Hydrodynamic and Microbiological Modelling of Water Quality in Drinking Water Sources

Licentiate thesis, 2011

Faecal contamination of drinking water sources poses risks for waterborne disease outbreaks. To manage these risks the fate and transport of faecal contamination in a drinking water source need to be understood and quantitatively described. In this study the fate and transport of faecal contamination in a drinking water source, Lake Rådasjön in Sweden, was simulated using a coupled hydrodynamic and microbiological modelling approach. To calibrate the microbiological model that describes the inactivation of faecal indicators as a function of temperature and sunlight, a microcosm experiment was performed. The experiment consisted of three outdoor microcosm trials performed in March, August and November 2010 to capture seasonal variations in the inactivation of faecal indicators. The indicators studied in the microcosm experiment included traditional faecal indicators (total coliforms, E. coli, enterococci, somatic coliphages) and Bacteroidales genetic markers (BacH and BacR) that can be used in microbial source tracking to determine the human or ruminant origin of faecal contamination. The spread of faecal contamination in the lake was simulated using E. coli and Bacteroidales genetic markers. The results indicated that hydrometeorological conditions such as wind, inflow to the lake and temperature stratification of the lake have a major impact on the spread of faecal contamination. The simulations showed that faecal contamination from the river Mölndalsån, emergency sewer overflow and on-site sewers can pose threats to the drinking water supply of the cities of Gothenburg and Mölndal. Moreover, modelling the fate and transport of Bacteroidales markers in a water body provided information about the contribution of different sources to the total concentration of these markers at the water intake. This can substantially improve the usefulness of Bacteroidales markers in microbial source tracking.