Micropollutants as internal probe compounds to assess UV fluence and hydroxyl radical exposure in UV/H2O2 treatment. (1st May 2021)

• Record Type: Journal Article
• Authors: Wünsch, Robin; Mayer, Carina; Plattner, Julia; Eugster, Fabienne; Wülser, Richard; Gebhardt, Jens; Hübner, Uwe; Canonica, Silvio; Wintgens, Thomas; von Gunten, Urs
• Is Part Of: Water research. Volume 195(2021)
• Publication Date: 2021-05-01
• Subjects: OH-radical exposure -- UV/H2O2 AOP -- in-situ probe compounds -- kinetic modeling -- sensitivity analysis -- water treatment; Abbreviations: A Pre-exponential factor [L mol−1 s−1] -- α2 Fraction of the deprotonated form of a micropollutant at a given pH [-] -- AOP Advanced oxidation process -- c Speed of light [m s−1] -- c0, MP Concentration of a micropollutant before UV/H2O2 treatment [mol L−1] -- cMP Concentration of a micropollutant after UV/H2O2 treatment [mol L−1] -- CBD Collimated beam device -- CTOH Hydroxyl radical exposure [mol L−1 s] -- DOC Dissolved organic carbon -- ε Decadic molar absorption coefficient at 254 nm [cm−1] -- ε1 Decadic molar absorption coefficient at 254 nm of the deprotonated form of a micropollutant [cm−1] -- ε2 Decadic molar absorption coefficient at 254 nm of the protonated form of a micropollutant [cm−1] -- E Ultraviolet fluence rate [W m−2] -- Ea Activation energy [J mol−1] -- h Planck's constant [J s] -- H Ultraviolet fluence [J m−2] -- kOH Second-order rate constant for the reaction with hydroxyl radicals [L mol−1 s−1] -- kUV Fluence-based rate constant for direct photolysis [m2 J−1] -- λ Wavelength [m] -- NA Avogadro number [einstein−1] -- MP Micropollutant -- OH Hydroxyl radical -- Φ Quantum yield at 254 nm [mol einstein−1] -- R Ideal gas constant [J K−1 mol−1] -- S Pseudo-first-order hydroxyl radical scavenging rate constant of matrix [s−1] -- T Absolute temperature [K] -- TIC Total inorganic carbon -- u2 Combined standard uncertainty [-] -- uc2 Combined standard variance [-] -- UV Ultraviolet -- UVA Ultraviolet absorbance at 254 nm normalized to the path length [m−1] -- Δ% Difference between % predicted abatement and % measured abatement [-]; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2021.116940
• Languages: English
• ISSNs: 0043-1354

Abstract

Highlights: UV fluence and OH exposure were calculated from abatements of two micropollutants The abatement of other micropollutants was predicted within ±20 % The model allowed estimations of k OH and k UV of co-existing micropollutants A sensitivity analysis showed limited effect of analytical errors if probe compounds were abated > 50% Abstract: 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/H2 O2 can be applied to abate these MPs. During UV/H2 O2 treatment, MPs are abated primarily by photolysis and reactions with hydroxyl radicals ( OH), which are produced in situ from H2 O2 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. Graphical abstract: Image, graphical abstract