@DoomsdaysCW
I wonder what the practicalities on this would be. Not wanting to rain (in any color of shower) - on your urea parade, I just like to think about these things:
- Would national pee production be enough to supply fertilizer needs?(actually probably yes, there’s plenty of NPK in pee)
- How would this resource be collected? Would it be feasible to separate it back out of sewage sourced from waste treatment plants; or would the urine need to be intercepted…
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@DoomsdaysCW
… pre-toilet and transported from individual homes, offices, etc?
- What would it take to process urine &/or sewage into urea acceptable as a precursor to fertilizer production?
Could existing plants be retooled to convert from some other process to the urine/urea conversion?

All excellent quesstions, @Gorfram ! I'll be doing some research!