Ultraviolet/Peracetic acid Advanced Oxidation for the Removal of Antidepressant Compounds and Disinfection Byproducts
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Advanced oxidation processes (AOPs) have gained attention for degrading trace organic contaminants (TrOCs) such as pharmaceuticals and disinfection byproducts for wastewater and potable water treatment. Antidepressants are of concern due to their prevalence in wastewater and receiving waters and potential adverse effects on aquatic species. Many disinfection by-products (DBPs) exhibit cyto- and genotoxicity; their occurrence in advanced treatment systems for potable water reuse has raised concern. Peracetic acid (PAA) is an organic peroxy acid that can be degraded by UV light to generate hydroxyl radical. This thesis project investigated UV/PAA, an emerging AOP, for the removal of three antidepressants (fluoxetine (FLX), sertraline (SER), and norsertraline (NSER)) and seven halogenated DBPs. The performance of UV/PAA was compared to UV/H2O2, the most established AOP. First, the three antidepressants (FLX, SER, and NSER) were subjected to 5 treatments: UV alone (254 nm), UV/PAA and its dark control (i.e., PAA alone), and UV/H2O2 and its dark control. The results showed that neither PAA nor H2O2 alone was effective in degrading FLX, SER, or NSER. For FLX, UV/PAA and UV/H2O2 exhibited similar performance. After 2 h, 88% and 93% of FLX was degraded under UV/PAA and UV/H2O2, respectively. However, much of the FLX removal was attributed to direct photolysis by UV, which alone achieved 87% degradation after 2 h. The pseudo-first-order rate constants for FLX degradation by UV/H2O2, UV/PAA, and UV were 0.023, 0.019, and 0.018 min-1 (6 mg/L oxidant if present, 0.48 W/cm2 fluence rate). For SER, UV/PAA treatment achieved 57% SER removal, while UV/H2O2 achieved 90% removal after 2 h. UV treatment alone did not lead to significant SER degradation, suggesting that radicals were the main contributor to SER degradation. For NSER, none of the treatment achieved significant removal after 2 h. Second, the removal of seven halogenated DBPs were evaluated in UV/PAA and UV/H2O2 processes. The two haloketones 1,1,1-trichloropropanone and 1,1-dichloropropanone were removed by less than 35% by UV/H2O2, while UV/PAA achieved 66% and 87% removal, respectively. One hundred percent removal was achieved for chloropicrin and four haloacetonitriles (bromochloroacetonitrile, dibromoacetonitrile, trichloroacetonitrile, and dichloroacetonitrile) after 3 h with 2 mg/L PAA dose and 0.31 mW/cm2 UV fluence rate. For these five DBPs, the pseudo-first-order decay rate constants from UV/PAA treatment was 1.3-3 times higher than those from UV/H2O2.