Modelling of Fate and Transport of Wastewater-Derived Contamination in European Rivers with the New wOtter Code

Wastewater-derived contamination is one of the key causes for surface water bodies failing the European Commission requirements for good chemical status. Assessment tools that determine the contamination of surface water are pivotal as they can help to identify the stretches where microcontaminants levels are estimated to be high and as they can support monitoring and mitigation strategies. The production and the centralization of sanitation and hydrological datasets. Notably: (i) WWTP discharge, (ii) river flow conditions, and (iii) monitoring observations (for calibration/validation) are valuable information layers allowing microcontaminants fate and transport (MFT) modelling of wastewater-derived contamination in rivers. wOtter is a recently released fast and open-source MFT code, capable of simulating contamination across the EU hydrographic network and fine-tuned for using the above mentioned publicly available datasets. The produced MFT model in its early release was calibrated for a lumped contaminant over 273 EU sites. This study presents an improved approach to modelling the attenuation of a multitude of microcontaminants at EU scale, by assuming that the attenuation rates follow a statistical distribution. This results in higher rates of attenuation when highly degradable compounds are present initially, and lower rates of attenuation when only persistent contaminants remain. The new attenuation formula recognizes this behavior, and is shown to improve model accuracy when persistent compounds are present.