Biofilm development in potable quality water

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Abstract
Instances of rapid failure of copper pipe in potable water systems in large municipal buildings in certain geographical areas have led to a review of alternative materials, including stainless steel. This study compares biofilms formed on the surfaces of stainless steel pipes of grades 304 and 316 2B and 2D. Biofilms developed on stainless steel for 1 year at a water flow rate of 0.32 m s‐1 were subjected to a new water flow rate of 0.96ms‐1 for 4 weeks. Total viable cell counts of all biofilms showed a general increase as a result of an increase in water flow rate. At no time were there any significant differences (P < 0.05) in the viable cell counts between grades and finishes of stainless steel. The sessile bacterial community observed on stainless steel 304 2B pipe consisted of predominately Gram‐negative bacteria, namely Pseudomonas spp., Alcaligenes sp., and Methylobacterium sp. and Gram‐positive bacteria of the Arthrobacier/Corynebacterium group. A change in the velocity from 0.32ms‐1 to 0.96ms‐1 did not result in any changes in the genera present within the biofilm. The viable cell counts on all stainless steel surfaces generally decreased within 1 week after changing the water velocity from 0.64ms‐1 to 1.75ms‐1. The viable cell counts were not significantly lower (p < 0.05) on grade 316 than on grade 304. Once a biofilm was well established on the surface of 2B or 2D grades of stainless steel detachment was not significant and there were no major changes in the composition of the microbiota. ‘Streamers’ were evident at the higher water velocities.