CN114873694A

CN114873694A - Method and device for treating PFASs wastewater by zinc-based electroflocculation in cooperation with electrocatalytic oxidation

Info

Publication number: CN114873694A
Application number: CN202210615092.9A
Authority: CN
Inventors: 林辉; 梁逸扬; 田君
Original assignee: Dongguan University of Technology
Current assignee: Dongguan University of Technology
Priority date: 2022-06-01
Filing date: 2022-06-01
Publication date: 2022-08-09
Anticipated expiration: 2042-06-01
Also published as: CN114873694B

Abstract

The invention discloses a method and a device for treating PFASs wastewater by zinc-based electroflocculation in cooperation with electrocatalytic oxidation, belonging to the technical field of water treatment. The invention uses Ti ₄ O ₇ And (2) taking the inert electrode as an anode material, taking the zinc sheet as a cathode, taking the zinc sheet as a bipolar electrode, passing through a three-electrode electrolytic tank, adding electrolyte into the wastewater of the electrolytic tank, applying constant current, magnetically stirring, adsorbing PFASs in the water by using zinc flocs electrolyzed by electric flocculation, and further reducing the PFASs in the water body to below 70ng/L by cooperating with an electrochemical oxidation technology. The invention utilizes the zinc hydroxide with good hydrophobicity, can quickly and efficiently adsorb PFASs, cooperates with the electrochemical oxidation technology, and canThe PFASs in the water body are further reduced, the inert electrode has the characteristics of more reaction potential, high oxygen evolution potential, large hydroxyl generation amount and the like, and is suitable for an anode for degrading the PFASs through electrochemical catalytic oxidation. The technology has the advantages of high current efficiency, large treatment capacity, low energy consumption and the like. Is suitable for purification treatment of fluorine industrial wastewater.

Description

Method and device for treating PFASs wastewater by zinc-based electroflocculation in cooperation with electrocatalytic oxidation

Technical Field

The invention belongs to the field of sewage treatment, and particularly discloses a method and a device for treating PFASs wastewater based on zinc-based electrocoagulation in cooperation with electrocatalytic oxidation.

Background

Polyfluorinated and perfluoroalkyl group substances (PFASs) are environmental priority pollutants and are widely used in industries or products which are closely related to production and life, such as fire-fighting foam extinguishing agents, metal plating, developing and printing, semiconductors, product coatings, packaging materials, insecticides, surfactants and the like. PFASs have special molecular structures and stable C-F bonds, so that the PFASs can resist various biochemical processes in natural environments such as high temperature, illumination, chemical oxidation-reduction, microbial metabolism and the like. Toxicology studies indicate that PFASs have toxicity to animal organs, immunity and endocrine toxicity, neurotoxicity, carcinogenicity, reproduction and development toxicity. The environmental pollution problem caused by it has therefore attracted global attention and value, and is listed in the stockholm convention on persistent organic pollutants, and the health counseling level of the sum of PFOA and PFOS in drinking water is determined to be 70ng/L by the united states Environmental Protection Agency (EPA).

At present, adsorption, micro-filtration, chemical degradation, photodegradation, microwave-assisted degradation, electrocatalysis advanced oxidation methods and the like are widely applied to the research of removing polyfluorine and perfluorinated compounds in industrial wastewater. The adsorption and membrane separation technology is proved to be capable of effectively treating the water body polluted by low-concentration polyfluorine and perfluorinated compounds, including granular activated carbon, ion exchange resin and the like. Granular activated carbon has problems such as a small adsorption capacity and poor adsorbent regenerability. The ion exchange resin can effectively remove polyfluorine and perfluorinated compounds with low concentration (ng/L-mu g/L), but is limited by adsorption capacity, adsorption rate and soluble organic matter (DOM) when treating polyfluorine and perfluorinated compounds with high concentration (mg/L), is easy to penetrate, needs frequent regeneration and is not suitable for treating high-concentration wastewater. Therefore, the treatment methods in the prior art are difficult to rapidly and effectively reduce the PFASs with high concentration to the standard of 70 ng/L.

The effective treatment of the high-concentration polyfluorinated and perfluorinated compound wastewater is a great challenge, and the zinc-based electroflocculation technology well solves the problem and can quickly and effectively treat the high-concentration PFASs.

Disclosure of Invention

The invention aims at overcoming the defects of the prior art and provides a method for treating PFASs wastewater by zinc-based electroflocculation in coordination with electrocatalytic oxidation, because PFASs can be effectively adsorbed by the zinc-based electroflocculation, but the concentration of the PFASs in a water body can only be reduced to mu g/L by single zinc-based electroflocculation, and the health counseling level determined by the United states Environmental Protection Agency (EPA) can not be reached to be less than 70ng/L, and the method for treating the PFASs wastewater by the zinc-based electroflocculation in coordination with electrocatalytic oxidation uses Ti ₄ O ₇ The inert electrode is used as an anode material, the zinc sheet is used as a cathode, the zinc sheet is used as a bipolar electrode, the electrolyte is added into the wastewater of the electrolytic cell through a three-electrode electrolytic cell, constant current is applied, magnetic stirring is carried out, the PFASs in the water are quickly adsorbed by the electrolytic zinc floc, and the PFASs in the water are further reduced to the human health level (70ng/L) by cooperating with the electrochemical oxidation technology. The zinc hydroxide has good hydrophobicity, can quickly and efficiently adsorb PFASs, is cooperated with an electrochemical oxidation technology, can further reduce the PFASs in the water body, and the inert electrode has the characteristics of many reaction sites, high oxygen evolution potential, large hydroxyl generation amount and the like. Has the advantages of high current efficiency, large treatment capacity, low energy consumption and the like.

The technical scheme adopted by the invention is as follows:

adding electrolyte salt into an electrolytic cell containing PFASs wastewater to form electrolyte, and soaking an anode, a cathode and a bipolar electrode into the electrolyte, wherein the anode is electrically connected with a positive electrode of a power supply, the cathode is electrically connected with a negative electrode of the power supply, the bipolar electrode is arranged between the anode and the cathode, the anode is an inert electrode, and the bipolar electrode and the cathode are made of metal zinc; and applying constant direct current voltage to the power supply, stirring the electrolyte, electrolyzing for a period of time until flocs generated in a reaction system are naturally deposited at the bottom of the electrolytic tank, filtering to realize solid-liquid separation, and obtaining liquid with PFASs concentration less than 70ng/L after separation.

The adsorption principle of PFASs adsorbed by the zinc-based floc is that compounds with strong hydrophobicity are easier to be adsorbed and removed by the zinc-based floc through hydrophobic action force, the oil-water distribution coefficient log P of PFOA is 4.46, which shows that PFOA has strong hydrophobicity, and the PFASs can be effectively adsorbed by the zinc-based floc through the hydrophobic action force. The zinc sheet is used as a bipolar electrode and a cathode, more zinc flocs can be precipitated in a short time, and the effect of rapidly reducing the concentration of PFASs in a short time is achieved. Meanwhile, an electrocatalytic oxidation technology of the electrocoagulation floc is utilized, so that PFASs in the water body can be further reduced, and the concentration of the PFASs in the water body is reduced to the health level of a human body. The inert anode has the characteristics of more reaction sites, high oxygen evolution potential, large hydroxyl generation amount and the like, and can effectively further reduce low-concentration PFASs.

The method for treating PFASs wastewater by zinc-based electroflocculation in cooperation with electrocatalytic oxidation mainly comprises two parts as follows: PFASs in the wastewater are quickly adsorbed by zinc-based electroflocculation, and the PFASs with high concentration are reduced to mu g/L; the low-concentration PFASs can be effectively mineralized by utilizing an electro-catalytic oxidation technology; the zinc-based electroflocculation is cooperated with the electrocatalytic oxidation technology to reduce PFASs to the human health level.

In a further technical scheme, the inert electrode is Ti ₄ O ₇ 、BDD、Ti/SnO ₂ Any one of-Sb, preferably Ti ₄ O ₇ . The inert anode has the characteristics of more reaction sites, high oxygen evolution potential, large hydroxyl generation amount and the like, and can effectively further reduce low-concentration PFASs. Ti ₄ O ₇ The inert anode can obtain high anode potential, and electrons can be transferred to PFASs by controlling the speed, so that the PFASs can be degraded. At the same time, Ti ₄ O ₇ When the inert electrode has more reaction sites, PFASs can be mineralized into CO by electrolyzing water to generate a large amount of hydroxyl groups ₂ And HF.

In a further technical scheme, the electrolyte salt is NaCl or Na ₂ SO ₄ 、NaNO ₃ Preferably, NaCl is used as the active ingredient.

In a further technical scheme, after the electrolyte salt is added, the concentration of the electrolyte salt in the electrolyte is more than 20mM, and preferably, the concentration of the electrolyte salt is 20-200 mM.

In a further technical scheme, the distance between the bipolar electrode and the anode and between the bipolar electrode and the cathode is 2-4 cm, more zinc flocs can be separated out in the connection mode under the conditions of low current density and short time, and the current density of the direct-current voltage applied by the power supply is 2-20 mA/cm ² 。

In a further technical scheme, the electrolysis time is 30min, and the precipitation amount of the metal zinc of the bipolar electrode and the cathode in the electrolysis process is 2.4-24.3 mg/cm ² 。

In a further technical scheme, the mass concentration of the PFASs wastewater is 25mg/L, and the method is particularly suitable for treating the wastewater with the mass concentration of 25mg/L of PFASs, and can realize a better removal effect.

In a further technical scheme, the initial pH of the electrolyte is 3-10, and a good adsorption effect can be obtained particularly under an acidic or alkaline condition.

In a further technical scheme, the adopted stirring method is magnetic stirring, the stirring speed is 400-800 r/min, the generated zinc floc is ensured to be fully contacted with the PFASs, and meanwhile, the PFASs are rapidly diffused to the surface of the inert anode, so that the adsorption capacity of the zinc floc and the PFASs degradation capacity of the inert anode can be improved.

In a further technical scheme, the waste water of the PFASs is fluorine industrial waste water mainly containing perfluorononanoic acid, perfluorooctanoic acid and perfluoroheptanoic acid.

In view of the defects of the prior art, another object of the present invention is to provide a PFASs wastewater treatment device, which comprises an electrolytic cell, an anode, a cathode, a bipolar electrode and a power supply, wherein the electrolytic cell contains an electrolyte solution composed of electrolyte salt and PFASs wastewater, the anode, the cathode and the bipolar electrode are all immersed in the electrolyte solution, the bipolar electrode is located between the anode and the cathode, the anode is made of an inert electrode, and the cathode and the bipolar electrode are made of zinc; the anode of the power supply is electrically connected with the anode, and the cathode of the power supply is electrically connected with the cathode.

The technical scheme of the invention has the following beneficial effects:

1. according to the method for treating PFASs wastewater by zinc-based electroflocculation in cooperation with electrocatalytic oxidation, provided by the invention, PFASs with high concentration in the wastewater are efficiently adsorbed by zinc-based flocs, and the concentration of the PFASs can be reduced to below 70ng/L by the zinc flocs within 30min, so that the method has the advantages of high current efficiency, large treatment capacity, low energy consumption and the like.

2. The reaction device has the advantages of simple and feasible structure, high current efficiency, large processing capacity and low energy consumption, meets the requirement of industrial development in the aspects of practicability and cost benefit, and has industrial utilization value.

3. The method for treating PFASs wastewater by zinc-based electroflocculation in cooperation with electrocatalytic oxidation has stable and feasible operation and has greater potential in the fluoride industrial wastewater treatment.

Drawings

FIG. 1 is a structural diagram of a zinc-based electroflocculation cooperated electrocatalytic oxidation device in the invention;

FIG. 2 is a graph of the quasi-first order kinetics of single zinc-based electroflocculation on the treatment of perfluorononanoic, perfluorooctanoic and perfluoroheptanoic acids in PFASs wastewater in an example of the present invention;

FIG. 3 is a graph of the quasi-first order kinetics of zinc-based electroflocculation in conjunction with electrocatalytic oxidation for perfluorononanoic acid, perfluorooctanoic acid, and perfluoroheptanoic acid treatment in PFASs wastewater in an example of the present invention;

description of reference numerals: 1-power supply, 2-electrolytic bath, 3-anode, 4-cathode and 5-bipolar electrode.

Detailed Description

The following detailed description of exemplary embodiments of the invention refers to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration exemplary embodiments in which the invention may be practiced, and in which features of the invention are identified by reference numerals. The following more detailed description of the embodiments of the invention is not intended to limit the scope of the invention, as claimed, but is presented for purposes of illustration only and not limitation to describe the features and characteristics of the invention, to set forth the best mode of carrying out the invention, and to sufficiently enable one skilled in the art to practice the invention. It will, however, be understood that various modifications and changes may be made without departing from the scope of the invention as defined in the appended claims. The detailed description and drawings are to be regarded as illustrative rather than restrictive, and any such modifications and variations are intended to be included within the scope of the present invention as described herein. Furthermore, the background is intended to be illustrative of the state of the art as developed and the meaning of the present technology and is not intended to limit the scope of the invention or the application and field of application of the invention.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs; the terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention; as used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

The examples, in which specific conditions are not specified, were carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

In order to make the technical problems, technical solutions and advantages of the present invention more apparent, the following detailed description is given with reference to the accompanying drawings and specific embodiments.

Adding electrolyte salt into an electrolytic cell containing PFASs wastewater to form electrolyte, wherein the PFASs wastewater is fluorine industrial wastewater mainly containing perfluorononanoic acid, perfluorooctanoic acid and perfluoroheptanoic acid, and the electrolyte salt is NaCl and Na ₂ SO ₄ 、NaNO ₃ Soaking an anode, a cathode and a bipolar electrode in the electrolyte, wherein the anode is electrically connected with a positive electrode of a power supply, the cathode is electrically connected with a negative electrode of the power supply, the bipolar electrode is arranged between the anode and the cathode, the anode is an inert electrode, and the bipolar electrode and the cathode are made of metal zinc; one surface of the bipolar electrode close to the anode and the anode form an electrocatalytic oxidation and electrocoagulation system, one surface of the bipolar electrode close to the cathode and the cathode form an electrocoagulation system, and the two systems are combined to increase the precipitation amount and shrinkage of zincShort reaction time. And applying constant direct current voltage to the power supply, stirring the electrolyte, electrolyzing for a period of time until flocs generated in a reaction system are naturally deposited at the bottom of the electrolytic cell, filtering to realize solid-liquid separation, and obtaining the liquid with PFASs concentration less than 70ng/L after separation.

The inert electrode is Ti ₄ O ₇ 、BDD、Ti/SnO ₂ -Sb, preferably Ti ₄ O ₇ . The inert anode has the characteristics of more reaction sites, high oxygen evolution potential, large hydroxyl generation amount and the like, and can effectively further reduce low-concentration PFASs. Ti ₄ O ₇ The inert anode can obtain high anode potential, and electrons can be transferred to PFASs by controlling the speed, so that the PFASs can be degraded. At the same time, Ti ₄ O ₇ When the inert electrode has more reaction sites, PFASs can be mineralized into CO by electrolyzing water to generate a large amount of hydroxyl groups ₂ And HF.

The electric flocculation technology takes soluble metal as an anode, metal ions dissolved under the action of an electric field are hydrolyzed to generate polyhydroxy hydroxide flocs, and the flocs remove pollutants in water through hydrophobic effect, electrostatic effect and the like. The cathode is usually made of graphite, stainless steel or the like, and a metal such as zinc, iron or aluminum may be used. And zinc is an amphoteric metal, can be dissolved in acid and alkali, so that zinc sheets can be separated out at the anode and the cathode. In the technology, the zinc sheet is used as a bipolar electrode, namely a cathode and an anode, so that the precipitation amount of zinc can be increased, the adsorption efficiency on PFASs is greatly improved, and meanwhile, the zinc sheet is used as the cathode, so that the adsorption efficiency on the PFASs is further improved. The main principle is as follows:

anode: zn-2e ^- →Zn ²⁺

2H ₂ O-4e ^- →O ₂ +4H ⁺

2H ⁺ +Zn→Zn ²⁺ +H ₂

Cathode: h ₂ O+2e ^- →H ₂ +OH ^-

The electrocatalytic oxidation has high current efficiency, can realize the capability of complete mineralization, is simple to operate, has good prospect and is widely applied to sewage treatment. Ti ₄ O ₇ The inert anode can obtain high anode potential, and electrons can be transferred to PFASs by controlling the speed, so that the PFASs can be degraded. At the same time, Ti ₄ O ₇ When the inert electrode has more reaction sites, PFASs can be mineralized into CO by electrolyzing water to generate a large amount of hydroxyl groups ₂ And HF. The reaction mechanism is as follows:

H ₂ O-e ^- →·OH+H ⁺

the PFASs degradation mechanism (PFOA as an example) is as follows:

C ₇ F ₁₅ COO ^- -e ^- →C ₇ F ₁₅ COO ^·

C ₇ F ₁₃ OF+H ₂ O→C ₆ F ₁₃ COO ^- +HF+H ⁺

after the electrolyte salt is added, the concentration of the electrolyte salt in the electrolyte is more than 20mM, and preferably, the concentration of the electrolyte salt is 20-200 mM. The electrolyte salt concentration is typically, but not limited to, set at 20mM, 40mM, 60mM, 80mM, 100mM, 120mM, 140mM, 160mM, 180mM, or 200 mM.

The distance between the bipolar electrode and the anode and between the bipolar electrode and the cathode is 2-4 cm, more zinc flocs can be separated out in the connection mode under the conditions of low current density and short time, and the current density of the direct-current voltage applied by the power supply is 2-20 mA/cm ² . The electrode spacing is typically, but not limited to, set at 2cm, 3cmOr 4 cm; the current density is typically but not exclusively set at 2mA/cm ² 、4mA/cm ² 、6mA/cm ² 、8mA/cm ² 、10mA/cm ² 、12mA/cm ² 、14mA/cm ² 、16mA/cm ² 、18mA/cm ² Or 20mA/cm ² 。

The electrolysis time is 30min, and the precipitation amount of the metal zinc of the bipolar electrode and the cathode in the electrolysis process is 2.4-24.3 mg/cm ² . When the mass concentration of the PFASs wastewater is 25mg/L, the solid-to-liquid ratio of the zinc-based floc production to the PFASs wastewater is 24-243 mg/L, PFASs can be efficiently removed; when the solid-to-liquid ratio of the zinc-based floc generation amount to PFASs wastewater is 100mg/L, the removal rate of perfluorononanoic acid, perfluorooctanoic acid and perfluoroheptanoic acid can reach more than 90%. After the synergy electrocatalytic oxidation technology, the removal rate of the perfluorononanoic acid, the perfluorooctanoic acid and the perfluoroheptanoic acid is further improved, and the current density is 20mA/cm ² When the method is used, the best removal effect of PFASs can be achieved, and the concentration of the PFASs is reduced to the level of human safety.

The initial pH of the electrolyte is 3-10, and a good adsorption effect can be obtained particularly under an acidic or alkaline condition. The initial pH of the electrolyte is typically, but not limited to, set to 3, 4, 5, 6, 7, 8, 9 or 10.

The stirring method is magnetic stirring, the stirring speed is 400-800 r/min, the produced zinc flocs are fully contacted with the PFASs, and meanwhile, the PFASs are rapidly diffused to the surface of the inert anode, so that the adsorption capacity of the zinc flocs and the PFASs degradation capacity of the inert anode can be improved. The stirring speed of the magnetic stirring is typically, but not exclusively, set to 400r/min, 450r/min, 500r/min, 550r/min, 600r/min, 650r/min, 700r/min, 750r/min or 800 r/min.

The following description is given with reference to specific examples.

Example 1

An electrocoagulation-electrocatalytic oxidation system is constructed, electrolyte is configured in an electrolytic cell 2, the electrolyte comprises full PFASs wastewater and electrolyte salt, the PFASs wastewater is fluorooctanoic acid (PFOA) wastewater, the initial concentration of the PFOA is 25mg/L, the concentration of the electrolyte salt is 20mM, the initial pH of the electrolyte is 3,Ti ₄ O ₇ the inert electrode is used as an anode 3, the cathode 4 and the bipolar electrode 5 are both made of metal zinc, and the electrode distance is 2 cm. The anode 3 is connected with the anode of an external power supply 1, the cathode 4 is connected with the cathode of the external power supply, the power supply is turned on, and the constant current density is 10mA/cm ² Adjusting the stirring speed to be 500r/min, electrifying for 30min, and recording data.

Example 2

In this example, in order to investigate the influence of the pH change on the PFOA removal rate, the initial pH of the electrolyte was adjusted to 7 under the same conditions as in example 1.

Constructing an electrocoagulation-electrocatalytic oxidation system, and preparing electrolyte in an electrolytic cell, wherein the electrolyte comprises waste water containing perfluorooctanoic acid (PFOA) and electrolyte salt, the initial concentration of the perfluorooctanoic acid is 25mg/L, the concentration of the electrolyte salt is 20mM, the initial pH of the electrolyte is 7, and Ti is added ₄ O ₇ The inert electrode is used as an anode, the cathode and the bipolar electrode are both made of metal zinc, and the electrode distance is 2 cm. The anode is connected with the anode of an external power supply, the cathode is connected with the cathode of the external power supply, the power supply is turned on, and the constant current density is 10mA/cm ² Adjusting the stirring speed to be 500r/min, electrifying for 30min, and recording data.

Example 3

In this example, in order to examine the influence of the pH change on the PFOA removal rate, the initial pH of the electrolyte was adjusted to 10 under the same conditions as in example 1.

Constructing an electrocoagulation-electrocatalytic oxidation system, and preparing electrolyte in an electrolytic cell, wherein the electrolyte comprises waste water containing perfluorooctanoic acid (PFOA) and electrolyte salt, the initial concentration of the perfluorooctanoic acid is 25mg/L, the concentration of the electrolyte salt is 20mM, the initial pH of the electrolyte is 10, and Ti is added ₄ O ₇ The inert electrode is used as an anode, the cathode and the bipolar electrode are both made of metal zinc, and the electrode distance is 2 cm. The anode is connected with the anode of an external power supply, the cathode is connected with the cathode of the external power supply, the power supply is turned on, and the constant current density is 10mA/cm ² Adjusting the stirring speed to be 500r/min, electrifying for 30min, and recording data.

The PFOA solution is treated by utilizing the treatment parameters, and the PFOA removal rates of the embodiments 1-3 are respectively 97.3%, 93.9% and 97.1% by calculating the wastewater after the measurement treatment by a UPLC-MS method. According to analysis, the pH influences the elution amount of zinc, the zinc is amphoteric metal and can generate chemical reaction under acid and alkaline conditions, the elution amount of a zinc electrode can be increased under alkaline or acidic conditions compared with neutral pH conditions, and the treatment of wastewater is facilitated under acid and alkaline conditions.

Example 4

This example was carried out to investigate the effect of the change in current density on the PFOA removal rate, and the current density was adjusted to 5mA/cm under the same conditions as in example 1 ² 。

Constructing an electrocoagulation-electrocatalytic oxidation system, and preparing electrolyte in an electrolytic cell, wherein the electrolyte comprises waste water containing perfluorooctanoic acid (PFOA) and electrolyte salt, the initial concentration of the perfluorooctanoic acid is 25mg/L, the concentration of the electrolyte salt is 20mM, the initial pH of the electrolyte is 3, and Ti is added ₄ O ₇ The inert electrode is used as an anode, the cathode and the bipolar electrode are both made of metal zinc, and the electrode distance is 2 cm. The anode is connected with the anode of an external power supply, the cathode is connected with the cathode of the external power supply, the power supply is turned on, and the constant current density is 5mA/cm ² Adjusting the stirring speed to be 500r/min, electrifying for 30min, and recording data.

Example 5

This example was carried out to investigate the effect of the change in current density on the PFOA removal rate, and the current density was adjusted to 15mA/cm under the same conditions as in example 1 ² 。

Constructing an electrocoagulation-electrocatalytic oxidation system, and preparing electrolyte in an electrolytic cell, wherein the electrolyte comprises waste water containing perfluorooctanoic acid (PFOA) and electrolyte salt, the initial concentration of the perfluorooctanoic acid is 25mg/L, the concentration of the electrolyte salt is 20mM, the initial pH of the electrolyte is 3, and Ti is added ₄ O ₇ The inert electrode is used as an anode, the cathode and the bipolar electrode are both made of metal zinc, and the electrode distance is 2 cm. The anode is connected with the anode of an external power supply, the cathode is connected with the cathode of the external power supply, the power supply is turned on, and the constant current density is 15mA/cm ² Adjusting the stirring speed to be 500r/min, electrifying for 30min, and recording data.

Example 6

This example was conducted to investigate the effect of the change in current density on the PFOA removal rate, and the current density was adjusted to 20mA/cm under the same conditions as in example 1 ² 。

Constructing an electrocoagulation-electrocatalytic oxidation system, and preparing electrolyte in an electrolytic cell, wherein the electrolyte comprises waste water containing perfluorooctanoic acid (PFOA) and electrolyte salt, the initial concentration of the perfluorooctanoic acid is 25mg/L, the concentration of the electrolyte salt is 20mM, the initial pH of the electrolyte is 3, and Ti is added ₄ O ₇ The inert electrode is used as an anode, the cathode and the bipolar electrode are both made of metal zinc, and the electrode distance is 2 cm. The anode is connected with the anode of an external power supply, the cathode is connected with the cathode of the external power supply, the power supply is turned on, and the constant current density is 20mA/cm ² Adjusting the stirring speed to be 500r/min, electrifying for 30min, and recording data.

The PFOA solution treated with the above treatment parameters gave PFOA removal rates of 95.2%, 99.9%, and 99.9% for examples 4-6, respectively. In general, the effect of the electroflocculation to remove PFOA increases with increasing current density for the same energization time, but too high a current density increases the amount of flocs produced and also promotes agglomeration between flocs, resulting in no significant change in the rate of contaminant removal by flocs.

Example 7

On the basis of example 5, the present example explores the treatment effect of the zinc-based electroflocculation in cooperation with the electrocatalytic oxidation system on PFSA wastewater with various chain lengths. Constructing a zinc-based electroflocculation and electrocatalytic oxidation system: ti ₄ O ₇ Using a zinc sheet as a cathode and a zinc sheet as a bipolar electrode at an electrode spacing of 2cm, treating a plurality of PFASs-containing wastewater, wherein the initial concentrations of perfluorononanoic acid, perfluorooctanoic acid and perfluoroheptanoic acid are 25mg/L, the pH value is 3, and the constant current density is 15mA/cm ² The concentration of the electrolyte salt was 20mM, and the sample was taken out and examined at a predetermined time by magnetic stirring.

The obtained result is shown in figure 3, the zinc-based electroflocculation is cooperated with the electrocatalytic oxidation technology, the removal efficiency of PFASs in the water body is effectively improved, and the removal efficiency is 10minThe balance is basically achieved, and the reaction rate constants are all more than 0.4min ^-1 Compared with a single electrocoagulation technology, the method is improved by more than one time, and shows that the removal of PFASs can be effectively accelerated by the zinc-based electrocoagulation cooperating with the electrocatalytic oxidation technology. After the reaction is carried out for 30min, the concentration of PFASs is reduced to the ng/L level, the surface zinc-based electroflocculation is cooperated with the electrocatalytic oxidation technology to effectively reduce the PFASs in the water body to the human body safety level, and the method has application prospect.

Comparative example 1

Constructing a single electric flocculation system: treating a plurality of PFASs-containing wastewater by using a zinc sheet as an anode and a zinc sheet as a cathode at an electrode spacing of 2cm, wherein the initial concentrations of perfluorononanoic acid, perfluorooctanoic acid, perfluoroheptanoic acid and perfluoroheptanoic acid are all 25mg/L, the pH value is 3, and the constant current density is 15mA/cm ² The concentration of the electrolyte salt was 20mM, and the sample was taken out and examined at a predetermined time by magnetic stirring.

The results are shown in fig. 2, the removal rate of PFAS and the reaction rate increase with the increase of the chain length of PFAS, because the zinc-based flocs are adsorbed by hydrophobic forces, and the hydrophobic forces increase with the increase of the chain length of PFAS. PFASs treated by the single zinc-based electroflocculation system reach balance basically within 12.5min, and the removal rate reaches over 95 percent. However, when the adsorption is balanced, the concentration of PFASs can only be reduced to mu g/L, and the safety level of human bodies cannot be reached, and the PFASs need to be further treated by combining other technologies.

Comparative example 2

On the basis of the comparative example 1, an independent electrocatalysis system is added, the electrocatalysis system comprises an electrocatalysis tank, the electrocatalysis tank is communicated with the electrocoagulation tank through a check valve, and an electrocatalysis anode (an inert electrode Ti is selected) which is respectively connected with the anode and the cathode of an external power supply is arranged in the electrocatalysis tank ₄ O ₇ ) And an electrocatalytic cathode (selected from metallic zinc). Firstly, PFASs wastewater is added into an electro-catalysis tank, the electro-catalysis reaction is carried out for 60min, the wastewater enters an electro-flocculation tank through a check valve, the reaction is carried out for 10min to reach balance, the removal rate is measured to be more than 95%, but only the PFASs concentration can be reduced to mu g/L, so that the PFASs concentration cannot be reduced to ng/L level by independent electro-catalysis and electro-flocculation, and the high-concentration wastewater is oxidized by independent electro-catalysisThe PFASs treatment needs a long time to reach the equilibrium state, and only can reduce the wastewater to mu g/L at most after the electric flocculation, which can not meet the standard of healthy use of drinking water.

More specifically, although exemplary embodiments of the invention have been described herein, the invention is not limited to these embodiments, but includes any and all embodiments modified, omitted, combined, e.g., between various embodiments, adapted and/or substituted, as would be recognized by those skilled in the art from the foregoing detailed description. The limitations in the claims are to be interpreted broadly based the language employed in the claims and not limited to examples described in the foregoing detailed description or during the prosecution of the application, which examples are to be construed as non-exclusive. Any steps recited in any method or process claims may be executed in any order and are not limited to the order presented in the claims. The scope of the invention should, therefore, be determined only by the appended claims and their legal equivalents, rather than by the descriptions and examples given above.

Claims

1. A method for treating PFASs waste water by zinc-based electroflocculation in cooperation with electrocatalytic oxidation is characterized in that electrolyte salt is added into an electrolytic bath containing PFASs waste water to form electrolyte, an anode, a cathode and a bipolar electrode are soaked in the electrolyte, the anode is electrically connected with a positive electrode of a power supply, the cathode is electrically connected with a negative electrode of the power supply, the bipolar electrode is arranged between the anode and the cathode, wherein the anode is an inert electrode, and the bipolar electrode and the cathode are made of metal zinc; and applying constant direct current voltage to the power supply, stirring the electrolyte, electrolyzing for a period of time until flocs generated in a reaction system are naturally deposited at the bottom of the electrolytic cell, filtering to realize solid-liquid separation, and obtaining the liquid with PFASs concentration less than 70ng/L after separation.

2. The method of claim 1, wherein the zinc-based electroflocculation is cooperated with electrocatalytic oxidation to treat PFASs wastewater, and the method comprises the following steps: the inert electrode is Ti ₄ O ₇ 、BDD、Ti/SnO ₂ Any one of-Sb, preferably Ti ₄ O ₇ 。

3. The method of claim 1, wherein the zinc-based electroflocculation is cooperated with electrocatalytic oxidation to treat PFASs wastewater, and the method comprises the following steps: the electrolyte salt is NaCl or Na ₂ SO ₄ 、NaNO ₃ Preferably, NaCl is used as the active ingredient.

4. The method of claim 3, wherein the zinc-based electroflocculation is cooperated with electrocatalytic oxidation to treat PFASs wastewater, and the method comprises the following steps: after the electrolyte salt is added, the concentration of the electrolyte salt in the electrolyte is more than 20mM, and preferably, the concentration of the electrolyte salt is 20-200 mM.

5. The method of claim 1, wherein the zinc-based electroflocculation is cooperated with electrocatalytic oxidation to treat PFASs wastewater, and the method comprises the following steps: the distance between the bipolar electrode and the anode and between the bipolar electrode and the cathode is 2-4 cm, and the current density of the direct-current voltage applied by the power supply is 2-20 mA/cm ² 。

6. The method of claim 5, wherein the zinc-based electroflocculation is cooperated with electrocatalytic oxidation to treat PFASs wastewater, and the method comprises the following steps: the electrolysis time is 30min, and the precipitation amount of the metal zinc of the bipolar electrode and the cathode in the electrolysis process is 2.4-24.3 mg/cm ² 。

7. The method of claim 6, wherein the zinc-based electroflocculation is cooperated with electrocatalytic oxidation to treat PFASs wastewater, and the method comprises the following steps: the mass concentration of the PFASs wastewater is 25 mg/L.

8. The method of claim 1, wherein the zinc-based electroflocculation is cooperated with electrocatalytic oxidation to treat PFASs wastewater, and the method comprises the following steps: the initial pH of the electrolyte is 3-10.

9. The method of claim 1, wherein the zinc-based electroflocculation is cooperated with electrocatalytic oxidation to treat PFASs wastewater, and the method comprises the following steps: the stirring method is magnetic stirring, and the stirring speed is 400-800 r/min.

10. A wastewater treatment plant for use in the method of any one of claims 1 to 9, characterized by: the electrolytic cell is internally provided with electrolyte consisting of electrolyte salt and PFASs wastewater, the anode, the cathode and the bipolar electrode are all soaked in the electrolyte, the bipolar electrode is positioned between the anode and the cathode, the anode is made of an inert electrode, and the cathode and the bipolar electrode are made of metal zinc; the anode of the power supply is electrically connected with the anode, and the cathode of the power supply is electrically connected with the cathode.