Transformation of organic micropollutants during river bank filtration: laboratory versus field data

This paper investigates the degradation behavior of 14 organic micropollutants (OMPs), selected for their different physico-chemical properties (e.g., molecular weight, hydrophobicity and charge), in soil columns simulating the conditions prevailing in the first meter of river bank filtration (RBF) media. The results from the column system are compared to RBF field data obtained from the Vitens drinking water company in The Netherlands. The study explores the role of sorption media (sand filled columns and polyethylene tubes) as carrier material for the biomass. Polyethylene tubes with the same specific surface area as sand in the columns, were operated under similar conditions to compare OMP removal in the two systems. Both the column and field data indicate that negatively charged OMPs with Log D ranging from 0.65 to 1.95, positively charged OMPs with Log D ranging from -0.59 to 0.21 and neutral OMPs with Log D (-1.9 to 1.12) were more susceptible to biodegradation. The compounds that persisted (carbamazepine, atrazine, phenytoin, lincomycin) were positively charged with lower Log D (-1.33) or neutral with higher Log D (1.56 to 2.64). Hydrochlorothiazide showed poor biodegradability despite being neutral and having a lower log D (-0.71); it is an exception to the above behavior for reasons that have not yet been identified. A comparison of OMP removal in a biologically active polyethylene tube with a biologically active column showed that the biomass established in either systems removed the same OMPs and to similar extent for a majority of the OMPs. This finding supports the use of polyethylene tubes as a simple, cheap and quick method for investigating the trends in OMP removal in RBF.