UV-induced degradation of contaminants of emerging concern in the presence of monobromoamine: Role of N-Br bond and degradation mechanisms

Abstract

The N-Br bond in monobromoamine (NH2Br) can be cleaved by UV irradiation to generate Br• and subsequently HO•, resulting in an advanced oxidation condition (i.e., UV/NH2Br). This study investigated the degradation of six contaminants of emerging concern (CECs) in the UV/NH2Br process, including the phenolic hydrocarbons phenol and bisphenol A (BPA), the amines aniline and sulfadiazine (SDZ), and the persistent organic pollutants ibuprofen (IBP) and carbamazepine (CBZ). The results showed that UV/NH2Br process significantly improved the degradation of CECs following pseudo-first order kinetics, and the degradation of CECs was enhanced with the increase of NH2Br dosage. UV/NH2Br was more efficient in degrading CECs containing phenolic hydroxyl groups (100 %), followed by those containing amine groups (> 95 %). The degradation efficiency was influenced by the pH value and was highest at pH 7. It was found that low concentrations of Cl− (< 0.5 mM) and HCO3− (< 0.5 mM) promoted the degradation of SDZ and IBP, but further increases in Cl− and HCO3− (0.5 ∼ 5.0 mM) resulted in inhibition. SDZ and IBP degradation was inhibited by photo absorption competition and free radical depletion in natural organic matter and actual water. Probe experiments showed that reactive bromine species (RBS), reactive nitrogen species (RNS), and hydroxyl radical (HO•) played a dominant role in CEC degradation. During the degradation of IBP by UV/NH2Br, hydroxylation, bromination, and quinylation were proposed as the primary reaction mechanisms. As compared to HOCl disinfection, NH2Cl disinfection after the UV/NH2Br process produced lower concentrations of disinfection by-products (DBPs).