coagulant aid is 0.5 mg / L. The flocculant is alum, aluminum chloride or ferric chloride, and the coagulant aid is chitosan or anionic polyacrylamide. Stir and flocculate for 15 min and precipitate for 20 min. The sewage after flocculation treatment is discharged through the drain pipe 33.

[0074] Example 8

[0075] The difference between this example and Example 6 is as follows:

[0076] S1. Electroflotation treatment: Inject the microplastic-polluted sewage into the electroflotation tank 1 through the water inlet pipe 11. Rectify the 220V alternating current into 10A direct current through the voltage stabilizer 12, and the electrolysis time is 40 min;

[0077] S3. Flocculation treatment: In the flocculation tank 3, a flocculant and a coagulant aid are added through the flocculant storage tank 31 and the coagulant aid storage tank 32. The dosage of the flocculant is 40 mg / L, and the dosage of the coagulant aid is 1 mg / L. The flocculant is ferric chloride, and the coagulant aid is anionic polyacrylamide. Stir and flocculate for 20 min and precipitate for 30 min, and then discharge the sewage after flocculation treatment through the drain pipe 33.

[0078] Note: When the total volume of the flocculation tank 3 is larger, the dosages of the flocculant and the coagulant aid should be appropriately increased while keeping them proper, and at the same time, the stirring and flocculation time and the precipitation time should be appropriately increased. Also, when the scale of the sewage to be treated is larger, the current in the electroflotation cell 1 is larger.

[0079] Next, we will briefly explain the working principle of the stirring assembly in the device part of the present invention in combination with the method of the present invention.

[0080] When performing S3 flocculation treatment, turn on each driving motor 5 to drive each second gear 52 to rotate. Then, under the meshing action of the gear and the second tooth groove 48, drive the rotating ring 41 to rotate. The upper slider 42 slides in the upper chute 36, the lower slider 43 slides in the lower chute 37, and the auxiliary roller 49 rolls in the limiting groove 38 and plays a certain supporting role. At the same time, during the rotation of the rotating ring 41, the first tooth groove 47 and the first gear 46 mesh to make the first gear 46 rotate, thereby driving each stirring rod 44 to rotate. When rotating, the stirring rod 44 maintains the seal and stability with the side wall of the flocculation tank 3, and then stirs the sewage inside the flocculation tank 3 through the rotation of the blade 45.

[0081] Experimental Example 1

[0082] First, we use indoor experiments to verify the feasibility of the device and method of the present invention and the treatment effect on microplastic sewage.

[0083] In the experiment, microplastic microspheres with a particle size of 5 μm and a concentration of 4 μg / L are used. The number of microplastics in the initial microplastic solution of 4 μg / L is 31270 MPs / L. Platinum electrodes are used for electroflotation, the current is set at 0.1 A, the plate spacing is 2 cm, and the electrolysis time is 30 min. The overall microplastic removal rate after electroflotation is only 1.78%. At this time, the number of microplastics drops to 30712 MPs / L. The subsequent effluent is flocculated, and 30 mg / L of PAC is added for mixed flocculation for 15 min. After precipitation for 20 min, the removal rate of microplastics can reach 98.9% at this time, and the number of microplastics in the field of view drops to 337 MPs / L, and no microplastics are significantly observed.

[0084] The experimental results show that although the electroflotation has a poor removal effect on microplastics, it can destroy the negative charge stability of microplastic colloidal particles, resulting in a reduction in surface charge and the formation of microflocs, which is more conducive to the subsequent use of PAC to achieve colloid destabilization, flocculation, and sedimentation for the removal of microplastics.

[0085] Experimental Example 2

[0086] We used the device and method of the present invention to conduct on-site treatment of a large volume of sewage. Multiple batches of sewage were divided into multiple treatment groups with a volume of 2t each. The number of microplastics in the initial microplastic solution was 40,000 - 50,000 MPs / L, and the treatment method in Example 6 was adopted.

[0087] When performing S2, after detecting the sewage treated by electroflotation in the first treatment group, it was found that the content of microplastics with a particle size greater than 20μm in the sewage accounted for 76% of the total microplastics. Therefore, S2-1 multi-stage cyclone treatment was carried out.

[0088] After detecting the sewage treated by electroflotation in the second treatment group, it was found that the content of microplastics with a particle size greater than 20μm in the sewage accounted for 62% of the total microplastics. Therefore, S2-1 multi-stage cyclone treatment was carried out.

[0089] After detecting the sewage treated by electroflotation in the first treatment group, it was found that the content of microplastics with a particle size greater than 20μm in the sewage accounted for 45% of the total microplastics. Therefore, S2-2 classification cyclone treatment was carried out.

[0090] At the same time, we also set up a control group. In the control group, only flocculation treatment was adopted, and an existing commercially available flocculation treatment cylinder (equipped with a stirring rod inside) was selected. The sewage was the same as that in the first treatment group, and the same flocculant and coagulant aid were used. The treatment results of the microplastic removal rate are shown in Table 1.

[0091] Table 1 Treatment results in each case

[0092] Case Microplastic removal rate % First treatment group 98.7 Second treatment group 97.4 Third treatment group 97.2 Control group 94.3

[0093] It can be found that after adopting the device and method of the present invention, the removal rate of microplastics in sewage has been significantly improved, which also confirms what we mentioned earlier: electroflotation can destroy the negative charge stability of microplastic colloidal particles, resulting in a reduction in surface charge and the formation of microflocs, which is more conducive to the subsequent use of PAC to achieve colloid destabilization, flocculation, and sedimentation for the removal of microplastics.

[0094] Among them, the removal rate of the second treatment group decreased slightly. This may be because the content of microplastics with a particle size greater than 20 μm in the sewage is lower than that of the first treatment group in the total microplastics, and the cyclone has a better removal effect on large-sized microplastics than on small-sized microplastics. Therefore, when the sewage after electroflotation treatment is detected, the larger the content of microplastics with a particle size greater than 20 μm in the sewage accounts for the total microplastics, the better the treatment effect of using S2-1 and multi-stage cyclone;

[0095] At the same time, in the third treatment group, the change in the microplastic removal rate was not obvious compared with the second treatment group. This is because the content of microplastics with a particle size greater than 20 μm in the sewage is relatively low, and there is no need to use cyclone treatment frequently. By increasing the speed of the sewage entering the flocculation tank 3 after electroflotation and shortening the time interval between electroflotation and flocculation, a high removal rate effect can also be maintained, indicating that the division of S2 in the method of the present invention is relatively scientific and reasonable.

Claims

1. An apparatus for removing microplastics in water by a combined process of flocculation and electroflotation, characterized in that, It includes an electroflotation tank (1), several cyclone tanks (2) and an annular flocculation tank (3). The electroflotation tank (1) is located at the middle position of the flocculation tank (3), and the cyclone tanks (2) are located between the electroflotation tank (1) and the flocculation tank (3) and are arranged at equal intervals. On one side of the top of the electroflotation tank (1), there is a water inlet pipe (11). On the top of the electroflotation tank (1), there is a voltage stabilizer (12). Inside the electroflotation tank (1), several anode electrode plates (13) and cathode electrode plates (14) are alternately arranged at equal intervals. On one side of the top of the electroflotation tank (1), there is a slag discharge tank (15). At the bottom of the electroflotation tank (1), on the side corresponding to each of the cyclone tanks (2), there is a first water outlet pipe (16). A diversion pump (17) is provided on the first water outlet pipe (16). Each first water outlet pipe (16) is connected to the upper side of one of the cyclone tanks (2) in a one-to-one correspondence. On the top of each of the cyclone tanks (2), there is a second water outlet pipe (21). On the top of the second water outlet pipe (21), there is a four-way solenoid valve (22). A conduit (23) is connected between the upper side wall of the cyclone tank (2) corresponding to the previous four-way solenoid valve (22) and the cyclone tank (2) corresponding to the next four-way solenoid valve (22). The outside of each four-way solenoid valve (22) is docked with the upper part of the flocculation tank (3) through a third water outlet pipe (24). Above the flocculation tank (3), there are a flocculant storage tank (31) and a coagulant aid storage tank (32). On the outer wall of the upper part of one side of the flocculation tank (3), there is a drain pipe (33). An annular stirring assembly (4) is provided on the outer periphery of the bottom of the flocculation tank (3). A rotating ring (41) provided on the stirring assembly (4) rotates along the outer wall of the flocculation tank (3). An upper slider (42) and a lower slider (43) which are slidably connected to the outer wall of the flocculation tank (3) are provided inside the rotating ring (41). Several stirring rods (44) are arranged at equal intervals on the inner side wall of the flocculation tank (3). At the front end of each of the stirring rods (44), there are several blades (45) for stirring the sewage inside the flocculation tank (3). The rear end of each stirring rod (44) extends through the flocculation tank (3) and then reaches the rotating ring (41). Each stirring rod (44) is rotationally and sealingly connected to the outer wall of the flocculation tank (3). A first gear (46) provided at the rear end of each stirring rod (44) is rotationally engaged with a first tooth groove (47) provided at the bottom of the upper slider (42).

2. The device for removing microplastics in water by using a combined process of flocculation and electroflotation according to claim 1, characterized in that, The flocculant storage tank (31) and the coagulant aid storage tank (32) are respectively arranged on both sides above the flocculation tank (3).

3. The device for removing microplastics in water by using a combined process of flocculation and electroflotation according to claim 1, characterized in that, There are three cyclone tanks (2), and the three cyclone tanks (2) and the slag discharge tank (15) respectively correspond to the four faces of the electroflotation tank (1).

4. The device for removing microplastics in water by using a combined process of flocculation and electroflotation according to claim 3, wherein, A filter screen (18) is provided inside the electroflotation tank (1) corresponding to the water inlet pipe (11). A first sludge discharge pipe (34) and a second sludge discharge pipe (35) are buried underground at the bottom of the flocculation tank (3). The first sludge discharge pipe (34) communicates with both sides of the bottom of the flocculation tank (3) and communicates with the bottoms of two symmetrically arranged swirl tanks (2). The second sludge discharge pipe (35) communicates with the bottom of another swirl tank (2) and communicates with one side of the bottom of the flocculation tank (3).

5. The device for removing microplastics in water by using a combined process of flocculation and electroflotation according to claim 1, wherein, A number of driving motors (5) are arranged on the ground outside the flocculation tank (3). A second gear (51) is provided on the top output shaft of each driving motor (5). Each second gear (51) is rotationally meshed with a circle of second tooth grooves (48) provided on the outer wall of the rotating ring (41). The upper slider (42) and the lower slider (43) slide in the upper chute (36) and the lower chute (37) provided on the outer wall of the flocculation tank (3) respectively. A number of auxiliary rollers (49) are equidistantly provided at the bottom of the lower slider (43). The auxiliary rollers (49) slide in the limiting groove (38) provided at the inner bottom of the lower chute (37).

6. The device for removing microplastics in water by a combined process of flocculation and electroflotation according to claim 5, characterized in that, There are 6 to 8 stirring rods (44), 3 to 4 blades (45) on each stirring rod (44), and 2 to 4 driving motors (5).

7. The device for removing microplastics in water by using a combined process of flocculation and electroflotation according to claim 1, characterized in that, A magnetic stirrer (19) is provided at the inner bottom of the electroflotation tank (1). The number of anode electrode plates (13) and cathode electrode plates (14) is the same, both being 4 to 16. The distance between the anode electrode plate (13) and the cathode electrode plate (14) is 2 to 20 cm. A slag scraper (151) is provided on one side of the slag discharge tank (15) corresponding to the upper part inside the electroflotation tank (1).

8. A method for removing microplastics in water by a combined process of flocculation and electroflotation, based on the device for removing microplastics in water by a combined process of flocculation and electroflotation according to any one of claims 1 to 7, characterized in that, It includes the following steps: S1. Electroflotation treatment: Inject the microplastic-polluted sewage into the electroflotation tank (1) through the water inlet pipe (11). Rectify 220V alternating current into direct current of 0.1 to 10A through a voltage stabilizer (12). The electrolysis time is 30 to 40 minutes. Generate bubbles to carry the microplastics in the sewage to the surface and discharge them through the slag discharge tank (15). Divert the treated sewage to the swirl tank (2) through a diversion pump (17) and a first water outlet pipe (16). S2. Swirl treatment: During the swirl treatment, it is divided into three different treatment situations according to the content of microplastics in the sewage. When the content of microplastics with a particle size greater than 20 µm in the sewage accounts for more than 60% of the total microplastics, perform S2-1 multi-stage swirl treatment. When the content of microplastics with a particle size greater than 20 µm in the sewage accounts for less than 60% of the total microplastics, perform S2-2 hierarchical swirl treatment; S2-1. Multi-stage cyclone treatment: The sewage enters the first cyclone tank (2). Under the action of cyclone centrifugal force and gravity, the sewage rotates downward along the inner wall of the cyclone tank (2) and then discharges upward from the middle, so that the microplastics with larger density sink to the bottom of the cyclone tank (2), and the microplastics with smaller density are discharged with the water flow through the second outlet pipe (21). By adjusting each four-way solenoid valve (22), after the sewage is first treated by the first cyclone tank (2), it is discharged from the top of the cyclone tank (2) and is guided by the four-way solenoid valve (22) and the conduit (23) to the next cyclone tank (2) for cyclone treatment again. After passing through each cyclone tank (2) in turn, it is discharged into the flocculation tank (3) by the four-way solenoid valve (22) and the third outlet pipe (24); S2-2. Hierarchical cyclone treatment: The sewage enters each first cyclone tank (2) respectively. Under the action of cyclone centrifugal force and gravity, the sewage rotates downward along the inner wall of the cyclone tank (2) and then discharges upward from the middle, so that the microplastics with larger density sink to the bottom of the cyclone tank (2), and the microplastics with smaller density are discharged with the water flow through the second outlet pipe (21). By adjusting each four-way solenoid valve (22), after the sewage in each cyclone tank (2) is subjected to one-time cyclone treatment, it is discharged into the flocculation tank (3) by the four-way solenoid valve (22) and the third outlet pipe (24) respectively; S3. Flocculation treatment: In the flocculation tank (3), a flocculant and a coagulant aid are added through the flocculant storage tank (31) and the coagulant aid storage tank (32). The dosage of the flocculant is 30 - 40 mg / L, and the dosage of the coagulant aid is 0.5 - 1 mg / L. The flocculant is alum, aluminum chloride or ferric chloride, and the coagulant aid is chitosan or anionic polyacrylamide. Stir and flocculate for 15 - 20 min and precipitate for 20 - 30 min, and then discharge the sewage after flocculation treatment through the drain pipe (33).

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