Assessing the Fate of Nitrosamine Precursors in Wastewater Treatment by Physicochemical Fractionation

Source control or elimination of precursors of NDMA and other nitrosamines in wastewater requires information on their physicochemical properties, which is still limited. Thus we developed a multistep fractionation method based on a combination of consecutive filtration steps to <1 mu m, <0.2 mu m urn, and <2.5 kDa followed by solid-phase extraction on a C18 column and validated it using model NDMA precursors covering a wide polarity range. The membrane filtration to <2.5 kDa was suitable to separate a low-molecular weight precursor fraction but partially removed hydrophobic compounds by sorption. Fractionation on a C18 column allowed distinguishing highly polar precursors (such as dimethylamine) from less polar ones (such as ranitidine or other pharmaceuticals). Application of the fractionation procedure together with the formation potential test revealed that in the influent of one studied wastewater treatment plant about 50% of all precursors were associated with colloids or macromolecules, suggesting that these fractions comprise sorbed hydrophobic precursors. During activated sludge treatment small polar and charged NDMA and other nitrosamines' precursors were removed to about 80%. In contrast, less polar precursors were more recalcitrant. In advanced treatment steps, only small fractions of the precursors were removed by the prechlorination/ultrafiltration step, while reverse osmosis removed >98% of all precursors.