Claude-Gilles Dussap

A Simple and reliable formula for assessment of maximum volumetric productivities in photobioreactors

This article establishes and discusses the consistency and the range of applicability of a simple but general and predictive analytical formula, enabling to easily assess the maximum volumetric biomass growth rates (the productivities) in several kinds of photobioreactors with more or less 15% of deviation. Experimental validations are performed on photobioreactors of very different conceptions and designs, cultivating the cyanobacterium Arthrospira platensis, on a wide range of volumes and hemispherical incident light fluxes. The practical usefulness of the proposed formula is demonstrated by the fact that it appears completely independent of the characteristics of the material phase (as the type of reactor, the kind of mixing, the biomass concentration…), according to the first principle of thermodynamics and to the Gauss‐Ostrogradsky theorem. Its ability to give the maximum (only) kinetic performance of photobioreactors cultivating many different photoautotrophic strains (cyanobacteria, green algae, eukaryotic microalgae) is theoretically discussed but experimental results are reported to a future work of the authors or to any other contribution arising from the scientific community working in the field of photobioreactor engineering and potentially interested by this approach.

Energy model and metabolic flux analysis for autotrophic nitrifiers

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.

Representation of vapour -liquid equilibria in water-alcohol-electrolyte mixtures with a modified UNIFAC group-contribution method

Abstract Achard, C., Dussap, C.G. and Gros J.B., 1994. Representation of vapour-liquid equilibria in water-alcohol-electrolyte mixtures with a modified UNIFAC group-contribution method. Fluid Phase Equilibria , 98: 71-89. A new method for the correlation and prediction of salt effects on vapour-liquid equilibria of mixed solvent systems is proposed. The model combines a term of the Debye-Huckel type with a modified UNIFAC equation and is based on the solvation concept. The model parameters are ion-specific and no ternary parameters are required. Group interaction parameters have been estimated between ions (Na + , K + , Li + , Mg 2+ , Ca 2+ , Co 2+ , Ba 2+ , Sr 2+ , NH + 4 , Cl − , Br − , F − , NO − 3 , SO 2− 4 ) and solvent groups (CH 3 OH, CH 2 , OH), while previously published group interaction parameters between solvent groups and between water and ionic species have been maintained. Application of this model to alcohol-water-salt mixtures shows that the change in vapour phase composition on adding salt to the liquid phase can be represented satisfactorily. The average expected accuracy of the total pressure or temperature is about 4% and of vapour phase mole fractions better than 4%. Since it is a group-contribution method, it has a much broader range of applicability than classical approaches based on local composition models such as NRTL or UNIQUAC

A model-based method for investigating bioenergetic processes in autotrophically growing eukaryotic microalgae: Application to the green algae Chlamydomonas reinhardtii

A constraint‐based modeling approach was developed to investigate the metabolic response of the eukaryotic microalgae Chlamydomonas reinhardtii under photoautotrophic conditions. The model explicitly includes thermodynamic and energetic constraints on the functioning metabolism. A mixed integer linear programming method was used to determine the optimal flux distributions with regard to this set of constraints. It enabled us, in particular, to highlight the existence of a light‐driven respiration depending on the incident photon flux density in photobioreactors functioning in physical light limitation.

A physical chemical UNIFAC model for aqueous solutions of sugars

Abstract A new physical chemical model is proposed to describe the thermodynamic properties of binary water-carbohydrate mixtures. The chemical part of the model takes into account the conformational equilibria of sugars and the solvation equilibria between water and sugars. The physical part of the model is a modified UNIFAC model where three new main groups (pyranose ring, furanose ring and osidic bond) are introduced to describe carbohydrate molecules. The coefficients of the model (six interaction parameters and one parameter describing the partial molar Gibbs energy of the hydrogen bond, all temperature dependent) are adjusted on seven binary water-sugar systems (glucose, mannose, galactose, fructose, sucrose, lactose, maltose). The experimental data include water activity, osmotic coefficients, activity coefficients, freezing and boiling temperatures, excess Gibbs energy and excess enthalpy. The model allows carbohydrate isomers to be distinguished and the excess Gibbs energy of systems not used in the coefficients estimation (xylose, raffinose) to be predicted.

Excess properties and solid-liquid equilibria for aqueous solutions of sugars using a UNIQUAC model

Abstract Catte M., Dussap C.-G., Achard C. and Gros J.-B., 1994. Excess properties and solid-liquid equilibria for aqueous solutions of sugars using a UNIQUAC model. Fluid Phase Equilibria, 96: 33-50. A modified UNIQUAC model was used to describe thermodynamic properties of binary water-carbohydrate mixtures. Interaction parameters are determined for glucose, fructose and sucrose. A new equation was developed to describe carbohydrate solubility in water from knowledge of dilution enthalpy rather than fusion enthalpy, and particularly when sugar crystallizes as a hydrated form. For all thermodynamic properties (water activity, osmotic coefficients, excess Gibbs energy, excess enthalpy, activity coefficients, boiling temperature, freezing temperature and solubility) the model agrees with experiments when reliable data are available. Good predictions are also obtained for water activity and osmotic coefficients in ternary systems (water-sucrose-glucose).

Modeling Stability of Photoheterotrophic Continuous Cultures in Photobioreactors

Continuous cultures of the purple non‐sulfur bacterium Rhodospirillum rubrum were grown in a cylindrical photobioreactor in photoheterotrophic conditions, using acetate as carbon source. A new kinetic and stoichiometric knowledge model was developed, and its ability to simulate experimental results obtained under varying incident light fluxes and residence times is discussed. The model accurately predicts the stable, unstable, or oscillating behavior observed for the reactor productivity. In particular, the values of residence time corresponding to a subcritical bifurcation with a typical hysteresis effect are calculated and analyzed. The robustness of the proposed model allows the engineering operating domain of the photobioreactor function to be set and offers a promising tool for the design and control of such photoheterotrophic processes.

Spectral kinetic modeling and long‐term behavior assessment of Arthrospira platensis growth in photobioreactor under red (620 nm) light illumination

The ability to cultivate the cyanobacterium Arhtrospira platensis in artificially lightened photobioreactors using high energetic efficiency (quasi‐monochromatic) red LED was investigated. To reach the same maximal productivities as with the polychromatic lightening control conditions (red + blue, P/2e− = 1.275), the need to work with an optimal range of wavelength around 620 nm was first established on batch and continuous cultures. The long‐term physiological and kinetic behavior was then verified in a continuous photobioreactor illuminated only with red (620 nm) LED, showing that the maximum productivities can be maintained over 30 residence times with only minor changes in the pigment content of the cells corresponding to a well‐known adaptation mechanism of the photosystems, but without any effect on growth and stoichiometry. For both poly and monochromatic incident light inputs, a predictive spectral knowledge model was proposed and validated for the first time, allowing the calculation of the kinetics and stoichiometry observed in any photobioreactor cultivating A. platensis, or other cyanobacteria if the parameters were updated. It is shown that the photon flux (with a specified wavelength) must be used instead of light energy flux as a relevant control variable for the growth. The experimental and theoretical results obtained in this study demonstrate that it is possible to save the energy consumed by the lightening device of photobioreactors using red LED, the spectral range of which is defined according to the action spectrum of photosynthesis. This appears to be crucial information for applications in which the energy must be rationalized, as it is the case for life support systems in closed environments like a permanent spatial base or a submarine.

Dynamic Aspects and Controllability of the MELiSSA Project: A Bioregenerative System to Provide Life Support in Space

Manmade ecosystems differ from their prototype biosphere by the principle of control. The Earth Biosphere is sustainable by stochastic control and very large time constants. By contrast, in a closed ecosystem such as the micro-ecological life support system alternative (MELiSSA system) developed by the European Space Agency for space exploration, a deterministic control is a prerequisite of sustainable existence. MELiSSA is an integrated sum of interconnected biological subsystems. On one hand, all unit operations in charge of the elementary functions constitutive of the entire life support system are studied until a thorough understanding and mathematical modelling. On the other hand, the systemic approach of complex, highly branched systems with feedback loops is performed. This leads to study in the same perspective, with the same degree of accuracy and with the same language, waste degradation, water recycling, atmosphere revitalisation and food production systems prior to the integration of knowledge-based control models. This paper presents the mathematical modelling of the MELiSSA system and the interface between the control strategy of the entire system and the control of the bioreactors.

Growth monitoring of Fibrobacter succinogenes by pressure measurement.

In life support systems, such as the MELiSSA (Micro-Ecological Life Support Alternative) project, developed by the European Space Agency, the aim is to understand and assemble artificial ecosystems for ensuring human subsistence in space. Fibrobacter succinogenes, an anaerobic bacterium, was used for the degradation of vegetable wastes produced in higher plants chambers, but the process does not allow the monitoring of biomass concentration and degradation rates. This study proposes a growth and a degradation monitoring technique using pressure measurements. First, volatile fatty acids (VFA) production was compared with biomass growth and with CO2 production. The experiments were carried out in batch and fed-batch processes on glucose and on vegetables. The results have shown that a link could be established between VFA production, degradation rate and gas pressure measurements. Thus, the pressure could be used both as a relevant variable for online evaluation of biomass growth and of degradation of complex vegetable wastes.