This student manual provides the textual material for a unit on rotating biological contactors (RBC's). Topic areas considered include: (1) flow patterns of water through RBC installations; (2) basic concepts (shaft and stage); (3) characteristics of biomass; (4) mechanical features (bearings, mechanical drive systems, and air drive systems); (5) design considerations (flow rates, organic and solid loads, industrial loading, and weather/environmental influences); (6) interaction of unit processes (preliminary treatment, primary clarifier, return streams, and secondary clarifier); (7) process monitoring and testing, focusing on the visual observation of the biomass; (8) process control for steady state operation (considering mechanical and air drive systems); and (9) making process control changes. A list of objectives, a glossary of key terms, a list of references, and student worksheets are included. It is assumed that students using this manual have had some experience in wastewater treatment and a basic understanding of biological treatment. (JN)