Micropollutants as internal probe compounds to assess UV fluence and hydroxyl radical exposure in UV/H 2 O 2 treatment

Organic micropollutants (MPs) are increasingly detected in water resources, which can be a concern for human health and the aquatic environment. Ultraviolet (UV) radiation based advanced oxidation processes (AOP) such as low-pressure mercury vapor arc lamp UV/H 2 O 2 can be applied to abate these MPs. During UV/H 2 O 2 treatment, MPs are abated primarily by photolysis and reactions with hydroxyl radicals ( 'OH), which are produced in situ from H 2 O 2 photolysis. Here, a model is presented that calculates the applied UV fluence ( H calc ) and the 'OH exposure ( C T ?OH , calc ) from the abatement of two selected MPs, which act as internal probe compounds. Quantification of the UV fluence and hydroxyl radical exposure was generally accurate when a UV susceptible and a UV resistant probe compound were selected, and both were abated at least by 50 %, e.g., iopamidol and 5-methyl-1H-benzotriazole. Based on these key parameters a model was developed to predict the abatement of other MPs. The prediction of abatement was verified in various waters (sand filtrates of rivers Rhine and Wiese, and a tertiary wastewater effluent) and at different scales (laboratory experiments, pilot plant). The accuracy to predict the abatement of other MPs was typically within ?20 % of the respective measured abatement. The model was further assessed for its ability to estimate unknown rate constants for direct photolysis ( k UV , MP ) and reactions with 'OH ( k ?OH , MP ). In most cases, the estimated rate constants agreed well with published values, considering the uncertainty of kinetic data determined in laboratory experiments. A sensitivity analysis revealed that in typical water treatment applications, the precision of kinetic parameters ( k UV , MP for UV susceptible and k ?OH , MP for UV resistant probe compounds) have the strongest impact on the model?s accuracy. ? 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )