DIG-L: Residential digester

[JDAVIDERICKSON@cs.com]

Hello,
I am new to the list and new to biogas, so forgive me if I ask ridiculous questions!

I live in an agricultural area (Sonoma County, CA, USA), and became interested in the potential for harvesting methane from livestock waste from the many dairies in the area.

Although biogas plants have been built on dairies to generate electricity, I was curious about the potential to use biogas as a natural gas or liquid propane replacement for residential cooking and heating use.

The question for the list I had was this:
Suppose one could build a low cost digester that would have enough capacity to generate sufficient biogas for cooking and heating for a typical residential household, using livestock manure slurry.  (I'm sure it's possible to easily calculate the required digester capacity, but I don't have the background to know how. Could someone point me to a reference on how to do this?)

I'm envisioning possibly a fiberglass digester tank with a motorized stirring system driven by a small photovoltaic array. The biogas would be used to heat the digester, so the whole thing could be completely self-contained, once it was up and running. It would have two chambers to allow continuous gas production. The digester could be buried and connected to the house's gas line.

The livestock waste from the dairies would be collected at a central point, where it would be turned into slurry, and stored  in tanks. Tank trucks would then take the slurry around to the residential digesters and charge them on an as-needed basis. The trucks could also collect the digested effluent.

Is a scheme like this totally far-fetched? Does it seem practical/economical? Is anyone doing anything like this?

Thank you for any input.

Dave Erickson