V. Lund et K. Ormerod, THE INFLUENCE OF DISINFECTION PROCESSES ON BIOFILM FORMATION IN WATERDISTRIBUTION-SYSTEMS, Water research, 29(4), 1995, pp. 1013-1021
Results of a 20 months pilot plant study of microbial regrowth after t
he action on humic water of three oxidative disinfection processes (ch
lorination, u.v. irradiation and ozonation) are reported. Regrowth was
detected as biofilm produced in 2.6 m lengths of PEH pipes. No biofil
m was formed from the chlorinated water containing a residual of 0.04-
0.05 mg/l free chlorine. The greatest production was found from the oz
onated water, closely followed by the control (microstrained) water. T
he u.v. irradiated water showed considerably less production of biofil
m. This may be the effect of a residual disinfectant, the presence of
which was also demonstrated by reduced biological oxygen demand compar
ed to the control. A higher oxygen demand in ozonated water indicated
an increase in the content of easily degradable organic molecules, whi
ch was confirmed by high performance size exclusion chromatography. Th
e chromatograms showed a rise in low molecular fractions in the ozonat
ed but not the u.v. irradiated water. Examination by a scanning electr
on microscope of biofilm on pieces of mica inserted in the pipe system
s, revealed a higher content and variety of bacteria in the ozonated t
han in the control system, indicating a lower microbial activity in th
e latter, which also showed the highest content of inorganic material.
The rate of biofilm formation was closely related to the seasonal flu
ctuations in water temperature. The bactericidal effect of the u.v. ir
radiated water was less pronounced during the last part of the experim
ental period. The residual free chlorine in the chlorinated water was,
however, sufficient to prevent biofilm formation during the whole exp
erimental period.