For bacterial control and water clarity, ozone (O3) or ultraviolet (UV) lamps or a combination of both can be applied. The task in RAS is usually not to completely disinfect the water but to keep the bacterial counts at a reasonable level.
UV light inactivates microorganisms through photochemical damage. The irradiance of UV lights at 254 nm damages the cellular RNA and DNA making the bacteria unable to replicate or infect. An advantage of UV is the lack of residues, because it is a physical process. The disadvantage is that the target organisms are only affected if the light can directly hit them.
