Chemical oxidation technique
Chemical oxidation technology is often used for pre-treatment of biological treatment. Generally, under the action of catalysts, chemical oxidants are used to treat organic wastewater to improve its biodegradability, or directly oxidize and degrade organic matter in wastewater to stabilize it.
1 Fenton oxidation method
The technology originated in the mid 1890s, proposed by French scientist H.J. Foron, under acidic conditions, H2O2 can effectively oxidize tartaric acid under the catalytic action of Fe2+ ions, and applied to the oxidation of malic acid. For a long time, people default that the main principle of Fenton is to use ferrous ion as a catalyst for hydrogen peroxide, and the reaction produces hydroxyl radical formula :Fe2++H2O2 -- Fe3++OH-+·OH, and most of the reactions are carried out under acidic conditions.
Among the chemical oxidation methods, Fenton process has shown certain advantages in the treatment of some difficult to degrade organic matter (such as phenol and aniline). With the deepening of research on Fenton process, ultraviolet light (UV) and oxalate have been introduced into Fenton process in recent years, which greatly enhances the oxidation capacity of Fenton process.
2 kinds of Fenton oxidation
In addition to Fe(Ⅱ), Fenton-like reaction is a general term for a class of reactions in which Fe(Ⅲ), iron-bearing minerals and some other transition metals such as Co, Cd, Cu, Ag, Mn and Ni can accelerate or replace Fe(Ⅱ) and catalyze H2O2.
Studies have shown that using homogeneous catalysts such as Fe3+ and Mn2+ and heterogeneous catalysts such as oxidizing minerals of iron powder, graphite, iron and manganese can also decompose H2O2 to produce ·OH, which is called Fenton-like system because its basic reaction process is similar to Fenton reagent. If Fe3+ is used instead of Fe2+, because Fe2+ is generated immediately, the chance of ·OH being reduced by Fe2+ is reduced, and the utilization efficiency of ·OH can be improved. If some complexing agents (such as C2O2-4, EDTA, etc.) are added to Fenton system, the removal rate of organic matter can be increased.
3 Ozone oxidation method
Ozone oxidation system has a high REDOX potential, can oxidize most of the organic pollutants in wastewater, and is widely used in industrial wastewater treatment. Ozone can oxidize many organic matter in water, but the reaction between ozone and organic matter is selective, and organic matter can not be completely decomposed into CO2 and H2O, and the products of ozone oxidation are often carboxylic acid organic matter.
The chemical properties of ozone are extremely unstable, especially in non-pure water, and the oxidation decomposition rate is measured in minutes. In wastewater treatment, ozone oxidation is usually not used as a separate treatment unit, and some strengthening means are usually added, such as photocatalytic ozonation, alkali catalytic ozonation and heterogeneous catalytic ozonation. In addition, the combination of ozone oxidation and other technologies is also the focus of research, such as ozone/ultrasonic method, ozone/biological activated carbon adsorption method.
