Meßmethoden in Fermentern unter sterilen Bedingungen

Measuring methods for fermentations under sterile conditions . In process development as well as in industrial production it is necessary to obtain information about the state of the process by the measurement of characteristic variables. This is true for bioengineering in the same way as for chemical processes in general. Characteristic variables to be taken into consideration include temperature, pressure, masses and mass-flow rates, operating parameters such as liquid level and impeller speed, and especially the concentrations of reactants, intermediates, and products. In contrast to other processes, a particular problem exists in fermentation because introduction of microorganisms, into the system by the measurement has to be prevented. Since taking samples from the reactor is hardly suitable for controlling the process for various reasons (amount of work, loss of time), this review considers only those methods which can be used for measurements directly in the fermentor. Essentially these are physical and physico-chemical methods, e. g. for concentrations (O₂ and CO₂ in gas and liquid phase, pH, biomass). Of special interest for future development are spectroscopic and enzymatic methods for fast determination of substrates and of important intermediates and products. Here the sterility required entails special problems in the case of enzyme electrodes. Important information on the state of the process can, of course, also be obtained from physical variables, such as gas hold-up, bubble size, viscosity, and turbulence properties of the medium. These variables are less critical with regard to sterility.     

INFLUENCE OF LIQUID PROPERTIES ON THE DETERMINATION OF THE VOLUMETRIC MASS TRANSFER COEFFICIENT WITH THE HYDRAZINE METHOD

The oxidation of hydrazine in aqueous solution by atmospheric oxygen in presence of a homogeneous catalyst (copper tetrasulphophthalocyanine) is well suited for the determination of volumetric mass transfer coefficients. In contrast to other chemical methods the hydrazine oxidation permits to vary coalescence behaviour of the liquid phase by adding electrolytes or organic compounds, because without these solutes the reaction liquid does not inhibit bubble coalescence. With appropriate high molecular additives the hydrazine method can also be used for mass transfer measurements in liquids of high viscosity. Compared to the dynamic method the hydrazine method as a steady state method is far less influenced by systematic errors originating from the evaluation model. For this reason the application of the hydrazine method for testing semi-industrial and industrial gas-liquid contacting devices should be especially attractive.     

Segregation in eastern German cities: Gentrification, downgrading of large estates, and suburbanization

The following discussion deals with the changes in eastern German cities following the “Wende,” or turning point, in 1989. Residential segregation existed on a very limited scale in the GDR; but it can be assumed, given the rapid differentiation of social structure and housing conditions in eastern German cities, that it will become a dominant structural characteristic of cities there as well. The following discussion will present selected results of an empirical study of the city of Magdeburg. The study shows that the process of segregation, now taking place in the city as a whole after a somewhat hesitant beginning, can be broken down into various partial processes. And though the expected selective migration of the economically better off to prestigious residential areas from the end of the last century is only in its beginnings, problems are growing in some areas of the newer large estates that were built in the 70s and early 1980s. The downgrading of the newer large estates has also been the result of a massive trend toward suburbanization based on social and spatial selectivity since the Wende.