Oxidation of 4-tert-butylphenol by potassium permanganate and reduced formation of disinfection byproducts from chlorination

Abstract

4-tert-butylphenol (4-tBP), a typical endocrine disruptor, is widely used as pharmaceutical and agricultural additive and has been detected in the aqueous environment. In this work, we systematically investigated the oxidation process of 4-tBP by potassium permanganate (KMnO4). The degradation condition was optimized by adjusting pH and oxidant dose. The removal efficiency could reach > 93% in 45 min under pH = 6.0–9.0 and [4-tBP]0:[KMnO4]0 = 1:2, where the maximum second-order reaction rate constant (kapp) was (2.48 ± 0.23) × 10−2 M−1 min−1. Common anions (Cl-, SO42-, NO3- and HCO3-) and cations (K+, Ca2+, Mg2+, Fe3+ and Cu2+) did not show apparent influence, while humic acid played a positive role in the degradation. A total of 20 products were identified and two main pathways of the oxidation process were proposed, which included hydroxylation and coupling. Through the theoretical calculations, the mechanism of the 4-tBP hydroxylation was explained as mono-oxygen transfer at the ortho site of the hydroxyl group and coupling was from the extraction of hydrogen at the hydroxyl group. Meanwhile, the toxicity assessment showed lowered biotoxicity of products as compared to the substrate. In addition, chlorination of degradation products would yield lower concentrations of disinfection byproducts (dichloroacetic acid, 4.5 μg/L; trichloroacetic acid, 4.7 μg/L, in ultrapure water) than the initial 4-tBP solution. These findings confirmed that KMnO4 could be used as a safe and promising technology for 4-tBP degradation.