I think the depolymerization plants hav ethe most promise, *and* get rid of biological wastes as well.
Mix that with a herd of small nuclear plants and some judicious hydro/wind/tidal power plants and we're all set. Later on we can manage with a heard of nuclear powered hydrogen generation plants, or maybe, just maybe, once there's a nuke site in every county across the US the people can stop being so exasperatingly paranoid about it and we can have electric cars with point-source recharging from small isotope generators onboard. Run the car out of juice? Just sit an hour or so and it's back on full charge ready to go. Heh, it'd bring back the advent of the sit-down restaurant too :-D