CN112358017B

CN112358017B - System and method for treating sewage by utilizing induced crystallization

Info

Publication number: CN112358017B
Application number: CN202011168128.0A
Authority: CN
Inventors: 王晓阳; 洪元堂; 谢晓朋; 周义
Original assignee: Beijing Hanqi Environment Technology Co ltd
Current assignee: Beijing Hanqi Environment Technology Co ltd
Priority date: 2020-10-27
Filing date: 2020-10-27
Publication date: 2023-12-19
Anticipated expiration: 2040-10-27
Also published as: CN112358017A

Abstract

The application relates to the technical field of sewage treatment, and particularly discloses a system and a method for treating sewage by utilizing induced crystallization. The system comprises a coagulation tank, a flocculation tank and a sedimentation separation tank which are sequentially communicated, wherein a guide cylinder is vertically arranged in the flocculation tank, and an upward-lifting type axial flow stirrer is arranged in the guide cylinder; the flocculation tank is internally provided with a water passing channel, the flocculation tank is communicated with the coagulation tank through the water passing channel, and the water passing channel is used for enabling the effluent at the top of the coagulation tank to enter the guide cylinder from the bottom of the guide cylinder; the water channel is communicated with a crystal nucleus adding device; and a reflux channel is arranged in the flocculation tank, surrounds the circumference of the guide cylinder and is used for refluxing part of sewage from the top of the guide cylinder to the bottom of the guide cylinder. The system has simple structure and easy control, is particularly suitable for recycling pollutants with utilization value in water, and the purity of the obtained recycled material crystal beads is higher; the treated sewage water has good quality and does not need secondary treatment; the cost of sewage treatment is lower.

Description

System and method for treating sewage by utilizing induced crystallization

Technical Field

The present application relates to the field of wastewater treatment technology, and more particularly, to a system and method for treating wastewater using induced crystallization.

Background

In the field of sewage treatment, a method of adding a chemical substance to wastewater to react the chemical substance with some dissolved substances in the wastewater to generate insoluble salts and precipitate the insoluble salts is called a chemical precipitation method. The formation of a precipitate in chemical precipitation is a process of progression from none to small to large, which is quite complex. The precipitate produced by the chemical precipitation process is often an amorphous precipitate formed by a plurality of tiny precipitate particles loosely gathered together, which are randomly arranged and often contain a large amount of moisture and other impurities, so that the precipitate is a loose flocculent precipitate and the volume of the whole precipitate is large.

In order to accelerate the formation of sediment, excessive dosing, dosing treatment agents and other measures are generally adopted, so that impurities are added in the sludge, the recycling value of the sediment sludge is greatly reduced, and the difficulty of sludge treatment is increased. Moreover, the sludge produced by the chemical precipitation process is often dangerous waste and needs to be specially treated, but the unit cost of the special treatment is very high, the water content of the waste sludge is as high as 60% -80%, the volume of the waste sludge is larger, and the treatment cost is further increased.

In order to solve the above-mentioned problem of sludge treatment, in recent years, the "induced crystallization precipitation technology" has been developed rapidly, which uses induced crystallization as a principle, and combines a fluidized bed or packed bed reactor to induce crystallization reaction of the substances to be removed on the seed crystal, thereby depositing on the seed crystal, and then discharging sludge through the bottom, thereby achieving the purpose of treatment and achieving effective recovery of some substances. Among these, the most common is a pellet reactor, which has the ability to remove some contaminants from the wastewater that can precipitate in crystalline form.

However, pellet reactors suffer from the following disadvantages: the effluent treated by the pellet reactor needs to be treated for the second time by adopting a sand filter and the like, so that the cost is too high; the pellet reactor has larger size and higher investment cost; meanwhile, in order to recycle the better pellets, the controlled reaction conditions are harsh, the process is unstable in actual operation, and the risk of unstable effluent quality exists.

Disclosure of Invention

In order to reduce sewage treatment costs, investment costs, and improve the stability of sewage treatment processes, the present application provides a system and method for treating sewage using induced crystallization.

In a first aspect, the present application provides a system for treating sewage by using induced crystallization, which adopts the following technical scheme:

a system for treating sewage by utilizing induced crystallization comprises a coagulation tank, a flocculation tank and a sedimentation separation tank which are sequentially communicated, wherein a guide cylinder is vertically arranged in the flocculation tank, and the inner diameter of the bottom of the guide cylinder is larger than the inner diameter of the top of the guide cylinder; an upward-lifting axial flow stirrer is arranged in the guide cylinder;

a water passing channel is arranged in the flocculation tank, the flocculation tank is communicated with the coagulation tank through the water passing channel, and the water passing channel is used for enabling the effluent at the top of the coagulation tank to enter the guide cylinder from the bottom of the guide cylinder;

the water passing channel is communicated with a crystal nucleus adding device;

and a reflux channel is arranged in the flocculation tank, surrounds the circumference of the guide cylinder and is used for refluxing part of sewage from the top of the guide cylinder to the bottom of the guide cylinder.

By adopting the technical scheme, sewage enters the coagulation tank, treatment chemical is put into the sewage, then the sewage enters the bottom of the guide cylinder from the water passage, at the moment, induction crystal nucleus is put into the water passage, the treatment chemical reacts with pollutants in the sewage, and generated precipitate substances are wrapped on the surface of the induction crystal nucleus to form embryonic crystal beads; after sewage enters the guide cylinder, flocculant is added into the flocculation tank, and pollutants to be removed in the sewage react with the flocculant again to continue to react on the formed embryonic crystal beads, so that the embryonic crystal beads become large. Under the action of the lifting axial flow stirrer, sewage in the guide cylinder flows out from the top of the guide cylinder, and at the moment, part of sewage containing larger crystal beads enters a sedimentation separation tank; part of sewage containing smaller crystal beads flows to the bottom of the guide cylinder along the backflow channel, and flows into the guide cylinder again from the bottom of the guide cylinder to form an internal circulation. In the circulation process, small crystal beads are larger and larger, become larger crystal beads, then flow into a sedimentation separation tank along with sewage, the larger crystal beads in the sedimentation separation tank serve as ballast, sludge can be quickly settled, mud-water separation is quickly realized, clear water is discharged from the top of the sludge tank, and sludge is discharged from the bottom of the sedimentation separation tank.

The sewage coming out through the system of the application can be directly discharged or utilized, and the sewage is not required to be subjected to secondary treatment such as sand filtration and the like, so that the sewage treatment cost is relatively low. The sediment obtained through the system of this application is crystal form sediment, and its structure is inseparable, easily deposits to the bottom of the pool, and mud volume reduces greatly, and the moisture content of mud is low, easily recycle or final handling.

The upward-lifting type axial flow stirrer combines a water flow mode of the guide cylinder in and out from the bottom, can generate a suspension effect and drive sewage to flow upwards, so that the driving force can be reduced, and the electric energy can be saved.

The system has simple structure, is easy to control and modify, and is particularly suitable for upgrading and modifying the existing sewage treatment plant. The sewage treatment system can be obtained by reforming the treatment tank of the original sewage treatment plant without additionally adding a pellet reactor, so that the cost can be saved, the occupied area can be reduced, and the cost and difficulty of sewage treatment can be reduced.

Preferably, a first retaining wall is arranged between the flocculation tank and the flocculation tank, and sewage can turn over the first retaining wall and enter the flocculation tank from the flocculation tank; a second retaining wall is arranged between the flocculation tank and the sedimentation separation tank, and sewage can turn over the second retaining wall and enter the sedimentation separation tank from the flocculation tank;

The flocculation tank is internally and vertically provided with a drainage plate, the drainage plate is positioned between the guide cylinder and the first retaining wall, one end of the drainage plate is fixed at the top of the flocculation tank and is used for preventing sewage which turns over the first retaining wall from entering the guide cylinder from the top of the guide cylinder, a gap is reserved between the other end of the drainage plate and the bottom of the flocculation tank, and a space between the drainage plate and the first retaining wall forms the water passing channel;

the side wall of the guide cylinder, the drainage plate and the annular space formed by the second retaining wall are the backflow channels.

Through adopting above-mentioned technical scheme, in this application, through reforming transform coagulation tank and flocculation tank, sedimentation separation tank, set up first barricade between flocculation tank and sedimentation separation tank, set up the second barricade between flocculation tank and sedimentation separation tank to and set up drainage board etc. can realize laying of water channel and backward flow passageway, the structure is exquisite, easily implements and reforms transform, practices thrift sewage treatment's cost and investment cost.

Preferably, at least two supporting blocks are arranged in the backflow channel and used for fixing the guide cylinder between the drainage plate and the second retaining wall;

a supporting rod is arranged in the flocculation tank, one end of the supporting rod is connected with the guide cylinder, and the other end of the supporting rod is connected with the bottom wall of the flocculation tank.

By adopting the technical scheme, the supporting block can stably support and fix the guide cylinder. The supporting rod is positioned below the guide cylinder, can stably support the guide cylinder, and is beneficial to the stable operation of the flocculation reactor. In the system, the supporting block and the supporting rod can not influence the circulation of sewage while supporting and fixing the guide cylinder, thereby being beneficial to improving the sewage treatment efficiency.

Preferably, the supporting block is vertically arranged, the top end of the supporting block is flush with the upper edge of the guide cylinder, and the length of the supporting block is smaller than the height of the guide cylinder;

a plurality of baffles are vertically arranged in the reflux channel along the radial direction of the guide cylinder, and the baffles are fixed between the outer wall of the guide cylinder and the inner wall of the flocculation tank;

the top end of the baffle plate is 30-50mm higher than the upper edge of the guide cylinder, and the bottom end of the baffle plate is positioned above the lower edge of the guide cylinder.

Through adopting above-mentioned technical scheme, the supporting shoe top flushes with the upper edge of draft tube, avoids the supporting shoe to block the sewage that comes out from the draft tube top and turns over the supporting shoe, is favorable to sewage circulation. The supporting blocks are vertically arranged, sewage from the top end of the guide cylinder flows to the bottom of the guide cylinder along the channel between the adjacent supporting blocks, and the circulating sewage can be prevented from generating vortex and rotational flow to a certain extent, so that the sewage circulating speed can be increased.

Sewage from the top end of the guide cylinder flows to the bottom of the guide cylinder along the channel between the adjacent baffles, and the circulating sewage can be prevented from generating vortex and rotational flow to a certain extent, so that the sewage circulating speed can be increased. The top of the baffle is 30-50mm higher than the upper edge of the guide cylinder, so that sewage from the top of the guide cylinder flows to the bottom of the guide cylinder uniformly, and the system can run stably.

Preferably, a medicament adding ring is fixedly arranged in the guide cylinder at a position 200-300mm away from the bottom of the lifting axial flow stirrer, and a medicament adding hole is formed in the medicament adding ring, and the opening of the medicament adding hole faces downwards.

Through adopting above-mentioned technical scheme, the medicament is thrown and is added the ring and set up in the bottom of lifting axial flow agitator, and the medicament is earlier with sewage mixing time, and the more even that mixes, flocculation effect is better. The dosing hole is downward, and the water flow direction is opposite to the dosing direction, so that the sewage and the medicament are fully mixed, and better flocculation is facilitated.

Preferably, a water separator is horizontally arranged below the medicament adding ring in the guide cylinder, and is fixedly connected with the side wall of the guide cylinder, wherein the water separator is circular, and the top surface of the water separator is in a shape like a Chinese character 'mi'.

Through adopting above-mentioned technical scheme, the water knockout drum can integrate the draft tube from the rivers of the different directions in bottom into along the vertical ascending direction flow of draft tube, has effectively avoided phenomenon such as the whirl of sewage, vortex, can make the better internal circulation of sewage. And the arrangement of the water separator can lead the sewage flowing into the guide cylinder to be more balanced, thereby being beneficial to flocculation.

Preferably, the flocculation tank is rectangular or circular;

when the flocculation tank is rectangular, the ratio of the depth to the width of the flocculation tank is (2-3): 1; the ratio (0.3-0.5) between the top inner diameter of the guide cylinder and the width of the flocculation tank: 1, a step of;

when the flocculation tank is circular, the ratio between the depth and the diameter of the flocculation tank is (2-3): 1; the ratio (0.3-0.5) between the top inner diameter of the guide cylinder and the diameter of the flocculation tank: 1, a step of;

the distance between the bottom end of the guide cylinder and the bottom wall of the flocculation tank is 1/3-2/3 of the inner diameter of the top of the guide cylinder.

Through adopting above-mentioned technical scheme, flocculation basin and draft tube are according to specific proportion design, satisfy specific specification, are favorable to better circulation of sewage, also can prevent the flocculating constituent to deposit in the flocculation basin, have improved flocculation efficiency, are favorable to the stable operation of system.

Preferably, a plurality of inclined pipes are obliquely arranged in the sedimentation separation tank, the inclined angle between the inclined pipes and the horizontal plane is 60-75 degrees, and the length of the inclined pipes is 0.75-1.5m;

the sedimentation separation tank is characterized in that a water collecting tank is arranged on the inner wall of the sedimentation separation tank, and a serrated overflow port is arranged at the top of the water collecting tank.

Through adopting above-mentioned technical scheme, through being provided with the inclined tube and collecting tank, be favorable to the muddy water quick separation in the sewage, improve sewage treatment's efficiency.

Preferably, the system for treating sewage by utilizing induced crystallization further comprises a sludge reflux pump, a hydrocyclone, a sludge pond, a crystal bead screening device and a crystal bead collecting device;

the inlet end of the sludge reflux pump is communicated with the bottom of the sedimentation separation tank, and the outlet end of the sludge reflux pump is communicated with the hydrocyclone;

the hydrocyclone is communicated with the sludge pond through a sludge discharge pipe;

the inlet end of the crystal bead screening device is communicated with the bottom end of the hydrocyclone, and the outlet end of the crystal bead screening device is communicated with the flocculation tank;

the crystal bead collecting device is communicated with the crystal bead screening device.

By adopting the technical scheme, the sludge (the mixed solution of the sludge and the crystal beads) at the bottom of the sedimentation separation tank is directly conveyed into the hydrocyclone by the sludge reflux pump, the crystal beads and the sludge are subjected to cyclone separation by the hydrocyclone, and the separated sludge can be directly discharged in the sludge tank; and the separated crystal beads are screened by a crystal bead screening device, the crystal beads with the particle size larger than 3mm are collected in a crystal bead collecting device, and the rest crystal beads can flow back to a flocculation tank to be used as induction crystal nuclei again, so that the resources are saved and the follow-up recovery of the crystal beads is facilitated.

In a second aspect, the present application provides a method for treating sewage by using induced crystallization, which adopts the following technical scheme:

a method for treating sewage by using induced crystallization, comprising the following steps:

introducing pretreated sewage into a coagulation tank, adding a treatment agent into the coagulation tank, staying the sewage in the coagulation tank for 2-12min, introducing the sewage into the bottom of a guide cylinder from a water channel, and at the moment, introducing 1000-3000mg/L of induction crystal nucleus into the water channel through a crystal nucleus adding device;

the sewage enters a guide cylinder, 1-5mg/L flocculant is added into a flocculation tank, and under the action of an upward-lifting axial flow stirrer, the sewage in the guide cylinder flows out from the top of the guide cylinder; at the moment, part of sewage containing the crystal beads passes through the second retaining wall and enters the sedimentation separation tank, and the rest of sewage containing the crystal beads flows to the bottom of the guide cylinder along the backflow channel and flows into the guide cylinder again from the bottom of the guide cylinder; sewage entering the sedimentation separation tank realizes mud-water separation, clean water flows out from the top of the separation tank, and sludge is discharged from the bottom of the separation tank.

By adopting the technical scheme, the pretreated sewage enters the coagulation tank, the treatment agent is added into the coagulation tank for reaction for 2-12min, then the sewage enters the bottom of the guide cylinder from the water passing channel, at the moment, the induction crystal nucleus is added into the water passing channel, the treatment agent or other agents react with pollutants in the sewage, and the generated precipitate substances are wrapped on the surface of the induction crystal nucleus to form embryonic crystal beads; after sewage enters the guide cylinder, flocculant is added into the flocculation tank, and pollutants to be removed in the sewage react with the flocculant again and continue to react on the formed embryonic crystal beads, so that the embryonic crystal beads become large; under the action of the lifting axial flow stirrer, sewage in the guide cylinder flows out from the top of the guide cylinder, and at the moment, part of sewage containing crystal beads turns over the retaining wall and enters the sedimentation separation tank; and the residual part of sewage containing the crystal beads flows to the bottom of the guide cylinder along the backflow channel, and flows into the guide cylinder again from the bottom of the guide cylinder. Forming a fluidization state of internal water flow in the flocculation tank by taking the guide cylinder as the center; can ensure that immature crystal pearl (the crystal pearl that the particle diameter is less than or equal to 3 mm) can carry out circulating fluidization in the draft tube inside, at circulating fluidization's in-process, immature crystal pearl has become great crystal pearl along with inside fluidization state is bigger and bigger, then along with sewage comes to sedimentation separation pond.

The original sewage is pretreated firstly to remove larger impurities or suspended matters in the sewage, and the pretreatment is conventional treatment in the field of sewage treatment.

In the method, through the system, the quality of the effluent can be improved only by controlling the dosage and the dosage of the induced crystal nucleus, and the crystal beads which are compact and have high purity are obtained. Compared with the process for treating sewage by using a pellet reactor, the process for treating sewage is simpler, the treatment condition is not harsh, the treatment capacity is high, the treatment efficiency is high, the control is easy, the risk of unstable water quality of effluent is small, and the sewage treatment process is stable.

Preferably, the sludge discharged from the bottom of the precipitation separation tank is refluxed by a sludge reflux pump, and the reflux amount of the sludge reflux pump is 3% -10% of the water inflow of the coagulation tank;

the sludge from the outlet end of the sludge reflux pump enters into the hydrocyclone, is swirled by the hydrocyclone, is discharged into the sludge tank through the sludge discharge pipe, and the crystal beads are sent to the crystal bead screening device, are screened by the crystal bead screening device, and are sent to the crystal bead collecting device, and the crystal beads with the particle size of less than or equal to 3mm flow back into the flocculation tank.

Through adopting above-mentioned technical scheme, sediment separation tank bottom exhaust mud (including mud and brilliant pearl) is carried in the hydrocyclone by mud reflux pump return current, obtains mud and brilliant pearl after the hydrocyclone revolves the branch, and at this moment, mud is discharged in the mud pond, and brilliant pearl is carried in the brilliant pearl sieving mechanism, and brilliant pearl sieving mechanism filters brilliant pearl, and the qualified brilliant pearl that the particle diameter is greater than 3mm sends into brilliant pearl collection device, and the unqualified brilliant pearl that the particle diameter is less than or equal to 3mm flows back to the flocculation tank. In the process, qualified crystal beads are screened out and recovered. And returning the unqualified crystal beads to the flocculation tank, using the unqualified crystal beads as induction crystal nuclei again, circulating in the flocculation tank, continuously fluidizing and growing until the unqualified crystal beads are changed into qualified crystal beads, and entering a precipitation separation tank. The induced crystal nucleus can be reused, so that the resources are saved and the environment is protected.

In summary, the present application has the following beneficial effects:

1. because the induced crystallization principle is adopted and matched with a special flocculation tank, part of sewage containing smaller crystal beads flows to the bottom of the guide cylinder along a backflow channel, and flows into the guide cylinder again from the bottom of the guide cylinder to form an internal circulation, in the process of the internal circulation, the smaller crystal beads (unqualified crystal beads) are larger and larger, and become larger crystal beads (qualified crystal beads), and the larger crystal beads can be rapidly precipitated in a precipitation separation tank, so that crystal form precipitation is obtained; compared with the common precipitation, the crystal form precipitation has the advantages of reduced volume, low water content, compact structure and easiness in precipitation to the bottom of the tank, so that the sludge separated from the crystal form precipitation is easy to recycle or finally treat, and meanwhile, the effluent water quality of the precipitation separation tank is better, and secondary treatment by a sand filter and the like is not needed, so that the cost of sewage treatment is reduced;

2. The system has simple structure, easy control and easy transformation, can be suitable for upgrading and transforming the existing sewage treatment plant without additionally adding a pellet reactor, and saves the investment and cost of sewage treatment;

3. the sewage treatment method used in the application has high treatment capacity, high treatment efficiency and relatively stable treatment process;

4. the system and the method are combined, and are particularly suitable for recycling pollutants with value in water, and the obtained recycled material crystal beads have higher purity and yield.

Drawings

Fig. 1 is a schematic structural view of the overall structure of the sewage treatment system of the present embodiment.

FIG. 2 is a cross-sectional view of the flocculation basin of the present embodiment taken along the height direction of two symmetrical support blocks.

FIG. 3 is a cross-sectional view of the flocculation basin of the present embodiment taken along the height of two symmetrical baffles.

FIG. 4 is a top view of the flocculation basin edge of the present embodiment.

Description of the drawings: 1. a coagulation tank; 11. a sewage inlet pipe; 12. a stirrer; 13. a dosing device; 2. a flocculation tank; 21. a guide cylinder; 211. an upward-lifting axial flow stirrer; 212. a medicament adding ring; 213. a water separator; 22. a water passing channel; 221. a crystal nucleus adding device; 23. a return passage; 24. a drainage plate; 25. a fixing frame; 26. a support block; 27. a support rod; 28. a baffle; 3. a sedimentation separation tank; 31. clear water is discharged from the ditch; 32. a pre-settling zone; 33. a sloped tube separation zone; 34. a water collection tank; 35. a mud scraper; 4. a sludge reflux pump; 5. a hydrocyclone; 6. a sludge pool; 7. a crystal bead screening device; 8. a crystal bead collecting device; 9. a first retaining wall; 10. and a second retaining wall.

Detailed Description

The present application is described in further detail below in conjunction with figures 1-4.

A system for treating sewage by utilizing induced crystallization, as shown in figure 1, comprises a coagulation tank 1, a flocculation tank 2, a sedimentation separation tank 3, a sludge reflux pump 4, a hydrocyclone 5, a sludge tank 6, a crystal bead screening device 7 and a crystal bead collecting device 8. The coagulation tank 1, the flocculation tank 2 and the sedimentation separation tank 3 are sequentially communicated, a sewage inlet pipe 11 is arranged at the bottom end of the coagulation tank 1, and a clear water outlet channel 31 is arranged at the top of the sedimentation separation tank 3. The inlet end of the sludge reflux pump 4 is communicated with the bottom of the sedimentation separation tank 3, and the outlet end of the sludge reflux pump 4 is communicated with the hydrocyclone 5. A sludge discharge pipe is arranged between the hydrocyclone 5 and the sludge tank 6 and is used for discharging the sludge separated by the hydrocyclone 5 into the sludge tank 6; the bottom of the hydrocyclone 5 is communicated with the crystal bead screening device 7, and the crystal beads separated by the hydrocyclone 5 are conveyed into the crystal bead screening device 7. The crystal bead screening device 7 is communicated with the flocculation tank 2, a crystal bead return pipe is arranged between the crystal bead screening device 7 and the crystal bead collecting device 8, the crystal bead screening device 7 screens crystal beads, qualified crystal beads (the grain diameter is greater than 3 mm) are collected in the crystal bead collecting device 8, and unqualified crystal beads (the grain diameter is less than or equal to 3 mm) are returned into the flocculation tank 2 for circulation.

As shown in fig. 1, a stirrer 12 is installed at the top of the coagulation tank 1, and the blades of the stirrer 12 are positioned at the central position of the coagulation tank 1; the coagulation tank 1 is connected to a dosing device 13 for dosing the coagulation tank 1 with a treatment agent, preferably from the top of the coagulation tank 1; the agitator 12 is used to agitate the wastewater to thoroughly mix the wastewater with the treatment chemical delivered.

In one embodiment, the coagulation tank 1 is connected to an acid-base regulator feeding device for feeding an appropriate acid or base to the coagulation tank 1, so that the pH value of the sewage in the coagulation tank 1 can be controlled. In one embodiment, an on-line pH meter is provided on the side wall of the coagulation tank 1 for monitoring the acidity and alkalinity of the sewage in the coagulation tank 1 in real time. And controlling the type and the dosage of the acid-base regulator put in the acid-base regulator putting device according to the reading of the pH meter.

As shown in fig. 1 and 2, a guide cylinder 21 is vertically arranged in the flocculation tank 2, and the inner diameter of the bottom of the guide cylinder 21 is larger than that of the top. In this embodiment, the guide cylinder 21 includes a cylindrical cylinder and a horn ring fixedly connected to the lower end of the cylindrical cylinder, and the edge of the narrower end of the horn ring is integrally connected with the cylindrical cylinder. The flocculation tank 2 is rectangular, and the ratio of the depth to the width of the flocculation tank 2 is (2-3): 1; the ratio between the inner diameter of the cylinder and the width of the flocculation tank 2 is (0.3-0.5): 1, a step of; the distance between the edge of the wider end of the horn ring and the bottom wall of the flocculation tank 2 is 1/3-2/3 of the inner diameter of the cylindrical barrel.

In one embodiment, flocculation basin 2 is circular, and the ratio between the depth and the diameter of flocculation basin 2 is (2-3): 1; the ratio between the inner diameter of the cylinder and the diameter of the flocculation basin 2 is (0.3-0.5): 1, a step of; the distance between the edge of the wider end of the horn ring and the bottom wall of the flocculation tank 2 is 1/3-2/3 of the inner diameter of the cylindrical barrel.

As shown in fig. 1 and 2, a first retaining wall 9 is arranged between the flocculation tank 2 and the flocculation tank 1, and sewage can pass through the first retaining wall 9 and enter the flocculation tank 2 from the flocculation tank 1; a second retaining wall 10 is arranged between the flocculation tank 2 and the sedimentation separation tank 3, and sewage can pass through the second retaining wall 10 and enter the sedimentation separation tank 3 from the flocculation tank 2.

As shown in fig. 1 and 2, a drainage plate 24 is vertically arranged in the flocculation tank 2, the drainage plate 24 is positioned between the guide cylinder 21 and the first retaining wall 9, and one end of the drainage plate 24 is fixed at the top of the flocculation tank 2 and is used for preventing sewage which turns over the first retaining wall 9 from entering the guide cylinder 21 from the top of the guide cylinder 21; a gap is reserved between the other end of the drainage plate 24 and the bottom wall of the flocculation tank 2, a water passing channel 22 is formed in the space between the drainage plate 24 and the first retaining wall 9, and the water passing channel 22 is used for enabling the effluent at the top of the flocculation tank 1 to enter the guide cylinder 21 from the bottom of the guide cylinder 21. The annular space formed by the side wall of the guide cylinder 21, the drainage plate 24 and the second retaining wall 10 is a backflow channel 23, and the backflow channel 23 is used for backflow of part of sewage from the top of the guide cylinder 21 to the bottom of the guide cylinder 21. In this embodiment, a fixing frame 25 for fixing the drainage plate 24 is provided on the top of the flocculation tank 2.

As shown in fig. 1 and 2, at least two supporting blocks 26 are disposed in the backflow channel 23, one end of each supporting block 26 is welded with the drainage plate 24 or the second retaining wall 10, the other end of each supporting block 26 is welded with the outer wall of the cylindrical barrel, and the supporting blocks 26 fix the guide cylinder 21 between the drainage plate 24 and the second retaining wall 10, so that stable installation of the guide cylinder 21 is facilitated. The supporting block 26 is vertically arranged, the length of the supporting block 26 is smaller than the height of the guide cylinder 21, in the embodiment, the height of the supporting block 26 is consistent with the height of the cylinder, the top end of the supporting block 26 is flush with the upper edge of the cylinder, and the bottom end of the supporting block 26 is flush with the junction of the cylinder and the horn ring. The sewage from the top end of the guide cylinder 21 flows to the bottom of the guide cylinder 21 along the channel between the adjacent supporting blocks 26, so that the circulating sewage is prevented from generating vortex and whirl, and the sewage circulating speed is increased.

As shown in fig. 1 and 2, a support rod 27 is provided in the flocculation tank 2, one end of the support rod 27 is fixed on the inner wall of the guide cylinder 21 (the junction of the cylindrical cylinder and the horn ring) by bolts, and the other end of the support rod 27 is fixedly connected on the bottom wall of the flocculation tank 2 by bolts. The number of the support bars 27 may be 4 to 8. The supporting rod 27 is matched with the supporting block 26, so that the guide cylinder 21 can be stably fixed in the flocculation tank 2. The supporting rod 27 is arranged at the bottom of the flocculation tank 2, and can support the guide cylinder 21 without influencing sewage to enter the guide cylinder 21.

As shown in fig. 1 and 2, the guide cylinder 21 is internally provided with an upward-lifting axial flow stirrer 211, the upward-lifting axial flow stirrer 211 comprises a stirring shaft and an impeller fixedly connected to the stirring shaft, and the impeller extends below the central position of the guide cylinder 21, so that better sewage mixing is facilitated. The upward-lifting type axial flow stirrer 211 can convey sewage at the bottom of the guide cylinder 21 upward, thereby facilitating the circulation of the sewage. The medicament adding ring 212 is arranged in the guide cylinder 21 at a position 200-300mm away from the bottom of the lifting axial flow stirrer 211, the medicament adding ring 212 is positioned at the bottom end of the guide cylinder 21, the mixing time of the medicament and the sewage entering from the bottom end of the guide cylinder 21 is relatively early, and the better the mixing and flocculating effects are; the medicine adding ring 212 is provided with a plurality of medicine adding holes, the openings of the medicine adding holes are downward, the water flow direction is opposite to the medicine adding direction, and the sewage and the medicine are fully mixed, so that better flocculation is facilitated.

As shown in fig. 1 and 2, a water separator 213 is horizontally installed below the medicament adding ring 212 in the guide cylinder 21, the water separator 213 is fixedly connected with the inner side wall of the guide cylinder 21, the water separator 213 is circular, and the top surface of the water separator 213 is in a shape of a Chinese character 'mi'. The water separator 213 integrates the sewage from the bottom of the guide cylinder 21 in different directions, changes the sewage from different directions into water flow along the vertical direction of the guide cylinder 21, effectively avoids phenomena such as rotational flow and vortex of the sewage, and ensures that the sewage circulates in the flocculation tank 2 better.

As shown in fig. 3 and 4, a plurality of baffles 28 are vertically arranged in the backflow channel 23 along the radial direction of the guide cylinder 21, and the baffles 28 may be arranged in 2-8 blocks, and in this embodiment, for convenience of illustration, the baffles 28 are arranged in 4 blocks. The baffle 28 is fixed between the outer wall of the guide cylinder 21 and the inner wall of the flocculation basin 2; the top end of the baffle 28 is 30-50mm higher than the upper edge of the guide cylinder 21, and the bottom end is positioned above the lower edge of the guide cylinder 21. Sewage from the top end of the guide cylinder 21 flows to the bottom of the guide cylinder 21 along the channel between the adjacent baffles 28, so that the circulating sewage is prevented from generating vortex and rotational flow, and the sewage circulating speed is increased.

As shown in fig. 1, a pre-sedimentation zone 32, an inclined tube separation zone 33 and a water collecting tank 34 are arranged in the sedimentation separation tank 3 along the water flow direction; the water flow speed of the pre-sedimentation zone 32 is set to be 30-80m/h; the inclined tube separation area 33 is internally provided with a plurality of inclined tubes in an inclined way, the length of each inclined tube is 0.75-1.5m, the inclined angle between each inclined tube and the water surface is 60-75 degrees, and each inclined tube is made of PE material; the top of the water collecting tank 34 is provided with a serrated overflow port which is communicated with the clean water outlet channel 31. A mud scraper 35 is arranged in the sedimentation separation tank 3, so that the sludge at the bottom of the tank can be cleaned conveniently.

The sewage treatment process comprises the following steps:

The sewage enters the coagulation tank 1 from the sewage inlet pipe 11, a treatment agent (the treatment agent can be aluminum salt, ferric salt or organic treatment agent, and the like, specifically can be calcium chloride or sodium sulfide, and the like) is put into the sewage through the dosing device 13, the sewage stays in the coagulation tank 1 for 2-12min, then the sewage turns over the first retaining wall 9, and enters the bottom of the guide cylinder 21 from the water channel 22; at this time, an induction crystal nucleus is put into the water channel 22 (the induction crystal nucleus is put into the water channel 22 through the crystal nucleus adding device 221 at the beginning, after the system stably operates, the induction crystal nucleus can be supplemented through the circulating crystal beads, when the circulating amount is insufficient, a new induction crystal nucleus is added through the crystal nucleus adding device 221), at this time, the treatment agent reacts with pollutants in the sewage, and the generated precipitate substances are wrapped on the surface of the induction crystal nucleus to form embryonic crystal beads;

after the sewage enters the guide cylinder 21, flocculant is added through the reagent adding ring 212, and the pollutants to be removed in the sewage react with the flocculant again and continue to react on the formed embryonic crystal beads, so that the embryonic crystal beads become large; under the action of the lifting axial flow stirrer 211, sewage in the guide cylinder 21 flows out from the top of the guide cylinder 21, and at the moment, part of sewage containing larger crystal beads turns over the second retaining wall 10 to enter the sedimentation separation tank 3;

Part of sewage containing smaller crystal beads flows to the bottom of the guide cylinder 21 along the backflow channel 23, flows into the guide cylinder 21 again from the bottom of the guide cylinder 21 to form an internal circulation, and in the circulation process, the smaller crystal beads become larger and larger crystal beads, and then enter the sedimentation separation tank 3 along with the sewage; in the sedimentation tank 3, the crystal beads are used as ballast, the sludge can be settled quickly, mud-water separation is realized quickly, clear water is discharged from a clear water outlet channel, and the sludge (the mixed solution of the sludge and the crystal beads) is discharged from the bottom of the sedimentation tank 3.

The sludge reflux pump 4 conveys sludge (mixed liquid of sludge and crystal beads) into the hydrocyclone 5, the hydrocyclone 5 carries out cyclone separation on the sludge, and the sludge separated by the hydrocyclone 5 is directly discharged into the sludge tank 6 through a sludge discharge pipe; the crystal beads separated by the hydrocyclone 5 enter a crystal bead screening device 7; the crystal bead screening device 7 screens the crystal beads, the crystal beads with the particle size larger than 3mm can be collected in the crystal bead collecting device 8, and the crystal beads with the particle size smaller than or equal to 3mm flow back to the flocculation tank 2 to be used as the induction crystal nucleus again.

The system has the advantages of simple structure, easy control of process conditions, stable water quality of the effluent, direct discharge or utilization of the effluent through the system, no need of secondary treatment through sand filter and the like, and relatively low cost of sewage treatment. The sediment obtained through the system of this application is crystal form sediment, and its structure is inseparable, easily deposits to the bottom of the pool, and the mud volume of discharging is reduced, the moisture content is low, easily recycle.

Application example 1

Some project of fluorine-containing wastewater, the treated water quantity is 200m ³ The specific treatment method is as follows:

firstly, sewage is pretreated by a high-efficiency sedimentation tank to remove a large amount of suspended matters in the water.

The pretreated sewage enters the coagulation tank 1 from the sewage inlet pipe 11, 3000mg/L calcium chloride solution and 210mg/L NaOH are added into the sewage through the dosing device 13, and the sewage stays in the coagulation tank 1 for reaction for 8min after being fully mixed by the stirrer 12. Then the sewage turns over the first retaining wall 9 and enters the water channel 22, and at the moment, 3000mg/L quartz sand (induced crystal nucleus) with the average grain diameter of 0.1-0.3mm is thrown into the water channel 22 through a crystal nucleus throwing device 221; the sewage flowing out of the water channel 22 enters the guide cylinder 21 from the bottom of the guide cylinder 21, and at the moment, tiny CaF is generated in the sewage ₂ And quartz sand is used as crystal nucleus and is adhered to the quartz sand to form the primary embryonic crystal beads.

The embryonic crystal beads enter the guide cylinder 21 along with the sewage, 1mg/L flocculant is added through the reagent adding ring 212, at the moment, under the action of the lifting axial flow stirrer 211, the sewage in the guide cylinder 21 flows out from the top of the guide cylinder 21, and at the moment, a part of sewage containing the crystal beads turns over the second retaining wall 10 to enter the sedimentation separation tank 3; the residual sewage containing the crystal beads flows to the bottom of the guide cylinder 21 along the backflow channel 23, flows into the guide cylinder 21 again from the bottom of the guide cylinder 21, forms a fluidization state of internal water flow in the flocculation tank 2 by taking the guide cylinder 21 as the center, and ensures that the immature crystal beads can be circularly fluidized in the guide cylinder 21; in the circulation process, the smaller crystal beads become larger with the internal fluidization state becoming larger and larger, and then enter the sedimentation separation tank 3 with the sewage.

The sewage entering the sedimentation separation tank 3 first passes through the preliminary sedimentation zone 32, the water flow speed of the preliminary sedimentation zone 32 is set to 30m/h, then passes through the inclined tube separation zone 33, and finally flows into the clean water outlet channel 31 from the zigzag overflow port of the water collection tank 34. Sewage is subjected to mud-water separation in the sedimentation separation tank 3, clear water flows out from the clear water outlet channel 31, and sludge is discharged from the bottom of the sedimentation separation tank 3. The sludge at the bottom of the sedimentation and separation tank 3 is conveyed into a hydrocyclone 5 by a sludge reflux pump 4 (the reflux amount of the sludge reflux pump 4 is 3 percent of the water inflow amount of a sewage inlet pipe 11), the separated sludge is conveyed into a sludge tank 6 after being separated by the hydrocyclone 5, and the separated crystal beads enter a crystal bead screening device 7; the crystal bead screening device 7 screens the crystal beads, qualified crystal beads with the particle size being more than 3mm enter the crystal bead recovery device, unqualified crystal beads with the particle size being less than or equal to 3mm return to the flocculation tank 2, and continue to fluidize and grow until the qualified crystal beads are formed.

The crystal beads recovered in the crystal bead recovery device are calcium fluoride crystal beads, namely fluorite.

The quality of the inlet water in the sewage inlet pipe 11 and the quality of the outlet water in the clean water outlet channel 31 in application example 1 were measured, and the measurement results are shown in table 2 below.

TABLE 1 intake and outlet Water quality detection Meter

Project	pH value of	Fluoride (mg/L)	SS(mg/L)
				Inflow of water	7-9	500-1000	100-200
Effluent water	7-9	8.4	15.3

The beads obtained in the bead recovery apparatus were examined, and the index of the recovered beads is shown in table 2 below.

Table 2 index of recovered beads

Project	Particle size (mm)	Purity of	Yield (kg/h)
				Crystal bead	＞3	92％	324

From an examination of tables 1 and 2, it can be seen that: the sewage treatment system and the sewage treatment method have the advantages that the sewage treatment effect is good, and the yield and purity of the recovered crystal beads are high.

The fluoride in the effluent is 8.4mg/L, the SS is 15.3mg/L, and the effluent quality of the sewage is good without secondary treatment; the purity of the recovered crystal beads is 92%, and the yield is 324kg/h; the yield is very high, which means that a large amount of pollutants in the sewage are attached to the surface of the crystal nucleus in a concentrated way instead of being mixed in the sludge, so that the cost and difficulty of sludge treatment can be effectively reduced; the high yield and purity indicate that the system and method of the present application are particularly useful for recovery of valuable contaminants in water.

Application example 2

Some project of phosphorus-containing wastewater, the treated water quantity is 100m ³ The specific treatment method is as follows:

The pretreated sewage enters the coagulation tank 1 from the sewage inlet pipe 11, and 350mg/L calcium chloride solution and 180mg/L calcium chloride solution are added into the sewage through the dosing device 13 NaOH, through the thorough mixing of the stirrer 12, the sewage stays in the coagulation tank 1 for reaction for 12min. Then the sewage turns over the first retaining wall 9 and enters the water channel 22, and at the moment, quartz sand (induced crystal nucleus) with the average grain diameter of 0.1-0.3mm and 1500mg/L is thrown into the water channel 22 through the crystal nucleus throwing device 221; the sewage flowing out of the water channel 22 enters the guide cylinder 21 from the bottom of the guide cylinder 21, and at the moment, tiny CaF is generated in the sewage ₂ And quartz sand is used as crystal nucleus and is adhered to the quartz sand to form the primary embryonic crystal beads.

The embryonic crystal beads enter the guide cylinder 21 along with the sewage, 5mg/L flocculant is added through the reagent adding ring 212, and at the moment, under the action of the lifting axial flow stirrer 211, the sewage in the guide cylinder 21 flows out from the top of the guide cylinder 21; at this time, a part of sewage containing crystal beads turns over the second retaining wall 10 to enter the sedimentation separation tank 3; part of the residual sewage containing the crystal beads flows to the bottom of the guide cylinder 21 along the backflow channel 23, flows into the guide cylinder 21 again from the bottom of the guide cylinder 21, forms a fluidization state of internal water flow in the whole flocculation basin 2 by taking the guide cylinder 21 as the center, and ensures that immature crystal beads can be circularly fluidized in the guide cylinder 21; in the circulation process, the smaller crystal beads become larger with the internal fluidization state becoming larger and larger, and then enter the sedimentation separation tank 3 with the sewage.

The sewage entering the sedimentation separation tank 3 first passes through the preliminary sedimentation zone 32, the water flow rate of the preliminary sedimentation zone 32 is set to 80m/h, then passes through the inclined tube separation zone 33, and finally flows into the clean water outlet channel 31 from the zigzag overflow port of the water collection tank 34. Sewage is subjected to mud-water separation in the sedimentation separation tank 3, clear water flows out from the clear water outlet channel 31, and sludge is discharged from the bottom of the sedimentation separation tank 3. The sludge at the bottom of the sedimentation separation tank 3 is conveyed into a hydrocyclone 5 by a sludge reflux pump 4 (the reflux amount of the sludge reflux pump 4 is 10 percent of the water inflow amount of a sewage inlet pipe 11), the separated sludge is conveyed into a sludge tank 6 after being separated by the hydrocyclone 5, and the separated crystal beads enter a crystal bead screening device 7; the crystal bead screening device 7 screens the crystal beads, qualified crystal beads with the particle size being more than 3mm enter the crystal bead recovery device, unqualified crystal beads with the particle size being less than or equal to 3mm return to the flocculation tank 2, and continue to fluidize and grow until the qualified crystal beads are formed.

The water quality of the inlet water in the sewage inlet pipe and the water quality of the outlet water in the clean water outlet channel in application example 2 were measured, and the measurement results are shown in the following table 3.

TABLE 3 quality of inlet water and outlet water quality detecting meter

Project	pH value of	Phosphate (mg/L)	SS(mg/L)
				Inflow of water	7-9	150	150
Effluent water	7-9	0.35	7.9

The beads obtained in the bead recovery apparatus were examined, and the index of the recovered beads is shown in table 4 below.

Table 4 index of recovered beads

Project	Particle size (mm)	Purity of	Yield (kg/h)
				Crystal bead	＞3	90％	21.5

From an examination of tables 3 and 4, it can be seen that: by utilizing the sewage treatment system and method, the sewage treatment effect is good, and the purity of the recovered crystal beads is high.

The phosphate in the effluent is 0.35mg/L, the SS is 7.9mg/L, and the quality of the sewage effluent is good without secondary treatment; the purity of the recovered crystal beads is 90%, and the yield is 21.5kg/h; the method has the advantages that a certain yield indicates that pollutants in sewage can be attached to the surface of crystal nucleus, and the cost and difficulty of sludge treatment can be reduced; the high purity indicates that the system and method of the present application are particularly useful for recovery of valuable contaminants in water.

Application example 3

Some project of copper-containing wastewater, the treated water quantity is 250m ³ The specific treatment method is as follows:

The pretreated sewage enters the coagulation tank 1 from the sewage inlet pipe 11, 200mg/L sodium sulfide solution and 65mg/L NaOH are added into the sewage through the dosing device 13, and the sewage stays in the coagulation tank 1 for reaction for 8min after being fully mixed by the stirrer 12. Then the sewage turns over the first retaining wall 9 and enters the water channel 22, at this time, 1000mg/L quartz sand (induced nucleus) with the average particle size of 0.2-0.5mm is thrown into the water channel 22 through a nucleus throwing device 221, and the generated fine CuS takes the quartz sand as the nucleus and adheres to the quartz sand to form preliminary embryonic crystal beads.

The embryonic crystal beads enter the guide cylinder 21 along with the sewage, 2mg/L flocculant is added through the reagent adding ring 212, at this time, under the action of the lifting axial flow stirrer 211, the sewage in the guide cylinder 21 flows out from the top of the guide cylinder 21, and at this time, part of the sewage containing the crystal beads turns over the second retaining wall 10 to enter the sedimentation separation tank 3; the residual sewage containing the crystal beads flows to the bottom of the guide cylinder 21 along the backflow channel 23, flows into the guide cylinder 21 again from the bottom of the guide cylinder 21, forms a fluidization state of internal water flow in the flocculation tank 2 by taking the guide cylinder 21 as the center, and ensures that immature crystal beads can be circularly fluidized in the guide cylinder 21; in the circulation process, the smaller crystal beads become larger with the internal fluidization state becoming larger and larger, and then enter the sedimentation separation tank 3 with the sewage.

The sewage entering the sedimentation separation tank 3 first passes through the preliminary sedimentation zone 32, the water flow rate of the preliminary sedimentation zone 32 is set to 50m/h, then passes through the inclined tube separation zone 33, and finally flows into the clean water outlet channel 31 from the zigzag overflow port of the water collection tank 34. Sewage is subjected to mud-water separation in the sedimentation separation tank 3, clear water flows out from the clear water outlet channel 31, and sludge is discharged from the bottom of the sedimentation separation tank 3. The sludge at the bottom of the sedimentation and separation tank 3 is conveyed into a hydrocyclone 5 by a sludge reflux pump 4 (the reflux amount of the sludge reflux pump 4 is 6 percent of the water inflow amount of a sewage inlet pipe 11), the separated sludge is conveyed into a sludge tank 6 after being separated by the hydrocyclone 5, and crystal beads after being separated enter a crystal bead screening device 7; the crystal bead screening device 7 screens the crystal beads, qualified crystal beads with the particle size being more than 3mm enter the crystal bead recovery device, unqualified crystal beads with the particle size being less than or equal to 3mm return to the flocculation tank 2, and continue to fluidize and grow until the qualified crystal beads are formed.

The crystal beads recovered in the crystal bead recovery device are calcium sulfide crystal beads.

The water quality of the inlet water in the sewage inlet pipe and the water quality of the outlet water in the clean water outlet channel in application example 3 were measured, and the measurement results are shown in the following table 5.

TABLE 5 quality of incoming water and outgoing water quality detection meter

Project	pH value of	Copper (mg/L)	SS(mg/L)
				Inflow of water	7-9	150	150
Effluent water	7-9	0.3	8.3

The beads obtained in the bead recovery apparatus were examined, and the index of the recovered beads is shown in table 6 below.

Table 6 index of recovered beads

Project	Particle size (mm)	Purity of	Yield (kg/h)
				Crystal bead	＞3	91.2％	56.5

From an examination of tables 5 and 6, it can be seen that: by utilizing the sewage treatment system and method, the sewage treatment effect is good, and the yield of the recovered crystal beads is high.

Copper in the effluent is 0.3mg/L, SS is 8.3mg/L, the quality of the effluent is good, and secondary treatment is not needed;

the purity of the recovered crystal beads is 91.2 percent, and the yield is 56.5kg/h; the higher yield indicates that the pollutants in the sewage are more intensively attached to the surface of the crystal nucleus, so that the cost and difficulty of sludge treatment can be reduced; the purity is very high, and the system and method disclosed by the application are particularly suitable for recovering pollutants with value in water.

The present embodiment is merely illustrative of the present application and is not intended to be limiting, and those skilled in the art, after having read the present specification, may make modifications to the present embodiment without creative contribution as required, but is protected by patent laws within the scope of the claims of the present application.

Claims

1. A system for treating sewage by utilizing induced crystallization, wherein the sewage is industrial wastewater from which impurities and suspended matters are removed after pretreatment, and the system comprises a coagulation tank (1), a flocculation tank (2) and a precipitation separation tank (3) which are sequentially communicated, and is characterized in that:

the coagulation tank (1) is communicated with a dosing device (13) and is used for throwing a treatment agent into the coagulation tank (1);

a guide cylinder (21) is vertically arranged in the flocculation tank (2), and the inner diameter of the bottom of the guide cylinder (21) is larger than the inner diameter of the top; an upward-lifting type axial flow stirrer (211) is arranged in the guide cylinder (21), a medicament adding ring (212) for adding a flocculating agent is fixedly arranged in the guide cylinder (21) at a position 200-300mm away from the bottom of the upward-lifting type axial flow stirrer (211), a medicament adding hole is formed in the medicament adding ring (212), and the opening of the medicament adding hole faces downwards;

a water passing channel (22) is arranged in the flocculation tank (2), the flocculation tank (2) is communicated with the flocculation tank (1) through the water passing channel (22), and the water passing channel (22) is used for enabling the effluent at the top of the flocculation tank (1) to enter the guide cylinder (21) from the bottom of the guide cylinder (21);

the water passing channel (22) is communicated with a crystal nucleus adding device (221);

a reflux channel (23) is arranged in the flocculation tank (2), and the reflux channel (23) surrounds the circumference of the guide cylinder (21) and is used for refluxing part of sewage from the top of the guide cylinder (21) to the bottom of the guide cylinder (21);

The device also comprises a sludge reflux pump (4), a hydrocyclone (5), a sludge tank (6), a crystal bead screening device (7) and a crystal bead collecting device (8);

the inlet end of the sludge reflux pump (4) is communicated with the bottom of the sedimentation separation tank (3), and the outlet end is communicated with the hydrocyclone (5);

the hydrocyclone (5) is communicated with the sludge pond (6) through a sludge discharge pipe;

the inlet end of the crystal bead screening device (7) is communicated with the bottom end of the hydrocyclone (5), and the outlet end is communicated with the flocculation tank (2);

the crystal bead collecting device (8) is communicated with the crystal bead screening device (7);

the industrial wastewater comprises fluorine-containing wastewater, phosphorus-containing wastewater and copper-containing wastewater, when the industrial wastewater is fluorine-containing wastewater, the treatment agents put into the dosing device (13) are calcium chloride solution and NaOH, and the crystal beads collected in the crystal bead collecting device are calcium fluoride crystal beads; when the industrial wastewater is phosphorus-containing wastewater, the treatment agent put into the dosing device (13) is a calcium chloride solution and NaOH, and the crystal beads collected in the crystal bead collecting device are calcium phosphate; when the industrial wastewater is copper-containing wastewater, a treatment agent which is sodium sulfide solution and NaOH is put into the dosing device (13), and the crystal beads collected in the crystal bead collecting device are copper sulfide.

2. The system for treating sewage by using induced crystallization according to claim 1, wherein: a first retaining wall (9) is arranged between the flocculation tank (2) and the flocculation tank (1), and sewage can turn over the first retaining wall (9) and enter the flocculation tank (2) from the flocculation tank (1); a second retaining wall (10) is arranged between the flocculation tank (2) and the sedimentation separation tank (3), and sewage can turn over the second retaining wall (10) and enter the sedimentation separation tank (3) from the flocculation tank (2);

a drainage plate (24) is vertically arranged in the flocculation tank (2), the drainage plate (24) is positioned between the guide cylinder (21) and the first retaining wall (9), one end of the drainage plate (24) is fixed at the top of the flocculation tank (2) and is used for preventing sewage which turns over the first retaining wall (9) from entering the guide cylinder (21) from the top of the guide cylinder (21), and a gap is reserved between the other end of the drainage plate (24) and the bottom of the flocculation tank (2); the space between the drainage plate (24) and the first retaining wall (9) forms the water passing channel (22);

the annular space formed by the side wall of the guide cylinder (21), the drainage plate (24) and the second retaining wall (10) is the backflow channel (23).

3. The system for treating sewage by using induced crystallization according to claim 2, wherein: at least two supporting blocks (26) are arranged in the backflow channel (23) and are used for fixing the guide cylinder (21) between the drainage plate (24) and the second retaining wall (10);

A supporting rod (27) is arranged in the flocculation tank (2), one end of the supporting rod (27) is connected with the guide cylinder (21), and the other end of the supporting rod is connected with the bottom wall of the flocculation tank (2).

4. A system for treating wastewater using induced crystallization according to claim 3 wherein: the supporting blocks (26) are vertically arranged, the top ends of the supporting blocks (26) are flush with the upper edge of the guide cylinder (21), and the length of the supporting blocks (26) is smaller than the height of the guide cylinder (21);

a plurality of baffles (28) are vertically arranged in the backflow channel (23) along the radial direction of the guide cylinder (21), and the baffles (28) are fixed between the outer wall of the guide cylinder (21) and the inner wall of the flocculation basin (2);

the top end of the baffle plate (28) is 30-50mm higher than the upper edge of the guide cylinder (21), and the bottom end of the baffle plate is positioned above the lower edge of the guide cylinder (21).

5. The system for treating sewage by using induced crystallization according to claim 1, wherein: the water knockout drum (213) is horizontally arranged below the medicament adding ring (212) in the guide cylinder (21), the water knockout drum (213) is fixedly connected with the side wall of the guide cylinder (21), the water knockout drum (213) is circular, and the top surface of the water knockout drum (213) is in a shape of a Chinese character 'mi'.

6. The system for treating wastewater using induced crystallization according to any one of claims 1-5, wherein: the flocculation tank (2) is rectangular or circular;

When the flocculation tank (2) is rectangular, the ratio of the depth to the width of the flocculation tank (2) is (2-3): 1; the ratio (0.3-0.5) between the top inner diameter of the guide cylinder (21) and the width of the flocculation tank (2): 1, a step of;

when the flocculation tank (2) is round, the ratio between the depth and the diameter of the flocculation tank (2) is (2-3): 1; the ratio (0.3-0.5) between the top inner diameter of the guide cylinder (21) and the diameter of the flocculation tank (2): 1, a step of;

the distance between the bottom end of the guide cylinder (21) and the bottom wall of the flocculation tank (2) is 1/3-2/3 of the inner diameter of the top of the guide cylinder (21).

7. The system for treating sewage by utilizing induced crystallization according to claim 1, wherein a plurality of inclined pipes are obliquely arranged in the sedimentation separation tank (3), the inclined angle between the inclined pipes and the horizontal plane is 60-75 degrees, and the length of the inclined pipes is 0.75-1.5m; the sedimentation separation tank is characterized in that a water collecting tank (34) is arranged on the inner wall of the sedimentation separation tank (3), and a serrated overflow port is arranged at the top of the water collecting tank (34).

8. A method for using the system for treating wastewater by induced crystallization according to any one of claims 2 to 4, wherein the wastewater is industrial wastewater from which impurities and suspended matters are removed after pretreatment, characterized in that: the method comprises the following steps:

the pretreated sewage enters a coagulation tank (1), a treatment agent is added into the coagulation tank (1), the sewage stays in the coagulation tank (1) for 2-12min, then the sewage enters the bottom of a guide cylinder (21) from a water passing channel (22), and at the moment, 1000-3000mg/L of induction crystal nucleus is added into the water passing channel (22) through a crystal nucleus adding device (221);

The sewage enters a guide cylinder (21), 1-5mg/L flocculant is added into a flocculation tank (2), and under the action of an upward-lifting type axial flow stirrer (211), the sewage in the guide cylinder (21) flows out from the top of the guide cylinder (21); at the moment, part of the sewage containing the crystal beads passes through the second retaining wall (10) and enters the sedimentation separation tank (3), and the rest of the sewage containing the crystal beads flows to the bottom of the guide cylinder (21) along the backflow channel (23) and flows into the guide cylinder (21) again from the bottom of the guide cylinder (21);

sewage entering the sedimentation separation tank (3) realizes mud-water separation, clean water flows out from the top of the separation tank (3), and sludge is discharged from the bottom of the separation tank (3); the sludge discharged from the bottom of the sedimentation separation tank (3) is refluxed by a sludge reflux pump (4), and the reflux amount of the sludge reflux pump (4) is 3% -10% of the water inflow of the coagulation tank (1);

the sludge from the outlet end of the sludge reflux pump (4) enters a hydrocyclone (5), is rotationally separated by the hydrocyclone (5), is discharged into a sludge tank (6) through a sludge discharge pipe, and is sent to a crystal bead screening device (7), and is sent to a crystal bead collecting device (8) after being screened by the crystal bead screening device (7), and the crystal beads with the particle size of more than 3mm are returned to a flocculation tank (2) through the crystal beads with the particle size of less than or equal to 3 mm;

9. The method for treating sewage by using induced crystallization according to claim 8, wherein: the grain diameter of the induction crystal nucleus is 0.1-0.5mm;

the induction crystal nucleus is selected from any one or more of quartz sand, silver sand, ore sand, garnet and marble.