Respirometers have been used for years to assess industrial wastewater treat ability, to evaluate biodegradation kinetics of specific chemicals, and to conduct research on biological growth reactions. The need to use respirometers to support plant operations is fast becoming a necessity because of new requirements to optimise plant control and the need to evaluate the impact of industrial discharges on treatment plant performance. Recent developments in respirometer design and function and investigations of new applications have caused renewed interest in their application for assisting in plant design and operation.