"Bill" wrote:

On a visit over 30 years ago, I saw methane gas being "siphoned" off
of the "settling pools" (surely the wrong word) as part of the
process at sewage treatment plants. I assume they are even better
at it now.
-----------------------------
Check out anaerobic digesters.

Standard bio-mass technology.

The State of Ohio has a pilot plant operation under test to collect
cow poop from farms, convert to methane, run turbine/generator to
generate electricity to run the Ag Experiment station located at
Wooster, OH.

The whole thing was less than $10Meg.


Lew