Impact of seasonality, redox conditions, travel distances and initial concentrations on micropollutant removal during riverbank filtration at four sites

Oberleitner O, Schulz W, Bergmann A, Achten C

Abstract

Riverbank filtration (RBF) is a reliable water purification technique that has proven to be suitable for theremoval of organic micropollutants. Its removal efficiency and dependency on a variety of factors such asredox conditions, temperatures, geology, travel times, level of initial micropollutant concentrations andseasonality were investigated during three seasonal sampling campaigns. Two anoxic (silty sand, Emsriver) and two oxic (gravel, Ruhr river) RBF sites in Germany with different travel distances (42e633 m)were studied. Micropollutant concentrations were examined using a large-volume direct injection liquidchromatography method coupled to high-resolution mass spectrometry. Seasonal differences in micropollutantconcentrations in the rivers were observed for chlorotolurone, diclofenac, terbuthylazine,mecoprop-P, MCPA (2-methyl-4-chlorophenoxyacetic acid) and propyphenazone. Redox dependencies inRBF were only found for sulfamethoxazole, propyphenazone, terbuthylazine and carbamazepine. Data foroxazepam, tramadol, N-desmethyl-tramadol, tilidin-desmethyl, carbamazepine and carbendazim indicatea required minimum travel distance of e.g. 100e200 m for the complete removal. Notably, traveltime did not seem to be a substantial factor for their removal. High conductivity aquifers are also wellsuited for micropollutant removal. Seasonal initial concentration level variations showed no impact onthe resulting abstraction well concentrations. Although the calculated removal efficiencies varied, theyproved to be improper for seasonal raw water quality comparison. Knowledge of micropollutant behaviorin riverbank filtration was broadened and RBF proved to be well suited for effective micropollutant