During the infiltration of surface water in the dunes and along river banks, natural processes in the soil can effectively remove micropollutants. In surface water infiltration systems, the bottom sludge layer is however regularly cleaned by drinking water utilities to prevent clogging of the bank. The question concerns the degree to which this measure has positive or negative effects on attenuation of pollutants.
Additional benefit of soil passage systems
Although bank filtration systems, such as dune infiltration and river-bank filtration, are not designed to remove various organic micropollutants (OMPs), they are very effective in doing so. Drinking water utilities are increasingly turning their attention to this additional benefit. By optimising the bank filtration systems, one can try to reduce the load of OMPs on the above-ground treatment plants. This raises the question of which OMPs are removed in the bottom sludge layer and river bank, and what role the sludge plays in this, including the interaction with microorganisms and the hydro-geochemical conditions. The sludge generally contains high contents of organic matter which results in more reduced redox conditions, but also in an increase in the sorption capacity for certain OMPs. For this reason, the removal of the sludge layer can lead to a better removal of OMPs that are degraded under oxygen-rich conditions, but also to a possible reduced sorption of certain OMPs.
Insight into underlying removal mechanisms
The primary objective of this project in the Joint Research Programme of KWR and the water utilities is a better understanding of the mechanisms underlying the removal of OMPs through sorption and/or biodegradation during soil passage in dune infiltration and river-bank filtration. The research will also offer an understanding of the microbial population in both systems. This involves examining the differences and/or similarities in the microbial population, and the development of the microbial population during soil passage. Lastly, an assessment will be made about whether the identified bacteria can be connected to the biotransformation of OMPs. This might clarify why certain compounds (pyrazole, metformin/guanylurea) are degraded or not in these systems.
Measures to follow clarification
Once the OMP removal mechanism is clarified, the possibility will exist to develop measures to stimulate these processes. If the research succeeds in identifying the bacteria that play a role here, these bacteria may be used specifically to attenuate OMPs