Biofilms, mains water and stainless steel

Abstract

There seems to be a general shift in the U.K. and the rest of Europe away from copper to the use of stainless steel piping for carrying particular “problem” waters in buildings where corrosion has been found to cause failures in copper. As stainless steel is a relatively new plumbing system few reports are available of its short term and long term performance in potable water environments and of differences between grades. Results of the development of biofilms on stainless steel grades 304 and 316, as an appendage to a large buildings plumbing distribution system, after 24 months exposure to potable water are presented. The viable cell counts on stainless steel grade 304 pipe after 24 months averaged 1.9×10 3 cfu cm −2 compared to 3.2×10 2 cfu cm −2 on 316 piping. The viable cell and total cell count on matt (2D) finished stainless steel were not significantly higher ( p<0.05) when compared to smooth (2B) stainless steel. Total carbohydrate levels and biomass dry weight levels were slightly higher on 304 stainless steel than 316 stainless steel, but were not significantly ( p<0.05) different. A mixture of biofilm bacteria attached to stainless steel were evident including, Pseudomonas spp., Alcaligenes sp. and Corynebacterium/Arthrobacter spp. Metal ions were evident in both 304 and 316 pipe biofilms. Scanning electron microscopy provided evidence of microcolony formation of rod-shaped bacteria and diatoms. Results of the development of biofilms on stainless steel grades 304 and 316, as an appendage to a large buildings plumbing distribution system, after 5 months exposure to mains water at watervelocities of 0.32, 0.96 and 1.75 m s −1 are also presented.