An electrode, electrocoagulation system and electrocoagulation method

Abstract

This invention provides an electrode, an electrocoagulation system, and an electrocoagulation method. The electrode comprises a tubular anode made of iron with a circular cross-section and a detachable cylindrical cathode made of non-reactive metal, fitted inside the anode. The ratio of the inner radius of the anode to the outer radius of the cathode is 2-4, with a difference of 1-2.5 cm. The electrocoagulation system includes an inlet tank, an outlet tank, two electrode groups, and two diode switches. Each electrode group includes one or more electrodes connected in parallel or series. The inlet tank is connected to the outlet tank through channels between the anode and cathode of each electrode. The circuit currents of the two electrode groups are connected in parallel with opposite directions. The two diode switches are respectively located at the anode interfaces of the two electrode groups. The inlet tank is equipped with a pH adjustment device to adjust the pH value of the water to 4-5. By using a special electrode setup combined with an appropriate anode current density, a suitable polarization deflection is achieved, and acid-assisted dissolution is used to solve the anode passivation problem.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to an electrode for electrocoagulation, an electrocoagulation system, and an electrocoagulation method. Background Technology

[0002] Iron anode electrocoagulation is a technology that utilizes the principle of electrolysis to release flocculants through anodic oxidation. With the increasing complexity of wastewater types and the growing demand for integrated wastewater treatment equipment, it is now widely used in wastewater treatment processes such as heavy metal treatment, dyeing and printing, papermaking, leather making, and drinking water defluorination and rainwater purification. However, the large-scale application of iron anode electrocoagulation technology is significantly hampered by inherent technical challenges. These challenges mainly involve two aspects related to the properties of current conduction: one is the obstruction caused by anode passivation. Anode passivation refers to the accumulation of metal ions generated at the metal anode under the polarization of the electric field, which react with other substances to form metal oxides or salts, adhering to the surface of the anode plate to form a dense passivation film. The presence of this passivation film prevents the dissolution of the metal plate and electron transfer, limiting flocculant production and significantly hindering the normal reaction. The other obstacle is the obstruction caused by cathode adsorption passivation. Wastewater contains cations such as calcium and magnesium, which move to the vicinity of the cathode under the influence of the electric field and react with free OH groups around the cathode. - The reaction produces hydroxide precipitate. In addition, CO3 in the wastewater... 2- HCO3 - It can also react with cations to form carbonate precipitates, affecting the reaction rate between the cathode and the reaction solution. In short, achieving passivation suppression of the anode and cathode of the iron anode battery during electrocoagulation is of great significance to the electrocoagulation process.

[0003] The electrocoagulation process has undergone a certain development process. In electrocoagulation, electrode connection methods are divided into unipolar and bipolar types. The characteristic of the unipolar type is that the two outermost plates are directly connected to an external power source, and each face of the middle plate has a completely opposite electrical polarity to its adjacent plates; the same plate exhibits two electrical polarities. In a unipolar electrode, the current always flows from one anode to the adjacent cathode, without bypassing the middle plate to flow to other cathodes. In a bipolar type, each plate is connected to an external power source, and the polarity of the plate electrode is the same as the power source polarity; the current flow is opposite to that of the unipolar type. Electrodes are the carriers of the electrocoagulation process, and plates are the most common electrode shape in electrocoagulation. Currently, electrode shapes are diverse, gradually evolving from plate-like shapes to spherical, rod-like, mesh-like, and tubular shapes, as well as three-stage electrodes composed of anodes, cathodes, and a third-dimensional electrode. The most commonly used power source in electrocoagulation is direct current (DC) power. However, DC power is susceptible to electrode passivation during operation. Therefore, some researchers have explored using novel power sources such as alternating current (AC) and pulsed power to replace traditional DC power supplies, which are beneficial for reaction diffusion and reduce electrode passivation. Compared to DC electrocoagulation, pulsed electrocoagulation reduces energy consumption. AC electrocoagulation, through the periodic transformation of the electric field, prevents charged particles from moving in a specific direction, thus mitigating the formation of a passivation film. Experiments show that periodic transformation can address electrode passivation to some extent while reducing energy consumption.

[0004] While existing electrocoagulation processes have made technical improvements in electrode shape and conduction methods, which have played a role in delaying electrode passivation, most of these improvements are based on concentration polarization considerations and neglect the polarization effect of the electrostatic field (conservative force field) on the aqueous medium, resulting in unsatisfactory effects. In particular, the current mainstream electrode conduction method, although it can delay the decay of anodic current to some extent, causes passivation products to coexist on both electrodes, which is detrimental to subsequent processing.

[0005] In conclusion, there is still a need to research technical solutions to address the passivation problem of the anode and cathode of iron anode batteries during electrocoagulation. Summary of the Invention

[0006] The purpose of this invention is to provide a technical solution that can solve the problem of passivation of the anode and cathode of iron anode batteries during electrocoagulation.

[0007] To achieve the above objectives, the present invention provides the following three technical solutions.

[0008] In a first aspect, the present invention provides an electrode, wherein the electrode includes a tubular anode and a detachable cylindrical cathode disposed inside the tubular anode, the central axis of the cylindrical cathode coinciding with the central axis of the tubular anode;

[0009] The cylindrical cathode is made of a non-reactive metal, the tubular anode is made of iron, the ratio of the inner radius of the tubular anode to the outer radius of the cylindrical cathode is 2-4, and the difference between the inner radius of the tubular anode and the outer radius of the cylindrical cathode is 1-2.5 cm.

[0010] The electrode provided by this invention is an electrode for electrocoagulation. By setting the ratio of the inner radius of the tubular iron anode to the outer radius of the cylindrical cathode to 2-4, and the difference between the inner radius of the tubular anode and the outer radius of the cylindrical cathode to 1-2.5 cm, a foundation is laid for achieving appropriate reverse polarization of the electrode, thereby avoiding anode passivation during electrocoagulation. It also increases the cathode's ability to treat hard wastewater. In addition, the detachable cylindrical cathode, which is fitted inside the tubular anode, is easy to disassemble and facilitates the removal of cathode passivation scale, which helps to control cathode adsorption passivation.

[0011] According to a preferred embodiment of the first aspect, the length of the portion of the cylindrical cathode and the tubular anode that are fitted together is 5 to 20 times the inner radius of the tubular anode.

[0012] According to a preferred embodiment of the first aspect, the inner radius of the tubular anode is 2-5 cm.

[0013] According to a preferred embodiment of the first aspect, the cylindrical cathode is made of stainless steel.

[0014] In a second aspect, the present invention provides an electrocoagulation system, wherein the electrocoagulation system comprises:

[0015] Water inlet tank, water outlet tank, electrode group A, electrode group B, diode switch A and diode switch B;

[0016] Electrode group A and electrode group B each include one or more electrodes connected in parallel or in series; each electrode adopts the electrode provided in the first aspect of the present invention;

[0017] The inlet tank is connected to the outlet tank through the channels formed between the tubular anodes and cylindrical cathodes of each electrode, thus realizing the parallel connection of the water passages between the inlet and outlet tanks.

[0018] One phase of the three-phase AC power supply is connected to the anode interface of electrode group A and the cathode interface of electrode group B, respectively. Diode switch A is located on the connection line between the anode interface of electrode group A and the three-phase AC power supply. The cathode interfaces of electrode group A and the anode interfaces of electrode group B are both connected to the neutral point of the three-phase AC power supply. Diode switch B is located on the connection line between the cathode interface of electrode group B and the three-phase AC power supply. This achieves reverse parallel connection of the circuit currents of electrode group A and electrode group B.

[0019] The inlet tank is equipped with a pH adjustment device to adjust the pH value of the water in the inlet tank to 4-5.

[0020] The electrocoagulation system provided by the invention achieves appropriate polarization deflection through special electrode settings, which, combined with acid-assisted dissolution, lays the foundation for effectively solving the anode passivation problem. At the same time, the appropriate polarization deflection increases the cathode's ability to treat hard wastewater, and the pluggable design of the cathode makes it easy to clean the passivation film, thereby effectively solving the cathode passivation problem.

[0021] According to the preferred embodiment of the second aspect, electrode group A and electrode group B are the same.

[0022] According to the preferred embodiment of the second aspect, all electrodes are identical.

[0023] According to the preferred embodiment of the second aspect, the inlet tank and the outlet tank are provided with multiple sleeves to fix the cylindrical cathode and tubular anode of each electrode.

[0024] More preferably, the inlet tank is provided with a plurality of cathode fixing sleeves penetrating two opposite sides of the inlet tank, and the outlet tank is provided with a plurality of cathode fixing sleeves penetrating two opposite sides of the outlet tank. The central axis of each cathode fixing sleeve is parallel to the central axis of the cylindrical cathode of the electrode, and the cathode fixing sleeves on the inlet tank and the cathode fixing sleeves on the outlet tank are arranged opposite to each other. The cylindrical cathode of each electrode is respectively inserted through one cathode fixing sleeve in the inlet tank and one cathode fixing sleeve in the outlet tank to fix the cylindrical cathode, and at least one end of the cylindrical cathode extends out of the cathode fixing sleeve to facilitate the insertion and removal of the cylindrical cathode. At least one of the inlet tank and the outlet tank is provided with a plurality of anode fixing sleeves to fix the tubular anode of each electrode.

[0025] According to the preferred embodiment of the second aspect, the inlet tank is connected to the outlet tank through a channel formed between the tubular anode and the cylindrical cathode of each electrode in the following manner:

[0026] The inlet tank, electrodes, and outlet tank are arranged from bottom to top;

[0027] The top surface of the water inlet tank is provided with multiple fluid channel openings that match the size of the tubular anodes of each electrode, and the fluid channel openings are provided with anode fixing sleeves. The water inlet tank is provided with multiple cathode fixing sleeves that penetrate the top and bottom surfaces of the water inlet tank and match the size of the tubular anodes of each electrode, and the cathode fixing sleeves are fixed to the bottom surface of the water inlet tank.

[0028] The bottom surface of the water outlet tank is provided with multiple fluid channel openings that match the size of the tubular anode of each electrode, and the fluid channel openings are provided with anode fixing sleeves. The water outlet tank is provided with multiple cathode fixing sleeves that penetrate the top and bottom surfaces of the water outlet tank and match the size of the tubular anode of each electrode, and the cathode fixing sleeves are fixed to the top surface of the water outlet tank.

[0029] The tubular anode of each electrode is fixed between the inlet tank and the outlet tank by an anode fixing sleeve in the inlet tank and an anode fixing sleeve in the outlet tank. The anode fixing sleeves in the inlet tank and the outlet tank can seal the interface between the tubular anode of each electrode and the inlet tank and the outlet tank to prevent water from overflowing from the interface.

[0030] Each cylindrical cathode is fixed by inserting into a cathode fixing sleeve in the inlet tank and a cathode fixing sleeve in the outlet tank, and at least one end of the cylindrical cathode extends out of the sleeve to facilitate insertion and removal of the cylindrical cathode.

[0031] Water in the inlet tank flows through the fluid channels on the top surface of the inlet tank to the channels formed between the tubular anode and the cylindrical cathode of each electrode, and then flows into the outlet tank through the fluid channels on the bottom surface of the outlet tank.

[0032] According to the preferred embodiment of the second aspect, the inlet tank and outlet tank are insulated water tanks.

[0033] According to the preferred embodiment of the second aspect, both the anode fixing sleeve and the cathode fixing sleeve are made of insulating sleeves.

[0034] According to the preferred embodiment of the second aspect, a pH adjustment device is provided at the outlet of the water tank to maintain the pH value of the water discharged from the water tank at 8-9 by adding alkaline substances.

[0035] According to the preferred embodiment of the second aspect, a turbulence impeller is provided at the inlet of the channel formed between the tubular anode and the cylindrical cathode of each electrode (i.e., the inlet near the end of the inlet tank). The turbulence impeller helps to reduce the effect of concentration polarization. Specifically, the turbulence blades make the water flow more uniform and generate lateral shear force, reducing the scaling and adhesion of suspended pollutants to the iron anode and increasing the flocculation efficiency.

[0036] Thirdly, the present invention provides an electrocoagulation method, wherein the method is performed using the electrocoagulation system provided in the second aspect of the present invention, and the method includes:

[0037] The wastewater to be treated is fed into the inlet tank and the pH value is adjusted to 4-5 to obtain the wastewater to be flocculated.

[0038] Alternating current is used to electrocoagulate the wastewater to be flocculated in the channel formed between the tubular anode and the cylindrical cathode, resulting in flocculated water. During the electrocoagulation process, the effective current density of the tubular anode (referring to the current density of the anode during the electrode conduction cycle) does not exceed 2.0 mA / cm². 2 ;

[0039] The water after flocculation treatment enters the outlet tank.

[0040] According to a preferred embodiment of the third aspect, the pH of the wastewater to be treated is adjusted to 4-5 by adding sulfuric acid.

[0041] According to a preferred embodiment of the third aspect, the method further includes: after the flocculated water enters the effluent tank, the pH value is adjusted to 8-9 before being discharged for coagulation and clarification; adjusting the pH value of the flocculated water to 8-9 can achieve the removal of Fe 2+ It is converted into Fe(OH)2 to further enhance flocculation;

[0042] More preferably, the pH of the flocculated water is adjusted to 8-9 by adding sodium hydroxide and / or potassium hydroxide.

[0043] According to the preferred embodiment of the third aspect, during the electrocoagulation process, the effective current density (referring to the current density of the anode during the electrode conduction cycle) of the tubular anode is 1-2 mA / cm². 2 .

[0044] According to a preferred embodiment of the third aspect, the method further includes: monitoring the effective current during electrocoagulation using alternating current in the channel formed between the tubular anode and cylindrical cathode of each electrode when the wastewater to be flocculated enters each electrode; and cleaning the cylindrical cathode of each electrode after the effective current decay reaches the current decay threshold.

[0045] More preferably, the current decay threshold is 10%-15% of the effective current when the electrode is operating normally.

[0046] According to the preferred embodiment of the third aspect, during the electrocoagulation process, the water flow velocity in the channel formed between the tubular anode and the cylindrical cathode of the electrode does not exceed 0.1 m / s;

[0047] More preferably, during the electrocoagulation process, the water flow velocity in the channel formed between the tubular anode and the cylindrical cathode of the electrode is 0.02-0.1 m / s.

[0048] According to the preferred embodiment of the third aspect, the frequency of the alternating current is 30-100 Hz.

[0049] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0050] 1. By using special electrode settings and appropriate anodic current density to achieve adequate polarization deflection, and then using acid-assisted dissolution, the problem of anodic passivation is effectively solved, thus solving the energy loss problem caused by anodic passivation.

[0051] 2. By using special electrode settings in conjunction with appropriate anode current density, a suitable polarization deflection is achieved. This suitable polarization deflection increases the cathode's ability to treat hard wastewater. Furthermore, the cylindrical pluggable cathode is easy to handle, effectively controlling cathode adsorption passivation and solving the energy loss problem caused by cathode passivation.

[0052] 3. No chemical cleaning is required, which significantly increases the operating cycle and avoids the problem of localized corrosion and damage to the iron anode caused by chemical cleaning.

[0053] 4. No electrode is used during the electrocoagulation process, thus avoiding the problem of cathode passivation products existing simultaneously at both electrodes due to electrode conduction.

[0054] 5. It has no strict requirements on wastewater indicators and has a wide range of applications. Attached Figure Description

[0055] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0056] Figure 1 This is a schematic diagram of the structure of an electrode provided in an embodiment of the present invention.

[0057] Figure 2 This is a schematic diagram of the structure of an electrocoagulation system provided in an embodiment of the present invention.

[0058] Figure 3 This is a schematic diagram illustrating polarization deflection.

[0059] Figure 4 This is a phase sampling diagram of the AC power supply.

[0060] Figure 5 This is a schematic diagram illustrating the electrode potential after rectification.

[0061] Figure 6 This is a schematic diagram of the electrocoagulation system provided in Example 1.

[0062] Figure 7 This is a schematic diagram illustrating the process of electrode A being turned on and electrode B being turned off.

[0063] Figure 8 This is a schematic diagram of the process where electrode B is turned on and electrode A is turned off.

[0064] Figure 9 This is a schematic diagram of a traditional plate-type DC electrocoagulation system.

[0065] Figure 10This is a schematic diagram of a traditional plate-type AC flocculation system. Detailed Implementation

[0066] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0067] Cathodic and anode passivation are common problems in iron anode electrocoagulation. These passivations severely hinder the successful implementation of electrocoagulation. Therefore, the inventors have dedicated themselves to solving the passivation problems of the anode and cathode in iron anode batteries during electrocoagulation. The specific reactions of anode and cathode passivation during iron anode electrocoagulation are as follows:

[0068] The reaction of anodic passivation:

[0069] (1)

[0070] (2)

[0071] (3)

[0072]

[0073] The reaction of cathodic adsorption passivation:

[0074]

[0075] (2)

[0076] (3) Mg 2+ +2OH - →Mg(OH)2, Ca 2+ +2OH - →Ca(OH)2

[0077] (4)

[0078] There is a fundamental difference between cathodic passivation and anodic passivation. Anodic passivation involves a reaction between the anode material and the ionization products of water. The anode material combines with oxygen and hydroxide ions to form passivation products with chemical bonds, which cannot be removed by mechanical or physical methods. Furthermore, the passivation product FeO is a p-type semiconductor material without a corresponding n-type semiconductor contact, thus hindering current conduction on the anode surface and increasing the risk of Fe degradation. 2+The difficulty in releasing the flocculant limits its production, and the electric field strength has a positive correlation with the passivation of the iron anode. The cathode adsorbent passivation products are unrelated to the cathode's bulk composition; they are produced by cathode byproduct reactions. These passivation products are a type of physical adsorption scale, which can be removed using mechanical methods, thereby eliminating the obstruction to current conduction.

[0079] While existing electrocoagulation processes have made technical improvements in electrode shape and conduction methods, playing a role in delaying electrode passivation, most are based on concentration polarization considerations, neglecting the polarization effect of the electrostatic field (conservative force field) on the water-electrolyte. Water molecules and hydroxide ions are dipoles. After the initial ionization of water molecules to form hydroxide ions, under the influence of an external electric field, an increase in the external electric field strength will lead to an increase in the polarization of OH groups in the Stern layer. - Atomic polarization. OH - The positively charged center of mass H moves in the direction of the electric field, while the negatively charged center of mass oxygen moves in the opposite direction, increasing the distance between the shared electron pairs and hydrogen atoms, thus causing OH... - The Coulomb force between the hydrogen atom and the shared electron pair weakens, while the Coulomb force between the oxygen atom and the shared electron pair strengthens. This change in the Coulomb force enhances the positive charge of the hydrogen atom and the negative charge of the oxygen atom. OH - The bonding mechanism between hydrogen and oxygen atoms changed from primarily Coulomb forces between shared electron pairs to primarily Coulomb forces between positive and negative ions. OH - The polar covalent bonds undergo heterolytic cleavage, reducing the Fe... 2+ With O 2- In OH - The potential energy barrier for the reaction. Because Fe 2+ and O 2- The Gibbs free energy of the reaction is much greater than that of H. + and O 2- The Gibbs free energy of the reaction, and the fact that matter always transforms into a more stable state, therefore, the Fe reaction occurs. 2+ Replace H + The reaction in Fe 2+ and O 2- They bond together and form a new surface film product, FeO. It is impossible to completely solve the problem of iron anode passivation without considering the electric field strength.

[0080] Based on this, the present invention improves the electrocoagulation process based on the principle of alternating current conduction, and establishes a completely new stack structure to make the cathode and anode polarization uniformly deflected, achieving weak anode polarization and strong cathode polarization; and in terms of cathode structure design, cathode polarization products can be easily mechanically or manually processed, thereby solving the problem of cathode passivation and anode passivation hindering the conduction of ferroelectric coagulation current.

[0081] See Figure 1 A specific embodiment of the present invention provides an electrode for electrocoagulation, wherein the electrode includes a tubular anode 11 and a detachable cylindrical cathode 12 sleeved inside the tubular anode, the central axis of the cylindrical cathode 12 coinciding with the central axis of the tubular anode 11.

[0082] The cylindrical cathode 12 is made of a metal that does not react with water, and the tubular anode 11 is made of iron. The ratio of the inner radius of the tubular anode 11 to the outer radius of the cylindrical cathode 12 is 2-4, and the difference between the inner radius of the tubular anode 11 and the outer radius of the cylindrical cathode 12 is 1-2.5 cm.

[0083] Furthermore, the length of the portion where the cylindrical cathode 12 and the tubular anode 11 are fitted together is 5-20 times the inner radius of the tubular anode 11.

[0084] Furthermore, the inner radius of the tubular anode 11 is 2-5 cm.

[0085] Furthermore, the cylindrical cathode 12 is made of stainless steel.

[0086] The aforementioned electrocoagulation electrode achieves a cathode interface field strength 2-4 times that of the anode interface by setting the ratio of the inner radius of the tubular iron anode 11 to the outer radius of the cylindrical cathode 12 to 2-4. Furthermore, the difference between the inner radius of the tubular anode 11 and the outer radius of the cylindrical cathode 12 is 1-2.5 cm. This lays the foundation for achieving appropriate reverse polarization of the electrode, thus preventing anode passivation during electrocoagulation and increasing the cathode's ability to treat hard wastewater. Additionally, the detachable cylindrical cathode 12, housed within the tubular anode 11, facilitates disassembly and removal of cathode passivation scale, helping to control cathode adsorption passivation.

[0087] See Figure 2 A specific embodiment of the present invention provides an electrocoagulation system, wherein the electrocoagulation system includes:

[0088] Water inlet tank 21, water outlet tank 22, A electrode group 23, B electrode group 24, A diode switch 25 and B diode switch 26;

[0089] Electrode group A 23 and electrode group B 24 each include one or more electrodes connected in parallel or in series; each electrode includes a tubular anode with a circular cross-section and a detachable cylindrical cathode fitted inside the tubular anode, the central axis of the cylindrical cathode coincides with the central axis of the tubular anode; the cylindrical cathode is made of a non-reactive metal, the tubular anode is made of iron, the ratio of the inner radius of the tubular anode to the outer radius of the cylindrical cathode is 2-4, and the difference between the inner radius of the tubular anode and the outer radius of the cylindrical cathode is 1-2.5 cm;

[0090] The inlet tank 21 is connected to the outlet tank 22 through the channels formed between the tubular anode and the cylindrical cathode of each electrode, so as to realize the parallel connection of the water passage between the inlet tank 21 and the outlet tank 22.

[0091] One phase of the three-phase AC power supply is connected to the anode interface of electrode group A 23 and the cathode interface of electrode group B 24, respectively. Diode switch A 25 is located on the connection line between the anode interface of electrode group A 23 and the three-phase AC power supply. The cathode interface of electrode group A 23 and the anode interface of electrode group B 24 are both connected to the neutral point of the three-phase AC power supply. Diode switch B 26 is located on the connection line between the anode interface of electrode group B 24 and the three-phase AC power supply. This achieves reverse parallel connection of the circuit currents of electrode group A 23 and electrode group B 24.

[0092] The inlet tank 21 is equipped with a pH adjustment device 211 to adjust the pH value of the water in the inlet tank to 4-5.

[0093] In the aforementioned electrocoagulation system, the use of special electrodes causes the electric field lines to deflect uniformly from the outside in, creating a closed loop, thereby driving the reverse deflection of the electric field strength. For example... Figure 3 As shown, electric field lines originate from positive charges and terminate at negative charges. According to Gauss's law, the formula for the electric field strength around any equipotential surface P of the cathode is: in, Let ∑q be the charge density per unit length of the cathode column, ∑q be the charge on the cylindrical electrode formed by the current intensity, l be the length of the portion of the cylindrical cathode and tubular anode that are connected together, i.e., the effective length of the conductive surface of the cylindrical electrode in contact with the water, R be the distance from the equipotential surface surrounding the cylindrical cathode to the center point of the cylindrical cathode, d be the inner radius of the tubular anode, r be the outer radius of the cylindrical cathode, and ε0 be the dielectric constant. The electric field strength is minimum when R = d (point Q) and maximum when R = r (point O). In the above electrocoagulation system, d / r is set to 2-4, so that the electric field strength at the cathode interface is 2-4 times that at the anode interface. Combined with the difference of 1-2.5 cm between the inner radius of the tubular anode and the outer radius of the cylindrical cathode, this lays the foundation for achieving appropriate reverse bias of the electrode polarization.

[0094] The aforementioned electrocoagulation system, together with any one phase and the neutral point of a three-phase AC power supply, forms a closed loop (see...). Figure 4 The design employs electrode group A (23) and electrode group B (24) connected to the two poles of the power supply. A diode switch is also installed at the output terminals of electrode groups A (23) and B (24). Under alternating current, electrode groups A (23) and B (24) achieve π-cycle cyclic conduction. (See [reference]). Figure 5 During the conduction process, the anodes of each electrode in electrode group A 23 and electrode group B 24 are always at a high potential rectifier terminal. The appropriate number of electrodes in electrode group A 23 and electrode group B 24 can be determined according to the wastewater treatment volume and connected in parallel in the same direction to form a water circuit. The circuit currents of electrode group A 23 and electrode group B 24 are connected in parallel in opposite directions.

[0095] Under alternating current, a peak field strength will inevitably be generated at the wave crest, promoting the formation of a small amount of FeO. At the same time, dissolved oxygen in the water will also cause non-dense oxidation of the iron body. By installing a pH adjustment device 211 in the inlet water tank 21 to maintain the pH value of the water in the inlet water tank at 4-5, when the stack is turned off, FeO dissolves to form Fe. 2+ H2O and other substances prevent the FeO passivation film from accumulating and thickening.

[0096] The aforementioned electrocoagulation system achieves appropriate polarization deflection through special electrode settings, which, combined with acid-assisted dissolution, lays the foundation for effectively solving the anode passivation problem. At the same time, the appropriate polarization deflection increases the cathode's ability to treat hard wastewater, and the pluggable design of the cathode makes it easy to clean the passivation film, thus effectively solving the cathode passivation problem.

[0097] Furthermore, the length of the portion where the cylindrical cathode and tubular anode are fitted together is 5-20 times the inner radius of the tubular anode.

[0098] Furthermore, the inner radius of the tubular anode is 2-5 cm.

[0099] Furthermore, the cylindrical cathode is made of stainless steel.

[0100] Furthermore, electrode group A 23 and electrode group B 24 are the same.

[0101] Furthermore, all electrodes are identical.

[0102] Furthermore, the inlet tank 21 and outlet tank 22 are equipped with multiple sleeves to fix the cylindrical cathodes and tubular anodes of each electrode. Specifically, the inlet tank 21 is provided with multiple cathode fixing sleeves penetrating two opposite sides of the inlet tank 21, and the outlet tank 22 is provided with multiple cathode fixing sleeves penetrating two opposite sides of the outlet tank 22. The central axis of each cathode fixing sleeve is parallel to the central axis of the cylindrical cathode of the electrode, and the cathode fixing sleeves on the inlet tank 21 and the outlet tank 22 are arranged opposite to each other. The cylindrical cathode of each electrode is respectively inserted through one cathode fixing sleeve in the inlet tank 21 and one cathode fixing sleeve in the outlet tank 22 to fix the cylindrical cathode, and at least one end of the cylindrical cathode extends out of the cathode fixing sleeve to facilitate the insertion and removal of the cylindrical cathode. At least one of the inlet tank 21 and the outlet tank 22 is provided with multiple anode fixing sleeves to fix the tubular anodes of each electrode.

[0103] Furthermore, the inlet tank 21 is connected to the outlet tank 22 through the channels formed between the tubular anode and the cylindrical cathode of each electrode in the following manner:

[0104] The inlet tank 21, each electrode, and the outlet tank 22 are arranged from bottom to top.

[0105] The top surface of the water inlet tank 21 is provided with multiple fluid channel openings that match the size of the tubular anode of each electrode, and the fluid channel openings are provided with anode fixing sleeves. The water inlet tank 21 is provided with multiple cathode fixing sleeves that penetrate the top and bottom surfaces of the water inlet tank 21 and match the size of the tubular anode of each electrode, and the cathode fixing sleeves are fixed to the bottom surface of the water inlet tank 21.

[0106] The bottom surface of the water outlet tank 22 is provided with multiple fluid channel openings that match the size of the tubular anode of each electrode, and the fluid channel openings are provided with anode fixing sleeves. The water outlet tank 22 is provided with multiple cathode fixing sleeves that penetrate the top and bottom surfaces of the water outlet tank 22 and match the size of the tubular anode of each electrode, and the cathode fixing sleeves are fixed to the top surface of the water outlet tank 22.

[0107] The tubular anode of each electrode is fixed between the inlet tank 21 and the outlet tank 22 by an anode fixing sleeve of the inlet tank 21 and an anode fixing sleeve of the outlet tank 22. The anode fixing sleeves of the inlet tank 21 and the outlet tank 22 can achieve the sealing of the interface between the tubular anode of each electrode and the inlet tank 21 and the outlet tank 22 to prevent water from overflowing from the interface.

[0108] Each cylindrical cathode is fixed by inserting into a cathode fixing sleeve in the inlet tank 21 and a cathode fixing sleeve in the outlet tank 22, and at least one end of the cylindrical cathode extends out of the sleeve to facilitate insertion and removal of the cylindrical cathode.

[0109] Water in the inlet tank 21 flows through the fluid channels on the top surface of the inlet tank 21 to the channels formed between the tubular anode and the cylindrical cathode of each electrode, and then flows into the outlet tank 22 through the fluid channels on the bottom surface of the outlet tank 22.

[0110] Furthermore, insulated water tanks are selected for inlet tank 21 and outlet tank 22.

[0111] Furthermore, insulating sleeves are selected for both the anode fixing sleeve and the cathode fixing sleeve.

[0112] Furthermore, a pH adjustment device 221 is provided at the outlet of the water tank 22 to maintain the pH value of the water discharged from the water tank 22 at 8-9 by adding alkaline substances.

[0113] Furthermore, a turbulence impeller is installed at the entrance of the channel formed between the tubular anode and the cylindrical cathode of each electrode (i.e., the entrance near the water inlet tank). The turbulence impeller helps to reduce the effect of concentration polarization. Specifically, the turbulence blades make the water flow more uniform and generate lateral shear force, reducing the scaling and adhesion of suspended pollutants to the iron anode and increasing flocculation efficiency.

[0114] A specific embodiment of the present invention provides an electrocoagulation method, wherein the method uses the electrocoagulation system provided in the above embodiments of the present invention, and the method includes:

[0115] The wastewater to be treated is fed into the inlet tank 21 and the pH value is adjusted to 4-5 to obtain the wastewater to be flocculated.

[0116] Alternating current is used to electrocoagulate the wastewater to be flocculated in the channel formed between the tubular anode and the cylindrical cathode, resulting in flocculated water. During the electrocoagulation process, the effective current density of the tubular anode (referring to the current density of the anode during the electrode conduction cycle) does not exceed 2.0 mA / cm². 2 ;

[0117] The water after flocculation treatment enters the outlet tank 22.

[0118] The aforementioned electrocoagulation method achieves appropriate polarization deflection through special electrode settings and suitable effective anode current density, which, combined with acid-assisted dissolution, effectively solves the anode passivation problem. At the same time, the polarization deflection increases the cathode's ability to treat hard wastewater, and the pluggable design of the cathode makes it easy to clean the passivation film, thus effectively solving the cathode passivation problem.

[0119] Furthermore, the pH of the wastewater to be treated is adjusted to 4-5 by adding sulfuric acid.

[0120] Furthermore, the method also includes: after the flocculation-treated water enters the effluent tank 22, the pH value is adjusted to 8-9 before being discharged for coagulation and clarification; adjusting the pH value of the flocculation-treated water to 8-9 can achieve the removal of Fe 2+ It is converted into Fe(OH)2 to further enhance flocculation;

[0121] Furthermore, the pH value is adjusted to 8-9 by adding sodium hydroxide and / or potassium hydroxide.

[0122] Furthermore, during the electrocoagulation process, the effective current density of the tubular anode (referring to the current density of the anode during the electrode conduction cycle) is 1-2 mA / cm². 2 .

[0123] Furthermore, the method also includes: monitoring the effective current during electrocoagulation using alternating current in the channel formed between the tubular anode and cylindrical cathode of each electrode when the wastewater to be flocculated enters. After the effective current decay reaches the current decay threshold, the cylindrical cathodes of each electrode are descaled. Further, the current decay threshold is 10%-15% of the effective current when the electrodes are working normally (i.e., when the cathode and anode are not scaled). Although polarization deflection prevents the formation of an anode passivation film, it cannot solve the cathode adsorption passivation problem. When the calcium and magnesium hardness in the wastewater is high, calcium and magnesium scale will inevitably be adsorbed at the cathode. Using the degree of current decay as a trigger condition to treat cathode scale can more scientifically and rationally solve the cathode passivation problem.

[0124] Furthermore, during the electrocoagulation process, the water flow velocity in the channel formed between the tubular anode and the cylindrical cathode of the electrode does not exceed 0.1 m / s;

[0125] Furthermore, during the electrocoagulation process, the water flow velocity in the channel formed between the tubular anode and the cylindrical cathode of the electrode is 0.02-0.1 m / s.

[0126] Furthermore, the frequency of alternating current is 30-100 Hz.

[0127] Example 1

[0128] This embodiment provides an electrode.

[0129] The electrode includes a tubular anode and a detachable cylindrical cathode fitted inside the tubular anode. The central axis of the cylindrical cathode coincides with the central axis of the tubular anode. The cylindrical cathode is made of 316 stainless steel, and the tubular anode is made of iron. The inner radius of the tubular anode is 3cm, the outer radius of the cylindrical cathode is 1cm, the length of the tubular anode is 20cm, and the cylindrical cathode is longer than the tubular anode. The length of the portion of the cylindrical cathode fitted inside the tubular anode is 20cm.

[0130] Example 2

[0131] This embodiment provides an electrocoagulation system.

[0132] like Figure 6 As shown, the electrocoagulation system includes an inlet tank, an outlet tank, an A electrode group, a B electrode group, an A diode switch, and a B diode switch; the A electrode group and the B electrode group each include an electrode provided in Embodiment 1, namely the A electrode and the B electrode, respectively. The A electrode group and the B electrode group are the same, and all electrodes are the same.

[0133] The inlet tank, electrodes, and outlet tank are arranged from bottom to top. The inlet tank is connected to the outlet tank through channels formed between the tubular anodes and cylindrical cathodes of each electrode. Specifically: the top surface of the inlet tank has multiple fluid channel openings matching the size of the tubular anodes of each electrode, and each fluid channel opening is equipped with an anode fixing sleeve; the inlet tank has multiple cathode fixing sleeves that penetrate the top and bottom surfaces of the inlet tank and match the size of the tubular anodes of each electrode, and these cathode fixing sleeves are fixed to the bottom surface of the inlet tank; the bottom surface of the outlet tank has multiple fluid channel openings matching the size of the tubular anodes of each electrode, and each fluid channel opening is equipped with an anode fixing sleeve; the outlet tank has multiple cathode fixing sleeves that penetrate the top and bottom surfaces of the outlet tank and match the size of the tubular anodes of each electrode, and these cathode fixing sleeves are fixed to the top surface of the outlet tank; the tubular anode of each electrode is fixed to the inlet tank through one anode fixing sleeve in the inlet tank and one anode fixing sleeve in the outlet tank. Between the inlet and outlet water tanks, and through the anode fixing sleeves of the inlet and outlet water tanks, the interfaces between the tubular anodes of each electrode and the inlet and outlet water tanks are sealed to prevent water from overflowing from the interfaces. The cylindrical cathode of each electrode is fixed by inserting into one cathode fixing sleeve of the inlet water tank and one cathode fixing sleeve of the outlet water tank, and at least one end of the cylindrical cathode protrudes from the sleeve to facilitate insertion and removal of the cylindrical cathode. Water in the inlet water tank flows through the fluid channel openings on the top surface of the inlet water tank to the channels formed between the tubular anodes and cylindrical cathodes of each electrode, and then flows into the outlet water tank through the fluid channel openings on the bottom surface of the outlet water tank. The inlet and outlet water tanks are made of insulated water tanks, and the anode fixing sleeves and cathode fixing sleeves are also made of insulated sleeves.

[0134] One phase of the three-phase AC power supply is connected to the anode interface of electrode A and the cathode interface of electrode B, respectively, and diode switch A is set on the connection line between the anode interface of electrode A and the three-phase AC power supply; the cathode interface of electrode A and the anode interface of electrode B are both connected to the neutral point of the three-phase AC power supply, and diode switch B is set on the connection line between the cathode interface of electrode A and the three-phase AC power supply.

[0135] The inlet tank is equipped with a pH adjustment device to adjust the pH value of the water in the inlet tank to 4-5.

[0136] A pH adjustment device is installed at the outlet of the water tank to maintain the pH value of the water discharged from the tank at 8-9 by adding alkaline substances.

[0137] A turbulence impeller is installed at the entrance of the channel formed between the tubular anode and the cylindrical cathode of each electrode (i.e., the entrance near the end of the water inlet tank).

[0138] Example 3

[0139] This embodiment provides an electrocoagulation method.

[0140] This method uses the electrocoagulation system provided in Example 2, and the method includes:

[0141] 1) Input the wastewater to be treated (domestic sewage and desulfurization wastewater effluent from the primary clarifier) ​​into the inlet tank and adjust the pH value to 4-5 by adding sulfuric acid to obtain the wastewater to be flocculated;

[0142] 2) Use alternating current to electrocoagulate the wastewater to be flocculated in the channel formed between the tubular anode and the cylindrical cathode of each electrode to obtain flocculated water; during the process, monitor the effective current of the wastewater to be flocculated in the channel formed between the tubular anode and the cylindrical cathode of each electrode during the electrocoagulation process using alternating current.

[0143] The total water flow rate is 1.8m. 3 The water flow rate within the channel formed between the tubular anode and cylindrical cathode of each electrode is 0.9 m³ / h. 3 / h (the water flow velocity in the channel formed between the tubular anode and the cylindrical cathode of each electrode is approximately 0.1m / s);

[0144] The effective current density during normal operation of the anode (referring to the current density of the anode during the electrode conduction cycle) is 2 mA / cm². 2 The frequency of alternating current is 50 Hz.

[0145] Among them, when the effective current decay reaches the current decay threshold (15% of the effective current when the electrode is working normally), the cylindrical cathodes of each electrode are cleaned.

[0146] 3) After flocculation treatment, the water enters the outlet tank, where carbon dioxide is added to adjust the pH value to 9 before being discharged into the coagulation and clarification equipment for coagulation and clarification.

[0147] In the electrocoagulation method provided in this embodiment, the current density generated when the anode is working normally is 2 mA / cm². 2 The effective current density formed at the cathode is 2 × 3 = 6 mA / cm². 2 The effective current intensity during the electrode conduction period is I = 2πdσ e ·l=2×3.14×3×2×20=753.6mA, and the total loop current decay threshold is approximately 753.6mA×15%=113mA.

[0148] In the electrocoagulation method provided in this embodiment, the turbulence impeller is passively rotated under the propulsion of water, so that the longitudinal straight water flow can achieve a spiral upward. The water flow enters the water tank from the inlet tank and finally flows out to the coagulation and clarification device.

[0149] In the electrocoagulation method provided in this embodiment, see [reference needed]. Figure 7 When the voltage on the power supply side is greater than the turn-on voltage of diode A, electrode A conducts, and the reverse potential of diode B is always greater than the forward potential, so electrode B is cut off. Within one 2π cycle, the AC power supply achieves a positive conduction angle of π. The iron anode is at a high potential, generating flocculated iron ions, while the 316L anode is at a low potential, corresponding to the loss of electrons at the anode, and hydrogen ions gain electrons to produce hydrogen gas. (See also...) Figure 8 When the voltage on the power supply side is greater than the turn-on voltage of diode B, electrode B conducts, and the reverse potential of diode A is always greater than the forward potential, so electrode A is cut off. Within one 2π cycle, the AC power supply achieves a negative conduction angle of π, with the iron anode at a high potential, generating flocculated iron ions, and the 316L electrode at a low potential, corresponding to the loss of electrons at the anode, while hydrogen ions gain electrons to produce hydrogen gas. In summary, within one 2π cycle, both electrodes A and B achieve high iron potential conduction, and this cycle repeats in 2π periods, as described in the diagram. Figure 5 ,accomplish

[0150]

[0151] In the electrocoagulation method provided in this embodiment, flocculant is released at the anode. The flocculant bridges and adsorbs impurities in the water to form colloidal clusters. These colloidal clusters interact with Fe(OH)2 generated under pH adjustment at the total outlet and flow into the coagulation and clarification device, achieving enhanced flocculation and solid-liquid separation. Water samples after solid-liquid separation are taken for analysis, and the results are shown in Tables 1 and 2.

[0152] Table 1 Domestic Sewage Treatment

[0153] Laboratory items Before processing After processing Removal rate <![CDATA[Total hardness / (mg·L -1 )]]> 490 263 46.33 Turbidity / degree 187.0 8.3 95.56 <![CDATA[COD / (mg·L -1 )]]> 793.5 280.2 64.69 <![CDATA[Suspended solids / (mg·L -1 )]]> 234.2 1.7 99.27

[0154] Table 2 Treatment of Effluent from Primary Clarification Tank for Desulfurization Wastewater

[0155] Laboratory items Before processing After processing Removal rate <![CDATA[Hardness (mg·L -1 )]]> 5330 1939 63.62 Turbidity / degree 77.0 2.2 97.14 <![CDATA[COD / (mg·L -1 )]]> 869.7 77.5 91.09 <![CDATA[Suspended solids / (mg·L -1 )]]> 107.2 1.1 98.97

[0156] The hardness and COD purification results of the effluent from the primary clarifier of desulfurization wastewater are better than those of domestic sewage. This is because the magnesium content in the effluent from the primary clarifier of desulfurization wastewater is relatively high. The final step of increasing the pH converts magnesium ions into magnesium hydroxide, and the interaction between magnesium hydroxide and flocs enhances the flocculation effect. Furthermore, unlike organic wastewater, the COD in the effluent from the primary clarifier of desulfurization wastewater is mainly formed by sulfites, which are easily removed by electrochemical methods. Additionally, during the treatment process of the effluent from the primary clarifier of desulfurization wastewater, the device operates for approximately 10 hours before the effective current decline reaches the current decline threshold. At this point, the system needs to be shut down to treat the cathode scaling, replace the cathode column with a new one, and the old cathode column is treated and put back into use.

[0157] When the system was shut down to treat the scale buildup on the cathode, the passivation status of the anode of the electrode was tested, and no passivation was detected on the anode.

[0158] Experimental Example 1

[0159] In this experimental example, methods one, two, three, and four were used to perform electrocoagulation treatment on a saturated sodium sulfate solution with zero hardness.

[0160] Method 1: Using the electrocoagulation system provided in Example 2;

[0161] The specific steps are as follows:

[0162] 1) Input the wastewater to be treated into the inlet tank and adjust the pH value to 4-5 by adding sulfuric acid to obtain the wastewater to be flocculated;

[0163] 2) Use alternating current to electrocoagulate the wastewater to be flocculated in the channel formed between the tubular anode and the cylindrical cathode of each electrode to obtain flocculated water; during the process, monitor the effective current of the wastewater to be flocculated in the channel formed between the tubular anode and the cylindrical cathode of each electrode using alternating current during electrocoagulation, and record the time it takes for the effective current to decline to 25% of the effective current when the electrode is working normally.

[0164] The water flow rate within the channel formed between the tubular anode and the cylindrical cathode of each electrode is 0.9 m³. 3 / h (the water flow velocity in the channel formed between the tubular anode and the cylindrical cathode of each electrode is approximately 0.1m / s);

[0165] The effective current density during the electrode conduction cycle when the anode is operating normally is controlled to be 2.45 mA / cm². 2 (i.e., effective current of 925mA during normal operation), 3.32mA / cm 2 (i.e., effective current of 1250mA during normal operation), 4.78mA / cm 2 (i.e., effective current of 1800mA during normal operation), 6.48mA / cm 2 (i.e., effective current of 2440mA during normal operation), 8.88mA / cm 2 (i.e., effective current of 3345mA during normal operation), 11.80mA / cm 2 (i.e., effective current of 4445mA during normal operation), 15.59mA / cm 2 (i.e., the effective current during normal operation is 5876mA); the frequency of the alternating current is 50Hz.

[0166] 3) After flocculation treatment, the water enters the outlet tank, where sodium hydroxide is added to adjust the pH value to 9.0 before being discharged for coagulation and clarification.

[0167] Method 2: The electrocoagulation system provided in Example 2 is used. The only difference between Method 1 and Method 2 is that the pH value of the wastewater to be treated is not adjusted when it enters the inlet tank, and the pH value of the water after flocculation treatment is not adjusted when it enters the outlet tank.

[0168] Method 3: Using a traditional plate-type DC electrocoagulation system, such as... Figure 9 As shown, the specific steps are as follows:

[0169] The wastewater to be treated enters the iron anode plate (the area of ​​the iron anode plate is 377 cm²). 2 Electrocoagulation is performed between the iron anode plate and the 316 stainless steel cathode plate to obtain flocculated water. During the process, the effective current of the wastewater to be treated entering the electrocoagulation process between the iron anode plate and the 316 stainless steel cathode plate is monitored, and the time taken for the effective current to decline to reach 25% of the effective current when working normally is recorded.

[0170] The total water flow velocity is 0.1 m / s;

[0171] Electrocoagulation was performed using direct current, with the effective current density controlled at 2.45 mA / cm² during normal anode operation. 2 (i.e., effective current of 925mA during normal operation), 3.32mA / cm 2 (i.e., effective current of 1250mA during normal operation), 4.78mA / cm 2 (i.e., effective current of 1800mA during normal operation), 6.48mA / cm 2 (i.e., effective current of 2440mA during normal operation), 8.88mA / cm 2 (i.e., effective current of 3345mA during normal operation), 11.8mA / cm 2 (i.e., effective current of 4445mA during normal operation), 15.59mA / cm 2 (i.e., the effective current during normal operation is 5876mA).

[0172] Method 4: Using a traditional plate-type AC flocculation system, such as... Figure 10 As shown, the specific steps are as follows:

[0173] The wastewater to be treated enters the iron anode plate (the area of ​​the iron anode plate is 377 cm²). 2 ) and iron cathode plate (the area of ​​the iron cathode plate is 377cm²) 2 Electrocoagulation is performed between the two iron plates to obtain flocculated water. During the process, the effective current between the two iron plates is monitored, and the time taken for the effective current to decline to reach 25% of the effective current when working normally is recorded.

[0174] The total water flow velocity is 0.1 m / s;

[0175] Electrocoagulation was performed using alternating current, with the effective current density controlled to be 2.45 mA / cm² during the electrode conduction cycle when the anode was operating normally. 2 (i.e., effective current of 925mA during normal operation), 3.32mA / cm 2 (i.e., effective current of 1250mA during normal operation), 4.78mA / cm 2 (i.e., effective current of 1800mA during normal operation), 6.48mA / cm 2 (i.e., effective current of 2440mA during normal operation), 8.88mA / cm 2 (i.e., effective current of 3345mA during normal operation), 11.8mA / cm 2 (i.e., effective current of 4445mA during normal operation), 15.59mA / cm 2 (i.e., the effective current during normal operation is 5876mA); the frequency of the alternating current is 50Hz.

[0176] The results are shown in Table 3. Under several methods, the monitoring current declined to varying degrees with increasing current density. In this experimental example, the hardness of the wastewater to be treated was zero, and there was almost no anion adsorption passivation during electrocoagulation. The decline in the monitoring current was due to anodic passivation. Method 3 showed the fastest decline, while Method 1 showed the slowest. This indicates that Method 3, with the iron anode, is the fastest way to grow the passivation film. Although Method 4 delayed the current decline time, it resulted in passivation on both electrodes, making the effect less than ideal. Method 2 significantly delayed the current decline time, but could not prevent the accumulation of passivation, making it inferior to Method 1 from an operational cycle perspective.

[0177] Table 3

[0178]

[0179] Experiment Example 2

[0180] In this experiment, electrocoagulation treatment was performed on a saturated sodium sulfate solution with a hardness of 200 mg / L using methods one, two, three, and four as described in Experiment Example 1.

[0181] In Method 1 and Method 2, the effective current density during the electrode conduction cycle when the anode is operating normally is controlled to be 2.33 mA / cm², respectively. 2 (i.e., effective current of 879mA during normal operation), 3.46mA / cm 2 (i.e., effective current of 1304mA during normal operation), 4.72mA / cm 2(i.e., the effective current during normal operation is 1779mA), and the frequency of the AC current is 50Hz; in method three, the effective current density of the anode during normal operation is controlled to be 2.33mA / cm². 2 (i.e., effective current of 879mA during normal operation), 3.46mA / cm 2 (i.e., effective current of 1304mA during normal operation), 4.72mA / cm 2 (i.e., the effective current during normal operation is 1779mA); in Method 4, the effective current density during normal operation of the anode is controlled to be 2.33mA / cm². 2 (i.e., effective current of 879mA during normal operation), 3.46mA / cm 2 (i.e., effective current of 1304mA during normal operation), 4.72mA / cm 2 (i.e., the effective current during normal operation is 1779mA), and the frequency of the alternating current is 50HZ.

[0182] The results are shown in Table 4.

[0183] Table 4

[0184]

[0185] The data from Experiments 1 and 2 show that the scaling time is shorter when treating hard water compared to treating non-hard water, especially in Methods 1 and 2. This is because the polarization deflection leads to stronger adsorption passivation of the columnar cathode, hindering current conduction. On the other hand, regarding the current decay caused by hardness, the current decay caused by adsorption passivation is much smaller than that caused by anodic passivation. This is because adsorption passivation is less dense than oxidative passivation.

[0186] Experimental Example 3

[0187] Current density is a necessary condition for passivation of iron anodes, but controlling passivation solely by current density is insufficient. This is similar to some engineering applications where, although current density is controlled, frequent overhauls and acid washing are still necessary to restore the flocculation capacity of the iron anode. The reason is that while hydroxyl ion fragmentation is influenced by the magnitude of the electric field, the fragmentation rate is limited by the rate of hydrogen ion commutation at the cathode. Changing the cathode inner diameter to create an asymmetric change in the overpotential between the anode and cathode, thereby weakening the oxygen ion generation rate and further reducing the accumulation of the passivation film on the anode, is crucial.

[0188] This experimental example studies the effects of the inner radius of different tubular anodes and the outer radius of cylindrical cathodes on anode passivation.

[0189] This experimental example uses an electrocoagulation system similar to that provided in Example 2 to electrocoagulate a saturated sodium sulfate solution with a hardness of 200 mg / L. The only difference between the electrocoagulation system used in this example and that in Example 2 is the outer radius r of the cylindrical cathode. The specific steps are as follows:

[0190] 1) Input the wastewater to be treated into the inlet tank and adjust the pH value to 4-5 by adding sulfuric acid to obtain the wastewater to be flocculated;

[0191] 2) The wastewater to be flocculated enters the channel formed between the tubular anode and the cylindrical cathode of each electrode using alternating current for electrocoagulation, and the wastewater to be flocculated is obtained by electrocoagulation using alternating current to obtain flocculated water. During the process, the effective current of the wastewater to be flocculated enters the channel formed between the tubular anode and the cylindrical cathode of each electrode for electrocoagulation using alternating current, and the time taken for the effective current to decline to reach 15% of the effective current when the electrode is working normally is recorded. The passivation of the cathode and anode is also detected when the current decline reaches 15% of the effective current when the electrode is working normally.

[0192] The water flow velocity in the channel formed between the tubular anode and the cylindrical cathode of each electrode is approximately 0.1 m / s.

[0193] The effective current density (referring to the current density of the anode during the electrode conduction cycle) for controlling normal anode operation is 2 mA / cm². 2 The frequency of the alternating current is 50 Hz;

[0194] 3) After flocculation treatment, the water enters the outlet tank, where sodium hydroxide is added to adjust the pH value to 9.0 before being discharged for coagulation and clarification.

[0195] The results are shown in Table 5.

[0196] Table 5

[0197] d(cm) r(cm) d / r Time (h) for current to decrease by 15% 3 2.50 1.2 59.3 3 1.76 1.7 85.2 3 1.50 2.0 >100 3 1.20 2.5 >100 3 1.00 3.0 >100 3 0.86 3.5 >100 3 0.75 4.0 >100 3 0.67 4.5 95.3 3 0.60 5.0 63.2 3 0.55 5.5 33.5 3 0.50 6.0 9.7

[0198] In this experimental example, dr = 0.5-2.5 cm was used as the mass transfer distance limit. When d / r < 2, anodic passivation was significant, becoming the main obstacle to current conduction. When d / r > 4, current generation rapidly declined, and cathode passivation was significant. This is because the excessively small cathode bearing area caused the adsorption passivation resistance to exhibit an exponential amplification effect. In addition, an excessively small cathode area is not conducive to the removal of hardness in water. d / r = 2-4 can effectively avoid anodic passivation, effectively control the degree of cathode passivation, and is beneficial to the removal of hardness in water.

[0199] Specific embodiments have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. An electrocoagulation system, characterized in that, The electrocoagulation system includes: Water inlet tank, water outlet tank, electrode group A, electrode group B, diode switch A and diode switch B; Electrode group A and electrode group B each include one or more electrodes connected in parallel or series; each electrode includes a tubular anode and a detachable cylindrical cathode fitted inside the tubular anode, the central axis of the cylindrical cathode coinciding with the central axis of the tubular anode; wherein, the cylindrical cathode is made of a non-reactive metal, the tubular anode is made of iron, the ratio of the inner radius of the tubular anode to the outer radius of the cylindrical cathode is 2-4, and the difference between the inner radius of the tubular anode and the outer radius of the cylindrical cathode is 1-2.5 cm; The inlet tank is connected to the outlet tank through the channels formed between the tubular anode and the cylindrical cathode of each electrode; One phase of the three-phase AC power supply is connected to the anode interface of electrode group A and the cathode interface of electrode group B, respectively, and diode switch A is set on the connection line between the anode interface of electrode group A and the three-phase AC power supply; the cathode interface of electrode group A and the anode interface of electrode group B are both connected to the neutral point of the three-phase AC power supply, and diode switch B is set on the connection line between the anode interface of electrode group B and the three-phase AC power supply. The inlet tank is equipped with a pH adjustment device to adjust the pH value of the water in the inlet tank to 4-5.

2. The system according to claim 1, characterized in that, The length of the portion where the cylindrical cathode and tubular anode are fitted together is 5-20 times the inner radius of the tubular anode.

3. The system according to claim 1 or 2, characterized in that, The inner radius of the tubular anode is 2-5 cm.

4. The system according to claim 1, characterized in that, Electrode group A and electrode group B are the same.

5. The system according to claim 1, characterized in that, The inlet tank is provided with multiple cathode fixing sleeves that penetrate two opposite sides of the inlet tank, and the outlet tank is provided with multiple cathode fixing sleeves that penetrate two opposite sides of the outlet tank. The central axis of each cathode fixing sleeve is parallel to the central axis of the cylindrical cathode of the electrode, and the cathode fixing sleeves on the inlet tank and the cathode fixing sleeves on the outlet tank are arranged opposite to each other. The cylindrical cathode of each electrode is respectively inserted through one cathode fixing sleeve in the inlet tank and one cathode fixing sleeve in the outlet tank to fix the cylindrical cathode, and at least one end of the cylindrical cathode extends out of the cathode fixing sleeve to facilitate the insertion and removal of the cylindrical cathode. At least one of the inlet tank and the outlet tank is provided with multiple anode fixing sleeves to fix the tubular anodes of each electrode.

6. The system according to claim 1, characterized in that, The inlet tank is connected to the outlet tank through channels formed between the tubular anodes and cylindrical cathodes of each electrode, as follows: The inlet tank, electrodes, and outlet tank are arranged from bottom to top; The top surface of the water inlet tank is provided with multiple fluid channel openings that match the size of the tubular anodes of each electrode, and the fluid channel openings are provided with anode fixing sleeves. The water inlet tank is provided with multiple cathode fixing sleeves that penetrate the top and bottom surfaces of the water inlet tank and match the size of the tubular anodes of each electrode, and the cathode fixing sleeves are fixed to the bottom surface of the water inlet tank. The bottom surface of the water outlet tank is provided with multiple fluid channel openings that match the size of the tubular anode of each electrode, and the fluid channel openings are provided with anode fixing sleeves. The water outlet tank is provided with multiple cathode fixing sleeves that penetrate the top and bottom surfaces of the water outlet tank and match the size of the tubular anode of each electrode, and the cathode fixing sleeves are fixed to the top surface of the water outlet tank. The tubular anode of each electrode is fixed between the inlet tank and the outlet tank by an anode fixing sleeve in the inlet tank and an anode fixing sleeve in the outlet tank. The anode fixing sleeves in the inlet tank and the outlet tank can seal the interface between the tubular anode of each electrode and the inlet tank and the outlet tank to prevent water from overflowing from the interface. Each cylindrical cathode is fixed by inserting into a cathode fixing sleeve in the inlet tank and a cathode fixing sleeve in the outlet tank, and at least one end of the cylindrical cathode extends out of the sleeve to facilitate insertion and removal of the cylindrical cathode. Water in the inlet tank can flow through the fluid channels on the top surface of the inlet tank to the channels formed between the tubular anode and the cylindrical cathode of each electrode, and then flow into the outlet tank through the fluid channels on the bottom surface of the outlet tank.

7. The system according to claim 5 or 6, characterized in that, Insulated water tanks are selected for both the inlet and outlet water tanks; Insulating sleeves are selected for both anode fixing and cathode fixing.

8. The system according to claim 1, characterized in that, A pH adjustment device is installed at the outlet of the water tank to maintain the pH value of the water discharged from the tank at 8-9 by adding alkaline substances.

9. The system according to claim 1, characterized in that, A turbulence impeller is installed at the entrance of the channel formed between the tubular anode and the cylindrical cathode of each electrode.

10. An electrocoagulation method, characterized in that, This method is performed using the electrocoagulation system according to any one of claims 1-9, and the method includes: The wastewater to be treated is fed into the inlet tank and the pH value is adjusted to 4-5 to obtain the wastewater to be flocculated. The wastewater to be flocculated is electrocoagulated using alternating current in the channel formed between the tubular anode and the cylindrical cathode of each electrode, resulting in flocculated water. During the electrocoagulation process, the effective current density of the tubular anode does not exceed 2 mA / cm². 2 ; The water after flocculation treatment enters the outlet tank.

11. The method according to claim 10, characterized in that, The pH of the wastewater to be treated is adjusted to 4-5 by adding sulfuric acid.

12. The method according to claim 10, characterized in that, The method also includes: after the flocculation treatment, the water enters the outlet tank and the pH value is adjusted to 8-9 before being discharged for coagulation and clarification.

13. The method according to claim 12, characterized in that, The pH of the flocculated water is adjusted to 8-9 by adding sodium hydroxide and / or potassium hydroxide.

14. The method according to claim 10, characterized in that, During electrocoagulation, the effective current density of the tubular anode electrode is 1-2 mA / cm². 2 .

15. The method according to claim 10, characterized in that, The method also includes: monitoring the effective current during electrocoagulation using alternating current in the channel formed between the tubular anode and cylindrical cathode of each electrode when the wastewater to be flocculated enters each electrode; and cleaning the cylindrical cathode of each electrode after the effective current decay reaches the current decay threshold.

16. The method according to claim 15, characterized in that, The current decay threshold is 10%-15% of the effective current when the electrode is working normally.

17. The method according to claim 16, characterized in that, During the electrocoagulation process, the water flow velocity in the channel formed between the tubular anode and the cylindrical cathode of the electrode does not exceed 0.1 m / s.

18. The method according to claim 17, characterized in that, During the electrocoagulation process, the water flow velocity in the channel formed between the tubular anode and the cylindrical cathode of the electrode is 0.02-0.1 m / s.

19. The method according to claim 18, characterized in that, The frequency of alternating current is 30-100Hz.

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