Announced 13 days in advance due to delays in Student Services processing.
Ph.D. Thesis Defense Announcement
Evaluating Peroxyacid and UV/Peroxyacid Disinfection: Pathogen Inactivation, Byproduct Formation, and Co-Removal of Micropollutants
By
Junyue (Holden) Wang
Advisor(s):
Dr. Ching-Hua Huang (CEE)
Committee Members:
Dr. Ching-Hua Huang (CEE), Dr. Yongsheng Chen (CEE), Dr. Ameet J. Pinto (CEE),
Dr. Xing Xie (CEE), Dr. Brian Hammer (Biological Science)
Date & Time: April 17th, 12:30 pm
Location: ES&T 3243ES&T 3243
Recently, peroxyacids (POAs) are extensively investigated and applied as an alternative disinfectant to chlorine. However, a dearth of information on the chemical properties of POA hinders the comprehensive understanding of their pathogen inactivation capabilities and byproduct mitigation mechanisms.
First, this study employed multidimensional bioanalysis, to unveil the bacterial and viral disinfection kinetics and mechanisms of POAs (i.e., performic acid (PFA), peracetic acid (PAA), and perpropionic acid (PPA)). Results showed that POAs exhibited satisfactory bacterial culturability inactivation, while the removal of enveloped and non-enveloped virus surrogates was mediocre. Furthermore, the bacterial inactivation was mainly attributed to intracellular accumulation and protein damage, rather than genome or cell integrity damage, resulting in a minimal bacterial inactivation count when the analytical methods were switched from cultivation to qPCR or flow cytometry. Finally, kinetic studies using simple biomolecules (i.e., amino acids and nucleotides) showed that POAs selectively reacted with S-containing compounds through sequential O-atom transfer reactions, suggesting that POA disinfection can be highly selective and dependent on the protein compositions of the microbes.
Second, the DBP formation potential of POAs was comprehensively studied at different background halide levels. Compared to chlorine, DBP formation by PAA and PFA was minimal in regular wastewater. However, during 24-h disinfection of saline wastewater, PAA
surprisingly produced more brominated and iodinated DBPs than chlorine, while PFA kept all tested DBPs at bay effectively. A kinetic model was developed based on literature and additional kinetic experiments to predict the DBP formation potential of POAs.
Moreover, as POAs themselves may not efficiently oxidize some microbes and organic contaminants due to their selective reactivity, research was conducted to investigate the potential of combing UV irradiation and POAs for co-removal of antibiotic resistance genes (ARGs) and organic micropollutants, with PAA as the representative POA. The photolysis of PAA under UV254 (254 nm) effectively generated hydroxyl radical (●OH) and multiple organic radicals (e.g., CH3C(O)OO●) and achieved synergistic degradation of ARGs and micropollutants. However, flow cytometry analysis demonstrated that cell membrane integrity could not be damaged by PAA or UV/PAA processes. In addition to ●OH, acetylperoxyl radical (CH3C(O)OO●), is also an important radical in UV/PAA system. This study employed different approaches to quantify its reactivity with different organic compounds and unveiled its remarkable role in UV/PAA.
Overall, this study demonstrated the promising potential of POAs for effective bacterial inactivation and DBP control, and delineated the underlying mechanisms. Results and methodologies developed by this study filled critical knowledge gaps for POAs and can be useful to facilitate future research.