A mixture containing the test substance, mineral nutrients and a relatively large amount of
activated sludge in aqueous medium is agitated and aerated at 20-25°C in the dark or in diffuse light
for up to 28 days. Blank controls, containing activated sludge and mineral nutrients but no test
substance, are run in parallel. The biodegradation process is monitored by determination of DOC (or
COD(2)) in filtered samples taken at daily or other time intervals. The ratio of eliminated DOC (or
COD), corrected for the blank, after each time interval, to the initial DOC value is expressed as the
percentage biodegradation at the sampling time. The percentage biodegradation is plotted against time
to give the biodegradation curve.