The main objective of this work is to compare the evolution of the metabolic activity of pure or enriched culture of nitrifying bacteria immobilized by two different methods: spontaneous attachment on solid surface and incorporation in alginate beads. Special attention will be made on the comparison of nutrient diffusion in these two biofilms, on population dynamics and on the changes of biofilm morphology. To obtain these objectives the research work is divided in four parts: (1) Preparation of nitrifying biofilms which consists on isolation of strains of nitrifying bacteria, characterisation of its specific activities, bacteria fixation on solid supports, incorporation of bacteria in alginate beads. Choice of appropriate gel matrix characterised by high mechanical stability and low diffusion limitations.
(2) Development of new methods to study diffusion limitations, fixed bacteria activity, population dynamics and spatial distribution of bacterial strains. This task will evaluate the influence of process conditions on multispecies bacteria population dynamics. In particular, a better understanding is sought of the competition between autotrophic and heterotrophic bacteria and their influence on reactor design and operation This specific research topic includes mass transfer study and evaluation of the mass fraction of active cells in the biofilm and its spatial distribution.
(3) Operation of the two biofilms in air-lift reactor and study of the evolution of biofilm properties and activities in comparison with the innoculum properties. The studies will be carried out in a new reactor, the Circulating Floating Bed Reactor, developed in the CIRSEE.
(4) Verification of the pertinence of this methodology at industrial scale for expertise of nitrifying biofilm in wastewater treatment systems. Links with industry / industrial relevance (22)