A pretreatment method and pretreatment device system for polysilicon production wastewater

Abstract

The present invention relates to a pretreatment method and a pretreatment device system for polysilicon production wastewater, wherein the pretreatment method comprises: subjecting the polysilicon production wastewater to the steps of primary reaction, primary coagulation, primary precipitation, secondary reaction, pH value adjustment, tertiary reaction, secondary coagulation, secondary precipitation and solid-liquid separation in sequence to obtain pretreated product water. The pretreatment method and pretreatment device system provided by the present invention can achieve the coordinated deep removal of various forms of silicon impurities, hardness, colloidal suspended matter and other impurities in the wastewater, provide a good water quality foundation for the long-term and stable operation of the rear-end concentration crystallization section, and meet the pretreatment water quality requirements of zero wastewater discharge.

Description

Technical Field

[0001] The invention relates to the technical field of industrial wastewater treatment, and in particular to a pretreatment method and a pretreatment device system for polysilicon production wastewater. Background Art

[0002] With the increase in production capacity of the polysilicon industry, the accompanying environmental problems have become increasingly prominent. Among them, the treatment of polysilicon production wastewater is the most critical and difficult, with high difficulty and cost, and is a hot topic and focus of attention in the industry. Polysilicon production wastewater mainly comes from the wastewater generated by washing various types of waste gases during the polysilicon production process. Polysilicon production wastewater has the characteristics of large output, high salinity, high hardness and high suspended matter concentration. The main ionic components include sodium ions, calcium ions, chloride ions, silicate ions, etc. The proportion of each ion concentration varies depending on the specific alkaline liquid substance used in the waste gas washing process. High-concentration suspended matter includes insoluble colloids or particulate impurities such as silicon dioxide, silicon powder, and calcium silicate.

[0003] Various forms of silicon impurities and calcium and magnesium hardness in the wastewater generated by exhaust gas washing will seriously affect the stable and long-term operation of the wastewater zero-discharge treatment process and equipment, especially in the membrane concentration and evaporation crystallization sections. The silicon scale and hard scale produced will cause scaling and clogging of the membrane components, and the heat exchange effect will be greatly reduced, which will eventually lead to frequent membrane replacement, clearing of blockages and scale in the device system, and a sharp increase in operating costs. It will also affect the continuity and safety of the device system operation.

[0004] At present, the removal of calcium and magnesium hardness in wastewater is usually done by dosing and ion exchange. The removal of silicon impurities in wastewater is usually done by coagulation, membrane, flotation and ion exchange. For polysilicon production wastewater, especially upstream waste gas washing liquid, the more cost-effective calcium hydroxide method is often used, resulting in downstream wastewater containing both high concentrations of calcium and magnesium hardness and high concentrations of silicon impurities, which is difficult to treat. It is difficult to achieve the pretreatment requirements of zero discharge of wastewater by using a single technology. For example, the ion exchange method is often used to remove active silicon in wastewater, but its ability to remove colloidal silicon is very weak. The membrane method is often used to remove colloidal silicon in wastewater, but the removal of active silicon is limited, and for high suspended solids systems, the membrane components are difficult to operate and have a short lifespan. The flotation method will also reduce the treatment effect when operating in a high suspended solids system, and it has limited removal of active silicon. It can be seen that the most economical pretreatment method for polysilicon production wastewater is to properly couple various technical processes, such as combining dosing and coagulation. However, the dosing coagulation and sedimentation process currently used in the market still has certain defects in treatment effect and operating costs, and it is difficult to achieve efficient and thorough pretreatment effects for removing hardness, silicon and suspended solids from wastewater.

[0005] The silicon impurities in polysilicon production wastewater are complex, including insoluble silicon dioxide, silicon powder, and colloids or particles of calcium silicate, as well as soluble active silicate ions. These different types of silicon impurities can also transform into each other under certain conditions, which not only makes it difficult to completely remove silicon by using a one-time silicon removal method, but also makes it difficult to achieve the expected silicon removal effect by simply replicating the silicon removal process without paying attention to the changes in intermediate water quality conditions (especially pH and the concentration of other interfering ions). For example, magnesium and aluminum agents are currently widely used in the coagulation method for silicon removal, that is, magnesium oxide, sodium aluminate and other agents are added to the system, and the effect of removing silicon impurities in the wastewater is achieved by controlling the appropriate pH value conditions. However, when excessive magnesium agents are added to the system, there is a risk of increasing the residual amount of magnesium hardness, which is not conducive to the zero-discharge disposal of high-silicon and high-hardness polysilicon production wastewater. In addition, when removing calcium and magnesium hardness from polysilicon production wastewater, the water quality is usually adjusted to a stronger alkalinity. At this time, the use of the aluminum agent sodium aluminate will inhibit its hydrolysis reaction, weaken the silicon removal ability, increase reagent loss and operating costs. When the conventional multi-stage chemical coagulation and silicon removal process is adopted, after the front-stage chemical coagulation and silicon removal, the colloid and suspended matter content in the wastewater system is at a lower value, that is, the floc core required for silicon removal is reduced, and the silicon removal effect through chemical coagulation in the final stage will be significantly reduced.

[0006] In addition, for the removal of calcium and magnesium hardness in polysilicon production wastewater, the chemical precipitation method of adding alkali solution is often used, and it is set separately from the silicon impurity removal section in the wastewater, that is, the hardness removal and silicon removal of the wastewater are considered separately, which not only leads to a long overall pretreatment process, but also a large consumption of reagents, and the overall effect of hardness removal and silicon removal is difficult to achieve the target. This is because the optimal water quality conditions for hardness removal and silicon removal are different. Mechanically coupling the hardness removal section and the silicon removal section together without considering the impact of changes in intermediate water quality conditions makes it difficult to achieve a satisfactory treatment effect.

[0007] Therefore, in response to the above-mentioned problems and shortcomings of the existing polysilicon production wastewater pretreatment process, combined with the water quality characteristics of polysilicon production wastewater, such as high hardness, high silicon impurities, and high suspended solids content, a synergistic and efficient wastewater pretreatment process for removing hardness and silicon is provided, which is conducive to the deep removal of calcium and magnesium hardness and silicon impurities in the wastewater, and meets the pretreatment water quality requirements for zero wastewater discharge, thereby ensuring the stable and long-term operation of the wastewater zero discharge back-end concentration and crystallization section system and equipment. Summary of the invention

[0008] In view of the above problems, the purpose of the present invention is to provide a pretreatment method and pretreatment device system for polysilicon production wastewater. Compared with the prior art, the pretreatment method and pretreatment device system provided by the present invention can achieve the coordinated deep removal of various forms of silicon impurities, hardness, colloidal suspended matter and other impurities in the wastewater, provide a good water quality foundation for the long-term and stable operation of the rear-end concentration and crystallization section, and meet the pretreatment water quality requirements for zero wastewater discharge.

[0009] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a method for pretreating polysilicon production wastewater, the pretreatment method comprising the following steps:

[0011] (1) subjecting polysilicon production wastewater and a precipitant to a primary reaction to obtain primary reaction water;

[0012] (2) subjecting the primary reaction water obtained in step (1) to primary coagulation and primary precipitation in sequence to obtain primary precipitation water;

[0013] (3) subjecting the primary precipitated water obtained in step (2) to a secondary reaction with a de-hardening agent to obtain secondary reaction water;

[0014] (4) adjusting the pH value of the secondary reaction water obtained in step (3) to obtain pH-adjusted water, and performing a tertiary reaction on the pH-adjusted water and a desiliconizing agent to obtain tertiary reaction water;

[0015] (5) subjecting the tertiary reaction water obtained in step (4) to secondary coagulation and secondary precipitation in sequence to obtain secondary precipitated water;

[0016] (6) The secondary precipitation water obtained in step (5) is subjected to solid-liquid separation to obtain pretreated product water.

[0017] The pretreatment method provided by the present invention can achieve the coordinated deep removal of impurities such as silicon impurities in various forms, hardness, colloidal suspended matter, etc. through the mutual coordination of the steps of primary reaction, primary coagulation, primary precipitation, secondary reaction, pH value adjustment, tertiary reaction, secondary coagulation, secondary precipitation and solid-liquid separation, and the process is simple, the operation is reliable, the amount of reagent added is small, the removal efficiency of hardness, silicon impurities and colloidal suspended matter is high, and the comprehensive investment and operation costs are low.

[0018] Preferably, the pH value of the polysilicon production wastewater in step (1) is 7-11, for example, it can be 7, 8, 9, 10 or 11, the total dissolved solids TDS content is 10000-50000 mg / L, for example, it can be 10000 mg / L, 15000 mg / L, 20000 mg / L, 25000 mg / L, 30000 mg / L, 35000 mg / L, 40000 mg / L, 45000 mg / L or 50000 mg / L; the suspended matter SS content is 1000-15000 mg / L, for example, it can be 1000 mg / L, 2000 mg / L, 4000 mg / L, 6000 mg / L, 8000 mg / L, 10000 mg / L, 12000 mg / L or 15000 mg / L; the calcium ion content is 500 -4000mg / L, for example, it can be 500mg / L, 1000mg / L, 1500mg / L, 2000mg / L, 2500mg / L, 3000mg / L, 3500mg / L or 4000mg / L; COD content <200mg / L, for example, it can be 180mg / L, 160mg / L, 140mg / L, 120mg / L, 100mg / L or 80mg / L; total silicon content is 1000-10000mg / L, for example, it can be 1000mg / L, 2000mg / L, 3000mg / L, 4000mg / L, 5000mg / L, 6000mg / L, 8000mg / L or 10000mg / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are equally applicable.

[0019] The polysilicon production wastewater described in the present invention mainly comes from the washing process of polysilicon production waste gas, wherein the polysilicon production waste gas generally includes chlorosilane, silane, silicon powder, hydrogen chloride, nitrogen and hydrogen, etc. The chemical reactions involved in the waste gas washing process generally include:

[0020] SiHCl3 / SiH2Cl2+H2O→SiO2+HCl+H2;

[0021] SiCl4+H2O→SiO2+HCl;

[0022] SiH4+H2O→SiO2+H2;

[0023] SiO2+NaOH / Ca(OH)2→Na2SiO3 / CaSiO3+H2O;

[0024] HCl+NaOH / Ca(OH)2→NaCl / CaCl2+H2O.

[0025] Preferably, the precipitating agent contains calcium hydroxide.

[0026] Preferably, the precipitant comprises lime milk obtained by reacting quicklime and water.

[0027] In the present invention, the mass concentration of the lime milk is generally 5-10%, for example, 5%, 6%, 7%, 8%, 9% or 10%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] In the present invention, calcium hydroxide is added to carry out a primary reaction. On the one hand, the impurity silicon can be promoted to be converted into active silicate under strong alkaline conditions. The high calcium hardness of the wastewater is utilized so that calcium ions are combined with silicate to generate calcium silicate particle precipitates. When calcium hydroxide is added, the calcium hardness in the wastewater system is increased, which is more conducive to the removal of silicate ions under strong alkaline conditions, thereby facilitating the removal of silicon impurities in the wastewater. On the other hand, magnesium impurities are entrained in the quicklime, which is hydrolyzed under strong alkaline conditions to generate magnesium hydroxide flocculent precipitates. While reducing the magnesium hardness, the quicklime can also adsorb colloidal silicon and silicon powder with a smaller particle size in the wastewater as flocs, which is conducive to removing silicon impurities in the system.

[0029] Preferably, the pH value of the water after the primary reaction is 11.5-12.5, for example, it can be 11.5, 11.6, 11.8, 12, 12.2, 12.4 or 12.5, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] Preferably, the coagulant used in the primary coagulation in step (2) includes polyferric sulfate.

[0031] In the present invention, the coagulant is generally added in the form of a polyferric sulfate solution, and the general mass concentration range is 10-20%, for example, it can be 10%, 12%, 14%, 16%, 18% or 20%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] Preferably, a flocculant is also added into the primary coagulation.

[0033] Preferably, the flocculant comprises polyacrylamide.

[0034] In the present invention, the flocculant is generally added in the form of polyacrylamide solution, and the general mass concentration range is 0.1-0.3%, for example, it can be 0.1%, 0.2% or 0.3%, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0035] In the present invention, the coagulant polyferric sulfate (PFS) added in the primary coagulation has good coagulation performance under strong alkaline conditions and less iron residue, and does not affect the subsequent treatment of wastewater; at the same time, the flocculant polyacrylamide (PAM) added in the primary coagulation aggregates small suspended particles of calcium silicate, silicon powder and the like in the wastewater with silicon impurity colloids into larger alum flowers through the effects of electrical neutralization, compression of double electric layers, adsorption bridging, net capture and sedimentation, etc., which is beneficial to rapid sedimentation and filtration, and enhances the coagulation and sedimentation effect.

[0036] Preferably, the suspended matter SS content of the water after the primary precipitation is 100-500 mg / L, for example, it can be 100 mg / L, 200 mg / L, 300 mg / L, 400 mg / L or 500 mg / L, the total silicon content is 200-500 mg / L, for example, it can be 200 mg / L, 300 mg / L, 400 mg / L or 500 mg / L, and the calcium ion content is 1000-2000 mg / L, for example, it can be 1000 mg / L, 1200 mg / L, 1400 mg / L, 1600 mg / L, 1800 mg / L or 2000 mg / L, but it is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0037] Preferably, after the primary sedimentation, primary sedimentation sludge is obtained, and the primary sedimentation sludge is concentrated and solid-liquid separated to obtain waste residue.

[0038] Preferably, the de-hardening agent in step (3) comprises sodium carbonate.

[0039] In the present invention, the de-hardening agent is generally added in the form of a sodium carbonate solution, and the mass concentration range of the sodium carbonate solution is generally 10-30%, for example, it can be 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28% or 30%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0040] Preferably, the calcium ion content of the water after the secondary reaction is 200-500 mg / L, for example, it can be 200 mg / L, 300 mg / L, 400 mg / L or 500 mg / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] In the present invention, based on the fact that the calcium and magnesium hardness in the wastewater is greatly reduced after the primary coagulation and the primary sedimentation, the amount of the de-hardening agent is reduced, and the amount of the de-hardening agent added is adjusted according to the back-end process. When a certain amount of residual calcium hardness is allowed in the back-end influent, by adjusting the amount of sodium carbonate added within a specific range, it is possible to provide a source of calcium ions for the formation of new seed calcium sulfate at the back end, thereby improving the treatment effect of the back end and reducing the amount and cost of the de-hardening agent added.

[0042] Preferably, the pH adjuster used for pH adjustment in step (4) comprises acid solution.

[0043] Preferably, the acid solution comprises hydrochloric acid and / or sulfuric acid.

[0044] In the present invention, the mass concentration range of the hydrochloric acid is generally 20-30%, for example, it can be 20%, 22%, 24%, 26%, 28% or 30%, but is not limited to the listed values, and other values ​​not listed in the numerical range are equally applicable. The mass concentration range of sulfuric acid is generally 90-98%, for example, it can be 90%, 92%, 94%, 96% or 98%, but is not limited to the listed values, and other values ​​not listed in the numerical range are equally applicable.

[0045] Preferably, the pH value of the water after the pH adjustment is 8-9, for example, 8, 8.2, 8.4, 8.6, 8.8 or 9, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0046] In the present invention, the pH value adjustment is beneficial to the subsequent addition of sodium aluminate for deep silicon removal operation on the one hand, and can remove the residual alkalinity of the system on the other hand. Generally, the wastewater entering the back-end zero-discharge process requires a pH value between 5 and 6, which can reduce the control difficulty of the back-end pH value directly adjusting from strong alkalinity to acidity.

[0047] Preferably, the desiliconizing agent comprises sodium metaaluminate.

[0048] In the present invention, the desiliconizer is generally added in the form of sodium aluminate solution, and the mass concentration range is generally 5-10%, for example, it can be 5%, 6%, 8% or 10%, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0049] In the present invention, sodium aluminate is added to carry out a tertiary reaction, and the sodium aluminate can be hydrolyzed under weakly alkaline conditions to form a silicon-containing precipitate, which is then removed through secondary coagulation and secondary precipitation to achieve a good deep silicon removal effect. On the one hand, most of the impure silicon is removed through the front-end primary coagulation and primary precipitation process, especially the fine silicon powder, calcium silicate and colloidal silica in the state of suspended particles, the suspended matter content of the system is greatly reduced, and the small amount of soluble silicon and colloidal silicon impurities remaining in the system are converted into colloidal silicon under weakly alkaline conditions; on the other hand, in the process of removing hardness by the secondary reaction of sodium carbonate at the front end, the insoluble calcium carbonate particles generated provide the floc core for deep silicon removal, which can further enhance the deep silicon removal effect of sodium aluminate.

[0050] Preferably, the coagulant used in the secondary coagulation in step (5) includes polyferric sulfate.

[0051] Preferably, a flocculant is also added into the secondary coagulation.

[0052] Preferably, the flocculant comprises polyacrylamide.

[0053] In the present invention, by adding a coagulant and a flocculant in the secondary coagulation, the colloidal silicon impurities, calcium carbonate and other trace suspended substances in the system can be quickly and efficiently aggregated and precipitated.

[0054] Preferably, the suspended matter SS content of the water after the secondary precipitation is less than 100 mg / L, for example, it can be 90 mg / L, 80 mg / L, 70 mg / L, 60 mg / L, 50 mg / L, 40 mg / L, 30 mg / L or 20 mg / L, but is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable; the total silicon content is less than 50 mg / L, for example, it can be 40 mg / L, 30 mg / L, 20 mg / L or 10 mg / L, but is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable.

[0055] Preferably, after the secondary precipitation, secondary precipitation sludge is obtained, and the secondary precipitation sludge is concentrated and solid-liquid separated to obtain waste residue.

[0056] Preferably, the solid-liquid separation method in step (6) includes any one of flotation separation, multi-media filtration or ultrafiltration membrane filtration.

[0057] Preferably, the suspended solids SS content of the pretreated water is less than 20 mg / L, for example, it can be 18 mg / L, 16 mg / L, 14 mg / L or 12 mg / L; the total silicon content is less than 20 mg / L, for example, it can be 18 mg / L, 16 mg / L, 14 mg / L or 12 mg / L; the calcium ion content is less than 500 mg / L, for example, it can be 400 mg / L, 300 mg / L, 200 mg / L or 100 mg / L, and other values ​​not listed in the numerical range are also applicable.

[0058] As a preferred technical solution of the first aspect of the present invention, the pretreatment method comprises the following steps:

[0059] (1) subjecting polysilicon production wastewater and lime milk to a primary reaction to obtain primary reaction water, wherein the pH value of the primary reaction water is 11.5-12.5;

[0060] The polysilicon production wastewater has a total dissolved solids TDS content of 10000-50000 mg / L, a suspended solids SS content of 1000-15000 mg / L, a calcium ion content of 500-4000 mg / L, a COD content of <200 mg / L, a pH value of 7-11, and a total silicon content of 1000-10000 mg / L;

[0061] (2) adding a coagulant, polyferric sulfate, and a flocculant, polyacrylamide to the primary reaction water obtained in step (1), and sequentially performing primary coagulation and primary precipitation to obtain primary precipitation water and primary precipitation sludge, wherein the primary precipitation sludge is sequentially concentrated and solid-liquid separated to obtain waste residue, wherein the suspended matter SS content of the primary precipitation water is 100-500 mg / L, the total silicon content is 200-500 mg / L, and the calcium ion content is 1000-2000 mg / L;

[0062] (3) adding sodium carbonate to the primary precipitated water obtained in step (2) to carry out a secondary reaction to obtain secondary reaction water, wherein the calcium ion content of the secondary reaction water is 200-500 mg / L;

[0063] (4) adding hydrochloric acid and / or sulfuric acid to the secondary reaction water obtained in step (3) to adjust the pH value to obtain pH-adjusted water having a pH value of 8-9, and adding sodium aluminate to the pH-adjusted water to carry out a tertiary reaction to obtain tertiary reaction water;

[0064] (5) adding a coagulant of polyferric sulfate and a flocculant of polyacrylamide to the water after the tertiary reaction obtained in step (4) to perform secondary coagulation and secondary precipitation in sequence to obtain water after secondary precipitation and sludge after secondary precipitation, wherein the sludge after secondary precipitation is successively concentrated and solid-liquid separated to obtain waste residue, wherein the suspended matter SS content of the water after secondary precipitation is less than 100 mg / L, and the total silicon content is less than 50 mg / L;

[0065] (6) The secondary precipitated water obtained in step (5) is subjected to flotation separation, multi-media filtration or ultrafiltration membrane filtration to obtain pretreated product water, wherein the suspended matter SS content of the pretreated product water is less than 20 mg / L, the total silicon content is less than 20 mg / L, and the calcium ion content is less than 500 mg / L.

[0066] In a second aspect, the present invention provides a pretreatment device system for polysilicon production wastewater, wherein the pretreatment device system is used in the pretreatment method for polysilicon production wastewater as described in the first aspect of the present invention;

[0067] The pretreatment device system includes a wastewater regulating tank, a primary reaction tank, a primary coagulation tank, a primary sedimentation tank, a secondary reaction tank, a pH value regulating tank, a tertiary reaction tank, a secondary coagulation sedimentation tank, a solid-liquid separation device and a pretreatment water production tank which are sequentially connected along the water flow direction.

[0068] The pretreatment device system provided by the present invention not only has a simple structure, stable operation, low comprehensive investment and operation costs, but also has high efficiency in removing hardness, silicon impurities and colloidal suspended matter in polysilicon production wastewater through the combination of various devices.

[0069] Preferably, the sludge outlets of the primary sedimentation tank and the secondary coagulation sedimentation tank are respectively connected to the sludge thickening tank.

[0070] Preferably, the outlet of the sludge thickening tank is connected to a filter press.

[0071] In the present invention, the filter press is preferably a plate and frame filter press. Generally, the water content of the waste residue obtained after filtration is less than 20%, which is conducive to external transportation and disposal.

[0072] Preferably, the primary sedimentation tank comprises any one of an inclined plate sedimentation tank, an inclined tube sedimentation tank or a vertical flow sedimentation tank.

[0073] Preferably, the solid-liquid separation device comprises any one of an air flotation machine, a multi-media filter or a tubular ultrafiltration membrane.

[0074] Preferably, the secondary coagulation sedimentation tank comprises a coagulation zone, a flocculation zone and a sedimentation zone which are sequentially connected along the water flow direction;

[0075] A clarification zone is arranged above the sedimentation zone, an inclined plate is arranged in the clarification zone, the lower end of the inclined plate is communicated with the sedimentation zone, the water outlet of the clarification zone is connected to a water outlet pipeline, and the water outlet pipeline is connected to the inlet of the solid-liquid separation device;

[0076] A coagulation agitator is provided in the coagulation zone, the water inlet of the coagulation zone is connected to a water inlet pipeline, the entrance of the coagulation zone is also connected to a coagulant dosing pipeline, and the water inlet pipeline is connected to a water outlet of the tertiary reaction tank;

[0077] The flocculation zone is provided with a guide tube, the guide tube is provided with a flocculation agitator, and the inlet of the flocculation zone is also connected to a flocculant dosing pipeline;

[0078] A sludge scraper is arranged at the bottom of the sedimentation zone, and the sludge outlet of the sedimentation zone is respectively connected to a sludge conveying pump and a sludge circulation pump, the outlet of the sludge conveying pump is connected to a sludge outlet pipeline, and the outlet of the sludge circulation pump is connected to the coagulation zone.

[0079] In the present invention, secondary coagulation and secondary sedimentation are coupled in a secondary coagulation sedimentation tank, and the structure of the secondary coagulation sedimentation tank is preferably set, which not only makes the device more compact and saves space, but also the secondary coagulation sedimentation tank can simultaneously set sludge return to the coagulation zone. By controlling the return amount of sludge, the appropriate suspended matter content can be maintained in the coagulation zone, which is beneficial to enhance the coagulation and sedimentation effect and make the upper clear liquid in the clarification zone meet the standards.

[0080] Compared with the prior art, the present invention has the following beneficial effects:

[0081] (1) The pretreatment method provided by the present invention controls and adjusts the intermediate water quality changes through the mutual coordination of the steps of primary reaction, primary coagulation, primary precipitation, secondary reaction, pH value adjustment, tertiary reaction, secondary coagulation, secondary precipitation and solid-liquid separation, thereby achieving the coordinated deep removal of various forms of silicon impurities, hardness, colloidal suspended matter and other impurities in the wastewater, providing a stable and beneficial preliminary water quality condition foundation for zero wastewater discharge and resource utilization, and the consumption of reagents is small, and the removal rate of hardness, silicon impurities and colloidal suspended matter is high.

[0082] (2) The pretreatment device system provided by the present invention is not only simple in structure and stable in operation through the combination of various devices, but also has low comprehensive investment and operation costs, and provides stable early water quality for the evaporation and crystallization section at the rear end of zero wastewater discharge. BRIEF DESCRIPTION OF THE DRAWINGS

[0083] Figure 1 This is a schematic diagram of the structure of the pretreatment device system described in Example 1 of the present invention;

[0084] Figure 2 This is a schematic diagram of the structure of the secondary coagulation sedimentation tank described in Example 1 of the present invention;

[0085] Among them, 1-wastewater regulating tank; 2-primary reaction tank; 3-primary coagulation tank; 4-primary sedimentation tank; 5-sludge concentration tank; 6-plate and frame filter press; 7-secondary reaction tank; 8-pH value adjustment tank; 9-tertiary reaction tank; 10-secondary coagulation sedimentation tank; 11-multi-media filter; 12-pretreatment water production tank;

[0086] 1001-coagulation zone; 1002-water inlet pipeline; 1003-coagulant dosing pipeline; 1004-coagulation agitator; 1005-flocculation zone; 1006-flocculant dosing pipeline; 1007-flocculation agitator; 1008-guide tube; 1009-clarification zone; 1010-inclined plate; 1011-water outlet pipeline; 1012-sedimentation zone; 1013-sludge scraper; 1014-sludge circulation pump; 1015-sludge transfer pump; 1016-sludge outlet pipeline. DETAILED DESCRIPTION

[0087] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0088] In a specific embodiment, the pretreatment method of polysilicon production wastewater provided by the present invention is carried out in a pretreatment device system, and the structural schematic diagram of the pretreatment device system is as follows: Figure 1As shown, the pretreatment device system includes a wastewater regulating tank 1, a primary reaction tank 2, a primary coagulation tank 3, a primary sedimentation tank 4, a secondary reaction tank 7, a pH value regulating tank 8, a tertiary reaction tank 9, a secondary coagulation sedimentation tank 10, a multi-media filter 11 and a pretreatment water production tank 12 which are sequentially connected along the water flow direction, the sludge outlets of the primary sedimentation tank 4 and the secondary coagulation sedimentation tank 10 are respectively connected to the sludge thickening tank 5, the outlet of the sludge thickening tank 5 is connected to the filter press, the filter press is a plate and frame filter press 6, and the primary sedimentation tank 4 is a vertical flow sedimentation tank.

[0089] The pretreatment device system provided by the present invention has the advantages of simple structure, stable operation, low comprehensive investment and operation costs, and high efficiency in removing hardness, silicon impurities and colloidal suspended matter in polysilicon production wastewater through the combination of various devices.

[0090] The structural diagram of the secondary coagulation sedimentation tank 10 is as follows: Figure 2 As shown, the secondary coagulation sedimentation tank 10 includes a coagulation zone 1001, a flocculation zone 1005 and a sedimentation zone 1012 which are sequentially connected along the water flow direction; a clarification zone 1009 is arranged above the sedimentation zone 1012, an inclined plate 1010 is arranged in the clarification zone 1009, the lower end of the inclined plate 1010 is connected to the sedimentation zone 1012, the water outlet of the clarification zone 1009 is connected to the outlet pipeline 1011, and the outlet pipeline 1011 is connected to the inlet of the multi-media filter 11; a coagulation agitator 1004 is arranged in the coagulation zone 1001, the water inlet of the coagulation zone 1001 is connected to the inlet pipeline 1002, and the inlet of the coagulation zone 1001 is connected to the inlet pipeline 1002. It is also connected to the coagulant dosing pipeline 1003, and the water inlet pipeline 1002 is connected to the water outlet of the tertiary reaction tank 9; a guide tube 1008 is provided in the flocculation zone 1005, and a flocculation agitator 1007 is provided in the guide tube 1008, and the inlet of the flocculation zone 1005 is also connected to the flocculant dosing pipeline 1006; a scraper 1013 is provided at the bottom of the sedimentation zone 1012, and the sludge outlet of the sedimentation zone 1012 is respectively connected to the sludge conveying pump 1015 and the sludge circulation pump 1014, the outlet of the sludge conveying pump 1015 is connected to the sludge outlet pipeline 1016, and the outlet of the sludge circulation pump 1014 is connected to the coagulation zone 1001.

[0091] In the present invention, secondary coagulation and secondary sedimentation are coupled in the secondary coagulation sedimentation tank 10. The secondary coagulation sedimentation tank 10 has a compact structure and can save space. It can also simultaneously arrange sludge return to the coagulation zone 1001 so that the appropriate suspended matter content is maintained in the coagulation zone 1001, which is beneficial to enhancing the coagulation and sedimentation effect and ensuring that the upper clear liquid in the clarification zone 1009 meets the standards.

[0092] Example 1

[0093] This embodiment provides a method for pretreating polysilicon production wastewater. The pretreating method is performed in a polysilicon production wastewater device system. The structural schematic diagram of the pretreating device system is shown in FIG. Figure 1 As shown, it includes a wastewater regulating tank 1, a primary reaction tank 2, a primary coagulation tank 3, a primary sedimentation tank 4, a secondary reaction tank 7, a pH value regulating tank 8, a tertiary reaction tank 9, a secondary coagulation sedimentation tank 10, a multi-media filter 11 and a pre-treatment water production tank 12 which are sequentially connected along the water flow direction. The structural schematic diagram of the secondary coagulation sedimentation tank 10 is shown in FIG. Figure 2 As shown, it includes a coagulation zone 1001, a flocculation zone 1005 and a sedimentation zone 1012 which are sequentially connected along the water flow direction, and a clarification zone 1009 is arranged above the sedimentation zone 1012.

[0094] In this embodiment, the polysilicon production wastewater comes from a polysilicon production enterprise. The wastewater discharged from each process section is collected in the wastewater regulating tank 1. The pH value of the wastewater in the regulating tank is about 9, the total dissolved solids TDS content is about 45000 mg / L, and the SS content of suspended matter such as a large amount of fine silicon powder is about 10000 mg / L, the calcium ion content is about 3500 mg / L, the total silicon content is about 6000 mg / L, and the COD content is about 100 mg / L. The pretreatment method includes the following steps:

[0095] (1) The polysilicon production wastewater in the wastewater regulating tank 1 is pumped into the primary reaction tank 2, in which a stirring device is installed, and lime milk with a mass concentration of 5% is added into the tank for primary reaction to obtain primary reaction water, wherein the pH value of the primary reaction water is 12;

[0096] Under the alkaline condition, the fine silicon powder and colloidal silicon in the wastewater are transformed into active soluble silicate, and combined with the original calcium ions in the system and the calcium ions introduced by the added lime milk to form calcium silicate particle precipitates. In addition, the lime milk introduces magnesium impurities, which are hydrolyzed under alkaline conditions to form magnesium hydroxide flocculent precipitates, which adsorb suspended impurities such as colloidal silicon and fine silicon powder in the wastewater.

[0097] (2) pumping the primary reaction water in the primary reaction tank 2 of step (1) into the primary coagulation tank 3, in which a stirring device is installed, and adding a 20% mass concentration of polyferric sulfate solution (dosage amount is about 50 mg / L) and a 0.1% mass concentration of polyacrylamide solution (dosage amount is about 2 mg / L) into the tank for primary coagulation;

[0098] In the primary coagulation, the addition of coagulants and flocculants enhances the effects of electrical neutralization, double electrical layer compression, adsorption bridging, net capture and sedimentation of insoluble impurities such as suspended particles and colloids in the wastewater, and aggregates small suspended particles of calcium silicate, silicon powder and silicon impurity colloids in the wastewater into larger alum flowers, which is conducive to rapid sedimentation and filtration, and enhances the coagulation and sedimentation effect;

[0099] Afterwards, the wastewater is pumped into a primary sedimentation tank 4 for primary sedimentation. The primary sedimentation tank 4 is a vertical flow sedimentation tank, and a scraper device is provided in the tank to obtain primary sedimentation water at the top and primary sedimentation sludge at the bottom. The suspended matter SS content of the primary sedimentation water is about 300 mg / L, the total silicon content is about 400 mg / L, and the calcium ion content is about 1500 mg / L. The primary sedimentation sludge is collected by the scraper device and transported to the sludge thickening tank 5 through a pipeline for further sedimentation and concentration. Afterwards, the sludge is dehydrated by a plate and frame filter press 6 to obtain waste residue with a moisture content of less than 20%, which is convenient for external transportation and disposal;

[0100] (3) transporting the primary precipitated water in the primary sedimentation tank 4 of step (2) to a secondary reaction tank 7 through a pipeline, wherein a stirring device is provided in the tank, and adding a sodium carbonate solution with a mass concentration of 30% to the tank for secondary reaction, wherein the amount of sodium carbonate added is about 3000 mg / L, so that carbonate radicals react with calcium ions to generate calcium carbonate precipitates, thereby obtaining secondary reaction water, wherein the calcium ion content of the secondary reaction water is about 500 mg / L;

[0101] (4) pumping the secondary reaction water in the secondary reaction tank 7 of step (3) into a pH adjustment tank 8, the tank is equipped with a stirring device, adding sulfuric acid with a mass concentration of 98% into the tank to adjust the pH value, and obtaining pH-adjusted water with a pH value of about 8.5, and pumping the pH-adjusted water into a tertiary reaction tank 9, the tank is equipped with a stirring device, and adding a sodium aluminate solution with a mass concentration of 10% into the tank for tertiary reaction, wherein the amount of sodium aluminate added is about 1000 mg / L, and obtaining tertiary reaction water;

[0102] In the three-stage reaction, the solid calcium carbonate particles generated in the secondary reaction tank 7 are used as the floc core, and the hydrolysis of sodium aluminate in the wastewater causes the hydrolysis product Al(OH)3 floc to absorb the remaining colloidal silicon impurities in the wastewater;

[0103] (5) The water after the tertiary reaction in the tertiary reaction tank 9 of step (4) is pumped into the secondary coagulation sedimentation tank 10 through the water inlet pipeline 1002, and a 20% polyferric sulfate solution (dosage is about 30 mg / L) is added to the coagulation zone 1001 through the coagulant dosing pipeline 1003. The wastewater is coagulated under the action of the coagulation agitator 1004. The coagulated wastewater enters the flocculation zone 1005 through the flow channel. In the flocculation zone 1005, a 0.1% polyacrylamide solution (dosage is about 1 mg / L) is added through the flocculant dosing pipeline 1006. The wastewater is flocculated under the action of the flocculation agitator 1007 and the guide tube 1008. The flocculated wastewater enters the sedimentation zone 1012 through the flow channel to achieve rapid sedimentation and separation of the wastewater, and the upper The clear liquid enters the clarification zone 1009, and fine suspended matter is further removed under the action of the inclined plate 1010. The wastewater in the clarification zone 1009 is discharged through the outlet pipeline 1011 to obtain secondary sedimentation water, wherein the suspended matter SS content of the secondary sedimentation water is about 50 mg / L, and the total silicon content is about 40 mg / L. The sludge obtained in the sedimentation zone 1012 is collected by the scraper 1013 and discharged into the sludge delivery pump 1015 and the sludge circulation pump 1014 through the sludge outlet. Part of the sludge is returned to the coagulation zone 1001 through the sludge circulation pump 1014, and part of the sludge is successively transported to the sludge thickening tank 5 through the sludge delivery pump 1015 and the mud outlet pipeline 1016 for further sedimentation and concentration, and then the sludge is dehydrated by the plate and frame filter press 6 to obtain waste residue with a moisture content of less than 20%, which is convenient for external transportation and disposal;

[0104] (6) The secondary precipitated water obtained in the secondary coagulation sedimentation tank 10 of step (5) is pumped into the multi-media filter 11 to further remove the insoluble suspended matter in the wastewater, and the pretreated water is obtained and stored in the pretreated water tank 12 to be disposed in the next stage, i.e., the evaporation and crystallization section at the rear end of the wastewater zero discharge.

[0105] Comparative Example 1

[0106] This comparative example provides a method for pretreating polysilicon production wastewater. The only difference compared with Example 1 is that step (3) is not performed, that is, sodium carbonate is not added for secondary reaction, and the primary precipitation water obtained in step (2) replaces the secondary reaction water in step (4) to directly adjust the pH value.

[0107] This comparative example provides a pretreatment device system used in the above-mentioned pretreatment method. The difference between the pretreatment device system and Example 1 is that no secondary reaction tank is provided, and the primary reaction tank is directly connected to the pH value adjustment tank.

[0108] Comparative Example 2

[0109] This comparative example provides a method for pretreating polysilicon production wastewater, which differs from Example 1 only in that pH adjustment is not performed in step (4), and the secondary reaction water obtained in step (3) directly undergoes a tertiary reaction with a sodium aluminate solution.

[0110] This comparative example provides a pretreatment device system used in the above-mentioned pretreatment method. The difference between the pretreatment device system and Example 1 is that no pH adjustment tank is provided, and the secondary reaction tank is directly connected to the tertiary reaction tank.

[0111] Comparative Example 3

[0112] This comparative example provides a method for pretreating polysilicon production wastewater. The only difference compared with Example 1 is that no tertiary reaction is performed in step (4), and the pH-adjusted water obtained in step (4) replaces the tertiary reaction water in step (5) to directly perform secondary coagulation.

[0113] This comparative example provides a pretreatment device system used in the above-mentioned pretreatment method. The difference between the pretreatment device system and Example 1 is that no tertiary reaction tank is provided, and the pH adjustment tank is directly connected to the secondary coagulation sedimentation tank.

[0114] Comparative Example 4

[0115] This comparative example provides a method for pretreating polysilicon production wastewater. The only difference compared with Example 1 is that step (5) is not performed, and the tertiary reaction water obtained in step (4) replaces the secondary precipitation water in step (6) to directly perform multi-media filtration.

[0116] This comparative example provides a pretreatment device system used in the above-mentioned pretreatment method. The difference between the pretreatment device system and Example 1 is that no secondary coagulation sedimentation tank is provided, and the tertiary reaction tank is directly connected to the multi-media filter.

[0117] Comparative Example 5

[0118] This comparative example provides a method for pretreating polysilicon production wastewater. The only difference compared with Example 1 is that step (6) is not performed, and the secondary precipitation water obtained in step (5) is the pretreated water.

[0119] This comparative example provides a pretreatment device system used in the above-mentioned pretreatment method. The difference between the pretreatment device system and Example 1 is that no multi-media filter is provided, and the secondary coagulation sedimentation tank is directly connected to the pretreatment water production tank through the outlet pipeline.

[0120] The pretreated produced water prepared in Example 1 and Comparative Examples 1-5 was measured, wherein the suspended matter SS content was measured by the "Gravimetric Method for Determination of Suspended Matter in Water Quality" (GB / T 11901-1989), the total silicon content was measured by the "Determination of Silicon in Industrial Circulating Cooling Water and Boiler Water" (GB / T 12149-2017), and the calcium ion content was measured by the "EDTA Titration Method for Determination of Calcium and Magnesium Ions in Industrial Circulating Cooling Water" (GB / T15452-2009). The results are shown in Table 1.

[0121] Table 1

[0122] Suspended matter SS content / (mg / L) Total silicon content / (mg / L) Calcium ion content / (mg / L) Example 1 10 13 450 Comparative Example 1 12 35 1400 Comparative Example 2 13 50 450 Comparative Example 3 13 150 440 Comparative Example 4 65 45 450 Comparative Example 5 50 40 450

[0123] From Table 1, we can see the following points:

[0124] (1) It can be seen from the data of Example 1 that the pretreatment method provided by the present invention can achieve the coordinated deep removal of various forms of silicon impurities, hardness and colloidal suspended matter. The SS content of the suspended matter in the obtained pretreated water reaches 10 mg / L, the total silicon content reaches 13 mg / L, and the calcium ion content reaches 450 mg / L. At the same time, the calcium ions contained can provide a source of calcium ions for the formation of new seed calcium sulfate at the back end, thereby improving the treatment effect of the back end.

[0125] (2) From the data of Example 1 and Comparative Example 1, it can be seen that the difference between Comparative Example 1 and Example 1 is that the hardness removal step of adding sodium carbonate is not performed. The calcium ion content and total silicon content of the pretreated water obtained in Example 1 are significantly lower than those in Comparative Example 1. It can be seen that the present invention can not only reduce the calcium ion content by adding sodium carbonate for the secondary reaction of hardness removal, but also the generated calcium carbonate solid particles can serve as the floc core, further improving the subsequent silicon removal effect.

[0126] (3) From the data of Example 1 and Comparative Example 2, it can be seen that the only difference between Comparative Example 2 and Example 1 is that the pH value is not adjusted. The total silicon content of the pretreated water produced in Example 1 is significantly lower than that in Comparative Example 2. It can be seen that the pH value adjustment of the present invention is beneficial to improving the silicon removal effect of sodium aluminate, thereby further reducing the total silicon content of the pretreated water.

[0127] (4) From the data of Example 1 and Comparative Example 3, it can be seen that the only difference between Comparative Example 3 and Example 1 is that the tertiary reaction is not performed. The total silicon content of the pretreated produced water obtained in Example 1 is significantly lower than that in Comparative Example 3. Therefore, it can be seen that the present invention can further reduce the total silicon content of the pretreated produced water by adding the desiliconizing agent sodium aluminate for desiliconization.

[0128] (5) From the data of Example 1 and Comparative Example 4, it can be seen that the only difference between Comparative Example 4 and Example 1 is that the secondary coagulation and secondary sedimentation are not performed. The suspended matter SS content and the total silicon content of the pretreated water produced in Example 1 are significantly lower than those in Comparative Example 4. It can be seen that the present invention can not only remove the suspended matter in the system by performing secondary coagulation and secondary sedimentation, but also avoid the interference of the suspended matter on the subsequent adsorption and precipitation of silicon impurities, thereby further improving the removal effect of suspended matter and silicon impurities.

[0129] (6) From the data of Example 1 and Comparative Example 5, it can be seen that the only difference between Comparative Example 5 and Example 1 is that the multi-media filter is not used for solid-liquid separation. The suspended matter SS content and total silicon content of the pretreated water produced in Example 1 are significantly lower than those in Comparative Example 5. It can be seen that the present invention can not only reduce the suspended matter content by using a multi-media filter for solid-liquid separation, but also further adsorb and retain silicon impurities in the system, thereby further reducing the total silicon content of the pretreated water.

[0130] In summary, the pretreatment method provided by the present invention controls and adjusts the intermediate water quality changes through the mutual coordination of the steps of primary reaction, primary coagulation, primary precipitation, secondary reaction, pH value adjustment, tertiary reaction, secondary coagulation, secondary precipitation and solid-liquid separation, thereby achieving the coordinated deep removal of various forms of silicon impurities, hardness, colloidal suspended matter and other impurities in the wastewater, providing a stable and beneficial preliminary water quality condition foundation for zero wastewater discharge and resource utilization.

[0131] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for pretreating polysilicon production wastewater, It is characterized in that The pretreatment method comprises the following steps: (1) subjecting polysilicon production wastewater and a precipitant to a primary reaction to obtain primary reaction water; the polysilicon production wastewater has a pH value of 7-11, a total dissolved solids TDS content of 10000-50000 mg / L, a suspended solids SS content of 1000-15000 mg / L, a calcium ion content of 500-4000 mg / L, a COD content of <200 mg / L, and a total silicon content of 1000-10000 mg / L; (2) subjecting the primary reaction water obtained in step (1) to primary coagulation and primary precipitation in sequence to obtain primary precipitation water; the primary precipitation water has a suspended matter SS content of 100-500 mg / L, a total silicon content of 200-500 mg / L, and a calcium ion content of 1000-2000 mg / L; (3) subjecting the primary precipitation water obtained in step (2) to a secondary reaction with a de-hardening agent to obtain secondary reaction water; the calcium ion content of the secondary reaction water is 200-500 mg / L; (4) adjusting the pH value of the secondary reaction water obtained in step (3) to obtain pH-adjusted water, and performing a tertiary reaction with a desiliconizing agent to obtain tertiary reaction water; (5) subjecting the tertiary reaction water obtained in step (4) to secondary coagulation and secondary sedimentation in sequence to obtain secondary sedimentation water; the suspended matter SS content of the secondary sedimentation water is less than 100 mg / L, and the total silicon content is less than 50 mg / L; (6) The secondary precipitated water obtained in step (5) is subjected to solid-liquid separation to obtain pretreated product water; the pretreated product water has a suspended matter SS content of less than 20 mg / L, a total silicon content of less than 20 mg / L, and a calcium ion content of less than 500 mg / L.

2. The pretreatment method according to claim 1, It is characterized in that The precipitant in step (1) contains calcium hydroxide.

3. The pretreatment method according to claim 1, It is characterized in that The precipitant in step (1) includes lime milk obtained by the reaction of quicklime and water.

4. The pretreatment method according to claim 1, It is characterized in that The pH value of the water after the primary reaction in step (1) is 11.5-12.

5.

5. The pretreatment method according to claim 1, It is characterized in that The coagulant used in the primary coagulation in step (2) includes polyferric sulfate.

6. The pretreatment method according to claim 1, It is characterized in that In step (2), a flocculant is also added to the primary coagulation.

7. The pretreatment method according to claim 6, It is characterized in that The flocculant includes polyacrylamide.

8. The pretreatment method according to claim 1, It is characterized in that After the primary precipitation in step (2), primary precipitation sludge is obtained, and the primary precipitation sludge is concentrated and solid-liquid separated to obtain waste residue.

9. The pretreatment method according to claim 1, It is characterized in that The de-hardening agent in step (3) includes sodium carbonate.

10. The pretreatment method according to claim 1, It is characterized in that The pH adjusting agent used for pH adjustment in step (4) includes acid solution.

11. The pretreatment method according to claim 10, It is characterized in that The acid solution includes hydrochloric acid and / or sulfuric acid.

12. The pretreatment method according to claim 1, It is characterized in that After the pH value is adjusted in step (4), the pH value of the water is 8-9.

13. The pretreatment method according to claim 1, It is characterized in that The silicon removal agent in step (4) includes sodium aluminate.

14. The pretreatment method according to claim 1, It is characterized in that The coagulant used in the secondary coagulation in step (5) includes polyferric sulfate.

15. The pretreatment method according to claim 1, It is characterized in that In step (5), a flocculant is also added to the secondary coagulation.

16. The pretreatment method according to claim 15, It is characterized in that The flocculant includes polyacrylamide.

17. The pretreatment method according to claim 1, It is characterized in that After the secondary precipitation in step (5), secondary precipitation sludge is obtained, and the secondary precipitation sludge is concentrated and solid-liquid separated to obtain waste residue.

18. The pretreatment method according to claim 1, It is characterized in that The solid-liquid separation method in step (6) includes any one of flotation separation, multi-media filtration or ultrafiltration membrane filtration.

19. A pretreatment device system for polysilicon production wastewater, It is characterized in that The pretreatment device system is used for the pretreatment method of polysilicon production wastewater as claimed in any one of claims 1 to 18; The pretreatment device system includes a wastewater regulating tank, a primary reaction tank, a primary coagulation tank, a primary sedimentation tank, a secondary reaction tank, a pH value regulating tank, a tertiary reaction tank, a secondary coagulation sedimentation tank, a solid-liquid separation device and a pretreatment water production tank which are sequentially connected along the water flow direction.

20. The pre-treatment device system according to claim 19, It is characterized in that The sludge outlets of the primary sedimentation tank and the secondary coagulation sedimentation tank are respectively connected to the sludge thickening tank.

21. The pre-treatment device system according to claim 20, It is characterized in that The outlet of the sludge thickening tank is connected to a filter press.

22. The pre-treatment device system according to claim 19, It is characterized in that The primary sedimentation tank includes any one of an inclined plate sedimentation tank, an inclined tube sedimentation tank or a vertical flow sedimentation tank.

23. The pre-treatment device system according to claim 19, It is characterized in that The solid-liquid separation device includes any one of an air floatation machine, a multi-media filter or a tubular ultrafiltration membrane.

24. The pre-treatment device system according to claim 19, It is characterized in that The secondary coagulation sedimentation tank comprises a coagulation zone, a flocculation zone and a sedimentation zone which are sequentially connected along the water flow direction; A clarification zone is arranged above the sedimentation zone, an inclined plate is arranged in the clarification zone, the lower end of the inclined plate is connected to the sedimentation zone, the water outlet of the clarification zone is connected to a water outlet pipeline, and the water outlet pipeline is connected to the inlet of the solid-liquid separation device; A coagulation agitator is provided in the coagulation zone, the water inlet of the coagulation zone is connected to a water inlet pipeline, the entrance of the coagulation zone is also connected to a coagulant dosing pipeline, and the water inlet pipeline is connected to a water outlet of the tertiary reaction tank; The flocculation zone is provided with a guide tube, the guide tube is provided with a flocculation agitator, and the inlet of the flocculation zone is also connected to a flocculant dosing pipeline; A sludge scraper is arranged at the bottom of the sedimentation zone, and the sludge outlet of the sedimentation zone is respectively connected to a sludge conveying pump and a sludge circulation pump, the outlet of the sludge conveying pump is connected to a sludge outlet pipeline, and the outlet of the sludge circulation pump is connected to the coagulation zone.

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