“Disinfection is the destruction, inactivation or removal of those micro-organisms likely to cause subsequent infection of people. Wastewater disinfection refers to the use of a process designed specifically to reduce the numbers of viable, infectious microbial organisms in an effluent, ...” (Wright, 1997). Because of its high oxidation potential and specific lethality, ozone is the most effective disinfectant (killing bacteria, inactivating viruses and protozoa).
O3 : 2.07 volt (pH = 7)
Cl2 : 1.36 volt (pH = 2 - 6)
ClO2 : 0.95 volt (pH = 7)
In addition to disinfection, wastewater treatment must address other factors such as lowering the COD (Chemical Oxygen Demand), and to a lesser extent sometimes the BOD (Biological Oxygen Demand), as well as making improvements in colour and odour. With ozone, oxidation of organic matter and precipitation of metals further improve the water quality and allow its reuse.