I am less of a bio-diesel advocate, the more I learn about it.

Emissions has always been a problem, and is probably not news to anyone considering this approach.

The eye-opener for me was learning that modern agriculture is fossil-fuel based, due to the high fertilizer requirements met by using natural gas. So the notions that bio-diesel is renewable, and a zero-contributor to CO2 are incorrect. To the extent that the Natural Gas is domestic, it improves the reliance on middle-east petroleum, but the same could be said of coal ..

On the current small scale that biodiesel is used, essentially scavenging waste products, it is OK. But attempts to scale upward do not seem a good idea.