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Effects of UV/H₂O₂ advanced oxidation on physical and chemical characteristics of natural organic matter in raw drinking water sources Sarathy, Siva Rajan

Abstract

This thesis focused on the physical and chemical transformations undergone by natural organic matter (NOM) in two natural waters (from British Columbia, Canada) during ultraviolet plus hydrogen peroxide (UV/H₂O₂) advanced oxidation treatment as a function of UV fluence (up to 2000 mJ cm⁻­­­­­²­) and initial H₂O₂ concentration (up to 20 mg L⁻­­­­­­¹­). Under these conditions NOM was not mineralized but the hydroxyl radical (•OH) partially oxidized NOM leading to reductions in the chromophoric natural organic matter (CNOM) (i.e., NOM absorbing at 254 nm). NOM was degraded into more readily biodegradable compounds, such as aldehydes. An appreciable reduction in the very hydrophobic acid (VHA) fraction of NOM was observed. Considerable reductions in the formation potentials of trihalomethanes (THMs) or haloacetic acids (HAAs) were not observed. An increase in alkalinity slowed down the rate of degradation of CNOM during UV/H₂O₂. A dynamic kinetic model was developed to predict the degradation of CNOM. Model parameters were developed using isolated aquatic NOM from Suwannee River. For the two natural waters, the model adequately predicted the degradation of CNOM as a function of initial H₂O₂ concentration, irradiation time (i.e., UV fluence). Including the reduction in CNOM improved the modeling of H₂O₂ degradation, but H₂O₂ degradation was still slightly under predicted. For water that had undergone ultrafiltration (UF), NOM was readily mineralized during UV/H₂O₂ treatment due to the absence of high molecular size NOM. For water from which the VHA fraction of NOM was removed, UV/H₂O₂ treatment led to mineralisation of NOM suggesting that, when coupled with a pre-treatment capable of removing a large portion of the VHA fraction, UV/H₂O₂ can achieve reductions in TOC. Combining UV/H₂O₂ with downstream biological activated carbon (BAC) filtration led to reductions in NOM and formation potentials of THMs and HAAs. Formaldehyde and H₂O₂ were effectively removed by BAC. Development of a method for the determination of assimilable organic carbon (AOC) in UV/H₂O₂ treated water concluded that manganese dioxide was a suitable agent for the removal of H₂O₂ prior to AOC analysis. The method was applied to observe an increase in AOC as fluence increased during UV/H₂O₂ treatment of raw water.

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Attribution-NonCommercial-NoDerivatives 4.0 International

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