Studies on the degradation of trace phenol and indole odorants by chlorine and permanganate in drinking water treatment

Abstract

The frequent detection of phenols and indoles in source water gives rise to concern about the taste and odor problems mainly caused by some chemicals. Exploration for the efficient removal of trace amounts of phenols and indoles in source water is imperative. This study investigated the removals and oxidation kinetics of 3-methylphenol (3-MP), 2,6-dichlorophenol (2,6-DCP), indole and 3-methylindole (3-MI) by NaClO and KMnO4. The results showed that the selected chemical odorants could be removed by NaClO and KMnO4. Meanwhile, the oxidation processes could be well described by the second-order kinetics model, in which kinetics constants of chemical odorants were from 1.44 × 104 to 1.45 × 106 L·mol−1·min−1 and followed the order 3-MI > indole> 3-MP> 2,6-DCP by NaClO. However, the kinetics constants for the selected chemical odorants were also determined from 1.10 × 103 to 2.25 × 104 L·mol−1·min−1 and in the order 2,6-DCP> 3-MI> 3-MP > indole by KMnO4. The phenols degradation mechanisms by NaClO are chlorine substitution, and the products generated are 3,4,6-trichloro-2-methylphenol, 2,4,6-trichlorophenol, etc. And that of indoles are chlorine substitution and hydroxylation by NaClO, which generated 6-chloroindole, 2,6-dichloroaniline, etc. The phenols degradation pathways are oxidative coupling reactions by KMnO4, and that of indoles are hydroxylation reactions by KMnO4. This study provides a further basis for NaClO and KMnO4 oxidation to remove trace phenols and indoles in drinking water pre-treatments.