Role of Reactive Halogen Species in Disinfection Byproduct Formation during Chlorine Photolysis

Abstract

The multiple reactive oxidants produced during chlorine photolysis effectively degrade organic contaminants during water treatment, but their role in disinfection byproduct (DBP) formation is unclear. The impact of chlorine photolysis on dissolved organic matter (DOM) composition and DBP formation is investigated using lake water collected after coagulation, flocculation, and filtration at pH 6.5 and pH 8.5 with irradiation at three wavelengths (254, 311, and 365 nm). The steady-state concentrations of hydroxyl radical and chlorine radical decrease by 38–100% in drinking water compared to ultrapure water, which is primarily attributed to radical scavenging by natural water constituents. Chlorine photolysis transforms DOM through multiple mechanisms to produce DOM that is more aliphatic in nature and contains novel high molecular weight chlorinated DBPs that are detected via high-resolution mass spectrometry. Quenching experiments demonstrate that reactive chlorine species are partially responsible for the formation of halogenated DOM, haloacetic acids, and haloacetonitriles, whereas trihalomethane formation decreases during chlorine photolysis. Furthermore, DOM transformation primarily due to direct photolysis alters DOM such that it is more reactive with chlorine, which also contributes to enhanced formation of novel DBPs during chlorine photolysis.

Molecular-Level Insights into the Formation of Traditional and Novel Halogenated Disinfection Byproducts

“…Chlorine concentrations were determined using 1,3,5-trimethoxybenzene (Section S1). , After 24 h, remaining chlorine was quenched with sodium thiosulfate (final concentration = 1 mM) and samples were extracted for FT-ICR MS analysis. Sodium thiosulfate was used over an organic quencher due to the potential for interference with FT-ICR MS analysis.…”

New 19F NMR methodology reveals structures of molecules in complex mixtures of fluorinated compounds

“…Ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) is making contributions to the characterisation of DBPs at the level of molecular formulae, compound class and functional group classification, including identification of compound classes with the highest DBP formation potential. [52][53][54][55][56][57][58] When ion fragmentation is used a more definite structural information can be obtained by MS. 49,51,59 On the other hand, the use of NMR spectroscopy in the structure determination of DBPs is rare and usually requires some form of compound separation. [60][61][62][63] Here we illustrate the power of 19 F-centred NMR structure elucidation of fluorinated molecules using a complex mixture of DBPs produced by chloramination of a single fluorine-containing molecule.…”

“…Ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) is making contributions to the characterisation of DBPs at the level of molecular formulae, compound class and functional group classification, including identification of compound classes with the highest DBP formation potential. 52–58 When ion fragmentation is used more definite structural information can be obtained by MS. 49,51,59…”

High-Efficiency and Ground-State Atomic Oxygen-Dominant Photodegradation of Carbamazepine by Coupling Chlorine and g-C3N4

“…Pharmaceuticals and personal care products (PPCPs) and their daughter products have been continually detected in the aquatic environment with the increase in the consumption of pharmaceuticals and PPCPs. , Carbamazepine (CBZ), a representative antiepileptic drug that is extensively used to treat neuropathic pain and trigeminal neuralgia, is one of the most durable drug contaminants due to its resistance to photodegradation and biodegradation. , Substantial amounts of CBZ and its metabolites are discharged into the environment given the wide application and mass production of CBZ; these compounds are difficult to remove via conventional adsorption, coagulation, sedimentation, and filtration methods . A large number of investigations have concentrated on the application of advanced oxidation processes (AOPs), such as Fenton oxidation, , wet air oxidation, ozonation, electrochemical oxidation, UV/H 2 O 2 , and photocatalytic degradation to eliminate CBZ from water bodies, , including surface water, rivers, lakes, sewage, and marine ecosystems, and even drinking water.…”

“…3,4 Substantial amounts of CBZ and its metabolites are discharged into the environment given the wide application and mass production of CBZ; these compounds are difficult to remove via conventional adsorption, coagulation, sedimentation, and filtration methods. 5 A large number of investigations have concentrated on the application of advanced oxidation processes (AOPs), such as Fenton oxidation, 6,7 wet air oxidation, 8 ozonation, 9 electrochemical oxidation, 10 UV/H 2 O 2 , 11 and photocatalytic degradation to eliminate CBZ from water bodies, 12,13 including surface water, rivers, lakes, sewage, and marine ecosystems, and even drinking water.…”