Water reuse via ozonation: an oxidation-driven approach for diverse applications

Introduction

With increasing stress on freshwater resources, water reuse has become a critical component of sustainable water management strategies. Among advanced treatment technologies, ozonation stands out due to its strong oxidative potential, enabling the transformation of a wide range of dissolved contaminants. When considered strictly from an oxidation perspective—excluding any disinfection-related aspects—ozone offers a versatile solution for improving water quality across multiple reuse scenarios.

Fundamentals of ozone-based oxidation

Ozone (O₃) is a highly reactive molecule characterized by a significant oxidation potential. In aqueous environments, it reacts through two main pathways:

• Direct oxidation, where ozone selectively reacts with specific chemical groups such as double bonds, activated aromatic compounds, amines, and sulfides.
• Indirect oxidation, involving the generation of hydroxyl radicals (•OH), especially under alkaline conditions, leading to faster and less selective reactions.

These mechanisms enable the breakdown of complex organic molecules into simpler compounds, often enhancing their biodegradability or reducing their environmental impact.

Objectives of ozonation in water reuse (oxidation focus only)

When applied purely for oxidation purposes, ozonation aims to:

• Degrade trace organic contaminants (e.g., pharmaceuticals, industrial chemicals, pesticides)
• Reduce dissolved organic matter (DOM)
• Convert persistent compounds into more biodegradable intermediates
• Remove substances responsible for color, taste, and odor
• Oxidize dissolved metals such as iron and manganese into removable forms

Application areas based on end uses

Agricultural irrigation

In irrigation reuse systems:

• Ozonation helps break down residual organic compounds that may accumulate in soils.
• It reduces clogging risks in irrigation systems, particularly drip irrigation, by oxidizing colloidal organic matter.
• It enhances the physicochemical compatibility of reclaimed water with agricultural use.

Industrial applications

For industrial reuse (cooling systems, process water, cleaning):

• Ozone reduces dissolved organic load, limiting fouling in equipment.
• It transforms compounds that contribute to scaling or deposit formation.
• It stabilizes water chemistry, which is essential for closed-loop systems.

Aquifer recharge and environmental uses

In managed aquifer recharge or environmental discharge:

• Ozonation converts micropollutants into forms more amenable to natural attenuation processes in soils.
• It reduces the persistence of problematic compounds in the environment.
• It improves aesthetic parameters such as color and aromatic content.

Urban non-potable uses

For urban applications (street cleaning, ornamental fountains, non-potable networks):

• Ozone enhances water clarity and overall appearance.
• It reduces organic compounds that may cause odor or deposits.
• It contributes to maintaining chemical stability during storage.

Integration into treatment trains

Ozonation is typically implemented as a tertiary or advanced treatment step, often combined with:

• Activated carbon filtration, to remove oxidation by-products
• Biological filtration, leveraging improved biodegradability
• Advanced oxidation processes (AOPs) for more demanding treatment objectives

System design depends on key parameters such as ozone dosage, contact time, influent water quality (DOC, alkalinity, pH), and targeted transformation goals.

Conclusion

When applied as an oxidation process, ozonation is a powerful technique for transforming contaminants in reclaimed water. By improving physicochemical quality and reducing the complexity of dissolved compounds, it broadens the range of potential reuse applications. However, its effectiveness relies on proper integration within a well-designed treatment scheme tailored to specific reuse objectives.