Date of Award
2026
Document Type
Campus Access Dissertation
Degree Name
Doctor of Philosophy in Environmental Engineering (PhD)
Administrative Home Department
Department of Civil, Environmental, and Geospatial Engineering
Advisor 1
Daisuke Minakata
Advisor 2
Michelle Jarvie-Eggart
Committee Member 1
Jiehong Guo
Committee Member 2
Marina Tanasova
Committee Member 3
Zhimin Song
Abstract
Filtered krypton chloride (KrCl*) excilamps emitting far UVC light centered at ~222 nm have emerged as a powerful disinfection tool for air, surfaces, and water following the COVID 19 pandemic. These lamps offer advantages over conventional 254 nm low pressure UV, reducing risk of harm to human skin and eyes while eliminating the risk of toxic mercury. This has prompted substantial research into treatment applications, particularly disinfection and advanced oxidation processes (AOPs) for organic pollutant removal via direct photolysis or indirect photolysis, where a precursor oxidant (e.g., hydrogen peroxide) is activated to produce reactive species such as hydroxyl radicals. Nitrate, commonly present at high concentrations in wastewater, absorbs strongly at 222 nm but negligibly at 254 nm. Its photolysis produces hydroxyl radicals and reactive nitrogen species (RNS) such as nitrogen dioxide radicals, nitric oxide radicals, and peroxynitrite (ONOO−), generating a de facto AOP (UV222/NO3−) without any added oxidant. This process has drawn interest because of its treatment advantages and its potential to convert organic pollutants into more toxic, nitrogenous byproducts. However, the role of certain RNS, particularly ONOO−, remains uncertain, especially regarding its direct photolysis at 222 nm and contribution to nitration. Separately, recent research shows dissolved oxygen and water can absorb photons and generate reactive species, contributing to observed photolysis rates without any added oxidant and suggesting many reported quantum yields may be overestimated.
This dissertation advances fundamental understanding of far UVC 222 nm treatment through two projects. First, I examined in situ reactive species production via 17 dissolved oxygen and water by varying the light these constituents absorbed relative to target compound concentration. This revealed increasing apparent quantum yields with decreasing initial concentration uniquely at 222 nm, confirming overestimation in prior reported values, and a kinetic model built from elementary reactions validated these findings. Second, I studied the phototransformation of phenol, a model aromatic compound, across varying sources of inorganic nitrogen to clarify the roles of different reactive species in nitration. Comparisons of degradation kinetics and product formation provided insight into the role of peroxynitrite and dominant mechanisms governing the UV222/NO3− AOP, offering a roadmap for future work.
Recommended Citation
Mohrhardt, Benjamin J., "MECHANISTIC INSIGHTS OF FAR-UVC 222 NM TREATMENT PROCESSES FOR ORGANIC CONTAMINANT REMOVAL AND TRANSFORMATION: ROLES OF DIRECT PHOTOLYSIS, REACTIVE OXYGEN SPECIES, AND REACTIVE NITROGEN SPECIES", Campus Access Dissertation, Michigan Technological University, 2026.
https://digitalcommons.mtu.edu/etdr/2155