Oxidation of As(III) to As(V) using ozone microbubbles

• The oxidation of As(III) to As(V) using ozone microbubbles was highly effective.
• The pH of the solution was an important parameter in the rate of oxidation.
• The rate of oxidation increased with increasing ozone generation rate.
• Hydroxyl radicals were involved in the oxidation of As(III) at low pH.
• The oxidation of As(III) followed an overall second-order kinetics.

The use of ozone in the treatment of water and wastewater is rapidly increasing due to its high oxidizing power. Arsenic is one the most toxic elements found in water. As(III) and As(V) are the major sources of arsenic poisoning. It is known that As(V) can be more easily removed from water by adsorptive methods than As(III). In this work, oxidation of more toxic As(III) to less toxic As(V) was studied in a pilot-plant by using ozone microbubbles. The microbubbles were effective in dissolving ozone in water. The oxidation was fast over a wide range of pH (e.g., 4–9). The role of hydroxyl radical in the oxidation of As(III) under acidic conditions was investigated by using 2-propanol as the hydroxyl radical scavenger. Under acidic conditions, the addition of 2-propanol slowed down the oxidation, which proves that hydroxyl radicals were involved in the oxidation process. The effect of carbonate ions on the rate of oxidation was investigated. It was found that the generation of carbonate ion radical from the carbonate ion accelerated the oxidation of As(III). The kinetics of oxidation of As(III) by ozone was studied.