The effect of turbulent flow and surface roughness on biofilm formation in drinking water

There is considerable interest in both Europe and the USA in the effects of microbiological fouling on stainless steels in potable water. However, little is known about the formation and effects of biofilms, on stainless steel in potable water environments, particularly in turbulent flow regimes. Results are presented on the development of biofilms on stainless steel grades 304 and 316 after exposure to potable water at velocities of 0.32, 0.96 and 1.75 m s(-1). Cell counts on slides of stainless steel grades 304 and 316 with both 2B (smooth) and 2D trough) finishes showed viable and total cell counts were higher at the higher flow rates of 0.96 and 1.75 m s(-1), compared to a flow rate of 0.32 m s(-1). Extracellular polysaccharide levels were not significantly different (P < 0.05) between each flow rate on all stainless steel surfaces studied. Higher levels were found at the higher water velocities. The biofilm attached to stainless steel was comprised of a mixed bacterial flora including Acinetobacter sp, Pseudomonas spp, Methylobacterium sp, and Corynebacterium/Arthrobacter spp. Epifluorescence microscopy provided evidence of rod-shaped bacteria and the formation of stands, possibly of extracellular material attached to stainless steel at high flow rates but not at low flow rates.