http://bioprocesos.unq.edu.ar/Biopro%20II/Paper%20escalado.pdf

Bioreactor scale-up and oxygen transfer rate in microbial processes: An overview

Pullulan: Microbial sources, production and applications

Pullulan is a linear glucosic polysaccharide produced by the polymorphic fungus Aureobasidium pullulans, which has long been applied for various applications from food additives to environmental remediation agents. This review article presents an overview of pullulan’s chemistry, biosynthesis, applications, state-of-the-art advances in the enhancement of pullulan production through the investigations of enzyme regulations, molecular properties, cultivation parameters, and bioreactor design. The enzyme regulations are intended to illustrate the influences of metabolic pathway on pullulan production and its structural composition. Molecular properties, such as molecular weight distribution and pure pullulan content, of pullulan are crucial for pullulan applications and vary with different fermentation parameters. Studies on the effects of environmental parameters and new bioreactor design for enhancing pullulan production are getting attention. Finally, the potential applications of pullulan through chemical modification as a novel biologically active derivative are also discussed.

Pullulan: Biosynthesis, production, and applications

Filamentous fungi are important organisms industrially and continue to attract research interest as microbiologists attempt to overcome the problems associated with their behavior in submerged culture. This review critically examines the literature describing these problems and where available suggests possible solutions to them. The influence of the chemical and physical environment on culture morphology, the process engineering challenges presented by different fungal morphologies, and the relationship between fungal morphology and metabolite production are all discussed.

Growth of filamentous fungi in submerged culture: problems and possible solutions

Current knowledge on biosynthesis, biological activity, and chemical modification of the exopolysaccharide, pullulan.

Power consumption, gas holdup and oxygen mass transfer in agitated gas-liquid columns have been studied for an air-water system. Measurements have been carried out in a reciprocating plate reactor using five different types of perforated plates and in a stirred tank reactor with one, two and three Rushton turbines, a helical ribbon impeller with and without surface baffles. Each mixing vessel had an identical geometry with a working volume of 17 L. For reciprocating plate stacks, the gas holdup is a complex function of the perforation diameter, the frequency of agitation and the gas superficial velocity. For radial-type mixing devices, the gas holdup increases more rapidly with the speed of rotation for the helical ribbon. The power imparted to the fluid by the mixing device is independent of the gas superficial velocity for the plate stacks and the helical ribbon impeller for a given frequency or speed of agitation whereas it decreases for Rushton turbines. The correlation of the power consumption obtained for all mixing devices plotted against the reciprocating frequency or speed of rotation to the third power shows a linear fit. KLa values were correlated very well with the power input per unit volume and superficial gas velocity for all mixing devices. At lower power input per unit volume, KLa is a function of only the gas superficial velocity. At higher input power per unit volume, KLa increases rapidly with an increase in the intensity of agitation. Reciprocating plates with larger diameter perforations led to higher KLa values whereas the lowest KLa were obtained with the helical ribbon impeller. Correlations for one and three Rushton impeller assemblies were almost identical whereas measured KLa were much higher for the two-impeller assembly due to the presence of a highly mixed zone in the vicinity of the dissolved oxygen probe.



La puissance consommee, la retention de gaz et le transfert d'oxygene dans une colonne agitee aeree ont ete etudies pour un systeme air-eau. Les mesures ont ete realisees dans un reacteur a plateaux a mouvement alternatif munis de cinq differents systemes de plateaux perfores. Pour le reacteur agite aere, ce sont des combinaisons de une, deux ou trois turbines Rushton ou d'un ruban helicoidal avec ou sans chicanes de surfaces qui ont ete evaluees. Les deux reacteurs ont une geometrie identique et un volume utile de 17 L. Pour les systemes de plateaux, la retention de gaz est une fonction complexe du diametre des perforations, de la frequence d'agitation et de la vitesse superficielle du gaz. Pour les systemes d'agitation de type radial, la retention de gaz augmente plus rapidement avec la vitesse de rotation pour le ruban helicoidal. La puissance fournie au fluide par le systeme d'agitation est independante de la vitesses superficielle de gaz pour les plateaux perfores et le ruban helicoidal pour une frequence ou une vitesse d'agitation donnee, tandis qu'elle diminue pour les turbines Rushton. La correlation de la puissance consommee obtenue pour tous les systemes d'agitation en fonction de la frequence d'agitation ou de la vitesse de rotation a la puissance trois est une regression lineaire. Les valeurs de KLa experimentales ont ete mises sous forme de correlations avec succes en fonction de la puissance par unite de volume et de la vitesse superficielle de gaz pour tous les systemes d'agitation. A faible puissance par unite de volume, le KLa est fonction uniquement de la vitesse superficielle de gaz pour tous les systemes d'agitaiton. A puissance par unite de volume eleve, le KLa augmente rapidement avec une augmentation de l'intensite d'agitation. Les plateaux avec un plus grand diametre de perforation entraǐnent des valeurs de KLa plus elevees tandis que les plus faibles KLa sont obtenus avec le ruban helicoidal. Les correlations obtenues pour les dispositifs utilisant une ou trois turbines Rushton sont presque identiques tandis que les valeurs de KLa obtenues a l'aide du dispositif muni de deux turbines Rushton sont plus elevees due a la presence d'une zone fortement agitee a proximite de la sonde d'oxygene dissous.

Power consumption and mass transfer in agitated gas‐liquid columns: A comparative study

Reciprocating plate bioreactors are particularly well suited for conducting fermentations which give rise to highly viscous broth. To evaluate their performance for polysaccharide fermentations, a series of pullulan fermentations were performed with a particular emphasis placed on the influence of aeration on both the quantity and quality of the product. Two experiments were conducted at constant aeration rates and two others with constant dissolved oxygen concentrations. For the latter two experiments, the dissolved oxygen concentration was controlled by manipulating either the aeration flow rate or the reciprocating frequency of the perforated plates.

Pullulan fermentation in a reciprocating plate bioreactor

This investigation was undertaken with the objective to compare experimentally the performance of four different mixing devices for the production of the polysaccharide pullulan with Aureobasidium pullulans (2552). Fermentations were performed using identical bioreactors with respectively an assembly of three Rushton turbines (RTB), a helical ribbon impeller (HR) and two different reciprocating plates (RPB1, RPB2). Each mixing vessel had identical geometry and working volume (18 L). These four fermentations were performed with an equal level of power input per unit volume (1000 W/m3) and gas flow rate (0.5 vvm, 9 L/min). For each system, the evolution of biomass, polysaccharide concentration, dissolved oxygen and agitation speed or frequency were recorded as a function of time along with the rheological properties of the culture broths. The type of mixing device used had a significant impact on the rate of biomass production and on polysaccharide physical properties. However, the rate of polysaccharide production appears to be less sensitive to the bioreactor design. The overall productivity, which represents the ability of micro-organisms to convert rapidly substrate into biomass and polysaccharide, was maximised using the RPB2 system. The quality of the synthesised polysaccharide, in terms of viscosity producing power, was highest using the HR system but the overall productivity was very low. Thus, the best compromise between productivity and product quality was achieved with the RPB2.

Polysaccharide production: Experimental comparison of the performance of four mixing devices

The environment in which live microorganisms has a major impact on their productivity. One important factor is the mechanical mixing that is used to promote good heat and mass transfer in bioreactors. In this paper, the performance of reciprocating plate bioreactors is first evaluated for their ability to produce high oxygen transfer coefficients. Pure water and a glycerol water (50∶50 wt%) solution are used for this evaluation. Then, the performance of reciprocating plate bioreactors for the production of an exocellular polysaccharide (pullulan) by yeast Aureobasidium pullulans is analyzed in terms of quantity and quality of the polysaccharide. Results clearly show that a more efficient substrate utilisation is achieved with reciprocating plate bioreactors.

Description and evaluation of reciprocating plate bioreactors

An experimental program has been initiated to use a reciprocating plate column for aerobic fermentations. This paper reports the results of the initial phase consisting of the hydrodynamic studies and the evaluation of the power consumption as a function of the level of agitation and gas superficial velocity. The variation of the gas holdup is presented and compared to a correlation. It is shown that a simple correlation can predict adequately the gas holdup when water is used. The power consumption, necessary for scale-up and design considerations, was evaluated using the pressure variation at the base of the column, the pressure difference across the column and the force exerted on the central shaft to reciprocate the plate stack. Results for the power consumed by the fluid mixture obtained with the three methods are presented and analyzed. The three methods give approximately the same value of the power consumption.



On a entrepris un programme experimental dans lequel on utilise une colonne a plateaux reciproques pour des fermentations aerobiques. On presente dans cet article les resultats de la phase initiale comprenant les etudes hydrodynamiques et ľevaluation de la consommation de puissance en fonction du degre ďagitation et de la vitesse superficielle du gaz. La variation de la retention de gaz est presentee et comparee a une correlation. On montre q'une simple correlation peut predire correctement la retention de gaz lorsque de ľeau est utilisee. La consommation de puissance, donnee necessaire pour des considerations de mise a ľechelle et de conception, a ete evaluee selon trois criteres: la variation de pression a la base de la colonne, la difference de pression dans la colonne et la force exercee sur ľaxe central pour faire osciller la pile de plateaux. On analyse les resultats de puissance consommee par le melange fluide pour les trois methodes. Les trois methodes donnent sensiblement la měme valeur pour la consommation de puissance.

Mustapha Lounes

Papers

Power consumption and mass transfer in agitated gas‐liquid columns: A comparative study

Pullulan fermentation in a reciprocating plate bioreactor

Polysaccharide production: Experimental comparison of the performance of four mixing devices

Description and evaluation of reciprocating plate bioreactors

Hydrodynamics and power consumption of a reciprocating plate gas–liquid column