Oxidation of natural organic matter with processes involving O3, H2O2 and UV light: formation of oxidation and disinfection by-products

Abstract

This study investigates the effects of UV photolysis, ozonation and different advanced oxidation processes (O₃/UV, H₂O₂/UV and O₃/H₂O₂/UV) on the oxidation of groundwater natural organic matter (NOM) and by-product formation. Although the investigated treatments only slightly reduce the total organic carbon content (4–15%), the NOM character was changed significantly. The fulvic acid fraction decreased and the content of the hydrophilic acid fraction increased in ozone treated water and even more noticeably in water treated by O₃/H₂O₂/UV. All treatments led to significant increases in polar oxidation by-products such as aldehydes (up to 8 times) and carboxylic acids (up to 34 times), with no clear relationship between the changes in concentrations of these by-products and the addition of H₂O₂ and the UV dose. Statistical analysis showed a good correlation between carboxylic acids with ozone applications and carboxylic acids and UV₂₅₄. Trihalomethane and haloacetic acid formation potentials were reduced best (43% for THMFP and 68% for HAAFP) during the O₃/H₂O₂/UV process (0.5 mg O₃ per mg DOC; 10 mg H₂O₂ per L: 600 mL cm⁻²) using the lower UV dose, and were also well correlated (R = 0.847) during all water treatments. Bromate formation was observed only in the processes involving ozone.