UV disinfection requires an excessive amount of energy.
UV lamps have low electrical efficiencies and thus are not "energy-conscious".
The energy costs alone make UV disinfection significantly more expensive (O&M) than chemical disinfection.
Environment / Safety
The mercury contained inside the UV lamp presents a hazard to end-users (or surface waters).
Mercury contained inside the UV lamp presents an environmental hazard after disposal of used lamps.
Lamps break frequently and release mercury to the environment.
UV systems present a safety risk to plant staff because of the potential of exposure to UV-C radiation.
The visible emissions from UV lamps will cause algal growth.
UV creates DBPs that have yet to be discovered.
Lamps are always burning out and require frequent replacement.
Between lamp replacement and lamp cleaning, operations staff will spend a significant amount of time maintaining a UV disinfection system.
Lamp ballasts are unreliable and require frequent maintenance/replacement.
UV disinfection cannot be cost effectively used for 4-log virus inactivation.
Since drinking water plants have to add chlorine/chloramines for virus inactivation and residual, adding a UV system does not make financial sense unless required for Cryptosporidium inactivation.
Microorganisms can "re-activate" following UV disinfection.
Regulators won’t approve UV disinfection without significant validation and pilot testing.