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Institut für Wasser- und Umweltsystemmodellierung - IWS



"Investigations on biofilm topography at hydraulic relevant scales"

Biofilm often grows at the interface between a fluid and a solid phase. It alters the appearance of surfaces by producing a biofilm matrix. A changed roughness impacts the hydraulic conditions, turbulence and velocity, to the extent that biofilm reduces the efficiency of hydraulic devices. As a first step, a non-destructive method is developed to measure biofilm topography at small scales to enable investigations on the reciprocal relationship of biofilm and ambient hydraulics in future. This feasibility study focuses on the measurement principle, calibration, and validation. The developed Laser Scanning Method (LSM) is based on the triangulation principle. Using the measurement data, the Digital Elevation Models (DEM) of the biofilm surface are generated and printed in 3D to create replica. The Laser Doppler Velocimetry (LDV), an established method, is applied in a comparative study for varying roughness conditions: (i) smooth, (ii) biofilm surface and (iii) 3D generated print in order to evaluate the hydraulic relevance. The hydraulic parameters: (i) Reynolds stresses, (ii) turbulence intensity, and (iii) velocity profiles are compared. This study shows that investigations on biofilm topography are possible using LSM clarifying its field of application. The hydraulic data demonstrates that the generated replica and the investigated biofilm cause comparable hydraulic conditions near the bed. This suggests that the presented method is able to capture the hydraulic relevant roughness of biofilm and therefore facilitates further studies about the mutual relationship of hydrophysical factors and biofilm.