Abstract

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In Germany, bank-filtered raw water and ground water is mainly used for drinking water conditioning. Microorganisms, which are neither retarded by the subsoil passage of the bank-filtration, nor by the different filtration and disinfection steps at the water works, cause the growth of biofilms on different materials originally used in drinking water distribution systems. The development, the phylogenetical diversity and the bacterial metabolic activities of biofilms on polyethylen (PE-HD), polyvinylchlorid (PVC), steel and copper were analyzed at different sampling points. The incubation experiments were performed under natural conditions using a flow device technique.

The devices were installed after the activated carbon filters and disinfection step at the water works and at two different house branch connections within the distribution system of the conditioned drinking water of the water works. The synthetic materials were colonized very rapidly within a few days in significant higher densities than steel and copper. The total bacterial cell counts of the biofilms were measured by DAPI (4′,6-diamidino-2-phenylindole) staining.

The metabolic activities of the bacteria were quantified by the use of the redox dye CTC (5-cyano-2,3-ditolyl tetrazolium chloride), which is frequently described as an indicator for respiration. The highest respiratory activities were observed in biofilms from synthetic materials grown after the activated carbon filters at the water works. A significant reduction of the total bacterial cell counts and respiratory activities of about 80% was measured due to the disinfection at the water works.

A time dependent growth of bacteria in biofilms was observed at the two sampling points within the distribution system, whereas the percentage of CTC-reducing cells stabilized at 35%. The in situ-hybridizations with fluorescence labelled, group-specific rRNA targeted oligonucleotide probes revealed the following: (i) bacteria of the Beta- and Gamma-subclass of Proteobacteria were found most frequently within the biofilm population, (ii) the percentage of the different subclasses depended on the used material, (iii) there were no significant changes in bacterial subclass composition of the biofilms taken from the water works and house branch connections.

In addition, polymerase chain reaction (PCR), southern blot hybridization and in situ hybridization were used to detect facultative pathogenic bacteria in biofilms. Non-pneumophila Legionella were found in a relative high percentage up to about 7% in many biofilms, whereas fecal streptococci were detected only in few biofilms of the drinking water distribution systems