BIOFILM DEVELOPMENT ON STAINLESS STEEL IN MAINS WATER

Biofilm development on stainless steel in mains water has been poorly documented to date. Results are presented of the development of potable-water biofilms over 12 months on stainless-steel grades 304 and 316, used as appendages to a large buildingʹs plumbing distribution system. The viable cell counts on grade 304 pipe after 12 months averaged 2.8 × 103 cfu cm−2, compared to 3.6 × 102 cfu cm−2 on grade 316 pipe. The viable cell and total cell count on matt (2D) stainless steel remained significantly higher (p < 0.05) when compared to smooth (2B) stainless steel after 4-months and 8-months biofilm development, but at month 12 the viable cell counts on the two steel finishes were not significantly different. Total carbohydrate levels and biomass dry weight levels were slightly but not significantly higher on grade 304 than on grade 316. A mixture of biofilm bacteria attached to stainless steel were evident, including Pseudomonas spp., Methylobacterium spp., Acinetobacter spp., Corynebacterium/Arthrobacter spp. and Micrococcus spp. Inductively coupled plasma spectrophotometer analysis of biofilms showed an accumulation of metal ions in both grades 304 and 316 pipe biofilms. Molybdenum (0.04 mg litre−1) was found to be associated with biofilms isolated from grade 316 after 4 months, and 0.05 mg litre−1 was found in the biofilms after 12-months exposure to mains water. Scanning electron microscopy provided evidence of microcolony formation of rod-shaped and coccoid-shaped bacteria and diatoms.