Eli5: what exactly does it mean when sewage is treated them released into a river?

Question

So the city it talking about treating sewage before dumping it into a river that I see tons of people swimming and fishing in. How does this work?

In: 11

Answer 1

Sewage treatment plants exist to convert raw sewage into relatively clean water.

The effluent of sewage treatment plants, particularly in developed countries with decent pollution regulations, is mostly just water — the nasty stuff was either left behind in a digester/settling tank or scraped off a semi-permeable membrane.