Biodegradation tests usually involve comparison of the oxygen uptake of a test sample – or gas production for anoxic or anaerobic tests – to that for a readily biodegradable control substrate (usually acetic acid, ethanol, or aniline). While biodegradation characteristics can vary among chemical types and wastewater sources, typical patterns are shown in Figure A. The curve labeled CONTROL represents oxygen uptake of readily biodegradable substances. The curve labeled INHIBITION represents oxygen uptake for chemicals that show toxic impacts or low rates of biodegradation. When acclimation is required, a delay in oxygen uptake will occur, but the initial rates of oxygen uptake will be similar to that for the seed culture. An example of the use a CES AER-200 respirometer system to evaluate biodegradability is shown in Figure B. In this case, 10 and 50 mL of an industrial waste were added to respective 500-mL seed cultures consisting of municipal wastewater and aerobic microorganisms. The 10-mL dose (2% by volume) caused no adverse impact on the oxygen uptake of the seed culture and acclimation occurred after about 70 hours of incubation. However, the 50 mL dose (10% by volume) of industrial waste showed inhibition of oxygen uptake early in the test followed by acclimation and biodegradation. Additional tests indicated that the industrial waste could be added to the municipal treatment process in quantities representing less than 5% of the municipal wastewater volume.