I'm not a scientist, I'm a city planner. But, first I saw this: http://ecojohn.com/ecojohn_sr.html I couldn't find a link, but somebody once posted on a city in southern California that converts its sewage into methanol. Putting 2 + 2 together, it occurred to me that the ash resulting from the incinerating toilet could be used as a fuel source. Anyway, there are people here who with much more scientific acumen than I. Could this be done at a microscale, i.e., using the toilet to power the home? Since methane is flammable, why not use it to heat gas stoves. Not a very pleasant thought going from the bathroom to the kitchen instead of the other way around, but is it conceivable?
There's a guy in Florida, who has figured out a way to turn 6 lbs(i think) of cow manure into 1 gallon of fuel for your car. You need a very simple tweak to the car. The problem he's having is scale.
Just doing some very simple research, I've come across this: http://en.wikipedia.org/wiki/Microbial_fuel_cell Someone please correct me if I'm wrong, but I would have thought that the major obstacle to a waste disposal system that is sustainable in terms of energy and doesn't need water would be the scale i.e., you would need a plant to do this. If I'm reading this right, this is a very doable project. I'm not an engineer so there must be something that I'm not seeing here.