Structure et propriétés hydrophobes des agrégats bactériens de boues activées

Abstract : Settling of microbial biomass formed during the "activated sludge" process is a key step of biological wastewater treatment. Its efficiency is know to be innuenced by filamentous bacteria. Besides this, evidence is present that this settleability is mainly governed by the physico-chemical structure of bacterial aggregates (" flocs"). Then, a better knowledge of the structure and the factors governing the floc formation is necessary to weil control the settling step. The hydrophobie character of activated sludge floc components has been studied to elucidated the effect on sludge settleability. Electronic microscopy and granulometric analysis of dispersed flocs, showed the heterogeneous structure. Flocs with an average diameter of 125 µm are constituted of 13 pm micro-aggregates and 2.5 pm particles. Some of the micro-flocs are bacterial colonies. The flocs are shown to consist of bacteria along exo-cellular polymers. Polymers, extraeted by ultrasonication, are found to be composed of proteins, sugars and DNA. Adsorption chromatography in acidic conditions with no ionic resins, showed the hydrophobie character of the soluble heteropolymers constitutiIig the floc matrix. By using the microbial adhesion test to octane, we demonstrated that "hydrophobie" and "hydrophilic" bacteria coexist into the sludges. The "hydrophobic / hydrophilic" character of some of these strains, changes as a funetion of the environmental parameters (nutrient load, oxygen concentration, ... ). The control of these parameters should be able by favouring the hydrophobic bacterial populations, or/and the production of hydrophobic polymers, to product flocs with good settleability. However, measurements of "biosorption" of organic matter in wastewater by activated sludges, comparing with other floc characteristics, showed that the floes with the nicest structure (best settlement), present the lower adsorption ability. AIso, it is necessary to find a compromise between the best settleability of sludge and the best biosorption properties.
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Frédéric Jorand. Structure et propriétés hydrophobes des agrégats bactériens de boues activées. Sciences agricoles. Université Henri Poincaré - Nancy 1, 1995. Français. ⟨NNT : 1995NAN10463⟩. ⟨tel-01747125⟩

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