Biofilm structure and influence on biofouling under laminar and turbulent flows

A flow system was designed so that biofilms could be grown simultaneously in parallel flow cells under laminar and turbulent flows using shared nutrients and inocula. The flow cells were made from rectangular glass tubing chosen to simulate flow in industrial pipes. The hydrodynamics in the flow cells were characterized using dye tracers and the relationship between the Fanning friction factor (f) and Reynolds number (Re). Flow was laminar at Re 100 and turbulent at Re 3000. Transition between flows occurred at approximately Re 1000. Biofilms from environmental inocula were grown on tap water or a minimal salts medium with 40 ppm glucose. Biofilms grown under laminar flow were patchy and consisted of cell clusters separated by interstitial voids. Biofilms grown under turbulent flow were filamentous. The filaments had a complex structure and were formed by the colonization of filamentous sheathed bacteria with microcolonies of non-filamentous bacteria. The filamentous bacteria were often tangled together and subsequent colonization by microcolonies resulted in the formation of cohesive structures that we termed “biofilm streamers”. The frictional loss coefficient (kf) across the flow cell colonized with biofilm grown under turbulent flow was almost twice the kf across the flow cell colonized with biofilm grown under laminar flow. There was little difference in kf across the flow cell colonized with biofilm grown under laminar flow and the kf across a clean flow cell