Showing papers in "Bioprocess Engineering in 1986"

Hydrodynamic effects on cells in agitated tissue culture reactors

Abstract: Tissue cells are known to be sensitive to mechanical stresses imposed on them by agitation in bioreactors. The amount of agitation provided in a microcarrier or suspension bioreactor should be only enough to provide an effective homogeneity. Three distinct flow regions can be identified in the reactor: bulk turbulent flow, bulk laminar flow, and boundary-layer flows. Possible mechanisms of cell damage are examined by analyzing the motion of microcarriers or free cells relative to the surrounding fluid, to each other, and to moving or stationary solid surfaces. The primary mechanisms of cell damage appear to result from (a) direct interaction between microcarriers and turbulent eddies, (b) collisions between microcarriers in turbulent flow, and (c) collisions against the impeller or other stationary surfaces. If the smallest eddies of turbulent flow are of the same size as the microcarrier beads, they may cause high shear stresses on the cells. Eddies the size of the average interbead spacing may cause bead-bead collisions which damage cells. The severity of the collisions increases when the eddies are also of the same size as the beads. Bead size and the interbead distance are virtually equal in typical microcarrier suspensions. Impeller collisions occur when the beads cannot avoid the impeller leading edge as it advances through the liquid. The implications of the results of this analysis on the design and operation of tissue culture bioreactors are also discussed.

Biological elimination of volatile xenobiotic compounds in biofilters

Abstract: Biofiltration is a technique which is frequently applied for the odour abatement of waste gases. This technique is based on the ability of microorganisms (generally bacteria, and to a small extent moulds and yeasts) to degrade several organic as well as inorganic compounds to mineral end-products, like water and carbon dioxide. In the case of biofiltration, microorganisms are attached to suited packing materials in the filter, which contain the inorganic nutrients necessary for microbial growth. In order to make biofiltration applicable on a larger scale in process industry, it is necessary to find microorganisms able to eliminate compounds which are strange to life, the so-called xenobiotics. At the Eindhoven University of Technology microorganisms were isolated for the elimination of a number of xenobiotics, e.g. aromatic compounds and chlorinated hydrocarbons.

Valuation of bioreactors for low viscous media and high oxygen transfer demand

Abstract: A strategy of a systematic comparison is developed in which the valuation parameters and the influencing parameters are put in order in a three dimensional matrix. The performance of a bioreactor construction is then evaluated with a biological test system that has representative medium properties and where all important parameters of microbial growth are known. This strategy is applied to four bioreactor constructions and to low viscous bacteria and yeast systems with and without foam formation. On the basis of this data set the performances of the different bioreactors are compared.

Microporous membranes in biotechnical application

Abstract: Crossflow microfiltration has become an established process for the separation of microparticles, bacteria and emulsion droplets in a variety of biotechnical applications. After the characterization of microporous membranes and explanation of the different microfiltration processes including the backpulse system, some applications in the biotechnical industry will be discussed in more detail. Special attention will be paid to the sterile filtration, cell mass retention, diafiltration and bubble-free gassing.

Coupling of microbial kinetics and oxygen transfer for analysis and optimization of gluconic acid production with Aspergillus niger

Abstract: Gluconic acid fermentation has been widely used for the analysis of various aspects of kinetics and gas liquid transfer of oxygen. Most of these studies are, however, restricted to processes with bacteria. Mathematical models for industrially important productions with fungi have not been elaborated. In the experimental part of this work computer coupled fermentations of gluconic acid production with Aspergillus niger NRRL 3 have been performed. Knowledge of the stoichiometric relationship in the key reaction (glucose oxidase) provides an excellent opportunity for on-line estimation of glucose, biomass and product gluconate from oxygen uptake and carbon dioxide evolution rates. Starting then from experimental observations on the pH-depending oxygen kinetics of gluconic acid formation and influences of product concentrations on the growth of Aspergillus niger a mathematical framework is developed in which the kinetics of growth and production are coupled with gas liquid oxygen transfer. The model can be successfully applied to simulations of the experimental results of gluconic acid fermentations with cyclic addition of glucose. An important aspect in the coupling of transport and microbial reaction in this model is the incorporation of the influence of sugar and gluconate on the solubility of oxygen and k La via changes of viscosities and molecular diffusivities. With the development of such a comprehensive model, it appears feasible to investigate the influence of various process conditions (sugar feeding, pressure, optimal pH profiles) and to study their possible impacts on the productivity of the overall process.

Aerobic two-stage biological degradation of organic carbon compounds and ammonium

Abstract: In a two-stage pilot plant biological processes effect substantial degradation of organic carbon compounds and the ammonium contained in highly contaminated waste waters at extremely short mean residence time in the bioreactor. This achievement is mainly due to employment of a newly-developed type of bioreactor — the reciprocating jet bioreactor.

Bioprocess engineering characteristics of the horizontal stirred tank

Abstract: Bioreactor performance studies of the recently developed “horizontal stirred tank” with a volume of 421 have been carried out for fermentation with Trichosporon cutaneum. Quantification on the basis of measured oxygen transfer capacity and power consumption is presented and compared with data for a conventional vertical tank bioreactor. During the experiments it has been observed that two different forms of morphology of Trichosporon, i.e. the “normal” yeast-form (Y) with single cells and a mycelium-form (M) with filamentous cells, are present in the horizontal stirred tank when working with the original strain (DSM 70698). After separation both forms were characterized and later on used for bioreactor performance studies in the horizontal and vertical stirred tank. Results of oxygen efficiency show the drastic effect of the morphology change on bioreactor performance. Finally different bioreactors are quantitatively compared on the basis of oxygen transfer, power consumption and productivity using the reference fermentation system Trichosporon cutaneum.

EPR and EXAFS studies of glucose isomerase activation by divalent metals

Abstract: The interactions of Mn2+ and Co2+ with glucose isomerases from three microbial sources have been studied using various direct physical methods. Co2+ was found to activate each enzyme, although the degree of activation varied significantly for enzymes from different organisms. EPR spectroscopy measurements revealed that dissimilarities in the coordination sphere of enzyme-bound Mn2+ accompanied the differences in enzyme activity. Variations in the EPR spectra of a nitroxide spin label coupled to two of the three isomerases, possibly near their active sites, were also observed. In no case was the EPR spectrum influenced by Co2+ addition, a result discordant with the hypothesis that Co2+ activates the enzyme by inducing a conformational change. The proximal biochemical environment of enzymebound Co2+ was also examined using EXAFS spectroscopy. This method showed that glucose causes notable changes in the ligand environment of the enzyme-bound metal, suggesting the formation of an enzyme-metal-substrate bridge complex. The significance of these results relative to possible reaction mechanisms is discussed.

Stability analysis of a binary culture chemostat experiencing biofilm formation

Abstract: Time-dependent biofilm formation effects on continuous fermenter operation are modelled here for a binary culture of microorganisms growing on a single substrate. Dynamic computer solutions are detailed for a mixed culture of one microbe a having a higher growth rate than a second microbe b for two hypothetical scenarios of microbe b having different magnitudes of cellular deposition rate. A stability analysis of the resultant steady-states is also provided. Biofilm effects on the estimation of kinetic and stoichiometric parameters in a chemostat plus the impact of biofilms on mixed culture dynamics are discussed.