The Application of Ozone in Sewage Treatment

In the surging wave of today's environmental protection cause, sewage treatment, as a crucial part of safeguarding the ecological environment, is constantly exploring innovative technologies. Ozone, with its unique properties, plays a significant role in the field of sewage treatment.

Ozone (O₃) has a light blue appearance, a special smell, and a unique molecular structure. Its oxidizing power far exceeds that of ordinary oxygen. Industrially, ozone is often produced by the dielectric barrier discharge method, which uses high-voltage alternating current to prompt the recombination of oxygen molecules, thus generating ozone.

The efficacy of ozone in sewage treatment is remarkable. Firstly, in terms of sterilization and disinfection, there are a large number of pathogenic microorganisms such as bacteria and viruses lurking in sewage, constantly threatening the water environment and human health. With its strong penetrability, ozone can break through the cell walls of microorganisms, directly target key biomacromolecules such as enzymes and nucleic acids inside the cells, destroy their structures and functions, and instantly render the microorganisms inactive, achieving efficient sterilization. Compared with traditional chlorine disinfection, ozone does not produce harmful chlorinated organic compounds, ensuring water quality safety.

In terms of decolorization, industrial wastewaters from printing and dyeing, papermaking, etc. are often deeply colored and contain a large number of hardly degradable colored organic substances. Ozone utilizes its strong oxidizing property to "attack" the colored groups, oxidatively decomposing the complex chromogenic structures and converting them into colorless or light-colored small molecules, effectively improving the appearance quality of the wastewater, and the decolorization effect is quite remarkable.

Its deodorization function is equally outstanding. The peculiar smell in sewage plants mainly originates from sulfur-containing compounds, nitrogen-containing compounds, and volatile organic substances. When ozone encounters them, it rapidly undergoes an oxidation reaction, converting these malodorous substances into odorless or substances with a low odor threshold, purifying the air from the source and improving the surrounding environment.

In addition, for organic pollutants in sewage, ozone first directly oxidizes some organic substances, decomposing them into carbon dioxide, water, and small molecular organic acids. At the same time, it initiates a free radical reaction to generate hydroxyl radicals, deeply mineralizing hardly degradable organic substances and improving the biodegradability of sewage, laying a good foundation for subsequent biological treatment processes.

However, after ozone completes its mission of purifying sewage, if the residual ozone is not properly treated, it will bring many disadvantages. On the one hand, residual ozone in water bodies will cause oxidative stress to aquatic organisms and damage the aquatic ecosystem. On the other hand, when it escapes into the air, it will irritate the mucous membranes of the human respiratory tract and other tissues, endangering health.

There are various methods for treating residual ozone. Natural decomposition is relatively slow and is greatly affected by environmental factors, making it unsuitable for large-scale sewage treatment plants. Although the chemical reduction method reacts rapidly, it requires continuous dosing of chemicals, resulting in high costs and easily introducing new salt pollution. The thermal decomposition method consumes a huge amount of energy, and the equipment investment and operating costs are prohibitive.

In comparison, the catalytic decomposition of residual ozone has obvious advantages. There are several common types of catalysts: metal oxide catalysts such as manganese dioxide and copper oxide have abundant surface active sites that can adsorb ozone molecules. Through electron transfer, the O - O bond within the ozone molecule is weakened, prompting its decomposition into oxygen, and the catalytic activity of nanostructured metal oxides is even better. Precious metal catalysts such as palladium and platinum have extremely high catalytic efficiencies and can easily adsorb and activate ozone, but their costs are extremely high, limiting their application. Activated carbon catalysts have a wide range of sources and are affordable, possessing both physical adsorption and chemical catalytic functions, and their performance can be further improved after modification.

Taking metal oxide catalysts as an example, during the catalytic process, ozone molecules are captured by the active sites on the catalyst surface, forming an adsorbed state. Subsequently, electron transfer occurs between the metal ions and the ozone molecules, causing the O - O bond to break, generating active oxygen species, and finally combining into oxygen.

In practical applications, fixed-bed reactors or fluidized-bed reactors are often used. The fixed-bed reactor has a simple structure and is convenient to operate. The catalyst is not easily lost, but it is prone to clogging and requires regular backwashing. The fluidized-bed reactor has high mass and heat transfer efficiencies, and the catalyst regeneration is convenient. However, it requires high equipment sealing, and the catalyst wears out quickly. During operation, parameters such as ozone concentration, water flow rate, and temperature should be monitored in real-time, and the reactor conditions should be flexibly adjusted according to the influent water quality and ozone dosage to ensure that the residual ozone meets the discharge standards.

Looking ahead, with the progress of materials science, ozone and related treatment technologies will surely continue to be optimized, injecting stronger impetus into sewage treatment and helping the ecological environment reach new heights.