methane?

So here's the science/facts:
-Methane is 21 more times more powerful a greenhouse gas than CO2.
-Its atmospheric concentration has more than doubled since pre-industrial times.
-The number one source for all of this methane? Animal Agriculture.

So i was inspired while in the bathroom (which is where most of my inspiration occurs), and i thought to myself: why aren't we using poop/feces as a fuel? Where does it get filtered to in treatment plants and what is done with it once separated? Cows are bastards that, while delicious, are screwing up our environment! There must be some way to separate methane in the air from other gases. Can't we put all the cows in a barn or something and suck out the air and use that fuel? Ok, no, that would be a bad idea. Not enough room for them plus it's dark and would be pretty gross.

Then it came to me:

Lots of cows in a bio-dome where we suck the air out and use it as fuel. We could even put them in the desert because, hello: bio-dome! This not only helps us migrate cow populations out of big cities where they are a nuisance (damn cows eating up my front lawn) but now we've got a useful fuel while saving the environment!

You're welcome humanity.