RESUMEN
Radical-induced disinfection byproduct (DBP) formation is drawing attention with increasing applications of advanced oxidation processes (AOPs). Cl2â¢- represents one of the extensively generated radicals in AOPs, whose behavior in DBP formation remains unknown. In this study, we found that aromatic structures serve as the main DBP precursors in Cl2â¢- reactions by employing diverse groups of model compounds. At a typical Cl2â¢- exposure of 1.2 × 10-9 M·s, the sum concentrations of 7 regulated aliphatic DBPs (e.g., trichloromethane, chloroacetic acids) are â¼0.10 to 0.48 µM for aromatic precursors and <0.05 µM for aliphatic ones. The DBP formation mechanisms from Cl2â¢- reactions involved the formation of chlorinated aromatics, radical-induced oxygen incorporation followed by ring cleavage, and the interactions of Cl2â¢- with ring-cleavage intermediates. In reacting with DOM, Cl2â¢- reactions produced much fewer aliphatic DBPs (5% of the total organochlorine vs 40% for chlorination) and chloroacetic acids dominated the aliphatic DBPs (usually trihalomethane for chlorination), which can be well interpreted by the precursors and mechanisms proposed. This work comprehensively reveals the precursors, formation patterns, and mechanisms of DBPs during the less-studied Cl2â¢- reactions, highlighting the importance of eliminating the aromatic structures of DOM before the AOPs.
RESUMEN
Transforming dissolved organic matter (DOM) is a crucial approach to alleviating the formation of disinfection byproducts (DBPs) in water treatment. Although catalytic ozonation effectively transforms DOM, increases in DBP formation potential are often observed due to the accumulation of aldehydes, ketones, and nitro compound intermediates during DOM transformation. In this study, we propose a novel strategy for the sequential oxidation of DOM, effectively reducing the levels of accumulation of these intermediates. This is achieved through the development of a catalyst with a tailored surface and nanoconfined active sites for catalytic ozonation. The catalyst features a unique confinement structure, wherein Mn-N4 moieties are uniformly anchored on the catalyst surface and within nanopores (5-20 Å). This design enables the degradation of the large molecular weight fraction of DOM on the catalyst surface, while the transformed smaller molecular weight fraction enters the nanopores and undergoes rapid degradation due to the confinement effect. The generation of *Oad as the dominant reactive species is essential for effectively reducing these ozone refractory intermediates. This resulted in over 70% removal of carbonaceous and nitrogenous DBP precursors as well as brominated DBP precursors. This study highlights the importance of the nanoscale sequential reactor design and provides new insights into eliminating DBP precursors by the catalytic ozonation process.
Asunto(s)
Desinfección , Ozono , Purificación del Agua , Ozono/química , Catálisis , Purificación del Agua/métodos , Contaminantes Químicos del Agua/químicaRESUMEN
Dissolved organic matter (DOM) is a major sink of radicals in advanced oxidation processes (AOPs) and the radical-induced DOM transformation influences the subsequent water treatment processes or receiving waters. In this study, we quantified and compared DOM transformation by tracking the changes of dissolved organic carbon (DOC), UVA254, and electron donating capacity (EDC) as functions of four one-electron oxidants (SO4â¢-, Cl2â¢-, Br2â¢-, and CO3â¢-) exposures as well as the changes of functional groups and molecule distribution. SO4â¢- had the highest DOC reduction while Cl2â¢- had the highest EDC reduction, which could be due to their preferential reaction pathways of decarboxylation and converting phenols to quinones, respectively. Br2â¢- and CO3â¢- induced less changes in DOC, UVA254, and EDC than SO4â¢- and Cl2â¢-. Additionally, DOM enriched with high aromatic contents tended to have higher DOC, UVA254, and EDC reductions. Decreases in hydroxyl and carboxyl groups and increases in carbonyl groups were observed in these four types of radicals treated DOM using Fourier transform infrared spectroscopy. High resolution mass spectrometry using FTICR-MS showed that one-electron oxidants preferred to attack unsaturated carbon skeletons and transformed into molecules featuring high saturation and low aromaticity. Moreover, SO4â¢- was inclined to decrease oxidation state of carbon and O/C of DOM due to its strong decarboxylation capacity. This study highlights the distinct DOM transformation by four one-electron oxidants and provides comprehensive insights into the reactions of one-electron oxidants with DOM.
Asunto(s)
Materia Orgánica Disuelta , Oxidantes , Antioxidantes , Electrones , Carbono/análisisRESUMEN
Radicals in advanced oxidation processes (AOPs) degrade micropollutants during water and wastewater treatment, but the transformation of dissolved organic matter (DOM) may be equally important. Ketone moieties in DOM are known disinfection byproduct precursors, but ketones themselves are intermediates produced during AOPs. We found that aromatic alcohols in DOM underwent transformation to ketones by one-electron oxidants (using SO4â¢- as a representative), and the formed ketones significantly increased trichloromethane (CHCl3) formation potential (FP) upon subsequent chlorination. CHCl3-FPs from aromatic ketones (Ar-CO-CH3, average of 22 mol/mol) were 6-24 times of CHCl3-FPs from aromatic alcohols (Ar-CH(OH)-CH3, average of 0.85 mol/mol). At a typical SO4â¢- exposure of 7.0 × 10-12 M·s, CHCl3-FPs from aromatic alcohol transformation increased by 24.8%-112% with an average increase of 53.4%. Notably, SO4â¢- oxidation of aliphatic alcohols resulted in minute changes in CHCl3-FPs due to their low reactivities with SO4â¢- (â¼107 M-1 s-1). Other one-electron oxidants (Cl2â¢-, Br2â¢-,and CO3â¢-) are present in AOPs and also lead to aromatic alcohol-ketone transformations similar to SO4â¢-. This study highlights that subtle changes in DOM physicochemical properties due to one-electron oxidants can greatly affect the reactivity with free chlorine and the formation of chlorinated byproducts.
Asunto(s)
Contaminantes Químicos del Agua , Purificación del Agua , Oxidantes , Materia Orgánica Disuelta , Cloroformo , Cetonas , Electrones , Contaminantes Químicos del Agua/análisis , Cloro/química , Purificación del Agua/métodos , Halogenación , Desinfección , Alcohol BenciloRESUMEN
Dissolved organic matter (DOM) scavenges sulfate radicals (SO4â¢-), and SO4â¢--induced DOM transformations influence disinfection byproduct (DBP) formation when chlorination follows advanced oxidation processes (AOPs) used for pollutant destruction during water and wastewater treatment. Competition kinetics experiments and transient kinetics experiments were conducted in the presence of 19 DOM fractions. Second-order reaction rate constants for DOM reactions with SO4â¢- (kDOM,SO4â¢-) ranged from (6.38 ± 0.53) × 106 M-1 s-1 to (3.68 ± 0.34) × 107 MC-1 s-1. kDOM,SO4â¢- correlated with specific absorbance at 254 nm (SUVA254) (R2 = 0.78) or total antioxidant capacity (R2 = 0.78), suggesting that DOM with more aromatics and antioxidative moieties reacted faster with SO4â¢-. SO4â¢- exposure activated DBP precursors and increased carbonaceous DBP (C-DBP) yields (e.g., trichloromethane, chloral hydrate, and 1,1,1-trichloropropanone) in humic acid and fulvic acid DOM fractions despite the great reduction in their organic carbon, chromophores, and fluorophores. Conversely, SO4â¢--induced reactions reduced nitrogenous DBP yields (e.g., dichloroacetonitrile and trichloronitromethane) in wastewater effluent organic matter and algal organic matter without forming more C-DBP precursors. DBP formation as a function of SO4â¢- exposure (concentration × time) provides guidance on optimization strategies for SO4â¢--based AOPs in realistic water matrices.