C. Chavarie

Effect of interparticle forces on the hydrodynamic behaviour of fluidized aerogels

Abstract Aerogel powders, particles of the group C according to the Geldart classification, are not particularly attractive as such for fluidized bed applications. The following study shows, however, that these fine solids form agglomerates above a minimum superficial velocity of 0.04 m/s and that the resulting new system fluidizes smoothly and homogeneously at room and at higher temperatures. A comprehensive model developed to represent the hydrodynamic behaviour of the system proposes that the agglomerate is a cluster of the original fixed bed materials and hence has the properties of the bulk matrix. Van der Waals forces on the elementary grains are used to predict the cluster size. This clustering process is finally analysed in the light of the classical fluidizability diagram.

PHB recovery by hypochlorite digestion of non-PHB biomass

Hypochlorite digestion of bacterial biomass from intracellular poly-β-hydroxybutyrate (PHB) has not been used on a large scale since it has been reported to severely degrade PHB. In this study, to minimize degradation, the initial biomass concentration, digestion time and pH of the hypochlorite solution were optimized. Consequently, PHB of 95% purity with a weight average molecular weight (MW) of 600,000 and a polydispersity index (PI) of 4.5 was recovered from biomass initially containing PHB with a MW of 1,200,000 and a PI of 3.

Extraction of poly-3-hydroxybutyrate using chlorinated solvents

Recovery of poly-3-hydroxybutyrate (PHB) in three chlorinated solvents with or without acetone pretreatment and degradation of extracted PHB (99% pure) in hot chloroform were studied. When lyophilized Alcaligenes eutrophus biomass was used, the best results were obtained with acetone pretreatment and solvent reflux for 15 min in methylene chloride or chloroform. Recovered PHB had a 95% purity and molecular weights (Mw) of 1,050,000 and 930,000 g/mol respectively. Further heating resulted in a serious Mw, loss at reflux temperatures. Degradation of extracted PHB at 110°C in chloroform was due to random and chain-end scission, the former being predominant.

Recovery of poly-3-hydroxyalkanoic acid granules by a surfactant-hypochlorite treatment

When Alcaligenes eutrophus biomass was treated with a surfactant and then washed with hypochlorite, the recovered poly-3-hydroxyalkanoic acid (PHA) granules were 97 to 98% pure with a molecular weight (MW) between 730,000 and 790,000, depending on the surfactant used. When treated with only surfactant, the MW was slightly higher than that obtained with the surfactant-hypochlorite treatment but the purity was 10% lower. PHA of higher purity but lower MW was obtained with just a hypochlorite treatment.

Optimization of fed-batch culture of hybridoma cells using dynamic programming: single and multi feed cases

The optimization of fed-batch culture of hybridoma cells is accomplished on a mathematical model using dynamic programming. Optimal feed trajectories are found using a seventh order model for a single feed stream containing both glucose and glutamine and for two separate feed streams of glucose and glutamine. Compared to a constant feed rate, optimal trajectories can improve the final MAb concentration by 11 % for the single feed case and by 20% for the multifeed case. Higher MAb concentrations can be expected for fed-batch optimization with feed enriched in nutrients.

Improvement of recombinant protein production with the human adenovirus/293S expression system using fed-batch strategies

The human adenovirus/293S cell expression system is used for the production of either recombinant protein or adenovirus vectors for use in gene therapy. In this work, the production of protein tyrosine phosphatase (PTP1C) was used as a model for the scale-up of both applications. Maximum specific production of 30 to 45 mug of active protein/10(6) cells was maintained upon infection with adenovirus vectors at cell densities between 2 x 10(6) to 3 x 10(6) cells/mL in a 3.5-L bioreactor. This was achieved by resuspending the culture in fresh medium at infection time. The pH was kept at 7.0 throughout the experiment and, at 24 h postinfection, glucose and essential amino acids were added. Attempts to replace the complete change of medium at the time of infection with nutrient supplementation of the used medium led to lower production levels, suggesting that protein expression was limited not by the absence of a key nutrient but by inhibitory factors. Two potentially inhibitory factors were investigated: lactic acid accumulation and increased osmolarity. Medium acidification such as that which would be brought about by lactic acid accumulation was shown to depress PTP1C production. The lactate molecule itself decreased the cell viability when added in concentrations of 20 mM or more. But the specific productivity was affected at higher lactate concentrations of 40 mM or more. Additions of glucose, amino acids, and NaHCO(3) used to control pH, led to increases in osmolarity. Osmolarities above 400 mOsm lowered cell density. However, specific production was not significantly affected below 500 mOsm. But, at 500 mOsm, PTP1C production peak was shifted from 48 to 72 hpi. Because of the cell loss, this per cell yield increase did not translate into higher volumetric production. When glucose concentrations was kept at 5 mM by fed-batch addition, lactate production and increases in osmolarity were reduced. In shake flasks, this method permitted maximum production with cells resuspended either in fresh or spent medium at infection. This fed-batch process was implemented successfully at the 3.5-L scale. Fed-batch with glucose may provide a means to increase infected-cell density beyond 3 x 10(6) cells/mL.

Catalytic storage of hydrogen: hydrogenation of toluene over a nickel/silica aerogel catalyst in integral flow conditions

Abstract The feasibility of the hydrogenation of toluene into methylcyclohexane over a Ni/SiO 2 aerogel catalyst in a flow fixed bed reactor has been demonstrated in the temperature range 90 to 150°C. In order to avoid thermal limitations the Ni/SiO 2 , aerogel had to be mechanically mixed with steel wool (in active by itself). In integral conditions of conversion the reaction mechanism obeyed the Langmuir-Hinshelwood model involving reactants both strongly adsorbed on specific sites and exhibiting a global reaction order of zero. The energy of activation was found to be 47 kJ/mol. The catalytic activity was found to be very stable with time on stream.

Fed-batch culture of hybridoma cells: comparison of optimal control approach and closed loop strategies

Control of fed-batch culture of hybridoma cells was investigated based on two approaches optimal control theory and feedback control. Experiments were conducted for both approaches-with a feed enriched in glutamine. The optimal feed trajectory, a decreasing one, yielded a final monoclonal antibody (MAb) concentration of 170 mg/l, a three-fold increase compared to a typical batch operation.The feedback strategy relied on the on-line estimation of the net specific growth rate of cells from the measurement of the CO2 production rate with a mass-spectrometer. A PI controller was then used to maintain the growth rate at a desired value by adjusting the dilution rate to the reactor. For the chosen set-point (0.1 d−1), the final MAb concentration achieved was about 100 mg/1. It was found that there was a delay in the assimilation of the glutamine that should be included in the model to explain the lower MAb production in feedback mode. A higher production can be expected also for a lower set-point in feedback operation.

Production of glomus intraradices propagules, an arbuscular mycorrhizal fungus, in an airlift bioreactor

This work addresses the symbiotic culture of the arbuscular mycorrhizal (AM) fungus Glomus intraradices with Daucus carota hairy roots transformed by Agrobacterium rhizogenes, in two submerged culture systems: Petri dish and airlift bioreactor. AM fungi play an active role in plant nutrition and protection against plant pathogens. These fungi are obligate biotrophs as they depend on a host plant for their needs in carbohydrates. The effect of the mycorrhizal roots inoculum-to-medium volume ratio on the growth of both symbionts was studied. A critical inoculating condition was observed at approximately 0.6 g dry biomass (DW). L-1 medium, above which root growth was significantly reduced when using a low-salt minimal (M) liquid medium previously developed for hairy root-AM fungi co-culture. Below critical inoculum conditions the maximum specific root growth and specific G. intraradices spore production rates of 0.021 and 0.035 d-1, respectively, were observed for Petri dish cultures. Maximum spore production in the airlift bioreactor was ten times lower than that of Petri dish cultures and obtained with the lowest inoculum assessed (0.13 g DW. L-1 medium) with 1.82 x 10(5) +/- 4.05 x 10(4) (SEM) spores (g DW inoculum)-1 (L medium)-1 in 107 d. This work proposes a second-generation bioprocess for AM fungi propagule production in bioreactors. Copyright 1999 John Wiley & Sons, Inc.

Design parameters and performance of a surface baffled helical ribbon impeller bioreactor for the culture of shear sensitive cells

A novel bioreactor equipped with a double helical ribbon impeller (HRI) and three surface baffles has been shown to be well adapted to shear sensitive suspension cultures. Data on power dissipation, mixing time, circulation time, mass transfer parameters (kL, KLa) were obtained at the 3 and 11 L scale. Rational design and scale-up of this type of unit are discussed. Performance of the HRI for the high density cultivation of plant cells (27g dry weight/L) and insect cells (6×106 cells/mL) are presented.