Device and method for removing micro-plastics in water by flocculation and electroflotation combined process

Abstract

The invention discloses a device and a method for removing micro-plastics in water by a flocculation and electroflotation combined process, the device comprises an electroflotation tank, a plurality of rotational flow tanks and an annular flocculation tank, the electroflotation tank is positioned in the middle of the flocculation tank, and the rotational flow tanks are positioned between the electroflotation tank and the flocculation tank and are arranged at equal intervals. The method comprises the following steps: S1, electroflotation treatment; s2, rotational flow treatment: S2-1, multi-stage rotational flow treatment; s2-2, carrying out graded rotational flow treatment; and S3, flocculation treatment. After the electroflotation tank, the rotational flow tank and the flocculation tank are integrated and optimized, rapid and efficient treatment of micro-plastics in sewage is realized, firstly, the negative charge stability of micro-plastic colloidal particles is destroyed through electroflotation, so that surface charges of the micro-plastics are reduced, and micro-floccules are formed; therefore, subsequent PAC is more facilitated to realize colloid destabilization, flocculation and sedimentation to remove the micro-plastic, and micro-plastic particle pollutants with different sizes can be effectively removed.

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] A device for removing microplastics in water by a flocculation and electrical flotation combined process, comprising an electrical flotation tank, a plurality of cyclone tanks and an annular flocculation tank, wherein the electrical flotation tank is located in the middle of the flocculation tank, and the cyclone tank is located between the electrical flotation tank and the flocculation tank and is arranged at equal intervals;

[0009] A water inlet pipe is provided on one side of the top of the electric floating pool, a voltage-stabilizing power supply is provided on the top of the electric floating pool, a plurality of anode electrode plates and cathode electrode plates are alternately and evenly spaced inside the electric floating pool, a slag discharge trough is provided on one side of the top of the electric floating pool, and a first water outlet pipe is provided on each side of the bottom of the electric floating pool corresponding to each cyclone pool, a flow guide pump is provided on the first water outlet pipe, and each first water outlet pipe is connected to one side of the upper part of the cyclone pool in a one-to-one correspondence;

[0010] A second water outlet pipe is provided on the top of each cyclone pool, a four-way solenoid valve is provided on the top of the second water outlet pipe, a conduit is connected between the upper side wall of the cyclone pool corresponding to the previous four-way solenoid valve and the next four-way solenoid valve, and the outer side of each four-way solenoid valve is connected to the top of the flocculation pool through a third water outlet pipe;

[0011] A flocculant storage tank and a coagulant aid storage tank are arranged above the flocculation tank, and a drainage pipe is arranged on the upper outer wall 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] Description: Add flocculants and coagulant aids into the flocculation tank through the flocculant storage tank and the coagulant aid storage tank, and reasonably adjust the distance between the two to improve the flocculation effect and stirring and mixing effect.

[0014] Furthermore, there are three cyclone pools, and the three cyclone pools and the slag discharge trough correspond to four surfaces of the electric floating pool respectively.

[0015] Note: By optimizing the number of cyclone pools, the placement can be more reasonable, and the balance between treatment effect and treatment time can be maximized to avoid redundant cyclone pools being idle or in a high-load state.

[0016] Furthermore, the water inlet pipe is provided with a filter screen inside the electric floating pool corresponding to the water inlet pipe, and the bottom of the flocculation pool is located under the ground and a first mud discharge pipe and a second mud discharge pipe are buried. The first mud discharge pipe is connected to both sides of the bottom of the flocculation pool and to the bottoms of two symmetrically arranged cyclone pools, and the second mud discharge pipe is connected to the bottom of another cyclone pool and to one side of the bottom of the flocculation pool.

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

[0018] Furthermore, an annular stirring assembly is provided at 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 are provided on the inner side of the rotating ring and are slidably connected to the outer wall of the flocculation tank, a plurality of stirring rods are provided at equal intervals on the inner side wall of the flocculation tank, a plurality of blades for stirring the sewage inside the flocculation tank are provided at the front end of each stirring rod, a plurality of blades for stirring the sewage inside the flocculation tank are provided at the rear end of each stirring rod and extend to the rotating ring after penetrating the flocculation tank, and each stirring rod is rotatably sealed and connected to the outer wall of the flocculation tank. A first gear provided at the rear end of each stirring rod is rotatably meshed with a first tooth groove provided at the bottom of the upper slider.

[0019] Note: By setting up the stirring component, the sewage inside the flocculation tank can be stirred to improve the flocculation effect.

[0020] Furthermore, a plurality of driving motors are arranged on the ground outside the flocculation tank, and a second gear is provided on the top output shaft of each driving motor, and each second gear is rotatably meshed with a circle of second tooth grooves provided on the outer wall of the rotating ring, and the upper slider and the lower slider slide in the upper slide groove and the lower slide groove provided on the outer wall of the flocculation tank respectively, and a plurality of auxiliary rollers are provided at equal intervals on the bottom of the lower slider, and the auxiliary rollers slide in the limiting groove provided at the bottom of the lower slide groove.

[0021] Description: The stirring assembly is driven by the driving motor driving the second gear.

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

[0023] Note: By optimizing the number of stirring rods, the entire stirring assembly can be ensured to operate stably, avoiding excessive loads that affect the stirring effect.

[0024] Furthermore, a magnetic stirrer is provided at the bottom of the electric floating pool, the anode electrode plates and cathode electrode plates are provided in the same number, both 4 to 16, the spacing between the anode electrode plates and the cathode electrode plates is 2 to 20 cm, and a scraper is provided on one side of the slag discharge trough corresponding to the upper part of the electric floating pool.

[0025] Note: Using direct current to generate electrolysis through electrode plates can produce tiny bubbles such as H2 and O2 to wrap microplastic particles, thereby carrying away small-sized microplastic particles in the sewage during the rising process of the bubbles.

[0026] A method for removing microplastics from water by combining flocculation and electrical flotation, based on the above-mentioned device for removing microplastics from water by combining flocculation and electrical flotation, comprises the following steps:

[0027] S1. Electrical flotation treatment: Inject microplastic-contaminated sewage into the electrical flotation tank through the water inlet pipe, rectify 220V AC into 0.1-10A DC through a voltage stabilizer, and electrolyze for 30-40 minutes. Bubbles are generated to carry microplastics in the sewage to the surface and discharge them through the slag discharge tank. The treated sewage is diverted to the cyclone tank through the diversion pump and the first outlet pipe;

[0028] S2, cyclone treatment: during cyclone treatment, it is divided into three different treatment conditions according to the content of microplastics in sewage. When the content of microplastics with a particle size greater than 20 μm in 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 20 μm in sewage accounts for less than 60% of the total microplastics, S2-2 graded cyclone treatment is carried out;

[0029] S2-1, multi-stage cyclone treatment: the sewage enters the first cyclone pool, and under the action of the cyclone centrifugal force and gravity, the sewage rotates downward along the inner wall of the cyclone pool, and then is discharged upward from the middle, so that the microplastics with higher density fall to the bottom of the cyclone pool, and the microplastics with lower density are discharged through the second outlet pipe with the water flow. By adjusting each four-way solenoid valve, the sewage is first processed by the first cyclone pool, and then discharged from the top of the cyclone pool and guided to the next cyclone pool through the four-way solenoid valve and the conduit, and then cyclone treatment is performed again, and after being processed in each cyclone pool in turn, it is discharged into the flocculation tank through the four-way solenoid valve and the third outlet pipe;

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

[0031] S3. Flocculation treatment: In the flocculation tank, flocculants and coagulant aids are added through the flocculant storage tank and the coagulant aid storage tank. The amount of flocculant added is 30-40 mg / L, and the amount of coagulant aid added 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 minutes, and settle for 20-30 minutes. Discharge the flocculated sewage through the drain pipe.

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

[0033] (2) The device of the present invention for removing microplastics in water by combining flocculation and electroflotation processes integrates and optimizes an electroflotation tank, a cyclone tank and a flocculation tank, thereby achieving rapid and efficient treatment of microplastics in sewage. First, the negative charge stability of the microplastic colloid particles is destroyed by electroflotation, resulting in a reduction in the surface charge of the microplastics and the formation of microflocs, which is more conducive to the subsequent PAC to achieve colloid destabilization flocculation sedimentation to remove microplastics. Compared with existing microplastic sewage treatment technologies, it can save more flocculants and has obvious advantages in cost control. It can effectively remove microplastic particle pollutants of different sizes and can be applied to microplastic sewage generated in various scenarios for a long time. The recovered microplastics have certain reuse value.

[0034] (3) The device for removing microplastics from water by combining flocculation and electrical flotation processes of the present invention stirs the sewage in the flocculation tank through a dedicated stirring component, which can ensure the best stirring effect using as little power source as possible, thereby saving costs.

[0035] (3) The method of removing microplastics from water by combining flocculation and electroflotation processes of the present invention distinguishes the proportion of microplastics of different particle sizes in wastewater after electroflotation treatment, and performs different cyclone treatment processes, which can improve the treatment efficiency while ensuring the treatment effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the overall structure of a device for removing microplastics in water by combining flocculation and electrical flotation process according to the present invention;

[0037] Figure 2 It is a top view of a device for removing microplastics in water by combining flocculation and electrical flotation process according to the present invention;

[0038] Figure 3 This is a schematic diagram of the internal structure after omitting the flocculation tank of a device for removing microplastics in water by combining flocculation and electrical flotation process of the present invention;

[0039] Figure 4 It is a front view of a device for removing microplastics in water by combining flocculation and electrical flotation process of the present invention, omitting the flocculation tank;

[0040] Figure 5 It is a schematic diagram of the internal structure of an electric flotation tank and a cyclone tank of a device for removing microplastics in water by a flocculation and electric flotation combined process of the present invention;

[0041] Figure 6 This is a schematic diagram of the internal structure of a stirring component of a device for removing microplastics in water using a flocculation and electrical flotation process according to the present invention.

[0042] Among them, 1-electric floating tank, 11-water inlet pipe, 12-voltage stabilizer, 13-anode electrode plate, 14-cathode electrode plate, 15-slag trough, 151-slag scraper, 16-first outlet pipe, 17-diversion pump, 18-filter screen, 19-magnetic agitator, 2-cyclone tank, 21-second outlet pipe, 22-four-way solenoid valve, 23-conduit, 24-third outlet pipe, 3-flocculation tank, 31-flocculation agent storage tank , 32-coagulant storage tank, 33-drain pipe, 34-first mud discharge pipe, 35-second mud discharge pipe, 36-upper slide, 37-lower slide, 38-limiting 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 DESCRIPTION

[0043] Example 1

[0044] like Figure 1 As shown, a device for removing microplastics in water by combining flocculation and electrical flotation processes comprises an electrical floating pool 1, three cyclone pools 2 and an annular flocculation pool 3, wherein the electrical floating pool 1 is located in the middle of the flocculation pool 3, and the cyclone pool 2 is located between the electrical floating pool 1 and the flocculation pool 3 and is arranged at equal intervals;

[0045] like Figure 2 and Figure 5 As shown, a water inlet pipe 11 is provided on one side of the top of the electric floating pool 1, and a filter screen 18 is provided inside the electric floating pool 1 corresponding to the water inlet pipe 11, a voltage-stabilizing power supply 12 is provided on the top of the electric floating pool 1, and four anode electrode plates 13 and cathode electrode plates 14 are alternately and evenly spaced inside the electric floating pool 1, and the anode electrode plates 13 and the cathode electrode plates 14 are connected to the voltage-stabilizing power supply 12, so as to obtain direct current to generate an electric floating process, a slag discharge trough 15 is provided on one side of the top of the electric floating pool 1, and a first water outlet pipe 16 is provided on each side of the bottom of the electric floating pool 1 corresponding to each cyclone pool 2, and a flow guide pump 17 is provided on the first water outlet pipe 16, and each first water outlet pipe 16 is connected to one side of the upper part of the cyclone pool 2 in a one-to-one correspondence, a magnetic stirrer 19 is provided at the bottom of the electric floating pool 1, and the number of anode electrode plates 13 and 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, and a scraper 151 is provided on one side of the slag discharge trough 15 corresponding to the upper part of the electric floating pool 1;

[0046] like 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] Eight anode electrode plates 13 and cathode electrode plates 14 are alternately and evenly spaced inside the electrical floating pond 1 , and the spacing between the anode electrode plates 13 and the cathode electrode plates 14 is 2 cm.

[0052] Example 3

[0053] The difference between this embodiment and embodiment 1 is that:

[0054] Sixteen anode electrode plates 13 and cathode electrode plates 14 are alternately and evenly spaced inside the electrical floating pond 1 , and the spacing between the anode electrode plates 13 and the cathode electrode plates 14 is 20 cm.

[0055] Example 4

[0056] The difference between this embodiment and embodiment 1 is that:

[0057] Seven stirring rods 44 are evenly spaced on the inner side wall of the flocculation tank 3 , and three blades 45 for stirring the sewage inside the flocculation tank 3 are arranged at the front end of each stirring rod 44 . Two driving motors 5 are arranged on the ground outside the flocculation tank 3 .

[0058] Example 5

[0059] The difference between this embodiment and embodiment 1 is that:

[0060] Eight stirring rods 44 are evenly spaced on the inner side wall of the flocculation tank 3 , and each stirring rod 44 has four blades 45 at the front end for stirring the sewage in the flocculation tank 3 . Four driving motors 5 are arranged on the outer ground of the flocculation tank 3 .

[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 sufficiently stirred.

[0062] Example 6

[0063] A method for removing microplastics from water by combining flocculation and electrical flotation, based on this embodiment, is a device for removing microplastics from water by combining flocculation and electrical flotation in embodiment 1, comprising the following steps:

[0064] S1, electrical flotation treatment: inject microplastic polluted sewage into the electrical flotation tank 1 through the water inlet pipe 11, rectify 220V AC into 0.5A DC through the voltage stabilizer 12, electrolyze for 35 minutes, 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 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 scraper 151 is used to separate the microplastic particle pollutants accumulated on the liquid surface, and divert the treated sewage to the cyclone tank 2 through the diversion pump 17 and the first outlet pipe 16;

[0065] S2, cyclone treatment: during cyclone treatment, it is divided into three different treatment conditions according to the content of microplastics in sewage. When the content of microplastics with a particle size greater than 20 μm in 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 20 μm in sewage accounts for less than 60% of the total microplastics, S2-2 graded cyclone treatment is carried out;

[0066] S2-1, multi-stage cyclone treatment: the sewage enters the first cyclone pool 2, and under the action of the cyclone centrifugal force and gravity, the sewage rotates downward along the inner wall of the cyclone pool 2, and then is discharged upward from the middle, so that the microplastics with higher density fall to the bottom of the cyclone pool 2, and the microplastics with lower density are discharged through the second outlet pipe 21 with the water flow. By adjusting each four-way solenoid valve 22, the sewage is first processed by the first cyclone pool 2, and then discharged from the top of the cyclone pool 2 and guided to the next cyclone pool 2 through the four-way solenoid valve 22 and the conduit 23, and then cyclone treatment is performed again, and after being processed by each cyclone pool 2 in turn, it is discharged into the flocculation pool 3 through the four-way solenoid valve 22 and the third outlet pipe 24;

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

[0068] Microplastic flocculated particles with larger density and smaller density are separated in the cyclone pool 2. Microplastic flocculated particles with larger density gradually fall to the bottom of the pool due to the cyclone action, and are finally discharged from the sand discharge port at the bottom of the cyclone pool 2 to the first mud discharge pipe 34 and the second mud discharge pipe 35; microplastic flocculated particles with smaller density gradually float up and flow out through the second water outlet pipe 21. Under the action of the cyclone pool, the separation of microplastic flocculated particles with larger density and microplastic flocculated particles with smaller density is achieved;

[0069] S3, flocculation treatment: in the flocculation tank 3, flocculants and coagulants are added through the flocculant storage tank 31 and the coagulant storage tank 32, the flocculant addition amount is 35 mg / L, the coagulant addition amount is 0.6 mg / L, the flocculant is alum, aluminum chloride or ferric chloride, the coagulant is chitosan or anionic polyacrylamide, the flocculation is stirred for 18 minutes, and the sedimentation is 25 minutes. Most of the microplastic particles are wrapped by the macromolecular complex formed by the flocculant and precipitated to the bottom and discharged from the first mud discharge pipe 34 and the second mud discharge pipe 35. The microplastic flocculation sediment is discharged in time through the external mud pump to ensure the normal operation of the device, 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 embodiment and embodiment 6 is that:

[0072] S1, electrical flotation treatment: inject the microplastic-contaminated wastewater into the electrical flotation tank 1 through the water inlet pipe 11, rectify the 220V AC into 0.1A DC through the voltage stabilizer 12, and the electrolysis time is 30 minutes;

[0073] S3, flocculation treatment: in the flocculation tank 3, flocculants and coagulants are added through the flocculant storage tank 31 and the coagulant storage tank 32, the flocculant addition amount is 30 mg / L, the coagulant addition amount is 0.5 mg / L, the flocculant is alum, aluminum chloride or ferric chloride, the coagulant is chitosan or anionic polyacrylamide, the flocculation is stirred for 15 minutes, the sedimentation is 20 minutes, and the sewage after flocculation treatment is discharged through the drain pipe 33.

[0074] Example 8

[0075] The difference between this embodiment and embodiment 6 is that:

[0076] S1, electrical flotation treatment: inject the microplastic-contaminated wastewater into the electrical flotation tank 1 through the water inlet pipe 11, rectify the 220V AC into 10A DC through the voltage stabilizer 12, and the electrolysis time is 40 minutes;

[0077] S3, flocculation treatment: in the flocculation tank 3, flocculants and coagulants are added through the flocculant storage tank 31 and the coagulant storage tank 32, the flocculant addition amount is 40 mg / L, the coagulant addition amount is 1 mg / L, the flocculant is ferric chloride, the coagulant is anionic polyacrylamide, the flocculation is stirred for 20 minutes, the sedimentation is 30 minutes, and the sewage after flocculation treatment is discharged through the drain pipe 33.

[0078] Note: When the total volume of the flocculation tank 3 is larger, the amount of flocculant and coagulant added is appropriately increased, and the stirring flocculation time and sedimentation time are appropriately increased. At the same time, the larger the scale of sewage to be treated, the larger the current in the electric floating tank 1.

[0079] Next, we briefly describe the working principle of the stirring component of the device of the present invention in combination with the method of the present invention.

[0080] When performing S3 flocculation treatment, each driving motor 5 is turned on to drive each second gear 52 to rotate, thereby driving the rotating ring 41 to rotate under the meshing action of the gear and the second tooth groove 48, the upper slider 42 slides in the upper slide groove 36, the lower slider 43 slides in the lower slide groove 37, and the auxiliary roller 49 rolls in the limit 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 rotate the first gear 46, thereby driving each stirring rod 44 to rotate. During rotation, the stirring rod 44 maintains a seal and stability with the side wall of the flocculation tank 3, and then the sewage inside the flocculation tank 3 is stirred by the rotation of the blade 45.

[0081] Experimental Example 1

[0082] We first used indoor experiments to verify the feasibility of the device and method of the present invention and its treatment effect on microplastic wastewater.

[0083] The experiment used microplastic microspheres with a particle size of 5μm and a concentration of 4μg / L. The number of microplastics in the initial 4μg / L microplastic solution was 31270MPs / L. Platinum electrodes were used for electroflotation, the current was set to 0.1A, the plate spacing was 2cm, and the electrolysis time was 30min. After electroflotation, the overall microplastic removal rate was only 1.78%, and the number of microplastics dropped to 30712MPs / L. The effluent was subsequently flocculated, and 30mg / L of PAC was added for mixed flocculation for 15min. After 20min of sedimentation, the removal rate of microplastics could reach 98.9%, and the number of microplastics in the field of view dropped to 337MPs / L, and no microplastics were obviously observed.

[0084] This experimental result shows that although electrical flotation is less effective in removing microplastics, it can destroy the negative charge stability of microplastic colloidal particles, resulting in a reduction in surface charge and the formation of microflocculates, which is more conducive to the subsequent PAC to achieve colloidal destabilization flocculation sedimentation to remove microplastics.

[0085] Experimental Example 2

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

[0087] When S2 was performed, the sewage after the electrical flotation treatment was tested in the first treatment group, and it was found that the content of microplastics with a particle size greater than 20 μm in the sewage accounted for 76% of the total microplastics, so S2-1 multi-stage cyclone treatment was performed;

[0088] In the second treatment group, after testing the sewage after the electroflotation treatment, it was found that the content of microplastics with a particle size greater than 20 μm in the sewage accounted for 62% of the total microplastics, so S2-1 multi-stage cyclone treatment was carried out;

[0089] In the first treatment group, after testing the sewage after the electroflotation treatment, it was found that the content of microplastics with a particle size greater than 20 μm in the sewage accounted for 45% of the total microplastics, so S2-2 graded cyclone treatment was carried out;

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

[0091] Table 1 Treatment results in each case

[0092] Case Microplastic removal rate % The first treatment group 98.7 The second treatment group 97.4 The third treatment group 97.2 Comparative Example 94.3

[0093] It can be found that by 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: electrical flotation can destroy the negative charge stability of microplastic colloid particles, resulting in a reduction in surface charge and the formation of microflocculates, which is more conducive to the subsequent PAC to achieve colloid destabilization flocculation sedimentation to remove microplastics.

[0094] Among them, the removal rate of the second treatment group decreased slightly, which may be because the content of microplastics with a particle size greater than 20μm in the sewage accounts for a lower proportion of the total microplastics than that in the first treatment group, and the cyclone is better at removing large-sized microplastics than small-sized microplastics. Therefore, when the sewage after electrical flotation treatment is tested, the greater the content of microplastics with a particle size greater than 20μm in the sewage accounts for the total microplastics, the better the treatment effect of using S2-1 and multi-stage cyclone is.

[0095] At the same time, in the third treatment group, the microplastic removal rate did not change significantly compared with the second treatment group. This is because the content of microplastics with a particle size greater than 20 μm in the sewage accounts for a relatively low proportion of the total microplastics, and there is no need to frequently use cyclone treatment. Increasing the speed at which sewage enters the flocculation tank 3 after passing through electrical flotation and shortening the time interval between electrical flotation and flocculation can also maintain a relatively high removal rate. This shows that the division of S2 in the method of the present invention is more scientific and reasonable.

Claims

1. A device for removing microplastics from water by combining flocculation and electrical flotation, characterized in that: The invention comprises an electric floating pool (1), a plurality of cyclone pools (2) and an annular flocculation pool (3), wherein the electric floating pool (1) is located in the middle of the flocculation pool (3), and the cyclone pool (2) is located between the electric floating pool (1) and the flocculation pool (3) and is arranged at equal intervals. A water inlet pipe (11) is provided on one side of the top of the electric floating pool (1), a voltage-stabilizing power supply (12) is provided on the top of the electric floating pool (1), a plurality of anode electrode plates (13) and cathode electrode plates (14) are alternately and evenly spaced inside the electric floating pool (1), a slag discharge trough (15) is provided on one side of the top of the electric floating pool (1), and a first water outlet pipe (16) is provided on each side of the bottom of the electric floating pool (1) corresponding to each cyclone pool (2), a flow guide pump (17) is provided on the first water outlet pipe (16), and each first water outlet pipe (16) is connected to one side of the upper part of the cyclone pool (2) in a one-to-one correspondence; A second water outlet pipe (21) is provided at the top of each cyclone pool (2), a four-way solenoid valve (22) is provided at the top of the second water outlet pipe (21), 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 via a conduit (23), and the outer side of each four-way solenoid valve (22) is connected to the top of the flocculation pool (3) via a third water outlet pipe (24); A flocculant storage tank (31) and a coagulant aid storage tank (32) are provided above the flocculation tank (3), and a drainage pipe (33) is provided on the upper outer wall of one side of the flocculation tank (3).

2. The device for removing microplastics in water by combining flocculation and electrical flotation 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 combining flocculation and electrical flotation according to claim 1, characterized in that: There are three cyclone pools (2), and the three cyclone pools (2) and the slag discharge trough (15) correspond to the four surfaces of the electric floating pool (1) respectively.

4. The device for removing microplastics in water by combining flocculation and electrical flotation according to claim 3, characterized in that: The water inlet pipe (11) is provided with a filter screen (18) corresponding to the electric floating pond (1). A first mud discharge pipe (34) and a second mud discharge pipe (35) are buried under the ground at the bottom of the flocculation pond (3). The first mud discharge pipe (34) is connected to both sides of the bottom of the flocculation pond (3) and is connected to the bottoms of two symmetrically arranged cyclone ponds (2). The second mud discharge pipe (35) is connected to the bottom of another cyclone pond (2) and is connected to one side of the bottom of the flocculation pond (3).

5. The device for removing microplastics in water by combining flocculation and electrical flotation according to claim 1, characterized in that: 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) are provided on the inner side of the rotating ring (41) and are slidably connected to the outer wall of the flocculation tank (3), a plurality of stirring rods (44) are provided at equal intervals on the inner side wall of the flocculation tank (3), a plurality of blades (45) for stirring the sewage inside the flocculation tank (3) are provided at the front end of each stirring rod (44), and a plurality of blades (45) for stirring the sewage inside the flocculation tank (3) are provided at the rear end of each stirring rod (44) after penetrating the flocculation tank (3) and extending to the rotating ring (41), and each stirring rod (44) is rotatably sealed and 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 rotatably meshed with a first tooth groove (47) provided at the bottom of the upper slider (42).

6. The device for removing microplastics in water by combining flocculation and electrical flotation according to claim 5, characterized in that: A plurality of drive motors (5) are arranged on the ground outside the flocculation tank (3), and a second gear (51) is provided on the top output shaft of each drive 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 evenly spaced at the bottom of the lower slider (43), and the auxiliary rollers (49) slide in the limiting grooves (38) provided at the bottom of the lower slide groove (37).

7. The device for removing microplastics in water by combining flocculation and electrical flotation according to claim 6, characterized in that: The number of the stirring rods (44) is 6 to 8, the number of the blades (45) on each stirring rod (44) is 3 to 4, and the number of the driving motors (5) is 2 to 4.

8. The device for removing microplastics in water by combining flocculation and electrical flotation according to claim 1, characterized in that: A magnetic stirrer (19) is provided at the bottom of the electric floating pool (1), the anode electrode plates (13) and the cathode electrode plates (14) are provided in the same number, 4 to 16, the spacing between the anode electrode plates (13) and the cathode electrode plates (14) is 2 to 20 cm, and a slag scraper (151) is provided on one side of the slag discharge trough (15) corresponding to the upper part of the electric floating pool (1).

9. A method for removing microplastics from water by combining flocculation and electrical flotation, based on a device for removing microplastics from water by combining flocculation and electrical flotation according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1, electrical flotation treatment: inject the microplastic-contaminated sewage into the electrical flotation tank (1) through the water inlet pipe (11), rectify the 220V AC power into 0.1-10A DC power through the voltage stabilizer (12), and electrolyze for 30-40 minutes, so that bubbles are generated to carry the microplastics in the sewage to the surface and discharge them through the slag discharge tank (15), and the treated sewage is diverted to the cyclone tank (2) through the diversion pump (17) and the first outlet pipe (16); S2, cyclone treatment: during cyclone treatment, it is divided into three different treatment conditions according to the content of microplastics in sewage. When the content of microplastics with a particle size greater than 20 μm in 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 20 μm in sewage accounts for less than 60% of the total microplastics, S2-2 graded cyclone treatment is carried out; S2-1, multi-stage cyclone treatment: the sewage enters the first cyclone pool (2), and under the action of the centrifugal force of the cyclone and gravity, the sewage rotates downward along the inner wall of the cyclone pool (2), and then is discharged upward from the middle, so that the microplastics with higher density fall to the bottom of the cyclone pool (2), and the microplastics with lower density are discharged through the second outlet pipe (21) along with the water flow. By adjusting each four-way solenoid valve (22), the sewage is first processed by the first cyclone pool (2), then discharged from the top of the cyclone pool (2), and guided to the next cyclone pool (2) through the four-way solenoid valve (22) and the conduit (23), and then cyclone treated again. After being processed by each cyclone pool (2) in turn, the sewage is discharged into the flocculation pool (3) through the four-way solenoid valve (22) and the third outlet pipe (24); S2-2, graded cyclone treatment: the sewage enters each first cyclone pool (2) respectively, and under the action of the cyclone centrifugal force and gravity, the sewage rotates downward along the inner wall of the cyclone pool (2) and is then discharged upward from the middle, so that microplastics with higher density fall to the bottom of the cyclone pool (2), and microplastics with lower density are discharged through the second outlet pipe (21) along with the water flow. By adjusting each four-way solenoid valve (22), the sewage in each cyclone pool (2) is discharged into the flocculation pool (3) through the four-way solenoid valve (22) and the third outlet pipe (24) after a cyclone treatment; S3, flocculation treatment: in the flocculation tank (3), flocculants and coagulants are added through the flocculant storage tank (31) and the coagulant storage tank (32), the amount of flocculant added is 30-40 mg / L, the amount of coagulant added is 0.5-1 mg / L, the flocculant is alum, aluminum chloride or ferric chloride, the coagulant is chitosan or anionic polyacrylamide, the flocculation is stirred for 15-20 minutes, the sedimentation is 20-30 minutes, and the sewage after flocculation treatment is discharged through the drain pipe (33).

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