Sammendrag
To prevent waterborne disease outbreaks and provide customers with safe drinking water, the
Drinking Water Regulations (FOR-2016-12-22-1868) require that the water supply must have sufficient
hygienic barriers. Hygienic barrier is a measure that reduces the burden of disease-causing microbes,
hereinafter referred to as pathogens. New knowledge is needed about the log-reductions that can be
achieved for various pathogens, especially viruses, at typical Norwegian water works, under Norwegian
conditions and operating conditions. There is also a need for more knowledge about the possible
presence of pathogens in return flows in coagulation filtration plants. This is essential for how these
flow lines are handled, e.g. whether maturation water can be used for flushing filters or returned to
raw water, as well as for hygienic assessments regarding the return flows to the recipient.
The knowledge of log reductions at Norwegian water works is largely missing because of a lack of good
and sensitive analytical methods for determining low levels of pathogens or good pathogen indicators.
In recent years, there has been significant method development for the analysis of various pathogens
or pathogen indicators. The new methods have made it possible to analyze a wider range of microbes,
including those that cannot be cultured, thus, acting as broader indicators of pathogenic bacteria and
viruses. Hygienic barriers are assessed based on the reduction of pathogens on a log10 scale. Raw water
normally has low concentrations of pathogens that are only sporadically detected by current methods,
thus, alternative methods or surrogates/indicators as a substitute for pathogens must be considered.
A peer review of available literature has been carried out for alternative methods for use in assessing
the barrier effect of the particle removal stage. The methods described in this report include assessing
different strategies for viruses, bacteria and parasites. For viruses, the use of model viruses such as
Pepper mild mottle virus as an alternative fecal indicator, spiked-in with somatic coliphages and
quantification of all viral particles in water with flow virometry are discussed. Alternative bacterial
methods described in the report include different methods of quantification of all bacteria in water:
by cell counting with flowcytometer, DNA quantification with digital PCR for the 16s gene of bacteria
and activity measuring adenosine triphosphate (ATP). In addition, one can analyze which bacteria are
present using sequencing of 16s. For parasites, some alternative surrogate parameters are described
as spore forming bacteria and microspheres.
Flow virometry for viruses and flow cytometry, digital droplet PCR and sequencing for bacteria have
been established and tested in this project for further use in an additional project. All these methods
provide information of the importance for the assessment of hygienic barriers. The various methods
have strengths and weaknesses; For example, both ATP analyses and flow cytometry are tested, but
they do not distinguish between bacteria originating from the raw water and bacteria that grow in the
water treatment plant. DNA-based measurement methods are a rapidly evolving field, however,
requiring some processing before they can be used for assessments of hygienic barrier effect at the
species level.
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