The primary purpose of wastewater treatment is biological material and nutrient removal, primarily nitrogen. Check out the wikipedia page for more details, I’m a biologist, not a chemist. https://en.wikipedia.org/wiki/Wastewater_treatment
So this is actually my industry - Wastewater Based Epidemiology or WBE. It is very anonymous. There is no way to pick out one person’s identity from the waste stream. What we get is a about 100mL of blend from 24 hour’s worth of shit water passing into the treatment plant. A tiny treatment plant is processing 100,000 gallons per day, while a top 10 plant is processing > 100 Million gallons per day.
It’s not strictly privacy-focused but The Goblin’s Notebook is designed exactly for your use-case. It has markdown, object connections, every object has a player visible setting, so your players can access known content while you keep secrets hidden. There’s a free tier, a mid tier at $1.50 and an unlimited tier at $3 dollars a month (managed via their patreon).
I also have been using podcast addict, probably for over 10 years now. You can autodownload new episodes (mine checks daily at 7a and 7p), create custom playlists for juggling multiple podcasts at once, has android auto support, and you don’t have to deal with the bs of Spotify.
I’m sure there are a 100 other features I don’t know about, but that’s what I use.
Every treatment plant in the country is already collecting samples of wastewater as it enters and leaves the plant as they have to take certain measurements every day to show compliance. To my knowledge, there is no way to identify/track individuals based on wastewater. There is a government database of everyone’s license plate.