This two-lesson unit on rotating biological contactors (RBC's) is designed to be used with students who have had some experience in wastewater treatment and a basic understanding of biological treatment. The first lesson provides information on the concepts and components of RBC treatment systems. The second lesson focuses on design operation and maintenance. The teaching guide includes: (1) an overview of the unit; (2) lesson plans; (3) lecture outlines; (4) overhead transparency masters for use with the second lesson; (5) student worksheets (with answers); and (6) two copies of a final quiz (with and without answers). The lecture outline for the first lesson includes reference to a set of slides developed for use with the lesson. Instructors are encouraged to add their own slides or to change the order of slides to fit their own teaching styles. (JN)