Advanced oxidation process of ozone
In recent years, advanced ozone oxidation technology has been rapidly developed in the wastewater treatment of various industries in various countries. Countries are paying more and more attention to the construction of environmentally friendly society. Ozone oxidation technology is used in printing and dyeing wastewater, coal chemical wastewater, reverse osmosis concentrated landfill leachate, and waste emulsion. Further progress has been made in other areas, and great progress has been made.
Keywords: ozone oxidation technology, industrial wastewater, ozone utilization rate
1. Ozone oxidation mechanism
1.1 Ozone properties
Ozone is an unstable gas with strong oxidizing property, which must be prepared and used on site. Ozone is an allotrope of oxygen, containing 3 oxygen atoms, sp2 hybrid orbitals, delocalized π bonds, V-shaped, polar molecules. Ozone is a light blue gas under normal temperature and pressure. The solubility in water is 9.2mlO3/L, which is higher than oxygen (42.87mg/L). When the dissolved concentration in water is higher than 20mg/L, it is purple-blue. Ozone has a strong oxidizing property, with an oxidation-reduction potential of 2.07V, which is only lower than F2 (3.06V) in the elemental substance.
1.2 The oxidation mechanism of ozone
Ozone can oxidize most organic substances, especially those that are difficult to degrade, with good effects. In the process of ozone reacting with organic matter in water, there are usually two ways of direct reaction and indirect reaction. The oxidation products of different reaction pathways are different, and the type of controlled reaction kinetics is also different.
(1) Direct oxidation reaction
The direct reaction of ozone is the direct oxidation of organic matter, the reaction rate is slow, the reaction is selective, and the reaction rate constant is in the range of 1.0~103M-1S-1. Due to the dipolarity, electrophilicity, and nucleophilicity of ozone molecules, the direct oxidation mechanism of ozone includes Criegree mechanism, electrophilic reaction, and nucleophilic reaction.
2 Influencing factors of ozone oxidation method
⑴ Ozone concentration
Since the solubility of ozone in water is relatively small, increasing the concentration of ozone can improve the dissolution balance of ozone in water, increase the concentration of ozone in water, and improve the effect of ozone oxidation.
⑵ pH of the system
The pH of the reaction system has a great influence on the oxidative degradation of ozone. The pH of the system will directly affect the production of various free radicals, mainly hydroxyl radicals.
⑶ Temperature of the system
The temperature of the system has a significant effect on the reaction rate. The increase in temperature helps to increase the concentration of free radicals generated by the self-decomposition of ozone molecules in the aqueous solution, and the increase in temperature helps to average the pollutant molecules and ozone molecules or free radicals in the aqueous solution. The molecular kinetic energy is conducive to the collision of pollutant molecules with ozone molecules or free radicals, thereby increasing the rate of oxidative degradation.
3 Combined process with ozone as the main body
Due to the practical application of ozone oxidation method, there are some problems: First, the cost of ozone generation is high, and the utilization rate of ozone is not high (at room temperature, the solubility of ozone in water is about 10mg/L); Second, the efficiency of ozone’s thorough mineralization of organic matter needs to be improved. In order to further improve the efficiency of the ozone oxidation method, increase the utilization rate of ozone, reduce the operating cost of ozone oxidation, and further improve the removal efficiency of pollutants, many scholars at home and abroad have begun to study advanced oxidation combined processes with ozone as the main body.
3.1 Catalytic Ozone Process
The addition of transition metal ions in the oxidation system can produce a significant catalytic effect on ozone oxidation, which can catalyze the self-decomposition of ozone in water, increase the ·OH concentration produced in the water, and thereby improve the ozone oxidation effect. At present, the catalytic ozone process is divided into two types: homogeneous ozone oxidation and heterogeneous ozone oxidation. Homogeneous ozone oxidation refers to the addition of some soluble transition metal ions in water to achieve the effect of catalyzing ozone oxidation.
3.2 H2O2/O3 process
When the dosage of ozone is low, continuously increasing the dosage of H2O2 can continuously improve the effect of oxidative degradation, but when the dosage of ozone is high, when the dosage of H2O2 reaches a certain value, continuing to increase its dosage is effective There is no obvious improvement in improving the catalytic effect. Yu] et al. pointed out that the use of H2O2 to catalyze the ozone degradation of 2,4-D, the experimental results indicated that it can effectively catalyze the self-decomposition of ozone to produce a higher concentration of ·OH, and effectively improve the mineralization of 2,4-D by ozone degradation. Rate.
3.3 Photocatalysis/O3 process
Studies have shown that photocatalysis technology can greatly improve the effect of ozone oxidation. Therefore, the photocatalysis/O3 process has been continuously studied and gradually applied by scholars at home and abroad, and has gradually developed into an independent advanced oxidation technology to treat.
3.4 Electrochemistry/O3 process
The product of the positive and negative reactions of the electrolysis process is usually the initiator of free radicals generated by the self-decomposition of ozone. This discovery provides a theoretical basis for the combined use of electrolysis and ozone oxidation, and some scholars at home and abroad have begun to study this technology, but there are not many studies in this field at present, and the analysis of the mechanism and treatment effects is not thorough enough.
4. Application of ozone oxidation technology in wastewater treatment
4.1 Ozone oxidation technology to treat printing and dyeing wastewater
Because printing and dyeing wastewater contains azo dyes and other components, the dyeing wastewater has high chroma and is difficult to biochemically treat. At present, more separation methods such as flocculation and adsorption are used to treat printing and dyeing wastewater. On the one hand, these methods are expensive, and on the other hand, they do not completely degrade and remove pollutants such as azo dyes in the wastewater, which may cause secondary pollution. Ozone oxidation method is suitable for the treatment of high chroma wastewater due to its high efficiency, and is gradually being used in the treatment of printing and dyeing wastewater.
4.2 Treatment of landfill leachate by ozone oxidation technology
Landfill leachate tends to decrease its biochemical performance as the “age” of the landfill grows. Often the leachate from old landfills has low biochemical properties and is not suitable for direct biological treatment. It usually requires physical and chemical treatment first. Its biochemical properties are then subjected to biological treatment; in addition, with the application of membrane treatment systems in the leachate, the produced membrane interception concentrated leachate often has very low biochemical properties, and physical and chemical treatment is required before further biological treatment . Therefore, in recent years, the treatment of landfill leachate by the ozone oxidation method has gradually become a research hotspot.
4.3 Treatment of coal chemical wastewater by ozone oxidation technology
The refractory organic matter and chromaticity in coal chemical wastewater are difficult to be removed by secondary treatment. After advanced ozone treatment, the removal effect is obvious, which can significantly reduce CODcr, improve the biodegradability of effluent, reduce chromaticity, and react quickly. The pH requirements are not strict. , Ozone in the effluent can be quickly decomposed and has little impact on subsequent treatment facilities. With the reduction of ozone production costs and the development of advanced ozone-related oxidation technologies, ozone has broad application prospects in the advanced treatment of coal chemical wastewater.
4.4 Treatment of waste emulsion with ozone oxidation technology
The waste emulsion is only used for the pretreatment of wastewater through conventional physical and chemical methods. The organic matter in the wastewater is not completely degraded, and it is difficult to meet the purification requirements, and the effluent has low biodegradability, which is not conducive to the subsequent biochemical treatment. The entire wastewater treatment process is considered to involve advanced oxidation treatment methods. The principle of advanced oxidation method is mainly to use the generated radical free radicals to react with the refractory organics in the water, thereby improving the biodegradability of wastewater. Advanced oxidation technology was first proposed by GLaze. It refers to a deep oxidation technology involving a large number of light radicals with strong oxidation performance during the oxidation process. It is currently an efficient and innovative sewage treatment technology at home and abroad.
Ozone oxidation is combined with other water treatment processes to form advanced oxidation treatment of ozone. Its essence is to produce hydroxyl radicals with stronger oxidation and lower selectivity, so it can degrade various types of wastewater with stable structure and biodegradability. The pollutants at the bottom do not form secondary pollution. It has broad prospects in wastewater treatment. At present, advanced ozone oxidation technology still has problems that can be solved, such as: high ozone energy consumption, low yield, and increasing ozone in water Solubility, etc., the research and application of ozone oxidation wastewater is still in its infancy at home and abroad, and its mechanism of action needs to be studied in depth. However, its application potential in the field of water treatment has attracted more and more attention. With the high efficiency and low consumption of new ozone The development of the generating device is that the advanced oxidation technology has a strong application advantage for the toxic, harmful and difficult-to-degrade pollutants in the water body. With its many advantages such as high efficiency, rapidity, and no secondary pollution, it creates a more beautiful and broad prospect.