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Significant role of UV and carbonate radical on the degradation of oxytetracycline in UV-AOPs: Kinetics and mechanism
- Source :
- Water research
- Publication Year :
- 2016
- Publisher :
- Elsevier BV, 2016.
-
Abstract
- Carbonate radical (CO3•-), a selective oxidant, reacts readily with electron-rich compounds through electron transfer and/or hydrogen abstraction. In this study, the role of CO3•- in degrading oxytetracycline (OTC) by UV only, UV/H2O2 and UV/persulfate (UV/PS) advanced oxidation processes (AOPs) in the presence of HCO3- or CO32- was investigated. For UV only process, the presence of photosensitizers, i.e., nitrate (NO3-) and natural organic matter (NOM), had different impacts on OTC degradation, i.e., an enhancing effect by NO3- due to the generation of HO• and a slight inhibiting effect by NOM possibly due to a light scattering effect. Differently for UV/H2O2 and UV/PS processes, the presence of NO3- hardly influenced the destruction of OTC. Generation of CO3•- presented a positive role on OTC degradation by UV/NO3-/HCO3-. Such influence was also observed in the two studied AOPs in the presence of both bicarbonate and other natural water constituents. When various natural water samples from different sources were used as reaction matrices, UV only and UV/H2O2 showed an inhibiting effect while UV/PS demonstrated a comparable or even promoting effect in OTC decomposition. After elucidating the potential contribution of UV direct photolysis via excited state OTC* at an elevated reaction pH condition, putative OTC transformation byproducts via CO3•- reaction were identified by ultra-high definition accurate-mass quadrupole time-of-flight tandem mass spectrometry (QTOF/MS). Five different reaction pathways were subsequently proposed, including hydroxylation (+16 Da), quinonization (+14 Da), demethylation (-14 Da), decarbonylation (-28 Da) and dehydration (-18 Da). The significant role of UV at high pH and CO3•- on OTC removal from contaminated water was therefore demonstrated both kinetically and mechanistically. •Generation of CO3•- enhanced the kinetics of OTC degradation in UV/NO3-/HCO3-.•CO3•- had a positive role in AOPs even in the presence of other water constituents.•Comparable or enhanced OTC removal was observed in natural waters using UV/S2O82-.•CO3•- and UV photolysis showed a different preferable mechanism than HO.• or SO4•-.•Paths, e.g., quinonization, demethylation and decarbonylation, etc., were proposed. 95 195 204
- Subjects :
- Environmental Engineering
Ultraviolet Rays
Bicarbonate
Kinetics
Inorganic chemistry
Carbonates
Oxytetracycline
02 engineering and technology
010501 environmental sciences
Hydrogen atom abstraction
Photochemistry
01 natural sciences
Hydroxylation
chemistry.chemical_compound
Oxytetracycline UV-254 nm
Carbonate radical
Advanced oxidation processes (AOPs)
Transformation products
Waste Management and Disposal
0105 earth and related environmental sciences
Water Science and Technology
Civil and Structural Engineering
Demethylation
Ecological Modeling
Decarbonylation
Photodissociation
Hydrogen Peroxide
021001 nanoscience & nanotechnology
Persulfate
Pollution
chemistry
0210 nano-technology
Water Pollutants, Chemical
Subjects
Details
- ISSN :
- 00431354
- Volume :
- 95
- Database :
- OpenAIRE
- Journal :
- Water Research
- Accession number :
- edsair.doi.dedup.....610fc5bd3d31f027f154040f7efa9783