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Jurnal Sains dan Teknologi Lingkungan
58 Ursula Ubst
drinking water such as Aquabacterium commune and Caulobacter crescentus could survive
radiation intensities of 100 J/m2, exceptionally up to 400 J/m2 (German technical standard).
Hygienically relevant bacteria such Pseudomonas aeruginosa and Enterococcus faecium, however,
could survive even stronger intensities up to 600 J/m2. Repair of DNA was not induced and did not
start until 2 hrs after disinfection so that immediatelly after disinfection (the regular point for
sampling and analysing) no repair or survival indicator could be detected. Repair started as recently
as during transport through the pipe system. Enterococcus faecium represented an extreme example
by starting repair after 27 hrs, being viable again at the point of drinking water use by the customer.
Thus, bacterial stress response proved to be an important factor for hygiene during drinking water
treatment and distribution which is mostly neglected up to now.
Table 1. Occurence of hygienically relevant bacteria in source water, during treatment and
distribution
Species
Surface
Raw Water Activated
Ultraviolet
Distribution
Water
Carbon
Radiation
Net
Filtration
Saprophytic atypical
positive
positive
positive
positive
positive
Mycobacteria
Pathogenic atypical
Mycobacteria
negative
negative
negative
positive
positive
Enterococci
(E. faecium/E. faecalis)
negative
negative
negative
negative
negative
Legionella spp.
positive
positive
positive
positive
positive
Legionella pneumophila
negative
negative
negative
negative
negative
Pseudomonas aeruginosa
positive
negative
negative
positive
positive
5. Water distribution
As drinking water is not sterile but has still low bacterial numbers, microbes also colonize the
distribution system and may form biofilms. These biofilms cannot be detected by the regular
controls using water sampling and cultivation techniques. Thus, we used devices specific for
biofilm sampling (Kalmbach et al., 1997; Schwartz et al., 2003a, Obst et al., 2007) consisting of
hollow stainless steel cylinders. Stainless steel bolts holding platelets of different materials (plastics,
metals) for biofilm settlement were screwed into place (fig. 2). The samplers were installed at