With regard to biogas, you should note that without supplementing with food or other material, the wastes from one person will not generate enough biogas to cook their own meals. This is because the feces and urine from one person will, on average, produce one cubic foot of biogas per day, which in turn is enough to run a one burner stove for about 10 minutes. (On my stove, it takes 12-15 minutes to heat enough water for three large cups of coffee, and cooking rice takes about 40-50 minutes.)
That means, in essence, that a community toilet facility which connects to a digester-- again, without supplementation with other wastes-- will most certainly not produce enough biogas to support pressurization of cylinders to distribute to anything except a small fraction of those who "contribute". (And it will take a good deal of the energy from the biogas to run the pump.) Further, it is wasteful to compress raw biogas, since it's about half carbon dioxide, and it is functionally impossible to liquefy it using low-cost pumps.
Again, though, where food or other digestible wastes are added to such a digester, then it could produce more (and perhaps far more) biogas.
You should also know that anaerobic digestion will not destroy some of the more persistent pathogens until the wastes have been allowed to remain anaerobic for 6 or more months. Where fresh material is mixed in, the clock must be restarted. Thus a community wastes digester must deal both with the issue of what to do with the effluent, and how to insure it is safe.
Propane, on burning, does /not/ produce fumes that are any nastier or more dangerous than butane or methane. And finally, butane, methane and
propane all require different-sized holes in the burner, so that one stove cannot be designed to efficiently burn any of the three. The issue of designing efficient stoves is indeed very important, but it has as much to do with the design of the pots that go on the stove as it does the stove itself. Quite good biogas stoves have been designed and are being sold, but I am not aware of any that have taken the step of designing pots that contribute to the capture of the heat produced.
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