The effects of UV disinfection on distribution pipe biofilm growth and pathogen incidence within the greater Stockholm area, Sweden

An assessment of the effects of the transition from conventional chlorination to UV disinfection on potable water biofilm growth and pathogen incidence was made. Two hydraulic systems were tested, one a 1.0 km polyethylene pilot-scale system within the Lovö waterworks, Stockholm, Sweden, as well as Hässelby and Nockeby municipal distribution systems within the greater Stockholm area. Biofilms were propagated on coupons and the amount of biomass analysed by standard culture and molecular methods. There was no measurable difference in biofilm biomass or pathogen incidence in the transition from conventional chlorination to UV-treatment in any system examined. With the exception of aeromonads, frank (salmonellae, enterobacteria) and opportunistic (legionellae) pathogens as well as indicator bacteria (E. coli, coliforms, enterococci) could not be detected within biofilms in either the pilot-scale or large-scale municipal system. Free-living protozoa were detected almost ubiquitously in biofilm samples in either experimental system though their exact significance and impact remains unknown and warrants further investigation.