Ozone gas is created inside a small unit and a tube feeds it into the return water. The circulating filter water, flowing through a venturi, sucks in the ozone just like a carburetor draws in gasoline. UV systems use one or two special fluorescent tubes inside an ozone chamber. Powerful UV rays break the air molecules down into ozone just like the sun does in the upper atmosphere. Corona discharge units create ozone like lightning in a thunder storm.
Ozone is the fresh smell outdoors after a thunder storm.
These units basically produce tiny lightning bolts inside of the ozone chamber. Although both designs are effective, UV is the simplest system. If the long-life tube ever burns out, just replace it. Neither design uses much electricity, but the CD systems are slightly more efficient to operate and they produce higher ozone concentrations for large pools. Instead of using chlorine chemicals for the residual level, consider a new salt system to generate its own chlorine.