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[Plant-education] RE: Alcohol from potatoes and such

David Walker via plant-ed%40net.bio.net (by d.a.walker from sheffield.ac.uk)
Thu May 15 13:51:25 EST 2008

Seems that most of my Email on this subject got lost in transmission. Here
it is again in its entirety. I will try to get back to those of you who have
kindly responded as soon as poss.

I'm pleased that my previous enquiry (about how much alcohol you can get
from potatoes) caused a few smiles but, sadly, I must return to more serious
matters. There are claims on the Net that if you are particularly kind to
algae (which seemingly grow many many times faster than any other green
organisms even if you are not particularly kind to them) they will reward
you with so much biofuel that a mere 4.5 million acres of algal bioreactors
could meet all of the road transport fuel requirements of the United States.

 My problem is that, in open- ponds, algae don¹t produce any more dry weight
in 100 days than do potatoes in a field and that the yield of bioethanol
from both (per acre) is about 400 U.K gallons (petrol/gasoline equivalent
270 U.K gallons). 

 I know that photosynthesis is not synonymous with growth. I learned as a
child about the man who told a grateful king that he would be happy to be
rewarded by a penny on the first square of a chess board, two on the next
square, 4 on the third and so on. (knowing, of course, that by the time that
you got to the last square even Bill Gates and Google together  would not
have nearly enough dollars to do that ).
Compound interest is a wonderful thing  but I can¹t quite figure out to make
by bank balance increase if I keep withdrawing the meagre interest on a
daily basis.

 I am sceptical about a bioreactor that produces more than 100gm (DW) per
square metre in a day because that in itself is right at the top of what the
laws of physics and chemistry allow. I am additionally sceptical about it
running at that rate for 100 days or more. But maybe I¹m missing something?

Best regards

>From David Alan Walker, FRS; Emeritus Professor of Photosynthesis,
University of Sheffield, UK.

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