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

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