How Ozone Conquers "Invisible Threats" in Wastewater

Ozone: The "Powerful Purifier" in Wastewater Treatment

In the "assembly line" of urban wastewater purification, ozone (O₃) is a special role with super strong oxidation capability. This unstable molecule composed of three oxygen atoms, though non-storable, non-transportable and requiring on-site generation, exerts an irreplaceable role in the advanced purification stage of wastewater treatment by virtue of its strong oxidizability, becoming a key force in safeguarding the water environment.

I. Ozone's Purification Principle: Dual Oxidation Attacks

The core reason for ozone's efficient pollutant removal lies in its unique oxidation mechanism, which mainly launches "attacks" on pollutants through two pathways to achieve purification goals.

1. Direct Oxidation: Precision Strike on Specific Pollutants

Ozone molecules themselves possess strong oxidizability and will directly target electron-rich structures (such as double bonds, amino groups, etc.) in pollutant molecules, decomposing them into small-molecule substances by breaking chemical bonds. This method has high specificity, being particularly suitable for treating chromaticity, odor-causing substances, and some easily oxidizable organic compounds, enabling rapid decolorization and deodorization of wastewater.

2. Indirect Reaction: Non-Selective Removal of Persistent Pollutants

Ozone decomposes rapidly in water to generate hydroxyl radicals (·OH) with stronger oxidizing power — this "ultimate oxidation weapon" has almost no selectivity and can non-selectively attack most refractory pollutants, including pharmaceutical residues, endocrine-disrupting compounds, and industrial refractory organic matter. Hydroxyl radicals react extremely fast; even in the face of low-concentration (ng/L to μg/L level) micro-pollutants, they can efficiently mineralize them into carbon dioxide and water, greatly enhancing the depth of wastewater purification. Notably, natural organic matter in water can also catalyze the generation of hydroxyl radicals, strengthening the purification effect.

II. Core Roles of Ozone in Wastewater Treatment

From disinfection and sterilization to advanced pollutant removal, ozone runs through multiple key links of wastewater treatment, solving many problems that are difficult to tackle with traditional processes.

1. Efficient Disinfection: Rapid Elimination of Pathogens

As a top-tier "disinfectant", ozone has much higher disinfection efficiency than chlorine disinfection and ultraviolet disinfection, with a shorter contact time. It can directly destroy the cell membranes and protein structures of bacteria and viruses, alter the three-dimensional morphology of viruses to prevent them from attaching to host cells, and break through the resistance of spore-forming microorganisms with a slightly higher concentration, achieving a pathogen removal rate of over 99%. Especially for resistant pathogens such as Cryptosporidium that are difficult to inactivate with chlorine disinfection, ozone can easily neutralize them — an effect verified by the U.S. Environmental Protection Agency (EPA) and incorporated into drinking water safety standards.

2. Degradation of Micro-Pollutants: Conquering "Invisible Threats"

With increasingly stringent environmental protection standards, the removal of micro-pollutants such as pharmaceutical residues, personal care products, and pesticides has become a key demand. Ozone and hydroxyl radicals can effectively decompose such substances; the European Union's 2024 Urban Wastewater Directive lists ozone oxidation as one of the core technologies for micro-pollutant removal. Experiments show that at a specific ozone dosage of 0.3g O₃/g DOC (Dissolved Organic Carbon), ozone direct reaction alone can remove 63%-86% of micro-pollutants, and the removal rate can be increased to 90% when combined with biological pretreatment.

3. Decolorization, Deodorization and Water Quality Optimization

The chromaticity in wastewater is mostly caused by chromophoric group-containing organic matter; ozone can accurately destroy these groups to achieve efficient decolorization. Meanwhile, it can oxidize odor-causing substances such as algal metabolites and sulfides, completely eliminating wastewater odor. In addition, ozone oxidation can decompose some surfactants to solve foaming problems in wastewater treatment, and simultaneously increase dissolved oxygen content in water to improve effluent quality.

4. Enhanced Sludge Treatment and Biodegradability Improvement

Ozone can not only treat wastewater but also "transform" sludge — by attacking the cell walls of bacteria in sludge, it converts solid sludge into treatable liquid waste, improving the efficiency of subsequent sludge treatment. At the same time, it can convert refractory macromolecular organic matter into small-molecule easily degradable substances, enhancing the biodegradability of wastewater and paving the way for subsequent biological treatment processes.

III. Mainstream Processes and Application Scenarios of Ozone Wastewater Treatment

Ozone treatment is not an isolated process; it needs to be combined with process design and combined technologies to maximize efficiency.

1. Core Structure: Ozone Contact Tank

The core site for ozone treatment is the ozone contact tank, usually located after biological treatment. It adopts a sealed reinforced concrete structure with multiple series-connected contact chambers inside to ensure sufficient reaction time between wastewater and ozone. The micro-porous aeration device in the tank can disperse ozone into fine bubbles, maximizing the gas-liquid contact area; the supporting off-gas destruction device decomposes unreacted ozone to avoid hazards caused by emission.

2. Mainstream Combined Process: Ozone-Biological Filtration

Single ozone treatment cannot completely mineralize pollutants; currently, the mainstream adopted process is the combined "ozone oxidation + biological filtration" process. Ozone first oxidizes complex organic matter into biodegradable substances, and then microorganisms in the biological activated carbon (BAC) filter further decompose residual pollutants, while removing heavy metals, disinfection by-products, etc. This combination not only improves purification efficiency but also reduces ozone dosage and operating costs, being widely used in scenarios such as municipal wastewater reuse and advanced drinking water treatment.

3. Exploration of Cutting-Edge Technologies

Researchers are breaking through the bottlenecks of ozone treatment through technological innovation. For example, the "bidirectional electron transfer tunnel regulation technology" developed by Sun Yat-sen University constructs a cluster-single atom synergistic catalyst to enable ozone to rapidly generate highly active oxygen species, with catalytic activity increased by 2-4 orders of magnitude compared with traditional materials, maintaining high efficiency after thousands of hours of continuous operation. There is also the new Ozone Strong Water (OSW) system, which achieves rapid ozone reaction within 2 seconds through efficient mixing, reducing bromate by-product generation and energy consumption.

IV. Advantages and Challenges of Ozone Treatment

1. Core Advantages

The greatest advantage of ozone treatment is its cleanliness and high efficiency — it only decomposes into oxygen after oxidation reaction, leaving no secondary pollution residues, which meets the demand for green wastewater treatment. It also has strong adaptability, being less affected by wastewater pH value and temperature, and can cope with different water quality scenarios. Meanwhile, its equipment has high integration, which can be flexibly integrated into existing wastewater treatment plants without large-scale reconstruction.

2. Existing Challenges

The popularization of ozone treatment is still restricted by multiple factors: first, high energy consumption — ozone needs to be generated on-site through corona discharge (applying 6-20 kV high voltage), with energy costs accounting for a large proportion; second, susceptibility to interference — suspended solids and sludge in wastewater will consume ozone, requiring adequate pretreatment to ensure effectiveness; third, potential by-product generation — for example, toxic bromate may be produced when bromine is present in water, which needs to be controlled through process optimization.

V. Future Outlook: Green Upgrade of Ozone Technology

With the increasing demand for water resource reuse and tighter environmental protection standards, ozone oxidation technology is developing towards high efficiency, energy saving, and low by-product generation. On the one hand, the research and development of new catalysts and high-efficiency ozone generators will continuously reduce energy consumption; on the other hand, intelligent control systems can adjust ozone dosage in real time according to water quality to achieve precise treatment. In the future, ozone technology will not only play a greater role in municipal wastewater and industrial wastewater treatment but also integrate with membrane separation, advanced oxidation and other technologies to build a more efficient wastewater treatment system, safeguarding the sustainable utilization of water resources.