Anaerobic Removal of Trace Organic Contaminants in Sewage Sludge: 15 Years of Experience

Trace organic contaminants (TOCs) correspond to a broad range of molecules generated either directly or indirectly by human activity. Even though TOCs are found at low concentrations in the environment, they often accumulate by biomagnification and bioaccumulation into biological organisms and cause irreversible damages in biological systems through direct or indirect toxic effects such as endocrine disruption and tumour initiation. This manuscript presents the main findings of over fifteen years of research focusing on biological removal of various TOCs found in sewage sludge from urban treatment plants. A special focus of the research was made on microbial processes in complex anaerobic ecosystems. Four families of compounds mostly retrieved in urban plants were studied: the polycyclic aromatic hydrocarbons (PAHs), the polychlorobiphenyls (PCBs), the phthalic acid esters (PAEs), and the nonylphenol ethoxylates (NPEs). It was observed that the microbial capability for removing low amounts of TOCs required a long adaptation time and was often limited by the bioavailability of these compounds. In fact, the overall biodegradation resulted from the numerous interactions existing between the matrix (organic matter) and the microbial ecosystems according to the physico-chemical sorption properties of these compounds. Mechanistic aspects were also tackled in depth and specific models were developed for better understanding the network of interactions between TOCs, microorganisms, and organic matter. These findings could be extrapolated to other ecosystems such as soils and sediments. Finally, it was shown that microbial cometabolism was essential for TOC removal, and the concept of bioavailability was not only dependent on the nature, the level, and the sorption properties of TOCs but was also strongly dependent on the nature and the concentration of the sludge organic matter. Specific parameters were proposed for better evaluating the fate of TOCs in microbial anaerobic processes and technological solutions for efficient removal of these compounds were also proposed

Catabolite repression of induction of aldose reductase activity and utilization of mixed hemicellulosic sugars in Candida guilliermondii

International audienc

Induction of aldose reductase activity in Candida guilliermondii by pentose sugars

International audienc

Modeling the alcoholic fermentation of xylose by Pichia stipitis using a qualitative reasoning approach

International audienc

Fermentation of D-xylose, D-glucose, L-arabinose mixture by Pichia stipitis; effect of the oxygen transfer rate on fermentation performance

25 ref.International audienc

Spectrum of assimilation of volatile fatty acids (VFA) for enhanced uptake of phosphorus by strains of Acinetobacter calcoaceticus

International audienc

Fermentation of D-xylose, D-glucose and L-arabinose mixture by Pichia stipitis Y 7124 : sugar tolerance

International audienceThe effect of substrate concentration (S 0) on the fermentation parameters of a sugar mixture byPichia stipitis Y 7124 was investigated under anaerobic and microaerobic conditions. Under microaerobiosisP. stipitis maintained high ethanol yield and productivity when initial substrate concentration did not exceed 150 g/l; ethanol yield of about 0.40 g/g and volumetric productivity up to 0.39 g/l per hour were obtained. Optimal specific ethanol productivity (0.2 g/g per hour) was observed withS 0=110 g/l. Under anaerobic conditionsP. stipitis exhibited the highest fermentative performances atS 0=20 g/l; it produced ethanol with a yield of 0.42 g/g, with a specific rate of 1.1 g/g per day. When the initial substrate level increased, specific ethanol productivity declined gradually and ethanol yield was dependent on the degree of utilization of each sugar in the mixture

Production d'éthanol à partir des sucres lignocellulosiques : fermentation alcoolique du glucose et du xylose par coculture levurienne

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Xylose metabolism by Pichia stipitis : the effect of ethanol

International audiencePichia stipitis Y7124 was grown anaerobically on d-xylose in the presence of an initial ethanol concentration (E0) varying from 0 to 40 g/l. When E0 increased, the yield of xylitol increased linearly, reaching a value of 0.20 mol xylitol/mol xylose at E0=40 g/l. When a hydrogen acceptor (acetoin) was added to the cultures, the cylitol yield decreased with the contaminant stoichiometric reduction of acetoin to 2,3-butanediol. Furthermore, it was demonstrated that xylitol dehydrogenase and acetoin reductase activities from cell-free extracts of P. stipitis Y7124 were NAD+ and NADH2-linked, respectively. A hypothesis is put forward explaining that the xylitol yield is dependent on the ethanol concentration. It is suggested that ethanol may cause a disturbed NAD+/NADH2 balance during anaerobic xylose metabolism by P. stipitis. Metabolic mechanisms are proposed and their validity is discussed