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A simple generalised two-flux approach is presented for modelling radiant light transfer in photobioreactors. A predictive method to obtain optical properties for the medium, based on the Lorenz-Mie theory is discussed. In the same way, a biochemically structured approach is proposed to predict stoichiometries of reactions, including energetic aspects. The formulation for coupling available light and kinetic rates is then proposed by defining a working illuminated volume. The obtained model, compared to experimental results in many different conditions, is proved to be a good tool for simulation, design and predictive control of photobioreactors.

An operational reactor has been designed for the fermentation of a pure culture of Fibrobacter succinogenes with the constraints of strict anaerobic condition. The process is controlled by measurements of pH, redox, temperature and CO2 pressure; it allows an efficient degradation (67%) of lignocellulosic wastes such as a mixture of wheat straw, soya bean cake and green cabbage.

The behavior of pure cultures of nitrifying microorganisms under autotrophic growth operating conditions was investigated and the relations between their energy metabolism and their anabolism analyzed by means of metabolic network computation. The description of the metabolism of the nitrifiers is extended to their energy metabolism by introducing compartmentalization (cytoplasmic and periplasmic sides) and studying coupling between the electron transport chain and the proton gradient generation. The energy model of Nitrosomonas and Nitrobacter was developed based on the oxidoreduction reactions known to be involved. The electron transport chains and the associated proton translocation for these models are described. Several possible hypotheses are analyzed and discussed concerning the thermodynamic consistency of all the oxidoreduction reactions. For Nitrosomonas, the most delicate point is the second step of hydroxylamine oxidation. For Nitrobacter a new energy model is proposed in which NO plays an important role as node in the distribution of electrons from NO(2)(-) oxidation to the membrane electron transport chain. The compartmentalization enables us to consider a proton gradient dissipation flux as the expression of the overall energy loss in metabolic analysis (the so-called maintenance phenomena). The energy model (electron transport chain, proton gradient) is associated with an overall description of the metabolism of Nitrosomonas and Nitrobacter in terms of metabolic flux calculation. This representation demonstrates that a maintenance in nitrifiers expressed as a proton leak is no higher than for other aerobes. The yields calculated from the energy models integrated with the metabolic models of nitrifiers are consistent with the experimental yields in the literature.

4 tables 1 graph.; International audience; Whole body respiration chambers are characterized by a relatively low turnover rate of air which is a handicap for measuring the energy expenditure associated with physiological phenomena of short duration. This paper presents several mathematical methods, based either on integration or on derivative approaches, which can be used to calculate the instantaneous rates of gas exchange. The methods were then used to calculate and compare total, daily, lying and standing energy expenditure of a steer with its energy cost of standing. The influence of the measurement frequency (1 vs. 5 min) was also tested. Total daily energy expenditure as well as rates over short periods (lying or standing), calculated on the basis of the integration approach, were influenced by the measurement frequency chosen. Additionally, the various equations derived from the integration approach yielded significantly different results. By contrast, the measurement frequency had little influence on the rates of energy expenditure calculated using the derivative approach. The best agreement between results obtained from the derivative approach was achieved at the 1 min measurement frequency, in particular with the higher order equations. This study showed the importance of the mathematical treatment of indirect calorimetry data and of the measurement frequency on the interpretation of instantaneous rates of energy expenditure and of the calculated energy cost of standing.

The distribution of carbon in the metabolic network of a bacterial cell was estimated by a mass-balance-based intracellular flux computation method. It was applied to the growth phase of Corynebacterium melassecola, a glutamic acid producing bacterium, using experimental production yields of biomass, lactate and acetate measured during batch cultures on glucose, fructose, and various mixtures of both sugars. This flux computation method identifies the direction of the 86 reactions that ensure proper metabolic function during the growth phase of C. melassecola. Flux ratios allow comparison of calculated and relevant experimental yields. The results highlight the key influence of the biomass production yield Y(X-O(2) ) on the overall distribution of carbon; the proportion of carbon drained in the pentose-P pathway fell from a value in the range of 54% to 47% on media containing glucose (Y(X-O(2) ) = 1.75 to 1.56 g X/g O(2)) to 37% on fructose medium (Y(X-O(2) ) = 1.36 g X/g O(2)). The highest maintenance requirement was calculated on fructose medium (J(m) = 290 mol ATP/100 mol fructose) which must be connected to a lower efficiency of cell multiplication observed on this substrate. Another important result was that the significant decreases in experimental values of production yields and rates observed on fructose medium which were related to the operation of the FBPase. In particular, it was estimated that, as long as the proportion of glucose in the carbon source remains above 22% (78% fructose), the operation of the FBPase is not necessary and the bacteria exhibit behavior similar to that observed on glucose alone; this result is consistent with experimental observations.

Resume La separation du melange n-heptane—toluene est realisee par pompage parametrique en mode direct fonctionnant en discontinu, c'est-a-dire a reflux total. La variable intensive utilisee est la temperature. L'adsorbant est du silica gel. Les resultats obtenus en faisant varier la duree du cycle, la difference de temperature d'un demi-cycle a l'autre et le volume des reservoirs confirment les resultats obtenus par Wilhelm et Sweed. L'analyse des resultats montre que l'hypothese considerant que l'equilibre est realise en chaque point de la colonne ne semble pas verifiee měme pour des durees de cycles de 120 minutes. Le modele propose par Grevillot et Tondeur, legerement modifie, permet de traduire les resultats experimentaux de facon satisfaisante au prix de deux parametres: nombre d'etages et volume mort dans les reservoirs. L'etude experimentale et les simulations mettent en evidence l'importance des effets d'extremites — melange dans les bacs, volumes morts — sur la separation.

This work concerns energy consumption and aeration efficiency in a 15 dm 3 concentric cylinder gas-lift fermentor with the ejector nozzle located at the base of the central tube. Pressures are measured at ejector input and output and in the fermentor, and are compared with those predicted using Bernoulli's theorem and momentum balance at different points in the apparatus. Energy consumption per unit volume is the sum of isothermal expansion and gas-jet kinetic energy terms, the second of which becomes dominant at volumetric aeration rates above 2 vvm (volume of gas per liquid volume per min). Energy consumed is always lower than that for a classical agitated aerated fermentor. Oxygen transfer rate is determined by the sodium sulphite technique (with cobalt catalyst). Transfer can be strongly enhanced by the chemical reaction. The specific interfacial area for mass transfer, a′, depends on the power dissipated according to a′ = 3.66 (E/V l ) 0.73 (S.I. units) This correlation accounts for results obtained by other authors for larger fermentors (0.06 – 2 m 3 ).

Female milk production was related to offspring water turnover, estimated by a tracer method (fig. 1). After deuterium oxide was injected into the blood of the offspring, we measured the decrease of its concentration in time. Milk intake was calculated by equations taking into account the weight gain of the offspring. The reliability of this method was checked in 28 bottle-fed lambs with known milk intake; the correlation between the actual intakes and our estimates was 0.98 with an error means of 5.6 p. 100. The error on the mean of 28 lambs was 0.5 p. 100 (table 1). The milk production of 6 heavy brood mares, estimated during the first week of lactation, varied from 12 to 20 kg per day between animals (table 2). This method did not interfere with the mother-offspring relationship nor with the usual suckling conditions; it can be used advantageously during the onset of lactation in species whose offspring suck frequently.