Degradation of Polar Organic Micropollutants during Riverbank Filtration: Complementary Results from Spatiotemporal Sampling and Push–Pull Tests

The fate of polar organic micropollutants (logDOW (pH 7) between -4.2 and +3.5) during riverbank filtration (RBF) at the river Thur was studied using both spatiotemporally resolved sampling and single-well push-pull tests (PPT), followed by LC-MS/MS analysis. The Thur is a dynamic prealpine river with an alluvial sandy-gravel aquifer, which is characterized by short groundwater travel times (a few days) from surface water infiltration to groundwater extraction. The spatiotemporal sampling allowed tracing concentration dynamics in the river and the groundwater and revealed persistence for the drug carbamazepine, while the herbicide MCPA (2-methyl-4-chloro-phenoxyacetic acid) and the drug 4-acetamidoantipyrine were very quickly degraded under the prevalent aerobic conditions. The corrosion inhibitor 1H-benzotriazole was degraded slightly, particularly in a transect influenced by river restoration measures. For the first time in situ first-order degradation rate constants for three pesticides and two pharmaceuticals were determined by PPTs, which confirmed the results of the spatiotemporal sampling. Atenolol was transformed almost completely to atenolol acid. Rate constants of 0.1-1.3 h(-1) for MCPA, 2,4-D, mecoprop, atenolol, and diclofenac, corresponding to half-lives of 0.6-6.3 h, demonstrated the great potential of RBF systems to degrade organic micropollutants and simultaneously the applicability of PPTs for micropollutants in such dynamic systems.