Enviroblogs writes about a new train in Sweden that runs on biogas:

Biogas refers to methane produced by the anaerobic digestion of biomass waste. (Aerobic decomposition, or composting, requires large amounts of oxygen and produces heat.)

Biogas produced in anaerobic digesters consists of methane (50%-80%), carbon dioxide (20%-50%), and trace levels of other gases such as hydrogen, carbon monoxide, nitrogen, oxygen, and hydrogen sulfide.

Now, if we could only figure out what to do with the 20%-50% carbon dioxide, CO, and H2S, this could be a moving solution to some of the waste we create.