Removal of Organic Micro Pollutants in Batch Experiments Mimicking Riverbank Filtration

The increasing occurrence of organic micro pollutants (OMPs) detected in river- and surface waters raises concerns for safe drinking water supply. Riverbank filtration (RBF) might be able to provide an effective barrier against most OMPs; however the removal mechanisms in the riverbank are not yet fully understood. The purpose of this study was to understand the main mechanism (biodegradation and/or sorption) for removal of OMPs during RBF. RBF was simulated by performing batch experiments using river water and riverbank sand from the river Lek near drinking water company Oasen in Bergambacht, the Netherlands. A distinction was made between biodegradation and sorption by comparing bottles treated with and without sodium azide, a biocide which inactivates the bioactivity. Furthermore different experimental conditions were studied; the effect of the river water matrix and the effect of dosing an additional C source (acetate) at regular intervals. The experiments were performed under oxic and anoxic conditions to mimic different redox zones in RBF. Anoxic conditions were present, established by the reduction of nitrate. No nutrient limitation was observed under oxic and anoxic conditions. Furthermore, results showed that the dose of 0.4 g/L sodium azide was too low to completely suppress the bioactivity. This led to an underestimation of the biodegradation of OMPs in this study. Therefore the determined biodegradation only gave an indication but did not represent reality; gemfibrozil, 2,4-D, diclofenac, and diuron showed the highest biodegradation. OMP removal did not vary significantly between different experimental conditions. This may indicate that the OMP dose per mass of sand was too low in the batch bottles; meaning that not enough OMPs were available for microorganisms to be able to determine differences in removal. Furthermore, this report showed that measuring parameters such as dissolved organic carbon (DOC), bioactivity (ATP) and extracellular polymeric substances (EPS) gave a better representation of the occurring processes in the batch bottles when measured in the sand phase than in the aqueous phase. Finally, it was concluded that the amount of proteins and carbohydrates present in the biofilm in riverbank sand was directly related to the bioactivity.Sanitary EngineeringWater ManagementCivil Engineering and Geoscience