I think a couple of people have already pointed out the process, but do you think we could actually make a measurable dent in our diesel fuel consumption from fast food resturants? Diesel is used for tractors and harvesters, semi trucks, trains, mixed with karosene and naptha (if I remember right) as part of making jet fuel, RVs and Diesel pickups (used for RVs, hotshot rigs and small deliveries), delivery trucks and personal automobiles. While the total produced by fast food recycling into biodiesel might help with the passenger cars and some RVs, there just is not enough from that source to make an appreciatable difference in out National Daily consumption of Diesel. We need massive amounts of it, and that would mean using corn, soybean and other vegetables to make it.
Does anyone know if you can make Biodiesel from a Yucca Cactus? If so, that would go a long way towards a good supply. Think of the Desert Southwest where most of the land is useless without massive and costley irrigation, yucca grows there.