The Role of Ozone in Multi-Barrier Processes for Drinking Water
A key tool to strengthen the safety, efficiency, and sustainability of modern DWTPs
1. Why talk about ozone in drinking water treatment today?
The water that reaches our homes is not simply the result of chemical treatment or filtration. It is the product of a comprehensive safety strategy based on multiple layers of control, redundancy, and complementary technologies—what we call a multi-barrier process.
Within this framework, ozone is no longer a secondary player. Once limited to supporting oxidation or tertiary treatment, ozone today plays a central role. In the face of emerging microcontaminants, chlorine-resistant pathogens, and regulatory limitations on chlorine, ozone now stands out as an active, versatile, and highly effective barrier.
This article offers a technical perspective—from the design and operation of drinking water treatment plants (DWTPs)—on how and where ozone can be integrated to maximize process performance, minimize public health risks, and enhance operational sustainability.
2. The multi-barrier concept: beyond disinfection
Traditional drinking water treatment follows sequential steps: pre-oxidation, coagulation, sedimentation, filtration, and chlorination. While this scheme has worked well, it is no longer sufficient.
Challenges such as refractory organic compounds, pesticides, disinfection by-products, and chlorine-resistant protozoa like Cryptosporidium demand reinforced treatment stages using complementary technologies.
This is where ozone proves essential—not as a replacement for chlorine or UV, but as a means to improve overall system effectiveness in both contaminant oxidation and disinfection without chemical residues.
3. What does ozone actually do in a DWTP?
Ozone (O₃) is an unstable gas with a higher oxidation potential and faster kinetics than chlorine or chlorine dioxide, making it an extremely powerful tool when applied properly.
As a primary oxidant (pre-ozonation):
Applied before coagulation, ozone can:
Oxidize natural organic matter (NOM), enhancing coagulant performance.
Break down aromatic structures and colloids, aiding sedimentation.
Oxidize Fe²⁺, Mn²⁺, H₂S, and odorous compounds.
Lower chemical oxygen demand (COD) of raw water.
Effect: Improved physicochemical treatment and reduced reagent consumption.
As an intermediate barrier (advanced oxidation):
Applied between filtration steps or ahead of adsorption, ozone can:
Remove emerging microcontaminants: pharmaceuticals, pesticides, industrial residues.
Oxidize refractory organics not removed by coagulation or activated carbon.
Reduce trihalomethane (THM) precursors via partial oxidation.
In combination with H₂O₂ or UV, ozone enables AOPs (Advanced Oxidation Processes) through hydroxyl radical generation (•OH), greatly expanding its action range.
As a final disinfectant:
At the end of the process, ozone allows for:
Rapid inactivation of viruses, bacteria, and protozoa (Giardia, Cryptosporidium).
Microbial load reduction prior to storage or distribution.
Minimal or no need for high chlorine residuals, thus reducing THMs and HAAs.
4. What sets ozone apart from other disinfectants or oxidants?
Ozone’s main advantages:
Fast reaction speed: seconds vs. minutes for chlorine.
Broad spectrum: effective against viruses, protozoa, metals, and organics.
No residuals: decomposes into oxygen.
No impact on taste, odor, or color.
While it doesn’t offer residual disinfection like chlorine, combining ozone with UV or low-dose chlorine ensures safety without compromising health or water quality.
5. Key design considerations for ozone barriers
Effective ozone systems require more than just gas injection. Design must include:
Ozone concentration in gas: ≥8–12% for high transfer efficiency.
CT value (concentration × time): >1.5–3 mg·min/L depending on goal.
Diffusion system: Venturis, ceramic diffusers, or pressurized chambers.
Off-gas control: Catalytic or thermal destruction units.
Bromate control: Especially important in bromide-rich waters—monitor pH and pre-treat as needed.
Automation integration is also crucial: sensors for ORP, O₃ concentration, and flow must be included to ensure precise, continuous dosing control.
6. Real-world applications
Many DWTPs worldwide successfully apply ozone as part of a multi-barrier system. Typical cases:
Eutrophic rivers with high organic load: improved coagulation, reduced PAC dosage.
Groundwater with iron and manganese: effective oxidation followed by filtration.
Sources with emerging contaminants: AOP + granular activated carbon (GAC).
Combined UV + O₃ + minimal chlorination: maximum microbial safety with no organoleptic impact.
7. Conclusion: an essential resource for modern drinking water treatment
Ozone is no longer a niche option. It is a proven, safe, and increasingly accessible technology enabling DWTPs to meet today’s challenges with:
High efficiency against resistant contaminants.
Effective taste and odor removal.
Heavy metal oxidation.
Reduced chemical use and waste generation.
Easier regulatory compliance.
More sustainable, flexible plant designs.
At Longking EnTech Europe, specialists in ozone technologies and water treatment processes, we help integrate ozone wherever it delivers the most value: as a primary oxidant, intermediate barrier, or final disinfectant—always tailored to the goals of each plant.
Because true water safety doesn’t lie in a single control point, but in the strength of the entire system.
If you're designing or upgrading an ozone system for drinking water, talk to our team at Longking EnTech Europe. We help you choose, size, and optimize the full process—not just the equipment—so your ozone system performs as it should: powerfully, efficiently, and safely.
Contact our commercial department at info@longkingeu.com
www.longkingeu.com