Miguel Angel Marazuela, Giovanni Formentin, Klaus Erlmeier, Thilo Hofmann

The persistence of the artificial sweetener acesulfame potassium (ACE) in wastewater treatment and subsequently in the aquatic environment has made it a widely used marker of wastewater in both surface water and groundwater. However, the recently observed biodegradation of ACE during wastewater treatment has questioned the validity of this application. In this study, we assessed the use of ACE not only as a marker of wastewater, but also as a transient wastewater tracer that allows both the calculation of mixing ratios and travel times through the aquifer as well as the calibration of transient groundwater flow and mass transport models. Our analysis was based on the data obtained in a nearly 8-year river water and groundwater sampling campaign along a confirmed wastewater-receiving riverbank filtration site located close to a drinking water supply system. We confirm that temperature controls ACE concentrations and thus their seasonal oscillation. River water data showed that ACE loads decreased from 1,500-4,000 μg·s−1 from December to June (cold season; T<10°C) to 0-500 μg·s−1 from July to November (warm season; T>10°C). This seasonal oscillation was transferred to the aquifer and preserved >3 km through the aquifer, with ACE concentrations oscillating between values below the detection limit in the warm season to 0.15 μg·L−1 in the cold season. The seasonal variation in ACE degradation during wastewater treatment enables the sweetener’s use as a transient tracer of wastewater inflows and riverbank filtration. In addition, the arrival time of the ACE concentration peak can be used to estimate groundwater flow velocity and mixing ratios, thereby demonstrating its potential in the calibration of groundwater numerical models.