This lesson is the first of a two-part series on anaerobic digestion. Topics discussed include the five basic functions of an anaerobic digester, basic theory of the biological processes involved, basic equipment necessary for digestion, and the products of digestion. The lesson includes an instructor's guide and student workbook. The instructor's guide contains a description of the lesson, estimated presentation time, instructional materials list, suggested sequence of presentation, reading lists, objectives, lecture outline, narrative of the slide/tape program used with the lesson, and student worksheet (with answers). The student workbook contains plant flow diagrams, objectives, glossary, discussion material, references, and worksheet. Discussion material is presented in four sections titled: digester function, basic equipment, theory--"the basics," and by-products of digestion. (JN)