Characterisation of activated sludge by automated image analysis

An automated image analysis procedure has been developed for the simultaneous characterisation of flocs (projected diameter and fractal dimension) and filamentous bacteria (filament length) of fresh activated sludge samples observed by optical microscopy. It has been used to monitor, over a period of I year, the activated sludge of a large municipal wastewater treatment plant, located in an area subject to mild continental weather. No relationship could be established between floc characteristics and the sludge volume index (SVI). Filamentous bulking events associated with variations of the SVI were detected from changes of total filament length, of filament number/image and of the proportion of filamentous bacteria with respect to the total activated sludge. The proposed automated method provides quantitative support for the classification of bulking events. (C) 2001 Elsevier Science B.V. All rights reserved.