SPATIAL ARRANGEMENT OF THE COMPONENTS OF ACTIVATED-SLUDGE FLOCS

The purpose of this work was to observe the internal structure of acti vated sludge flocs and the relationship between the different componen ts. Activated sludge flocs from the municipal sewage treatment plant a t Nancy (France) were physically stabilized and solidified in an epoxy resin. The flocs were sliced into 0.1 mu m thick sections and stained for characterisation of components and exopolymers by transmission el ectron microscopy, one small floc (10 mu m x 20 mu m), embedded in res in, was chosen and studied using a laser scanning confocal microscope. The focal plane was incremented in steps of 2 mu m along the z axis o f the microaggregate. In order to extract quantitative data (number of cells, flee size) a numerical treatment of the images was applied. A typical flee exhibits an unhomogeneous distribution of the mass and of the exocellular polymer matrix (mainly polysaccharides). This matrix maintains the integrity of the flee and connects most of the component s. These components are isolated bacteria, waste and debris inherited from the effluent and microcolonies. The structure of the microflocs i s fractal with a fractal dimension Df approximate to 3. This large val ue implies that the growth of the small aggregates is possibly generat ed by cellular division and polymer production.