"can be done with human waste"
It is, LA County runs all the deisel pumps/generator that support thier eerrr, wastewater treatment facilities from methane. The airport uses food waste to generate methane as well.
FOr more on the technology & how YOU can use it, see http://journeytoforever.org/biofuel_library/MethaneDigesters/MD1.html
Since I was a kid, Milwaukee solid waste has been marketed as fertilizer under the label Milorganite.