Interactions bactéries - ANTIBIotiques dans les installations de traitement des EAUx usées – ANTIBI-EAU

Scientific background and objectives: The presence in the environment of pharmaceutical substances is a public health problem. These biologically active, hydrophilic and persistent substances are introduced in the water cycle by wastewater and are discharged in the environment, if the barrier constituted by wastewater treatment units is not sufficiently efficient. Then it is possible to find them in drinking water produced from surface or ground water. Groundwater resources can be recharged by reclaimed wastewater. Some of these pharmaceutical products as well as their metabolites are classified as endocrine disruptors and are a risk for human beings and animals. The case of antibiotics is more complex as they can interfere, due to their bactericide and bacteriostatic nature, with bacteria used in biological wastewater treatment systems, such as those by activated sludge, which are used in most urban communities. At longer term, the adaptation of these bacteria to an antibiotic is not excluded, with risk of resistance transfer to pathogens.Activated sludge is constituted of flocs of filamentous and non filamentous bacteria, whose cohesion is due to polymeric substances excreted by the bacteria (EPS). The transport and transfer of a toxic substance from wastewater to bacteria contained in flocs is done by diffusion of the substance through EPS. These phenomena depend upon the spatial arrangement of bacteria and EPS. The project aims at developing a multi-scale model of the floc, taking into account the type of bacteria and EPS, as well as their localization in the floc, in order to be able to predict the action of an antibiotic in function of the wastewater treatment operating conditions. The application is focused on a macrolide, erythromycin.Description of project, methodology: To reach this goal a set of methods which allow a multi-scale characterization of flocs will be applied. The spatial distribution and the nature of filamentous and non filamentous bacteria and EPS, as well as the transfer of the antibiotic will be studied by optical microscopy (brightfield, epifluorescence), confocal laser and multiphotonic laser, using markers (membrane integrity, EPS type, labelled antibiotic, etc) and by infra-red and Raman microscopy. EPS will be also characterized after extraction and chromatographic separation by spectroscopy (fluorescence in liquid phase, infra-red and Raman after crystallization). These methods will be use during batch toxicity tests on activated sludge obtained in different operation conditions (full-scale sludge conditioned with iron chloride, polyelectrolytes, by freezing/thawing cycles, lab-scale sludge obtained in reactors fed with synthetic substrate (reactor-clarifier systems and membrane reactor). The data will be used to identify the parameters of a multi-scale model able to represent the attack of bacteria inside the floc by the antibiotic and the loss of treatment efficiency. The model will take into account the nature of bacteria (filamentous, non filamentous, nitrifiers) and of EPS, as well as their localization.Expected results: This model should be able to help to the development of new systems and the optimization of existing systems for wastewater treatment, in order to be able to discharge without any danger in the aquatic environment waster polluted by pharmaceutical substances and in particular by antibiotics.