1. Research on three-dimensional electrolysis
(1) Research direction:
The rapid development of the modern chemical industry has caused more and more types of organic matter in wastewater, and the treatment of organic wastewater with high toxicity, high concentration and difficult to biodegradation has become a hot spot in water treatment research at home and abroad. In recent years, deep oxidation technology has been used as a treatment An important way of this kind of organic pollutants has attracted widespread attention. This technology is mainly through the addition, substitution and electrons between the highly oxidizing • OH, [O], O3, H2O2 oxygen radicals and organic matter. Mineralization of pollutants by transfer, etc. At present, the main methods of generating OH radicals are chemical oxidation, electrochemical methods, photooxidation and ultrasonic methods, among which the method of electrochemically generating OH radicals is favored. Because of this method The advanced oxidation process of wastewater has the advantages of relatively easy control, easy establishment of closed circulation and no secondary pollution. It is expected to develop into a new technology of high-efficiency organic wastewater treatment that reflects the "green" characteristics. At present, the relevant research is mostly limited For a two-dimensional flat electrode, this traditional flat electrode has a small specific surface area ratio, so the mass transfer problem cannot be fundamentally solved, the current efficiency is low, and the energy consumption Therefore, it is not widely used in practice. In contrast, the three-dimensional electrode has a large specific surface area ratio, a small distance between ions, and a good mass transfer effect. The electrochemical reactor designed by this method is used in electro-organic synthesis and There are already successful application cases in metal ion-containing treatment and other aspects.
However, the three-dimensional electrode electro-induced OH radical and its application in organic wastewater treatment have not been reported before the operation of our difficult sewage treatment equipment in Zhejiang.
Our system has conducted in-depth exploration and research on the three-dimensional electrode electrochemical reactor and mechanism of electro-induced OH, [O], O3, H2O2 oxygen radicals. The optimized design and process of the refractory organic wastewater treatment reactor Adjustment.
(2) Research content
1. Printing and dyeing wastewater: it has large amount of water, high content of organic pollutants, deep color, large alkalinity, and large changes in water quality.
2. Leather wastewater: high COD content, deep color, high heavy metal content, and high toxicity.
3. Pharmaceutical wastewater: high toxicity, high COD content, many solid suspended solids, and extremely difficult to biochemically. It is a difficult industrial wastewater.
In recent years, due to the development of new chemical fiber fabrics, the rise of artificial silk and the improvement of printing and dyeing finishing technology, PVA pulp, oleic acid, new additives and other difficult biodegradable organic substances have entered the printing and dyeing wastewater in large quantities, and their COD concentration has also been changed from the original The 400 ～ 1 000 mg / L of the crude oil rises to 2 000 ～ 3 000 mg / L, thereby reducing the COD removal rate of the original biological treatment system from 70% to about 50%, or even lower. With the progress of the process, the new Auxiliary agents and other biodegradable organic substances enter a large amount of leather wastewater. The content of heavy metals and complexes is high. The cost of toxic sludge treatment is too high. Traditional chemical and biological treatment processes have been seriously challenged. The traditional coagulation and oxidation methods of pharmaceutical wastewater have a COD removal rate of only about 30%. Therefore, the development of cost-effective wastewater treatment technology has increasingly become a topic of concern in today's environmental protection industry.
The three-dimensional electrode method is a technical improvement in the application of the original electrochemical treatment method. The three-dimensional electrode is also called the ternary electrode. It is a new type of electrochemical reactor. It is filled with granular electrode material between the electrodes of the traditional two-dimensional electrolytic cell and electrochemical reaction occurs on the surface of the material. The three-dimensional electrode method is used to treat difficult-to-degrade wastewater It has the characteristics of simple treatment, small footprint, convenient management, small amount of sludge, and low processing cost.
2. Three-dimensional electrolysis mechanism
1. Three-dimensional electrode reactor
As shown in Figure 1, the experimental device is a rectangular single-chamber three-dimensional electrode electrochemical reactor. It is mainly composed of two flat electrodes (anode and cathode), particle electrode, compressed air and tank. It acts as a feed electrode The flat anode is a DSA electrode, and the cathode is a stainless steel electrode. The particle electrode is an efficient, non-toxic and inexpensive special granular material. They are used as working electrodes to be filled between two flat electrodes to form a three-dimensional electric level. The body is welded by PVC material. Compressed air passes through the bottom of the reactor To the reactor
Figure 1 Schematic diagram of a three-dimensional electrode electrochemical reactor
2. The reaction mechanism of the three-dimensional electrode electrochemical reactor
In the three-dimensional electrode electrochemical reactor, hydroxyl radicals are generated according to the following electrochemical reaction mechanism:
O2 + 2H + + 2e vH2O2 (1)
H2O2 + Fe2 + vHO • + HO-+ Fe3 + (2)
Fe3 + + e vFe2 + (3)
First, oxygen is generated on the cathode by two-electron reduction to produce hydrogen peroxide, and the generated hydrogen peroxide rapidly reacts with Fe2 + present in the solution to produce OH and Fe3 +. Since the reduction potential of Fe3 + is more positive than the initial reduction potential of O2, Therefore, Fe3 + can be regenerated to Fe2 + during the reduction of O2 on the cathode. The oxygen required for the above reaction is provided by the compressed air passing through the reactor.
Experiments show that molecular oxygen plays a large role in the process of electrooxidation. On the one hand, hydrogen peroxide is generated by trapping electrons, on the other hand, the mass transfer effect of • OH radicals and other reactants is increased. Due to • OH radicals The life span of the product is very short, and it is difficult to directly detect its ESR signal, so this paper uses the spin capture technology to measure. The OH radical trapping agent used is DMPO, which can interact with the OH radical to generate a longer life nitrogen and oxygen free Based on the agreement, it is proved that the three-dimensional electrode reactor used in this experiment can indeed induce OH radicals.
Under acidic conditions, O2 is easier to reduce to produce H2O2, and with the presence of Fe2 +, the rate of conversion of H2O2 to OH radicals is accelerated, and the removal is increased, which means that the effect is better under acidic conditions. The effect of the rate is that the removal rate gradually increases with the extension of the treatment time, and the removal rate reaches more than 90% within 60 minutes.
3. Three-dimensional electrolysis experiment conclusion
1), The electrochemical-like reactor is a high-efficiency, non-toxic and inexpensive granular special material filled between two plates, and its organic matter removal mechanism is mainly based on the oxidation of generated hydrogen peroxide and hydroxyl radicals .
2) The OH radicals generated by the electrochemical process can directly degrade organic pollutants in wastewater into carbon dioxide, water and simple organic matter without selectivity, and the treatment process does not produce or basically does not produce secondary pollution.
This technology has been successfully applied in water treatment, and actual industrial wastewater such as urban domestic sewage, printing and dyeing, leather, and pharmaceuticals has been treated with satisfactory results. Compared with flat electrodes, three-dimensional electrodes have increased the volume of a unit cell. The electrode surface area and electrode electrode pitch are randomly and dynamically changed, which can provide greater instantaneous current intensity at a lower current density. Produces highly oxidizing complex oxygen radicals • OH, [O], O3, and H2O2 electrolyze hypochlorite and other oxidizing substances NaCl + H2O, NaClO + H2 ↑ from the simultaneous use of high-concentration wastewater containing high salt characteristics; Improve the electrolysis efficiency and treatment capacity of wastewater.
Three, three-dimensional electrolysis practical application
The oxidation capacity of oxygen radicals (• OH) produced by three-dimensional electrolysis is second only to F2, and its oxidation capacity is far superior to other oxidants, but F2 is very harmful to humans and the environment and is not suitable as an oxidant for sewage treatment. Advanced oxidation technology mainly produces large amounts of OH to rapidly "burn" organic matter, oxidize and decompose into CO2 and H2O, which greatly reduces the COD value of organic sewage and achieves the purpose of water treatment. The reaction rate of OH to most organic molecules reaches 107 ~ 1010M-1S-1, and no selectivity for organic pollutants.
Three-dimensional electrolytic electrocatalytic degradation technology is the production of OH, [O], O3, H2O2 oxygen radicals to degrade organic matter. Table 2 compares various advanced oxidation methods. The electrocatalytic oxidation method has many advantages that other advanced oxidation methods cannot compare with:
Table 2. Comparison of various advanced oxidation methods
|Advanced oxidation technology||advantage||Disadvantages|
|Fenton试剂||Standard Fenton reagent||Strong oxidizing property, no selectivity to organic matter, no secondary pollution of products||The degree of mineralization of organic matter is not high! A large amount of H2O2 is consumed during operation, the cost is high, and it is difficult to be practical|
|Light-Fenton reagent||It has strong oxidizability, no selectivity for organic matter, no secondary pollution of the product, and has a larger total organic matter removal rate and a faster reaction speed||System light absorption efficiency is not high, the cost of equipment is very high|
|Ligand-Fenton reagent||Organic matter degrades faster||Need to add ligand chemicals, which is easy to cause secondary pollution and high cost|
|Nano-photocatalytic oxidation||Suspended||Large contact area with sewage, high organic matter degradation efficiency||TiO2 particles are difficult to recycle and reuse, and need to be separated and recovered by membrane technology, which increases the investment cost|
|Fixed||TiO2 is fixed on the carrier or made into a film to treat wastewater, no additional equipment can be used to reuse TiO2||Small contact area with sewage, low organic matter degradation efficiency|
|Ultrasonic oxidation||Degradation of organic matter through three ways: · OH oxidation, combustion decomposition in bubbles, and supercritical water oxidation, with large processing capacity||Large energy consumption and large equipment investment|
|Electrolytic oxidation||Organic compounds are degraded by · OH, · O2, H2O2, no chemicals such as oxidants and reducing agents need to be added to the system, the processing capacity per unit volume of equipment is large, the reaction process is controllable, and the system operating costs are low||Further improve the catalytic activity, oxygen evolution overpotential and stability of the anode electrode, and further improve the electrode reaction efficiency through the design of the reactor|
From the comparison of various advanced oxidation methods in the above table, it can be seen that the Fenton method requires the addition of a large amount of chemical agents (H2O2, Fe2 +, etc.), and requires complex equipment investment (UV light source), and the investment cost and operating cost are high; The method is not suitable for large-scale application; the ultrasonic oxidation method has large equipment investment and large energy consumption; the electrocatalytic oxidation method has many advantages that other advanced oxidation methods cannot compare with:
(1) The main reagent for the degradation of pollutants is electrons, no need to add oxidants, and no secondary pollution will occur.
(2) The pollutants are degraded at normal temperature and pressure, the reaction conditions are mild, and the energy efficiency is high;
(3) It has the functions of air flotation, flocculation and sterilization, and can improve the removal effect of pollutants by removing suspended matter in water.
(4) Simple device, flexible process, strong controllability, easy automation, low investment and operating cost.
In recent years, the electrocatalytic oxidation method has been applied in the fields of sewage purification, landfill leachate, tanning wastewater, printing and dyeing wastewater, pharmaceutical wastewater, oil refining wastewater, etc.
Fourth, the characteristics of the three-dimensional electrode method
The three-dimensional electrode method is developed based on the two-dimensional planar electrode. Compared with other processing methods, the method has the following characteristics:
1. Compared with the traditional two-dimensional planar electrode, the three-dimensional electrode can increase the face-to-body ratio of the electrolytic cell, and increase the mass transfer speed of the substance due to the small spacing between the filled particles, and improve the current efficiency and processing effect.
2. The three-dimensional electrode reactor equipment is relatively simple and compact, and it occupies less area. The particle electrode does not require regeneration treatment for a long time, the operation cost is low, it is easy to control, and it is easy to achieve industrialization;
3. There is no need to add chemicals during the treatment. The post-treatment is simple and there is no secondary pollution. It is called "environmentally friendly treatment technology";
V. Application and prospect of 3D electrolysis market
1. The three-dimensional electrode makes full use of the characteristics of the reaction of the solution on the surface of the electrode, which increases the contact surface between the solution and the electrode. Its particle spacing is small, the mass transfer effect is greatly improved, and it has higher current efficiency and unit space-time yield. In order to improve the volumetric efficiency of the reactor and improve the effect of sewage treatment, its application will become increasingly widespread.
2. Through experimental analysis, the electrode of three-dimensional electrolysis is much larger than the surface of two-dimensional electrolysis, the mass transfer speed and reaction speed are fast, the current efficiency and space-time efficiency are high, the energy consumption is low, and the chromaticity and heavy metals can be effectively removed. To improve the biodegradability of wastewater, so that it has extremely important value in the research and application of high-concentration wastewater treatment. The decolorization rate of the three-dimensional electrode is over 95%, and the removal rate of COD is about 80%. This endows the system with great practical significance. The technology is widely used in the fields of ship domestic sewage, drinking water purification, high-concentration refractory wastewater, etc. It has the advantages of strong treatment capacity, no secondary pollution, and mild reaction conditions.
3. With the intensification of environmental pollution in rural areas, the three-dimensional electrolysis treatment technology will be adapted to the rapid treatment of rural groundwater, rural or high-manganese, high-arsenic, high-heavy metal area water reform projects.
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