[permaculture] The energy-efficient homestead.

Lawrence F. London, Jr. lflj at intrex.net
Thu Dec 27 17:14:39 EST 2007


David wrote:

> 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 
> http://www.wrc.org.za/archives/watersa%20archive/2004/Jan-04/16.pdf), 

Thanks for the links.

> 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

I wasn't suggesting using algae or duckweed as biogas substrate. As they are
easy to grow in ponds that store ag runoff water and easy to harvest it would be best used
as mulch, fertilizer and soil conditioning on land used to grow the crops actually used to generate biogas, i.e. corn, 
harvest the ears then make biogas out of the stalks. Then return the spent slurry to the land.
This would represent a more efficient energy audit trail. Are you familiar with the Emergy concept:
 From Wikipedia:
"The term Emergy was originally coined by David M. Scienceman in collaboration with the late Howard T. Odum. H.T.Odum 
used 'emergy' to mean both sequestered energy and emergent property of energy use. However Scienceman also used the term 
'emergy' to refer to the concept of energy memory, a concept which motivated Scienceman and B.M. El-Youssef (1993) to 
propose the addition of a new dimension to physics, [P] for "past". Some researchers maintain that it can be expressed 
as a scientific unit which is called the "emjoule", a contraction of "emergy joule"."

(D.M. Scienceman, indeed. must really be his real name . Wonder if he is the original Mr. Science you hear about 
frequently? :----))


> fodder, then putting the livestock manure through a digester.

As appropriate technology, keeping this system as simple as possible is a good thing. Not everyone has livestock, for 
various reasons, predators being one. Stopping the cycling of the aquatic plants as soil amdenment makes a lot more 
sense to me. You're producing a harvestable crop with chaff used for biogas production and you are recycling nutrients 
and water that originated in the garden in the first place. A second best option as far as I can tell would be to feed 
to auatic plants to the livestock to gain food and manure for biogas and fertilizer. Actually I would grow food and 
forage crops with the aquatic plants for human use and livestock feed then return the manure to the garden to help start 
the nutrient cycling once again. Using only crop residues for biogas might be the most efficient system, also since 
you'll have them on hand anyway, also using manure for biogas would make the gas generating system more complex and the 
process more difficult. If you set up one fixed system to use year after year that might be more reliable and more 
easily replicated around communities. Equipment for this type of system could be improved upon and tailored for plant 
residues. I am assuming the using plant material and manure require different handling methods and maintenance.
So you have with my system:
1) channelling water runoff from farmland and homestead, forest and field to catchment ponds
2) grow aquatic plants in these ponds (you're also creating another ecosystem plus wildlife habitat)
3) harvest the aquatic plants and apply them directly to the land as mulch (also represents fertilizer top dressing)
4) grow food, forage, grass, grain, legume, herb, fruit crops on thios land
5) harvest crops and return crop residues to the biogas digester
6) return the biogas digester residue to the land or to a compost pile
6) feed forage crops to livestock and return their manure to the field or to a compost pile, along with some of the
    aquatic plants harvested and some of the harvested crop residue from the fields; also add compostable materials from
    fields and pastures and from the forests
7) growing field crops for pigs to harvest as forage would be a good thing also, their manure could be field applied,
    added to compost or if sufficient quantities were available used for biogas production. Having a diversity of
    livestock would be important using cows for compost, pigs for biogas, poultry for compost. Channelling runoff from
    around all areas that the livestock use would be a good thing as their manure would get washed into the
    algae/duckweed ponds to add nutrients to be recycled. I would think cattails, water hyacinths and possibly papyrus
    (all cold hardy excpet the hyacinth) could be turned into biogas directly. I know that water hyacinths are used for
    this purpose. Anyway, you'll have to have cattails in the ponds to extract nutrients from bottom sludge so you may as
    well find a good use for them, mulch for crops being one of many.

> 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.

Just Google it and you'll see lots of instances of use for biogas. John Todd's
Ocean Arks International is a fascinating organization doing great work. They evolved from the New Alchemy Institute.
You probably are familiar with them.

LL
-- 
Lawrence F. London, Jr.
lflj at intrex.net
lflj at bellsouth.net
venaurafarm at bellsouth.net
Venaura Farm http://venaurafarm.blogspot.com
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