Ozone, with its strong oxidation capacity, no secondary pollution residue, and high process adaptability, has become a core advanced oxidation process (AOP) in the field of sewage treatment. It can targeted solve industry pain points such as removal of refractory organic compounds, elimination of chromaticity and odor, and inactivation of pathogenic microorganisms in sewage. It is widely used in pretreatment, advanced treatment, and standard upgrade and retrofitting links of various sewage treatment scenarios including municipal sewage and industrial wastewater.
Core Mechanisms of Ozone in Sewage Treatment
The role of ozone in sewage treatment mainly relies on two reaction pathways: direct oxidation and indirect oxidation. The two pathways work synergistically to achieve efficient degradation of various pollutants in sewage.
Direct Oxidation by Ozone
Ozone molecules themselves have extremely strong oxidation performance, with an oxidation-reduction potential (ORP) of 2.07 V.
It can directly undergo selective oxidation reactions with pollutants in sewage.
It can directly attack unsaturated bonds and aromatic ring structures in organic molecules.
It can quickly break long-chain organic compounds, and decompose macromolecular refractory organic compounds into small-molecule biodegradable substances.
It can directly oxidize and decompose chromophoric groups and odor-causing substances in sewage, to achieve decolorization and deodorization effects.
The direct oxidation reaction can occur at normal temperature and pressure, with a controllable reaction path and strong targeting.
Indirect Oxidation by Ozone
Ozone in water can generate hydroxyl radicals with stronger oxidation capacity through decomposition and catalytic reactions.
Hydroxyl radicals have an ORP of 2.80 V, with non-selective oxidation capacity and faster reaction rate.
It can attack almost all organic pollutants in sewage without discrimination, to achieve thorough oxidative decomposition.
It can degrade persistent organic pollutants, trace pollutants such as antibiotics that are difficult to remove by direct ozone oxidation.
The indirect oxidation reaction can greatly improve the pollutant removal efficiency of ozone, and broaden the application scope of the technology.
Core Application Scenarios of Ozone in Sewage Treatment
Ozone technology can adapt to sewage treatment needs of different water quality and different treatment standards. It is a core technical means for current sewage discharge standard compliance and standard upgrading, with core application scenarios concentrated in five major fields.
Advanced Treatment for Municipal Sewage Standard Upgrade and Retrofitting
After conventional biochemical treatment in municipal sewage treatment plants, the effluent still retains part of refractory organic compounds, chromaticity and microorganisms.
Ozone technology is one of the mainstream technologies for municipal sewage standard upgrade and retrofitting, which can meet the requirements of Class 1A discharge standard and higher emission specifications.
It can efficiently remove COD and BOD in biochemical effluent, and improve the stability of effluent quality.
It can completely remove the chromaticity of effluent, and solve the problem of yellowing and color rendering of effluent after biochemical treatment.
It can replace chlorine-containing disinfectants to achieve efficient disinfection of sewage, and avoid the generation of disinfection by-products such as trihalomethanes (THMs).
Supporting the ozone-biological activated carbon process can further improve the pollutant removal effect and reduce operating costs.
At present, most municipal sewage plant standard upgrade and retrofitting projects in China have been equipped with ozone advanced treatment units.
Advanced Treatment and Discharge Standard Compliance of Industrial Wastewater
Industrial wastewater has complex components, often containing high-concentration, refractory, toxic and harmful organic pollutants, which are difficult to meet the discharge standard by conventional processes.
Ozone technology can adapt to the treatment needs of various types of industrial wastewater, and is a core technical means for industrial wastewater discharge standard compliance.
In printing and dyeing wastewater treatment, ozone can quickly decompose chromophoric groups such as azo dyes, with a decolorization rate of more than 90%. At the same time, it can degrade refractory organic compounds in wastewater and improve biodegradability.
In pharmaceutical wastewater treatment, ozone can destroy the molecular structure of antibiotics and drug intermediates, reduce the biotoxicity of wastewater, and solve the problem of low treatment efficiency of conventional biochemical processes.
In chemical wastewater treatment, ozone can decompose persistent organic pollutants such as aromatic hydrocarbons and halogenated hydrocarbons, reduce COD and toxicity of wastewater, and meet industry discharge standards.
In papermaking wastewater treatment, ozone can remove lignin derivatives and chromogenic substances in wastewater, and solve the pain points of high chromaticity and difficult biochemical degradation of wastewater.
Pretreatment of Refractory Organic Wastewater
For high-concentration organic wastewater with extremely poor biodegradability, ozone technology can be used as a pretreatment process.
Through the oxidation of ozone, macromolecular refractory organic compounds in wastewater can be decomposed into small-molecule biodegradable substances such as organic acids and alcohols.
It can greatly improve the BOD/COD ratio of wastewater, improve the biodegradability of wastewater, and create conditions for subsequent biochemical treatment.
It can destroy toxic and harmful substances in wastewater, reduce the biotoxicity of wastewater, and avoid inhibition of microorganisms in the biochemical system.
This pretreatment mode has been widely used in the treatment of high-difficulty wastewater from coal chemical, fine chemical, pharmaceutical intermediate and other industries.
Sewage Disinfection and Inactivation of Pathogenic Microorganisms
Ozone has an extremely strong bactericidal and disinfection effect, and can efficiently inactivate various pathogenic microorganisms including bacteria, viruses, spores and fungi.
Its disinfection principle is to destroy the cell membrane, nucleic acid and enzyme system of microorganisms through oxidation, to achieve irreversible inactivation.
Compared with chlorine-containing disinfectants, ozone disinfection has faster reaction speed, higher bactericidal efficiency, and is less affected by the pH value and temperature of sewage.
After disinfection, ozone can quickly decompose into oxygen by itself, without toxic and harmful residues, and will not produce disinfection by-products.
It can be applied to disinfection treatment of hospital sewage, municipal sewage, reclaimed water and other scenarios, to meet the relevant health standard requirements.
Special Removal of Sewage Odor and Chromaticity
The odor in sewage mainly comes from odor-causing substances such as sulfides, ammonia nitrogen, and volatile organic acids.
Ozone can quickly oxidize and decompose these odor-causing substances, eliminate sewage odor from the root, and improve the surrounding environment of the treatment plant.
The chromaticity in sewage mainly comes from organic chromophoric groups, heavy metal complexes and other substances.
Ozone can destroy the molecular structure of chromophoric groups to achieve efficient decolorization. Compared with traditional decolorization agents, it has no sludge increase and no secondary pollution.
This technology can be targeted applied to sewage treatment scenarios with prominent chromaticity and odor problems such as printing and dyeing, papermaking, and landfill leachate.
Mainstream Combined Processes of Ozone Sewage Treatment
The single ozone oxidation process has problems such as low ozone utilization rate, high operating cost, and incomplete degradation of some pollutants. In current industry applications, the combination mode of ozone and other processes is mostly adopted to achieve dual optimization of treatment effect and economy.
Ozone-Biological Activated Carbon (O3-BAC) Process
This process is the most widely used combined process in advanced sewage treatment at present.
First, through ozone oxidation, macromolecular refractory organic compounds in sewage are decomposed into small-molecule substances.
Then through the adsorption of activated carbon, small-molecule organic compounds and ozone oxidation products are enriched.
Relying on the biofilm attached to the surface of activated carbon, the enriched organic compounds are biodegraded to achieve complete removal of pollutants.
This process can greatly improve the utilization efficiency of ozone, and reduce ozone dosage and operating cost.
It can simultaneously achieve multiple effects such as COD removal, decolorization and deodorization, and disinfection, with strong stability of effluent quality.
It is widely used in municipal sewage standard upgrade, reclaimed water treatment, industrial wastewater advanced treatment and other scenarios.
Heterogeneous Ozone Catalytic Oxidation Process
This process strengthens the decomposition of ozone and the generation of hydroxyl radicals by adding solid catalysts.
Most catalysts use activated carbon, alumina, molecular sieve as carriers, and load active metal components such as iron, manganese and copper.
Under the action of the catalyst, ozone can quickly generate a large number of hydroxyl radicals, improving the oxidation reaction efficiency and pollutant removal effect.
It can greatly reduce ozone dosage, improve ozone utilization rate, and reduce operating energy consumption.
Compared with homogeneous catalytic oxidation, it has no reagent addition, no sludge increase, no secondary pollution, and simpler process operation and maintenance.
It is the mainstream upgrading technology in the field of high-difficulty industrial wastewater treatment and sewage standard upgrade and retrofitting.
Ozone-Fenton Synergistic Oxidation Process
This process combines the technical advantages of ozone oxidation and Fenton oxidation, targeting high-concentration, high-toxicity and refractory wastewater.
Ozone can promote the conversion of Fe³+ to Fe²+ in the Fenton reaction system, and improve the generation efficiency of hydroxyl radicals.
The intermediate products of the Fenton reaction can further promote the decomposition of ozone, forming a synergistic reaction effect.
Compared with a single process, the synergistic process has higher pollutant degradation efficiency and more thorough removal of refractory organic compounds.
It can greatly reduce the dosage of reagents and sludge output, and reduce the overall operating cost.
It is mainly used in the treatment of high-difficulty wastewater such as fine chemical, pharmaceutical, and landfill leachate.
Ozone-Membrane Treatment Combined Process
This process combines ozone oxidation with membrane treatment technologies such as ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO).
Ozone can oxidize and decompose macromolecular organic compounds and colloidal substances in sewage in advance, reducing the risk of membrane fouling.
It can reduce the cleaning frequency of membrane modules, extend the service life of membranes, and reduce the operation and maintenance cost of the membrane treatment system.
The membrane treatment process can further intercept residual pollutants after ozone oxidation, to ensure the effluent quality meets the standard.
This combined process is widely used in sewage reclamation and reuse, ultrapure water preparation, high-salinity wastewater treatment and other scenarios.
Advantages and Existing Bottlenecks of Ozone Sewage Treatment Technology
Core Application Advantages
Strong oxidation capacity. Ozone and the generated hydroxyl radicals can degrade most organic pollutants, and solve pollution problems that are difficult to handle by conventional processes.
No secondary pollution. The final decomposition product of ozone is oxygen, without toxic and harmful residues, no new sludge output, and no secondary pollution to the water body.
Fast reaction speed. The oxidation reaction can be completed within a few minutes, with short equipment retention time, small floor area, and suitable for the upgrade and retrofitting of existing sewage treatment plants.
Strong process adaptability. It can be used alone or combined with various processes such as biochemistry, adsorption, and membrane treatment, to adapt to the treatment needs of different water quality and different discharge standards.
Diversified functions. It can simultaneously achieve multiple treatment effects such as organic matter degradation, decolorization and deodorization, and sterilization and disinfection, reducing treatment units and simplifying the process flow.
Existing Technical Bottlenecks
Low ozone utilization rate. Under normal temperature and pressure, the solubility of ozone in water is limited. Traditional aeration methods are easy to cause ozone escape, resulting in insufficient actual utilization rate.
High operating energy consumption and cost. Ozone production requires a lot of electric energy, and electricity accounts for more than 80% of the operating cost of the ozone system, which limits its popularization in large-scale sewage treatment.
Limited removal effect on some pollutants. For some persistent organic pollutants such as perfluorinated compounds and polychlorinated biphenyls, the degradation effect of a single ozone oxidation process is poor, and a supporting catalytic process is required.
High safety control requirements. Ozone has strong irritation, excessive escape will affect human health and the surrounding environment, and has strict requirements on system sealing, tail gas treatment and safety monitoring.
High equipment operation and maintenance threshold. Ozone generation equipment, dosing system, and catalytic system require professional personnel for operation and maintenance. The problems of equipment stability and catalyst deactivation in long-term operation still need continuous optimization.
Industry Development Trend of Ozone Sewage Treatment Technology
With the continuous tightening of environmental protection discharge standards and the improvement of prevention and control requirements for refractory new pollutants, ozone sewage treatment technology is developing towards the direction of low energy consumption, high efficiency, intelligence and precision.
Upgrading of low-energy ozone production equipment. The industry is accelerating the research and development of high-frequency, high-voltage, low-energy ozone generation devices, to improve ozone production efficiency and reduce the power consumption and production cost per unit of ozone.
Iterative research and development of high-efficiency catalytic materials. For the ozone catalytic oxidation process, research and develop heterogeneous catalysts with high activity, high stability and long service life, to improve the generation efficiency of hydroxyl radicals and reduce the use cost of catalysts.
Intelligent and precise dosing control system. Combined with online water quality monitoring and AI algorithm, it can realize real-time dynamic adjustment of ozone dosage, adapt to the fluctuation of influent water quality, and minimize ozone dosage and operating energy consumption on the premise of ensuring effluent compliance.
Research and development of targeted new pollutant removal technology. For new pollutants in water such as antibiotics, microplastics, endocrine disrupting chemicals, and persistent organic pollutants, research and develop ozone targeted oxidation technology to improve the removal efficiency of trace new pollutants.
Carbon neutrality adaptation process optimization. Combined with biogas power generation, waste heat utilization and other technologies of sewage plants, reduce the carbon emission of the ozone system; optimize the resource utilization of ozone oxidation by-products, and promote the low-carbon transformation of sewage treatment processes.
Construction of multi-technology coupling collaborative system. Promote the deep coupling of ozone oxidation with biochemical treatment, membrane separation, advanced reduction and other technologies, build a whole-process collaborative system of “pretreatment-core treatment-advanced treatment”, and achieve the comprehensive optimization of treatment effect, operating cost and carbon emission.
