Advance Oxidation Process (AOP) For Water Treatment

The Advance Oxidation Process (AOP) is a water treatment technology that utilizes powerful oxidizing agents to remove contaminants from water. AOP creates hydroxyl radicals, a powerful secondary oxidant. This secondary oxidant can cause the oxidation of most organic compounds until they are fully mineralized as carbon dioxide and water. The hydroxyl radical has a much higher oxidation potential than hydrogen peroxide. Ozone usually reacts at least one million times faster, leading to a lower contact time and footprint.

Oxidation water treatment

Most water purification plants worldwide use chlorine for disinfection. In recent research, however, it has been suggested that chlorine produces THMs, such as chloroform, when it mixes with organic molecules. Free radicals produced by THMs are highly carcinogenic (Díaz et al., 2011). According to the United States Council on Environmental Quality, chlorinated water users face a 93% higher cancer risk than non-users (Yan et al., 2021). Therefore, many water purification and wastewater facilities now disinfect water with O3. The most widely applied advanced oxidation processes (AOP) combine Ozone, Ultraviolet Light, and Hydrogen Peroxide.

Advantages and Limitations of Advanced Oxidation Processes For Water Treatment:

• High Degradation Efficiency: Advanced Oxidation Processes can kill viruses and microorganisms in just a few seconds due to their high oxidizing strength and quick response time.
• Environmentally friendly: Ozone is generated in situ and leaves no harmful residue after disinfection. This procedure adds oxygen to the water.
• Chemical-free: Unlike other water treatment methods that may rely on chemical additives.
• Broad Spectrum of Contaminant Removal: Advanced Oxidation Processes effectively remove many contaminants, including organic compounds, pesticides, pharmaceuticals, and microplastic pollutants. They can degrade contaminants into smaller, less harmful molecules or mineralize them into harmless byproducts, thereby reducing the environmental impact of water pollution.
• Operational Costs: While AOPs may have higher upfront costs due to the equipment and energy requirements, they can offer lower operating costs than conventional water treatment methods.

However, there are some limitations to the use of ozone in AOPs, such as:

• pH and temperature dependence: The efficiency of ozone oxidation can be affected by the pH and temperature of the water, requiring careful control and optimization for optimal performance.
• Bromate formation: Ozone can react with bromide ions in water to form bromate. This regulated disinfection byproduct needs to be carefully managed.

Chemical Principes for the oxidation processes

Despite its highly reactive properties, ozone is a gas with limited solubility in water. Due to this complexity, ozone reactions in the aqueous system are highly complicated, involving gas-liquid mass transfer, self-decomposition, and reactions with dissolved and suspended organic contaminants and inorganic constituents. Ozone’s high redox potential allows it to oxidize numerous compounds, including iron, manganese, nitrate, sulfides, and bromide.

In many cases, ozone oxidation reactions are characterized by oxygen transfer from the ozone to the reactant. In water, ozone primarily reacts with:

O3 + HO− → HO2− + O2 (reaction between O3 and a hydroxyl ion leads to the formation of H2O2 (in charged form))

O3 + HO2− → HO2· + O3−· (a second O3 molecule reacts with the HO2− to produce the ozonide radical)

O3−· + H+ → HO3· (this radical gives to ·OH upon protonation)

HO3· → ·OH + O2

Some of the Applications in Advanced Oxidation Processes in Wastewater treatment

• Removal of Aromatic Compounds From Wastewater
• Removal of Dyes From Wastewater
• Removal of Pharmaceutical Compounds
• Removal of Pesticides
• Removal of Organic compounds

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