CHEMICAL AND STRUCTURAL (2D) LINKAGE BETWEEN BACTERIA WITHIN ACTIVATED-SLUDGE FLOCS

This study describes the complexity of the activated sludge flee structure using four methods: (i) microscopic observation of flocs in situ and after specific staining, (ii) optimization of flee dispersion by sonication of pure bacterial strains, (iii) analysis of polymers released from sonicated sludges, and (iv) flee size distributions after different sonication times. The sonication of activated sludge at 37 W for 60s was found to be best for dispersing flocs and minimizing bacterial cell lysis. The polymers released from Aocs were mainly proteins, with polysaccharides and DNA. Electron microscopy showed that a polysaccharide gel connected the cells together. Raw activated sludges give a continuous distribution of particle sizes (1.2-600 mu m). The flee size distribution in sonicated sludge samples was used to build a model of floc structure showing that the predominating macroflocs (125 mu m) are formed from 13 mu m microfloc aggregates, which are made up of smaller particles (2.5 mu m).