Biological waste treatment in the activated sludge process is based on the ability of microorganisms to use dissolved oxygen in breaking down soluble organic substances. The oxygen uptake test is a means of measuring the respiration rate of microorganisms in this process. Designed for individuals who have completed National Pollutant Discharge Elimination System (NPDES) level 1 laboratory training skills, this module provides waste water treatment plant operators with the basic skills and information needed to: (1) successfully run the oxygen uptake test; (2) graph its results; (3) properly perform calculations for slope, oxygen uptake rates, and specific uptake rates; and (4) obtain reliable data from the test procedure. The instructor's manual contains a statement of instructional goals, lists of instructor/student activities and instructional materials, narrative of the slide/tape program used with the module, overhead transparency masters, and student worksheet (with answers). The student workbook contains objectives, prerequisite skills needed before the module is started, sources of dissolved oxygen meters, laboratory procedures (oxygen uptake test, stabilization test, suspended solids, and volatile suspended solids), and worksheet. (Author/JN)