Bill Mollison writes about making use of biogas in his Permaculture Principles described in "Introduction to Permaculture" and elsewhere. It is a critical - not to mention fun! - process for recycling nutrients for agriculture while producing 100% natural, clean-burning renewable energy for cooking or fueling generators or pumps. 

For permaculture design instructors and other educators as well as anyone interested in learning about biogas, we offer biogas experimentation kits that include everything needed to produce a safe and usable amount of biogas for classroom demonstrations.

The kits are $109 USD + shipping available from our website shipped via Fedex Ground... 

http://hestiahomebiogas.com/products/

And can also be found on Ebay with your choice of shipping method...

http://www.ebay.com/itm/191085368222?ssPageName=STRK:MESOX:IT&_trksid=p3984.m1561.l2648

If you are not in the US or cannot afford a kit, please contact me and I can get you the material list and instruction booklet to make your own.