permaculture

[Marimike6@cs.com]

Doug and Lora--

Manure effluent does contain a lot of CO2, plus traces of other gases. A good 
overview and assay can be found here:

http://www.eere.energy.gov/consumerinfo/factsheets/ab5.html

I think the basic point to most collection-digester systems is that by 
containing the manure for a period, usually around twenty days, you capture 
the 
gases that usually escape into the air, making your animal operation possibly 
obnoxious to your neighbors or to yourself. 

A sensible approach, if you're thinking of building one yourself, is to start 
with a solids separator-- a sieve or slat system that will allow the urine to 
be collected separately. I would just batch the manure itself into the 
digester. If you have large amounts of rotten vegetables, like unsold 
pumpkins, 
lying around you can use them. But don't bother to put straw or grass 
clippings 
in. They have very little potential for outgassing, and have better uses 
around 
the farm.

Depending on the size of your operation, you can collect and pipe enough for 
your cooking needs, and possibly for heating your water. But if you want to 
heat a Wisconsin farmhouse in winter, I think you'll need a lot of cows.

Down here at NCSU the guys in the lab coats have looked very closely at 
biogas for the past few years. I think the consensus is that even in a very 
concentrated operation (they're looking at CAFO's like pig, turkey and 
chicken farms) 
it doesn't really pay to develop a system around gas sales. They're looking 
at other directions in post-manure products, like high protein animal feeds. 
Black soldier fly larva would be an example. If you want to check out one of 
the 
really good research schools on the subject, start here:

http://www.cals.ncsu.edu/an_sci/annrep95/swine/swin9514.html 

http://www.bae.ncsu.edu/programs/extension/publicat/wqwm/ebae071_80.html 

http://www.hydroponics.com.au/back_issues/issue59.html 

http://www.epa.gov/agstar/pdf/ag_fund_doc.pdf 

Finally, here's something from the middle of a long conversation on another 
list about the subect. Scroll forward or backward and you can find much 
useful 
info:

http://listserv.repp.org/pipermail/digestion/2004-May/000406.html