Smittspridning från avloppsreningsverk – QMRA som beslutsstöd vid ombyggnation av Arvidstorps reningsverk / Pathogen dispersion from wastewater treatment plants – QMRA as decision support in the renovation of Arvidstorp treatment plant
Source water contamination is a main cause of waterborne disease outbreaks in Sweden and municipal sewage discharges often end up in water sources. At Arvidstorp wastewater treatment plant in Trollhättan, a disc filter has been installed with the primary aim of improving phosphorus reduction. To give permission, the County Administrative Board of Västra Götaland called for an investigation into the plant’s microbial load to the Göta River and its health consequences for drinking water consumers. With a pore size of 10 μm in the disc filters, there should be no high expectations of microbial removal. Mechanical separation would require the micro-organisms to be particulate bound, and by precipitation or polymer additives the microbiological separation of the disc filter can be increased. A QMRA model was set up to analyze pathogen dispersion, where indicator organism data were combined with factors such as disease occurrence, operating conditions at the treatment plant, flows and microbiological inactivation in the river. The model was used to calculate the risk of infection for water consumers with respect to Campylobacter, Salmonella, norovirus, Giardia and Cryptosporidium and how this is affected by the disc filter. The QMRA model, which is based on stochastic modeling, has provided a decision support for operational strategies at the sewage treatment plant and has also met the investigation requirements.