Ozone

Oxygen in the air (O2) is composed of two oxygen atoms.  Under certain conditions, three oxygen atoms can be bound together instead, forming ozone (O3).

Ozone molecule.

Ozone has many advantages as a disinfectant.  It kills all pathogenic organisms by a direct effect on their DNA.  Disinfection with ozone occurs 30,000 times faster than with chlorine, so a prolonged contact time is unnecessary.  And there is no harmful residual left in the system.

The disadvantages of an ozone disinfection system include a corrosive nature, a high cost for the initial set-up, and a high electricity consumption.