ENVIRONMETRICS Environmetrics 2005; 16: 589–601 Published online 21 April 2005 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/env.724 Toxic event detection by respirometry and adaptive principal components analysis Se ´bastien Le Bonte ´ 1,2 , Olivier Potier 1 and Marie-Noe ¨lle Pons 1 * ,y 1 Laboratoire des Sciences du Ge ´nie Chimique, CNRS-ENSIC-INPL, 1, rue Grandville, BP 451, F-54001 Nancy cedex, France 2 Laboratoire des Sciences de l’Eau et de l’Environnement, Parc ESTER technopo ˆle, 16 rue Atlantis, BP 6804, 87068 Limoges cedex, France SUMMARY Two methods based on adaptive principal components analysis (APCA) are compared to extract, from primary measurements, information related to the changes of wastewater characteristics induced by variable weather conditions and/or to the presence of toxic substances. The primary measurements are activated sludge respiratory data obtained by short-term experiments in an on-line batch respirometer, combined with indirect information on soluble pollution (UV-visible absorbance, turbidity, pH, etc.) and wastewater flow rate. The Benchmark Simulation Model 1 (BSM1), which simulates the functioning of a large wastewater treatment plant by activated sludge, has been used to obtain large data sets and to test the proposed APCA method, which has then been applied to real wastewater characteristics. Copyright # 2005 John Wiley & Sons, Ltd. key words: principal components analysis; monitoring; respirometry; UV-visible absorbance; toxicant; inhibition INTRODUCTION Activated sludge systems are largely used for the treatment of domestic, industrial or mixed wastewater. Although they have proven their efficiency for many years, their principal drawback is the fragility of the microbial population. These plants are prone to variations in flow and load due mainly to predictable changes in urban activity (normal diurnal cycle, week-end and vacation periods). Their general trend can be forecasted, but voluntary or involuntary spillages of toxic compounds in the sewer networks and weather related changes (storm, long rain periods) may also occur, that are not, or badly, predicted. They may be considered as critical events, which require steps to be taken to protect especially the biological stage of the treatment plant: their rapid detection can be used in the control strategy of the plant to trigger the opening of gates and to direct part or the totality of the flow towards a temporary storage tank (Copp and Spanjers, 2004). As regulators require the treatment of all Received 8 June 2004 Copyright # 2005 John Wiley & Sons, Ltd. Accepted 25 November 2004 *Correspondence to: M.-N. Pons, Laboratoire des Sciences du Ge ´nie Chimique, CNRS-ENSIC-INPL, 1, rue Grandville, BP 451, F-54001 Nancy cedex, France. y E-mail: Marie-Noelle.Pons@ensic.inpl-nancy.fr Contract/grant sponsor: Ministry of Education and Research, France.