Food Microbiology

Biological rapid sand filters (RSF) are commonly used for drinking water production at waterworks in Denmark, Europe and worldwide. RSF is a place where natural groundwater pollutants (e.g. ammonium) are removed. The native microorganisms in RSFs have a significant role in the removal of pollutants, where a sudden change in e.g. ammonium removal suggests a misbalance in a microbial community. The aim of current work was to get a deeper insight in the physiological needs of main microbial groups at RSF to micronutrients (trace elements). Waterworks frequently receive groundwater with different chemical properties (incl. micronutrients) from distant water-wells, which allows the creation of well-defined inlet-water blend. qPCR based approach revealed that sand filters were microbial rich environments, harboring ca. 3 billion bacteria per gram sand. The ammonium oxidizing bacteria (AOB) stayed for 1-3% of the bacterial population. AOB was up to 50-times more abundant in pre-filter units than in respective after-filter units. The abundance of ammonium oxidizing archaea was trivially low, suggesting that AOB stayed for full ammonium removal in RSF. Both the laboratory column-experiments and full-scale trials at waterworks suggested that certain sand filters at a waterworks naturally possessed an extra NH4- removal capacity. A fine blending of inlet water from chosen water-wells, focusing on copper and nickel at low (0.1 – 1.0 ug/L) concentrations, shown a high (>50%) and persistent stimulating effect on NH4 removal by ammonium oxidizing bacteria. A sudden stimulating-effect of nickel and copper appeared to be the product of increased catabolic abilities of the existing AOB cells.