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Institut für Wasser- und Umweltsystemmodellierung - IWS

Abstract

 
   

"Das Messprinzip von MagPI zur Bestimmung der Adhäsion von Biofilmen"

In the last few decades, sediment stability has become a big focus of interest in hydrodynamics. It was identified, that biochemical processes in bio films on water/solid interfaces contribute a lot to stabilize river sediments. Microorganisms embedded in biofilms secrete extracellular polymeric substances (EPS), which glue sediment particles together. In river systems biofilms perform great ecosystem functions. They absorb pollutants and add to the river self-purification. The impairment of herbicides on biofilm growth is analysed in this thesis through an experiment. Biofilms were grown on dioxin polluted sediments and exposed to different Mecoprop concentrations. The development of the microcolonies was recorded using Magnetic Particle Induction (MagPI) [Larson et al., 2009]. The results show a big influence by mecoprop on the biofillm formation. While MagPI measurements of the control sample (0 g{l Mecoprop) reveal an increase in sediment stability, the other samples indicate a loss of adhesion. Furthermore, the methodology of MagPI is the focus of this study. Because of the common declaration of data in mA (current) or in mT (magnetic flux density), it is difficult to compare measurements recorded by different MagPIs. With the aid of a demonstration experiment, it is shown that the gradient of the magnetic flux density grad B is the physically correct parameter, which enables the comparison of measurements. Particles in a strong, homogeneous magnetic field did not move until the induction of a gradient of the magnetic flux density grad B. The acting force F, that makes the magnetic particles take o , depends on two parameters: (a) the gradient of the magnetic field grad B and (b) the magnetic moment of the particles. With increasing magnetization of the particles in a magnetic field, the magnetic moment is enhanced as well. Therefore, to generate the same force F, a smaller grad B is needed.