You can compost human waste, but you have to be patient - it can take a couple of years to complete the process. Alternatively, if you have enough waste, less time, and some concrete, you can harvest biogas (methane) a useful fuel
see
http://www.cityfarmer.org/biogasPaul.html
According to article above you also get a very useful byproduct
The effluent from the reactors is an odourless dark coloured slurry. The primary application of the effluent is as an agricultural fertilizer. Other applications include as a feed supplement for pigs, mushroom growing media, fertilizer for fish ponds, worm rearing media (the worms are then fed to chickens), and media for soaking seeds prior to germination
BTW, you can use methane aka biogas in diesel engines
http://www.guardian.co.uk/environmen...methane-energy