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Volatile organic compounds (VOCs), representing a wide range of products mainly generated by industrial activity, are involved in air pollution. This study deals with a new biological treatment process of gaseous effluent combining a gas/liquid contactor called an "aero-ejector" and a membrane bioreactor. Combining these two innovative technologies enables a high elimination efficiency to be reached. We first focus on transfer phenomena characterization in a pilot installation on a laboratory scale, using a gaseous effluent polluted with a low ethanol concentration (7.1 x 10(-3) kg.m(-3)). These experiments demonstrated the good transfer performances since 90% of the ethanol was absorbed in the liquid phase in one step. After this physical characterization, the biological aspect of the system was studied using the yeast Candida utilis as microorganism. During the experiment, no ethanol was measured in the fermentation broth nor in the outlet gas, confirming the efficiency of ethanol elimination by C. utilis. The experimental procedure emerging from the present study strongly validates the suitability of this process for ethanol removal from air.

This article focuses on the characterization of slug-flow hydrodynamics in two sizes of tubular membrane diameters (6 and 15 mm) to quantify the main mechanical phenomena involved in the limitation of particle fouling during cross-flow filtration of suspensions. By using a conductance probe technique, the flow structure was accurately identified for two geometries, and noticeable differences were observed in terms of void fractions, velocities and lengths of Taylor bubbles, and liquid slugs. This characterization allowed some data to be theoretically estimated (wall shear stress, “falling” film velocity, film thickness) thanks to the application of a phenomenological model initially developed for oil pipes. The results obtained in a 15-mm tube showed that the ultrafiltration flux improvement, experimentally achieved with bentonite and yeast suspensions, was partly due to the increase in the wall shear stress, induced by continuous gas sparging inside the tubular filtration module. Other hydrodynamic phenomena linked to the quasi-periodic succession of Taylor bubbles and liquid slugs were also involved in the control of the particle entrainment: intermittency frequency, reversal of the wall shear stress, instantaneous pressure variations in the long bubble wake with a higher level of turbulence, and an enhanced local mixing.

This study deals with the use of an upward gas/liquid slug flow to reduce tubular mineral membrane fouling. The injection of air into the feedstream is designed to create hydrodynamic conditions that destabilize the cake layer over the membrane surface inside the filtration module complex. Experimental study was carried out by filtering a biological suspension (yeast) through different tubular mineral membranes. The effects of operating parameters, including the nature of the membrane, liquid and gas flowrates, and transmembrane pressure, were examined. When external fouling was the main limiting phenomenon, flux enhancements of a factor of three could be achieved with gas sparging compared with single liquid phase crossflow filtration. The economic benefits of this unsteady technique have also been examined. To investigate the possibility of long-term operation of the two-phase flow principle, dense cell perfusion cultures of Saccharomyces cerevisiae were carried out in a fermentor coupled with an ultrafiltration module. The air injection allowed a high and stable flux to be maintained over 100 h of fermentation, with a final cell concentration of 150 g dry weight/L. At equal biomass level, a twofold gain in flux could be attained compared with classical steady crossflow filtration at half the cost.

International audience; The present work was focused on elucidating biochemical changes in the model bacterium Escherichia coli exposed to ionic silver mediated stress, at a single-cell scale. In order to achieve this, in situ synchrotron Fourier-transform infrared (sFTIR) microspectroscopy was performed, for the first time, on individual cells by attenuated total reflectance (ATR) combined with the use of zinc-selenide hemisphere for high spatial resolution. In a first part, the potential of the method was evaluated on bacteria subjected to a lethal 100 μM AgNO3 concentration for 2 h compared to untreated 100 % viable cells. Differences in cell composition were assessed for the C–H stretching and protein spectral regions, indicating that the inhibitory action was targeted against both fatty acids and proteins. Transmission electron microscopy (TEM) confirmed morphological damages of the cell ultrastructure. The relevance of ATR-sFTIR microspectroscopy for highlighting the heterogeneity in Ag+-mediated effects within a given bacterial population was also pointed out. In a second part, cells were exposed to sub-lethal Ag+ concentrations (

A membrane bioreactor (MBR), an association of a bioreactor with a crossflow filtration unit, enables continuous processes with total cell retention within the reactor to be realized. Provided that high dilution rates can be applied and that inhibition processes are avoided, very high biomass concentrations can be reached, thereby improving the volumetric productivities. These membrane bioreactors have been successfully applied to various microbial bioconversion, such as alcoholic fermentation, solvents, organic acid production, starters, and wastewater treatment. On the basis of the biological reaction characteristics and bibliographic results, the potentialities and bottlenecks of this methodology are discussed. Depending on the application, it is shown how the performance of the membrane bioreactor can be enhanced by acting either on the biological reaction achievement, by controlling the balance between cell growth and death, or on the dilution rate, by increasing the permeate flux through the filtration unit. This discussion is based on results obtained in specific biological treatments applied to polluted liquid and gas.

Among processes developed to increase biological performances, membrane bioreactors have provided the best results. The membrane bioreactor combines a continuous fermentor and a crossflow filtration module enabling separation of cells from liquid media. Very high biomass concentrations have thus been reached and important bioconversion yields obtained. However the potentiality of this process is mainly limited by the rapid decline in permeate flux due to membrane fouling. In our laboratory, various technological solutions, based on unsteady hydrodynamics inside the tubular filters to limit the external fouling, have been developed and applied during cell cultures in membrane bioreactors. The biological model was alcoholic fermentation. The first kind of flow unsteadiness was based on an air injection at the membrane inlet to create a gas/liquid slug flow. For the same energy consumption, this process enabled a mean twofold gain in ultrafiltration flux with a lower efficiency for microfiltration due to pore blocking by cell debris. The impact of an unsteady jet generated by a pneumatically controlled valve was also evaluated. Although the strong physico–chemical affinity between the membrane material and the culture medium, a flux enhancement of 1.3 was achieved at the end of fermentation. It was also pointed out that when the formation of a cell cake layer was expected to be the main mechanism for flux decline, flow unsteadiness failed to disrupt a previously built-up deposit and for a maximal efficiency it had to be started at the very beginning of the filtration operation. After these feasibility studies on a relatively simple and well-known biological model, further applications on environmental problems were carried out. The interest of a gas/liquid slug flow as a means to increase both the permeate flux and the oxygen transfer rate was demonstrated during continuous phenol degradation by Ralstonia eutropha . The active biomass could be doubled without encountering oxygen depletion while the permeate flux was 75% higher. This led to the complete degradation of a high phenol load higher than 70 kg m −3 day −1 . Finally, a new biological treatment process combining a gas/liquid contactor (‘aero-ejector’) and a membrane bioreactor was developed in order to ensure total microbial degradation of pollutants which were initially present in industrial gaseous effluents. The ‘aero-ejector’ technology allowed the solubilisation of gaseous compounds (here ethanol) in a liquid phase before their degradation in the bioreactor itself. During aerobic cultures of Candida utilis , almost all injected ethanol was transferred and degraded over 350 h of culture.