I'm just finishing writing a program for an automated small to medium scale biogas
systems. It is modeled after Comercial biogas systems. The digester is kept warm
with its own gas and is agitated periodically to prevent caking. Gas is passed filtered and dried and compressed for storage. Yes compressed....don't panic. The collection system is always under positive pressure preventing oxygen from entering the collection system. Failure to produce positive pressure shuts the system down. End goal is to be able to use normal natural gas appliances with the standard regulators and controls.
The key to biogas is consistent temperature. Then feedstock.
I'm hoping to have my first trial system up running this (2016) summer. My findings will be documented on my youtube channel (good or bad) user name, dadigitechman.