Biofilm development on stainless steel and pvc surfaces in drinking water

Abstract

Surfaces of electro-polished, bright annealed and matt stainless steel and of lead stabilized PVC were exposed to running municipal drinking water (10 cm s −1) for 167 days. The total number of micro-organisms growing on the surfaces was examined with an acridine orange direct count technique at 7 sampling times. The growth was exponential with a doubling time of 11 days between 0–122 days which increased to 47 days between 123–167 days. The mean number of micro-organisms on the surfaces after 167 days was 4.90 × 10 6 cells cm −2. There was no difference in the amount of cells on the hydrophilic glossy steel surfaces and the hydrophobic PVC surface. The biofilm processes of growth, product formation and debris entrapment seemed to dominate over the initial surface energy dependent attachment processes. The matt steel surface is rougher than the other surfaces and had an average of 4.07 × 10 6 bacteria cm −2 during the last 45 days, which is 1.44 times more micro-organisms than the electro-polished steel had. Two reasons support this observation. Detachment due to shear forces from the flow will be reduced on the rougher surface since the cells can be shielded from the bulk flow and more substratum surface area may be available for the biofilm. Micro-flagellates were grazing the bacteria on the test surfaces after 122 days. This might explain why the doubling time decreased to 47 days between 123–167 days. It suggests that microbial biofilms in drinking waters are grazed and thereby partly controlled by protozoa.