Learning texts for acquiring knowledge and techniques related to biogas. - Title: The Book of Biogas - Author: Masahiko Kawashima - Theme: Biogas - Content: Knowledge about energy generation - Target audience: Learning text - Title: Practical Biogas Technology - Theme: Biogas technology - Target audience: Practical guide - Illustrations: Colorful illustrations and diagrams - Language: Japanese Please note that there are many writings and folded corners on the pages, but these are considered important points for those who understand.