A wastewater treatment system and a process system for recycling water and salt in electroplating wastewater

Abstract

This invention provides a wastewater treatment system and a process system for the resource recovery of water and salt from electroplating wastewater, belonging to the field of wastewater treatment technology. The wastewater treatment system provided by this invention includes a wastewater pretreatment unit, a wastewater solid-liquid separation unit, a wastewater oxidation unit, a wastewater biochemical treatment unit, a wastewater multivalent metal ion removal unit, and a membrane treatment system, connected in sequence. In the wastewater treatment system provided by this invention, the total amount of divalent and higher-valent metal ions in the effluent from the multivalent metal ion removal unit is ≤5 ppm, with the total amount of multivalent metal ions ≤2 ppm, and calcium and magnesium ≤5 ppm. The significantly reduced multivalent metal ion content avoids fouling of the subsequent membrane system, thereby effectively ensuring the reuse of water resources and maximizing the value of salt resources in subsequent process systems.

Description

Technical Field

[0001] This utility model relates to the field of wastewater treatment technology, and in particular to a wastewater treatment system and a process system for the resource utilization of water and salt in electroplating wastewater. Background Technology

[0002] Electroplating wastewater has a complex composition, containing heavy metal ions such as chromium, zinc, copper, nickel, and cadmium, as well as highly toxic impurities such as acids, alkalis, and cyanides. If discharged directly without treatment, it will cause great pollution to the surrounding water bodies, thereby endangering aquatic plants and animals, as well as the crops, animals, and humans on which they depend for survival.

[0003] Electroplating wastewater exhibits significant variations in water quality, and the wastewater from various production lines contains diverse and complex pollutants, making its treatment challenging. While the related research, "A System and Method for Water and Salt Resource Utilization in Electroplating Wastewater," achieved deep purification of chemical pollutants in electroplating wastewater, yielding RO permeate (freshwater), and simultaneously separating industrial chloride and sulfate salts, effectively ensuring water resource reuse and maximizing the value of salt resources, the treatment process also resulted in the formation of colloids, precipitates, and suspended solids from polyvalent metal ion solutions. This fouling of the membrane treatment system increased the treatment pressure and losses within the membrane system. Utility Model Content

[0004] The purpose of this invention is to provide a wastewater treatment system and a process system for the resource recovery of water and salt in electroplating wastewater. The wastewater treatment system provided by this invention can effectively avoid membrane clogging in wastewater treatment, reducing the treatment pressure and membrane system wear of subsequent process systems for wastewater and waste liquid.

[0005] To achieve the above-mentioned objectives, this utility model provides the following technical solution:

[0006] This utility model provides a wastewater treatment system, characterized in that it includes a wastewater pretreatment unit, a wastewater solid-liquid separation unit, a wastewater oxidation unit, a wastewater biochemical treatment unit, a wastewater multivalent metal ion removal unit, and a membrane treatment system connected in sequence.

[0007] Preferably, the effluent pH value of the wastewater pretreatment unit is 8.5 to 11.5.

[0008] Preferably, the wastewater solid-liquid separation unit includes a gravity sedimentation tank and a plate and frame filter; the supernatant outlet of the gravity sedimentation tank is connected to the inlet of the wastewater oxidation treatment unit; and the bottom sludge outlet of the gravity sedimentation tank is connected to the inlet of the plate and frame filter.

[0009] Preferably, the wastewater oxidation unit includes a complex-breaking oxidation unit and an advanced oxidation unit connected in sequence.

[0010] Preferably, the wastewater multivalent metal ion removal unit is equipped with a metal ion adsorption material; the metal ion adsorption material includes special resin adsorption material, multifunctional fiber material adsorption material, porous sponge adsorption material, or porous gel adsorption material.

[0011] Preferably, the membrane treatment system includes a wastewater nanofiltration desalination unit, a first wastewater salt concentration and separation unit connected to the concentrate outlet of the wastewater nanofiltration desalination unit, a first reverse osmosis unit connected to the desalination outlet of the first wastewater salt concentration and separation unit, a second wastewater salt concentration and separation unit connected to the desalination outlet of the wastewater nanofiltration desalination unit, and a second reverse osmosis unit connected to the desalination outlet of the second wastewater salt concentration and separation unit.

[0012] The concentrate outlet of the first reverse osmosis unit is connected to the inlet of the first wastewater salt concentration and separation unit;

[0013] The concentrate outlet of the second reverse osmosis unit is connected to the inlet of the second wastewater salt concentration and separation unit.

[0014] Preferably, the first wastewater salt concentration and separation unit and the second wastewater salt concentration and separation unit are equipped with an electrodialysis device;

[0015] The concentrate conductivity of both the first and second wastewater salt concentration and separation units is 1–1.5 × 10⁻⁶. 5 μs / cm, and the conductivity of freshwater is 1000~3000μs / cm.

[0016] Preferably, both the first and second reverse osmosis units are low-pressure reverse osmosis devices; the operating pressure of each low-pressure reverse osmosis device is less than 1.5 MPa.

[0017] This utility model also provides a process system for the resource utilization of water and salt in electroplating wastewater, including the wastewater treatment system described in the above claims and a first waste liquid treatment system and a second waste liquid treatment system connected to the membrane treatment system in the wastewater treatment system.

[0018] Preferably, the first waste liquid treatment system includes a first concentrated liquid collection unit, a first concentrated liquid pretreatment unit, a first concentrated liquid solid-liquid separation unit, and a first evaporation unit connected in sequence; the concentrated water outlet of the first wastewater salt concentration and separation unit is connected to the inlet of the first concentrated liquid collection unit.

[0019] The second waste liquid treatment system includes a second concentrated liquid collection unit, a second concentrated liquid pretreatment unit, a second concentrated liquid solid-liquid separation unit, and a second evaporation unit connected in sequence; the concentrated water outlet of the second wastewater salt concentration and separation unit is connected to the inlet of the second concentrated liquid collection unit.

[0020] This utility model provides a wastewater treatment system, including a wastewater pretreatment unit, a wastewater solid-liquid separation unit, a wastewater oxidation unit, a wastewater biochemical treatment unit, a wastewater multivalent metal ion removal unit, and a membrane treatment system connected in sequence. This invention pre-treats wastewater through a wastewater pretreatment unit, which precipitates most of the heavy metals in the wastewater. The wastewater oxidation unit deeply removes cyanide and complexed heavy metal ions through oxidation, and also pre-oxidizes organic matter, improving its biodegradability. The wastewater biochemical treatment unit achieves deep removal of biodegradable organic matter, total phosphorus, and total nitrogen from the wastewater, while simultaneously breaking down organic complexes. The wastewater multivalent metal ion removal unit removes calcium, magnesium, and residual iron, nickel, copper, zinc, aluminum, and other multivalent metal ions from the solution, preventing subsequent fouling of the membrane treatment system. Through the organic coupling of multiple units, deep purification of chemical pollutants in electroplating wastewater is achieved, avoiding fouling of the membrane system in subsequent wastewater treatment. When used in a process system for the resource recovery of water and salt in electroplating wastewater, it can reduce the pressure on the process system for treating wastewater and waste liquid. The results of the embodiments show that in the wastewater treatment system provided by this utility model, the total amount of divalent and higher metal ions in the effluent of the wastewater polyvalent metal ion removal unit is ≤5ppm, of which the total amount of polyvalent metal ions is ≤2ppm, and calcium and magnesium are ≤5ppm. The content of polyvalent metal ions is significantly reduced, which can avoid fouling of the subsequent membrane system and thus effectively ensure the reuse of water resources and the maximization of the value of salt resources in the subsequent process system. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the process system for resource utilization of water and salt in electroplating wastewater in this embodiment of the present invention. Detailed Implementation

[0022] This utility model provides a wastewater treatment system, including a wastewater pretreatment unit, a wastewater solid-liquid separation unit, a wastewater oxidation unit, a wastewater biochemical treatment unit, a wastewater multivalent metal ion removal unit, and a membrane treatment system connected in sequence.

[0023] As one embodiment of the present invention, the wastewater treatment system may further include a wastewater collection unit; the wastewater collection unit collects the electroplating wastewater generated during the electroplating process, and then passes it into the wastewater pretreatment unit for treatment.

[0024] In this invention, the electroplating wastewater composition may be: conductivity 2000-10000 μs / cm, suspended solids 50-200 mg / L, COD (chemical oxygen demand) 50-800 mg / L, ammonia nitrogen 8-200 mg / L, total nitrogen 15-500 mg / L, total phosphorus 0.5-200 mg / L, copper 0.5-500 mg / L, total chromium 0.5-500 mg / L, nickel 0.1-200 mg / L, zinc 1.0-500 mg / L, iron 2.0-800 mg / L, and calcium and magnesium 5.0-100 mg / L.

[0025] The wastewater treatment system provided by this utility model includes a wastewater pretreatment unit. In one embodiment of this utility model, when the wastewater treatment system includes a wastewater collection unit, the outlet of the wastewater collection unit is connected to the inlet of the wastewater pretreatment unit. This utility model, by sending wastewater into the wastewater pretreatment unit for pretreatment, can cause most of the heavy metals in the wastewater to precipitate out.

[0026] In one embodiment of this invention, the wastewater pretreatment unit may be equipped with a sodium hydroxide dosing device, a heavy metal precipitator dosing device, a flocculant dosing device, and a coagulant aid dosing device. By setting up the aforementioned dosing devices, this invention adjusts the pH of the wastewater, which is beneficial for the precipitation of heavy metal ions. The addition of sodium hydroxide and heavy metal precipitator can initially cause most of the heavy metal ions to precipitate, while a small amount of complexed heavy metal ions remain in the clear liquid. The addition of flocculant and coagulant aid can cause the precipitate to form larger flocs, which is beneficial for subsequent solid-liquid separation.

[0027] In one embodiment of this utility model, the wastewater is introduced into the wastewater pretreatment unit, where sodium hydroxide is first added for pH adjustment, then a precipitating agent is added, and finally a flocculant and a coagulant aid are added.

[0028] In one embodiment of this invention, the amount of sodium hydroxide added is sufficient to adjust the pH of the wastewater in the wastewater pretreatment unit to 8.5–11.5; the amount of the heavy metal precipitator added can be adjusted accordingly based on the heavy metal ion content in the wastewater. This invention does not specifically limit the types of heavy metal precipitators, flocculants, and coagulants; commonly used types of heavy metal precipitators, flocculants, and coagulants by those skilled in the art can be used.

[0029] In the embodiments of this utility model, the pH value of the effluent from the wastewater pretreatment unit can be 8.5-11.5 or 9.5-10.5; the total concentration of metal ions in the effluent from the wastewater pretreatment unit can be less than 5 ppm.

[0030] The wastewater treatment system provided by this utility model further includes a wastewater solid-liquid separation unit connected to the wastewater pretreatment unit. By connecting the wastewater pretreatment unit and the wastewater solid-liquid separation unit, this utility model enables the pretreated wastewater to be sent to the wastewater solid-liquid separation unit for solid-liquid separation.

[0031] In one embodiment of this invention, the wastewater solid-liquid separation unit may include a gravity sedimentation tank and a plate and frame filter. In this invention, pretreated wastewater undergoes sedimentation and separation in the gravity sedimentation tank to obtain bottom sludge and supernatant. In another embodiment, the supernatant outlet of the gravity sedimentation tank is connected to the inlet of the wastewater oxidation treatment unit, enabling the supernatant to be sent to the wastewater oxidation treatment unit for oxidation treatment; the bottom sludge outlet of the gravity sedimentation tank is connected to the inlet of the plate and frame filter, enabling the bottom sludge to be sent to the plate and frame filter for pressure filtration separation and collection before outsourced processing. This invention achieves solid-liquid separation through the wastewater solid-liquid separation unit, removing most of the heavy metal ions from the wastewater.

[0032] The wastewater treatment system provided by this utility model also includes a wastewater oxidation unit connected to the wastewater solid-liquid separation unit. By connecting the wastewater solid-liquid separation unit and the wastewater oxidation unit, this utility model can send the supernatant in the gravity sedimentation tank into the wastewater oxidation treatment unit for oxidation treatment.

[0033] As one embodiment of this utility model, the wastewater oxidation unit may include a complex-breaking oxidation unit and an advanced oxidation unit connected in sequence.

[0034] In one embodiment of this invention, the complex-breaking oxidation unit may be equipped with an oxidant dosing device; the oxidation method used in the complex-breaking oxidation unit may include sodium hypochlorite oxidation, ozone oxidation, (Fenton-like) oxidation, or Inco process; the advanced oxidation unit may be equipped with an electrocatalytic oxidation device. This invention can deeply remove cyanide and complexed heavy metal ions through the complex-breaking oxidation unit, resulting in cyanide complex concentrations of less than 0.1 mg / L. The advanced oxidation unit can preliminarily oxidize organic matter, converting large organic molecules into smaller ones, thus improving the biodegradability of the organic matter. After passing through the advanced oxidation unit, COD ≤ 250 mg / L, total phosphorus ≤ 5 mg / L, and ammonia nitrogen ≤ 25 mg / L.

[0035] In this invention, the total removal rate of ammonia nitrogen, the total removal rate of COD, the total removal rate of pigments, and the total removal rate of oil in the wastewater treated by the wastewater oxidation unit are ≥50%, ≥60%, ≥90%, and ≥90%, respectively.

[0036] The wastewater treatment system provided by this utility model also includes a wastewater biochemical treatment unit connected to the wastewater oxidation unit. By connecting the wastewater oxidation unit and the wastewater biochemical treatment unit, this utility model can send the oxidized wastewater into the wastewater biochemical treatment unit for biochemical treatment.

[0037] In one embodiment of this invention, the wastewater biochemical treatment unit can be a membrane bioreactor. This invention does not specifically limit the type and parameter settings of the membrane bioreactor; any type and parameter settings commonly used by those skilled in the art can be employed. This invention can simultaneously achieve membrane separation and biological treatment functions through a membrane bioreactor.

[0038] This invention utilizes a wastewater biochemical treatment unit to deeply remove BOD (biochemical oxygen demand), total nitrogen, and total phosphorus, yielding biochemical sludge and a first supernatant. The biochemical sludge is collected and then outsourced for further treatment. In this invention, the effluent from the wastewater biochemical treatment unit has oil ≤1 mg / L, COD ≤150 mg / L, ammonia nitrogen ≤8 mg / L, and conductivity of 2000–12000 μS / cm.

[0039] The wastewater treatment system provided by this utility model also includes a wastewater polyvalent metal ion removal unit connected to the wastewater biochemical treatment unit. By connecting the wastewater biochemical treatment unit and the wastewater polyvalent metal ion removal unit, this utility model enables the first clarified liquid obtained from biochemical treatment to be sent to the wastewater polyvalent metal ion removal unit to remove polyvalent metal ions.

[0040] In one embodiment of this invention, the wastewater multivalent metal ion removal unit may include a metal ion adsorption material; the metal ion adsorption material may include special resin adsorption material, multifunctional fiber material adsorption material, porous sponge adsorption material, or porous gel adsorption material. In this invention, suitable metal ion adsorption materials can be selected according to the type of metal ions based on common knowledge in the art. This invention uses a wastewater multivalent metal ion removal unit to adsorb calcium, magnesium, and residual iron, nickel, copper, zinc, aluminum, and other multivalent heavy metal ions in the solution onto the material, preventing subsequent fouling of the membrane system. In this invention, the total amount of divalent or higher metal ions in the effluent of the wastewater multivalent metal ion removal unit is ≤5 ppm, of which the total amount of multivalent heavy metal ions is ≤2 ppm, and calcium and magnesium are ≤5 ppm. In one embodiment of this invention, the multivalent heavy metal ions include iron ions and aluminum ions.

[0041] The wastewater treatment system provided by this invention also includes a membrane treatment system connected to the wastewater multivalent metal ion removal unit. By connecting the wastewater multivalent metal ion removal unit to the membrane treatment system, this invention enables further treatment of the wastewater.

[0042] As one embodiment of the present invention, the membrane treatment system may include a wastewater nanofiltration desalination unit, a first wastewater salt concentration and separation unit connected to the concentrate outlet of the wastewater nanofiltration desalination unit and a first reverse osmosis unit connected to the desalination outlet of the first wastewater salt concentration and separation unit, a second wastewater salt concentration and separation unit connected to the desalination outlet of the wastewater nanofiltration desalination unit and a second reverse osmosis unit connected to the desalination outlet of the second wastewater salt concentration and separation unit.

[0043] In one embodiment of this invention, the membrane treatment system includes a wastewater nanofiltration desalination unit. In another embodiment, the inlet of the wastewater nanofiltration desalination unit is connected to the outlet of the wastewater polyvalent metal ion removal unit. By connecting the wastewater polyvalent metal ion removal unit and the wastewater nanofiltration desalination unit, this invention enables wastewater with removed polyvalent metal ions to be fed into the wastewater nanofiltration desalination unit for nanofiltration desalination treatment, resulting in nanofiltration concentrate containing sulfates and nanofiltration desalination water containing chlorides.

[0044] In one embodiment of this invention, the wastewater nanofiltration desalination unit can have two nanofiltration stages. In another embodiment, the pH value of the wastewater at the influent stage can be 4.5–6.5; the bactericide dosage in the wastewater nanofiltration desalination unit can be a non-oxidizing bactericide. This invention, through two-stage nanofiltration, can achieve a retention rate of greater than ≥95% for divalent and higher-valent cations and an ≤5% for monovalent ions. The nanofiltration membrane system in this invention, by controlling the influent pH and bactericide dosage, inhibits microbial activity and improves the effectiveness of the nanofiltration membrane. In this invention, the concentrated water of the wastewater nanofiltration desalination unit has a conductivity of 33000 μs / cm, sulfate ≥20 g / L, chloride ≤500 mg / L, heavy metal ions ≤20 ppm, and calcium and magnesium ≤50 ppm; the freshwater of the wastewater nanofiltration desalination unit has a conductivity of 5000 μs / cm, chloride 2 g / L, sulfate 100 mg / L, total heavy metal ions ≤0.2 ppm, and calcium and magnesium ≤0.5 ppm.

[0045] In one embodiment of this invention, the membrane treatment system further includes a first wastewater salt concentration and separation unit connected to the concentrate outlet of the wastewater nanofiltration desalination unit. By connecting the concentrate outlet of the wastewater nanofiltration desalination unit to the first wastewater salt concentration and separation unit, this invention enables the nanofiltration concentrate to be fed into the first wastewater salt concentration and separation unit, achieving deep concentration of sulfate.

[0046] In one embodiment of this utility model, the first wastewater salt concentration and separation unit may be equipped with an electrodialysis device; the conductivity of the concentrated water in the first wastewater salt concentration and separation unit can be between 1 and 1.5 × 10⁻⁶.5 μs / cm, and can also be 1~1.2×10 5 μs / cm; the conductivity of the freshwater in the first wastewater salt concentration and separation unit can be 1000-3000 μs / cm, or even 1000-2000 μs / cm. In this invention, the freshwater in the first wastewater salt concentration and separation unit contains copper <0.05 mg / L, nickel <0.5 mg / L, chromium <0.05 mg / L, zinc <0.05 mg / L, iron <0.05 mg / L, aluminum <0.05 mg / L, cadmium <0.05 mg / L, silver <0.5 mg / L, lead <0.05 mg / L, calcium <1.0 mg / L, ammonia nitrogen <2.0 mg / L, and total nitrogen <40 mg / L. Total phosphorus <1.0 mg / L; the concentrated water from the first wastewater salt concentration and separation unit contains copper <0.5 mg / L, nickel <5.0 mg / L, chromium <8.5 mg / L, zinc <20 mg / L, iron <20 mg / L, aluminum <25 mg / L, cadmium <2 mg / L, silver <1.5 mg / L, lead <1.0 mg / L, calcium <50 mg / L, ammonia nitrogen <100 mg / L, total nitrogen <200 mg / L, and total phosphorus <1.0 mg / L.

[0047] In one embodiment of this invention, the membrane treatment system further includes a first reverse osmosis unit connected to the freshwater outlet of the first wastewater salt concentration and separation unit. By connecting the freshwater outlet of the first wastewater salt concentration and separation unit to the first reverse osmosis unit, the freshwater separated by the first wastewater salt concentration and separation unit can be sent to the first reverse osmosis unit.

[0048] In one embodiment of this invention, the first reverse osmosis unit can be a low-pressure reverse osmosis device; the operating pressure of the low-pressure reverse osmosis device can be below 1.5 MPa. This invention limits the operating voltage of the low-pressure reverse osmosis device to the above-mentioned range to obtain high-purity water.

[0049] The concentrate outlet of the first reverse osmosis unit of this invention is connected to the first wastewater salt concentration and separation unit. By connecting the concentrate outlet of the first reverse osmosis unit to the first wastewater salt concentration and separation unit, this invention can further treat the concentrate separated by the first reverse osmosis unit, achieving water recycling and maximum resource utilization of salt.

[0050] In this invention, the freshwater from the first reverse osmosis unit contains copper <0.02 mg / L, nickel <0.01 mg / L, chromium <0.01 mg / L, zinc <0.01 mg / L, iron <0.01 mg / L, aluminum <0.08 mg / L, cadmium <0.001 mg / L, silver <0.001 mg / L, lead <0.01 mg / L, mercury <0.0001 mg / L, total nitrogen <2.0 mg / L, total phosphorus <0.1 mg / L, COD <30 mg / L, and conductivity of [missing information]. <150μs / cm; the concentrate from the first reverse osmosis unit contains copper <0.5mg / L, nickel <0.5mg / L, chromium <0.5mg / L, zinc <1mg / L, iron <0.5mg / L, aluminum <0.5mg / L, cadmium <0.01mg / L, silver <0.1mg / L, lead <0.1mg / L, mercury <0.001mg / L, total nitrogen <10mg / L, ammonia nitrogen <20mg / L, total phosphorus <0.5mg / L, and has a conductivity of 3000~5000μs / cm.

[0051] The first product water obtained from the freshwater outlet of the first reverse osmosis unit of this invention meets the standards for production line cleaning and reuse water or Class IV surface water. The first product water obtained from the freshwater outlet of the first reverse osmosis unit of this invention enables water reuse.

[0052] In one embodiment of this invention, the membrane treatment system further includes a second wastewater salt concentration and separation unit connected to the freshwater outlet of the wastewater nanofiltration desalination unit. By connecting the freshwater outlet of the wastewater nanofiltration desalination unit to the second wastewater salt concentration and separation unit, this invention enables the nanofiltration freshwater to be fed into the second wastewater salt concentration and separation unit, achieving deep concentration of chloride salts.

[0053] In one embodiment of this utility model, the second wastewater salt concentration and separation unit may include an electrodialysis device; the conductivity of the concentrated water in the second wastewater salt concentration and separation unit may be 1 to 1.5 × 10⁻⁶. 5μs / cm; the conductivity of the freshwater in the second wastewater salt concentration and separation unit can be 1000-3000 μs / cm. The freshwater in the second wastewater salt concentration and separation unit of this invention contains copper <0.05 mg / L, nickel <0.5 mg / L, chromium <0.05 mg / L, zinc <0.05 mg / L, iron <0.05 mg / L, aluminum <0.05 mg / L, cadmium <0.05 mg / L, silver <0.5 mg / L, lead <0.05 mg / L, calcium <0.5 mg / L, ammonia nitrogen <2.0 mg / L, and total nitrogen <40 mg / L. Total phosphorus <1.0 mg / L; the concentrated water from the second wastewater salt concentration and separation unit contains copper <2 mg / L, nickel <2 mg / L, chromium <2.5 mg / L, zinc <2.5 mg / L, iron <2 mg / L, aluminum <25 mg / L, cadmium <2 mg / L, silver <1.5 mg / L, lead <1.0 mg / L, calcium <40 mg / L, ammonia nitrogen <50 mg / L, total nitrogen <80 mg / L, and total phosphorus <1.0 mg / L. This invention achieves deep concentration of chloride salts through the second wastewater salt concentration and separation unit.

[0054] In one embodiment of this invention, the membrane treatment system further includes a second reverse osmosis unit connected to the freshwater outlet of the second wastewater salt concentration and separation unit. By connecting the freshwater outlet of the second wastewater salt concentration and separation unit to the second reverse osmosis unit, the freshwater separated by the second wastewater salt concentration and separation unit can be sent to the second reverse osmosis unit.

[0055] In one embodiment of this invention, the second reverse osmosis unit can be a low-pressure reverse osmosis device; the operating pressure of the low-pressure reverse osmosis device can be below 1.5 MPa, or even below 1.0 MPa. This invention limits the operating voltage of the low-pressure reverse osmosis device to the above range to obtain high-purity water.

[0056] The concentrate outlet of the second reverse osmosis unit of this invention is connected to the second wastewater salt concentration and separation unit. By connecting the concentrate outlet of the second reverse osmosis unit to the second wastewater salt concentration and separation unit, this invention can further treat the concentrate separated by the second reverse osmosis unit, achieving water recycling and maximum resource utilization of salt.

[0057] In this invention, the freshwater from the second reverse osmosis unit contains copper <0.02 mg / L, nickel <0.01 mg / L, chromium <0.01 mg / L, zinc <0.01 mg / L, iron <0.01 mg / L, aluminum <0.08 mg / L, cadmium <0.001 mg / L, silver <0.001 mg / L, lead <0.01 mg / L, mercury <0.0001 mg / L, total nitrogen <2.0 mg / L, total phosphorus <0.1 mg / L, and COD <30 mg / L. mg / L, conductivity <200μs / cm; the concentrate of the second reverse osmosis unit contains copper <0.5mg / L, nickel <0.5mg / L, chromium <0.5mg / L, zinc <1mg / L, iron <0.5mg / L, aluminum <0.5mg / L, cadmium <0.01mg / L, silver <0.1mg / L, lead <0.1mg / L, mercury <0.001mg / L, total nitrogen <10mg / L, ammonia nitrogen <20mg / L, and total phosphorus <0.5mg / L.

[0058] The second product water obtained from the freshwater outlet of the second reverse osmosis unit of this invention meets the standards for production line cleaning and reuse water or Class IV surface water. The second product water obtained from the freshwater outlet of the second reverse osmosis unit of this invention enables water reuse.

[0059] In one embodiment of this utility model, the quality of the water produced in the first and second reverse osmosis units can be as follows: heavy metals copper <0.02mg / L, nickel <0.01mg / L, chromium <0.01mg / L, zinc <0.01mg / L, iron <0.01mg / L, aluminum <0.08mg / L, cadmium <0.001mg / L, silver <0.001mg / L, lead <0.01mg / L, mercury <0.0001mg / L, total nitrogen <2.0mg / L, total phosphorus <0.1mg / L, and conductivity <200μs / cm.

[0060] This invention pre-treats wastewater through a wastewater pretreatment unit, which precipitates most of the heavy metals in the wastewater. The wastewater oxidation unit deeply removes cyanide and complexed heavy metal ions through oxidation, and also pre-oxidizes organic matter, improving its biodegradability. The wastewater biochemical treatment unit achieves deep removal of biodegradable organic matter, total phosphorus, and total nitrogen from the wastewater, while simultaneously breaking down organic complexes. The wastewater multivalent metal ion removal unit removes calcium, magnesium, and residual iron, nickel, copper, zinc, aluminum, and other multivalent metal ions from the solution, preventing subsequent fouling of the membrane treatment system. Through the organic coupling of multiple units, deep purification of chemical pollutants in electroplating wastewater is achieved, avoiding fouling of the membrane system in subsequent wastewater treatment. When used in a process system for the resource recovery of water and salt in electroplating wastewater, it can reduce the pressure on subsequent wastewater and waste liquid treatment systems.

[0061] This utility model also provides a process system for the resource utilization of water and salt in electroplating wastewater, including the wastewater treatment system described in the above technical solution and a first waste liquid treatment system and a second waste liquid treatment system connected to the membrane treatment system in the wastewater treatment system.

[0062] The process system for resource utilization of water and salt in electroplating wastewater provided by this utility model includes the wastewater treatment system described in the above technical solution; the first concentrated water separated by the first wastewater salt concentration and separation unit and the second concentrated water separated by the second wastewater salt concentration and separation unit in the wastewater treatment system need to be further treated in the first waste liquid treatment system and the second waste liquid treatment system.

[0063] The process system for resource recovery of water and salt in electroplating wastewater provided by this utility model also includes a first waste liquid treatment system connected to the wastewater treatment system. As one embodiment of this utility model, the concentrated water outlet of the first wastewater salt concentration and separation unit in the wastewater treatment system is connected to the inlet of the first waste liquid treatment system.

[0064] As one embodiment of the present invention, the first waste liquid treatment system includes a first concentrated liquid collection unit, a first concentrated liquid pretreatment unit, a first concentrated liquid solid-liquid separation unit, and a first evaporation unit connected in sequence.

[0065] In one embodiment of this invention, the concentrated water outlet of the first wastewater salt concentration and separation unit is connected to the inlet of the first concentrated liquid collection unit. By connecting the concentrated water outlet of the first wastewater salt concentration and separation unit to the inlet of the first concentrated liquid collection unit, this invention enables the first concentrated water separated by the first wastewater salt concentration and separation unit to be collected in the first concentrated liquid collection unit.

[0066] In one embodiment of this utility model, the conductivity of the first concentrated water separated by the first wastewater salt concentration and separation unit is 1 to 1.5 × 10⁻⁶. 5 μs / cm, containing copper <0.5mg / L, nickel <5.0mg / L, chromium <8.5mg / L, zinc <20mg / L, iron <20mg / L, aluminum <25mg / L, cadmium <2mg / L, silver <1.5mg / L, lead <1.0mg / L, calcium <50mg / L, ammonia nitrogen <100mg / L, total nitrogen <200mg / L, and total phosphorus <1.0mg / L.

[0067] In one embodiment of this invention, the first wastewater treatment system further includes a first concentrated liquid pretreatment unit connected to the first concentrated liquid collection unit. By connecting the first concentrated liquid collection unit to the first concentrated liquid pretreatment unit, this invention enables the first concentrated liquid collected by the first concentrated liquid collection unit to be sent to the wastewater pretreatment unit for pretreatment.

[0068] In one embodiment of this invention, the first concentrated liquid sent to the wastewater pretreatment unit may be equipped with a sodium hydroxide dosing device and a heavy metal precipitator dosing device. By setting up the aforementioned dosing devices, this invention uses sodium hydroxide to adjust the pH of the first concentrated liquid, which is beneficial for the precipitation of heavy metal ions; by adding sodium hydroxide and a heavy metal precipitator, most of the heavy metal ions can be precipitated out.

[0069] In one embodiment of this utility model, the pH value of the effluent from the first concentrated liquid pretreatment unit can be 9 to 11.

[0070] In one embodiment of this utility model, the first concentrated liquid is introduced into the first concentrated liquid pretreatment unit, sodium hydroxide is added first for pH adjustment, and then a heavy precipitator is added.

[0071] In one embodiment of this invention, the amount of sodium hydroxide added is sufficient to adjust the pH of the liquid in the first concentrated liquid pretreatment unit to 9-11; the amount of the heavy metal ion precipitant added can be adjusted accordingly based on the heavy metal ion content in the wastewater. In a specific embodiment of this invention, the sodium hydroxide in the sodium hydroxide dosing device of the first concentrated liquid pretreatment unit can be added in the form of liquid alkali; the concentration of the liquid alkali is 30 wt%. This invention does not have a special limitation on the type of heavy metal precipitant; any type of heavy metal precipitant commonly used by those skilled in the art can be used.

[0072] In one embodiment of this invention, the first waste liquid treatment system further includes a first concentrated liquid solid-liquid separation unit connected to the first concentrated liquid pretreatment unit. By connecting the first concentrated liquid pretreatment unit to the first concentrated liquid solid-liquid separation unit, this invention enables the pretreated concentrated liquid to be sent to the first concentrated liquid solid-liquid separation unit for solid-liquid separation.

[0073] In this invention, the first concentrated liquid solid-liquid separation unit can separate solids and liquids to obtain a first solution and a first sludge. In this invention, the first solution is passed into a first evaporation unit for further processing; the first sludge can be collected and outsourced for further treatment.

[0074] In one embodiment of this invention, the first waste liquid treatment system further includes a first evaporation unit connected to the first concentrated liquid solid-liquid separation unit. By connecting the first concentrated liquid solid-liquid separation unit to the first evaporation unit, this invention enables the first solution obtained from the first concentrated liquid solid-liquid separation unit to be sent to the first evaporation unit for evaporation and concentration.

[0075] In one embodiment of this invention, the first evaporation unit can be a mechanical vapor recompression evaporator. In this invention, the first evaporation unit evaporates and concentrates the first solution separated by the first concentrated liquid solid-liquid separation unit to obtain first evaporation condensate and industrial by-product sodium sulfate. The first evaporation condensate of this invention contains copper <0.02 mg / L, nickel <0.01 mg / L, chromium <0.01 mg / L, zinc <0.01 mg / L, iron <0.01 mg / L, aluminum <0.08 mg / L, cadmium <0.001 mg / L, silver <0.001 mg / L, lead <0.01 mg / L, mercury <0.0001 mg / L, ammonia nitrogen <40 mg / L, total phosphorus <0.5 mg / L, COD <40 mg / L, and conductivity <200 μS / cm.

[0076] In one embodiment of this invention, the first waste liquid treatment system further includes a first distilled water unit connected to the first evaporation unit. By connecting the first evaporation unit to the first distilled water unit, this invention enables the collection of the first evaporation condensate obtained from the first evaporation unit.

[0077] In one embodiment of this invention, the first waste liquid treatment system may further include a first industrial by-product salt recovery unit connected to the salt outlet of the first evaporation unit. By connecting the salt outlet of the first evaporation unit to the first industrial by-product salt recovery unit, this invention enables the collection of sodium sulfate, an industrial by-product salt obtained from the first evaporation unit.

[0078] In one embodiment of this utility model, the first distilled water unit can be connected to the inlet of the first reverse osmosis unit to realize the recycling and utilization of water resources.

[0079] The process system for resource recovery of water and salt in electroplating wastewater provided by this utility model also includes a second waste liquid treatment system connected to the wastewater treatment system. In one embodiment of this utility model, the concentrated water outlet of the second wastewater salt concentration and separation unit in the wastewater treatment system is connected to the inlet of the second waste liquid treatment system.

[0080] As one embodiment of the present invention, the second waste liquid treatment system includes a second concentrated liquid collection unit, a second concentrated liquid pretreatment unit, a second concentrated liquid solid-liquid separation unit, and a second evaporation unit connected in sequence.

[0081] In one embodiment of this invention, the concentrated water outlet of the second wastewater salt concentration and separation unit is connected to the inlet of the second concentrated liquid collection unit. By connecting the concentrated water outlet of the second wastewater salt concentration and separation unit to the inlet of the second concentrated liquid collection unit, this invention enables the collection of the second concentrated water separated by the second wastewater salt concentration and separation unit into the second concentrated liquid collection unit.

[0082] In one embodiment of this utility model, the conductivity of the second concentrated water separated by the second wastewater salt concentration and separation unit is 1 to 1.5 × 10⁻⁶. 5 μs / cm, containing copper <2mg / L, nickel <2mg / L, chromium <2.5mg / L, zinc <2.5mg / L, iron <2mg / L, aluminum <25mg / L, cadmium <2mg / L, silver <1.5mg / L, lead <1.0mg / L, calcium <40mg / L, ammonia nitrogen <50mg / L, total nitrogen <80mg / L, and total phosphorus <1.0mg / L.

[0083] In one embodiment of this invention, the second wastewater treatment system further includes a second concentrated liquid pretreatment unit connected to the second concentrated liquid collection unit. By connecting the second concentrated liquid collection unit to the second concentrated liquid pretreatment unit, this invention enables the second concentrated liquid collected by the second concentrated liquid collection unit to be sent to the wastewater pretreatment unit for pretreatment.

[0084] In one embodiment of this invention, the second concentrated liquid fed into the wastewater pretreatment unit may be equipped with a sodium hydroxide dosing device and a heavy metal precipitator dosing device. By setting up the aforementioned dosing devices, this invention uses sodium hydroxide to adjust the pH of the second concentrated liquid, which is beneficial for the precipitation of heavy metal ions; by adding sodium hydroxide and a heavy metal precipitator, most of the heavy metal ions can be precipitated out.

[0085] In one embodiment of this utility model, the pH value of the effluent from the second concentrated liquid pretreatment unit can be 9 to 11.

[0086] In one embodiment of this utility model, the second concentrated liquid is introduced into the second concentrated liquid pretreatment unit, sodium hydroxide is added first for pH adjustment, and then a heavy precipitant is added.

[0087] In one embodiment of this invention, the amount of sodium hydroxide added is sufficient to adjust the pH of the liquid in the second concentrated liquid pretreatment unit to 9-11; the amount of the heavy metal ion precipitant added can be adjusted accordingly based on the heavy metal ion content in the wastewater. In a specific embodiment of this invention, the sodium hydroxide in the sodium hydroxide dosing device of the second concentrated liquid pretreatment unit can be added in the form of liquid alkali; the concentration of the liquid alkali is 30 wt%. This invention does not have a special limitation on the type of heavy metal precipitant; any type of heavy metal precipitant commonly used by those skilled in the art can be used.

[0088] In one embodiment of this invention, the second waste liquid treatment system further includes a second concentrated liquid solid-liquid separation unit connected to the second concentrated liquid pretreatment unit. By connecting the second concentrated liquid pretreatment unit to the second concentrated liquid solid-liquid separation unit, this invention enables the pretreated concentrated liquid to be fed into the second concentrated liquid solid-liquid separation unit for solid-liquid separation.

[0089] In this invention, the second concentrated liquid solid-liquid separation unit can achieve solid-liquid separation to obtain a second solution and a second sludge. In this invention, the second solution is passed into the first evaporation unit for further processing; the second sludge can be collected and outsourced for further treatment.

[0090] In one embodiment of this invention, the second waste liquid treatment system further includes a second evaporation unit connected to the second concentrated liquid solid-liquid separation unit. By connecting the second concentrated liquid solid-liquid separation unit to the second evaporation unit, this invention enables the second solution obtained from the second concentrated liquid solid-liquid separation unit to be sent to the second evaporation unit for evaporation and concentration.

[0091] In one embodiment of this invention, the second evaporation unit can be a mechanical vapor recompression evaporator. In this invention, the second evaporation unit evaporates and concentrates the second solution separated by the second concentrated liquid solid-liquid separation unit to obtain second evaporation condensate and industrial by-product sodium chloride. The second evaporation condensate of this invention contains copper <0.02 mg / L, nickel <0.01 mg / L, chromium <0.01 mg / L, zinc <0.01 mg / L, iron <0.01 mg / L, aluminum <0.08 mg / L, cadmium <0.001 mg / L, silver <0.001 mg / L, lead <0.01 mg / L, mercury <0.0001 mg / L, ammonia nitrogen <40 mg / L, total phosphorus <0.5 mg / L, COD <40 mg / L, and conductivity <200 μS / cm.

[0092] In one embodiment of this invention, the second wastewater treatment system further includes a second distilled water unit connected to the second evaporation unit. By connecting the second evaporation unit to the second distilled water unit, this invention enables the collection of the second evaporation condensate obtained from the second evaporation unit.

[0093] In one embodiment of this invention, the second wastewater treatment system may further include a second industrial by-product salt recovery unit connected to the salt outlet of the second evaporation unit. By connecting the salt outlet of the second evaporation unit to the second industrial by-product salt recovery unit, this invention enables the collection of sodium chloride, an industrial by-product salt obtained from the second evaporation unit.

[0094] In one embodiment of this utility model, the second distilled water unit can be connected to the inlet of the second reverse osmosis unit to realize the recycling and utilization of water resources.

[0095] In this invention, the sodium sulfate and sodium chloride produced by industrial by-products contain more than 95% sodium sulfate and more than 95% sodium chloride, respectively, and have a water content of less than 5%. Furthermore, the sodium sulfate and sodium chloride produced by industrial by-products contain less than 0.003% copper, less than 0.003% nickel, less than 0.003% chromium, less than 0.02% zinc, less than 0.05% iron, less than 0.1% aluminum, and less than 0.0004% cadmium.

[0096] This invention can effectively remove calcium, magnesium, and residual iron, nickel, copper, zinc, aluminum, and other polyvalent metal ions from the solution through a wastewater treatment system, preventing subsequent clogging of the nanofiltration system. Through a waste liquid treatment system, it can achieve deep purification of chemical pollutants in electroplating wastewater, obtaining RO permeate (reclaimed water), while separating industrial chloride and sulfate salts, effectively ensuring the reuse of water resources and maximizing the value of salt resources.

[0097] In a specific embodiment of this utility model, the process system for resource recovery of water and salt in electroplating wastewater is as follows: Figure 1 As shown:

[0098] from Figure 1 As can be seen, electroplating wastewater enters the wastewater collection unit, which is connected to the wastewater pretreatment unit. The wastewater pretreatment unit is connected to the wastewater solid-liquid separation unit. In the solid-liquid separation unit, bottom sludge and supernatant are separated. The supernatant enters the wastewater oxidation treatment unit for oxidation treatment. The wastewater oxidation treatment unit is then connected to the wastewater biological treatment unit, where biological sludge and the first supernatant are obtained. The wastewater biological treatment unit is connected to the wastewater multivalent metal ion removal unit (the first supernatant enters the wastewater multivalent metal ion removal unit). The wastewater multivalent metal ion removal unit is connected to the nanofiltration desalination unit. The concentrated water from the nanofiltration desalination unit is connected to the first wastewater salt concentration and separation unit. The freshwater from the wastewater salt concentration and separation unit is connected to the first reverse osmosis unit. The first product water obtained from the freshwater outlet of the first reverse osmosis unit is connected to the production line for reuse. The concentrated water outlet of the first reverse osmosis unit is connected to the first wastewater salt concentration and separation unit. The concentrated water outlet of the first wastewater salt concentration and separation unit is connected to the first concentrated liquid collection unit. The freshwater outlet of the wastewater nanofiltration desalination unit is connected to the second wastewater salt concentration and separation unit. The freshwater outlet of the second wastewater salt concentration and separation unit is connected to the second reverse osmosis unit. The freshwater outlet of the second reverse osmosis unit is connected to the production line. The concentrated water outlet of the second reverse osmosis unit is connected to the second wastewater salt concentration and separation unit. The concentrated water outlet of the second wastewater salt concentration and separation unit is connected to the second concentrated liquid collection unit.

[0099] The first concentrated liquid collection unit is connected to the first concentrated liquid pretreatment unit, and the first concentrated liquid pretreatment unit is connected to the first concentrated liquid solid-liquid separation unit. First sludge and first solution are separated in the first concentrated liquid solid-liquid separation unit. The first concentrated liquid solid-liquid separation unit is connected to the inlet of the first evaporation unit (the first solution enters the first evaporation unit). The first evaporation unit is connected to the first distilled water unit. The salt outlet of the first evaporation unit is connected to the first industrial by-product salt recovery unit. The first distilled water unit is connected to the first reverse osmosis unit. The second concentrated liquid collection unit is connected to the second concentrated liquid pretreatment unit, and the second concentrated liquid pretreatment unit is connected to the second concentrated liquid solid-liquid separation unit. Second sludge and second solution are separated in the second concentrated liquid solid-liquid separation unit. The second concentrated liquid solid-liquid separation unit is connected to the second evaporation unit (the second solution enters the second evaporation unit). The second evaporation unit is connected to the second distilled water unit. The salt outlet of the second evaporation unit is connected to the second industrial by-product salt recovery unit. The second distilled water unit is connected to the second reverse osmosis unit.

[0100] The technical solutions of this utility model will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this utility model, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this utility model without creative effort are within the scope of protection of this utility model.

[0101] Example 1

[0102] A wastewater treatment system comprises, in sequence, a wastewater collection unit, a wastewater pretreatment unit, a wastewater solid-liquid separation unit, a wastewater oxidation unit, a wastewater biochemical treatment unit, a wastewater multivalent metal ion removal unit, and a membrane treatment system.

[0103] The membrane treatment system comprises a wastewater nanofiltration desalination unit, a first wastewater salt concentration and separation unit, and a first reverse osmosis unit connected in sequence; the concentrate outlet of the first reverse osmosis unit is connected to the first wastewater salt concentration and separation unit; the desalination outlet of the wastewater nanofiltration desalination unit is connected in sequence to the second wastewater salt concentration and separation unit and the second reverse osmosis unit; the concentrate outlet of the second reverse osmosis unit is connected to the second wastewater salt concentration and separation unit.

[0104] The specific usage method is as follows: Electroplating wastewater enters the wastewater collection unit, and the outlet of the wastewater collection unit is connected to the inlet of the wastewater pretreatment unit. The collected electroplating wastewater is sent to the wastewater pretreatment unit. In the wastewater pretreatment unit, 500 mg / L of sodium hydroxide is added to adjust the pH of the wastewater to 11. Then, 200 mg / L of a flocculant is added, followed by 100 mg / L of flocculant (polyaluminum chloride) and 2 mg / L of coagulant aid (polyacrylamide). The outlet of the wastewater pretreatment unit is connected to the inlet of the wastewater solid-liquid separation unit. The pretreated wastewater is then sent to the wastewater pretreatment unit. The wastewater is fed into a solid-liquid separation unit, where bottom sludge and supernatant are separated. The supernatant then enters a wastewater oxidation treatment unit (a complex-breaking oxidation unit and an advanced oxidation unit) for oxidation treatment (oxidation is performed using the Inco process in the complex-breaking oxidation unit and electrochemical oxidation using an electrocatalytic oxidation device in the advanced oxidation unit). The outlet of the wastewater oxidation treatment unit is then connected to the inlet of a wastewater biological treatment unit (membrane bioreactor). In the wastewater biological treatment unit, biological sludge and a first supernatant are obtained. The outlet of the wastewater biological treatment unit is connected to... The inlet of the wastewater multivalent metal ion removal unit (porous sponge ion exchange adsorption material) is connected to the inlet of the wastewater multivalent metal ion removal unit (the first clear liquid enters the wastewater multivalent metal ion removal unit). The outlet of the wastewater multivalent metal ion removal unit is connected to the inlet of the wastewater nanofiltration desalination unit (two-stage nanofiltration). The concentrated water outlet of the wastewater nanofiltration desalination unit is connected to the inlet of the first wastewater salt concentration and separation unit (equipped with an electrodialysis device). The desalinated water outlet of the first wastewater salt concentration and separation unit is connected to the inlet of the first reverse osmosis unit (low-pressure reverse osmosis device, operating pressure below 1.5 MPa). The freshwater outlet of the first reverse osmosis unit is connected to the production line; the concentrated water outlet of the first reverse osmosis unit is connected to the inlet of the first wastewater salt concentration and separation unit; the freshwater outlet of the wastewater nanofiltration and desalination unit is connected to the inlet of the second wastewater salt concentration and separation unit (equipped with an electrodialysis device); the freshwater outlet of the second wastewater salt concentration and separation unit is connected to the inlet of the second reverse osmosis unit (low-pressure reverse osmosis device, operating pressure below 1.5 MPa); the freshwater outlet of the second reverse osmosis unit is connected to the production line; and the concentrated water outlet of the second reverse osmosis unit is connected to the inlet of the second wastewater salt concentration and separation unit.

[0105] The electroplating wastewater has the following composition: pH 2.2, conductivity 9500 μs / cm, COD (chemical oxygen demand) 500 mg / L, CN (total cyanide) 10 mg / L, ammonia nitrogen 48 mg / L, total nitrogen 55 mg / L, total phosphorus 70 mg / L, copper 125 mg / L, chromium 80 mg / L, nickel 140 mg / L, zinc 40 mg / L, and calcium and magnesium 40 mg / L.

[0106] The concentrations of the main ions in the effluent of each unit in Example 1 are shown in Table 1.

[0107] Table 1. Concentration of major ions in the effluent of each unit in Example 1

[0108]

[0109]

[0110]

[0111]

[0112] Example 2

[0113] A process system for the resource utilization of water and salt in electroplating wastewater comprises the wastewater treatment system described in Example 1, and a first waste liquid treatment system and a second waste liquid treatment system connected to the membrane treatment system in the wastewater treatment system.

[0114] The first waste liquid treatment system comprises a first concentrated liquid collection unit, a first concentrated liquid pretreatment unit, a first concentrated liquid solid-liquid separation unit, and a first evaporation unit connected in sequence; the concentrated water outlet of the first wastewater salt concentration and separation unit is connected to the inlet of the first concentrated liquid collection unit.

[0115] The second waste liquid treatment system consists of a second concentrated liquid collection unit, a second concentrated liquid pretreatment unit, a second concentrated liquid solid-liquid separation unit, and a second evaporation unit connected in sequence; the concentrated water outlet of the second wastewater salt concentration and separation unit is connected to the inlet of the second concentrated liquid collection unit.

[0116] The specific usage method is as follows: The first concentrated water separated by the first wastewater salt concentration and separation unit in Example 1 is connected to the inlet of the first concentrated liquid collection unit through the concentrated water outlet and enters the first waste liquid treatment system. The outlet of the first concentrated liquid collection unit is connected to the inlet of the first concentrated liquid pretreatment unit. 30% liquid alkali 14000mg / L is added to the first concentrated liquid pretreatment unit to adjust the pH of the wastewater to 10, and then 250mg / L of heavy precipitant is added for pretreatment. The outlet of the first concentrated liquid pretreatment unit is connected to the inlet of the first concentrated liquid solid-liquid separation unit. The first sludge and the first solution are separated in the first concentrated liquid solid-liquid separation unit. The first solution is connected to the inlet of the first evaporation unit (mechanical vapor recompression evaporator) through the outlet of the first concentrated liquid solid-liquid separation unit (the first solution enters the first evaporation unit). The outlet of the first evaporation unit is connected to the first distilled water unit (collecting the first evaporation condensate). The salt outlet of the first evaporation unit is connected to the inlet of the first industrial by-product salt recovery unit (obtaining industrial by-product salt sodium sulfate). The outlet of the first distilled water unit is connected to the inlet of the first reverse osmosis unit, realizing the recycling of water resources.

[0117] The second concentrated water separated from the second wastewater salt concentration and separation unit in Example 1 is connected to the inlet of the second concentrated liquid collection unit through the concentrated water outlet and enters the second waste liquid treatment system. The outlet of the second concentrated liquid collection unit is connected to the inlet of the second concentrated liquid pretreatment unit. In the second concentrated liquid pretreatment unit, 30% liquid alkali (15000 mg / L) is added to adjust the pH of the wastewater to 10.5, and then 50 mg / L of heavy precipitant is added for pretreatment. The outlet of the second concentrated liquid pretreatment unit is connected to the inlet of the second concentrated liquid solid-liquid separation unit. In the second concentrated liquid solid-liquid separation unit, the second sludge and the second solution are separated. The second solution is connected to the inlet of the second evaporation unit (mechanical vapor recompression evaporator) through the outlet of the second concentrated liquid solid-liquid separation unit (the second solution enters the second evaporation unit). The outlet of the second evaporation unit is connected to the second distillation water unit (collecting the first evaporation condensate). The salt outlet of the second evaporation unit is connected to the inlet of the second industrial by-product salt recovery unit (obtaining industrial by-product sodium chloride). The outlet of the second distillation water unit is connected to the inlet of the second reverse osmosis unit, realizing the recycling of water resources.

[0118] The bottom sludge obtained from the wastewater solid-liquid separation unit, the biochemical sludge obtained from the wastewater biochemical treatment unit, the first sludge obtained from the first concentrated liquid solid-liquid separation unit, and the second sludge obtained from the second concentrated liquid solid-liquid separation unit are outsourced for treatment.

[0119] The composition of the first concentrated water separated by the first wastewater salt concentration and separation unit is as follows: pH value 4.2, conductivity 98300μs / cm, COD (chemical oxygen demand) 460mg / L, CNND mg / L, ammonia nitrogen 5mg / L, total nitrogen 15mg / L, total phosphorus 5mg / L, copper 0.5mg / L, chromium ND mg / L, nickel 0.62mg / L, zinc 0.5mg / L and calcium and magnesium 68mg / L;

[0120] The composition of the second concentrated water separated by the second wastewater salt concentration and separation unit is as follows: pH value 5.2, conductivity 95300μs / cm, COD (chemical oxygen demand) 60mg / L, CNND mg / L, ammonia nitrogen 43mg / L, total nitrogen 150mg / L, total phosphorus 0.45mg / L, copper 0.1mg / L, chromium ND mg / L, nickel 0.3mg / L, zinc 2.5mg / L, and calcium and magnesium 4.8mg / L.

[0121] The concentrations of the main ions in the effluent of the main unit in Example 2 are shown in Table 2.

[0122] Table 2 shows the main units and the concentration of main ions in the effluent of Example 2.

[0123]

[0124]

[0125] As can be seen from Tables 1 and 2, the final effluent contains copper <0.02 mg / L, nickel <0.01 mg / L, chromium <0.01 mg / L, zinc <0.01 mg / L, pH 6–7.5, COD <40 mg / L, total phosphorus <0.1 mg / L, and total nitrogen <2 mg / L, enabling the entire wastewater treatment process to achieve water reuse. Furthermore, the final effluent obtained by this invention contains iron <0.01 mg / L, aluminum <0.08 mg / L, cadmium <0.001 mg / L, silver <0.001 mg / L, lead <0.01 mg / L, and mercury <0.0001 mg / L. Simultaneously, the chloride and sulfate salts enriched in the concentrated water were concentrated and crystallized to obtain the corresponding industrial by-product salts (industrial by-product sodium sulfate and industrial by-product sodium chloride). The sodium sulfate and sodium chloride contents in the industrial by-product sodium sulfate and industrial by-product sodium chloride are above 95% and the water content is below 5%, respectively. Moreover, the industrial by-product sodium sulfate and industrial by-product sodium chloride contain copper <0.003%, nickel <0.003%, chromium <0.003%, zinc <0.02%, iron <0.05%, aluminum <0.1%, and cadmium <0.0004%, thus enabling the recycling of salt resources.

[0126] After various treatments and concentrations, the wastewater produced by this invention has a conductivity of ≤100μs / cm, COD of ≤45mg / L, and heavy metal content below the background level. It can be directly reused in the production line. The concentrated liquid is treated and then enters the evaporation unit. The distilled water is treated and then reused. The crystallized salt is mainly sodium sulfate and sodium chloride, which are industrial by-products. The sludge is disposed of by an external contractor, thus achieving true zero discharge.

[0127] The above description is only a preferred embodiment of the present utility model. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present utility model, and these improvements and modifications should also be considered within the protection scope of the present utility model.

Claims

1. A wastewater treatment system, characterized in that, It includes a wastewater pretreatment unit, a wastewater solid-liquid separation unit, a wastewater oxidation unit, a wastewater biochemical treatment unit, a wastewater multivalent metal ion removal unit, and a membrane treatment system connected in sequence. The membrane treatment system includes a wastewater nanofiltration desalination unit, a first wastewater salt concentration and separation unit connected to the concentrate outlet of the wastewater nanofiltration desalination unit, a first reverse osmosis unit connected to the desalination outlet of the first wastewater salt concentration and separation unit, a second wastewater salt concentration and separation unit connected to the desalination outlet of the wastewater nanofiltration desalination unit, and a second reverse osmosis unit connected to the desalination outlet of the second wastewater salt concentration and separation unit. The concentrate outlet of the first reverse osmosis unit is connected to the inlet of the first wastewater salt concentration and separation unit; The concentrate outlet of the second reverse osmosis unit is connected to the inlet of the second wastewater salt concentration and separation unit.

2. The wastewater treatment system according to claim 1, characterized in that, The effluent pH value of the wastewater pretreatment unit is 8.5~11.

5.

3. The wastewater treatment system according to claim 1, characterized in that, The wastewater solid-liquid separation unit includes a gravity sedimentation tank and a plate and frame filter; the supernatant outlet of the gravity sedimentation tank is connected to the inlet of the wastewater oxidation treatment unit; the bottom sludge outlet of the gravity sedimentation tank is connected to the inlet of the plate and frame filter.

4. The wastewater treatment system according to claim 1, characterized in that, The wastewater oxidation unit includes a complex-breaking oxidation unit and an advanced oxidation unit connected in sequence.

5. The wastewater treatment system according to claim 1, characterized in that, The first wastewater salt concentration and separation unit and the second wastewater salt concentration and separation unit are equipped with an electrodialysis device; The concentrate conductivity of both the first and second wastewater salt concentration and separation units is 1~1.5×10⁻⁶. 5 μs / cm, and the conductivity of freshwater is 1000~3000μs / cm.

6. The wastewater treatment system according to claim 1, characterized in that, The first and second reverse osmosis units are both low-pressure reverse osmosis devices; the operating pressure of the low-pressure reverse osmosis devices is lower than 1.5 MPa.

7. A process system for the resource utilization of water and salt in electroplating wastewater, comprising the wastewater treatment system as described in any one of claims 1 to 6, and a first waste liquid treatment system and a second waste liquid treatment system connected to the membrane treatment system in the wastewater treatment system.

8. The process system according to claim 7, characterized in that, The first waste liquid treatment system includes a first concentrated liquid collection unit, a first concentrated liquid pretreatment unit, a first concentrated liquid solid-liquid separation unit, and a first evaporation unit connected in sequence; the concentrated water outlet of the first wastewater salt concentration and separation unit is connected to the inlet of the first concentrated liquid collection unit. The second waste liquid treatment system includes a second concentrated liquid collection unit, a second concentrated liquid pretreatment unit, a second concentrated liquid solid-liquid separation unit, and a second evaporation unit connected in sequence; the concentrated water outlet of the second wastewater salt concentration and separation unit is connected to the inlet of the second concentrated liquid collection unit.

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