Monitoring the active sessile-colonisation of two drinking water distribution systems based on the protein contents in native biofilm samples

Biofilms are present to a greater or lesser degree in virtually all drinking water distribution systems. In order to investigate the relative intensity and the spatial and temporal distributions of the active sessile-colonization, protein was determined in native biofilm samples from the Oeiras-Amadora (OADS) and the Almada (ADS) distribution systems in Portugal. Samples (25 cm²) were taken from lengths of asbestos cement pipes of different ages and diameters. Protein was detected at levels from 0.3 to 68 μg/cm² in samples from all analysed pipe diameters and ages. At OADS, protein was found at 0.3 to 1 mg/cm² in 99% of the samples. At ADS, protein was only found in 30% of the samples, but at significantly higher levels (0.3 to 68 mg/cm²). In addition to displaying a more intense and scattered active colonization, ADS's oldest-pipes (in use for over 30 years) solely exhibited protein at the highest levels found (>19 mg/cm²), in contrast with the younger pipes where protein levels ranged from 0.3 to 19 mg/cm². Observed results suggest that the spatial and temporal distribution patterns of the active biofilm colonization may vary significantly among drinking water networks and may have a rather slow evolution, possibly at the decades scale.