Issue 1, 2022

Direct and nitrite-sensitized indirect photolysis of effluent-derived phenolic contaminants under UV254 irradiation

Abstract

UV254 photolysis has increasingly been utilized for disinfection of water-born pathogens in wastewater. During disinfection, wastewater-derived trace organic contaminants, such as pharmaceuticals and personal care products (PPCPs), may be subjected to direct photolysis and indirect photolysis sensitized by wastewater constituents such as nitrite (NO2). Herein, we reported the direct photolysis and NO2-sensitized indirect photolysis of four phenolic contaminants commonly observed in wastewaters (i.e., bisphenol A (BPA), acetaminophen (ATP), salbutamol (SAL), and 2,4-dihydroxybenzophenone (BP1)). Spectroscopic characterization and quantum yield measurement were carried out to evaluate the photochemical reactivity of these phenolic compounds. In NO2-sensitized photolysis, the relative contribution of direct and indirect photolysis was quantified by light screening factor calculation and radical quenching studies. The experimental results highlight the important roles of HO˙ and NO2˙ in the NO2-sensitized photolysis of phenolic compounds. A series of intermediate products, including hydroxylated, nitrated, nitrosated, dimerized, and alkyl chain cleavage products, were identified by solid phase extraction (SPE) combined with high-resolution mass spectrometry (HRMS) analyses. On the basis of identified products, the underlying mechanisms and transformation pathways for NO2-sensitized photolysis of these phenolic compounds were elucidated. The second-order rate constants of BPA, SAL, BP1 with NO2˙ were calculated to be 2.25 × 104, 1.35 × 104 and 2.44 × 104 M−1 s−1, respectively, by kinetic modeling. Suwanee River natural organic matter (SRNOM) played complex roles in the direct and NO2-sensitized photolysis of phenolic compounds by serving as a photosensitizer, light screening and radical quenching agent. Wastewater constituents, such as NO3 and EfOM, could accelerate direct and NO2-sensitized photolysis of BPA, SAL, and BP1 in the wastewater matrix. Our results suggest that NO2 at the WWTP effluent-relevant level can sensitize the photolysis of effluent-derived phenolic contaminants during the UV254 disinfection process; however, the formation of potentially carcinogenic and mutagenic nitrated/nitrosated derivatives should be scrutinized.

Graphical abstract: Direct and nitrite-sensitized indirect photolysis of effluent-derived phenolic contaminants under UV254 irradiation

Supplementary files

Article information

Article type
Paper
Submitted
09 Sep 2021
Accepted
02 Dec 2021
First published
04 Dec 2021

Environ. Sci.: Processes Impacts, 2022,24, 127-139

Direct and nitrite-sensitized indirect photolysis of effluent-derived phenolic contaminants under UV254 irradiation

Y. Li, L. Wang, H. Xu, J. Lu, J. Chovelon and Y. Ji, Environ. Sci.: Processes Impacts, 2022, 24, 127 DOI: 10.1039/D1EM00381J

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