Depends on the source of course. McDonalds in the UK claim to fuel about half their fleet of delivery vehicle with the used oil from their own restaurants. If

Depends on the source of course. McDonalds in the UK claim to fuel about half their fleet of delivery vehicle with the used oil from their own restaurants. If you get the source right, biofuels are great. But as you say, get it wrong (e.g. the EU policy of encouraging bioethanol) and it is disastrous for biodiversity. I'm surprised we are not doing more with sewage, but I suspect that is to do with the difficulty of processing such a mixed substance, and the amount of infrastructure that would have to be changed.