Vice did a good documentary on NYC's effort to do just this

You Don't Know Shit https://www.youtube.com/watch?v=ZiNiBZiR_uA https://www.youtube.com/watch?v=EVGdmE4_h4c https://www.youtube.com/watch?v=Ra47l7fihZU

Interesting, it looks like most of the liquid gets separated out early on in the process and released downstream(with processing???). Seems like a good opportunity to collect the pee part.

From my understanding, it's better for making biomethane if you separate them. The methane comes from feces, and bacteria digest parts of urine into ammonia, which slows down the bacteria that convert feces into methane.

> Using an inoculum acclimated to high ammonia concentrations was critical to successful biogas production at these high TAN concentrations.

That's what this part is talking about. They intentionally introduced bacteria that were tolerant of high ammonia levels to work around all the ammonia the urine gives off. The wild-type bacteria aren't tolerant of those levels of ammonia, and do a poor job of digesting the feces when mixed.