Projet de thèse en Sciences et Techniques de l'Environnement
Sous la direction de Stéphanie Rossano.
Thèses en préparation à Paris Est en cotutelle avec l'Erasmus Mundus ETeCoS3 , dans le cadre de SIE - Sciences, Ingénierie et Environnement , en partenariat avec LGE - Laboratoire Géomatériaux et Environnement (laboratoire) depuis le 01-11-2010 .
Granules that develop in upflow anaerobic sludge bed (UASB) bioreactors are dense conglomerates. UASB bioreactors are designed to produce biogas from organic matter which require trace metal dosage for optimal methane production (Zandvoort et al., 2003) or to remove metal from wastewater (De Lima et al., 2001). The granules consist of microorganisms, their microbial produced components like extracellular polymeric substances (EPS) and bio-minerals (iron sulfide, calcium carbonate, ). Their microbiological and chemical composition depends on the seed sludge and the chemical composition of the wastewater (Batstone et al., 2004). In anaerobic bioreactors, precipitation and adsorption phenomena of trace metals with sulfides or carbonates minerals may dramatically affect their bioavailability (Zayed and Winter, 2000 and Zandvoort et al., 2005a). The behaviour of metals in anaerobic sludge granules is further affected by their biosorption to EPS (Shen et al., 1993). EPS are mainly composed of polysaccharides, proteins, humic substances, nucleic acids and lipids (Flemming and Leis, 2002) containing ionisable functional groups such as carboxyl, phosphoric, amine and hydroxyl groups. The charge-carrying nature of these functional groups enables EPS to sequester minerals, nutrients and toxic metals (Rudd et al., 1984). Weakly acidic functional groups present in the EPS are involved in the mechanism proposed above. In addition to those groups, polysaccharides and amino acids present in the basic structure of the cell wall contain polarizable groups (sites), such as phosphate, carboxyl, hydroxyl and amino-groups capable of interaction with cations. Also these sites may contribute to the reversible metal binding capacity of the granular sludge (Flemming and Leis, 2002). Even if the influence of the nature of the substrates on the EPS composition and production has been reported in the literature (Bhatti et al., 1995 and Veiga et al., 1997), little is known regarding the relation between these compounds and their metal retention capacity, either at trace or at toxic concentrations. This PhD work aims to get insight in the sorption mechanisms of cationic metals by anaerobic granular sludge. However the mineralogy of the granular biofilm is poorly describe in the literature. Sulfur, phosphate, iron, aluminium and calcium are the main elements present in granular biofilms. It is therefore required to know their speciation and their mineralogy. Such type of study required the use of XRD to determine the crystalline structure of the minerals present in the biofilm. In addition X-ray absorption spectroscopy studies should be conducted to know about the chemistry coordination of the previously mentioned elements. For such study, research proposals will be submitted at several synchrotron (Soleil, ESRF, SLS) beamlines in order to perform such work. In previous work performed by D'abzac et al., he investigated the different type of EPS present in granular biofilm. The effects of the extraction procedure of extracellular polymeric substances (EPS) on their proton/metal binding properties were studied. Nine extraction procedures (one control, four physical and four chemical procedures) were applied to four types of anaerobic granular sludges. The binding capacities between the EPS and lead or cadmium were investigated at pH 7 by a polarographic method. Knowing that EPS still contain a significant amount of mineral phases. It is therefore required to discriminate which fraction is involved in the sorption of heavy metals (mineral phase or EPS). Size exclusion chromatography (Simon et al., 2009, 2010) coupled to an ICP-MS may be used to investigate which size of the EPS in involved in the sorption of heavy metal. Such work could be performed in collaboration with Markus Lenz (http://www.fhnw.ch/lifesciences/iec/personen/markus.lenz, Switzerland). To investigate the interactions Metal and EPS we can also apply for beamtime on Samba beamline (Soleil Synchrotron) and Superxafs (SLS synchrotron). Pb and Cd studies may be performed to investigate such interactions.
Removal of heavy metals in upflow anaerobic packed bed (UASB) reactors: a better understanding of the sorption mechanisms involved for optimized applications
Pas de résumé disponible.