Ozone (O₃) is one of the strongest oxidizing agents that is readily available. It is used to reduce color, eliminate organic waste, reduce odor and reduce total organic carbon in water.

Ozone is created in a number of different ways, including ultra violet (UV) light, corona discharge of electricity through an oxygen stream (including air), and several others. In treating small quantities of waste, the UV ozonators are the most common, while large-scale systems use either corona discharge or other bulk ozone-producing methods.

Ozone is formed as oxygen (O₂) is struck by a source of energy. The bonds that hold the O₂ together are broken and three O₂ molecules are combined to form two O₃ molecules. The ozone begins to break down fairly quickly, and as it does so, it reverts back into O₂. The bonds that hold the O atoms together are very weak, which is why ozone acts as a strong oxidant as readily as it does.