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All restaurant could produce much of their own energy from bathroom & food waste converted to biogas and fertilizer closing the loop.
Just from all the food waste a restaurant produces it could produce several hours worth of biogas (methane). If the waste from the bathroom were added a restaurant could produce enough biogas to cut their bill anywhere from 1/3 to 1/2 - it all depends on how efficiently it is used and how much is wasted. Not only is methane produced in the process but a very valuable fertilizer that can be put right back on the farm land to feed plants organically.
I've seen discussions about restaurants composting but why not first make an energy source - gas, that a restaurant can use as it without much filtering or cleaning.
If a home can produce all it's own cooking gas with some extra for lighting then a restaurant can at least cut its use of natural gas and through better efficiency (wiser use) the biogas could go a long way to cutting fossil fuel use.