Fate of persistent and mobile substances in drinking water treatment: A systematic comparison of treatment options

Persistent and mobile (PM) substances are suspected to pass drinking water treatment; however, the extent of the treatment gap remains uncertain. This study aimed to determine the elimination of 115 potentially persistent and mobile substances (PM candidates) for four established (biological filtration, adsorption onto activated carbon, ozonation, reverse osmosis (RO)) and one developing treatment method (reductive treatment represented by catalytic hydrogenation) for drinking water supply individually and in combinations. In systematic lab-scale experiments, less than half of all PM candidates were eliminated above 80% by adsorption or ozonation at typical doses (10 mg/L with 48 h contact time, 0.67 mg O₃/mg DOC), whereby adsorption indicated slightly higher elimination. Overall, RO achieved the highest elimination, exceeding 80% removal for 96% of all PM candidates. In three common combined treatment sequences, 16 PM candidates remained below 50% elimination and were therefore identified as critical for drinking water treatment, among them six halomethanesulfonates and seven components of ionic liquids. For adsorption onto activated carbon, polarizability, logD and solubility showed strong correlations with PM candidate eliminations, whereas for RO, strong correlations were observed between PM candidate eliminations, and molar mass and polarizability. These correlations provide suitable and readily accessible molecular properties to feed predictive models for the assessment of PM candidate elimination.