Biogas Volume 3: A Chinese Biogas Manual by Michael Cook
This book describes ways the Chinese perfected the process of making farm-scale daily methane from organic material, using pits.
The manual shows you how to dig a hole, make a brick or earth wall, and then cover it for continuous production of free methane from the digesting material.
This is a beautiful, very low-maintenance system that you can build in your own backyard. The Chinese had over 6 million working biodigesters of this type in the late 1970s/early ’80s.