THESIS
2022
1 online resource (xii, 88 pages) : illustrations (some color)
Abstract
Advanced oxidation processes (AOPs) combining chlorine-based oxidants (e.g., free chlorine,
monochloramine, and chlorine dioxide (ClO
2)) with UVC irradiation at 254 nm are
increasingly used for micropollutant degradation in water and wastewater. However, these
AOPs suffer from the use of energy-intensive and mercury-based UVC lamps, chloro-organic
byproduct formation, and the low yields of reactive species in the UVC/ClO
2 AOP. This thesis
work reports a novel UVA/ClO
2 AOP based on the photolysis of ClO
2 using energy-efficient
UV radiation sources in the UVA range (e.g., UVA-LEDs) by taking advantage of the high UV
absorbance of ClO
2 in the UVA range. At a ClO
2 dosage of 74 μM (5.0 mg L
–1 as ClO
2) and a
UV fluence at 47.5 mJ cm
–2, the UVA
365/ClO
2 AOP generated a spectrum of reactive spec...[
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Advanced oxidation processes (AOPs) combining chlorine-based oxidants (e.g., free chlorine,
monochloramine, and chlorine dioxide (ClO
2)) with UVC irradiation at 254 nm are
increasingly used for micropollutant degradation in water and wastewater. However, these
AOPs suffer from the use of energy-intensive and mercury-based UVC lamps, chloro-organic
byproduct formation, and the low yields of reactive species in the UVC/ClO
2 AOP. This thesis
work reports a novel UVA/ClO
2 AOP based on the photolysis of ClO
2 using energy-efficient
UV radiation sources in the UVA range (e.g., UVA-LEDs) by taking advantage of the high UV
absorbance of ClO
2 in the UVA range. At a ClO
2 dosage of 74 μM (5.0 mg L
–1 as ClO
2) and a
UV fluence at 47.5 mJ cm
–2, the UVA
365/ClO
2 AOP generated a spectrum of reactive species,
including chlorine oxide radicals (ClO
•), chlorine atoms (Cl
•), hydroxyl radicals (HO
•), and
ozone at a concentration of ~10
–13, ~10
–15, ~10
–14, and ~10
–7 M, respectively. The
concentrations of the generated reactive species were barely affected by the changes in pH,
with changes of less than 20% as pH increased from 6.0 to 8.0. A kinetic model to simulate the
reactive species generation in the UVA
365/ClO
2 AOP was established, validated against the experimental results, and used to predict the pseudo-first-order rate constants and relative
contributions of different reactive species to the degradation of 19 micropollutants in the
UVA
365/ClO
2 AOP. The presence of NOM increased chlorite but decreased chlorate formation
in the UVA
365/ClO
2 AOP. The molar yields of chlorite and chlorate, together with the second-order
rate constants of NOM towards ClO
2 and reactive species, were determined by
experiments and kinetic modelling, which enables accurate prediction of chlorite and chlorate
formation in the UVA
365/ClO
2 AOP in the presence of NOM. Compared to the well-documented
UVC
254/chlorine AOP, the UVA
365/ClO
2 AOP produced similar levels of reactive
species at similar oxidant dosages but was much less pH-dependent and required much lower
energy input, with a much lower formation of chloro-organic byproducts and marginal
formation of chlorite and chlorate.
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