Re: like pavement power...you are looking at am absolute max of 5W per person.
Voyna, I took it for granted that we all know the relationship between energy and power.
You are right, of course, that with my max. 5W and your entirely reasonable 10% efficiency, you could power a moderately busy smartphone all day. But I still think that unless you are processing vast quantities of urine a day, you are going to struggle to get enough energy out to do more than manage the material handling and bioculture maintenaince.
There's better, and less sticky and smelly, ways of getting a few kJ of energy when you are off grid.
BTW, according to this urine solids are about 1700 kcal/kg so the 2000 max I "picked from empty air" doesn't look too shabby.