If you read up on refining biodiesel, you'll find that the byproduct is
simply a biodegradable vegetable glycerin.
This glycerin can be composted and may serve as a fertilizer for the plants
grown to produce the next batch of fuel. The glycerin can also be used to
make soaps. As far as power plants burning biological material, "biological
material" or "renewable fuels" can mean anything. Raw vegetable oil is not
very clean when burned, contrary to the "greasels" out there. Same with
burning straight crude vs refined petroleum. Once the vegetable oil is
transesterified (refined), it is very clean burning and the byproduct is
inert. You won't get much better than that until we're electrolyzing
hydrogen from water using solar power. It's pretty expensive to run an
economy on subsidized agriculture. Biodiesel is a good start and much better
than the Bush plan to make hydrogen from petroleum. My goal is to not have
any gas consuming vehicles by this time next year.

-Steven Dodson
Kneeland, CA
"Inga" the 87 Syncro

-----Original Message-----
Date:    Tue, 11 May 2004 23:52:53 -0400
From:    Joy Hecht <jhecht@ALUM.MIT.EDU>
Subject: Re: Diesels on NPR this morning

There is a question, though, about what kind of biological material is used
to make the fuel.  I don't know how auto fuel is made, but with power plants
that burn biological material, it's not clear that they are that much better
than petroleum.  They put out GHG emissions, and if the fuel isn't grown
organically, its cultivation generates a lot of water pollution from ag
runoff.  Is the biological matter used to make biodiesel the waste from some
other ag process or grown specifically for fuel?  In the former case, what
is now done with that waste.  If it's excess nutrients that we've found a
new use for, great.  But if it was returned to the soil to enrich it for
future agriculture, then we'll have to replace it.  If it was grown just for
making fuel, then how?  Growing biofuels organically is pretty expensive.

All of which isn't to say that they aren't a good idea, just that they may
not be financially viable, and they also may not be environmentally
preferable to the alternatives.

Joy