Micropollutants present in the aquatic environment may affect human health via exposure to and consumption of potable water. Advanced oxidation processes (AOPs) are promising technologies for micropollutant abatement in drinking water treatment and potable water reuse. Chlorine dioxide (C1O
2) has a great potential to be used to formulate a new AOP under UV irradiation or work collectively with other AOPs, for micropollutant abatement. This thesis work demonstrates the pros and cons of using C1O
2 in the UV-based AOPs in two cases: 1) when C1O
2 is used as an oxidant precursor in a UV/C1O
2 AOP, the reactive species generation and byproduct formation from UV photolysis of C1O
2 are investigated. This novel UV/C1O
2 process is compared with the UV/chlorine and UV/NH
2C1 processes; and 2) when C...[
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Micropollutants present in the aquatic environment may affect human health via exposure to and consumption of potable water. Advanced oxidation processes (AOPs) are promising technologies for micropollutant abatement in drinking water treatment and potable water reuse. Chlorine dioxide (C1O
2) has a great potential to be used to formulate a new AOP under UV irradiation or work collectively with other AOPs, for micropollutant abatement. This thesis work demonstrates the pros and cons of using C1O
2 in the UV-based AOPs in two cases: 1) when C1O
2 is used as an oxidant precursor in a UV/C1O
2 AOP, the reactive species generation and byproduct formation from UV photolysis of C1O
2 are investigated. This novel UV/C1O
2 process is compared with the UV/chlorine and UV/NH
2C1 processes; and 2) when C1O
2 is used for pre-oxidation, the multiple effects of chlorite (C1O
2-), the major byproduct of C1O
2 oxidation, on the reactive species generation and byproduct formation in the post-UV-AOP (e.g., UV/chlorine process) are evaluated.
In the first case where C1O
2 was used as an oxidant precursor, reactive species, including ozone, C1O
•, HO
•, and C1
• were generated in the UV/C1O
2 process under the drinking water treatment conditions, and their concentrations followed the order of ozone > C1O
• > HO
• > C1
•. The concentrations of organic byproducts formed in the UV/C1O2 process were low, while a significant amount of chlorate (C1O
3-) was formed. The concentrations of radicals (HO
•, C1
•, and C1O
•) in the UV/chlorine, UV/NH
2C1 and UV/C1O
2 AOPs followed the order of UV/chlorine > UV/NH
2C1 > UV/CIO
2 at the same initial chemical dose of 70 μM, the same irradiation wavelength of 254 nm, and in the deionized water buffered at pH 7.5. The concentration of ozone generated in the UV/C1O
2 process was higher than that in the UV/chlorine process, while a negligible amount of ozone was generated in the UV/NH
2C1 process. Radical and ozone concentrations in the UV/chlorine process were strongly pH dependent, while those in the UV/C1O
2 and UV/NH
2C1 processes were less. Radical and ozone concentrations in the UV/C1O
2 and UV/chlorine processes increased with increasing radiation UV wavelength from 254 to 285 and 300 nm, while those in the UV/NH
2C1 process showed an opposite wavelength dependency. When the three UV-AOPs were used individually to treat the same NOM-containing water, the formation of total organic chlorine (TOC1) followed the order of UV/chlorine > UV/NH
2C1 > UV/C1O
2.
Where C1O
2 was used for pre-oxidation, the effects of chlorite (C1O
2- ), the degradation product of C1O
2, on the concentrations of reactive species and the formation of byproducts in the subsequent UV/chlorine process were investigated. The results showed that the concentration of C1O
• in the UV/chlorine process remarkably decreased by 98.20-100.00% in the presence of C1O
2- at concentrations of 0.1-1.0 mg L
-1 as NaC1O
2. The concentrations of HO
• and ozone decreased by 42.71-65.42% and by 22.02-64.31%, respectively, while the concentration of C1
• was less affected (i.e., 31.00-36.21% reduction). The overall concentrations of the reactive species were differentially impacted by C1O
2- multiple roles in the process. UV photolysis of C1O
2- generated HO
• but not C1
•, C1O
• or ozone under the drinking water relevant conditions. C1O
2- also competed with chlorine for UV photons but this effect was minor (< 1.0%). The radicals/ozone scavenging by C1O
2- outcompeted the above two to lead to the overall decreasing concentrations of the reactive species, in consistency with the trends predicted by a kinetic model. C1O
2- reacted with radicals and ozone to form chlorate (C1O
3- ) but not perchlorate (C1O
4- ). HO
• played a dominant role in the C1O
3- formation. This thesis work improves the fundamental understanding on micropollutant abatement and byproduct formation during the use of C1O
2 in UV-AOPs. It also offers information useful for selection and operation of UV-AOPs for micropollutant abatement in water treatment.
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