It's certainly doable. Raise the cost of commercial fish sky high. Good to some, bad to the majority who buy fish to eat. Same with hatcheries for fisheries. Significant increase in cost, which is license fees.

It is a problem of volume. Like as has been said, metro sewage discharges (like hatcheries) have low levels of nutrients but they make it up in volume. Getting the last couple ppm or ppb out of a waste stream is very speedy.

Plus, I don't think any of the ozone or UV treatments are 100% effective. 99.9999 still lets some out and that one survivor may successfully find a host and spread.

This whole argument revolves around risk versus cost.