Last time we talked the Physical law method.Today is Chemical oxidation method.
Advanced oxidation technology referred to as AOPs, its principle is the use of electricity, light radiation, catalysts and other reactions in the production of highly active free radicals (such as hydroxyl radicals • OH), through the addition of free radicals and organic compounds, Electron transfer, bond breaking, etc., make the macromolecule refractory organic matter in water body oxidize and degrade into low-toxic or non-toxic small molecule material, and even directly degrade into CO2 and H2O, close to complete mineralization, so that the CODcr value of organic sewage is greatly Reduce, its high stability in water, refractory organic pollutants is particularly effective. Advanced oxidation technology includes photocatalytic oxidation, Fenton oxidation, supercritical water oxidation, etc. Now that water treatment technology has become a hot research.
1) advanced wet oxidation method
2) Photocatalytic oxidation method
3) Fenton oxidation method
4) supercritical water oxidation method
5) Ozone oxidation method
6) Persulfate oxidation
1) advanced wet oxidation method
Wet oxidation is a high-level oxidation treatment of high concentration of biodegradable organic wastewater. It refers to oxidation of organic pollutants to oxygen or air at high temperature (125-320 ℃) under high pressure (0.5-20MPa) Organic small molecule material or its mineralized into carbon dioxide and water and other inorganic chemical processes. It has gone through the traditional wet air oxidation, catalytic wet oxidation, wet peroxide oxidation, supercritical water oxidation and catalytic supercritical water oxidation process. The method has the characteristics of fast oxidation, no secondary pollution and high treatment efficiency.
The wastewater containing polyvinyl alcohol was treated by wet oxidation method, the reaction temperature was controlled at 220 ℃ and the reaction pressure was 10.0MPa. Under the reaction conditions, stirring at 300r / min for 1h, the COD in waste water was controlled by 11800mg / L reduced to 2150mg / L
2) Photocatalytic oxidation method
The photocatalytic oxidation method uses the energy generated by light to promote the energy level transition of the catalyst or the oxide. The resulting free radical or empty orbit has strong oxidation and can react with the organic pollutants in the wastewater to achieve the removal of pollutants purpose. Photocatalytic oxidation has the advantages of fast reaction and good effect, and it is a key technology to develop and apply a chemically stable, cheap and non-toxic photocatalyst.
Photocatalytic oxidation is an optical degradation in the presence of a catalyst, which can be divided into two types: homogeneous and heterogeneous. Homogeneous photocatalytic oxidative degradation of Fe2 + or Fe3 + and H2O2 as a medium, by light-assisted Fenton hydroxyl radical degradation. Heterogeneous catalytic degradation is a certain amount of photosensitive semiconductor material put into the pollution system, combined with light radiation, so that the photosensitive semiconductor under the irradiation of light to generate electron-hole pairs, adsorbed on the semiconductor dissolved oxygen, water molecules and electrons Cavitation, resulting in OH • Extremely oxidizing free radicals.
3) Fenton oxidation method
Fenton reagent consists of ferrous salt and H2O2. Under acidic conditions (pH = 4 ~ 5) and Fe2 + catalysis, H2O2 decomposes to produce • OH, • OH, which directly reacts with pollutants in wastewater to decompose it into CO2, H2O and harmless. Because H2O2 decomposition mechanism is similar to that of Fenton reagent, UV, H2O2, UV + Fe2 ++ H2O2, H2O2 + Fe2 ++ O2, H2O2 + UV + O2, H2O2 + Fe2 ++ UV + O2 are collectively referred to as Fenton-like reagent.
Fenton reagent has strong oxidizing ability, which is composed of Fe2 + and hydrogen peroxide. Under acidic conditions, H2O2 is catalytically decomposed by Fe2 + ions and produces OH • radicals with high oxidizing power, which can oxidize wastewater with no choice Most organic matter. The wastewater treatment mainly through the oxidation of organic matter and coagulation and sedimentation, compared with the conventional oxidant treatment of organic wastewater, with rapid response, temperature and pressure conditions such as the reaction temperature advantages. On the basis of ordinary Fenton reagent oxidation method, the oxidation methods of light-Fenton, electro-
4) supercritical water oxidation method
Supercritical water oxidation (SCWO) uses the characteristics of water in supercritical state (374.3 ℃, critical pressure 22.05MPa) to make organic pollutants and oxidants (air, O2 and hydrogen peroxide, etc.) in homogeneous water in supercritical water The oxidation reaction removes it. SCWO has the advantages of thorough removal of contaminants, direct reuse of effluent, and recovery of inorganic salts in solid form. However, the corrosion of equipment and the blockage of pipes have hindered its development.
5), Ozone oxidation method
Ozone is a strong oxidizing agent that is highly oxidizing and produces less polluting substances. Its oxidation process is mainly through direct oxidation and indirect oxidation. Direct oxidation is achieved by cycloaddition, electrophilic reaction and nucleophilic reaction with pollutants, which is selective to the oxidation of pollutants. Indirect oxidation is the reaction of ozone in aqueous solution to induce self-decomposition and generate strong oxidant through chain reaction - Hydroxyl radicals, which are then oxidized by hydroxyl radicals.
Based on the ozone oxidation method, other oxidants such as O3 / H2O2, O3 / UV and O3 / US are added to other oxidants or ultraviolet light or ultrasonic waves are introduced. Jing Guohua and others conducted experimental research on ozonized polyvinyl alcohol wastewater and compared the results with those of ozone alone using O3 / UV and O3 / US methods. The results showed that after 12min treatment, the degradation rate of PVA under O3 / UV and O3 / US synergistic effect was significantly higher than 63.2% ozone oxidation alone, showing a good synergistic effect.
6), Persulfate oxidation
Because of its strong oxidizing properties, non-selective reaction and stable property at room temperature, persulfates become a substitute for conventional oxidants in pollutant oxidation reactions. In addition, the persulfate ions can form sulfate radical SO4- • with stronger oxidation ability under the action of heating, metal ions and UV irradiation, and can form hydroxyl radical OH •. In the wastewater system , Two kinds of free radicals can jointly participate in the oxidation of pollutants.
S2O82- + heat / UV → 2SO42-S2O82- + Men + → SO42- + Me (n + 1) ++ SO42-SO42- + H2O ← → OH + H ++ SO42-SO42- + OH- → SO42- + OH
The potassium persulfate oxidant was used to oxidize the PVA solution under the condition of heating and adding Fe2 + or Fe (0). The results showed that K2S2O8250mg / L was added at the initial temperature of 46.5 ~ 51.9mg / L, the temperature was controlled at 200C, and Fe2 + or Fe (Fe2 +) was added at a molar ratio of S2O82- to Fe2 + or Fe 0), the reaction 2h, PVA completely oxidized. The GC-MS was used to detect and prove that PVA was converted to C4H6O2.
Using ammonium sulfate or sodium salt, polyvinyl alcohol is oxidized to a water-insoluble resin to be removed. When COD 800mg / L containing polyvinyl alcohol wastewater, and 2000mg / L ammonium persulfate at 80 ~ 100 ℃ heated 1h, remove the spongy brown resin, COD removal rate> 99%.
