Mapping of Bacteria with Flow Cytometry – before, during and after treatment of drinking water

Sammanfattning: In order to produce drinking water of high quality, surface water works apply extensive treatment processes. In this study, flow cytometry and heterotrophic plate counting was utilized to study water quality before, during and after treatment in Görvälnverket in Stockholm, Sweden. Samples were collected and analysed throughout the treatment process, mapping the reduction of total and intact cell counts as well as bacteria possessing high nucleic acid content, which is a characteristic of some pathogens. Total and intact cell counts decline throughout autumn and stabilize at the end of December. At the same time, the number of bacteria with high nucleic acid content increase, possibly displaying circulation in the lake and therefore intake of sediment bacteria. The treatment of flocculation and sedimentation decrease bacterial counts to a large extent. Samples taken after sand filtration, carbon filtration and finished drinking water display similar counts. According to this data, the number of effluent bacteria from sand filters depend heavily on maintenance timing. Carbon filtration does not seem to alter the numbers of bacteria. Lastly, biostability was evaluated and compared to commercially sold bottled water. Norrvatten’s produced drinking water yield the least cfu and display sufficient biostability. The reason seems to be monochloramine addition and UV radiation that disinfects and inhibits bacterial regrowth, respectively.