Electrochemical treatment system and method for removing hardness from water and preventing cathode fouling

Abstract

The application discloses an electrochemical treatment system and method for removing hardness in water and preventing cathode fouling. The treatment system comprises a reactor, an anode plate and a cathode plate arranged in the reactor, a water inlet arranged at the bottom of one side of the reactor, and a water outlet arranged at the top of the other side of the reactor. The anode plate and the cathode plate are electrically connected with a direct current power supply. The outer periphery of the cathode plate is covered with cloth. The application aims to reduce the fouling at the cathode in electrochemical softening, thereby long-term and sustainedly maintaining the high-efficiency water treatment capacity of the system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of water treatment, in particular to an electrochemical treatment system and method for removing hardness in water and preventing cathode fouling. BACKGROUND

[0002] The nanofiltration concentrated water has the characteristics of high content of inorganic salt ions Ca 2+ , Mg 2+ , Cl- and SO4 2- , and large changes in water quality and quantity, and the hardness in the nanofiltration concentrated water is caused by the existence of inorganic salt ions Ca 2+ and Mg 2+ . If it is directly discharged without treatment, it will cause fouling of drainage pipes and equipment. Therefore, it is of great significance to effectively remove the hardness in the nanofiltration concentrated water. Currently, methods such as adding scale inhibitors, chemical precipitation, ion exchange and reverse osmosis are commonly used to prevent fouling. However, these technologies all have inherent shortcomings, for example, scale inhibitors are usually chelating agents, which can only delay precipitation and cannot effectively remove hardness ions, in addition to introducing organic pollutants. Chemical precipitation first needs to increase the pH value to promote the precipitation of CaCO3 or Mg(OH)2, and then reduce the pH value to neutral to recycle. The cost of chemical agents, large amount of precipitation and increase of salinity are all undesirable. Ion exchange must be backwashed with high salinity water, causing high cost and discharge burden. Reverse osmosis cannot avoid membrane fouling and high energy consumption.

[0003] The characteristics of electrochemical softening in the field of scale inhibition are that no chemical reagents need to be introduced and it is easy to automate operation. This method relies on the OH - produced by the cathode in the water electrolysis process to convert HCO3 - to CO3 2- , and further combine with Ca 2+ to form CaCO3, or directly combine with Mg 2+ to form Mg(OH)2, thereby reducing the hardness of the water. However, since OH- is directly produced at the cathode, the production process of OH- and the precipitation process of calcium and magnesium ions are synchronized on the cathode surface, so most of the solid precipitate is directly deposited on the cathode surface. During continuous operation, the scale on the cathode accumulates continuously, and after long-term operation of the system, a large amount of sediment will cover the active area on the surface of the cathode, thereby reducing the scale removal efficiency, increasing the energy consumption, and even causing the risk of short circuit between the cathode and the anode, which may lead to safety accidents and limit the practical application of electrochemical softening technology. SUMMARY

[0004] The present application aims to provide an electrochemical treatment system and method for removing hardness in water and preventing cathode fouling, reducing the fouling at the cathode in electrochemical softening, and thereby long-term and continuously maintaining the high efficiency of water treatment capacity of the system.

[0005] To solve the above technical problems, the application adopts the specific scheme of an electrochemical treatment system for removing hardness in water and preventing cathode scaling, comprising a reactor and an anode plate and a cathode plate arranged in the reactor, the bottom of one side of the reactor is provided with a water inlet, the top of the other side is provided with a water outlet, the anode plate and the cathode plate are electrically connected with a direct current power supply, and the outer periphery of the cathode plate is covered with cloth.

[0006] Preferably, the cloth is non-woven fabric, cotton cloth, linen, polyester, silk or nylon cloth.

[0007] Preferably, the cloth is polypropylene non-woven fabric, with a specification of 28-32 g / m 2 and a thickness of 0.1-0.5 mm.

[0008] Preferably, the cathode plate is a plate-shaped or mesh-shaped electrode made of any one or several of nickel, stainless steel, iron, aluminum, copper, graphite, carbon, platinum, titanium, ruthenium, palladium, iridium and titanium suboxide.

[0009] Preferably, the anode plate is a plate-shaped or mesh-shaped ruthenium iridium titanium-based electrode plate, platinum titanium-based electrode plate, lead dioxide, tin dioxide, iridium dioxide, ruthenium dioxide, boron-doped diamond or titanium suboxide electrode plate.

[0010] Preferably, the effective areas of the anode plate and the cathode plate are the same.

[0011] Preferably, the cathode plate is located close to the water inlet, and the anode plate is located close to the water outlet.

[0012] Preferably, the water inlet is connected with a peristaltic pump.

[0013] An electrochemical treatment method for removing hardness in water and preventing cathode scaling, in which OH- generated by electrolysis of water at the cathode plate precipitates calcium and magnesium ions in the water to form magnesium hydroxide and calcium carbonate precipitates, the cathode plate is wrapped with cloth, and the formation process of OH - at the cathode plate and the precipitation process of magnesium hydroxide and calcium carbonate precipitates are separated by the cloth.

[0014] Preferably, the cathode plate is wrapped with polypropylene non-woven fabric, so that the magnesium hydroxide and calcium carbonate precipitates automatically separate from the cloth and settle.

[0015] The present application uses cloth to wrap the cathode plate, separates the formation process of OH- at the cathode plate and the precipitation process of magnesium hydroxide and calcium carbonate precipitation by the cloth, thereby continuously generating OH- at the cathode plate and passing through the cloth, providing an alkaline microenvironment outside the cloth to make the calcium and magnesium ions react and precipitate. Due to the wrapping effect of the cloth, the precipitation of calcium carbonate and magnesium hydroxide does not adhere to the surface of the cathode plate, thereby effectively preventing the problem of cathode fouling, achieving effective use and protection of the cathode plate, and facilitating the continuous and long-term performance of the descaling reaction, thereby reducing the operation cost in the wastewater treatment process.

[0016] In the preferred embodiment of the present application, the cathode plate is wrapped with non-woven cloth or other materials made of hydrophobic materials, so that the generated calcium carbonate and magnesium hydroxide automatically slip off the cloth and settle at the bottom of the reactor, on the one hand, creating a microenvironment outside the cloth with low precipitation and high calcium and magnesium ion concentration, ensuring the speed of the precipitation reaction outside the cloth, and on the other hand, avoiding the deposition of the precipitate on the cloth, so that the cloth can be continuously and long-term used, further facilitating the continuous and long-term performance of the descaling reaction.

[0017] In summary, compared with the conventional electrochemical softening water treatment technology, the present application has the following beneficial effects:

[0018] (1) The present application can replace the traditional intermittent system with a continuous water flow operation mode, thereby improving the treatment efficiency.

[0019] (2) The cathode plate is wrapped with cloth, which can effectively separate the generation and crystallization process of OH - , the cathode can continuously generate OH-, and provide an alkaline microenvironment, which is conducive to the descaling reaction.

[0020] (3) It is conducive to preventing the cathode from fouling, achieving effective use and protection of the cathode, and does not require additional descaling device, thereby reducing the operation cost in the wastewater treatment process.

[0021] (4) The present application is simple to operate, easy to automate, and the cloth is inexpensive, which is conducive to industrialization and scale-up operation. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 Figure 1 is a structural schematic diagram of an electrochemical treatment system for removing hardness in water and preventing cathode fouling according to the present application;

[0023] In the figure, 1 is a sewage pool, 2 is a peristaltic pump, 3 is a direct current power supply, 4 is a drain, 5 is a reactor, 6 is an anode plate, 7 is a cathode plate, 8 is cloth, and 9 is a water inlet. DETAILED DESCRIPTION

[0024] As Figure 1As shown, the electrochemical treatment system for removing hardness and preventing cathode fouling in water of the present application mainly comprises a reactor 5, and an anode plate 6 and a cathode plate 7 arranged in parallel in the reactor 5.

[0025] The reactor 5 is a cylindrical shell with a capacity of 2L. The reactor 5 is provided with a water inlet 9 at the lower left, which is connected to the sewage pool 1 through a peristaltic pump 2; and a water outlet 4 at the upper right, which is connected to a discharge pipeline.

[0026] The size of the cathode plate 7 and the anode plate 6 is 150mm x 50mm x 1mm, and the spacing between the anode plate 6 and the cathode plate 7 is 20mm. The anode plate 6 is a ruthenium iridium titanium plate, and the cathode plate 7 is a titanium plate. The cathode plate 7 is wrapped with a cloth 8 of the same size to close it. In this embodiment, the material of the non-woven fabric cloth 8 is polypropylene, with a specification of 30g / m 2 , and a thickness of 0.3mm. The anode plate 6 and the cathode plate 7 are connected to a direct current power supply 3 arranged outside the reactor 5.

[0027] The specific implementation process of this embodiment is as follows:

[0028] The nanofiltration concentrated water to be treated is pumped into the reactor 5 through the water inlet 9 by the peristaltic pump 2. Under the action of the electric field provided by the direct current power supply 3 to the cathode plate 7 and the anode plate 6, water is electrolyzed on the cathode plate 7 to produce OH - , which reacts with HCO3 - to generate CO3 2- . At this time, calcium and magnesium ions in the water react with OH - and CO3 2- to generate calcium carbonate and magnesium hydroxide precipitates. Due to the wrapping effect of the cloth 8, the calcium carbonate and magnesium hydroxide generated near the cathode plate 7 are precipitated at the bottom of the reactor 5 and do not adhere to the surface of the cathode plate 7 and the cloth 8, effectively preventing the problem of cathode fouling. Under the action of the electric field, H + ions are generated at the anode plate 6, and after the wastewater flows through the anode plate 6 and reacts with the H + ions generated near the anode plate 6, it is discharged through the water outlet 4 after neutralization.

[0029] Example 1: The nanofiltration concentrate with hardness of 1600 mg / L, alkalinity of 750 mg / L and pH of 8.4 is pumped into the reactor 5 by the peristaltic pump 2, and the removal rate of hardness is 92% and the pH of the effluent is 7.6 when the applied current is 0.1 A and the hydraulic retention time is 8 h (the hydraulic retention time is the average residence time of the nanofiltration concentrate to be treated in the electrochemical reactor 5). The distribution of calcium hardness after electrochemical treatment is as follows: the proportion of calcium hardness on the cathode plate 7 is 0.01%, the proportion of calcium hardness on the cloth 8 is 0.023%, and the proportion of calcium hardness in the reactor 5 is 96.7%.

[0030] Example 2: The nanofiltration concentrate with hardness of 1600 mg / L, alkalinity of 750 mg / L and pH of 8.4 is pumped into the reactor 5 by the peristaltic pump 2, and the removal rate of hardness is 96% and the pH of the effluent is 7.8 when the applied current is 0.5 A and the hydraulic retention time is 12 h. The distribution of calcium hardness after electrochemical treatment is as follows: the proportion of calcium hardness on the cathode plate 7 is 0.015%, the proportion of calcium hardness on the cloth 8 is 0.05%, and the proportion of calcium hardness in the reactor 5 is 93.5%.

Claims

1. An electrochemical treatment system for removing hardness from water and preventing cathode scaling, characterized by: The invention comprises a reactor (5) and an anode plate (6) and a cathode plate (7) arranged in the reactor (5); a water inlet (9) is provided at the bottom of one side of the reactor (5); a drain outlet (4) is provided at the top of the other side; the anode plate (6) and the cathode plate (7) are electrically connected to a DC power supply (3); and the outer periphery of the cathode plate (7) is covered with a fabric (8); the fabric (8) is a polypropylene non-woven fabric with a specification of 28-32 g / m 2 , thickness is 0.1-0.5mm.

2. The electrochemical treatment system for removing hardness in water and preventing cathode scaling according to claim 1, characterized in that: The cathode plate (7) is a plate-shaped or mesh-shaped electrode made of any one or more materials of nickel, stainless steel, iron, aluminum, copper, carbon, platinum, titanium, ruthenium, palladium, and iridium.

3. The electrochemical treatment system for removing hardness in water and preventing cathode scaling according to claim 1, characterized in that: The anode plate (6) is a plate-shaped or mesh-shaped ruthenium-iridium-titanium-based electrode plate, a platinum-titanium-based electrode plate, lead dioxide, tin dioxide, iridium dioxide, ruthenium dioxide, boron-doped diamond or titanium dioxide electrode plate.

4. The electrochemical treatment system for removing hardness in water and preventing cathode scaling according to claim 1, characterized in that: The effective areas of the anode plate (6) and the cathode plate (7) are the same.

5. The electrochemical treatment system for removing hardness in water and preventing cathode scaling according to claim 1, characterized in that: The cathode plate (7) is located near the water inlet (9), and the anode plate (6) is located near the water outlet (4).

6. The electrochemical treatment system for removing hardness in water and preventing cathode scaling according to claim 1, characterized in that: The water inlet (9) is connected to a peristaltic pump (2).

7. An electrochemical treatment method for removing hardness from water and preventing cathode scaling, characterized by: The electrochemical treatment system for removing hardness in water and preventing cathode scaling as described in any one of claims 1 to 6 is used for treatment, and OH generated by electrolysis of water at the cathode plate (7) is used. - Calcium and magnesium ions in water are precipitated to form magnesium hydroxide and calcium carbonate precipitates. A cloth (8) is used to wrap the cathode plate (7). The cloth (8) separates the OH at the cathode plate (7). - The formation process and the precipitation process of magnesium hydroxide and calcium carbonate precipitation make the magnesium hydroxide and calcium carbonate precipitation automatically separate from the cloth (8) and settle. The cloth is made of polypropylene non-woven fabric.

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