Patrick Legentilhomme

Harvesting of Cyanobacterium Arthrospira platensis Using Inorganic Filtration Membranes

Abstract The present work deals with the concentration and the separation of Arthrospira platensis from a diluted culture medium. Among the different ways to operate this liquid/solid separation, this paper is focused on the membrane alternative. The general framework of this experimental study is the MELISSA project from the European Space Agency (ESA) for the development of life support systems in Space. The performances of fourteen inorganic membranes (microfiltration and ultrafiltration) were evaluated. According to the results, the operating conditions and the influence of phycocyanin and exopolysaccharides on the fouling phenomenon were investigated on the best membrane. A critical aspect to monitor along the process is the quality of the product in terms of composition of the main cell macro‐components, such as proteins and exopolysaccharides. The ultrafiltration membrane ATZ‐50 kD exhibited the best permeation flux and cleanability. An increase of fluid velocity and transmembrane pressure is energy‐consuming. A good compromise between this consideration and the gain in terms of permeation flux is close to 3 m · s−1 and 2 · 105 Pa with the selected membrane and with a cyanobacteria suspension concentration ranging from 50 mg · L−1 to 1 g · L−1.

Suction effect on the shear stress at a plane ultrafiltration ceramic membrane surface

Wall shear stresses are determined at the surface of a plane ceramic ultrafiltration membrane using an electrochemical method. Twenty microelectrodes are mounted flush to this ceramic membrane and maps of shear stress and turbulent intensity rate are determined for three inlet/outlet distributors configurations. The experimental results are compared to that obtained previously in the same configurations without permeation. Thus, the wall shear rates and the turbulent intensity rates obtained with a transmembrane pressure of 50 kPa and a ratio of the permeation Reynolds number (more commonly called wall Reynolds number) to the channel Reynolds numbers, Re w/Re, ranged between 1.3×10−5 and 6.4×10−4, show the influence of the permeation on the velocity profile at the wall of a plane channel. Furthermore, the suction effect induces a softening of the incidence of the inlet/outlet configurations. Indeed, the average wall shear rate value is 15,000 sec−1 and the average turbulent intensity rate value is about 15% for the three distributors investigated.

Numerical Study of the Flow and Mass Transfer in Micromixers

Computational fluid dynamic simulations are used to characterize the flow and the liquid mixing quality in a micromixer as a function of the Reynolds number. Two micromixers are studied in steady flow conditions; they are based on two geometries, respectively T-shaped and cross-type (⊤ and + shapes). Simulations allow, in the case of ⊤ micromixers, to chart the topology of the flow and to describe the evolution of species concentration downstream the intersection. The streamline layout and the mixing quality curves reveal the three characteristic types of flow, depending on Reynolds number: stratified, vortex and engulfment flows. Vortices appear after impingement, in the exit channel. They become asymmetrical and gain in length with an increase in Re making the flow unsteady, which induces an enhancement of the mass transfer by advection between the two liquids. In the case of cross-type micromixers, the structure of the flow is strongly three-dimensional. It is characterized by symmetrical vortices in both output channels. In the zone close to the impingement, a back flow is observed which induces strong shear stresses. The results show that the + shaped system can improve the mixing process in comparison with the micromixers having ⊤ geometry. The numerical study also allows to select the locations of the most relevant zones of study, from an experimental point of view. It will allow to choose the location of PIV planes and local non intrusive sensors, such as electrochemical microprobes, in order to experimentally investigate the flow.© 2008 ASME

Numerical modeling of the dynamic response of a bioluminescent bacterial biosensor.

Water quality and water management are worldwide issues. The analysis of pollutants and in particular, heavy metals, is generally conducted by sensitive but expensive physicochemical methods. Other alternative methods of analysis, such as microbial biosensors, have been developed for their potential simplicity and expected moderate cost. Using a biosensor for a long time generates many changes in the growth of the immobilized bacteria and consequently alters the robustness of the detection. This work simulated the operation of a biosensor for the long-term detection of cadmium and improved our understanding of the bioluminescence reaction dynamics of bioreporter bacteria inside an agarose matrix. The choice of the numerical tools is justified by the difficulty to measure experimentally in every condition the biosensor functioning during a long time (several days). The numerical simulation of a biomass profile is made by coupling the diffusion equation and the consumption/reaction of the nutrients by the bacteria. The numerical results show very good agreement with the experimental profiles. The growth model verified that the bacterial growth is conditioned by both the diffusion and the consumption of the nutrients. Thus, there is a high bacterial density in the first millimeter of the immobilization matrix. The growth model has been very useful for the development of the bioluminescence model inside the gel and shows that a concentration of oxygen greater than or equal to 22xa0% of saturation is required to maintain a significant level of bioluminescence. A continuous feeding of nutrients during the process of detection of cadmium leads to a biofilm which reduces the diffusion of nutrients and restricts the presence of oxygen from the first layer of the agarose (1xa0mm) and affects the intensity of the bioluminescent reaction. The main advantage of this work is to link experimental works with numerical models of growth and bioluminescence in order to provide a general purpose model to understand, anticipate, or predict the dysfunction of a biosensor using immobilized bioluminescent bioreporter in a matrix.