Degradation of odorous sulfide compounds by different oxidation processes in drinking water: Performance, reaction kinetics and mechanism

Abstract

Swampy/septic odor caused by various sulfides is one of the most frequently encountered odor problems in drinking water. However, even though it is much more offensive, few studies have specifically focused on swampy/septic odor compared to the extensively studied musty/earthy problems. In this work, four sulfide odorants, diamyl sulfide (DAS), dipropyl sulfide (DPS), dimethyl disulfide (DMDS) and diethyl disulfide (DEDS), were selected to evaluate the treatment performance of different oxidation processes in drinking water. The results demonstrated that DMDS, DEDS, DPS and DAS could be oxidized effectively by KMnO4, NaClO and ClO2. The oxidation processes could be well described by the second-order kinetic model, in which k values of selected sulfides followed the order DMDS≈DEDS ≪ DPS≈DAS. As for the three oxidants, the order of reactivity was KMnO4 ≪ ClO2 < NaClO, which was also verified in raw water. The results of oxidation treatability, reaction kinetics and mechanisms confirmed that the characteristics of the central sulfur atom rather than the side chain is the decisive factor in controlling the oxidation rate and transformation pathway of sulfides. The transformation products and pathways were significantly different for the three oxidants. Sulfones (DPSO, DASO) were always formed by cycloaddition reactions during KMnO4 oxidation, yet recombination reactions proceeded during ClO2 oxidation and formed more products, such as MADS, DADS and EADS. Density functional theory (DFT) calculations confirmed that the differences in transformation pathways were caused by the variations in the activity of the oxidants and sulfides. Finally, NaClO was certified as the most effective oxidant for controlling sulfide odorants in drinking water treatment.