Hmm I wonder what that would smell like... gross but I suppose they would burn. But then if you're doing that it would make more sense to burn the waste that they were eating in the first place, less efficiency loss there actually. The key is drying it and burning it cleanly. Biomass is biomass!
"And Lord, we are especially thankful for nuclear power, the cleanest, safest energy source there is. Except for solar, which is just a pipe dream." Homer Simpson, 1990