The Impact of Biofilm Development on Pipe Roughness and Velocity Profile

The unpredictable impact of biofilms on friction in pipes causes difficulty in accurately designing for pipe roughness in biofouled pipes. The effects of biofilm growth on pipe roughness were experimentally investigated with the variation of growth conditions of velocity, diameter and water source. The results showed that differences in the growth velocity and source water altered the equivalent sand grain roughness of the biofouled pipes. The variation of the friction factor with Reynolds number in these biofouled pipes was not as expected for a rough surface and did not follow the traditional pipe friction equations. In addition, the change to the pipe velocity profile once biofilm had developed was analysed. One of the most important findings was that the Von Karman constant was significantly lower than normal in the biofouled pipes and that it varied with velocity. This enabled a modified version of the Colebrook-White equation to be created to describe the friction factor variation with Reynolds number in biofouled pipes. This research provides a basis for a method to predict the impact of biofilm development on pipe roughness.