www.build-a-biogas-plant.com/small-sc...s-design/
Biogas is a clean cooking and lighting fuel that can be produced at varying scales; from small household systems to large-scale commercial plants producing several thousand cubic metres a day. Biogas can be used for electricity generation, heating, cooking, process steam and powering farm equipment.
This link contains a number of papers that can be downloaded for small scale biogas design, suited to domestic applications. Refer to the Design page to download designs for other larger or community systems.