Byproduct formation (chlorate, bromate, organic halogen,
etc.)
during sulfate radical (SO4
•–)-based
processes like ultraviolet/peroxymonosulfate (UV/PMS) has aroused
widespread concern. However, hypohalous acid (HOCl and HOBr) can form
via two-electron transfer directly from PMS, thus leading to the formation
of organic halogenated byproducts as well. This study found both PMS
alone and UV/PMS can increase the toxicity to mammalian cells of wastewater,
while the UV/H2O2 decreased the toxicity. Cytotoxicity
of two wastewater samples increased from 5.6–8.3 to 15.7–29.9
mg-phenol/L, and genotoxicity increased from 2.8–3.1 to 5.8–12.8
μg 4-NQO/L after PMS treatment because of organic halogen formation.
Organic halogen formation from bromide rather than chloride was found
to dominate the toxicity increase. The SO4
•–-based process UV/PMS led to the formation of both organic halogen
and inorganic bromate and chlorate. However, because of the very low
concentration (<20 μg/L) and relatively low toxicity of bromate
and chlorate, contributions of inorganic byproducts to toxicity increase
were negligible. PMS would not form chlorate and bromate, but it generated
a higher concentration of total organic halogen, thus leading to a
more toxic treated wastewater than UV/PMS. UV/PMS formed less organic
halogen and toxicity because of the destruction of byproducts by UV
irradiation and the removal of byproduct precursors. Currently, many
studies focused on the byproducts bromate and chlorate during SO4
•–-based oxidation processes. This
work revealed that the oxidant PMS even needs more attention because
it caused higher toxicity due to more organic halogen formation.
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