Advance Oxidation Processes (AOP) is an oxidation method consisting of highly reactive species used in the oxidative destruction of target pollutants. In 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 ozone or hydrogen peroxide. Ozone usually reacts at least one million times more quickly, leading to a lower contact time and footprint.
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% increased risk of cancer than non-users (Yan et al., 2021). Therefore, many water purification facilities now disinfect water with O3.
Benefits of AOP For Water Treatment:
- It can kill viruses and microorganisms in just a few seconds due to its high oxidizing strength and quick response time.
- After disinfection, this procedure adds oxygen to the water.
- There is no need for additional chemicals.
- It has no odor or flavor.
- It is pretty effective in eliminating germs.
- It can kill bacteria, molds, organic substances, and other contaminants in water.
- O3 is swiftly converted into oxygen and disappears after use.
- It can reduce COD with low operational costs.
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 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 the transfer of oxygen 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 wastewater
- Removal of Aromatic Compounds From Wastewater
- Removal of Dyes From Wastewater
- Removal of Pharmaceutical Compounds
- Removal of Pesticides
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