[permaculture] The energy-efficient homestead.
david at h4c.org
Thu Dec 27 16:28:51 EST 2007
Lawrence F. London, Jr. wrote:
> I was thinking about generating methane from algae tonight and remembered
> David's suggestion to use higher plants for this purpose.
Thanks for the heads up.
Some research has been done on this. One of my favorite quotes is from
Boruff and Buswell, who did a great deal of research in the subject area
in the 30's:
"the present estimate is that from 5 to 10 cubic feet of gas can be
obtained per pound of cornstalks, and that the rate of production
will be from ½ to 1 cubic foot of gas per day per cubic foot of tank
volume. Taking the lower figure, a ton of cornstalks would furnish
gas for 400 people for one day, allowing 25 cubic feet per capita
per day. From the data given by Weber for yields from regions where
30 percent of the land is planted to corn, an area with an 8-mile
radius will produce enough cornstalks to supply a city of 80,000
inhabitants continuously. *In other words, the cornstalks from one
acre will produce the gas for one person for a year." *[emphasis added]
With regard to water-based or aquaculture situations, I have been
thinking a lot of duckweed (which you mentioned) in this regard (see
but I have not yet done research on potential problems of duckweed as a
biogas substrate. Algae, in this regard, can provide some problems
because unless the cell membrane is compromised, a good portion of it
may go through the digester essentially intact. Duckweed is only about
7% dry matter (i.e. 93% water), so this may provide a challenge, since
everything about biogas-- including, for example, heating systems-- has
to scale with increasing dilution of the slurry. In either case, albeit
more probably with duckweed, it may be that the plant could serve as
fodder, then putting the livestock manure through a digester.
An interesting comparison of duckweed and algae is found at
http://library.wur.nl/wda/dissertations/dis3362.pdf (There is really
quite a bit of good stuff available on the web about duckweed.)
Water hyacinth appears to be another promising candidate.
David William House
"The Complete Biogas Handbook" www.completebiogas.com
"No matter how far the material world advances, it cannot
establish the happiness of mankind. Only when material and
spiritual civilization are linked and coordinated will
happiness be assured. Then material civilization will not
contribute its energies to the forces of evil in destroying
the oneness of humanity, for in material civilization good
and evil advance together and maintain the same pace."
'Abdu'l-Baha, The Promulgation of Universal Peace, p. 109
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