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In the early 1960s, with the rapid development of the power industry, electrolysis began to attract people's attention. Traditional electrolysis reactors use two-dimensional plate electrodes. The effective electrode area of such reactors is very small, and the mass transfer problem cannot be well solved. In industrial production, high electrode reaction speed is required, so it is objectively necessary to develop new and efficient electrolysis reactors.
In 1969, Backnurst et al. proposed the design of fluidized bed electrode (FBE). This electrode is different from the flat electrode, has a certain three-dimensional configuration, the specific surface area is dozens or even hundreds of times that of the flat electrode, the electrolyte flows in the pores, and the mass transfer process in the electrolysis reactor is greatly improved.
In 1973, m.fleischm amm and f.goodridge successfully developed bipolar fixed bed electrode (bipolar packed bed electrode for short bpbe). The inner electrode material is repolarized under the action of a high gradient electric field to form bipolar particles, and oxidation-reduction reactions occur at both ends of the small particles, each of which is equivalent to a micro-electrolytic cell. Migration is easily achieved due to the small distance between the cathode and anode of each microelectrolysis cell. At the same time, since the entire electrolytic cell is equivalent to a series of numerous micro-electrolytic cells, the efficiency is greatly improved.
The basic principle of electrochemical water treatment technology is to make pollutants undergo direct electrochemical reaction or indirect electrochemical transformation on the electrode, that is, direct electrolysis and indirect electrolysis.
1. Direct electrolysis
Direct electrolysis means that pollutants are directly oxidized or reduced on the electrodes to remove them from wastewater. Direct electrolysis can be divided into anodic process and cathodic process. The anode process is the oxidation of pollutants on the surface of the anode to convert them into less toxic substances or easily biodegradable substances, and even inorganic organic matter, so as to achieve the purpose of reducing and removing pollutants. The cathode process is the reduction of pollutants on the cathode surface to remove them, which is mainly used for the reduction and dehalogenation of halogenated hydrocarbons and the recovery of heavy metals.
2. Indirect electrolysis
Indirect electrolysis refers to the use of electrochemically generated redox substances as reactants or catalysts to convert pollutants into less toxic substances. Indirect electrolysis is divided into reversible and irreversible processes. A reversible process (mediated electrochemical oxidation) means that the redox can be electrochemically regenerated and recycled during electrolysis. Irreversible process refers to the use of irreversible electrochemical reactions to produce substances, such as the process of oxidizing organic compounds such as chlorate, hypochlorite, h2o2 and o3 with strong oxidizing properties, and can also use electrochemical reactions to generate strong oxidizing intermediates. , including solvated electrons, ·ho, ·ho2, o2- and other radicals. At the same time, you can view more technical documents on China Sewage Treatment Engineering Network.
1. Electrocoagulation electric float method
Under the action of external voltage, the soluble anode (iron or aluminum) is oxidized to generate a large number of cations and then form a colloid to coagulate the dirt in the wastewater. The method is called electro-coagulation electro-floating. In electrocoagulation, iron and aluminum are often used as anode materials.
2. Electrodeposition
Using the potential difference of different metal components in the electrolyte, the dissolved metals in the free state or the bound state are precipitated at the cathode. Appropriate electrical potential is the key to electrodeposition. No matter what state the metal is in, the potential level can be determined by the Nernst equation according to the ionic activity in the solution, and the solution composition, temperature, overpotential and electrode materials will also affect the electrodeposition process.
3. Electrochemical oxidation
Electrochemical oxidation is divided into two types: direct oxidation and indirect oxidation, which belong to the anodic process. Direct oxidation is to directly convert pollutants into harmless substances through anodic oxidation; indirect oxidation is to generate intermediate substances with strong oxidizing effect through anodic reaction or intermediate reactions other than anodic reaction to oxidize the treated pollutants, ** eventually transformed into harmless substances. For direct anodic oxidation, the electrochemical surface reaction is limited by the mass transfer step if the reactant concentration is too low; for indirect oxidation, this limitation does not exist. In the process of direct or indirect oxidation, the side reaction of precipitation of h2 or o2 is generally accompanied, but the side reaction can be suppressed by the selection of electrode materials and potential control.
4. Photoelectrochemical oxidation
By absorbing the energy of visible light and ultraviolet light through semiconductor materials, generating "electron-hole" pairs, and storing excess energy, the semiconductor particles can overcome the barriers of thermodynamic reactions and use them as catalysts to carry out some catalytic reactions.
5. Electrodialysis
Relying on the unique function of selectively permeating the membrane under the action of an electric field, ions can pass from one solution into another solution to achieve the separation and concentration of ionized pollutants. When electrodialysis is used to treat metal ions, solid metal cannot be directly recovered, but concentrated salt solution can be obtained, and the quality of effluent can be significantly improved. At present, the most researched method is single-cation membrane electrodialysis.
6. Electrochemical membrane separation
A separation process that utilizes the potential difference across the membrane. Often used for the separation of gaseous pollutants.
(1) The oh free radicals generated in the process can directly react with organic pollutants in wastewater, and degrade them into carbon dioxide, water and simple organic matter, with no or little secondary pollution, which is an environmentally friendly technology (environm ent friendly technology);
(2) The energy efficiency is high, and the electrochemical process can generally be carried out at normal temperature and pressure;
(3) Electrochemical methods can be used alone or in combination with other treatment methods, such as pre-treatment methods, which can improve the biodegradability of wastewater;
(4) The electrolysis equipment and its operation are generally relatively simple and the cost is low.
