Good link to information about biogas and digesters

I was looking for different ideas for building a digester and found this .pdf file. It is old, but the information is good.

http://c.ymcdn.com/sites/www.echocommunity.org/resource/collection/C01889C5-4BB2-424C-962F-F5B14EF26E69/Biogas.08.pdf

I was considering the sliding barrel method, but now I am thinking about using a sealed barrel with an inlet and outlet and having the gas going to inner-tubes or bladders to supply the pressure. The biggest issue with biogas is keeping out the oxygen, so using a bladder with a sealed barrel should make the process easier/safer.

Thanks Chris

the way google is going to do it... solve for X

http://nextbigfuture.com/2013/02/converting-municipal-waste-to-energy.html#more