Advancing Seawater Treatment Through Halide-Specific Oxidation Chemistry

In high-salinity environments, water treatment is both a technical challenge and a chemical balancing act. As ozone becomes the oxidant of choice for advanced disinfection, understanding its behavior in the presence of halide ions, specifically bromide and iodide, is essential. Halide-Aware Ozone Use in Seawater Disinfection is critical to achieving effective microbial control while minimizing unwanted by-products.

At Pinnacle Ozone Solutions, our focus on halide-aware oxidation strategies stems from a deep understanding of seawater chemistry. Ozone’s effectiveness in marine systems is undeniable, but it must be applied with precision to manage complex reaction chains and avoid unintended by-products.

This article provides a focused overview of ozone’s reactivity with bromide and iodide, its implications for disinfection and by-product control, and the importance of engineered process design in seawater applications.

Ozone and Bromide in Seawater: The Primary Disinfection Pathway

Bromide (Br^–) is abundant in seawater, typically around 65 mg/L. When ozone is introduced, the following sequential reactions occur:

1. Oxidation to Hypobromite and Hypobromous Acid

   O₃ + Br^– → OBr^– + O₂
   OBr^– + H₂O ⇌ HOBr + OH^–

   These products hypobromite (OBr^–) and hypobromous acid (HOBr) act as highly effective secondary oxidants. They broaden ozone’s disinfectant spectrum and are frequently the dominant agents in pathogen inactivation, especially in seawater systems.

2. Further Oxidation to Bromate

   HOBr + O₃ → BrO₃^– + H⁺

   Continued oxidation leads to the formation of bromate (BrO₃^–), a persistent disinfection by-product regulated in many jurisdictions. Bromate formation is a function of pH, ozone dose, temperature, and reaction time. It also contributes hydrogen ions, potentially lowering pH in systems with limited buffering capacity.

Comparative Advantage: Ozone vs. Chlorination in Marine Systems

While chlorination of seawater is well established, it produces halogenated organic by-products such as trihalomethanes (THMs) and haloacetic acids (HAAs). Ozone, by contrast, reacts more cleanly, rapidly decomposing and producing fewer persistent organohalogens. The oxidation products formed, primarily bromine species are effective disinfectants with lower toxicity profiles.

Furthermore, ozone achieves microbial reductions without requiring the long contact times associated with chlorination, making it more efficient and responsive in dynamic flow-through systems.

Ozone and Iodide: A Secondary Oxidation Route with Minimal Disinfection Impact

Though less abundant than bromide, iodide (I^–) is still chemically relevant in seawater. Ozone oxidizes iodide through the following sequence:

1. Primary Reaction

   O₃ + I^– → IO^– + O₂
   IO^– + I^– + 2H⁺ → I₂ + H₂O

   This results in hypoiodite (IO^–) and elemental iodine (I₂). While iodine has some disinfectant properties, it is significantly weaker than brominated species.

2. Final Oxidation to Iodate

   IO^– + O₃ → IO₃^–

   The terminal product, iodate (IO₃^–), is stable and non-toxic, with no current regulatory thresholds. Its formation has negligible impact on seawater pH, though it may contribute to subtle shifts in iodine speciation and trace nutrient balance in marine ecosystems.

Implications for System Design and Process Control

Ozone’s interaction with halides is rapid, pH-sensitive, and highly dependent on reactor hydraulics. In seawater systems, precise control of contact time, ozone mass transfer, and residence time distribution is essential to:

• Maximize inactivation of microbial pathogens
• Limit bromate formation
• Preserve equilibrium in complex seawater matrices
• Avoid excessive acidification in low-alkalinity conditions

These objectives require more than just ozone delivery. They demand reactor geometry matched to hydraulic loading, integrated oxidation-reduction potential (ORP) feedback, and selective post-treatment to remove residual oxidants before process water reaches sensitive biological endpoints.

Engineering Leadership in Halide-Aware Ozone Application

At Pinnacle Ozone Solutions, we treat ozone not just as a chemical input, but as a reactive system. Our approach to seawater treatment is based on:

• Fundamental reaction kinetics
• Mass transfer modeling specific to halide-rich water
• Real-time process control using advanced sensors and oxidation potential feedback
• Validation against published seawater disinfection data

We do not treat bromide and iodide as limitations. We treat them as parameters to be understood, modeled, and managed. Halide-Aware Ozone Use in Seawater Disinfection is the foundation of our strategies in recirculating aquaculture systems, desalination pre-treatment, ballast water disinfection, and coastal effluent polishing.

Conclusion: From Reaction Chemistry to System Reliability

Ozone’s reactions with bromide and iodide define its performance and risk profile in saline environments. These reactions are not trivial. But when understood and controlled, they unlock disinfection capabilities that chlorine cannot match.

Pinnacle Ozone Solutions continues to advance seawater oxidation through applied science, engineered systems, and field-proven methodologies. Our leadership in the ozone industry is built not only on technology, but on chemistry, data, and precision. Contact Us to learn how Pinnacle Ozone Solutions can help you implement halide-aware ozone systems for your seawater or high-salinity applications.