CN101531411A - Method for electrochemically disinfecting gas diffusion electrode system - Google Patents

Abstract

A method for electrochemical water treatment and disinfection of gas diffusion electrode system, which adopts an electrolysis system without a diaphragm, uses an activated carbon/PTFE gas diffusion electrode with a membrane structure as a cathode, and uses a metal stable electrode or a graphite pole plate as an anode, and uses Simple and practical aeration in environmental engineering, control the electrolysis current density below 15mA/cm ² , control the oxygen flow rate in the range of 15-75L/h, use the reducing ability of the cathode, and use electrocatalysis to generate H ₂ O ₂ , and make It decomposes to generate hydroxyl radicals to sterilize, so as to achieve safe and non-toxic sterilization, reduce equipment investment and improve treatment effect. The system has a relatively wide range of pH values, and is expected to be used for disinfection treatment of tap water or secondary sedimentation tank effluent of sewage treatment plants.

Description

Method for Electrochemical Disinfection of Gas Diffusion Electrode System

technical field

The invention belongs to the field of environmental protection and energy saving, and relates to an electrochemical water treatment and disinfection method, in particular to an electrochemical water treatment and disinfection method using a gas diffusion electrode system.

Background technique

At present, commonly used disinfection processes include traditional chlorine disinfection, ultraviolet disinfection and ozone disinfection. Chlorination disinfection technology occupies a dominant position in the field of water treatment, but its main defect is that chlorine gas, the raw material for preparing chlorine disinfectants, is not only highly toxic, but also prone to fires, explosions, and even casualties during storage and transportation. At the same time, when it was discovered that chlorine disinfection would produce more carcinogens, the use of chlorine became more and more cautious. However, ozone disinfection and ultraviolet disinfection have disadvantages such as high technical difficulty, large investment, and no continuous sterilization effect, and their practical application has certain limitations. The on-site preparation of disinfectant technology solves the high-risk problem of chlorine gas in the storage and transportation process, so it has always been the focus of attention. The electrochemical disinfection method is one of the important methods for preparing disinfectants on site. The so-called electrochemical disinfection method is to allow the object to be sterilized to pass through an electrochemical device to achieve the purpose of sterilization and disinfection. The advantages of using electrochemical disinfection methods are: first, electrochemical methods can kill a variety of harmful microorganisms; second, electrode oxidation or reduction characteristics can be used to remove various ionic impurities in water; third, electrochemical disinfection systems have continuous sterilization capabilities , After the electric field disappears, it can still kill bacteria and algae. Moreover, the operation and management of the electrochemical method is simple, safe and reliable, and it has been verified by experiments that the sterilization speed is fast. Lower power consumption. The amount of trichloromethane generated by electrochemical method is lower than that generated by chlorine disinfection, even if the water containing more THMs (trihalomethane) precursor substances, the content of trihalomethane in water after electrochemical treatment Still lower than the value stipulated in the national standard (Shangyu et al. Feasibility study on the treatment of reused water by electrochemical disinfection, Environmental Pollution Control Technology and Equipment, 2002, Vol.3: 46-50).

There have been many research reports and practical use cases on electric sterilization, but so far, this technology has not been widely used on a large scale. Various types of electrochemical reactors are only used to produce chlorine gas or ozone as a disinfectant, and the research on the disinfection of organic wastewater and drinking water by electrochemical methods is only concentrated on the anode. A variety of shape-stable electrodes (DSA) have been used as anodes, such as Ti/IrO ₂ , Ti/RuO ₂ , etc., which are widely used in water treatment and disinfection. But only in the aqueous solution with higher Cl-concentration can obtain relatively high bactericidal rate; in the water without ^Cl- , mainly rely on the active groups generated on the electrode to realize the bactericidal effect.

The current passes through the water to be treated, and the HClO produced by Cl ^- oxidation on the anode is the main disinfection substance. At the same time, a large amount of oxygen overflows on the anode, and a useless hydrogen evolution reaction occurs on the cathode. This hydrogen mixes with the oxygen produced at the anode, potentially forming an explosive hydrogen and oxygen mixture. Moreover, the accumulation of large amounts of hydrogen in the pipes can disrupt the normal flow of water. Hydrogen gas is capable of penetrating many metals, causing hydrogen corrosion, which makes the metal brittle. In addition, operating costs are also expensive due to useless hydrogen evolution (compared to liquid chlorine disinfection).

H ₂ O ₂ has been successfully used to treat and disinfect drinking water and various types of sewage. Its oxidation reaction does not leave any reaction by-products in the water, and the reaction itself is not dangerous and is carried out under mild conditions. The peroxidation reaction on the electrode will not produce carcinogens, no need to add any chemical agents, and the operating cost will be reduced. The turbidity and chromaticity are basically completely removed, and the removal of turbidity is mainly due to the oxidation of organic matter and bacteria. The H ₂ O ₂ produced on the surface of the cathode can penetrate the cell membrane and reach the nucleus, and it has also been proved to have a continuous disinfection effect (Drogui, et al., Wat. Res., 2001, Vol. 35: 3235-3241). _Booch and Stocklin (German patent: DE19631842) used oxygen-consuming cathodes to generate _H2O2 on-site to sterilize drinking water. On the oxygen-consuming cathode, oxygen is reduced to H ₂ O ₂ and OH ⁻ . Compared with other disinfection substances, the oxidation-reduction potential of H ₂ O ₂ is lower, but the sterilization efficiency is basically not improved, because the H ₂ O ₂ formed on the oxygen-consuming cathode reacts with the free residual chlorine generated on the anode to generate HCl . Another disadvantage of oxygen-consuming cathodes is that only oxygen dissolved in water can generate H ₂ O ₂ . The solubility of oxygen in water is very low, only 8-10mg/L when P=1 atmospheric pressure. If pure oxygen is used for oxygenation, the concentration of dissolved oxygen in the water should be <25mg/L. Therefore, the yield of H ₂ O ₂ is very low, and the efficiency of generating H ₂ O ₂ at the cathode is very low, so it is difficult to be practically applied in the field of wastewater and drinking water disinfection, and therefore oxygen-consuming electrodes have not been widely used.

Contents of the invention

The object of the present invention is to address the deficiencies of the prior art, to provide an efficient, safe and non-toxic water treatment and disinfection method by using a gas diffusion electrode system for electrochemical water treatment and disinfection.

In order to achieve the above purpose, the solution adopted by the present invention is to use a composite gas diffusion electrode system for electrochemical water treatment and disinfection, the essence of which is to generate H ₂ O ₂ and highly active hydroxyl radicals in the electrochemical process to kill bacteria .

The present invention has the following characteristics:

The composite gas diffusion electrode used as the cathode in the electrolysis process of the present invention consists of two parts, a conductive skeleton and a diffusion catalytic layer. Use any one of C, Fe, Ni, Cu and other elements or their alloys as the conductive and supporting framework, and use carbon elements with a large specific surface area, including powdered activated carbon, graphite powder, acetylene black, carbon black, carbon fiber, etc. Any of them A kind of material is used as the base material of the diffusion catalytic layer, and any material or alloy thereof of Pt, Au, Ag, Cu, Fe, Ni, Mn and other elements is used as the catalyst in the diffusion layer, and the base material of the catalyst and the diffusion catalytic layer The mass ratio is 0-5‰. The diffusion catalytic layer also contains a certain amount of low-temperature pore forming agent NH ₄ HCO ₃ or (NH ₄ ) ₂ CO ₃ , and the mass ratio of the pore forming agent to the base material of the diffusion catalytic layer is 0-70%.

The electrolysis process is carried out under the external direct current, and the current density is controlled below 15mA/cm ² . If the current density is too high, the current efficiency will be reduced, and if the current density is too small, the generation rate of free radicals will be affected.

The electrochemical water treatment and disinfection process is carried out in a reactor with a gas diffusion electrode, and the anode uses a graphite plate or a shape-stable electrode. Oxygen produced by electrolysis or fed oxygen undergoes a reduction reaction on the diffusion electrode, and the flow rate of fed oxygen is controlled within the range of 15-75 L/h. Through the gas diffusion electrode, the voltage difference between the electrode plates can be reduced, the occurrence of side reactions such as oxygen evolution or hydrogen evolution can be reduced, and the current efficiency can be improved.

After the raw water was reacted for 10-30 minutes, the total number of bacteria was greatly reduced. The invention is expected to be used in electrochemical disinfection water treatment.

Owing to adopted above-mentioned scheme, the present invention has following advantage:

1. The operation is carried out at normal temperature and pressure, with simple operation and simple equipment.

2. Using this technology for electrochemical water treatment and disinfection has the advantages of low investment, good treatment effect, stable operation, safety and non-toxicity.

3. The pH value of the system is applicable to a wide range.

4. This equipment is especially suitable for the sterilization and disinfection of drinking water with low bacterial content. Its water flow stays for a short time and the equipment occupies a small area.

Description of drawings

Fig. 1 is a schematic diagram of the equipment device of the embodiment of the present invention.

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with specific embodiments.

The electrolytic reaction device is shown in Fig. 1, and is mainly composed of three parts: an oxygen cylinder 1, a flow meter 2, an electrolytic cell 3, and a DC stabilized voltage and stabilized current power supply 7. The above self-made activated carbon/PTFE gas diffusion electrode 4 is used as the cathode, and the anode is made of ordinary graphite plate 5 or a metal-shaped stable electrode, and O ₂ is electrolytically reduced to generate H ₂ O ₂ . A rectangular anode and a rectangular cathode are located in the middle of the electrolytic cell with a distance of 10mm and a plate thickness of 5mm.

Sterilization principle:

Cathode: Oxygen is reduced by two electrons to generate H ₂ O ₂ :

O ₂ +2H ⁺ +2e ^- →H ₂ O ₂ (1)

When the cathode uses activated carbon material with strong adsorption, the bacteria are adsorbed to the surface of the electrode, and then sterilized on the surface of the electrode.

Embodiment 1 carries out electrochemical disinfection with the composite gas diffusion electrode not containing pore-forming agent and catalyst as cathode

In the present invention, the water distribution containing the total number of bacteria of 10 ⁶ CFU/mL is electrolyzed under the action of the composite gas diffusion cathode without pore-forming agent and catalyst, and the current density is controlled at 6.6mA/cm ² , and the oxygen flow rate is 30L/h. Samples were taken at different times, and the total number of bacteria was detected after culturing for 24 hours by the standard plate method. It can be seen from the table below that when the energy consumption is equal to 0.62W·h/L, the sterilization efficiency is only 63.27%.

time (min) Energy Consumption(W·h/L) Bactericidal efficiency (%) 5 0.10 7.14 10 0.21 19.39 15 0.31 28.57 20 0.41 37.76 25 0.52 50.00 30 0.62 63.27

Example 2 Electrochemical Disinfection Using Composite Gas Diffusion Electrode Containing Porogen NH ₄ HCO ₃ as Cathode

The present invention electrolyzes the distributed water containing 10 ⁶ CFU/mL of total bacteria under the action of a composite gas diffusion electrode with a pore-forming agent content of 30%. Other conditions are the same as application example 1. It can be seen from the table below that when the energy consumption is equal to 0.63W·h/L, the sterilization efficiency reaches more than 77%.

time (min) Energy Consumption(W·h/L) Bactericidal efficiency (%) 5 0.10 25.00 10 0.21 39.58 15 0.31 50.00 20 0.42 58.33 25 0.52 66.67 30 0.63 77.92

Under the action of a composite diffusion electrode with a pore-forming agent content of 40%, other reaction conditions are the same as above, and the electrolysis is carried out to obtain the following results:

time (min) Energy Consumption(W·h/L) Bactericidal efficiency (%) 5 0.10 25.53 10 0.22 42.55 15 0.32 57.45 20 0.42 72.09 25 0.53 85.93 30 0.64 93.62

Under the action of a composite diffusion electrode with a pore-forming agent content of 40%, the bactericidal efficiency reaches more than 93% when the energy consumption is equal to 0.64W·h/L.

Under the action of a composite diffusion electrode with a pore-forming agent content of 70%, other reaction conditions are the same as above, and electrolysis is carried out to obtain the following results:

time (min) Energy Consumption(W·h/L) Bactericidal efficiency (%) 5 0.11 31.11 10 0.22 45.19 15 0.33 62.96

20 0.44 79.26 25 0.55 90.03 30 0.66 97.04

Under the action of a composite diffusion electrode with a pore-forming agent content of 70%, the sterilization efficiency reaches over 97% when the energy consumption is equal to 0.66W·h/L. The increase of pore forming agent obviously improved the bactericidal effect.

Embodiment 3 carries out electrochemical disinfection with the composite gas diffusion electrode containing catalyst Pt as cathode

The present invention electrolyzes the distribution water containing 106 CFU/mL of total bacteria under the action of a composite gas diffusion electrode with a catalyst Pt content of 2‰. Other conditions are the same as application example 1. It can be seen from the table below that when the energy consumption is equal to 0.58W·h/L, the sterilization efficiency reaches more than 79%.

time (min) Energy Consumption(W·h/L) Bactericidal efficiency (%) 5 0.10 14.63 10 0.20 32.93 15 0.29 48.78 20 0.39 58.54 25 049 67.07 30 0.58 79.27

Under the action of a composite diffusion electrode with a catalyst Pt content of 3‰, other reaction conditions were the same as above, and the electrolysis was carried out to obtain the following results:

time (min) Energy Consumption(W·h/L) Bactericidal efficiency (%) 5 0.10 15.92 10 0.20 41.78 15 0.30 57.21 20 0.40 65.67 25 0.50 75.64 30 0.60 89.05

Under the action of a composite diffusion electrode with a catalyst Pt content of 3‰, the sterilization efficiency reaches over 89% when the energy consumption is equal to 0.60W·h/L. Catalyst Pt can improve the current efficiency of H ₂ O ₂ production, the higher its loading, the more Pt in the active position, and the better the bactericidal effect.

Example 4 Under different oxygen flow rates, a composite gas diffusion electrode with a catalyst Pt content of 3‰ was used as the cathode for electrochemical disinfection

The present invention electrolyzes the distribution water containing 106 CFU/mL of total bacteria under the action of a composite gas diffusion electrode with a catalyst content of 3‰. Control the oxygen flow rate at 15L/h, and other conditions are the same as application example 1. It can be seen from the table below that when the energy consumption is equal to 0.60W·h/L, the sterilization efficiency reaches ~80%.

time (min) Energy Consumption(W·h/L) Bactericidal efficiency (%) 5 0.10 10.47 10 0.20 34.88 15 0.30 48.26 20 0.40 58.14 25 0.50 68.02 30 0.60 79.65

Under the action of a composite diffusion electrode with a catalyst content of 3‰, the oxygen flow rate was controlled at 30L/h, and other reaction conditions were the same as above, and the following results were obtained:

time (min) Energy Consumption(W·h/L) Bactericidal efficiency (%) 5 0.10 22.17 10 0.20 47.78 15 0.30 61.58 20 0.40 76.35 25 0.50 84.24 30 0.60 91.13

Under the action of a composite gas diffusion electrode with a catalyst content of 3‰, the oxygen flow rate is 30L/h, and the sterilization efficiency reaches above 91% when the energy consumption is equal to 0.60W·h/L.

Under the action of a composite diffusion electrode with a catalyst content of 3‰, the oxygen flow rate was controlled at 75L/h, and other reaction conditions were the same as above, and the following results were obtained:

time (min) Energy Consumption(W·h/L) Bactericidal efficiency (%) 5 0.11 45.00 10 0.22 71.11 15 0.33 89.17 20 0.44 92.78 25 0.55 94.44 30 0.66 97.83

Under the action of a composite gas diffusion electrode with a catalyst content of 3‰, the bactericidal efficiency reaches 97.83% when the oxygen flow rate is 75L/h and the energy consumption is equal to 0.66W·h/L. On the one hand, the increase of oxygen flow rate improves the sterilization effect to a certain extent, shortens the processing time, thereby reducing equipment investment; on the other hand, the increase of oxygen flow rate increases the energy consumption of sterilization, thus increasing the operating cost of the system for sterilization .

Example 5 At different pH values, a composite gas diffusion electrode with a catalyst Pt content of 3‰ was used as the cathode for electrochemical disinfection

The present invention electrolyzes the distribution water containing 106 CFU/mL of total bacteria under the action of a composite gas diffusion electrode with a catalyst content of 3‰. Raw water pH=5. Other conditions are the same as application example 1. The results are as follows:

time (min) Energy Consumption(W·h/L) Bactericidal efficiency (%) 5 0.10 41.68 10 0.22 58.46 15 0.32 76.35 20 0.42 85.54 25 0.53 89.90 30 0.64 92.31

Under the action of a composite diffusion electrode with a catalyst content of 3‰, the pH of the raw water is 6, and the other reaction conditions are the same as above, and the following results are obtained:

time (min) Energy Consumption(W·h/L) Bactericidal efficiency (%) 5 0.10 37.34 10 0.22 45.43 15 0.32 53.55 20 0.42 58.80 25 0.53 67.60

30 0.64 88.30

Under the action of a composite diffusion electrode with a catalyst content of 3‰, the pH of the raw water is 8, and the other reaction conditions are the same as above, and the following results are obtained:

time (min) Energy Consumption(W·h/L) Bactericidal efficiency (%) 5 0.10 30.87 10 0.22 38.70 15 0.32 46.43 20 0.42 52.39 25 0.53 58.91 30 0.64 85.81

The bactericidal efficiency decreased with the increase of pH, but the range of change was not large. When the pH is 5-8, the bactericidal efficiency can reach more than 85% after electrolysis for 30 minutes. The total number of bacteria in the effluent of the secondary sedimentation tank of the general sewage plant is ~104CFU/mL, which is far less than the total number of bacteria in the experimental water. Using this system for electrochemical disinfection water treatment is expected to achieve better results in a shorter treatment time. Therefore, this system is expected to be used for the sterilization and disinfection of the effluent of the secondary sedimentation tank of the sewage plant and the tap water.

Example 6 Using a composite gas diffusion electrode with a catalyst Pt content of 3‰ as the cathode for electrochemical disinfection at different current densities

The present invention controls the current density of 3.3mA/cm ² to carry out electrolysis on the distribution water containing 106 CFU/mL of bacteria in total under the action of a composite gas diffusion electrode with a catalyst content of 3‰. Other conditions are the same as application example 1. The results are as follows:

time (min) Energy Consumption(W·h/L) Bactericidal efficiency (%) 5 0.04 14.75 10 0.08 33.33 15 0.12 43.72 20 0.15 57.92 25 0.19 71.04 30 0.23 82.51

Under the action of a composite diffusion electrode with a catalyst content of 3‰, the current density is controlled at 10mA/cm ² , and other reaction conditions are the same as above, and the following results are obtained:

time (min) Energy Consumption(W·h/L) Bactericidal efficiency (%) 5 0.16 35.30 10 0.33 52.42 15 0.49 69.39 20 0.65 83.94 25 0.81 91.45 30 0.98 95.85

The above description of the embodiments is for those of ordinary skill in the art to understand and apply the present invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments, and apply the general principles described here to other embodiments without creative effort. Therefore, the present invention is not limited to the embodiments herein, and improvements and modifications made by those skilled in the art according to the disclosure of the present invention should fall within the protection scope of the present invention.

Claims (5)

1. A water treatment and disinfection method, characterized in that: a composite gas diffusion electrode system is used for electrochemical water treatment and disinfection, and H ₂ O ₂ and highly active hydroxyl radicals are generated during the electrochemical process to kill bacteria. 2. The water treatment and disinfection method according to claim 1, characterized in that: an electrolysis system without a diaphragm is adopted, a membrane-structured activated carbon/PTFE gas diffusion electrode is used as the cathode, a metal shape-stable electrode or a graphite pole plate is used as the anode, and the The side of the cathode is aerated. 3. The water treatment and disinfection method according to claim 1, characterized in that: the composite gas diffusion electrode is composed of a conductive framework and a diffusion catalytic layer, and any material among C, Fe, Ni, and Cu elements is used Or its alloy is used as the conductive and supporting skeleton, and any one of powdered activated carbon, graphite powder, acetylene black, carbon black, and carbon fiber is used as the base material of the diffusion catalytic layer, and Pt, Au, Ag, Cu, Fe, Ni, Any material in the Mn element or its alloy is used as the catalyst in the diffusion layer. The mass ratio of the catalyst to the base material of the diffusion catalyst layer is within 5‰, and the diffusion catalyst layer also contains a low-temperature pore-forming agent NH ₄ HCO ₃ or (NH ₄ ) The mass ratio of ₂ CO ₃ , the pore forming agent and the base material of the diffusion catalyst layer is less than 70%. 4. The water treatment and disinfection method according to claim 1, characterized in that: the electrolysis process is carried out under the external direct current, and the current density is controlled below 15mA/cm ² . 5. The water treatment and disinfection method according to claim 1, characterized in that: the oxygen generated by electrolysis or the oxygen passed in undergoes a reduction reaction on the diffusion electrode, and the flow rate of the oxygen passed in is controlled within the range of 15-75L/h .

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