INTEGRATION OF PERFORMANCE, MOLECULAR-BIOLOGY AND MODELING TO DESCRIBE THE ACTIVATED-SLUDGE PROCESS

To study process performance and population dynamics in activated slud ge, a pilot-scale Membrane Bioreactor (MBR) was installed in a municip al wastewater treatment plant (Aubergenville, France), Since no solids losses occur in the MBR effluent, the sludge residence time (SRT) can be: i) easily controlled by means of the sludge withdrawal, and ii) d issociated from the hydraulic residence time (HRT). A complete charact erization of this activated sludge system was performed at three sludg e ages (5, 10 and 20 days). Raw and treated wastewater quality, as wel l as sludge concentration, was analyzed, nucleic probe analysis was pe rformed to determine the heterotrophic and nitrifier populations, and the results were compared to the output from a multispecies model that integrates substrate removal kinetics and soluble microbial products (SMP) production/consumption. This paper presents an integrated analys is of the activated sludge process based on chemical, molecular biolog y, and mathematical tools. The model was able to describe the MBR syst em with a high degree of accuracy, in terms of COD removal and nitrifi cation, as well as sludge production and population dynamics through t he ratio of active nitrifiers/bacteria. Both steady-state and transien t conditions could be described accurately by the model, except for te chnical problems or sudden variations in the wastewater composition. ( C) 1998 IAWQ. Published by Elsevier Science Ltd.