Prediction of Iron Release during Riverbank Filtration

At many sites, anoxic conditions and dissolution of iron and manganese are already present, or are likely to develop during riverbank filtration (RBF). A prediction of iron and manganese mobilization during riverbank filtration is required to evaluate the need for further water treatment. Different methods have been tested at RBF sites in Germany: water and sediment analysis, batch and column experiments using river water, sequential extraction, and the mass balance approach. At these sites, a wash out effect was observed, resulting in a gradual decrease in iron concentrations between the riverbank and the abstraction well over two decades. Hydrogeochemical exchange processes in the aquifer can cause a long-term release of iron and manganese even if the organics concentration in the river water is low. Contrary to common expectations, high iron concentrations are often dominated by the portion of landside groundwater, whereas iron concentrations in bank filtrate often undergo a long-term decline.