Water quality modelling, monitoring and microbial source tracking for microbial risk assessment of a drinking water source

Conference poster, 2012

To prevent waterborne disease outbreaks, mitigation of faecal contamination of drinking water sources and sufficient treatment of water at the drinking water treatment plant (DWTP) are required. The aim of this study was to combine and apply several tools to investigate the raw water quality and determine the risk for waterborne infections in a drinking water source for the cities of Mölndal and Gothenburg in Sweden, Lake Rådasjön. To identify the major contamination sources around the lake and their contribution to the faecal contamination at the water intakes of DWTPs, monitoring of faecal indicators and pathogens was combined with microbial source tracking and water quality modelling. The microbial source tracking was performed to determine the human or ruminant origin of faecal contamination using host-specific Bacteroidales genetic markers. The decay of these genetic markers in relation to the decay of traditional faecal indicators in water environment was investigated in outdoor microcosm trials performed in different seasons. Using measured concentrations of Bacteroidales genetic markers the pathogen (norovirus and Cryptosporidium) concentrations in faecal contamination sources around the lake were estimated for endemic and epidemic conditions. Afterwards, the fate and transport of faecal indicators and pathogens within the lake were simulated using a three-dimensional coupled hydrodynamic and microbiological model, which was calibrated based on the decay data from the microcosm trials. Based on the obtained results a microbial risk assessment of a conventional DWTP was conducted using two different approaches – optimal disinfection practices (ODP) and quantitative microbial risk assessment (QMRA). The results showed that the on-site sewers were the source that contributed the most to the pathogen concentrations at the water intakes under both endemic and epidemic conditions. The results from both the ODP and QMRA risk assessments indicated that the barrier efficiency against Cryptosporidium and possibly viruses may be too low at a conventional DWTP. This study demonstrated how different approaches and tools can be applied to evaluate the risks for waterborne infections and prioritise mitigation measures related to faecal contamination of surface drinking water sources.