Diaphragm-free electrochemical sewage treatment method and device

Abstract

The invention provides a diaphragm-free electrochemical sewage treatment method and device, and belongs to the technical field of sewage treatment. A sewage stock solution, an oxidizing agent and a catalyst are mixed, the mixed solution flows parallel to an anode and perpendicular to a cathode at the same time, a dynamic and stable anode acid zone, a dynamic and stable cathode alkaline zone and a dynamic and stable metal ion metastable zone are presented in a reactor by regulating and controlling a flow field and an electric field, and the mixed solution flows through an anode compression acid diffusion layer in parallel to promote the anode reaction efficiency; the alkaline diffusion layer vertically penetrating through the porous cathode efficiently reduces high-valence metal ions into low-valence metal ions, metal oxides and nano metal particles; hydroxyl free radicals and high-valence metal complexes are generated through a Fenton or Fenton-like catalytic reaction to degrade and mineralize refractory organic pollutants in the sewage stock solution, a large amount of acid and alkali does not need to be added before and after the reaction to adjust the pH value of the sewage stock solution, and the yield of active species is high; and cyclic utilization of the catalyst can be realized through intermittent backwashing of the porous cathode.

Description

Technical Field

[0001] The invention belongs to the technical field of sewage treatment, and in particular relates to a diaphragm-free electrochemical sewage treatment method and device. Background Art

[0002] Refractory organic pollutants are organic substances with low biodegradability and difficult to be effectively removed using conventional biotechnology. Fenton oxidation is a process that uses Fenton reagent (Fe 2+ / H2O2) to produce reactive oxygen species (ROS) with strong oxidative ability to degrade pollutants. As an advanced oxidation process, Fenton oxidation is an important component method for treating refractory organic pollutants. However, Fenton oxidation requires Fe 2+ As a catalyst, Fe 2+ It can only exist stably under strong acidic conditions of pH 2.8 to 3. When treating neutral and alkaline solutions, the pH value needs to be adjusted to 2.8 to 3 in advance. Its applicable pH range is extremely narrow. After Fenton oxidation, the pH value of the treated liquid needs to be further adjusted to neutral. A large amount of iron sludge (iron-containing precipitate) will be produced in this process. It takes a long time to precipitate and separate the iron sludge, and the sedimentation tank occupies a large area, which increases the treatment construction cost.

[0003] As an improved process of the Fenton oxidation method, the electro-Fenton method has a more complete mechanism for automatically generating H2O2. In addition to the oxidation of hydroxyl radicals, there are also mechanisms such as anodic oxidation and electrosorption. Chinese patent CN107337301A discloses a method for treating wastewater with electro-Fenton by adding hydrogen peroxide. This invention method adjusts the pH value of the wastewater to acidic to obtain acidic wastewater; the acidic wastewater is subjected to continuous flow decontamination treatment to obtain oxidized wastewater; and the oxidized wastewater is also subjected to flocculation and precipitation treatment. However, the above-mentioned prior art requires the addition of an acid regulator to maintain the system reaction pH = 3 to 5. At the same time, the wastewater needs to be subjected to flocculation and precipitation treatment. There are problems such as the narrow applicable pH range of the Fenton oxidation method, the low electrochemical reaction efficiency caused by electrode concentration polarization, and the difficulty in treating iron mud precipitation. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a diaphragm-free electrochemical sewage treatment method and device. The sewage treatment method provided by the present invention couples the flow field and the electric field to compress the diffusion layer on the electrode surface, thereby avoiding the influence of the concentration polarization on the electrode surface on the electrochemical reaction efficiency. At the same time, through the electrolysis of water at the anode and the cathode, a local anode acidic area and a cathode alkaline area are formed, thereby solving the problem that the traditional electro-Fenton reaction requires frequent addition of acid and alkali to adjust the pH value. In addition, when the mixed liquid vertically penetrates the alkaline diffusion layer of the porous cathode, the reducing HO generated by the electroreduction and the ionization of hydrogen peroxide under alkaline conditions 2-High-valent metal ions are efficiently reduced to low-valent metal ions, metal oxides and metal element particles, thereby forming a metastable zone of metal ions, achieving repeated and efficient utilization of the catalyst. The applicable pH range is 1 to 14, and the applicable pH range is wide and there is no need for subsequent treatment of the metal sludge precipitation.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] The present invention provides a diaphragm-free electrochemical sewage treatment method, comprising the following steps: mixing a sewage stock solution, an oxidant and a catalyst, passing part of the obtained mixed solution into an electrochemical reactor for electrochemical reaction and cross-flow filtration, wherein the product obtained by the electrochemical reaction flows parallel to the anode and perpendicular to the cathode, flows through the anode to obtain reflux concentrated water, and penetrates the cathode to obtain purified water; the anode used in the electrochemical reactor is a flat plate electrode, and the cathode is a porous filter membrane electrode;

[0007] The reflux concentrated water is refluxed, mixed with the remaining mixed solution, and then cyclically subjected to electrochemical reaction, cross-flow filtration, reflux and mixing; the pH value of the sewage raw solution is 1 to 14;

[0008] No diaphragm is arranged between the anode and the cathode used in the electrochemical reaction.

[0009] Preferably, the oxidant includes one or more of hydrogen peroxide, peroxymonosulfate, peroxydisulfate, percarbonate, potassium permanganate, ferrate, periodate, sodium hypochlorite, chlorine dioxide, ozone and oxygen.

[0010] Preferably, the catalyst comprises one or more of metal element particles, metal oxides and metal salts;

[0011] The metal single substance particles include one or more of iron single substance particles, copper single substance particles, cobalt single substance particles and aluminum single substance particles;

[0012] The metal oxide includes one or more of iron oxide, copper oxide, cerium oxide, tin oxide, vanadium oxide and manganese dioxide;

[0013] The metal ions in the metal salt include one or more of divalent metal ions, trivalent metal ions, tetravalent metal ions and hexavalent metal ions.

[0014] Preferably, the divalent metal ions include one or more of divalent iron ions, divalent copper ions, divalent cobalt ions, divalent manganese ions, divalent chromium ions and divalent ruthenium ions;

[0015] The trivalent metal ions include one or more of trivalent iron ions, trivalent cobalt ions, trivalent cerium ions, trivalent chromium ions, trivalent ruthenium ions, trivalent titanium ions and trivalent vanadium ions;

[0016] The tetravalent metal ions include one or more of tetravalent manganese ions, tetravalent molybdenum ions, tetravalent cerium ions, tetravalent titanium ions, tetravalent vanadium ions and tetravalent tungsten ions;

[0017] The hexavalent metal ions include one or more of hexavalent molybdenum ions, hexavalent chromium ions and hexavalent tungsten ions.

[0018] Preferably, the sewage raw liquid also includes electrolytes; the electrolytes include one or more of sulfates, chlorides, carbonates, phosphates and nitrates.

[0019] Preferably, in the mixed solution obtained by mixing the sewage stock solution, the oxidant and the catalyst, the concentration of the oxidant is 0.01 to 2000 mmol / L, and the concentration of the catalyst is 0.01 to 1000 mmol / L.

[0020] Preferably, the transmembrane pressure of the cross-flow filtration is 0.05 to 5 MPa.

[0021] Preferably, the current density of the electrochemical reaction is 1 to 2000 mA / cm 2 .

[0022] The present invention also provides a device used in the diaphragm-free electrochemical sewage treatment method described in the above technical solution, characterized in that it includes an electrochemical reactor, wherein the electrochemical reactor is provided with a sewage raw liquid inlet, a purified water outlet and a reflux concentrated water outlet;

[0023] The electrochemical reactor is also provided with a cathode and an anode; the anode is a non-penetrating plate electrode, and the cathode is a penetrating porous filter membrane electrode; no diaphragm is provided between the cathode and the anode;

[0024] The purified water outlet is below the cathode;

[0025] The sewage raw liquid inlet and the reflux concentrated water outlet are located between the cathode and the anode;

[0026] The reflux concentrated water outlet is connected to the sewage raw liquid tank; the sewage raw liquid tank is also connected to the sewage raw liquid inlet.

[0027] Preferably, it also includes a purified water tank and a high-pressure pump;

[0028] The sewage raw liquid tank is provided with a feed inlet, a sewage raw liquid outlet and a return concentrated water inlet; the return concentrated water inlet is connected to the sewage raw liquid outlet;

[0029] The high-pressure pump is arranged on a pipeline connecting the sewage raw liquid outlet and the sewage raw liquid inlet;

[0030] The inlet of the purified water tank is communicated with the purified water outlet.

[0031] The present invention provides a diaphragm-free electrochemical sewage treatment method. During the electrochemical reaction, no diaphragm is arranged between the anode and cathode, so that the mixed solution containing the sewage raw solution, the catalyst and the oxidant can flow in parallel to the anode and perpendicular to the cathode at the same time, and after the electrochemical reaction, the reactor presents a dynamically stable anode acidic region, cathode alkaline region and metal ion metastable region: the mixed solution undergoes an oxygen evolution reaction at the anode to generate active oxygen species and hydrogen ions, so that the reflux concentrated water is acidic, the influence of the formation of metal ion-hydroxyl complexes or metal ion-organic complexes under neutral conditions is reduced, and highly active oxygen substances mainly composed of hydroxyl free radicals and high-valent metal complexes are generated to degrade and mineralize the difficult-to-degrade organic pollutants in the sewage raw solution. No additional acid or alkali is required before and after the reaction to adjust the pH value of the sewage raw solution, and the applicable pH value range is The range is as wide as 1 to 14, and the free radical yield is high. The acidic environment presented by the reflux concentrated water also effectively alleviates the problem of metal mud generation and the long separation time of metal mud and water; purified water is obtained through the cathode, and the catalyst (such as metal ion colloid, metal nano-element particles, metal oxides, metal hydroxides) and high-valent metal complexes are intercepted by the cathode including the filter membrane in the process of cross-flow filtration inside the reactor, and return to the sewage raw liquid together with the high-concentration reflux concentrated water, preventing the problem of concentration reduction due to effluent loss, maintaining the concentration of homogeneous / heterogeneous catalysts in the reactor, and no need to continue to add catalysts after the initial addition, reducing the treatment cost, and providing a new way to efficiently treat difficult-to-degrade organic matter in water to solve the problems of narrow pH treatment range, large sludge production, and low free radical yield of the existing electro-Fenton method. At the same time, the efficient electrochemical reaction can degrade most of the pollutants on the surface of the filter membrane, reduce the deposition of pollutants on the membrane surface, thereby alleviating membrane pollution, and making the pollution layer generated on the membrane surface more loose, which is convenient for the recycling of the membrane.

[0032] The invention provides a sewage treatment device. Compared with the traditional electro-Fenton method, the invention uses electrolysis-electrochemical reaction-composite cathode membrane as a sewage treatment system, and utilizes the coupling effect among the three. When the device provided by the invention is used for sewage treatment, the electric field and the flow field are regulated to form a dynamically stable anode acidic region, a cathode alkaline region and a metal ion metastable region, thereby realizing efficient reuse of the catalyst and maintaining the concentration of the catalyst in the reactor; the formed metal nano-single substance, metal oxide and metal ion colloid and high-valent metal complex are accumulated on the surface or inside of the cathode electrode when passing through the alkaline diffusion layer and the filter membrane in the cathode, which can not only realize the cyclic regeneration of the catalyst and maintain the continuous progress of the electrochemical reaction, but also provide more active sites through the catalyst surface to enhance the decomposition of the oxidant, and shorten the attack distance of the active species through the confined catalytic oxidation, thereby improving the degradation efficiency of the difficult-to-degrade organic matter and shortening the water treatment residence time. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the structure of a sewage treatment device, wherein 1-sewage raw liquid tank, 2-high pressure pump, 3-purified water tank, 4-electrochemical reactor, 5-sewage raw liquid inlet, 6-concentrated water outlet (exhaust port), 7-purified water outlet, 8-anode connection, 9-cathode connection;

[0034] Figure 2 The schematic diagram of the reactor membrane assembly structure, wherein: 1-ruthenium-iridium electrode; 2-conductive titanium ring; 3-conductive carbon fiber cloth; 4-ultrafiltration membrane; 5-filter cloth; 6-titanium mesh; 7-water inlet; 8-water outlet;

[0035] Figure 3 The degradation curves of atrazine in Example 1 and Comparative Examples 1-2;

[0036] Figure 4 It is a bar graph of the mineralization rate of atrazine in Example 1 and Comparative Examples 1-2;

[0037] Figure 5 Fe in Example 1 and Comparative Example 1 2+ Conversion rate bar graph;

[0038] Figure 6 is Fe in Example 1 2+ Concentration, Fe 3+ Concentration and total iron ion concentration change with time. DETAILED DESCRIPTION

[0039] The present invention provides a diaphragm-free electrochemical sewage treatment method, comprising the following steps:

[0040] The sewage raw liquid, oxidant and catalyst are mixed, and part of the obtained mixed liquid is passed into an electrochemical reactor for electrochemical reaction and cross-flow filtration, wherein the product obtained by the electrochemical reaction flows parallel to the anode and perpendicular to the cathode, flows through the anode to obtain reflux concentrated water, and penetrates the cathode to obtain purified water; the anode used in the electrochemical reactor is a flat electrode, and the cathode is a porous filter membrane electrode;

[0041] The reflux concentrated water is refluxed, mixed with the remaining mixed solution, and then cyclically subjected to electrochemical reaction, cross-flow filtration, reflux and mixing; the pH value of the sewage raw solution is 1 to 14;

[0042] No diaphragm is arranged between the anode and the cathode used in the electrochemical reaction.

[0043] In the present invention, unless otherwise specified, the required materials are commercially available products well known to those skilled in the art.

[0044] In the present invention, the mixing preferably includes: after a first mixing of the sewage raw liquid and the catalyst, passing the mixture into the device used for the electrochemical reaction for reflux circulation, after the partial mixture obtained by the first mixing is refluxed to the remaining mixture, the mixture obtained by the reflux circulation is mixed with the oxidant for a second time.

[0045] In the present invention, the second mixing is preferably carried out under the action of a direct current electric field, the current of which may be 50 to 8000 mA, and in a specific embodiment, may be 50 mA, 100 mA, 500 mA, 1000 mA, 2000 mA or 8000 mA; the current density may be 1 to 2000 mA / cm 2 In a specific embodiment, it can be 1 mA / cm 2 , 20mA / cm 2 , 100mA / cm 2 , 200mA / cm 2 , 400mA / cm 2 , 500mA / cm 2 , 1000mA / cm 2 , 1200mA / cm 2 , 1600mA / cm 2 、1800mA / cm 2 or 2000mA / cm 2 .

[0046] In the present invention, the current of the electrochemical reaction may be 50 to 8000 mA, and in a specific embodiment, may be 50 mA, 100 mA, 500 mA, 1000 mA, 2000 mA or 8000 mA; the current density of the electrochemical reaction may be 1 to 2000 mA / cm 2In a specific embodiment, it can be 1 mA / cm 2 , 20mA / cm 2 , 100mA / cm 2 , 200mA / cm 2 , 400mA / cm 2 , 500mA / cm 2 , 1000mA / cm 2 , 1200mA / cm 2 , 1600mA / cm 2 、1800mA / cm 2 or 2000mA / cm 2 In the present invention, the electrochemical reaction may last for 1 to 360 minutes, and in specific embodiments, may last for 1 minute, 60 minutes, 120 minutes, 180 minutes, 300 minutes or 360 minutes.

[0047] In the present invention, the sewage stock solution may include refractory organic pollutants; the pH value of the sewage stock solution is 1 to 14, and in a specific embodiment, it may be 1, 2, 3, 4, 6, 8, 10, 11, 12, 13 or 14. The sewage treatment method provided by the present invention has a good removal effect on acidic, neutral and alkaline sewage stock solutions, and does not need to adjust the pH of the sewage stock solution, and the pH range of the applicable sewage stock solution is wide.

[0048] In the present invention, the sewage stock solution may further include an electrolyte; the electrolyte may include one or more of sulfate, chloride, carbonate, phosphate and nitrate. In a specific embodiment, the electrolyte may include one or more of potassium sulfate, sodium chloride, ferric chloride, sodium carbonate, potassium chloride, sodium nitrate, ferric nitrate and potassium nitrate. In a specific embodiment, the electrolyte may be sodium sulfate, specifically anhydrous sodium sulfate. The present invention improves the current utilization efficiency of the reaction process by adding electrolytes to the sewage stock solution.

[0049] In the present invention, the oxidant may include one or more of hydrogen peroxide, permonosulfate, peroxydisulfate, percarbonate, potassium permanganate, ferrate, periodate, sodium hypochlorite, chlorine dioxide, ozone and oxygen, and in a specific embodiment, it may be hydrogen peroxide. In the present invention, the concentration of the oxidant in the mixed solution obtained by mixing the sewage stock solution, the oxidant and the catalyst may be 0.01 to 2000 mmol / L, and in a specific embodiment, it may be 0.01 mmol / L, 10 mmol / L, 100 mmol / L, 500 mmol / L, 1000 mmol / L or 2000 mmol / L.

[0050] In the present invention, the catalyst may include one or more of metal element particles, metal oxides and metal salts; the metal element may include one or more of iron element particles, copper element particles, cobalt element particles and aluminum element particles; the metal oxide may include one or more of iron oxide, copper oxide, cerium oxide, tin oxide, vanadium oxide and manganese dioxide; in the present invention, the iron oxide preferably includes one or more of Fe3O4, α-Fe2O3, β-Fe2O3, γ-Fe2O3, α-FeOOH, β-FeOOH, γ-FeOOH; the anion in the metal salt may be sulfate ion; the metal ion in the metal salt may include divalent metal ion, trivalent metal ion, tetravalent metal ion and One or more of hexavalent metal ions; the divalent metal ions may include one or more of divalent iron ions, divalent copper ions, divalent cobalt ions, divalent manganese ions, divalent chromium ions and divalent ruthenium ions; the trivalent metal ions may include one or more of trivalent iron ions, trivalent cobalt ions, trivalent cerium ions, trivalent aluminum ions, trivalent chromium ions, trivalent ruthenium ions, trivalent titanium ions and trivalent vanadium ions; the tetravalent metal ions may include one or more of tetravalent manganese ions, tetravalent molybdenum ions, tetravalent cerium ions, tetravalent titanium ions, tetravalent vanadium ions and tetravalent tungsten ions, and the metal compound corresponding to the tetravalent manganese ions may be colloidal manganese dioxide; the hexavalent metal ions may include one or more of hexavalent molybdenum ions, hexavalent chromium ions and hexavalent tungsten ions. When the catalyst is a metal salt, the metal ions and the mixed solution are separated by adsorption or ion exchange after the reaction, and the metal ions after adsorption or ion exchange are used for the next round of water treatment by desorption, thereby realizing the reuse of the metal salt.

[0051] In a specific embodiment, the catalyst is ferric sulfate. In the present invention, the concentration of the catalyst in the mixed solution obtained by mixing the sewage stock solution, the oxidant and the catalyst can be 0.01 to 1000 mmol / L, and in a specific embodiment, can be 0.01 mmol / L, 0.1 mmol / L, 1 mmol / L, 10 mmol / L, 100 mmol / L, 200 mmol / L, 500 mmol / L, 800 mmol / L or 1000 mmol / L.

[0052] Taking hydrogen peroxide as the oxidant, ferric sulfate as the catalyst, and sodium sulfate as the electrolyte as an example, the principle of the electrochemical reaction in the present invention is as follows: the present invention mixes sewage raw liquid, ferric sulfate, hydrogen peroxide and anhydrous sodium sulfate, the anode is a non-penetrating flat plate electrode, the cathode is a penetrating porous filter membrane electrode, and no diaphragm is required between the anode and the cathode, so that the mixed liquid of sewage raw liquid, catalyst and oxidant can flow parallel to the anode and perpendicular to the cathode at the same time, and the flow state of the mixed liquid and the electrolysis reaction process are controlled to make the reactor present a dynamically stable anode acidic region and cathode alkaline region and a metal ion metastable region. In the anode acidic region, the catalyst (Fe 2+ ) can produce a large number of highly oxidizing hydroxyl radicals (·OH), Fe(IV)-complexes or Fe(V)-complexes and other active oxidizing species through catalytic oxidants (H2O2). These active oxidizing species can efficiently degrade and mineralize the difficult-to-degrade organic pollutants in the sewage raw liquid. At the same time, the oxidant (H2O2) is more likely to be ionized in the cathode alkaline zone to generate reductive peroxide ions (HO 2- ), which together with the cathode electron reduction reaction can enhance the Fe 3+ Reduction reaction occurs to generate Fe 2+ , thus greatly accelerating the rate-limiting step of the Fenton reaction. The catalyst produced in the metastable region (such as zero-valent iron or iron oxide form) can not only promote Fe 3+ Regeneration to Fe 2+ , maintaining the continuous progress of the reaction, and at the same time providing more active sites on the catalyst surface to enhance the decomposition of H2O2, and can also replace part of Fe 2 + Fenton reaction is carried out to achieve the reuse of the catalyst. In addition, this method does not require additional addition of acid or alkali to adjust the pH value of the sewage before and after the reaction, and is applicable to the pH value range of the sewage raw solution as wide as 1 to 14; the acidic environment presented by the mixed solution also effectively avoids the generation of iron sludge, and the presence of the alkaline diffusion layer and the ultrafiltration membrane enables the catalyst and water to be efficiently separated. At the cathode, the purified water passes through the cathode, and the formed catalyst and high-valent metal complex are intercepted inside the reactor during the cross-flow filtration process, maintaining the concentration of homogeneous / heterogeneous catalysts in the reactor, without the need to continuously add catalysts, and reducing treatment costs. At the same time, efficient redox reactions (electrochemical reactions) can degrade most of the pollutants on the surface of the filter membrane, reduce the deposition of pollutants on the membrane surface, thereby alleviating membrane pollution, and making the pollution layer generated on the membrane surface looser, which is convenient for the long-term and continuous use of the membrane.

[0053] In the present invention, the valence change, reaction process and active oxidation species of the catalyst during the catalytic process are shown in Table 1.

[0054] Table 1 Valence changes, reaction process and active oxidative species of catalysts during catalysis

[0055]

[0056]

[0057]

[0058] Note: “≡” indicates adsorption on an electrode or solid surface. Specifically, this symbol is used to indicate that a chemical substance is associated with the surface of an electrode or a solid material such as a catalyst. 4+ and Ce 3+ ) are ions adsorbed on electrodes or solid surfaces, rather than free ions existing alone in the solution.

[0059] In the present invention, the standard redox potentials of the oxidant and the catalyst are shown in Table 2 (V vs. NHE).

[0060] Table 2 Standard redox potentials of oxidants and catalysts (V vs. NHE)

[0061]

[0062]

[0063] In the present invention, the mixing may include stirring mixing; the rotation speed of the stirring mixing may be 200 to 2000 rpm, and in a specific embodiment, may be 200 rpm, 400 rpm, 800 rpm, 1200 rpm, 1600 rpm or 2000 rpm.

[0064] In the present invention, the transmembrane pressure of the cross-flow filtration may be 0.05 to 5 MPa. In specific embodiments, it may be 0.05 MPa, 0.1 MPa, 1 MPa, 2 MPa, 3 MPa, 4 MPa or 5 MPa.

[0065] In the present invention, the filter membrane may include a macrofiltration membrane, an ultrafiltration membrane, a microfiltration membrane, a nanofiltration membrane or a reverse osmosis membrane, and in a specific embodiment, it may be an ultrafiltration membrane. The present invention adopts a cross-flow filtration method, and the water flow does not directly pass through the membrane during the reaction. The addition of the cathode membrane reduces the impact of the hydraulic force on the membrane, reduces the possibility of membrane clogging, and prolongs the service life of the membrane.

[0066] In the present invention, the reflux rate of the concentrated water can be 0.5-40 L / min, and in a specific embodiment, it can be 0.5 L / min, 1 L / min, 1.5 L / min, 2 L / min, 5 L / min, 10 L / min, 20 L / min, 30 L / min or 40 L / min. The present invention adopts the concentrated water reflux mode, has stable effluent, simple structure, strong operability of the sewage treatment method, and convenient operation and management.

[0067] In the present invention, the metal ions remaining in the reflux concentrated water obtained by the last sequential circulation can be recovered and reused by an adsorbent. In the present invention, the adsorbent can include nanocellulose and / or macroporous adsorption resin.

[0068] The present invention provides a device used in the sewage treatment method described in the above technical solution, comprising an electrochemical reactor, wherein the electrochemical reactor is provided with a sewage raw liquid inlet, a purified water outlet and a reflux concentrated water outlet;

[0069] The electrochemical reactor is also provided with a cathode and an anode; the anode is a non-penetrating plate electrode, the cathode is a penetrating porous filter membrane electrode; there is no cathode and anode between the cathode and the anode.

[0070] Place diaphragm;

[0071] The purified water outlet is below the cathode;

[0072] The sewage raw liquid inlet and the reflux concentrated water outlet are located between the cathode and the anode;

[0073] The reflux concentrated water outlet is connected to the sewage raw liquid tank; the sewage raw liquid tank is also connected to the sewage raw liquid inlet.

[0074] The device provided by the present invention comprises an electrochemical reactor, wherein the electrochemical reactor is provided with a sewage raw liquid inlet, a purified water outlet and a return concentrated water outlet; a sewage raw liquid tank connected to the return concentrated water outlet; the sewage raw liquid tank is also connected to the sewage raw liquid inlet; the purified water outlet is below the cathode; the sewage raw liquid inlet and the return concentrated water outlet are located between the cathode and the anode. The return concentrated water outlet can also be used as a gas outlet.

[0075] In the present invention, the device preferably includes a purified water tank and a high-pressure pump; the high-pressure pump may include a high-pressure diaphragm pump.

[0076] In the present invention, the sewage raw liquid tank is provided with a feed inlet, a sewage raw liquid outlet and a return concentrated water inlet. In the present invention, the return concentrated water inlet can be connected to the sewage raw liquid outlet. In the present invention, the high-pressure pump can be arranged on a pipeline connecting the sewage raw liquid outlet and the sewage raw liquid inlet.

[0077] The electrochemical reactor is provided with a cathode and an anode; the anode is a non-penetrating flat plate electrode, and the cathode is a penetrating porous filter membrane electrode; and no diaphragm is provided between the cathode and the anode.

[0078] In the present invention, the cathode preferably includes a conductive coil, a conductive porous electrode, a filter membrane, a filter cloth and a titanium mesh stacked in sequence; in the present invention, the conductive porous electrode includes one or more of conductive carbon fiber cloth, graphite carbon felt, activated carbon fiber, graphene, carbon nanotubes, carbon black gas diffusion electrode, foam iron, foam nickel and foam copper, and the filter membrane includes one or more of macrofiltration membrane, ultrafiltration membrane, microfiltration membrane, nanofiltration membrane and reverse osmosis membrane, and in a specific embodiment, it can be an ultrafiltration membrane. The electrochemical reactor provided by the present invention is applicable to a variety of electro-Fenton reaction types and a variety of filter membranes. A suitable electro-Fenton reaction can be designed according to actual conditions and a suitable filter membrane can be selected, which has good applicability and removal effect. In the present invention, the conductive coil, the conductive porous electrode and the filter membrane can be tightly stacked.

[0079] In the present invention, the anode can be arranged on the side of the conductive coil in the cathode away from the filter membrane; the sewage raw liquid inlet and the reflux concentrated water outlet can be independently arranged between the conductive coil and the anode in the cathode; the purified water outlet can be arranged on the side of the filter membrane in the cathode away from the conductive carbon cloth.

[0080] In the present invention, the anode may include a ruthenium-iridium electrode. In the present invention, the anode is preferably a non-penetrating plate electrode, and the cathode is a penetrating porous membrane electrode. When the anode is a non-penetrating plate electrode and the cathode is a penetrating porous membrane electrode, a better technical effect can be achieved.

[0081] The device provided by the present invention may further include a purified water tank, wherein the inlet of the purified water tank is connected to the purified water outlet.

[0082] Taking hydrogen peroxide as the oxidant and ferric sulfate as the catalyst as an example, when the device provided by the present invention is used for sewage treatment, the filter membrane can effectively intercept ferric hydroxide, ferrous hydroxide colloid and iron oxide in the effluent, achieving Fe 2+ , Fe 3+ The efficient separation of ions and water and the recovery of catalysts maintain the stability of the concentration of chemical reagents (oxidants and catalysts) in the mixed solution, improve the utilization rate of chemical reagents, and ensure the efficient activation efficiency of the oxidant.

[0083] Figure 1 This is a schematic diagram of the sewage treatment device structure. Figure 1 The specific method of using the sewage treatment device provided by the present invention to treat sewage may include the following steps:

[0084] A mixture of sewage raw liquid and catalyst or a mixture of sewage raw liquid, catalyst and electrolyte is transported to the electrochemical reactor through the sewage raw liquid outlet by a high-pressure pump, and then the oxidant is transported to the sewage raw liquid tank through the feed port for a second mixing to obtain a mixed liquid; the mixed liquid is subjected to an electrochemical reaction and then cross-flow filtration to obtain purified water and reflux concentrated water; the reflux concentrated water is refluxed to the sewage raw liquid tank through the reflux concentrated water outlet to be mixed with the sewage raw liquid.

[0085] In the present invention, the purified water can be delivered to a purified water tank through a purified water outlet.

[0086] In the present invention, the filter membrane can be pre-pressed with ultrapure water before use. In the present invention, the pre-pressing time can be 10 to 60 minutes, and in a specific embodiment, it can be 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes or 60 minutes.

[0087] In the present invention, before the electrochemical reaction, the mixture of the sewage stock solution and the catalyst or the mixture of the sewage stock solution, the catalyst and the electrolyte (i.e., the mixture obtained by the first mixing) is preferably refluxed. Specifically, when the mixture flows through the cathode and flows back into the sewage stock solution tank, a DC electric field is started to be applied and the oxidant is transported to the sewage stock solution tank through the feed port for a second mixing to obtain a mixed solution.

[0088] In order to further illustrate the present invention, a diaphragm-free electrochemical sewage treatment method and device provided by the present invention are described in detail below in conjunction with the accompanying drawings and embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0089] The device used in the embodiment is composed of the following components:

[0090] An electrochemical reactor, wherein the electrochemical reactor is provided with a sewage raw liquid inlet, a purified water outlet and a reflux concentrated water outlet; a sewage raw liquid tank connected to the reflux concentrated water outlet; the sewage raw liquid tank is also connected to the sewage raw liquid inlet; the purified water outlet is below the cathode; the sewage raw liquid inlet and the reflux concentrated water outlet are located between the cathode and the anode. The reflux concentrated water outlet can also be used as a gas outlet;

[0091] Purified water tank, high pressure pump;

[0092] The sewage raw liquid tank is provided with a feed inlet, a sewage raw liquid outlet and a reflux concentrated water inlet; the reflux concentrated water inlet is connected to the sewage raw liquid outlet; the high-pressure pump is arranged on a pipeline connected to the sewage raw liquid outlet and the sewage raw liquid inlet; the inlet of the purified water tank is connected to the purified water outlet;

[0093] The electrochemical reactor is provided with a cathode and an anode; the anode is a non-penetrating flat plate electrode, and the cathode is a penetrating porous filter membrane electrode; and no diaphragm is provided between the cathode and the anode.

[0094] Example 1

[0095] use Figure 1 The device shown performs sewage treatment. Figure 2 The schematic diagram of the reactor membrane assembly structure, where 1-ruthenium-iridium electrode; 2-conductive titanium ring; 3-conductive carbon fiber cloth (density 0.1g / cm 3 , with a specific surface area of ​​2.2 to 4 m 2 / g); 4-ultrafiltration membrane (pore size 5nm); 5-filter cloth (2300 mesh); 6-titanium mesh (1×3mm); 7-water inlet; 8-water outlet. The specific processing steps are as follows:

[0096] The ultrafiltration membrane in the electrochemical reactor was pre-pressed with ultrapure water for 30 minutes, and 250 mL of organic wastewater containing the target pollutant atrazine (ATZ) was injected into a beaker and continuously stirred with magnetic force at a speed of 800 rpm. The concentration of atrazine in the organic wastewater was 10 mg / L, the concentration of FeSO4 was 30 mg / L, the concentration of anhydrous sodium sulfate was 50 mmol / L, and the pH was 7.

[0097] The high-pressure diaphragm pump provides pressure to drive the organic wastewater into the electrochemical reactor and maintain the transmembrane pressure at 0.1 MPa. When the organic wastewater flows from the constant current chamber (the chamber in the middle of the reactor) of the electrochemical reactor through the cathode and flows back to the beaker containing the organic wastewater, the DC power supply is immediately turned on to apply an electric field and the current density is adjusted to 10 mA / cm 2 , the current is 500mA, and then 460μL of 10mmol / L hydrogen peroxide is added to the beaker, and the electrochemical reaction is followed by cross-flow filtration. The reflux concentrated water is refluxed into the beaker containing the organic wastewater at a rate of 1.5L / min.

[0098] When the reaction time is 0min, 1min, 3min, 5min, 10min, 15min, 20min and 30min, the samples were sampled using a syringe, and the samples were refrigerated at 3°C. 1mL of the refrigerated sample was taken, filtered through a 0.22μm PTFE filter membrane, and added to a liquid phase bottle containing 0.2mL of methanol (which can quench the residual free radicals in the liquid phase vial and ensure the stability of the treatment effect before the test). The concentration of atrazine in the organic wastewater was detected by high performance liquid chromatography and the TOC concentration before and after treatment was detected by a total organic carbon analyzer, and the removal rate and mineralization rate of atrazine were calculated. Among them, the calculation formula of the mineralization rate is: Mineralization rate = 1-C x / C 初始, C x is the TOC concentration after treatment for x min, C 初始 is the initial TOC concentration.

[0099] When the reaction time is 0min, 1min, 2min, 3min, 5min, 10min, 15min, 20min, 25min and 30min, two samples are taken respectively using a pipette, and the obtained samples are added to 10mL colorimetric tubes, one of which is added with 1mL of 10mmol / L hydroxylamine hydrochloride, and the other is not added, and then 1mL of ammonium acetate buffer (the buffer preparation method is: weigh 100g of ammonium acetate, add 125mL of glacial acetic acid and dilute to 250mL with pure water) and 2mL of 5% o-phenanthroline solution are added respectively, and then pure water is added to make the volume to 10mL, mixed evenly and color developed for 15min, and the absorbance is measured at a wavelength of 510nm. Each group of data is measured twice in parallel and the average value is taken to calculate the total iron concentration and Fe 2+ Ion concentration, and calculate Fe 3+ Concentration and Fe 2+ conversion rate.

[0100] After calculation, after 30 minutes of treatment, the removal rate of atrazine was 99.14%, the mineralization rate was 66.33%, and the Fe 2+ The conversion rate was 70.25%.

[0101] Example 2

[0102] The organic wastewater was treated by the sewage treatment method of Example 1, and the only difference from Example 1 was that the Fe2(SO4)3 concentration in the organic wastewater was 15 mg / L. The atrazine removal rate was calculated to be 99.07%.

[0103] Example 3

[0104] The organic wastewater was treated by the sewage treatment method of Example 1, the only difference from Example 1 being that the amount of hydrogen peroxide added was 230 μL. The removal rate of atrazine was calculated to be 99.04%.

[0105] Example 4

[0106] The organic wastewater was treated by the sewage treatment method of Example 1, the only difference from Example 1 being that the pH value of the organic wastewater was adjusted to 3 with a 1M sulfuric acid solution. The atrazine removal rate was calculated to be 99.05%.

[0107] Example 5

[0108] The organic wastewater was treated by the sewage treatment method of Example 1, and the only difference from Example 1 was that the pH value of the organic wastewater was adjusted to 12 with a 1M sodium hydroxide solution. The atrazine removal rate was calculated to be 99.03%.

[0109] It can be seen from Examples 1, 4 and 5 that the organic wastewater is acidic, neutral and alkaline, and the degradation effect on atrazine is stably maintained at more than 99%, and the treatment effect is good; it can be seen that the initial pH value has little effect on the degradation of the target pollutants by the system, and has a wider pH applicability.

[0110] Comparative Example 1

[0111] 250 mL of organic wastewater containing the target pollutant atrazine was injected into a beaker and continuously stirred with magnetic force at a speed of 800 rpm. The concentration of atrazine in the organic wastewater was 10 mg / L, and Fe 3+ The concentration is 60 mg / L, the concentration of anhydrous sodium sulfate is 50 mmol / L, and the pH is 7.

[0112] The high-pressure diaphragm pump provides pressure to drive the organic wastewater into the electrochemical reactor (the difference from Example 1 is that the cathode is a penetrating porous electrode and no ultrafiltration membrane is provided). When the organic wastewater flows from the constant current chamber of the electrochemical reactor through the cathode and flows back to the beaker containing the organic wastewater, the DC power supply is immediately turned on to apply the electrochemical reaction, and the current is adjusted to 500 mA and the current density is 10 mA / cm 2 Then, 460 μL of 10 mmol / L hydrogen peroxide was added to the beaker, and the electrochemical reaction was followed by cross-flow filtration. The reflux concentrated water was refluxed into the beaker containing the organic wastewater at a rate of 1.5 L / min.

[0113] When the reaction time is 0min, 1min, 3min, 5min, 10min, 15min, 20min and 30min, the samples were sampled by syringe, and the samples were refrigerated at 3°C. 1mL of the refrigerated samples were taken, filtered through a 0.22μm PTFE filter membrane, and added to a liquid phase bottle containing 0.2mL of methanol (which can quench the residual free radicals in the liquid phase vial and ensure the stability of the treatment effect before the test). The concentration of atrazine in the organic wastewater was detected by high performance liquid chromatography, and the TOC concentration before and after treatment was detected by a total organic carbon analyzer, and the removal rate and mineralization rate of atrazine were calculated.

[0114] When the reaction time is 0min, 1min, 2min, 3min, 5min, 10min, 15min, 20min, 25min and 30min, two samples are taken respectively using a pipette, and the obtained samples are added to 10mL colorimetric tubes, one of which is added with 1mL of 10mmol / L hydroxylamine hydrochloride, and the other is not added, and then 1mL of ammonium acetate buffer (the buffer preparation method is: weigh 100g of ammonium acetate, add 125mL of glacial acetic acid and dilute to 250mL with pure water) and 2mL of 5% 1,10-phenanthroline solution are added respectively, and then pure water is added to make the volume to 10mL, mixed evenly and color developed for 15min, and the absorbance is measured at a wavelength of 510nm. Each group of data is measured twice in parallel and the average value is taken to calculate the total iron concentration and Fe 2+ Ion concentration, and calculate Fe 3+ Concentration and Fe 2+ conversion rate.

[0115] After calculation, after 30 minutes of treatment, the removal rate of atrazine was 48.54%, the mineralization rate was 37.18%, and the Fe 2+ The conversion rate was 70.25%.

[0116] Comparative Example 2

[0117] 250 mL of organic wastewater containing the target pollutant atrazine was injected into a beaker and continuously stirred with magnetic force at a speed of 800 rpm. The concentration of atrazine in the organic wastewater was 10 mg / L, the concentration of anhydrous sodium sulfate was 50 mmol / L, and the pH was 7.

[0118] The high-pressure diaphragm pump provides pressure to drive the organic wastewater into the device used in Example 1. When the organic wastewater flows from the constant current chamber of the electrochemical reactor through the cathode and flows back to the beaker containing the organic wastewater, the DC power supply is immediately turned on to apply an electric field for electrochemical reaction. The current is adjusted to 500 mA and the current density is 10 mA / cm 2 After the electrolysis reaction, cross-flow filtration is performed and the reflux concentrated water is refluxed into the beaker containing organic wastewater at a rate of 1.5 L / min.

[0119] When the reaction time is 0min, 1min, 3min, 5min, 10min, 15min, 20min and 30min, the samples were sampled by syringe, and the samples were refrigerated at 3°C. 1mL of the refrigerated samples were taken, filtered through a 0.22μm PTFE filter membrane, and added to a liquid phase bottle containing 0.2mL of methanol (which can quench the residual free radicals in the liquid phase vial and ensure the stability of the treatment effect before the test). The concentration of atrazine in the organic wastewater was detected by high performance liquid chromatography, and the TOC concentration before and after treatment was detected by a total organic carbon analyzer, and the removal rate and mineralization rate of atrazine were calculated.

[0120] It was calculated that after 30 minutes of treatment, the removal rate of atrazine was 20.04% and the mineralization rate was 24.23%.

[0121] Figure 3 The degradation curves of atrazine in Example 1 and Comparative Examples 1-2 are Example 1, Comparative Example 1 and Comparative Example 2 from top to bottom;

[0122] Figure 4 It is a bar graph of the mineralization rate of atrazine in Example 1 and Comparative Examples 1-2, from left to right are Comparative Example 2, Comparative Example 1 and Example 1;

[0123] Figure 5 Fe in Example 1 and Comparative Example 1 2+ Conversion rate bar graph, from left to right, Comparative Example 1 and Example 1;

[0124] Figure 6 is Fe in Example 1 2+ Concentration, Fe 3+ Concentration and total iron ion concentration change with time.

[0125] Depend on Figure 3 to Figure 6 It can be seen that under the same conditions, the treatment method provided in Example 1 (electrolysis-Fenton-cathode composite membrane system) increased the removal rate of atrazine by 50.58% and the mineralization rate by 29.15% compared with Comparative Example 1. 2+ The conversion rate increased by 36.44%; compared with Comparative Example 2, the removal rate of atrazine increased by 79.07%, and the mineralization rate increased by 42.1%. The sewage treatment effect was significantly better than that of the electrolysis-Fenton system in Comparative Example 1 and the electrolysis system in Comparative Example 2.

[0126] It can be seen that the present invention creatively uses electrolysis-Fenton-composite cathode membrane as a sewage treatment system, utilizes the coupling effect between the three, enhances the interaction and utilization rate of electrolytes, oxidants and catalysts, increases the generation rate of active oxidative species, and maximizes the utilization rate and degradation efficiency of added compounds, thereby greatly improving the removal rate of difficult-to-degrade organic pollutants such as atrazine in sewage, and solves the problems of low free radical yield, large oxidant dosage and weak treatment capacity in the prior art degradation method of difficult-to-degrade organic pollutants.

[0127] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A diaphragm-free electrochemical sewage treatment method, characterized in that: The following steps are involved: The sewage raw liquid, oxidant and catalyst are mixed, and part of the obtained mixed liquid is passed into an electrochemical reactor for electrochemical reaction and cross-flow filtration, wherein the product obtained by the electrochemical reaction flows parallel to the anode and perpendicular to the cathode, flows through the anode to obtain reflux concentrated water, and penetrates the cathode to obtain purified water; the anode used in the electrochemical reactor is a flat plate electrode, and the cathode is a penetrating porous membrane electrode; The reflux concentrated water is refluxed, mixed with the remaining mixed solution, and then cyclically subjected to electrochemical reaction, cross-flow filtration, reflux and mixing; the pH value of the sewage raw solution is 1 to 14; No diaphragm is arranged between the anode and the cathode used in the electrochemical reaction.

2. The diaphragm-free electrochemical sewage treatment method according to claim 1, characterized in that: The oxidant includes one or more of hydrogen peroxide, peroxymonosulfate, peroxydisulfate, percarbonate, potassium permanganate, ferrate, periodate, sodium hypochlorite, chlorine dioxide, ozone and oxygen.

3. The diaphragm-free electrochemical sewage treatment method according to claim 1, characterized in that: The catalyst includes one or more of metal element particles, metal oxides and metal salts; The metal single substance particles include one or more of iron single substance particles, copper single substance particles, cobalt single substance particles and aluminum single substance particles; The metal oxide includes one or more of iron oxide, copper oxide, cerium oxide, tin oxide, vanadium oxide and manganese dioxide; The metal ions in the metal salt include one or more of divalent metal ions, trivalent metal ions, tetravalent metal ions and hexavalent metal ions.

4. The diaphragm-free electrochemical sewage treatment method according to claim 3, characterized in that: The divalent metal ions include one or more of divalent iron ions, divalent copper ions, divalent cobalt ions, divalent manganese ions, divalent chromium ions and divalent ruthenium ions; The trivalent metal ions include one or more of trivalent iron ions, trivalent cobalt ions, trivalent cerium ions, trivalent chromium ions, trivalent ruthenium ions, trivalent titanium ions and trivalent vanadium ions; The tetravalent metal ions include one or more of tetravalent manganese ions, tetravalent molybdenum ions, tetravalent cerium ions, tetravalent titanium ions, tetravalent vanadium ions and tetravalent tungsten ions; The hexavalent metal ions include one or more of hexavalent molybdenum ions, hexavalent chromium ions and hexavalent tungsten ions.

5. The diaphragm-free electrochemical sewage treatment method according to claim 1, 2 or 3, characterized in that: The sewage raw liquid also includes electrolytes; the electrolytes include one or more of sulfates, chlorides, carbonates, phosphates and nitrates.

6. The diaphragm-free electrochemical sewage treatment method according to claim 1, characterized in that: In the mixed solution obtained by mixing the sewage stock solution, the oxidant and the catalyst, the concentration of the oxidant is 0.01 to 2000 mmol / L, and the concentration of the catalyst is 0.01 to 1000 mmol / L.

7. The diaphragm-free electrochemical sewage treatment method according to claim 1, characterized in that: The transmembrane pressure of the cross-flow filtration is 0.05-5 MPa.

8. The diaphragm-free electrochemical sewage treatment method according to claim 1, characterized in that: The current density of the electrochemical reaction is 1-2000 mA / cm 2 .

9. The device used in the diaphragm-free electrochemical sewage treatment method according to any one of claims 1 to 8, characterized in that: It comprises an electrochemical reactor, wherein the electrochemical reactor is provided with a sewage raw liquid inlet, a purified water outlet and a reflux concentrated water outlet; The electrochemical reactor is also provided with a cathode and an anode; the anode is a non-penetrating plate electrode, and the cathode is a penetrating porous filter membrane electrode; no diaphragm is provided between the cathode and the anode; The purified water outlet is below the cathode; The sewage raw liquid inlet and the reflux concentrated water outlet are located between the cathode and the anode; The reflux concentrated water outlet is connected to the sewage raw liquid tank; the sewage raw liquid tank is also connected to the sewage raw liquid inlet.

10. The device according to claim 9, characterized in that It also includes a purified water tank and a high-pressure pump; The sewage raw liquid tank is provided with a feed inlet, a sewage raw liquid outlet and a return concentrated water inlet; the return concentrated water inlet is connected to the sewage raw liquid outlet; The high-pressure pump is arranged on a pipeline connecting the sewage raw liquid outlet and the sewage raw liquid inlet; The inlet of the purified water tank is communicated with the purified water outlet.

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