Treatment of wastewater with high COD by catalytic ozone oxidation
Mechanism of reducing COD in wastewater by catalytic ozone oxidation
Ozone oxidation: Ozone itself has a strong oxidation effect, and its REDOX potential is 2.07eV. Ozone oxidation is mainly divided into two aspects: the direct oxidation of ozone molecules reacting with pollutants; Indirect oxidation of hydroxyl radicals resulting from ozonolysis reacting with pollutant molecules. Although pure ozone oxidation can remove organic matter to a certain extent, the single ozone utilization rate is low and the treatment of pollutants is not complete.
Ozone catalytic oxidation: By adding a catalyst in the ozone system, it can significantly improve the decomposition capacity of ozone, generate a large number of ·O H, non-selective degradation of organic matter in water, is a new technology developed for the low efficiency of ozone oxidation alone.
Ozone catalyst can catalyze the conversion of ozone into hydroxyl free radicals with stronger oxidation capacity , thereby improving the oxidation efficiency of ozone.
The principle of ozone catalyst is to use the action of catalyst, to convert ozone, a strong oxidizing agent, into non-selective oxidation of hydroxyl free radicals (·OH) . hydroxyl radical has stronger oxidation capacity than ozone molecules, and the reaction is non-selective, can oxidize and decompose a large number of organic pollutants in sewage. Under the catalytic action, ozone gas enters the catalytic oxidation tower together with wastewater, rises through the catalytic bed, produces a lot of hydroxyl free radicals. These hydroxyl radicals can effectively transform macromolecular refractory organic compounds in wastewater into small molecules by chain breaking, ring opening, etc., and then further mineralized into carbon dioxide and water. ozone decomposition produces oxygen, will not cause secondary pollution, to ensure that the treated wastewater discharge standards.
Ozone catalysts can be divided into homogeneous catalysts and heterogeneous catalysts according to different forms. homogeneous catalysts are mainly catalyzed by metal ( ion) in solution, while heterogeneous catalysts are mainly catalyzed by solid metals, metal oxides or supported metals or metal oxides. These catalysts can catalyze ozone to directly oxidize organic matter in water to CO2 and H2O, or oxidize macromolecules of organic matter into smaller molecules, make it more easily degraded.
The introduction of ozone catalyst greatly improves the utilization rate of ozone and the organic mineralization ability of ozone. The composite porous high strength Si-Al-Ti is used as the carrier, and doped with the catalytic component which is not easy to be lost, improves the stability and mechanical strength of the catalyst, has a long service life, and does not need to be added regularly. In addition, the ozone oxidation catalyst has a large specific surface area, treatment wastewater flux, increases the contact time between wastewater and catalyst, reduces the footprint, can be adjusted according to the change of water quality and quantity, has strong adaptability, and has strong impact load resistance.
Common ozone catalysts on the market are divided into the following categories according to the carrier:
Ceramide/clay: combination of physical bonds, poor physical strength, easy loss of catalyst, short life;
Activated carbon: the combination of physical bonds, the catalyst is easy to lose, the life is short, and the column type increases the head loss of backwashing;
Silica-aluminum composite materials: on the basis of traditional ceramics, part of the alumina molding is introduced as a carrier, which is an upgraded version of the ceramic carrier catalyst, with the characteristics of low production cost, relatively large strength, higher hardness, relatively low wear relative to ceramics, but it is still easy to wear off the powder, some filler off the powder will make the water color.
Activated alumina: The substrate and catalytic components are chemically bonded, the catalytic components are not easy to lose, long life, strong anti-pollution ability under neutral conditions, and the effect is stable.
Shenzhen Keli uses a variety of transition metal oxides and precious metals as catalytic components, which has excellent adaptability and high catalytic activity to different wastewater, catalyzing the efficient conversion of ozone to produce ·OH, and the oxidation efficiency is 2-5 times higher than that of traditional ozone catalytic oxidation, and the adoption of this technology can effectively reduce the COD of sewage.
Key technological innovation points of efficient heterogeneous catalyst:
(1) A variety of transition metal oxides are used as catalytic components, and the ratio of materials is adjusted to make the catalyst have poles for different wastewater through a large number of experiments and engineering verification
Excellent adaptability while providing high catalytic activity;
(2) The use of low-temperature sintering technology, while ensuring the active group, effectively reduce production energy consumption and the loss rate during the use of catalysts, to prevent secondary pollution;
(3) The high active component material is used as the catalyst carrier, the porous structure has a high specific surface area, and the doping is not easy to lose the catalytic component, to improve the stability of the catalyst. The carrier has high mechanical strength and long service life.
(4) The catalyst can effectively reduce the activation energy of the reaction, so as to achieve the purpose of deep oxidation and maximum removal of organic pollutants.
(5) It can accelerate the self-decomposition of ozone in water, increase the concentration of ·0H produced in water, thereby improving the ozone oxidation effect, and the oxidation efficiency is 2-5 times higher than that of simple ozone oxidation.
(6) Using atomic deposition to modify the catalyst technology, the catalyst carrier has super hydrophilicity, the catalyst is not easy to pollute, scale and clog, and can run for a long period.
