[permaculture] The energy-efficient homestead.

David 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 
http://www.fao.org/ag/AGAinfo/resources/documents/DW/Dw2.htm and 
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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