Modelling the fate of organic micropollutants during river bank filtration

Emerging organic contaminants (EOCs) are frequently detected in urban surface water and adjacent groundwater, and are therefore an increasing problem for potable water quality.

River bank filtration (RBF) is a beneficial pretreatment step to improve surface water quality for potable use. Removal is mainly caused by microbial degradation of micropollutants, while sorption retards the transport. But there has been little field-scale quantification of biodegradation and adsorption parameters for EOCs.

In this German study, the fate and behaviour of a range of organic compounds during RBF were investigated using a 2D numerical flow and transport model. The database used came from a project conducted in Berlin, called NASRI: Natural and Artificial Systems for Recharge and Infiltration.

Oxygen isotope signatures and hydraulic head data were used for model calibration. Then 12 organic micropollutants were simulated with a reactive transport model.

Three compounds (primidone, EDTA, and AMDOPH) showed conservative behaviour, i.e. no biodegradation or sorption. Degradation and/or sorption was observed for the nine remaining compounds: 1.5 NDSA, AOX, AOI, MTBE, carbamazepine, clindamycin, phenazone, diclofenac, and sulfamethoxazole.

It was found that 1.5 NDSA and AOX were not sorbed, but slightly degraded, and MTBE could be well characterised. Carbamazepine degraded with a half-life of about 66 days under certain conditions.

Breakthrough curves of clindamycin, phenazone, diclofenac, and sulfamethoxazole could be fitted less well, probably due to the dependency of degradation on temperature and redox conditions, which are highly transient at the RBF site. Conditions ranged from oxic to anoxic (up to iron-reducing), with the oxic and denitrifying zones moving spatially back and forth over time.

Journal of Contaminant Hydrology, Volume 156, January 2014, Pages 78–92.