Behavior of bulk organics and trace pollutants during bank filtration and groundwater recharge of wastewater-impacted surface waters

Behavior of bulk organics and trace pollutants during bank filtration and groundwater recharge of wastewater-impacted surface waters

Bank fillration provides an important drinking water source to the city of Berlin. 56% of the drinking water is derived from bank filtration (the remainder is 14% replenished groundwater and 30% natural groundwater) [1]. At most bank filtration sites, the surface water contains portions of sewage treatment plant effluent (Lake Tegel 10-30%, [2]). Due to water recycling, the introduction of effluent organic matter (EfON) and persistent trace pollutants in the drinking water may be a concern. The project “Organic Substances in Bank filtration and Groundwater Recharge Process Studies” at the Department for Water Quality Control (DWQC) at the Technical University of Berlin is part of the “Natural and Artificial Systems for Recharge and lnfiltration (NASRI)’ - project of the Berlin Centre of Competence for Water [3]. The research objectives of this part of the project are to study the removal of bulk organics (dissolved organic carbon (DOC) and EfOM) and trace organics at three field sites with different characteristics. Since the processes during bank filtration are very complex, it is difficult to predict bulk organic composition in the bank filtrale or to estimate important factors of influence for the degradation of trace compounds. For instance, it was shown in previous studies, that iodinated x-ray contrast medias are deiodinated under teductive conditions. Therefore, a bank filtration under anoxic or even anaerobic conditions would provide the removal of these trace pollutants. In addition to lhe redox state, factors such as retention time, initial degradable carbon . concentration, soil properties and hydrogeologlcal conditions may affect the final concentration. In order to be able to prevent the intrusion of persistent pollutants into the drinking water, lhe factors of influence are studied for a few model compounds that represent groups of trace pollutants. This will provide a tool that can be merged with hydrogeological models and soil properties to predict the removal efficiency of a given field site. To fulfill these objectives this research is presently investating: (i) the differences in bulk organic composition and trace organic concentration related to bank filtration conditions at three different field sites in Berlin, (ii) the simulation of a bank filtration site with a 30m soil column (elimination of hydrogeological variables).