This paper discusses treatment and emergent pathogens:
"The Role of Wastewater Treatment in Protecting Water Supplies Against Emerging Pathogens"
https://www.jstor.org/stable/23803199
I thought direct chlorination played a larger role, it seems it doesn't.
(Heavy chlorination of water does result in post-treatment chlorine compounds being present, these are themselves an environmental concern. The bulk of the chlorine evaporates or is reacted relatively quickly. Chlorine also negatively impacts "digestors" which process residual organic matter in wastewater.)
UV, oxygenation, sunlight, filtration, and dilution are all utilised as well.
Viruses tend not to survive long periods of environmental exposure outside a host in most circumstances, though I'm not knowledgeable on specifics or exceptions.
I wouldn't be too worried about catching COVID from the water.
But it's not really necessary most of the time.
It's often done more for political reasons than technical ones, because it's easier for the public to understand and trust UV disinfection than the other, much more complex processes that are typically used.
Cobb County GA is an example of a plant that has large scale UV treatment right before discharge into the Chattahoochee River. But it's effluent is cleaner than the water getting pumped into their water supply.