It occurs to me that I throw away enough food, both spoiled leftovers, and stuff that we bought and didn’t eat, to power an efficient automobile if it were converted into ethanol. I would think there might be some way to collect that and turn it into ethanol. God, what a stinky, nightmarish mess it would be, though. Ugh!!
I’d say that a few additions to the sewer system might allow the ability to tap the massive quantities of methane that’s anyway produced, to be scrubbed, and bottled as fuel.