Pergamon 0045-6535(94)00400-5 Chemosphere, Vol. 30, No. 2, pp. 327-338, 1995 Copyright O 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0045-6535/95 $9.50+0.00 BIOLOGICAL TEST SYSTEMS FOR MONITORING THE OPERATION OF WASTEWATER TREATMENT PLANTS Uwe J. Strotmann 1., Andreas Keinath 1,2 and Stefan H. Hfittenhain2 1 BASF AG, Ecology Laboratory, 67056 Ludwigshafen, Germany 2 Fachhochschule Darmstadt, Chemical Technology, 64289 Darmstadt, Germany (Received in Germany 24 June 1994; accepted 12 August 1994) Abstract Four different biological test systems were used for monitoring the biological activity of a labo- ratory-scale wastewater treatment plant which was operated with municipal wastewater. The heterotrophic respiration activity test (HRA), dehydrogenase activity test (DHA) and nitrifica- tion activity test were used for monitoring the biological activity of the activated sludge, and the luminescent bacteria test was used for screening the effluent of the treatment plant. In shock loading experiments with 2.3-dichlorophenol and 3.5-dichlorophenol it was shown that both the nitrification and heterotrophic respiration activities and the TOC degradation in the treatment plant were significantly reduced, whereas no clear effect on dehydrogenase activity was found. Screening of the effluent revealed a clear increase in luminescent bacteria inhibition during the shock loading experiments. Keywords Activated sludge, toxicity monitoring, respiration activity, dehydrogenase activity, nitrification activity, luminescent bacteria test, chlorinated phenols (*): Corresponding author 327