Detection of Microbial Pathogens and Indicators in Sewage Effluent and River Water During the Temporary Interruption of a Wastewater Treatment Plant.

In this case study, the impact of a temporary (4 days) interruption of a sewage treatment works on the microbial quality of a drinking water source in SE Norway to which the sewage was discharged was investigated. Samples of wastewater and river water were taken before and during the interruption of the sewage treatment and analysed for various microbial indicators and pathogens: faecal indicator bacteria (E. coli and total coliforms); F-specific RNA bacteriophages; pathogenic viruses (norovirus GI and GII, adenovirus); protozoan parasites (Giardia and Cryptosporidium). Water at the inlet to the drinking water treatment plant, 20 km downstream from the sewage discharge, was not found to be significantly affected with respect to bacteria and parasites, with higher concentrations measured prior to the sewage treatment interruption, probably associated with a period of heavy rainfall. For viruses, however, the heavy rainfall appeared to be of lesser relevance to the contamination levels. These data demonstrate the importance of water providers having a clear overview not only of sewage discharge in water catchment areas but also of other potential sources of contamination with different pathogens and indicators, and the effects of weather conditions on contamination events.